18,710 research outputs found
Statistical emulation of a tsunami model for sensitivity analysis and uncertainty quantification
Due to the catastrophic consequences of tsunamis, early warnings need to be
issued quickly in order to mitigate the hazard. Additionally, there is a need
to represent the uncertainty in the predictions of tsunami characteristics
corresponding to the uncertain trigger features (e.g. either position, shape
and speed of a landslide, or sea floor deformation associated with an
earthquake). Unfortunately, computer models are expensive to run. This leads to
significant delays in predictions and makes the uncertainty quantification
impractical. Statistical emulators run almost instantaneously and may represent
well the outputs of the computer model. In this paper, we use the Outer Product
Emulator to build a fast statistical surrogate of a landslide-generated tsunami
computer model. This Bayesian framework enables us to build the emulator by
combining prior knowledge of the computer model properties with a few carefully
chosen model evaluations. The good performance of the emulator is validated
using the Leave-One-Out method
Renormalization Group and Conformal Symmetry Breaking in the Chern-Simons Theory Coupled to Matter
The three-dimensional Abelian Chern-Simons theory coupled to a scalar and a
fermionic field of arbitrary charge is considered in order to study conformal
symmetry breakdown and the effective potential stability. We present an
improved effective potential computation based on two-loop calculations and the
renormalization group equation: the later allows us to sum up series of terms
in the effective potential where the power of the logarithms are one, two and
three units smaller than the total power of coupling constants (i.e., leading,
next-to-leading and next-to-next-to-leading logarithms). For the sake of this
calculation we determined the beta function of the
fermion-fermion-scalar-scalar interaction and the anomalous dimension of the
scalar field. We shown that the improved effective potential provides a much
more precise determination of the properties of the theory in the broken phase,
compared to the standard effective potential obtained directly from the loop
calculations. This happens because the region of the parameter space where
dynamical symmetry breaking occurs is drastically reduced by the improvement
discussed here.Comment: 29 pages, 10 figures, 1 tabl
Crop Flexibility in Dryland Corn and Soybeans Using Predicted Yields and Prices
Crop Production/Industries,
Non-perturbative fixed points and renormalization group improved effective potential
The stability conditions of a renormalization group improved effective
potential have been discussed in the case of scalar QED and QCD with a
colorless scalar. We calculate the same potential in these models assuming the
existence of non-perturbative fixed points associated to a conformal phase. In
the case of scalar QED the barrier of instability found previously is barely
displaced as we approach the fixed point, and in the case of QCD with a
colorless scalar not only the barrier is changed but the local minimum of the
potential is also changed.Comment: 6 pages, 8 figures, References added. Matching the journal versio
Fitting isochrones to open cluster photometric data III. Estimating metallicities from UBV photometry
The metallicity is a critical parameter that affects the correct
determination fundamental characteristics stellar cluster and has important
implications in Galactic and Stellar evolution research. Fewer than 10 % of the
2174 currently catalog open clusters have their metallicity determined in the
literature. In this work we present a method for estimating the metallicity of
open clusters via non-subjective isochrone fitting using the cross-entropy
global optimization algorithm applied to UBV photometric data. The free
parameters distance, reddening, age, and metallicity simultaneously determined
by the fitting method. The fitting procedure uses weights for the observational
data based on the estimation of membership likelihood for each star, which
considers the observational magnitude limit, the density profile of stars as a
function of radius from the center of the cluster, and the density of stars in
multi-dimensional magnitude space. We present results of [Fe/H] for nine
well-studied open clusters based on 15 distinct UBV data sets. The [Fe/H]
values obtained in the ten cases for which spectroscopic determinations were
available in the literature agree, indicating that our method provides a good
alternative to determining [Fe/H] by using an objective isochrone fitting. Our
results show that the typical precision is about 0.1 dex
Enhancement of the Benjamin-Feir instability with dissipation
It is shown that there is an overlooked mechanism whereby some kinds of
dissipation can enhance the Benjamin-Feir instability of water waves. This
observation is new, and although it is counterintuitive, it is due to the fact
that the Benjamin-Feir instability involves the collision of modes with
opposite energy sign (relative to the carrier wave), and it is the negative
energy perturbations which are enhanced.Comment: 15 pages, 2 figures To download more papers, go to
http://www.cmla.ens-cachan.fr/~dias. Physics of Fluids (2007) to appea
Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario
We study the perturbative generation of higher-derivative operators as
corrections to the photon effective action, which are originated from a Lorentz
violation background. Such corrections are obtained, at one-loop order, through
the proper-time method, using the zeta function regularization. We focus over
the lowest order corrections and investigate their influence in the propagation
of electromagnetic waves through the vacuum, in the presence of a strong,
constant magnetic field. This is a setting of experimental relevance, since it
bases active efforts to measure non linear electromagnetic effects. After
surprising cancellations of Lorentz violating corrections to the Maxwell's
equation, we show that no effects of the kind of Lorentz violation we consider
can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main
results unchanged and are now obtained in a simpler way. To appear in PL
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