Showing papers by "Bar-Ilan University published in 2000"

Resilience of the internet to random breakdowns

Abstract: A common property of many large networks, including the Internet, is that the connectivity of the various nodes follows a scale-free power-law distribution, P(k) = ck(-alpha). We study the stability of such networks with respect to crashes, such as random removal of sites. Our approach, based on percolation theory, leads to a general condition for the critical fraction of nodes, p(c), that needs to be removed before the network disintegrates. We show analytically and numerically that for alpha 0.99.

Prototype systems for rechargeable magnesium batteries

Abstract: The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, because it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems Moreover, in contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and safe to handle But the development of Mg batteries has been hindered by two problems First, owing to the chemical activity of Mg, only solutions that neither donate nor accept protons are suitable as electrolytes; but most of these solutions allow the growth of passivating surface films, which inhibit any electrochemical reaction Second, the choice of cathode materials has been limited by the difficulty of intercalating Mg ions in many hosts Following previous studies of the electrochemistry of Mg electrodes in various non-aqueous solutions, and of a variety of intercalation electrodes, we have now developed rechargeable Mg battery systems that show promise for applications The systems comprise electrolyte solutions based on Mg organohaloaluminate salts, and Mg(x)Mo3S4 cathodes, into which Mg ions can be intercalated reversibly, and with relatively fast kinetics We expect that further improvements in the energy density will make these batteries a viable alternative to existing systems

Diffusion and Reactions in Fractals and Disordered Systems

Abstract: Preface Part I. Basic Concepts: 1. Fractals 2. Percolation 3. Random walks and diffusion 4. Beyond random walks Part II. Anomalous Diffusion: 5. Diffusion in the Sierpinski gasket 6. Diffusion in percolation clusters 7. Diffusion in loopless structures 8. Disordered transition rates 9. Biased anomalous diffusion 10. Excluded-volume interactions Part III. Diffusion-Limited Reactions: 11. Classical models of reactions 12. Trapping 13. Simple reaction models 14. Reaction-diffusion fronts Part IV. Diffusion-Limited Coalescence: An Exactly Solvable Model: 15. Coalescence and the IPDF method 16. Irreversible coalescence 17. Reversible coalescence 18. Complete representations of coalescence 19. Finite reaction rates Appendix A. Fractal dimension Appendix B. Number of distinct sites visited by random walks Appendix C. Exact enumeration Appendix D. Long-range correlations References Index.

Loneliness and friendship in high-functioning children with autism.

Abstract: Loneliness and friendship were examined in 22 high-functioning children with autism and 19 typically developing children equated with the autistic children for IQ, CA, gender, mother's education, and ethnicity. Children between the ages of 8 and 14 were asked to report on both their understanding and feelings of loneliness and the quality of their friendship. Compared to typically developing children, children with autism were both lonelier and had less complete understandings of loneliness. Although all children with autism reported having at least one friend, the quality of their friendships was poorer in terms of companionship, security, and help. Fewer associations were found between loneliness and friendship for the autistic than for the non-autistic children, suggesting less understanding of the relation between loneliness and friendship. Implications of these results are discussed for conceptualizing the social deficits in autism.

Sonochemical Synthesis and Characterization of Nanometer-Size Transition Metal Oxides from Metal Acetates

Abstract: Transition metal oxide nanoparticles have been synthesized sonochemically from metal acetates. The metal oxide nanoparticles are characterized using X-ray diffraction (XRD), diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM), and BET nitrogen adsorption. The results of DRS are analyzed in detail, and the band gap energies for CuO, ZnO, and Co3O4 are seen to be 2.18, 3.35, and 2.26 (3.40), respectively. Different particle sizes, morphology, and yields are observed when water and 10% water−N,N-dimethylformamide (DMF) are used as solvents, and the possible mechanisms are discussed.

Correlated and uncorrelated regions in heart-rate fluctuations during sleep.

Abstract: Healthy sleep consists of several stages: deep sleep, light sleep, and rapid eye movement (REM) sleep. Here we show that these sleep stages can be characterized and distinguished by correlations of heart rates separated by $n$ beats. Using the detrended fluctuation analysis (DFA) up to fourth order we find that long-range correlations reminiscent to the wake phase are present only in the REM phase. In the non-REM phases, the heart rates are uncorrelated above the typical breathing cycle time, pointing to a random regulation of the heartbeat during non-REM sleep.

