A stochastic differential equation SIS epidemic model

In this paper we extend the classical susceptible-infected-susceptible epidemic model from a deterministic framework to a stochastic one and formulate it as a stochastic differential equation (SDE) for the number of infectious individuals $I(t)$. We then prove that this SDE has a unique global positive solution $I(t)$ and establish conditions for extinction and persistence of $I(t)$. We discuss perturbation by stochastic noise. In the case of persistence we show the existence of a stationary distribution and derive expressions for its mean and variance. The results are illustrated by computer simulations, including two examples based on real-life diseases

Modeling and migration of 2-D georadar data: A stationary phase approach

Copyright © 2006 IEEE This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.This paper presents the basic kinematic and dynamic imaging and migration equations for zero-offset two-dimensional georadar profiling. The kinematic equations are derived from simple considerations of spatial impulse responses and a generating function. The dynamic equations follow from a multidimensional stationary phase approximation to the infinite spectral integrals. They show how the radar signal (amplitude and phase) depends on the shape and curvature of the reflector. The imaging equations are evaluated for the special cases of a point scatterer, a continuous reflector, and a terminating reflector. A general formula is developed by which to migrate an arbitrary shaped event of variable amplitude on the georadar section.Stewart A. Greenhalgh and Laurent Maresco

Authors' reply to comments by Takuya Sakamoto, Shouhei Kidera, and Toru Sato on "seabed algorithm and comments on 'modeling and migration of 2-D georadar data: A stationary phase approach"

Copyright © 2008 IEEES. A. Greenhalgh and L. Maresco

Electric Potential and Fréchet Derivatives for a Uniform Anisotropic Medium with a Tilted Axis of Symmetry

In this paper we develop analytic solutions for the electric potential, current density and Fréchet derivatives at any interior point within a 3-D transversely isotropic medium having a tilted axis of symmetry. The current electrode is assumed to be on the surface of the Earth and the plane of stratification given arbitrary strike and dip. Profiles can be computed for any azimuth. The equipotentials exhibit an elliptical pattern and are not orthogonal to the current density vectors, which are strongly angle dependent. Current density reaches its maximum value in a direction parallel to the longitudinal conductivity direction. Illustrative examples of the Fréchet derivatives are given for the 2.5-D problem, in which the profile is taken perpendicular to strike. All three derivatives of the Green's function with respect to longitudinal conductivity, transverse resistivity and dip angle of the symmetry axis (dG/dσl, dG/dσt, dG/dθ0) show a strongly asymmetric pattern compared to the isotropic case. The patterns are aligned in the direction of the tilt angle. Such sensitivity patterns are useful in real-time experimental design as well as in the fast inversion of resistivity data collected over an anisotropic eart

Influence of surface on impact shock experienced during a fencing lunge

The purpose of this study was to investigate the effect of sports surface on the magnitude of impact shock experienced during a lunge movement. Thirteen experienced, competitive fencers (age 32.4 +/- 4.6 years; Height 178.4 +/- 7.2 cm; Mass 74.4 +/- 9.1 kg) performed ten lunges on four different surfaces: concrete with an overlaid vinyl layer (COVL); wooden sprung court surface (WSCS); metallic carpet fencing piste overlaid on the WSCS and: aluminium fencing piste overlaid on the WSCS. An accelerometer measured accelerations along the longitudinal axis of the tibia at 1000Hz. The results identified a significantly (P < 0.05) larger impact shock magnitude was experienced during a lunge on the COVL (14.88 +/- 8.45g) compared to the WSCS (11.61 +/- 7.30g), WSCS with metallic carpet piste (11.14 +/- 6.38g) and WSCS with aluminium piste (11.95 +/- 7.21g). Furthermore, the two types of piste used had no significant effect the impact shock magnitude measured when overlaid on the WSCS compared to the WSCS on its own. The results of this investigation suggest that occurrences of injuries related to increased levels of impact shock, may be reduced through the utilization of a WSCS as opposed to a COVL surface, during fencing participation

A novel human glucocorticoid receptor SNP results in increased transactivation potential.

