Showing papers by "Bar-Ilan University published in 1987"

Diffusion in disordered media

Abstract: Diffusion in disordered systems does not follow the classical laws which describe transport in ordered crystalline media, and this leads to many anomalous physical properties. Since the application of percolation theory, the main advances in the understanding of these processes have come from fractal theory. Scaling theories and numerical simulations are important tools to describe diffusion processes (random walks: the 'ant in the labyrinth') on percolation systems and fractals. Different types of disordered systems exhibiting anomalous diffusion are presented (the incipient infinite percolation cluster, diffusion-limited aggregation clusters, lattice animals, and random combs), and scaling theories as well as numerical simulations of greater sophistication are described. Also, diffusion in the presence of singular distributions of transition rates is discussed and related to anomalous diffusion on disordered structures.

On weighted shapley values

Abstract: Nonwmmetric Shapley values for coalitional form games with transferable utility are studied. The nonsymmetries are modeled through nonsymmetric weight systems defined on the players of the games. It is shown axiomatically that two families of solutions of this type are possible. These families are strongly related to each other through the duality relationship on games. While the first family lends itself to applications of nonsymmetric revenue sharing problems the second family is suitable for applications of cost allocation problems. The intersection of these two families consists essentially of the symmetric Shapley value. These families are also char- acterized by a prObabilistic arrival time to the game approach. It is also demonstrated that lack of symmetries may arise naturally when players in a game represent nonequal size constituencies.

Cancer incidence in a cohort of infertile women

Abstract: To explore further the relation between infertility and breast and female reproductive cancers, cancer incidence among 2,632 Israeli women treated for infertility between 1964 and 1974 was evaluated. Cancer incidence through December 1981 was determined by matching the study cohort to the Israel Cancer Registry. The observed number of cancers was compared with sex-age-ethnic and calendar-year, site-specific national cancer rates. There were 42 cancers observed compared with 37.4 expected, yielding a standardized incidence ratio of 1.1 (95% confidence interval (CI) = 0.8-1.5). Analysis by infertility diagnosis demonstrated no significant excess of total cancer incidence; the standardized incidence ratio was 1.3 (95% CI = 0.8-1.8) for infertility due to hormonal deficiency, 0.7 (95% CI = 0.3-1.4) for mechanical infertility, 1.6 (95% CI = 0.6-3.6) for infertility of the male partner, and 1.1 (95% CI = 0.5-2.2) for unclassified diagnosis. Site-specific analyses revealed a significantly increased risk (8.0; 95% CI = 2.5-19.3; four cases observed, 0.50 expected) of endometrial cancer for the hormonal group and a nonsignificant excess of breast cancer and melanoma. Although numbers were small, women with disorders causing unopposed estrogen production had a risk of 1.4 (95% CI = 0.8-2.2) for all cancer sites, which reached 10.3 (95% CI = 2.6-28.2; three cases observed, 0.29 expected) for endometrial cancer and 1.8 (95% CI = 0.8-3.4; eight cases observed, 4.43 expected) for breast cancer. Among women with nonhormonal infertility, there was a suggestion of increased risks of carcinoma of the ovary (3.2; 95% CI = 0.3-32.9; two cases observed, 0.63 expected) and thyroid (3.0; 95% CI = 0.3-24.6; two cases observed; 0.67 expected). No evidence of an association between ovulation-inducing drugs and cancer was found. This study supports the hypothesis that infertility caused by hormone deficiency is a risk factor for uterine cancer, but is inconclusive regarding breast cancer.

