Showing papers by "Ben-Gurion University of the Negev published in 1989"
TL;DR: In this paper, it was pointed out that neutron-star collisions should synthesize neutron-rich heavy elements, thought to be formed by rapid neutron capture (the r-process), and these collisions should produce neutrino bursts and resultant bursts of gamma rays; the latter should comprise a subclass of observable gamma-ray bursts.
Abstract: It is pointed out here that neutron-star collisions should synthesize neutron-rich heavy elements, thought to be formed by rapid neutron capture (the r-process). Furthermore, these collisions should produce neutrino bursts and resultant bursts of gamma rays; the latter should comprise a subclass of observable gamma-ray bursts. It is argued that observed r-process abundances and gamma-ray burst rates predict rates for these collisions that are both significant and consistent with other estimates.
1,986 citations
TL;DR: With further study, ultrasound may prove useful as a way of externally regulating release rates from polymers in a variety of situations where on-demand release is required.
Abstract: The effect of ultrasound on the degradation of polymers and the release rate of incorporated molecules within those polymers was examined. Up to 5-fold reversible increases in degradation rate and up to 20-fold reversible increases in release rate of incorporated molecules were observed with biodegradable polyanhydrides, polyglycolides, and polylactides. Up to 10-fold reversible increases in release rate of incorporated molecules within nonerodible ethylene/vinyl acetate copolymer were also observed. The release rate increased in proportion to the intensity of ultrasound. Temperature and mixing were relatively unimportant in effecting enhanced polymer degradation, whereas cavitation appeared to play a significant role. Increased release rates were also observed when ultrasound was applied to biodegradable polymers implanted in rats. Histological examination revealed no differences between normal rat skin and rat skin that had been exposed to ultrasonic radiation for 1 hr. With further study, ultrasound may prove useful as a way of externally regulating release rates from polymers in a variety of situations where on-demand release is required.
321 citations
TL;DR: In their review, portrayed as a mosaic, Yehuda Shoenfeld and David Isenberg illustrate the complexity of conditions, outlining the many pieces, genetic, hormonal, immunological and environmental that contribute to auto-immunity and show how their varying combinations lead to diverse diseases.
274 citations
TL;DR: In nitrate-fed wheat, raising the calcium concentration from 2 to 12 mM in the presence of 60 mM salinity produced an 11% increase in growth, which is ascribed to improved nitrate uptake due to calcium protection of the nitrate transporter and was not evident in ammonium-grown wheat.
Abstract: summary
The effect of ammonium and nitrate nutrition on maize and wheat grown hydroponically and salinity stressed was assessed from measurements of growth rate and gas exchange. In both maize and wheat the ammonium-grown plains were much more sensitive to salinity toxicity than nitrate-grown plants particularly when exposed to 60–80 mM salinity. Shoot growth was retarded to a far greater extent than root growth in salinity-stressed plants of both wheat and maize with either nitrogen source.
There was no significant decrease of photosynthetic rate in salinity-stressed plants of either species fed nitrate or ammonium, except in severely wilted plants of both species fed nitrate or ammonium at the highest (80 mM) salinity concentration. The same was true for stomatal conductance, transpiration rate and transpiration ratio (water use efficiency). In nitrate-fed wheat, raising the calcium concentration from 2 to 12 mM in the presence of 60 mM salinity produced an 11% increase in growth. This effect is ascribed to improved nitrate uptake due to calcium protection of the nitrate transporter and was not evident in ammonium-grown wheat. Possible reasons for the differential effects of ammonium and nitrate nutrition are discussed.
151 citations
TL;DR: In this paper, a review of the morphodynamic and genetic classifications of linear dunes is presented, which substantiates three different simple linear dune types: lee dunes, seifs and vegetated linear, each having a different shape and mechanism of formation and elongation.
Abstract: Most geomorphologists and geologists do not differentiate the various types of linear dune and refer to them as one dune type mainly in the terms of linear, longitudinal or seif dunes. In recent morphodynamic and genetic classifications of dunes, all types of linear dunes are lumped under the heading of longitudinal dunes (Wasson and Hyde, 1983; Hunter et al., 1983). This review, however, substantiates three different simple linear dunes - lee dunes, seifs and vegetated- linear - each of which has a different shape and mechanism of formation and elongation.
