9,106 research outputs found
Sharp-Interface Limit of a Fluctuating Phase-Field Model
We present a derivation of the sharp-interface limit of a generic fluctuating
phase-field model for solidification. As a main result, we obtain a
sharp-interface projection which presents noise terms in both the diffusion
equation and in the moving boundary conditions. The presented procedure does
not rely on the fluctuation-dissipation theorem, and can therefore be applied
to account for both internal and external fluctuations in either variational or
non-variational phase-field formulations. In particular, it can be used to
introduce thermodynamical fluctuations in non-variational formulations of the
phase-field model, which permit to reach better computational efficiency and
provide more flexibility for describing some features of specific physical
situations. This opens the possibility of performing quantitative phase-field
simulations in crystal growth while accounting for the proper fluctuations of
the system.Comment: 21 pages, 1 figure, submitted to Phys. Rev.
Inflation from IIB Superstrings with Fluxes
We study the conditions needed to have an early epoch of inflationary
expansion with a potential coming from IIB superstring theory with fluxes
involving two moduli fields. The phenomenology of this potential is different
from the usual hybrid inflation scenario and we analize the possibility that
the system of field equations undergo a period of inflation in three different
regimes with the dynamics modified by a Randall-Sundrum II term in the
Friedmann equation. We find that the system can produce inflation and due to
the modification of the dynamics, a period of accelerated contraction can
follow or preceed this inflationary stage depending on the sign of one of the
parameters of the potential. We discuss on the viability of this model in a
cosmological context.Comment: 10 pages, 6 figure
A Radial Velocity Study of the Intermediate Polar EX Hydrae
A study on the intermediate polar EX Hya is presented, based on simultaneous
photometry and high dispersion spectroscopic observations, during four
consecutive nights. The strong photometric modulation related to with the
67-min spin period of the primary star is clearly present, as well as the
narrow eclipses associated to the orbital modulation. Since our eclipse timings
have been obtained almost 91,000 cycles since the last reported observations,
we present new linear ephemeris, although we cannot rule out a sinusoidal
variation suggested by previous authors. The system mainly shows double-peaked
H, H and HeI 5876 \AA emission lines. From the profile
of the H line, we find two components; one with a steep rise and
velocities not larger than 1000 km s and another broader component
extending up to 2000 km s, which we interpret as coming mainly
from the inner disc. A strong and variable hotspot is found and a stream-like
structure is seen at times. We show that the best solution correspond to km s from H, from the two emission components, which
are both in phase with the orbital modulation. We remark on a peculiar effect
in the radial velocity curve around phase zero, which could be interpreted as a
Rositter-MacLaughlin-like effect, which has been taken into account before
deriving . This value is compatible with the values found in
high-resolution both in the ultraviolet and X-ray. We find: M, M and
R. Doppler Tomography has been applied, to construct six Doppler
tomograms for single orbital cycles spanning the four days of observations to
support our conclusions. Our results indicate that EX Hya has a well formed
disc and that the magnetosphere should extend only to about
.Comment: 16 pages, 14 figures, accepted for publication in MNRA
How Far Do Shocks Move Across Borders? Examining Volatility Transmission in Major Agricultural Futures Markets
This paper examines the level of interdependence and volatility transmission in global agricultural futures markets. We follow a multivariate GARCH approach to explore the dynamics and cross-dynamics of volatility across major exchanges of corn, wheat, and soybeans between the United States, Europe, and Asia. We account for the potential bias that may arise when considering exchanges with different closing times. The results indicate that agricultural markets are highly interrelated and there are both own- and cross- volatility spillovers and dependence among most of the exchanges. The results also show the major role Chicago plays in terms of spillover effects over the other markets, particularly for corn and wheat. Additionally, the level of interdependence between exchanges has only increased in recent years for some of the commodities.Volatility transmission, agricultural commodities, futures markets, Multivariate GARCH.
