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  • 1
    Electronic Resource
    Electronic Resource
    High critical temperature by resonant quantum confinement: Evidence for polarons ordering atT*≈1.5T c in Bi-2212 and La-214 by EXAFS (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1815-1820 
    Details
    ISSN: 0392-6737
    Keywords: Insulator-superconductor transitions ; unconventional mechanisms of high-T c superconductivity ; Other topics in superconductivity ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The temperature dependence of local Cu site conformations in single-domain crystals of Bi2Sr2CaCu2O8+y (Bi-2212) and La1.85Sr0.15CuO4 (La-214) has been determined by EXAFS (Extended X-ray Absorption Fine Structure), a fast (10−15 s) and local probe. Two sets of Cu site conformations characterized by the Cu−O(apical) bond distances and tilting of copper square plane have been found atT〈T*∼1.5T c . The difference between the long and short Cu−O(apical) distance appeared to be 0.17 Å and 0.12 Å atT〈T* in Bi-2212 and La-214 systems, respectively. The polarons are associated with the short Cu−O(apical) bond distance. The ratio between the number of short and the total number of Cu−O(apical) bonds (N short/N tot∼0.42 in both systems) is a measure of the relative area of distorted and undistorted domains. By using this result we have been able to show the polaronic nature of the one-dimensional structural anharmonic modulation of the CuO2 plane in Bi-2212 where the polarons have dimensionW=(11±1) Å atT〈T*≈1.4T c and are condensed into a one-dimensional generalized Wigner charge density wave (CDW). It appears that superconductivity is stabilized at thigh temperature by resonant quantum confinement in a superlattice of stripe widthL wherek Fx ∼k Fy ∼π/L.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462179
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  • 2
    Electronic Resource
    Electronic Resource
    A study of the d.c. susceptibility of granular superconductors by means of Josephson-junction array models (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1851-1856 
    Details
    ISSN: 0392-6737
    Keywords: Magnetization curves ; Meissner effect ; penetration depth ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The field-cooled d.c. susceptibility of granular superconductors is studied by means of simple Josephson-junction array models. It is shown that a paramagnetic behaviour after field cooling for these systems, for certain ranges of the applied field, is a natural consequence of their topological structure and of the presence of weak superconducting coupling between grains. In this way, the recently detected positive field-cooled d.c. susceptibility is interpreted by means of a traditional Josephson-junction network approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462184
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  • 3
    Electronic Resource
    Electronic Resource
    Large single-crystal growth of RBa2Cu3O7−x by the flux method (R=Y and rare earths) (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1679-1683 
    Details
    ISSN: 0392-6737
    Keywords: Thermodynamic properties ; thermal conductivity ; Methods of crystals growth and purification ; Phase diagrams of other materials ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this work the thermal conditions required for single-crystal growth in RBa2Cu3O7−x systems (R=Y or rare earths apart from Ce and Tb) have been systematically revised in order to improve the size of crystals obtainable by the flux method. Large single crystals of NdBCO, SmBCO and EuBCO have been actually obtained and characterized by XRD, oxygen content and electrical resistivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462159
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  • 4
    Electronic Resource
    Electronic Resource
    The peculiarities ofc-axis transport in the normal phase of high-T c materials (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1821-1826 
    Details
    ISSN: 0392-6737
    Keywords: Superconductivity: general properties ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Thec-axis transport of impure layered metals is discussed in the cases of clean and dirty limits. The crossover from the Drude regime to the hopping regime in transverse conductivity is treated qualitatively as the change from anisotropic diffusion to Zener oscillations of electrons. It is shown that the superconducting fluctuations in strongly anisotropic layered superconductors substantially affect the transport coefficients above the transition temperature. In a wide temperature range aboveT c the main effect of these fluctuations is to create a virtual gap in the electron spectrum, causing an increase of transverse electric and heat resistivities and decrease of thermoelectric power. This effect turns out to be specially competitive due to the suppression of paraconductivity along thec-axis direction due to the hopping character of electron motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462180
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of thermal treatment and oxygen stoichiometry on paraconductivity of YBa2Cu3O7−δ pellets (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1843-1849 
    Details
    ISSN: 0392-6737
    Keywords: Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary This work is focused on how oxygen stoichiometry and distribution affects the pretransitional region in YBa2Cu3O7−δ pellets prepared by different thermal treatments starting from the same batch with oxygen content 6.94. We find that slightly deoxygenated samples, which show higherT c and narrower transition than the starting material, also exhibit a more pronounced rounding of the resistivity extending towards higher temperatures. We analyse the presence and the extension of regions with different power law behaviour of excess conductivityvs. temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462183
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  • 6
    Electronic Resource
    Electronic Resource
    DTA study for clarifying the role of silver in the formation of Bi-2223 phase in Ag-Sheathed tapes (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1665-1670 
    Details
    ISSN: 0392-6737
    Keywords: Superconducting magnets and magnetic levitation devices ; superconducting cables and conductors ; Superconducting perovskites and related structures ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The role of silver in catalysing and promoting the textured growth of 2223 phase in Ag-sheathed (Powder In Tube) tapes, starting from a precursor «bi-component» powder, constituted by Bi-2212 and other mixed oxides, was investigated in detail by means of DTA and X-ray analyses at the different stages of the annealing of the tapes. By monitoring the reaction it was possible to show how the presence of silver modifies the thermal behaviour of the reactants. The reduction of the temperature at which a liquid phase is formed is believed to be the key mechanism through which the presence of silver enhances the overall conversion to 2223 phase. This temperature decrease was shown (for the first time, to our knowledge) to be active only as long as some precursor (unreacted) powder was present, and not on fully reacted 2223 phase. Further investigation on 2212 phase and the other mixed oxides, separately analysed by DTA, clarified that only the thermal behaviour of the former was modified by the presence of silver. An explanation based on oxygen unbalancing in the material possibly induced, at the annealing temperature, by the presence of silver, is suggested: as a consequence of the very high solubility of oxygen in silver at high temperature, O2 would be «pumped off» the superconducting 2212 phase, with the result of lowering its melting point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462157
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  • 7
    Electronic Resource
    Electronic Resource
    Sticky model of charged colloids (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 703-709 
    Details
    ISSN: 0392-6737
    Keywords: Theory and models of liquid structure ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We use the Sticky Electrolyte Model, which we solved before in PY/MSA, to obtain the equation of state of a charge colloid taking into account both sticky and charge contribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456715
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  • 8
    Electronic Resource
    Electronic Resource
    Novel approaches to parallelism in soft-matter problems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 831-834 
    Details
    ISSN: 0392-6737
    Keywords: Renormalization-group, fractal and percolation studies of phase transitions ; Chemical kinetics: Computational modelling: simulation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We outline a novel method of exploiting distributed computational resources to study problems in soft-matter science. We have applied our method to simulations of polymers, including hydrodynamic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456731
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  • 9
    Electronic Resource
    Electronic Resource
    Study of the far-infrared and mm-wave conductivity of YBCO in the normal state (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1803-1807 
    Details
    ISSN: 0392-6737
    Keywords: Response to electromagnetic fields ; nuclear magnetic resonance ; ultrasonic attenuation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary An accurate determination of the optical conductivity σ(ν) of high-T c materials at low frequencies (ν〈100 cm−1) is still an open problem. In the present paper we report new far-infrared data showing that the LaAlO3 crystal, on which high-quality YBCO films can be deposited, is well transparent at low frequencies. Test measurements have also been performed by employing the ENEA compact FEL facility; preliminary reslts indicate the possibility to obtain high-accuracy spectroscopic data in the mm-wave region. On the basis of these results, we have in program mm-wave and far-infrared transmittance measurements on thin YBCO films on LaAlO3, in order to get new information on the low-frequency behaviour of σ(ν).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462177
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  • 10
    Electronic Resource
    Electronic Resource
    Tunnel spectroscopy into the YBa2Cu4O8 compound (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1885-1888 
    Details
    ISSN: 0392-6737
    Keywords: Proximity effects, tunneling phenomena and Josephson effects ; Y-based compounds ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have realized planar tunnel junctions using both Y123 and Y124 single crystals as base electrodes and Pb as counterelectrode. The crystals, withT c =90 K (Y123) andT c =80 K (Y124), have been chemically etched and natural barriers were formed by a short air exposure. We have compared the tunneling spectra obtained on both systems. The features at about±18mV of the Y123 compound are still observed in the Y124, while the low-bias structures at ±5 mV are not present in the tunneling characteristics of the Y124 system. Linearity of the background conductance is also observed, with less steep slopes in Y124 that might indicate a reduced interlayer coupling in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462189
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  • 11
    Electronic Resource
    Electronic Resource
    Scaling in dispersion rheology (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1193-1197 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Statistical mechanics ; Linear viscoelasticity ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A nonequilibrium fluid lattice model of concentrated colloidal dispersions is presented to predict the effects of the microstructure, particle interactions, volume fraction (ϕ), frequency (ω), and the longest viscoelastic relaxation time on the complex shear viscosity. In addition to the pair interactions between colloidal particles, the many-body interactions between the particles and the equilibrium microstructure have to be included in the analysis. As ϕ approaches a critical valueφ c, the fluidity of concentrated dispersions slows down drastically. This percolation thresholdφ c scales ad (AP)−0.5, whereA andP are related to the repulsive interparticle potential and microstructure, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458800
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  • 12
    Electronic Resource
    Electronic Resource
    Analytic study of a model of diffusion on random comb-like structures (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1223-1230 
    Details
    ISSN: 0392-6737
    Keywords: Order-disorder and statistical mechanics of model systems ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary An analytic study of a model of diffusion on random comb-like structures in which a bias field may or not exist along the backbone is presented. First, when no bias is present, the method allows to compute in an exact manner, for any given disordered structure, the asymptotic behaviour at large time of the probability of presence of the particle at its initial site and on the backbone, and of the particle position and dispersion. The expressions of these quantities are shown to coincide asymptotically with those derived in simple «mean-field» treatments. The results for any given sample do not depend on the particular configuration (self-averaging property). When a bias field is present along the backbone, one can also compute directly in an exact manner the asymptotic behaviour at large time of the disorder average of the probability of presence of the particle at its initial site. As for the particle position and dispersion, they can be computed in a periodized system of arbitrary periodN. The corresponding quantities for the random system can then be obtained by taking the limitN→∞. As a result, in both cases the behaviours strongly depend on the distribution of the lengths of the branches. With an exponential distribution transport is normal while anomalous drift and diffusion may take place for a power law distribution (when long branches are present with sufficiently high weights).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458804
