429 research outputs found
Neutron Moderation in the Oklo Natural Reactor and the Time Variation of alpha
In the analysis of the Oklo (gabon) natural reactor to test for a possible
time variation of the fine structure constant alpha, a Maxwell-Boltzmann low
energy neutron spectrum was assumed. We present here an analysis where a more
realistic spectrum is employed and show that the most recent isotopic analysis
of samples implies a non-zero change in alpha, over the last two billion years
since the reactor was operating, of \Delta\alpha/\alpha\geq 4.5\times 10^{-8}
(6\sigma confidence). Issues regarding the interpretation of the shifts of the
low energy neutron resonances are discussed.Comment: 7 pages, 4 figures; version 2 included reference to Flambaum/Shuryak
work and corrects error in abstract version three corrects a few points and
adds discussion on hydrogen and impurity concentration
Curvature in causal BD-type inflationary cosmology
We study a closed model of the universe filled with viscous fluid and
quintessence matter components in a Brans-Dicke type cosmological model. The
dynamical equations imply that the universe may look like an accelerated flat
Friedmann-Robertson-Walker universe at low redshift. We consider here
dissipative processes which follow a causal thermodynamics. The theory is
applied to viscous fluid inflation, where accepted values for the total entropy
in the observable universe is obtained.Comment: 11 pages, revtex 4. For a festschrift honoring Alberto Garcia. To be
publishen in Gen. Rel. Gra
Charged vortices in superfluid systems with pairing of spatially separated carriers
It is shown that in a magnetic field the vortices in superfluid electron-hole
systems carry a real electrical charge. The charge value depends on the
relation between the magnetic length and the Bohr radiuses of electrons and
holes. In double layer systems at equal electron and hole filling factors in
the case of the electron and hole Bohr radiuses much larger than the magnetic
length the vortex charge is equal to the universal value (electron charge times
the filling factor).Comment: 4 page
Rip/singularity free cosmology models with bulk viscosity
In this paper we present two concrete models of non-perfect fluid with bulk
viscosity to interpret the observed cosmic accelerating expansion phenomena,
avoiding the introduction of exotic dark energy. The first model we inspect has
a viscosity of the form by
taking into account of the decelerating parameter q, and the other model is of
the form . We give out the
exact solutions of such models and further constrain them with the latest
Union2 data as well as the currently observed Hubble-parameter dataset (OHD),
then we discuss the fate of universe evolution in these models, which confronts
neither future singularity nor little/pseudo rip. From the resulting curves by
best fittings we find a much more flexible evolution processing due to the
presence of viscosity while being consistent with the observational data in the
region of data fitting. With the bulk viscosity considered, a more realistic
universe scenario is characterized comparable with the {\Lambda}CDM model but
without introducing the mysterious dark energy.Comment: 9 pages, 6 figures, submitted to EPJ-
Quintessence and variation of the fine structure constant in the CMBR
We study dependence of the CMB temperature anisotropy spectrum on the value
of the fine structure constant and the equation of state of the dark
energy component of the total density of the universe. We find that bounds
imposed on the variation of from the analysis of currently available
CMB data sets can be significantly relaxed if one also allows for a change in
the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos
corrected in the revised versio
Bulk viscosity driving the acceleration of the Universe
The possibility that the present acceleration of the universe is driven by a
kind of viscous fluid is exploited. At background level this model is similar
to the generalized Chaplygin gas model (GCGM). But, at perturbative level, the
viscous fluid exhibits interesting properties. In particular the oscillations
in the power spectrum that plagues the GCGM are not present. Possible
fundamental descriptions for this viscous dark energy are discussed.Comment: Latex file, 8 pages, 3 eps figure
Decomposition and nutrient release of leguminous plants in coffee agroforestry systems.
Leguminous plants used as green manure are an important nutrient source for coffee plantations, especially for soils with low nutrient levels. Field experiments were conducted in the Zona da Mata of Minas Gerais State, Brazil to evaluate the decomposition and nutrient release rates of four leguminous species used as green manures (Arachis pintoi, Calopogonium mucunoides, Stizolobium aterrimum and
Stylosanthes guianensis) in a coffee agroforestry system under two different climate conditions. The initial N contents in plant residues varied from 25.7 to 37.0 g kg-1 and P from 2.4 to 3.0 g kg-1. The lignin/N, lignin/polyphenol and(lignin+polyphenol)/N ratios were low in all residues studied. Mass loss rates were highest in the first 15 days, when 25 % of the residues were decomposed. From 15 to 30 days, the decomposition rate decreased on both farms. On the farm in Pedra Dourada (PD), the decomposition constant k increased in the order C. mucunoides < S. aterrimum < S. guianensis < A. pintoi. On the farm in Araponga (ARA), there was no difference in the decomposition rate among leguminous plants. The N release rates varied from 0.0036 to 0.0096 d-1. Around 32 % of the total N content in the plant material was released in the first 15 days. In ARA, the N concentration in the S. aterrimum residues was always significantly higher than in the other residues. At the end of 360 days, the N released was 78 % in ARA and 89 % in PD of the initial content. Phosphorus was the most rapidly released nutrient (k values from 0.0165 to 0.0394 d-1). Residue decomposition and nutrient release did not correlate with initial residue chemistry and biochemistry, but differences in climatic conditions between the two study sites modified the decomposition rate constants
Spatial evolution of an AMD stream in the Iberian Pyrite Belt: process characterization and control factors on the hydrochemistry
This paper presents hydrochemical data of an AMD stream in the Iberian Pyrite Belt, obtained from its source, in the Poderosa Mine Portal, till its confluence at the Odiel River. The main objective is to establish potential interdependent relations between sulfate and metalsâ loads and the following physical-chemical variables: pH, electric conductivity (EC), redox potential (EH), and dissolved oxygen (O2). All the parameters show a global increasing tendency since the tunnelâs exit to the confluence at Odiel River. The TDS and EC are two relevant exceptions. They behave similarly, showing a decreasing trend and a strong inflection that describes a minimum immediately after the discharging point. The spatial analysis combined with statistical tools put in evidence the typical AMD processes and the respective physical-chemical implications. Inputs with distinctive hydrochemical signatures impose relevant modifications in the Poderosa creek waters. This indicates low hydrochemical inertia and high vulnerability to external stimulus.Financial support for this research was provided by DGCICYT National Plan, project CGL2010-21268-C02-01 and the Andalusian Autonomous Government Excellence Projects, Project RNM-6570
Scenario of Accelerating Universe from the Phenomenological \Lambda- Models
Dark matter, the major component of the matter content of the Universe,
played a significant role at early stages during structure formation. But at
present the Universe is dark energy dominated as well as accelerating. Here,
the presence of dark energy has been established by including a time-dependent
term in the Einstein's field equations. This model is compatible with
the idea of an accelerating Universe so far as the value of the deceleration
parameter is concerned. Possibility of a change in sign of the deceleration
parameter is also discussed. The impact of considering the speed of light as
variable in the field equations has also been investigated by using a well
known time-dependent model.Comment: Latex, 9 pages, Major change
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