2,587 research outputs found
Birefringent Electroweak Textures
The behaviour of electromagnetic waves propagating through an electroweak
homilia string network is examined. This string network is topologically stable
as a cosmic texture, and is characterized by the spatial variation of the
isospin rotation of the Higgs field. As a consequence the photon field couples
to the intermediate vector bosons, producing a finite range electromagnetic
field. It is found that the propagation speed of the photon depends on its
polarization vector, whence an homilia string network acts as a birefringent
medium. We estimate the birefringent scale for this texture and show that it
depends on the frequency of the electromagnetic wave and the length scale of
the homilia string network.Comment: 10 page
Why national health research systems matter
Some of the most outstanding problems in Computer Science (e.g. access to heterogeneous information sources, use of different e-commerce standards, ontology translation, etc.) are often approached through the identification of ontology mappings. A manual mapping generation slows down, or even makes unfeasible, the solution of particular cases of the aforementioned problems via ontology mappings. Some algorithms and formal models for partial tasks of automatic generation of mappings have been proposed. However, an integrated system to solve this problem is still missing. In this paper, we present AMON, a platform for automatic ontology mapping generation. First of all, we show the general structure. Then, we describe the current version of the system, including the ontology in which it is based, the similarity measures that it uses, the access to external sources, etc
The effect of soy phytoestrogen supplementation on thyroid status and cardiovascular risk markers in patients with subclinical hypothyroidism: A randomized, double-blind, crossover study
Context: There is concern whether soy phytoestrogens may affect thyroid function. If true, soy phytoestrogens may be expected to have a greater impact in subjects with subclinical hypothyroidism. Objective: The primary aim was to determine the effect of soy phytoestrogen supplementation on thyroid function, with a secondary aim of assessing the effects on cardiovascular risk indices in patients with subclinical hypothyroidism. Design and Setting: We conducted a randomized, double-blind, crossover study in a tertiary care setting. Participants: Sixty patients with subclinical hypothyroidism participated in the study. Intervention: Patients were randomly assigned to either low-dose phytoestrogen (30 g soy protein with 2 mg phytoestrogens, representative of a Western diet) or high-dose phytoestrogen (30 g soy protein with 16 mg phytoestrogens, representative of a vegetarian diet) supplementation for 8 wk, then crossed over after an 8-wk washout period. Main Outcome Measures: The primary outcome was progression to overt hypothyroidism, with secondary outcome measures of blood pressure, insulin resistance, lipids, and highly sensitive C-reactive protein (hsCRP). Results: Six female patients in the study progressed into overt hypothyroidism with a standardized rate ratio of 3.6 (95% confidence interval, 1.9, 6.2) after 16-mg phytoestrogen supplementation. Both systolic and diastolic blood pressure decreased with 16 mg phytoestrogens, whereas systolic pressure alone decreased with 2 mg phytoestrogens. Insulin resistance (homeostasis model assessment of insulin resistance, 3.5 ± 0.09 vs. 2.6 ± 0.08; P < 0.02) and hsCRP (4.9 ± 0.04 vs. 3.9 ± 0.03; P < 0.01) decreased with 16 mg phytoestrogens. Lipid profile remained unchanged. Conclusion: There is a 3-fold increased risk of developing overt hypothyroidism with dietary supplementation of 16 mg soy phytoestrogens with subclinical hypothyroidism. However, 16-mg soy phytoestrogen supplementation significantly reduces the insulin resistance, hsCRP, and blood pressure in these patients. Copyright © 2011 by The Endocrine Society
Stability of string defects in models of non-Abelian symmetry breaking
In this paper we describe a new type of topological defect, called a homilia
string, which is stabilized via interactions with the string network. Using
analytical and numerical techniques, we investigate the stability and dynamics
of homilia strings, and show that they can form stable electroweak strings. In
SU(2)xU(1) models of symmetry breaking the intersection of two homilia strings
is identified with a sphaleron. Due to repulsive forces, the homilia strings
seperate, resulting in sphaleron annihilation. It is shown that electroweak
homilia string loops cannot stabilize as vortons, which circumvents the adverse
cosmological problems associated with stable loops. The consequences for GUT
scale homilia strings are also discussed.Comment: 15 pages, revtex, with 8 figures. Submitted to PR
Exotic spacetimes, superconducting strings with linear momentum, and (not quite) all that
We derive the general exact vacuum metrics associated with a stationary (non
static), non rotating, cylindrically symmetric source. An analysis of the
geometry described by these vacuum metrics shows that they contain a subfamily
of metrics that, although admitting a consistent time orientation, display
"exotic" properties, such as "trapping" of geodesics and closed causal curves
through every point. The possibility that such spacetimes could be generated by
a superconducting string, endowed with a neutral current and momentum, has
recently been considered by Thatcher and Morgan. Our results, however, differ
from those found by Thatcher and Morgan, and the discrepancy is explained. We
also analyze the general possibility of constructing physical sources for the
exotic metrics, and find that, under certain restrictions, they must always
violate the dominant energy condition (DEC). We illustrate our results by
explicitly analyzing the case of concentric shells, where we find that in all
cases the external vacuum metric is non exotic if the matter in the shells
satisfies the DEC.Comment: 13 pages with no figures. Accepted in PR
Real world and tropical cyclone world. Part I: high-resolution climate model verification
Recent global climate models with sufficient resolution and physics offer a promising approach for simulating
real-world tropical cyclone (TC) statistics and their changing relationship with climate. In the first part
of this study, we examine the performance of a high-resolution (;40-km horizontal grid) global climate
model, the atmospheric component of the Australian Community Climate and Earth System Simulator
(ACCESS) based on the Met Office Unified Model (UM8.5) Global Atmosphere (GA6.0). The atmospheric
model is forced with observed sea surface temperature, and 20 years of integrations (1990â2009) are analyzed
for evaluating the simulated TC statistics compared with observations. The model reproduces the observed
climatology, geographical distribution, and interhemispheric asymmetry of global TC formation rates reasonably
well. The annual cycle of regional TC formation rates over most basins is also well captured.
However, there are some regional biases in the geographical distribution of TC formation rates. To identify
the sources of these biases, a suite of model-simulated large-scale climate conditions that critically modulate
TC formation rates are further evaluated, including the assessment of a multivariate genesis potential index.
Results indicate that the model TC genesis biases correspond well to the inherent biases in the simulated
large-scale climatic states, although the relative effects on TC genesis of some variables differs between
basins. This highlights the modelâs mean-state dependency in simulating accurate TC formation rates
- âŠ