1,285 research outputs found
Failure of vaccination to prevent outbreaks of foot-and-mouth disease
Outbreaks of foot-and-mouth disease persist in dairy cattle herds in Saudi Arabia despite revaccination at intervals of 4-6 months. Vaccine trials provide data on antibody responses following vaccination. Using this information we developed a mathematical model of the decay of protective antibodies with which we estimated the fraction of susceptible animals at a given time after vaccination. The model describes the data well, suggesting over 95% take with an antibody half-life of 43 days. Farm records provided data on the time course of five outbreaks. We applied a 'SLIR' epidemiological model to these data, fitting a single parameter representing disease transmission rate. The analysis provides estimates of the basic reproduction number R(0), which may exceed 70 in some cases. We conclude that the critical intervaccination interval which would provide herd immunity against FMDV is unrealistically short, especially for heterologous challenge. We suggest that it may not be possible to prevent foot-and-mouth disease outbreaks on these farms using currently available vaccines
Relativistic eikonal description of A(p,pN) reactions
The authors present a relativistic and cross-section factorized framework for
computing quasielastic A(p,pN) observables at intermediate and high energies.
The model is based on the eikonal approximation and can accomodate both optical
potentials and the Glauber method for dealing with the initial- and final-state
interactions (IFSI). At lower nucleon energies, the optical-potential
philosophy is preferred, whereas at higher energies the Glauber method is more
natural. This versatility in dealing with the IFSI allows one to describe
A(p,pN) reactions in a wide energy range. Most results presented here use
optical potentials as this approach is argued to be the optimum choice for the
kinematics of the experiments considered in the present paper. The properties
of the IFSI factor, a function wherein the entire effect of the IFSI is
contained, are studied in detail. The predictions of the presented framework
are compared with two kinematically different experiments. First, differential
cross sections for quasielastic proton scattering at 1 GeV off 12C, 16O, and
40Ca target nuclei are computed and compared to data from PNPI. Second, the
formalism is applied to the analysis of a 4He(p,2p) experiment at 250 MeV. The
optical-potential calculations are found to be in good agreement with the data
from both experiments, showing the reliability of the adopted model in a wide
energy range.Comment: 34 pages, 14 figures, accepted for publication in Phys. Rev.
Estimating the Integrated Bispectrum from Weak Lensing Maps
We use a recently introduced statistic called {\em Integrated Bispectrum}
(IB) to probe the gravity-induced non-Gaussianity at the level of the
bispectrum from weak lensing convergence or maps. We generalize the
concept of the IB to spherical coordinates. This result is next connected to
the response function approach. Finally, we use the Euclid Flagship simulations
to compute the IB as a function of redshift and wave number. We also outline
how the IB can be computed using a variety of analytical approaches including
the ones based on Effective Field Theory (EFT), {\em Halo models} and models
based on the {\em Separate Universe approach} in projection or two-dimension
(2D). Comparing these results against simulations we find that the existing
theoretical models tend to over-predict the numerical value of the IB. We
emphasize the role of the finite volume effect in the numerical estimation of
the IB. We introduced the concept of squeezed and collapsed tripsectrum for 2D
maps. We derive the IB for many parameterized theories of modified
gravity including the Horndeskii and beyond-Horndeskii theories specifically
for the non-degenerate scenarios that are also known as the
Gleyzes-Langlois-Piazza-Venizzi or GPLV theories. In addition, the cosmological
models with clustering quintessence and models involving massive neutrinos are
also derived.Comment: 49 pages, 8 figures, To appear in JCA
On the unique possibility to increase significantly the contrast of dark resonances on D1 line of Rb
We propose and study, theoretically and experimentally, a new scheme of
excitation of a coherent population trapping resonance for D1 line of alakli
atoms with nuclear spin by bichromatic linearly polarized light ({\em
lin}{\em lin} field) at the conditions of spectral resolution of the
excited state. The unique properties of this scheme result in a high contrast
of dark resonance for D1 line of Rb.Comment: 9 pages, 7 figures. This material has been partially presented on
ICONO-2005, 14 May 2005, St. Petersburg, Russia. v2 references added; text is
changed a bi
Finding Evidence for Massive Neutrinos using 3D Weak Lensing
In this paper we investigate the potential of 3D cosmic shear to constrain
massive neutrino parameters. We find that if the total mass is substantial
(near the upper limits from LSS, but setting aside the Ly alpha limit for now),
then 3D cosmic shear + Planck is very sensitive to neutrino mass and one may
expect that a next generation photometric redshift survey could constrain the
number of neutrinos N_nu and the sum of their masses m_nu to an accuracy of
dN_nu ~ 0.08 and dm_nu ~ 0.03 eV respectively. If in fact the masses are close
to zero, then the errors weaken to dN_nu ~ 0.10 and dm_nu~0.07 eV. In either
case there is a factor 4 improvement over Planck alone. We use a Bayesian
evidence method to predict joint expected evidence for N_nu and m_nu. We find
that 3D cosmic shear combined with a Planck prior could provide `substantial'
evidence for massive neutrinos and be able to distinguish `decisively' between
many competing massive neutrino models. This technique should `decisively'
distinguish between models in which there are no massive neutrinos and models
in which there are massive neutrinos with |N_nu-3| > 0.35 and m_nu > 0.25 eV.
