1,878 research outputs found
Quantifying the Effects of Measures to Control Highly Pathogenic Avian Influenza H5N1 in Poultry in Southeast Asia
Despite the ongoing efforts to contain its spread, H5N1 is now considered endemic within
poultry in various settings worldwide, threatening both the livelihoods of those involved in
poultry production in affected countries and posing a continuous public health risk. The
reasons for the varying levels of success in controlling H5N1 in Southeast Asia need to be
better understood. In this thesis, various different methods of quantifying the effects of
individual control measures, using the types of data available in various different contexts,
are discussed and applied. In the first half of this thesis a spatio-temporal survival model is
fitted to H5N1 outbreak surveillance data from Vietnam and Thailand using a Bayesian
framework in order to account for unobserved infection times. Following vaccination in
Vietnam it was found that transmissibility had been successfully reduced but, during a wave
of outbreaks in 2007, that this coincided with a reduction in the rate of at which outbreaks
were reported following the introduction of infection, limiting the overall impact this
reduction in transmissibility had on the total epidemic size. In Thailand, active surveillance
was found to be successful in contributing to the control of infection. Furthermore,
backyard producers, whilst responsible for the majority of outbreaks, were, on average, less
likely to transmit infection than those involved in more intensive production. In the second
half of the thesis, the use of final size methods to assess the effectiveness of vaccination
from trial data is explored. This involved an investigation into the effects of different
assumptions regarding the action by which vaccination confers immunity and fitting
estimates of transmissibility to data collected from outbreak investigations in the context of
a field trial of vaccination in Indonesia, where, making strong assumptions about the
underlying infection process, a reduction in both within and between flock transmissibility
was detected for outbreaks occurring in areas where vaccination was being carried out
Development of the Base Support Plan Process Model for Evaluation of Proposed Process Improvement Initiatives
The primary role of the United States Air Force (USAF) logistics planner is to plan for war. For the wing level logistics planner, an important war planning product they are responsible for is the base support plan (BSP). The BSP is the installation level plan to support unified and specified command wartime operations plans, as well as MAJCOM supporting plans. Two Armstrong Laboratory sponsored initiatives exist to automate and enhance some of the BSP processes: the Survey Tool for Employment Planning (STEP) and Beddown Capability and Assessment Tool (BCAT). This research explored the BSP process and improvement initiatives by (1) flowcharting the current process, (2) establishing where in the current process STEP and BCAT play a role, (3) developing a spreadsheet model of the process using Microsoft Excel and the program evaluation and review technique (PERT) for quantifying any possible BSP scenario, and (4) computing the estimated time savings STEP and BCAT can provide the USAF in one of its areas of responsibility. The results of this research are threefold. First, a detailed BSP process map now exists filling a void experienced by logistics planners at all levels. Second, a model using Excel and PERT is available for users interested in improving their BSP process. This model can be adapted to any BSP scenario. And, finally, the model showed the average time to complete a BSP with and without STEP and BCAT are significantly different
Domain walls and instantons in N=1, d=4 supergravity
We study the supersymmetric sources of (multi-) domain-wall and (multi-)
instanton solutions of generic N=1, d=4 supergravities, that is: the
worldvolume effective actions for said supersymmetric topological defects. The
domain-wall solutions naturally couple to the two 3-forms recently found as
part of the N=1, d=4 tensor hierarchy (i.e. they have two charges in general)
and their tension is the absolute value of the superpotential section L. The
introduction of sources (we study sources with finite and vanishing thickness)
is equivalent to the introduction of local coupling constants and results in
dramatic changes of the solutions. Our results call for a democratic
reformulation of N=1,d=4 supergravity in which coupling constants are,
off-shell, scalar fields. The effective actions for the instantons are always
proportional to the coordinate orthogonal to the twist-free embedding of the
null-geodesic (in the Wick-rotated scalar manifold) describing the instanton.
