1,004 research outputs found
Existence and Stability of Symmetric Periodic Simultaneous Binary Collision Orbits in the Planar Pairwise Symmetric Four-Body Problem
We extend our previous analytic existence of a symmetric periodic
simultaneous binary collision orbit in a regularized fully symmetric equal mass
four-body problem to the analytic existence of a symmetric periodic
simultaneous binary collision orbit in a regularized planar pairwise symmetric
equal mass four-body problem. We then use a continuation method to numerically
find symmetric periodic simultaneous binary collision orbits in a regularized
planar pairwise symmetric 1, m, 1, m four-body problem for between 0 and 1.
Numerical estimates of the the characteristic multipliers show that these
periodic orbits are linearly stability when , and are
linearly unstable when .Comment: 6 figure
Discrete Laplace Cycles of Period Four
We study discrete conjugate nets whose Laplace sequence is of period four.
Corresponding points of opposite nets in this cyclic sequence have equal
osculating planes in different net directions, that is, they correspond in an
asymptotic transformation. We show that this implies that the connecting lines
of corresponding points form a discrete W-congruence. We derive some properties
of discrete Laplace cycles of period four and describe two explicit methods for
their construction
Surgical Treatment of Kawasaki Disease with Intestinal Pseudo-obstruction
A 5-year-old boy suffering from abdominal pain accompanied by a fever of up to 39.5 degrees C for 2 days was admitted to the hospital. Although Flomoxef was administered following admission, the boy's fever persisted and abdominal distension gradually worsened. On the 4th day, dry lips, red eyes and a strawberry tongue were noted. An echocardiogram revealed pericoronary enhancement with mild mitral valve regurgitation and a small degree of pericardial effusion, characteristics compatible with Kawasaki disease. Although intravenous immunoglobulin was administered, the fever and abdominal distension persisted. On the 8th day, a pediatric surgeon was consulted and an exploratory laparotomy was arranged. During the operation, intestinal pseudo-obstruction and fibrin coatings around the intestine near the splenic flexure were found. A colostomy was performed for decompression of the dilated bowel and a biopsy of the lymph node surrounding the splenic flexure was taken. The fever subsided dramatically after decompression of the bowel and the recovery course was uneventful. The pathologic report revealed necrotic lymphadenitis. We report this rare case and review the literature
Collective Modes of Soliton-Lattice States in Double-Quantum-Well Systems
In strong perpendicular magnetic fields double-quantum-well systems can
sometimes occur in unusual broken symmetry states which have interwell phase
coherence in the absence of interwell hopping. When hopping is present in such
systems and the magnetic field is tilted away from the normal to the quantum
well planes, a related soliton-lattice state can occur which has kinks in the
dependence of the relative phase between electrons in opposite layers on the
coordinate perpendicular to the in-plane component of the magnetic field. In
this article we evaluate the collective modes of this soliton-lattice state in
the generalized random-phase aproximation. We find that, in addition to the
Goldstone modes associated with the broken translational symmetry of the
soliton-lattice state, higher energy collective modes occur which are closely
related to the Goldstone modes present in the spontaneously phase-coherent
state. We study the evolution of these collective modes as a function of the
strength of the in-plane magnetic field and comment on the possibility of using
the in-plane field to generate a finite wave probe of the spontaneously
phase-coherent state.Comment: REVTEX, 37 pages (text) and 15 uuencoded postscript figure
Dark Synergy: Gravitational Lensing and the CMB
Power spectra and cross-correlation measurements from the weak gravitational
lensing of the cosmic microwave background (CMB) and the cosmic shearing of
faint galaxies images will help shed light on quantities hidden from the CMB
temperature anisotropies: the dark energy, the end of the dark ages, and the
inflationary gravitational wave amplitude. Even with modest surveys, both types
of lensing power spectra break CMB degeneracies and they can ultimately improve
constraints on the dark energy equation of state w by over an order of
magnitude. In its cross correlation with the integrated Sachs-Wolfe effect, CMB
lensing offers a unique opportunity for a more direct detection of the dark
energy and enables study of its clustering properties. By obtaining source
redshifts and cross-correlations with CMB lensing, cosmic shear surveys provide
tomographic handles on the evolution of clustering correspondingly better
precision on the dark energy equation of state and density. Both can indirectly
provide detections of the reionization optical depth and modest improvements in
gravitational wave constraints which we compare to more direct constraints.