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  • 13
    Electronic Resource
    Electronic Resource
    Diffusion of testing particles in turbulent nematic liquid crystals (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1253-1258 
    Details
    ISSN: 0392-6737
    Keywords: Liquid crystals ; Turbulence, fluid dynamics ; Diffusion and ionic conduction in liquids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report on the diffusive motion of dielectric testing particles floating in a turbulent nematic fluid under the effect of an external oscillating electric field. The particle is viewed as a tracer of the underlying turbulence. We calculate the diffusion coefficients and the probability distribution of the particle displacements, thus showing that the motion of the particle is a classical Brownian diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458809
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  • 14
    Electronic Resource
    Electronic Resource
    Longitudinal collective modes in liquid water (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 817-824 
    Details
    ISSN: 0392-6737
    Keywords: Computer simulation of static and dynamic behavior ; Liquid metals and liquid alloys ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Results of extensive computer simulations performed in liquid water are reported in order to clarify the main features of dynamical density correlations in this system. Puzzling aspects, such as the anomalous sound wave propagation at finite wave vectors, are related to the peculiar structural aspects of this hydrogen-bonded liquid. Additional features (such as the evolution of the relevant memory functions at increasing wave vectors and the emergency of a second mode in the longitudinal current spectra) are also discussed in some detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456729
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  • 15
    Electronic Resource
    Electronic Resource
    Analysis of dynamic light scattering of poly(N-isopropylacrylamide) across the collapse transition (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 711-720 
    Details
    ISSN: 0392-6737
    Keywords: Polymer reactions and polymerization ; Brillouin and Rayleigh scattering ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We analyse data from the dynamic light scattering of poly(N-isopropylacrilamide) in water solution as we cross the collapse transition. Experimental data are interpreted by the Gaussian self-consistent Zimm model that takes into account two- and three-body excluded-volume effects, and Oseen hydrodynamic interactions, as well as by the standard cumulant and Contin analyses. By fitting the dynamic structure factor we extract the temperature dependence of the diffusion coefficientD and the first relaxation time τ1 across the collapse transition for a range of scattering angles. The relaxation time τ1 possesses a characteristic peak at about 32.4 °C due to slowing of the internal motions of the polymer at the theta-point, and a minimum at 33.4 °C. We interpret this as a combination of collapse closely followed by the growth of critical correlations. At large scattering angles we reach the universalk 3 regime, and observe that this behaviour vanishes at the onset of collapse transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456716
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  • 16
    Electronic Resource
    Electronic Resource
    Aggregating block copolymers as model systems to study polymer brush dynamics (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 747-755 
    Details
    ISSN: 0392-6737
    Keywords: Neutron scattering techniques (including small-angle scattering) ; Polymers, elastomers, and plastics ; Fluctuation phenomena, random processes and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A-B block copolymers in a selective solvent—good for the B-species and bad for the A-species—form micellar aggregates with a compact A-core with a corona (brush) of B «hairs» reaching into the solvent. Whereas polystyrene(PS)-polyisoprene(PI) in decane forms spherical micelles with a PS core of about 10 nm radius, polyethylene(PE)-polyethylenepropylene(PEP) forms micellar platelets, the shape of which is goverend by the habitus of PE crystallites forming the core. These planar aggregates have large (several hundred nanometers) lateral extension and a core thickness in the range of 10 nm. Both systems are model systems for polymer brushes, either on a spherical surface or planar. Neutron spin-echo experiments allow for the investigation of the dynamics of the brushes which reflects their viscoelastic properties. Results of neutron small-angle and spin-echo investigations are reported. The brush dynamics is explained using a model based on an idea of de Gennes describing the brush properties in terms of scaling relations for osmotic pressure and viscosity of a semi-dilute solution with inhomogeneous density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456720
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  • 17
    Electronic Resource
    Electronic Resource
    Cluster description of water-in-oil microemulsions near the critical and percolation points (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1419-1431 
    Details
    ISSN: 0392-6737
    Keywords: Phase equilibria, phase transitions, and critical points of specific substances ; Optical properties of bulk materials ; Statistical theory of liquid structure ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures. In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering. The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent complex dielectric constant of this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462026
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  • 18
    Electronic Resource
    Electronic Resource
    Scale-dependent elastic response of closed phospholipid bilayers to transmembrane molecular pumping activity: a key for exo-endocytosis physiological process (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1457-1470 
    Details
    ISSN: 0392-6737
    Keywords: Active transport processes across biological membranes cellular and subcellular transmembrane electrochemical potentials intracellular electron transport and energy transduction ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The question is asked on the physiological role of the universal molecular biological function activity of lipid transmembrane translocation in living-cell membranes. The elastic response of closed bilayers to phospholipid translocation is theoretically found to be scale dependent, leading to vesiculation for plasma membrane characteristic-size bilayers (R m≈10 μm), and to dilation strain for endocytic-vesicles characteristic-size bilayers (R m≈0.1 μm). Both vesiculation and dilation effects are experimentally proved. On the basis of this scaledependent behaviour, it is argued that transmembrane pumping activity could control both the vesiculation and the fusion processin vivo, namely the exo-endocytic cellular-membrane traffic process itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462030
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  • 19
    Electronic Resource
    Electronic Resource
    Exact treatment of interface fluctuations in a two-dimensional emulsion (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1595-1599 
    Details
    ISSN: 0392-6737
    Keywords: Thermodynamics of surfaces and interfaces ; Disperse systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present a model for a polydisperse ensemble of two-dimensional droplets wich accounts for the effects of arbitrarily large distortions of the droplet shape. Interactions within a droplet include bending rigidity and spontaneous curvature. Interactions between droplets are omitted. Even at high temperatures, the effects of the shape fluctuations on the droplet size distribution remain small, as they are dominated by the contributions from the mixing entropy. In contrast, shape fluctuations lead to a pronounced peak in thermodynamic quantities like specific heat. This peak occurs at temperatures where thermal excitations become of the order of the bending energies of the droplet surface. The fluctuation-dominated regime extends to temperatures far lower than expected from a mean-field calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462047
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  • 20
    Electronic Resource
    Electronic Resource
    Small-angle light scattering in dense microemulsions, transition from droplet to bicontinuous phase (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1627-1633 
    Details
    ISSN: 0392-6737
    Keywords: Brillouin and Rayleigh scattering ; Liquids ; Emulsions and suspensions ; Order-disorder and statistical mechanics of model systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have performed extensive small-angle light scattering (SALS) measurements on a three-component microemulsion (AOT/decane/water) as a function of the dispersed phase concentration and the temperature. All samples have a water/AOT molar fractionw=40.8. Such a system presents a very complex phase diagram with many structural configurations. With the SALS technique, we have been able to observe all the phase separation lines. In particular we give details on the system structure on the percolation phenomenon and on the bicontinuous phase recently observed. In particular we show that the percolation is driven by a long-scale aggregation between microemulsion droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462051
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  • 21
    Electronic Resource
    Electronic Resource
    Low-temperature specific heats of lanthanum and yttrium phosphate glasses (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1277-1284 
    Details
    ISSN: 0392-6737
    Keywords: Vibrational states in disordered systems ; Heat capacities of solids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The specific heats of (R2O3) x (P2O5)1−x glasses containing high concentrations of La3+ and Y3+ ions have been measured between 1.5K and 30K. It is shown that, in addition to the usual Debye contribution, there is an excess specific heat arising from localized vibrational states which has been discussed in terms of two distinct models. The first predicts a maximum in the temperature dependence of the excess specific heat associated with the crossover frequency from phonon to fracton behaviour. The phonon-fracton density of states used to fit the excess specific heat gives rise to model parameters having the same magnitudes as those found previously for other glasses including samarium phosphates. The second model, formulated on the basis of soft vibrations in glasses, predicts a minimum in the excess specific heat, which is also observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458813
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  • 22
    Electronic Resource
    Electronic Resource
    Freeze-fracture electron microscopy and light scattering studies on polyethylcyanoacrylate nanocapsule colloidal suspensions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1271-1276 
    Details
    ISSN: 0392-6737
    Keywords: Granular materials: aggregation characteristics (e.g., grain size, particle size distribution, porosity) ; Polymer reactions and polymerization ; Colloids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Nanocapsule preparative procedures are able to change the availability of drugs from delivery devices. In particular, the influence of the organic solvent, used in the interfacial polymerisation process, on the shape, mean particle size, size distribution and type of colloidal suspension was investigated. The organic solvents employed in the preparation of PECA nanocapsules were ethanol, acetone or acetonitrile. A non-ionic surfactant (Pluronic F68) was used during the preparation process. The amount of monomer represented another variable, capable of influencing the final carrier properties of PECA nanocapsules. The presence of ethanol achieved the formation of both nanoparticles and nanocapsules. However, the presence of acetone or acetonitrile achieved not only a highly homogeneous size colloidal system, but also the formation of only one type of PECA nanosphere (nanocapsule). The different amount of monomer led to the formation of nanocapsules with a wall thickness proportional to the initial concentration of the polymerising agent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458812
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  • 23
    Electronic Resource
    Electronic Resource
    Continuum Monte Carlo simulation of phase transitions in rod-like molecules at surfaces (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1297-1303 
    Details
    ISSN: 0392-6737
    Keywords: Fluid surfaces and fluid-fluid interfaces ; Liquid thin films ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Stiff rod-like chain molecules with harmonic bond length potentials and trigonometric bond angle potentials are used to model Langmuir monolayers at high densities. One end of the rod-like molecules is strongly bound to a flat two-dimensional substrate which represents the air-water interface. A ground-state analysis is performed which suggests phase transitions between phases with and without collective uniform tilt. Large-scale off-lattice Monte Carlo simulations over a wide temperature range show in addition to the tilting transition the presence of a strongly constrained melting transition at high temperatures. The latter transition appears to be related to two-dimensional melting of the head group lattice. These findings show that the model contains both, two- and three-dimensional ergodicity breaking solidification transitions. We discuss our findings with respect to experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458816
