Showing papers by "Bar-Ilan University published in 1981"

Light-shade adaptation of Stylophora pistillata, a hermatypic coral from the Gulf of Eilat

Abstract: All reef-forming, or hermatypic, corals harbour photosynthetic endosymbiotic algae called zooxanthellae1–5, which are assumed to be predominantly a single dinoflagellate species, Gymnodinium microadriaticum Freudenthal6. The zooxan-thellae are essential for the well-being of their hosts7–9; nevertheless, little is known about how light affects the symbiotic association, especially regarding the numbers of zooxanthellae, their photosynthetic responses, and their overall productivity10–14. On the reefs of the Gulf of Eilat, Stylophora pistillata is an abundant hermatypic coral15; it is unique in that region in that it can adapt to a wide range of light intensities. In the high light intensities of lagoons or the upper areas of reefs, the corals are markedly lighter in colour than those living under ledges, in grottos, or near the reef floor (∼ 15 m; Fig. 1). We report here on the biochemical and physiological adaptations of S. pistillata to variations in light intensity spanning more than two orders of magnitude.

Impartiality, Justice and Fairness: The Ethics of Concurrent Termination

Abstract: The method of well founded structures for proving termination of programs is extended to concurrent programs. The more complicated case is when a program terminates only for fair executions. Different versions of fairness are introduced: Impartiality, Fairness and Justice, and Methods for proving their termination are presented.

Environmental control of the immune response in fish

Abstract: This review deals essentially with the influence of environmental temperature on the immune response of fish and on their immune resistance to pathogens. The first part of this paper (Sections II and III) is concerned with the resistance of fish to infections and the influence of different natural or experimental stresses, including the influence of the environmental temperature, on both the humoral immune response and the phagocytic apparatus. On the basis of the reported data, as well as field observations, an attempt was made to explain the mechanism of infection in fish. It was stated that microbial contamination, environmental stresses, temperature, and specific immunity are the major determining factors in the infection of fish. Specific immunity may have a palliative action enabling the fish to surmount infection despite the stress; however, it could be reduced or abolished at low temperatures. The second part of this review deals with temperature control of experimentally induced humoral immune re...

Optical second‐harmonic scattering in rat‐tail tendon

Abstract: The angular dependence of optical second-harmonic generation by native, wet, rat-tail tendon is found to display a sharp, intense, forward peak superimposed on a broad background. The sharp peak is shown to imply long-range polar order, while the broad background corresponds to that predicted for the random “up”/“down” array of collagen fibrils seen with the electron microscope. The degree of polar order is determined, and the dependence of the fibril diameter distribution on age and state of hydration is measured. The coherence length of tendon for harmonic generation and the absolute magnitude of the nonlinear susceptibility of the collagen fibril are also determined. The biological significance of these various findings is discussed.

Max-Min Tree Partitioning

Abstract: The max-rain k-partition algorithm may be formulated as follows: Given a tree T with n edges and a nonnegative weight associated with each vertex, assign a cut to each of k distinct edges of T so as to maximize the weight of the lightest resulting connected subtree. An algorithm for this problem is presented which initially assigns all k cuts to one edge incident with a terminal vertex of T; thereafter the cuts are shifted from edge to adjacent edge on the basis of local information. An efficient implementation with complexity O(k 2. rd(T) + kn), where rd(T) is the number of edges in the radius of T, is described. An algorithm for a simpler problem, namely, the partitioning of Tinto the maximum number of connected components whose weight is bounded below, is then described. Combined with the technique of binary search, it yields an alternative algorithm for the max-rain k-partition problem with complexity dependent on the range of the given weights.

Cytokinin interaction with free radical metabolism and senescence: Effects on endogenous lipoxygenase and purine oxidation

Abstract: A typical system comprising xanthine-xanthine oxidase, which produces superoxide free radicals, significantly increased endogenous levels of the senescence-associated lipoxygenase enzyme while cytokinin reversed this effect. It is suggested that in its interaction with free radicals cytokinin may have a dual effect: a) it may inhibit purine oxidation by the formation of a 2,8 dihydroxy purine which lowers the substrate affinity of xanthine oxidase; b) it may act as a direct free radical scavenger by virtue of H abstraction from the α-carbon atom in the amine bond.

Expressive Functional Completeness in Tense Logic (Preliminary report)

Abstract: Consider a partially ordered set (T, <, =), where T is non-empty, < is an irreflexive and transitive relation on T and = is equality. We can regard T as a set of moments of time and < as the earlier-later relation. We refer to any fixed (T, <, =) as a flow of time.

Subgroups of free profinite groups and large subfields of\(\mathop Q\limits^ \sim \)

Abstract: We prove that many subgroups of free profinite groups are free, and use this to give new examples of pseudo-algebraically closed subfields of\(\mathop Q\limits^ \sim \) satisfying Hilbert’s Irreducibility Theorem, and to solve problems posed by M. Jarden and A. Macintyre. We also find a subfield of\(\mathop Q\limits^ \sim \) which does not satisfy Hilbert’s Irreducibility Theorem, but all of whose proper finite extensions do.