Glucocorticoids are one of the most widely used therapeutics in the treatment of a variety of inflammatory disorders. However, it is known that there are variable patient responses to glucocorticoid treatment; there are responders and non-responders, or those that need higher dosages. Polymorphisms in the glucocorticoid receptor (GR) have been implicated in this variability. In this study, ninety-seven volunteers were surveyed for polymorphisms in the human GR-alpha (hGRα), the accepted biologically active reference isoform. One isoform identified in our survey, named hGR DL-2, had four single nucleotide polymorphisms (SNPs), one synonymous and three non-synonymous, and a four base pair deletion resulting in a frame shift and early termination to produce a 743 amino acid putative protein. hGR DL-2 had a decrease in transactivation potential of more than 90%. Upon further analysis of the individual SNPs and deletion, one SNP, A829G, which results in a lysine to glutamic acid amino acid change at position 277, was found to increase the transactivation potential of hGR more than eight times the full-length reference. Furthermore, the hGRα-A829G isoform had a differential hyperactive response to various exogenous steroids. Increasing our knowledge as to how various SNPs affect hGR activity may help in understanding the unpredictable patient response to steroid treatment, and is a step towards personalizing patient care

On the dynamic tensile behaviour of thermoplastic composite carbon/polyamide 6.6 using split Hopkinson pressure bar

A dynamic tensile experiment was performed on a rectangular specimen of a non-crimp fabric (NCF) thermoplastic composite T700 carbon/polyamide 6.6 specimens using a split Hopkinson pressure (Kolsky) bar (SHPB). The experiment successfully provided useful information on the strain-rate sensitivity of the NCF carbon/thermoplastic material system. The average tensile strength at three varying strain rates: 700, 1400, and 2100/s was calculated and compared to the tensile strength measured from a standardized (quasi-static) procedure. The increase in tensile strength was found to be 3.5, 24.2, and 45.1% at 700, 1400, and 2100/s strain rate, respectively. The experimental findings were used as input parameters for the numerical model developed using a commercial finite element (FE) explicit solver LS-DYNA®. The dynamic FE model was validated against experimental gathering and used to predict the composite system’s behavior in various engineering applications under high strain-rate loading conditions. The SHPB tension test detailed in this study provided the enhanced understanding of the T700/polyamide 6.6 composite material’s behavior under different strain rates and allowed for the prediction of the material’s behavior under real-world, dynamic loading conditions, such as low-velocity and high-velocity impact

Referral management centres as a means of reducing outpatients attendances: how do they work and what influences successful implementation and perceived effectiveness?

Abstract Background The rising volume of referrals to secondary care is a continuing concern in the NHS in England, with considerable resource implications. Referral management centres (RMCs) are one of a range of initiatives brought in to curtail this rise, but there is currently limited evidence for their effectiveness, and little is known about their mechanisms of action. This study aimed to gain a better understanding of how RMCs operate and the factors contributing to the achievement of their goals. Drawing on the principles of realist evaluation, we sought to elicit programme theories (the ideas and assumptions about how a programme works) and to identify the key issues to be considered when establishing or evaluating such schemes. Methods Qualitative study with a purposive sample of health professionals and managers involved in the commissioning, set-up and running of four referral management centres in England and with GPs referring through these centres. Semi-structured interviews were conducted with 18 participants. Interviews were audio-recorded and transcribed. Data were analysed thematically. Results Interview data highlighted the diverse aims and functions of RMCs, reflecting a range of underlying programme theories. These included the overarching theory that RMCs work by ensuring the best use of limited resources and three sub-theories, relating to how this could be achieved, namely, improving the quality of referrals and patient care, reducing referrals, and increasing efficiency in the referral process. The aims of the schemes, however, varied between sites and between stakeholders, and evolved significantly over time. Three themes were identified relating to the context in which RMCs were implemented and managed: the impact of practical and administrative difficulties; the importance and challenge of stakeholder buy-in; and the dependence of perceived effectiveness on the aims and priorities of the scheme. Many RMCs were described as successful by those involved, despite limited evidence of reduced referrals or cost-savings. Conclusions The findings of this study have a number of implications for the development of similar schemes, with respect to the need to ensure clarity of aims and to identify indicators of success from the outset, to anticipate scheme evolution and plan for potential changes with respect to IT systems and referral processes. Also identified, is the need for further research that evaluates the effectiveness and cost effectiveness of particular models of RMC