Über den Einfluss der Oberflächeneigenschaften von Halbleitern auf ihre Eiskeimfähigkeit

The factors controlling the ice nucleation efficiency are studied in this paper on suitably chosen model substances, in particular on silicon. It is found that the critical supersaturation for the growth of ice on a (111)-plane of GaAs is 25% at –25°C; this quantity as well as the number of growing ice crystals (cm^–2) were found to be independent of the dislocation density. The critical supersaturation for the growth of ice on the (111)-plane of Si is strongly dependent on the electrical conductivity of the crystals, but independent of the sign of the majority charge carriers. Epitaxial growth is observed on the hexagonal substrate GaSe only, but not on the cubic GaAs and Si.On the basis of the classical nucleation theory the free energy of adsorption of H₂O on GaSe G _ads =0,48 eV and the specific interfacial free energy _SL =23,2 erg · cm^–2 are evaluated. This indicates that the outermost layer of the ice embryo is in a liquid-like state.Water adsorption isotherms were measured gravimetrically down to –20°C and were found to be of type II (BET, [33]). The amount of adsorbed water and the isosteric heat of adsorption at a given relative pressure depend on the doping of the sample.From this it is concluded that low conductivity material had more adsorption sites than high conductivity material, but these fewer sites on the high conductivity samples were more active in collecting water molecules. The larger water clusters are formed on high conductivity samples in agreement with the higher nucleation efficiency observed in mixing cloud chamber experiments.The electrical conductivity and the sign of the thermoelectric effect of a thin silicon on sapphire film have been measured as a function of oxygen and water vapor pressures. It is found that band bending towards ann-type surface occurred during water chemisorption on Si.This indicates that chemisorbed water molecules act as donor surface states. The charge exchanged between adsorbate and adsorbent is larger on high conductivity samples on account of their higher initial surface potential.Chemisorption sites on Si are proportional to the doping concentration and they produce relatively large water clusters. Hence doping results in a higher nucleation efficiency.     

A type of mechanically anisotropic,optically sensitive material

The technology for obtaining a mechanically anisotropic, optically sensitive material that can be used in photoelastic stress analysis is described. The mechanically anisotropic, photoelastic materials obtained by this method (method 3) are free of initial birefringence, have a sufficiently high degree of mechanical anisotropy, and possess high optical sensitivity. The elastic and piezooptic properties of specimens of orthotropic material have been investigated and it has been found that the isochromatics (lines of equal path differences ) are lines of equal principal strain differences. Experimental results are presented for the stress distribution in an orthotropic disk compressed by a pair of opposing concentrated forces.Translated from Mekhanika Polimerov, No. 5, pp. 835–839, September–October, 1971.     

Water hammer in a viscoelastic pipe

The problem of water hammer in a pipe made of material whose mechanical behavior is described by the Boltzmann model has been solved numerically on a Minsk-22 computer using Fourier transforms. The phase velocity and phase difference functions for low-density poly-ethylene over a broad range of vibration frequencies are used in the solution.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 908–912, September–October, 1970.     

On Perfect Codes and Related Concepts

The concept of diameter perfect codes, which seems to be a natural generalization of perfect codes (codesattaining the sphere–packing bound) is introduced. This was motivated by the code–anticode bound of Delsartein distance regular graphs. This bound in conjunction with the recent complete solutions of diametric problems in the Hamming graph _q(n) and the Johnson graph J(n,k)gives a sharpening of the sphere–packing bound. Some necessaryconditions for the existence of diameter perfect codes are given.In the Hamming graph all diameter perfect codes over alphabetsof prime power size are characterized. The problem of tilingof the vertex set of J(n,k) with caps (and maximalanticodes) is also examined.     

The optico-deformation effect in irradiated polyethylene

The absorption of light by polyethylene film subjected to extension and electron bombardment has been investigated on the wavelength interval 220–800 nm. It is shown that irradiation and illumination by a xenon lamp during extension reduce the stresses corresponding to the beginning of high-elastic deformation of the polyethylene. It is established that deformation and electron bombardment lead to an increase in the light absorption of the polyethylene film with absorption maxima at 245 and 290 nm. It is assumed that the nature of the effect is associated with reorientation of the macromolecule chains under the influence of mechanical stress and the appearance of allyl radicals-CH₂-CH CH-H-CH₂-.Institute of Physical Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 451–455, May–June, 1972.     

Buildup of failures in polymers on micro- and macrolevels

The buildup of damage in polymers has been studied by mechanical and structural—analytical methods. A method of programmed loading has been developed which makes it possible to make an estimate of damage buildup in macroscopic experiments. A comparison has been performed of kinetic curves of failure buildup on molecular and macroscopic levels. It is shown that the kinetic equations where the rate of failure is basically initiated by true stress qualitatively follow the experimental curves for failure buildup on micro- and macrolevels."Plastpolimer" Scientific-Manufacturing Association, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 263–268, March–April, 1976.     

