427 research outputs found
Shell Crossing Singularities in Quasi-Spherical Szekeres Models
We investigate the occurrence of shell crossing singularities in
quasi-spherical Szekeres dust models with or without a cosmological constant.
We study the conditions for shell crossing singularity both from physical and
geometrical point of view and they are in agreement.Comment: 10 latex pages, RevTex style, no figure
Holographic Dark Energy Scenario and Variable Modified Chaplygin Gas
In this letter, we have considered that the universe is filled with normal
matter and variable modified Chaplygin gas. Also we have considered the
interaction between normal matter and variable modified Chaplygin gas in FRW
universe. Then we have considered a correspondence between the holographic dark
energy density and interacting variable modified Chaplygin gas energy density.
Then we have reconstructed the potential of the scalar field which describes
the variable modified Chaplygin cosmology.Comment: 4 latex pages, no figures, RevTeX styl
Density Evolution in the New Modified Chaplygin Gas Model
In this paper, we have considered new modified Chaplygin gas (NMCG) model
which interpolates between radiation at early stage and CDM at late
stage. This model is regarded as a unification of dark energy and dark matter
(with general form of matter). We have derived the density parameters from the
equation of motion for the interaction between dark energy and dark matter.
Also we have studied the evolution of the various components of density
parameters.Comment: 6 Latex pages, 4 figures, RevTex styl
Collapse Dynamics of a Star of Dark Matter and Dark Energy
In this work, we study the collapse dynamics of an inhomogeneous spherically
symmetric star made of dark matter (DM) and dark energy (DE). The dark matter
is taken in the form of a dust cloud while anisotropic fluid is chosen as the
candidate for dark energy. It is investigated how dark energy modifies the
collapsing process and is examined whether dark energy has any effect on the
Cosmic Censorship Conjecture. The collapsing star is assumed to be of finite
radius and the space time is divided into three distinct regions and
, where represents the boundary of the star and
denotes the interior (exterior) of the star. The junction
conditions for matching over are specified. Role of Dark
energy in the formation of apparent horizon is studied and central singularity
is analyzed.Comment: 13 page
Instruments of RT-2 Experiment onboard CORONAS-PHOTON and their test and evaluation II: RT-2/CZT payload
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high
resolution devices for hard X-ray imaging and spectroscopic studies. The new
series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical
Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the
CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of
20 keV to 150 keV, are used to image solar flares in hard X-rays. Since these
modules are essentially manufactured for commercial applications, we have
carried out a series of comprehensive tests on these modules so that they can
be confidently used in space-borne systems. These tests lead us to select the
best three pieces of the 'Gold' modules for the RT-2/CZT payload. This paper
presents the characterization of CZT modules and the criteria followed for
selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries,
along with three CZT modules, a high spatial resolution CMOS detector for high
resolution imaging of transient X-ray events. Therefore, we discuss the
characterization of the CMOS detector as well.Comment: 26 pages, 19 figures, Accepted for publication in Experimental
Astronomy (in press
Naked Singularities in Higher Dimensional Szekeres Space-time
In this paper we study the quasi-spherical gravitational collapse of (n+2)
dimensional Szekeres space-time. The nature of the central shell focusing
singularity so formed is analyzed by studying both the radial null and
time-like geodesic originated from it. We follow the approach of Barve et al to
analyze the null geodesic and find naked singularity in different situations.Comment: 11 Latex Pages, 4 figures, RevTex styl
Occurrence of functional single-lobed ovary in Cirrhinus mrigala (Hamilton,1822) brood fish from Assam, India
Occurrence of abnormally developed gonads in fish is rather more uncommon in freshwater fish than marine fish. It is therefore worthwhile to disseminate the information of occurrence of a single-lobed ovary in Cirrhinus mrigala brood fish as an abnormal phenomenon. During April 2011 to March 2013, around 500 brood fish samples of Indian major carps (Labeo rohita, Catla and C. mrigala) were collected from different government and private fish farms of Assam and Tripura located in the Northeast of India. Among them, one C. mrigala specimen measuring 41 cm in total length and 640 g in weight collected from Ulubari fish seed farm of Guwahati, Assam during June, 2012 was found to have a single-lobed ovary instead of the normal bilobed structure. The ovary occupied the entire body cavity and the majority of ova were round and translucent. The ovary contributed substantially to the total body weight with gonado-somatic index of 32.81 which was the highest among all the mrigal specimens examined. The study indicates possibility of artificially inducing development of single-lobed ovary in C. mrigala for achieving possible higher spawn outputs in induced breeding of the cultivable species
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People-centric Emission Reduction in Buildings: A Data-driven and Network Topology-based Investigation
There is a growing consensus among policymakers that we need a human-centric low-carbon transition. There are few studies on how to do it effectively, especially in the context of emissions reduction in the building sector. It is critical to investigate public sentiment and attitudes towards this aspect of climate action, as the building and construction sector accounts for 40% of global carbon emissions. Our methodology involves a multi-method approach, using a data-driven exploration of public sentiment using 256,717 tweets containing #emission and #building between 2009 - 2021. Using graph theory-led metrics, a network topology-based investigation of hashtag co-occurrences was used to extract highly influential hashtags. Our results show that public sentiment is reactive to global climate policy events. Between 2009-2012, #greenbuilding, #emissions were highly influential, shaping the public discourse towards climate action. In 2013-2016, #lowcarbon, #construction and #energyefficiency had high centrality scores, which were replaced by hashtags like #climatetec, #netzero, #climateaction, #circulareconomy, and #masstimber, #climatejustice in 2017-2021. Results suggest that the current building emission reduction context emphasises the social and environmental justice dimensions, which is pivotal to an effective people-centric policymaking
A New Variable Modified Chaplygin Gas Model Interacting with Scalar Field
In this letter we present a new form of the well known Chaplygin gas model by
introducing inhomogeneity in the EOS. This model explains crossing.
Also we have given a graphical representation of the model using
parameters. We have also considered an interaction of this model with the
scalar field by introducing a phenomenological coupling function and have shown
that the potential decays with time.Comment: 7 pages, 3 figure
Gravitational Collapse in Higher Dimensional Husain Space-Time
We investigate exact solution in higher dimensional Husain model for a null
fluid source with pressure and density are related by the following
relations (i) , (ii) (variable
modified Chaplygin) and (iii) (polytropic). We have studied
the nature of singularity in gravitational collapse for the above equations of
state and also for different choices of the of the parameters and
namely, (i) , constant (generalized Chaplygin), (ii) constant
(modified Chaplygin). It is found that the nature of singularity is independent
of these choices of different equation of state except for variable Chaplygin
model. Choices of various parameters are shown in tabular form. Finally,
matching of Szekeres model with exterior Husain space-time is done.Comment: 12 latex pages, No figure, RevTex styl
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