Showing papers by "Bar-Ilan University published in 1988"

Memory effects in propagation of optical waves through disordered media.

Abstract: We verify experimentally for optical waves the striking memory effect predicted very recently by Feng, Kane, Lee, and Stone. We present data for both transmission and reflection, and find general agreement with the theoretical predictions for the linear scale dependence and asymptotic exponential falloff of the memory effect. The theoretical and experimental results suggest that significant information about the spatial variation of the incident waveform is preserved during passage through a highly disordered, strongly multiply scattering medium.

Chapter 7 Patterns of structural change

Abstract: Publisher Summary This chapter presents a discussion on the patterns of structural transformation during the transition from a low income, agrarian rural economy to an industrial urban economy with substantially higher per capita income. The chapter presents a review on the basic concepts of the empirical research program into the economic structure of developing countries during the transition process, which originated with the monumental work of Simon Kuznets. The chapter discusses methodological issues of empirical research on structural transformation. A summary of the main stylized facts of development, with emphasis on growth, accumulation, and sector proportions is presented. Attempts to model and explain the transformation are also presented. The chapter also discusses relative prices and the role of the state in facilitating, fostering, or at times hampering, an efficient transformation. Development economics can be characterized as dealing with issues of structure and growth in less developed countries. Analysis of structure appears in two variants. The first, and more recent, is concerned with the functioning of economies, their markets, institutions, mechanisms for allocating resources, income generation and its distribution, and so on. In the second variant, economic development is seen as an interrelated set of long-run processes of structural transformation that accompany growth. The central features of this approach are economy-wide phenomena such as industrialization, urbanization, and agricultural transformation, regarded as elements of what Kuznets identified as “modern economic growth.”

Social support and self-esteem in adolescence.

Abstract: This study assessed contingencies in the effect of social support from parents and friends on adolescent self-esteem Questionnaires were administered to 76 Israeli adolescents regarding self-esteem, stressful life events, and perceived level of support from mother, father, and friends Maternal support had a strong effect on self-esteem Aid from friends was influential primarily when that of mothers was absent Paternal support had little effect, once other support sources were controlled Despite the negative influence of stress on self-esteem, support and stress had no interactive effects These findings, consistent with attachment theory and social provision theories, were contrary to cross-pressure or separate world models of peer/parent influence

Potts-glass models of neural networks.

Abstract: The theory of neural networks is extended to include discrete neurons with more than two discrete states. The dynamics of such systems are studied. The maximum number of storage patterns is found to be proportional to Nq(q-1), where q is the number of Potts states and N is the size of the network. The properties of the Potts neural network are compared with the Ising case, and the similarity between the Potts neural network and a diluted multineuron interacting Hopfield model is discussed.

Labour Migration as a Response to Relative Deprivation

Abstract: In this paper we define the relative deprivation of a person with income y as an increasing function of the percentage of individuals in the person's reference group whose income is larger than y. We obtain his satisfaction by adding up the marginal utilities of income over the range of income a person possesses. We model migration from one reference group to another as a response to relative deprivation and satisfaction: We say that a strong incentive to migrate exists if relative deprivation decreases while satisfaction rises with migration and that a weak incentive exists if the individual increases or decreases his satisfaction and deprivation at the same time by migrating. We derive conditions under which different incentives, weak or strong, hold for different individuals. We obtain the result that in general the richest individual in a society will not have a strong incentive to migrate but may have a weak incentive to migrate, whereas the poorest individual may have a strong incentive to migrate and also a weak incentive to migrate. Our analysis enables us to explain several perplexing migratory phenomena, identify income inequality as a distinct explanatory variable of migration and establish an incentive to migrate in situations where the utility-social welfare approach does not.

Labour migration as a response to relative deprivation.

Abstract: In this paper we define the relative deprivation of a person with income y as an increasing function of the percentage of individuals in the person's reference group whose income is larger than y. We obtain his satisfaction by adding up the marginal utilities of income over the range of income a person possesses. We model migration from one reference group to another as a response to relative deprivation and satisfaction: We say that a strong incentive to migrate exists if relative deprivation decreases while satisfaction rises with migration and that a weak incentive exists if the individual increases or decreases his satisfaction and deprivation at the same time by migrating. We derive conditions under which different incentives, weak or strong, hold for different individuals. We obtain the result that in general the richest individual in a society will not have a strong incentive to migrate but may have a weak incentive to migrate, whereas the poorest individual may have a strong incentive to migrate and also a weak incentive to migrate. Our analysis enables us to explain several perplexing migratory phenomena, identify income inequality as a distinct explanatory variable of migration and establish an incentive to migrate in situations where the utility-social welfare approach does not.

