1,556 research outputs found
On the question of deconfinement in noncommutative Schwinger Model
The 1+1 dimensional bosonised Schwinger model with a generalized gauge
invariant regularisation has been studied in a noncommutative scenario to
investigate the fate of the transition from confinement to deconfinement
observed in the commutative setting. We show that though the fuzziness of space
time introduces new features in the confinement scenario, it does not affect
the deconfining limit.Comment: 4 pages, revTe
Thin-shell wormholes from black holes with dilaton and monopole fields
We provide a new type of thin-shell wormhole from the black holes with
dilaton and monopole fields. The dilaton and monopole that built the black
holes may supply fuel to construct the wormholes. Several characteristics of
this thin-shell wormhole have been discussed. Finally, we discuss the stability
of the thin-shell wormholes with a "phantom-like" equation of state for the
exotic matter at the throat.Comment: 6 pages and 3 figures, some typos are corrected and accepted in
Int.J.Theor.Phy
Gravitational Lensing by Rotating Naked Singularities
We model massive compact objects in galactic nuclei as stationary,
axially-symmetric naked singularities in the Einstein-massless scalar field
theory and study the resulting gravitational lensing. In the weak deflection
limit we study analytically the position of the two weak field images, the
corresponding signed and absolute magnifications as well as the centroid up to
post-Newtonian order. We show that there are a static post-Newtonian
corrections to the signed magnification and their sum as well as to the
critical curves, which are function of the scalar charge. The shift of the
critical curves as a function of the lens angular momentum is found, and it is
shown that they decrease slightingly for the weakly naked and vastly for the
strongly naked singularities with the increase of the scalar charge. The
point-like caustics drift away from the optical axis and do not depend on the
scalar charge. In the strong deflection limit approximation we compute
numerically the position of the relativistic images and their separability for
weakly naked singularities. All of the lensing quantities are compared to
particular cases as Schwarzschild and Kerr black holes as well as
Janis--Newman--Winicour naked singularities.Comment: 35 pages, 30 figure
The Influence Of Neutron Capture Rates On The Rare Earth Region Of The r-Process Abundance Pattern
We study the sensitivity of the r-process abundance pattern to neutron
capture rates along the rare earth region (A~150 to A~180). We introduce the
concepts of large nuclear flow and flow saturation which determine the neutron
capture rates that are influential in setting the rare earth abundances. We
illustrate the value of the two concepts by considering high entropy conditions
favorable for rare earth peak production and identifying important neutron
capture rates among the rare earth isotopes. We also show how these rates
influence nuclear flow and specific sections of the abundance pattern.Comment: 14 pages, 7 figures, submitted to PR
Can electro-magnetic field, anisotropic source and varying be sufficient to produce wormhole spacetime ?
It is well known that solutions of general relativity which allow for
traversable wormholes require the existence of exotic matter (matter that
violates weak or null energy conditions [WEC or NEC]). In this article, we
provide a class of exact solution for Einstein-Maxwell field equations
describing wormholes assuming the erstwhile cosmological term to be
space variable, viz., .
The source considered here not only a matter entirely but a sum of matters
i.e. anisotropic matter distribution, electromagnetic field and cosmological
constant whose effective parts obey all energy conditions out side the wormhole
throat. Here violation of energy conditions can be compensated by varying
cosmological constant. The important feature of this article is that one can
get wormhole structure, at least theoretically, comprising with physically
acceptable matters.Comment: Some changes have been mad
Induced hypotension for functional endoscopic sinus surgery: comparison between dexmedetomidine and nitro-glycerine
Background: Functional endoscopic sinus surgery (FESS) is a minimally invasive technique used to restore sinus ventilation and normal function by opening sinus air cells and ostia. FESS requires bloodless field, several techniques and drugs have been used in the past for achieving controlled hypotension such as nitroglycerine, esmolol, remifentanil, dexmedetomidine, isoflurane, propofol. Therefore, this study was conducted to compare between dexmedetomidine and nitroglycerine for controlled hypotension for FESS. Primary aim to compare quality of surgical field using average category scale and surgeon satisfaction and secondary aim to compare arterial pressure and heart rate changes between dexmedetomidine and nitroglycerine when used to induce hypotension.Methods: This study was conducted in 40 consenting adult patients posted for FESS and were randomly divided into two groups, group D received dexmedetomidine 1 mcg/kg and group N received nitroglycerine 0.5 mcg/kg/min, both infusions started 10 min after induction. Parameters such as quality of surgical field by average category scale, heart rate and mean arterial pressure (MAP) recorded every 10 minutes.Results: Dexmedetomidine and nitroglycerine both had comparable quality of surgical field. ACS grading of 1 or 2 were found among both the groups. Dexmedetomidine group had better mean arterial pressure at 10th, 20th, 30th, 40th, 50th, 60th and 70th min and heart rate at 10th, 20th, 30th, 40th, 50th, 60th and 70th min when compared to nitroglycerine group.Conclusions: Dexmedetomidine and nitroglycerine both were found to be safe to use for controlled hypotension in functional endoscopic sinus surgeries
Bell's inequalities in the tomographic representation
The tomographic approach to quantum mechanics is revisited as a direct tool
to investigate violation of Bell-like inequalities. Since quantum tomograms are
well defined probability distributions, the tomographic approach is emphasized
to be the most natural one to compare the predictions of classical and quantum
theory. Examples of inequalities for two qubits an two qutrits are considered
in the tomographic probability representation of spin states.Comment: 11 pages, comments and references adde
Higher Dimensional Dust Cosmological Implications of a Decay Law for Term : Expressions for Some Observable Quantities
In this paper we have considered the multidimensional cosmological
implications of a decay law for term that is proportional to , where is a constant and is the scale factor
of RW-space time. We discuss the cosmological consequences of a model for the
vanishing pressure for the case . It has been observed that such models
are compatible with the result of recent observations and cosmological term
gradually reduces as the universe expands. In this model
varies as the inverse square of time, which matches its natural units. The
proper distance, the luminosity distance-redshift, the angular diameter
distance-redshift, and look back time-redshift for the model are presented in
the frame work of higher dimensional space time. The model of the Freese {\it
et al.} ({\it Nucl. Phys. B} {\bf 287}, 797 (1987)) for is retrieved for
the particular choice of and also Einstein-de Sitter model is obtained
for . This work has thus generalized to higher dimensions the
well-know result in four dimensional space time. It is found that there may be
significant difference in principle at least, from the analogous situation in
four dimensional space time.Comment: 10 pages, no figure, to be appear in IJMP
New structural and magnetic aspects of the nanotube system Na2V3O7
We present new experimental results of low temperature x-ray synchrotron
diffraction, neutron scattering and very low temperature (mK-range) bulk
measurements on the nanotube system {\tube}. The crystal structure determined
from our data is similar to the previously proposed model (P. Millet {\it et
al.} J. Solid State Chem. , 676 (1999)), but also deviates from it in
significant details. The structure comprises nanotubes along the c-axis formed
by stacking units of two V-rings buckled in the -plane. The space group is
P and the composition is nonstoichiometric, Na(2-x)V3O7, x=0.17. The
thermal evolution of the lattice parameters reveals anisotropic lattice
compression on cooling. Neutron scattering experiments monitor a very weak
magnetic signal at energies from -20 to 9 meV. New magnetic susceptibility,
specific heat measurements and decay of remanent magnetization in the 30 mK -
300 mK range reveal that the previously observed transition at ~76 mK is
spin-glass like with no long-range order. Presented experimental observations
do not support models of isolated clusters, but are compatible with a model of
odd-legged S=1/2 spin tubes possibly segmented into fragments with different
lengths
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