8,369 research outputs found
An improved fitting algorithm for parametric macromodeling from tabulated data
This paper introduces a new scheme for the identification of multivariate behavioral maeromodels from tabulated frequencydomain data. The method produces closed-form parametric expressions that reproduce with excellent accuracy the external port behavior of the structure, both as function of frequency and one or more external parmeters. The numerical robustness of the main algorithm is demonstrated on two significant examples
Geometric model of black hole quantum -portrait, extradimensions and thermodynamics
Recently a short scale modified black hole metric, known as holographic
metric, has been proposed in order to capture the self-complete character of
gravity. In this paper we show that such a metric can reproduce some geometric
features expected from the quantum -portrait beyond the semi-classical
limit. We show that for a generic this corresponds to having an effective
energy momentum tensor in Einstein equations or, equivalently, non-local terms
in the gravity action. We also consider the higher dimensional extension of the
metric and the case of an AdS cosmological term. We provide a detailed
thermodynamic analysis of both cases, with particular reference to the
repercussions on the Hawking-Page phase transition.Comment: 36 pages, 8 figures, invited paper to the special issue "Entropy in
Quantum Gravity and Quantum Cosmology" edited by R. Garattini for the journal
"Entropy", accepted for publication; v2 version matching that published on
the journa
Unparticle Casimir effect
In this paper we present the un-Casimir effect, namely the study of the
Casimir energy in the presence of an unparticle component in addition to the
electromagnetic field contribution. The distinctive feature of the un-Casimir
effect is a fractalization of metallic plates. This result emerges through a
new dependence of the Casimir energy on the plate separation that scales with a
continuous power controlled by the unparticle dimension. As long as the perfect
conductor approximation is valid, we find bounds on the unparticle scale that
are independent of the effective coupling constant between the scale invariant
sector and ordinary matter. We find regions of the parameter space such that
for plate distances around m and larger the un-Casimir bound wins over
the other bounds.Comment: 13 pages, 3 figures; v2: improved discussion, additional references,
v3: title slightly changed, version matching that in press on Physics Letters
Concentration fluctuations of large Stokes number particles in a one-dimensional random velocity field
We analyze the behavior of an ensemble of inertial particles in a
one-dimensional smooth Gaussian velocity field, in the limit of large inertia,
but considering a finite correlation time for the random field. We derive in
this limit a perturbative scheme for the calculation of the concentration
correlation and of the particle relative velocity distribution, providing
analytical expressions for the concentration fluctuation amplitude, its
correlation length, and the modification in the particle pair relative velocity
variance. The amplitude of the concentration fluctuations is characterized by
slow decay at large inertia and a much larger correlation length than that of
the random field. The fluctuation structure in velocity space is very different
from predictions from short-time correlated random velocity fields, with only
few particle pairs crossing at sufficiently small relative velocity to produce
correlations. Concentration fluctuations are associated with depletion of the
relative velocity variance of colliding particles.Comment: 8 pages, 1 figure, revtex
Did Going North Give Us Migraine? An Evolutionary Approach on Understanding Latitudinal Differences in Migraine Epidemiology
This commentary discusses a recent publication by evolutionary biologists with strong implications for migraine experts. The Authors showed that a gene polymorphism associated with migraine gave our ancestors an evolutionary advantage when colonizing northern, and thus colder, territories. They then highlight that the prevalence of migraine may differ among countries because of climatic adaptation. These results may prove useful in planning both epidemiological and physiological studies in the field of migraine
Return times for Stochastic processes with power-law scaling
An analytical study of the return time distribution of extreme events for
stochastic processes with power-law correlation has been carried on. The
calculation is based on an epsilon-expansion in the correlation exponent:
C(t)=|t|^{-1+epsilon}. The fixed point of the theory is associated with
stretched exponential scaling of the distribution; analytical expressions,
valid in the pre-asymptotic regime, have been provided. Also the permanence
time distribution appears to be characterized by stretched exponential scaling.
The conditions for application of the theory to non-Gaussian processes have
been analyzed and the relations with the issue of return times in the case of
multifractal measures have been discussed.Comment: 9 pages, 5 figures, revtex
Implications of a New Solar System Population of Neutralinos on Indirect Detection Rates
Recently, a new Solar System population of weakly interacting massive
particle (WIMP) dark matter has been proposed to exist. We investigate the
implications of this population on indirect signals in neutrino telescopes (due
to WIMP annihilations in the Earth) for the case when the WIMP is the lightest
neutralino of the MSSM, the minimal supersymmetric extension of the standard
model. The velocity distribution and capture rate of this new population is
evaluated and the flux of neutrino-induced muons from the center of the Earth
in neutrino telescopes is calculated. The strength of the signal is very
sensitive to the velocity distribution of the new population. We analytically
estimate this distribution using the approximate conservation of the component
of the WIMP angular momentum orthogonal to the ecliptic plane. The non-linear
problem of combining a fixed capture rate from the standard galactic WIMP
population with one rising linearly with time from the new population to obtain
the present-day annihilation rate in the Earth is also solved analytically. We
show that the effects of the new population can be crucial for masses below
around 150 GeV, where enhancements of the predicted muon flux from the center
of the Earth by up to a factor of 100 compared to previously published
estimates occur. As a result of the new WIMP population, the next generation of
neutrino telescopes should be able to probe a much larger region of parameter
space in the mass range 60-130 GeV.Comment: 21 pages, 5 eps figures, uses JHEP.cls. Figures made more readable,
references updated. Matches published versio
Forcing anomalous scaling on demographic fluctuations
We discuss the conditions under which a population of anomalously diffusing
individuals can be characterized by demographic fluctuations that are
anomalously scaling themselves. Two examples are provided in the case of
individuals migrating by Gaussian diffusion, and by a sequence of L\'evy
flights.Comment: 5 pages 2 figure
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