124 citations
TL;DR: Fission track analysis in combination with subsidence data from the Gulf of Suez basin, indicate that the onset of rift-flank uplift in the northern Red Sea area occurred between 21 and 23 m.y. ago as discussed by the authors.
107 citations
TL;DR: In this paper, the effect of retrogression and reaging on the dislocation structure of 7000-type aluminum alloys was studied using transmission electron microscopy (TEM) and a clear relationship has been found between the presence of dislocations adjacent to grain boundaries and the susceptibility to stress corrosion of 775-type aluminium alloys.
Abstract: The 7000-type aluminum alloys in the T6 temper are known to be highly susceptible to stress-corrosion cracking (SCC). Some years ago, a heat treatment known as retrogression and reaging (RR) was developed by one of the authors (B.C.), providing for enhanced stress-corrosion resistance without any sacrifice of yield or tensile strength in 7075 aluminum alloy. The idea behind the process was based on the suggestion that dislocations developed during quenching from the solution treatment were responsible for susceptibility to stress corrosion. In spite of considerable practical development of the RR process, the above basic hypothesis as to the role of dislocations has never been investigated. In the present work, the effect of the RR treatments on the dislocation structure of 7000-type aluminum alloys was studied using transmission electron microscopy (TEM). A clear relationship has been found between the presence of dislocations adjacent to grain boundaries and the susceptibility to stress corrosion of 7000-type aluminum alloys. The beneficial effect of the RR treatment on the SCC of 7000-type aluminum alloys in the T6 temper is believed to be due to the disappearance of the above dislocations as a result of RR treatment.
104 citations
03 Apr 1989
101 citations
TL;DR: A detailed computational model for learning spatial networks is presented, called the Traveller, which displays the well-known transition from route level to survey level knowledge in learning a new network.
Abstract: A detailed computational model for learning spatial networks is presented. Information is kept in a distributed, modular format: "condition-actions pairs." Knowledge of individual routes consists i...
98 citations
TL;DR: The solubilities of ascorbic, 2-furancarboxylic, glutaric, pimelic, salicylic, and ophthalic acids in water in the 279.15 to 342.15 K temperature range and the apparent molar volumes of the ascorbinic, glutaraic, and pimelic acids at 298.15 k have been determined.
96 citations
TL;DR: In this article, a complete description of determinantal representations of smooth irreducible curves over any algebraically closed field is presented. Butler et al. used the notion of the class of divisors of the vector bundle corresponding to a determinant-al representation; they proved that two determinant representations of a smooth curve F are equivalent if and only if the classes of the corresponding vector bundles coincide.
TL;DR: In this article, the authors considered increasing the heat dissipation of annular fin at a denned magnitude of mass, and four different cross-section shapes were examined, including constant thickness, constant area for heat flow, triangular and parabolic fin shapes.
TL;DR: Experimental data indicate that the relations developed are capable not only of accurately describing the chip temperature for a variety of thermal management strategies, but also of highlighting the impact of specific thermal design features.
Abstract: It is noted that there has been increased use of theta /sub jc/ for the thermal characterization of chip packages. The longevity of theta /sub jc/ can be traced to its simplicity, its utility as a figure of merit, and its convenient use in numerical analysis of packaging configurations. To enhance the utility of this parameter, the distinct contribution of various segments of the 'case' area to the junction temperature is recognized, and this dependence is embodied in a modified- theta /sub jc/ relation. The analytical basis and methodology to be used in obtaining this relation are presented and illustrated by the use of detailed chip package temperatures obtained from numerical analysis of a generic PLCC (plastic leaded clip carrier) package. >
TL;DR: In this paper, a simple model of drug trapping, based on a modification to percolation theory, is proposed, which is qualitatively in agreement with the data, but are unable to predict certain quantitative features.
TL;DR: The results suggest that the idiotypic network and particularly anti‐idiotypic antibodies specific for anti‐DNA common idiotypes found in SLE, play an important role in the induction of SLE in mice.
