942 research outputs found
Subresultants in multiple roots: an extremal case
We provide explicit formulae for the coefficients of the order-d polynomial
subresultant of (x-\alpha)^m and (x-\beta)^n with respect to the set of
Bernstein polynomials \{(x-\alpha)^j(x-\beta)^{d-j}, \, 0\le j\le d\}. They are
given by hypergeometric expressions arising from determinants of binomial
Hankel matrices.Comment: 18 pages, uses elsart. Revised version accepted for publication at
Linear Algebra and its Application
Graphical Markov models, unifying results and their interpretation
Graphical Markov models combine conditional independence constraints with
graphical representations of stepwise data generating processes.The models
started to be formulated about 40 years ago and vigorous development is
ongoing. Longitudinal observational studies as well as intervention studies are
best modeled via a subclass called regression graph models and, especially
traceable regressions. Regression graphs include two types of undirected graph
and directed acyclic graphs in ordered sequences of joint responses. Response
components may correspond to discrete or continuous random variables and may
depend exclusively on variables which have been generated earlier. These
aspects are essential when causal hypothesis are the motivation for the
planning of empirical studies.
To turn the graphs into useful tools for tracing developmental pathways and
for predicting structure in alternative models, the generated distributions
have to mimic some properties of joint Gaussian distributions. Here, relevant
results concerning these aspects are spelled out and illustrated by examples.
With regression graph models, it becomes feasible, for the first time, to
derive structural effects of (1) ignoring some of the variables, of (2)
selecting subpopulations via fixed levels of some other variables or of (3)
changing the order in which the variables might get generated. Thus, the most
important future applications of these models will aim at the best possible
integration of knowledge from related studies.Comment: 34 Pages, 11 figures, 1 tabl
A compendium and functional characterization of mammalian genes involved in adaptation to Arctic or Antarctic environments
Many mammals are well adapted to surviving in extremely cold environments. These species have likely accumulated genetic changes that help them efficiently cope with low temperatures. It is not known whether the same genes related to cold adaptation in one species would be under selection in another species. The aims of this study therefore were: to create a compendium of mammalian genes related to adaptations to a low temperature environment; to identify genes related to cold tolerance that have been subjected to independent positive selection in several species; to determine promising candidate genes/pathways/organs for further empirical research on cold adaptation in mammals
Lepton Acceleration in Pulsar Wind Nebulae
Pulsar Wind Nebulae (PWNe) act as calorimeters for the relativistic pair
winds emanating from within the pulsar light cylinder. Their radiative
dissipation in various wavebands is significantly different from that of their
pulsar central engines: the broadband spectra of PWNe possess characteristics
distinct from those of pulsars, thereby demanding a site of lepton acceleration
remote from the pulsar magnetosphere. A principal candidate for this locale is
the pulsar wind termination shock, a putatively highly-oblique,
ultra-relativistic MHD discontinuity. This paper summarizes key characteristics
of relativistic shock acceleration germane to PWNe, using predominantly Monte
Carlo simulation techniques that compare well with semi-analytic solutions of
the diffusion-convection equation. The array of potential spectral indices for
the pair distribution function is explored, defining how these depend
critically on the parameters of the turbulent plasma in the shock environs.
Injection efficiencies into the acceleration process are also addressed.
Informative constraints on the frequency of particle scattering and the level
of field turbulence are identified using the multiwavelength observations of
selected PWNe. These suggest that the termination shock can be comfortably
invoked as a principal injector of energetic leptons into PWNe without
resorting to unrealistic properties for the shock layer turbulence or MHD
structure.Comment: 19 pages, 5 figures, invited review to appear in Proc. of the
inaugural ICREA Workshop on "The High-Energy Emission from Pulsars and their
Systems" (2010), eds. N. Rea and D. Torres, (Springer Astrophysics and Space
Science series
Effect of oat bran on time to exhaustion, glycogen content and serum cytokine profile following exhaustive exercise
The aim of this study was to evaluate the effect of oat bran supplementation on time to exhaustion, glycogen stores and cytokines in rats submitted to training. The animals were divided into 3 groups: sedentary control group (C), an exercise group that received a control chow (EX) and an exercise group that received a chow supplemented with oat bran (EX-O). Exercised groups were submitted to an eight weeks swimming training protocol. In the last training session, the animals performed exercise to exhaustion, (e.g. incapable to continue the exercise). After the euthanasia of the animals, blood, muscle and hepatic tissue were collected. Plasma cytokines and corticosterone were evaluated. Glycogen concentrations was measured in the soleus and gastrocnemius muscles, and liver. Glycogen synthetase-α gene expression was evaluated in the soleus muscle. Statistical analysis was performed using a factorial ANOVA. Time to exhaustion of the EX-O group was 20% higher (515 ± 3 minutes) when compared with EX group (425 ± 3 minutes) (p = 0.034). For hepatic glycogen, the EX-O group had a 67% higher concentrations when compared with EX (p = 0.022). In the soleus muscle, EX-O group presented a 59.4% higher glycogen concentrations when compared with EX group (p = 0.021). TNF-α was decreased, IL-6, IL-10 and corticosterone increased after exercise, and EX-O presented lower levels of IL-6, IL-10 and corticosterone levels in comparison with EX group. It was concluded that the chow rich in oat bran increase muscle and hepatic glycogen concentrations. The higher glycogen storage may improve endurance performance during training and competitions, and a lower post-exercise inflammatory response can accelerate recovery
Gamma-Ray Bursts and Magnetars as Possible Sources of Ultra High Energy Cosmic Rays: Correlation of Cosmic Ray Event Positions with IRAS Galaxies
We use the two-dimensional Kolmogorov-Smirnov (KS) test to study the
correlation between the 60 cosmic ray events above 4x10^19 eV from the AGASA
experiment and the positions of infrared luminous galaxies from the IRAS PSCz
catalog. These galaxies are expected to be hosts to gamma ray bursts (GRB) and
magnetars, both of which are associated with core collapse supernovae and have
been proposed as possible acceleration sites for ultra high energy cosmic rays.
We find consistency between the models and the AGASA events to have been drawn
from the same underlying distribution of positions on the sky with KS
probabilities ~50%. Application of the same test to the 11 highest AGASA events
above 10^20 eV, however, yields a KS probability of < 0.5%, rejecting the
models at >99.5% significance level. Taken at face value, these highest energy
results suggest that the existing cosmic ray events above 10^20 eV do not owe
their origin to long burst GRBs, rapidly rotating magnetars, or any other
events associated with core collapse supernovae. The larger data set expected
from the AUGER experiment will test whether this conclusion is real or is a
statistical fluke that we estimate to be at the 2 sigma level.Comment: 15 pages, 4 figures. Final Version to be published in Phys. Rev.
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