Showing papers by "Ben-Gurion University of the Negev published in 1994"

Determinants of stated willingness to pay for public goods: A study in the headline method.

Abstract: Respondents were shown brief statements ("headlines") referring to various threats to the environment or to public health, and other public issues. An intervention to deal with each problem was also introduced by a single sentence. Some respondents were asked to indicate their willingness to pay for the interventions by voluntary contributions. Others indicated their opinion of the intervention on a conventional rating scale, rated the personal satisfaction of contributing to it, or rated the importance of the problem. Group averages of these response measures were obtained for a large set of issues. Computed over issues, the rank-order correlations between the different measures were very high, suggesting that group averages of WTP and of other opinion statements are measures of the same public attitudes. Observed preference reversals and violations of monotonicity in contributions are better explained by a concept of attitude than by the notion of economic value that underlies the contingent valuation method. Contributions and purchases do not follow the same logic. Possible implications for the contingent valuation method are discussed.

Regular linear systems with feedback

Abstract: We consider a rather general class of infinite-dimensional linear systems, called regular linear systems, for which convenient representations are known to exist both in time and in the frequency domain. We introduce and study the concept of admissible feedback operator for such a system and of well-posedness radius. We show that the closed-loop system obtained from a regular linear system with an admissible feedback operator is again regular and we describe the relationship between the generating operators of the open-loop and closed-loop systems.

Strategies of seed dispersal and germination in plants inhabiting deserts

Abstract: Massive seed consumption is typical in many deserts. The “escape” or “protection” strategies of seed dispersal are important, as they prevent massive seed consumption. The more extreme the desert, the more unpredictable the low amounts and distribution of the rains as well as the beginning and length of the season or seasons with rains. Seeds, which have the highest resistance to extreme environmental conditions, develop during germination into seedlings, which are the most sensitive. Therefore, germination of parts of the seed population at their respective proper times spreads the risk over time and is thus very important for plant survival, especially in those plants inhabiting the more extreme deserts. Each of the plant species studied was found to have its own survival strategies of seed dispersal and germination. At least two extreme seed-dispersal and germination strategies have been observed: 1) the “escape” seed dispersal and “opportunistic” portioned seed-germination strategies, such as inSchismus arabicas andSpergularia diandra, and 2) the “cautious” portioned dispersal by rain of the protected seeds, such as inAsteriscus hierochunticus and portioned dispersal and rapid germination strategies such as inBlepharis spp. The fate of future generations, as far as the germinability of seeds of some species is concerned, depends on the influences of maternal and environmental factors when the seeds are still on the mother plant, mostly during the final stage of seed maturation, as inTrigonella arabica. It may even depend on the position of the caryopsis from which the mother plant originated, as inAegilops geniculata. The dry post-maturation conditions and the environmental factors during seed wetting and germination may also affect the percentage of seed germination, as inSchismus arabicus.

Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements

Abstract: Ground-based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California. Stratospheric aerosol was introduced after the eruption of Mount Pinatubo in June 1991. Therefore measurements taken before the eruption are used to analyze the properties of tropospheric aerosol; measurements from 1992 are also used to detect the particle size and concentration of stratospheric aerosol. The measurements are used to retrieve the size distribution and the scattering phase function at large scattering angles of the undisturbed aerosol particles. The retrieved properties represent an average on the entire atmospheric column. A comparison between the retrieved phase function for a scattering angle of 120 deg, with phase function predicted from the retrieved size distribution, is used to test the assumption of particle homogeneity and sphericity in radiative transfer models (Mie theory). The effect was found to be small (20% +/- 15%). For the stratospheric aerosol (sulfates), as expected, the phase function was very well predicted using the Mie theory. A model with a power law distribution, based on the spectral dependence of the optical thickness, alpha, cannot estimate accurately the phase function (up to 50% error for lambda = 0.87 microns). Before the Pinatubo eruption the ratio between the volumes of sulfate and coarse particles was very well correlated with alpha. The Pinatubo stratospheric aerosol destroyed this correlation. The aerosol optical properties are compared with analysis of the size, shape, and composition of the individual particles by electron microscopy of in situ samples. The measured volume size distribution before the injection of stratospheric aerosol consistently show two modes, sulfate particles with r(sub m) less than 0.2 microns and coarse paritcles with r(sub m) greater than 0.7 microns. The 'window' in the tropospheric aerosol in this radius range was used to observe a stable stratospheric aerosol in 1992, with r(sub m) approximately 0.5 microns. A combination of such optical thickness and sky measurements can be used to assess the direct forcing and the climatic impact of aerosol. Systematic inversion for the key aerosol types (sulfates, smoke, dust, and maritime aerosol) of the size distribution and phase function can give the relationship between the aerosol physical and optical properties that can be used to compute the radiative forcing. This forcing can be validated in dedicated field experiments.