The Study of Surface Phenomena Related to Electrochemical Lithium Intercalation into Li x MO y Host Materials (M = Ni, Mn)

Abstract: The authors report herein on the comparative study of LiNiO{sub 2} and LiMn{sub 2}O{sub 4} electrodes in three salt solutions, namely, LiAsF{sub 6}, LiPF{sub 6}, and LiC(SO{sub 2}CF{sub 3}){sub 3} in a mixture of the commonly used ethylene and dimethyl carbonates. The surface chemistry of the electrodes in these solutions was studied by surface-sensitive Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray analysis, and their electrochemical behavior was studied by variable-scan-rate voltammetry and impedance spectroscopy. It was found that the electrochemical behavior of these electrodes is strongly dependent on their surface chemistry. Complicated reactions between the active mass and solution components, which include the solvents, the salt anions, and unavoidable contaminants such as HF and perhaps, HSO{sub 3}CF{sub 3}, lead to the precipitation of surface films through which the Li ion has to migrate in order to reach the active mass. The impedance spectroscopy of these electrodes clearly reflects their surface chemistry. It demonstrates the serial nature of the Li insertion-deinsertion processes, which includes, in addition to solid-state diffusion and accumulation, Li-ion migration through surface films and their charge transfer across the surface film/active mass interface, which strongly depends on the chemical composition of the surface films andmore » hence, the solution chosen. LiNiO{sub 2} is considerably more reactive with these solutions than LiMn{sub 2}O{sub 4}, probably due to its stronger nucleophilic nature. In addition, in LiPF{sub 6} solutions, the electrodes' impedance is higher due to precipitation of films comprising LiF, which is highly relative to Li ion transport (probably produced by reactions of the Li{sub x}Mo{sub y} active mass with trace HF).« less

Shape-Controlled Synthesis of Silver Nanoparticles by Pulse Sonoelectrochemical Methods

Abstract: Shaped silver nanoparticles with spheres, rods, and dendrites have been prepared by a pulse sonoelectrochemical technique from an aqueous solution of AgNO3 in the presence of nitrilotriacetate N(CH2COOH)3-NTA. The silver nanoparticles were characterized by using transmission electron microscopy, X-ray diffraction, and absorption spectroscopy. The effects of electrosonic time on particle shape have been discussed. It was found that the concentration of AgNO3 and NTA affects the shape of the nanoparticles.

Exploring individual differences in reactions to mortality salience: does attachment style regulate terror management mechanisms?

Abstract: Five studies examined the contribution of attachment style to mortality salience effects. In Study 1, mortality salience led to more severe judgments of transgressions only among anxious-ambivalent and avoidant persons but not among secure persons. In addition, whereas anxious-ambivalent persons showed immediate and delayed increases in severity judgments, avoidant persons showed this response only after a delay period. In Study 2, anxious-ambivalent persons showed immediate and delayed increases in death-thought accessibility after death reminders. Avoidant and secure persons showed this effect only after a delay period. Study 3 revealed that worldview defense in response to mortality salience reduced death-thought accessibility only among avoidant persons. Studies 4-5 revealed that mortality salience led to an increase in the sense of symbolic immortality as well as in the desire of intimacy only among secure persons, but not among avoidant and anxious-ambivalent persons.

Traces and determinants of linear operators

Abstract: A general theory of tracestr D A and determinantsdet D (I+A) in normed algebrasD of operators acting in Banach spacesB is proposed. In this approach trace and determinant are defined as continuous extensions of the corresponding functionals from finite dimensional operators. We characterize the algebras for which such extensions exist and describe sets of possible values of traces and determinants for the same operator in different algebras. In spite of the fact that the extended traces and determinants may differ in different algebrasD, operatorI+A (withA ∈D) is invertible inB if and only ifdet D (I+A) does not vanish. Cramer's rule and formulas for the resolvent are obtained and they are expressed in different algebras by the same formulas viadet D (I+A) andtr D (A). A large set of examples and illustrations are also presented.

