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  • Artikel: DFG Deutsche Nationallizenzen  (174)
  • 1
    Digitale Medien
    Digitale Medien
    Quantum dynamical calculations in clusters of spin 1/2 particles: Resonant coherent quantum tunneling on the magnetization reversal : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6110-6112 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigate the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few (N) spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian at T=0. The temporal evolution is calculated by a numerically exact solution of the time-dependent Schrödinger equation, and the mean value in time of each spin component is computed as a function of the magnetic field. The correlation function and the spectrum are analyzed in terms of the macroscopic quantum coherence. Our calculations demonstrate that this model for small (N〈11) magnetic particles exhibit collective tunneling of the magnetization only for some specific resonant values of the applied magnetic field, at variance with the Stoner–Wohlfarth model. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362103
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  • 2
    Digitale Medien
    Digitale Medien
    Nonhomogeneous magnetization reversal in 2D Ising clusters : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6019-6021 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed Monte Carlo simulations on 2D circular Ising clusters, studying the distribution of the magnetization within the cluster as well as the magnetization reversal process when an applied external field is suddenly changed. We have shown that for highly anisotropic systems (the Ising-like limit), the magnetization reversal process is not uniform in a wide range of temperatures. Spins having a lower coordination at cluster edges drive the reversal process, acting as nucleation centers. We have found that there is a connection between the roughness transition temperature and the differences in the time evolution patterns of the magnetization. Our simulations agree with experimental results on magnetization reversal of single domain particles. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362139
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  • 3
    Digitale Medien
    Digitale Medien
    O/W emulsion and W/O/W multiple emulsion: physical characterization and skin pharmacokinetic comparison in the delivery process of caffeine (1998)
    Dordrecht, The Netherlands : Kluwer Academic Publishers
    International journal of cosmetic science 20 (1998), S. 0 
    Details
    ISSN: 1468-2494
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: The aim of this study was to compare the characteristics of an O/W emulsion and a W/O/W emulsion, formulated with similar ingredients. The physical properties of these two types of vehicles were characterized first. Using three types of in vitro models, human skin biopsies, nitrate acetate cellulose membranes and human reconstituted epidermis, the delivery potential of each vehicle for one hydrophilic drug, caffeine, was compared. The assessment of physical parameters, such as particle size, conductivity and rheological behavior enabled the nature of the test emulsions to be clearly identified. Clear differences were observed in the ability of each type of emulsion to deliver caffeine. Whatever the nature of the membrane used for the pharmacokinetic study, the absorption of caffeine was roughly two-fold lower (2.6 for human skin) when the W/O/W multiple emulsion was used as the vehicle. The concomitant determination of physical and kinetic properties of these two test emulsions allowed the W/O/W multiple emulsion and a simple O/W emulsion to be clearly differentiated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1467-2494.1998.181621.x
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  • 4
    Digitale Medien
    Digitale Medien
    Characterization of the barrier function in a reconstituted human epidermis cultivated in chemically defined medium (2002)
    Oxford, UK : Blackwell Science, Ltd
    International journal of cosmetic science 24 (2002), S. 0 
    Details
    ISSN: 1468-2494
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: The aim of the study was to characterize and assess the maturation process of the barrier function in a reconstituted human epidermis (REp) cultivated in a chemically defined medium. For this purpose histo-morphological analysis, percutaneous absorption studies and non-invasive measurements were performed. In order to understand the time course of the barrier development, REp cultivated from the same pool of normal human keratinocytes were harvested and measured after several increasing periods of exposure at the air–liquid interface. From these results we concluded that a maturation period of at least 16 days at the air–liquid interface was required for an optimal barrier function development of REp. At this time point, the permeability of the skin cultures for caffeine (CAF) was 20–25-fold higher than that of normal human skin (NHS) biopsies. Non-invasive measurements of skin water content, transepidermal water loss (TEWL) and pH were achieved after the same period of time. Results showed that the stratum corneum (SC) of REp was slightly more hydrated than that of ex vivo and in vivo, human skin. TEWL was slightly higher through REp than through NHS, and the pH of the REp models was very close to that of in vivo, normal human skin. In the latter part, assuming that this type of model could be routinely used, we quantified over a 1-year period the barrier function variability of this skin culture model between batches. The satisfactory results obtained with a 20% coefficient of variation indicated that this REp model has a consistent and reproducible barrier function. This leads us to suggest that the skin model might be considered an alternative membrane to normal human skin for permeation screening tests.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.0412-5463.2001.00112.x
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  • 5
    Digitale Medien
    Digitale Medien
