Mean exposure fractions of human body solar UV exposure patterns for application in different ambient climates

In this research, the erythemally effective UV measured using miniaturized polysulphone dosimeters to over 1250 individual body sites and collected over a 4-year period is presented relative to the total exposed skin surface area (SSA) of a life-size manikin model. A new term is also introduced, the mean exposure fraction (MEF). The MEF is used to weight modeled or measured horizontal plane UV exposures to the total unprotected SSA of an individual and is defined as the ratio of exposure per unit area received by the unprotected skin surfaces of the body relative to the exposure received on a horizontal plane. The MEF has been calculated for a range of solar zenith angles (SZA) to provide a sunburning energy data set weighted to the actual SSA of a typically clothed individual. For this research, the MEF was determined as 0.15, 0.26 and 0.41 in the SZA ranges 0°-30°, 30°-50° and 50°-80° providing information that can be used in a variety of different ambient, latitudinal and seasonal climates where total human body UV exposure information is not available.     

Neighborhood preferences in random matching problems

We consider a class of random matching problems where the distance between two points has a probability law which, for a small distance l, goes like l^r. In the framework of the cavity method, in the limit of an infinite number of points, we derive equations for p_k, the probability for some given point to be matched to its kth nearest neighbor in the optimal configuration. These equations are solved in two limiting cases: r = 0 -- where we recover p _k = 1/2^k, as numerically conjectured by Houdayer et al. and recently rigorously proved by Aldous -- and r→ + ∞. For 0 < r < + ∞, we are not able to solve the equations analytically, but we compute the leading behavior of p_k for large k. Received 14 February 2001     

On the distribution of the overlaps at given disorder

We prove a rigorous version of the following heuristic statement: if, in a spin glass model, the extended Ghirlanda–Guerra identities are valid, at given disorder the distribution of the overlap of two configurations is discrete, and its support (the smallest closed set that carries this distribution) is non-random. To cite this article: G. Parisi, M. Talagrand, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Interplanetary disturbances during Forbush decreases

Summary The interplanetary perturbations associated with Forbush decreases (FDs) during the period 1965–1974 are studied. The systematic appearance of the results obtained confirms once again that type-IV solar flares are the origin of these perturbations. The front perturbation is a wide (∼100° in longitude) driven shock followed by a magnetic blob and a high-speed plasma cloud of about 0.5 A.U. average radial dimension at the Earth orbit, emitted in a short time interval (<15 h) immediately following the beginning of the type-IV burst. The FD-modulated region is found to be included between two boundary streams which rotate with the Sun; therefore the FD can be observed also in the interplanetary regions which were not swept by the front perturbation. The FD amplitude appears to be correlated with an empiric parameter which caters for the importance of the shock and magnetic blob at the front perturbation.

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Riassunto Le perturbazioni interplanetarie associate alle diminuzioni di Forbush (FDs) sono state studiate per il periodo 1965–1974. L’insieme dei risultati ottenuti conferma che i brillamenti solari accompagnati da radioemissione di tipo IV sono all’origine di queste perturbazioni. II fronte della perturbazione è un’onda d’urto di estensione ∼100° in longitudine seguita da campo magnetico esaltato (?magnetic blob?) e da una nuvola di plasma ad alta velocità, di dimensione media radiale ∼0.5 A.U. all’orbita della Terra, emessa per un intervallo di tempo breve (,15 ore) dopo l’inizio della radioemissione di tipo IV. Si trova che la regione modulata della FD è limitata da due fasci di vento solare veloce che coruotano con il Sole; la FD può essere perciò anche osservata nelle regioni di spazio interplanetario che non sono state investite direttamente dal fronte della perturbazione. L’ampiezza della FD appare correlata con un parametro empirico che tiene conto dell’importanza dell’onda d’urto e del ?magnetic blob? presenti al fronte della perturbazione.

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Резюме Исследуются межпланетные возмущения, связанные с убываниями Форбуша в течение периода 1965–1974 г.г. Получается систематическое подтверждение того факта, что солнечные вспышки типа IV связаны с этими возмущениями. Фронт возмущения представляет широкую (∼100° по долготе) ударную волну, за которой следует магнитое ?пятно? и плазменное облако со средним радиальным размером 0.5 а.е.д. на орбите Земли, испускаемые в течение короткого временного интервала (<15 часов) непосредственно за началом вспышки типа IV. Область, модулированная убываниями Форбуша, заключена между двумя граничными потоками, которые вращаются вокруг Солнца. Таким образом, убывания Форбуша могут наблюдаться также в межпланетных областях, через которые не проходит фронт возмущения. Оказывается, что амплтуда убываний Форбуша коррелирует с змпирическим параметром, который определяет значимость ударной волны и магнитного ?пятна? на возмущение Форбуша.

     

Imaging of self-generated multifilamentary current patterns in GaAs

Two-dimensional imaging of current filament patterns generated in homogeneousn-type GaAs during avalanche breakdown at low temperatures is reported. The self-generated formation and subsequent growth behavior of distinct single- and multifilament configurations could globally be visualized by means of a scanning electron microscope equipped with a liquid-helium stage. From local conductivity measurements in the smallest possible filaments (typical diameter of about 10 m) carrier mobilities as high as about 4·10⁶ cm²/Vs at 4.2 K were estimated. Such high-mobility filament channels may become interesting for applications in ultrafast electronic circuits.     

An estimation of biological hazards due to solar radiation

A spectrum evaluator based on four different dosimeter materials has been employed to estimate the spectral irradiances of solar radiation for exposed humans. The result is used to calculate the biologically effective irradiance using the erythemal action spectrum and a fish melanoma action spectrum. Measurements are made in winter at a sub-tropical site on the chest and shoulder of subjects during normal daily activities. Up to 95% of the total UV exposure received is in the UV-A waveband (320-400 nm). The UV-A waveband is found to contribute approximately 14% of the erythemal UV and 93% of the biologically effective UV for fish melanoma. Extrapolation to humans suggests that exposure to the UV-A band will contribute to photodamage in human skin during exposure to solar radiation.     

On the investigation of the low-energy conformational space of molecules

A new perspective on traditional energy minimization problems is provided by a connection between statistical thermodynamics and combinatorial optimization (finding the minimum of a function depending on many variables). The joint use of a new method for uncovering the global minimum of intramolecular potential energy functions, based on following the asymptotic behavior of a system of stochastic differential equations, and an iterative-improvement technique, whereby a search for relative minima is made by carrying out local quasi-Newton minimizations starting from many distinct points of the energy hypersurface, proved most effective for investigating the low-energy conformational space of molecules.