Showing papers by "Ben-Gurion University of the Negev published in 1993"

Sliding order and sliding accuracy in sliding mode control

Abstract: The synthesis of a control algorithm that stirs a nonlinear system to a given manifold and keeps it within this constraint is considered. Usually, what is called sliding mode is employed in such synthesis. This sliding mode is characterized, in practice, by a high-frequency switching of the control. It turns out that the deviation of the system from its prescribed constraints (sliding accuracy) is proportional to the switching time delay. A new class of sliding modes and algorithms is presented and the concept of sliding mode order is introduced. These algorithms feature a bounded control continuously depending on time, with discontinuities only in the control derivative. It is also shown that the sliding accuracy is proportional to the square of the switching time delay.

Stated Willingness to Pay for Public Goods: A Psychological Perspective

Abstract: In the contingent valuation method for the valuation of public goods, survey respondents are asked to indicate the amount they are willing to pay (WTP) for the provision of a good. We contrast economic and psychological analyses of WTP and describe a study in which respondents indicated their WTP to prevent or to remedy threats to public health or to the environment, attributed either to human or to natural causes. WTP was significantly higher when the cause of a harm was human, though the effect was not large. The means of WTP for 16 issues were highly correlated with the means of other measures of attitude, including a simple rating of the importance of the threat. The responses are better described as expressions of attitudes than as indications of economic value, contrary to the assumptions of the contingent valuation method.

Quantitative remote sensing methods for real-time monitoring of inland waters quality

Abstract: Spaceborne remote sensing of inland water quality is based on the assumption that the relationship between the reflectance and the concentration of relevant water quality constituents is known a priori. Simultaneous measurements of the upwelling and downwelling irradiances, along with phytoplankton chlorophyll-a, suspended matter and dissolved organic matter concentration at over 20 water bodies throughout former USSR, Hungary, Germany and Bulgaria, are reported in this article. The measurements cover different trophic states of water bodies, from oligotrophic to hypertrophic, and different climatic conditions. The range of chlorophyll-a is 0·1 to 350 mgm-3, suspended matter is 0·1 to 66mg1-1, and dissolved organic matter absorption at the wavelength 380nm is 0·1 to 12m-1. All radiometric measurements are performed with a single radiometer in the 400-750 nm range with spectral resolution better than 1 nm. Factor and signature analysis, as well as multi-spectral statistical modelling of water qual...

ECG compression using long-term prediction

Abstract: A new algorithm for ECG signal compression is introduced. The compression system is based on the subautoregression (SAR) model, known also as the long-term prediction (LTP) model. The periodicity of the ECG signal is employed in order to further reduce redundancy, thus yielding high compression ratios. The suggested algorithm was evaluated using an in-house database. Very low bit rates on the order of 70 b/s are achieved with a relatively low reconstruction error (percent RMS difference-PRD) of less than 10%. The algorithm was compared, using the same database, with the conventional linear prediction (short-term prediction-STP) method, and was found superior at any bit rate. The suggested algorithm can be considered a generalization of the recently published average beat subtraction method. >

Perceived Political Climate and Job Attitudes

Abstract: The present study examines the relationships between perceived Organizational Politics (OP) and job attitudes. Questionnaires containing scales of perceived OP climate and job attitudes were administered to a sample of 200 employees in several organizations. It was found that variables reflecting on the employee's status in the organization such as Gender and Supervisory Position moderate the relationships between perceptions of organizational politics and job attitudes. The association between climate and negative job attitudes was stronger for employees of lower status than for those of a higher status. It was speculated that organizational politics has a potentially damaging effect on lower status employees, who react to a climate of politics by showing increasingly negative attitudes towards the organization.

