158 research outputs found
Studies in Structure Formation in theories with a repulsive long range gravitational force
This article reports on emergence of structures in a class of alternative
theories of gravity. These theories do not have any horizon, flatness, initial
cosmological singularity and (possibly) quantization problems. The model is
characterised by a dynamically induced gravitational constant with a ``wrong''
sign corresponding to repulsive gravitation on the large scale. A non - minimal
coupling of a scalar field in the model can give rise to non - topological
solitons in the theory. This results in domains (gravity - balls) inside which
an effective, canonical, attractive gravitational constant is induced. We
consider simulations of the formation and evolution of such solutions. Starting
with a single gravity - ball, we consider its fragmentation into smaller (lower
mass) balls - evolving by mutual repulsion. After several runs, we have been
able to identify two parameters: the strength of the long range gravitational
constant and the size of the gravity balls, which can be used to generate
appropriate two point correlations of the distribution of these balls.Comment: Normal Tex, 7 pages, 5 figures available from the author
Etiology of male infertility: a review
Infertility is one of the major health issues and a socially destabilizing condition for couples often causing marital disharmony. Infertility refers to the biological inability of an individual to contribute to conception over the course of one year of continuous unprotected intercourse. There are numerous factors such as anatomical, physiological, environmental, lifestyle and genetic factors that cause infertility. Male infertility can be diagnosed by different tools, for instance, physical examination, semen analysis, testicular biopsy, hormonal tests, urine test, immunobead test, sperm functional tests, sperm chromatin and abnormal deoxyribonucleic acid (DNA) assays, chromosome and genetic studies. There are diverse treatment options available for male infertility inclusive of hormonal, pharmacological, non-pharmacological, antioxidants, anti-inflammatory therapy, surgical, assisted reproductive technologies (ART), combination and herbal supplement with lifestyle changes. The infertility of known etiology has ample treatment success rate that vary by age, accurate diagnosis and effective therapy along with shared decision-making which can facilitate achievement of fertility goals. Thus, the review summarizes classification, causes, and diagnosis with treatment modalities of male infertility
MARBLER: An Open Platform for Standarized Evaluation of Multi-Robot Reinforcement Learning Algorithms
Multi-agent reinforcement learning (MARL) has enjoyed significant recent
progress, thanks to deep learning. This is naturally starting to benefit
multi-robot systems (MRS) in the form of multi-robot RL (MRRL). However,
existing infrastructure to train and evaluate policies predominantly focus on
challenges in coordinating virtual agents, and ignore characteristics important
to robotic systems. Few platforms support realistic robot dynamics, and fewer
still can evaluate Sim2Real performance of learned behavior. To address these
issues, we contribute MARBLER: Multi-Agent RL Benchmark and Learning
Environment for the Robotarium. MARBLER offers a robust and comprehensive
evaluation platform for MRRL by marrying Georgia Tech's Robotarium (which
enables rapid prototyping on physical MRS) and OpenAI's Gym framework (which
facilitates standardized use of modern learning algorithms). MARBLER offers a
highly controllable environment with realistic dynamics, including barrier
certificate-based obstacle avoidance. It allows anyone across the world to
train and deploy MRRL algorithms on a physical testbed with reproducibility.
Further, we introduce five novel scenarios inspired by common challenges in MRS
and provide support for new custom scenarios. Finally, we use MARBLER to
evaluate popular MARL algorithms and provide insights into their suitability
for MRRL. In summary, MARBLER can be a valuable tool to the MRS research
community by facilitating comprehensive and standardized evaluation of learning
algorithms on realistic simulations and physical hardware. Links to our
open-source framework and the videos of real-world experiments can be found at
https://shubhlohiya.github.io/MARBLER/.Comment: 7 pages, 3 figures, submitted to MRS 2023, for the associated
website, see https://shubhlohiya.github.io/MARBLER
de Sitter spacetime: effects of metric perturbations on geodesic motion
Gravitational perturbations of the de Sitter spacetime are investigated using
the Regge--Wheeler formalism. The set of perturbation equations is reduced to a
single second order differential equation of the Heun-type for both electric
and magnetic multipoles. The solution so obtained is used to study the
deviation from an initially radial geodesic due to the perturbation. The
spectral properties of the perturbed metric are also analyzed. Finally, gauge-
and tetrad-invariant first-order massless perturbations of any spin are
explored following the approach of Teukolsky. The existence of closed-form,
i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation
is discussed.Comment: IOP macros, 10 figure
A program for a problem free Cosmology within a framework of a rich class of scalar tensor theories
A search for a problem free cosmology within the framework of an effective
non - minimally coupled scalar tensor theory is suggested. With appropriate
choice of couplings in variants of a Lee - Wick model [as also in a model
supporting Q - ball solutions], non topological solutions [NTS's], varying in
size upto 10 kpc to 1 Mpc can exist. We explore the properties of a ``toy''
Milne model containing a distribution of NTS domains. The interior of these
domains would be regions where effective gravitational effects would be
indistinguishable from those expected in standard Einstein theory. For a large
class of non - minimal coupling terms and the scalar effective potential, the
effective cosmological constant identically vanishes. The model passes
classical cosmological tests and we describe reasons to expect it to fare well
as regards nucleosynthesis and structure formation.Comment: 20 pages, Plain Tex, references added and expanded the previous
version of article, 2 figures available from [email protected]
Hawking Radiation of a Quantum Black Hole in an Inflationary Universe
The quantum stress-energy tensor of a massless scalar field propagating in
the two-dimensional Vaidya-de Sitter metric, which describes a classical model
spacetime for a dynamical evaporating black hole in an inflationary universe,
is analyzed. We present a possible way to obtain the Hawking radiation terms
for the model with arbitrary functions of mass. It is used to see how the
expansion of universe will affect the dynamical process of black hole
evaporation. The results show that the cosmological inflation has an
inclination to depress the black hole evaporation. However, if the cosmological
constant is sufficiently large then the back-reaction effect has the
inclination to increase the black hole evaporation. We also present a simple
method to show that it will always produce a divergent flux of outgoing
radiation along the Cauchy horizon where the curvature is a finite value. This
means that the Hawking radiation will be very large in there and shall modify
the classical spacetime drastically. Therefore the black hole evaporation
cannot be discussed self-consistently on the classical Vaidya-type spacetime.
Our method can also be applied to analyze the quantum stress-energy tensor in
the more general Vaidya-type spacetimes.Comment: Proper boundary will lead to anti-evaporation of schwarzschild-de
Sitter black holes, as corrected in Class. Quantum Grav. 11 (1994) 28
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