Global Convergence of Conjugate Gradient Methods without Line Search

Global convergence results are derived for well-known conjugate gradient methods in which the line search step is replaced by a step whose length is determined by a formula. The results include the following cases: (1) The Fletcher–Reeves method, the Hestenes–Stiefel method, and the Dai–Yuan method applied to a strongly convex LC ¹ objective function; (2) The Polak–Ribière method and the Conjugate Descent method applied to a general, not necessarily convex, LC ¹ objective function.     

Statistical analysis of some characteristics of cylindrical glass-fiber-reinforced plastic materials

The results are given of a statistical treatment of experimental data on several characteristics of glass-fiber-reinforced plastic cylindrical shells, prepared from glass fabric TS8/3-250 and epoxide binder IF-ÉD-6 (TU-26-59) at the "Électroizolit" factory by winding an impregnated fabric cloth on a mandrel. The experim ental data on the mechanical properties of the glass-fiber-reinforced plastic material were obtained in tests on representative samples cut from the margin of the cylindrical shells. The results of the statistical analysis can be used to evaluate the mechanical reliability of structures made of glass-fiber-reinforced plastic material of the above type.Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 906–910, September–October, 1973.     

A fuzzy adaptive network approach to parameter estimation in cases where independent variables come from an exponential distribution

In a regression analysis, it is assumed that the observations come from a single class in a data cluster and the simple functional relationship between the dependent and independent variables can be expressed using the general model; Y=f(X)+ε. However; a data cluster may consist of a combination of observations that have different distributions that are derived from different clusters. When faced with issues of estimating a regression model for fuzzy inputs that have been derived from different distributions, this regression model has been termed the ‘switching regression model’ and it is expressed with . Here l_i indicates the class number of each independent variable and p is indicative of the number of independent variables [J.R. Jang, ANFIS: Adaptive-network-based fuzzy inference system, IEEE Transaction on Systems, Man and Cybernetics 23 (3) (1993) 665–685; M. Michel, Fuzzy clustering and switching regression models using ambiguity and distance rejects, Fuzzy Sets and Systems 122 (2001) 363–399; E.Q. Richard, A new approach to estimating switching regressions, Journal of the American Statistical Association 67 (338) (1972) 306–310].In this study, adaptive networks have been used to construct a model that has been formed by gathering obtained models. There are methods that suggest the class numbers of independent variables heuristically. Alternatively, in defining the optimal class number of independent variables, the use of suggested validity criterion for fuzzy clustering has been aimed. In the case that independent variables have an exponential distribution, an algorithm has been suggested for defining the unknown parameter of the switching regression model and for obtaining the estimated values after obtaining an optimal membership function, which is suitable for exponential distribution.     

Variable stepsize schemes for effective order methods and enhanced order composition methods

The interest in the concept of effective order has been revived by its rediscovery in applications to symplectic problems. In this paper we revert to the original application, the construction of explicit Runge–Kutta methods. Changing stepsize is a characteristic difficulty with effective order methods and we propose a way of overcoming this difficulty. We also consider the possible cancellation of local truncation errors of two methods over two successive steps. Using the algebraic approach for deriving these results gives us further insight into these methods and compositions of methods. A particular sixth stage Runge–Kutta pair is derived in the paper and is shown to be competitive.     

Solution of Index 2 Implicit Differential-Algebraic Equations by Lobatto Runge-Kutta Methods

We consider the numerical solution of systems of index 2 implicit differential-algebraic equations (DAEs) by a class of super partitioned additive Runge–Kutta (SPARK) methods. The families of Lobatto IIIA-B-C-C^*-D methods are included. We show super-convergence of optimal order 2s–2 for the s-stage Lobatto families provided the constraints are treated in a particular way which strongly relies on specific properties of the SPARK coefficients. Moreover, reversibility properties of the flow can still be preserved provided certain SPARK coefficients are symmetric.     

Temperature-time analogy applied to thermorheologically complex polymer materials. 2. Mixtures of thermoplastic and thermosetting polymers (polymer-oligomer composites)

Conclusions 1. Stress-relaxation curves have been obtained for polymer-oligomer composites over a wide temperature range, and the temperature-time characteristics of properties of mixtures have been analyzed. The effect of each component on the mechanical characteristics of a mixture has also been examined.2. We have studied the temperature depenence of viscoelastic properties of mixtures of tetrafluoroethylene and vinylidene fluoride copolymer with epoxide-diphenylene propane resin. We have demonstrated that polymer-oligomer composites do not conform to the concept of thermorheologically simple behavior.3. The parameters of the temperature-time analogy were calculated with the aid of a computer for polymer-oligomer composites, examples of thermorheologically complex materials. It has been established, as a result, that the reduction factor depends strongly on time and the relaxation function depends strongly on the ratio of components.For communication 1, see [7].Okhtinsk Scientific-Industrial Combine, Plastpolimer, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 430–434, May–June, 1978.     

