Fitting Effective Diffusion Models to Data Associated with a "Glassy Potential": Estimation, Classical Inference Procedures and Some Heuristics

A variety of researchers have successfully obtained the parameters of low dimensional diffusion models using the data that comes out of atomistic simulations. This naturally raises a variety of questions about efficient estimation, goodness-of-fit tests, and confidence interval estimation. The first part of this article uses maximum likelihood estimation to obtain the parameters of a diffusion model from a scalar time series. I address numerical issues associated with attempting to realize asymptotic statistics results with moderate sample sizes in the presence of exact and approximated transition densities. Approximate transition densities are used because the analytic solution of a transition density associated with a parametric diffusion model is often unknown.I am primarily interested in how well the deterministic transition density expansions of Ait-Sahalia capture the curvature of the transition density in (idealized) situations that occur when one carries out simulations in the presence of a "glassy" interaction potential. Accurate approximation of the curvature of the transition density is desirable because it can be used to quantify the goodness-of-fit of the model and to calculate asymptotic confidence intervals of the estimated parameters. The second part of this paper contributes a heuristic estimation technique for approximating a nonlinear diffusion model. A "global" nonlinear model is obtained by taking a batch of time series and applying simple local models to portions of the data. I demonstrate the technique on a diffusion model with a known transition density and on data generated by the Stochastic Simulation Algorithm.Comment: 30 pages 10 figures Submitted to SIAM MMS (typos removed and slightly shortened

Spreading of virulence regarding spatial distribution resistant cultivars inferred from population modeling coupled with genetics

One of the control strategies of fungal crop diseases is planting highly resistant varieties. However selection pressure on the pathogen, imposed by major resistance genes, leads to the development of new virulent races. In most cases breakdown of resistance has been reported for crop-pathogen systems with a genetically uniform crop distributed over large areas [2]. Des choix stratégiques en matière de construction et de déploiement de génotypes résistants combinant des gènes de résistance se pose aujourd’hui de manière aigüe afin de tendre vers une agriculture à résistance durable. To reach this objective, we start a study that combined population modeling with genetics to (1) identify keys traits of life of the pathogen involved in resistance breakdown (2) simulate virulence spreading regarding spatial host distribution

Strongly correlating liquids and their isomorphs

This paper summarizes the properties of strongly correlating liquids, i.e., liquids with strong correlations between virial and potential energy equilibrium fluctuations at constant volume. We proceed to focus on the experimental predictions for strongly correlating glass-forming liquids. These predictions include i) density scaling, ii) isochronal superposition, iii) that there is a single function from which all frequency-dependent viscoelastic response functions may be calculated, iv) that strongly correlating liquids are approximately single-parameter liquids with close to unity Prigogine-Defay ratio, and v) that the fictive temperature initially decreases for an isobaric temperature up jump. The "isomorph filter", which allows one to test for universality of theories for the non-Arrhenius temperature dependence of the relaxation time, is also briefly discussed

Discovery of high-performance low-cost n-type Mg3Sb2-based thermoelectric materials with multi-valley conduction bands

Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg(3)Sb(1.5)Bi(0.5), that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300−725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg(3)Sb(1.5)Bi(0.5) a promising candidate for the low- and intermediate-temperature thermoelectric applications

Variation in general practitioners' information-seeking behaviour:a cross-sectional study on the influence of gender, age and practice form

