784 research outputs found

    On the continuous spectral component of the Floquet operator for a periodically kicked quantum system

    Full text link
    By a straightforward generalisation, we extend the work of Combescure from rank-1 to rank-N perturbations. The requirement for the Floquet operator to be pure point is established and compared to that in Combescure. The result matches that in McCaw. The method here is an alternative to that work. We show that if the condition for the Floquet operator to be pure point is relaxed, then in the case of the delta-kicked Harmonic oscillator, a singularly continuous component of the Floquet operator spectrum exists. We also provide an in depth discussion of the conjecture presented in Combescure of the case where the unperturbed Hamiltonian is more general. We link the physics conjecture directly to a number-theoretic conjecture of Vinogradov and show that a solution of Vinogradov's conjecture solves the physics conjecture. The result is extended to the rank-N case. The relationship between our work and the work of Bourget on the physics conjecture is discussed.Comment: 25 pages, published in Journal of Mathematical Physic

    Characterising pandemic severity and transmissibility from data collected during first few hundred studies

    Get PDF
    Early estimation of the probable impact of a pandemic influenza outbreak can assist public health authorities to ensure that response measures are proportionate to the scale of the threat. Recently, frameworks based on transmissibility and severity have been proposed for initial characterization of pandemic impact. Data requirements to inform this assessment may be provided by "First Few Hundred" (FF100) studies, which involve surveillance-possibly in person, or via telephone-of household members of confirmed cases. This process of enhanced case finding enables detection of cases across the full spectrum of clinical severity, including the date of symptom onset. Such surveillance is continued until data for a few hundred cases, or satisfactory characterization of the pandemic strain, has been achieved. We present a method for analysing these data, at the household level, to provide a posterior distribution for the parameters of a model that can be interpreted in terms of severity and transmissibility of a pandemic strain. We account for imperfect case detection, where individuals are only observed with some probability that can increase after a first case is detected. Furthermore, we test this methodology using simulated data generated by an independent model, developed for a different purpose and incorporating more complex disease and social dynamics. Our method recovers transmissibility and severity parameters to a high degree of accuracy and provides a computationally efficient approach to estimating the impact of an outbreak in its early stages.Andrew J. Black, Nicholas Gear, James M. McCaw, Jodie McVernon, Joshua V. Ros

    Modelling the economic efficiency of using different strategies to control Porcine Reproductive & Respiratory Syndrome at herd level

    Get PDF
    PRRS is among the diseases with the highest economic impact in pig production worldwide. Different strategies have been developed and applied to combat PRRS at farm level. The broad variety of available intervention strategies makes it difficult to decide on the most cost-efficient strategy for a given farm situation, as it depends on many farm-individual factors like disease severity, prices or farm structure. Aim of this study was to create a simulation tool to estimate the cost-efficiency of different control strategies at individual farm level. Baseline is a model that estimates the costs of PRRS, based on changes in health and productivity, in a specific farm setting (e.g. farm type, herd size, type of batch farrowing). The model evaluates different intervention scenarios: depopulation/repopulation (D/R), close & roll-over (C&R), mass vaccination of sows (MS), mass vaccination of sows and vaccination of piglets (MS + piglets), improvements in internal biosecurity (BSM), and combinations of vaccinations with BSM. Data on improvement in health and productivity parameters for each intervention were obtained through literature review and from expert opinions. The economic efficiency of the different strategies was assessed over 5 years through investment appraisals: the resulting expected value (EV) indicated the most cost-effective strategy. Calculations were performed for 5 example scenarios with varying farm type (farrow-to-finish – breeding herd), disease severity (slightly – moderately – severely affected) and PRRSV detection (yes – no). The assumed herd size was 1000 sows with farm and price structure as commonly found in Germany. In a moderately affected (moderate deviations in health and productivity parameters from what could be expected in an average negative herd), unstable farrow-to-finish herd, the most cost-efficient strategies according to their median EV were C&R (€1′126′807) and MS + piglets (€ 1′114′649). In a slightly affected farrow-to-finish herd, no virus detected, the highest median EV was for MS + piglets (€ 721′745) and MS (€ 664′111). Results indicate that the expected benefits of interventions and the most efficient strategy depend on the individual farm situation, e.g. disease severity. The model provides new insights regarding the cost-efficiency of various PRRSV intervention strategies at farm level. It is a valuable tool for farmers and veterinarians to estimate expected economic consequences of an intervention for a specific farm setting and thus enables a better informed decision

