811 research outputs found
Effective action for scalar fields and generalised zeta-function regularisation
Motivated by the study of quantum fields in a Friedman-Robertson-Walker (FRW)
spacetime, the one-loop effective action for a scalar field defined in the
ultrastatic manifold , being the finite
volume, non-compact, hyperbolic spatial section, is investigated by a
generalisation of zeta-function regularisation. It is shown that additional
divergences may appear at one-loop level. The one-loop renormalisability of the
model is discussed and making use of a generalisation of zeta-function
regularisation, the one-loop renormalisation group equations are derived.Comment: Latex, 16 pages, no figures; Latex mistakes corrected; accepted for
publication in Physical Review
The (2+1)-dimensional charged gravastars
This is a continuation and generalization of our earlier work on {\it
gravastar} in (2+1) anti-de Sitter space-time to 2+1 dimensional solution of
charged gravastar. Morphologically this gravastar contains three regions
namely: (i) charged interior, (ii) charged shell and (iii) electrovacuum
exterior. We have studied different characteristics in terms of Length and
Energy, Entropy, and Junction conditions of the spherical charged distribution.
It is shown that the present model of charged gravastar is non-singular and
represents itself an alternative of Black Hole.Comment: 14 pages, Accepted in Phys. Lett.
The Hitchin functionals and the topological B-model at one loop
The quantization in quadratic order of the Hitchin functional, which defines
by critical points a Calabi-Yau structure on a six-dimensional manifold, is
performed. The conjectured relation between the topological B-model and the
Hitchin functional is studied at one loop. It is found that the genus one free
energy of the topological B-model disagrees with the one-loop free energy of
the minimal Hitchin functional. However, the topological B-model does agree at
one-loop order with the extended Hitchin functional, which also defines by
critical points a generalized Calabi-Yau structure. The dependence of the
one-loop result on a background metric is studied, and a gravitational anomaly
is found for both the B-model and the extended Hitchin model. The anomaly
reduces to a volume-dependent factor if one computes for only Ricci-flat Kahler
metrics.Comment: 33 pages, LaTe
Higher Dimensional Dark Energy Investigation with Variable and
Time variable and are studied here under a phenomenological
model of through an () dimensional analysis. The relation of
Zeldovich (1968) between and is
employed here, where is the proton mass and is Planck's constant. In
the present investigation some key issues of modern cosmology, viz. the age
problem, the amount of variation of and the nature of expansion of the
Universe have been addressed.Comment: 7 Latex pages with few change
Phenomenology of -CDM model: a possibility of accelerating Universe with positive pressure
Among various phenomenological models, a time-dependent model is selected here to investigate the -CDM cosmology.
Using this model the expressions for the time-dependent equation of state
parameter and other physical parameters are derived. It is shown that
in model accelerated expansion of the Universe takes place at negative
energy density, but with a positive pressure. It has also been possible to
obtain the change of sign of the deceleration parameter during cosmic
evolution.Comment: 16 Latex pages, 11 figures, Considerable modifications in the text;
Accepted in IJT
Scenario of Accelerating Universe from the Phenomenological \Lambda- Models
Dark matter, the major component of the matter content of the Universe,
played a significant role at early stages during structure formation. But at
present the Universe is dark energy dominated as well as accelerating. Here,
the presence of dark energy has been established by including a time-dependent
term in the Einstein's field equations. This model is compatible with
the idea of an accelerating Universe so far as the value of the deceleration
parameter is concerned. Possibility of a change in sign of the deceleration
parameter is also discussed. The impact of considering the speed of light as
variable in the field equations has also been investigated by using a well
known time-dependent model.Comment: Latex, 9 pages, Major change
Phase diagram and influence of defects in the double perovskites
The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo
O_6 is analyzed, with and without disorder due to antisites. In addition to an
homogeneous half metallic ferrimagnetic phase in the absence of doping and
