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Selected AbstractsInfluence of the Wall Characteristics on the Development of MARFE in TokamaksCONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006O. Marchuk Abstract Multifaceted asymmetric radiation from the edge (MARFE) normally develops in fusion devices close to the density limit. MARFE is considered a result of thermal instabilities excited under critical conditions through different mechanisms: impurity radiation, recycling of neutral particles, anomalous transport of charged particles and energy. Recent experiments on tokamaks TEXTOR and JET show that plasma-wall interaction, leading to release of recycling neutrals and impurities, plays a very important role for the formation of MARFE. In the present contribution we develop further the MARFE models based on the instability of particle recycling on the tokamak wall by including a simple description for the release of recycling neutrals from the wall surface into the plasma. This development takes into account the time delay between the out flow of charged particles from the plasma and in flux of neutrals. The linear stability analysis shows that this does not change the critical plasma density for the MARFE formation but modifies significantly the growth rate of unstable perturbations developing when the density exceeds the threshold. These findings are confirmed in a non-linear consideration by solving the equations for the particle, momentum and energy transfer in the plasma coupled with the wall particle balance equations. This is done in a one-dimensional approximation by taking into account the variation of the main plasma parameters in the poloidal direction and making averaging in the radial direction over the plasma edge width of the penetration depth of neutrals. The intrinsic poloidal asymmetry of the system, defining the MARFE localization, is introduced by the Shafranov shift of magnetic flux surfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Body waves in a weakly anisotropic medium,II.GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001P waves from a centre of rotation, S waves from a centre of expansion Summary A perturbation theory is presented, providing a simple description of the S wave from a centre of expansion and the P wave from a centre of rotation. The relationships between the directivities of these waves and polarization anomalies of plane waves are established. The effect of anisotropy on the generation of these waves is compared with that of a smooth inhomogeneity. [source] Statistical morphological analysis of hippocampal principal neurons indicates cell-specific repulsion of dendrites from their own cellJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2003Alexei V. Samsonovich Abstract Traditionally, the sources of guidance cues for dendritic outgrowth are mainly associated with external bodies (A) rather than with the same neuron from which dendrites originate (B). To quantify the relationship between factors A and B as determinants of the adult dendritic shape, the morphology of 83 intracellularly characterized, stained, completely reconstructed, and digitized principal neurons of the rat hippocampus was statistically analyzed using Bayesian optimization. It was found that the dominant directional preference (tropism) manifested in dendritic turns is to grow away from the soma rather than toward the incoming fibers or in any other fixed direction; therefore, B is predominant. Results are robust and consistent for all examined morphological classes (dentate gyrus granule cells, basal and apical trees of CA3 and CA1 pyramidal cells). In addition, computer remodeling of neurons based on the measured parameters produced virtual structures consistent with real morphologies, as confirmed by measurement of several global emergent parameters. Thus, the simple description of dendritic shape based on dendrites' tendency to grow straight, away from their own soma, and with additional random deflections, proves remarkably accurate and complete. Although based on adult neurons, these results suggest that dendritic guidance during development may be associated primarily with the host cell. This possibility challenges the traditional concept of dendritic guidance: in that hippocampal cells are densely packed and have highly overlapping dendritic fields, the somatodendritic repulsion must be cell specific. Plausible mechanisms involving extracellular effects of spikes are discussed, together with feasible experimental tests and predicted results. © 2002 Wiley-Liss, Inc. [source] Redetermination of hydronium perchlorate at 193 and 293,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2003Azhar A. Rahman A sample of hydronium perchlorate, H3O+·ClO4,, crystallized from ethanol at ambient temperature, was found to be orthorhombic (space group Pnma) at both 193 and 293,K, with no phase transition observed in this temperature range. This contrasts with the earlier observation [Nordman (1962). Acta Cryst. 15, 18,23] of a monoclinic phase (space group P21/n) at 193,K for crystals grown at that temperature from perchloric acid. The hydronium and perchlorate ions lie across a mirror plane but it is not possible to define at either temperature a simple description of the H-atom positions due to the three-dimensional tumbling of the hydronium cation. [source] REVIEW: Questionnaires in ecology: a review of past use and recommendations for best practiceJOURNAL OF APPLIED ECOLOGY, Issue 3 2005PIRAN C. L. WHITE Summary 1Questionnaires, or social surveys, are used increasingly as a means of collecting data in ecology. We present a critical review of their use and give recommendations for good practice. 2We searched for papers in which questionnaires were used in 57 ecological academic journals, published over the period 1991,2003 inclusive. This provided a total sample size of 168 questionnaires from 127 papers published in 22 academic journals. 3Most questionnaires were carried out in North America and western Europe, and addressed species-level issues, principally focusing on mammals. The majority were concerned with impacts of species and/or their conservation, and just under half with human,wildlife interactions. 4Postal survey was the method used most frequently to carry out the questionnaires, followed by in-person interviews. Some questionnaires were conducted by telephone, and none was web-based. 5Most questionnaires were concerned with obtaining factual information or perceptions of facts. Ground-truthing (independent verification of the facts) was carried out in less than 10% of questionnaires. 6The mean (± SE) sample size (number of respondents) per questionnaire was 1422 ± 261 and the average (± SE) response rate was 63 ± 3%. These figures varied widely depending on the methods used to conduct the questionnaire. 7The analysis of data was mostly descriptive. Simple univariate methods were the most frequently used statistical tools, and data from a third of questionnaires were not subjected to any analysis beyond simple descriptions of the results. 8Synthesis and applications. We provide recommendations for best practice in the future use of questionnaires in ecology, as follows: (i) the definition of the target population, any hypotheses to be tested and procedures for the selection of participants should be clearly documented; (ii) questionnaires should be piloted prior to their use; (iii) the sample size should be sufficient for the statistical analysis; (iv) the rationale for the choice of survey method should be clearly stated; (v) the number of non-respondents should be minimized; (vi) the question and answer format should be kept as simple as possible; (vii) the structure of the questionnaire and the data emerging from it should be unambiguously shown in any publication; (viii) bias arising from non-response should be quantified; (ix) the accuracy of data should be assessed by ground-truthing where relevant; (x) the analysis of potentially interrelated data should be done by means of modelling. Researchers should also consider whether alternative, interpretative methods, such as in-depth interviews or participatory approaches, may be more appropriate, for example where the focus is on elucidating motivations or perceptions rather than testing factual hypotheses. [source] Contributions of A. Roberto Frisancho to human population biology: An introduction,AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009William R. Leonard Over the span of his career, A. Roberto Frisancho has been one of the prime architects of the development and expansion of human population biology. His research and scholarly publications have helped to move the field beyond simple descriptions of human variation to address the nature and evolutionary origins of human biological diversity. Frisancho's early work in the Peruvian Andes elegantly demonstrated the importance of developmental acclimatization for promoting adaptive responses to the multiple stressors of high-altitude environments. Since mid-1970s, he has played a major role in developing and expanding the use of anthropometric techniques for assessing physical growth and nutritional status. Frisancho's influential publications have helped to make the use of anthropometric methods commonplace in the fields of nutritional science and public health. Throughout his career, Frisancho's work has examined how environmental, genetic, and developmental factors interact to influence human health and nutritional status. His research has addressed topics ranging from the determinants of low-birth weight infants in teenage mothers to the origins of obesity and associated metabolic diseases in populations of the developing world. Both the breadth and impact of Frisancho's work have been truly remarkable. The field of human population biology owes much to the tremendous contributions of A. Roberto Frisancho. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||