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    Electronic Resource
    Electronic Resource
    Theoretical and experimental approaches to kinetics at the collapse transition of a homopolymer (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 675-687 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Polymer reactions and polymerization ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss some recent theoretical studies of the kinetics of the collapse transition in homopolymers. An isolated polymer is modelled using computer simulation, and a time-dependent mean-field theory. The mean-field theory is analysed analytically for early stages, and for short polymers the equations are studied numerically. The results of simulation and theory are compared yielding, we argue, a consistent physical picture. Quantitative comparisons are not yet given, but seem relatively promising.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456712
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    Electronic Resource
    Electronic Resource
    Polymers inO(N) symmetric quantum field theory in the double-scaling limit (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 697-702 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Field theory ; Spontaneous and radiative symmetry breaking ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Filamentary-surfaces randomly branched polymers can be represented byO(N) symmetric quantum field theories in the limit whereN→∞ and the coupling constantg→g c in a correlated manner. The statistical systems of randomly branched polymers are realized as dual diagrams of the Feynman graphs of the underlyingO(N) symmetric quantum field theory. The purpose of these studies is to gain intuition for the long-lasting search for a possible description of quantum field theory in terms of extended objects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456714
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  • 26
    Electronic Resource
    Electronic Resource
    Sol-gel transition in worm-like micelles (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 771-781 
    Details
    ISSN: 0392-6737
    Keywords: Neutron scattering techniques (including small-angle scattering) ; Gels and sols ; Brillouin and Rayleigh scattering ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The statical and dynamical properties of lecithin/H2O/cyclohexane cylindrical reverse micelles are investigated as a function of lecithin volume fraction, ϕ, and temperature at fixed water/lecithin ratio,w 0. The viscosity data are well fitted by the Cates model when the breathing mode of micelles is taken into consideration, overlapping with the breaking and reforming mechanisms. We present some results from Brillouin-scattering experiment, performed across the sol-gel transition. In order to explain the experimentally observed ϕ-dependence of the hyperacoustic parameters, a mechanical model was developed from which the ϕ-dependence of the micelle size distribution was obtained. From a comparison with the viscosity data the entanglement length was estimated. Furthermore some new results from an incoherent quasi-elastic neutron scattering experiment are presented. The whole body of the experimental results suggests for a sol-gel transition triggered by topologic phenomena. When the lecithin volume fraction increases, the kinetic equilibrium between the breaking and reforming mechanisms of the micelles shifts the mean micelle length towards higher values and the entanglement of the micelles becomes highly favourable. The obtained results are discussed and compared with other findings in literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456723
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  • 27
    Electronic Resource
    Electronic Resource
    Pattern formation at the traveling liquid-crystal twist grain boundary-smectic a interface (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 765-770 
    Details
    ISSN: 0392-6737
    Keywords: Experimental determinations of smectic, nematic, cholesteric, and lyotropic structures ; Specialized material fabrications and fabrication techniques ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Pattern formation at phase boundaries moving in a temperature gradient is one of the major areas of nonequilibrium physics attracting considerable attention. While most of the early work concentrated on the moving solid-liquid interface, now the focus has changed to phase transitions characterized by broken continuous symmetry. Most recently we investigated consequences to interfacial patterns of a chirality-induced equilibrium length. Here we study patterns at another chiral interface where one of the phases has a chirality-induced defect lattice, the twist grain boundary (TGB) phase. The TGB state is analogous to the vortex lattice in Type-II superconductors predicted by the Gennes’ analogy between the nematic (N)-smectic A (A) transition and the normal-superconducting transition. In this analogy, a cholesteric A transition is analogous to the normal-superconducting transition in an external magnetic field and a theory has been developed for its analogous vortex lattice, the TGB phase, when this transition is Type II. We study patterns formed at the traveling TGB-A phase boundary. Different patterns are observed depending on whether TGB grows into A or A into TGB. Indeed, this maybe the first time a steady-state pattern is observed in directional melting (i.e. TGB growing into A). As these patterns have a broad band of wavelengths, they are difficult to characterize physically. Thus, we introduced a novel analysis (most simply but not rigorously described as) measuring the fractal dimension of the patterns at these traveling interfaces. Two lengths emerged from this analysis: a longer one set by sample thickness and a shorter one set by the smallest TGB unit that can grow into an oriented smectic A phase. We invoke our old dynamic arguments to account for why TGB cannot propagate at a second-order TGB-cholesteric phase transition so it is eventually squeezed out leaving behind a direct cholesteric-A transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456722
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    Electronic Resource
    Electronic Resource
    The fusion of ethylene oxide polymers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 825-830 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Anelasticity, internal friction, and mechanical resonances ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Calorimetric measurements by DSC technique have been made in pure polyethylene glycol (PEG) and oxide (PEO) polymers having a very wide molecular-weight range (from 600 to 4000 000) and in PEO (MW 600 000)-NaSCN complexes. It was found that the melting temperature increases with increasing molecular weight, ranging from 293 K in the polymer with MW=600 to 340 K in that with MW=4000 000. The behaviour of the heats of fusion with increasing molecular weight reflects the trend expected in systems, in which the increase of the main chain length produces a relevant growth of the degree of crystallinity. A distinct maximum of the heat of fusion has been found at about MW=10000, this result being an evidence of the high amount of crystalline regions building up the structure of that system. The dependence of the melting temperature on molecular weight has been nicely accounted for by using the expression of Flory, deduced from the statistical theory of polymers having the most probable molecular-weight distribution. The addition of sodium thiocyanate to PEO modifies the morphology of the host polymer and, for salt concentrations higher than 0.03 molar fraction, gives rise to the formation of a PEO-salt crystalline complex characterized by a high melting temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456730
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  • 29
    Electronic Resource
    Electronic Resource
    Frequency dependence of the complex dielectric constant of poly(ethylene oxide) under hydrostatic pressure (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 855-864 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Mechanics and rheology of solids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Electrical-impedance measurements have been made in the frequency range 5 Hz to10 MHz in pure poly(ethylene oxide) having a molecular weight of 600 000 from 254 K nearly up to the melting point of the crystalline phase (about 330 K). As the temperature approaches the melting point there are large increases in the realε′ and imaginaryε″ parts of the dielectric constant. The frequency dependence ofε′ is characterized by a primary-relaxation process, whose frequency increases with increasing temperature as a consequence of decrease of the average structural relaxation time. There is strong evidence that this low-frequency dispersion rises mainly from the diffusive transport of localised charge carriers rather than a purely orientation relaxation process. In addition the effects of hydrostatic pressure (0–25 Gpa) on the frequency dependences of the realε′ and imaginaryε″ parts of the dielectric constant have been measured in the same temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456735
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    Electronic Resource
    Electronic Resource
    A design and performance test of the visualization within a capillary pumped loop (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 883-893 
    Details
    ISSN: 0392-6737
    Keywords: Diffusion and ionic conduction in liquids ; Studies of specific liquid structures ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Capillary Pumped Loop (CPL) is a thermal management device for advanced spacecrafts. This paper presents the operating principles of a CPL and the design characteristics of the components. Another purpose of this experiment was to build up a transparent loop in order to better determine and observe the internal thermofluid dynamics. The results indicated that the CPL could be in normal operation under various heat modes. Observation also told Non-Condensed Gas (NCG) was moving and collecting to somewhere between the condenser section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456739
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    Electronic Resource
    Dynamical properties of water-methanol solutions: Brillouin and depolarized Rayleigh scattering (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 923-931 
    Details
    ISSN: 0392-6737
    Keywords: Brillouin and Rayleigh scattering ; Ultrasonic relaxation processes in gases, liquids, and solids ; Structure of associated liquids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have performed Brillouin and depolarized Rayleigh light scattering on water-methanol solutions as a function of methanol molar fraction and temperature. For this system, molecular-dynamics (MD) simulation predicts that a shell of water forms around a methanol molecule, prediction which has been recently confirmed by neutron diffraction experiments. The results obtained by light scattering and presented here confirm previous observations and show, in addition, an increase of the stability in time of the water structure in the shells when temperature decreases and methanol concentration approaches a particular value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456743
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    Electronic Resource
    Electronic Resource
    Monte carlo studies of phase transitions in polymer blends and block copolymer melts (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 653-660 
    Details
    ISSN: 0392-6737
    Keywords: Macromolecular and polymer solutions (solubility, swelling, etc.) ; polymer melts ; Critical point phenomena ; Liquid-liquid transitions ; Monte Carlo and statistical methods ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The unmixing transition of both symmetrical polymer blends AB (i.e. chain lengthsN A=N B=N) and asymmetrical ones (N B/N A=2,3) is studied by large-scale Monte Carlo simulations of the bond fluctuation model. Combination of semi-grand-canonical simulation techniques, «histogram reweighting» and finitesize scaling allows an accurate location of the coexistence curve in the critical region. The variation of the critical temperature with chain length (N) is studied and compared to theoretical predictions. For the symmetrical case, use of chain lengths up toN=512 allows a rough estimation of crossover scaling functions for the crossover from Ising to mean-field exponents. The order-disorder transitions in melts of both symmetric (compositionf=N A/(N A+N B)=1/2) and asymmetric (f=3/4) block copolymers is studied for very short chains (16≤N≤60). The interplay between structure and chain configuration is emphasized. Qualitative evidence for «dumbell formation» of chains and vacancy enrichment in A-B-interfaces and near hard walls is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456709
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    Electronic Resource
    Electronic Resource
    Cooperative diffusion in concentrated polymer solutions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 661-667 
    Details
    ISSN: 0392-6737
    Keywords: Diffusive momentum transport (including viscosity of liquids) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Concentrated solutions of polystyrene in dioctylphthalate have been examined as a function of temperature over the concentration range 0.2 to 0.9 g/ml. The static screening length and the hydrodynamic screening length evaluated from the cooperative-diffusion coefficient are compared with the predictions of current models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456710
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  • 34
    Electronic Resource
    Electronic Resource
