696 research outputs found
Numerical study of scars in a chaotic billiard
We study numerically the scaling properties of scars in stadium billiard.
Using the semiclassical criterion, we have searched systematically the scars of
the same type through a very wide range, from ground state to as high as the 1
millionth state. We have analyzed the integrated probability density along the
periodic orbit. The numerical results confirm that the average intensity of
certain types of scars is independent of rather than scales with
. Our findings confirm the theoretical predictions of Robnik
(1989).Comment: 7 pages in Revtex 3.1, 5 PS figures available upon request. To appear
in Phys. Rev. E, Vol. 55, No. 5, 199
Wigner--Dyson statistics for a class of integrable models
We construct an ensemble of second--quantized Hamiltonians with two bosonic
degrees of freedom, whose members display with probability one GOE or GUE
statistics. Nevertheless, these Hamiltonians have a second integral of motion,
namely the boson number, and thus are integrable. To construct this ensemble we
use some ``reverse engineering'' starting from the fact that --bosons in a
two--level system with random interactions have an integrable classical limit
by the old Heisenberg association of boson operators to actions and angles. By
choosing an --body random interaction and degenerate levels we end up with
GOE or GUE Hamiltonians. Ergodicity of these ensembles completes the example.Comment: 3 pages, 1 figur
Viscosity in the escape-rate formalism
We apply the escape-rate formalism to compute the shear viscosity in terms of
the chaotic properties of the underlying microscopic dynamics. A first passage
problem is set up for the escape of the Helfand moment associated with
viscosity out of an interval delimited by absorbing boundaries. At the
microscopic level of description, the absorbing boundaries generate a fractal
repeller. The fractal dimensions of this repeller are directly related to the
shear viscosity and the Lyapunov exponent, which allows us to compute its
values. We apply this method to the Bunimovich-Spohn minimal model of viscosity
which is composed of two hard disks in elastic collision on a torus. These
values are in excellent agreement with the values obtained by other methods
such as the Green-Kubo and Einstein-Helfand formulas.Comment: 16 pages, 16 figures (accepted in Phys. Rev. E; October 2003
Business ethics : practical proposals
While most people agree that the inculcation of ethical awareness is desirable, the means of stimulating this awareness vary among companies, industries and cultures. The fundamental question surrounding the difference between social responsibility and ethics is addressed. Guidelines for establishing ethical priorities from both the individual, group and organisational perspectives are provided. <br /
Level statistics and eigenfunctions of pseudointegrable systems: dependence on energy and genus number
We study the level statistics (second half moment and rigidity
) and the eigenfunctions of pseudointegrable systems with rough
boundaries of different genus numbers . We find that the levels form energy
intervals with a characteristic behavior of the level statistics and the
eigenfunctions in each interval. At low enough energies, the boundary roughness
is not resolved and accordingly, the eigenfunctions are quite regular functions
and the level statistics shows Poisson-like behavior. At higher energies, the
level statistics of most systems moves from Poisson-like towards Wigner-like
behavior with increasing . Investigating the wavefunctions, we find many
chaotic functions that can be described as a random superposition of regular
wavefunctions. The amplitude distribution of these chaotic functions
was found to be Gaussian with the typical value of the localization volume
. For systems with periodic boundaries we find
several additional energy regimes, where is relatively close to the
Poisson-limit. In these regimes, the eigenfunctions are either regular or
localized functions, where is close to the distribution of a sine or
cosine function in the first case and strongly peaked in the second case. Also
an interesting intermediate case between chaotic and localized eigenfunctions
appears
Chaotic self-similar wave maps coupled to gravity
We continue our studies of spherically symmetric self-similar solutions in
the SU(2) sigma model coupled to gravity. For some values of the coupling
constant we present numerical evidence for the chaotic solution and the fractal
threshold behavior. We explain this phenomenon in terms of horseshoe-like
dynamics and heteroclinic intersections.Comment: 25 pages, 17 figure
Chaos and Quantum Thermalization
We show that a bounded, isolated quantum system of many particles in a
specific initial state will approach thermal equilibrium if the energy
eigenfunctions which are superposed to form that state obey {\it Berry's
