Showing papers by "Tel Aviv University published in 1974"

Baring high-albedo soils by overgrazing: a hypothesized desertification mechanism.

Abstract: Observations are reported of high-albedo soils denuded by overgrazing which appear bright, in high contrast to regions covered by natural vegetation. Measurements and modeling show that the denuded surfaces are cooler, when compared under sunlit conditions. This observed "thermal depression" eflect should, on theoretical grounds, result in a decreased lifting of air necessary for cloud formation and precipitation, and thus lead to regional climatic desertification.

Stable reduced-order models using Padé-type approximations

Abstract: An algorithm is introduced which ensures that the reduced-order model derived by equating time-moments and by continued fraction synthesis will be stable, assuming the high-order system is stable.

Optimal flows in networks with multiple sources and sinks

Abstract: The concept of an optimal flow in a multiple source, multiple sink network is defined. It generalizes maximal flow in a single source, single sink network. An existence proof and an algorithm are given.

Vacuum polarization and the absence of free quarks

Abstract: This paper is addressed to the question of why isolated quark partons are not seen. It is argued that in vector gauge theories it is possible to have the short-distance and light-cone behavior of quark fields without real quark production in deep-inelastic reactions. The physical mechanism involved is the flow of vacuum-polarization currents which neutralize any outgoing quarks. Our ideas are inspired by arguments due to Schwinger and an intuitive picture of Bjorken. Two-dimensional (1 space, 1 time) vector gauge field theories provide exactly soluble examples of this phenomenon. The resulting picture of deep-inelastic final states predicts jets of hadrons and logarithmically rising multiplicities as conjectured by Bjorken and Feynman.

A Difficulty in the Concept of Fairness

Abstract: This note raises a new difficulty concerning the possibility of satisfying equity and Pareto efficiency objectives simultaneously. When interpersonal comparisons of utility are ruled out, which is the case considered here, there is no natural way to define the concept of equity. An appropriate criterion for equity discussed in the literature seems to be that of fairness. An allocation is said to be fair (equitable) if no individual in the society prefers the bundle allocated to anyone else over the bundle allocated to him (Dubins and Spanier [2], Foley [3] and Sen [5]). We present here two examples of economies in which no Pareto optimal allocation is fair, even in the absence of externalities, non convexities or other deviations from the classical Arrow-Debreu environment. In the first example there are two consumers, one consumption good and two kinds of labour (one for each consumer). The production possibilities of the economy are characterized by the constant returns to scale technology set {(x, y, z) E R3 I x ul(x,, 0, z1) for x1 >0 and (0, 0, z1 +x1), (0, Y2, z2) is also feasible. Similarly, Y2 0 is incompatible with Pareto optimality because u2(0, Y2+s, Z2-8/10)>U2(0, Y2, Z2) for any 0 u2(0, Y2, 0) as z1 > 1 _ Y2. We are left with the case of Y2 = 1 where any Pareto optimal allocation is of the form (0, 0, z1), (0, 1, z2) and Z +Z2 = 1. Noting that the definition of fairness means that each consumer evaluates the bundles of other consumers from his own point of view, the first individual will look at the bundle (0, 1, Z2) of the second as involving the consumption of one unit of leisure and Z2 units of the consumption good (i.e. as though it were (1, 0, Z2)). Therefore, in order for the allocations under consideration to be fair from the point of view of the first individual, it must be true that 1 Iz1/l0 ? 1 + 1 lz2/10. Similarly, fairness from the point of view of the second individual requires 1+ 2z2 > 2z1. These two inequalities are incompatible (as they imply 1/2+ z2 > z1 ? 10/Il +Z2). This completes our first counterexample. In our second example, in order to illustrate that the result does not depend on permuting commodities when applying the fairness criterion, utility is assumed to depend only on consumption goods. Leisure as such does not yield direct utility but as the consumption (as well as the production) process is time-consuming, leisure time is a necessary input to the welfare of consumers. There are now five commodities: time, two types of labour services and two different consumption goods. Along the lines of the previous example,

Membrane-active polypeptides from snake venom: Cardiotoxins and haemocytotoxins

Abstract: On a isole a partir du venin de serpents un nombre de polypeptides fortement basiques, a poids moleculaire reduit, qui n'exhibent pas d'activite enzymatique, ne sont pas neurotoxiques et ont un effet lethal modere. Neanmoins, ces polypeptides sont hemolytiques, cytotoxiques et cardiotoxiques. Il semble que ces polypeptides excercent leur action au niveau de la membrane cellulaire en modifiant sa structure. Ces modifications structurales sont a la base des changements des proprietes membranaires telles que permeabilite, transport, excitabilite et activite enzymatique. De plus, les polypeptides basiques excercent une action synergique avec un enzyme present dans le venin, la phospholipase A2. Sous l'action combinee des polypeptides et de la phospholipase, les phospholipides membranaires deviennent susceptibles a l'hydrolyse par l'enzyme. Deux mecanismes permettant d'expliquer le mode d'action des polypeptides sur les membranes cellulaires ont ete proposes: 1. les polypeptides, grâce a leur structure reunissant basicite et residus lipophyliques, modifient la membrane en la penetrant; 2. l'alteration de la membrane est la consequence d'une interaction des groupes S-S des polypeptides avec les groupes-SH membranaires.

