595 research outputs found
Inclusion of Diffraction Effects in the Gutzwiller Trace Formula
The Gutzwiller trace formula is extended to include diffraction effects. The
new trace formula involves periodic rays which have non-geometrical segments as
a result of diffraction on the surfaces and edges of the scatter.Comment: 4 pages, LaTeX, 1 ps figur
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The Measurement of Sexual Selection Using Bateman's Principles: An Experimental Test in the Sex-Role-Reversed Pipefish Syngnathus typhle.
Angus J. Bateman's classic study of sexual selection in Drosophila melanogaster has had a major influence on the development of sexual selection theory. In some ways, Bateman's study has served a catalytic role by stimulating debate on sex roles, sexual conflict and other topics in sexual selection. However, there is still considerable disagreement regarding whether or not "Bateman's principles" are helpful in the study of sexual selection. Here, we test the idea that Bateman's principles provide the basis for a useful method to quantify and compare mating systems. In this study, we focus on the sex-role-reversed pipefish Syngnathus typhle as a model system to study the measurement of sexual selection. We set up artificial breeding assemblages of pipefish in the laboratory and used microsatellite markers to resolve parentage. Three different sex-ratio treatments (female-biased, even and male-biased) were used to manipulate the expected intensity of sexual selection. Measures of the mating system based on Bateman's principles were calculated and compared to the expected changes in the intensity of sexual selection. We also compare the results of this study to the results of a similar study of Bateman's principles in the rough-skinned newt, a species with conventional sex roles. The results of this experiment show that measures of the mating system based on Bateman's principles do accurately capture the relative intensities of sexual selection in the different treatments and species. Thus, widespread use of Bateman's principles to quantify mating systems in nature would facilitate comparative studies of sexual selection and mating system evolution
Small Disks and Semiclassical Resonances
We study the effect on quantum spectra of the existence of small circular
disks in a billiard system. In the limit where the disk radii vanish there is
no effect, however this limit is approached very slowly so that even very small
radii have comparatively large effects. We include diffractive orbits which
scatter off the small disks in the periodic orbit expansion. This situation is
formally similar to edge diffraction except that the disk radii introduce a
length scale in the problem such that for wave lengths smaller than the order
of the disk radius we recover the usual semi-classical approximation; however,
for wave lengths larger than the order of the disk radius there is a
qualitatively different behaviour. We test the theory by successfully
estimating the positions of scattering resonances in geometries consisting of
three and four small disks.Comment: Final published version - some changes in the discussion and the
labels on one figure are correcte
Geometrical theory of diffraction and spectral statistics
We investigate the influence of diffraction on the statistics of energy
levels in quantum systems with a chaotic classical limit. By applying the
geometrical theory of diffraction we show that diffraction on singularities of
the potential can lead to modifications in semiclassical approximations for
spectral statistics that persist in the semiclassical limit . This
result is obtained by deriving a classical sum rule for trajectories that
connect two points in coordinate space.Comment: 14 pages, no figure, to appear in J. Phys.
Policy Recommendations for Tobacco Taxation in the European Union Integrated Research Findings from the PPACTE Project
Three disks in a row: A two-dimensional scattering analog of the double-well problem
We investigate the scattering off three nonoverlapping disks equidistantly
spaced along a line in the two-dimensional plane with the radii of the outer
disks equal and the radius of the inner disk varied. This system is a
two-dimensional scattering analog to the double-well-potential (bound state)
problem in one dimension. In both systems the symmetry splittings between
symmetric and antisymmetric states or resonances, respectively, have to be
traced back to tunneling effects, as semiclassically the geometrical periodic
orbits have no contact with the vertical symmetry axis. We construct the
leading semiclassical ``creeping'' orbits that are responsible for the symmetry
splitting of the resonances in this system. The collinear three-disk-system is
not only one of the simplest but also one of the most effective systems for
detecting creeping phenomena. While in symmetrically placed n-disk systems
creeping corrections affect the subleading resonances, they here alone
determine the symmetry splitting of the 3-disk resonances in the semiclassical
calculation. It should therefore be considered as a paradigm for the study of
creeping effects. PACS numbers: 03.65.Sq, 03.20.+i, 05.45.+bComment: replaced with published version (minor misprints corrected and
references updated); 23 pages, LaTeX plus 8 Postscript figures, uses
epsfig.sty, espf.sty, and epsf.te
Uniform approximation for diffractive contributions to the trace formula in billiard systems
We derive contributions to the trace formula for the spectral density
accounting for the role of diffractive orbits in two-dimensional billiard
systems with corners. This is achieved by using the exact Sommerfeld solution
for the Green function of a wedge. We obtain a uniformly valid formula which
interpolates between formerly separate approaches (the geometrical theory of
diffraction and Gutzwiller's trace formula). It yields excellent numerical
agreement with exact quantum results, also in cases where other methods fail.Comment: LaTeX, 41 pages including 12 PostScript figures, submitted to Phys.
Rev.
Investigating Salmonella Eko from Various Sources in Nigeria by Whole Genome Sequencing to Identify the Source of Human Infections
Twenty-six Salmonella enterica serovar Eko isolated from various sources in Nigeria were investigated by whole genome sequencing to identify the source of human infections. Diversity among the isolates was observed and camel and cattle were identified as the primary reservoirs and the most likely source of the human infections
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