Associative recall of memory without errors

Abstract: A neural network which is capable of recalling without errors any set of linearly independent patterns is studied. The network is based on a Hamiltonian version of the model of Personnaz et al. The energy of a state of N (\ifmmode\pm\else\textpm\fi{}1) neurons is the square of the Euclidean distance\char22{}in phase space\char22{}between the state and the linear subspace spanned by the patterns. This energy corresponds to nonlocal updatings of the synapses in the learning mode. Results of the mean-field theory (MFT) of the system as well as computer simulations are presented. The stable and metastable states of the network are studied as a function of ``temperature'' T and \ensuremath{\alpha}=p/N, where p is the number of embedded patterns. The maximum capacity of the network is \ensuremath{\alpha}=1. For all \ensuremath{\alpha} (0\ensuremath{\le}\ensuremath{\alpha}l1) the embedded patterns are not only locally stable but are global minima of the energy. The patterns appear, as metastable states, below a temperature T=${T}_{M}$(\ensuremath{\alpha}). The temperature ${T}_{M}$(\ensuremath{\alpha}) decreases to zero as \ensuremath{\alpha}\ensuremath{\rightarrow}1. The spurious states of the network are studied in detail in the case of random uncorrelated patterns. At finite p, they are identical to the mixture states of Hopfield's model. At finite \ensuremath{\alpha}, a spin-glass phase exists as a metastable state. According to the replica symmetric MFT the spin-glass state becomes degenerate with the patterns at \ensuremath{\alpha}=${\ensuremath{\alpha}}_{g}$=1-2/\ensuremath{\pi} and disappears above it. Possible interpretations of this unusual result are discussed. The average radius of attraction R of the patterns has been determined by computer simulations, for sizes up to N=400. The value of R for 0l\ensuremath{\alpha}l1 depends on the details of the dynamics. Results for both parallel and serial dynamics are presented. In both cases R is unity (the largest distance in phase space by definition) at \ensuremath{\alpha}\ensuremath{\rightarrow}0 and decreases monotonically to zero as \ensuremath{\alpha}\ensuremath{\rightarrow}1. Contrary to the MFT, simulations have not revealed, so far, any singularity in the properties of the spurious states at an intermediate value of \ensuremath{\alpha}.

Destruction of erythroleukaemic cells by photoactivation of endogenous porphyrins

Abstract: Selective destruction of Friend erythroleukaemic cells (FELC) was potentiated by stimulation of endogenous porphyrin synthesis followed by light sensitization. Endogenous porphyrin biosynthesis in FELC was induced by supplementation of 5-amino levulinic acid (5-ALA) at a concentration of 5 X 10(-4) M. The main accumulated product, after 4 days culture, was uroporphyrin, while after 8 days culture the cells were loaded with protoporphyrin, up to 1.5 micrograms 10(-7) cells. Photoirradiation of the cells for 2 min, accumulating endogenous porphyrins, induced cardinal deformations and cell disintegration in greater than 95% of the cells, as examined by scanning electron microscopy (SEM). The photodynamic destruction effects were dependent on cultivation time with 5-ALA. Flow cytometry analysis showed an immediate expansion of cell volume subsequent to irradiation, presumably a consequence of water influx. Transmission electron microscopy (TEM) of photosensitized cells after different time intervals of culture in 5-ALA medium, revealed initial damage to mitochondria and water influx into the nuclear envelope, after 2 days. After 3-4 days in culture the water influx phenomenon was pronounced, chromatin condensation took place and slight rupture of the outer membrane was detected. Cells photosensitized after 5-6 days of culture were completely disintegrated leaving a nuclear remnant and an enormously swollen nuclear envelope. The culture time dependence of the process, showed an interrelationship between the photodynamic effect and porphyrin accumulation sites in cellular compartments. The study presents a specific method for erythroleukaemic cell inactivation.

Dissipation of contestable rents by small numbers of contenders

Abstract: The theory of rent seeking with its origins in the observations of Gordon Tullock (1967) - or to use Jagdish Bhagwati's (1982) proposed term, the theory of directly unproductive profit-seeking activities - is concerned with the potentially adverse effects on resource allocation of incentives to cap- ture and defend artificially-contrived rents and transfers. The scope for so- cial loss proposed by the theory derives from the relation between the value of a contestable prize and the value of the resources attracted into the con- test to determine the beneficiary of the prize. Underlying this social loss is a specification of how rational behavior by optimizing agents links the value of the prize sought to the resources expended. It has been traditional to assume competitive behavior in describing the activities of lobbying and influence seeking. Then, if some further condi- tions are satisfied, l the total value of the resources expended precisely equals the value of the prize sought, so dissipation is complete. 2 Conse- quently, the social cost associated with contestability of a rent can be in- ferred from the value of the rent itself, and the detailed and hard-to-come- by information on individual outlays made in the course of the contest be- comes unnecessary. By basing their analyses on competitive dissipation, contributors to the rent seeking literature (see the review by Robert Tollison, 1982) have been able to presume that the observed value of a contested rent is an exact measure of the associated social cost of monopoly power or regu- lation. Similarly, in the trade-theoretic literature where the rights contested are to quota premia or revenues from trade taxes (Krueger, 1974; Bhagwati

Seeking rents by setting rents: the political economy of rent seeking*

Abstract: In recent years, there has been a large number of papers on the subject of rent seeking. Most such works on rent seeking have taken the rent as exogenously determined by regulators. Regulators, howeve r, may also be expected (and indeed have been shown) to be rent seeke rs and hence the determination of the rent itself should be endogeniz ed to reflect the fact that the rent setters are, themselves, rent se ekers. In this paper, the authors do this by presenting an analysis o f the interaction of regulators, firms, and consumers within a rent-s eeking framework where all three groups are assumed to be self-motiva ted. The analysis is carried out under alternative assumptions regard ing the nature of the market and the reaction functions of the partic ipants. Policy implications are drawn where appropriate. Copyright 1987 by Royal Economic Society.

