4,059 research outputs found
Bogomol'nyi solitons in a gauged sigma model
The scale invariance of the sigma model can be broken by gauging a
subgroup of the symmetry and including a Maxwell term for the
gauge field in the Lagrangian. Adding also a suitable potential one obtains a
field theory of Bogomol'nyi type with topological solitons. These solitons are
stable against rescaling and carry magnetic flux which can take arbitrary
values in some finite interval. The soliton mass is independent of the flux,
but the soliton size depends on it. However, dynamically changing the flux
requires infinite energy, so the flux, and hence the soliton size, remains
constant during time evolution.Comment: 10 pages, Latex, 2 postscript figure
Cyclic torsion testing
Torsional fatigue testing and data analysis procedures are described. Since there are no standards governing cyclic torsion testing that are generally accepted on a widespread basis by the technical community, the different approaches that dominate current experimental activity, and the ramifications of each are discussed. Particular attention is given to the theoretical and experimental difficulties that have paced refinement and general acceptance of test procedures. Finally, specific quantities and nomenclature modelled after analagous axial fatigue properties are suggested as an effective way to communicate torsional fatigue results until accepted standards are established
Cyclic labellings with constraints at two distances
Motivated by problems in radio channel assignment, we consider the vertex-labelling of graphs with non-negative integers. The objective is to minimise the span of the labelling, subject to constraints imposed at graph distances one and two. We show that the minimum span is (up to rounding) a piecewise linear function of the constraints, and give a complete specification, together with associated optimal assignments, for trees and cycles
Human embryos from overweight and obese women display phenotypic and metabolic abnormalities
STUDY QUESTION Is the developmental timing and metabolic regulation disrupted in embryos from overweight or obese women? SUMMARY ANSWER Oocytes from overweight or obese women are smaller than those from women of healthy weight, yet post-fertilization they reach the morula stage faster and, as blastocysts, show reduced glucose consumption and elevated endogenous triglyceride levels. WHAT IS KNOWN ALREADY Female overweight and obesity is associated with infertility. Moreover, being overweight or obese around conception may have significant consequences for the unborn child, since there are widely acknowledged links between events occurring during early development and the incidence of a number of adult disorders. STUDY DESIGN, SIZE, DURATION We have performed a retrospective, observational analysis of oocyte size and the subsequent developmental kinetics of 218 oocytes from 29 consecutive women attending for ICSI treatment and have related time to reach key developmental stages to maternal bodyweight. In addition, we have measured non-invasively the metabolic activity of 150 IVF/ICSI embryos from a further 29 consecutive women who donated their surplus embryos to research, and have related the data retrospectively to their body mass index (BMI). PARTICIPANTS/MATERIALS, SETTING, METHODS In a clinical IVF setting, we compared oocyte morphology and developmental kinetics of supernumerary embryos collected from overweight and obese women, with a BMI in excess of 25 kg/m2 to those from women of healthy weight. A Primovision Time-Lapse system was used to measure developmental kinetics and the non-invasive COnsumption/RElese of glucose, pyruvate, amino acids and lactate were measured on spent droplets of culture medium. Total triglyceride levels within individual embryos were also determined. MAIN RESULTS AND THE ROLE OF CHANCE Human oocytes from women presenting for fertility treatment with a BMI exceeding 25 kg/m2 are smaller (R2 = −0.45; P = 0.001) and therefore less likely to complete development post-fertilization (P < 0.001). Those embryos that do develop reach the morula stage faster than embryos from women of a BMI < 25 kg/m2
Frequency reassignment in cellular phone networks
In cellular communications networks, cells use beacon frequencies to ensure the smooth operation of the network, for example in handling call handovers from one cell to another. These frequencies are assigned according to a frequency plan, which is updated from time to time, in response to evolving network requirements. The migration from one frequency plan to a new one proceeds in stages, governed by the network's base station controllers. Existing methods result in periods of reduced network availability or performance during the reassgnment process.
The problem posed to the Study Group was to develop a dynamic reassignment algorithm for implementing a new frequency plan so that there is little or no disruption of the network's performance during the transition. This problem was naturally formulated in terms of graph colouring and an effective algorithm was developed based on a straightforward approach of search and random colouring
Primary care groups - Modernising primary and community health services
Developing primary and community health
services is a key component of the government's
plans for modernising the NHS.
Primary care groups and trusts have a vital part to
play in overcoming the variability, fragmentation,
and isolation that have been the weaknesses of
primary health care in the NHS.
Primary care groups and trusts have introduced
initiatives to promote greater collaboration
between general practices and to share expertise
and resources.
Improving access to care is an important feature
of the modernisation plan, and most groups and
trusts are actively promoting access, particularly
for people who have been poorly served
traditionally.
Groups and trusts are tackling staff shortages by
using clinical specialists and promoting extended
roles for nurses and pharmacist
Topological and Nontopological Solitons in a Gauged O(3) Sigma Model with Chern-Simons term
The nonlinear sigma model with its subgroup gauged, where the
gauge field dynamics is solely governed by a Chern-Simons term, admits both
topological as well as nontopological self-dual soliton solutions for a
specific choice of the potential. It turns out that the topological solitons
are infinitely degenerate in any given sector.Comment: Few minor changes have been made. To appear in Phys. Lett.
Remarks on gauge vortex scattering
In the abelian Higgs model, among other situations, it has recently been
realized that the head-on scattering of solitons distributed symmetrically
around the point of scattering is by an angle , independant of various
details of the scattering. In this note, it is first observed that this result
is in fact not entirely surprising: the above is one of only two possible
outcomes. Then, a generalization of an argument given by Ruback for the case of
two gauge theory vortices in the Bogomol'nyi limit is used to show that in the
geodesic approximation the above result follows from purely geometric
considerations.Comment: 6 pages, revtex, missing authors added to one referenc
Effects of surface chemistry on hot corrosion life
This program has its primary objective: the development of hot corrosion life prediction methodology based on a combination of laboratory test data and evaluation of field service turbine components which show evidence of hot corrosion. The laboratory program comprises burner rig testing by TRW. A summary of results is given for two series of burner rig tests. The life prediction methodology parameters to be appraised in a final campaign of burner rig tests are outlined
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