Showing papers by "Tel Aviv University published in 1985"

Generalized many-channel conductance formula with application to small rings.

Abstract: The conductance of a sample scattering elastically and coupled to leads with many channels is derived. We assume that all the incident channels on one side of the sample are fed from the same chemical potential. The transmitted and reflected streams are determined by the incident streams through the multichannel scattering properties of the sample. We do not assume that the channels equilibrate with each other. Our result differs from those given earlier by other authors, except for that of Azbel [J. Phys. C 14, L225 (1981)], which is confirmed. We point out that a similar result is obtained for the conductance in a single channel at a temperature above zero. As an application, we obtain the dependence on channel number N of the contributions to the conductance of a small ring, periodic in the Aharonov-Bohm flux through it. Terms whose period is h/e as well as those with period h/2e vary with N as 1/N.

The Nash bargaining solution in economic modelling

Abstract: This article establishes the relationship between the static axiomatic theory of bargaining and the sequential strategic approach to bargaining. We consider two strategic models of alternating offers. The models differ in the source of the incentive of the bargaining parties to reach agreement: the bargainers' time preference and the risk of breakdown of negotiations. Each of the models has a unique perfect equilibrium. When the motivation to reach agreement is made negligible, in each model the unique perfect equilibrium outcome approaches the Nash bargaining solution with utilities that reflect the incentive to settle and with the proper disagreement point chosen. The results provide a guide for the application of the Nash bargaining solution in economic modelling.

Clustering Countries on Attitudinal Dimensions: A Review and Synthesis

Abstract: Eight empirical studies using attitudinal data to cluster countries are reviewed. The major dimensions accounting for similarities among countries are discussed, and a final synthesis of clusters is presented.

Checking that finite state concurrent programs satisfy their linear specification

Abstract: We present an algorithm for checking satisfiability of a linear time temporal logic formula over a finite state concurrent program. The running time of the algorithm is exponential in the size of the formula but linear in the size of the checked program. The algorithm yields also a formal proof in case the formula is valid over the program. The algorithm has four versions that check satisfiability by unrestricted, impartial, just and fair computations of the given program.

The Glory of the Past

Abstract: An extension of propositional temporal logic that includes operators referring to a bounded past is considered. An exponential time decision procedure and a complete axiomatic system are presented. A suggested normal form leads to a syntactic classification of safety and liveness formulae. The adequacy of temporal logic to modular verification is examined. Finally we present the notion of α-fairness which is proved to fully capture the behavior of probabilistic finite state programs.

The role of implicit models in solving verbal problems in multiplication and division

Abstract: Arithmetical operations were assumed to remain attached to primitive behavioral models that influence tacitly the choice of an operation even after the learner has had solid formal-algorithmic training. The model for multiplication was conjectured to be repeated addition, and two primitive models (partitive and quotative) were seen as linked to division. A total of 623 pupils enrolled in 13 Italian schools (Grades 5, 7, and 9) were asked to choose the operation needed to solve 26 multiplication and division word problems. Violations by the numerical data of the constraints imposed by the assumed tacit models (for instance, when the operator was a decimal number) constituted particular sources of difficulty at all three grade levels. The findings seemed to confirm the impact of the repeated addition model on multiplication and of the partitive model on division. The quotative division model influenced the pupils' choices only at the ninth-grade level. The present study was inspired by previous findings on the difficulties children encounter when faced with verbal problems in multiplication and division. Bell, Swan, and Taylor (1981) have shown that when children are presented with a series of problems with the same content, they may change their minds about the operation needed to solve the problem, depending on the specific numerical data that are given. For instance, 12- to 15-year-old

Implicit TVD schemes for hyperbolic conservation laws in curvilinear coordinates

Abstract: The Harten (1983, 1984) total variation-diminishing (TVD) schemes, constituting a one-parameter explicit and implicit, second-order-accurate family, have the property of not generating spurious oscillations when applied to one-dimensional, nonlinear scalar hyperbolic conservation laws and constant coefficient hyperbolic systems. These methods are presently extended to the multidimensional hyperbolic conservation laws in curvilinear coordinates. Means by which to linearize the implicit operator and solution strategies, in order to improve the computation efficiency of the implicit algorithm, are discussed. Numerical experiments with steady state airfoil calculations indicate that the proposed linearized implicit TVD schemes are accurate and robust.

Large-scale structures in a forced turbulent mixing layer

Abstract: The large-scale structures that occur in a forced turbulent mixing layer at moderately high Reynolds numbers have been modelled by linear inviscid stability theory incorporating first-order corrections for slow spatial variations of the mean flow. The perturbation stream function for a spatially growing time-periodic travelling wave has been numerically evaluated for the measured linearly diverging mean flow. In an accompanying experiment periodic oscillations were imposed on the turbulent mixing layer by the motion of a small flap at the trailing edge of the splitter plate that separated the two uniform streams of different velocity. The results of the numerical computations are compared with experimental measurements.When the comparison between experimental data and the computational model was made on a purely local basis, agreement in both the amplitude and phase distribution across the mixing layer was excellent. Comparisons on a global scale revealed, not unexpectedly, less good accuracy in predicting the overall amplification.

