Fractal behavior in trapping and reaction: A random walk study

We investigate the trapping of a random walker in fractal structures (Sierpinski gaskets) with randomly distributed traps. The survival probability is determined from the number of distinct sites visited in the trap-free fractals. We show that the short-time behavior and the long-time tails of the survival probability are governed by the spectral dimensiond. We interpolate between these two limits by introducing a scaling law. An extension of the theory, which includes a continuous-time random walk on fractals, is discussed as well as the case of direct trapping. The latter case is shown to be governed by the fractal dimensiond.     

EXAFS spectroscopy,from one perspective

Summary Extended X-ray absorption fine-structure (EXAFS) spectroscopy has been demonstrated to be a most useful probe of short-range interatomic correlations in a wide variety of materials. The theory of the EXAFS is presented in its simplest form so as to provide the basis for a discussion about the kind and quality of the structural information which can be extracted from EXAFS data. The adequacy of several of the approximations commonly incorporated in this theory is examined with emphasis on those areas of the theory which bear most directly on the analysis of EXAFS data. Paper presented at the Workshop on ?EXAFS Data Analysis in Disordered Systems?, held in Parma, October 5–7, 1981.     

The dynamics of random interfaces in phase transitions

A review is given of recent developments involving the dynamics of random interfaces formed in the evolution of metastable and unstable systems. Topics which are discussed include interface growth and nonequilibrium dynamical scaling. The possibility of there being dynamical universality classes in first-order phase transitions is also discussed. There are a large number of systems of experimental interest which include binary alloys, binary fluids, and polymer mixtures. Other systems studied by computer simulation include the kinetic Ising, Potts, andZ _N models.Work supported by NSF grant No. DMR-8013700.     

Geometry and combinatorics of Julia sets of real quadratic maps

For real a correspondence is made between the Julia setB forz(z–)², in the hyperbolic case, and the set of-chains±(±(±..., with the aid of Cremer's theorem. It is shown how a number of features ofB can be understood in terms of-chains. The structure ofB is determined by certain equivalence classes of-chains, fixed by orders of visitation of certain real cycles; and the bifurcation history of a given cycle can be conveniently computed via the combinatorics of-chains. The functional equations obeyed by attractive cycles are investigated, and their relation to-chains is given. The first cascade of period-doubling bifurcations is described from the point of view of the associated Julia sets and-chains. Certain Julia sets associated with the Feigenbaum function and some theorems of Lanford are discussed.Supported by NSF grant No. MCS-8104862.Supported by NSF grant No. MCS-8203325.     

Biostimulation of HeLa cells by low-intensity visible light

Summary The action spectra of low-intensity light in the range from 300 to 900 nm on the synthesis rate of nucleic acids in the culture of HeLa cells has been measured. The synthesis of DNA and RNA is stimulated in several spectral intervals with maxima nearby 400, 630, 680, 760 and 820 nm. The stimulation effect is very sensitive to the irradiation duration (light intensity) at a fixed dose. The dose that causes the maximal stimulation is approximately 10 times smaller in the near-UV blue region than in red-IR region.

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Riassunto Si è misurato lo spettro d’azione della luce a bassa intensità nell’intervallo da 300 a 900 nm sul tasso di sintesi degli acidi nucleici in culture di cellule HeLa. La sintesi di DNA ed RNA è stimolata in parecchi intervalli spetrali con massimi vicino a 400, 630, 680, 760 e 820 nm. L’effetto di stimolazione è molto sensibile alla durata d’irradiazione (intensità della luce) ad una dose fissa. La dose che causa la stimolazione massima è approssimativamente dieci volte piú piccola nella regione blu dell’ultravioletto vicino che nella regione del rosso-infrarosso.

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Резюме Измерен спектр действия низкоинтенсивного света в диапазоне (300⋎900) нм на скорость синтеза нуклеиновых кислот в культуре клеток HeLa 1.5 часа после облучения. Синтез ДНК и РНК стимулируется в несколбких спектральных интервалах с максимумами вблизи 400, 630, 680, 760 и 820 нм. Эффект стимуляции очень чувствителен к продолжительности облуения (интенсивности света) при фиксированной дозе. Доза, при которой наблюдается максимальная стимудяция, в несколько ваз меньше в ближнеи УФ-синей области с максимумом около 400 нм.

     

Comments on the mean spherical approximation for hard-core and soft potentials and an application to the one-component plasma

The thermodynamic properties of the mean spherical (MSA), Percus-Yevick (PY), and hypernetted-chain (HNC) approximations are derived by a simple and unified approach by considering the RPA free-energy functionalF and employing an Ewald-type identity. It is demonstrated that with decreasing relative contribution of the hard-core insertion to the thermodynamic functions, the MSA changes its nature from PY-like to HNC-like, withF changing its role from excess pressure to excess free energy, respectively. It is found that the condition of continuity of the MSA pair functions is equivalent to a stationarity condition forF and leads to thermodynamic consistency between the virial and energy equations of state for the (thus defined) soft-MSA (SMSA), withF playing the role of the excess free energy. It is shown that the PY-compressibility and virial equations of state forD-dimensional hard spheres may be simply obtained one from the other without knowing any details of the solution of the model. Using this relation we find an indication that the PY approximation for hard spheres becomes less accurate with increasing dimensionality. A general variational formulation is presented for the application of the MSA for soft potentials, and results for the one-component plasma are discussed and extended.On sabbatical leave from the Nuclear Research Center-Negev, P.O. Box 9001, Beer Sheva, Israel.     

Electromagnetic radiation from a conducting tether moving in the ionosphere

Summary We set up a model to compute electromagnetic radiation associated with the motion of a conductor through a magnetized plasma. Calculations are carried out, in the framework of cold-plasma theory, for radiation near the ion cyclotron frequency. Results are applied to the TSS (Tethered Satellite System) project presently under development.

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Riassunto S’imposta il formalismo generale per il calcolo della radiazione elettromagnetica associata con il moto di un conduttore in moto attraverso un plasma magnetizzato. I calcoli sono poi fatti specificamente per la radiazione nelle vicinanze della frequenza di ciclotrone degli ioni. I risultati sono applicati ai parametri del progetto spaziale TSS (Tethered Satellite System) che è attualmente in fase di sviluppo.

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Резюме Мы предлагаем модель для вычисления электромагнитного излучения, связанного с движением проводника через намагниченныю плазму. Вычисления проводятся в рамках теории холодной плазмы для изучения вблизи ионной циклотронной частоты. Полученные результаты применяются к ТСС (связанная система спутников), проект которой разрабатывается в настояцее время.

     

The representation of thermodynamic properties at high pressures

It is sometimes advantageous to have an expression for the Gibbs energy, G_m(T,P), from which one can analytically derive an expression for the Heimholtz energy, F_m(T, V_m). Such an expression is suggested for solid substances and it is shown how expressions for other physical properties can be derived from it.     

非圆截面环流器硬X射线辐射强度的绝对测量

本文给出了逃逸电子在孔拦上轰击出的硬X射线能谱及其辐射强度,描述了硬X射线闪烁谱还原成能谱的分析处理法,并对NaI(T1)探测器的绝对光峰效率进行了测量。     

椭圆截面等离子体柱离子回旋频率附近的本征振荡

本文用椭圆柱座标系导出了波导管中和自由边界情况下波的色散关系,计算了椭圆截面波导管中快磁流体波和慢波的本征模。通过计算得出,在时,快波可以在等离子体的高密度区域传播,而慢波只能在低密度区域传播。