532 research outputs found
MARKETING OF COTTON FIBER IN THE PRESENCE OF YIELD AND PRICE RISK
An expected utility model and a chance constrained linear programming model were used to analyze four marketing strategies and seven crop insurance alternatives in cotton marketing in Georgia. The results obtained suggest that the existing marketing tools and insurance alternatives can be used successfully as a substitute for government support.Demand and Price Analysis, Marketing, Risk and Uncertainty,
Generalized exponential and logarithmic functions
AbstractGeneralizations of the exponential and logarithmic functions are defined and an investigation is made of two possible versions of these functions. Some applications are described, including computer arithmetic, properties of very large and very small numbers, and the determination of functional roots
Fiber depolymerization
Depolymerization is, by definition, a crucial process in the reversible assembly of various biopolymers. It may also be an important factor in the pathology of sickle cell disease. If sickle hemoglobin fibers fail to depolymerize fully during passage through the lungs then they will reintroduce aggregates into the systemic circulation and eliminate or shorten the protective delay (nucleation) time for the subsequent growth of fibers. We study how depolymerization depends on the rates of end- and side-depolymerization, kend and kside, which are, respectively, the rates at which fiber length is lost at each end and the rate at which new breaks appear per unit fiber length. We present both an analytic mean field theory and supporting simulations showing that the characteristic fiber depolymerization time View the MathML source depends on both rates, but not on the fiber length L, in a large intermediate regime 1 much less-than ksideL2/kend much less-than (L/d)2, with d the fiber diameter. We present new experimental data which confirms that both mechanisms are important and shows how the rate of side depolymerization depends strongly on the concentration of CO, acting as a proxy for oxygen. Our theory remains rather general and could be applied to the depolymerization of an entire class of linear aggregates, not just sickle hemoglobin fibers
Damping of Tensor Modes in Cosmology
An analytic formula is given for the traceless transverse part of the
anisotropic stress tensor due to free streaming neutrinos, and used to derive
an integro-differential equation for the propagation of cosmological
gravitational waves. The solution shows that anisotropic stress reduces the
squared amplitude by 35.6 % for wavelengths that enter the horizon during the
radiation-dominated phase, independent of any cosmological parameters. This
decreases the tensor temperature and polarization correlation functions for
these wavelengths by the same amount. The effect is less for wavelengths that
enter the horizon at later times. At the longest wavelengths the decrease in
the tensor correlation functions due to neutrino free streaming ranges from
10.7% for to 9.0% for . An Appendix gives a
general proof that tensor as well as scalar modes satisfy a conservation law
for perturbations outside the horizon, even when the anisotropic stress tensor
is not negligible.Comment: 14 pages. The original version of this paper has been expanded to
deal with perturbations of any wavelength. While for wavelengths short enough
to enter the horizon during radiation dominance, temperature and polarization
correlations are damped by 35.6%, at the longest wavelengths the damping is
from 9.0% to 11%. An added Appendix gives a general proof that tensor as well
as scalar modes satisfy a conservation law outside the horizon, even during
neutrino decoupling. Some references are also adde
Exponential-Potential Scalar Field Universes I: The Bianchi I Models
We obtain a general exact solution of the Einstein field equations for the
anisotropic Bianchi type I universes filled with an exponential-potential
scalar field and study their dynamics. It is shown, in agreement with previous
studies, that for a wide range of initial conditions the late-time behaviour of
the models is that of a power-law inflating FRW universe. This property, does
not hold, in contrast, when some degree of inhomogeneity is introduced, as
discussed in our following paper II.Comment: 16 pages, Plain LaTeX, 1 Figure to be sent on request, to appear in
Phys. Rev.
Shear and Mixing in Oscillatory Doubly Diffusive Convection
To investigate the mechanism of mixing in oscillatory doubly diffusive (ODD)
convection, we truncate the horizontal modal expansion of the Boussinesq
equations to obtain a simplified model of the process. In the astrophysically
interesting case with low Prandtl number, large-scale shears are generated as
in ordinary thermal convection. The interplay between the shear and the
oscillatory convection produces intermittent overturning of the fluid with
significant mixing. By contrast, in the parameter regime appropriate to sea
water, large-scale flows are not generated by the convection. However, if such
flows are imposed externally, intermittent overturning with enhanced mixing is
observed.Comment: 24 pages, 16 figures, Accepted for publication in Geophysical and
Astrophysical Fluid Dynamic
On the Circular Orbit Approximation for Binary Compact Objects In General Relativity
One often-used approximation in the study of binary compact objects (i.e.,
black holes and neutron stars) in general relativity is the instantaneously
circular orbit assumption. This approximation has been used extensively, from
the calculation of innermost circular orbits to the construction of initial
data for numerical relativity calculations. While this assumption is
inconsistent with generic general relativistic astrophysical inspiral phenomena
where the dissipative effects of gravitational radiation cause the separation
of the compact objects to decrease in time, it is usually argued that the
timescale of this dissipation is much longer than the orbital timescale so that
the approximation of circular orbits is valid. Here, we quantitatively analyze
this approximation using a post-Newtonian approach that includes terms up to
order ({Gm/(rc^2)})^{9/2} for non-spinning particles. By calculating the
evolution of equal mass black hole / black hole binary systems starting with
circular orbit configurations and comparing them to the more astrophysically
relevant quasicircular solutions, we show that a minimum initial separation
corresponding to at least 6 (3.5) orbits before plunge is required in order to
bound the detection event loss rate in gravitational wave detectors to < 5%
(20%). In addition, we show that the detection event loss rate is > 95% for a
range of initial separations that include all modern calculations of the
innermost circular orbit (ICO).Comment: 10 pages, 12 figures, revtex
Can a matter-dominated model with constant bulk viscosity drive the accelerated expansion of the universe?
