14,148 research outputs found
Environmental factors influencing the spread of the highly pathogenic avian influenza H5N1 virus in wild birds in Europe
A large number of occurrences of the highly pathogenic avian influenza (HPAI) H5N1 virus in wild birds were reported in Europe. The relationship between the occurrence pattern and environmental factors has, however, not yet been explored. This research uses logistic regression to quantify the relationships between anthropogenic or physical environmental factors and HPAI H5N1 occurrences. Our results indicate that HPAI H5N1 occurrences are highly correlated with the following: the increased normalized difference vegetation index (NDVI) in December; intermediate NDVI in March; lower elevations; increased minimum temperatures in January; and reduced precipitation in January. A predictive risk map of HPAI H5N1 occurrences in wild birds in Europe was generated on the basis of five key environmental factors. Independent validation of the risk map showed the predictive model to be of high accuracy (79%). The analysis suggests that HPAI H5N1 occurrences in wild birds are strongly influenced by the availability of food resources and are facilitated by increased temperatures and reduced precipitation. We therefore deduced that HPAI H5N1 occurrences in wild birds in Europe are probably caused by contact with other wild birds and not by contact with domestic poultry. These findings are important considerations for the global surveillance of HPAI H5N1 occurrences in wild birds
The coupling of a hearing aid loudspeaker membrane to visco-thermal air layers
Hearing aids and their components are becoming smaller. This presents new problems for the acoustical components, such as the loudspeaker. A circular membrane of a hearing aid loudspeaker is modeled in this paper. Neglecting air influences, the membrane and its suspension behave as a mass spring system. However, under operating conditions, thin layers of air on both sides of the membrane influence its behavior. Air can enter and leave these layers at certain locations on the circular edge of the layer. Since these air layers are thin, visco-thermal effects may have to be taken into account. Therefore, the air layers are not modeled by the wave equation, but by the low reduced frequency model that takes these visco-thermal effects into account. The equations of this model are solved in a polar coordinate system, using a wave-based method. The other acoustical parts of the hearing aid loudspeaker, and the membrane itself are modeled by simple lumped models. The emphasis in this paper is on the coupling of the viscothermal air layer model to the mechanical model of the membrane. Coupling of the air layer to other acoustical parts by using an impedance as boundary condition for the layer model, is also described. The resulting model is verified by experiments. The model and the measurements match reasonably well, considering the level of approximation with lumped parts
Higher order correlations for fluctuations in the presence of fields
The higher order moments of the fluctuations for the thermodynamical systems
in the presence of fields are investigated in the framework of a theoretical
method. The metod uses a generalized statistical ensemble consonant with the
adequate expression for the generalized internal energy. The applications refer
to the case of a system in magnetoquasistatic field. In the case of linear
magnetic media one finds that for the description of the magnetic induction
fluctuations the Gaussian approximation is good enough. For nonlinear media the
coresponding fluctuations are non-Gaussian, they having a non-null asymmetry.
Aditionally the respective fluctuations have characteristics of leptokurtic,
mesokurtic and platykurtic type, depending of the value of the magnetic field
strength comparatively with a scaling factor of the magnetization curve.Comment: 10 pages, REVTe
Chiral-Odd Contribution to Single-Transverse Spin Asymmetry in Hadronic Pion Production
A formula for the single transverse spin asymmetry in the large- pion
production in the nucleon-nucleon collision is derived. We focuss on the
chiral-odd contribution where the transversity distribution and the chiral-odd
spin-independent twist-3 distribution contributes. This contribution is
expected to give rise to a large effect at .Comment: Latex file 10 pages + 2 figures attached as PS and EPS files. A minor
correction is include
Fluctuations in the presence of fields -Phenomenological Gaussian approximation and a new class of thermodynamic inequalities-
The work approaches the study of the fluctuations for the thermodynamic
systems in the presence of the fields. The approach is of phenomenological
nature and developed in a Gaussian approximation. The study is exemplified on
the cases of a magnetizable continuum in a magnetoquasistatic field, as well as
for the so called discrete systems. In the last case one finds that the
fluctuations estimators depends both on the intrinsic properties of the system
and on the characteristics of the environment. Following some earlier ideas of
one of the authors we present a new class of thermodynamic inequalities for the
systems investigated in this paper. In the case of two variables the mentioned
inequalities are nothing but non-quantum analogues of the well known quantum
Heisenberg (''uncertainty'') relations. Also the obtained fluctuations
estimators support the idea that the Boltzmann's constant k has the
signification of a generic indicator of stochasticity for thermodynamic
systems.
Pacs number(s): 05.20.-y, 05.40.-a, 05.70.-a, 41.20.GzComment: preprint, 24 page
Optical excitation and external photoluminescence quantum efficiency of Eu3+ in GaN
We investigate photoluminescence of Eu-related emission in a GaN host consisting of thin layers grown by organometallic vapor-phase epitaxy. By comparing it with a reference sample of Eu-doped Y2O3, we find that the fraction of Eu3+ ions that can emit light upon optical excitation is of the order of 1%. We also measure the quantum yield of the Eu-related photoluminescence and find this to reach (similar to 10%) and (similar to 3%) under continuous wave and pulsed excitation, respectively.Stichting voor de Technologische Wetenschappen (STW); Japan Society for the Promotion of Science [19GS1209, 24226009]; Ministry of Education, Culture, Sports, Science and Technology of Japaninfo:eu-repo/semantics/publishedVersio
Detection of a very bright optical flare from a gamma-ray burst at redshift 6.29
In this letter we discuss the flux and the behavior of the bright optical
flare emission detected by the 25 cm TAROT robotic telescope during the prompt
high-energy emission and the early afterglow. We combine our data with
simultaneous observations performed in X-rays and we analyze the broad-band
spectrum. These observations lead us to emphasize the similarity of GRB 050904
with GRB 990123, a remarkable gamma-ray burst whose optical emission reached
9th magnitude. While GRB 990123 was, until now, considered as a unique event,
this observation suggests the existence of a population of GRBs which have very
large isotropic equivalent energies and extremely bright optical counterparts.
The luminosity of these GRBs is such that they are easily detectable through
the entire universe. Since we can detect them to very high redshift even with
small aperture telescopes like TAROT, they will constitute powerful tools for
the exploration of the high-redshift Universe and might be used to probe the
first generation of stars.Comment: 9 pages, 3 figures. Accepted in ApJ
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