Sonochemical Synthesis of SnO2 Nanoparticles and Their Preliminary Study as Li Insertion Electrodes

Abstract: SnO2 semiconductor nanoparticles were synthesized by an ultrasonic irradiation of an aqueous solution of SnCl4 and azodicarbonamide under ambient air. These nanoparticles are ∼3−5 nm in size, as calculated using the Debye−Scherrer formula, and as observed by TEM. The SnO2 nanoparticles were also characterized by powder X-ray diffraction (XRD), reflection spectroscopy and FT-IR spectroscopy, transmission electron microscopy (TEM), DSC, and TGA. The band gap was calculated from reflection spectroscopy. Electrochemical tests were performed using the SnO2 nanoparticles as the electrode's materials in nonaqueous Li salt solutions. The results showed promising reversibility, cycle life and high capacity for lithium insertion into the SnO2 nanoparticles.

Pleistocene milestones on the out-of-Africa corridor at Gesher Benot Ya'aqov, israel.

Abstract: The Acheulean site of Gesher Benot Ya'aqov in the Dead Sea Rift of Israel documents hominin movements and technological development on a corridor between Africa and Eurasia. New age data place the site at 780,000 years ago (oxygen isotope stage 19), considerably older than previous estimates. The archaeological data from the site portray strong affinities with African stone tool traditions. The findings also reflect adroit technical skills and in-depth planning abilities, more advanced and complex than those of earlier archaeological occurrences in the Levant.

Microwave Assisted Preparation of CdSe, PbSe, and Cu2-xSe Nanoparticles

Abstract: Nanoparticles of various dimensions of II−VI binary chalcogenides CdSe, PbSe, and Cu2-xSe, have been prepared by a very simple fast reaction between acetates or sulfates of Cd, Pb, and Cu and Na2SeSO3 in the presence of complexating agents, using microwave irradiation. The nanoparticles were analyzed by X-ray diffraction (XRD), electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).

Micromorphological Studies of Lithium Electrodes in Alkyl Carbonate Solutions Using in Situ Atomic Force Microscopy

Abstract: The morphology of lithium electrodes in a variety of alkyl carbonate solutions was studied using in situ atomic force microscopy (AFM). We made use of a workstation specially built for the study of...

Factors Which Limit the Cycle Life of Rechargeable Lithium (Metal) Batteries

Abstract: Failure mechanisms due to high charging rates of rechargeable lithium batteries comprised of Li metal anodes, cathodes (tunneled structure), and electrolyte solutions based on the combination of 1,3‐dioxolane (DN), , and tributylamine (antipolymerization stabilizer) were explored with the aid of postmortem analysis. It was found that at high charging rates, lithium deposition produces small grains, which are too reactive toward the electrolyte solution, in spite of the excellent passivation of lithium in this solution. In practical batteries such as AA cells with spirally wound configurations, the amount of solution is relatively small, and the solution is spread throughout the battery in a thin layer. Therefore, upon cycling, the Li‐solution reactions deplete the amount of the solution below a critical value, so that only part of the active materials continues to function. This leads to a pronounced increase in the internal resistance of these batteries, which fail as a result of their high impedance and the decrease in the effective working electrodes area. Another failure mechanism relates to the extremely high charge‐discharge current densities developed as the active electrode area decreases. These high currents, developed after prolonged cycling, lead to the formation of dendrites that short‐circuit the battery, thus terminating its life. © 2000 The Electrochemical Society. All rights reserved.

Sonochemical synthesis and characterization of pure nanometer-sized Fe3O4 particles

Abstract: Sonochemical synthesis of pure nanometer-size Fe3O4 powder with particle size of ca 10 nm is reported in this article. Fe3O4 can be simply synthesized by sonication of iron(II)acetate in water under an argon atmosphere. The properties of pure nanometer-size Fe3O4 particles were characterized by X-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA) with an external magnetic field, and quantum design SQUID magnetization measurements. The prepared Fe3O4 nanoparticles are superparamagnetic and its magnetization at room temperature is very low (

Stress and accessibility of proximity-related thoughts: exploring the normative and intraindividual components of attachment theory.

Abstract: Three studies examine the effects of stress on the accessibility of proximity-related thoughts. In all the studies, participants reported on their attachment style, and the accessibility of proximity themes and worries in a lexical decision task was assessed upon the priming of a stress or neutral word. In Study 2, the primed stress word was semantically related to attachment themes. In Study 3, lexical decisions were made under low or high cognitive load conditions. Overall, the priming of a stress word led to increased accessibility of proximity themes, regardless of attachment style. Anxious-ambivalent people also showed high accessibility to proximity themes and worries in both neutral and stress contexts. In most conditions, avoidant persons' reactions were similar to those of secure persons. However, they showed no accessibility to proximity worries even after the priming of a semantically related word and reacted with high accessibility to these worries upon the addition of cognitive load.

