2,317 research outputs found
Predicting spatial spread of rabies in skunk populations using surveillance data reported by the public
Background:
Prevention and control of wildlife disease invasions relies on the ability to predict spatio-temporal dynamics and understand the role of factors driving spread rates, such as seasonality and transmission distance. Passive disease surveillance (i.e., case reports by public) is a common method of monitoring emergence of wildlife diseases, but can be challenging to interpret due to spatial biases and limitations in data quantity and quality.
Methodology/Principal findings:
We obtained passive rabies surveillance data from dead striped skunks (Mephitis mephitis) in an epizootic in northern Colorado, USA. We developed a dynamic patch-occupancy model which predicts spatio-temporal spreading while accounting for heterogeneous sampling. We estimated the distance travelled per transmission event, direction of invasion, rate of spatial spread, and effects of infection density and season. We also estimated mean transmission distance and rates of spatial spread using a phylogeographic approach on a subsample of viral sequences from the same epizootic. Both the occupancy and phylogeographic approaches predicted similar rates of spatio-temporal spread. Estimated mean transmission distances were 2.3 km (95% Highest Posterior Density (HPD95): 0.02, 11.9; phylogeographic) and 3.9 km (95% credible intervals (CI95): 1.4, 11.3; occupancy). Estimated rates of spatial spread in km/year were: 29.8 (HPD95: 20.8, 39.8; phylogeographic, branch velocity, homogenous model), 22.6 (HPD95: 15.3, 29.7; phylogeographic, diffusion rate, homogenous model) and 21.1 (CI95: 16.7, 25.5; occupancy). Initial colonization probability was twice as high in spring relative to fall.
Conclusions/Significance:
Skunk-to-skunk transmission was primarily local (< 4 km) suggesting that if interventions were needed, they could be applied at the wave front. Slower viral invasions of skunk rabies in western USA compared to a similar epizootic in raccoons in the eastern USA implies host species or landscape factors underlie the dynamics of rabies invasions. Our framework provides a straightforward method for estimating rates of spatial spread of wildlife diseases
The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV)
acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV
trend), hinting at the existence of a distant orbiting companion. We have
obtained high-contrast adaptive optics images of the star using NIRC2 at Keck
Observatory and report the direct detection of the body that causes the
acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than
its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14
(J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU).
Follow-up astrometric measurements obtained over an 1.1 year time baseline
demonstrate physical association through common parallactic and proper motion.
We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion
mass from orbital dynamics using a combination of Doppler observations and
imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a
gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a
much older age of Gyr, which corresponds to a mass of
m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude
are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of
[Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is
the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with
a measured RV acceleration.Comment: Updated to reflect ApJ versio
The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity
The companion to the G0V star HR7672 directly imaged by Liu et al. (2002) has
moved measurably along its orbit since the discovery epoch, making it possible
to determine its dynamical properties. Originally targeted with adaptive optics
because it showed a long-term radial velocity acceleration (trend), we have
monitored this star with precise Doppler measurements and have now established
a 24 year time baseline. The radial velocity variations show significant
curvature (change in the acceleration) including an inflection point. We have
also obtained a recent image of HR7672B with NIRC2 at Keck. The astrometry also
shows curvature. In this paper, we use jointly-fitted Doppler and astrometric
models to calculate the three-dimensional orbit and dynamical mass of the
companion. The mass of the host star is determined using a direct radius
measurement from CHARA interferometry in combination with high resolution
spectroscopic modeling. We find that HR7672B has a highly eccentric,
, near edge-on, deg, orbit with
semimajor axis, AU. The mass of the companion is
at the 68.2% confidence level. HR7672B thus resides
near the substellar boundary, just below the hydrogen-fusing limit. These
measurements of the companion mass are independent of its brightness and
spectrum and establish HR7672B as a rare and precious "benchmark" brown dwarf
with a well-determined mass, age, and metallicity essential for testing
theoretical evolutionary models and synthetic spectral models. It is presently
the only directly imaged L,T,Y-dwarf known to produce an RV trend around a
solar-type star.Comment: accepted to Ap
Roles of the color antisymmetric ghost propagator in the infrared QCD
The results of Coulomb gauge and Landau gauge lattice QCD simulation do not
agree completely with continuum theory. There are indications that the ghost
propagator in the infrared region is not purely color diagonal as in high
energy region. After presenting lattice simulation of configurations produced
with Kogut-Susskind fermion (MILC collaboration) and those with domain wall
fermion (RBC/UKQCD collaboration), I investigate in triple gluon vertex and the
ghost-gluon-ghost vertex how the square of the color antisymmetric ghost
contributes. Then the effect of the vertex correction to the gluon propagator
and the ghost propagator is investigated.
