Showing papers by "Tel Aviv University published in 1978"

The Glutathione Status of Cells

Abstract: Publisher Summary Glutathione (GSH) is the most important nonprotein thiol in living systems and is of widespread occurrence in the intracellular milieu of animals, plants, and microorganisms GSH was isolated and named by the English biochemist Frederick Gowland Hopkins This chapter discusses GSH status, the biologically relevant chemistry of GSH, the forms in which GSH can be present within the cell, along with the GSH content of cells and the methods for analysis of this substance GSH-related biochemical reactions and the biological roles of GSH are discussed in the chapter The use of perturbations in GSH status as a means for investigating GSH-related phenomena and an analysis of the consequences of perturbation are presented A short summary of genetic lesions related to GSH is also included Like chemically induced perturbations in GSH status, genetic lesions provide valuable insights into the role of GSH in normal functions and processes in cells The chapter concludes with some brief comments about the future of the relationship of GSH status to cellular processes

A method to produce uniform plane-stress states with applications to fiber-reinforced materials

Abstract: This work is concerned with a new method for testing material properties under uniform plane-stress conditions by means of a specially designed plane specimen. Photoelastic analysis showed that in the significant section of the specimen it is possible to produce uniform plane stress, with high accuracy, subject to the limitation that the principal stresses are of different signs. An important special case of loading produces pure shear on the significant section. The specimen is of particular importance for fiber-composite testing. The experimental results presented are encouraging.

Egalitarian Equivalent Allocations: A New Concept of Economic Equity

Abstract: Foreword, 671. — I. Introduction, 671. — II. The concept of Pareto-efficient-egalitarian-equivalent-allocations (PEEEA), 674. — III. PEEEA as a fair arbitration scheme for allocations, 676. — IV. Maximin properties of PEEEA, 678. — V. PEEEA in economies with production, 680. — Mathematical appendices, 682.

Order and disorder in gauge systems and magnets

Abstract: We show how phase transitions in Abelian two-dimensional spin and four-dimensional gauge systems can be understood in terms of condensation of topological objects. In the spin systems these objects are kinks and in the gauge systems either magnetic monopoles or fluxoids (quantized lines of magnetic flux). Four models are studied: two-dimensional Ising and $\mathrm{XY}$ models and four-dimensional ${Z}_{2}$ and U(1) gauge systems.

Tricritical points in systems with random fields

Abstract: Mean-field theory and renormalization-group arguments are used to show that the phase transition in a system with a random ordering field becomes first order at sufficiently low transition temperature, provided the (symmetric) random-field distribution function has a minimum at zero field. The first-order region is separated from the second-order region by a tricritical point. Both the critical and the tricritical exponents at $dg4$ dimensions are shown to be the same as for the pure system at $d\ensuremath{-}2$ dimensions. The relevance to spin glasses and other systems is discussed. The new tricritical point is very different from all previously studied tricritical points, as it deviates from mean-field theory at $d=5$, and not at $d=3$. Although quantitative results are calculated only at $d=5\ensuremath{-}\ensuremath{\epsilon}$ dimensions, the qualitative results are expected to apply at $d=3$.

Computational Complexity of the Game Theory Approach to Cost Allocation for a Tree

Abstract: In the game theory approach to the problem of allocating cost, the users of a facility are viewed as players in a cooperative n-person game. It is the nature of cooperative games that the power of each one of the 2n-1 possible coalitions is taken into account. Thus, practical problems of allocating cost may be intractable in the game theory approach because of the computational complexity involved. However, it is shown that good algorithms do exist for the nucleolus and the Shapley value allocations for a tree. The nucleolus can be computed within On3 operations and the Shapley allocation in On operations.

Combinatorial optimization with rational objective functions

Abstract: Let A be the problem of minimizing c1x1+...+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[p(n)] comparisons and O[q(n)] additions, then B is solvable in time O[p(n)(q(n)+p(n))]. 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 within 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.