Existence of salt glands in various genera of the gramineae

Abstract: SUMMARY Salt glands were observed in twenty-five species belonging to the Chlorideae, Sporoboleae and Aeluropodeae tribes of the Gramineae. Most of those species are presently glycophytes, and the possession of salt glands suggests that they had a common halophytic ancestor.

Vacuum Polarization and the Absence of Free Quarks in Four-Dimensions

Abstract: We speculate that the mechanism of one-dimensional quantum electrodynamics for prohibiting quark production can be generalized to three-dimensional space. The important feature of one-dimensional gauge theories which trap quarks is that electric flux lines cannot spread out and can only end on a charge. The generalization to three dimensions involves dynamical nonlinearities which trap electric flux lines into tubelike configurations. It is suggested that the required nonlinearities arise in Yang-Mills theories of "colored" quarks. The large-scale properties of hadrons would be described by a stringlike model similar to the conventional dual model.

The Rādhānite Merchants and the Land of Rādhān

Abstract: The Rddhdnites: From east to west. It is now more than ioo years since Ibn Khurdldhbe's book was first edited, by the French orientalist Barbier de Meynard. Seventeen years before this first edition, the fragment dealing with the "Jewish merchants called Rddhdnites" had been translated by another French orientalist, J. T. Reinaud, and thus brought to the attention of western scholarship. That fragment has since been the subject of a continuous discussion among scholars. According to Ibn Khurdddhbe, who wrote around the middle of the ninth century, these Rddhdnite merchants operated along several routes, stretching from the lands of Firanja and Andalus, i.e. Western Europe, to China in the Far East. The ramifications of these routes reached to the

High-order concept formation in the pigeon.

Abstract: After 30 days of operant training, with pecking responses to aerial photographs containing man-made objects reinforced with food, and no food reinforcement for pecking on photographs not containing man-made objects, a discrimination to the two classes of photographs was obtained. The discriminative response generalized to photographs with which the pigeons had no previous experience. This study demonstrates that pigeons are capable of forming relatively high-order concepts. Some possible stimulus properties controlling the discrimination are discussed.

Superconducting phase transitions in granular systems

Abstract: We consider a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers. We obtain systematically the various critical regions, critical temperature shifts, and crossover regions between zero- and three-dimensional behavior as functions of measurable sample parameters. The qualitative behavior of the system in the various regimes is analyzed and results for the specific heat and fluctuation conductivity in the Gaussian region above ${T}_{c}$ are obtained. The possibility of obtaining large critical regions is emphasized. The conditions for observing the phase-locking transition distinct from quasiordering within the grains are found. Theoretical predictions are compared with existing experimental results.

Human Pancreatic Proteolytic Enzymes and Protein Inhibitors

Abstract: The purification of human proteolytic enzymes, i.e. two trypsins, two chymotrypsins and at least one elastase from activated extracts of human pancreas has been accomplished by a combination of affinity chromatography and conventional ion-exchange chromatography on SE-Sephadex. The enzymes thus obtained were homogeneous by several criteria: gel electrophoresis, equilibrium sedimentation and immunological assay. The molecular weight and amino-acid composition of each preparation was determined and compared with those of other mammalian enzymes. The two trypsins showed only partial immunological identity while the two chymotrypsins were identical immunologically. The data raises the question of the number of the zymogens present in the human pancreas. In addition to the proteolytic enzymes, four protein inhibitors of proteolytic enzymes were also isolated from human pancreas. The procedure consisted of several steps that included gel filtration, affinity chromatography and isoelectric focusing. The two major components which accounted for most of the trypsin inhibitory activity were characterized and were apparently of the Kazal type. The more basic human pancreatic inhibitor had a pI of 8.7 and contained 48 amino acids with a molecular weight of 5200. The more acidic inhibitor had a pI of 6.5 and contained 39 amino acids with a molecular weight of 4300. Both inhibitors were capable of inhibiting bovine and two human trypsins. They did not inhibit two human chymotrypsins but had a weak capacity to inhibit bovine chymotrypsin.

Dose dependence of thermoluminescence peaks

Abstract: The dependence on the excitation dose of the maximum thermoluminescence intensity as well as of the peak temperature are investigated theoretically. It is shown that certain irregularities of the dose dependences can be explained by assuming the existence of a trapping level, the transition into which competes with the retrapping and recombination of the free carriers. By numerical solution of the appropriate equations, it is demonstrated that the maximum thermoluminescence intensity may depend super-linearly on the excitation dose. The power of the dose dependence was found to be 2 under certain circumstances at low doses, and reached even higher values before saturation of the competing level. The maximum temperature sometimes behaved in an unusual way; namely, it increased with increasing dose. The relation between the area under a glow peak and its maximum intensity is also studied; it is shown that the latter can usually serve as a measure for the former. This finding is of practical importance, especially in thermoluminescent dosimetry, since the evaluation of the maximum intensity is obviously more convenient than that of the area.

