370 research outputs found
Vaccination against Foot-and-Mouth Disease : differentiating strategies and their epidemiological and economic consequences
The effectiveness of different control strategies against Foot-and-Mouth Disease (FMD) were investigated using epidemiological and economic models. A quick and large-scale vaccination within a radius of at least 2km is as effective as preemptive 1-km ring culling to mitigate FMD epidemics. Control measures should primarily target cattle farms. After the epidemic, most seropositive animals are expected on sheep farms and vaccinated cattle farms. An effective end-screening strategy should focus on these farms. Market acceptance by trade partners of products of vaccinated animals can limit the economic consequences of outbreaks of FMD.De effectiviteit van bestrijdingstrategieën tegen Mond-en-Klauwzeer (MKZ) is onderzochtmet behulp van epidemiologische en economische modellen. Het blijkt dat snelle en op grote schaal toegepaste vaccinatie in een straal van 2 km rond geïnfecteerde bedrijven net zo effectief is als ruimen in een straal van 1 km rond geïnfecteerde bedrijven bij het bestrijden van MKZ-uitbraken. Controlemaatregelen moeten vooral worden gericht op rundveebedrijven. Na de epidemie zijn de meeste seropositieve dieren te verwachten. De eindscreening zal zich op schapenbedrijven en gevaccineerde rundveebedrijven moeten richten. Acceptatie door internationale handelspartners van producten van gevaccineerde dieren kan de economische gevolgen van een uitbraak van MKZ beperken
Monte-Carlo calculation of longitudinal and transverse resistivities in a model Type-II superconductor
We study the effect of a transport current on the vortex-line lattice in
isotropic type-II superconductors in the presence of strong thermal
fluctuations by means of 'driven-diffusion' Monte Carlo simulations of a
discretized London theory with finite magnetic penetration depth. We calculate
the current-voltage (I-V) characteristics for various temperatures, for
transverse as well as longitudinal currents I. From these characteristics, we
estimate the linear resistivities R_xx=R_yy and R_zz and compare these with
equilibrium results for the vortex-lattice structure factor and the helicity
moduli. From this comparison a consistent picture arises, in which the melting
of the flux-line lattice occurs in two stages for the system size considered.
In the first stage of the melting, at a temperature T_m, the structure factor
drops to zero and R_xx becomes finite. For a higher temperature T_z, the second
stage takes place, in which the longitudinal superconducting coherence is lost,
and R_zz becomes finite as well. We compare our results with related recent
numerical work and experiments on cuprate superconductors.Comment: 4 pages, with eps figure
Effects of Electronic Correlations on the Thermoelectric Power of the Cuprates
We show that important anomalous features of the normal-state thermoelectric
power S of high-Tc materials can be understood as being caused by doping
dependent short-range antiferromagnetic correlations. The theory is based on
the fluctuation-exchange approximation applied to Hubbard model in the
framework of the Kubo formalism. Firstly, the characteristic maximum of S as
function of temperature can be explained by the anomalous momentum dependence
of the single-particle scattering rate. Secondly, we discuss the role of the
actual Fermi surface shape for the occurrence of a sign change of S as a
function of temperature and doping.Comment: 4 pages, with eps figure
Improving the evaluation of worldwide biomedical research output: classification method and standardised bibliometric indicators by disease
Merit, Expertise and Measuremen
Transverse depinning and melting of a moving vortex lattice in driven periodic Josephson junction arrays
We study the effect of thermal fluctuations in a vortex lattice driven in the
periodic pinning of a Josephson junction array. The phase diagram current ()
vs. temperature () is studied. Above the critical current we find a
moving vortex lattice (MVL) with anisotropic Bragg peaks. For large currents
, there is a melting transition of the MVL at . When
applying a small transverse current to the MVL, there is no dissipation at low
. We find an onset of transverse vortex motion at a transverse depinning
temperature .Comment: 4 pages, 4 figures, Figure 2 changed, added new reference
Orientational pinning and transverse voltage: Simulations and experiments in square Josephson junction arrays
We study the dependence of the transport properties of square Josephson
Junctions arrays with the direction of the applied dc current, both
experimentally and numerically. We present computational simulations of
current-voltage curves at finite temperatures for a single vortex in the array
(), and experimental measurements in
arrays under a low magnetic field corresponding to . We find that
the transverse voltage vanishes only in the directions of maximum symmetry of
the square lattice: the [10] and [01] direction (parallel bias) and the [11]
direction (diagonal bias). For orientations different than the symmetry
directions, we find a finite transverse voltage which depends strongly on the
angle of the current. We find that vortex motion is pinned in the [10]
direction (), meaning that the voltage response is insensitive to small
changes in the orientation of the current near . We call this
phenomenon orientational pinning. This leads to a finite transverse critical
current for a bias at and to a transverse voltage for a bias at
. On the other hand, for diagonal bias in the [11] direction the
behavior is highly unstable against small variations of , leading to a
rapid change from zero transverse voltage to a large transverse voltage within
a few degrees. This last behavior is in good agreement with our measurements in
arrays with a quasi-diagonal current drive.Comment: 9 pages, 9 figure
Numerical studies of the phase diagram of layered type II superconductors in a magnetic field
We report on simulations of layered superconductors using the
Lawrence-Doniach model in the framework of the lowest Landau level
approximation. We find a first order phase transition with a dependence
which agrees very well with the experimental ``melting'' line in YBaCuO. The
transition is not associated with vortex lattice melting, but separates two
vortex liquid states characterised by different degrees of short-range
crystalline order and different length scales of correlations between vortices
in different layers. The transition line ends at a critical end-point at low
fields. We find the magnetization discontinuity and the location of the lower
critical magnetic field to be in good agreement with experiments in YBaCuO.
