11,633 research outputs found
Bose-Einstein correlations in thermal field theory
Two-particle correlation functions are calculated for bosons emitted from a
localized thermal source (the ``glow'' of a ``hot spot''). In contrast to
existing work, non-equilibrium effects up to first order in gradients of the
particle distribution function are taken into account. The spectral width of
the bosons is shown to be an important quantity: If it is too small, they do
not equilibrate locally and therefore strongly increase the measured
correlation radius. In memoriam of Eugene Wigner and Hiroomi Umezawa.Comment: Paper in LaTeX. Figures and complete paper available via anonymous
ftp, ftp://tpri6c.gsi.de/pub/phenning/hhbr9
Existence and Vanishing of the Breathing Mode in Strongly Correlated Finite Systems
One of the fundamental eigenmodes of finite interacting systems is the mode
of {\em uniform radial expansion and contraction} -- the ``breathing'' mode
(BM). Here we show in a general way that this mode exists only under special
conditions: i) for harmonically trapped systems with interaction potentials of
the form or , or ii) for
some systems with special symmetry such as single shell systems forming
platonic bodies. Deviations from the BM are demonstrated for two examples:
clusters interacting with a Lennard-Jones potential and parabolically trapped
systems with Yukawa repulsion. We also show that vanishing of the BM leads to
the occurence of multiple monopole oscillations which is of importance for
experiments
Detecting multi-atomic composite states in optical lattices
We propose and discuss methods for detecting quasi-molecular complexes which
are expected to form in strongly interacting optical lattice systems.
Particular emphasis is placed on the detection of composite fermions forming in
Bose-Fermi mixtures. We argue that, as an indirect indication of the composite
fermions and a generic consequence of strong interactions, periodic
correlations must appear in the atom shot noise of bosonic absorption images,
similar to the bosonic Mott insulator [S. F\"olling, et al., Nature {\bf 434},
481 (2005)]. The composites can also be detected directly and their
quasi-momentum distribution measured. This method -- an extension of the
technique of noise correlation interferometry [E. Altman et al., Phys. Rev. A
{\bf 79}, 013603 (2004)] -- relies on measuring higher order correlations
between the bosonic and fermionic shot noise in the absorption images. However,
it fails for complexes consisting of more than three atoms.Comment: 9 revtex page
Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems
We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks. © 2012 American Institute of Physics
Dust rings and filaments around the isolated young star V1331 Cygni
We characterize the small and large scale environment of the young star V1331
Cygni with high resolution HST/WFPC2 and Digitized Sky Survey images. In
addition to a previously known outer dust ring (~30'' in diameter), the
HST/WFPC2 scattered light image reveals an inner dust ring for the first time.
This ring has a maximum radius of 6.5'' and is possibly related to a molecular
envelope. Large-scale optical images show that V1331 Cyg is located at the tip
of a long dust filament linking it to the dark cloud LDN 981. We discuss the
origin of the observed dust morphology and analyze the object's relation to its
parent dark cloud LDN 981. Finally, based on recent results from the
literature, we investigate the properties of V1331 Cyg and conclude that in its
current state the object does not show suffcient evidence to be characterized
as an FU Ori object.Comment: 15 pages ApJ preprint style including 3 figures, accepted for
publication in ApJ (Feb. 2007
On the methanol emission detection in the TW Hya disc: the role of grain surface chemistry and non-LTE excitation
The recent detection of gas-phase methanol (CHOH) lines in the disc of TW
Hya by Walsh et al. provided the first observational constraints on the complex
O-bearing organic content in protoplanetary discs. The emission has a ring-like
morphology, with a peak at au and an inferred column density of
cm. A low CHOH fractional abundance of (with respect to H) is derived, depending on the
assumed vertical location of the CHOH molecular layer. In this study, we
use a thermo-chemical model of the TW Hya disc, coupled with the ALCHEMIC
gas-grain chemical model, assuming laboratory-motivated, fast diffusivities of
the surface molecules to interpret the CHOH detection. Based on this disc
model, we performed radiative transfer calculations with the LIME code and
simulations of the observations with the CASA simulator. We found that our
model allows to reproduce the observations well. The CHOH emission in our
model appears as a ring with radius of au. Synthetic and observed line
flux densities are equal within the rms noise level of observations. The
synthetic CHOH spectra calculated assuming local thermodynamic equilibrium
(LTE) can differ by up to a factor of 3.5 from the non-LTE spectra. For the
strongest lines, the differences between LTE and non-LTE flux densities are
very small and practically negligible. Variations in the diffusivity of the
surface molecules can lead to variations of the CHOH abundance and,
therefore, line flux densities by an order of magnitude.Comment: Accepted for publication in MNRAS, 8 pages, 8 figure
- …