Conversely, polarization B-mode contamination from CMB lensing, like any other
residual foreground, darkens the prospects for ultra-high precision on
gravitational waves through CMB polarization requiring large areas of sky for
statistical subtraction. To evaluate these effects we provide fitting formula
for the evolution and transfer function of the Newtonian gravitational
potential.Comment: 16 pages, 11 figures submitted to PR
Franck-Condon Effect in Central Spin System
We study the quantum transitions of a central spin surrounded by a
collective-spin environment. It is found that the influence of the
environmental spins on the absorption spectrum of the central spin can be
explained with the analog of the Franck-Condon (FC) effect in conventional
electron-phonon interaction system. Here, the collective spins of the
environment behave as the vibrational mode, which makes the electron to be
transitioned mainly with the so-called "vertical transitions" in the
conventional FC effect. The "vertical transition" for the central spin in the
spin environment manifests as, the certain collective spin states of the
environment is favored, which corresponds to the minimal change in the average
of the total spin angular momentum.Comment: 8 pages, 8 figure
Large Scale Pressure Fluctuations and Sunyaev-Zel'dovich Effect
The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of
the large scale structure gas distribution will be probed with current and
upcoming wide-field small angular scale cosmic microwave background
experiments. We study the generation of pressure fluctuations by baryons which
are present in virialized dark matter halos and by baryons present in small
overdensities. For collapsed halos, assuming the gas distribution is in
hydrostatic equilibrium with matter density distribution, we predict the
pressure power spectrum and bispectrum associated with the large scale
structure gas distribution by extending the dark matter halo approach which
describes the density field in terms of correlations between and within halos.
The projected pressure power spectrum allows a determination of the resulting
SZ power spectrum due to virialized structures. The unshocked photoionized
baryons present in smaller overdensities trace the Jeans-scale smoothed dark
matter distribution. They provide a lower limit to the SZ effect due to large
scale structure in the absence of massive collapsed halos. We extend our
calculations to discuss higher order statistics, such as bispectrum and
skewness in SZ data. The SZ-weak lensing cross-correlation is suggested as a
probe of correlations between dark matter and baryon density fields, while the
probability distribution functions of peak statistics of SZ halos in wide field
CMB data can be used as a probe of cosmology and non-Gaussian evolution of
large scale structure pressure fluctuations.Comment: 16 pages, 9 figures; Revised with expanded discussions. Phys. Rev. D.
(in press
Constraining the dark energy dynamics with the cosmic microwave background bispectrum
We consider the influence of the dark energy dynamics at the onset of cosmic
acceleration on the Cosmic Microwave Background (CMB) bispectrum, through the
weak lensing effect induced by structure formation. We study the line of sight
behavior of the contribution to the bispectrum signal at a given angular
multipole : we show that it is non-zero in a narrow interval centered at a
redshift satisfying the relation , where the
wavenumber corresponds to the scale entering the non-linear phase, and is
the cosmological comoving distance. The relevant redshift interval is in the
range 0.1\lsim z\lsim 2 for multipoles 1000\gsim\ell\gsim 100; the signal
amplitude, reflecting the perturbation dynamics, is a function of the
cosmological expansion rate at those epochs, probing the dark energy equation
of state redshift dependence independently on its present value. We provide a
worked example by considering tracking inverse power law and SUGRA Quintessence
scenarios, having sensibly different redshift dynamics and respecting all the
present observational constraints. For scenarios having the same present
equation of state, we find that the effect described above induces a projection
feature which makes the bispectra shifted by several tens of multipoles, about
10 times more than the corresponding effect on the ordinary CMB angular power
spectrum.Comment: 15 pages, 7 figures, matching version accepted by Physical Review D,
one figure improve
WMAP constraints on inflationary models with global defects
We use the cosmic microwave background angular power spectra to place upper
limits on the degree to which global defects may have aided cosmic structure
formation. We explore this under the inflationary paradigm, but with the
addition of textures resulting from the breaking of a global O(4) symmetry
during the early stages of the Universe. As a measure of their contribution, we
use the fraction of the temperature power spectrum that is attributed to the
defects at a multipole of 10. However, we find a parameter degeneracy enabling
a fit to the first-year WMAP data to be made even with a significant defect
fraction. This degeneracy involves the baryon fraction and the Hubble constant,
plus the normalization and tilt of the primordial power spectrum. Hence,
constraints on these cosmological parameters are weakened. Combining the WMAP
data with a constraint on the physical baryon fraction from big bang
nucleosynthesis calculations and high-redshift deuterium abundance, limits the
extent of the degeneracy and gives an upper bound on the defect fraction of
0.13 (95% confidence).Comment: 10pp LaTeX/RevTeX, 6 eps figs; matches accepted versio
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