24,016 research outputs found
Interacting scalar and spinor fields in Bianchi type I universe filled with magneto-fluid
Self-consistent system of spinor, scalar and BI gravitational fields in
presence of magneto-fluid and -term is considered. Assuming that the
expansion of the BI universe is proportional to the component of
the shear tensor, exact solutions for the metric functions, as well as for
scalar and spinor fields are obtained. For a non-positive the
initially anisotropic space-time becomes isotropic one in the process of
expansion, whereas, for an oscillatory mode of expansion of the
BI model occurs.Comment: RevTex4, 8 pages, no figure
Nonlinear Spinor Fields and its role in Cosmology
Different characteristic of matter influencing the evolution of the Universe
has been simulated by means of a nonlinear spinor field. Exploiting the spinor
description of perfect fluid and dark energy evolution of the Universe given by
an anisotropic Bianchi type-VI, VI, V, III, I or isotropic
Friedmann-Robertson-Walker (FRW) one has been studied. It is shown that due to
some restrictions on metric functions, initial anisotropy in the models Bianchi
type-VI, VI, V and III does not die away, while the anisotropic Bianchi
type-I models evolves into the isotropic one.Comment: 22 pages, 12 Figure
Comparative study between two quantum spin systems KCuCl and TlCuCl
We have performed an {\it ab initio} study of the electronic structure of two
isostructural quantum spin systems, KCuCl and TlCuCl, which have
recently attracted much attention due to their unconventional magnetic
properties. Our first-principles analysis shows unambiguously the role of Tl,
as opposed to structural differences between the two compounds, in making
TlCuCl a {\it strongly} coupled s=1/2 dimer system compared to
KCuCl which shows a {\it weakly} coupled s=1/2 dimer behavior. Good
agreement with the existing analysis of inelastic neutron scattering results
has been observed.Comment: minor changes in text with additional references; in EPL forma
Pixelated Lenses and H_0 from Time-delay QSOs
Observed time delays between images of a lensed QSO lead to the determination
of the Hubble constant by Refsdal's method, provided the mass distribution in
the lensing galaxy is reasonably well known. Since the two or four QSO images
usually observed are woefully inadequate by themselves to provide a unique
reconstruction of the galaxy mass, most previous reconstructions have been
limited to simple parameterized models, which may lead to large systematic
errors in the derived H_0 by failing to consider enough possibilities for the
mass distribution of the lens. We use non-parametric modeling of galaxy lenses
to better explore physically plausible but not overly constrained galaxy mass
maps, all of which reproduce the lensing observables exactly, and derive the
corresponding distribution of H_0's. Blind tests - where one of us simulated
galaxy lenses, lensing observables, and a value for H_0, and the other applied
our modeling technique to estimate H_0 indicate that our procedure is reliable.
For four simulated lensed QSOs the distribution of inferred H_0 have an
uncertainty of \simeq 10% at 90% confidence. Application to published
observations of the two best constrained time-delay lenses, PG1115+080 and
B1608+656, yields H_0=61 +/- 11 km/s/Mpc at 68% confidence and 61 +/- 18
km/s/Mpc at 90% confidence.Comment: 27 pages, including 17 figs, LaTeX; accepted to A
Understanding Job Stress among Healthcare Staff
Introduction: Job life is an important part of a person’s daily life. There are many aspects of a job. A person may be satisfied with one or more aspects of his/her job but at the same time may be unhappy with other things related to the job. Objective: To evaluate the sources of job stress (stressful aspects of work) among the staff of a super specialty hospital & to suggest measures to decrease level of job stress. Methodology: Descriptive study employing 381 staff members of a super specialty hospital using a structured personal interview questionnaire consisting of 21 sources of stress. The hospital staff was asked to rate each item according to the extent to which it had contributed to their stress as experienced in their jobs in the past few months on a scale of 0 (not at all),1(a little), 2(quite a bit), 3 (a lot). A global rating of stress was also obtained. Result: The prime sources of stress were found to be underpayment (76%), excessive workload (70.3%), inadequate staff (48.6), & being involved in the emotional distress of patients (46.7%). Conclusion: The staffs of the hospital were in moderate stress due to the prime stressors so adequate measures should be taken to alleviate these stressors. This could be achieved through workload management, job redesign, & by offering occupational health education
Augmented space recursion for partially disordered systems
Off-stoichiometric alloys exhibit partial disorder, in the sense that only
some of the sublattices of the stoichiometric ordered alloy become disordered.
This paper puts forward a generalization of the augmented space recursion (ASR)
(introduced earlier by one of us (Mookerjee et al 1997(*))) for systems with
many atoms per unit cell. In order to justify the convergence properties of ASR
we have studied the convergence of various moments of local density of states
and other physical quantities like Fermi energy and band energy. We have also
looked at the convergence of the magnetic moment of Ni, which is very sensitive
to numerical approximations towards the k-space value 0.6 with the
number of recursion steps prior to termination.Comment: Latex 2e, 21 Pages, 13 Figures, iopb style file attache
Qualitative Theory for Lensed QSOs
We show that some characteristics of multiply-imaged QSO systems are very
model-independent and can be deduced accurately by simply scrutinizing the
relative positions of images and galaxy-lens center. These include the
time-ordering of the images, the orientation of the lens potential, and the
rough morphology of any ring. Other features can differ considerably between
specific models; H_0 is an example. Surprisingly, properties inherited from a
circularly symmetric lens system are model-dependent, whereas features that
arise from the breaking of circular symmetry are model-independent. We first
develop these results from some abstract geometrical ideas, then illustrate
them for some well-known systems (the quads Q2237+030, H1413+117,
HST14113+5211, PG1115+080, MG0414+0534, B1608+656, B1422+231, and RXJ0911+0551,
and the ten-image system B1933+507), and finally remark on two systems
(B1359+154 and PMN J0134-0931) where the lens properties are more complex. We
also introduce a Java applet which produces simple lens systems, and helps
further illustrate the concepts.Comment: 26 pages, incl. 15 figs; accepted to AJ; java applet available at
http://ankh-morpork.maths.qmw.ac.uk/~saha/astron/lens
Valley-Selective Landau-Zener Oscillations in Semi-Dirac p-n Junctions
We study transport across p-n junctions of gapped two-dimensional semi-Dirac
materials: nodal semimetals whose energy bands disperse quadratically and
linearly along distinct crystal axes. The resulting electronic properties ---
relevant to materials such as TiO/VO multilayers and
-(BEDT-TTF)I salts --- continuously interpolate between those
of mono- and bi-layer graphene as a function of propagation angle. We
demonstrate that tunneling across the junction depends on the orientation of
the tunnel barrier relative to the crystalline axes, leading to strongly
non-monotonic current-voltage characteristics, including negative differential
conductance in some regimes. In multi-valley systems these features provide a
natural route to engineering valley-selective transport.Comment: 7 pages, 7 figures, appendice
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