5,166 research outputs found
A CM based equalizer for space-time spreading over channels with inter-Symbol interference
Space-time block coding (STBC) and a number of derivative techniques have been developed to maximize the diversity gain of a multi-input multi-output (MIMO) channel. This was later generalized for multi-user DS-CDMA systems through space-time spreading (STS), [3] and [4], which assumed flat fading as well as the availability of full channel state information (CSI) at the receiver. This paper focuses on the development of a blind chip-rate method for the equalization of STS over channels with inter-symbol interference (ISI). Simulation results are presented to demonstrate the convergence and noise resilience of the derived algorithm
Spectral Properties of M87 Using Two-Component Flow
We fit the observational data for M87 using two-component advective disk
model. We show that the flat spectrum from the nucleus of M87 is due to
synchrotron radiation produced by non-thermal electrons in the CENBOL. The
non-thermal distribution is produced due to acceleration of electrons across
the shock in a sub-Keplerian flow.Comment: 4 Pages, 1 Figures, Proceeding of the 2nd Kolkata Conference on
"Observational Evidence for the Black Holes in the Universe", Published in
AIP, 200
Consistent 3D Quantum Gravity on Lens Spaces
We study non-perturbative quantization of 3d gravity with positive
cosmological constant (de Sitter space being the prototype vacuum solution,
whose Euclideanization of course gives the three sphere) on the background
topology of lens space, which is a three spheres modulo a discrete group.
Instead of the strategy followed by a recent work \cite{Castro:2011xb}, which
compares results in the second and first order formulations of gravity, we
concentrate on the later solely. We note, as a striking feature, that the
quantization, that relies heavily on the axiomatics of topological quantum
field theory (TQFT) can only be consistently carried by augmenting the
conventional theory by an additional topological term coupled through a
dimensionless parameter. More importantly the introduction of this additional
parameter renders the theory finite.Comment: New section and references added. Accepted in Phys. Rev. D for
publicatio
Boosts, Schwarzschild Black Holes and Absorption cross-sections in M theory
dimensional neutral black strings wrapped on a circle are related to
dimensional charged black holes by boosts. We show that the boost has
to be performed in the covering space and the boosted coordinate has to be
compactified on a circle with a Lorentz contracted radius. Using this fact we
show that the transition between Schwarzschild black holes to black p-branes
observed recently in M theory is the well-known black hole- black string
transition viewed in a boosted frame. In a similar way the correspondence point
where an excited string state goes over to a neutral black hole is mapped
exactly to the correspondence point for black p-branes. In terms of the
brane quantities the equation of state for an excited string state becomes
identical to that of a 3+1 dimensional massless gas for all . Finally, we
show how boosts can be used to relate Hawking radiation rates. Using the known
microscopic derivation of absorption by extremal 3-branes and near-extremal 5D
holes with three large charges we provide a microscopic derivation of
absorption of 0-branes by seven and five dimensional Schwarzschild black holes
in a certain regime.Comment: Some references added, minor clarifications (harvmac, 16 pages
Zero-point quantum swing of magnetic couples
Quantum fluctuations are ubiquitous in physics. Ranging from conventional
examples like the harmonic oscillator to intricate theories on the origin of
the universe, they alter virtually all aspects of matter -- including
superconductivity, phase transitions and nanoscale processes. As a rule of
thumb, the smaller the object, the larger their impact. This poses a serious
challenge to modern nanotechnology, which aims total control via atom-by-atom
engineered devices. In magnetic nanostructures, high stability of the magnetic
signal is crucial when targeting realistic applications in information
technology, e.g. miniaturized bits. Here, we demonstrate that zero-point
spin-fluctuations are paramount in determining the fundamental magnetic
exchange interactions that dictate the nature and stability of the magnetic
state. Hinging on the fluctuation-dissipation theorem, we establish that
quantum fluctuations correctly account for the large overestimation of the
interactions as obtained from conventional static first-principles frameworks,
filling in a crucial gap between theory and experiment [1,2]. Our analysis
further reveals that zero-point spin-fluctuations tend to promote the
non-collinearity and stability of chiral magnetic textures such as skyrmions --
a counter-intuitive quantum effect that inspires practical guidelines for
designing disruptive nanodevices
Bound on Hardy's non-locality from the principle of Information Causality
Recently,the principle of nonviolation of information causality [Nature
461,1101 (2009)], has been proposed as one of the foundational properties of
nature. We explore the Hardy's nonlocality theorem for two qubit systems, in
the context of generalised probability theory, restricted by the principle of
nonviolation of information causality. Applying, a sufficient condition for
information causality violation, we derive an upper bound on the maximum
success probability of Hardy's nonlocality argument. We find that the bound
achieved here is higher than that allowed by quantum mechanics,but still much
less than what the nosignaling condition permits. We also study the Cabello
type nonlocality argument (a generalization of Hardy's argument) in this
context.Comment: Abstract modified, changes made in the conclusion, throughout the
paper we clarified that the condition used by us is protocal based and is
only a sufficient condition for the violation of information causalit
Do the mildly superluminal VLBI knots exclude ultrarelativistic blazar jets?
We compute the effective values of apparent transverse velocity and flux
boosting factors for the VLBI radio knots of blazar jets, by integrating over
the angular distributions of these quantities across the widths of jets with
finite opening angles but constant velocities. For high bulk Lorentz factors
(Gamma > 10) variations across the jet can be quite large if the opening angle,
omega, is even a few degrees on sub-parsec scales. The resulting apparent
speeds are often much lower than those obtained from the usual analyses that
ignore the finite jet opening angles. We can thus reconcile the usually
observed subluminal or mildly superluminal speeds with the very high (>~ 20)
Gamma factors, required by the inverse Compton origin and rapid variability of
TeV fluxes, as well as by intraday radio variability. Thus it is possible to
associate the VLBI radio knots directly with shocks in the ultra-relativistic
main jet flow, without invoking very rapid jet deceleration on parsec scales,
or extremely unlikely viewing angles.Comment: 10 pages, 1 figure, to appear in ApJ Letters, Nov. 10 2004 issu
Nonlocality without inequality for spin-s system
We analyze Hardy's non-locality argument for two spin-s systems and show that
earlier solution in this regard was restricted due to imposition of some
conditions which have no role in the argument of non-locality. We provide a
compact form of non-locality condition for two spin-s systems and extend it to
n number of spin-s particles. We also apply more general kind of non-locality
argument still without inequality, to higher spin system.Comment: 6 page
The Reciprocal Reshaping of the American Dream and American Religion
Religion has played an important role in the creation and dissemination of the idea now called the American Dream since the discovery of the North American continent. The first iteration of the American Dream manifested in the sixteenth century as a Return to Eden. The next phase was best represented by the Puritan quest for freedom of religion. In the eighteenth century, independence was the object of the American Dream. This was supported by the First Great Awakening. The nineteenth century American Dream can be characterized as opportunity as evidenced by immigration, westward migration, and the growth of commercial enterprise. The twentieth century American Dream began under the banner of achievement. After World War I, the advertising sector shanghaied the American Dream so that the measure of success was the acquisition of wealth and material goods. Religion, through acts of omission and acts of commission enabled the American Dream to become individual, materialistic, and debt-ridden. The twenty-first century war on terror, ascent of China, and economic collapse has called to question the future of the American Dream. There is a dire need for a fundamental recast of the next chapter of the American Dream. By guiding a return to the earlier American Dreams, religion could play a seminal role in this endeavor
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