53,540 research outputs found
Radiating spherical collapse with heat flow
We present here a simple model of radiative gravitational collapse with
radial heat flux which describes qualitatively the stages close to the
formation of a superdense cold star. Starting with a static general solution
for a cold star, the model can generate solutions for the earlier evolutionary
stages. The temporal evolution of the model is specified by solving the
junction conditions appropriate for radiating gravitational collapse.Comment: 13 pages, including 3 figures, submitted to IJMP-
Schr\"{o}dinger cat state of trapped ions in harmonic and anharmonic oscillator traps
We examine the time evolution of a two level ion interacting with a light
field in harmonic oscillator trap and in a trap with anharmonicities. The
anharmonicities of the trap are quantified in terms of the deformation
parameter characterizing the q-analog of the harmonic oscillator trap.
Initially the ion is prepared in a Schr\"{o}dinger cat state. The entanglement
of the center of mass motional states and the internal degrees of freedom of
the ion results in characteristic collapse and revival pattern. We calculate
numerically the population inversion I(t), quasi-probabilities and
partial mutual quantum entropy S(P), for the system as a function of time.
Interestingly, small deformations of the trap enhance the contrast between
population inversion collapse and revival peaks as compared to the zero
deformation case. For \beta =3 and determines the average number
of trap quanta linked to center of mass motion) the best collapse and revival
sequence is obtained for \tau =0.0047 and \tau =0.004 respectively. For large
values of \tau decoherence sets in accompanied by loss of amplitude of
population inversion and for \tau \sim 0.1 the collapse and revival phenomenon
disappear. Each collapse or revival of population inversion is characterized by
a peak in S(P) versus t plot. During the transition from collapse to revival
and vice-versa we have minimum mutual entropy value that is S(P)=0. Successive
revival peaks show a lowering of the local maximum point indicating a
dissipative irreversible change in the ionic state. Improved definition of
collapse and revival pattern as the anharminicity of the trapping potential
increases is also reflected in the Quasi- probability versus t plots.Comment: Revised version, 16 pages,6 figures. Revte
The generalized gradient approximation kernel in time-dependent density functional theory
A complete understanding of a material requires both knowledge of the excited
states as well as of the ground state. In particular, the low energy
excitations are of utmost importance while studying the electronic, magnetic,
dynamical, and thermodynamical properties of the material. Time-Dependent
Density Functional Theory (TDDFT), within the linear regime, is a successful
\textit{ab-initio} method to access the electronic charge and spin excitations.
However, it requires an approximation to the exchange-correlation (XC) kernel
which encapsulates the effect of electron-electron interactions in the
many-body system. In this work we derive and implement the spin-polarized XC
kernel for semi-local approximations such as the adiabatic Generalized Gradient
Approximation (AGGA). This kernel has a quadratic dependence on the wavevector,
{\bf q}, of the perturbation, however the impact of this on the electron energy
loss spectra (EELS) is small. Although the GGA functional is good in predicting
structural properties, it generality overestimates the exchange spin-splitting.
This leads to higher magnon energies, as compared to both ALDA and experiment.
In addition, interaction with the Stoner spin-flip continuum is enhanced by
AGGA, which strongly suppresses the intensity of spin-waves.Comment: 11 pages, 7 figure
High-Symmetry Polarization Domains in Low-Symmetry Ferroelectrics
We present experimental evidence for hexagonal domain faceting in the
ferroelectric polymer PVDF-TrFE films having the lower orthorhombic
crystallographic symmetry. This effect can arise from purely electrostatic
depolarizing forces. We show that in contrast to magnetic bubble shape domains
where such type of deformation instability has a predominantly elliptical
character, the emergence of more symmetrical circular harmonics is favored in
ferroelectrics with high dielectric constant
Pathological remodelling of the athlete’s heart
Engaging in regular physical activity affords significant health benefits,
while a lack of exercise is associated with increased cardiovascular morbidity
and mortality. The amount of physical activity required to achieve
these benefits is relatively modest, equating to 20–30 minutes of moderate
intensity exercise per day. Most athletes far exceed these recommendations
and now perform athletic feats previously considered insurmountable.
Studies in veteran athletes have demonstrated favourable outcomes
such as reduced incidence of cardiac disease and a greater lifespan. However,
in asymptomatic athletes concealing underlying cardiac disease,
intense exercise may be associated with sudden cardiac death. Despite the
devastating and highly visible effects of life-threatening arrhythmias,
exercise has retained its reputation as a prolonger of life as it is not the
primary cause of death but merely a trigger for such catastrophes. More
recent studies, however, have suggested that the effects of regular intense
exercise may result in adverse remodelling in otherwise healthy hearts.
This article will explore this concept and whether chronic intensive exercise
can adversely impact cardiovascular health
Analysis of Genetic Diversity in White Clover (\u3cem\u3eTrifolium Repens\u3c/em\u3e) Breeding Populations Using Agro-Morphological and RAPD Markers
White clover is an important forage legume for temperate regions, but very little is known about the genetic organisation of its breeding populations. The low amount of variability in the Indian collections of white clover for genetic improvement warrants the introduction of new germplasm and collecting local ecotypes for characterisation, utilisation and conservation. Several molecular techniques have been used for germplasm characterisation, variety identification, marker development and identification, molecular diagnostics, phylogenetic studies and diversity analysis. Because of its simplicity, rapidity and reliability, the RAPD technique has been used extensively for diversity analysis. The present study aims at characterising white clover genotypes of distinct geographical origin using standard descriptors and RAPD markers
Interface induced perpendicular magnetic anisotropy in Co/CoO/Co thin film structure: An in-situ MOKE investigation
Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic
properties have been investigated using in-situ magneto-optic Kerr effect
during growth of the sample. Magnetic anisotropy with easy axis perpendicular
to the film surface has been observed in top Co layer, whereas bottom layer was
found to be soft with in-plane magnetization without any influence of top
layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that
the growth of Co on oxidized interface takes place with preferential
orientation of c-axis perpendicular to the film plane, which results in the
observed perpendicular magnetic anisotropy. Texturing of the c-axis is expected
to be a result of minimization of the interface energy due to hybridization
between Co and oxygen at the interface.Comment: 9 pages, 3 figures, under review in IOP journa
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