980 research outputs found
Feeding and working strategies for oxen used for draft purposes in semi-arid West Africa
This study was conducted to determine the energy expenditure of draft oxen working on sandy soils, performing common agricultural tasks, so that energy requirements could be determined; to establish the relationships between work and intake and digestibility of roughages by draft oxen; to investigate the effect of body condition before work and liveweight losses during work on work performance, and to investigate the implications of heat stress on draft oxen in semi-arid areas. This information will allow informed decisions to be made on the feeding and management of draft animals in semi-arid areas. Four experiments were conducted. Experiment 1 investigated the energy costs of walking on soils of different consistencies and the efficiencies of doing work. Experiment 2 and 3 were designed to establish the effect of work on intake, digestibility and rate of passage of feeds (millet stover) in the digestive tract. Experiment 4 looked at the effect of body condition before work and weight losses during work on work performance. The effect of heat stress was also investigated in experiment 2, 3 and 4. This report gives details of these experiments, the results obtained and, based on these, the recommendations made regarding feeding and working strategies for draft oxen in semi-arid areas
Sound Emissions by a Laboratory Bubble Cloud
This paper presents the results obtained from a detailed study of the sound field within and around a cylindrical column of bubbles generated at the center of an experimental water tank. The bubbles were produced by forcing air through a circular array of hypodermic needles. As they separated from the needles the ââbirthing wailsââ produced were found to excite the column into normal modes of oscillation whose spatial pressure?amplitude distribution could be tracked in the vertical and horizontal directions. The frequencies of vibration were predicted from theoretical calculations based on a collective oscillation model and showed close agreement with the experimentally measured values. On the basis of a model of the column excitation, absolute sound levels were analytically calculated with results again in agreement with the measured values. These findings provide considerable new evidence to support the notion that bubble plumes can be a major source of underwater sound around frequencies of a few hundred hertz
Anomaly Cancellation in Supergravity with Fayet-Iliopoulos Couplings
We review and clarify the cancellation conditions for gauge anomalies which
occur when N=1, D=4 supergravity is coupled to a Kahler non-linear sigma-model
with gauged isometries and Fayet-Iliopoulos couplings. For a flat sigma-model
target space and vanishing Fayet-Iliopoulos couplings, consistency requires
just the conventional anomaly cancellation conditions. A consistent model with
non-vanishing Fayet-Iliopoulos couplings is unlikely unless the Green-Schwarz
mechanism is used. In this case the U(1) gauge boson becomes massive and the
D-term potential receives corrections. A Green-Schwarz mechanism can remove
both the abelian and certain non-abelian anomalies in models with a gauge
non-invariant Kahler potential.Comment: 27 page
The rate of cosmic ray showers at large zenith angles: a step towards the detection of ultra-high energy neutrinos by the Pierre Auger Observatory
It is anticipated that the Pierre Auger Observatory can be used to detect
cosmic neutrinos of >10^19 eV that arrive at very large zenith angles. However
showers created by neutrino interactions close to the detector must be picked
out against a background of similar events initiated by cosmic ray nuclei. As a
step towards understanding this background, we have made the first detailed
analysis of air showers recorded at Haverah Park (an array which used similar
detectors to those planned for the Auger Observatory) with zenith angles above
60 degs. We find that the differential shower rate from 60 degs to 80 degs. can
be predicted accurately when we adopt the known primary energy spectrum above
10^17 eV and assume the QGSJET model and proton primaries. Details of the
calculation are given.Comment: 22 pages, 12 figures, to appear in Astroparticle Physic
Pressure Induced Change in the Magnetic Modulation of CeRhIn5
We report the results of a high pressure neutron diffraction study of the
heavy fermion compound CeRhIn5 down to 1.8 K. CeRhIn5 is known to order
magnetically below 3.8 K with an incommensurate structure. The application of
hydrostatic pressure up to 8.6 kbar produces no change in the magnetic wave
vector qm. At 10 kbar of pressure however, a sudden change in the magnetic
structure occurs. Although the magnetic transition temperature remains the
same, qm increases from (0.5, 0.5, 0.298) to (0.5, 0.5, 0.396). This change in
the magnetic modulation may be the outcome of a change in the electronic
character of this material at 10 kbar.Comment: 4 pages, 3 figures include
The inverse moment problem for convex polytopes
The goal of this paper is to present a general and novel approach for the
reconstruction of any convex d-dimensional polytope P, from knowledge of its
moments. In particular, we show that the vertices of an N-vertex polytope in
R^d can be reconstructed from the knowledge of O(DN) axial moments (w.r.t. to
an unknown polynomial measure od degree D) in d+1 distinct generic directions.
Our approach is based on the collection of moment formulas due to Brion,
Lawrence, Khovanskii-Pukhikov, and Barvinok that arise in the discrete geometry
of polytopes, and what variously known as Prony's method, or Vandermonde
factorization of finite rank Hankel matrices.Comment: LaTeX2e, 24 pages including 1 appendi
Superstring partition functions in the doubled formalism
Computation of superstring partition function for the non-linear sigma model
on the product of a two-torus and its dual within the scope of the doubled
formalism is presented. We verify that it reproduces the partition functions of
the toroidally compactified type--IIA and type--IIB theories for appropriate
choices of the GSO projection.Comment: 15 page
Flux Compactifications of M-Theory on Twisted Tori
We find the bosonic sector of the gauged supergravities that are obtained
from 11-dimensional supergravity by Scherk-Schwarz dimensional reduction with
flux to any dimension D. We show that, if certain obstructions are absent, the
Scherk-Schwarz ansatz for a finite set of D-dimensional fields can be extended
to a full compactification of M-theory, including an infinite tower of
Kaluza-Klein fields. The internal space is obtained from a group manifold
(which may be non-compact) by a discrete identification. We discuss the
symmetry algebra and the symmetry breaking patterns and illustrate these with
particular examples. We discuss the action of U-duality on these theories in
terms of symmetries of the D-dimensional supergravity, and argue that in
general it will take geometric flux compactifications to M-theory on
non-geometric backgrounds, such as U-folds with U-duality transition functions.Comment: Latex, 47 page
Reconnection of Colliding Cosmic Strings
For vortex strings in the Abelian Higgs model and D-strings in superstring
theory, both of which can be regarded as cosmic strings, we give analytical
study of reconnection (recombination, inter-commutation) when they collide, by
using effective field theories on the strings. First, for the vortex strings,
via a string sigma model, we verify analytically that the reconnection is
classically inevitable for small collision velocity and small relative angle.
Evolution of the shape of the reconnected strings provides an upper bound on
the collision velocity in order for the reconnection to occur. These analytical
results are in agreement with previous numerical results. On the other hand,
reconnection of the D-strings is not classical but probabilistic. We show that
a quantum calculation of the reconnection probability using a D-string action
reproduces the nonperturbative nature of the worldsheet results by Jackson,
Jones and Polchinski. The difference on the reconnection -- classically
inevitable for the vortex strings while quantum mechanical for the D-strings --
is suggested to originate from the difference between the effective field
theories on the strings.Comment: 29 pages, 14 eps figures, JHEP style; references added, typos
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