Showing papers by "Bar-Ilan University published in 1999"

Multifractality in human heartbeat dynamics

Abstract: There is evidence that physiological signals under healthy conditions may have a fractal temporal structure. Here we investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system, the healthy human heartbeat, and show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.

Optimizing the success of random searches

Abstract: We address the general question of what is the best statistical strategy to adapt in order to search efficiently for randomly located objects ('target sites'). It is often assumed in foraging theory that the flight lengths of a forager have a characteristic scale: from this assumption gaussian, Rayleigh and other classical distributions with well-defined variances have arisen. However, such theories cannot explain the long-tailed power-law distributions of flight lengths or flight times that are observed experimentally. Here we study how the search efficiency depends on the probability distribution of flight lengths taken by a forager that can detect target sites only in its limited vicinity. We show that, when the target sites are sparse and can be visited any number of times, an inverse square power-law distribution of flight lengths, corresponding to Levy flight motion, is an optimal strategy. We test the theory by analysing experimental foraging data on selected insect, mammal and bird species, and find that they are consistent with the predicted inverse square power-law distributions.

Ageing, fitness and neurocognitive function.

Abstract: In the ageing process, neural areas1,2 and cognitive processes3,4 do not degrade uniformly. Executive control processes and the prefrontal and frontal brain regions that support them show large and disproportionate changes with age. Studies of adult animals indicate that metabolic5 and neurochemical6 functions improve with aerobic fitness. We therefore investigated whether greater aerobic fitness in adults would result in selective improvements in executive control processes, such as planning, scheduling, inhibition and working memory. Over a period of six months, we studied 124 previously sedentary adults, 60 to 75 years old, who were randomly assigned to either aerobic (walking) or anaerobic (stretching and toning) exercise. We found that those who received aerobic training showed substantial improvements in performance on tasks requiring executive control compared with anaerobically trained subjects.

Solid‐State Electrochemical Kinetics of Li‐Ion Intercalation into Li1 − x CoO2: Simultaneous Application of Electroanalytical Techniques SSCV, PITT, and EIS

Abstract: The electroanalytical behavior of thin electrodes is elucidated by the simultaneous application of three electroanalytical techniques: slow‐scan‐rate cyclic voltammetry (SSCV), potentiostatic intermittent titration technique, and electrochemical impedance spectroscopy. The data were treated within the framework of a simple model expressed by a Frumkin‐type sorption isotherm. The experimental SSCV curves were well described by an equation combining such an isotherm with the Butler‐Volmer equation for slow interfacial Li‐ion transfer. The apparent attraction constant was −4.2, which is characteristic of a quasi‐equilibrium, first‐order phase transition. Impedance spectra reflected a process with the following steps: ion migration in solution, ion migration through surface films, strongly potential‐dependent charge‐transfer resistance, solid‐state diffusion, and accumulation of the intercalants into the host materials. An excellent fit was found between these spectra and an equivalent circuit, including a Voigt‐type analog ( migration through multilayer surface films and charge transfer) in series with a finite‐length Warburg‐type element ( solid‐state diffusion), and a capacitor (Li accumulation). In this paper, we compare the solid‐state diffusion time constants and the differential intercalation capacities obtained by the three electroanalytical techniques. © 1999 The Electrochemical Society. All rights reserved.

Mother-infant affect synchrony as an antecedent of the emergence of self-control

Abstract: This study examined relations between mother-infant affect synchrony and the emergence of children's self-control. Mother-infant face-to-face play and infant difficult temperament were examined at 3 and 9 months. Maternal and infant affective states at play were coded in 0.25-s frames, and synchrony was computed with cross-correlation functions. Self-control, verbal IQ, and maternal warm discipline were assessed at 2 years. Maternal synchrony with infant affect at 3 months (infant-leads-mother-follows relation) and mutual synchrony at 9 months (cross-dependence between maternal and infant affect) were each related to self-control at 2 years when temperament, IQ, and maternal style were partialed. Infant temperament moderated the relations of synchrony and self-control, and closer associations were found between mutual synchrony and self-control for difficult infants. Shorter lags to maternal synchrony at 3 months were independently related to self-control. The mutual regulation of affect in infancy, as moderated by temperament, is proposed as an important contributor to the emergence of self-regulation.