Moisture and low temperature impact on the properties of a polyether glass-reinforced plastic

The cyclic action of water and the combined action of water and low temperatures on the physical-mechanical properties of a polyether glass-reinforced plastic are studied. For experimental investigations, methods of sorption, thermogravimetry, and mechanical testing in static bending were used. It was found that the most aggressive external factor for the glass-reinforced plastic was the cyclic action of water, but not the change in its phase state at cooling. The process of sorption-desorption of the glass-reinforced plastic is irreversible.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Non-Metallic Materials, Siberian Branch of the Russian Academy of Sciences, Yakutsk, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 519–524, July–August, 1998.     

Change in the properties of impact polystyrene during multiple processing

It has been shown experimentally that the multiple extrusion of grade UP-1E impact polystyrene (5–7 cycles) has almost no effect on most of the physicomechanical properties, the content of volatiles and helium or the residual monomer content. Multiple processing of the same polystyrene by injection molding (10 cycles) causes partial degradation of the material and the destruction of its crosslinked fraction, which results in increased fluidity, reduced molecular weight, and a partial improvement in mechanical properties (approximately up to the fifth or sixth cycle).Mekhanika Polimerov, Vol. 3, No. 1, pp. 156–160, 1967     

Implicit function theorems for generalized equations

We show that Lipschitz and differentiability properties of a solution to a parameterized generalized equation 0 f(x, y) + F(x), wheref is a function andF is a set-valued map acting in Banach spaces, are determined by the corresponding Lipschitz and differentiability properties of a solution toz g(x) + F(x), whereg strongly approximatesf in the sense of Robinson. In particular, the inverse map (f + F)^–1 has a local selection which is Lipschitz continuous nearx ₀ and Fréchet (Gateaux, Bouligand, directionally) differentiable atx ₀ if and only if the linearization inverse (f (x ₀) + f (x₀) (× – x₀) + F(×))^–1 has the same properties. As an application, we study directional differentiability of a solution to a variational inequality.This work was supported by National Science Foundation Grant Number DMS 9404431.     

Extensions of an inequality of Bonnesen toD-dimensional space and curvature conditions for convex bodies

For convex bodies inE ^d (d 3) with diameter 2 we consider inequalitiesW _i – W _d–1 +( - 1) W _d 0 (i = 0, , d – 2) whereW _j are the quermassintegrals. In addition, for a ball, equality is attained for a body of revolution for which the elementary symmetric functions _d–1–i of main curvature radii is constant. The inequality is actually proved fori = d – 2 by means of Weierstrass's fundamental theorem of the calculus of variations.Dedicated to Professor Otto Haupt with best wishes on his 100th birthday     

Reversible linear systems and their versal deformations

Let R be a fixed linear involution (R ²=id) of the spaceR ⁿ . A linear operator M is said to bereversible with respect to R if RM R=M^–1 and infinitesimally reversible with respect to R if M R=–RM. A linear differential equation dx/dt=B(t)x is said to be reversible with respect to R if V(t)R –RV(–t). We construct normal forms and versal deformations for reversible and infinitesimally reversible operators. The results are applied to describe the homotopy classes of strongly stable reversible linear differential equations with periodic coefficients. The analogous theory for linear Hamiltonian systems was developed by J. Williamson, M. G. Krein, I.M. Gel'fand, V. B. Lidskii, D. M. Galin, and H. Koçak.Translated fromTrudy Seminara imeni I. G. Petrovskogo, No. 15, pp. 33–54, 1991. Original article submitted April 27, 1988.     

Study of the process of unstable flow of elastomers in open and closed channels and its connection with mechanical characteristics of the material

The unstable flow process has been studied for examples of a series of unvulcanized rubbers of different structures by a complex of methods — capillary, tribometric, and dynamic methods. A connection has been found between the critical parameters which characterize the onset of this process and the dynamic mechanical characteristics. The possibility of modeling the unstable flow process in open channels is shown.A. V. Topchiev Institute for Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 530–536, May–June, 1970.     

High-frequency periodic deformation of polymers in the viscous-flow state

The propagation of high-frequency periodic vibrations in melts and solutions is considered in the case where the acoustic characteristics of the material are determined by the deformation amplitude. It is shown that in sufficiently large specimens the consequences of periodic deformation are concentrated near the vibration source, as a result of which a layer of material with strongly modified mechanical characteristics develops. It is suggested that when periodic high-frequency deformation is superimposed on steady-state flow, owing to the presence of a boundary layer there is effective slippages of the material at the vibration-emitting surfaces.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 722–728, July–August, 1973.