Different brain areas mediate the analgesic and epileptic properties of enkephalin

Abstract: Single injections of 120 micrograms of methionine-enkephalin were made into various midbrain and forebrain structures in the rat Analgesia was observed after injections into or near the ventral, caudal midbrain periaqueductal gray matter Seizures and other pathological electroencephalogram (EEG) changes were seen with injections into or near the forebrain dorsomedial nucleus of the thalamus No animals with midbrain injection sites showed EEG changes, and none with forebrain injection sites were analgesic These data, taken together with other lines of evidence, suggest that enkephalin-induced analgesia and enkephalin-induced seizures are mediated by opiate receptors that are located in different brain areas and that are pharmacologically different

Joint changes after overuse and peak overloading of rabbit knees in vivo.

Abstract: The effect of overuse and overuse combined with axial peak overloading on the knee joints of living rabbits has been investigated. A specially constructed apparatus was used for this purpose. Physical and biochemical changes are reported and include:1. Early and progressive damage to the articular cartilage surface shown by the scanning electron microscope.2. The presence of an increased amount of prostaglandin E in the synovial fluid.3. A reduction of cyclic 3′-5′ adenosine monophosphate in the subchondral bone.4. Late changes which were consistent with osteoarthritis.These changes were found only in the joints subjected to simultaneous overuse and peak overloading.The results suggest that:1. Cartilage damage and chemical changes in the subchondral bone are simultaneous and are both responsible for eventual degenerative changes.2. Frictional overuse alone does not seem to be responsible for the production of osteoarthritis.

Interdependence of Gas Conductance, Incubation Length, and Weight of the Avian Egg

Abstract: Allometric relationships of incubation length (I), water vapor conductance (\({{\text{G}}_{{{\text{H}}_{\text{2}}}{\text{O}}}}\)), and total functional pore area (Ap) as a function of egg weight (W), were established in 90 species of birds. A constant was derived which expresses the interrelationship between three variables.Thus (\({{\text{G}}_{{{\text{H}}_{\text{2}}}{\text{O}}}}\) · I)/W = 5.13 ± 0.86 S.D. [mg/(g·torr)]. Similar constants were derived for O2 and CO2 conductances and discussed in relation to the metabolic requirements and water loss of eggs during incubation. It is proposed that the total quantity of water lost and the total quantity of O2 taken up per gram of egg is independent of egg size and incubation period.

Gauge theory of gravity and supergravity on a group manifold

Abstract: The natural arena for the physics of gravity, supergravity and their enlargements appears to be the group manifold of the Poincare group P, the graded Poincare group GP of supersymmetry, and the corresponding enlargements. The dynamics of these theories correspond to geometrical algorithms in P and GP. Differential geometry on Lie groups is reviewed and results applied to P and GP. Curvature, gauge transformations and factorization are introduced. Also reviewed is the general coordinate transformation group and a hybrid gauge transformation, the anholonomized G.C.T. gauge. A study is made of the construction of an action, including the introduction of a set of special 2 forms, the ''pseudo curvatures.'' The possibilities of factorization in supersymmetry are analyzed. The version of supergravity is present which has now become a completely geometrical theory.

On the Hotel Overbooking Problem---An Inventory System with Stochastic Cancellations

Abstract: M hotel rooms are available at a date n periods from now. Reservations are made by customers for that date, which is at the peak of the high season. Typically, for such a time period, a policy of overbooking is exercised by the hotel management. Customers, however, may cancel their previously confirmed reservations at any time prior to their arrival, with no penalty. On the other hand, new requests for rooms for that particular date are generated anew. At the end of each period the hotel management reviews both the “inventory” level of remaining uncanceled previously confirmed reservations and the total number of not-yet-confirmed new requests. At that time a decision is made regarding the inventory level of confirmed reservations with which to start the next period. A decision is one of three actions: i to keep the inventory at its present level i.e., declining all new requests; ii to increase the level of overbooking by confirming some of the new requests and, if necessary, by trying to obtain some additional reservations at some extra cost; iii to decrease the level of inventory by canceling some of the previously confirmed reservations incurring a penalty for each such cancellation. Each occupied room at the target day carries a given profit, while each unhonored reservation at that time incurs a penalty. The problem is to find the optimal over-booking strategy that will maximize net profit. For both criteria, maximization of the expected total net profit, and maximization of the expected discounted net profit, it is shown that the optimal strategy is a 3-region policy as follows: For each period there exist upper and lower bounds and an intermediate point such that, a if the overbooking level at the end of a period is greater than the upper bound, it should be decreased to that bound; b if the inventory level is below the lower bound, two cases may occur: i if the discrepancy is greater than the number of new requests, all new requests should be confirmed and additional reservations should be acquired such that the inventory level will be equal to the lower bound; and ii if the discrepancy is smaller than the number of new requests, some of the new requests are confirmed but the inventory level may not exceed the intermediate point; c if the inventory level is between the two bounds there are two possibilities: i if it is above the intermediate point none of the new requests are confirmed, but ii if it is below that point, some of the new requests should be confirmed provided that the new inventory level will not exceed the intermediate point.