Similarity-Based Models of Word Cooccurrence Probabilities

Abstract: In many applications of natural language processing (NLP) it is necessary to determine the likelihood of a given word combination For example, a speech recognizer may need to determine which of the two word combinations “eat a peach” and ”eat a beach” is more likely Statistical NLP methods determine the likelihood of a word combination from its frequency in a training corpus However, the nature of language is such that many word combinations are infrequent and do not occur in any given corpus In this work we propose a method for estimating the probability of such previously unseen word combinations using available information on “most similar” words We describe probabilistic word association models based on distributional word similarity, and apply them to two tasks, language modeling and pseudo-word disambiguation In the language modeling task, a similarity-based model is used to improve probability estimates for unseen bigrams in a back-off language model The similarity-based method yields a 20% perplexity improvement in the prediction of unseen bigrams and statistically significant reductions in speech-recognition error We also compare four similarity-based estimation methods against back-off and maximum-likelihood estimation methods on a pseudo-word sense disambiguation task in which we controlled for both unigram and bigram frequency to avoid giving too much weight to easy-to-disambiguate high-frequency configurations The similarity-based methods perform up to 40% better on this particular task

Attentional Biases for Facial Expressions in Social Phobia: The Face-in-the-Crowd Paradigm

Abstract: The present study examines the attentional bias hypothesis for individuals with generalised social phobia (GSPs). Socially phobic individuals were hypothesised to exhibit attentional bias towards threat stimuli relevant to interpersonal situations. This hypothesis was tested using the face-in-the-crowd paradigm. GSPs and nonanxious controls (NACs) detected an angry, happy, neutral, or disgust target face in a crowd of 12 distracter photographs. Results indicated that, compared to NACs, GSPs exhibited greater attentional biases for angry than for happy faces in a neutral crowd. GSPs were more slowed down in their performance by happy and angry versus neutral distracters; NACs did not exhibit such sensitivity to distracter type. Finally, GSPs were faster in detecting anger than disgust expressions; NACs detected both types of faces equally quickly. Implications of these findings for the maintenance of social phobia are discussed.

Statistical physics and physiology: monofractal and multifractal approaches.

Abstract: Even under healthy, basal conditions, physiologic systems show erratic fluctuations resembling those found in dynamical systems driven away from a single equilibrium state. Do such "nonequilibrium" fluctuations simply reflect the fact that physiologic systems are being constantly perturbed by external and intrinsic noise? Or, do these fluctuations actually, contain useful, "hidden" information about the underlying nonequilibrium control mechanisms? We report some recent attempts to understand the dynamics of complex physiologic fluctuations by adapting and extending concepts and methods developed very recently in statistical physics. Specifically, we focus on interbeat interval variability as an important quantity to help elucidate possibly non-homeostatic physiologic variability because (i) the heart rate is under direct neuroautonomic control, (ii) interbeat interval variability is readily measured by noninvasive means, and (iii) analysis of these heart rate dynamics may provide important practical diagnostic and prognostic information not obtainable with current approaches. The analytic tools we discuss may be used on a wider range of physiologic signals. We first review recent progress using two analysis methods--detrended fluctuation analysis and wavelets--sufficient for quantifying monofractual structures. We then describe recent work that quantifies multifractal features of interbeat interval series, and the discovery that the multifractal structure of healthy subjects is different than that of diseased subjects.

The impact of mortality salience on reckless driving: A test of terror management mechanisms.

Abstract: A series of 4 studies, based on terror management theory (TMT), examined the effects of mortality salience on risk taking while driving. In all the studies, participants (N = 603) reported on the relevance of driving to their self-esteem. Then half of them were exposed to various mortality salience inductions, and the remaining to a control condition. The dependent measures were either self-reported behavioral intentions of risky driving or driving speed in a car simulator. In Study 4, half of the participants in each condition received positive feedback about their quality of driving. Findings showed that mortality salience inductions led to more risky driving than the control condition only among individuals who perceived driving as relevant to their self-esteem. The introduction of positive feedback about driving eliminated this effect. The results were discussed in light of the self-enhancing mechanisms proposed by TMT.

The nature of the mother's tie to her infant: maternal bonding under conditions of proximity, separation, and potential loss.

