19,494 research outputs found
Properties of Information Carrying Waves in Cosmology
Recently we studied the effects of information carrying waves propagating
through isotropic cosmologies. By information carrying we mean that the waves
have an arbitrary dependence on a function. We found that the waves introduce
shear and anisotropic stress into the universe. We then constructed explicit
examples of pure gravity wave perturbations for which the presence of this
anisotropic stress is essential and the null hypersurfaces playing the role of
the histories of the wave-fronts in the background space-time are shear-free.
Motivated by this result we now prove that these two properties are true for
all information carrying waves in isotropic cosmologies.Comment: 15 pages, Latex File, accepted for publication in Physical Review
Further Evidence Suggestive of a Solar Influence on Nuclear Decay Rates
Recent analyses of nuclear decay data show evidence of variations suggestive
of a solar influence. Analyses of datasets acquired at the Brookhaven National
Laboratory (BNL) and at the Physikalisch-Technische Bundesanstalt (PTB) both
show evidence of an annual periodicity and of periodicities with sidereal
frequencies in the neighborhood of 12.25 year^{-1} (at a significance level
that we have estimated to be 10^{-17}). It is notable that this implied
rotation rate is lower than that attributed to the solar radiative zone,
suggestive of a slowly rotating solar core. This leads us to hypothesize that
there may be an "inner tachocline" separating the core from the radiative zone,
analogous to the "outer tachocline" that separates the radiative zone from the
convection zone. The Rieger periodicity (which has a period of about 154 days,
corresponding to a frequency of 2.37 year^{-1}) may be attributed to an r-mode
oscillation with spherical-harmonic indices l=3, m=1, located in the outer
tachocline. This suggests that we may test the hypothesis of a solar influence
on nuclear decay rates by searching BNL and PTB data for evidence of a
"Rieger-like" r-mode oscillation, with l=3, m=1, in the inner tachocline. The
appropriate search band for such an oscillation is estimated to be 2.00-2.28
year^{-1}. We find, in both datasets, strong evidence of a periodicity at 2.11
year^{-1}. We estimate that the probability of obtaining these results by
chance is 10^{-12}.Comment: 12 pages, 6 figures, v2 has a color corrected Fig 6, a corrected
reference, and a corrected typ
Metric Perturbation Approach to Gravitational Waves in Isotropic Cosmologies
Gravitational waves in isotropic cosmologies were recently studied using the
gauge-invariant approach of Ellis-Bruni. We now construct the linearised metric
perturbations of the background Robertson-Walker space-time which reproduce the
results obtained in that study. The analysis carried out here also facilitates
an easy comparison with Bardeen.Comment: 29 pages, Latex file, accepted for publication in Physical Review
Relating Green-Schwarz and Extended Pure Spinor Formalisms by Similarity Transformation
In order to gain deeper understanding of pure-spinor-based formalisms of
superstring, an explicit similarity transformation is constructed which
provides operator mapping between the light-cone Green-Schwarz (LCGS) formalism
and the extended pure spinor (EPS) formalism, a recently proposed
generalization of the Berkovits' formalism in an enlarged space. By applying a
systematic procedure developed in our previous work, we first construct an
analogous mapping in the bosonic string relating the BRST and the light-cone
formulations. This provides sufficient insights and allows us to construct the
desired mapping in the more intricate case of superstring as well. The success
of the construction owes much to the enlarged field space where pure spinor
constraints are removed and to the existence of the ``B-ghost'' in the EPS
formalism.Comment: 37pages, no figur
THE NIGERIAN AGRICULTURE AND POVERTY INCIDENCE: THE NEED FOR PRIVATE SECTOR EMPOWERMENT
Poverty in Nigeria is concentrated in rural areas. Low resource or resource-poor farmers characterized by preponderance of small farm units, fragile soils, rain-dependent, minimum inputs and poor yield dominate the agricultural sector. The incidence of poverty is highest among households in which the head is engaged in agriculture as the main source of income. Agricultural growth is therefore important to the eradication of extreme poverty and hunger in Nigeria. Conscious policy efforts by government towards poverty alleviation began during the SAP era. Some companies like Shell and certain State Governments have shown real interest in alleviating poverty through their agricultural programmes and policy statements. Nigeria’s current vision for agricultural development is expressed in the National Economic Empowerment and Development Strategy (NEEDS), the New Agricultural Policy (NAP), and the Rural Sector Development Strategy (RSDS). This paper posits that provision of electricity, potable water, health centres and formal schools will facilitate the sustainability of any impact of poverty alleviation programmes in Nigeria. Encouraging community development projects evolved by the communities themselves will minimize poverty incidence. Increasing the access of the poor to land and other productive resources will reduce poverty and generate employment. Development of infrastructural facilities in the rural areas has the two pronged approach of reducing poverty and developing the rural areas. Encouraging processing through adequate incentives to SMEs will also further empower the private sector.Farm Management, Food Security and Poverty,