Multinational Corporations and Trade Structure

Abstract: First, a model of horizontally and vertically integrated firms is developed. These firms are then embedded in a general equilibrium model of trading countries. It is shown how multinational corporations emerge as a result of differences across countries in factor compositions. Intersectoral, intraindustry, and intrafirm trade can coexist, and intrafirm trade takes place in invisibles (headquarter services) and intermediate inputs. It is shown how the various trade components depend on the structure of the world economy. The model predicts trade patterns which are close to observed trade patterns. The importance of multinational corporations in the conduct of foreign trade has been recognized for many years. Nevertheless, there exists no well articulated theory that explains the conditions for their emergence and predicts under these conditions a structure of trade that comes close to observed trade patterns. I have developed in Helpman (1984) a theory which is designed to fill in this gap and it is the purpose of this paper to extend it in order to make it better fit reality. My earlier work builds on the standard theory of monopolistic competition in differentiated products in which every firm produces a single variety. The distinguishing feature of that study is the interpretation of the technology so as to allow for specialized inputs which service plants that are geographically separated from the location of the inputs' employment. In particular, those inputs can be located in one country and service plants located in other countries. Management and product specific RD multinational corporations have often production facilities in several countries (see, for example, U.S. Tariff Commission (1973, Chapter III)). Moreover, in my earlier work all intra-firm trade consisted of trade in the services of the specialized inputs; i.e. in headquarter services, while empirically a large part of intra-firm trade takes place in intermediate inputs (see Buckley and Pearce (1979)). Hence, there is a need to extend the theory in order to take account of these missing features and in order to evaluate their contribution to the explanation of trade patterns. This task is undertaken in the following sections by incorporating the model of the horizontally and vertically integrated firm from Helpman (1983) into the theory of

Coherence multiplexing of fiber-optic interferometric sensors

Abstract: This paper describes a method of multiplexing several optical signals onto a single spatial channel (eg, a single-mode fiber) using a short coherence length continuous wave light source Several system configurations which utilize this technique are proposed, and some design considerations are discussed Experimental results for a single sensor and receiver are presented and compared with theoretical predictions

Nucleotide sequence evidence for relationship of AIDS retrovirus to lentiviruses

Abstract: Lentiviruses are a subfamily of retroviruses which have been aetiologically linked to the induction of arthritis, encephalitis, progressive pneumonia and slow neurological diseases in certain species1. Relatively little is known about their genome structure, mechanisms of pathogenesis or evolutionary relationships with other retroviral subfamilies. In an effort to understand better the mechanisms by which these viruses induce such a variety of chronic diseases, we have molecularly cloned and physically characterized the genomes of caprine arthritis-encephalitis virus (CAEV)2 and equine infectious anaemia virus (EIAV) (A.Y. et al., in preparation). The latter, which bears some morphological similarity to the lentiviruses, has yet to be classified definitively as one3. Here, we have determined the nucleotide sequence of a highly conserved region within the CAEV and EIAV pol genes. We demonstrate a much closer relationship of their predicted pol gene products to that of the presumed aetiological agent of human acquired immune deficiency syndrome (AIDS) than to those of other retroviruses. Additional pairwise comparisons allowed us to generate an evolutionary tree showing that the pol genes of lentiviruses and oncoviruses have evolved from a common progenitor.

Inositol 1,4,5-trisphosphate mimics muscarinic response in Xenopus oocytes.

Abstract: The enhanced metabolism of phosphoinositides, which is associated with a wide variety of stimuli and physiological responses, has been studied intensively. Berridge and his collaborators1–3 demonstrated that the first measurable reaction following cell membrane receptor activation is a rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), and that the product of this reaction, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), could cause a release of non-mitochondrial calcium. These findings have been verified in other systems4–6. Although the relationship between the hydrolysis of PtdIns(4,5)P2 and the mobilization of intracellular calcium was clearly demonstrated, the direct link between Ins(1,4,5)P3 production and the physiological response was only implied. We have investigated the possibility that the intracellular release of Ins(1,4,5)P3 mediates the muscarinic–cholinergic response is Xenopus oocytes, and we show here that intracellularly injected Ins(1,4,5)P3 mimics the muscarinic depolarizing chloride current in Xenopus oocytes. This is the first demonstration of a direct link between phosphoinositides metabolism and a neuro-transmitter-induced physiological response.

Coral community reproductive patterns: red sea versus the great barrier reef.

Abstract: In contrast to many corals of the Great Barrier Reef, Australia, which are synchronous multispecific spawners, the abundant coral species in the northern Red Sea, Israel, exhibit temporal reproductive isolation. Spawning dates of 12 of the 13 Red Sea species followed lunar periodicity and were consistent throughout 3 years of study. Spawning periods of all species occurred in different seasons, different months, or different lunar phases within the same month. The high abundance of the corals studied at Eilat may be due in part to the advantages gained through not having overlapping spawning periods and settlement times.