Abstract: Attachment has generally been examined from the infant's perspective. We focused on mothers' post-partum thoughts and behaviors. Guided by an ethological approach, maternal bonding was examined under conditions of proximity, separation, and potential loss. Ninety-one mothers were interviewed: mothers of full-term infants who maintained continuous proximity to the infant, mothers of healthy premature infants who were separated from the infant, and mothers of very low birthweight infants who experienced potential loss and prolonged separation. Mothers of term infants reported medium-to-high levels of preoccupations with thoughts of infant safety and well-being. Preoccupations increased with separation (Group 2) and significantly decreased with impending loss (Group 3). Attachment behaviors and representations were the highest among mothers of term infants and declined linearly with the duration of mother-infant separation. Maternal trait anxiety and depression were related respectively to higher levels of preoccupations and reduced attachment behaviors and representations, independent of the infant medical condition and mother-child separation. Discussion focused on the comparability of maternal and infant attachment in relation to the neurobiological system underlying bond formation.

Essential fatty acids are mediators of brain biochemistry and cognitive functions.

Abstract: Major advances have been made in understanding the biochemistry of essential fatty acids (FA) and their interactions with metabolic pathways leading to the production of longer and more complex fatty acids and lipids. Less understood are the roles played by FA which are known to affect neurotransmitters, peptides, releasing factors, hormones, and a variety of physiological and cognitive processes. Based on empirical findings we propose that (a) FA exert a controlling function in the modulation of neuronal membrane fluidity, and (b) the critical factor in FA action and efficacy is not absolute level but rather the ratio between various groups of FA. This approach unifies the biochemical and cognitive results obtained from many different and unrelated fields of research.

Surface Synthesis of Zinc Sulfide Nanoparticles on Silica Microspheres: Sonochemical Preparation, Characterization, and Optical Properties

Abstract: Ultrasonic irradiation of a slurry of amorphous silica microspheres, zinc acetate, and thioacetamide in an aqueous medium for 3 h under ambient air yields zinc sulfide coated on silica. The powder X-ray diffraction of the initial zinc sulfide−silica (ZSS) powder yields diffraction peaks corresponding to the ZnS phase. The TEM image of ZSS shows that the porous ZnS nanoparticles (diameter 1−5 nm) coated the silica (SiO2) surface as thin layers or nanoclusters, depending on the reactant concentration. Infrared spectroscopy illustrates the structural changes that occurred in the siloxane network and surface silanol groups of SiO2 upon the ultrasonic deposition of ZnS. The optical absorption of porous ZnS shows a broad band at around 610 nm, ascribed to unusual surface state transition. The absorption energy of the surface state transition is lower than the band gap of the ZnS particles and probably stems from the dangling surface bonds or defects. On the other hand, the ZSS does not show the surface state tr...

Intraspecific classification of melons ( Cucumis melo L.) in view of their phenotypic and molecular variation

Abstract: Cucumis melo L. (melon) genotypes differ widely in morphological and biochemical traits. Intra-specific classification of such variability has been difficult, and most taxonomists still rely on the work of NAUDIN (1859). A collection of 54 accessions representing diverse genotypes from 23 countries was surveyed. Morphological traits related to the vegetative and flowering stages and mature fruit morphology and quality parameters, e.g., taste, aroma, sugar composition and pH, were scored. These were used to construct a "botanical-morphological" dendrogram that generally reflected the classification of Cucumis melo into several horticultural varieties. DNA polymorphism among the accessions was assessed using the Inter-SSR-PCR and RAPD techniques that detected abundant DNA polymorphism among melon genotypes. Cluster analysis indicated that the largest divergence was between North American and European cantalupensis and inodorus cultivars as one group, and the more "exotic" varieties: conomon, chito, dudaim, agrestis and momordica, as a second group. The molecular phylogeny agreed, broadly, with the classification of melon into two subspecies, and did not contradict the division into "horticultural varieties". It was apparent, however, that the infra-specific division is rather loose, molecular variation being distributed continuously between and within cultivar groups. We suggest that despite the morphological diversity, separation between varietal-groups may be based on a too small number of genes to enable unambiguous infra-specific classification based on DNA diversity.

Sleep-wake differences in scaling behavior of the human heartbeat: analysis of terrestrial and long-term space flight data

Abstract: We compare scaling properties of the cardiac dynamics during sleep and wake periods for healthy individuals, cosmonauts during orbital flight, and subjects with severe heart disease. For all three groups, we find a greater degree of anticorrelation in the heartbeat fluctuations during sleep compared to wake periods. The sleep-wake difference in the scaling exponents for the three groups is comparable to the difference between healthy and diseased individuals. The observed scaling differences are not accounted for simply by different levels of activity, but appear related to intrinsic changes in the neuroautonomic control of the heartbeat.