Light utilization by phytoplankton in Lake Kinneret (Israel)

Abstract: Seasonal changes in light penetration, photosynthesis, and. related processes were measured in Lake Kinneret, Israel. The efficiency of penetrating ‘light utilization for the trophogenie water column ranged from 0.33 to 4.01% and was highest when cells in high concentrations were close to the surface. The lowest specific photosynthetic assimilation values were associated with the major bloom-forming dinoflagellate, Peridinium cinctum, which dominated the phytoplankton from February to June. On all occasions, in situ photosynthetic efficiencies increased steadily with depth as light intensity decreased in the euphotic zone. The various types of light utilization efficiencies are defined.

An experimental approach for evaluation of the O2 balance in local myocardial regions in vivo.

Abstract: Quantitative evaluation of myocardial oxygen balance can be accomplished by measurement of oxygen supply, demand, and intracellular oxygen concentration. Experimentally, these parameters are often related to coronary blood flow, cardiac contractility, and mitochondrial NADH redox level, respectively. Methods were developed to measure these three parameters in a local region on the myocardial surface in open-chest dogs. Local coronary blood supply was measured with the aid of a small surface thermistor, and cardiac work with a miniature strain gauge arch. NADH oxidation--reduction state was recorded using surface fluorometry through a fibre optic light guide. Transient anoxia produced by nitrogen breathing caused a rapid but reversible elevation in NADH levels, which was not always accompanied by a concomitant change in contractile force. Elevation of heart rate resulted in a rise in intramitochondrial NADH followed by an increase in coronary flow. In spite of the increased flow, NADH levels remained elevated, indicating a change in the O2 balance; this may indicate that autoregulation does not necessarily result in total compensation.

Some Common Characteristics of Latency‐Age Suicidal Children: A Tentative Model Based on Case Study Analyses

Abstract: Eleven latency-age (6 1/2 to 12 1/2) boys and girls who attempted or threatened suicide were investigated by means of the following information: intensive interviews, therapeutic meetings, direct observation in school, meetings with teachers, and survey of school records. The families of the children were also interviewed. In spite of the many differences between the children's personalities and backgrounds, some common dynamic features seemed to emerge: (a) There was a suicidal parent in the family, in most cases the mother; (b) Most of the families of these children were engaged in a major crisis, not necessarily centered around the suicidal child; (c) The children experienced demands by the parents to assume responsibilities which the children perceived as being beyond their capability; (d) There was a lack of satisfying relationships with adults; (e) Most children perceived death in a paradoxical way, believing that death was a need satisfying state yet fearing death; (f) The children showed strong positive strivings to say alive and were able to experience joy and happiness in spite of feelings of desperation and depression. A model based on the above multifaceted forces is presented. These forces consist of attractiveness of life, repulsiveness of life, attractiveness of death, and repulsiveness of death. Some of diagnostic and predictive uses of this model are elaborated.

Study of conformation and intramolecular motility of polypeptides in solution by a novel fluorescence method

Abstract: Linear oligomer and polymer molecules do not as a rule possess a futed conformation in solution. Because of the thermal motion of the chain segments, the overall conformation of each molecule varies constantly, and the distance between the chain ends changes ceaselessly. The extent and rate of such movements depend on the length of the chain, the nature of the backbone. the nature of the end groups, the temperature, the viscosity of the solvent, etc. In the following, we shall adopt the concept of static flexibility to express the repertoire of molecular conformations possessed by an ensemble of linear oligomer or polymer chain molecules at any given instant. This characteristic is essentially time independent. This is distinguished from the concept of dynamic flexibility, which expresses kinetic changes in conformation in a single molecule or a chosen subgroup of molecules in the ensemble. The dynamic flexibility of the chain obviously determines the rate of thermal movements of the chain ends. Conformational transitions in chain molecules predominantly involve rotations around bonds. However, if rotations around a single bond were the only process occurring at a given time. a large part of the chain would have to swing through the viscous medium. The probability of such a process occurring is very low. It was therefore suggested that changes in conformation in polymer chains take place by correlated transitions of a number of bonds. The motions are restricted to a short segment, while the major portion of the chain remains undisturbed.' The common methods used for studying the dimensions of polymeric molecules, such as viscosity, light scattering, or ultracentrifugal sedimentation, are not applicable to oligomers of relatively small molecular weight. The conformations of such molecules are, however, of considerable interest, since they are more amenable to computational analysis by fast computers. Furthermore, since many low molecular weight oligomers, such as some of the native and synthetic peptides, show biological activity, information about their conformation in solution seems of particular interest. Stryer and Haugland2 have suggested that distances of the order of 15-20 8, between definite sites on macromolecules can be derived from the efficiency of transfer of electronic excitation energy by the Forster mechanism3 between suitably chosen chromophoric groups that have been attached to these sites. This is made possible by the relationship given in Equation 1, in which E denotes the efficiency of energy transfer, and r is the distance between the participating chromophores.

