347,227 research outputs found

    Wildlife disease elimination and 1 density dependence

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    Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent transmission, is ineffective for controlling diseases that are subject to frequency-dependent transmission. We investigate control for horizontally transmitted diseases with frequency-dependent transmission where the control is via nonselective (for infected animals) culling or harvesting and the population can compensate through density-dependent recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are frequency-dependent. E 24 radication can be achieved under frequency-dependent transmission when density-dependent population regulation induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination and there is high enough transmission coefficient, application of both controls may be less efficient than when vaccination alone is used. We illustrate the effects of these control approaches on disease prevalence using assumed parameters for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment

    Femtosecond dynamics of hydrogen elimination: benzene formation from cyclohexadiene

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    Using femtosecond-resolved mass spectrometry in a molecular beam, we report real-time study of the hydrogen elimination reaction of 1,4-cyclohexadiene. The experimental observation of the ultrafast stepwise H-elimination elucidates the reaction dynamics and mechanism. With density-functional theory (ground-state) calculations, the nature of the reaction (multiple) pathways is examined. With the help of recent conical-intersection calculations, the excited-state and ground-state pathways are correlated. From these experimental and theoretical results we provide a unifying picture of the thermochemistry, photochemistry and the stereochemistry observed in the condensed phase

    Designing programs for eliminating canine rabies from islands: Bali, Indonesia as a case study

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    <p>Background: Canine rabies is one of the most important and feared zoonotic diseases in the world. In some regions rabies elimination is being successfully coordinated, whereas in others rabies is endemic and continues to spread to uninfected areas. As epidemics emerge, both accepted and contentious control methods are used, as questions remain over the most effective strategy to eliminate rabies. The Indonesian island of Bali was rabies-free until 2008 when an epidemic in domestic dogs began, resulting in the deaths of over 100 people. Here we analyze data from the epidemic and compare the effectiveness of control methods at eliminating rabies.</p> <p>Methodology/Principal Findings: Using data from Bali, we estimated the basic reproductive number, R0, of rabies in dogs, to be ~1·2, almost identical to that obtained in ten–fold less dense dog populations and suggesting rabies will not be effectively controlled by reducing dog density. We then developed a model to compare options for mass dog vaccination. Comprehensive high coverage was the single most important factor for achieving elimination, with omission of even small areas (<0.5% of the dog population) jeopardizing success. Parameterizing the model with data from the 2010 and 2011 vaccination campaigns, we show that a comprehensive high coverage campaign in 2012 would likely result in elimination, saving ~550 human lives and ~$15 million in prophylaxis costs over the next ten years.</p> <p>Conclusions/Significance: The elimination of rabies from Bali will not be achieved through achievable reductions in dog density. To ensure elimination, concerted high coverage, repeated, mass dog vaccination campaigns are necessary and the cooperation of all regions of the island is critical. Momentum is building towards development of a strategy for the global elimination of canine rabies, and this study offers valuable new insights about the dynamics and control of this disease, with immediate practical relevance.</p&gt

    Algebraic Density Functionals

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    A systematic strategy for the calculation of density functionals (DFs) consists in coding informations about the density and the energy into polynomials of the degrees of freedom of wave functions. DFs and Kohn-Sham potentials (KSPs) are then obtained by standard elimination procedures of such degrees of freedom between the polynomials. Numerical examples illustrate the formalism.Comment: 7 pages, 2 figures, changes to extend discussion of Kohn-Sham potentials, and also for interacting particles. Accepted for publication in Physics Letters

    Probabilistic Analysis of Edge Elimination for Euclidean TSP

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    One way to speed up the calculation of optimal TSP tours in practice is eliminating edges that are certainly not in the optimal tour as a preprocessing step. In order to do so several edge elimination approaches have been proposed in the past. In this work we investigate two of them in the scenario where the input consists of nn independently distributed random points in the 2-dimensional unit square with bounded density function from above and below by arbitrary positive constants. We show that after the edge elimination procedure of Hougardy and Schroeder the expected number of remaining edges is Θ(n)\Theta(n), while after that the the non-recursive part of Jonker and Volgenant the expected number of remaining edges is Θ(n2)\Theta(n^2)

    On the possibility of a maximum fundamental density and the elimination of gravitational singularities

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    With this note we want to point out that already in the early days of cosmology it was understood that negative pressure could eliminate gravitational singularities in a natural way e.g. E.B. Gliner, Sov. Phys. JETP 22(1966)378 and M.A. Markov, Pis'ma Zh. Eksp. Teor. Fiz. 36, No 6, 214-216 (20 Sept. 1982). Today, with the discovery of dark energy and the strong evidence in favor of an inflationary start of the Big Bang, the existence of negative pressure is widely accepted. In fundamental physics, phase transitions are generally thought to be reversible (Cf. Ellis, New Astronomy Reviews Volume 46, Issue 11, October 2002, P. 645). It seems likely then that if inflation has occurred, the process should be reversible. I.e. when the increasing density in a collapsing universe or star reaches a certain limit it should go through a phase transition to a medium with an equation of state of the type p=ωρp=\omega \rho, where 1<ω<1/3-1< \omega <-1/3. If this phase transition is fundamental, i.e. occurs for all energy densities, a collapse will always reach a minimum radius and bounce. If the phase transition is symmetric, the result will lead to oscillating universes. If however the phase transition is associated with an hysteresis effect, a collapsing star may, succeeding the bounce inflate into a new universe with a subsequent phase transition becomes dominated by ordinary relativistic matter. The aim of this note is study the time development of a model which mimics this process.Comment: 5 pages, 2 figures. Replaced since the Abstract is updated and further references are included. There are also some minor changes in the tex
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