Validity of self‐assessment: a field evaluation

Abstract: This study evaluated the validity of self-assessment in a natural setting. It also addressed the possibility of improving the utility of self-assessment by cautioning subjects that their responses could be compared with other existing data on them. Subjects were 357 males, aged 18–19 years, who were being screened for a prestigious military course. During the screening, they participated in small groups for nine days of tests, class exercises, and field simulations supervised by veteran commanders. On the ninth day, ratings were collected from commanders, peer group members, and the subjects themselves on dimensions related to eventual success in the training course. The experimental group was told their reports would be compared with those from other sources; the control group was not. Predictive and convergent validities were examined on three criteria: course success, commander ratings, and peer evaluations. Self-assessments from both experimental and control group were valid; however, those of the experimental group did not yield consistently higher validities. Findings are discussed in regard to their practical ramifications.

Reactance and helplessness following exposure to unsolvable problems: The effects of attributional style.

Abstract: I assessed the effects of internal-external attributional style and amount of unsolvable problems on subsequent task performance. Undergraduate subjects were divided according to their attributional style for bad events into internal, nondefined, and external attributors and were exposed to either one, four, or no unsolvable problems. Following exposure to a single unsolvable problem, internal attributors exhibited greater frustration and hostility and better performance in a subsequent cognitive task than did external attributors. Following exposure to four unsolvable problems, internal attributors exhibited stronger feelings of incompetence and a decrease in performance compared with external attributors. The results are discussed in terms of Wortman and Brehm's (1975) approach to reactance and helplessness.

Photon migration in layered media

Abstract: Surface emission profiles and related functions are computed for particles (photons) migrating within a semiinfinite medium containing a surface layer whose absorbance differs from that of the underlying layer Photons are assumed to be inserted at a single point on the surface In certain cases distinct features appear in the emission profiles which enable determination of the thickness of the top layer and of the absorption coefficients of both layers Computations are performed to provide estimates of parameter ranges for which the presence of one layer distorts photon emission profiles from the other Several ancillary functions are calculated, including the absorbance profile as a function of depth, the expected path length of photons that are reemitted at a distance rho from the point of insertion, and the average depth probed by those reemitted photons

The topology of performance curves during 72 hours of sleep loss: A memory and search task

Abstract: Three levels of working memory load of a visual search (Memory and Search) task were tested in a 72-hour sleep deprivation paradigm. General performance and accuracy decrease over time with monoton...

Molecular-dynamics study of Rayleigh-Bénard convection.

Abstract: Fully developed convective rolls have been observed in microscopic simulations of a hard-disk fluid driven by opposed temperature and gravitational fields. Under certain conditions a relatively long-lived mode with higher wave number is found to occur instead of the familiar square-cross-section rolls; this mode eventually undergoes a transition to the preferred square-roll state.

The in-vivo-nerve response to direct low-energy-laser irradiation.

Abstract: To study the in-vivo effects of direct Low-Energy Laser Irradiation (LELI) on the Peripheral Nervous System, the sciatic nerve in rats was surgically exposed, crushed and then subjected to the direct irradiation of either of two continuous-wave HeNe lasers--0.3 mW or 17 mW. We found that the 0.3 mW laser significantly boosts the electrical activity in both the injured and non-injured nerves. The temperature changes of the nerve were measured during irradiation, and no thermal effect was detected. These findings could have direct therapeutic applications in various surgical situations.

Stability and change in interaction of Israeli mothers and infants

Abstract: The current study describes the developmental trends of specific nurturant behaviors, defined as mediated learning experience (MLE), of mothers towards their infants over a period of 18 months and compares them across different caregiving situations Observations of molar sequences of meaningful behaviors, preselected on the basis of Feuerstein's theory of MLE (1979a) were conducted in unstructured home environments of 40 middle-class Israeli infants when they were 6, 12, and 24 months of age Each observation consisted of mother-infant interactions during a feeding, a bathing, and a play situation The MLEs were generally found to increase with age between 6 and 24 months, regardless of the different caregiving situations studied Exceptions were noted at age 24 months, when significantly more MLEs were observed at play than in the other caregiving situations, and at 12 months, when mediated feelings of competence during feeding were found to be more frequent than at 6 or 24 months Mothers were also highly consistent in the amount of MLE they provided at each age level and for the various situations Finally, differences in styles of mediation were observed between mothers identified as either high or low mediators The results demonstrate the advantages of a molar, rather than molecular, approach to monitoring parent-infant interactions that are critical to the child's healthy psychosocial development

Duration measures for specific term structure estimations and applications to bond portfolio immunization

Abstract: This paper explores duration measures which are induced by a polynomial approximation to the stochastic process that governs the term structure. The paper reaches two main conclusions: (1) Complete immunization is possible only by holding a zero coupon bond if the polynomial is of a degree which is not less than two. Hence, for such polynomials, measures of immunization risk should be used to construct portfolios so as to minimize these risks. (2) The paper derives risk measures based on the polynomial stochastic process. It explores their connection to the Fong– Vasicek risk measure. This measure is a particular case of the risk measures developed here and is shown not to measure risk effectively for some stochastic processes.