Objective: To assess general practitioners’ (GPs’) information-seeking behaviour and perceived importance of sources of scientific medical information and to investigate associations with GP characteristics. Design: A national cross-sectional survey was distributed electronically in December 2013. Setting: Danish general practice. Subjects: A population of 3440 GPs (corresponding to approximately 96% of all Danish GPs). Main outcome measures: GPs’ use and perceived importance of information sources. Multilevel mixed-effects logit models were used to investigate associations with GP characteristics after adjusting for relevant covariates. Results: A total of 1580 GPs (46.4%) responded to the questionnaire. GPs’ information-seeking behaviour is associated with gender, age and practice form. Single-handed GPs use their colleagues as an information source significantly less than GPs working in partnership practices and they do not use other sources more frequently. Compared with their younger colleagues, GPs aged above 44 years are less likely to seek information from colleagues, guidelines and websites, but more likely to seek information from medical journals. Male and female GPs seek information equally frequently. However, whereas male GPs are more likely than female GPs to find that pharmaceutical sales representative and non-refundable CME meetings are important, they are less likely to find that colleagues, refundable CME meetings, guidelines and websites are important. Conclusion: Results from this study indicate that GP characteristics should be taken into consideration when disseminating scientific medical information, to ensure that patients receive medically updated, high-quality care.KEY POINTS Research indicates that information-seeking behaviour is associated with GP characteristics. Further insights could provide opportunities for targeting information dissemination strategies. Single-handed GPs seek information from colleagues less frequently than GPs in partnerships and do not use other sources more frequently. GPs aged above 44 years do not seek information as frequently as their younger colleagues and prefer other information sources. Male and female GPs seek information equally frequently, but do not consider information sources equally important in keeping medically updated

Grating-assisted superresolution of slow waves in Fourier space

We present a far-field optical technique allowing measurements of the dispersion relation of electromagnetic fields propagating under the light cone in photonic nanostructures. It relies on the use of a one-dimensional grating to probe the evanescent tail of the guided field in combination with a high-numerical-aperture Fourier- space imaging setup. A high-resolution spectroscopy of the far-field emission diagram allows us to accurately and efficiently determine the dispersion curve and the group-index dispersion of planar photonic crystal waveguides operating in the slow-light regime

Radioactive heat production of six geologically important nuclides

Heat production rates for the geologically important nuclides ${}^{26}$Al, ${}^{40}$K, ${}^{60}$Fe, ${}^{232}$Th, ${}^{235}$U, and ${}^{238}$U are calculated on the basis of recent data on atomic and nuclear properties. The revised data differ by several per cent from some older values, but indicate that more recent analyses converge toward values with an accuracy sufficient for all common geoscience applications, although some possibilities for improvement still remain, especially in the case of ${}^{40}$K and with regard to the determination of half-lives. A Python script is provided for calculating heat production (https://github.com/trg818/radheat).Comment: 14 pages, 1 figur

Prolonged low flow reduces reactive hyperemia and augments low flow mediated constriction in the brachial artery independent of the menstrual cycle

© 2013 Rakobowchuk et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Non-invasive forearm ischemia-reperfusion injury and low flow induced vascular dysfunction models provide methods to evaluate vascular function. The role of oestrogen, an endogenous anti-oxidant on recovery from ischemia-reperfusion injury has not been evaluated nor has the impact of prolonged low flow on vascular function been established. Eight healthy women (33610 yr) attended the lab during the follicular, ovulatory and mid-luteal phases of their menstrual cycles. After 30 minutes of rest, brachial artery vascular function was assessed by ultrasound measurements of diameter changes during 5 minutes of forearm ischemia and 3 minutes after. Subsequently, a 20-minute forearm ischemia period was completed. Further, vascular function assessments were completed 15, 30 and 45 minutes into recovery. Flow-mediated dilation, lowflow-mediated constriction, and reactive hyperaemia proximal to the area of ischemia were determined. Flow-mediated dilation was reduced at 15 minutes of recovery but recovered at 30 and 45 minutes (PRE: 7.161.0%, POST15:4.560.6%, POST30:5. 560.7% POST45:5.960.4%, p,0.01). Conversely, low-flow mediated constriction increased (PRE: 21.360.4%, POST15: 23.360.6%, POST30: 22.560.5% POST45: 21.560.12%, p,0.01). Reactive hyperaemia was reduced throughout recovery (p,0.05). Data were unaffected by menstrual phase. Prolonged low flow altered vascular function and may relate as much to increased vasoconstriction as with decreased vasodilation. Reductions in anterograde shear and greater retrograde shear likely modulate the brachial artery response, but the reduced total shear also plays an important role. The data suggest substantial alterations in vascular function proximal to areas of ischemia with potential clinical implications following reperfusion.British Heart Foundation (PG/08/060/25340),a Physiological Society summer studentship to SG, and a Wellcome Trust Vacation Studentship to EP