Showing papers by "Tel Aviv University published in 2001"

Validation of a New General Self-Efficacy Scale:

Abstract: Researchers have suggested that general self-efficacy (GSE) can substantially contribute to organizational theory, research, and practice. Unfortunately, the limited construct validity work conduct...

The NBER Patent Citation Data File: Lessons, Insights and Methodological Tools

Abstract: This paper describes the database on U.S. patents that we have developed over the past decade, with the goal of making it widely accessible for research. We present main trends in U. S. patenting over the last 30 years, including a variety of original measures constructed with citation data, such as backward and forward citation lags, indices of 'originality' and 'generality', self-citations, etc. Many of these measures exhibit interesting differences across the six main technological categories that we have developed (comprising Computers and Communications, Drugs and Medical, Electrical and Electronics, Chemical, Mechanical and Others), differences that call for further research. To stimulate such research, the entire database about 3 million patents and 16 million citations is now available on the NBER website. We discuss key issues that arise in the use of patent citations data, and suggest ways of addressing them. In particular, significant changes over time in the rate of patenting and in the number of citations made, as well as the inevitable truncation of the data, make it very hard to use the raw number of citations received by different patents directly in a meaningful way. To remedy this problem we suggest two alternative approaches: the fixed-effects approach involves scaling citations by the average citation count for a group of patents to which the patent of interest belongs; the quasi-structural approach attempts to distinguish the multiple effects on citation rates via econometric estimation.

Talk of the Network: A Complex Systems Look at the Underlying Process of Word-of-Mouth

Abstract: Though word-of-mouth (w-o-m) communications is a pervasive and intriguing phenomenon, little is known on its underlying process of personal communications. Moreover as marketers are getting more interested in harnessing the power of w-o-m, for e-business and other net related activities, the effects of the different communications types on macro level marketing is becoming critical. In particular we are interested in the breakdown of the personal communication between closer and stronger communications that are within an individual's own personal group (strong ties) and weaker and less personal communications that an individual makes with a wide set of other acquaintances and colleagues (weak ties). We use a technique borrowed from Complex Systems Analysis called stochastic cellular automata in order to generate data and analyze the results so that answers to our main research issues could be ascertained. The following summarizes the impact of strong and weak ties on the speed of acceptance of a new product: ••The influence of weak ties is at least as strong as the influence of strong ties. Despite the relative inferiority of the weak tie parameter in the model's assumptions, their effect approximates or exceeds that of strong ties, in all stages of the product life cycle. ••External marketing efforts (e.g., advertising) are effective. However, beyond a relatively early stage of the growth cycle of the new product, their efficacy quickly diminishes and strong and weak ties become the main forces propelling growth. The results clearly indicate that information dissemination is dominated by both weak and strong w-o-m, rather than by advertising. ••The effect of strong ties diminishes as personal network size decreases. Market attributes were also found to mediate the effects of weak and strong ties. When personal networks are small, weak ties were found to have a stronger impact on information dissemination than strong ties.

Coral bleaching: the winners and the losers

Abstract: Sea surface temperatures were warmer throughout 1998 at Sesoko Island, Japan, than in the 10 preceding years. Temperatures peaked at 2.8 °C above average, resulting in extensive coral bleaching and subsequent coral mortality. Using random quadrat surveys, we quantitatively documented the coral community structure one year before and one year after the bleaching event. The 1998 bleaching event reduced coral species richness by 61% and reduced coral cover by 85%. Colony morphology affected bleaching vulnerability and subsequent coral mortality. Finely branched corals were most susceptible, while massive and encrusting colonies survived. Most heavily impacted were the branched Acropora and pocilloporid corals, some of which showed local extinction. We suggest two hypotheses whose synergistic effect may partially explain observed mortality patterns (i.e. preferential survival of thick-tissued species, and shape-dependent differences in colony mass-transfer efficiency). A community-structural shift occurred on Okinawan reefs, resulting in an increase in the relative abundance of massive and encrusting coral species.

