Showing papers by "Tel Aviv University published in 1979"

The Electrochemical Behavior of Alkali and Alkaline Earth Metals in Nonaqueous Battery Systems—The Solid Electrolyte Interphase Model

Abstract: It is suggested that in practical nonaqueous battery systems the alkali and alkaline earth metals are always covered by a surface layer which is instantly formed by the reaction of the metal with the electrolyte. This layer, which acts as an interphase between the metal and the solution, has the properties of a solid electrolyte. The corrosion rate of the metal, the mechanism of the deposition‐dissolution process, the kinetic parameters, the quality of the metal deposit, and the half‐cell potential depend on the character of the solid electrolyte interphase (SEI).

Combinatorial Optimization with Rational Objective Functions

Abstract: Let A be the problem of minimizing c1, x1, +... + cnxn subject to certain constraints on x = x1,..., xn, and let B be the problem of minimizing a0 + a1x1 +... + anxn/b0 + b1x1 +... + bnxn subject to the same constraints, assuming the denominator is always positive. It is shown that if A is solvable within O[pn] comparisons and O[qn] additions, then B is solvable in time O[pnqn + pn]. This applies to most of the “network” algorithms. Consequently, minimum ratio cycles, minimum ratio spanning trees, minimum ratio simple paths, maximum ratio weighted matchings, etc., can be computed withing polynomial-time in the number of variables. This improves a result of E. L. Lawler, namely, that a minimum ratio cycle can be computed within a time bound which is polynomial in the number of bits required to specify an instance of the problem. A recent result on minimum ratio spanning trees by R. Chandrasekaran is also improved by the general arguments presented in this paper. Algorithms of time-complexity O|E| · |V|2 · log|V| for a minimum ratio cycle and O|E| · log2|V| · log log |V| for a minimum ratio spanning tree are developed.

Analysis of Properties of Fiber Composites With Anisotropic Constituents

Abstract: Expressions and bounds for the five effective elastic moduli of a unidirectional fiber composite, consisting of transversely isotropic fibers and matrix, are derived on the basis of analogies between isotropic and transversely isotropic elasticity equations. Application of results for determination of the five elastic moduli of graphite fibers is discussed. Effective thermal expansion coefficients are derived on the basis of a general theorem. Effective conductivities, dielectric constants, and magnetic permeabilities are derived by use of certain mathematical analogies.

Influence of quenched impurities on first-order phase transitions

Abstract: Microscopic random quenched impurities may or may not produce rounding of a first-order phase transition. We derive a criterion for the appearance of rounding due to local fluctuations in thermodynamic phase. Such fluctuations occur when the free-energy lowering due to taking advantage of local fluctuations in impurity density more than offsets the free-energy cost of the interface produced. The argument also predicts the spatial scale of such phase fluctuations, when they occur. In some situations this scale is just the coherence length $\ensuremath{\xi}$; in others, the inhomogeneity develops over "domains," which may be much larger than $\ensuremath{\xi}$. Near a second-order transition our criterion reduces to the one due to Harris. We specifically discuss what happens when a first-order transition becomes second order as an external parameter is varied.

Chromoelectric-flux-tube model of particle production

Abstract: Quark confinement is assumed to be implemented by the generation of chromoelectric flux tubes with uniform energy density. Approximate formulas for the production of quark pairs in these tubes by tunneling are derived and various observable implications are studied. The non-Abelian nature of the SU(3) color group is taken partially into account thus yielding a quantitative estimate for the baryons-to-mesons ratio. Reasonable agreement with experiment is obtained.

Ground state of a spin-½ charged particle in a two-dimensional magnetic field

Abstract: We prove that a spin-\textonehalf{} charged particle moving in a plane under the influence of a perpendicular magnetic field has ($N\ensuremath{-}1$) zero-energy states, where $N$ is the closest integer to the total flux in units of the flux quantum. The ($N\ensuremath{-}1$) independent wave functions are calculated explicitly. The result, which is extremely simple to prove, is an example of the Atiyah-Singer index theorem when applied to the Euclidean two-dimensional Dirac equation.

Lattice models of quark confinement at high temperature

Abstract: We consider the behavior of lattice models of quark confinement at high temperature. We find that confinement is strictly a low-temperature phenomenon. At high temperatures a transition to a plasma-like phase occurs. In this phase free gluons form a plasma which Debye screens the quarks.

