18,004 research outputs found
Quantum evolution of scalar fields in Robertson-Walker space-time
We study the field theory in a flat Robertson-Walker
space-time using the functional Sch\"odinger picture. We introduce a simple
Gaussian approximation to analyze the time evolution of pure states and we
establish the renormalizability of the approximation. We also show that the
energy-momentum tensor in this approximation is finite once we consider the
usual mass and coupling constant renormalizations.Comment: Revtex file, 19 pages, no figures. Compressed ps version available at
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-912.ps.
Quantum Evolution of Inhomogeneities in Curved Space
We obtain the renormalized equations of motion for matter and semi-classical
gravity in an inhomogeneous space-time. We use the functional Schrodinger
picture and a simple Gaussian approximation to analyze the time evolution of
the model, and we establish the renormalizability of this
non-perturbative approximation. We also show that the energy-momentum tensor in
this approximation is finite once we consider the usual mass and coupling
constant renormalizations, without the need of further geometrical
counter-terms.Comment: 22 page
Preheating in Quintessential Inflation
We perform a numerical study of the preheating mechanism of particle production in models of quintessential inflation and compare it with the usual gravitational production mechanism. We find that even for a very small coupling between the inflaton field and a massless scalar field, g > 10^{-9}, preheating dominates over gravitational particle production. Reheating temperatures in the range 10^{-2} GeV < T_{rh} < 10^{15} GeV can be easily obtained
Phases of granular segregation in a binary mixture
We present results from an extensive experimental investigation into granular
segregation of a shallow binary mixture in which particles are driven by
frictional interactions with the surface of a vibrating horizontal tray. Three
distinct phases of the mixture are established viz; binary gas (unsegregated),
segregation liquid and segregation crystal. Their ranges of existence are
mapped out as a function of the system's primary control parameters using a
number of measures based on Voronoi tessellation. We study the associated
transitions and show that segregation can be suppressed is the total filling
fraction of the granular layer, , is decreased below a critical value,
, or if the dimensionless acceleration of the driving, , is
increased above a value .Comment: 12 pages, 12 figures, submitted to Phys. Rev.
Tratamento químico de sementes de trigo para o controle de Bipolaris sorokiniana.
bitstream/item/39597/1/COT37-98.pd
Evaluation of microclimatic data in the mango crop for epidemiological studies.
Data of air temperature, relative humidity and wind velocity were collected inside and outside a mango orchard cv. Tommy Atkins, irrigated by microsprinklers, in order to complement epidemiological studies in Petrolina, Pernambuco State, Brazil
Finite size analysis of a two-dimensional Ising model within a nonextensive approach
In this work we present a thorough analysis of the phase transitions that
occur in a ferromagnetic 2D Ising model, with only nearest-neighbors
interactions, in the framework of the Tsallis nonextensive statistics. We
performed Monte Carlo simulations on square lattices with linear sizes L
ranging from 32 up to 512. The statistical weight of the Metropolis algorithm
was changed according to the nonextensive statistics. Discontinuities in the
m(T) curve are observed for . However, we have verified only one
peak on the energy histograms at the critical temperatures, indicating the
occurrence of continuous phase transitions. For the regime, we
have found continuous phase transitions between the ordered and the disordered
phases, and determined the critical exponents via finite-size scaling. We
verified that the critical exponents , and depend
on the entropic index in the range in the form , and . On the other hand, the critical exponent does not
depend on . This suggests a violation of the scaling relations and and a nonuniversality of the
critical exponents along the ferro-paramagnetic frontier.Comment: accepted for publication in Phys. Rev.
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