Searching for galactic sources in the Swift GRB catalog
Since the early 1990s Gamma Ray Bursts have been accepted to be of
extra-galactic origin due to the isotropic distribution observed by BATSE and
the redshifts observed via absorption line spectroscopy. Nevertheless, upon
further examination at least one case turned out to be of galactic origin. This
particular event presented a Fast Rise, Exponential Decay (FRED) structure
which leads us to believe that other FRED sources might also be Galactic. This
study was set out to estimate the most probable degree of contamination by
galactic sources that certain samples of FREDs have. In order to quantify the
degree of anisotropy the average dipolar and quadripolar moments of each sample
of GRBs with respect to the galactic plane were calculated. This was then
compared to the probability distribution of simulated samples comprised of a
combination of isotropically generated sources and galactic sources. We observe
that the dipolar and quadripolar moments of the selected subsamples of FREDs
are found more than two standard deviations outside those of random
isotropically generated samples.The most probable degree of contamination by
galactic sources for the FRED GRBs of the Swift catalog detected until February
2011 that do not have a known redshift is about 21 out of 77 sources which is
roughly equal to 27%. Furthermore we observe, that by removing from this sample
those bursts that may have any type of indirect redshift indicator and multiple
peaks gives the most probable contamination increases up to 34% (17 out of 49
sources). It is probable that a high degree of contamination by galactic
sources occurs among the single peak FREDs observed by Swift.Comment: Published to A&A, 4 pages, 5 figures, this arXiv version includes
appended table with all the bursts considered in this stud
Genetic study in patients operated dentally and anesthetized with articaine-epinephrine
Aims: In this study we wanted to figure out if there was a correlation between OPRM1 N40D, TRPV1 I316M, TRPV1 I585V, NOS3 â786T>C and IL6 â174C>G polymorphisms and the response to locally applied articaine-epinephrine anesthetic.
Methods: In this observational study, 114 oral cell samples of patients anesthetized with articaine-epinephrine (54 from men 60 from women), were collected from dental centers in Madrid (Spain). High molecular weight DNA was obtained from oral mucosa cells. The analysis of OPRM1 N40D (rs1799971), TRPV1 I316M (rs222747), TRPV1 I585V (rs8065080) and IL6 â174C>G polymorphism was performed through real-time PCR allelic discrimination using TaqMan probes. Polymorphism NOS3 â786T> C (rs2070744) was analyzed using RFLP-PCR.
Results: The studied polymorphisms are involved neither in the response to the anesthetic, nor in the intensity of perceived dental pain. However, in a subset of female patients we found that TRPV1 I316M was associated with a delayed onset of anesthesia.
Conclusions: There is no association among these polymorphisms and the time elapsed between the application of the anesthetic and the onset of its effect
The frequency map for billiards inside ellipsoids
The billiard motion inside an ellipsoid Q \subset \Rset^{n+1} is completely
integrable. Its phase space is a symplectic manifold of dimension , which
is mostly foliated with Liouville tori of dimension . The motion on each
Liouville torus becomes just a parallel translation with some frequency
that varies with the torus. Besides, any billiard trajectory inside
is tangent to caustics , so the
caustic parameters are integrals of the
billiard map. The frequency map is a key tool to
understand the structure of periodic billiard trajectories. In principle, it is
well-defined only for nonsingular values of the caustic parameters. We present
four conjectures, fully supported by numerical experiments. The last one gives
rise to some lower bounds on the periods. These bounds only depend on the type
of the caustics. We describe the geometric meaning, domain, and range of
. The map can be continuously extended to singular values of
the caustic parameters, although it becomes "exponentially sharp" at some of
them. Finally, we study triaxial ellipsoids of \Rset^3. We compute
numerically the bifurcation curves in the parameter space on which the
Liouville tori with a fixed frequency disappear. We determine which ellipsoids
have more periodic trajectories. We check that the previous lower bounds on the
periods are optimal, by displaying periodic trajectories with periods four,
five, and six whose caustics have the right types. We also give some new
insights for ellipses of \Rset^2.Comment: 50 pages, 13 figure
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