    From mixing-demixing to condensation-evaporation phase transition in binary liquids (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1205-1216 
    Details
    ISSN: 0392-6737
    Keywords: Statistical theories of liquid structure ; Computer simulation of static and dynamic behavior ; General studies of phase transitions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Binary-fluid mixtures show first-order phase transition phenomena which are either classified as mixing-demixing (phase separation), or as condensation-evaporation. The localization of the transition lines, the characterization of the new phases, and the analysis of the parameters which force model systems to choose one of the two transition mechanisms is the aim of this study. We performed both parallel-molecular-dynamics simulations and integral-equation theory calculations on binary mixtures of Lennard-Jones particles. By fixing the composition and by varying the interaction strength, we found a continuous change between the two kinds of transition mechanisms. Theoretical and simulation results are compared with each other and a quantitative agreement i8s found. However, the simultation analysis appears to be more promising since, in contrast to the integral-equation theory in which the spinodal lines can only be approched, information on the microscopic structure of the new phases can be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458802
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    Electronic Resource
    Depolarized light scattering study of equilibrium sedimentation profiles of colloidal dispersions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1091-1101 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Brillouin and Rayleigh scattering ; General theory of equations of state and phase equilibria ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Equilibrium sedimentation profiles of concentrated suspensions of charged optically anisotropic colloids are accurately determined by performing depolarized light scattering measurements. From the data we derive the osmotic pressure πvs. the particle volume fraction Φ. The π(Φ) values obtained with strongly screened colloids are in excellent agreement with the predicted hard-sphere equation of state. The data suggest that, besides gravitation, there is an additional force acting on the particles, probably due to the build-up of an electrostatic sedimentation potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458789
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    Electronic Resource
    Phase behaviour of colloid-polymer mixtures (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1127-1139 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Solubility, segregation, and mixing ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We review the phase behaviour of mixtures of colloids and non-adsorbing polymers. The exclusion of polymer molecules from overlapping «depletion zones» between two neighbouring colloidal particles results in an unbalanced osmotic pressure pushing the particles together. This depletion potential is separately tunable in range and depth. Theory predicts that the resulting phase behaviour is sensitive to ξ=r g/R, the ratio of the radius of gyration of a polymer molecule, to the radius of the colloid. At large ξ, a stable colloidalliquid phase becomes possible. This has been confirmed by recent experiments. The formation of non-equilibrium «transient gel» states when the size ratio is small (≈0.08) is also introduced briefly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458793
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    Electronic Resource
    Chemically controlled pattern formation in phase-separating materials (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1171-1176 
    Details
    ISSN: 0392-6737
    Keywords: Thermal expansion and thermomechanical effects ; Lattice theory and statistic ; Ising problems ; Polymer reactions and polymerization ; General studies of phase transitions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The role of chemical reactions in the selection of patterns in phase-separating mixtures is presented. Linearized theory and computer simulation show that the initial long-wavelength instability characteristic of spinodal decomposition is suppressed by chemical reactions, which restrict domain growth to intermediate length scales even in the late stages of phase separation. Our findings suggest that chemical reactions may provide a novel way to stabilize and tune the steady-state morphology of phase-separating materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458797
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    Electronic Resource
    Periodic structures and scaling Laws in a magnetic colloid (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1199-1204 
    Details
    ISSN: 0392-6737
    Keywords: Magnetic liquids ; Pattern selection ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Phase separation was found in an eicosane-based ferrofluid in zero applied field. Upon applying a magnetic field, the condensed phase breaks up to form a lattice of periodic columns. The periodicity λ scales with the layer thicknessL. Two scaling regimes were found. When thickness is small, where no branching is observed, λ ∞L 1/2. In the large-thickness regime, a tree type of structure develops at the tail of each column, and the columns are separated by side bands while the scaling relation crosses over to λ ∞L 2/3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458801
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    Electronic Resource
    Kerr effect from fractal aggregates of polystyrene microspheres (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1237-1241 
    Details
    ISSN: 0392-6737
    Keywords: Birefringence (including stress birefringence, flow birefringence, etc. ; Fluctuation phenomena, random processes, and Brownian motion ; Extinction, absorption, scattering, and transmission coefficients, emissivity ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We study the slow aggregation of aqueous suspensions of optically isotropic microspheres by means of transient electric birefringence. Aggregating clusters exhibit large Kerr constants, and consequently we provide direct experimental evidence that the clusters do posses form anisotropy. From the birefringence relaxation time we derive information on the average cluster size and on the size distribution, and determine their evolution during the aggregation process. Static and dynamic light scattering data confirm the validity of the transient electric birefringence results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458806
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    Electronic Resource
    Generalized percolation models for frustrated spin systems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1259-1264 
    Details
    ISSN: 0392-6737
    Keywords: Crystal-field theory and spin Hamiltonians ; Monte Carlo and statistical methods ; Lattice theory and statistics ; Ising problems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A brief review on how to study frustrated spin models by mapping them into generalized percolation models is given. The percolation models associated to a number of deterministic frustrated models are discussed with particular attention on the properties of critical clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458810
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    Electronic Resource
    Evidence of large-angle reorientation in supercooledo-terphenyl (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1285-1289 
    Details
    ISSN: 0392-6737
    Keywords: Amorphous materials, glasses ; Free radicals ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We study the reorientation process of a paramagnetic radical dissolved in supercooledo-terphenyl around and belowT g via the Electron Spin Resonance spectroscopy. The experimental results are at variance with the hypothesis of diffusive reorientation of the radical. Instead, the ESR lineshapes are fairly well reproduced by assuming that the radical reorientates via large angular jumps with a width Δϕ=80° −5° +10° . The results are compared with previous2H NMR studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458814
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  • 42
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    Electronic Resource
    Experimental results on quadratic maps using generalized complex numbers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1311-1324 
    Details
    ISSN: 0392-6737
    Keywords: Hydrodynamic stability ; Theory and models of chaotic systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Some results obtained introducing two-unit generalized complex numbers to determine Mandelbrot and Julia sets for quadratic maps are presented. We also highlight some analogies and differences between classic complex numbers and one of the proposed extensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458818
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    Phase transitions in diglyceride monolayers studied by computer simulations, pressure-area isotherms and X-ray diffraction (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1479-1485 
    Details
    ISSN: 0392-6737
    Keywords: Surface energy (surface tension, interface tension, angle of contact, etc.) ; Phase transitions and critical phenomena ; Constant-composition solid-solid phase transformations: polymorphic ; massive, and order-disorder ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary 1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found between the simulations and experiments. The Langmuir film undergoes two phase transitions occurring at 38.3 and 39.8 Å2/molecule. The transition at low surface density is associated with a tilt of ≈14° in the direction close to nearest neighbour. The first transition is unique for the diglyceride molecules and has not been observed for other amphiphilic molecules. It is driven by a competition of hydrophobic/hydrophilic and intra/intermolecular forces and can be pictured as a «seesaw» mechanism. Due to the close packing of the chains at high surface pressure, thesn-1 ester group aligns with the alkyl chain, and only thesn-2 ester group is favoured to lay at the aqueous interface. Hydrophilic forces attract thesn-1 ester group, but its motion towards the aqueous subphase is hindered by intra- and intermolecular chain interactions. On expansion, the intermolecular interaction decreases, and at the first transition, the intramolecular interaction between the two chains is strong enough to cause a «swelling» of the molecules. The diffraction pattern determined in the different mesophases reveals that the layer maintains its hexagonal structure up to the second phase. Concomitant with the tilt, the structure relaxed from a hexagonal to a distorted hexagonal lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462032
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    Electronic Resource
    Interaction with DNA of the novel cationic complex (2, 2′: 6′, 2″-terpyridine)methyl platinum(II) (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1523-1528 
    Details
    ISSN: 0392-6737
    Keywords: Molecular biophysics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The planarity and electron delocalization of the 2, 2′:6′, 2″-terpyridine (terpy) moiety in salts of the type [Pt(terpy)Me]X leads to extensive stacking interactions in aqueous solution. UV/VIS,1H NMR and resonance light scattering spectra provide evidence for the tendency of the complex to form large aggregates even under low ionic strength conditions. The interaction of the cationic complex with calf thymus DNA was investigated by spectroscopic techniques and mobility assays. At highr f ratios the complex seems to form extended aggregates on the surface of the nucleic acid but at lowerr f evidence was obtained for intercalation.
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    URL: http://dx.doi.org/10.1007/BF02462037
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  • 45
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    Electronic Resource
    Monolayers of proteins: β-lactoglobulin and its interactions with phospholipids (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1529-1536 
    Details
    ISSN: 0392-6737
    Keywords: Surface energy ; thermodynamic properties ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Monolayers of a protein β-lactoglobulin (βL) and two lipids distearoylphosphatidylcholine (DSPC) and dimirystoylphosphatidylcholine (DMPC) on aqueous subphase containing Na+ or Ca2+ ions are studied. The spreading isotherms and the ATR-FTIR spectra of LB plurilayers transferred, allow to deduce that α-helix conformation of β-lactoglobulin is the prevailing form. The study of bidimensional mixtures between βL with DSPC and with DMPC shows that the components are incompatible at the W/A interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462038
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  • 46
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    Electronic Resource
    Evidence of ionic adsorption on C12E6 non-ionic micellar solutions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1613-1618 
    Details
    ISSN: 0392-6737
    Keywords: Surface energy ; thermodynamic properties ; Permittivity ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this paper we present conductivity measurements on different concentrations of C12E6 non-ionic surfactant solutions as a function of temperature and buffer ionic strength. The experimental data were analysed by means of Looyenga equation. The isothermal slopes of the linearized Looyenga equation depend on the ionic strength, showing saturation effect. Our results indicate that one of the basic hypotheses of the mixture equations is not fulfilled. Adsorption of light ions at micellar interface is necessary to justify the experimental data. Then for non-ionic surfactant solutions the ion adsorption prevents any explicit computation of the micellar hydrated volume.