We test a cosmological model which the only component is a pressureless fluid
with a constant bulk viscosity as an explanation for the present accelerated
expansion of the universe. We classify all the possible scenarios for the
universe predicted by the model according to their past, present and future
evolution and we test its viability performing a Bayesian statistical analysis
using the SCP ``Union'' data set (307 SNe Ia), imposing the second law of
thermodynamics on the dimensionless constant bulk viscous coefficient \zeta and
comparing the predicted age of the universe by the model with the constraints
coming from the oldest globular clusters.
The best estimated values found for \zeta and the Hubble constant Ho are:
\zeta=1.922 \pm 0.089 and Ho=69.62 \pm 0.59 km/s/Mpc with a \chi^2=314. The age
of the universe is found to be 14.95 \pm 0.42 Gyr. We see that the estimated
value of Ho as well as of \chi^2 are very similar to those obtained from LCDM
model using the same SNe Ia data set. The estimated age of the universe is in
agreement with the constraints coming from the oldest globular clusters.
Moreover, the estimated value of \zeta is positive in agreement with the second
law of thermodynamics (SLT).
On the other hand, we perform different forms of marginalization over the
parameter Ho in order to study the sensibility of the results to the way how Ho
is marginalized. We found that it is almost negligible the dependence between
the best estimated values of the free parameters of this model and the way how
Ho is marginalized in the present work. Therefore, this simple model might be a
viable candidate to explain the present acceleration in the expansion of the
universe.Comment: 31 pages, 12 figures and 2 tables. Accepted to be published in the
Journal of Cosmology and Astroparticle Physics. Analysis using the new SCP
"Union" SNe Ia dataset instead of the Gold 2006 and ESSENCE datasets and
without changes in the conclusions. Added references. Related works:
arXiv:0801.1686 and arXiv:0810.030
Accretion among preplanetary bodies: the many faces of runaway growth
(abridged) When preplanetary bodies reach proportions of ~1 km or larger in
size, their accretion rate is enhanced due to gravitational focusing (GF). We
have developed a new numerical model to calculate the collisional evolution of
the gravitationally-enhanced growth stage. We validate our approach against
existing N-body and statistical codes. Using the numerical model, we explore
the characteristics of the runaway growth and the oligarchic growth accretion
phases starting from an initial population of single planetesimal radius R_0.
In models where the initial random velocity dispersion (as derived from their
eccentricity) starts out below the escape speed of the planetesimal bodies, the
system experiences runaway growth. We find that during the runaway growth phase
the size distribution remains continuous but evolves into a power-law at the
high mass end, consistent with previous studies. Furthermore, we find that the
largest body accretes from all mass bins; a simple two component approximation
is inapplicable during this stage. However, with growth the runaway body stirs
up the random motions of the planetesimal population from which it is
accreting. Ultimately, this feedback stops the fast growth and the system
passes into oligarchy, where competitor bodies from neighboring zones catch up
in terms of mass. Compared to previous estimates, we find that the system
leaves the runaway growth phase at a somewhat larger radius. Furthermore, we
assess the relevance of small, single-size fragments on the growth process. In
classical models, where the initial velocity dispersion of bodies is small,
these do not play a critical role during the runaway growth; however, in models
that are characterized by large initial relative velocities due to external
stirring of their random motions, a situation can emerge where fragments
dominate the accretion.Comment: Accepted for publication in Icaru
Creating a community of praxis: integrating global citizenship and development education across campus at University College Cork
The Praxis Project, established at University College Cork (UCC), Ireland, in 2018, seeks to assess possible models of best practice with regard to the integration of global citizenship and development education (GCDE) into a cross-disciplinary, cross-campus, interwoven set of subject area pedagogies, policies and practices. This study â the first part of an eventual three-part framework â asserts that the themes, theories, values, skills, approaches and methodologies relevant to transformative pedagogical work are best underpinned by ongoing staff dialogue in order to build communities of support around such systemic pedagogical change. This article is based on a collaborative study with the first cohort of UCC staff (2020â1), which demonstrates many ways in which staff and students realised that smaller actions and carefully directed attention to specific issues opened doors to transformative thinking and action in surprising ways. From this viewpoint, the striking need emerged for taking a strategic approach to how GCDE is, and should be, integrated into learning across subject areas
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