85 research outputs found
Wormhole solutions in gravity
In this work, we intend to explore wormhole geometries in the framework of
gravity. We derive the field equations for the generic
function by assuming the static and spherically symmetric Morris-Thorne
wormhole metric. Then we consider two non-linear model,
specifically, and
, where and are free
model parameters. We obtain the wormhole solutions by assuming three cases,
namely, a linear barotropic EoS, anisotropic EoS, and isotropic EoS
corresponding to model I. We observe that for both barotropic and anisotropic
cases, the corresponding wormhole solutions obey the flaring-out condition
under asymptotic background, while for the isotropic case, the shape function
does not follow the flatness condition. Also, we find that the null energy
condition exhibits negative behavior in the vicinity of the throat. Further, we
consider two different shape functions to investigate the behavior of model II.
We find some constraints on the model parameter for which the violation of the
null energy condition exhibits. Finally, we employ the volume integral
quantifier to calculate the amount of exotic matter required near the wormhole
throat for both models. We conclude that the modification of standard GR can
efficiently minimize the use of exotic matter and provide stable traversable
wormhole solutions.Comment: Chinese Journal of Physics published versio
Dynamical system analysis of scalar field cosmology in coincident gravity
In this article, we investigate scalar field cosmology in the coincident
gravity formalism. We calculate the motion equations of gravity
under the flat Friedmann-Lema\^{i}tre-Robertson-Walker background in the
presence of a scalar field. We consider a non-linear model, particularly
, which is nothing but a polynomial correction to the STEGR
case. Further, we assumed two well-known specific forms of the potential
function, specifically the exponential from and
the power-law form . We employ some phase-space
variables and transform the cosmological field equations into an autonomous
system. We calculate the critical points of the corresponding autonomous
systems and examine their stability behaviors. We discuss the physical
significance corresponding to the exponential case for parameter values
and with , and with . Moreover, we
discuss the same corresponding to the power-law case for the parameter value
and . We also analyze the behavior of corresponding cosmological
parameters such as scalar field and dark energy density, deceleration, and the
effective equation of state parameter. Corresponding to the exponential case,
we find that the results obtained for the parameter constraints in Case III is
better among all three cases, and that represents the evolution of the universe
from a decelerated stiff era to an accelerated de-Sitter era via
matter-dominated epoch. Further, in the power-law case, we find that all
trajectories exhibit identical behavior, representing the evolution of the
universe from a decelerated stiff era to an accelerated de-Sitter era. Lastly,
we conclude that the exponential case shows better evolution as compared to the
power-law case.Comment: Comments are welcom
Viscous fluid cosmology in symmetric teleparallel gravity
In this manuscript, we analyze the viscous fluid cosmological model in the
framework of recently proposed gravity by assuming three different forms
of bulk viscosity coefficients, specifically, , , and and a linear
model, particularly, where is free model
parameter. We estimate the bulk viscosity coefficients and the model parameter
values using the combined H(z)+Pantheon+BAO data set. We study the asymptotic
behavior of our cosmological bulk viscous model by utilizing the phase space
method. We find that corresponding to all three cases, our model depicts the
evolution of the universe from matter dominated decelerated epoch (a past
attractor) to a stable de-sitter accelerated epoch ( a future attractor).
Further, we study the physical behavior of effective pressure, effective
equation of state (EoS), and the statefinder parameters. We find that the
pressure component in the presence of bulk viscosity shows negative behavior
and the effective EoS parameter predicts the accelerated expansion phase of the
universe for all three cases. Moreover, we obtain that the trajectories of our
model lie in the quintessence region and it converges to the CDM fixed
point in the far future. Thus we can conclude that our viscous fluid
cosmological model can efficiently describe late time accelerated expansion
phase of the universe corresponding to all three cases.Comment: Comments are welcom
gravity, its covariant formulation, energy conservation and phase-space analysis
In the present article we analyze the matter-geometry coupled theory
of gravity. We offer the fully covariant formulation of the theory, with which
we construct the correct energy balance equation and employ it to conduct a
dynamical system analysis in a spatially flat
Friedmann-Lema\^{i}tre-Robertson-Walker spacetime. We consider three different
functional forms of the function, specifically, , , and .
We attempt to investigate the physical capabilities of these models to describe
various cosmological epochs. We calculate Friedmann-like equations in each case
and introduce some phase space variables to simplify the equations in more
concise forms. We observe that the linear model with
is completely equivalent to the GR case without cosmological constant
. Further, we find that the model with
successfully depicts the observed transition from decelerated
phase to an accelerated phase of the universe. Lastly, we find that the model
with represents an accelerated
de-Sitter epoch for the constraints or .Comment: EPJC accepted versio
Bulk viscous fluid in symmetric teleparallel cosmology: theory versus experiment
The standard formulation of General Relativity Theory, in the absence of a
cosmological constant, is unable to explain the responsible mechanism for the
observed late-time cosmic acceleration. On the other hand, by inserting the
cosmological constant in Einstein's field equations it is possible to describe
the cosmic acceleration, but the cosmological constant suffers from an
unprecedented fine-tunning problem. This motivates one to modify Einstein's
space-time geometry of General Relativity. The modified theory of
gravity is an alternative theory to General Relativity, where the non-metricity
scalar is the responsible candidate for gravitational interactions. In the
present work we consider a Friedmann-Lem\^aitre-Robertson-Walker cosmological
model dominated by bulk viscous cosmic fluid in gravity with the
functional form , where and are free parameters
of the model. We constrain our model with the recent Pantheon supernovae data
set of 1048 data points, Hubble data set of 31 data points and baryon acoustic
oscillations data set consisting of six points. For higher values of redshift,
it is clear that the cosmology better fits data than standard cosmology.