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    URL: http://dx.doi.org/10.1007/BF02462049
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    Preliminary results for YBCO thick films sprayed on stainless steel with the HVOF technique, and for multilayers using Ag or CuO (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2119-2126 
    Details
    ISSN: 0392-6737
    Keywords: Other low-power superconducting devices ; Superconducting films ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary YBCO thick films were sprayed on amagnetic stainless steel containing chromium with the continuous-detonation spray technique. The presence of chromium requires a buffer layer to be sprayed between the metal and the superconductor. Preliminary results using a nickel-based buffer layer are reported, which show a shielding effectiveness comparable with that of coatings made with the same technique on silver. Preliminary results on multilayers, using YBCO and either silver or CuO as interspacing layer, are reported. The main problem which arises is the lack of full oxygenation of the underneath YBCO layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471876
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  • 48
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    Electronic Resource
    Critical behaviour in solutions of branched polymers and swollen gels as studied by static and dynamic light scattering (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 689-696 
    Details
    ISSN: 0392-6737
    Keywords: Gels and sols ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present results of static and dynamic light scattering study of the critical phenomena in semi-dilute solutions and gels of poly(methyl methacrylate) (PMMA) prepared by radical copolymerization of methyl methacrylate and ethylene dimethacrylate in the θ-solvent (4-heptanone). The correlation length ξ and the extrapolated zero-angle scattering intensityI c,0 of the solutions with degree of cross-linkingf c≤1% diverge at the pseudospinodal temperature with exponents ofv=0.5 and γ=1, respectively, characteristic of mean-field behaviour. The values ofv and y for samples withf c≥1.5% are about 0.6 and 1.2, respectively, indicating that the phase transition in solutions of branched PMMA molecules and PMMA gels can be classified to the 3D Ising model. The pseudospinodal temperaturesT s, for semi-dilute solutions of branched molecules and gels were found as a function of the degree of cross-linking,f c. The time autocorrelation functions consist of two contributions of which the faster one is attributed to the cooperative motions of the polymer matrix, while the broad slow mode is due to the dynamics of the partly penetrating polydisperse clusters and can be interpreted in terms of a simple cluster diffusion model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456713
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    Polyelectrolyte solutions + multivalent salts = phase separation (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 727-736 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Phase equilibria, phase transitions, and critical points of specific substances ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A queous solutions of highly charged flexible polyelectrolytes phase separate in the presence of multivalent counterions. We present a theoretical model which explains this behavior in terms of electrostatic bridging between monomers via the condensed counterions. The «Polymer Reference Interaction Site Model» with the Debye-Hückel closure (equivalent to the «Random Phase Approximation») is sufficient to understand the crucial role of the valency of the counterions, to predict a demixion above a given valency and a redissolution of the precipitate in excess of added salt. The model successfully reproduces the different experimental phase diagrams of polystyrene sulfonate suspensions with different added electrolytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456718
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  • 50
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    Neutron reflectivity study of adsorbed diblock copolymers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 721-726 
    Details
    ISSN: 0392-6737
    Keywords: Neutron scattering techniques (including small-angle scattering) ; Macromolecular and polymer solutions (solubility, swelling, etc.) ; polymer melts ; Solid-fluid interfaces ; Structure and morphology ; thickness ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this paper, we summarize our cumulative work on neutron reflectivity studies of polystyrene-poly(vinyl-2-pyridine) (PS-PVP) and polystyrene-polyethylene oxide (PS-PEO) adsorbed at a quartz-solvent interface. Deuterated toluene was chosen as the solvent since it is a good solvent for PS and a poor one for either of the other two blocks. In this case, the polystyrene dangles into the solvent while the other block acts as an anchor. The neutron reflectivity studies reveal that the form of the polymer density profile normal to the substrate may be varied from an extended «brush» to a condensed «mushroom» conformation by manipulating the ratio of the molecular weights of the two blocks. In addition, we present new data on the PS-PEO system in a poor solvent, deuterated cyclohexane, under conditions of shear flow in Poiseuille geometry. We find that when the PS-PEO diblock is absorbed from cyclohexane and is allowed to relax, the PS chain takes on a «mushroom» conformation. However, when the shear is applied, the layer shear thickens due to the PS chains extending to nearly twice their original lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456717
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    Scaling behaviour of polyelectrolytes and polyelectrolyte brushes (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 803-807 
    Details
    ISSN: 0392-6737
    Keywords: Conformation (statistics and dynamics) ; Polymers and plastics ; Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc ; Thermodynamics of surfaces and interfaces ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Simulation results as well as experimental data indicate that full stretching of flexible polyelectrolytes will not occur under experimentally realizable conditions. Using density-dependent swelling exponents ν(ϕ) as suggested by Stevens and Kremer from the results of a MD simulation study, we present an Alexander-de Gennes-like scaling picture for the behaviour of charged brushes. The brush height is found to become dependent on the grafting density as soon as internal stretching is incomplete. For a particular anchoring technique used in experimental studies the grafting density itself becomes dependent on the chain length. The resulting modified overall chain length dependence of the brush height is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456727
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    Molar-mass dependence of the lamellar thickness in symmetric diblock copolymers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 835-842 
    Details
    ISSN: 0392-6737
    Keywords: Order-disorder and statistical mechanics of model systems ; Small-angle scattering, EDXD, EXAFS, and other techniques ; Layer structures, intercalation compounds, and superlattices: growth, structure, and nonelectronic properties ; Polymers, elastomers, and plastic ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A homologous series of nine symmetric poly(styrene)-block-poly(butadieme) diblock copolymers was synthesized and characterized. The scaling of the lamellar thickness,D, with the chain lengthN(DαN δ ) was investigated with small-angle X-ray scattering. Different sample preparation methods were used: annealing, solvent-casting and shear alignment. We find that the lamellar thickness and thus the value of the exponent δ depends on the preparation method used,i.e. care must be taken to ensure that the samples investigated are in thermodynamic equilibrium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456732
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    Interactions between poly(diallyldimethylammonium chloride) and poly(acrylic acid) in dependence on polymer concentration (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 865-871 
    Details
    ISSN: 0392-6737
    Keywords: Disperse systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The phase diagram of the ternary system,i.e. poly(diallyldimethylammonium chloride), poly(acrylic acid, sodium salt), and water was investigated by varying the molecular weight of the components. In general, a range of phase separation is surrounded by a one-phase system. The range of phase separation can be subdivided into a region of flocculation and/or coacervation in contrast to stable symplex dispersions. By increasing the molecular weight of the components the range of phase separation is increased and phenomena of flocculation followed by coacervation were observed predominantly. Above a molecular weight of 10 000 g/mol the transition to concentrated macroscopic homogeneous one-phase systems was observed at a constant ionic strength of 2 mol/l coinciding with the «critical ionic strength» for Coulombic interactions in this system. That means the transition to concentrated one-phase systems can be understood by the disappearance of Coulombic forces above a system-specific ionic strength resulting in a quite additive behaviour of the mixtures with regard to the components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456736
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    Planar nematic anchoring on SiO-coated substrates (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 895-900 
    Details
    ISSN: 0392-6737
    Keywords: Liquid crystals ; Interface elasticity, viscosity, and viscoelasticity ; ther topics in the structure and nonelectronic properties of surfaces and thin films ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The nematic planar anchoring is usually explained by using simple elastic models: the surface easy axis corresponds to the surface direction that minimizes the excess of nematic elastic energy. When anisotropic rough substrates are used to align nematic liquid crystals, due to the complex surface morphology, usual elastic models are not directly applicable. This paper presents quantitative topographical data of rough substrates, obtained with oblique SiO evaporation under vacuum for nematic planar anchoring. Experimental data are obtained by means of Atomic Force Microscopy and they are used to demonstrate the self-affine nature of these substrates and to relate the nematic anchoring with the anisotropy of the local fractal properties of the substrate itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456740
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    The primary-relaxation process in a supercooled liquid (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 933-937 
    Details
    ISSN: 0392-6737
    Keywords: Phase equilibria, phase transitions, and critical points of specific substances ; Dielectric loss and relaxation ; Amorphous materials ; glasses ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Dielectric and ultrasonic measurements have been performed in the temperature and in the frequency domain to investigate the α (or primary) relaxation in the supercooled state of a «fragile» molecular liquid. This relaxation is strictly connected with the phenomenon of the glass transition and therefore an understanding of the former is a prerequisite for the explanation of the latter. The dynamic susceptibilities relative to these probes have been analysed with the Cole-Davidson function employing (where required) a Vogel-Fulcher-Tamman law to relate the main relaxation time to temperature. The results obtained are consistent with the dynamic behaviour of liquids of high fragility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456744
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    Anomalous dynamics in reaction-diffusion systems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1039-1051 
    Details
    ISSN: 0392-6737
    Keywords: Renormalization-group ; fractal ; and percolation studies of phase transitions ; Fluctuation phenomena ; random processes ; and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We review recent developments in the study of the diffusion reaction systems of the type A+B→C in which the reactants are initially separated. We consider the case where the A and B particles are initially placed uniformly in Euclidean space atx〉0 andx〈0, respectively. We find that whereas ford≥2 the mean-field exponent characterizes the width of the reaction zone, fluctuations are relevant in the one-dimensional system. We also presented analytical and numerical results for the reaction rate on fractals and percolation systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458786
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    Anomalous ionic transport in glassy electrolytes (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1053-1063 
    Details
    ISSN: 0392-6737
    Keywords: Amorphous materials ; glasses ; Theory of diffusion and ionic conduction in solids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss the dynamic structure model recently introduced by Bunde, Maass and Ingram to account for the anomalies of ionic transport in glassy ionic conductors. The model is based on the experimental evidence that ions in glass maintain their distinct local environments. Key features include a site memory effect that introduces vacancies appropriate to each kind of mobile ion, and a mismatch energy that emerges whenever an ion attempts to enter a different kind of site, the combination of both leads to the formation of fluctuating percolation pathways. The connectivity of these pathways determines the ion mobility in the glassy network. The exploration of this model by numerical methods leads i) to a power law relationship between ionic conductivity and cation content (now confirmed in the literature) and ii) to the elucidation of many facets of the mixed alkali effect. It is suggested that the model could form the basis for a comprehensive theory of vitreous electrolytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458787
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    Light scattering studies of Brownian motion in confined geometries (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1111-1118 
    Details
    ISSN: 0392-6737
    Keywords: Propagation and transmission in homogeneous media ; Fluctuation phenomena, random processes, and Brownian motion ; Disperse systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Dynamic light scattering can be a useful tool to determine the confinement of Brownian particles whose motion is restricted to dimensions comparable to the wavelength of the light. The theoretical form of the correlation function of the electric field scattered from such trapped particles has been derived and compared with the signal obtained both in a simulated experiment and in a real experiment where the particles are trapped in a glass wedge. This new result can be of relevance for particles trapped in various media such as a porous (transparent) media, a gel, a suspension of lamellar phases or even a concentrated colloidal suspension where a particle is «trapped» by its neighbours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458791
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    Self-organization in aggregating colloids (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1141-1148 
    Details
    ISSN: 0392-6737
    Keywords: Order-disorder and statistical mechanics of model systems ; Solubility, segregation and mixing ; Colloids ; Fluctuation phenomena, random processes and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The interceluster organization of a two-dimensional colloidal system undergoing diffusion-limited cluster-cluster aggregation is considered. During this process the system evolves into a stationary, scaling state. In this state the organization arises from effective intercluster repulsion due to the mutually exclusive depletion zones surrounding each cluster. It is shown that in the scaling regime the relevant size of the depletion zones is determined by the separation between clusters, rather than the cluster size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458794