We introduce the notion of marginalised and conditional evidence when
considering evidence for individual parameter values within a multi-parameter
model.Comment: 9 pages, 2 Figures, 2 Tables, submitted to Physical Review
Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes
For nearly fifty years theoretical and experimental efforts in
nucleon-nucleon bremsstrahlung (NN) have been devoted to measuring
off-shell amplitudes and distinguishing among various NN potentials on the
basis of their off-shell behavior. New experiments are underway, designed
specifically to attain kinematics further off shell than in the past, and thus
to be more sensitive to the off-shell behavior. This letter shows that,
contrary to these expectations, and due to the invariance of the S-matrix under
transformations of the fields, the off-shell NN amplitude is as a matter of
principle an unmeasurable quantity in NN.Comment: 9 pages, Latex, using RevTeX; Minor wording changes, title changed,
version to be published in Phys. Rev. Letter
A magneto-optic trap using a reversible, solid-state alkali-metal source
We demonstrate a novel way to form and deplete a vapor-cell magneto-optic
trap (MOT) using a reversible, solid-state alkali-metal source (AMS) via an
applied polarized voltage. Using ~100 mW of electrical power, a trapped-atom
number of 5x10^6 has been achieved starting from near zero and the timescales
of the MOT formation and depletion of ~1 s. This fast, reversible, and low
power alkali-atom source is desirable in both tabletop and portable cold-atom
systems. The core technology of this device should translate readily to other
alkali and alkaline-earth elements that could find a wide range of uses in
cold-atom systems and instruments.Comment: 7 page
Dynamic characterization of an alkali-ion battery as a source for laser-cooled atoms
We investigate a solid-state, reversible, alkali-ion battery (AIB) capable of
regulating the density of alkali atoms in a vacuum system used for the
production of laser-cooled atoms. The cold-atom sample can be used with
in-vacuum chronoamperometry as a diagnostic for the voltage-controlled
electrochemical reaction that sources or sinks alkali atoms into the vapor. In
a combined reaction-diffusion-limited regime, we show that the number of
laser-cooled atoms in a magneto-optical trap can be increased both by initially
loading the AIB from the vapor for longer, and by using higher voltages across
the AIB when atoms are subsequently sourced back into the vapor. The time
constants associated with the change in atom number in response to a change in
AIB voltage are in the range of 0.5 s - 40 s. The AIB alkali reservoir is
demonstrated to survive oxidization during atmospheric exposure, simplifying
reservoir loading prior to vacuum implementation as a replacement for
traditional resistively-heated dispensers. The AIB capabilities may provide an
improved atom number stability in next-generation atomic clocks and sensors,
while also facilitating fast loading and increased interrogation times.Comment: 7 pages, 5 figure
VIS: the visible imager for Euclid
Euclid-VIS is a large format visible imager for the ESA Euclid space mission
in their Cosmic Vision program, scheduled for launch in 2019. Together with the
near infrared imaging within the NISP instrument it forms the basis of the weak
lensing measurements of Euclid. VIS will image in a single r+i+z band from
550-900 nm over a field of view of ~0.5 deg2. By combining 4 exposures with a
total of 2240 sec, VIS will reach to V=24.5 (10{\sigma}) for sources with
extent ~0.3 arcsec. The image sampling is 0.1 arcsec. VIS will provide deep
imaging with a tightly controlled and stable point spread function (PSF) over a
wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5
billion galaxies to high levels of accuracy, from which the cosmological
parameters will be measured. In addition, VIS will also provide a legacy
imaging dataset with an unprecedented combination of spatial resolution, depth
and area covering most of the extra-Galactic sky. Here we will present the
results of the study carried out by the Euclid Consortium during the Euclid
Definition phase.Comment: 10 pages, 6 figure
- …