3,042 research outputs found
Power filtration of CMB observational data
We propose a power filter Gp for linear reconstruction of the CMB signal from
observational maps. This Gp filter preserves the power spectrum of the CMB
signal in contrast to the Wiener filter which diminishes the power spectrum of
the reconstructed CMB signal. We demonstrate how peak statistics and a cluster
analysis can be used to estimate the probability of the presence of a CMB
signal in observational records. The efficiency of the Gp filter is
demonstrated on a toy model of an observational record consisting of a CMB
signal and noise in the form of foreground point sources.Comment: 17 pages; 4 figures; submitted to International Journal of Modern
Physic
Two-dimensional algebro-geometric difference operators
A generalized inverse problem for a two-dimensional difference operator is
introduced. A new construction of the algebro-geometric difference operators of
two types first considered by I.M.Krichever and S.P.Novikov is proposedComment: 11 pages; added references, enlarged introduction, rewritten abstrac
On the numerical closeness of the effective phenomenological electroweak mixing angle and the \MS parameter
It happens that and are equal with 0.1% accuracy, though
they are split by radiative corrections and a natural estimate for their
difference is 1%. This degeneracy occurs only for value close to
170\GeV, so no deep physical reason can be attributed to it. However, another
puzzle of the Standard Model, the degeneracy of s_\Eff^2 and , is not
independent of the previous one since a good physical reason exists for
s_\Eff^2 and degeneracy. We present explicit formulas which relate
these three angles.Comment: 10 pages, latex, 3 figures included; published on MPLA. A few
numerical estimates are improved; journal-ref is adde
Testing for Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe Data: Minkowski Functionals and the Length of the Skeleton
The three Minkowski functionals and the recently defined length of the
skeleton are estimated for the co-added first-year Wilkinson Microwave
Anisotropy Probe (WMAP) data and compared with 5000 Monte Carlo simulations,
based on Gaussian fluctuations with the a-priori best-fit running-index power
spectrum and WMAP-like beam and noise properties. Several power
spectrum-dependent quantities, such as the number of stationary points, the
total length of the skeleton, and a spectral parameter, gamma, are also
estimated. While the area and length Minkowski functionals and the length of
the skeleton show no evidence for departures from the Gaussian hypothesis, the
northern hemisphere genus has a chi^2 that is large at the 95% level for all
scales. For the particular smoothing scale of 3.40 degrees FWHM it is larger
than that found in 99.5% of the simulations. In addition, the WMAP genus for
negative thresholds in the northern hemisphere has an amplitude that is larger
than in the simulations with a significance of more than 3 sigma. On the
smallest angular scales considered, the number of extrema in the WMAP data is
high at the 3 sigma level. However, this can probably be attributed to the
effect of point sources. Finally, the spectral parameter gamma is high at the
99% level in the northern Galactic hemisphere, while perfectly acceptable in
the southern hemisphere. The results provide strong evidence for the presence
of both non-Gaussian behavior and an unexpected power asymmetry between the
northern and southern hemispheres in the WMAP data.Comment: 17 pages, 10 figures, accepted for publication in Ap
Efficiency at maximum power of thermally coupled heat engines
We study the efficiency at maximum power of two coupled heat engines, using
thermoelectric generators (TEGs) as engines. Assuming that the heat and
electric charge fluxes in the TEGs are strongly coupled, we simulate
numerically the dependence of the behavior of the global system on the
electrical load resistance of each generator in order to obtain the working
condition that permits maximization of the output power. It turns out that this
condition is not unique. We derive a simple analytic expression giving the
relation between the electrical load resistance of each generator permitting
output power maximization. We then focuse on the efficiency at maximum power
(EMP) of the whole system to demonstrate that the Curzon-Ahlborn efficiency may
not always be recovered: the EMP varies with the specific working conditions of
each generator but remains in the range predicted by irreversible
thermodynamics theory. We finally discuss our results in light of non-ideal
Carnot engine behavior.Comment: 11 pages, 7 figure
Topological Phenomena in the Real Periodic Sine-Gordon Theory
The set of real finite-gap Sine-Gordon solutions corresponding to a fixed
spectral curve consists of several connected components. A simple explicit
description of these components obtained by the authors recently is used to
study the consequences of this property. In particular this description allows
to calculate the topological charge of solutions (the averaging of the
-derivative of the potential) and to show that the averaging of other
standard conservation laws is the same for all components.Comment: LaTeX, 18 pages, 3 figure
Squeezars: Tidally powered stars orbiting a massive black hole
We propose that there exists a class of transient sources, "squeezars", which
are stars caught in highly eccentric orbits around a massive (m<10^8 Mo) black
hole (MBH), whose atypically high luminosity (up to a significant fraction of
their Eddington luminosity) is powered by tidal interactions with the MBH.
Their existence follows from the presence of a mass sink, the MBH, in the
galactic center, which drives a flow of stars into nearly radial orbits to
replace those it has destroyed. We consider two limits for the stellar response
to tidal heating: surface heating with radiative cooling ("hot squeezars") and
bulk heating with adiabatic expansion ("cold squeezars"), and calculate the
evolution of the squeezar orbit, size, luminosity and effective temperature.
The squeezar formation rate is only ~0.05 that of tidal disruption flares, but
squeezar lifetimes are many orders of magnitude longer, and so future
observations of squeezars in nearby galaxies can probe the tidal process that
feeds MBHs and the effects of extreme tides on stars. The mean number of
squeezars orbiting the Galactic MBH is estimated at 0.1-1.Comment: ApJ Lett. accepted. 4 pp. 1 fi
New global stability estimates for the Gel'fand-Calderon inverse problem
We prove new global stability estimates for the Gel'fand-Calderon inverse
problem in 3D. For sufficiently regular potentials this result of the present
work is a principal improvement of the result of [G. Alessandrini, Stable
determination of conductivity by boundary measurements, Appl. Anal. 27 (1988),
153-172]
- …