A new immunomodulating compound (AS-101) with potential therapeutic application

Abstract: There has been interest in the potential of synthetic compounds to modify immune responses by imitation of cytokine action. Direct administration of interleukin 2 (IL-2) in conjunction with adoptive transfer of lymphokine activated killer cells has been used in the treatment of cancer, but there are toxic effects resulting from the high doses of IL-2 required. We have developed a new synthetic compound, ammonium tri-chloro(dioxoethylene-O,O'-)tellurate (AS-101), which has immunomodulating properties and minimal toxicity. The effects of AS-101 on the activation and function of immunocompetent cells have been assessed. We have found that AS-101 induces proliferation and IL-2 production by human lymphocytes in vitro, and enhances the production of IL-2 and colony-stimulating factor by mouse spleen cells. Splenocytes of BALB/c mice injected with AS-101 increased production of IL-2 and CSF in vitro in the presence of mitogen. Mononuclear cells of normal donors acquired responsiveness to recombinant IL-2 and bound monoclonal antibody to IL-2 receptor after incubation with AS-101. Splenocytes of mice treated in vivo with AS-101 expressed high levels of IL-2 receptor. The stimulation of lymphocytes by AS-101 apparently involves an increase in intracellular free calcium. AS-101 administered systemically to mice mediated antitumour effects which could be attributable to its immunomodulatory properties. In addition, AS-101 could directly enhance the ratio of OKT4 to OKT8-positive cells in cultured mononuclear cells from AIDS (acquired immune deficiency syndrome) patients. These results indicate that AS-101 is potentially useful in the treatment of clinical conditions involving immunosuppression.

International migration under asymmetric information.

Abstract: International migration under asymmetric information usually differs from international migration under symmetric information and often quite dramatically so and in counterintuitive ways. Since in real life information is indeed asymmetric it is somewhat surprising that hitherto the study of international migration has by and large proceeded without explicit recognition of the effect of informational asymmetry. In this paper we show that when at the lowest skill level migration is desirable; i.e. if the (discounted) wage differential is positive for the lowest skill level the introduction of asymmetric information results in a reduction of the quality and quantity of international migration or has no effect at all. When at the lowest skill level migration is not desirable--the (discounted) differential is not positive at the lowest skill level--the introduction of asymmetric information may either result in migration by all or none. When under asymmetric information workers can at some cost to themselves report to foreign employers their individual skill--thus dissociate themselves from the group effect--then provided the cost is small either a U pattern of migration with respect to skill level emerges or migration is uniformly pursued by all though some do and some do not invest in signalling. When the source consists of more than 1 (poor) country it is impossible to predict migration under asymmetric information from a given country without explicitly accounting for changes in the parameters of the other. For example a favorable change (encouraging less migration) taking place in 1 country will through a distinct impact on the overall composition of migration reduce migration from the other country. Finally allowing employers to discover after a while the true productivity of individual migrant workers we obtain the somewhat surprising result that (under a reasonable set of assumptions) eventual discovery may increase the quantity and quality of migration and also increase the wage enjoyed by the low quality migrants. Eventual discovery serves to mitigate the impact of group averaging that deters migration by the high skill workers. Due to migration of some such workers the prediscovery wage of the low skill workers arises in our case sufficiently to outweigh the effect of the future wage decline due to discovery. (authors)

Effect of irrigation on nematode population dynamics and activity in desert soils

Abstract: The nematode community in litter and soil was examined for a year in the Chihuahuan desert, before and after supplemental rainfall application. Proportions of nematode-active or anhydrobiotic forms and population densities were determined for 3 treatments: control (natural rainfall), a single, large (25-mm) monthly irrigation pulse, and 4 smaller (6-mm) irrigations spaced at weekly intervals. In litter the greatest nematode abundance was in the 6 mm week−1 treatment (48 nematodes 20 g−1 litter). Bacteriovores and fungivores accounted for approximately 95% of the numbers and biomass in all treatments. In soil, water amendments had no significant effect (P < 0.05) on annual mean densities of total nematodes, fungivores, bacterivores, or omnivore predators. Phytophage densities were greater on both irrigation treatments, with highest densities (9268 m−2) in the 6 mm week−1 soils, which was 5.9% of the total soil nematode density. Total densities of individual trophic groups were not significantly different before or after rainfall. Soil nematode densities fluctuated independently with trophic group, month, and season. Bacterial feeders and omnivore predators were the largest contributor to total soil nematode density and biomass. Prior to irrigation, there were no differences in the percentage of anhydrobiotes on the three treatments. Anhydrobiotes decreased after irrigation in all treatments, and were significantly lower in soils of the larger, monthly irrigation. Nematodes were inactive (anhydrobiotic) and decoupled from decomposition processes when soil water matric potentials reached −0.4 MPa.

