517 research outputs found
Tunneling in a Cosmological Model with Violation of Strong Energy Condition
The tunneling rate, with exact prefactor, is calculated to first order in
\hbar for a closed FRW universe filled with perfect fluid violating the strong
energy condition. The calculations are performed by applying the
dilute-instanton approximation on the corresponding Duru-Kleinert path
integral. It is shown that a closed FRW universe filled with a perfect fluid
with small violation of strong energy condition is more probable to tunnel than
the same universe with large violation of strong energy condition.Comment: 11 pages, LaTe
63PFATTY ACID COMPOSITION OF TISSUE CULTURED BREAST CARCINOMA: EFFECT OF STEAROYL-COA DESATURASE-1 (SCD-1) INHIBITOR
Casimir effect for a spherical shell in de Sitter spacetime with signature change
The Casimir stress on a spherical shell in de Sitter signature changing
background for massless scalar field satisfying Dirichlet boundary conditions
on the shell is calculated. The Casimir stress is calculated for inside and
outside of the shell with different backgrounds corresponding to different
metric signatures and cosmological constants. An important contribution appears
due to signature change which leads to a transient rapid expansion of the
bubbles in this background.Comment: 8 pages, no figure
Casimir effect in a two dimensional signature changing spacetime
We study the Casimir effect for free massless scalar fields propagating on a
two-dimensional cylinder with a metric that admits a change of signature from
Lorentzian to Euclidean. We obtain a nonzero pressure, on the hypersurfaces of
signature change, which destabilizes the signature changing region and so
alters the energy spectrum of scalar fields. The modified region and spectrum,
themselves, back react on the pressure. Moreover, the central term of
diffeomorphism algebra of corresponding infinite conserved charges changes
correspondingly.Comment: 14 pages, abstract and text extended, references added, to appear in
JM
Classical and quantum spinor cosmology with signature change
We study the classical and quantum cosmology of a universe in which the
matter source is a massive Dirac spinor field and consider cases where such
fields are either free or self-interacting. We focus attention on the spatially
flat Robertson-Walker cosmology and classify the solutions of the
Einstein-Dirac system in the case of zero, negative and positive cosmological
constant . For , these solutions exhibit signature
transitions from a Euclidean to a Lorentzian domain. In the case of massless
spinor fields it is found that signature changing solutions do not exist when
the field is free while in the case of a self-interacting spinor field such
solutions may exist. The resulting quantum cosmology and the corresponding
Wheeler-DeWitt equation are also studied for both free and self interacting
spinor fields and closed form expressions for the wavefunction of the universe
are presented. These solutions suggest a quantization rule for the energy.Comment: 13 pages, 4 figure
On Signature Transition and Compactification in Kaluza-Klein Cosmology
We consider an empty (4+1) dimensional Kaluza-Klein universe with a negative
cosmological constant and a Robertson-Walker type metric. It is shown that the
solutions to Einstein field equations have degenerate metric and exhibit
transitioins from a Euclidean to a Lorentzian domain. We then suggest a
mechanism, based on signature transition which leads to compactification of the
internal space in the Lorentzian region as . With the
assumption of a very small value for the cosmological constant we find that the
size of the universe and the internal scale factor would be related
according to in the Lorentzian region. The corresponding
Wheeler-DeWitt equation has exact solution in the mini-superspace giving rise
to a quantum state which peaks in the vicinity of the classical solutions
undergoing signature transition.Comment: 13 pages, 3 figure
Quantum Stephani Universe in vicinity of the symmetry center
We study a class of spherically symmetric Stephani cosmological models in the
presence of a self-interacting scalar field in both classical and quantum
domains. We discuss the construction of `canonical' wave packets resulting from
the solutions of a class of Wheeler-DeWitt equations in the Stephani Universe.
We suggest appropriate initial conditions which result in wave packets
containing some desirable properties, most importantly good classical and
quantum correspondence. We also study the situation from de-Broglie Bohm
interpretation of quantum mechanics to recover the notion of time and compare
the classical and Bohmian results. We exhibit that the usage of the canonical
prescription and appropriate choices of expansion coefficients result in the
suppression of the quantum potential and coincidence between classical and
Bohmian results. We show that, in some cases, contrary to
Friedmann-Robertson-Walker case, the bound state solutions also exist for all
positive values of the cosmological constant.Comment: 22 pages, 19 figures, to appear in JCA
Quantum Corrections for a Braneworld Black Hole
By using the quantum tunneling approach over semiclassical approximations, we
study the quantum corrections to the Hawking temperature, entropy and
Bekenstein-Hawking entropy-area relation for a black hole lying on a brane.Comment: 8 pages, accepted for publication in IJTP, references adde
Diffeomorphism algebra of two dimensional free massless scalar field with signature change
We study a model of free massless scalar fields on a two dimensional cylinder
with metric that admits a change of signature between Lorentzian and Euclidean
type (ET), across the two timelike hypersurfaces (with respect to Lorentzian
region). Considering a long strip-shaped region of the cylinder, denoted by an
angle \theta, as the signature changed region it is shown that the energy
spectrum depends on the angle \theta and in a sense differs from ordinary one
for low energies. Morever diffeomorphism algebra of corresponding infinite
conserved charges is different from '' Virasoro'' algebra and approaches to it
at higher energies. The central term is also modified but does not approach to
the ordinary one at higher energies.Comment: 18 pages, Latex, 2 ps figure
Stress among UK academics : identifying who copes best?
This paper examined the levels of stress and coping strategies among UK academics. Adopting a positive psychology approach, the influence of the character strengths of hope, optimism, gratitude and self-efficacy, on stress, subjective well-being (SWB), and mental health (GHQ) was examined in 216 academics in a UK university. The study explored the relationship between coping styles and work-coping variables of sense of coherence and work locus of control and stress. No significant differences on the stress, well-being and mental health measures were found for participants' gender, whether in full-time or part-time employment and level of seniority within the university. Participants using problem-focussed coping experienced lower levels of stress while dysfunctional coping was a positive predictor of stress. Hope agency, hope pathway, gratitude, optimism and self-efficacy were the strongest positive predictors of satisfaction with life (SWL), while levels of perceived stress negatively predicted SWL. Gratitude, hope agency and self-efficacy positively predicted positive affect, while stress was a negative predictor. Gratitude, hope agency, self-efficacy and optimism were negative significant predictors of negative affect while stress was a positive predictor. Gratitude positively predicted mental health, while stress was a negative predictor and optimism was a significant moderator of the relationship between stress and mental health. Academics with higher levels of gratitude, self-efficacy, hope and optimism report lower levels of stress at work and higher levels of well-being as measured by higher life satisfaction, higher positive affect and lower negative affect. New approaches to stress management training are suggested based on these findings
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