7,372 research outputs found
Spacetime torsion and parity violation: a gauge invariant formulation
The possibility of parity violation through spacetime torsion has been
explored in a scenario containing fields with different spins. Taking the
Kalb-Ramond field as the source of torsion, an explicitly parity violating
gauge invariant theory has been constructed by extending the KR
field with a Chern-Simons term.Comment: 4 pages, RevTe
Gravitational Redshift in Einstein-Kalb-Ramond Spacetime and Randall-Sundrum Scenario
It is shown that the gravitational redshift as predicted by Einstein's
theory, is modified in presence of second rank antisymmetric tensor
(Kalb-Ramond) field in a string inspired background spacetime.In presence of
extra dimensions, the Randall-Sundrum brane world scenario is found to play a
crucial role in suppressing this additional shift. The bound on the value of
the warp factor is determined from the redshift data and is found to be in good
agreement with that determined from the requirements of Standard model.Comment: 4 Pages, Revtex, No figures, version thoroughly revise
Finite Thermal Wave Propagation in a Half-Space Due to Variable Thermal Loading
The thermoelastic interaction for the dual-phase-lag (DP) heat conduction in a thermoelastic half space is studied in the light of two-temperature generalized thermoelasticity theory (2TT). The medium is assumed to be initially quiescent. Using Laplace transform, the fundamental equations are expressed in the form of a vector-matrix differential equation which is then solved by statespace approach. The obtained general solution is then applied to the mechanical loading and various types of thermal loading (the thermal shock and the ramp-type heating). The numerical inversion of the Laplace transforms are carried out by the method of Fourier series expansion technique. The numerical results are computed for copper like material. Significant dissimilarities between two models (the two-temperature Lord-Shulman (2TLS) and the two temperature Dual-phase-lag model (2TDP)) are shown graphically. Because of the short duration of the second sound effect, the small-time solutions are analyzed and the discontinuities that occur at the wave fronts are also discussed. The effects of two-temperature and ramping parameters are studied
An Experimental Comparison of Tradeoffs in Using Compliant Manipulators for Robotic Grasping Tasks
Controllers developed for control of flexible-link robots in hybrid
force-position control tasks by a new singular perturbation analysis
of flexible manipulators are implemented on an experimental two-robot
grasping setup. Performance criteria are defined for the grasping
task. We present preliminary experimental data to show the tradeoffs
between controller complexity and performance enhancement as we deal
with greater flexibility. Various performance criteria are set up and
experimental results are discussed within that setting. We conclude
that large flexibility can be controlled and can lead to reasonable
performances
Observable signals in a string inspired axion-dilaton background and Randall-Sundrum scenario
Rotation angle of the plane of polarization of the distant galactic radio
waves has been estimated in a string inspired axion-dilaton background. It is
found that the axion,dual to the field strength of the second rank
antisymmetric massless Kalb-Ramond field in the string spectrum, produces a
wavelength independent optical rotation which is much larger than that produced
by the dilaton. Detection of such rotation has been reported in some recent
cosmological experiments. The observed value has been compared with our
estimated theoretical value following various cosmological constraints. The
effects of warped extra dimensions in a braneworld scenario on such an optical
rotation have been investigated.Comment: 17 Pages, Latex, article revised, To appear in Physical Review
Where are the degrees of freedom responsible for black hole entropy?
Considering the entanglement between quantum field degrees of freedom inside
and outside the horizon as a plausible source of black hole entropy, we address
the question: {\it where are the degrees of freedom that give rise to this
entropy located?} When the field is in ground state, the black hole area law is
obeyed and the degrees of freedom near the horizon contribute most to the
entropy. However, for excited state, or a superposition of ground state and
excited state, power-law corrections to the area law are obtained, and more
significant contributions from the degrees of freedom far from the horizon are
shown.Comment: 6 pages, 4 figures, Invited talk at Theory Canada III, Edmonton,
Alberta, Canada, June 16, 200
Cosmic optical activity from an inhomogeneous Kalb-Ramond field
The effects of introducing a harmonic spatial inhomogeneity into the
Kalb-Ramond field, interacting with the Maxwell field according to a
`string-inspired' proposal made in earlier work are investigated. We examine in
particular the effects on the polarization of synchrotron radiation from
cosmologically distant (i.e. of redshift greater than 2) galaxies, as well as
the relation between the electric and magnetic components of the radiation
field. The rotation of the polarization plane of linearly polarized radiation
is seen to acquire an additional contribution proportional to the square of the
frequency of the dual Kalb-Ramond axion wave, assuming that it is far smaller
compared to the frequency of the radiation field.Comment: 9 pages, Revtex, no figure
Spectroscopic Characteristics and Biological Activity against Ehrlich Ascites Carcinoma Cells of some Phenanthrenic Alkaloids
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