Wave propagation in media having negative permittivity and permeability

Abstract: Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explored with wideband pulse excitations. These FDTD results show conclusively that the square root choice leading to a negative index of refraction and positive wave impedance is the correct one, and that this choice is consistent with the overall causality of the response. An analytical, exact frequency domain solution to the scattering of a wave from a DNG slab is also given and is used to characterize several physical effects. This solution is independent of the choice of the square roots for the index of refraction and the wave impedance, and thus avoids any controversy that may arise in connection with the signs of these constituents. The DNG slab solution is used to critically examine the perfect lens concept suggested recently by Pendry. It is shown that the perfect lens effect exists only under the special case of a DNG medium with $\ensuremath{\epsilon}(\ensuremath{\omega})=\ensuremath{\mu}(\ensuremath{\omega})=\ensuremath{-}1$ that is both lossless and nondispersive. Otherwise, the closed form solutions for the field structure reveal that the DNG slab converts an incident spherical wave into a localized beam field whose parameters depend on the values of $\ensuremath{\epsilon}$ and $\ensuremath{\mu}.$ This beam field is characterized with a paraxial approximation of the exact DNG slab solution. These monochromatic concepts are again explored numerically via a causal two-dimensional FDTD simulation of the scattering of a pulsed cylindrical wave by a matched, lossy Drude model DNG slab. These FDTD results demonstrate conclusively that the monochromatic electromagnetic power flow through the DNG slab is channeled into beams rather then being focused and, hence, the Pendry perfect lens effect is not realizable with any realistic metamaterial.

Confounding and effect modification in the short-term effects of ambient particles on total mortality: Results from 29 European cities within the APHEA2 project

Abstract: We present the results of the Air Pollution and Health: A European Approach 2 (APHEA2) project on short-term effects of ambient particles on mortality with emphasis on effect modification. We used daily measurements for particulate matter less than 10 microm in aerodynamic diameter (PM10) and/or black smoke from 29 European cities. We considered confounding from other pollutants as well as meteorologic and chronologic variables. We investigated several variables describing the cities' pollution, climate, population, and geography as potential effect modifiers. For the individual city analysis, generalized additive models extending Poisson regression, using a smoother to control for seasonal patterns, were applied. To provide quantitative summaries of the results and explain remaining heterogeneity, we applied second-stage regression models. The estimated increase in the daily number of deaths for all ages for a 10 microg/m3 increase in daily PM10 or black smoke concentrations was 0.6% [95% confidence interval (CI) = 0.4-0.8%], whereas for the elderly it was slightly higher. We found important effect modification for several of the variables studied. Thus, in a city with low average NO2, the estimated increase in daily mortality for an increase of 10 microg/m3 in PM10 was 0.19 (95% CI = 0.00-0.41), whereas in a city with high average NO2 it was 0.80% (95% CI = 0.67-0.93%); in a relatively cold climate the corresponding effect was 0.29% (95% CI = 0.16-0.42), whereas in a warm climate it was 0.82% (95% CI = 0.69-0.96); in a city with low standardized mortality rate it was 0.80% (95% CI = 0.65-0.95%), and in one with a high rate it was 0.43% (95% CI = 0.24-0.62). Our results confirm those previously reported on the effects of ambient particles on mortality. Furthermore, they show that the heterogeneity found in the effect parameters among cities reflects real effect modification, which is explained by specific city characteristics.

Discrimination in a Segmented Society: An Experimental Approach

Abstract: This paper proposes an experimental approach to studying different aspects of discrimination. We let participants play various games with opponents of distinct ethnic affiliation. Strategies based upon such ethnic affiliation provide direct evidence of ethnic discrimination. This approach was utilized to study ethnic discrimination in Israeli Jewish society. Using the “trust game,” we detected a systematic mistrust toward men of Eastern origin. A “dictator game” experiment indicated that this discrimination was due to (mistaken) ethnic stereotypes and not to a “taste for discrimination.” The “ultimatum game” enabled us to trace another ethnic stereotype that reversed the discrimination’s direction. One of the surprising results is that this ethnic discrimination is an entirely male phenomenon.

