2,879 research outputs found
A review of bovine Johne's disease control activities in 6 endemically infected countries
Mycobacterium avium subspecies paratuberculosis (MAP) is endemic in the bovine populations of many countries and can cause a significant reduction in animal welfare and production efficiency making control desirable. Effective control has proved very difficult to achieve despite multiple regionally coordinated programmes being in existence since the 1920s. The international community increasingly recognises the value in learning from the collective experiences of existing programmes to improve the effectiveness of control. The aim of this review is to outline key aspects of bovine Johne's disease control activities across 6 endemically infected countries to facilitate comparison of current international practice. The background, control activities and monitoring components of programmes in Australia, Canada, Denmark, the Netherlands, the United Kingdom and the United States of America were individually reviewed. Factual accuracy of each review was checked by individuals involved in the respective programmes before the reviews were condensed and combined into a single document presented here, with the complete reviews of each programme available as supplementary material. There was considerable heterogeneity in key aspects of control activity design including goals, responses to declining participation, herd classification, recommended control measures and associated test requirements. The data presented will be of interest to organisations that are involved in developing new or existing regionally coordinated BJD control activities
A spectral function tour of electron-phonon coupling outside the Migdal limit
We simulate spectral functions for electron-phonon coupling in a filled band
system - far from the asymptotic limit often assumed where the phonon energy is
very small compared to the Fermi energy in a parabolic band and the Migdal
theorem predicting 1+lambda quasiparticle renormalizations is valid. These
spectral functions are examined over a wide range of parameter space through
techniques often used in angle-resolved photoemission spectroscopy (ARPES).
Analyzing over 1200 simulations we consider variations of the microscopic
coupling strength, phonon energy and dimensionality for two models: a
momentum-independent Holstein model, and momentum-dependent coupling to a
breathing mode phonon. In this limit we find that any `effective coupling',
lambda_eff, inferred from the quasiparticle renormalizations differs from the
microscopic dimensionless coupling characterizing these Hamiltonians, lambda,
and could drastically either over- or under-estimate it depending on the
particular parameters and model. In contrast, we show that perturbation theory
retains good predictive power for low coupling and small momenta, and that the
momentum-dependence of the self-energy can be revealed via the relationship
between velocity renormalization and quasiparticle strength. Additionally we
find that (although not strictly valid) it is often possible to infer the
self-energy and bare electronic structure through a self-consistent
Kramers-Kronig bare-band fitting; and also that through lineshape alone, when
Lorentzian, it is possible to reliably extract the shape of the imaginary part
of a momentum-dependent self-energy without reference to the bare-band.Comment: 15 pages, 11 figures. High resolution available here:
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/sf_tour.pd
Distanciamiento social ante la COVID-19: Simulación del aforo máximo de personas mediante PHP
Population confluence in internal or external areas considerably increases transmission of COVID-19, due to not respecting the social distancing established by the health system. The objective of this work was to make use of programming techniques,
using the PHP language (hypertext preprocessor), for the development of an application that simulates the maximum capacity of people who can enter an internal or external area. The methodology allowed recognizing common internal and external areas, configurating to the development environment, coding, simulation proposing and executing of the simulator where a practical case and ten places were evaluated to determine its reliability. The simulator provided the maximum capacity of people who can enter an internal or external area, complying with the social distancing of 2 m. The results made it possible to know that the use of information technologies through programming techniques and the PHP language contributed to being a technological alternative for the fight against the spread of the virus.La confluencia poblacional en áreas internas o externas incrementa considerablemente la trasmisión de la COVID-19, por no respetar el distanciamiento social que establece el sistema de salud. El objetivo de este trabajo fue hacer uso de técnicas de programación, empleando el lenguaje PHP (preprocesador de hipertexto), para el desarrollo de una aplicación que simule el aforo máximo de personas que pueden ingresar a un área interna o externa. La metodología permitió el reconocimiento de áreas internas y externas comunes, configuración al entorno de desarrollo, codificación, propuesta de simulación y ejecución del simulador donde se ha evaluado un caso práctico y diez lugares para determinar su confiabilidad. El simulador brindó el aforo máximo de personas que pueden ingresar a un lugar de área interna o externa cumpliendo el distanciamiento social de 2 m. Los resultados permitieron conocer que el uso de las tecnologías de información a través de las técnicas de programación y el lenguaje PHP contribuyó en ser una alternativa tecnológica para la lucha contra la propagación del virus
Characterization of Melt Infiltrated SiC/SiC Composite Combustor Liners Using Meso- and Micro-NDE Techniques
Melt-infiltrated ceramic matrix composite SiC/SiC material systems are under development for use in combustor liners for low-emission advanced gas turbines. Uncertainty in repeatability of processing methods for these large components (33--76 cm diameter), and hence possible reduced reliability for the end user. This requires that appropriate test methods, at both meso- and micro-scale, be used to ensure that the liners are acceptable for use. Nondestructive evaluation (NDE) methods, if demonstrated to reliably detect changes caused by processing, would be of significant benefit to both manufacturer and end user. This paper describes the NDE methods and their applications in detecting a process upset in a melt-infiltrated 33 cm combustor liner and how high-resolution scanning electron microscopy was used to verify the NDE data
Characterizing SL2S galaxy groups using the Einstein radius
We analyzed the Einstein radius, , in our sample of SL2S galaxy
groups, and compared it with (the distance from the arcs to the center of
the lens), using three different approaches: 1.- the velocity dispersion
obtained from weak lensing assuming a Singular Isothermal Sphere profile
(), 2.- a strong lensing analytical method ()
combined with a velocity dispersion-concentration relation derived from
numerical simulations designed to mimic our group sample, 3.- strong lensing
modeling () of eleven groups (with four new models presented in
this work) using HST and CFHT images. Finally, was analyzed as a function
of redshift to investigate possible correlations with L, N, and the
richness-to-luminosity ratio (N/L). We found a correlation between
and , but with large scatter. We estimate = (2.2 0.9)
+ (0.7 0.2), = (0.4 1.5) + (1.1
0.4), and = (0.4 1.5) + (0.9 0.3) for
each method respectively. We found a weak evidence of anti-correlation between
and , with Log = (0.580.06) - (0.040.1), suggesting
a possible evolution of the Einstein radius with , as reported previously by
other authors. Our results also show that is correlated with L and N
(more luminous and richer groups have greater ), and a possible
correlation between and the N/L ratio. Our analysis indicates that
is correlated with in our sample, making useful to
characterize properties like L and N (and possible N/L) in galaxy groups.
Additionally, we present evidence suggesting that the Einstein radius evolves
with .Comment: Accepted for publication in Astronomy & Astrophysics. Typos correcte
Instabilities in the Nuclear Energy Density Functional
In the field of Energy Density Functionals (EDF) used in nuclear structure
and dynamics, one of the unsolved issues is the stability of the functional.
Numerical issues aside, some EDFs are unstable with respect to particular
perturbations of the nuclear ground-state density. The aim of this contribution
is to raise questions about the origin and nature of these instabilities, the
techniques used to diagnose and prevent them, and the domain of density
functions in which one should expect a nuclear EDF to be stable.Comment: Special issue "Open Problems in Nuclear Structure Theory" of
Jour.Phys.G - accepted. 7 pages, 2 figure
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