The Evolution of Sharedplans

Abstract: Rational agents often need to work together. There are jobs that cannot be done by one agent—for example, singing a duet or operating a computer network—and jobs that are more efficiently done by more than one agent—for example, hanging a door or searching the Internet. Collaborative behavior—coordinated activity in which the participants work jointly with each other to satisfy a shared goal—is more than the sum of individual acts [24, 8] and may be distinguished from both interaction and simple coordination in terms of the commitments agents make to each other [4, 10, 9]. A theory of collaboration must therefore treat not only the intentions, abilities, and knowledge about action of individual agents, but also their coordination in group planning and acting. It also must account for the ways in which plans are incrementally formed and executed by the participants.

Attachment working models and cognitive openness in close relationships: A test of chronic and temporary accessibility effects.

Abstract: In 3 studies the authors explored the impact of chronic and temporary accessibility of attachment working models on cognitive openness in the realm of close relationships. In Study 1, participants rated their attachment style and perceptions of their romantic partner. In Study 2, they recalled a relationship defined by a particular attachment orientation and rated perceptions of the targeted partner. Study 3 was similar to Study 1, but secure attachment was primed for half of the participants. In all the studies, cognitive openness was assessed by changes in the perception of the partner after being exposed to information that disconfirmed expectations. Secure attachment was related to higher cognitive openness and better recall of expectation-incongruent information, mainly when this information was positively valued. The discussion emphasizes the implications of the chronic and contextual aspects of attachment working models for information processing.

Parental Perspectives on Inclusion: Effects of Autism and Down Syndrome.

Abstract: This study examined the effects of the child's diagnosis (autism vs. Down syndrome), age, and current educational placement on parental perceptions toward inclusion for their child with disabilities. Parents of children with autism and with Down syndrome completed surveys regarding their opinions on their child's current educational placement, their desire for changing the current placement, and their views on inclusive education. Results indicated that diagnosis, age, and current placement influenced parental opinion on the ideal educational placement for their child. Parents of children with Down syndrome were significantly more likely to endorse inclusion (full-time placement in general education) as the ideal educational program for their child whereas parents of children with autism were more likely to endorse mainstreaming (consistent part-time placement with general education students). Parents of younger children and parents whose children were already placed in general education programs were more positive towards inclusion than parents of older children or students currently in special education. Findings are discussed in terms of child characteristics and prevailing educational practices.

Adult attachment style and the perception of others: the role of projective mechanisms.

Abstract: In 3 reported studies the authors examined attachment-style differences in the perception of others and the hypothesis that projective mechanisms underlie these differences. In these studies, participants reported on their attachment style and generated actual-self-traits and unwanted-self-traits. Then, a 2nd session was conducted, in which impression formation about new persons (Study 1), the ease of retrieval of memories about known persons (Study 2), or memory inferences about learned features of fictional persons (Study 3) were assessed. Findings indicate that whereas anxious-ambivalent persons' impression formation, memory retrieval, and inferences about others reflected the projection of their actual-self-traits, avoidant persons' responses reflected the projection of their unwanted-self-traits. Findings are discussed in terms of the regulatory goals and strategies that characterize the mental representations of each attachment style.

Ownership Structure and Firm Performance: Evidence from Israel

Abstract: The study examines the effect of ownership structure on firm performance. We distinguish between family firms, firms controlled by partnerships of individuals, concern controlled firms, and firms where blockholders have less than 50% of the vote. The empirical work analyzes data on 280 Israeli firms and employs the technique of Data Envelopment Analysis. It is found that owner-manager firms are less efficient in generating net income than firms managed by a professional (non-owner) manager, and that family firms run by their owners perform (relatively) the worst. This evidence suggests that the modern form of business organization, namely the open corporation with disperse ownership and non-owner managers, promotes firm performance.

X-ray photoelectron spectroscopy study of surface films formed on Li electrodes freshly prepared in alkyl carbonate solutions

Abstract: Li samples were freshly prepared (shearing) and stored (2 days) in dimethyl carbonate (DMC), and ethyl carbonate−diethyl carbonate (EC−DEC), and dry (20 ppm of H2O) and wet (500 ppm of H2O) EC−DMC solutions of LiAsF6 (1 M), and were then studied by X-ray photoelectron spectroscopy (XPS). The XPS analysis, including depth profiling of these surface films, appears to be reliable on the qualitative level only, because both the X-ray beam and sputtering should be suspected as being partially destructive to the surface films on lithium. These studies basically confirm previous conclusions obtained by Fourier transform infrared spectroscopy spectroscopic studies of Li surfaces. Surface films formed on Li in alkyl carbonate solutions of LiAsF6 are comprised of ROCO2Li, Li2CO3, LiF, LixAsFy, and Li oxides. XPS could also detect surface species with Li−C bonds (e.g., LiCH2CH2OCO2Li). When EC is present, its reduction dominates the surface film formation. The presence of water suppresses both solvent and salt anion...

