4,062 research outputs found
-dimensional charged Anti-de-Sitter black holes in gravity
We present a -dimensional charged Anti-de-Sitter black hole solutions in
gravity, where and . These solutions are
characterized by flat or cylindrical horizons. The interesting feature of these
solutions is the existence of inseparable electric monopole and quadrupole
terms in the potential which share related momenta, in contrast with most of
the known charged black hole solutions in General Relativity and its
extensions. Furthermore, these solutions have curvature singularities which are
milder than those of the known charged black hole solutions in General
Relativity and Teleparallel Gravity. This feature can be shown by calculating
some invariants of curvature and torsion tensors. Furthermore, we calculate the
total energy of these black holes using the energy-momentum tensor. Finally, we
show that these charged black hole solutions violate the first law of
thermodynamics in agreement with previous results.Comment: 11 Pages, will appear in JHE
Rotating charged AdS solutions in quadratic gravity
We present a class of asymptotically anti-de Sitter charged rotating black
hole solutions in gravity in -dimensions, where . These solutions are nontrivial extensions of the solutions presented in
\cite{Lemos:1994xp} and \cite{Awad:2002cz} in the context of general
relativity. They are characterized by cylindrical, toroidal or flat horizons,
depending on global identifications. The static charged black hole
configurations obtained in \cite{Awad:2017tyz} are recovered as special cases
when the rotation parameters vanish. Similar to \cite{Awad:2017tyz} the static
black holes solutions have two different electric multipole terms in the
potential with related moments. Furthermore, these solutions have milder
singularities compared to their general relativity counterparts. Using the
conserved charges expressions obtained in \cite{Ulhoa:2013gca} and
\cite{Maluf:2008ug} we calculate the total mass/energy and the angular momentum
of these solutions.Comment: 11 pages, Version accepted in EPJ
Phase Portraits of general f(T) Cosmology
We use dynamical system methods to explore the general behaviour of
cosmology. In contrast to the standard applications of dynamical analysis, we
present a way to transform the equations into a one-dimensional autonomous
system, taking advantage of the crucial property that the torsion scalar in
flat FRW geometry is just a function of the Hubble function, thus the field
equations include only up to first derivatives of it, and therefore in a
general cosmological scenario every quantity is expressed only in terms
of the Hubble function. The great advantage is that for one-dimensional systems
it is easy to construct the phase space portraits, and thus extract information
and explore in detail the features and possible behaviours of cosmology.
We utilize the phase space portraits and we show that cosmology can
describe the universe evolution in agreement with observations, namely starting
from a Big Bang singularity, evolving into the subsequent thermal history and
the matter domination, entering into a late-time accelerated expansion, and
resulting to the de Sitter phase in the far future. Nevertheless,
cosmology can present a rich class of more exotic behaviours, such as the
cosmological bounce and turnaround, the phantom-divide crossing, the Big Brake
and the Big Crunch, and it may exhibit various singularities, including the
non-harmful ones of type II and type IV. We study the phase space of three
specific viable models offering a complete picture. Moreover, we present
a new model of gravity that can lead to a universe in agreement with
observations, free of perturbative instabilities, and applying the Om(z)
diagnostic test we confirm that it is in agreement with the combination of
SNIa, BAO and CMB data at 1 confidence level.Comment: 39 pages, 12 figures, version published in JCA
A new optimization approach to the design of one-dimensional and two-dimensional finite impulse response digital filters
The theory for designing finite impulse response (FIR) frequency sampling digital filters can be extended to two-dimensions. The linear phase frequency response can be represented as a linear combination of individual frequency responses corresponding to the filter\u27s bands. The design of two-dimensional frequency sampling filters (FSF) has been treated in the past by using the technique of linear programming to find the optimal values of the transition samples. Although in theory the method guarantees an optimal solution, convergence problems occurred; This paper will introduce some detail of a one-dimensional FSF design technique and then extend these concepts to the two-dimensional problem. The mean of the squared error in both the stopband and the passband is minimized subject to constraints on the filter\u27s stopband. The filter\u27s coefficients can be calculated by solving a linear system of equations
First Law, Counterterms and Kerr-AdS_5 Black Holes
We apply the counterterm subtraction technique to calculate the action and
other quantities for the Kerr--AdS black hole in five dimensions using two
boundary metrics; the Einstein universe and rotating Einstein universe with
arbitrary angular velocity. In both cases, the resulting thermodynamic
quantities satisfy the first law of thermodynamics. We point out that the
reason for the violation of the first law in previous calculations is that the
rotating Einstein universe, used as a boundary metric, was rotating with an
angular velocity that depends on the black hole rotation parameter. Using a new
coordinate system with a boundary metric that has an arbitrary angular
velocity, one can show that the resulting physical quantities satisfy the first
law.Comment: 19 pages, 1 figur
Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars
Broadband magnetization response of coupled vortex state magnetic dots in
layered nanopillars was explored as a function of in-plane magnetic field and
interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25
nm) nanopillars of 600 nm diameter, a small in-plane field splits the
eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition
between in-phase and out-of-phase kinds of the low-lying coupled spin wave
modes. The critical field for this splitting is determined by antiparallel
chiralities of the vortices in the layers. Qualitatively similar (although more
gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25
nm) tri-layer nanopillars. These findings are in qualitative agreement with
micromagnetic dynamic simulations
Heat and mass transfer in unsteady rotating fluid flow with binary chemical reaction and activation energy
In this study, the Spectral Relaxation Method (SRM) is used to solve the coupled highly nonlinear system of partial differential equations due to an unsteady flow over a stretching surface in an incompressible rotating viscous fluid in presence of binary chemical reaction and Arrhenius activation energy. The velocity, temperature and concentration distributions as well as the skin-friction, heat and mass transfer coefficients have been obtained and discussed for various physical parametric values. The numerical results obtained by (SRM) are then presented graphically and discussed to highlight the physical implications of the simulations
Nonlinear nanofluid flow over heated vertical surface with sinusoidal wall temperature variations
The nonlinear density temperature variations in two-dimensional nanofluid flow over heated vertical surface with a sinusoidal wall temperature are investigated. The model includes the effects of Brownian motion and thermophoresis. Using the boundary layer approximation, the two-dimensional momentum, heat, and mass transfer equations are transferred to nonlinear partial differential equations form and solved numerically using a new method called spectral local linearisation method.The effects of the governing parameters on the fluid properties and on the heat and nanomass transfer coefficients are determined and shown graphically
Generation of Probabilistic Synthetic Data for Serious Games: A Case Study on Cyberbullying
Synthetic data generation has been a growing area of research in recent
years. However, its potential applications in serious games have not been
thoroughly explored. Advances in this field could anticipate data modelling and
analysis, as well as speed up the development process. The COVID-19 pandemic
has enlarged such a phenomenon, To try to fill this gap in the literature, we
propose a simulator architecture for generating probabilistic synthetic data
for serious games based on interactive narratives. This architecture is
designed to be generic and modular so that it can be used by other researchers
on similar problems. To simulate the interaction of synthetic players with
questions, we use a cognitive testing model based on the Item Response Theory
framework. We also show how probabilistic graphical models (in particular
Bayesian networks) can be used to introduce expert knowledge and external data
into the simulation. Finally, we apply the proposed architecture and methods in
a use case of a serious game focused on cyberbullying. We perform Bayesian
inference experiments using a hierarchical model to demonstrate the
identifiability and robustness of the generated data
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