The Pseudomonas aeruginosa Lectins PA-IL and PA-IIL Are Controlled by Quorum Sensing and by RpoS

Abstract: In Pseudomonas aeruginosa , many exoproduct virulence determinants are regulated via a hierarchical quorum-sensing cascade involving the transcriptional regulators LasR and RhlR and their cognate activators, N -(3-oxododecanoyl)-l-homoserine lactone (3O-C12-HSL) and N -butanoyl-l-homoserine lactone (C4-HSL). In this paper, we demonstrate that the cytotoxic lectins PA-IL and PA-IIL are regulated via quorum sensing. Using immunoblot analysis, the production of both lectins was found to be directly dependent on the rhl locus while, in a lasR mutant, the onset of lectin synthesis was delayed but not abolished. The PA-IL structural gene, lecA , was cloned and sequenced. Transcript analysis indicated a monocistronic organization with a transcriptional start site 70 bp upstream of the lecA translational start codon. A lux box-type element together with RpoS (ς S ) consensus sequences was identified upstream of the putative promoter region. In Escherichia coli , expression of a lecA :: lux reporter fusion was activated by RhlR/C4-HSL, but not by LasR/3O-C12-HSL, confirming direct regulation by RhlR/C4-HSL. Similarly, in P. aeruginosa PAO1, the expression of a chromosomal lecA :: lux fusion was enhanced but not advanced by the addition of exogenous C4-HSL but not 3O-C12-HSL. Furthermore, mutation of rpoS abolished lectin synthesis in P. aeruginosa , demonstrating that both RpoS and RhlR/C4-HSL are required. Although the C4-HSL-dependent expression of the lecA :: lux reporter in E. coli could be inhibited by the presence of 3O-C12-HSL, this did not occur in P. aeruginosa . This suggests that, in the homologous genetic background, 3O-C12-HSL does not function as a posttranslational regulator of the RhlR/C4-HSL-dependent activation of lecA expression.

On the clique-width of some perfect graph classes

Abstract: Graphs of clique–width at most k were introduced by Courcelle, Engelfriet and Rozenberg (1993) as graphs which can be defined by k-expressions based on graph operations which use k vertex labels. In this paper we study the clique–width of perfect graph classes. On one hand, we show that every distance–hereditary graph, has clique–width at most 3, and a 3–expression defining it can be obtained in linear time. On the other hand, we show that the classes of unit interval and permutation graphs are not of bounded clique–width. More precisely, we show that for every $n\in {\mathcal N}$ there is a unit interval graph In and a permutation graph Hn having n2 vertices, each of whose clique–width is at least n. These results allow us to see the border within the hierarchy of perfect graphs between classes whose clique–width is bounded and classes whose clique–width is unbounded. Finally we show that every n×n square grid, $n\in {\mathcal N}$, n ≥ 3, has clique–width exactly n+1.

Classic kaposi sarcoma: epidemiology and risk factors.

Abstract: BACKGROUND Although Kaposi sarcoma (KS) initially was described over a century ago, its biology remains enigmatic and conflicting. Whereas the classic type occurs mainly in older men of Mediterranean or Eastern European backgrounds and is not linked to impairment of the host immune response, iatrogenic and human immunodeficiency virus (HIV)-associated KS are linked to such conditions. A recently discovered pathogen, KS-associated herpesvirus (KSHV) (also known as human herpesvirus 8 [HHV8]), is found in tissues from all four forms of KS (classic, iatrogenic, endemic [African], and HIV-associated). This universal detection of KSHV/HHV8 suggests a central role for the virus in the development of KS and a common etiology for all KS types. The epidemiology and risk factors of classic KS, along with the biology of KSHV/HHV8 and the prevalence of the virus among different populations, is presented. METHODS The current review is based on multiple information sources, electronic health data in all languages from 1966 onward, and previously published scientific reports from the Americas, Europe, and Africa. RESULTS Nearly 5000 cases of morphologically characterized classic KS have been reported in Europe, Mediterranean countries, and the Americas up to 1998. Geographic location, ethnicity, time interval, age, and gender heavily influence the incidence rate of classic KS. The rate of incidence of nonacquired immunodeficiency syndrome-associated KS correlates with the KSHV/HHV8 seroprevalence in the general population. CONCLUSIONS Many contributory factors undoubtedly have etiologic and pathogenic significance in the development of classic KS; however, the interplay between these factors has complicated the understanding of the induction and development of the disease as well as the significance of each factor. As with other cell-transforming human DNA viruses, infection with KSHV/HHV8 alone is not sufficient for the development of KS and additional cofactors are required. Cancer 2000;88:500–17. © 2000 American Cancer Society.