Optimal Priority-Purchasing and Pricing Decisions in Nonmonopoly and Monopoly Queues

Abstract: An M/M/1 service station computer center consists of M separate queues. The ith i = 1, 2, ', M queue has priority over the jth iff i

Biosociology and ecology of pomacentrid fishes around the Sinai Peninsula (northern Red Sea)

Abstract: Pomacentrid fishes inhabiting the coral formations along the Red Sea coast of Sinai Peninsula form specific groups of species on various habitats. Amphirion bicinctus, Dascyllus aruanus, D. marginatus and Pomacentrus trichourus are typical for the backreef lagoon; Pomacentrus sulfureus, Abudefduf melanopus and A. melas are common along the rearreef wall; Pomacentrus albicaudatus, P. tripunctatus, Abudefduf lacrymatus, A. leucozona and A. annulatus dominate the coral reef table. The forereef wall is occupied by Abudefduf saxatilis, A. sexfasciatus and A. leucogaster. The lower part of the forereef and coral knolls along it are inhabited by groups of Abudefduf azysron, Chromis dimidiatus, C. caeruleus, C. ternatensis and of the Dascyllus trimaculatus. Among the fishes observed a part are living in groups or schools, whereas others are typical solitary, permanent territory holders. Most of them are polygamous, breeding in colonies, or solitary in nests, guarded by males. The variation in feeding behaviour as well as in sociobiology, enables the high diversity of these fishes on various parts of the habitat.

Ecology of the northern Red Sea crinoids and their Epi- and Endozoic fauna

Abstract: Fourteen crinoid species are found along the coral reefs of the northern Red Sea that form aggregations of different species at various depths. The shallowest aggregation consists partly of Lamprometra klunzingeri and Capillaster multiradiatus, occurring subtidal to a depth of 2 to 5 m. Of this group, Heterometra savignii inhabits depths down to 12–15 m. Further down, another group of 10-armed crinoids occurs, dominated by Decametra chadwicki and Oligometra serripinna. The deepest aggregation of crinoids occurs at 45 m; its most common members are Colobometra arabica and Comaster distinctus. Feeding on micro- and nanoplankton, shallow-water crinoids show a circadian activity rhythm; in deeper aggregations (10 to 12 m), this behaviour changes with decreasing illumination, to a diurnal activity rhythm. The symbiotic animals living on crinoids comprise 27 taxons, among them Copepoda (6 species), Mollusca (2 species), Polychaeta (11 species, especially Myzostomida); Ophiurida (1 species), Crustacea, Decapoda (6 species); and the clingfish Lepadichthys lineatus. These symbiotic animals form food webs at various depths, according to the distribution of their crinoid host. The occurrence of Indo-West Pacific and Mediterranean commensals on the same crinoid in the Gulf of Aqaba is of special interest.

Chiral magnetism (or magnetohadrochironics)

Abstract: In the infinite-momentum frame a hadron may be viewed as a one-dimensional stringlike structure composed of many constituents We consider the dynamics of such a system and show how a spontaneous breakdown of chiral symmetry may occur The effect is very similar to ferromagnetism We formulate the theory of the distribution of quantum numbers in hadrons and establish the relation between this theory, chiral magnetism, soft-pion theorems, Regge behavior, and duality In particular we show how the Harari-Gilman-Weinberg theory of chiral representation mixing follows from an approximation analogous to the treatment of a magnetic impurity in a ferromagnetic system The first stage of approximation, when applied to a quark-parton system leads to a $\overline{q}q$ meson model We demonstrate the need for spin-orbit coupling in the infinite-momentum quark system Higher approximations are expected to lead to exotic states A necessary consequence of our theory of spontaneous chiral-symmetry breakdown is the existence of a Pomeron-like vacuum trajectory with unit intercept The natural order of magnitude of high-energy meson-meson total cross sections turns out to be ${{f}_{\ensuremath{\pi}}}^{\ensuremath{-}2}=10$ mb, as conjectured by Pagels A specific model included in an appendix yields ${\ensuremath{\sigma}}_{\mathrm{tot}}(\ensuremath{\pi}\ensuremath{\pi})=2{{f}_{\ensuremath{\pi}}}^{\ensuremath{-}2}$ We do not explicitly deal with strangeness, or S${\mathrm{U}}_{3}$

Simple siliceous pneumoconiosis in Negev Bedouins.

Abstract: The purpose of this retrospective study is to evaluate the siliceous dust content in the lungs of a population for whom the Negev formed permanent habitat. The material consisted of 54 Bedouin autopsy lung specimens. The microscopical study revealed the presence of silica dust particles in the lung tissue distributed in the lymphatic bed in early involvement and in fibrous scars in advanced involvement. No classical collagenous silicotic nodules could be observed. The preponderant involvement of Bedouin women was explained by their habitual higher exposure to siliceous desert dust. It is suggested that the harmlessness of the dust accumulated in Bedouin lungs is due to its being “old dust” particles less than 5μ in diameter that had originated from dunes of the Negev desert. The benignity of this nonclinical entity prompted us to name it simple siliceous pneumoconiosis.