39,660 research outputs found
Bright solitons in asymmetrically trapped Bose-Einstein condensate
We study the dynamics of bright solitons in a Bose-Einstein condensate (BEC)
confined in a highly asymmetric trap. While working within the f ramework of a
variational approach we carry out the stability analysis o f BEC solitons
against collapse. When the number of atoms in the soliton exceeds a critical
number , it undergoes the so called primary col lapse. We find an
analytical expression for in terms of appropriat e experimental
quantities that are used to produce and confine the conde nsate. We further
demonstrate that, in the geometry of the problem consi dered, the width of the
soliton varies inversely as the number of consti tuent atoms.Comment: 5 pages, 1 figure
A Survey of Techniques for Improving Security of GPUs
Graphics processing unit (GPU), although a powerful performance-booster, also
has many security vulnerabilities. Due to these, the GPU can act as a
safe-haven for stealthy malware and the weakest `link' in the security `chain'.
In this paper, we present a survey of techniques for analyzing and improving
GPU security. We classify the works on key attributes to highlight their
similarities and differences. More than informing users and researchers about
GPU security techniques, this survey aims to increase their awareness about GPU
security vulnerabilities and potential countermeasures
What will anisotropies in the clustering pattern in redshifted 21 cm maps tell us?
The clustering pattern in high redshift HI maps is expected to be anisotropic
due to two distinct reasons, the
Alcock-Paczynski effect and the peculiar velocities, both of which are
sensitive to the cosmological parameters. The signal is also expected to be
sensitive to the details of the HI distribution at the epoch when the radiation
originated. We use simple models for the HI distribution at the epoch of
reionizaation and the post-reionization era to investigate exactly what we hope
to learn from future observations of the anisotropy pattern in HI maps. We find
that such observations will probably tell us more about the HI distribution
than about the background cosmological model. Assuming that reionization can be
described by spherical, ionized bubbles all of the same size with their centers
possibly being biased with respect to the dark matter, we find that the
anisotropy pattern at small angles is expected to have a bump at the
characteristic angular size of the individual bubbles whereas the large scale
anisotropy pattern will reflect the size and the bias of the bubbles. The
anisotropy also depends on the background cosmological parameters, but the
dependence is much weaker. Under the assumption that the HI in the
post-reionization era traces the dark matter with a possible bias, we find that
changing the bias and changing the background cosmology has similar effects on
the anisotropy pattern. Combining observations of the anisotropy with
independent estimates of the bias, possibly from the bi-spectrum, may allow
these observations to constrain cosmological parameters.Comment: Minor changes, Accepted to MNRA
Nonlinear Realization of the Local Conform-Affine Symmetry Group for Gravity in the Composite Fiber Bundle Formalism
A gauge theory of gravity based on a nonlinear realization (NLR) of the local
Conform-Affine (CA) group of symmetry transformations is presented. The coframe
fields and gauge connections of the theory are obtained. The tetrads and
Lorentz group metric are used to induce a spacetime metric. The inhomogenously
transforming (under the Lorentz group) connection coefficients serve as
gravitational gauge potentials used to define covariant derivatives
accommodating minimal coupling of matter and gauge fields. On the other hand,
the tensor valued connection forms serve as auxillary dynamical fields
associated with the dilation, special conformal and deformational (shear)
degrees of freedom inherent in the bundle manifold. The bundle curvature of the
theory is determined. Boundary topological invariants are constructed. They
serve as a prototype (source free) gravitational Lagrangian. The Bianchi
identities, covariant field equations and gauge currents are obtained.Comment: 24 pages. to appear in IJGMM
Squeezed States and Hermite polynomials in a Complex Variable
Following the lines of the recent paper of J.-P. Gazeau and F. H. Szafraniec
[J. Phys. A: Math. Theor. 44, 495201 (2011)], we construct here three types of
coherent states, related to the Hermite polynomials in a complex variable which
are orthogonal with respect to a non-rotationally invariant measure. We
investigate relations between these coherent states and obtain the relationship
between them and the squeezed states of quantum optics. We also obtain a second
realization of the canonical coherent states in the Bargmann space of analytic
functions, in terms of a squeezed basis. All this is done in the flavor of the
classical approach of V. Bargmann [Commun. Pur. Appl. Math. 14, 187 (1961)].Comment: 15 page
Design and Implementation of Position Estimator Algorithm on Voice Coil Motor
Voice Coil Motors (VCMs) have been an inevitable element in the mechanisms that have been used for precise positioning in the applications like 3D printing., micro-stereolithography., etc. These voice coil motors translate in a linear direction and require a high accuracy position sensor that amounts for a major part in the budget. In this research work., an effort has been made to design and implement an algorithm that would predict the displacement of VCM and eliminate the need of high cost sensors. VCM was integrated with dSPACE DS1104 R&D controller via linear current amplifier (LCAM) which acts as a driver circuit for VCM. Sine input was given to VCM with various amplitude and frequency and the corresponding displacement is measured by using linear variable differential transformer (LVDT). The position estimator algorithm is also implemented at the same time on VCM and its output is compared with that of LVDT. It is observed that there is 97.8 % accuracy in between algorithm output and LVDT output. Further., PID controller is used in integration with the novel algorithm to minimize the error. The estimator algorithm is tested for various amplitudes and frequencies and it is found that it has a very good agreement of 99.2% with the actual displacement measured with the help of LVDT
Slow test charge response in a dusty plasma with Kappa distributed electrons and ions
The electrostatic potential around a slowly moving test charge is studied in a dusty plasma where the ions and electrons follow a powerlaw Kappa distribution in velocity space. A test charge moving with a speed much smaller than the dust thermal speed gives rise to a short-scale Debye-Hueckel potential as well as a long-range far-field potential decreasing as inverse cube of the distance to the test charge along the propagation direction. The potentials are significantly modified in the presence of high-energy tails, modeled by lower spectral indices in the ion and electron Kappa distribution functions. Plasma parameters relevant to laboratory dusty plasmas are discussed
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