Effects of temperature and day length on the mass balance of Antarctic phytoplankton

Abstract: Photosynthesis and respiratory carbon losses of freshly collected Antarctic phytoplankton were measured in incubators at 5 temperatures between-2° C and +8°C. The results were used to predict daily growth rates and to define temperature and daylength boundary conditions under which the net balance between photosynthesis and respiration would be positive and allow increases in standing stock. Whereas the Q10 of photosynthesis was 1.4–2.2, the Q10 of respiratory losses exhibited a wide range and higher maxima (2.3–12). Model calculations sugest that under ample light energy supply during long summer days, potential daily growth rates are not severely affected by the low temperatures prevailing in the Southern Ocean. If energy supply is restricted by short days and deep water column mixing, substantially reduced respiration rates at low temperatures may allow the algae to survive.

A theoretical overview and empirical study of mediated learning experience: Prediction of preschool performance from mother‐infant interaction patterns

Abstract: This research is based on a 4-year longitudinal study of 51 normal, low SES infants and their mothers. It was conducted at the Clinical Infant Development Program sponsored by the Clinical Infant-Child Development Research Center (NIMH-HRSA). Infants' free-play sessions with their mothers were analyzed at 4, 8, 12, 24, and 36 months of age by use of an observation method based on Feuerstein's theory of Mediated Learning Experience (MLE). The participating children were tested with the Bayley Scales (to age 2 years) and the McCarthy Scales (at 36 and 48 months). Ten-minute observations of motherchild interactions, which used molar criteria of observation based on MLE theory, predicted cognitive performance at 2, 3, and 4 years of age. The observation made at 12 months was most predictive of long-term cognitive performance. Mother-infant interaction patterns were less predictive of cognitive performance in infancy than they were of performance at 2, 3, and 4 years of age. Each of the observed MLE criteria increased with age, although the frequency of some of the criteria remained low throughout the study. Stability of all MLE criteria was significant across most comparisons over time.

Elucidation of the two-dimensional structure of an α-amino acid surfactant monolayer on water using synchrotron X-ray diffraction

Abstract: Recently it has been demonstrated that a compressed monolayer of palmitoyl-(R)-lysine (Fig. 1) on the surface of water induces the orientated growth of α-glyeine crystals1. This effect was inter-preted to be a structural match between the monolayer and the α-glycine. To test this hypothesis we undertook to determine the packing arrangement of the monolayer by grazing incidence X-ray diffraction and reflection. These techniques2 use the unique proper-ties of synchrotron radiation: high intensity within a small natural collimation3. In the diffraction experiment two peaks were detect-able in the two-dimensional powder pattern from a monolayer of palmitoyl-(R)-lysine. The positions and intensities of these peaks allowed us to choose between various models and determine the monolayer structure. This is the first time that the crystal structure of a compressed surfactant monolayer at the air–water interface has been determined. The same techniques could be used for structural characterization of other monolayers of interest in fields as diverse as biological membranes4 and optical second harmonic generation5. The packing arrangement of the α-amino acid head groups in the model proved to be very similar to that found in the crystal structures of α-glycine and several hydrophobic α-amino acids.

Specificity of the fucose-binding lectin of Pseudomonas aeruginosa

Abstract: PA-II lectin of Pseudomonas aeruginosa , purified by affinity chromatography, was examined for its relative affinity to various carbohydrates using equilibrium dialysis and hemagglutination inhibition tests. This lectin was found to exhibit a high affinity for l-fucose and its derivatives. Among them, p-nitrophentl-α-l-fucose was the strongest inhibitor, followed by l-fucose →l-fucosylamine l-galactose →d-mannose →?→d-fructose. The association constant ( K a) of l-focuse for PA-II was 1.5 × 106· M−1 and the number of the l-fucose-binding sites per protein subunit was approximately 1. The K a of d-mannose for PA-II was 3.1 × 10−2· M−1 and a value of 0.84 was obtained as the number of its binding sites per mole protein subunit.

