5,411 research outputs found
Symmetric Instantons and Skyrme Fields
By explicit construction of the ADHM data, we prove the existence of a charge
seven instanton with icosahedral symmetry. By computing the holonomy of this
instanton we obtain a Skyrme field which approximates the minimal energy charge
seven Skyrmion. We also present a one parameter family of tetrahedrally
symmetric instantons whose holonomy gives a family of Skyrme fields which
models a Skyrmion scattering process, where seven well-separated Skyrmions
collide to form the icosahedrally symmetric Skyrmion.Comment: 22 pages plus 1 figure in GIF forma
A note on the discontinuity stresses at the junction of a pressurised spherical shell and a cylinder
An analysis has been made of the forces and moments occurring at the
junction of a pressurised spherical shell with an intersecting cylinder.
The additional effects of having a temperature gradient along the
length of the cylinder and the effect of a jointing ring have been
considered
The design of a multi-cell box in pure bending for minimum weight
The optimum skin thickness, web thickness and web pitch to
be used for a multi-cell box of given depth under a given
bending load are obtained by two different methods, resulting
in a graph where the optimum geometry is plotted against
the structural index for a given materia
Symmetric Skyrmions
We present candidates for the global minimum energy solitons of charge one to
nine in the Skyrme model, generated using sophisticated numerical algorithms.
Assuming the Skyrme model accurately represents the low energy limit of QCD,
these configurations correspond to the classical nuclear ground states of the
light elements. The solitons found are particularly symmetric, for example, the
charge seven skyrmion has icosahedral symmetry, and the shapes are shown to fit
a remarkable sequence defined by a geometric energy minimization (GEM) rule. We
also calculate the energies and sizes to within at least a few percent
accuracy. These calculations provide the basis for a future investigation of
the low energy vibrational modes of skyrmions and hence the possibility of
testing the Skyrme model against experiment.Comment: latex, 9 pages, 1 figure (fig1.gif
Basins of attraction of metastable states of the spherical -spin model
We study the basins of attraction of metastable states in the spherical
-spin spin glass model, starting the relaxation dynamics at a given distance
from a thermalized condition. Weighting the initial condition with the
Boltzmann distribution we find a finite size for the basins. On the contrary, a
white weighting of the initial condition implies vanishing basins of
attraction. We make the corresponding of our results with the ones of a
recently constructed effective potential.Comment: LaTeX, 7 pages, 7 eps figure
New hyper-Kaehler manifolds by fixing monopoles
The construction of new hyper-Kaehler manifolds by taking the infinite
monopole mass limit of certain Bogomol'nyi-Prasad-Sommerfield monopole moduli
spaces is considered. The one-parameter family of hyperkaehler manifolds due to
Dancer is shown to be an example of such manifolds. A new family of fixed
monopole spaces is constructed. They are the moduli spaces of four SU(4)
monopoles, in the infinite mass limit of two of the monopoles. These manifolds
are shown to be nonsingular when the fixed monopole positions are distinct.Comment: Version in Phys. Rev. D. 11 pp, RevTeX, 14 Postscript diagram
TWINLATIN: Twinning European and Latin-American river basins for research enabling sustainable water resources management. Combined Report D3.1 Hydrological modelling report and D3.2 Evaluation report
Water use has almost tripled over the past 50 years and in some regions the water demand already
exceeds supply (Vorosmarty et al., 2000). The world is facing a “global water crisis”; in many
countries, current levels of water use are unsustainable, with systems vulnerable to collapse from even
small changes in water availability. The need for a scientifically-based assessment of the potential
impacts on water resources of future changes, as a basis for society to adapt to such changes, is strong
for most parts of the world. Although the focus of such assessments has tended to be climate change,
socio-economic changes can have as significant an impact on water availability across the four main
use sectors i.e. domestic, agricultural, industrial (including energy) and environmental. Withdrawal
and consumption of water is expected to continue to grow substantially over the next 20-50 years
(Cosgrove & Rijsberman, 2002), and consequent changes in availability may drastically affect society
and economies.
One of the most needed improvements in Latin American river basin management is a higher level of
detail in hydrological modelling and erosion risk assessment, as a basis for identification and analysis
of mitigation actions, as well as for analysis of global change scenarios. Flow measurements are too
costly to be realised at more than a few locations, which means that modelled data are required for the
rest of the basin. Hence, TWINLATIN Work Package 3 “Hydrological modelling and extremes” was
formulated to provide methods and tools to be used by other WPs, in particular WP6 on “Pollution
pressure and impact analysis” and WP8 on “Change effects and vulnerability assessment”. With an
emphasis on high and low flows and their impacts, WP3 was originally called “Hydrological
modelling, flooding, erosion, water scarcity and water abstraction”. However, at the TWINLATIN
kick-off meeting it was agreed that some of these issues resided more appropriately in WP6 and WP8,
and so WP3 was renamed to focus on hydrological modelling and hydrological extremes.
The specific objectives of WP3 as set out in the Description of Work are
Quasiparticle thermal conductivity in the vortex state of high-T cuprates
We present the results of a microscopic calculation of the longitudinal
thermal conductivity, , of a d-wave superconductor in the mixed state.
Our results show an increase in the thermal conductivity with the applied field
at low temperatures, and a decrease followed by a nearly field independent
at higher temperatures, in qualitative agreement with the
experimental results. We discuss the relationship between the slope of the
superconducting gap and the plateau in .Comment: 4 pages, 3 figures, very minor changes to text, published versio
Single-Particle Green Functions in Exactly Solvable Models of Bose and Fermi Liquids
Based on a class of exactly solvable models of interacting bose and fermi
liquids, we compute the single-particle propagators of these systems exactly
for all wavelengths and energies and in any number of spatial dimensions. The
field operators are expressed in terms of bose fields that correspond to
displacements of the condensate in the bose case and displacements of the fermi
sea in the fermi case.
Unlike some of the previous attempts, the present attempt reduces the answer
for the spectral function in any dimension in both fermi and bose systems to
quadratures.
It is shown that when only the lowest order sea-displacement terms are
included, the random phase approximation in its many guises is recovered in the
fermi case, and Bogoliubov's theory in the bose case. The momentum distribution
is evaluated using two different approaches, exact diagonalisation and the
equation of motion approach.
The novelty being of course, the exact computation of single-particle
properties including short wavelength behaviour.Comment: Latest version to be published in Phys. Rev. B. enlarged to around 40
page
- …