Committee-based sample selection for probabilistic classifiers

Abstract: In many real-world learning tasks it is expensive to acquire a sufficient number of labeled examples for training This paper investigates methods for reducing annotation cost by sample selection In this approach, during training the learning program examines many unlabeled examples and selects for labeling only those that are most informative at each stage This avoids redundantly labeling examples that contribute little new information Our work follows on previous research on Query By Committee, and extends the committee-based paradigm to the context of probabilistic classification We describe a family of empirical methods for committee-based sample selection in probabilistic classification models, which evaluate the informativeness of an example by measuring the degree of disagreement between several model variants These variants (the committee) are drawn randomly from a probability distribution conditioned by the training set labeled so far The method was applied to the real-world natural language processing task of stochastic part-of-speech tagging We find that all variants of the method achieve a significant reduction in annotation cost, although their computational efficiency differs In particular, the simplest variant, a two member committee with no parameters to tune, gives excellent results We also show that sample selection yields a significant reduction in the size of the model used by the tagger

Stochastic resonance in linear systems subject to multiplicative and additive noise

Abstract: Exact expressions have been found for the first two moments and the correlation function for an overdamped linear system subject to an external periodic field as well as to multiplicative and additive noise. Stochastic resonance is absent for Gaussian white noise. However, when the multiplicative noise has the form of an asymmetric dichotomous noise, the signal-to-noise ratio (SNR) becomes a nonmonotonic function of the correlation time and the asymmetry of noise. Moreover, the SNR turns out to be a nonmonotonic function of the frequency of the external field as well as strongly depending on the strength of the cross correlation between multiplicative and additive noise.

Facets of Personal Values: A Structural Analysis of Life and Work Values

Abstract: On a traditionnellement enquete sur les valeurs generales de vie et les valeurs de travail separement. L'objectif de la presente etude etait de suggerer une definition a plusieurs facettes des valeurs personnelles, integrant a la fois les valeurs de vie et de travail et de la tester empiriquement. Des donnees recueillies a partir d'un echantillon de 165 directeurs et employes Israeliens viennent a l'appui des hypotheses structurelles de l'etude. Une structure empirique conique tridimensionnelle a ete mise en evidence au moyen d'une analyse spatiale fine (Smallest Space Analysis). Les valeurs relatives a la vie et celles relatives au travail y occupent deux regions distinctes pouvant etre toutes deux decoupees plus avant selon la modalite (materielle, affective et cognitive) et la focalisation (focalisee ou diffuse) des facettes des valeurs personnelles. La sante, le bonheur, et l'amour etaient, pour cet echantillon, les valeurs de vie les plus importantes, tandis que l'interet pour le poste, la responsabilite, un chef equitable venaient au premier rang dans la hierarchie des valeurs de travail. Les resultats sont discutes dans le cadre d'hypotheses de compensation ou de report concernant la question des rapports entre travail et non travail.

Coating Carboxylic Acids on Amorphous Iron Nanoparticles

Abstract: Nanophased amorphous iron particles were coated by various carboxylic acids and their physical properties (differential scanning calorimetry, thermogravimetric analysis, temperature-programmed desorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and magnetism) were measured. The various properties were measured as a function of the alkyl chain length. The desorption pattern at 400 °C revealed a keto derivative.

Feasible Formation of Coalitions Among Autonomous Agents in Nonsuperadditive Environments

Abstract: Cooperating and sharing resources by creating coalitions of agents are important ways for autonomous agents to execute tasks and to maximize payoff. Such coalitions will form only if each member of a coalition gains more by joining the coalition than it could gain otherwise. There are several ways of creating such coalitions and dividing the joint payoff among the members. In this paper we present algorithms for coalition formation and payoff distribution in nonsuperadditive environments. We focus on a low-complexity kernel-oriented coalition formation algorithm. The properties of this algorithm were examined via simulations. These have shown that the model increases the benefits of the agents within a reasonable time period, and more coalition formations provide more benefits to the agents.