Hydrophobic docking: A proposed enhancement to molecular recognition techniques

Abstract: In the classical procedures for predicting the structure of protein complexes two molecules are brought in contact at multiple relative positions, the extent of complementarity (geometric and/or energy) at the surface of contact is assessed at each position, and the best fits are retrieved. In view of the higher occurrence of hydrophobic groups at contact sites, their contribution results in more intermolecular atom-atom contacts per unit area for correct matches than for false positive fits. The hydrophobic groups are also potentially less flexible at the surface. Thus, from a practical point of view, a partial representation of the molecules based on hydrophobic groups should improve the quality of the results in finding molecular recognition sites, as compared to full representation. We tested this proposal by applying the idea to an existing geometric fit procedure and compared the results obtained with full vs. hydrophobic representations of molecules in known molecular complexes. The hydrophobic docking yielded distinctly higher signal-to-noise ratio so that the correct match is discriminated better from false positive fits. It appears that nonhydrophobic groups contribute more to false matches. The results are discussed in terms of their relevance to molecular recognition techniques as compared to energy calculations.

Referrals for alternative therapies.

Abstract: Background The purpose of this study was to examine how allopathic physicians participate in the decision to refer patients for alternative therapies. Methods A pretested, self-administered, structured questionnaire was distributed simultaneously to all area physicians at community locations in Washington State, New Mexico, and southern Israel. The primary outcome measures were monthly and yearly rates of referral to alternative therapies. Results More than 60% of all physicians made referrals to alternative providers at least once in the preceding year and 38% in the preceding month. Referrals were generally based on patient requests, synergy between the alternative therapy and the patients' cultural beliefs, failure of conventional treatment, and the belief that patients have "nonorganic" or "psychological" disease. There was no relationship between the rate of referral and the referring physician's level of knowledge about, beliefs about the effectiveness of, or familiarity with alternative therapies. Conclusions Primary care physicians are more likely than other medical specialists to be knowledgeable about, personally subscribe to, and refer patients for alternative therapies. Physicians who use alternative techniques for themselves and their families or who adopt complementary therapies into their practices have higher rates of referrals. Referral rates and patterns were similar between sites despite considerable cross-cultural and health system differences. Given the high rate of referral and the absence of an apparent internal logic for such recommendations, guidelines and physician education may be advisable.

Marginal conditional stochastic dominance

Abstract: This paper introduces the concept of Marginal Conditional Stochastic Dominance MCSD, which states the conditions under which all risk-averse individuals, when presented with a given portfolio, prefer to increase the share of one risky asset over that of another. MCSD rules also answer the question of whether all risk-averse individuals include a new asset in their portfolio when assets' returns are correlated. MCSD criteria are expressed in terms of the probability distributions of the assets and of the underlying portfolio. An empirical application of MCSD is provided using stocks traded on the New York Stock Exchange. MCSD rules are used to show that, in the long run, one cannot assert that the market portfolio is inefficient.

A current-controlled variable-inductor for high frequency resonant power circuits

Abstract: The practicality of designing a bias-controlled inductor, suitable for high frequency resonant mode inverters and converters, was investigated theoretically and experimentally. The proposed variable inductor is built around a double 'E' core structure with zero mutual coupling between the main inductor windings and the bias windings. The theoretical analysis of this study lead to a simple equivalent circuit and closed form equations that express the relationship between the inductance and the controlling bias current. Excellent agreement was found between model predictions and experimental results. >

Endogenously generated and visually guided saccades after lesions of the human frontal eye fields