disorder, we find antiferromagnetic phases at large dopings, and other
ferrimagnetic phases with lower saturation magnetization, in the presence of
disorder.Comment: 4 pages, 3 postscript figures, some errata correcte
Effective interaction between helical bio-molecules
The effective interaction between two parallel strands of helical
bio-molecules, such as deoxyribose nucleic acids (DNA), is calculated using
computer simulations of the "primitive" model of electrolytes. In particular we
study a simple model for B-DNA incorporating explicitly its charge pattern as a
double-helix structure. The effective force and the effective torque exerted
onto the molecules depend on the central distance and on the relative
orientation. The contributions of nonlinear screening by monovalent counterions
to these forces and torques are analyzed and calculated for different salt
concentrations. As a result, we find that the sign of the force depends
sensitively on the relative orientation. For intermolecular distances smaller
than it can be both attractive and repulsive. Furthermore we report a
nonmonotonic behaviour of the effective force for increasing salt
concentration. Both features cannot be described within linear screening
theories. For large distances, on the other hand, the results agree with linear
screening theories provided the charge of the bio-molecules is suitably
renormalized.Comment: 18 pages, 18 figures included in text, 100 bibliog
Defects and glassy dynamics in solid He-4: Perspectives and current status
We review the anomalous behavior of solid He-4 at low temperatures with
particular attention to the role of structural defects present in solid. The
discussion centers around the possible role of two level systems and structural
glassy components for inducing the observed anomalies. We propose that the
origin of glassy behavior is due to the dynamics of defects like dislocations
formed in He-4. Within the developed framework of glassy components in a solid,
we give a summary of the results and predictions for the effects that cover the
mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of
the glassy response of solid He-4. Our proposed glass model for solid He-4 has
several implications: (1) The anomalous properties of He-4 can be accounted for
by allowing defects to freeze out at lowest temperatures. The dynamics of solid
He-4 is governed by glasslike (glassy) relaxation processes and the
distribution of relaxation times varies significantly between different
torsional oscillator, shear modulus, and dielectric function experiments. (2)
Any defect freeze-out will be accompanied by thermodynamic signatures
consistent with entropy contributions from defects. It follows that such
entropy contribution is much smaller than the required superfluid fraction, yet
it is sufficient to account for excess entropy at lowest temperatures. (3) We
predict a Cole-Cole type relation between the real and imaginary part of the
response functions for rotational and planar shear that is occurring due to the
dynamics of defects. Similar results apply for other response functions. (4)
Using the framework of glassy dynamics, we predict low-frequency yet to be
measured electro-elastic features in defect rich He-4 crystals. These
predictions allow one to directly test the ideas and very presence of glassy
contributions in He-4.Comment: 33 pages, 13 figure
PELATIHAN PUBLIC SPEAKING DAN PENGENALAN TEKNOLOGI INFORMASI DI PANTI ASUHAN KHOIRUL UMMAH
Pengabdian masyarakat ini bertujuan untuk meningkatkan kepercayaan diri anak-anak Panti Asuhan Khoirul Ummah saat berkomunikasi dan pengenalan lebih dalam mengenai penggunaan teknologi dalam kehidupan. Mitra pengabdian kegiatan ini yaitu Panti Asuhan Khoirul Ummah yang berlokasi di Jl. Lange IV, Br.Batannyuh, Pemecutan Kelod Denpasar Barat, Bali. Metode yang digunakan dalam pelaksanaan kegiatan adalah pelatihan secara tatap muka dengan jumlah peserta kegiatan sebanyak 18 anak. Tahap pelaksanaan kegiatan meliputi, survei, analisis permasalahan mitra, pelatihan dan sharing session, pengisian kuesioner pra dan pasca pelatihan, dan evaluasi hasil pelaksanaan. Hasil kegiatan pengabdian menunjukan peningkatan persentase pemahaman public speaking sebesar 16,05% dengan nilai persentase awal 54,54% meningkat menjadi 70,59%. Sedangkan untuk peningkatan persentase pemahaman teknologi sebesar 17,26% dari persentase awal 45,09% menjadi 62,35%. Hasil-hasil tersebut menunjukkan bahwa terdapat peningkatan pemahaman anak-anak terhadap public speaking dan pengenalan teknologi informasi yang disampaikan pada pelatihan
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