We present the evolution of our deceleration parameter with redshift and it
properly predicts a transition from decelerated to accelerated phases of the
universe expansion. Also, we present the evolution of density, bulk viscous
pressure and the effective equation of state parameter with redshift. Those
show that bulk viscosity in a cosmic fluid is a valid candidate to acquire the
negative pressure to drive the cosmic expansion efficiently.We also examine the
behavior of different energy conditions to test the viability of our
cosmological model. Furthermore, the statefinder diagnostics are also
investigated in order to distinguish among different dark energy models.Comment: Comments are welcom
Scalar field evolution at background and perturbation levels for a broad class of potentials
In this paper, we investigate a non-interacting scalar field cosmology with
an arbitrary potential using the -deviser method that relies on the
differentiability properties of the potential. Using this alternative
mathematical approach, we present a unified dynamical system analysis at a
scalar field's background and perturbation levels with arbitrary potentials.
For illustration, we consider a monomial and double exponential potentials.
These two classes of potentials comprise the asymptotic behaviour of several
classes of scalar field potentials, and, therefore, they provide the skeleton
for the typical behaviour of arbitrary potentials. Moreover, we analyse the
linear cosmological perturbations in the matterless case by considering three
scalar perturbations: the evolution of the Bardeen potentials, the comoving
curvature perturbation, the so-called Sasaki-Mukhanov variable, or the scalar
field perturbation in uniform curvature gauge. Finally, an exhaustive dynamical
system analysis for each scalar perturbation is presented.Comment: 65 pages, 8 compound figures. Major revision. References adde
ROTIFERS ABUNDANCE AND THEIR RELATIONSHIP TO WATER QUALITY IN THE PANDU LAKE, BODHAN, TELANGANA, INDIA
Abstract: In the present study an attempt has been made to evaluate water quality and related density of rotifers for a period of two years, August 2002 to July 2004. A few water quality parameters such as dissolved Oxygen, biological oxygen demand, phosphates, and nitrates are presented here to relate with the abundance or cessation of rotifers. The present study has given an understanding that lake is transforming into nutrient rich water body
Gastrointestinal Tuberculosis Presenting as Malnutrition and Distal Colonic Bowel Obstruction
Gastrointestinal (GI) tuberculosis (TB) is rare and can occur in the context of active pulmonary disease or as a primary infection with no pulmonary symptoms. It typically presents with vague abdominal symptoms, making it difficult to discern from alternative disease processes. Although the ileocecal region is the most commonly affected site, tuberculous enteritis can involve any aspect of the GI tract. To demonstrate the importance of maintaining a high clinical suspicion for the disease, we present a case of GI TB presenting as severe malnutrition and segmental colitis of the left colon
Gastrointestinal haemorrhage in extracorporeal membrane oxygenation: insights from the national inpatient sample
INTRODUCTION: Extracorporeal membrane oxygenation (ECMO) is associated with gastrointestinal haemorrhage (GIH), which may result from coagulopathy, systemic inflammation, reduced gastric perfusion, and arteriovenous malformation from non-pulsatile blood flow. Data are limited regarding the burden of this complication in the United States.
MATERIAL AND METHODS: We analysed the National Inpatient Sample (NIS) database for the years 2007 to 2011 to identify hospitalisations in which an ECMO procedure was performed. Hospitalizations complicated by GIH in this cohort were then identified by relevant codes.
RESULTS: Between 2007 and 2011, ECMO hospitalisations increased from 1869 to 3799 (p \u3c 0.01). The proportion of hospitalisations complicated by GIH increased from 2.12% in 2007 to 7.46% in 2011 (p \u3c 0.01). Gastrointestinal haemorrhage was more common in men (56.7%) and in Caucasians (57.4%). Common comorbidities in this population were renal failure (71%), anaemia (55%), and hypertension (26%). All-cause inpatient mortality showed a numerical but nonsignificant increase from 56.7% to 61.9% (p = 0.49). The average cost of care per hospitalisation with GIH associated with ECMO use increased from 215,673 in 2011 (p \u3c 0.01).
CONCLUSIONS: Gastrointestinal haemorrhage during ECMO hospitalisations occurred in small but significantly increasing proportions. The inpatient mortality rate and costs associated with GIH were substantial and increased significantly during the study period
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