Plasma Observations Near Uranus: Initial Results from Voyager 2

Abstract: Extensive measurements of low-energy positive ions and electrons in the vicinity of Uranus have revealed a fully developed magnetosphere. The magnetospheric plasma has a warm component with a temperature of 4 to 50 electron volts and a peak density of roughly 2 protons per cubic centimeter, and a hot component, with a temperature of a few kiloelectron volts and a peak density of roughly 0.1 proton per cubic centimeter. The warm component is observed both inside and outside of L = 5, whereas the hot component is excluded from the region inside of that L shell. Possible sources of the plasma in the magnetosphere are the extended hydrogen corona, the solar wind, and the ionosphere. The Uranian moons do not appear to be a significant plasma source. The boundary of the hot plasma component at L = 5 may be associated either with Miranda or with the inner limit of a deeply penetrating, solar wind-driven magnetospheric convection system. The Voyager 2 spacecraft repeatedly encountered the plasma sheet in the magnetotail at locations that are consistent with a geometric model for the plasma sheet similar to that at Earth.

Nuclear gamma-rays from energetic particle interactions.

Abstract: Gamma ray line emission from nuclear deexcitation following energetic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made.

Market Expansion Strategies in Multinational Marketing

Abstract: This paper presents a framework for planning and evaluation of multinational expansion strategies focusing on the rate of entry into new markets and the allocation of efforts among markets. Two maj...

Inefficacy of Digitalis in the Control of Heart Rate in Patients With Chronic Atrial Fibrillation: Beneficial Effect of an Added Beta Adrenergic Blocking Agent

Abstract: The role of digoxin and the new beta adrenergic blocking agent, timolol, in controlling heart rate at rest and during exercise was investigated in 28 patients with chronic atrial fibrillation. Digoxin failed to prevent excessively rapid heart rates during mild to moderate exercise. Increasing digoxin blood levels from a mean of 0.6 to 1.8 ng/ml had no effect on heart rate either at rest or during exercise. The addition of timolol, 20 to 30 mg/day, resulted in a satisfactory and significant attenuation of the rapid heart rates both at rest and during exercise. Heart rates at rest were 91 and 98 beats/min in the patients with low and high digoxin dosage and rose to 135 and 139 beats/min, respectively, during exercise. Timolol reduced the heart rate to 67 at rest and to 92 beats/min during exercise. The effect of beta adrenergic blockade at rest was less pronounced in patients whose initial heart rates were below 90 beats/min. Digoxin alone may not suffice to control excessive heart rate in patients with chronic atrial fibrillation. The additional beta adrenergic blockade actually normalizes the heart rate response in these patients.

Emulsifier of Arthrobacter RAG-1: Chemical and Physical Properties

Abstract: The extracellular emulsifier of Arthrobacter RAG-1 was deproteinized by hot phenol treatment and purified by fractional precipitation with (NH4)2SO4. The active fraction, precipitating between 30 and 35% saturation [EF-RAG(UET) WA], appeared to be homogeneous by immunodiffusion and sedimentation analysis. EF-RAG(UET) WA had an intrinsic viscosity of 750 cm3/g, a sedimentation constant of 6.06S, a diffusion constant of 5.25 × 10−8 cm2 s−1, and a partial molar volume of 0.712 cm3 g−1. From these data a weight average molecular weight of 9.76 × 105 and a viscosity average molecular weight of 9.88 × 105 were calculated. EF-RAG(UET)WA contained 46.7% C, 7.01% H, and 6.06% N. Titration of the nonreducing polymer gave a single inflection point (pK′ = 3.05), corresponding to 1.5 μmol of carboxyl groups per mg. Direct estimation of O-ester and hexose content of the highly acidic polymer yielded 0.65 and 0.29 μmol/mg, respectively. Mild alkaline hydrolysis released fatty acids with an average molecular weight of about 231. Strong acid hydrolysis of EF-RAG(UET)WA yielded d-glucose (minor), d-galactosamine (major), and an unidentified amino uronic acid (major).