Novel mechanism of Wnt signalling inhibition mediated by Dickkopf-1 interaction with LRP6/Arrow.

Abstract: Wnt signalling has an important role in cell fate determination, tissue patterning and tumorigenesis. Secreted antagonists of Wnt include Frizzled (Fz)-related proteins (FRPs), Cerberus, Wnt inhibitory factor (WIF) and Dickkopf (Dkk). FRPs, Cerberus and WIF have all been shown to act by binding and sequestering Wnt. We report a novel mechanism of Wnt-signalling inhibition by human Dkk-1. Dkk-1 demonstrated no interaction with Wnt but bound a single cell surface site with high affinity (K(D) = 0.39 nM). Its receptor was detectable in a complex with a relative molecular mass of 240,000 (M(r) 240K) with [(125)I] Dkk-1 by covalent affinity cross-linking. Wnt signalling through beta-catenin is mediated by the Fz receptor and a recently identified low-density-lipoprotein-receptor-related co-receptor, LRP6/Arrow. Overproduction of the 200K LRP6 protein, but not of Fz, strikingly increased Dkk-1 binding as well as the amount of the 240K cross-linked complex, which was shown to be composed of Dkk-1 and LRP6. Moreover, Dkk-1 function was completely independent of Fz but LRP6 dramatically interfered with the Dkk-1 inhibition of Wnt signalling. Thus, unlike Wnt antagonists, which exert their effects by molecular mimicry of Fz or Wnt sequestration through other mechanisms, Dkk-1 specifically inhibits canonical Wnt signalling by binding to the LRP6 component of the receptor complex.

Point set surfaces

Abstract: We advocate the use of point sets to represent shapes. We provide a definition of a smooth manifold surface from a set of points close to the original surface. The definition is based on local maps from differential geometry, which are approximated by the method of moving least squares (MLS). We present tools to increase or decrease the density of the points, thus, allowing an adjustment of the spacing among the points to control the fidelity of the representation. To display the point set surface, we introduce a novel point rendering technique. The idea is to evaluate the local maps according to the image resolution. This results in high quality shading effects and smooth silhouettes at interactive frame rates.

Natural roles of biosurfactants

Abstract: Microorganisms produce a variety of surface-active agents (or surfactants) These can be divided into low-molecular-weight molecules that lower surface and interfacial tensions efficiently and high-molecular-weight polymers that bind tightly to surfaces These surfactants, produced by a wide variety of microorganisms, have very different chemical structures and surface properties It is therefore reasonable to assume that different groups of biosurfactants have different natural roles in the growth of the producing microorganisms Moreover, as their chemical structures and surface properties are so different, each emulsifier probably provides advantages in a particular ecological niche Several bioemulsifiers have antibacterial or antifungal activities Other bioemulsifiers enhance the growth of bacteria on hydrophobic water-insoluble substrates by increasing their bioavailability, presumably by increasing their surface area, desorbing them from surfaces and increasing their apparent solubility Bioemulsifiers also play an important role in regulating the attachment-detachment of microorganisms to and from surfaces In addition, emulsifiers are involved in bacterial pathogenesis, quorum sensing and biofilm formation Recent experiments indicate that a high-molecular-weight bioemulsifier that coats the bacterial surface can be transferred horizontally to other bacteria, thereby changing their surface properties and interactions with the environment

Signal enhancement using beamforming and nonstationarity with applications to speech

