8,343 research outputs found
Unifying Type II Supernova Light Curves with Dense Circumstellar Material
A longstanding problem in the study of supernovae (SNe) has been the
relationship between the Type IIP and Type IIL subclasses. Whether they come
from distinct progenitors or they are from similar stars with some property
that smoothly transitions from one class to another has been the subject of
much debate. Here we show using one-dimensional radiation-hydrodynamic SN
models that the multi-band light curves of SNe IIL are well fit by ordinary red
supergiants surrounded by dense circumstellar material (CSM). The inferred
extent of this material, coupled with a typical wind velocity of ~10-100 km/s,
suggests enhanced activity by these stars during the last ~months to ~years of
their lives, which may be connected with advanced stages of nuclear burning.
Furthermore, we find that even for more plateau-like SNe that dense CSM
provides a better fit to the first ~20 days of their light curves, indicating
that the presence of such material may be more widespread than previously
appreciated. Here we choose to model the CSM with a wind-like density profile,
but it is unclear whether this just generally represents some other mass
distribution, such as a recent mass ejection, thick disk, or even inflated
envelope material. Better understanding the exact geometry and density
distribution of this material will be an important question for future studies.Comment: 9 pages, 7 figures, submitted for publication in The Astrophysical
Journa
Stabilization of quantum metastable states by dissipation
Normally, quantum fluctuations enhance the escape from metastable states in
the presence of dissipation. Here we show that dissipation can enhance the
stability of a quantum metastable system, consisting of a particle moving in a
strongly asymmetric double well potential, interacting with a thermal bath. We
find that the escape time from the metastable state has a nonmonotonic behavior
versus the system-bath coupling and the temperature, producing a stabilizing
effect.Comment: 4 pages, 3 figures, submitted to Phys. Rev.
Moment Equations for a Spatially Extended System of Two Competing Species
The dynamics of a spatially extended system of two competing species in the
presence of two noise sources is studied. A correlated dichotomous noise acts
on the interaction parameter and a multiplicative white noise affects directly
the dynamics of the two species. To describe the spatial distribution of the
species we use a model based on Lotka-Volterra (LV) equations. By writing them
in a mean field form, the corresponding moment equations for the species
concentrations are obtained in Gaussian approximation. In this formalism the
system dynamics is analyzed for different values of the multiplicative noise
intensity. Finally by comparing these results with those obtained by direct
simulations of the time discrete version of LV equations, that is coupled map
lattice (CML) model, we conclude that the anticorrelated oscillations of the
species densities are strictly related to non-overlapping spatial patterns.Comment: 10 pages, 3 figure
Space Shuttle Main Engine radio frequency emissions
Several approaches to develop a diagnostics system for monitoring the operational health of the Space Shuttle Main Engine (SSME) are being evaluated. The ultimate goal is providing protection for the SSME as well as improving ground and flight test techniques. One scenario with some potential is measuring radio frequency (RF) emissions (if present) in the exhaust plume and correlating the data to engine health. An RF emissions detection system was therefore designed, the equipment leased, and the components integrated and checked out to conduct a quick-look investigation of RF emissions in the SSME exhaust plume. The system was installed on the A-1 Test Stand at Stennis Space Center, MS, and data were successfully acquired during SSME firings from May 3 to September 15, 1988. The experiments indicated that emitted radiation in the RF (20 to 470 MHz) spectrum definitely exists in the SSME exhaust plume, and is of such magnitude that it can be distinguished during the firing from background noise. Although additional efforts are necessary to assess the merit of this approach as a health monitoring technique, the potential is significant, and additional studies are recommended
Lifetime of the superconductive state in short and long Josephson junctions
We study the transient statistical properties of short and long Josephson
junctions under the influence of thermal and correlated fluctuations. In
particular, we investigate the lifetime of the superconductive metastable state
finding the presence of noise induced phenomena. For short Josephson junctions
we investigate the lifetime as a function both of the frequency of the current
driving signal and the noise intensity and we find how these noise-induced
effects are modified by the presence of a correlated noise source. For long
Josephson junctions we integrate numerically the sine-Gordon equation
calculating the lifetime as a function of the length of the junction both for
inhomogeneous and homogeneous bias current distributions. We obtain a
nonmonotonic behavior of the lifetime as a function of the frequency of the
current driving signal and the correlation time of the noise. Moreover we find
two maxima in the nonmonotonic behaviour of the mean escape time as a function
