505 research outputs found
Modelling the social and structural determinants of tuberculosis: opportunities and challenges
INTRODUCTION: Despite the close link between tuberculosis (TB) and poverty, most mathematical models of TB have not addressed underlying social and structural determinants.
OBJECTIVE: To review studies employing mathematical modelling to evaluate the epidemiological impact of the structural determinants of TB.
METHODS: We systematically searched PubMed and personal libraries to identify eligible articles. We extracted data on the modelling techniques employed, research question, types of structural determinants modelled and setting.
RESULTS: From 232 records identified, we included eight articles published between 2008 and 2015; six employed population-based dynamic TB transmission models and two non-dynamic analytic models. Seven studies focused on proximal TB determinants (four on nutritional status, one on wealth, one on indoor air pollution, and one examined overcrowding, socio-economic and nutritional status), and one focused on macro-economic influences.
CONCLUSIONS: Few modelling studies have attempted to evaluate structural determinants of TB, resulting in key knowledge gaps. Despite the challenges of modelling such a complex system, models must broaden their scope to remain useful for policy making. Given the intersectoral nature of the interrelations between structural determinants and TB outcomes, this work will require multidisciplinary collaborations. A useful starting point would be to focus on developing relatively simple models that can strengthen our knowledge regarding the potential effect of the structural determinants on TB outcomes
Estimation of vortex density after superconducting film quench
This paper addresses the problem of vortex formation during a rapid quench in
a superconducting film. It builds on previous work showing that in a local
gauge theory there are two distinct mechanisms of defect formation, based on
fluctuations of the scalar and gauge fields, respectively. We show how vortex
formation in a thin film differs from the fully two-dimensional case, on which
most theoretical studies have focused. We discuss ways of testing theoretical
predictions in superconductor experiments and analyse the results of recent
experiments in this light.Comment: 7 pages, no figure
Study of ATLAS sensitivity to FCNC top decays
The ATLAS experiment sensitivity to top quark Flavour Changing Neutral
Current (FCNC) decays was studied at LHC using ttbar events. While one of the
top quarks is expected to follow the dominant Standard Model decay t->bW, the
other decays through a FCNC channel, i.e. t-> Z u(c), t-> gamma u(c) or t-> g
u(c). Different types of analyses, applied to each FCNC decay mode, were
compared. The FCNC branching ratio sensitivity (assuming a 5sigma signal
significance) and 95% confidence level limits on the branching ratios (in the
hypothesis of signal absence) were obtained
The Ginzburg regime and its effects on topological defect formation
The Ginzburg temperature has historically been proposed as the energy scale
of formation of topological defects at a second order symmetry breaking phase
transition. More recently alternative proposals which compute the time of
formation of defects from the critical dynamics of the system, have been
gaining both theoretical and experimental support. We investigate, using a
canonical model for string formation, how these two pictures compare. In
particular we show that prolonged exposure of a critical field configuration to
the Ginzburg regime results in no substantial suppression of the final density
of defects formed. These results dismiss the recently proposed role of the
Ginzburg regime in explaining the absence of topological defects in 4He
pressure quench experiments.Comment: 8 pages, 5 ps figure
Energetics and Possible Formation and Decay Mechanisms of Vortices in Helium Nanodroplets
The energy and angular momentum of both straight and curved vortex states of
a helium nanodroplet are examined as a function of droplet size. For droplets
in the size range of many experiments, it is found that during the pickup of
heavy solutes, a significant fraction of events deposit sufficient energy and
angular momentum to form a straight vortex line. Curved vortex lines exist down
to nearly zero angular momentum and energy, and thus could in principle form in
almost any collision. Further, the coalescence of smaller droplets during the
cooling by expansion could also deposit sufficient angular momentum to form
vortex lines. Despite their high energy, most vortices are predicted to be
stable at the final temperature (0.38 K) of helium nanodroplets due to lack of
decay channels that conserve both energy and angular momentum.Comment: 10 pages, 8 figures, RevTex 4, submitted to Phys. Rev.
Lagrangian evolution of global strings
We establish a method to trace the Lagrangian evolution of extended objects
consisting of a multicomponent scalar field in terms of a numerical calculation
of field equations in three dimensional Eulerian meshes. We apply our method to
the cosmological evolution of global strings and evaluate the energy density,
peculiar velocity, Lorentz factor, formation rate of loops, and emission rate
of Nambu-Goldstone (NG) bosons. We confirm the scaling behavior with a number
of long strings per horizon volume smaller than the case of local strings by a
factor of 10. The strategy and the method established here are
applicable to a variety of fields in physics.Comment: 5 pages, 2 figure
Measuring Cosmic Defect Correlations in Liquid Crystals
From the theory of topological defect formation proposed for the early
universe, the so called Kibble mechanism, it follows that the density
correlation functions of defects and anti-defects in a given system should be
completely determined in terms of a single length scale , the relevant
domain size. Thus, when lengths are expressed in units of , these
distributions should show universal behavior, depending only on the symmetry of
the order parameter, and space dimensions. We have verified this prediction by
analyzing the distributions of defects/anti-defects formed in the
isotropic-nematic phase transition in a thin layer of nematic liquid crystals.
Our experimental results confirm this prediction and are in reasonable
agreement with the results of numerical simulations.Comment: 15 pages, 4 figures, minor changes, few new references adde
Search for Spontaneous Nucleation of Magnetic Flux During Rapid Cooling of YBCO films Through Tc
We describe an experimental search for spontaneous formation of flux lines
during a rapid quench of thin YBaCuO films through Tc. This effect is expected
according to the Kibble-Zurek mechanism of a creation of topological defects of
the order parameter during a symmetry breaking phase transition. Spontaneously
formed vortices were previously observed in superfluid 3He, while a similar
experiment in superfluid 4He gave negative results. Using a high Tc SQUID, we
measured both the magnetic flux in the sample during a quench with a
sensitivity of 20 phi-0/cm^2, and the field noise which one would expect from
flux lines pinned in the film. The sensitivity was sufficient to detect
spontaneous flux at a level corresponding to 10^(-3) of the prediction. Within
our resolution, we saw no evidence for this effect.Comment: Manuscript and 4 figure
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