4,687 research outputs found
Mean field analysis of quantum phase transitions in a periodic optical superlattice
In this paper we analyze the various phases exhibited by a system of
ultracold bosons in a periodic optical superlattice using the mean field
decoupling approximation. We investigate for a wide range of commensurate and
incommensurate densities. We find the gapless superfluid phase, the gapped Mott
insulator phase, and gapped insulator phases with distinct density wave orders.Comment: 6 pages, 7 figures, 4 table
Detection of gravitational waves using a network of detectors
We formulate the data analysis problem for the detection of the Newtonian
coalescing-binary signal by a network of laser interferometric gravitational
wave detectors that have arbitrary orientations, but are located at the same
site. We use the maximum likelihood method for optimizing the detection
problem. We show that for networks comprising of up to three detectors, the
optimal statistic is essentially the magnitude of the network correlation
vector constructed from the matched network-filter. Alternatively, it is simply
a linear combination of the signal-to-noise ratios of the individual detectors.
This statistic, therefore, can be interpreted as the signal-to-noise ratio of
the network. The overall sensitivity of the network is shown to increase
roughly as the square-root of the number of detectors in the network. We
further show that these results continue to hold even for the restricted
post-Newtonian filters. Finally, our formalism is general enough to be extended
to address the problem of detection of such waves from other sources by some
other types of detectors, e.g., bars or spheres, or even by networks of
spatially well-separated detectors.Comment: 14 pages, RevTex, 1 postscript figure. Based on talk given at
Workshop on Cosmology: Observations confront theories, IIT-Kharagpur, India
(January 1999
DMRG studies on linear-exchange quantum spin models in one dimension
We study a class of spin-1/2 quantum antiferromagnetic chains using DMRG
technique. The exchange interaction in these models decreases linearly as a
function of the separation between the spins, for . For the separations beyond , the interaction is zero. The range
parameter takes positive integer values. The models corresponding to all
the odd values of are known to have the same exact doubly degenerate dimer
ground state as for the Majumdar-Ghosh (MG) model. In fact, R=3 is the MG
model. For even , the exact ground state is not known in general, except for
R=2 (the Bethe ansatz solvable Heisenberg chain) and in the asymptotic limit of
where the two MG dimer states again emerge as the exact ground state. In
the present work, we numerically investigate the even- models whose ground
state is not known analytically. In particular, for R=4, 6 and 8, we have
computed a number of ground state properties. We find that, unlike R=2, the
higher even- models are spin-gapped, and show strong dimer-dimer
correlations of the MG type. Moreover, the spin-spin correlations decay very
rapidly, albeit showing weak periodic revivals.Comment: 8 pages, 12 figure
Supersolid in a one-dimensional model of hard-core bosons
We study a system of hardcore boson on a one-dimensional lattice with
frustrated next-nearest neighbor hopping and nearest neighbor interaction. At
half filling, for equal magnitude of nearest and next-nearest neighbor hopping,
the ground state of this system exhibits a first order phase transition from a
Bond-Ordered (BO) solid to a Charge-Density-Wave(CDW) solid as a function of
the nearest neighbor interaction. Moving away from half filling we investigate
the system at incommensurate densities, where we find a SuperSolid (SS) phase
which has concurrent off-diagonal long range order and density wave order which
is unusual in a system of hardcore bosons in one dimension. Using the
finite-size Density-Matrix Renormalization Group (DMRG) method, we obtain the
complete phase diagram for this model
Phases and phase transitions of frustrated hard-core bosons on a triangular ladder
We study hardcore bosons on a triangular ladder at half filling in the
presence of a frustrating hopping term and a competing nearest neighbor
repulsion which promotes crystallization. Using the finite-size
density-matrix renormalization group method, we obtain the phase diagram which
contains three phases: a uniform superfluid (SF), an insulating charge density
wave (CDW) crystal and a bond ordered insulator (BO). We find that the
transitions from SF to CDW and SF to BO are continuous in nature, with critical
exponents varying continously along the phase boundaries, while the transition
from CDW to BO is found to be first order. The phase diagram is also shown to
contain an exactly solvable Majumdar Ghosh point, and re-entrant SF to CDW
phase transitions.Comment: 10 pages, 16 figure
Axillary Arch (Of Langer): Incidence, Innervation, Importance
The present study was planned to find out the incidence of accessory muscle arches in the axilla of 68 upper limb (38 right and 30 left) dissections. Langer’s arch was observed in one right limb out of the 68 limbs, total incidence was 1.47%. The arch extended from the latissimus dorsi to the fascia covering the biceps brachii. The incidence is low in South Indian population (Dravidians) compared to the various other populations reported in literature. A branch from the lateral cord of brachial plexus supplied it in contrast with the previous reports. The surgical significance of this muscle is reviewe
Radiation Pressure Induced Instabilities in Laser Interferometric Detectors of Gravitational Waves
The large scale interferometric gravitational wave detectors consist of
Fabry-Perot cavities operating at very high powers ranging from tens of kW to
MW for next generations. The high powers may result in several nonlinear
effects which would affect the performance of the detector. In this paper, we
investigate the effects of radiation pressure, which tend to displace the
mirrors from their resonant position resulting in the detuning of the cavity.
We observe a remarkable effect, namely, that the freely hanging mirrors gain
energy continuously and swing with increasing amplitude. It is found that the
`time delay', that is, the time taken for the field to adjust to its
instantaneous equilibrium value, when the mirrors are in motion, is responsible
for this effect. This effect is likely to be important in the optimal operation
of the full-scale interferometers such as VIRGO and LIGO.Comment: 27 pages, 11 figures, RevTex styl
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