557 research outputs found
A fractional Brownian motion model for the turbulent refractive index in lightwave propagation
It is discussed the limitations of the widely used markovian approximation
applied to model the turbulent refractive index in lightwave propagation.
It is well-known the index is a passive scalar field. Thus, the actual
knowledge about these quantities is used to propose an alternative stochastic
process to the markovian approximation: the fractional Brownian motion. This
generalizes the former introducing memory; that is, there is correlation along
the propagation path.Comment: 11 pages, no figures. Submitted and revised for Optics Communication
Strong Coupling vs. 4-D Locality in Induced Gravity
We re-examine the problem of strong coupling in a regularized version of DGP
(or ``brane-induced'') gravity. We find that the regularization of ref.
hep-th/0304148 differs from DGP in that it does not exhibit strong coupling or
ghosts up to cubic order in the interactions. We suggest that the nonlocal
nature of the theory, when written in terms of the 4-D metric, is a plausible
reason for this phenomenon. Finally, we briefly discuss the possible behavior
of the model at higher-order in perturbation theory.Comment: 19 pages, accepted for publication in PR
Nonlinear Properties of Vielbein Massive Gravity
We propose a non-linear extension of the Fierz-Pauli mass for the graviton
through a functional of the vielbein and an external Minkowski background. The
functional generalizes the notion of the measure, since it reduces to a
cosmological constant if the external background is formally sent to zero. Such
a term and the explicit external background, emerge dynamically from a
bi--gravity theory, having both a massless and a massive graviton in its
spectrum, in a specific limit in which the massless mode decouples, while the
massive one couples universally to matter. We investigate the massive theory
using the Stueckelberg method and providing a 't Hooft-Feynman gauge fixing in
which the tensor, vector and scalar Stueckelberg fields decouple. We show that
this model has the softest possible ultraviolet behavior which can be expected
from any generic (Lorentz invariant) theory of massive gravity, namely that it
becomes strong only at the scale Lambda_3 = (m_g^2 M_P)^{1/3}.Comment: 23+1 pages LaTeX, 3 figures, few typos correcte
BF models, Duality and Bosonization on higher genus surfaces
The generating functional of two dimensional field theories coupled to
fermionic fields and conserved currents is computed in the general case when
the base manifold is a genus g compact Riemann surface. The lagrangian density
is written in terms of a globally defined 1-form and a
multi-valued scalar field . Consistency conditions on the periods of
have to be imposed. It is shown that there exist a non-trivial dependence of
the generating functional on the topological restrictions imposed to . In
particular if the periods of the field are constrained to take values , with any integer, then the partition function is independent of the
chosen spin structure and may be written as a sum over all the spin structures
associated to the fermions even when one started with a fixed spin structure.
These results are then applied to the functional bosonization of fermionic
fields on higher genus surfaces. A bosonized form of the partition function
which takes care of the chosen spin structure is obtainedComment: 17 page
Salinity tolerance of diapausing eggs of freshwater zooplankton
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73091/1/j.1365-2427.2004.01185.x.pd
Multimessenger astronomy with the Einstein Telescope
Gravitational waves (GWs) are expected to play a crucial role in the
development of multimessenger astrophysics. The combination of GW observations
with other astrophysical triggers, such as from gamma-ray and X-ray satellites,
optical/radio telescopes, and neutrino detectors allows us to decipher science
that would otherwise be inaccessible. In this paper, we provide a broad review
from the multimessenger perspective of the science reach offered by the third
generation interferometric GW detectors and by the Einstein Telescope (ET) in
particular. We focus on cosmic transients, and base our estimates on the
results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope.
Minor corrections include
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Epidemic centrality - is there an underestimated epidemic impact of network peripheral nodes?
In the study of disease spreading on empirical complex networks in SIR model,
initially infected nodes can be ranked according to some measure of their
epidemic impact. The highest ranked nodes, also referred to as
"superspreaders", are associated to dominant epidemic risks and therefore
deserve special attention. In simulations on studied empirical complex
networks, it is shown that the ranking depends on the dynamical regime of the
disease spreading. A possible mechanism leading to this dependence is
illustrated in an analytically tractable example. In systems where the
allocation of resources to counter disease spreading to individual nodes is
based on their ranking, the dynamical regime of disease spreading is frequently
not known before the outbreak of the disease. Therefore, we introduce a
quantity called epidemic centrality as an average over all relevant regimes of
disease spreading as a basis of the ranking. A recently introduced concept of
phase diagram of epidemic spreading is used as a framework in which several
types of averaging are studied. The epidemic centrality is compared to
structural properties of nodes such as node degree, k-cores and betweenness.
There is a growing trend of epidemic centrality with degree and k-cores values,
but the variation of epidemic centrality is much smaller than the variation of
degree or k-cores value. It is found that the epidemic centrality of the
structurally peripheral nodes is of the same order of magnitude as the epidemic
centrality of the structurally central nodes. The implications of these
findings for the distributions of resources to counter disease spreading are
discussed
Infrastructure for Detector Research and Development towards the International Linear Collider
The EUDET-project was launched to create an infrastructure for developing and
testing new and advanced detector technologies to be used at a future linear
collider. The aim was to make possible experimentation and analysis of data for
institutes, which otherwise could not be realized due to lack of resources. The
infrastructure comprised an analysis and software network, and instrumentation
infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture
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