Very high rates of bedload sediment transport by ephemeral desert rivers

Abstract: GEOMORPHOLOGISTS have thought for some time that rates of sediment transfer might differ markedly in ephemeral and perennial rivers, and have used this idea to explain both the changing character of sedimentary successions and the morphology of rivers in sub-humid or semi-arid areas that have experienced significant shifts in climate during the Quaternary period1−5 But until now there has been a lack of suitable field data to confirm this suggestion, mainly because floods in arid zones are infrequent and unpredictable Here we present bedload sediment transport data for an ephemeral river in Israel, which show it to be, on average, as much as 400 times more efficient at transporting coarse material than its perennial counterparts in humid zones This suggests that existing predictive sediment transport equations24, developed and calibrated exclusively with data obtained in perennial rivers, are inadequate for application to rivers in arid environments It also suggests that areas that are at risk of shifting from sub-humid to semi-arid conditions as a result of prospective global changes in climate may suffer severe sedimentation problems

Lichenoid drug eruptions.

Abstract: Lichen planus-like or lichenoid eruptions from certain drugs and compounds can closely mimic idiopathic lichen planus. The patient's history and physical examination, histopathologic criteria, and certain tests can assist in the differentiation between a lichenoid drug eruption and idiopathic lichen planus and in the identification of the offending drug.

A new tubular reactor for mass production of microalgae outdoors

Abstract: A novel reactor for outdoor production of microalgae is described. Air-lift is used for circulation of the culture in transparent tubes lying on the ground and interconnected by a manifold. Dissolved O2 is removed through a gas-separator placed 2.0 m above the tubes and water-spray is used for cooling. The manifold permits short-run durations between leaving the gas separator and re-entering it, preventing thereby damaging accumulation of dissolved oxygen. Day temperature control in summer is attained using water-spray. In winter, temperature in the tubes rises rapidly in the morning, as compared to an open raceway even if placed in a greenhouse. The number of hours along which optimal temperature prevails in the culture throughout the year increased significantly. Very high daily productivity computed on a volumetric basis (e.g. 550 mg dry wt l−1 culture) was obtained and preliminary observations indicate that a significantly higher output, e.g. 1500 mg dry wt l−1 d−1 is attainable. Much more research is required to assess the year-round, sustained productivity attainable in this reactor.

Regenerative Activity in Apical Dendrites of Pyramidal Cells in Neocortex

Abstract: In intracellular recordings from three neocortical pyramidal cells in vitro, intracellular dye injection identified the impalement site as the primary trunk of the apical dendrite. Dendritic recordings displayed two types of regenerative events: relatively fast, low-threshold spikes with amplitudes of 12-69 mV, and slower, higher-threshold spikes up to 80 mV in amplitude. This distinctive dendritic firing pattern was also encountered in six recordings without dye-filled electrodes. Fast spike frequency was extremely sensitive to small changes in membrane potential at the recording site. In one recording, the fast spikes were blocked by 1 microM TTX, while slow events were spared. A computational model of a pyramidal cell was constructed to assist in interpreting the recordings. Simulations suggested that the fast spikes were generated primarily by active Na+ conductance concentrated at a distance from the impalement site, probably in the region of the soma. The low threshold of the fast spikes suggested that Na+ channels also exist in the apical dendrites, where they have a relatively low density. The data strongly imply that there are Ca2+ channels in the apical dendrites.

Linkage of Bardet-Biedl syndrome to chromosome 16q and evidence for non-allelic genetic heterogeneity.

Abstract: Bardet–Biedl syndrome is an autosomal recessive disorder characterized by mental retardation, obesity, retinitis pigmentosa, polydactyly and hypogonadism. Other findings include hypertension, diabetes mellitus and renal and cardiovascular anomalies. We have performed a genome–wide search for linkage in a large inbred Bedouin family. Pairwise analysis established linkage with the locus D16S408 with no recombination and a lod score of 4.2. A multilocus lod score of 5.3 was observed. By demonstrating homozygosity, in all affected individuals, for the same allele of marker D16S408, further support for linkage is found, and the utility of homozygosity mapping using inbred families is demonstrated. In a second family, linkage was excluded at this locus, suggesting non–allelic genetic heterogeneity in this disorder.

