12,267 research outputs found
Periodic Orbits in Polygonal Billiards
We review some properties of periodic orbit families in polygonal billiards
and discuss in particular a sum rule that they obey. In addition, we provide
algorithms to determine periodic orbit families and present numerical results
that shed new light on the proliferation law and its variation with the genus
of the invariant surface. Finally, we deal with correlations in the length
spectrum and find that long orbits display Poisson fluctuations.Comment: 30 pages (Latex) including 11 figure
The CWKB Method of Particle Production in Periodic Potential
In this work we study the particle production in time dependent periodic
potential using the method of complex time WKB (CWKB) approximation. In the
inflationary cosmology at the end of inflationary stage, the potential becomes
time dependent as well as periodic. Reheating occurs due to particle production
by the oscillating inflaton field. Using CWKB we obtain almost identical
results on catastrophic particle production as obtained by others.Comment: 17 pages, latex, 2 figure
The Complex Time WKB Approximation And Particle Production
The complex time WKB (CWKB) approximation has been an effective technique to
understand particle production in curved as well as in flat spacetime. Earlier
we obtained the standard results on particle production in time dependent gauge
in various curved spacetime. In the present work we generalize the technique of
CWKB to the equivalent problems in space dependent gauge. Using CWKB, we first
obtain the gauge invariant result for particle production in Minkowski
spacetime in strong electric field. We then carry out particle production in
de-Sitter spacetime in space dependent gauge and obtain the same result that we
obtained earlier in time dependent gauge. The results obtained for de-Sitter
spacetime has a obvious extension to particle production in black hole
spacetime. It is found that the origin of Planckian spectrum is due to repeated
reflections between the turning points. As mentioned earlier, it is now
explicitly shown that particle production is accompanied by rotation of
currents.Comment: 12 pages, Revte
Quantum Gravity Equation In Schroedinger Form In Minisuperspace Description
We start from classical Hamiltonian constraint of general relativity to
obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter
prescription demanding that geometry itself determines the time, not the matter
field, such that the time so defined being equivalent to the time that enters
into the Schroedinger equation. Without any reference to the Wheeler-DeWitt
equation and without invoking the expansion of exponent in WKB wavefunction in
powers of Planck mass, we obtain an equation for quantum gravity in
Schroedinger form containing time. We restrict ourselves to a minisuperspace
description. Unlike matter field equation our equation is equivalent to the
Wheeler-DeWitt equation in the sense that our solutions reproduce also the
wavefunction of the Wheeler-DeWitt equation provided one evaluates the
normalization constant according to the wormhole dominance proposal recently
proposed by us.Comment: 11 Pages, ReVTeX, no figur
Wiggles in the cosmic microwave background radiation: echoes from non-singular cyclic-inflation
In this paper we consider a unique model of inflation where the universe
undergoes rapid asymmetric oscillations, each cycle lasting millions of Planck
time. Over many-many cycles the space-time expands to mimic the standard
inflationary scenario. Moreover, these rapid oscillations leave a distinctive
periodic signature in ln(k) in the primordial power spectrum, where k denotes
the comoving scale. The best fit parameters of the cyclic-inflation model
provides a very good fit to the 7-year WMAP data.Comment: Computational details and a figure adde
High-Q Gold and Silicon Nitride Bilayer Nanostrings
Low-mass, high-Q, silicon nitride nanostrings are at the cutting edge of
nanomechanical devices for sensing applications. Here we show that the addition
of a chemically functionalizable gold overlayer does not adversely affect the Q
of the fundamental out-of-plane mode. Instead the device retains its mechanical
responsiveness while gaining sensitivity to molecular bonding. Furthermore,
differences in thermal expansion within the bilayer give rise to internal
stresses that can be electrically controlled. In particular, an alternating
current excites resonant motion of the nanostring. This AC thermoelastic
actuation is simple, robust, and provides an integrated approach to sensor
actuation.Comment: 5 pages, 4 figures + supplementary materia
Experimentally Constrained Molecular Relaxation: The case of hydrogenated amorphous silicon
We have extended our experimentally constrained molecular relaxation
technique (P. Biswas {\it et al}, Phys. Rev. B {\bf 71} 54204 (2005)) to
hydrogenated amorphous silicon: a 540-atom model with 7.4 % hydrogen and a
611-atom model with 22 % hydrogen were constructed. Starting from a random
configuration, using physically relevant constraints, {\it ab initio}
interactions and the experimental static structure factor, we construct
realistic models of hydrogenated amorphous silicon. Our models confirm the
presence of a high frequency localized band in the vibrational density of
states due to Si-H vibration that has been observed in a recent vibrational
transient grating measurements on plasma enhanced chemical vapor deposited
films of hydrogenated amorphous silicon.Comment: 13 pages, 4 figure
Opinion dynamics model with domain size dependent dynamics: novel features and new universality class
A model for opinion dynamics (Model I) has been recently introduced in which
the binary opinions of the individuals are determined according to the size of
their neighboring domains (population having the same opinion). The coarsening
dynamics of the equivalent Ising model shows power law behavior and has been
found to belong to a new universality class with the dynamic exponent and persistence exponent in one dimension. The
critical behavior has been found to be robust for a large variety of annealed
disorder that has been studied. Further, by mapping Model I to a system of
random walkers in one dimension with a tendency to walk towards their nearest
neighbour with probability , we find that for any ,
the Model I dynamical behaviour is prevalent at long times.Comment: 12 pages, 10 figures. To be published in "Journal of Physics :
Conference Series" (2011
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