Application of the group-theoretical method to physical problems

The concept of the theory of continuous groups of transformations has attracted the attention of applied mathematicians and engineers to solve many physical problems in the engineering sciences. Three applications are presented in this paper. The first one is the problem of time-dependent vertical temperature distribution in a stagnant lake. Two cases have been considered for the forms of the water parameters, namely water density and thermal conductivity. The second application is the unsteady free-convective boundary-layer flow on a non-isothermal vertical flat plate. The third application is the study of the dispersion of gaseous pollutants in the presence of a temperature inversion. The results are found in closed form and the effect of parameters are discussed

X-ray Photoemission Spectroscopy Of Pt-cu: A Canonical Alloy

The possibility of employing x-ray photoemission valence-band spectra in a quantitative fashion for elucidation of valence-electron structure changes induced by alloying is examined. The special, or "canonical," property of Pt1-xCux, that one of the components, Pt, displays no measurable core-level shift, permits extraction of such changes from core-level and valence-band data alone. A relation between the d-resonant level shifts and the centroid of the valence-band spectra is derived and comparison of the centroid and core-level shifts leads to the desired information. The analysis indicates that there is no charge transfer in the system and that only Cu has significant valence occupation changes upon alloying, corresponding to dehybridization. Furthermore, information regarding Fermi-energy shifts is extracted and not required as input the results suggest that the shifts of the Fermi levels cannot be identified with those of the work functions as in other work. Model calculations indicate that dehybridization is to be expected as an "antihybridization" effect for a narrow d-band metal in a wide d-band one. © 1981 The American Physical Society.2373177318

Auditory perception in individuals with Friedreich’s Ataxia

INTRODUCTION: Friedreich's ataxia (FRDA) is an inherited ataxia with a range of progressive features including axonal degeneration of sensory nerves. The aim of this study was to investigate auditory perception in affected individuals. METHODS: Fourteen subjects with genetically defined FRDA participated. Two control groups, one consisting of healthy, normally hearing individuals and another comprised of subjects with sensorineural hearing loss, were also assessed. Auditory processing was evaluated using structured tasks designed to reveal the listeners' ability to perceive temporal and spectral cues. Findings were then correlated with open-set speech understanding. RESULTS: Nine of 14 individuals with FRDA showed evidence of auditory processing disorder. Gap and amplitude modulation detection levels in these subjects were significantly elevated, indicating impaired encoding of rapid signal changes. Electrophysiologic findings (auditory brainstem response, ABR) also reflected disrupted neural activity. Speech understanding was significantly affected in these listeners and the degree of disruption was related to temporal processing ability. Speech analyses indicated that timing cues (notably consonant voice onset time and vowel duration) were most affected. CONCLUSION: The results suggest that auditory pathway abnormality is a relatively common consequence of FRDA. Regular auditory evaluation should therefore be part of the management regime for all affected individuals. This assessment should include both ABR testing, which can provide insights into the degree to which auditory neural activity is disrupted, and some functional measure of hearing capacity such as speech perception assessment, which can quantify the disorder and provide a basis for interventio

Cloud microphysical effects of turbulent mixing and entrainment

Turbulent mixing and entrainment at the boundary of a cloud is studied by means of direct numerical simulations that couple the Eulerian description of the turbulent velocity and water vapor fields with a Lagrangian ensemble of cloud water droplets that can grow and shrink by condensation and evaporation, respectively. The focus is on detailed analysis of the relaxation process of the droplet ensemble during the entrainment of subsaturated air, in particular the dependence on turbulence time scales, droplet number density, initial droplet radius and particle inertia. We find that the droplet evolution during the entrainment process is captured best by a phase relaxation time that is based on the droplet number density with respect to the entire simulation domain and the initial droplet radius. Even under conditions favoring homogeneous mixing, the probability density function of supersaturation at droplet locations exhibits initially strong negative skewness, consistent with droplets near the cloud boundary being suddenly mixed into clear air, but rapidly approaches a narrower, symmetric shape. The droplet size distribution, which is initialized as perfectly monodisperse, broadens and also becomes somewhat negatively skewed. Particle inertia and gravitational settling lead to a more rapid initial evaporation, but ultimately only to slight depletion of both tails of the droplet size distribution. The Reynolds number dependence of the mixing process remained weak over the parameter range studied, most probably due to the fact that the inhomogeneous mixing regime could not be fully accessed when phase relaxation times based on global number density are considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in reduced quality), to appear in Theoretical Computational Fluid Dynamic

Quinta evaluación de genotipos de espárrago en invernadero y respuesta a técnicas de envasado

