Apparent suppression of turbulent magnetic dynamo action by a dc magnetic field

Numerical studies of the effect of a dc magnetic field on dynamo action (development of magnetic fields with large spatial scales), due to helically-driven magnetohydrodynamic turbulence, are reported. The apparent effect of the dc magnetic field is to suppress the dynamo action, above a relatively low threshold. However, the possibility that the suppression results from an improper combination of rectangular triply spatially-periodic boundary conditions and a uniform dc magnetic field is addressed: heretofore a common and convenient computational convention in turbulence investigations. Physical reasons for the observed suppression are suggested. Other geometries and boundary conditions are offered for which the dynamo action is expected not to be suppressed by the presence of a dc magnetic field component.Comment: To appear in Physics of Plasma

Intermittency in Hall-magnetohydrodynamics with a strong guide field

We present a detailed study of intermittency in the velocity and magnetic field fluctuations of compressible Hall-magnetohydrodynamic turbulence with an external guide field. To solve the equations numerically, a reduced model valid when a strong guide field is present is used. Different values for the ion skin depth are considered in the simulations. The resulting data is analyzed computing field increments in several directions perpendicular to the guide field, and building structure functions and probability density functions. In the magnetohydrodynamic limit we recover the usual results with the magnetic field being more intermittent than the velocity field. In the presence of the Hall effect, field fluctuations at scales smaller than the ion skin depth show a substantial decrease in the level of intermittency, with close to monofractal scaling.Comment: 10 pages, 8 figure

Examining Community-Based Research as an Application for Public Health Training

The University of Michigan School of Public Health provided community-based research (CBR) opportunities to masters-level students through week-long field experiences in two communities in Mississippi through interdisciplinary collaboration with Delta State University. This article examines the learning outcomes of those field experiences in the context of CBR and the value that those experiences added to their public health proficiency. Quantitative and qualitative data from post-deployment evaluations were examined to determine strengths and weaknesses of this approach to the public health learning process. Overall, students found this approach to provide a rich context for research, help put a face to the numbers, and broaden their perspective of how research is of value to communities and community organizations

Use of a simple pain model to evaluate analgesic activity of ibuprofen versus paracetamol

Objective: To evaluate the analgesic activity of ibuprofen against paracetamol using a simple pain model.Design: A double-blind study.Setting: Twenty general practitioners in Harare, Zimbabwe.Patients: Adults with acute sore throat of a maximum of two days’ duration.Interventions: One hundred and thirteen patients with acute pain associated with tonsillopharyngitis randomly received either 400mg ibuprofen or 1000mg paracetamol. The study design included repeated administration up to 48 hours to assess tolerability.Main outcome measures: At hourly intervals for six hours after the first dose of treatment, the patients evaluated pain intensity on swallowing, difficulty in swallowing and global pain relief according to visual analogue scales.Results: Ibuprofen 400mg was significantly more effective than paracetamol 1000mg in all three ratings, at all time-points for pain intensity and difficulty in swallowing, and from two hours onwards for pain relief. There were no serious adverse effects and no statisticallysignificant difference in the incidence of adverse effects in the two treatment groups.Conclusions: Sore throat pain provided a sensitive model to assess the analgesic efficacy of class I analgesics and discriminated between the analgesic efficacy of ibuprofen and paracetamol

Continuity of Optimal Control Costs and its application to Weak KAM Theory

We prove continuity of certain cost functions arising from optimal control of affine control systems. We give sharp sufficient conditions for this continuity. As an application, we prove a version of weak KAM theorem and consider the Aubry-Mather problems corresponding to these systems.Comment: 23 pages, 1 figures, added explanations in the proofs of the main theorem and the exampl

AN ORTHOPEDIC EXAM FOR ATHLETIC INJURY RISK FACTORS

Athletic injuries, in particular stress fractures, are common among U.S. Navy SEAL trainees during their extensive program of upper and lower body physical training. Between 1980 and 1986 there were over 200 stress fractures, accounting for almost halfof all medical dropouts from the program. Most of the injuries are overuse related, and potentially preventable. In an attempt to identify physical risk factors that could be used in a pre-selection process, a simple reproducible physical exam emphasizing biomechanical factors was devised and used to evaluate men about to begin training

A Bayesian approach to the estimation of maps between riemannian manifolds

Let \Theta be a smooth compact oriented manifold without boundary, embedded in a euclidean space and let \gamma be a smooth map \Theta into a riemannian manifold \Lambda. An unknown state \theta \in \Theta is observed via X=\theta+\epsilon \xi where \epsilon>0 is a small parameter and \xi is a white Gaussian noise. For a given smooth prior on \Theta and smooth estimator g of the map \gamma we derive a second-order asymptotic expansion for the related Bayesian risk. The calculation involves the geometry of the underlying spaces \Theta and \Lambda, in particular, the integration-by-parts formula. Using this result, a second-order minimax estimator of \gamma is found based on the modern theory of harmonic maps and hypo-elliptic differential operators.Comment: 20 pages, no figures published version includes correction to eq.s 31, 41, 4

Towards a common thread in Complexity: an accuracy-based approach

The complexity of a system, in general, makes it difficult to determine some or almost all matrix elements of its operators. The lack of accuracy acts as a source of randomness for the matrix elements which are also subjected to an external potential due to existing system conditions. The fluctuation of accuracy due to varying system-conditions leads to a diffusion of the matrix elements. We show that, for the single well potentials, the diffusion can be described by a common mathematical formulation where system information enters through a single parameter. This further leads to a characterization of physical properties by an infinite range of single parametric universality classes