Rigorous Study (rigorous + study)

Distribution by Scientific Domains


Selected Abstracts


What really happens with the electron gas in the famous Franck-Hertz experiment?

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2003
F. Sigeneger
Abstract The interpretation of the anode current characteristics obtained in the famous Franck-Hertz experiment of 1914 led to the verification of Bohr's predictions of quantised atomic states. This fundamental experiment has been often repeated, and nowadays is generally part of the curriculum in modern physics education. However, the interpretation of the experiment is typically based upon significant simplifying assumptions, some quite unrealistic. This is the case especially in relation to the kinetics of the electron gas, which is in reality quite complex, due mainly to non-uniformities in the electric field, caused by a combination of accelerating and retarding components. This non-uniformity leads to a potential energy valley in which the electrons are trapped. The present state of understanding of such effects, and their influence upon the anode characteristics, is quite unsatisfactory. In this article a rigorous study of a cylindrical Franck-Hertz experiment is presented, using mercury vapour, the aim being to reveal and explain what really happens with the electrons under realistic experimental conditions. In particular, the anode current characteristics are investigated over a range of mercury vapour pressures appropriate to the experiment to clearly elaborate the effects of elastic collisions (ignored in typical discussions) on the power budget, and the trapping of electrons in the potential energy valley. [source]


Headache and Psychological Functioning in Children and Adolescents

HEADACHE, Issue 9 2006
Scott W. Powers PhD
Headache can affect all aspects of a child's functioning, leading to negative affective states (eg, anxiety, depression, anger) and increased psychosocial problems (for instance, school absences, problematic social interactions). For children and adolescents who experience frequent headache problems, comorbid psychological issues are a well-recognized, but poorly understood, clinical phenomenon. The confusion surrounding the relationship between pediatric headache and psychopathology exists for several reasons. First, in some cases, headache has been inappropriately attributed to psychological or personality features based on anecdotal observations or interpretations that go beyond the available data. Additionally, measures of psychopathology have not always adhered to the American Psychiatric Association's diagnostic criteria, thus reducing the reliability of diagnostic judgments. Furthermore, the diagnosis of headache has not always followed standard criteria, and has been complicated by the emergence of new terms and evolving measures. Finally, methodological shortcomings, such as incomplete descriptions of the procedures and criteria used for the study, inadequate descriptions of headache severity, lack of a control group for comparison with individuals without headaches, reliance primarily on cross-sectional research designs that are often discussed with inferences to causal hypotheses, and the use of unstandardized assessment measures, have significantly limited the validity of research findings. The goal of the current review is to examine the extant literature to provide the most up-to-date picture on what the research has made available about the magnitude, specificity, and causes of psychopathology in children and adolescents with headache, in an effort to further elucidate their relationship and prompt a more methodologically rigorous study of these issues. [source]


Finite element and sensitivity analysis of thermally induced flow instabilities

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2010
Jean-Serge Gigučre
Abstract This paper presents a finite element algorithm for the simulation of thermo-hydrodynamic instabilities causing manufacturing defects in injection molding of plastic and metal powder. Mold-filling parameters determine the flow pattern during filling, which in turn influences the quality of the final part. Insufficiently, well-controlled operating conditions may generate inhomogeneities, empty spaces or unusable parts. An understanding of the flow behavior will enable manufacturers to reduce or even eliminate defects and improve their competitiveness. This work presents a rigorous study using numerical simulation and sensitivity analysis. The problem is modeled by the Navier,Stokes equations, the energy equation and a generalized Newtonian viscosity model. The solution algorithm is applied to a simple flow in a symmetrical gate geometry. This problem exhibits both symmetrical and non-symmetrical solutions depending on the values taken by flow parameters. Under particular combinations of operating conditions, the flow was stable and symmetric, while some other combinations leading to large thermally induced viscosity gradients produce unstable and asymmetric flow. Based on the numerical results, a stability chart of the flow was established, identifying the boundaries between regions of stable and unstable flow in terms of the Graetz number (ratio of thermal conduction time to the convection time scale) and B, a dimensionless ratio indicating the sensitivity of viscosity to temperature changes. Sensitivities with respect to flow parameters are then computed using the continuous sensitivity equations method. We demonstrate that sensitivities are able to detect the transition between the stable and unstable flow regimes and correctly indicate how parameters should change in order to increase the stability of the flow. Copyright © 2009 John Wiley & Sons, Ltd. [source]


On the convergence of the finite integration technique for the anisotropic boundary value problem of magnetic tomography

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 9 2003
Roland Potthast
The reconstruction of a current distribution from measurements of the magnetic field is an important problem of current research in inverse problems. Here, we study an appropriate solution to the forward problem, i.e. the calculation of a current distribution given some resistance or conductivity distribution, respectively, and prescribed boundary currents. We briefly describe the well-known solution of the continuous problem, then employ the finite integration technique as developed by Weiland et al. since 1977 for the solution of the problem. Since this method can be physically realized it offers the possibility to develop special tests in the area of inverse problems. Our main point is to provide a new and rigorous study of convergence for the boundary value problem under consideration. In particular, we will show how the arguments which are used in the proof of the continuous case can be carried over to study the finite-dimensional numerical scheme. Finally, we will describe a program package which has been developed for the numerical implementation of the scheme using Matlab. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Surgical e-learning: validation of multimedia web-based lectures