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    Aggregated colloids under flow (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1177-1180 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Renormalization-group, fractal, and percolation studies of phase transitions ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have recently reported on a new scaling theory of the rupture of colloid aggregates. The scaling theory is compared with a simulation study of the transient response of sheared 2d aggregates. In this paper we discuss the origins of deviations from the predicted scaling behaviour. We also report some of the steady-state configurations formed post rupture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458798
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    Characterization of non-exponential relaxation via linear ESR (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1217-1221 
    Details
    ISSN: 0392-6737
    Keywords: General theory of resonances and relaxations ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effect of non-exponential relaxation on the lineshape of the linear Electron Spin Resonance spectroscopy is discussed. In the simple case of a paramagnetic system withS=1/2 it is found that the lineshape is mainly affected by the tails of the correlation function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458803
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    Correlation and anticorrelation of fractal aggregates. A model for «spinodal-type» aggregation (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1243-1246 
    Details
    ISSN: 0392-6737
    Keywords: Granular materials: aggregation characteristics (e.g., grain size, particle size distribution, porosity) ; Order-disorder and statistical mechanics of model systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present a simple phenomenological model, based on mass conservation arguments, in order to describe aggregation in dense solutions. It has been previously shown that fordiffusion-limited processes scattered intensity distributions exhibit a peak atq≠0 which grows in time and moves to smaller and smallerq vectors. According to the model, each aggregate is surrounded by a depletion region whose size depends on the aggregation kinetics. The form factor for such a cluster should satisfy local mass conservation and hence exhibit a pronounced depression atq=0. the initial stages of aggregation, when the clusters are far apart, are accounted on the basis of a form factor alone. The model shows good agreement with the data and also explains the experimental evidence that the peak does not appear inreaction-limited conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458807
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    On anomalous diffusion of fractal clusters under certain realistic physical conditions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1265-1270 
    Details
    ISSN: 0392-6737
    Keywords: Renormalization-group, fractal, and percolation studies of phase transitions ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Diffusion of a fractal cluster of dimensiond f in a three-dimensional space is investigated. The diffusion process is assumed to be modelled by a standard parabolic diffusion equation, although a more general case represented by the Fokker-Planck-Kolmogoroff equation is also introduced. The mean-square displacement of the cluster mass centre is analysed and its anomalous behaviour is presented and critically discussed. The results obtained can be applied to describe some effects which may occur during the diffusion-limited cluster-cluster aggregation process, especially when the viscosity of the solvent is changed in time and/or a directed transport of clusters is present in the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458811
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    Scaling behavior in the dynamics of a supercooled Lennard-Jones mixture (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1291-1295 
    Details
    ISSN: 0392-6737
    Keywords: Time-dependent properties ; Computer simulation of static and dynamic behavior ; Molecular dynamics and particle methods ; Glass transitions ; PACS 01.30.Cc ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present the results of a large-scale molecular-dynamics computer simulation of a binary, supercooled Lennard-Jones fluid. At low temperatures and intermediate times the time dependence of the intermediate scattering function is well described by a von Schweidler law. The von Schweidler exponent is independent of temperature and depends only weakly on the type of correlator. For long times the correlation functions show a Kohlrausch behavior with an exponent β that is independent of temperature. This dynamical behavior is in accordance with the mode-coupling theory of supercooled liquids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458815
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    Slow dynamics in glasses (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 939-947 
    Details
    ISSN: 0392-6737
    Keywords: Spin-glass and other random models ; Glass transitions ; PACS 01.30.Cc ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We will review some of the theoretical progresses that have been recently done in the study of slow dynamics of glassy systems: the general techniques used for studying the dynamics in the mean-field approximation and the emergence of a pure dynamical transition in some of these systems. We show how the results obtained for a random Hamiltonian may be also applied to a given Hamiltonian. These two results open the way to a better understanding of the glassy transition in real systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458780
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    A kinetic model for Brownian motion (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 981-991 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Kinetic theory ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The Fokker-Planck equation for the distribution function of a Brownian sphere is derived from the exact hierarchy of kinetic equations for a massive sphere in a bath of smaller spheres, using a multiple-time-scale analysis. Our earlier derivation is specialized to the limiting cases where the bath is either an ideal or Boltzmann gas. The resulting simplifications allow more physical insight, and lead to explicit expressions for the friction coefficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458783
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    Geometry of bicontinuous microemulsions as revealed by SANS and simulations (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1357-1366 
    Details
    ISSN: 0392-6737
    Keywords: Fluid surfaces and fluid-fluid interfaces ; Neutron scattering techniques (including small-angle scattering) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Water-octane-C10E4 microemulsions in both the isotropic and lamellar phases were measured using small-angle neutron scattering. Varying the scattering length density of both the water and oil through hydrogen-deuterium substitution enabled us to isolate the scattering contributions of the surfactant monolayers and the water-surfactant and oil-surfactant interfaces. Analyses of the resulting scattering patterns allow us to directly determine the small mean curvature of the surfactant film as a function of temperature and correlate this quantity with the overall phase behavior. A simulation using a Gaussian random field yields the three-dimensional structure of the bicontinuous microemulsion having a surfactant monolayer with zero mean curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462020
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    Mucin: Aggregation and colloidal interactions of relevance to some biomedical problems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1411-1418 
    Details
    ISSN: 0392-6737
    Keywords: Physical chemistry of solutions of biological macromolecules ; Colloids ; Gels and sols ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Mucus is the viscoelastic secretion that lines, most epithelial surfaces forming a protective, lubricating barrier. The viscoelastic properties of mucus arise from mucin, a glycoprotein of molecular weight ranging from 2–10 million. In this paper we address two problems where the aggregation and interactions of mucin with colloidal particles is of physiological relevance. The first deals with gastric mucin and the question of the mechanisms that prevent the stomach from digesting itself. Using dynamic light scattering techniques we show that solutions of gastric mucin aggregate belowpH 4. Very large aggregates with 100-fold slower diffusion constants than the mucin monomer are observed atpH 2. Viscosity measurements indicate that mucin will eventually gel at lowpH, thus acting as a diffusional, barrier and protecting the stomach. The second problem is concerned with the role of mucin in the nucleation of cholesterol crystals which lead to gallstone formation. Using dynamic light scattering we have shown that mucin at relatively low concentrations (4 mg/ml) promotes the fusion of phospholipid + cholesterol vesicles. The time evolution of the fusion process was measured. No changes in the aggregation state of the gallbladder mucin were observed during the fusion process, suggesting that this phenomenon is related to physico-chemical interactions between the polymer (mucin) and the colloidal particle (vesicle).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462025
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    Scaling in the aggregation behaviour of zinc-free insulin studied by small-angle neutron scattering (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1447-1455 
    Details
    ISSN: 0392-6737
    Keywords: Disperse systems ; Molecular biophysics ; Physical chemistry of solutions of biological macromolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The aggregation behaviour of zinc-free insulin has been studied by small-angle neutron scattering as a function of protein concentration,pH, and ionic strength of the solution. The distance distribution functions for the 12 samples have been obtained by indirect Fourier transformation. The weight-averaged molecular mass and thez-averaged radius of gyration were determined. Both quantities vary systematically with the experimental conditions. They increase with decreasingpH and with increasing ionic strength. The radius of gyration scales as a power law of the weight-average mass with the exponent 0.44. A similar scaling is found for a set of oligomers structures based on the crystal structure of zinc-free insulin. The mass distribution between the oligomers was determined by a model based on these oligomers. The results from this model and the Fourier transformations have been compared to an equilibrium model recently introduced by Kadimaet al. The model takes into account the variation of the effective charge of the monomer withpH and ionic strength. The neutron scattering results agree well with the predictions of the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462029
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  • 70
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    Structure in protein solution changing thepH (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1493-1498 
    Details
    ISSN: 0392-6737
    Keywords: Physical chemistry of solutions of biological macromolecules ; Macromolecular and polymer solutions (solubility, swelling, etc.), polymer melts ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this paper we present a small-angle neutron scattering measurement on concentrated aqueous solutions of lysozyme. The ranges for thepH and for the ionic strength of the solutions are chosen in order to match the physiological values at which the enzymatic activity of the protein is at his maximum. The net charge has been determined by separate tritation experiment. The form factor and the structure factor were extracted from the experimental data. The structure factor is quantitatively reproduced within a hard-sphere model with an attractive Yukawa-tail potential. The importance in this kind of systems of the attractive interaction, even at far from zero net charge is highlighted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462034
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  • 71
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    SANS and light scattering of nonylammonium chloride micelles in aqueous solutions of sodium chloride (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1515-1522 
    Details
    ISSN: 0392-6737
    Keywords: Colloids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Aqueous solutions of nonylammonium chloride (NAC) containing sodium chloride were studied by using light scattering and small-angle neutron scattering (SANS) techniques. It was found that the aggregation number of NAC is independent of the surfactant concentration and increases smoothly with increasing the ionic strength. Micelles of NAC in D2O with [NaCl]=0.3422 have prolate ellipsoidal shape and their average aggregation number is greater than that found in H2O at the same ionic strength. A possible explanation of this difference may arise from a solvent effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462036
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  • 72
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    Interactions of metal ions with monolayers and with Langmuir-Blodgett films (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1579-1584 
    Details
    ISSN: 0392-6737
    Keywords: Fluid surfaces and fluid-fluid interfaces ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Oriented systems such as monolayers and Langmuir-Blodgett multilayers constitute supramolecular structures appropriate for ion detection. In fact, they are sensitive to small quantities of ions since they have specifically oriented ligand head groups that can easily combine with the ions to be detected in solution. We investigated monolayers of dioctadecyldithiocarbamate (DODTC) specificially synthesized and we studied the interactions of the monolayers with transition metal ions such as Ni2+ dissolved in the subphase. The spreading isotherms, the surface potential-area isotherms and the spectroscopic measurements (UV-Vis absorption and ESCA spectroscopy) show that the metal ions can combine with the DODTC monolayers. The present findings show that it is possible to employ these systems to build chemical sensors for transition metal ions
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462045
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  • 73
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    Structural variations induced by magnesium ions and temperature in the large ribosomal subunit from the extreme thermophileSulfolobus solfataricus (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1573-1577 
    Details
    ISSN: 0392-6737
    Keywords: Molecular interactions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Small-angle neutron scattering (SANS) measurements on the large 50S ribosomal subunit of the extreme thermophile archaebacteriumSulfolobus solfataricus are presented. The structural effects induced by magnesium ions and temperature are investigated. Supramolecular aggregation was present in all the investigated conditions. Removal of magnesium ions and increase of temperature reduce the intensity of the scattering atQ=0. This reduction is discussed looking at the Fourier inversion of the scattering intensity, which includes both inter- and intra-particle contributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462044