Abstract: We consider a sensor array located in an enclosure, where arbitrary transfer functions (TFs) relate the source signal and the sensors. The array is used for enhancing a signal contaminated by interference. Constrained minimum power adaptive beamforming, which has been suggested by Frost (1972) and, in particular, the generalized sidelobe canceler (GSC) version, which has been developed by Griffiths and Jim (1982), are the most widely used beamforming techniques. These methods rely on the assumption that the received signals are simple delayed versions of the source signal. The good interference suppression attained under this assumption is severely impaired in complicated acoustic environments, where arbitrary TFs may be encountered. In this paper, we consider the arbitrary TF case. We propose a GSC solution, which is adapted to the general TF case. We derive a suboptimal algorithm that can be implemented by estimating the TFs ratios, instead of estimating the TFs. The TF ratios are estimated by exploiting the nonstationarity characteristics of the desired signal. The algorithm is applied to the problem of speech enhancement in a reverberating room. The discussion is supported by an experimental study using speech and noise signals recorded in an actual room acoustics environment.

Center-periphery organization of human object areas.

Abstract: The organizing principles that govern the layout of human object-related areas are largely unknown. Here we propose a new organizing principle in which object representations are arranged according to a central versus peripheral visual field bias. The proposal is based on the finding that building-related regions overlap periphery-biased visual field representations, whereas face-related regions are associated with center-biased representations. Furthermore, the eccentricity maps encompass essentially the entire extent of object-related occipito-temporal cortex, indicating that most object representations are organized with respect to retinal eccentricity. A control experiment ruled out the possibility that the results are due exclusively to unequal feature distribution in these images. We hypothesize that brain regions representing object categories that rely on detailed central scrutiny (such as faces) are more strongly associated with processing of central information, compared to representations of objects that may be recognized by more peripheral information (such as buildings or scenes).

Approximate distance oracles

Abstract: Let G=(V,E) be an undirected weighted graph with |V|=n and |E|=m. Let k\ge 1 be an integer. We show that G=(V,E) can be preprocessed in O(kmn^{1/k}) expected time, constructing a data structure of size O(kn^{1+1/k}), such that any subsequent distance query can be answered, approximately, in O(k) time. The approximate distance returned is of stretch at most 2k-1, i.e., the quotient obtained by dividing the estimated distance by the actual distance lies between 1 and 2k-1. We show that a 1963 girth conjecture of Erd{\H{o}}s, implies that ω(n^{1+1/k}) space is needed in the worst case for any real stretch strictly smaller than 2k+1. The space requirement of our algorithm is, therefore, essentially optimal. The most impressive feature of our data structure is its constant query time, hence the name oracle. Previously, data structures that used only O(n^{1+1/k}) space had a query time of ω(n^{1/k}) and a slightly larger, non-optimal, stretch. Our algorithms are extremely simple and easy to implement efficiently. They also provide faster constructions of sparse spanners of weighted graphs, and improved tree covers and distance labelings of weighted or unweighted graphs.}

Compact routing schemes

Abstract: We describe several compact routing schemes for general weighted undirected networks. Our schemes are simple and easy to implement. The routing tables stored at the nodes of the network are all very small. The headers attached to the routed messages, including the name of the destination, are extremely short. The routing decision at each node takes constant time. Yet, the stretch of these routing schemes, i.e., the worst ratio between the cost of the path on which a packet is routed and the cost of the cheapest path from source to destination, is a small constant. Our schemes achieve a near-optimal tradeoff between the size of the routing tables used and the resulting stretch. More specifically, we obtain: A routing scheme that uses only O (n 1/2) bits of memory at each node of an n-node network that has stretch 3. The space is optimal, up to logarithmic factors, in the sense that every routing scheme with stretch n2), and every routing scheme with stretch n3/2). The headers used are only (1 + O(1)) log2> n-bits long and each routing decision takes constant time. A variant of this scheme with [log2 n] -bit headers makes routing decisions in O(log log n) time. Also, for every integer k > 2, a general handshaking based routing scheme that uses O (n1/k) bits of memory at each node that has stretch 2k - 1. A conjecture of Erdos from 1963, settled for k = 3, 5, implies that the routing tables are of near-optimal size relative to the stretch. The handshaking is similar in spirit to a DNS lookup in TCP/IP. Headers are O(log2 n) bits long and each routing decision takes constant time. Without handshaking, the stretch of the scheme increases to 4k - 5. One ingredient used to obtain the routing schemes mentioned above, may be of independent practical and theoretical interest: A shortest path routing scheme for trees of arbitrary degree and diameter that assigns each vertex of an n-node tree a (1 + O(1)) log2 n-bit label. Given the label of a source node and the label of a destination it is possible to compute, in constant time, the port number of the edge from the source that heads in the direction of the destination. The general scheme for k > 2 also uses a clustering technique introduced recently by the authors. The clusters obtained using this technique induce a sparse and low stretch tree cover of the network. This essentially reduces routing in general networks into routing problems in trees that could be solved using the above technique.