Assessment of nonarticular tenderness and prevalence of fibromyalgia in children.

Abstract: Fibromyalgia syndrome (FS) is most common in midlife, but may be seen at any age. Its prevalence and assessment of tenderness in healthy children is not known. We assessed 338 healthy schoolchildren for tenderness thresholds and prevalence of FS. In all children a point count of 18 tender points (TP) was conducted by thumb palpation and tenderness of some of the TP sites as well as control point sites was further assessed using a Chatillon dolorimeter. All children and their parents were questioned about the presence of widespread pain or aching. Children were considered to have FS if they met the American College of Rheumatology (ACR) criteria for diagnosis of FS. Of the 338 children, 21 (6.2%) had FS. Thresholds of tenderness of 9 TP were 5.0 (1.2) (kg) [mean (standard deviation)] for boys vs 3.6 (0.8) (kg) for girls (p < 0.001). Thresholds of tenderness of the control point sites were 7.1 (1.4) (kg) for boys vs 5.5 (1.1) (kg) for girls (p < 0.001). Thresholds of tenderness of TP and control points in the children with FS were 2.5 (0.4) (kg) and 4.2 (0.5) (kg) vs 4.5 (1.2) (kg) and 6.6 (1.4) (kg) respectively in the children without FS (p < 0.001). We suggest that FS is common in the pediatric age group. Boys have lower tenderness than girls; children with FS have lower thresholds for tenderness both at control and TP compared to the subjects without FS.

A controlled trial of the retraining of the sensory function of the hand in stroke patients.

Abstract: A controlled trial of retraining of the sensory function of the hand was undertaken in hemiplegic patients after the period of spontaneous recovery. Twenty hemiplegic patients with sensory deficit in the hand, two or more years after stroke, received systematic retraining three times a week for six weeks. Sensation in the plegic hand was tested before and after this period in these patients and in 19 untreated control patients. The treated group showed large and significant gains on all sensory tests (P < 0.001), while no change occurred in the control group. It is concluded that somatosensory deficit can be alleviated even years after stroke and that rehabilitation for stroke patients should include sensory retraining for those with sensory deficit.

Oviposition habitat selection by the mosquito, Culiseta longiareolata: effects of conspecifics, food and green toad tadpoles

Abstract: . 1. Ovipositing females should choose egg-laying sites which maximize the growth and survivorship of their offspring. Accordingly, they should avoid habitats with high densities of competitors and predators and should choose sites with adequate food. We tested experimentally the oviposition response of the mosquito, Culiseta longiareolata Macquart, to extra food and two species which are both potential competitors and predators of its offspring: conspecific larvae and green toad (Bufo viridis) tadpoles. 2. We conducted the experiment in outdoor artificial pools where wild C. longiareolata females were presented with choices of all combinations of the presence or absence of: (1) C.longiareolata larvae, (2) B.viridis tadpoles, and (3) extra food (a mixture of ground fish food and mouse chow). 3. Oviposition rates averaged approximately 4 times greater in response to extra food. 4. The presence of the tadpoles, particularly later in the experiment when they were larger, caused a significant reduction (approximately 50%) in oviposition rate. 5. We did not detect a statistically significant effect of conspecific larvae on oviposition habitat selection. 6. Our results indicate that Culiseta females choose habitats for oviposition based on food availability. They also tend to avoid habitats containing Bufo tadpoles, presumably to avoid predation and/or competition.