Abstract: We have recently reported the induction of experimental systemic lupus erythematosus (SLE) in mice by a human anti-DNA monoclonal antibody (mAb) that bears a common idiotype, the 16/6 Id. In the present report we investigated the role of the idiotypic network in the induction of experimental SLE by using a murine anti-idiotypic mAb specific for the 16/6 Id. This anti-idiotypic mAb induced experimental SLE similarly to the 16/6 Id. Thus, following immunization, in addition to 16/6 Id+ antibodies, the mice produced antibodies to various nuclear antigens: single-stranded DNA, double-stranded DNA, poly(I), poly(G), Ro, La, Sm and ribonucleoproteins. Similarly to the 16/6 Id-immunized mice, the mice injected with the anti-16/6 Id mAb exhibited elevated erythrocyte sedimentation rate and leukopenia. The murine anti-16/6 Id mAb was found to be more effective than the 16/6 Id, in causing earlier onset of proteinuria and renal damage. These results suggest that the idiotypic network and particularly anti-idiotypic antibodies specific for anti-DNA common idiotypes found in SLE, play an important role in the induction of SLE in mice.
TL;DR: It seems that polyethylene sleeves have the following advantages over open ponds: high light availability, high rate of heating and cooling, improved turbulence, relative lack of contamination, and prevention of evaporation and hence of fluctuation in salinity.
01 Sep 1989
TL;DR: The possibility of integrating human visual intelligence into the process of encrypting sensitive information by presenting certain visual information to the recipient's eye is discussed, which adds a new dimension to the cryptocomplexity of such a process.
Abstract: The possibility of integrating human visual intelligence into the process of encrypting sensitive information by presenting certain visual information to the recipient's eye is discussed. This adds a new dimension to the cryptocomplexity of such a process. Two implementations are based on this principle are described. The first shows how keys used for encryption can be randomly generated by the transmitter, without the necessity of exchanging them with the legitimate recipient. The keys are 'embedded' in a master key and are recovered from it by the intelligence of the legitimate recipient after he or she uses the master key. No human intelligence can be helpful to a user who does not possess the master key. The second implementation concerns the possibility of creating a secret connection between a numerical key and a specific image (e.g. a face). Such a scheme can be used, for example, in validating the identity of the users of credit cards. >
TL;DR: Activated charcoal adsorption, ultrafiltration and spray drying were used effectively to produce a high quality colourant grade phycocyanin, while activated charcoal adsoreption, ammonium sulphate precipitation, dialysis and chromatography were effective in preparing reagent grade phytochemical.
Abstract: Spirulina biomass was separated into two fractions which may have various uses. A phycocyanin fraction may provide a food colourant and biomarkers, and a protein-rich leftover may be useful as aquaculture feed. Activated charcoal adsorption, ultrafiltration and spray drying were used effectively to produce a high quality colourant grade phycocyanin, while activated charcoal adsorption, ammonium sulphate precipitation, dialysis and chromatography were effective in preparing reagent grade phycocyanin.
TL;DR: The concept that these new LH-RH antagonists can directly inhibit the growth of human mammary tumors and thus might be suitable for the treatment of breast cancer is supported.
Abstract: Various studies support the view that analogs of luteinizing hormone-releasing hormone (LH-RH) exert some direct effects on mammary tumor cells. Recently, new LH-RH antagonists [Ac-D-Nal(2)1,D-Phe(pCl)2,D-Trp3,D-Hci6,D-Ala10]-LH-RH (SB-29) and [Ac-D-Nal(2)1,D-Phe(pCl)2,D-Trp3,D-Cit6,D-Ala10]LH-RH (SB-30), which are devoid of edematogenic effects, were synthesized. In this study, we examined whether these LH-RH antagonists inhibit the proliferation of MDA-MB-231 human mammary tumor cells in culture. [3H]Thymidine incorporation into DNA and cell number were measured. The antagonists induced up to 40% inhibition of [3H]thymidine incorporation in MDA-MB-231 cells. This inhibition was dose-dependent in the 0.3-30 microM range and could be demonstrated after 2 days of incubation in the presence of the peptides. An older antagonist, [Ac-D-Phe(pCl)1,2,D-Trp3,D-Arg6,D-Ala10]-LH-RH (ORG 30276), had a lesser effect, and the agonist des-Gly10-[D-Ser(tBu)6]LH-RH ethylamide (buserelin) had no effect. The antagonists SB-29 and SB-30 also inhibited the rate of cell growth, as measured by cell number, while the LH-RH agonist buserelin had no significant effect. These results support the concept that these new LH-RH antagonists can directly inhibit the growth of human mammary tumors and thus might be suitable for the treatment of breast cancer.