Recent Dyson-Schwinger equation analysis suggests the ghost dressing function
finite and no infrared enhancement or . But the ghost
propagator renormalized by the loop containing a product of color antisymmetric
ghost is expected to behave as with
with , if the fixed point
scenario is valid. I interpret the solution should contain a
vertex correction. The infrared exponent of our lattice Landau gauge gluon
propagator of the RBC/UKQCD is and that of MILC is about
-0.7.
The implication for the Kugo-Ojima color confinement criterion, QCD effective
coupling and the Slavnov identity are given.Comment: 13 pages 10 figures, references added and revised. version to be
published in Few-Body System
The TRENDS High-contrast Imaging Survey. I. Three Benchmark M Dwarfs Orbiting Solar-type Stars
We present initial results from a new high-contrast imaging program dedicated to stars that exhibit long-term Doppler radial velocity accelerations (or "trends"). The goal of the TRENDS (TaRgetting bENchmark-objects with Doppler Spectroscopy) imaging survey is to directly detect and study the companions responsible for accelerating their host star. In this first paper of the series, we report the discovery of low-mass stellar companions orbiting HD 53665, HD 68017, and HD 71881 using NIRC2 adaptive optics (AO) observations at Keck. Follow-up imaging demonstrates association through common proper motion. These comoving companions have red colors with estimated spectral types of K7-M0, M5, and M3-M4, respectively. We determine a firm lower limit to their mass from Doppler and astrometric measurements. In the near future, it will be possible to construct three-dimensional orbits and calculate the dynamical mass of HD 68017 B and possibly HD 71881 B. We already detect astrometric orbital motion of HD 68017 B, which has a projected separation of 13.0 AU. Each companion is amenable to AO-assisted direct spectroscopy. Further, each companion orbits a solar-type star, making it possible to infer metallicity and age from the primary. Such benchmark objects are essential for testing theoretical models of cool dwarf atmospheres
The TRENDS High-contrast Imaging Survey. II. Direct Detection of the HD 8375 Tertiary
We present the direct imaging detection of a faint tertiary companion to the single-lined spectroscopic binary HD 8375 AB. Initially noticed as an 53 m s^–1 yr^–1 Doppler acceleration by Bowler et al., we have obtained high-contrast adaptive optics observations at Keck using NIRC2 that spatially resolve HD 8375 C from its host(s). Astrometric measurements demonstrate that the companion shares a common proper-motion. We detect orbital motion in a clockwise direction. Multiband relative photometry measurements are consistent with an early M-dwarf spectral type (~M1V). Our combined Doppler and imaging observations place a lower-limit of m ≥ 0.297 M_☉ on its dynamical mass. We also provide a refined orbit for the inner pair using recent radial velocity measurements obtained with the High Resolution Echelle Spectrometer. HD 8375 is one of many triple-star systems that are apparently missing in the solar neighborhood
The impact of the demographic transition on dengue in Thailand: Insights from a statistical analysis and mathematical modeling
Background: An increase in the average age of dengue hemorrhagic fever (DHF) cases has been reported in Thailand. The cause of this increase is not known. Possible explanations include a reduction in transmission due to declining mosquito populations, declining contact between human and mosquito, and changes in reporting. We propose that a demographic shift toward lower birth and death rates has reduced dengue transmission and lengthened the interval between large epidemics. Methods and Findings: Using data from each of the 72 provinces of Thailand, we looked for associations between force of infection (a measure of hazard, defined as the rate per capita at which susceptible individuals become infected) and demographic and climactic variables. We estimated the force of infection from the age distribution of cases from 1985 to 2005. We find that the force of infection has declined by 2% each year since a peak in the late 1970s and early 1980s. Contrary to recent findings suggesting that