Novel argumentation and attitude change: The case of polarization following group discussion

Abstract: This study is concerned with attitude polarization as a function of two properties of a persuasive message: (a) its validity or acceptability and (b) its novelty. The latter is defined as the extent to which the message contains new arguments unlikely to have been already considered by the individual. Acceptability is assumed to be a necessary condition for inducing attitude change; the impact of novelty, therefore, was expected to be most pronounced for arguments of high validity. This hypothesis was tested in two related studies using arguments produced in response to choice dilemma items, widely used in research on polarization. First, it was shown that arguments rated as both valid and novel were perceived as more persuasive than arguments rated either as highly valid but obvious (non-novel) or as low in validity (non-valid) but novel. Second, when subjects read samples of valid arguments, their attitudes polarized in the direction advocated by the novel arguments rather than by the non-novel ones. These findings are considered relevant to the polarization of attitudes in groups. Other research demonstrates that this phenomenon is the result of persuasive arguments raised during group discussion, The present study suggests why such arguments may be persuasive.

The plane turbulent impinging jet

Abstract: This paper presents an experimental study of the turbulent structure on the centre-line of a two-dimensional impinging jet. The mean velocity, turbulent stresses, triple velocity products and temporal derivatives were measured and the energy balances for the three fluctuating components were calculated. The results indicate a selective stretching of vortices in the direction in which the streamlines spread near the wall, causing anisotropy in this region. The distribution of energy among various frequencies was found from spectral measurements. These measurements revealed the existence of a neutral frequency above which the energy was attenuated by viscous dissipation and below which it was augmented by a vortex-stretching mechanism.

Strategic Planning for Management Information Systems

Abstract: This paper deals with strategic planning for management information systems. Specifically, those variables of the strategic plan which impact on the success or failure of MIS are identified, and propositions are formulated relating states of the variables to system conditions. The variables concerned are the system development strategy, the purpose of MIS, the priority scheme, functions assigned the system, goals, definitions of requirements and documentation of the strategic plan. Two factors predominate in determining the appropriateness of strategic plans for MIS explicitness the degree to which the process is conscious, formal and documented and situational fit the degree to which the MIS is compatible with the specific organization and its members. It is concluded that there is no one optimal, strategic plan for MIS. Each organization must develop that strategy which best fits its particular situation.

The evolution of parental care in birds.

Abstract: The data on which this work is based were accumulated mainly from the existing literature. A substantial amount of data on body weight, egg weight, clutch size and incubation length was first gathered by Heinroth (1922). His list contained 436 bird species, on the majority of which he has all the above data. In addition to that, Heinroth added information on egg characteristics, mainly yolk content of 57 of the above 436 species. In a series of short papers published in 1929-1930, Harms (1929/30) gave such data on 14 bird species, some of which had already been mentioned by Heinroth. Data on the yolk and albumin weights of nine species were given by Asmundson et al. (1943). Thirteen species were listed by Romanoff and Romanoff (1949), and 24 species of Anatidae (some of which were mentioned by the former authors) by Lack (1968). We gathered such data on 37 species (Appendix 1), mainly from Aberdeenshire, Scotland, and the Tel-Aviv University Research Zoo. In order to complete the information needed for this work and not given by the above authors, we referred to various works on fauna or specific systematic groups (Ali and Ripley, 1968-1974; Delacour, 1954-1964; Dementiev et al., 1967; Harrison, 1975; Heinzel et al., 1972; Macworth Praed and Grant, 1953; Merom, 1960; Schonwetter, 1960-1972; Witherby et al., 1938-1941), where we found evoludata on female body weight, egg weight,