TL;DR: Etude de l'impact potentiel du cannibalisme sur la taille and the structure d'une population captive de carpe (Cyprinus carpio) elevee uniquement avec des aliments secs.
Abstract: Etude de l'impact potentiel du cannibalisme sur la taille et la structure d'une population captive de carpe (Cyprinus carpio) elevee uniquement avec des aliments secs.Discussion des consequences du cannibalisme en pisciculture
TL;DR: A mechanism is proposed for the enzyme that involves irreversible and rate-determining reaction of pyruvate, at a site which accepts 2-ketobutyrate poorly, if at all, to form an intermediate common to all the reactions.
Abstract: Acetohydroxy acid synthase (AHAS, EC 4.1.3.18) isozyme III from Escherichia coli has been studied in steady-state kinetic experiments in which the rates of formation of acetolactate (AL) and acetohydroxybutyrate (AHB) have been determined simultaneously. The ratio between the rates of production of the two alternative products and the concentrations of the substrates pyruvate and 2-ketobutyrate (2KB) leading to them, R, VAHB/VAL = R[( 2KB]/[pyruvate]), was found to be 40 +/- 3 under a wide variety of conditions. Because pyruvate is a common substrate in the reactions leading to both products and competes with 2-ketobutyrate to determine whether AL or AHB is formed, steady-state kinetic studies are unusually informative for this enzyme. At a given pyruvate concentration, the sum of the rates of formation of AL and AHB was nearly independent of the 2-ketobutyrate concentration. On the basis of these results, a mechanism is proposed for the enzyme that involves irreversible and rate-determining reaction of pyruvate, at a site which accepts 2-ketobutyrate poorly, if at all, to form an intermediate common to all the reactions. In the second phase of the reaction, various 2-keto acids can compete for this intermediate to form the respective acetohydroxy acids. 2-Keto acids other than the natural substrates pyruvate and 2-ketobutyrate may also compete, to a greater or lesser extent, in the second phase of the reaction to yield alternative products, e.g., 2-ketovalerate is preferred by about 2.5-fold over pyruvate. However, the presence of an additional keto acid does not affect the relative specificity of the enzyme for pyruvate and 2-ketobutyrate; this further supports the proposed mechanism. The substrate specificity in the second phase is an intrinsic property of the enzyme, unaffected by pH or feedback inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The average daily incidence of stroke was about twice as great on relatively warm days as on relatively cold ones, and this increase may be explained by increases in thromboembolic mechanisms secondary to physiologic changes in response to heat.
Abstract: Clinical observations of the apparent clustering of daily stroke admissions to a regional hospital in an arid climate prompted our investigation of possible meteorologic factors associated with stroke admissions. Daily hospitalization and meteorologic data were studied for 895 patients with stroke admitted to Soroka Medical Center, Beer-Sheva, Israel, during 1981, 1982, and 1983. The average daily incidence of stroke was about twice as great on relatively warm days as on relatively cold ones. This increase may be explained by increases in thromboembolic mechanisms secondary to physiologic changes in response to heat. When heat waves are predicted, information on the added risk for stroke needs to be disseminated to both the population and to health care providers so preventive measures can be instituted. Special attention should be devoted to air conditioning and adequate consumption of liquids, and antiplatelet aggregation medication such as aspirin should be considered.
Journal Article•
TL;DR: It seems that appearance of autoantibodies to ribonucleoproteins in sera of patients infected with Leishmania is not only due to simply polyclonal activation of lymphocytes, but is also the result of a molecular mimicry between leishmanial antigens and ribon nucleoprotein.
