3,014 research outputs found
Finite size corrections to the blackbody radiation laws
We investigate the radiation of a blackbody in a cavity of finite size. For a
given geometry, we use semiclassical techniques to obtain explicit expressions
of the modified Planck's and Stefan-Boltzmann's blackbody radiation laws as a
function of the size and shape of the cavity. We determine the range of
parameters (temperature, size and shape of the cavity) for which these effects
are accessible to experimental verification. Finally we discuss potential
applications of our findings in the physics of the cosmic microwave background
and sonoluminescence.Comment: 5 pages, 1 figure, journal versio
Closed-orbit theory for spatial density oscillations
We briefly review a recently developed semiclassical theory for quantum
oscillations in the spatial (particle and kinetic energy) densities of finite
fermion systems and present some examples of its results. We then discuss the
inclusion of correlations (finite temperatures, pairing correlations) in the
semiclassical theory.Comment: LaTeX, 10pp., 2 figure
Some Calculable Contributions to Entanglement Entropy
Entanglement entropy appears as a central property of quantum systems in
broad areas of physics. However, its precise value is often sensitive to
unknown microphysics, rendering it incalculable. By considering parametric
dependence on correlation length, we extract finite, calculable contributions
to the entanglement entropy for a scalar field between the interior and
exterior of a spatial domain of arbitrary shape. The leading term is
proportional to the area of the dividing boundary; we also extract finite
subleading contributions for a field defined in the bulk interior of a
waveguide in 3+1 dimensions, including terms proportional to the waveguide's
cross-sectional geometry; its area, perimeter length, and integrated curvature.
We also consider related quantities at criticality and suggest a class of
systems for which these contributions might be measurable.Comment: 4+ pages, 1 figure. v2: Some clarifications and more references;
updated to resemble version published in PR
Stochastic Quantization and Casimir Forces: Pistons of Arbitrary Cross Section
Recently, a method based on stochastic quantization has been proposed to
compute the Casimir force and its fluctuations in arbitrary geometries. It
relies on the spectral decomposition of the Laplacian operator in the given
geometry. Both quantum and thermal fluctuations are considered. Here we use
such method to compute the Casimir force on the plates of a finite piston of
arbitrary cross section. Asymptotic expressions valid at low and high
temperatures and short and long distances are obtained. The case of a piston
with triangular cross section is analysed in detail. The regularization of the
divergent stress tensor is described.Comment: 10 pages and 4 figures. Accepted for publication in the Proceedings
of the tenth conference on Quantum Field Theory under the influence of
external conditions - QFEXT'1
Application of the Trace Formula in Pseudointegrable Systems
We apply periodic-orbit theory to calculate the integrated density of states
from the periodic orbits of pseudointegrable polygon and barrier
billiards. We show that the results agree so well with the results obtained
from direct diagonalization of the Schr\"odinger equation, that about the first
100 eigenvalues can be obtained directly from the periodic-orbit calculations
in good accuracy.Comment: 5 Pages, 4 Figures, submitted to Phys. Rev.
Quantal Consequences of Perturbations Which Destroy Structurally Unstable Orbits in Chaotic Billiards
Non-generic contributions to the quantal level-density from parallel segments
in billiards are investigated. These contributions are due to the existence of
marginally stable families of periodic orbits, which are structurally unstable,
in the sense that small perturbations, such as a slight tilt of one of the
segments, destroy them completely. We investigate the effects of such
perturbation on the corresponding quantum spectra, and demonstrate them for the
stadium billiard
Resonance Patterns in a Stadium-shaped Microcavity
We investigate resonance patterns in a stadium-shaped microcavity around
, where is the refractive index, the vacuum
wavenumber, and the radius of the circular part of the cavity. We find that
the patterns of high resonances can be classified, even though the
classical dynamics of the stadium system is chaotic. The patterns of the high
resonances are consistent with the ray dynamical consideration, and appears
as the stationary lasing modes with low pumping rate in the nonlinear dynamical
model. All resonance patterns are presented in a finite range of .Comment: 8 pages, 9 figure
Elementary Teachers’ Use of 1:1 Tablets in Lesson Planning and Presentation on a Western Pacific Island
The Ministry of Education on a Western Pacific island invested in an expensive 1:1 tablet program providing elementary teachers and students with a tablet but had not determined if the program produced desired positive changes in the teachers’ instructional practices of lesson planning and lesson presentation. Guided by experiential learning theory, this causal–comparative study’s purpose was to determine if the 1:1 tablet program resulted in changes in elementary teachers’ use of technology in their lesson planning and lesson presentation practices. We analyzed pre and postimplementation lesson planning and lesson presentation data, collected from 63 elementary teachers, using repeated measures t-tests. Results showed teachers’ use of technology in lesson planning and lesson presentation increased significantly following implementation of the 1:1 tablet initiative. These findings suggest that the 1:1 tablet program created an environment that positively supported technology-driven instruction for teachers as well as students. In light of these results, the 1:1 tablet program appears to be a worthwhile initiative for the education system on the island that should be continued and possibly expanded even if public financial resources are scarce
Attractive Casimir Forces in a Closed Geometry
We study the Casimir force acting on a conducting piston with arbitrary cross
section. We find the exact solution for a rectangular cross section and the
first three terms in the asymptotic expansion for small height to width ratio
when the cross section is arbitrary. Though weakened by the presence of the
walls, the Casimir force turns out to be always attractive. Claims of repulsive
Casimir forces for related configurations, like the cube, are invalidated by
cutoff dependence.Comment: An updated version to coincide with the one published December 2005
in PRL. 4 pages, 2 figure
- …