The Avian Egg: Mass and Strength

Abstract: In a series of recent works, attention has been paid to the functional properties of the avian eggshell: water vapor and respiratory gas conductances, water loss, metabolic rate and incubation time-all these major physiological characteristics of eggs may be closely and intimately related to egg mass, which, in turn, is allometrically related to eggshell structural properties such as thickness, porosity, mass, density and surface area (Wangensteen 1972, Ar et al. 1974, Rahn and Ar 1974, Paganelli et al. 1974, Rahn et al. 1974, Ar and Rahn 1978). These structural and functional relations of bird eggs reveal some variables of importance to the physiology of the embryo, including the gradient in water vapor pressure between egg and nest, the fractional water loss constant, the constancy of gas composition in the air cell, and total oxygen consumption per gram egg during incubation. The ability to hatch successfully is the outcome of a delicate equilibrium among several factors, some of which are inherited in the structure and function of the egg itself, while others are either imposed on the egg by the environment or controlled by the incubating parents. The eggshell provides the egg with an external “skeletal” support that utilizes the dome principle to obtain strength with economy in building material and without need for internal supporting posts. It must satisfy conflicting demands: On the one hand, it must be strong enough to support the incubating bird’ s mass plus the egg’ s own mass and to protect and prevent it from being crushed during incubation. On the other hand, it must not be too strong for the hatchling to break its way out, a problem that may become crucial in bigger eggs where shell thickness increases and the specific metabolic rate of the embryo decreases (Paganelli et al. 1974, Rahn et al. 1974). The ratio of total shell pore area to shell thickness is largely evolved to meet the forthcoming metabolic demands of the growing embryo, which in turn, are a function of mass (Ar et al. 1974). Adding to this the belief that any saving in building material should benefit the laying bird, we hypothesize that eggshell strength should be related to egg mass. Eggshells have been subjected to numerous strength tests in the past. They have been crushed, cracked, pierced, snapped, compressed, bent and deformed in various ways. Force has been applied inwards and outwards, on whole eggs and on pieces of shells. Various methods and instrumentations have been used (Brooks 1960, Tyler and Geake 1963, 1964, Tyler and Coundon 1965, Tyler and Thomas 1966, Carter 1971, Scott et al. 1971). However, most of these studies were designed to establish practical “quality” criteria as they are understood by the poultry industry (Petersen 1965). As a result, most of the research has been concentrated on domestic hen (Gallus domesticus) eggs and little has been published on other species (Romanoff and Romanoff 1949, Brooks 1960, Tyler 1969a, Radcliffe 1970, Peakall et al. 1973). Strength has been correlated with factors such as calcium diet, diet in general, insecticides, shell microstructure, specific gravity, incubation period and shape index (e.g., Sluka et al. 1967, Wells 1967a, b, Vanderstoep and Richards 1969, Connor and Arnold 1972, King and Robinson 1972, Cooke 1973, Carter 1976). However, Tyler (196913) clearly demonstrated that the main factor affecting strength in hen eggs is shell thickness, where strength is a function of shell thickness squared. It is our purpose here to describe how egg strength scales with mass. We do not try to explain the relationship, but rather attempt to define the common principles that emerge from this relationship.

BRAM: The Broadcast Recognizing Access Method

Abstract: In this paper, we first present the broadcast recognizing access method (BRAM), an access protocol suitable for regulating internode communication in either a radio or (coaxial or fiber) cable based communication system. The method avoids collisions, imposes negligible computational requirements on the nodes attempting to transmit, and is fair in the sense that no node will be indefinitely prevented from transmitting. Next we introduce parametric BRAM which attempts to balance the length of inserted channel idle periods, resulting from scheduling effects, against the probability of allowed message collisions. We show that parametric BRAM can be used to realize a method which balances inserted channel idle time against the probability of message collision to yield enhanced performance. For high message loads, parametric BRAM converges to BRAM, while for low and medium loadings it yields throughputs in excess of BRAM, and other methods. Both BRAM and parametric BRAM are discussed under the assumption of homogeneous message arrival rates at the nodes. We conclude by showing how the parametric BRAM can be applied when the nodes operate with heterogeneous or mixed message arrival rates.

Localization of heavy metals and other elements accumulated in the lichen thallus

Abstract: Summary This study demonstrates the extracellular deposition of particulate metallic fall-out accumulated in the lichen Caloplaca aurantia with the aid of scanning and transmission electron microscopy and the application of energy dispersive X-ray analyses. The elemental composition of particles integrated in the lichen tissue was compared with the elemental composition of dust particles collected from the surface of the lichen colonies. The different effect of heavy metals in particulate form or in solution, as reflected by lichen's tolerance or sensitivity, is discussed.

Quantum Particle in One-Dimensional Potentials with Incommensurate Periods

Abstract: The energy spectrum and wave functions for a particle in periodic potentials with incommensurate periods are obtained analytically and reduced to specific phase trajectories. The spectrum is of the devil's-stairs type. States may be extended and localized, separated by mobility edges. These results are applicable to incommensurate linear chain structures (such as those in Hg/sub 3-delta/AsF/sub 6/) and to the fine structure of de Haas--van Alphen oscillations.

On the perseverance of a quasi-two-dimensional eddy-structure in a turbulent mixing layer

Abstract: Strong external disturbances were introduced into a mixing layer in order to test the formation of the quasi two-dimensional coherent eddies and their survival under less than ideal conditions. Velocity and temperature correlation measurements, flow visualization, and the simultaneous use of a large number of sensors suggest that these eddies are very stable in the range of Reynolds numbers considered and they persevere in spite of the external buffeting imposed. Some measurements were carried out in a mixing layer between two parallel streams and some in a mixing layer entraining quiescent surrounding fluid. In both cases the large eddies could be described. as vortex rolls spanning the test section; these rolls may be contorted and sometimes skewed, but they are basically two-dimensional.

On improving the worst case running time of the Boyer-Moore string matching algorithm

Abstract: It is shown how to modify the Boyer-Moore string matching algorithm so that its worst case running time is linear even when multiple occurrences of the pattern are present in the text.