Reduced bovine pancreatic trypsin inhibitor has a compact structure.

Abstract: The conformation of reduced bovine pancreatic trypsin inhibitor (R-BPTI) under reducing conditions was monitored by measurements of nonradiative excitation energy-transfer efficiencies (E) between a donor probe attached to the N-terminal Arg1 residue and an acceptor attached to one of the lysine residues (15, 26, 41, or 46) [Amir, D., & Haas, E. (1987) Biochemistry 26, 2162-2175]. High-excitation energy-transfer efficiencies that approach those found in the native state were obtained for the reduced labeled BPTI derivatives in 0.5 M guanidine hydrochloride (Gdn.HCl) and 4 mM DTT. Unlike the dependence expected for a random coil chain, E does not decrease as a function of the number of residues between the labeled sites. The efficiency of energy transfer between probes attached to residues 1 and 15 in the reduced state is higher than that found for the same pair of sites in the native state or reduced unfolded (in 6 M Gdn.HCl) state. This segment also shows high dynamic flexibility. These results indicate that the overall structure of reduced BPTI under folding (but still reducing) conditions shows a high population of conformers with interprobe distances similar to those of the native state. Reduced BPTI seems to be in a molten globule state characterized by a flexible, compact structure, which probably reorganizes into the native structure when the folding is allowed to proceed under oxidizing conditions.

Real Shocks, Efficient Risk Sharing, and the Duration of Labor Contracts

Abstract: It is widely believed that increased uncertainty leads to shorter duration of labor contracts. This is indeed also the result obtained in the formal analysis in Gray [1978], who concludes that "[a]s expected, increased variability-regardless of source-shortens contract length" [1978, p. 8]. The basic argument is that production is inefficient, unless the real wage happens to equate the demand and supply of labor, and that the loss due to inefficient production increases with the deviation of the actual real wage from the real wage that would equate the demand and supply of labor. It is assumed that the economy is exposed to both aggregate real shocks and nominal shocks, but that the wage can only be indexed to the general price level, an imperfect signal of the underlying shocks. Since uncertainty is greater for more distant periods, the deviation of the actual real wage from the real wage that would equate the demand and supply also tends to be greater for more distant periods, and it follows that the per period expected loss due to inefficient production increases with contract duration. Consequently, increased uncertainty provides an incentive to reduce contract durations. The reason contracts do not become arbitrarily short is the existence of a fixed contracting cost that militates against shortening the contract duration. The oil-price hikes of 1973 and 1978 presumably increased the a priori importance of aggregate real shocks, and the efficientproduction hypothesis therefore leads one to expect a decrease in contract durations in the years following the price hikes. The empirical fact, however, is that there has been no such tendency, at least not in the United States. This is clearly brought out in Table I, which shows that the average duration of major collective bargaining settlements negotiated in 1972-1987 has remained roughly constant.'

Does contact with the mentally ill affect nurses' attitudes to mental illness?

Abstract: This study examines the effects of contact on nurses' attitudes towards psychiatric patients. Three groups of nurses with differing degrees of contact answered the Attitude towards Mental Illness (AMI) questionnaire. No differences were found among the three groups. Practical nurses, nurses with less experience and religious nurses held more positive attitudes.

Causal attribution, cognitive interference, and the generalization of learned helplessness.

Abstract: We assessed the role of off-task cognitions in mediating the performance effects of global and specific attributions for failure. In Experiment 1, subjects were divided into global and specific attributors and were exposed to either no feedback or failure feedback. In Experiment 2, subjects were exposed to no feedback or to unsolvable problems wherein they received attribution for failure to specific or global causes. Experiment 3 added a condition in which subjects were restrained from engaging in off-task cognitions. Results showed that exposure to unsolvable problems deteriorated performance and increased off-task cognitions mainly among subjects who attributed failure to global causes. In addition, the enhancement of off-task cognitions interfered with performance following unsolvable problems. The introduction of instructions that discouraged subjects from engaging in off-task cognitions eliminated the detrimental effects of global attribution. Results are discussed in terms of test anxiety and excuse-making conceptualizations of learned helplessness.