    Cost of care of chronic non-communicable diseases in Jamaican patients: the role of obesity

    Get PDF
    OBJECTIVE: To estimate the economic cost of Chronic Non-Communicable Diseases (CNCDs) and the portion attributable to obesity among patients in Jamaica.METHODS: The cost-of-illness approach was used to estimate the cost of care in a hospital setting in Jamaica for type 2 diabetes mellitus, hypertension, coronary heart disease, stroke, gallbladder disease, breast cancer, colon cancer, osteoarthritis, and high cholesterol. Cost and service utilization data were collected from the hospital records of all patients with these diseases who visited the University Hospital of the West Indies (UHWI) during 2006. Patients were included in the study if they were between15 and 74 years of age and if female, were not pregnant during that year. Costs were categorized as direct or indirect. Direct costs included costs for prescription drugs, consultation visits (emergency and clinic visits), hospitalizations, allied health services, diagnostic and treatment procedures. Indirect costs included costs attributed to premature mortality, disability (permanent and temporary), and absenteeism. Indirect costs were discounted at 3% rate.RESULTS: The sample consisted of 554 patients (40%) males (60%) females. The economic burden of the nine diseases was estimated at US5,672,618(males37 5,672,618 (males 37%; females 63%) and the portion attributable to obesity amounted to US 1,157,173 (males 23%; females 77%). Total direct cost was estimated at US3,740,377withfemalepatientsaccountingfor69.9 3,740,377 with female patients accounting for 69.9% of this cost. Total indirect cost was estimated at US 1,932,241 with female patients accounting for 50.6% of this cost. The greater cost among women was not found to be statistically significant. Overall, on a per capita basis, males and females accrued similar costs-of-illness (US9,451.75vs.US 9,451.75 vs. US 10,758.18).CONCLUSIONS: In a country with per capita GDP of less than US5,300,apercapitaannualcostofillnessofUS 5,300, a per capita annual cost of illness of US 10,239 for CNCDs is excessive and has detrimental implications for the health and development of Jamaica

    Model-Informed Risk Assessment and Decision Making for an Emerging Infectious Disease in the Asia-Pacific Region

    Get PDF
    Background: Effective response to emerging infectious disease (EID) threats relies on health care systems that can detect and contain localised outbreaks before they reach a national or international scale. The Asia-Pacific region contains low and middle income countries in which the risk of EID outbreaks is elevated and whose health care systems may require international support to effectively detect and respond to such events. The absence of comprehensive data on populations, health care systems and disease characteristics in this region makes risk assessment and decisions about the provision of such support challenging.\ud \ud Methodology/principal findings: We describe a mathematical modelling framework that can inform this process by integrating available data sources, systematically explore the effects of uncertainty, and provide estimates of outbreak risk under a range of intervention scenarios. We illustrate the use of this framework in the context of a potential importation of Ebola Virus Disease into the Asia-Pacific region. Results suggest that, across a wide range of plausible scenarios, preemptive interventions supporting the timely detection of early cases provide substantially greater reductions in the probability of large outbreaks than interventions that support health care system capacity after an outbreak has commenced.\ud \ud Conclusions/significance: Our study demonstrates how, in the presence of substantial uncertainty about health care system infrastructure and other relevant aspects of disease control, mathematical models can be used to assess the constraints that limited resources place upon the ability of local health care systems to detect and respond to EID outbreaks in a timely and effective fashion. Our framework can help evaluate the relative impact of these constraints to identify resourcing priorities for health care system support, in order to inform principled and quantifiable decision making

    Correspondence to General William Robertson Boggs, 1860s: October 28, 1867 - February 18, 1869

    Get PDF
    Box 1, Folder 1: W.R. Boggs Family Papers Correspondence to General William Robertson Boggs, 1860s: October 28, 1867 - February 18, 1869https://digitalcommons.wofford.edu/littlejohnboggs/1000/thumbnail.jp
    corecore