El espárrago es una hortaliza perecedera, que en Argentina se requiere extender el período de oferta y optimizar su productividad y presentación, imple-mentando diferentes estrategias como la comercialización de turiones cortos y el empleo de bolsas y bandejas de IV Gama. A tal fin, se realizó un ensayo con el objetivo de evaluar el comportamiento (5º año), de los genotipos italianos Ítalo, Zeno, Eros y Ercole, versus UC-157, norteamericano, como testigo. Se estudiaron diferencias en t totales y comerciales, Nº turiones totales y comerciales y distribución de calibres y defectos encontrados (turiones espigados y cortos). Se obtuvieron 578015 turiones.ha-1 totales, siendo la producción comercial/cosecha: 59 kg.ha-1. En pos-cosecha, se evaluó la evolución del peso fresco y tres tipos de envasado: atados, bandejas y bolsas para turiones cortos. El híbrido Ítalo presentó mejor adaptación para primicia. Sobre la evolución productiva, se encontró que es posible adelantar el período de cosecha un mes comparado con la producción a campo. Además se recomienda cosechar diariamente el cultivo para evitar turiones espigados. En poscosecha se consideró la conveniencia del empleo de la técnica de IV Gama, mediante la utilización de bolsas o bandejas, para la optimización de la calidad del producto final y para extender la vida de anaquel. De esta forma se demostró la importancia de una adecuada planificación que incluye la elección criteriosa del híbrido y el acondicionamiento y presentación del producto final.Asparagus is a perishable vegetable that in Argentina requires its period of supply to be extended and the optimisation of its productivity and presentation, implementing different strategies such as the presentation of short spears (turions) and the use of bags and trays for Category IV products. To this end, the behaviour of the genotypes Ítalo, Zeno, Eros and Ercole, of Italian origin, versus UC-157, from the USA, as a control, was evaluated in the fifth year of productivity. Differences in the following characters were studied: total and commercial spear yield, number of total and commercial spears, calibre distribution and the proportion of defects observed (spiked and short spears). The following mean values were obtained: 578015 spears.ha-1, with a commercial production of 59 kg.ha-1. In postharvest, the evolution of fresh weight was evaluated, plus the influence of three types of packaging: tied bundles, trays and bags for short spears. The hybrid Ítalo demonstrated superior behaviour for primary production performance. Regarding production evolution, it was shown that it is possible to forward the harvest period by one month compared to field production. Additionally, daily harvesting is recommended in the glasshouse to avoid spiked spears. In postharvest the desirability of using bags and trays for Category IV was considered, in order to optimise the quality of the final product and to extend shelf-life. By these means, the importance of adequate planning before crop planting, including judicious choice of hybrid and the conditioning and presentation of the final product, was demonstrated.Fil: Giménez Azara C.. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Agrarias; ArgentinaFil: Castagnino A.M.. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Agrarias; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Diaz, Karina Elizabeth. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Tarantino, M.B.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Rogers, William John. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Cientifico Tecnolológico Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología. Laboratorio de Biología Funcional y Biotecnología; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; Argentin

Solidification of Al-Sn-Cu based immiscible alloys under intense shearing

The official published version of the Article can be accessed from the link below - Copyright @ 2009 The Minerals, Metals & Materials Society and ASM InternationalThe growing importance of Al-Sn based alloys as materials for engineering applications necessitates the development of uniform microstructures with improved performance. Guided by the recently thermodynamically assessed Al-Sn-Cu system, two model immiscible alloys, Al-45Sn-10Cu and Al-20Sn-10Cu, were selected to investigate the effects of intensive melt shearing provided by the novel melt conditioning by advanced shear technology (MCAST) unit on the uniform dispersion of the soft Sn phase in a hard Al matrix. Our experimental results have confirmed that intensive melt shearing is an effective way to achieve fine and uniform dispersion of the soft phase without macro-demixing, and that such dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm and 60 seconds will be adequate to produce fine and uniform dispersion of the Sn phase, and that higher shearing speed and prolonged shearing time can only achieve minor further refinement.This work is funded by the EPSRC and DT

Percolation model for structural phase transitions in Li1−x_{1-x}Hx_xIO3_3 mixed crystals

A percolation model is proposed to explain the structural phase transitions found in Li$_{1-x}$H$_x$IO$_3$ mixed crystals as a function of the concentration parameter $x$. The percolation thresholds are obtained from Monte Carlo simulations on the specific lattices occupied by lithium atoms and hydrogen bonds. The theoretical results strongly suggest that percolating lithium vacancies and hydrogen bonds are indeed responsible for the solid solution observed in the experimental range $0.22 < x < 0.36$.Comment: 4 pages, 2 figure

Selberg Supertrace Formula for Super Riemann Surfaces III: Bordered Super Riemann Surfaces

This paper is the third in a sequel to develop a super-analogue of the classical Selberg trace formula, the Selberg supertrace formula. It deals with bordered super Riemann surfaces. The theory of bordered super Riemann surfaces is outlined, and the corresponding Selberg supertrace formula is developed. The analytic properties of the Selberg super zeta-functions on bordered super Riemann surfaces are discussed, and super-determinants of Dirac-Laplace operators on bordered super Riemann surfaces are calculated in terms of Selberg super zeta-functions.Comment: 43 pages, amste

Spatial correlations in vote statistics: a diffusive field model for decision-making

We study the statistics of turnout rates and results of the French elections since 1992. We find that the distribution of turnout rates across towns is surprisingly stable over time. The spatial correlation of the turnout rates, or of the fraction of winning votes, is found to decay logarithmically with the distance between towns. Based on these empirical observations and on the analogy with a two-dimensional random diffusion equation, we propose that individual decisions can be rationalised in terms of an underlying "cultural" field, that locally biases the decision of the population of a given region, on top of an idiosyncratic, town-dependent field, with short range correlations. Using symmetry considerations and a set of plausible assumptions, we suggest that this cultural field obeys a random diffusion equation.Comment: 18 pages, 5 figures; added sociophysics references

Students as co-creators of teaching approaches, course design and curricula: implications for academic developers

Within higher education, students’ voices are frequently overlooked in the design of teaching approaches, courses and curricula. In this paper we outline the theoretical background to arguments for including students as partners in pedagogical planning processes. We present examples where students have worked collaboratively in design processes along with the beneficial outcomes of these examples. Finally we focus on some of the implications and opportunities for academic developers of proposing collaborative approaches to pedagogical planning