Abstract: Nine patients with chronic, unilateral lesions of the dorso-lateral prefrontal cortex including the frontal eye fields (FEF) made saccades toward contralesional and ipsilesional fields. The saccades were either voluntarily directed in response to arrows in the center of a visual display, or were reflexively summoned by a peripheral visual signal. Saccade latencies were compared to those made by seven neurologic control patients with chronic, unilateral lesions of dorsolateral prefrontal cortex sparing the FEF, and by 13 normal control subjects. In both the normal and neurologic control subjects, reflexive saccades had shorter Latencies than voluntary saccades. In the FEF lesion patients, voluntary saccades had longer latencies toward the contralesional field than toward the ipsilesional field. The opposite pattern was found for reflexive saccades: latencies of saccades to targets in the contralesional field were shorter than saccades summoned to ipsilesional targets. Reflexive saccades toward the ipsilesional field had abnormally prolonged latencies; they were comparable to the latencies observed for voluntary Saccades. The effect of FEF lesions on saccacles contrasted with those observed in a second experiment requiring a key press response: FEF lesion patients were slower in making key press responses to signals detected in the contralesional field. To assess covert attention and preparatory set the effects of precues providing advance information were measured in both saccade and key press experiments. Neither patient group showed any deficiency in using precues to shift attention or to prepare saccades. The FEF facilitates the generation of voluntary saccatles and also inhibits reflexive saccades to exogenous signals. FEF lesions may disinhibit the ipsilesional midbrain which in turn may inhibit the opposite colliculus to slow reflexive saccades toward the ipsilesional field.

The requirement for phospholipase A2 for activation of the assembled NADPH oxidase in human neutrophils.

Abstract: Phospholipase A2 (PLA2) inhibitors suppressed simultaneously, in a dose-dependent manner, the activation of NADPH oxidase and the release of 3H-labelled arachidonic acid ([3H]AA) stimulated by either phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan (OZ) in human neutrophils. In spite of total inhibition of superoxide production in the presence of the PLA2 inhibitors, 10 microM bromophenacyl bromide (BPB) or 20 microM quinacrine, a maximal phosphorylation of p47 and translocation of p47 and p67 to the neutrophil membranes induced by PMA or OZ was observed. Addition of 10 microM free AA, which by itself did not stimulate superoxide generation, restored oxidase activity in neutrophils treated with PLA2 inhibitors. These findings indicate that phosphorylation and translocation of the cytosolic factors to the membranes are not sufficient for generating superoxide; a functional PLA2 is also needed to stimulate the oxidase activity. The inhibition of PLA2 activity did not prevent the phosphorylation of p47, suggesting that the location of PLA2 is downstream of and does not activate protein kinase C.

Core and Peripheral-Populations and Global Climate-Change

Abstract: Environmental conditions outside the periphery of a species' distribution prevent population persistence, hence peripheral populations live under conditions different from those of core populations. Peripheral areas are characterized by variable and unstable conditions, relative to core areas. Peripheral populations are expected to be genetically more variable, since the variable conditions induce fluctuating selection, which maintains high genetic diversity. Alternatively, due to marginal ecological conditions at the periphery, populations there are small and isolated; the within-population diversity is low, but the between-population genetic diversity is high due to genetic drift. It is also likely that peripheral populations evolve resistance to extreme conditions. Thus, peripheral populations rather than core ones may be resistant to environmental extremes and changes, such as global climate change induced by the anthropogenically emitted ''greenhouse gases''. They should be treated as a biogenetic resource used for rehabilitation and restoration of damaged ecosystems. Climatic transition zones are characterized by a high incidence of species represented by peripheral populations, and therefore should be conserved now as repositories of these resources, to be used in the future for mitigating undesirable effects of global climate change. Preliminary research revealed high phenotypic variability and high genetic diversity in peripheral populations relative to core populations of wild barley and the chukar partridge, respectively.

Proximity clouds—an acceleration technique for 3D grid traversal

Abstract: In this paper we present a new method for the acceleration of ray traversal through a regular 3D grid. A distance transformation is precomputed and mapped onto the empty grid space. A ray traversing the empty space is assisted by the distance values which permit it to perform long skips along the ray direction. We show that the City-Block metric simplifies the preprocessing with no penalty at the traversal phase. Different schemes are discussed and the trade-off between the preprocessing time and the speed-up is analyzed.

Types of Roles in Small Groups A Bit of History and a Current Perspective

Abstract: The types of roles played by members of small groups have been describedfrom a number of different perspectives. Most of the research has been based on laboratory or therapy-like groups in their "t...

Cardiac abnormalities in the Bardet-Biedl syndrome: echocardiographic studies of 22 patients.