We show their supersymmetry and find the associated supersymmetric (multi-)
instanton solutions.Comment: 34 pages, 4 figures, references adde
ULF waves in the low‐latitude boundary layer and their relationship to magnetospheric pulsations: A multisatellite observation
On April 30 (day 120), 1985, the magnetosphere was compressed at 0923 UT and the subsolar magnetopause remained near 7 REgeocentric for ∼2 hours, during which the four spacecraft Spacecraft Charging At High Altitude (SCATHA), GOES 5, GOES 6, and Active Magnetospheric Particle Tracer Explorers (AMPTE) CCE were all in the magnetosphere on the morning side. SCATHA was in the low-latitude boundary layer (LLBL) in the second half of this period. The interplanetary magnetic field was inferred to be northward from the characteristics of precipitating particle fluxes as observed by the low-altitude satellite Defense Meteorological Satellite Program (DMSP) F7 and also from absence of substorms. We used magnetic field and particle data from this unique interval to study ULF waves in the LLBL and their relationship to magnetic pulsations in the magnetosphere. The LLBL was identified from the properties of particles, including bidirectional field-aligned electron beams at ∼200 eV. In the boundary layer the magnetic field exhibited both a 5–10 min irregular compressional oscillation and a broadband (Δƒ/ƒ ∼ 1) primarily transverse oscillations with a mean period of ∼50 s and a left-hand sense of polarization about the mean field. The former can be observed by other satellites and is likely due to pressure variations in the solar wind, while the latter is likely due to a Kelvin-Helmholtz (K.-H.) instability occurring in the LLBL or on the magnetopause. Also, a strongly transverse ∼3-s oscillation was observed in the LLBL. The magnetospheric pulsations, which exhibited position dependent frequencies, may be explained in terms of field line resonance with a broadband source wave, that is, either the pressure-induced compressional wave or the K.-H. wave generated in or near the boundary layer
Optical and Near-Infrared Observations of the Peculiar Type Ia Supernova 1999ac
We present 39 nights of optical photometry, 34 nights of infrared photometry,
and 4 nights of optical spectroscopy of the Type Ia SN 1999ac. This supernova
was discovered two weeks before maximum light, and observations were begun
shortly thereafter. At early times its spectra resembled the unusual SN 1999aa
and were characterized by very high velocities in the Ca II H and K lines, but
very low velocities in the Si II 6355 A line. The optical photometry showed a
slow rise to peak brightness but, quite peculiarly, was followed by a more
rapid decline from maximum. Thus, the B- and V-band light curves cannot be
characterized by a single stretch factor. We argue that the best measure of the
nature of this object is not the decline rate parameter Delta m_15 (B). The B-V
colors were unusual from 30 to 90 days after maximum light in that they evolved
to bluer values at a much slower rate than normal Type Ia supernovae. The
spectra and bolometric light curve indicate that this event was similar to the
spectroscopically peculiar slow decliner SN 1999aa.Comment: 42 pages, 14 figures, accepted for publication in the Astronomical
Journal (January 28, 2006
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Biases in the perceived timing of perisaccadic perceptual and motor events
Subjects typically experience the temporal interval immediately following a saccade as longer than a comparable control interval. One explanation of this effect is that the brain antedates the perceptual onset of a saccade target to around the time of saccade initiation. This could explain the apparent continuity of visual perception across eye movements. Thisantedating account was tested in three experiments in which subjects made saccades of differing extents and then judged either the duration or the temporal order of key events. Postsaccadic stimuli underwent subjective temporal lengthening and had early perceived onsets. A temporally advanced awareness of saccade completion was also found, independently of antedating effects. These results provide convergent evidence supporting antedating and differentiating it from other temporal biases
Human Resources and the Resource Based View of the Firm
The resource-based view (RBV) of the firm has influenced the field of strategic human resource management (SHRM) in a number of ways. This paper explores the impact of the RBV on the theoretical and empirical development of SHRM. It explores how the fields of strategy and SHRM are beginning to converge around a number of issues, and proposes a number of implications of this convergence
Resonant nonlinear magneto-optical effects in atoms
In this article, we review the history, current status, physical mechanisms,
experimental methods, and applications of nonlinear magneto-optical effects in
atomic vapors. We begin by describing the pioneering work of Macaluso and
Corbino over a century ago on linear magneto-optical effects (in which the
properties of the medium do not depend on the light power) in the vicinity of
atomic resonances, and contrast these effects with various nonlinear
magneto-optical phenomena that have been studied both theoretically and
experimentally since the late 1960s. In recent years, the field of nonlinear
magneto-optics has experienced a revival of interest that has led to a number
of developments, including the observation of ultra-narrow (1-Hz)
magneto-optical resonances, applications in sensitive magnetometry, nonlinear
magneto-optical tomography, and the possibility of a search for parity- and
time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002,
Figure added, typos corrected, text edited for clarit
A Bayesian approach to quantifying the effects of mass poultry vaccination upon the spatial and temporal dynamics of H5N1 in Northern Vietnam.
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