908 research outputs found
Conformal Ricci collineations of static spherically symmetric spacetimes
Conformal Ricci collineations of static spherically symmetric spacetimes are
studied. The general form of the vector fields generating conformal Ricci
collineations is found when the Ricci tensor is non-degenerate, in which case
the number of independent conformal Ricci collineations is \emph{fifteen}; the
maximum number for 4-dimensional manifolds. In the degenerate case it is found
that the static spherically symmetric spacetimes always have an infinite number
of conformal Ricci collineations. Some examples are provided which admit
non-trivial conformal Ricci collineations, and perfect fluid source of the
matter
Uniqueness of Flat Spherically Symmetric Spacelike Hypersurfaces Admitted by Spherically Symmetric Static Spactimes
It is known that spherically symmetric static spacetimes admit a foliation by
{\deg}at hypersurfaces. Such foliations have explicitly been constructed for
some spacetimes, using different approaches, but none of them have proved or
even discussed the uniqueness of these foliations. The issue of uniqueness
becomes more important due to suitability of {\deg}at foliations for studying
black hole physics. Here {\deg}at spherically symmetric spacelike hy-
persurfaces are obtained by a direct method. It is found that spherically
symmetric static spacetimes admit {\deg}at spherically symmetric hypersurfaces,
and that these hypersurfaces are unique up to translation under the time- like
Killing vector. This result guarantees the uniqueness of {\deg}at spherically
symmetric foliations for such spacetimes.Comment: 10 page
Fluxon analogues and dark solitons in linearly coupled Bose-Einstein condensates
Two effectively one-dimensional parallel coupled Bose-Einstein condensates in
the presence of external potentials are studied. The system is modelled by
linearly coupled Gross-Pitaevskii equations. In particular, grey-soliton-like
solutions representing analogues of superconducting Josephson fluxons as well
as coupled dark solitons are discussed. Theoretical approximations based on
variational formulations are derived. It is found that the presence of a
magnetic trap can destabilize the fluxon analogues. However, stabilization is
possible by controlling the effective linear coupling between the condensates.Comment: 14 pages, 7 figures, The paper is to appear in Journal of Physics
Foliation of the Kottler-Schwarzschild-De Sitter Spacetime by Flat Spacelike Hypersurfaces
There exist Kruskal like coordinates for the Reissner-Nordstrom (RN) black
hole spacetime which are regular at coordinate singularities. Non existence of
such coordinates for the extreme RN black hole spacetime has already been
shown. Also the Carter coordinates available for the extreme case are not
manifestly regular at the coordinate singularity, therefore, a numerical
procedure was developed to obtain free fall geodesics and flat foliation for
the extreme RN black hole spacetime. The Kottler-Schwarzschild-de Sitter
(KSSdS) spacetime geometry is similar to the RN geometry in the sense that,
like the RN case, there exist non-singular coordinates when there are two
distinct coordinate singularities. There are no manifestly regular coordinates
for the extreme KSSdS case. In this paper foliation of all the cases of the
KSSdS spacetime by flat spacelike hypersurfaces is obtained by introducing a
non-singular time coordinate.Comment: 12 pages, 4 figure
Asymptotic Behaviour of the Proper Length and Volume of the Schwarzschild Singularity
Though popular presentations give the Schwarzschild singularity as a point it
is known that it is spacelike and not timelike. Thus it has a "length" and is
not a "point". In fact, its length must necessarily be infinite. It has been
proved that the proper length of the Qadir-Wheeler suture model goes to
infinity [1], while its proper volume shrinks to zero, and the asymptotic
behaviour of the length and volume have been calculated. That model consists of
two Friedmann sections connected by a Schwarzschild "suture". The question
arises whether a similar analysis could provide the asymptotic behaviour of the
Schwarzschild black hole near the singularity. It is proved here that, unlike
the behaviour for the suture model, for the Schwarzschild essential singularity
and , where
is the mean extrinsic curvature, or the York time.Comment: 13 pages, 1 figur
Note on flat foliations of spherically symmetric spacetimes
It is known that spherically symmetric spacetimes admit flat spacelike
foliations. We point out a simple method of seeing this result via the
Hamiltonian constraints of general relativity. The method yields explicit
formulas for the extrinsic curvatures of the slicings.Comment: 4 pages, to appear in PRD, reference added, typos correcte
RNAi: An emerging field of molecular research
RNA silencing, named as co-suppression or post transcriptional gene silencing (PTGS) was found in transgenic plants which was the result of cellular mRNA degradation and silencing of gene expression.RNA interference (RNAi) is a specific technique using only a few double stranded RNA (dsRNA) molecules to stop the expression which has made it one of the important areas in molecular biology. By introducing a gene into the host genome which is highly homologous to an endogenous gene, the RNA silencing is initiated. Double-stranded RNA (dsRNA) is cut by the enzyme âDicerâ producing small interfering RNAs (siRNAs) which combine with RNA-induced silencing complex (RISC). RISC, a protein complex, binds one strand of siRNA with mRNA of native target gene for destruction, resulting in gene silencing. The mechanism of RNAi offers a quick and easy way to determine the function of a gene. In this review, we discuss the history, components, mechanism and the application of RNA interference
Energy-aware Theft Detection based on IoT Energy Consumption Data
With the advent of modern smart grid networks, advanced metering infrastructure provides real-time information from smart meters (SM) and sensors to energy companies and consumers. The smart grid is indeed a paradigm that is enabled by the Internet of Things (IoT) and in which the SM acts as an IoT device that collects and transmits data over the Internet to enable intelligent applications. However, IoT data communicated over the smart grid could however be maliciously altered, resulting in energy theft due to unbilled energy consumption. Machine learning (ML) techniques for energy theft detection (ETD) based on IoT data are promising but are nonetheless constrained by the poor quality of data and particularly its imbalanced nature (which emerges from the dominant representation of honest users and poor representation of the rare theft cases). Leading ML-based ETD methods employ synthetic data generation to balance the training the dataset. However, these are trained to maximise average correct detection instead of ETD. In this work, we formulate an energy-aware evaluation framework that guides the model training to maximise ETD and minimise the revenue loss due to mis-classification. We propose a convolution neural network with positive bias (CNN-B) and another with focal loss CNN (CNN-FL) to mitigate the data imbalance impact. These outperform the state of the art and the CNN-B achieves the highest ETD and the minimum revenue loss with a loss reduction of 30.4% compared to the highest loss incurred by these methods
Towards Smart Sensing Systems: A New Approach to Environmental Monitoring Systems by Using LoRaWAN
The proliferation of monitoring in unpredictable
environments has aided the world in solving challenges that were
previously thought to be insurmountable. Drastic advancement
has been pinpointed in the way we live, work, and play; however,
the data odyssey has yet started. From sensing to monitoring,
the endless possibility enabled by LoRa, the long-range low
power solution has made its mark on the technological world.
With the adoption of the LoRaWAN, the long-range low power
wide area network has appeared in existence to cope with the
constraints associated with the Internet of Things (IoT) infrastructure. This paper presents a practical experiment for sensing
the environmental condition using the LoRaWAN solution. The
proposed work allows the users to check the environmental
effects (temperature, and humidity) online. Furthermore, the
signal behavior has been recorded and cross-verified by using
MATLAB software implementation
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