the incidence of DHF has increased in Thailand, we find a small but statistically significant decline in DHF incidence since 1985 in a majority of provinces. The strongest predictor of the change in force of infection and the mean force of infection is the median age of the population. Using mathematical simulations of dengue transmission we show that a reduced birth rate and a shift in the population's age structure can explain the shift in the age distribution of cases, reduction of the force of infection, and increase in the periodicity of multiannual oscillations of DHF incidence in the absence of other changes. Conclusions: Lower birth and death rates decrease the flow of susceptible individuals into the population and increase the longevity of immune individuals. The increase in the proportion of the population that is immune increases the likelihood that an infectious mosquito will feed on an immune individual, reducing the force of infection. Though the force of infection has decreased by half, we find that the critical vaccination fraction has not changed significantly, declining from an average of 85% to 80%. Clinical guidelines should consider the impact of continued increases in the age of dengue cases in Thailand. Countries in the region lagging behind Thailand in the demographic transition may experience the same increase as their population ages. The impact of demographic changes on the force of infection has been hypothesized for other diseases, but, to our knowledge, this is the first observation of this phenomenon
Summing up the perturbation series in the Schwinger Model
Perturbation series for the electron propagator in the Schwinger Model is
summed up in a direct way by adding contributions coming from individual
Feynman diagrams. The calculation shows the complete agreement between
nonperturbative and perturbative approaches.Comment: 10 pages (in REVTEX
The Gribov problem and QCD dynamics
In 1967, Faddeev and Popov were able to quantize the Yang-Mills theory by
introducing new particles called ghost through the introduction of a gauge.
Ever since, this quantization has become a standard textbook item. Some years
later, Gribov discovered that the gauge fixing was not complete, gauge copies
called Gribov copies were still present and could affect the infrared region of
quantities like the gauge dependent gluon and ghost propagator. This feature
was often in literature related to confinement. Some years later, the
semi-classical approach of Gribov was generalized to all orders and the
so-called GZ action was born. Ever since, many related articles were published.
This review tends to give a pedagogic review of the ideas of Gribov and the
subsequent construction of the GZ action, including many other toipics related
to the Gribov region. It is shown how the GZ action can be viewed as a
non-perturbative tool which has relations with other approaches towards
confinement. Many different features related to the GZ action shall be
discussed in detail, such as BRST breaking, the KO criterion, the propagators,
etc. We shall also compare with the lattice data and other non-perturbative
approaches, including stochastic quantization.Comment: 121 pages, 12 figures, Review article, references adde
Higher-order non-symmetric counterterms in pure Yang-Mills theory
We analyze the restoration of the Slavnov-Taylor (ST) identities for pure
massless Yang-Mills theory in the Landau gauge within the BPHZL renormalization
scheme with IR regulator. We obtain the most general form of the action-like
part of the symmetric regularized action, obeying the relevant ST identities
and all other relevant symmetries of the model, to all orders in the loop
expansion. We also give a cohomological characterization of the fulfillment of
BPHZL IR power-counting criterion, guaranteeing the existence of the limit
where the IR regulator goes to zero. The technique analyzed in this paper is
needed in the study of the restoration of the ST identities for those models,
like the MSSM, where massless particles are present and no invariant
regularization scheme is known to preserve the full set of ST identities of the
theory.Comment: Final version published in the journa
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