2,071 research outputs found
Surface spin waves in superconducting and insulating ferromagnets
Surface magnetization waves are studied on a semi-infinite magnetic medium in
the perpendicular geometry. Both superconducting and insulating ferromagnets
are considered. Exchange and dipole energies are taken into account, as well as
retardation effects. At large wave vectors, the spectrum for a superconductor
and insulator is the same, though for the former the branch is terminated much
earlier than for the latter due to excitation of plasmons. At small wave
vectors, the surface wave is more robust in the superconductor since it is
separated from the bulk continuum by a finite gap.Comment: 4 pages, 2 figure
Oscillating Nernst-Ettingshausen effect in Bismuth across the quantum limit
In elemental Bismuth, 10 atoms share a single itinerant electron.
Therefore, a moderate magnetic field can confine electrons to the lowest Landau
level. We report on the first study of metallic thermoelectricity in this
regime. The main thermoelectric response is off-diagonal with an oscillating
component several times larger than the non-oscillating background. When the
first Landau level attains the Fermi Energy, both the Nernst and the
Ettingshausen coefficients sharply peak, and the latter attains a
temperature-independent maximum. A qualitative agreement with a theory invoking
current-carrying edge excitations is observed.Comment: Final published versio
Boundary conditions at spatial infinity for fields in Casimir calculations
The importance of imposing proper boundary conditions for fields at spatial
infinity in the Casimir calculations is elucidated.Comment: 8 pages, 1 figure, submitted to the Proceedings of The Seventh
Workshop QFEXT'05 (Barcelona, September 5-9, 2005
Radiative damping: a case study
We are interested in the motion of a classical charge coupled to the Maxwell
self-field and subject to a uniform external magnetic field, B. This is a
physically relevant, but difficult dynamical problem, to which contributions
range over more than one hundred years. Specifically, we will study the
Sommerfeld-Page approximation which assumes an extended charge distribution at
small velocities. The memory equation is then linear and many details become
available. We discuss how the friction equation arises in the limit of "small"
B and contrast this result with the standard Taylor expansion resulting in a
second order equation for the velocity of the charge.Comment: 4 figure
Recovery of chaotic tunneling due to destruction of dynamical localization by external noise
Quantum tunneling in the presence of chaos is analyzed, focusing especially
on the interplay between quantum tunneling and dynamical localization. We
observed flooding of potentially existing tunneling amplitude by adding noise
to the chaotic sea to attenuate the destructive interference generating
dynamical localization. This phenomenon is related to the nature of complex
orbits describing tunneling between torus and chaotic regions. The tunneling
rate is found to obey a perturbative scaling with noise intensity when the
noise intensity is sufficiently small and then saturate in a large noise
intensity regime. A relation between the tunneling rate and the localization
length of the chaotic states is also demonstrated. It is shown that due to the
competition between dynamical tunneling and dynamical localization, the
tunneling rate is not a monotonically increasing function of Planck's constant.
The above results are obtained for a system with a sharp border between torus
and chaotic regions. The validity of the results for a system with a smoothed
border is also explained.Comment: 14 pages, 15 figure
Formation of shock waves in a Bose-Einstein condensate
We consider propagation of density wave packets in a Bose-Einstein
condensate. We show that the shape of initially broad, laser-induced, density
perturbation changes in the course of free time evolution so that a shock wave
front finally forms. Our results are well beyond predictions of commonly used
zero-amplitude approach, so they can be useful in extraction of a speed of
sound from experimental data. We discuss a simple experimental setup for shock
propagation and point out possible limitations of the mean-field approach for
description of shock phenomena in a BEC.Comment: 8 pages & 6 figures, minor changes, more references, to appear in
Phys. Rev.
Formation of ions by high energy photons
We calculate the electron energy spectrum of ionization by a high energy
photon, accompanied by creation of electron-positron pair. The total cross
section of the process is also obtained. The asymptotics of the cross section
does not depend on the photon energies. At the photon energies exceeding a
certain value this appeares to to be the dominant mechanism of
formation of the ions. The dependence of on the value of nuclear
charge is obtained. Our results are consistent with experimental data.Comment: 16 pages, 6 figure
Carbohydrate-derived amphiphilic macromolecules: a biophysical structural characterization and analysis of binding behaviors to model membranes.
The design and synthesis of enhanced membrane-intercalating biomaterials for drug delivery or vascular membrane targeting is currently challenged by the lack of screening and prediction tools. The present work demonstrates the generation of a Quantitative Structural Activity Relationship model (QSAR) to make a priori predictions. Amphiphilic macromolecules (AMs) "stealth lipids" built on aldaric and uronic acids frameworks attached to poly(ethylene glycol) (PEG) polymer tails were developed to form self-assembling micelles. In the present study, a defined set of novel AM structures were investigated in terms of their binding to lipid membrane bilayers using Quartz Crystal Microbalance with Dissipation (QCM-D) experiments coupled with computational coarse-grained molecular dynamics (CG MD) and all-atom MD (AA MD) simulations. The CG MD simulations capture the insertion dynamics of the AM lipophilic backbones into the lipid bilayer with the PEGylated tail directed into bulk water. QCM-D measurements with Voigt viscoelastic model analysis enabled the quantitation of the mass gain and rate of interaction between the AM and the lipid bilayer surface. Thus, this study yielded insights about variations in the functional activity of AM materials with minute compositional or stereochemical differences based on membrane binding, which has translational potential for transplanting these materials in vivo. More broadly, it demonstrates an integrated computational-experimental approach, which can offer a promising strategy for the in silico design and screening of therapeutic candidate materials
Matter Wave Scattering and Guiding by Atomic Arrays
We investigate the possibility that linear arrays of atoms can guide matter
waves, much as fiber optics guide light. We model the atomic line as a quasi-1D
array of s wave point scatterers embedded in 2D. Our theoretical study reveals
how matter wave guiding arises from the interplay of scattering phenomena with
bands and conduction along the array. We discuss the conditions under which a
straight or curved array of atoms can guide a beam focused at one end of the
array.Comment: Submitted to Phys. Rev.
On the mutual polarization of two He-4 atoms
We propose a simple method based on the standard quantum-mechanical
perturbation theory to calculate the mutual polarization of two atoms He^4.Comment: 9 pages, 1 table; the article is revised and the calculation is
essentially refined; v4: final version, the Introduction is delete
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