MEDICAL EDUCATION, Issue 2 2007
Paul F Ridgway
Background, Distance learning has been advocated increasingly as a modern efficient method of teaching surgery. Efficiency of knowledge transfer and validity of web-based courses have not been subjected to rigorous study to date. Methods, An entirely web-based surgical 5-week lecture course was designed. Fifty per cent of the lectures were prepared as HTML slides with voice-over while the other group was presented in the text-only form. Only written material presented was examined. The lectures were presented via an educational web module. The lecture series was balanced specifically to reduce the pre-existent knowledge bias. Web usage was estimated utilising surrogates, including the number of hits as well as log-on timing. Face validity was assessed by a standardised questionnaire. Results, Eighty-eight students took part in the lecture series and subsequent examination and questionnaire. Median multiple choice questionnaire (MCQ) marks were significantly higher in the aural lecture-derived stems versus the non-aural (P = 0.012, Mann,Whitney U -test). There was widespread approval of web-based learning as an adjunct to conventional teaching. Usage rates were augmented significantly in the final week when compared to the previous 4 weeks (mean total hits weeks 1,4 ± SEM: 100.9 ± 9.7 and mean total hits week 5: 152.1 ± 13.1; P < 0.001, Kruskal,Wallis). However, total hits did not correlate with overall examination results (r2 = 0.16). The aural lectures demonstrated higher face validity than the non-aural for content and presentation (P < 0.05, Kruskal,Wallis). Conclusions, The addition of aural files to the novel web-based lecture series is face valid and results in significantly increased examination performance. [source]


A new compact band-pass filter based on an asymmetric short-circuited spurline resonator

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2010
P. Rodriguez-Cepeda
Abstract In this letter, a new compact two-pole band-pass filter (BPF) based on an asymmetric short-circuited spurline resonator is presented. The filter is modeled by means of a new multimodal circuit model for a microstrip to three-line-microstrip cross, which allows a rigorous study of a very generic new family of filters. A BPF centered at 1.9 GHz has been designed, measured, and simulated using this multimodal model. A good agreement between measurements and simulations has been obtained. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1328,1331, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25161 [source]


Highlights in Emergency Medicine Medical Education Research: 2008

ACADEMIC EMERGENCY MEDICINE, Issue 12 2009
Susan E. Farrell MD
Abstract Objectives:, The purpose of this article is to highlight medical education research studies published in 2008 that were methodologically superior and whose outcomes were pertinent to teaching and education in emergency medicine. Methods:, Through a PubMed search of the English language literature in 2008, 30 medical education research studies were independently identified as hypothesis-testing investigations and measurements of educational interventions. Six reviewers independently rated and scored all articles based on eight anchors, four of which related to methodologic criteria. Articles were ranked according to their total rating score. A ranking agreement among the reviewers of 83% was established a priori as a minimum for highlighting articles in this review. Results:, Five medical education research studies met the a priori criteria for inclusion and are reviewed and summarized here. Four of these employed experimental or quasi-experimental methodology. Although technology was not a component of the structured literature search employed to identify the candidate articles for this review, 14 of the articles identified, including four of the five highlighted articles, employed or studied technology as a focus of the educational research. Overall, 36% of the reviewed studies were supported by funding; three of the highlighted articles were funded studies. Conclusions:, This review highlights quality medical education research studies published in 2008, with outcomes of relevance to teaching and education in emergency medicine. It focuses on research methodology, notes current trends in the use of technology for learning in emergency medicine, and suggests future avenues for continued rigorous study in education. [source]


Control of Cell Volume in Skeletal Muscle

BIOLOGICAL REVIEWS, Issue 1 2009
Juliet A. Usher-Smith
Abstract Regulation of cell volume is a fundamental property of all animal cells and is of particular importance in skeletal muscle where exercise is associated with a wide range of cellular changes that would be expected to influence cell volume. These complex electrical, metabolic and osmotic changes, however, make rigorous study of the consequences of individual factors on muscle volume difficult despite their likely importance during exercise. Recent charge-difference modelling of cell volume distinguishes three major aspects to processes underlying cell volume control: (i) determination by intracellular impermeant solute; (ii) maintenance by metabolically dependent processes directly balancing passive solute and water fluxes that would otherwise cause cell swelling under the influence of intracellular membrane-impermeant solutes; and (iii) volume regulation often involving reversible short-term transmembrane solute transport processes correcting cell volumes towards their normal baselines in response to imposed discrete perturbations. This review covers, in turn, the main predictions from such quantitative analysis and the experimental consequences of comparable alterations in extracellular pH, lactate concentration, membrane potential and extracellular tonicity. The effects of such alterations in the extracellular environment in resting amphibian muscles are then used to reproduce the intracellular changes that occur in each case in exercising muscle. The relative contributions of these various factors to the control of cell volume in resting and exercising skeletal muscle are thus described. [source]