Length scales of order parameter correlations parallel and perpendicular to the
magnetic field increase exponentially as 1/T at low temperatures. The dominant
relaxation time scales grow roughly exponentially with these correlation
lengths. We find that the first order phase transition persists in the presence
of weak random point disorder but can be suppressed entirely by strong
disorder. No vortex glass or Bragg glass state is found in the presence of
disorder. The consistency of our numerical results with various experimental
features in YBaCuO, including the dependence on anisotropy, and the temperature
dependence of the structure factor at the Bragg peaks in neutron scattering
experiments is demonstrated.Comment: 25 pages (revtex), 19 figures included, submitted to PR
Epidemiological Characteristics of Classical Scrapie Outbreaks in 30 Sheep Flocks in the United Kingdom
Most previous analyses of scrapie outbreaks have focused on flocks run by research institutes, which may not reflect the field situation. Within this study, we attempt to rectify this deficit by describing the epidemiological characteristics of 30 sheep flocks naturally-infected with classical scrapie, and by exploring possible underlying causes of variation in the characteristics between flocks, including flock-level prion protein (PrP) genotype profile. In total, the study involved PrP genotype data for nearly 8600 animals and over 400 scrapie cases.We found that most scrapie cases were restricted to just two PrP genotypes (ARQ/VRQ and VRQ/VRQ), though two flocks had markedly different affected genotypes, despite having similar underlying genotype profiles to other flocks of the same breed; we identified differences amongst flocks in the age of cases of certain PrP genotypes; we found that the age-at-onset of clinical signs depended on peak incidence and flock type; we found evidence that purchasing infected animals is an important means of introducing scrapie to a flock; we found some evidence that flock-level PrP genotype profile and flock size account for variation in outbreak characteristics; identified seasonality in cases associated with lambing time in certain flocks; and we identified one case that was homozygous for phenylalanine at codon 141, a polymorphism associated with a very high risk of atypical scrapie, and 28 cases that were heterozygous at this codon.This paper presents the largest study to date on commercially-run sheep flocks naturally-infected with classical scrapie, involving 30 study flocks, more than 400 scrapie cases and over 8500 PrP genotypes. We show that some of the observed variation in epidemiological characteristics between farms is related to differences in their PrP genotype profile; although much remains unexplained and may instead be attributed to the stochastic nature of scrapie dynamics
Epidemiological Characteristics of Classical Scrapie Outbreaks in 30 Sheep Flocks in the United Kingdom
Most previous analyses of scrapie outbreaks have focused on flocks run by research institutes, which may not reflect the field situation. Within this study, we attempt to rectify this deficit by describing the epidemiological characteristics of 30 sheep flocks naturally-infected with classical scrapie, and by exploring possible underlying causes of variation in the characteristics between flocks, including flock-level prion protein (PrP) genotype profile. In total, the study involved PrP genotype data for nearly 8600 animals and over 400 scrapie cases.We found that most scrapie cases were restricted to just two PrP genotypes (ARQ/VRQ and VRQ/VRQ), though two flocks had markedly different affected genotypes, despite having similar underlying genotype profiles to other flocks of the same breed; we identified differences amongst flocks in the age of cases of certain PrP genotypes; we found that the age-at-onset of clinical signs depended on peak incidence and flock type; we found evidence that purchasing infected animals is an important means of introducing scrapie to a flock; we found some evidence that flock-level PrP genotype profile and flock size account for variation in outbreak characteristics; identified seasonality in cases associated with lambing time in certain flocks; and we identified one case that was homozygous for phenylalanine at codon 141, a polymorphism associated with a very high risk of atypical scrapie, and 28 cases that were heterozygous at this codon.This paper presents the largest study to date on commercially-run sheep flocks naturally-infected with classical scrapie, involving 30 study flocks, more than 400 scrapie cases and over 8500 PrP genotypes. We show that some of the observed variation in epidemiological characteristics between farms is related to differences in their PrP genotype profile; although much remains unexplained and may instead be attributed to the stochastic nature of scrapie dynamics
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