of the correlated noise intensity.Comment: 12 pages, 9 figure
High-resolution CRIRES spectra of Terzan1: a metal-poor globular cluster toward the inner bulge
Containing the oldest stars in the Galaxy, globular clusters toward the bulge
can be used to trace its dynamical and chemical evolution. In the bulge
direction, there are ~50 clusters, but only about 20% have been subject of
high-resolution spectroscopic investigations. So far, the sample observed at
high resolution spans a moderate-to-high metallicity regime. In this sample,
however, very few are located in the innermost region (1.5\,Kpc and
). To constrain the chemical evolution enrichment of the
innermost region of Galaxy, accurate abundances and abundance patterns of key
elements based on high-resolution spectroscopy are necessary. Here we present
the results we obtained for Terzan 1, a metal-poor cluster located in the
innermost bulge region. Using the near-infrared spectrograph CRIRES at ESO/VLT,
we obtained high-resolution (R50,000) H-band spectra of 16 bright
giant stars in the innermost region () of Terzan1. Full spectral
synthesis techniques and equivalent width measurements of selected lines,
isolated and free of significant blending and/or contamination by telluric
lines, allowed accurate chemical abundances and radial velocities to be
derived. Fifteen out of 16 observed stars are likely cluster members, with an
average heliocentric radial velocity of +571.8\,km/s and mean iron
abundance of [Fe/H]=--1.260.03\,dex. For these stars we measured some
[/Fe] abundance ratios, finding average values of
[O/Fe]=+0.390.02\,dex, [Mg/Fe]=+0.420.02\,dex,
[Si/Fe]=+0.310.04\,dex, and [Ti/Fe]=+0.150.04\,dex The
enhancement (\,dex) found in the observed giant stars of Terzan1
is consistent with previous measurements on other, more metal-rich bulge
clusters, which suggests a rapid chemical enrichment.Comment: 7, pages, 6 figures, accepted for publication on A&
Uncovering the genetics of cirrhosis: New plots for the usual suspects
Cirrhosis is the end\u2010stage and the turning point in the natural history of liver disease, as is the major determinant of hepatic decompensation and cancer. Chronic viral hepatitis, alcohol abuse and dysmetabolism are the major causes of this condition. However, individuals respond differently to liver damage triggers, and inherited factors and family history have a large role in explaining this variability
Moment equations in a Lotka-Volterra extended system with time correlated noise
A spatially extended Lotka-Volterra system of two competing species in the
presence of two correlated noise sources is analyzed: (i) an external
multiplicative time correlated noise, which mimics the interaction between the
system and the environment; (ii) a dichotomous stochastic process, whose jump
rate is a periodic function, which represents the interaction parameter between
the species. The moment equations for the species densities are derived in
Gaussian approximation, using a mean field approach. Within this formalism we
study the effect of the external time correlated noise on the ecosystem
dynamics. We find that the time behavior of the order moments are
independent on the multiplicative noise source. However the behavior of the
order moments is strongly affected both by the intensity and the
correlation time of the multiplicative noise. Finally we compare our results
with those obtained studying the system dynamics by a coupled map lattice
model.Comment: 12 pages, 7 figures, to appear in Acta Phys. Pol.
The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip
We present new empirical calibrations of the Red Giant Branch (RGB) Bump and
Tip based on a homogeneous near-Infrared database of 24 Galactic Globular
Clusters. The luminosities of the RGB Bump and Tip in the J, H and K bands and
their dependence on the cluster metallicity have been studied, yielding
empirical relationships. By using recent transformations between the
observational and theoretical planes, we also derived similar calibrations in
terms of bolometric luminosity. Direct comparison between updated theoretical
models and observations show an excellent agreement. The empirical calibration
of the RGB Tip luminosity in the near-Infrared passbands presented here is a
fundamental tool to derive distances to far galaxies beyond the Local Group, in
view of using the new ground-based adaptive optics facilities and, in the next
future, the James Webb Space Telescope.Comment: 7 pages, 7 figures, accepted for publication in MNRA
High resolution near-IR spectra of NGC 6624 and NGC 6569
We present the first abundances analysis based on high-resolution infrared
(IR) echelle spectra of NGC 6569 and NGC 6624, two moderately reddened globular
clusters located in the outer bulge of the Galaxy. We find
[Fe/H]=-0.790.02 dex and [Fe/H]=-0.690.02 dex for NGC 6569 and NGC
6624, respectively and an average -elements enhancement of
+0.430.02 dex and +0.390.02 dex, consistent with previous
measurements on other metal-rich Bulge clusters. We measure accurate radial
velocities of and
and velocity dispersions of and for NGC 6569 and NGC 6624, respectively. Finally, we find very low
isotopics ratio (7 in NGC 6624 and 5 in NGC
6569), confirming the presence extra-mixing mechanisms during the red giant
branch evolution phase.Comment: 7 pages, 3 figures, accepted for publication on MNRA
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