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  • 74
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    Sound propagation and viscosity in water short-chain amphiphiles solutions, evidence of percolation phenomena (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1619-1625 
    Details
    ISSN: 0392-6737
    Keywords: Brillouin and Rayleigh scattering ; Ultrasonic relaxation processes in gases, liquids, and solids ; Acoustical properties of liquids ; Order-disorder and statistical mechanics of model systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A water/butoxyethanol solution has been investigated by means of several techniques (viscosity, ultrasound and hypersound) as a function of concentration and temperature. The butoxyethanol molar fraction range investigated was situated between 0.015 and 0.09, while temperature ranged between −10°C and +45°C. We observed the building-up of large structures lowering the temperature, in particular below +15°C. All data coming from different techniques seem to confirm such a picture and indicate that this aggregation phenomenon is a percolation-like process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462050
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  • 75
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    Modulation of HTSC characteristics induced by proton irradiation (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1933-1939 
    Details
    ISSN: 0392-6737
    Keywords: Flux pinning, flux creep, and flux-line lattice dynamics ; Critical currents ; Material effects onT c, κ, critical currents (including impurities, ion implantation, etc.) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Bulk slabs of sintered YBCO were irradiated with monoenergetic protons at different energies (3.5 and 6.5 MeV) and different fluences, ranging from 1.8·1016 to 8.6·1016 p/cm2. The effects on intergrain critical currents of protons crossing the sample and the effects of protons implanting in the specimen, has been studied by means of a.c. susceptibility characterizations. D.c. hysteresis cycles were measured in low fields in order to investigate the modifications in the intergrain critical current density due to proton implantation. The main result is the evidence that the intergrainJ c response to the applied field can be modulated by means of the proton irradiation. Resistive measurements were also performed in order to investigate the complex transport phenomena in polycrystalline materials. Irradiation-induced effects on both superconducting- and normal-state resistivity are studied. The addition of extrinsic defects can lead to enhanced transport properties, emerging especially when a magnetic field is applied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462196
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  • 76
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    Generation of subharmonic shapiro steps in ladder arrays of overdamped superconducting junctions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2053-2059 
    Details
    ISSN: 0392-6737
    Keywords: Proximity effects tunneling phenomena, and Josephson effects ; Amorphous, highly disordered, and granular superconductors ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Subharmonic Shapiro Steps (SSS) are usually observed in 2D arrays of superconducting junctions when their dynamical states are perturbed by factors like disorder, frustration, current inhomogeneities and so on. In order to clarify the conditions under which SSS can be generated we decided to investigate arrays of very simple shape like the ladder ones. In particular we have studied the influence of the frustration (i.e. of an external magnetic field) on the time evolution of the vortex configuration and the commensurability of the latter with the geometry and the dimension of the array. Ladders, parallel or perpendicular to the bias current, turn out to be systems where the properties of the square arrays can be suitably tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471866
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  • 77
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    High-T c superconducting magnetic bearings for rotation-based devices (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2061-2065 
    Details
    ISSN: 0392-6737
    Keywords: Superconducting materials ; Superconducting magnets and magnetic levitation devices ; superconducting cables and conductors ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A Modified-Melt-Powder-Melt-Growth (MMPMG) technique has been developed for the preparation of melt-textured Y-Ba−Cu−O pellets. To test their performances, the samples were characterized with respect to their microstructure, pinning strength and interaction force with permanent magnets. A superconducting magnetic bearing was built and integrated in a levitating flywheel system for energy storage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471867
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  • 78
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    Key differences in material requirement and technology for large electromagnetic shields, with respect to other large-scale applications of high-T c superconductors (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2079-2086 
    Details
    ISSN: 0392-6737
    Keywords: Other low-power superconducting devices ; Superconducting films ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The main specifications for the use of high-T c superconductors in the realization of extended surfaces to be used for the fabrication of electromagnetic shields are illustrated. In particular, the differences are stressed between the specifications required by this application and those required by other large-scale applications, namely electrotechnical machinery and magnetic levitation. From these premises, the approach to the fabrication technology of shields is briefly discussed, which also shows important differences with respect to other applications. The analysis is supported by examples of the solutions which are being developed and adopted in the world and in Torino.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471870
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  • 79
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    Influence of a presintering treatment on melt-textured Y−Ba−Cu−O growth (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2107-2111 
    Details
    ISSN: 0392-6737
    Keywords: Y-based compounds ; Granular, melt-textured and amorphous superconductors ; powders ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The influence of a presintering treatment on Y-Ba-Cu-O prepared by a modified MPMG process was investigated. The sinterization, reducing the material porosity, was found to enhance the homogeneity of the Y2BaCuO5 (Y-211) particles distribution during the partial melting at 1100°C. As a consequence, the melttextured YBa2Cu3O7−x (Y-123) grows more uniformly producing oriented domain up to 3cm in size. Microstructural and diffractometrical analyses were performed on samples quenched at different stages during the thermal treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471874
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  • 80
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    Polaron formation in superconducting cuprates: Evidence from the infrared reflectivity (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1735-1741 
    Details
    ISSN: 0392-6737
    Keywords: Response to electromagnetic fields ; nuclear magnetic resonance ; ultrasonic attenuation ; Scattering by phonons, magnons, and other nonlocalized excitations ; Superconducting perovskites and related structures ; Refractive index, reflectivity, critical angle, dispersive power ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Evidence of polaron formation in superconducting cuprates is provided by infrared reflectivity spectra. In the Nd−Ce−Cu−O withT c≈20 K, polaron formation corresponds to vibrational local modes in the far-infrared and to a band in the mid-infrared built up through overtones and combination bands of these modes. A comparison with infrared spectra taken by different groups on Y−Ba−Cu−O, and Tl−Sr−Ca−Cu−O suggests that polarons survive in the highest-T c superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462168
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  • 81
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    Substitutions in YBa2Cu3O7−y and their influence on the magnetic penetration depth, its anisotropy andT c: Muon spin rotation (μSR) (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1755-1760 
    Details
    ISSN: 0392-6737
    Keywords: La-based compounds ; Tl-based compounds ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Deterioration of the superconducting properties of HTC materials, induced by different substitutions, offers a key towards the understanding of the basic HTC interactions. Similar effects are obtained either by doping of layers of the perovskite not directly involved in the superconducting mechanism, or by direct substitution of the copper itself. However, this apparent similarity is misleading. In YBCO, for instance, in the first case the oxygen content or the substitution of Y with Pr4+ appear to control essentially the carrier density,n, while in the second case the direct substitution of Cu in the bilayers by Zn or Ni affects more extensively the overall electronic structure of the material. A sensitive experimental tool, such as μSR, detects correspondingly different behaviours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462170
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    An overview on recent NMR-NQR studies of high-T c superconductors and of their precursors AF (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1743-1753 
    Details
    ISSN: 0392-6737
    Keywords: Superconducting materials (excluding high-T c cuprates) ; Nuclear magnetic resonance and relaxation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary An overview on some works recently carried out by means of pulsed NMR-NQR experiments is given. The choice of the arguments is aimed at providing a flash on the topics and phenomena most tipically studied with the afore-mentioned approach: from the antiferromagnets (AF) precursors of high-temperature superconductors upon charge and spin doping (such as CuO-doped Li, La2CuO4-doped Sr and Zn) to the doping regime leading to superconductivity in LASCO and YBCO with the related issues involving the comparison with the Fermi-liquid behaviour, the possible opening of a pseudo-spin-gap aboveT c and the anisotropy and field effect ratios belowT c, the latter also in relation to thes-wave ord-wave orbital coupling. Finally, the topic of the motions of the flux lines in YBCO is addressed, in particular by discussing some experiments based on spin-echo dephasing due to thermal excitations and in the presence of d.c. currents and pulsed magnetic fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462169
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  • 83
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    Hole doping dependence of the effective exchange in La2−δSrδCuO4 (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1769-1776 
    Details
    ISSN: 0392-6737
    Keywords: Insulator-superconductor transitions ; unconventional mechanisms of high-T c superconductivity ; Exchange and superexchange interactions ; Narrow-band systems ; heavy-fermion metals ; intermediate-valence solids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We provide a microscopic modelling of the strong variation of the effective exchange interactionJ eff between Cu2+ spins as a function of hole doping δ in La2-δSrδCuO4, as derived from complementary Raman scattering and paramagnetic susceptibility data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462172
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  • 84
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    Dynamical mechanical measurements in dry PHEMA and its hydrogels (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 849-854 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Anelasticity, internal friction, and mechanical resonances ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The elastic modulus and tg δ of poly(2-hydroxyethyl methacrylate) (PHEMA) and its hydrogels have been measured over, the frequency range 0.3–30Hz and the temperature range 120–450 K. The mechanical spectra reveal the presence of a low-temperature γ-relaxation plus a shoulder (β-relaxation) that merges into the α-relaxation. The absorbed water lowers the temperature and rises the hight of the lowest temperature peak (the γ-peak for dry PHEMA) while lowering both temperature and height of the α-peak. This behaviour is interpreted in terms of hydrogen-bonding effects between water and polymer which weaken the intra- and/or interchain interactions. Furthermore, the calorimetric analysis in dry polymer is consistent with the mechanical behaviour in the higher-temeprature region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456734
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    Fluctuation effects on microphase separation in random copolymers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 879-882 
    Details
    ISSN: 0392-6737
    Keywords: Order-disorder and statistical mechanics of model systems ; Multicritical points ; Macromolecules and polymer molecules: Constitution (chains and sequences) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We study random copolymers consisting of two kinds of monomers with attraction between similar kinds. The mean-field analysis of this system indicates a continuous phase transition into a phase with periodic microdomain structure. It is shown that the inverse of the renormalized propagator has a minimum at non-zero wave numbers. Consequently, there is an anomalously large contribution of fluctuations that make the disordered phase locally stable. However, below a certain temperature, the ordered phase is shown to be locally stable and a weak first-order transition is possible, with qualitative differences from the weak crystallization theory developed by Brazovskii. These differences are due to the peculiar form of the fourth-order vertex of the effective Hamiltonian for the system. We calculated the temperature region for the validity of the mean-field estimates of the amplitude and the scale of microphase separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456738
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    Structural relaxation and anharmonicity in polymer electrolytes: Effect of the thermal history (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 911-921 
    Details
    ISSN: 0392-6737
    Keywords: Polymers, elastomers, and plastics ; Anelasticity, internal friction, and mechanical resonances ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effects of the storage at room temperature of PEO-KSCN polymer electrolytes have been studied by differential scanning calorimetry (DSC) and dynamical mechanical analysis. It has been revealed that, over the explored time interval, the annealing causes small variations in the anharmonic and relaxation properties of the samples, which are to be ascribed to changes in the relative amount of the phases building up the structure. The elastic and anelastic characteristics show a well-defined dependence on the degree of crystallinity of the polymer, which grows slightly with increasing annealing time. The application of a simplified version of a quasi-harmonic model and of the Kolrausch-Williams-Watts stretched exponential function permits to describe the temperature behaviour of the elastic modulusE′ and to obtain an anharmonicity parameter characterizing the polymeric system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456742
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    Multiblock copolymers at interfaces (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 641-652 
    Details
    ISSN: 0392-6737