Two-year effects of alendronate on bone mineral density and vertebral fracture in patients receiving glucocorticoids: a randomized, double-blind, placebo-controlled extension trial.

Abstract: OBJECTIVE: To evaluate the continued efficacy and safety of alendronate (ALN) for up to 2 years in patients receiving glucocorticoids. METHODS: This is a 12-month extension of a previously completed 1-year trial of daily ALN, performed to evaluate the effects of ALN over a total of 2 years in 66 men and 142 women continuing to receive at least 7.5 mg of prednisone or equivalent daily. All patients received supplemental calcium and vitamin D. The primary end point was the mean percentage change in lumbar spine bone mineral density (BMD) from baseline to 24 months. Other outcomes included changes in hip and total body BMD, biochemical markers of bone turnover, radiographic joint damage of the hands, and vertebral fracture incidence. RESULTS: The mean (+/-SEM) lumbar spine BMD increased by 2.8 +/- 0.6%, 3.9 +/- 0.7%, and 3.7 +/- 0.6%, respectively, in the groups that received 5 mg, 10 mg, and 2.5/10 mg of ALN daily (P < or = 0.001) and decreased by -0.8 +/- 0.6% in the placebo group (P not significant) over 24 months. In patients receiving any dose of ALN, BMD was increased at the trochanter (P < or = 0.05) and maintained at the femoral neck. Total body BMD was increased in patients receiving 5 or 10 mg ALN (P < or = 0.01). These 2 dose levels of ALN were more effective than placebo at all sites (P < or = 0.05). Bone turnover markers (N-telopeptides of type I collagen and bone-specific alkaline phosphatase) decreased 60% and 25%, respectively, during treatment with ALN (P < or = 0.05). There were fewer patients with new vertebral fractures in the ALN group versus the placebo group (0.7% versus 6.8%; P = 0.026). The safety profile was similar between treatment groups. CONCLUSION: Alendronate is an effective, well-tolerated therapy for the prevention and treatment of glucocorticoid-induced osteoporosis, with sustained treatment advantages for up to 2 years.

IDMaps: a global internet host distance estimation service

Abstract: There is an increasing need to quickly and efficiently learn network distances, in terms of metrics such as latency or bandwidth, between Internet hosts. For example, Internet content providers often place data and server mirrors throughout the Internet to improve access latency for clients, and it is necessary to direct clients to the nearest mirrors based on some distance metric in order to realize the benefit of the mirrors. We suggest a scalable Internet-wide architecture, called IDMaps, which measures and disseminates distance information on the global Internet. Higher level services can collect such distance information to build a virtual distance map of the Internet and estimate the distance between any pair of IP addresses. We present our solutions to the measurement server placement and distance map construction problems in IDMaps. We show that IDMaps can indeed provide useful distance estimations to applications such as nearest mirror selection.

