56,620 research outputs found
Effects of f(R) Model on the Dynamical Instability of Expansionfree Gravitational Collapse
Dark energy models based on f(R) theory have been extensively studied in
literature to realize the late time acceleration. In this paper, we have chosen
a viable f(R) model and discussed its effects on the dynamical instability of
expansionfree fluid evolution generating a central vacuum cavity. For this
purpose, contracted Bianchi identities are obtained for both the usual matter
as well as dark source. The term dark source is named to the higher order
curvature corrections arising from f(R) gravity. The perturbation scheme is
applied and different terms belonging to Newtonian and post Newtonian regimes
are identified. It is found that instability range of expansionfree fluid on
external boundary as well as on internal vacuum cavity is independent of
adiabatic index but depends upon the density profile, pressure
anisotropy and f(R) model.Comment: 26 pages, no figure. arXiv admin note: text overlap with
arXiv:1108.266
Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group
We present a state interaction spin-orbit coupling method to calculate
electron paramagnetic resonance (EPR) -tensors from density matrix
renormalization group wavefunctions. We apply the technique to compute
-tensors for the \ce{TiF3} and \ce{CuCl4^2-} complexes, a [2Fe-2S] model of
the active center of ferredoxins, and a \ce{Mn4CaO5} model of the S2 state of
the oxygen evolving complex. These calculations raise the prospects of
determining -tensors in multireference calculations with a large number of
open shells.Comment: 19 page
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Doping Nanocrystals And The Role Of Quantum Confinement
Recent progress in developing algorithms for solving the electronic structure problem for nanostructures is illustrated. Key ingredients in this approach include pseudopotentials implemented on a real space grid and the use of density functional theory. This procedure allows one to predict electronic properties for many materials across the nano-regime, i.e., from atoms to nanocrystals of sufficient size to replicate bulk properties. We will illustrate this method for doping silicon nanocrystals with phosphorous.Institute for Computational Engineering and Sciences (ICES
Radiating Shear-Free Gravitational Collapse with Charge
We present a new shear free model for the gravitational collapse of a
spherically symmetric charged body. We propose a dissipative contraction with
radiation emitted outwards. The Einstein field equations, using the junction
conditions and an ansatz, are integrated numerically. A check of the energy
conditions is also performed. We obtain that the charge delays the black hole
formation and it can even halt the collapse.Comment: 22 pages, 9 figures. It has been corrected several typos and included
several references. Accepted for publication in GR
Tensor factorizations of local second-order M{\o}ller Plesset theory
Efficient electronic structure methods can be built around efficient tensor
representations of the wavefunction. Here we describe a general view of tensor
factorization for the compact representation of electronic wavefunctions. We
use these ideas to construct low-complexity representations of the doubles
amplitudes in local second order M{\o}ller-Plesset perturbation theory. We
introduce two approximations - the direct orbital specific virtual
approximation and the full orbital specific virtual approximation. In these
approximations, each occupied orbital is associated with a small set of
correlating virtual orbitals. Conceptually, the representation lies between the
projected atomic orbital representation in Pulay-Saeb{\o} local correlation
theories and pair natural orbital correlation theories. We have tested the
orbital specific virtual approximations on a variety of systems and properties
including total energies, reaction energies, and potential energy curves.
Compared to the Pulay-Saeb{\o} ansatz, we find that these approximations
exhibit favourable accuracy and computational times, while yielding smooth
potential energy curves
Proposed New Test of Spin Effects in General Relativity
The recent discovery of a double-pulsar PSR J0737-3039A/B provides an
opportunity of unequivocally observing, for the first time, spin effects in
general relativity. Existing efforts involve detection of the precession of the
spinning body itself. However, for a close binary system, spin effects on the
orbit may also be discernable. Not only do they add to the advance of the
periastron (by an amount which is small compared to the conventional
contribution) but they also give rise to a precession of the orbit about the
spin direction. The measurement of such an effect would also give information
on the moment of inertia of pulsars
Synchrotron brightness distribution of turbulent radio jets
Radio jets are considered as turbulent mixing regions and it is proposed that the essential small scale viscous dissipation in these jets is by emission of MHD waves and by their subsequent strong damping due, at least partly, to gyro-resonant acceleration of supra-thermal particles. A formula relating the synchrotron surface brightness of a radio jet to the turbulent power input is deduced from physical postulates, and is tested against the data for NGC315 and 3C31 (NGC383). The predicted brightness depends essentially on the collimation behavior of the jet, and, to a lesser extent, on the CH picture of a 'high' nozzle with accelerating flow. The conditions for forming a large scale jet at a high nozzle from a much smaller scale jet are discussed. The effect of entrainment on the prediction is discussed with the use of similarity solutions. Although entrainment is inevitably associated with the turbulent jet, it may or may not be a dominant factor depending on the ambient density profile
Conservation of statistical results under the reduction of pair-contact interactions to solvation interactions
We show that the hydrophobicity of sequences is the leading term in
Miyazawa-Jernigan interactions. Being the source of additive (solvation) terms
in pair-contact interactions, they were used to reduce the energy parameters
while resulting in a clear vector manipulation of energy. The reduced
(additive) potential performs considerably successful in predicting the
statistical properties of arbitrary structures. The evaluated designabilities
of the structures by both models are highly correlated. Suggesting
geometrically non-degenerate vectors (structures) as protein-like structures,
the additive model is a powerful tool for protein design. Moreover, a crossing
point in the log-linear diagram of designability-ranking shows that about 1/e
of the structures have designabilities above the average, independent on the
used model.Comment: 17 pages and 10 figure
Comparison of computed tomography pulmonary angiography and point-of-care tests for pulmonary thromboembolism diagnosis in dogs
An Efficient Block Circulant Preconditioner For Simulating Fracture Using Large Fuse Networks
{\it Critical slowing down} associated with the iterative solvers close to
the critical point often hinders large-scale numerical simulation of fracture
using discrete lattice networks. This paper presents a block circlant
preconditioner for iterative solvers for the simulation of progressive fracture
in disordered, quasi-brittle materials using large discrete lattice networks.
The average computational cost of the present alorithm per iteration is , where the stiffness matrix is partioned into
-by- blocks such that each block is an -by- matrix, and
represents the operational count associated with solving a block-diagonal
matrix with -by- dense matrix blocks. This algorithm using the block
circulant preconditioner is faster than the Fourier accelerated preconditioned
conjugate gradient (PCG) algorithm, and alleviates the {\it critical slowing
down} that is especially severe close to the critical point. Numerical results
using random resistor networks substantiate the efficiency of the present
algorithm.Comment: 16 pages including 2 figure
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