    Keywords: Macromolecular and polymer solutions (solubility, swelling, etc.) ; polymer melts ; Thermodynamics of surfaces and interfaces ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We consider the configurations and the various regimes when an alternating, symmetric, multiblock copolymer made of successive sequences of A and B monomers with equal lengthZ is at the interface between two immiscible solvents that are respectively good for one of the sequences and poor for the other one. We find two semi-dilute regimes, when the copolymers overlap. For monomer concentrations belowГ **, we find a first range where the thickness of the copolymers is constant and equal to the radius of a sequence. For concentrations larger thanГ **, a second regime appears, where the seqeunces stretch our and adopt a conformation similar to what was reported for grafted polymers. Finally at a concentrationГ sat, the interface is completely saturated, and the copolymers form micelles in the bulk: it becomes energetically more favourable to have copolymers in the bulk than at interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456708
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  • 88
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    Frustrated percolation, spin glasses and glasses (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1027-1037 
    Details
    ISSN: 0392-6737
    Keywords: Glass transitions ; Renormalization-group ,fractal, and percolation studies of phase transitions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The static and dynamic properties of the frustrated percolation model are investigated. This model, which contains frustration as an essential ingredient, exhibits two transitions: a percolation transition at a temperatureT p with critical exponents of the ferromagnetic (s=1/2)-state Potts model, and a second transition at a lower temperatureT g in the same universality class of the Ising spin glass model. AboveT p the time-dependent autocorrelation function is characterized by a single exponential, while forT p〉T〉T g preliminary numerical results show a broad shoulder or plateau typical of a structural glass transition. BelowT g the system is in glassy state with an infinitely long relaxation time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458785
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    Chaos, complexity and morphogenesis: Optical-pattern formation and recognition (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1065-1089 
    Details
    ISSN: 0392-6737
    Keywords: Optical chaos ; Classical mechanics of continuous media: general methematical aspects ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In 1952 A. Turing introduced the concept of chemical morphogenesis. A medium with at least two interacting and diffusing components (activator and inhibitor) can be subjected to spontaneous pattern formation, with a scale length independent of the boundary conditions, and thus maintained even in the infinite volume limit. This is at variance with pattern formation in fluids (as,e.g., Rayleigh-Benard and Faraday instabilities) where the size is imposed by the boundary geometry. In non-linear optics, patterns emerge from the coupling of a diffractive equation describing electromagnetic propagation with a diffusion equation describing the local modification of the polarizability in a medium. As we adjust an extensive parameter (the so-called Fresnel numberF) corresponding to the optical aspect ratio, we observe a transition from a regime dominated by the boundary constraints to a Turing-type regime dominated by the bulk parameter. This is equivalent to saying that the preminent role is due to the diffractive equation in one case and to the diffusive one in the other. Morphogenesis for lowF arises from the non-linear competition among a small number of degrees of freedom, giving rise to a space-uniform excitation with a low-dimensional dynamics. This gives rise to the different scenarios of chaos. Their properties have been explored in the past decade. In the large-F case, the space-time instabilities rapidly evolve toward complex patterns, not reducible to a few indicators. In the case of two-dimensional fields, global characterization is achieved via the statistics of the topological defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458788
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  • 90
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    Fractal time and space in complex fluids (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1119-1125 
    Details
    ISSN: 0392-6737
    Keywords: Dielectric loss and relaxation ; Fluctuation phenomena, random processes, and Brownian motion ; Turbulent diffusion ; Chaos ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We investigate transport in complex fluids including glassy materials and turbulent flows. We focus on regimes where fractal hierarchical scaling exists in time, space or both simultaneously.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458792
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  • 91
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    Cluster-cluster correlation during irreversible diffusion-limited aggregation (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1159-1169 
    Details
    ISSN: 0392-6737
    Keywords: Order-disorder and statistical mechanics of model systems ; Fluctuation phenomena, random processes, and Brownian motion ; Colloids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this paper, we discuss the evolution of the scattered intensityI(q) during irreversible diffusion-limited cluster-cluster aggregation. We analyse twodimensional simulations and interpret the results within the framework of a recently proposed theoretical approach. The theory describes the correlation among different clusters which develops during the irreversible aggregation process. The model is based on two coupled differential equations, controlling the growth of the average cluster mass and the time dependence of the probability of finding pairs of clusters as a function of their distance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458796
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  • 92
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    Some considerations on error influence in the evolution of dynamical systems (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1305-1309 
    Details
    ISSN: 0392-6737
    Keywords: Systems displaying chaotic behaviour ; Theory and models of chaotic systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The finiteness of observational and computational precision suggests that not only the initial condition (as usually assumed) but also the evolution law of dynamical systems is affected by unavoidable uncertainties. The consequences are explored by suitably generalizing the concept of the Lyapunov exponent. The relation between the results obtained and the shadowing problem is discussed as well as some implications concerning the Kolmogorov entropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458817
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  • 93
    Electronic Resource
    Electronic Resource
    Analytical and numerical solutions of some integral equations in radiation transport theory (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1325-1338 
    Details
    ISSN: 0392-6737
    Keywords: Free-electron lasers ; Integral equations ; Functional analysis ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss some mathematical and computational problems relevant to the solutions of both linear and non-linear integral equations arising in radiation transport. By means of a functional-operator approach, analytic solutions for the FEL (Free Electron Laser) integral equations are found in terms of Bessel-Clifford functions. As for applications of this method to non-linear equations, the same technique allows us to obtain an efficient yet simple algorithm for the numerical solution of the Ambartsumian-ChandrasekharH-equation corresponding to a Neumann-series expansion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458819
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  • 94
    Electronic Resource
    Electronic Resource
    Rheological behaviour of worm-like micelles: Effect of electrostatic interactions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1401-1410 
    Details
    ISSN: 0392-6737
    Keywords: Mechanical properties of liquids ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Both linear and non-linear viscoelasticity experiments have been performed in semi-dilute micellar aqueous solutions of ethanediyl-α,ω-bis (dodecylmethylammonium bromide) as a function of solution chloride (NaCl) concentration. The results suggest that both linear and non-linear properties are affected by the electrostatic interactions. In particular, the plateau modulusG′∞ and the ratioσ m/G′∞, whereσ m represents the plateau value in a stress-shear rate experiment, are enhanced as the electrostatic interactions are screened by addition of salt. The zero-shear viscosity is lowered upon addition of NaCl, due likely to an exchange of the Cl− ions with the Br− counterions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462024
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  • 95
    Electronic Resource
    Electronic Resource
    Transport properties of long monofilamentary Bi(2223) tapes (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 2073-2077 
    Details
    ISSN: 0392-6737
    Keywords: Superconducting magnets and magnetic levitation devices ; superconducting cables and conductors ; Critical currents ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Monofilamentary Bi(2223) tapes withJ c(77 K, 0 tesla) up to 30 000 A/cm2 have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the oxide density and to reduce sausaging effects on the oxide thickness. The transport properties of these tapes have been studied in a wide range of temperature (4.2K-T c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K fields of 0.5 T and 1 T parallel to the tape surface are 10 000 A/cm2 and 5400 A/cm2, respectively. At 4.2 K theJ c value decreases from 1.6·105 A/cm2 at 0 T to 6·104 A/cm2 at 15 T. At fields higher than 15 tesla a very low field dependence ofJ c has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes of good quality (J c (77 K, 0 T)〉20000 A/cm2), theJ c distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the latter exhibiting much higherJ c (46000 A/cm2) than in the centre (18000 A/cm2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471869
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  • 96
    Electronic Resource
    Electronic Resource
    Influence of charge distribution on the conformation of neutral polyampholytes (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 669-674 
    Details
    ISSN: 0392-6737
    Keywords: Polymer reactions and polymerization ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Two polyampholyte copolymers based on sodium-2-acrylamido-2-methylsulfonate (NaAMPS) and methacryloyloxyethyltrimethylammonium chloride (MADQUAT) have been prepared either in homogeneous solution or by an inverse microemulsion polymerization technique. The copolymer microstructure was shown to depend on the method of preparation. The microemulsion polymerization yields copolymers with a monomer sequence distribution not far from random while those obtained by polymerization in solution have a strong tendency to alternation. The aqueous-solution properties of the two samples have been investigated by viscometry. The results show that the charge distribution along the copolymer chain affects considerably its conformation, in good agreement with recent theoretical studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456711
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  • 97
    Electronic Resource
    Electronic Resource
    Self-association behaviour of alcohols in diluted aqueous solutions (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1499-1514 
    Details
    ISSN: 0392-6737
    Keywords: Studies of specific liquid structures ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Our recent studies related to the properties of alcohol/water mixtures show the occurrence of some kind of molecular aggregation in the water-rich region of composition beyond a threshold alcohol concentrationx 2 *. The observed behaviour suggests that forx 2〈x 2 * the alcohol molecules are essentially dispersed and surrounded by «water cages» where the short-range order and microdynamic of water molecules are changed with respect to those of pure water. Alcohol molecules are in mutual contact at higher concentration only when almost all water is involved in hydration shells of alcohol molecules. The structural transition atx 2 * resembles, for some aspect, the micellization process. The main results of these investigations are reviewed and discussed in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462035
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  • 98
    Electronic Resource
    Electronic Resource
    Influence of a hydrophilic spacer on the structure of a phospholipid monolayer (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1545-1550 
    Details
    ISSN: 0392-6737
    Keywords: Thin films: growth, structure, epitaxy, and nonelectronic properties ; Structure and Morphology, thickness ; Structure, bonding, stereochemistry, and isomerism of biomolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present the results of thermodynamical and X-ray grazing incidence diffraction experiments performed on Langmuir monolayers of ether lipids with hydrophilic spacers between the glycerol backbone and the phosphatidylcholine head group: DHPC, DH-E01-PC, and DH-E02-PC. As a spacer the oxy-ethylene group is used, which is a typical hydrophilic unit of non-ionic tensides. It turns out that the introduction of the hydrophilic spacers leads to a fluidization of the monolayer and reduces the tilt angle of the chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462040
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  • 99
    Electronic Resource
    Electronic Resource
    A comparison of DMPC membranes mixed with melittin or C12E5 (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1585-1594 
    Details
    ISSN: 0392-6737
    Keywords: Molecular biophysics ; Defects in liquid crystals ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effect of adding the defect-forming molecules melittin and C12E5 to DMPC membranes has been studied and the corresponding phase diagrams established. Light, X-ray and neutron small-angle scattering have been used to characterize the mixed membranes. Both systems show a melting of the lamellar Lα into an isotropic phase upon addition of the second membrane constituent. The molar ratio, where the melting occurs is the same in concentrated and dilute samples. For the DMPC/C12E5 system not only membrane composition, but also temperature can be used to induce a transition from an isotropic to a lamellar phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462046
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  • 100
    Electronic Resource
    Electronic Resource
    Structure of water-in-oil microemulsions of AOT by infrared spectroscopy (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1601-1611 
    Details
    ISSN: 0392-6737
    Keywords: Electron correlation calculations for atoms and molecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The structure of water in water/AOT/n-heptane reverse micelles has been studied as a function of the [H2O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm−1 range. The results show that the IR spectra can be expressed as a sum of contributions from bound- and bulk-like water. The fraction of water in the two «regions» within the water pool was evaluated as a function ofW. The «bound» water region seems to hold 3.5 water molecules (corresponding to 7 O−H oscillators) per AOT molecule and its formation is nearly complete atW〉6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462048
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