8,966 research outputs found
Uniform semiclassical approximations on a topologically non-trivial configuration space: The hydrogen atom in an electric field
Semiclassical periodic-orbit theory and closed-orbit theory represent a
quantum spectrum as a superposition of contributions from individual classical
orbits. Close to a bifurcation, these contributions diverge and have to be
replaced with a uniform approximation. Its construction requires a normal form
that provides a local description of the bifurcation scenario. Usually, the
normal form is constructed in flat space. We present an example taken from the
hydrogen atom in an electric field where the normal form must be chosen to be
defined on a sphere instead of a Euclidean plane. In the example, the necessity
to base the normal form on a topologically non-trivial configuration space
reveals a subtle interplay between local and global aspects of the phase space
structure. We show that a uniform approximation for a bifurcation scenario with
non-trivial topology can be constructed using the established uniformization
techniques. Semiclassical photo-absorption spectra of the hydrogen atom in an
electric field are significantly improved when based on the extended uniform
approximations
Hybrid propulsion systems for motor vehicles with predominantly intermittent modes of operation
A small delivery vehicle was equipped with a flywheel-hybrid drive and compared in test stand and driving tests with a conventional drive vehicle. It turned out that with the hybrid drive, energy can be saved and exhaust emissions can be reduced
Semiclassical quantization of the hydrogen atom in crossed electric and magnetic fields
The S-matrix theory formulation of closed-orbit theory recently proposed by
Granger and Greene is extended to atoms in crossed electric and magnetic
fields. We then present a semiclassical quantization of the hydrogen atom in
crossed fields, which succeeds in resolving individual lines in the spectrum,
but is restricted to the strongest lines of each n-manifold. By means of a
detailed semiclassical analysis of the quantum spectrum, we demonstrate that it
is the abundance of bifurcations of closed orbits that precludes the resolution
of finer details. They necessitate the inclusion of uniform semiclassical
approximations into the quantization process. Uniform approximations for the
generic types of closed-orbit bifurcation are derived, and a general method for
including them in a high-resolution semiclassical quantization is devised
The hydrogen atom in an electric field: Closed-orbit theory with bifurcating orbits
Closed-orbit theory provides a general approach to the semiclassical
description of photo-absorption spectra of arbitrary atoms in external fields,
the simplest of which is the hydrogen atom in an electric field. Yet, despite
its apparent simplicity, a semiclassical quantization of this system by means
of closed-orbit theory has not been achieved so far. It is the aim of this
paper to close that gap. We first present a detailed analytic study of the
closed classical orbits and their bifurcations. We then derive a simple form of
the uniform semiclassical approximation for the bifurcations that is suitable
for an inclusion into a closed-orbit summation. By means of a generalized
version of the semiclassical quantization by harmonic inversion, we succeed in
calculating high-quality semiclassical spectra for the hydrogen atom in an
electric field
Boltzmann-type approach to transport in weakly interacting one-dimensional fermionic systems
We investigate transport properties of one-dimensional fermionic tight
binding models featuring nearest and next-nearest neighbor hopping, where the
fermions are additionally subject to a weak short range mutual interaction. To
this end we employ a pertinent approach which allows for a mapping of the
underlying Schr\"odinger dynamics onto an adequate linear quantum Boltzmann
equation. This approach is based on a suitable projection operator method. From
this Boltzmann equation we are able to numerically obtain diffusion
coefficients in the case of non-vanishing next-nearest neighbor hopping, i.e.,
the non-integrable case, whereas the diffusion coefficient diverges without
next-nearest neighbor hopping. For the latter case we analytically investigate
the decay behavior of the current with the result that arbitrarily small parts
of the current relax arbitrarily slowly which suggests anomalous diffusive
transport behavior within the scope of our approach.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
Photoabsorption spectra of the diamagnetic hydrogen atom in the transition regime to chaos: Closed orbit theory with bifurcating orbits
With increasing energy the diamagnetic hydrogen atom undergoes a transition
from regular to chaotic classical dynamics, and the closed orbits pass through
various cascades of bifurcations. Closed orbit theory allows for the
semiclassical calculation of photoabsorption spectra of the diamagnetic
hydrogen atom. However, at the bifurcations the closed orbit contributions
diverge. The singularities can be removed with the help of uniform
semiclassical approximations which are constructed over a wide energy range for
different types of codimension one and two catastrophes. Using the uniform
approximations and applying the high-resolution harmonic inversion method we
calculate fully resolved semiclassical photoabsorption spectra, i.e.,
individual eigenenergies and transition matrix elements at laboratory magnetic
field strengths, and compare them with the results of exact quantum
calculations.Comment: 26 pages, 9 figures, submitted to J. Phys.
Smoking Experimentation in Adolescents. Is There a Risk for Health?
peer reviewedIt is clear that even low rate smoking is hazardous for health, the risk being independently increased by the daily number of cigarettes smoked and by the duration of smoking. The question raised is thus: will an adolescent experimenter be a non smoker, an experimenter for ever, a regular smoker, light or heavy? This short review shows that there are numerous factors from genetics, to familial environment not limited to tobacco issues, smoking situation at school as well as school performances of the student, and also individual psychological characteristics. The experimenter is a very good target for smoking cessation actions and should deserve particular attention from preventive medicine and, thus, from school medicine, before he becomes a regular smoker, who will be more resistant to smoking cessation programs
Quantitative performance characterization of three-dimensional noncontact fluorescence molecular tomography
© 2016 The Authors.Fluorescent proteins and dyes are routine tools for biological research to describe the behavior of genes, proteins, and cells, as well as more complex physiological dynamics such as vessel permeability and pharmacokinetics. The use of these probes in whole body in vivo imaging would allow extending the range and scope of current biomedical applications and would be of great interest. In order to comply with a wide variety of application demands, in vivo imaging platform requirements span from wide spectral coverage to precise quantification capabilities. Fluorescence molecular tomography (FMT) detects and reconstructs in three dimensions the distribution of a fluorophore in vivo. Noncontact FMT allows fast scanning of an excitation source and noninvasive measurement of emitted fluorescent light using a virtual array detector operating in free space. Here, a rigorous process is defined that fully characterizes the performance of a custom-built horizontal noncontact FMT setup. Dynamic range, sensitivity, and quantitative accuracy across the visible spectrum were evaluated using fluorophores with emissions between 520 and 660 nm. These results demonstrate that high-performance quantitative three-dimensional visible light FMT allowed the detection of challenging mesenteric lymph nodes in vivo and the comparison of spectrally distinct fluorescent reporters in cell culture
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