Abstract: The Bardet-Biedl syndrome is an autosomal recessive disorder of polydactyly, obesity, tapetoretinal degeneration, mental retardation, hypogenitalism, and renal involvement. A high incidence of congenital and acquired heart disease was reported in the former "Laurence-Moon-Biedl-Bardet" syndrome. However, since the establishment of the Bardet-Biedl syndrome as a separate clinical entity, cardiac involvement has not been evaluated in this disorder. We have performed echocardiographic studies on 22 patients with the Bardet-Biedl syndrome from three extended, highly inbred Bedouin families. In addition to previously reported congenital heart defects we have observed hypertrophy of the interventricular septum and dilated cardiomyopathy. Our findings of cardiac involvement in 50% of the cases suggest that echocardiographic examination should be included in the clinical evaluation and follow-up of patients with Bardet-Biedl syndrome.

Foraging Under Predation - a Comparison of Energetic and Predation Costs in Rodent Communities of the Negev and Sonoran Deserts

Abstract: We used patch-use theory, giving-up densities in experimental food patches, and harvest-rate measurements within these patches to determine the relative contributions of predation risk and energy to foraging costs in four species of rodents from communities in the Sonoran and Negev deserts. To partition costs into components of energy and predation, we converted field measurements of giving-up densities into harvest rates (J min(-1)), used these harvest rates as an estimate of total foraging costs, estimated energetic foraging costs from published physiological measurements of activity and thermoregulatory costs, and assumed that missed opportunity costs were either zero or negative. Our results showed that predation costs predominate. Energetic costs represented only 24%, 19%, 16% and 13% of the foraging costs for Merriam's kangaroo rat (Dipodornys merriami; Sonoran), the round-tailed ground squirrel (Spermophilus tereticaudus; Sonoran), the greater Egyptian sand gerbil (Gerbillus pyramidum; Negev), and Allenby's gerbil (G. allenbyi; Negev), respectively. Equally important were predation-risk differences between bush and open microhabitats; the microhabitat differences in predation cost were often 2-4 times larger than the animals' energetic costs. Seasonal patterns in foraging costs also were predominantly influenced by predation rather than energetic costs. Predation costs appear to be greater in the Negev Desert, but rodents of the Sonoran desert experience greater seasonal and microhabitat variability in predation costs. As a result, predation risk may contribute more towards species coexistence in the community of the Sonoran Desert than that of the Negev Desert.

The Role of Predation in Shaping the Behavior, Morphology and Community Organization of Desert Rodents

Abstract: Predation greatly influences many aspects of the ecology of desert rodents, from foraging behaviour to mechanisms of species coexistence to the evolution of specialised morphologies. Using a foraging-theory approach, we examine consequences of predation for assemblages of desert rodents from North America and the Middle East. In particular, we review experimental evidence that examines the influence of predation on foraging costs and foraging behaviour, explore how predation can act to structure communities, and discuss the role that predation may have played in the evolution of bipedal locomotion. Finally, we compare the importance of predation for the evolution of anti-predator behaviours and morphology, for population dynamics, and for community processes, with its magnitude and heterogeneity. In regard to foraging behaviour, desert rodents treat the risk of predation as a cost of foraging. They combine assessments of food and safety to arrive at foraging decisions, exploiting resource patches less intensively in response to increased predatory risk. The cost of predation can be up to 91% of the foraging costs of desert rodents, but the proportion is greater for Middle Eastern rodents than for North American rodents. In regard to community structure, predation can provide the niche axis as well as the necessary tradeoff for species coexistence. Despite the importance of predation in shaping the foraging behaviour of desert rodents, predation may not always influence species coexistence. Predation contributes to species coexistence at sites in the Sonoran and Great Basin deserts. But in the Negev Desert, where predation costs are the greatest, predation does not provide a mechanism of species coexistence. In regard to bipedal locomotion, predation most likely confers superior ability to avoid predators by improving sprint speed and ability to take evasive action, but at the expense of foraging ability in safe microhabitats. The evolution of bipedality will be favoured by situations where the risk of predation is great: the open microhabitat is riskier than the bush, the richest patches are found in the riskiest places, and rich patches are far apart. The magnitude of predatory risk will affect the evolution of anti-predator behaviour and morphologies. However, the importance of predation in community processes is not determined by its magnitude, but by its heterogeneity in time and space relative to the abilities of potentially coexisting species.