A Critical Survey of the Literature

Abstract: This chapter discusses the ex-ante trading decisions and ex-post commodity trading decisions. Three types of uncertainty considered include uncertainty in prices, in technology, and in preferences. In the ex-ante trading models, trading decisions are made before the resolution of uncertainty. In particular, these models assume price uncertainty and when an export or import commitment is made, the price that will be paid or received is unknown. In the ex-post trading models, trading decisions are made after uncertainty resolves. In both types of models, input decisions are made before the resolution of uncertainty. This means that in the presence of technological uncertainty, inputs do not determine a certain output level but rather the distribution of output. It is observed that in the case in which production decisions are consistent with consumption preferences, the first-best policy consists of no government intervention.

Risk Considerations in Insurance Ratemaking

Abstract: This paper examines insurance pricing and its regulation in the context of efficient capital markets. Starting with an aggregated model and generalizing results reported recently in the literature about “proper” underwriting profit, the paper turns to disaggregation of the model with m insurance lines. The main result is that no unique set of rates exists that regulators may impose to avoid disturbing market equilibrium. Preliminary empirical evidence presented shows that the “systematic risk” of underwriting profits approaches zero in most lines. Thus an intuitive solution for underwriting profit rates in these lines equal to minus the riskless interest rate, is reasonable.

Spin-flop multicritical points in systems with random fields and in spin glasses

Abstract: Mean-field theory and renormalization-group arguments are used to study the phase diagram of an anisotropic $n$-component $d$-dimensional magnetic system with a uniaxially random magnetic field. The resulting phase diagram is shown to be very similar to that of anisotropic antiferromagnets in a uniform field: For small random fields, the system orders along the direction of uniaxial anisotropy, with exponents which are related to those of nonrandom Ising systems in $d\ensuremath{-}2$ dimensions. For larger random fields, parallel to the direction of uniaxial anisotropy, the transverse $n\ensuremath{-}1$ spin components order, with exponents which are unaffected by the random field. The two regions are separated by a spin-flop first-order line, by an intermediate "mixed" phase, and by a tetracritical (or bicritical) point. The exponents at this multicritical point are shown to coincide, near $d=6$, with those of the random-field Ising model. This phase diagram is shown to describe the behavior of random-site spin glasses in a uniform magnetic field. Other types of anisotropic random fields, related experimental realizations and other generalizations are also mentioned. Although some of the quantitative results are found only near $d=6$, qualitative results are believed to apply at $d=3$ as well.

Cost allocation for steiner trees

Abstract: A set of points, called consumers, and another point called central supplier, are located in a Euclidean plane. The cost of constructing a connection between two points is proportional to the distance between them. The minimum cost required for connecting all the consumers to the supplier is given by a minimal Steiner tree. An example is given in which for every allocation of the total cost of the tree to the consumers, a coalition of consumers exists, which is charged more than the cost required for connecting its members to the central supplier.

Evidence from auditory nerve and brainstem evoked responses for an organic brain lesion in children with autistic traits.

Abstract: In an attempt to resolve the question as to whether children with autistic traits have an organic nervous system lesion, auditory nerve and brainstem evoked responses were recorded in a group of 15 children with autistic traits. The most obvious results included a longer response latency of the auditory nerve and a longer brainstem transmission time, compared to normal children. Five of the autistic children were found to be profoundly deaf. These results strengthen the theory that an organic lesion of the nervous system can give rise to autistic traits.

Gravity and supergravity as gauge theories on a group manifold

Abstract: We construct generalizations of gravity, including supergravity, by writing the theory on the group manifold (Poincare for gravity, the graded-Poincare group for supergravity). The action involves forms over the group, restricted to a 4-dimensional submanifold. The equations of motion produce a Lorentz gauge in gravity and supergravity, and an additional anholonomic supersymmetric coordinate transformation which reduces to the “local supersymmetry” of supergravity.