Cross-Cultural Differences in Directionality

Abstract: The assumption that the directions of writing single letters and series of letters in a given language affect the directional preferences for reproducing single and multiple stimuli, respectively, was tested on three groups of subjects with different reading and writing habits; English readers, Hebrew readers, and Arabic readers. The subjects were presented with single stimuli and with series of stimuli for reproduction, and the horizontal directions of their responses were recorded. Confirming the hypothesis, the data pointed to the complexities of the effects of reading and writing habits on directional preferences among readers of different languages.

Ultrastructural studies of cyanidwm caldarium: contribution to phylogenesis

Abstract: Cyanidium caldarium, a eukaryotic unicellular alga, has served as a model of an algal pioneer in the dispute concerning the evolutionary relationships among algae.1-7 Indeed, this greenish-bluish fascinating genus has (or lacks) certain analogous homologous cellular phylogenetic markers which tempt its investigators to place this paradoxical organism between the prokaryotic bluegreen and the primitive eukaryotic red Others claim this organism to be an endosymbiont cyanophyte within an unknown host originally lacking chloroplasts.*, l7 Such cyanophytic origin of plastids was fmt proposed nearly 100 years ago.lS My personal interest and involvement in this organism started about a dozen years ago. I was asked by Prof. W. F. Libby of the University of California at Los Angeles to study the possibilities of life on the planet Venus. Our aim was to demonstrate that terrestrial photosynthetic organisms are able to tolerate and survive extreme conditions such as were believed to exist on Venus polar 11 Such organisms had to indicate growth in an atmosphere of pure CO, and at elevated temperature and pressure, as well as in a very acidic media. During our initial investigation with several representatives of the plant kingdom, I received a letter from Prof. L. Bogorad who suggested that we try his \"favorite organism Cyanidium caldarium\" as a candidate for the Venusian project. William N. Doemel, then a graduate student of Prof. T. D. Brock (at Indiana University), sent us axenic cultures of Cyanidium, isolated from samples collected at Norris Geyser Basin of Yellowstone National Park. The primary results of algal growth and physiology in high concentration of C02, elevated temperature, and acidic media were reported to the Eleventh International Botanical Congress (Seattle, Wash., 1969) and elsewhere.ll9 l2 At that Congress I met Prof. R. M. Klein (University of Vermont) who indicated strong interest and was quite excited with our electron micrographs of Cyanidium caldarium. It was he who inspired me to consider a publication on the ultrastructural observations with a taxonomic approach to this topic.s Later, in Jerusalem with Prof. R. Ikan, we studied the fatty acids and sterols of Cyanidium as chemosystematic tools for assessing its position among the algae.9~ l3 The present report and our recent observations at Bar-Ilan University on the micromorphological features of Cyanidium could not have taken place without the perpetual 4, s,

Aggression and its Escalation

Abstract: Physical aggression, its escalation, and felt responsibility for it, were compared in group and individual action of Israeli natives and of European Russian, Caucasian, and Georgian new immigrants to Israel. The experimental paradigm was a modified Buss aggression machine paradigm for measuring physical aggression. Generally, aggression was greater and escalated faster, and felt responsibility was lower, in groups than in individuals. Georgians were the most aggressive and European Russians were the least so. Diffusion of responsibility and its disinhibitory role in collective action was the major explanation. The ethnic differences were seen as reflecting the influence of sociocultural training in aggression (Georgians) versus that of a history of severe punishment for aggression (European Russians).

Personality Characteristics of Sexually Dysfunctioning Males and Their Wives

Abstract: It was hypothesized that males experiencing erectile and/or ejaculatory difficulties would exhibit higher levels of hostility, intrapunitiveness, submis‐siveness, be more sensitive to rejection, and perceive their fate as being dictated largely by external forces (locus of control), when compared to a control group Similar differences were predicted between the dysfunctional males and their wives Further predictions were made concerning differences between wives of the dysfunctioning males and the control wives The sample of 19 dysfunctioning males and their wives were compared with a sample of 25 control males and their wives All were Israeli Jews The predicted differences between patients and controls were found for all variables except submissiveness Sensitivity to rejection and the guilt subtest were particularly important predictors Patients' wives and control wives differed only in aspects of hostility The patients were also more sensitive to rejection than their own wives and regar

Personality Type, Life Events and Sudden Cerebrovascular Attack

Abstract: The severity of cerebrovascular attack (CVA) in patients having no known history of cardiovascular problems tends to be influenced by two factors: (a) recent life events; and (b) “type A” personali...