1,135 research outputs found
Influence of the 2014 West African Ebola epidemic on essential health service utilization in a Liberian district
Force-Extension Relations for Polymers with Sliding Links
Topological entanglements in polymers are mimicked by sliding rings
(slip-links) which enforce pair contacts between monomers. We study the
force-extension curve for linear polymers in which slip-links create additional
loops of variable size. For a single loop in a phantom chain, we obtain exact
expressions for the average end-to-end separation: The linear response to a
small force is related to the properties of the unstressed chain, while for a
large force the polymer backbone can be treated as a sequence of Pincus--de
Gennes blobs, the constraint effecting only a single blob. Generalizing this
picture, scaling arguments are used to include self-avoiding effects.Comment: 4 pages, 5 figures; accepted to Phys. Rev. E (Brief Report
Dynamical structure factor of the anisotropic Heisenberg chain in a transverse field
We consider the anisotropic Heisenberg spin-1/2 chain in a transverse
magnetic field at zero temperature. We first determine all components of the
dynamical structure factor by combining exact results with a mean-field
approximation recently proposed by Dmitriev {\it et al}., JETP 95, 538 (2002).
We then turn to the small anisotropy limit, in which we use field theory
methods to obtain exact results. We discuss the relevance of our results to
Neutron scattering experiments on the 1D Heisenberg chain compound .Comment: 13 pages, 14 figure
Experimental String Field Theory
We develop efficient algorithms for level-truncation computations in open
bosonic string field theory. We determine the classical action in the universal
subspace to level (18,54) and apply this knowledge to numerical evaluations of
the tachyon condensate string field. We obtain two main sets of results. First,
we directly compute the solutions up to level L=18 by extremizing the
level-truncated action. Second, we obtain predictions for the solutions for L >
18 from an extrapolation to higher levels of the functional form of the tachyon
effective action. We find that the energy of the stable vacuum overshoots -1
(in units of the brane tension) at L=14, reaches a minimum E_min = -1.00063 at
L ~ 28 and approaches with spectacular accuracy the predicted answer of -1 as L
-> infinity. Our data are entirely consistent with the recent perturbative
analysis of Taylor and strongly support the idea that level-truncation is a
convergent approximation scheme. We also check systematically that our
numerical solution, which obeys the Siegel gauge condition, actually satisfies
the full gauge-invariant equations of motion. Finally we investigate the
presence of analytic patterns in the coefficients of the tachyon string field,
which we are able to reliably estimate in the L -> infinity limit.Comment: 37 pages, 6 figure
A paradigm of open/closed duality: Liouville D-branes and the Kontsevich model
We argue that topological matrix models (matrix models of the Kontsevich
type) are examples of exact open/closed duality. The duality works at finite N
and for generic `t Hooft couplings. We consider in detail the paradigm of the
Kontsevich model for two-dimensional topological gravity. We demonstrate that
the Kontsevich model arises by topological localization of cubic open string
field theory on N stable branes. Our analysis is based on standard worldsheet
methods in the context of non-critical bosonic string theory. The stable branes
have Neumann (FZZT) boundary conditions in the Liouville direction. Several
generalizations are possible.Comment: v2: References added; a new section with generalization to non-zero
bulk cosmological constant; expanded discussion on topological localization;
added some comment
Ethnic armies and ethnic conflict in Burma – Reconsidering the history of colonial militarization in the Kachin region of Burma during the Second World War
The electron heating rate and ion chemistry in the thermosphere above Wallops Island during the solar eclipse of 7 March 1970
An identical pair of thermosphere probes measured the N2 concentration and temperature, the ion composition and concentrations and the electron temperature up to 290 km about 30 min and 5 min before totality during the 7 March 1970 eclipse at Wallops Island. The rockets travelled similar trajectories thus permitting the purely temporal changes between nights to be resolved. The neutral temperature and N2 concentration changed little but the electron temperature decreased by as much as 20 per cent in the lower F-region. The ion concentration decreased by about 30 per cent in the F-region and about 50 per cent in the E-region, with little change in relative ion composition. The electron cooling rates decreased by a factor of 6 in the lower F-region, approximately in proportion to the change in visible solar disc. A smaller than expected decrease in the cooling rate below 150 km between the two flights indicates a hardening of the solar spectrum and suggests a significant heat contribution from the solar corona near totality. The ion composition measurements were consistent with solutions of the ion continuity equations. A proper fit required a factor of three enhancement of the flux below 200 A, an amount also consistent with the electron heat balance analysis. Reactions involving the minor ions N+ and N2+ were found to be important for the ion chemistry of the major ions O2+ and NO+, especially at the time of eclipse. The negligible response of the neutral atmosphere to the eclipse is reasonable considering the long time constants for the conductive and convective transport processes and the local nature of the disturbance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34133/1/0000417.pd
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Cellular interference in craniofrontonasal syndrome: Males mosaic for mutations in the x-linked EFNB1 gene are more severely affected than true hemizygotes
Craniofrontonasal syndrome (CFNS), an X-linked disorder caused by loss-of-function mutations of EFNB1, exhibits a paradoxical sex reversal in phenotypic severity: females characteristically have frontonasal dysplasia, craniosynostosis and additional minor malformations, but males are usually more mildly affected with hypertelorism as the only feature. X-inactivation is proposed to explain the more severe outcome in heterozygous females, as this leads to functional mosaicism for cells with differing expression of EPHRIN-B1, generating abnormal tissue boundariesa process that cannot occur in hemizygous males. Apparently challenging this model, males occasionally present with a more severe female-like CFNS phenotype. We hypothesized that such individuals might be mosaic for EFNB1 mutations and investigated this possibility in multiple tissue samples from six sporadically presenting males. Using denaturing high performance liquid chromatography, massively parallel sequencing and multiplex-ligation-dependent probe amplification (MLPA) to increase sensitivity above standard dideoxy sequencing, we identified mosaic mutations of EFNB1 in all cases, comprising three missense changes, two gene deletions and a novel point mutation within the 5 untranslated region (UTR). Quantification by Pyrosequencing and MLPA demonstrated levels of mutant cells between 15 and 69. The 5 UTR variant mutates the stop codon of a small upstream open reading frame that, using a dual-luciferase reporter construct, was demonstrated to exacerbate interference with translation of the wild-type protein. These results demonstrate a more severe outcome in mosaic than in constitutionally deficient males in an X-linked dominant disorder and provide further support for the cellular interference mechanism, normally related to X-inactivation in females. © The Author 2013. Published by Oxford University Press. All rights reserved
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