2,989 research outputs found
Forecasting cosmological constraints from age of high-z galaxies
We perform Monte Carlo simulations based on current age estimates of high-z
objects to forecast constraints on the equation of state (EoS) of the dark
energy. In our analysis, we use two different EoS parameterizations, namely,
the so-called CPL and its uncorrelated form and calculate the improvements on
the figure of merit for both cases. Although there is a clear dependence of the
FoM with the size and accuracy of the synthetic age samples, we find that the
most substantial gain in FoM comes from a joint analysis involving age and
baryon acoustic oscillation data.Comment: 4 pages, 13 figures, late
Total integrated dose testing of solid-state scientific CD4011, CD4013, and CD4060 devices by irradiation with CO-60 gamma rays
The total integrated dose response of three CMOS devices manufactured by Solid State Scientific has been measured using CO-60 gamma rays. Key parameter measurements were made and compared for each device type. The data show that the CD4011, CD4013, and CD4060 produced by this manufacturers should not be used in any environments where radiation levels might exceed 1,000 rad(Si)
A comparative study for the pair-creation contact process using series expansions
A comparative study between two distinct perturbative series expansions for
the pair-creation contact process is presented. In contrast to the ordinary
contact process, whose supercritical series expansions provide accurate
estimates for its critical behavior, the supercritical approach does not work
properly when applied to the pair-creation process. To circumvent this problem
a procedure is introduced in which one-site creation is added to the
pair-creation. An alternative method is the generation of subcritical series
expansions which works even for the case of the pure pair-creation process.
Differently from the supercritical case, the subcritical series yields
estimates that are compatible with numerical simulations
Crossovers from parity conserving to directed percolation universality
The crossover behavior of various models exhibiting phase transition to
absorbing phase with parity conserving class has been investigated by numerical
simulations and cluster mean-field method. In case of models exhibiting Z_2
symmetric absorbing phases (the NEKIMCA and Grassberger's A stochastic cellular
automaton) the introduction of an external symmetry breaking field causes a
crossover to kink parity conserving models characterized by dynamical scaling
of the directed percolation (DP) and the crossover exponent: 1/\phi ~ 0.53(2).
In case an even offspringed branching and annihilating random walk model (dual
to NEKIMCA) the introduction of spontaneous particle decay destroys the parity
conservation and results in a crossover to the DP class characterized by the
crossover exponent: 1/\phi\simeq 0.205(5). The two different kinds of crossover
operators can't be mapped onto each other and the resulting models show a
diversity within the DP universality class in one dimension. These
'sub-classes' differ in cluster scaling exponents.Comment: 6 pages, 6 figures, accepted version in PR
Gravitational Mesoscopic Constraints in Cosmological Dark Matter Halos
We present an analysis of the behaviour of the `coarse-grained'
(`mesoscopic') rank partitioning of the mean energy of collections of particles
composing virialized dark matter halos in a Lambda-CDM cosmological simulation.
We find evidence that rank preservation depends on halo mass, in the sense that
more massive halos show more rank preservation than less massive ones. We find
that the most massive halos obey Arnold's theorem (on the ordering of the
characteristic frequencies of the system) more frequently than less massive
halos. This method may be useful to evaluate the coarse-graining level (minimum
number of particles per energy cell) necessary to reasonably measure signatures
of `mesoscopic' rank orderings in a gravitational system.Comment: LaTeX, 15 pages, 3 figures. Accepted for publication in Celestial
Mechanics and Dynamical Astronomy Journa
Observational constraints on late-time Lambda(t) cosmology
The cosmological constant, i.e., the energy density stored in the true vacuum
state of all existing fields in the Universe, is the simplest and the most
natural possibility to describe the current cosmic acceleration. However,
despite its observational successes, such a possibility exacerbates the well
known cosmological constant problem, requiring a natural explanation for its
small, but nonzero, value. In this paper we study cosmological consequences of
a scenario driven by a varying cosmological term, in which the vacuum energy
density decays linearly with the Hubble parameter. We test the viability of
this scenario and study a possible way to distinguish it from the current
standard cosmological model by using recent observations of type Ia supernova
(Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic
oscillation from the Sloan Digital Sky Survey and the position of the first
peak of the cosmic microwave background angular spectrum from the three-year
Wilkinson Microwave Anisotropy Probe.Comment: Some important revisions. To appear in Physical Review
Surface Effects on the Mechanical Elongation of AuCu Nanowires: De-alloying and the Formation of Mixed Suspended Atomic Chains
We report here an atomistic study of the mechanical deformation of AuxCu(1-x)
atomic-size wires (NWs) by means of high resolution transmission electron
microscopy (HRTEM) experiments. Molecular dynamics simulations were also
carried out in order to obtain deeper insights on the dynamical properties of
stretched NWs. The mechanical properties are significantly dependent on the
chemical composition that evolves in time at the junction; some structures
exhibit a remarkable de-alloying behavior. Also, our results represent the
first experimental realization of mixed linear atomic chains (LACs) among
transition and noble metals; in particular, surface energies induce chemical
gradients on NW surfaces that can be exploited to control the relative LAC
compositions (different number of gold and copper atoms). The implications of
these results for nanocatalysis and spin transport of one-atom-thick metal
wires are addressed.Comment: Accepted to Journal of Applied Physics (JAP
Nuclear Phenomenology: A Conceptual Proposal for High School Teaching
The discovery of atomic nucleus by E. Rutherford, at the beginning of the
twentieth century, was the Nuclear Physics original landmark. From then, a
series of experiments in which beams of particles composed of neutrons, protons
and others, brought to collide with a nucleus in order to unravel its structure
or produce artificial elements through nuclear transmutation, were triggered.
With the development of experimental equipment, a number of other nuclear
phenomena have been observed, such as beta decay, nuclear fission and fusion,
M\"oesbauer effect, etc. In view of the global political and economic landscape
and the contemporary educational trends, this work suggest alternative topics
in nuclear physics that can be discussed at the conceptual level in high school
teaching, where the main focus lies in the historical and technological
importance of such phenomena in society.Comment: 8 pages, 8 figure
A supercritical series analysis for the generalized contact process with diffusion
We study a model that generalizes the CP with diffusion. An additional
transition is included in the model so that at a particular point of its phase
diagram a crossover from the directed percolation to the compact directed
percolation class will happen. We are particularly interested in the effect of
diffusion on the properties of the crossover between the universality classes.
To address this point, we develop a supercritical series expansion for the
ultimate survival probability and analyse this series using d-log Pad\'e and
partial differential approximants. We also obtain approximate solutions in the
one- and two-site dynamical mean-field approximations. We find evidences that,
at variance to what happens in mean-field approximations, the crossover
exponent remains close to even for quite high diffusion rates, and
therefore the critical line in the neighborhood of the multicritical point
apparently does not reproduce the mean-field result (which leads to )
as the diffusion rate grows without bound
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