Mechanisms of species coexistence of optimal foragers: temporal partitioning by two species of sand dune gerbils

Abstract: Mechanistic approaches to understanding species coexistence and community structure have recently proved highly successful. We apply this approach to a sand dune community containing two common species of gerbils, Gerbillus allenbyi and G. pyramidum. Previous work suggested that coexistence is based on temporal variability in seed resource density on a daily time scale and a tradeoff of foraging efficiency at high versus low resource abundances. We tested the predictions of this mechanism by quantifying rodent foraging activity and its timing during the night over 6 nights using sand tracking plots, sand tracking strips, and seed trays. We demonstrated temporal partitioning with all three methods

The influence of snakes on the foraging behavior of gerbils

Abstract: Predation may have profound effects on the behavior of prey individuals with consequences for population dynamics and community structure. Here, we report on an experiment in which we examine the response of two gerbil species (Gerbillus allenbyi and G. pyramidum) to the presence of a snake predator, the desert diadema snake (Spalerosophus diadema), and to added illumination (a factor associated with increased risk of predation from owls). We measured rodent foraging behavior by the number of seed trays foraged in each microhabitat and amount of seed resources left in patches following exploitation by gerbils (giving-up densities; GUDs). Fewer seed trays foraged and higher GUDs are indicative of higher perceived predatory risk

New mechanism for electron heating in shocks.

Abstract: Electron trajectories diverge exponentially in a sufficiently small-scale electrostatic field with a static external magnetic field. This electron trajectory instability results in the electron heating in field structure typical for the collisionless shock front ramp. The magnitude of the effect is sufficient to explain the observed heating at the Earth's bow shock and interplanetary shocks. The heating features are consistent with the observations.

Stepwise repolarization from Ca2+ plateaus in neocortical pyramidal cells: evidence for nonhomogeneous distribution of HVA Ca2+ channels in dendrites.

Abstract: Although cortical dendrites have classically been thought of as passive structures, recent evidence suggests that active conductances, including Ca2+ conductance, are also present in the dendritic membrane. To investigate this, we have recorded intracellularly in slices of rat neocortex bathed in 24 mM tetraethylammonium chloride and 1 microM TTX. Under these conditions, pyramidal neurons generated prolonged Ca2+ spikes. In computer simulations, the breakpoint voltage from which the plateau level began to repolarize was closely related to a specific region on the voltage/activation curve of the high-voltage-activated Ca2+ conductance underlying the spike. This modeling result was supported by the experimental observation that substituting Ba2+ for Ca2+ caused a hyperpolarizing shift in breakpoint voltage by 8-10 mV. Often there was stepwise repolarization from the Ca2+ spike to one or more additional plateau levels. In compartmental computer models, this could be simulated by two different mechanisms: (1) the presence of multiple, electrotonically separated sites of Ca2+ spike electrogenesis in the dendritic tree, and (2) the presence of Ca2+ channels with different voltage dependencies in the same compartment. In experiments, brief hyperpolarizing pulses could cut short the high-amplitude plateau without terminating the smaller "steps." This result could be simulated by both computer models. However, only the multicompartmental model could simulate effects of prolonged depolarizing and hyperpolarizing currents on the breakpoint. Thus, the more depolarized the breakpoint, and hence the closer the spike initiation zone to the recording site, the less it was affected by the injected current. In experiments, the ratio of the breakpoint voltages for the different plateau levels was equal to the ratio of the highest repolarization rates. These data indicate that the breakpoint voltage and the time course of repolarization were the same at all the sites of Ca2+ electrogenesis. Our findings provide strong evidence that Ca2+ spike initiation occurs at electrotonically separated "hot spots" in the dendrites, and that voltage dependence of the Ca2+ channels that underlie the spikes is the same at all sites.

Intuitions about penalties and compensation in the context of tort law

Abstract: Students, retired judges, economists, and others made judgments of appropriate penalties and compensation for hypothetical injuries. In some scenarios, compensation was paid by the government and penalties were paid to the government, so the two could differ. Penalties were generally uninfluenced by their deterrent effect on future behavior. Penalties were greater when they were paid directly to the victim than when they were paid to the government. Compensation was affected by whether injuries were caused by people or by nature, or by acts vs. omissions. These effects are not justified according to consequentialist views of penalties and compensation. We suggest that people are overgeneralizing reasonable rules and that such overgeneralization may be involved in perverse effects of tort law.