Insulin-like growth factor 1 (IGF-1): a growth hormone

Abstract: Aim —To contribute to the debate about whether growth hormone (GH) and insulin-like growth factor 1 (IGF-1) act independently on the growth process. Methods —To describe growth in human and animal models of isolated IGF-1 deficiency (IGHD), such as in Laron syndrome (LS; primary IGF-1 deficiency and GH resistance) and IGF-1 gene or GH receptor gene knockout (KO) mice. Results —Since the description of LS in 1966, 51 patients were followed, many since infancy. Newborns with LS are shorter (42–47 cm) than healthy babies (49–52 cm), suggesting that IGF-1 has some influence on intrauterine growth. Newborn mice with IGF-1 gene KO are 30% smaller. The postnatal growth rate of patients with LS is very slow, the distance from the lowest normal centile increasing progressively. If untreated, the final height is 100–136 cm for female and 109–138 cm for male patients. They have acromicia, organomicria including the brain, heart, gonads, genitalia, and retardation of skeletal maturation. The availability of biosynthetic IGF-1 since 1988 has enabled it to be administered to children with LS. It accelerated linear growth rates to 8–9 cm in the first year of treatment, compared with 10–12 cm/year during GH treatment of IGHD. The growth rate in following years was 5–6.5 cm/year. Conclusion —IGF-1 is an important growth hormone, mediating the protein anabolic and linear growth promoting effect of pituitary GH. It has a GH independent growth stimulating effect, which with respect to cartilage cells is possibly optimised by the synergistic action with GH.

A myosignal-based powered exoskeleton system

Abstract: This paper studies the integration of a human arm with a powered exoskeleton (orthotic device) and its experimental implementation in an elbow joint, naturally controlled by the human. The human-machine interface was set at the neuromuscular level, by using the neuromuscular signal (EMG) as the primary command signal for the exoskeleton system. The EMG signal along with the joint kinematics were fed into a myoprocessor which in turn predicted the muscle moments on the elbow joint. The moment-based control system integrated myoprocessor moment prediction with feedback moments measured at the human arm/exoskeleton and external load/exoskeleton interfaces. The exoskeleton structure under study was a two-link, two-joint mechanism, corresponding to the arm limbs and joints, which was mechanically linked by the human operator. Four indices of performance were used to define the quality of the human/machine integration and to evaluate the operational envelope of the system. Experimental results indicate the feasibility of an EMG-based power exoskeleton system as an integrated human-machine system using high-level neurological signals.

Biomonitoring Atmospheric Heavy Metals with Lichens: Theory and Application

Abstract: Recent records of environmental contamination noted a moderate decrease of SO2 pollution, whereas the burden of atmospheric heavy metals is still considerable. The present review refers to the entrapment, uptake, and accumulation of heavy metals by lichen thalli, made apparent by parameters of lichen vitality and stress. The particulate nature of airborne heavy metals is made evident by parameters referring to the entrapment of heavy-metal containing particles by lichen thalli. The mechanism of uptake of heavy metals, investigated by means of controlled experiments, refers to extracellular and intracellular uptake. The rate of absorption and the accumulation of heavy metals is dependent on morphological features of lichen thalli in addition to kind and intensity of emission sources and to nonanthropogenic factors such as climate and topography. The role of lichens as biomonitors is demonstrated by the case of lead. In contrast to data obtained by retrospective studies, using lichens as biomonitors of heav...

A Possible Role for CXCR4 and Its Ligand, the CXC Chemokine Stromal Cell-Derived Factor-1, in the Development of Bone Marrow Metastases in Neuroblastoma