Abstract: Sera from 29 patients with visceral leishmaniasis and 14 patients with cutaneous leishmaniasis were tested against a panel of nine nuclear antigens employing an enzyme-linked immunosorbent assay (ELISA). Anti- Sm, RNP, SS-A and SS-B antibodies were present in high titres in 83, 86, 36 and 73 per cent of the patients with visceral leishmaniasis and in 7, 14, 25 and 25 per cent of the patients with cutaneous leishmaniasis. One serum from a patient with visceral leishmaniasis which reacted strongly with Sm, RNP, SS-A and SS-B was examined by immunoblotting on extractable nuclear antigen from Hela cells. This serum binds to nine different antigenic bands (16, 23, 29, 30, 40, 50, 58, 100 and 115 kD). These same antigens were recognized by serum from a patient with systemic lupus erythematosus. The binding of visceral leishmaniasis serum antibodies to ribonucleoproteins was inhibited by prior incubation of serum with either leishmanial membrane antigens, from four different species of Leishmania, or intact cells of Leishmania donovani, implying molecular resemblance between common leishmanial antigens and ribonuclear antigens. It seems that appearance of autoantibodies to ribonucleoproteins in sera of patients infected with Leishmania is not only due to simply polyclonal activation of lymphocytes, but is also the result of a molecular mimicry between leishmanial antigens and ribonucleoproteins.
TL;DR: Pertussis toxin-blockable, carbamylcholine-induced increases in GTP binding capacity were found to be mediated through M1 muscarinic receptors, as M1-selective antagonists were 100-fold more effective than M2 selective antagonists in blocking carbamelcholine effects.
26 Jun 1989
TL;DR: The bilinear model can be used as a simulation tool for fast and efficient computer-aided analysis and design and for the design of microprocessor-based controllers for switched mode converters, with improved transient response.
Abstract: A sampled data model of a switched mode converter applicable for the low-frequency range is presented. The assumption made is that the sampling rate is sufficiently high, as dictated by the sampling theorem. It is shown that the models are linear for small signal operation but represent a bilinear discrete system under large signal conditions. The models could be useful for the design of microprocessor-based controllers for switched mode converters, with improved transient response. Two examples of possible applications of the model are discussed: as a fast and efficient time-domain simulator and as a tool for the analysis and design of a fast turn-on boost converter. Experimental measurement and computer simulation of the responses to large steps of the duty ratio in a boost converter demonstrate the accuracy of the model at the tested low-frequency region. The bilinear model can be used as a simulation tool for fast and efficient computer-aided analysis and design. The main limitation of the model is its restriction to the low-frequency range. >
TL;DR: Investigation of farmers' fields in Ghana and Ivory Coast found the impact of Phenacoccus manihoti Matile-Ferrero on growth and tuber yield of cassava, and the results of its biological control by the exotic parasitoid Epidinocarsis lopezi (De Santis) were investigated.
Abstract: The impact of Phenacoccus manihoti Matile-Ferrero on growth and tuber yield of cassava, and the results of its biological control by the exotic parasitoid Epidinocarsis lopezi (De Santis) were investigated in a survey of 60 farmers' fields in Ghana and Ivory Coast over an area of 180 000 km2 of the savana and forest ecosystems. Twenty-nine variables associated with plant growth, agronomic and environmental factors, and insect populations were recorded. Densities of P. manihoti were closely correlated with stunting of the cassava shoot tips and, less so, with the rate of stunting early in the growing season. With increasing mealybug infestations, average harvest indices declined and populations of E. lopezi and of indigenous coccinellids increased, but parasitoids were found at lower host levels than were predators. The length of time E. lopezi had been present in an area was the most important factor influencing mealybug densities. Thus, P. manihoti populations were significantly lower where E. lopezi had been present for more than half the planting season than in areas where E. lopezi was lacking or had been only recently introduced. A significant proportion of the farmers in the savanna zone, where P. manihoti populations were much higher than in the forest zone, had observed this decline due to E. lopezi. Tuber yield losses due to P. manihoti in the absence of E. lopezi were tentatively estimated at 463 g/plant in the savanna zone. No significant effect was found in the forest region. When E. lopezi was present, average P. manihoti damage scores were reduced significantly, both in the savanna and forest regions. The increase in yields was 228g/plant or about 2.48 t/ha in the savanna region.
TL;DR: In this article, the authors measured the relative viscosities of suspensions of randomly oriented rods in a Newtonian fluid using falling-ball rheometry, and found that the specific viscosity increased with the cube of the volume fraction.