Normal Families and Shared Values

Abstract: For f a meromorphic function on the plane domain D and a ∈ [Copf ], let Ēf(a) = {z ∈ D[ratio ]f(z) = a}. Let [Fscr ] be a family of meromorphic functions on D, all of whose zeros are of multiplicity at least k. If there exist b ≠ 0 and h > 0 such that for every f ∈ [Fscr ], Ēf(0) = Ēf(k)(b) and 0 < [mid ]f(k+1)(z)[mid ] [les ] h whenever z ∈ Ēf(0), then [Fscr ] is a normal family on D. The case Ēf(0) = O is a celebrated result of Gu [5].

Differences in viral dynamics between genotypes 1 and 2 of hepatitis C virus.

Abstract: Many studies have shown that patients infected with hepatitis C virus (HCV) of genotype 2 have better response to interferon (IFN)-alpha treatment than genotype 1 patients; however, the mechanisms responsible for this difference are not understood. In this study, viral dynamics during high-dose IFN induction treatment were compared between the genotypes. Patients in each group received 10 MU of IFN-alpha2b for 14 days, and HCV RNA levels were frequently determined. Nonlinear fitting, both individually for each patient and using a mixed-effects approach, of the viral kinetic data to a mathematical model of the IFN effect on HCV infection was performed. The antiviral effectiveness of IFN in blocking virus production, the free virion clearance rate, and the HCV-infected cell death rate were all significantly higher for genotype 2 patients than for genotype 1 patients. Thus, the better response rate of patients infected with HCV genotype 2 is multifactorial. This is the first finding of a difference in viral dynamics between subtypes of the same virus and demonstrates the importance of subtype-specific virus-host-drug interactions.

Faster algorithms for string matching with k mismatches

Abstract: The string matching with mismatches problem is that of finding the number of mismatches between a pattern P of length m and every length m substring of the text T. Currently, the fastest algorithms for this problem are the following. The Galil-Giancarlo algorithm finds all locations where the pattern has at most k errors (where k is part of the input) in time O(nk). The Abrahamson algorithm finds the number of mismatches at every location in time O(n√ m log m). We present an algorithm that is faster than both. Our algorithm finds all locations where the pattern has at most k errors in time O(n√k log k). We also show an algorithm that solves the above problem in time O((n + (nk3)/m) log k).

Lévy flights in random searches

Abstract: We review the general search problem of how to find randomly located objects that can only be detected in the limited vicinity of a forager, and discuss its quantitative description using the theory of random walks. We illustrate Levy flight foraging by comparison to Brownian random walks and discuss experimental observations of Levy flights in biological foraging. We review recent findings suggesting that an inverse square probability density distribution P(l)∼l−2 of step lengths l can lead to optimal searches. Finally, we survey the explanations put forth to account for these unexpected findings.

Childless in the Land of Imperative Motherhood: Stigma and Coping Among Infertile Israeli Women

Abstract: Drawing on Goffman's stigma framework, this in-depth study explored the experiences of 26 infertile Jewish women in Israel, the country with a strong pronatalist ideology, both institutional and popular. The findings are in line with the key postulates of the stigma concept: women's coping strategies included selective disclosure, avoidance of exposure of their “hidden disability,” and other information management techniques. Infertility became a “master status” for these women, undermining any other merits and achievements they might have. Most women fully internalized and endorsed the pronatalist discourse by way of pursuing long-term and burdensome infertility treatments, at any personal cost. The paper argues that resistance to stigma of infertility is only possible where women dare question the motherhood imperative, which is clearly not the case with most Israelis. Material and mental resources needed for resisting the stigma of infertility are found among few educated professional women. The paper suggests three theoretical inferences: (a) stigma as a psychological response is graded by the extent of individual's conformity with the dominant norms; (b) the stigma of childlessness is most devastating for the less educated women without career or other nonfamilial aspirations; and (c) in pronatalist societies, the coping and management approach to the study of infertility is more relevant than the resistance approach suggested by some authors.