Towards Pure Spinor Type Covariant Description of Supermembrane -- An Approach from the Double Spinor Formalism --
In a previous work, we have constructed a reparametrization invariant
worldsheet action from which one can derive the super-Poincare covariant pure
spinor formalism for the superstring at the fully quantum level. The main idea
was the doubling of the spinor degrees of freedom in the Green-Schwarz
formulation together with the introduction of a new compensating local
fermionic symmetry. In this paper, we extend this "double spinor" formalism to
the case of the supermembrane in 11 dimensions at the classical level. The
basic scheme works in parallel with the string case and we are able to
construct the closed algebra of first class constraints which governs the
entire dynamics of the system. A notable difference from the string case is
that this algebra is first order reducible and the associated BRST operator
must be constructed accordingly. The remaining problems which need to be solved
for the quantization will also be discussed.Comment: 40 pages, no figure, uses wick.sty; v2: a reference added, published
versio
Shear-Free Gravitational Waves in an Anisotropic Universe
We study gravitational waves propagating through an anisotropic Bianchi I
dust-filled universe (containing the Einstein-de-Sitter universe as a special
case). The waves are modeled as small perturbations of this background
cosmological model and we choose a family of null hypersurfaces in this
space-time to act as the histories of the wavefronts of the radiation. We find
that the perturbations we generate can describe pure gravitational radiation if
and only if the null hypersurfaces are shear-free. We calculate the
gauge-invariant small perturbations explicitly in this case. How these differ
from the corresponding perturbations when the background space-time is
isotropic is clearly exhibited.Comment: 32 pages, accepted for publication in Physical Review
Nocturnal activity by the primarily diurnal Central American agouti (Dasyprocta punctata) in relation to environmental conditions, resource abundance and predation risk
An animal's fitness is in part based on its ability to manage the inherent risks (foraging costs, predation, exposure to disease) with the benefits (resource gain, access to mates, social interactions) of activity (Abrams 1991, Altizer et al. 2003, Lima & Bednekoff 1999, Rubenstein & Hohmann 1989, Wikelski et al. 2001). Thus, understanding an animal's pattern of activity is key to understanding behavioural and ecological processes. However, while numerous laboratory methodologies are available to continuously quantify activity over long periods of time, logistical difficulties have greatly hindered activity studies of animals in the field (DeCoursey 1990)
Effective Coupling for Open Billiards
We derive an explicit expression for the coupling constants of individual
eigenstates of a closed billiard which is opened by attaching a waveguide. The
Wigner time delay and the resonance positions resulting from the coupling
constants are compared to an exact numerical calculation. Deviations can be
attributed to evanescent modes in the waveguide and to the finite number of
eigenstates taken into account. The influence of the shape of the billiard and
of the boundary conditions at the mouth of the waveguide are also discussed.
Finally we show that the mean value of the dimensionless coupling constants
tends to the critical value when the eigenstates of the billiard follow
random-matrix theory
A New First Class Algebra, Homological Perturbation and Extension of Pure Spinor Formalism for Superstring
Based on a novel first class algebra, we develop an extension of the pure
spinor (PS) formalism of Berkovits, in which the PS constraints are removed. By
using the homological perturbation theory in an essential way, the BRST-like
charge of the conventional PS formalism is promoted to a bona fide
nilpotent charge , the cohomology of which is equivalent to the
constrained cohomology of . This construction requires only a minimum number
(five) of additional fermionic ghost-antighost pairs and the vertex operators
for the massless modes of open string are obtained in a systematic way.
Furthermore, we present a simple composite "-ghost" field which
realizes the important relation , with the
Virasoro operator, and apply it to facilitate the construction of the
integrated vertex. The present formalism utilizes U(5) parametrization and the
manifest Lorentz covariance is yet to be achieved.Comment: 38 pages, no figure. Proof of triviality of delta-homology improved
and a reference adde
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