10,861 research outputs found
Smoothed Affine Wigner Transform
We study a generalization of Husimi function in the context of wavelets. This
leads to a nonnegative density on phase-space for which we compute the
evolution equation corresponding to a Schr\"Aodinger equation
Multifractal wave functions of simple quantum maps
We study numerically multifractal properties of two models of one-dimensional
quantum maps, a map with pseudointegrable dynamics and intermediate spectral
statistics, and a map with an Anderson-like transition recently implemented
with cold atoms. Using extensive numerical simulations, we compute the
multifractal exponents of quantum wave functions and study their properties,
with the help of two different numerical methods used for classical
multifractal systems (box-counting method and wavelet method). We compare the
results of the two methods over a wide range of values. We show that the wave
functions of the Anderson map display a multifractal behavior similar to
eigenfunctions of the three-dimensional Anderson transition but of a weaker
type. Wave functions of the intermediate map share some common properties with
eigenfunctions at the Anderson transition (two sets of multifractal exponents,
with similar asymptotic behavior), but other properties are markedly different
(large linear regime for multifractal exponents even for strong
multifractality, different distributions of moments of wave functions, absence
of symmetry of the exponents). Our results thus indicate that the intermediate
map presents original properties, different from certain characteristics of the
Anderson transition derived from the nonlinear sigma model. We also discuss the
importance of finite-size effects.Comment: 15 pages, 21 figure
Mean-field magnetization relaxation in conducting ferromagnets
Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
"spin-pumping" and the "breathing Fermi-surface" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.Comment: 4 pages, 1 figur
Modeling growing confluent tissues using a lattice Boltzmann method: interface stability and fluctuations
Tissue growth underpins a wide array of biological and developmental processes, and numerical modeling of growing systems has been shown to be a useful tool for understanding these processes. However, the phenomena that can be captured are often limited by the size of systems that can be modeled. Here, we address this limitation by introducing a lattice Boltzmann method (LBM) for a growing system that is able to efficiently model hydrodynamic length scales. The model incorporates a bounce-back approach to describing the growing front of a tissue, which we use to investigate the dynamics of the interface of growing model tissues. We find that the interface grows with scaling in agreement with the Kardar-Parisi-Zhang (KPZ) universality class when growth in the system is bulk driven. Interestingly, we also find the emergence of a previously unreported hydrodynamic instability when proliferation is restricted to the tissue edge. We then develop an analytical theory to show that the instability arises due to a coupling between the number of cells actively proliferating and the position of the interface
Bounded Determinization of Timed Automata with Silent Transitions
Deterministic timed automata are strictly less expressive than their
non-deterministic counterparts, which are again less expressive than those with
silent transitions. As a consequence, timed automata are in general
non-determinizable. This is unfortunate since deterministic automata play a
major role in model-based testing, observability and implementability. However,
by bounding the length of the traces in the automaton, effective
determinization becomes possible. We propose a novel procedure for bounded
determinization of timed automata. The procedure unfolds the automata to
bounded trees, removes all silent transitions and determinizes via disjunction
of guards. The proposed algorithms are optimized to the bounded setting and
thus are more efficient and can handle a larger class of timed automata than
the general algorithms. The approach is implemented in a prototype tool and
evaluated on several examples. To our best knowledge, this is the first
implementation of this type of procedure for timed automata.Comment: 25 page
Cytochrome spectra of cytoplasmic mutants
Cytochrome spectra of cytoplasmic mutant
Coherent QED, Giant Resonances and Pairs in High Energy Nucleus-Nucleus Collisions
We show that the coherent oscillations of the e.m. field induced by the
collective quantum fluctuations of the nuclear matter field associated with the
giant resonances, with frequencies MeV, give
rise to a significant pair production in high energy Heavy Ion
collisions. The approximate parameterless calculation of such yield is in good
agreement with recent experimental observations.Comment: 27 pages, 13 figure
Out-of-plane spin polarization from in-plane electric and magnetic fields
We show that the joint effect of spin-orbit and magnetic fields leads to a
spin polarization perpendicular to the plane of a two-dimensional electron
system with Rashba spin-orbit coupling and in-plane parallel dc magnetic and
electric fields, for angle-dependent impurity scattering or nonparabolic energy
spectrum, while only in-plane polarization persists for simplified models. We
derive Bloch equations, describing the main features of recent experiments,
including the magnetic field dependence of static and dynamic responses.Comment: 5 pages and 1 figure in main text, 5 pages in appendi
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