21,981 research outputs found
Semiclassical transition probabilities by an asymptotic evaluation of the S matrix for elastic and inelastic collisions. Bessel uniform approximation
It has been observed in the past that the usual Airy uniform approximation gives probabilities greater than one, especially for near elastic collisions. By mapping the phase onto −ζ cos y + ky + A rather than (1∕3)y^3 − ζy + A one obtains a uniform approximation involving Bessel functions of the first kind, which approaches unity for the elastic collision. This Bessel uniform approximation is no more complicated than the Airy and also gives good agreement with exact quantum results, even if probabilities are large
The dynamical Casimir effect in braneworlds
In braneworld cosmology the expanding Universe is realized as a brane moving
through a warped higher-dimensional spacetime. Like a moving mirror causes the
creation of photons out of vacuum fluctuations, a moving brane leads to
graviton production. We show that, very generically, Kaluza-Klein (KK)
particles scale like stiff matter with the expansion of the Universe and can
therefore not represent the dark matter in a warped braneworld. We present
results for the production of massless and KK gravitons for bouncing branes in
five-dimensional anti de Sitter space. We find that for a realistic bounce the
back reaction from the generated gravitons will be most likely relevant. This
letter summarizes the main results and conclusions from numerical simulations
which are presented in detail in a long paper [M.Ruser and R. Durrer, Phys.
Rev. D 76, 104014 (2007), arXiv:0704.0790]Comment: misprints corrected, matches published versio
Intramolecular dynamics. I. Curvilinear normal modes, local modes, molecular anharmonic Hamiltonian, and application to benzene
The Hamiltonian based on curvilinear normal modes and local modes (CNLM) is discussed using Wilson's exact vibrational Hamiltonian as basis, the CNLM representation diagonalizing only the normal mode block of FG matrix in curvilinear internal coordinates. Using CNLM the kinetic and potential energy operators for benzene are given, including cubic and quartic anharmonicity in the potential energy and cubic and quartic terms in the kinetic energy expansion in curvilinear coordinates. Using symmetrized coordinates and cubic and higher force constants the number and identity of the independent symmetry allowed (A1g) such force constants are obtained. The relation to conventional anharmonic force constants is then given and the allowed contributions of the latter are obtained. The results are applied to CH overtone spectra and intramolecular vibrational dynamics in Part III of this series
Bound States in the Continuum Realized in the One-Dimensional Two-Particle Hubbard Model with an Impurity
We report a bound state of the one-dimensional two-particle (bosonic or
fermionic) Hubbard model with an impurity potential. This state has the
Bethe-ansatz form, although the model is nonintegrable. Moreover, for a wide
region in parameter space, its energy is located in the continuum band. A
remarkable advantage of this state with respect to similar states in other
systems is the simple analytical form of the wave function and eigenvalue. This
state can be tuned in and out of the continuum continuously.Comment: A semi-exactly solvable model (half of the eigenstates are in the
Bethe form
Lifetimes and Gj factors in excited states of chromium. Hyperfine structure of Cr53
Electronic and nuclear properties of excited chromium isotopes using level crossing and double resonance spectroscopy technique
Application of High-precision Timing Systems to Distributed Survey Systems
In any hydrographic survey system that consists of more than one computer, one of the most difficult integration problems is to ensure that all components maintain a coherent sense of time. Since virtually all modern survey systems are of this type, timekeeping and synchronized timestamping of data as it is created is of significant concern. This paper describes a method for resolving this problem based on the IEEE 1588 Precise Time Protocol (PTP) implemented by hardware devices, layered with some custom software called the Software Grandmaster (SWGM) algorithm. This combination of hardware and software maintains a coherent sense of time between multiple ethernet-connected computers, on the order of 100 ns (rms) in the best case, of the timebase established by the local GPS-receiver clock. We illustrate the performance of this techniques in a practical survey system using a Reson 7P sonar processor connected to a Reson 7125 Multibeam Echosounder (MBES), integrated with an Applanix POS/MV 320 V4 and a conventional data capture computer. Using the timing capabilities of the PTP hardware implementations, we show that the timepieces achieve mean (hardware based) synchronization and timestamping within 100-150 ns (rms), and that the data created at the Reson 7P without hardware timestamps has a latency variability of 28 µs (rms) due to software constraints within the capture system. This compares to 288 ms (rms) using Reson’s standard hybrid hardware/software solution, and 13.6 ms (rms) using a conventional single-oscillator timestamping model
Dynamical Casimir effect for gravitons in bouncing braneworlds
We consider a two-brane system in a five-dimensional anti-de Sitter
spacetime. We study particle creation due to the motion of the physical brane
which first approaches the second static brane (contraction) and then recedes
from it(expansion). The spectrum and the energy density of the generated
gravitons are calculated. We show that the massless gravitons have a blue
spectrum and that their energy density satisfies the nucleosynthesis bound with
very mild constraints on the parameters. We also show that the Kaluza-Klein
modes cannot provide the dark matter in an anti-de-Sitter braneworld. However,
for natural choices of parameters, backreaction from the Kaluza-Klein gravitons
may well become important. The main findings of this work have been published
in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601
(2007), arXiv:0704.0756].Comment: 40 pages, 34 figures, improved and extended version, matches
published versio
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