    Observation of magnetic forces by the atomic force microscope (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4293-4295 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a new way to observe the surface domain distribution of a magnetic sample at a submicrometer scale. This magnetic microscopy is based on the idea of measuring magnetic forces with the recently developed atomic force microscope (AFM). We study the magnetic forces involved in the interaction between a single-domain microtip and the sample surface magnetic domains. The influence of the experimental conditions on the performance of the AFM as a magnetic profiling device is also discussed. Preliminary experimental results are reported.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.339105
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  • 6
    Digitale Medien
    Digitale Medien
    Magnetism in metastable bcc and fcc iron-copper alloys : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6580-6582 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present linearized augmented plane-wave calculations for FeCu fcc and bcc metastable phases using the local density approximation. Curves for the density of states (without including the spin-polarization effects) at several Fe concentrations are given, noticing that the density of states at the Fermi level for determinated fcc alloys suffers significant large increases in relation to the fcc Fe. This fact provides an explanation to the magnetic character found in some fcc FeCu alloys. The magnetization is calculated at different compositions by applying the Stoner criteria, assuming a simple behavior for the magnetic exchange integral, and including the effect of randomness in a simple way. We find that the magnetic moment per Fe atom is similar to that of bcc Fe for some fcc FeCu alloys.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356901
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  • 7
    Digitale Medien
    Digitale Medien
    Magnetoresistance of paramagnetic metallic layers sandwiched between ferromagnetic layers : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5861-5863 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental results on magnetoresistance of Fe/Cr/Fe trilayers and multilayers show a large enhancement of this magnitude for a thickness of approximately 10 layers and decreases exponentially with the number of layers. In this work it is proposed that the key point to understand these experiments may lay in the fact that the exchange field of the ferromagnets penetrates in the paramagnet as has recently been proposed by the authors to explain coupling energies in trilayers. Even if the decay length of the penetrating field is small, of the order of nearest neighbors in Fe, its magnitude is large (1000 T), larger than any applied saturation field. The ferromagnetic and antiferromagnetic configurations give rise to two different field configurations and therefore to two different values of the resistance. In the opinion of the authors this is controlled by the effective section that the electrons can go. Also, it is not doubtful that the magnetoresistance is large but that the magnetic field (scattering spin potential) that the electrons see is large. It is found that the magnetoresistance is very much structure or roughness dependent and increases, in first approximation, with its amplitude. The magnetoresistance depends exponentially with the number of paramagnetic layers with a 10–20-A(ring) decay length, but does not oscillate; it is a smooth function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350137
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  • 8
    Digitale Medien
    Digitale Medien
    Erratum: The structure of liquid 1,2 dichloroethane by neutron diffraction. I. Molecular structure, full pair correlation function, and temperature effects [J. Chem. Phys. 87, 7171 (1987)] (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6680-6681 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454760
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  • 9
    Digitale Medien
    Digitale Medien
    The structure of liquid 1,2 dichloroethane by neutron diffraction. I. Molecular structure, full pair correlation function, and temperature effects (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 7171-7178 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Neutron diffraction measurements have been made in liquid 1,2 dichloroethane-d4 (DCE) at temperatures of −20, 21, and 70 °C. The intramolecular structural parameters have been determined by analysis of the high momentum transfer region of the derived structure factor as well as the relative populations of trans and gauche conformers. The separation between intra- and intermolecular contributions is achieved by means of previously reported procedures based upon maximum entropy estimation techniques. The full (composite) single-particle pair correlation function has been evaluated and show significant structural features up to 15 A(ring). A tentative assignment is made based upon results from a Monte Carlo simulation. The temperature variation produced some marked changes due to both the density decrease at high temperatures as well as to the displacement of the conformational equilibrium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.453360
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  • 10
    Digitale Medien
    Digitale Medien
    Correlation effects on Raman scattering from low-energy vibrational modes in fractal and disordered systems. I. Theory (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2040-2045 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: In disordered fractal or nonfractal systems, the disorder induces rapid fluctuations of the acoustical vibrational wave functions, so that statistics can be used to resolve the problem of Raman scattering from localized low-energy vibrations. We derive the expressions of light-vibration coupling coefficient, C(ω), as a function of the frequency ω, in the case of the dipole-induced dipole mechanism of susceptibility fluctuation and for different types of correlation, from full correlation to no-correlation. The results are compared to the existing numerical calculations. The expressions of C(ω) are determined for other mechanisms of susceptibility fluctuations, depending on an interaction propagating in the fractal.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465267
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