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The evaluation of losses in maize stored on a selection of small farms in Zambia with particular reference to the development of methodology (G109)
The terms of reference for this project were: (1) to develop a satisfactory methodology to evaluate the extent of losses; (2) to establish reasonably reliable cost- benefit relationships for a simple improved farm storage technique; and (3) to recommend whether a longer term project should be undertaken over a wider area to evaluate cost-benefit relationships of improved storage techniques for the purpose of planning development programmes.
Following these criteria the report makes a detailed study of various methods of assessing losses. These methods are then applied to maize stored by small farmers in selected areas of Zambia and an evaluation made of the costs and benefits to these farmers of adopting an improved storage technique
Hill's Equation with Random Forcing Parameters: Determination of Growth Rates through Random Matrices
This paper derives expressions for the growth rates for the random 2 x 2
matrices that result from solutions to the random Hill's equation. The
parameters that appear in Hill's equation include the forcing strength and
oscillation frequency. The development of the solutions to this periodic
differential equation can be described by a discrete map, where the matrix
elements are given by the principal solutions for each cycle. Variations in the
forcing strength and oscillation frequency lead to matrix elements that vary
from cycle to cycle. This paper presents an analysis of the growth rates
including cases where all of the cycles are highly unstable, where some cycles
are near the stability border, and where the map would be stable in the absence
of fluctuations. For all of these regimes, we provide expressions for the
growth rates of the matrices that describe the solutions.Comment: 22 pages, 3 figure
Twisted K-Theory from Monodromies
RR fluxes representing different cohomology classes may correspond to the
same twisted K-theory class. We argue that such fluxes are related by
monodromies, generalizing and sometimes T-dual to the familiar monodromies of a
D7-brane. A generalized theta angle is also transformed, but changes by a
multiple of 2pi. As an application, NS5-brane monodromies modify the twisted
K-theory classification of fluxes. Furthermore, in the noncompact case K-theory
does not distinguish flux configurations in which dG is nontrivial in compactly
supported cohomology. Such fluxes are realized as the decay products of
unstable D-branes that wrapped nontrivial cycles. This is interpreted using the
E8 bundle formalism.Comment: 24 Pages, 6 eps figure
Inflationary cosmology in the central region of String/M-theory moduli space
The "central" region of moduli space of M- and string theories is where the
string coupling is about unity and the volume of compact dimensions is about
the string volume. Here we argue that in this region the non-perturbative
potential which is suggested by membrane instanton effects has the correct
scaling and shape to allow for enough slow-roll inflation, and to produce the
correct amplitude of CMB anisotropies. Thus, the well known theoretical
obstacles for achieving viable slow-roll inflation in the framework of
perturbative string theory are overcome. Limited knowledge of some generic
properties of the induced potential is sufficient to determine the simplest
type of consistent inflationary model and its predictions about the spectrum of
cosmic microwave background anisotropies: a red spectrum of scalar
perturbations, and negligible amount of tensor perturbations.Comment: 9 pages, 1 figur
Toda systems in closed string tachyon condensation
We consider equations appearing in the study of localized tachyon
condensations. They are described by various Toda system when we consider the
condensation by the lowest tachyon corresponding to the monomial . The
tachyon potential is calculated as a solution to these equations. The Toda
system appearing in the deformation of \C^2/\Z_n by is identical to that
of singularity deformed by . For \C^3/\Z_n with deformation,
we find only generic non-simple form, similar to the case appearing in
\C/\Z_5\to \C/\Z_3 and we discuss the difficulties in these cases.Comment: 20 pages, no figur
Bulk perturbations of N=2 branes
The evolution of supersymmetric A-type D-branes under the bulk
renormalization group flow between two different N=2 minimal models is studied.
Using the Landau-Ginzburg description we show that a specific set of branes
decouples from the infrared theory, and we make detailed predictions for the
behavior of the remaining branes. The Landau-Ginzburg picture is then checked
against a direct conformal field theory analysis. In particular we construct a
natural index pairing which is preserved by the RG flow, and show that the
branes that decouple have vanishing index with the surviving branes.Comment: 35 pages (30 pages plus title and references), 8 figure
Loop Groups, Kaluza-Klein Reduction and M-Theory
We show that the data of a principal G-bundle over a principal circle bundle
is equivalent to that of a \hat{LG} = U(1) |x LG bundle over the base of the
circle bundle. We apply this to the Kaluza-Klein reduction of M-theory to IIA
and show that certain generalized characteristic classes of the loop group
bundle encode the Bianchi identities of the antisymmetric tensor fields of IIA
supergravity. We further show that the low dimensional characteristic classes
of the central extension of the loop group encode the Bianchi identities of
massive IIA, thereby adding support to the conjectures of hep-th/0203218.Comment: 26 pages, LaTeX, utarticle.cls, v2:clarifications and refs adde
D1-D5 on ALE Space
We construct a two-dimensional N=(0,4) quiver gauge theory on D1-brane
probing D5-branes on ALE space, and study its IR behavior. This can be thought
of as a gauged linear sigma model for the NS5-branes on ALE space.Comment: 17 pages, 1 figure, lanlmac; v2: reference adde
Depinning of a superfluid vortex line by Kelvin waves
We measure the interaction of a single superfluid vortex with surface
irregularities. While vortex pinning in superconductors usually becomes weaker
at higher temperatures, we find the opposite behavior. The pinning steadily
increases throughout our measurement range, from 0.15Tc to over 0.5Tc. We also
find that moving the other end of the vortex decreases the pinning, so we
propose Kelvin waves along the vortex as a depinning mechanism.Comment: 5 figures; substantial revision including 2 new figure
k-Essence, superluminal propagation, causality and emergent geometry
The k-essence theories admit in general the superluminal propagation of the
perturbations on classical backgrounds. We show that in spite of the
superluminal propagation the causal paradoxes do not arise in these theories
and in this respect they are not less safe than General Relativity.Comment: 34 pages, 5 figure
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