Abstract: The homing of hemopoietic stem cells to the bone marrow is mediated by specific interactions occurring between CXCR4, which is expressed on hemopoietic stem cells, and its ligand, stromal cell-derived factor-1 (SDF-1), a CXC chemokine secreted by bone marrow stromal cells. In the present study we evaluated the possibility that neuroblastoma cells use a mechanism similar to that used by hemopoietic stem cells to home to the bone marrow and adhere to bone marrow stromal cells. Our study suggests that CXCR4 expression may be a general characteristic of neuroblastoma cells. SH-SY5Y neuroblastoma cells express not only CXCR4, but also its ligand, SDF-1. CXCR4 expression on SH-SY5Y neuroblastoma cells is tightly regulated by tumor cell-derived SDF-1, as demonstrated by the ability of neutralizing Abs against human SDF-1alpha to up-regulate CXCR4 expression on the tumor cells. The reduction in CXCR4 expression following short term exposure to recombinant human SDF-1alpha can be recovered as a result of de novo receptor synthesis. Recombinant human SDF-1alpha induces the migration of CXCR4-expressing SH-SY5Y neuroblastoma cells in CXCR4- and heterotrimeric G protein-dependent manners. Furthermore, SH-SY5Y cells interact at multiple levels with bone marrow components, as evidenced by the fact that bone marrow-derived constituents promote SH-SY5Y cell migration, adhesion to bone marrow stromal cells, and proliferation. These results suggest that SH-SY5Y neuroblastoma cells are equipped with adequate machinery to support their homing to the bone marrow. Therefore, the ability of neuroblastoma tumors to preferentially form metastases in the bone marrow may be influenced by a set of complex CXCR4-SDF-1 interactions.

Why does fear override hope in societies engulfed by intractable conflict, as it does in the Israeli society?

Abstract: The question of why fear overrides hope in societies embarked on the road of peacemaking after years of intractable conflict is answered on the basis of accumulated knowledge in the psychology and sociology of emotions. This knowledge suggests that fear is an automatic emotion, grounded in the perceived present and often based on the memorized past (also processed unconsciously), that leads to freezing of beliefs, conservatism, and sometimes preemptive aggression. Hope, in contrast, involves mostly cognitive activity, which requires the search for new ideas and thus is based on creativity and flexibility. Because hope is based on thinking, it can be seriously impeded by the spontaneous and unconscious interference of fear. Both fear and hope can become collective emotional orientations that organize society’s views and direct its forms of action. It is assumed that societies involved in intractable conflict are dominated by a collective emotional orientation of fear, which is functional in their coping with the stressful and demanding situation. But such an orientation serves as a psychological obstacle to a peace process once it starts. The Israeli Jewish case of collective fear orientation is offered as an example. The presentation includes the roots of this orientation, the ways in which it is reflected and disseminated, and its expressions among the Israeli Jewish public; it ends optimistically with the suggestion that societies can determine to overcome their fear and establish a collective orientation of hope for peace.

Residue frequencies and pairing preferences at protein–protein interfaces

Abstract: We used a nonredundant set of 621 protein-protein interfaces of known high-resolution structure to derive residue composition and residue-residue contact preferences. The residue composition at the interfaces, in entire proteins and in whole genomes correlates well, indicating the statistical strength of the data set. Differences between amino acid distributions were observed for interfaces with buried surface area of less than 1,000 A(2) versus interfaces with area of more than 5,000 A(2). Hydrophobic residues were abundant in large interfaces while polar residues were more abundant in small interfaces. The largest residue-residue preferences at the interface were recorded for interactions between pairs of large hydrophobic residues, such as Trp and Leu, and the smallest preferences for pairs of small residues, such as Gly and Ala. On average, contacts between pairs of hydrophobic and polar residues were unfavorable, and the charged residues tended to pair subject to charge complementarity, in agreement with previous reports. A bootstrap procedure, lacking from previous studies, was used for error estimation. It showed that the statistical errors in the set of pairing preferences are generally small; the average standard error is approximately 0.2, i.e., about 8% of the average value of the pairwise index (2.9). However, for a few pairs (e.g., Ser-Ser and Glu-Asp) the standard error is larger in magnitude than the pairing index, which makes it impossible to tell whether contact formation is favorable or unfavorable. The results are interpreted using physicochemical factors and their implications for the energetics of complex formation and for protein docking are discussed. Proteins 2001;43:89-102.