2,580,774 research outputs found
Correlations in a BEC collision: First-principles quantum dynamics with 150 000 atoms
The quantum dynamics of colliding Bose-Einstein condensates with 150 000
atoms are simulated directly from the Hamiltonian using the stochastic
positive-P method. Two-body correlations between the scattered atoms and their
velocity distribution are found for experimentally accessible parameters.
Hanbury Brown-Twiss or thermal-like correlations are seen for copropagating
atoms, while number correlations for counterpropagating atoms are even stronger
than thermal correlations at short times. The coherent phase grains grow in
size as the collision progresses with the onset of growth coinciding with the
beginning of stimulated scattering. The method is versatile and usable for a
range of cold atom systems.Comment: 4 pages, 4 figures. v2: Rewording and style changes, minor except for
rewrite of background on the positive-P representation. Original research
unchange
Platelet Collapse Model of Pulsar Glitches
A platelet collapse model of starquakes is introduced. It displays
self-organized criticality with a robust power-law behavior. The simulations
indicate a near-constant exponent, whenever scaling is present.Comment: Figures available by sending request to Ivan Schmidt:
[email protected]
Newtonian Limit of Conformal Gravity
We study the weak-field limit of the static spherically symmetric solution of
the locally conformally invariant theory advocated in the recent past by
Mannheim and Kazanas as an alternative to Einstein's General Relativity. In
contrast with the previous works, we consider the physically relevant case
where the scalar field that breaks conformal symmetry and generates fermion
masses is nonzero. In the physical gauge, in which this scalar field is
constant in space-time, the solution reproduces the weak-field limit of the
Schwarzschild--(anti)DeSitter solution modified by an additional term that,
depending on the sign of the Weyl term in the action, is either oscillatory or
exponential as a function of the radial distance. Such behavior reflects the
presence of, correspondingly, either a tachion or a massive ghost in the
spectrum, which is a serious drawback of the theory under discussion.Comment: 9 pages, comments and references added; the version to be published
in Phys. Rev.
Local and global gravity
Our long experience with Newtonian potentials has inured us to the view that
gravity only produces local effects. In this paper we challenge this quite
deeply ingrained notion and explicitly identify some intrinsically global
gravitational effects. In particular we show that the global cosmological
Hubble flow can actually modify the motions of stars and gas within individual
galaxies, and even do so in a way which can apparently eliminate the need for
galactic dark matter. Also we show that a classical light wave acquires an
observable, global, path dependent phase in traversing a gravitational field.
Both of these effects serve to underscore the intrinsic difference between
non-relativistic and relativistic gravity.Comment: LaTeX, 20 pages plus three figures in two postscript files. To appear
in a special issue of Foundations of Physics honoring Professor Lawrence
Horwitz on the occasion of his 65th birthday; A. van der Merwe and S. Raby,
Editors, Plenum Publishing Company, N.Y., 199
A note on dissipation in helical turbulence
In helical turbulence a linear cascade of helicity accompanying the energy
cascade has been suggested. Since energy and helicity have different
dimensionality we suggest the existence of a characteristic inner scale,
, for helicity dissipation in a regime of hydrodynamic fully
developed turbulence and estimate it on dimensional grounds. This scale is
always larger than the Kolmogorov scale, , and their ratio vanishes in the high Reynolds number limit, so the flow will always be
helicity free in the small scales.Comment: 2 pages, submitted to Phys. Fluid
Bose-Einstein condensation of trapped atoms with dipole interactions
The path integral Monte Carlo method is used to simulate dilute trapped Bose
gases and to investigate the equilibrium properties at finite temperatures. The
quantum particles have a long-range dipole-dipole interaction and a short-range
s-wave interaction. Using an anisotropic pseudopotential for the long-range
dipolar interaction and a hard-sphere potential for the short-range s-wave
interaction, we calculate the energetics and structural properties as a
function of temperature and the number of particles. Also, in order to
determine the effects of dipole-dipole forces and the influence of the trapping
field on the dipolar condensate, we use two cylindrically symmetric harmonic
confinements (a cigar-shaped trap and a disk-shaped trap). We find that the net
effect of dipole-dipole interactions is governed by the trapping geometry. For
a cigar-shaped trap, the net contribution of dipolar interactions is attractive
and the shrinking of the density profiles is observed. For a disk-shaped trap,
the net effect of long-range dipolar forces is repulsive and the density
profiles expand
Diagonal quantum Bianchi type IX models in N=1 supergravity
We take the general quantum constraints of N=1 supergravity in the special
case of a Bianchi metric, with gravitino fields constant in the invariant
basis. We construct the most general possible wave function which solves the
Lorentz constraints and study the supersymmetry constraints in the Bianchi
Class A Models. For the Bianchi-IX cases, both the Hartle-Hawking state and
wormhole state are found to exist in the middle fermion levels.Comment: plain LaTex, 17 pages, accepted for publication in Classical Quantum
Gravit
Implications of Cosmic Repulsion for Gravitational Theory
In this paper we present a general, model independent analysis of a recently
detected apparent cosmic repulsion, and discuss its potential implications for
gravitational theory. In particular, we show that a negatively spatially curved
universe acts like a diverging refractive medium, to thus naturally cause
galaxies to accelerate away from each other. Additionally, we show that it is
possible for a cosmic acceleration to only be temporary, with some accelerating
universes actually being able to subsequently recontract.Comment: RevTeX, 13 page
Grover's search algorithm: An optical approach
The essential operations of a quantum computer can be accomplished using
solely optical elements, with different polarization or spatial modes
representing the individual qubits. We present a simple all-optical
implementation of Grover's algorithm for efficient searching, in which a
database of four elements is searched with a single query. By `compiling' the
actual setup, we have reduced the required number of optical elements from 24
to only 12. We discuss the extension to larger databases, and the limitations
of these techniques.Comment: 6 pages, 5 figures. To appear in a special issue of the Journal of
Modern Optics -- "The Physics of Quantum Information
Characteristic and Correlation Between TIME and Complication After Destructive Eye Procedure Patient at Plastic and Reconstruction Division Sanglah Hospital\u27s Eye Clinic Bali-Indonesia
Destructive eye procedure can be carried out by enucleation, evisceration and excenteration. Some efforts have been developed to reduce the complications, but it still occur within several years after the operation. This research aims to find out the characteristic and correlation between time and complications in patient after destructive eye procedure at Plastic and Reconstruction Division Sanglah Hospital\u27s Eye Clinic. For addition, characteristic of other patients in plastic and reconstruction also provided. This report is an analytical cross sectional study. Data were collected retrospectively from medical report of patients with history of destructive eye procedure in Sanglah Hospital\u27s eye clinic from January 1st until December 31st 2010. Patient\u27s characteristics were presented as frequency, percentage, mean, and standard deviation. Correlations between variables were statistically analyzed with Correlation of Lambda. Eye trauma, anophthalmic socket and nasolacrimal duct obstruction were the most common diagnosis at plastic and reconstruction division Sanglah Hospital\u27s eye clinic. There were 17 patients with history of destructive eye procedure in this report, including 76.5% male and 23.5% female. There is 58.8% destructive eye procedure held in age 13-50 year, mean 30.75 (SD 19.81). Infection (35.3%), trauma (23.5%) and tumor (11.8%) were the most common cause of destructive eye procedure in this study. Complications of destructive eye procedure occur in 70.6% of patient with contracted socket was the most common complication (58.3%). There was medium correlation between time and complication after the procedure, but the correlation was not statistically significant (r = 0.40; p > 0.05). In conclusion, from this study we obtained that there was medium correlation between time and complication after the procedure, but the correlation was not statistically significant
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