11,210 research outputs found
Isolated and Dynamical Horizons and Their Applications
Over the past three decades, black holes have played an important role in quantum gravity, mathematical physics, numerical relativity and gravitational wave phenomenology. However, conceptual settings and mathematical models used to discuss them have varied considerably from one area to another. Over the last five years a new, quasi-local framework was introduced to analyze diverse facets of black holes in an unified manner. In this framework, evolving black holes are modeled by dynamical horizons and black holes in equilibrium by isolated horizons. We review basic properties of these horizons and summarize applications to mathematical physics, numerical relativity and quantum gravity. This paradigm has led to significant generalizations of several results in black hole physics. Specifically, it has introduced a more physical setting for black hole thermodynamics and for black hole entropy calculations in quantum gravity; suggested a phenomenological model for hairy black holes; provided novel techniques to extract physics from numerical simulations; and led to new laws governing the dynamics of black holes in exact general relativity
Uplink Linear Receivers for Multi-cell Multiuser MIMO with Pilot Contamination: Large System Analysis
Base stations with a large number of transmit antennas have the potential to
serve a large number of users at high rates. However, the receiver processing
in the uplink relies on channel estimates which are known to suffer from pilot
interference. In this work, making use of the similarity of the uplink received
signal in CDMA with that of a multi-cell multi-antenna system, we perform a
large system analysis when the receiver employs an MMSE filter with a pilot
contaminated estimate. We assume a Rayleigh fading channel with different
received powers from users. We find the asymptotic Signal to Interference plus
Noise Ratio (SINR) as the number of antennas and number of users per base
station grow large while maintaining a fixed ratio. Through the SINR expression
we explore the scenario where the number of users being served are comparable
to the number of antennas at the base station. The SINR explicitly captures the
effect of pilot contamination and is found to be the same as that employing a
matched filter with a pilot contaminated estimate. We also find the exact
expression for the interference suppression obtained using an MMSE filter which
is an important factor when there are significant number of users in the system
as compared to the number of antennas. In a typical set up, in terms of the
five percentile SINR, the MMSE filter is shown to provide significant gains
over matched filtering and is within 5 dB of MMSE filter with perfect channel
estimate. Simulation results for achievable rates are close to large system
limits for even a 10-antenna base station with 3 or more users per cell.Comment: Accepted for publication in IEEE Transactions on Wireless
Communication
The slicing dependence of non-spherically symmetric quasi-local horizons in Vaidya Spacetimes
It is well known that quasi-local black hole horizons depend on the choice of
a time coordinate in a spacetime. This has implications for notions such as the
surface of the black hole and also on quasi-local physical quantities such as
horizon measures of mass and angular momentum. In this paper, we compare
different horizons on non-spherically symmetric slicings of Vaidya spacetimes.
The spacetimes we investigate include both accreting and evaporating black
holes. For some simple choices of the Vaidya mass function function
corresponding to collapse of a hollow shell, we compare the area for the
numerically found axisymmetric trapping horizons with the area of the
spherically symmetric trapping horizon and event horizon. We find that as
expected, both the location and area are dependent on the choice of foliation.
However, the area variation is not large, of order for a slowly
evolving horizon with . We also calculate analytically the
difference in area between the spherically symmetric quasi-local horizon and
event horizon for a slowly accreting black hole. We find that the difference
can be many orders of magnitude larger than the Planck area for sufficiently
large black holes.Comment: 10 pages, 5 figures, corrected minor typo
Extreme throat initial data set and horizon area--angular momentum inequality for axisymmetric black holes
We present a formula that relates the variations of the area of extreme
throat initial data with the variation of an appropriate defined mass
functional. From this expression we deduce that the first variation, with fixed
angular momentum, of the area is zero and the second variation is positive
definite evaluated at the extreme Kerr throat initial data. This indicates that
the area of the extreme Kerr throat initial data is a minimum among this class
of data. And hence the area of generic throat initial data is bounded from
below by the angular momentum. Also, this result strongly suggests that the
inequality between area and angular momentum holds for generic asymptotically
flat axially symmetric black holes. As an application, we prove this inequality
in the non trivial family of spinning Bowen-York initial data.Comment: 11 pages. Changes in presentation and typos correction
β-n-oxalyl-l-α, β -diaminopropionic acid (β -odap) content in lathyrus sativus: The integration of nitrogen and sulfur metabolism through β -cyanoalanine synthase
Grass pea (Lathyrus sativus L.) is an important legume crop grown mainly in South Asia and Sub-Saharan Africa. This underutilized legume can withstand harsh environmental conditions including drought and flooding. During drought-induced famines, this protein-rich legume serves as a food source for poor farmers when other crops fail under harsh environmental conditions; however, its use is limited because of the presence of an endogenous neurotoxic nonprotein amino acid β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP). Long-term consumption of Lathyrus and β-ODAP is linked to lathyrism, which is a degenerative motor neuron syndrome. Pharmacological studies indicate that nutritional deficiencies in methionine and cysteine may aggravate the neurotoxicity of β-ODAP. The biosynthetic pathway leading to the production of β-ODAP is poorly understood, but is linked to sulfur metabolism. To date, only a limited number of studies have been conducted in grass pea on the sulfur assimilatory enzymes and how these enzymes regulate the biosynthesis of β-ODAP. Here, we review the current knowledge on the role of sulfur metabolism in grass pea and its contribution to β-ODAP biosynthesis. Unraveling the fundamental steps and regulation of β-ODAP biosynthesis in grass pea will be vital for the development of improved varieties of this underutilized legume
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