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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 866-869 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The photoluminescence characteristics (peak intensity, peak wavelength and full width at half maximum of the emission band) of p-type porous silicon have been measured as a function of the etching time. Experimental data are discussed in the light of a pore nucleation and growth mechanism recently proposed by the authors. The steps of the formation of the porous layer are clearly apparent in the photoluminescence characteristic evolution. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1324-1330 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An experimental setup to measure "in situ" the amount of H that a Pd cathode absorbs during the electrolysis of aqueous solutions has been built up and tested. The setup implements a volumetric technique, i.e., it involves the measurement of the rate of H2 generation by the cathode. The pros and cons of this type of techniques against other procedures, the measurement of the variation of the cathode electrical resistance or of its dilation during the electrolysis, are briefly discussed. A careful analysis of the setup error sources is done by using two non-H-absorbing Pt electrodes. Neither any significant recombination of the electrolysis gases (H2 and O2), nor any deviation of a 100% electrolysis efficiency have been observed. It has been found that gas (air) release and H2 and O2 absorption by the solution, in the first stage of the electrolysis, seriously affect the measurement of the rate of H absorption by the cathode. Several improvements of the experimental installation and an operation protocol of saturation of H2 and O2 and of exhaustion of air in the solution, before starting the electrolysis, allowed overcoming those limitations. Finally, we present the results obtained in the measurement of the rate of H uptake by a Pd cathode during electrolysis. The reliability of the measurement has been confirmed by electrochemically deloading the Pd cathode. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3274-3278 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed numerical calculations for the random field (H) ferromagnetic Ising model in two dimensions. To study equilibrium properties, we have used the transfer matrix technique, thus bypassing serious equilibration problems which would arise in a Monte Carlo calculation for random systems. We have calculated the structure factor S vs H. Our results are consistent with S∼exp(c/H2) as predicted by theories which yield a lower critical dimension dc=2, whereas the expected behavior for dc=3, S∼H−4, is inconsistent with our results. To study dynamic properties we have used Monte Carlo simulations to determine the equilibration of Ising systems in random fields at low temperatures T following a quench from high T. The rate at which domains grow with time is determined as a function of the random field strength H, the linear dimension of the system L and temperature T. Domains are found to grow logarithmically with time. For small systems, L≤L*=(4J/H)2, the exponents a and b of the exponential equilibration time τ∼exp[(H/T)aLb] are found to be a(approximately-equal-to)1.0 and b(approximately-equal-to)0.5, in agreement with recent calculations based on approximate interface models. We tested the L and H/T dependence of τ in 3D and found a(approximately-equal-to)1.0, b(approximately-equal-to)0.5 also in 3D.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6940-6942 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A theory of the magnetic relaxation of a large spin (S=10) having a large uniaxial magnetocrystalline anisotropy is outlined. The theory explains magnetic relaxation observed in Mn12 acetate. The joint action of local fields and a fourth order distortion of the magnetocrystalline anisotropy is necessary to account for the tunneling that is observed, between the m=−4 and m=4 unperturbed states. Even in resonance, tunneling takes place mainly incoherently in Mn12 acetate. It proceeds through the lowest energy state doublet which is not blocked by longitudinal local fields. The relaxation rate Γ has been calculated using a master equation. The model gives magnetization hysteresis loops and ac magnetic susceptibility curves which are in quantitative agreement with experimental results. For temperatures below 0.5 K approximately, nonresonant tunneling from the ground state becomes the dominant relaxation mechanism. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1432-0819
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract A dynamic model for the activity of Poas Volcano, Costa Rica, is proposed. Data collected during a three-year period show that the volcanic processes occur within a small hydrothermal system. Heat is supplied by a magma body in the conduit and is transferred to the surface by fluid convection. Within a given volume of rock, pore pressure builds up due to the upward motion of fluids and the increase in vapor pressure when the temperature rises above the boiling point. Ultimately, the system becomes unstable when the pore pressure overcomes the total pressure. This leads to the assumption that the kinetic and thermal energies are proportional to the depth at which the mechanical equilibrium is disturbed. Laboratory experiments were performed by heating samples of the crater lake deposits. The preliminary results of these experiments show significant analogies with the low-energy activity of the volcano. Following this model we estimated that a phreatic explosion which reaches 200 m in height (comparable to the one observed by Francis et al. in 1978) originates at a depth of 70 m and a temperature of 180° C; these values agree with those reported in the literature. In addition, “magmatic” sulfur, which partitions into the rising hydrothermal fluids, reacts at lower temperature and higher $$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{f} O_2$$ to produce pockets of liquid sulfur in the conduit deposits and the lava dome. These pockets are subsequently erupted forming the pyroclastic sulfur.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 16 (1997), S. 1512-1515 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 17 (1997), S. 153-155 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 7 (1996), S. 55-60 
    ISSN: 1573-482X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Notizen: Abstract A PZT 53/47 was obtained by a modified chemical route. Small-particle-size powders were allowed to obtain high solid content, non-aqueous slips with Newtonian behaviour. The use of both the tape-casting technique and the common multilayer ceramic fabrication process led to a high-density multilayer ceramic body without cracks or delaminations, and a homogeneous microstructure. The architecture of multilayer piezoelectrics has an important effect on the clamping of resonance modes, particularly on planar modes, by modifying the nature of the electrode and the effect of the polarization procedure. This fact is corroborated by the dielectric and piezoelectric properties measured.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 18 (1999), S. 1297-1299 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 31 (1996), S. 949-955 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Submicronic powders of Bi4Ti3O12 with different morphologies were prepared by both the oxalate coprecipitation and the conventional mixing oxides methods. Compacts of the two calcined powders were sintered at 850–1100 °C in air, and the densification process was studied by non-isothermal and dilatometric experiments. A rapid densification (〉 97% theoretical density) below 875 °C took place in the Bi4Ti3O12 oxalate powder which was attributed to an extremely uniform pore-size distribution in the green compact. The possible formation of a transient liquid which promotes densification also was taken into account. The development of plate-like morphology in the conventional Bi4Ti3O12 powder, broad pore-size distribution, and the plate-like colony formation, hindered rapid densification of the green compacts at low temperature. Microstructural development was studied; preliminary dielectric and electrical results are also reported.
    Materialart: Digitale Medien
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