Production of F1 and F2 diploid gynogenetic tilapias and analysis of the Hertwig curve obtained using ultraviolet irradiated sperm

Abstract: In this study, a Hertwig effect with a non-typical biphasic curve was obtained using sperm irradiated with increasing intensities of UV. The first phase of the UV curve appeared to be quite different from that normally demonstrated using γ or x-ray irradiation. This difference is characterised throughout the length of the first phase by (1) low and stable embryo hatching rates of about 3.5%, and (2) exclusive formation of haploid embryos at any irradiation intensity. Additionally, at both phases, the ability of the sperm to induce morula formation was not affected at all, and no aneuploidy nor chromosomal fragments could be seen. Therefore, it was suggested that in this fish the lethal effect of UV irradition on sperm is mainly expressed on early differentiative events during embryogenesis, which lead to a degeneration of the embryos during early stages of their development. The possible mechanism by which haploidy is achieved during the first phase is discussed. Two generations of diploid gynogenetic tilapias were induced by activating Oreochromis aureus eggs with UV-irradiated O. niloticus sperm and by using the heat-shock technique, at optimized conditions, for the prevention of the second polar body extrusion. Species specific dominant genetic markers (serum esterases and tail striation) were used to confirm the exclusive content of the maternal genome in gynogenetic offspring. Very low survival rates (0.36%) were shown in F1 gynogenetic fish as well as a high incidence of malformations among survivors. In the second gynogenetic generation, both significantly higher survival rates (3.6%) and a considerably reduced incidence of malformations were obtained. We suggest that low frequencies of recombination occur in this species and cause a rapid increase in the inbreeding level. This is followed by the expression of lethal and defective genes that are considerably reduced after second generation selection.

Photoinduced degradation and modification of Photofrin II in cells in vitro.

Abstract: — Human cells of the line NHIK 3025 were incubated with Photofrin II (PII) and exposed to light. Fluorescence- and absorption spectra of PII in the cells were measured. Light exposure resulted in a degradation of PII in the cells and changes in the shape of the fluorescence spectra. These changes are probably partly due to a photochemical modification of PII and to a relocalization of PII in the cells. Notably, a destruction of binding sites for PII on or close to proteins was caused by the light exposure. The rate of the light-induced decay of the porphyrin fluorescence intensity was only slightly increasing with the PII concentration, indicating that each porphyrin molecule is mainly degraded by photoproducts originating from itself. On the other hand, the rate of the degradation of porphyrin binding sites on the proteins increased with increasing PII concentrations. The excitation spectrum of PII in cells has a peak at285–290 nm attributed to energy transfer from proteins to porphyrins located close to the proteins. The intensity of this peak relative to the intensity of the Soret band increases with decreasing porphyrin concentrations. This might indicate that some of the binding sites close to proteins have a higher affinity for the porphyrin than binding sites at longer distances from the proteins.

Bridging the Gap: A General Theory of Second Language Learning

Abstract: This article explores the requirements for a general theory of second language learning that can account both for the fact that people can learn more than one language and for the generalizable individual differences that occur in such learning. Such a general theory will be able to explain and describe differences between second and foreign language learning, between learning for general and special purposes, between formal and informal learning, and between developing knowledge and skills. It will need to be precise and clear on the nature of the goals and outcomes of learning and to recognize the complexity of the concept of knowing a second language, which can vary almost without restriction in both kind and amount. The model must be integrated and interactive, to assume that all or many parts of it apply to any specific kind of learning and that there is close interaction among the various parts. The theory proposed allows for a formally valued eclecticism, provided by the use of a preference model. This article considers the formalization of such a model in an expert system and the more recent implications of the Parallel Distributed Processing model.

Decomposition process in Negev ecosystems.

Abstract: The effects of supplemental water and natural rainfall on decomposition were studied in the Negev Highland desert, Israel. There was a mass loss of approximately 40% in Hammada scoparia leaves and Salsola inermis litter placed on the soil surface and buried in fine mesh bags. There was an annual mass loss of 80% in S. inermis litter buried in large fiberglass mesh bags. Supplemental water provided during the wet season (January to March) did not result in more rapid decomposition of litter of the annual grass Stipa capensis but irrigation during the dry season (August to September) produced a marked increase in the decomposition rate of S. capensis. These data suggest that rain events, not water quantity, are the most important regulators of decomposition in the Negev. Annual rates of decomposition were higher than predicted by models utilizing actual evapotranspiration and lignin content as regulating variables. Rates of decomposition were equal to those reported for tropical wet forests.