28,273 research outputs found
Test of Chemical freeze-out at RHIC
We present the results of a systematic test applying statistical thermal
model fits in a consistent way for different particle ratios, and different
system sizes using the various particle yields measured in the STAR experiment.
Comparison between central and peripheral Au+Au and Cu+Cu collisions with data
from p+p collisions provides an interesting tool to verify the dependence with
the system size. We also present a study of the rapidity dependence of the
thermal fit parameters using available data from RHIC in the forward rapidity
regions and also using different parameterization for the rapidity distribution
of different particles.Comment: SQM2008 conference proceeding
Tidal effects and the Proximity decay of nuclei
We examine the decay of the 3.03 MeV state of Be evaporated from an
excited projectile-like fragment following a peripheral heavy-ion collision.
The relative energy of the daughter particles exhibits a dependence on
the decay angle of the Be, indicative of a tidal effect. Comparison of
the measured tidal effect with a purely Coulomb model suggests the influence of
a measurable nuclear proximity interaction.Comment: 5 pages, 4 figure
The Overlooked Potential of Generalized Linear Models in Astronomy - I: Binomial Regression
Revealing hidden patterns in astronomical data is often the path to
fundamental scientific breakthroughs; meanwhile the complexity of scientific
inquiry increases as more subtle relationships are sought. Contemporary data
analysis problems often elude the capabilities of classical statistical
techniques, suggesting the use of cutting edge statistical methods. In this
light, astronomers have overlooked a whole family of statistical techniques for
exploratory data analysis and robust regression, the so-called Generalized
Linear Models (GLMs). In this paper -- the first in a series aimed at
illustrating the power of these methods in astronomical applications -- we
elucidate the potential of a particular class of GLMs for handling
binary/binomial data, the so-called logit and probit regression techniques,
from both a maximum likelihood and a Bayesian perspective. As a case in point,
we present the use of these GLMs to explore the conditions of star formation
activity and metal enrichment in primordial minihaloes from cosmological
hydro-simulations including detailed chemistry, gas physics, and stellar
feedback. We predict that for a dark mini-halo with metallicity , an increase of in the gas
molecular fraction, increases the probability of star formation occurrence by a
factor of 75%. Finally, we highlight the use of receiver operating
characteristic curves as a diagnostic for binary classifiers, and ultimately we
use these to demonstrate the competitive predictive performance of GLMs against
the popular technique of artificial neural networks.Comment: 20 pages, 10 figures, 3 tables, accepted for publication in Astronomy
and Computin
Trichogramma spp. (Hymenoptera: Trichogrammatidae) associados a ovos de Helicoverpa zea (Lepidoptera: Noctuidae) em milho no Estado de São Paulo.
Autoria: QUERINO [i.e. SILVA], R. B. Q. da. RANYSE BARBOSA QUERINO DA SILV
Evaluation of Tropical and Subtropical Forage Grasses in the Northwest Region of Rio Grande Do Sul, Brazil
A collection of 137 accessions of tropical and subtropical grasses of Pennisetum purpureum (53), Panicum maximum (10), Brachiaria spp. (9), Hemarthria altissima (19), Setaria spp. (11), Digitaria spp. (22), Cynodon spp.(7) and Paspalum spp. (6) was evaluated for frost tolerance (FT), dry matter yield per cut (DMYC), number of cuts (NC) and accumulated dry matter yield per year (ADMY). Crude protein content (CPC), leaf/stem ratio (L/S), pubescence (P) and animal preference under grazing (AP) were also recorded in 20 entries of in P. purpureum. Data exploration involved cluster analysis and ordination, revealing the most promising entries among and within genus. In general ADMY and FT were the most important variables to discriminate entries. Pennisetum, Panicum and Hemarthria were the most productive genus with high FT. Cynodon and Paspalum showed high FT
Polarization and Strong Infra-Red Activity in Compressed Solid Hydrogen
Under a pressure of ~150 GPa solid molecular hydrogen undergoes a phase
transition accompanied by a dramatic rise in infra-red absorption in the vibron
frequency range. We use the Berry's phase approach to calculate the electric
polarization in several candidate structures finding large, anisotropic dynamic
charges and strongly IR-active vibron modes. The polarization is shown to be
greatly affected by the overlap between the molecules in the crystal, so that
the commonly used Clausius-Mossotti description in terms of polarizable,
non-overlapping molecular charge densities is inadequate already at low
pressures and even more so for the compressed solid.Comment: To appear in Phys. Rev. Let
EVALUATION OF ACCIDENTS WITH DOMINO EFFECT IN LPG STORAGE AREAS
The term domino effect denotes a chain of accidents, or situations, in which a fire/explosion
load generated by an accident in one unit in an industry causes secondary and higher order
accidents in other units. Such chains of accidents have a greater propensity to cause damage
than stand-alone accidents. Most of the past risk assessment studies deal with accident in
a single industry, more so in one of the units of an industry. But, often, accident in one unit
causes a secondary accident in a nearby unit, which in turn may trigger a tertiary accident,
and so on. The probability of occurrence and adverse impacts of such domino or
cascading effects are increasing due to increasing congestion in industrial complexes
and increasing density of human population around such complexes. Accidents with domino
effect are seldom studied. LPG storage areas could produce the worst possible consequences
in the event of an unforeseen incident. This work illustrates the application of models to
evaluate the impacts of events with fire and explosion in LPG tanks on other similar units
in the park and the possibility of occurrence of a domino effect. The criteria for occurrence
of accidents with domino effect adopted in this work were 37.5 kW/m2 in case of fire
radiation and an overpressure of 0.7 atm in explosion cases in a receptor body. The spacing
between LPG tanks was evaluated. The results show that such spacing is minimal and
does not represent, as it should, a parameter indicating a safe distance able to prevent the
propagation of an accident with domino effect
Local mapping of dissipative vortex motion
We explore, with unprecedented single vortex resolution, the dissipation and
motion of vortices in a superconducting ribbon under the influence of an
external alternating magnetic field. This is achieved by combing the phase
sensitive character of ac-susceptibility, allowing to distinguish between the
inductive-and dissipative response, with the local power of scanning Hall probe
microscopy. Whereas the induced reversible screening currents contribute only
inductively, the vortices do leave a fingerprint in the out-of-phase component.
The observed large phase-lag demonstrates the dissipation of vortices at
timescales comparable to the period of the driving force (i.e. 13 ms). These
results indicate the presence of slow microscopic loss mechanisms mediated by
thermally activated hopping transport of vortices between metastable states.Comment: 5 pages, 2 figure
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