912 research outputs found
Separation of the first- and second-order contributions in magneto-optic Kerr effect magnetometry of epitaxial FeMn/NiFe bilayers
The influence of second-order magneto-optic effects on Kerr effect
magnetometry of epitaxial exchange coupled FeMn/NiFe-bilayers is investigated.
A procedure for separation of the first- and second-order contributions is
presented. The full angular dependence of both contributions during the
magnetization reversal is extracted from the experimental data and presented
using gray scaled magnetization reversal diagrams. The theoretical description
of the investigated system is based on an extended Stoner-Wohlfarth model,
which includes an induced unidirectional and fourfold anisotropy in the
ferromagnet, caused by the coupling to the antiferromagnet. The agreement
between the experimental data and the theoretical model for both the first- and
second-order contributions are good, although a coherent reversal of the
magnetization is assumed in the model.Comment: 6 pages, 7 figures, submitted to J. Appl. Phy
The Phenion (R) Full-Thickness Skin Model for Percutaneous Absorption Testing
In recent years many efforts have been made to replace dermal toxicity testing of chemicals in the animal by in vitro assays. As a member of a German research consortium, we have previously contributed to the validation of an in vitro test protocol for percutaneous absorption studies on the basis of reconstructed human epidermis and both human and pig skin ex vivo. Aiming to assess the barrier properties of a newly developed reconstructed skin model, this protocol has now been transferred to the Phenion (R) Full-Thickness Skin Model (FT model). The permeation of testosterone and caffeine was quantified in parallel to that of pig skin using Franz-type diffusion cells. In addition, the permeation of benzoic acid and nicotine was studied. As expected, the FT model is more permeable than pig skin, yet its barrier properties are well in accordance with those of reconstructed human epidermis when compared to previous data. In fact, the FT model most efficiently retards testosterone as the compound of highest lipophilicity, which can be explained by an additional uptake by a reservoir formed by the dermis equivalent. Thus, the structure closely parallels human skin. In consequence, the Phenion FT model appears to be suitable for percutaneous absorption studies in hazard analysis and should be subjected to a catch-up validation study. Copyright (C) 2009 S. Karger AG, Base
Hydrodynamic flow of expanding Bose-Einstein condensates
We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC)
after switching off the confining harmonic potential. Exact solution of
dynamical equations is obtained in framework of the hydrodynamic approximation
and it is compared with the direct numerical simulation of the full problem
showing excellent agreement at realistic values of physical parameters. We
analyze the maximum of the current density and estimate the velocity of
expansion. The results of the 1D analysis provides also qualitative
understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review
Atom optical elements for Bose condensates
A simple model for atom optical elements for Bose condensate of trapped,
dilute alkali atomns is proposed and numerical simulations are presented to
illustrate its characteristics. We demonstrate ways of focusing and splitting
the condensate by modifying experimentally adjustable parameters. We show that
there are at least two ways of implementing atom optical elements: one may
modulate the interatomic scattering length in space, or alternatively, use a
sinusoidal, externally applied potential.Comment: 7 pages, 10 figure
Switching Distributions for Perpendicular Spin-Torque Devices within the Macrospin Approximation
We model "soft" error rates for writing (WSER) and for reading (RSER) for
perpendicular spin-torque memory devices by solving the Fokker-Planck equation
for the probability distribution of the angle that the free layer magnetization
makes with the normal to the plane of the film. We obtain: (1) an exact, closed
form, analytical expression for the zero-temperature switching time as a
function of initial angle; (2) an approximate analytical expression for the
exponential decay of the WSER as a function of the time the current is applied;
(3) comparison of the approximate analytical expression for the WSER to
numerical solutions of the Fokker-Planck equation; (4) an approximate
analytical expression for the linear increase in RSER with current applied for
reading; (5) comparison of the approximate analytical formula for the RSER to
the numerical solution of the Fokker-Planck equation; and (6) confirmation of
the accuracy of the Fokker-Planck solutions by comparison with results of
direct simulation using the single-macrospin Landau-Lifshitz-Gilbert (LLG)
equations with a random fluctuating field in the short-time regime for which
the latter is practical
Energy relaxation pathways between light-matter states revealed by coherent two-dimensional spectroscopy
Coupling matter excitations to electromagnetic modes inside nano-scale optical resonators leads to the formation of hybrid light-matter states, so-called polaritons, allowing the controlled manipulation of material properties. Here, we investigate the photo-induced dynamics of a prototypical strongly-coupled molecular exciton-microcavity system using broadband two-dimensional Fourier transform spectroscopy and unravel the mechanistic details of its ultrafast photo-induced dynamics. We find evidence for a direct energy relaxation pathway from the upper to the lower polariton state that initially bypasses the excitonic manifold of states, which is often assumed to act as an intermediate energy reservoir, under certain experimental conditions. This observation provides new insight into polariton photophysics and could potentially aid the development of applications that rely on controlling the energy relaxation mechanism, such as in solar energy harvesting, manipulating chemical reactivity, the creation of Bose–Einstein condensates and quantum computing
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