conjecture}. Berry's conjecture is expected to hold only if the corresponding
classical system is chaotic, and essentially states that the energy
eigenfunctions behave as if they were gaussian random variables. We review the
existing evidence, and show that previously neglected effects substantially
strengthen the case for Berry's conjecture. We study a rarefied hard-sphere gas
as an explicit example of a many-body system which is known to be classically
chaotic, and show that an energy eigenstate which obeys Berry's conjecture
predicts a Maxwell--Boltzmann, Bose--Einstein, or Fermi--Dirac distribution for
the momentum of each constituent particle, depending on whether the wave
functions are taken to be nonsymmetric, completely symmetric, or completely
antisymmetric functions of the positions of the particles. We call this
phenomenon {\it eigenstate thermalization}. We show that a generic initial
state will approach thermal equilibrium at least as fast as
, where is the uncertainty in the total energy
of the gas. This result holds for an individual initial state; in contrast to
the classical theory, no averaging over an ensemble of initial states is
needed. We argue that these results constitute a new foundation for quantum
statistical mechanics.Comment: 28 pages in Plain TeX plus 2 uuencoded PS figures (included); minor
corrections only, this version will be published in Phys. Rev. E;
UCSB-TH-94-1
Childhood Adversity Moderates Change in Latent Patterns of Psychological Adjustment during the COVID-19 Pandemic: Results of a Survey of U.S. Adults
Emerging evidence suggests that the consequences of childhood adversity impact later psychopathology by increasing individuals’ risk of experiencing difficulties in adjusting to stressful situations later in life. The goals of this study were to: (a) identify sociodemographic factors associated with subgroups of psychological adjustment prior to and after the onset of the COVID-19 pandemic and (b) examine whether and to what extent types of childhood adversity predict transition probabilities. Participants were recruited via multiple social media platforms and listservs. Data were collected via an internet-based survey. Our analyses reflect 1942 adults (M = 39.68 years); 39.8% reported experiencing at least one form of childhood adversity. Latent profile analyses (LPAs) and latent transition analyses (LTAs) were conducted to determine patterns of psychological adjustment and the effects of childhood adversity on transition probabilities over time. We identified five subgroups of psychological adjustment characterized by symptom severity level. Participants who were younger in age and those who endorsed marginalized identities exhibited poorer psychological adjustment during the pandemic. Childhood exposure to family and community violence and having basic needs met as a child (e.g., food, shelter) significantly moderated the relation between latent profile membership over time. Clinical and research implications are discussed
Affleck-Dine dynamics and the dark sector of pangenesis
Pangenesis is the mechanism for jointly producing the visible and dark matter
asymmetries via Affleck-Dine dynamics in a baryon-symmetric universe. The
baryon-symmetric feature means that the dark asymmetry cancels the visible
baryon asymmetry and thus enforces a tight relationship between the visible and
dark matter number densities. The purpose of this paper is to analyse the
general dynamics of this scenario in more detail and to construct specific
models. After reviewing the simple symmetry structure that underpins all
baryon-symmetric models, we turn to a detailed analysis of the required
Affleck-Dine dynamics. Both gravity-mediated and gauge-mediated supersymmetry
breaking are considered, with the messenger scale left arbitrary in the latter,
and the viable regions of parameter space are determined. In the gauge-mediated
case where gravitinos are light and stable, the regime where they constitute a
small fraction of the dark matter density is identified. We discuss the
formation of Q-balls, and delineate various regimes in the parameter space of
the Affleck-Dine potential with respect to their stability or lifetime and
their decay modes. We outline the regions in which Q-ball formation and decay
is consistent with successful pangenesis. Examples of viable dark sectors are
presented, and constraints are derived from big bang nucleosynthesis, large
scale structure formation and the Bullet cluster. Collider signatures and
implications for direct dark matter detection experiments are briefly
discussed. The following would constitute evidence for pangenesis:
supersymmetry, GeV-scale dark matter mass(es) and a Z' boson with a significant
invisible width into the dark sector.Comment: 51 pages, 7 figures; v2: minor modifications, comments and references
added; v3: minor changes, matches published versio
- …