2,382 research outputs found
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
Density of states of helium droplets
Accurate analytical expressions for the state densities of liquid He-4
droplets are derived, incorporating the ripplon and phonon degrees of freedom.
The microcanonical temperature and the ripplon angular momentum level density
are also evaluated. The approach is based on inversions and systematic
expansions of canonical thermodynamic properties.Comment: 20 pages, 5 figure
Fractal Weyl law behavior in an open, chaotic Hamiltonian system
We numerically show fractal Weyl law behavior in an open Hamiltonian system
that is described by a smooth potential and which supports numerous
above-barrier resonances. This behavior holds even relatively far away from the
classical limit. The complex resonance wave functions are found to be localized
on the fractal classical repeller.Comment: 4 pages, 3 figures. to appear in 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
Conceptual mechanization studies for a horizon definition spacecraft electrical power subsystem
Solar cell-battery electrical power subsystem for horizon definition spacecraf
Chaotic Scattering in the Regime of Weakly Overlapping Resonances
We measure the transmission and reflection amplitudes of microwaves in a
resonator coupled to two antennas at room temperature in the regime of weakly
overlapping resonances and in a frequency range of 3 to 16 GHz. Below 10.1 GHz
the resonator simulates a chaotic quantum system. The distribution of the
elements of the scattering matrix S is not Gaussian. The Fourier coefficients
of S are used for a best fit of the autocorrelation function if S to a
theoretical expression based on random--matrix theory. We find very good
agreement below but not above 10.1 GHz
Discrete Symmetries in the Weyl Expansion for Quantum Billiards
We consider two and three-dimensional quantum billiards with discrete
symmetries. We derive the first terms of the Weyl expansion for the level
density projected onto the irreducible representations of the symmetry group.
As an illustration the method is applied to the icosahedral billiard. The paper
was published in J. Phys. A /27/ (1994) 4317-4323Comment: 8 printed pages Latex fil
Average ground-state energy of finite Fermi systems
Semiclassical theories like the Thomas-Fermi and Wigner-Kirkwood methods give
a good description of the smooth average part of the total energy of a Fermi
gas in some external potential when the chemical potential is varied. However,
in systems with a fixed number of particles N, these methods overbind the
actual average of the quantum energy as N is varied. We describe a theory that
accounts for this effect. Numerical illustrations are discussed for fermions
trapped in a harmonic oscillator potential and in a hard wall cavity, and for
self-consistent calculations of atomic nuclei. In the latter case, the
influence of deformations on the average behavior of the energy is also
considered.Comment: 10 pages, 8 figure
Hybrid Spiking Neural Network Fine-tuning for Hippocampus Segmentation
Over the past decade, artificial neural networks (ANNs) have made tremendous
advances, in part due to the increased availability of annotated data. However,
ANNs typically require significant power and memory consumptions to reach their
full potential. Spiking neural networks (SNNs) have recently emerged as a
low-power alternative to ANNs due to their sparsity nature. SNN, however, are
not as easy to train as ANNs. In this work, we propose a hybrid SNN training
scheme and apply it to segment human hippocampi from magnetic resonance images.
Our approach takes ANN-SNN conversion as an initialization step and relies on
spike-based backpropagation to fine-tune the network. Compared with the
conversion and direct training solutions, our method has advantages in both
segmentation accuracy and training efficiency. Experiments demonstrate the
effectiveness of our model in achieving the design goals.Comment: Accepted to ISBI 2023 conferenc
Quantum Chaotic Scattering in Microwave Resonators
In a frequency range where a microwave resonator simulates a chaotic quantum
billiard, we have measured moduli and phases of reflection and transmission
amplitudes in the regimes of both isolated and of weakly overlapping resonances
and for resonators with and without time-reversal invariance. Statistical
measures for S-matrix fluctuations were determined from the data and compared
with extant and/or newly derived theoretical results obtained from the
random-matrix approach to quantum chaotic scattering. The latter contained a
small number of fit parameters. The large data sets taken made it possible to
test the theoretical expressions with unprecedented accuracy. The theory is
confirmed by both, a goodness-of-fit-test and the agreement of predicted values
for those statistical measures that were not used for the fits, with the data
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