Are Social Psychological Laws Cross-Culturally Valid?:

Abstract: The purpose of this study was to evaluate the reproducibility of social psychological findings across cultures and subcultures in order to evaluate the cross-cultural validity of empirically based social psychological laws. Six studies were sampled from four major social psychological journals. Each study was replicated on two Israeli samples, one similar to that of the original study and the other differing in some respect. Results indicate that those original findings that were replicated primarily involved main effects. Interactions were generally not replicated. Those interactions that proved significant were usually in directions different from those obtained in the original studies. These findings indicate the necessity for replications on both cross-cultural and intracultural levels. Methodological aspects of such studies are discussed.

Perceptual and memorial constructs in children's judgments of quantity: a law of across-representation invariance.

Abstract: Children at three different ages made judgments of physically presented (perceptual estimation) or symbolically represented (memorial estimation) rectangles. Height and width were integrated according to different, age-dependent algebraic rules. Memorial data obeyed the same integration rules that operated in the original perceptual judgments even when younger children and older children used completely different combination models. Valuation operations were the same in perception and memory for the youngest group (6-year-olds) but became discriminably different at older ages (for the 8- and 10-year olds). Three additional experiments on judgments of volume, liquid quantity, and visual length yielded strong cross-validation support for the general invariance claim (with respect to integration rule theory) but less strong support for the specific invariance claim (with respect to valuation function for the 6-year-old subjects). Results are interpreted as demonstrating lawful and long-enduring ecological constraints on internal representation.

On the reinforcing value of helping behavior in a positive mood

Abstract: In two separate experiments, each utilizing 33 male high school students, it was found that (a) after offering help, subjects reported that they were in a more positive mood than subjects who were not given the opportunity to help and (b) the proportion of helpers among subjects who expected their positive mood to continue was smaller than among those who did not share such an expectation. These findings are discussed in terms of the Negative State Relief model describing the relationship between mood and helping behavior.

Light absorption and utilization among hermatypic corals: a study in Jamaica, West Indies

Abstract: The chlorophyll specific absorption coefficient ( $$\bar k$$ c) was measured for zooxanthellae from six hermatypic coral species obtained, where possible, from four depths (1, 10, 30, 50 m) on reef sites near Discovery Bay, Jamaica in February and March 1983. Measurements of photosynthetic rates versus irradiance, as well as cellular and areal chlorophyll a, were also performed on these colonies or sister colonies. Together the data were used to compare minimum quantum requirements (1/Φ m) among species and depths and to assess the importance of light utilization to the growth and depth distribution of these corals. Our data suggest that, although $$\bar k$$ c was found to decrease with depth, interspecific differences in $$\bar k$$ c do not occur for zooxanthellae from the corals investigated. Minimum quantum requirements (1/Φ m) decreased significantly with depth, thereby reflecting an increase in photosynthetic light utilization efficiency with decreasing irradiance. Interspecific differences in 1/Φ m determinations were suggested but not statistically conclusive. We conclude that interspecific differences in gross photosynthesis, and perhaps growth and depth distribution, are primarily attributable to differences in the light utilization capacity of the whole coral, as reflected by the product of $$\bar k$$ c ′ and chlorophyll per unit surface area, and in-situ quantum efficiencies.

Photodynamic effects of deuteroporphyrin on Gram-positive bacteria

Abstract: The photodynamic effects of deuteroporphyrin (DT) on the growth and viability ofStaphylococcus aureus, Streptococcus faecalis, andBacillus cereus are described. By exposure to light and DT, the growth ofSta. aureus andStr. Faecalis strains was markedly inhibited, whereasB. cereus was undergoing lysis. Counting the viable bacteria during the DT treatment revealed that more than 99% of the initial bacterial population was killed within the first 30 min of treatment. The pH dependence of the photodynamic inhibitory effect shows that it is best obtained at pH 6.5. No temperature dependence in the range of 37°–44°C could be detected. The best photodynamic effect was achieved when the culture was in the mid-log phase. DT-treated bacteria, when grown in the dark or in the presence of horse serum albumin, were unaffected by the porphyrin action. Electron microscopic examinations ofSta. aureus andStr. faecalis showed the appearance of well-developed mesosomes within the cell cytoplasm.B. cereus preparations have not shown any mesosome formation but showed some lysed cells as well as some spores. None of the mentioned effects by DT and light could be observed on Gramnegative bacteria such asEscherchia coli orPseudomonas aeruginosa.