Abstract: The relative viscosities of suspensions of randomly oriented rods in a Newtonian fluid were measured using falling-ball rheometry. The rods were monodisperse and sufficiently large to render colloidal and Brownian forces negligible. Steel and brass ball bearings were dropped along the centreline of cylindrical columns containing the suspensions. The terminal velocities of the falling balls were measured and used to determine the average viscosities of the suspensions. The suspensions behaved as Newtonian fluids in that they were characterized by a constant viscosity. They exhibited a linear relative viscosity-volume fraction relationship for volume fractions less than 0.125, and, for volume fractions between 0.125 and 0.2315, the specific viscosity increased with the cube of the volume fraction. The relative viscosity was found to be independent of falling-ball size for a ratio of falling ball to fibre length greater than 0.3. It was found to be independent of the diameter of the containing cylindrical column for a ratio of column diameter to fibre length greater than 3.2. The value determined for the intrinsic viscosity is in good agreement with theoretical predictions for suspensions of randomly oriented rods.
TL;DR: Response properties of neurons in brain slices of guinea pig parietal neocortex were examined following intracellular injection of the Ca2+ chelators, EGTA and BAPTA, and chelator injection induced 81% of neurons encountered at all sub‐pial depths to become ‘bursters’.
Abstract: Response properties of neurons in brain slices of guinea pig parietal neocortex were examined following intracellular injection of the Ca2+ chelators, EGTA and BAPTA. Although chelator injection did not cause any consistent change in passive membrane properties, it did induce 81% of neurons encountered at all sub-pial depths to become ‘bursters’, in that just-threshold depolarizing current pulses triggered all-or-none bursts of 2–5 fast action potentials. Transition to ‘burstiness’ was associated with disappearance of an AHP and appearance of a DAP. Although chelator caused a slight increase in steady-state firing rate, marked accommodation persisted. Extracellular Co2+ or Mn2+ had an effect on steady-state firing rate similar to that of the intracellular chelators; however, exposure to these Ca2+ channel blockers also caused steady state depolarization, increased resting input resistance and time constant, and profound spike broadening. This treatment never induced transition to ‘burstiness’. Chelator-injected neurons ceased to generate bursts when Ca2+ was replaced by Mn2+ in the Ringer's solution. During exposure to 10−6 M TTX and 20 mM TEA, 50–200 msec Ca2+ spikes followed brief depolarizing pulses. As chelator was injected into the cell, there was progressive prolongation of the Ca2+ plateaus, which was associated with slowing of the rate at which membrane resistance gradually recovered following the initial increase in conductance.
These findings indicate that under normal conditions, activity-related increases in intracellular Ca2+ activate processes which prevent most neocortical neurons from being bursters. These processes probably include Ca2+ -dependent K+ currents, and Ca2+ -dependent Ca2+ channel inactivation.
TL;DR: A study of trait-anxiety and sense of coherence on a group of medical students over 18 mo. shows that, although both characteristics are rather stable over time, the measure of sense ofCoherence is more sensitive to stressors than A-trait and is better predicted by A-Trait than the opposite.
Abstract: A study of trait-anxiety and sense of coherence on a group of medical students over 18 mo. shows that, although both characteristics are rather stable over time, the measure of sense of coherence is more sensitive to stressors than A-trait and is better predicted by A-trait than the opposite.
01 Jan 1989
TL;DR: This study presents a microlevel simulation model for radiological evacuation which incorporates behavioural input and can be used to test traffic management schemes for emergency evacuations much more realistically than the purely engineering-type models.
Abstract: Several radiological and industrial accidents which occurred during the last decade refocussed the attention of various authorities to evacuation preparedness and consequently, elaborate network simulation models have been developed. The modellers, however, recognise that critical variables relating to behaviorual aspects of the evacuees are still missing. This study presents a microlevel simulation model for radiological evacuation which incorporates such behavioural input. Using the SLAM II language to develop a network algorithm, the model estimates network clearance time for two scenarios—early evening and late night, and the role of the behavioural data is examined. The model can be used to test traffic management schemes for emergency evacuations much more realistically than the purely engineering-type models.