International Mediation: Conflict Resolution and Power Politics

Abstract: This study examines mediation as an exercise in which the mediator has interests and operates in a context of power politics and cost-benefit calculation. It is based on eight cases of international mediation-the U.S.S.R. between India and Pakistan (1966), Algeria between Iran and Iraq (1975), the United States and Great Britain in Rhodesia (1975–1979), the five Western States in Namibia (1977–1983), Algeria between the United States and Iran (1980–1981), and the ongoing activities of the Organization of African Unity, The Organization of American States, and the International Committee of the Red Cross. It was found that a mediator intervenes because of its interest in the conflict or in obtaining an outcome, and it can play three roles-communicator, formulator, manipulator- in accomplishing its objectives. The mediator is accepted by the parties, not because of its neutrality but because of its ability to produce an attractive outcome. The mediator's power, or leverage, comes from the parties' need for a solution, from its ability to shift weight among parties, and from side payments.

The Freezing and Unfreezing of Impressional Primacy Effects of the Need for Structure and the Fear of Invalidity

Abstract: Three constructive replications were executed to test the hypotheses that primary effects in impression formation are more pronounced when the individual feels (1) high versus low need for cognitive structure and (2) low versus high fear of invalidity. The experiments differed partially among themselves in the particular operational definitions of the structure and validity needs. In the first experiment need for structure was manipulated via demands for unidimensional (hence, global and undifferentiated) versus multidimensional judgments; and the fear of invalidity, via potential costs to the target person of subject's judgmental mistake. In the second experiment fear of invalidity was manipulated as in the first experiment and need for structure, via degrees of time pressure. In the third experiment need for structure was manipulated as in the first experiment and fear of invalidity, via degrees of evaluation apprehension. The research hypotheses were strongly confirmed in all three experiments. These r...

Generalized hopping model for frequency-dependent transport in a dynamically disordered medium, with applications to polymer solid electrolytes

Abstract: Protonic diffusion in hydrogen-bonded networks, ionic conduction in polymeric solid electrolytes, and other processes in which the carrier transport mechanism involves motion of the host medium on a time scale comparable to that of the carrier motion itself require generalization of the usual models based on carrier hopping in a static medium. Under the assumption that this concurrent motion of the host can be modeled by a random reassignment (or ``renewal'') of hopping probabilities, with a constant probability \ensuremath{\lambda} per unit time for renewal to occur, the effects of host motion on the frequency-dependent diffusion coefficient D(\ensuremath{\omega}) are now considered. We consider both the dynamic bond-percolation model (in which the site-to-site hopping probability is randomly assigned either the value w or the value 0) and the more general model based on a possibly continuous distribution of hopping rates randomly assigned between different pairs of sites. Under these assumptions, the diffusion coefficient D(\ensuremath{\omega}) with renewal is shown to be obtainable from D(\ensuremath{\omega}) without renewal through the formal substitution i\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\lambda}+i\ensuremath{\omega}. For the \ensuremath{\omega}=0 limit, an expression is obtained for the time-dependent mean-square displacement with renewal in terms of the mean-square displacement without renewal. These general formal results are applied to the one-dimensional dynamic percolation model, for which specific exact analytic results are thereby obtained, and D(\ensuremath{\omega}) is calculated and studied for this case.

Surgical decompression of anterior and posterior malignant epidural tumors compressing the spinal cord: a prospective study.

Abstract: Of 167 episodes of spinal epidural neoplastic compression, 86 were treated by operation. The surgical approach was prospectively selected according to the location of the tumor in the spinal canal. Decompression was achieved by 61 vertebral body resections (VBRs) and by 25 laminectomies. The indications for operation were: neurological relapse after previous radiotherapy, the need to make a tissue diagnosis, a radioresistant tumor, and neurological deterioration during radiotherapy. Before VBR, 28% (17 of 61) were still able to walk, 51% (31 of 61) were parAparetic, and 21% (13 of 61) were paraplegic. Bowel and bladder dysfunction was present in 49% (30 of 61). After VBR, the outcome of only 57 procedures was available for evaluation because of the postoperative death of 4 patients. Eighty per cent (46 of 57) were able to walk, 18% (10 of 57) were paraparetic, and 2% (1 of 57) were paraplegic. Ninety-three per cent had normal sphincter control. Before laminectomy, 8% (2 of 25) were ambulatory, 84% (21 of 25) were paraparetic, and 8% (2 of 25) were paraplegic. Bowel and bladder dysfunction was present in 76% (19 of 25). After laminectomy, only 23 procedures were evaluated because of the postoperative death of 2 patients. Thirty-nine per cent (9 of 23) were ambulatory, 35% (8 of 23) were paraparetic, and 26% (6 of 23) were paraplegic. Fifty-seven per cent regained normal sphincter control. The operative mortality was 7% (4 of 61) in VBR and 8% (2 of 25) in laminectomy.(ABSTRACT TRUNCATED AT 250 WORDS)