Showing papers by "Tel Aviv University published in 1986"

Eigen values and expanders

Abstract: Linear expanders have numerous applications to theoretical computer science Here we show that a regular bipartite graph is an expanderif and only if the second largest eigenvalue of its adjacency matrix is well separated from the first This result, which has an analytic analogue for Riemannian manifolds enables one to generate expanders randomly and check efficiently their expanding properties It also supplies an efficient algorithm for approximating the expanding properties of a graph The exact determination of these properties is known to be coNP-complete

An Efficient Algorithm for Spectral Analysis of Heart Rate Variability

Abstract: We present a simple efficient algorithm for the derivation of a heart rate signal from the electrocardiogram. We demonstrate that the amplitude spectrum of this heart rate signal more closely matches that of the input signal to an integral pulse frequency modulation (IPFM) model of the heart's pacemaker than do the spectra of other ECG-derived heart rate signals. The applicability of this algorithm in cross-spectral analysis between heart rate and other physiologic signals is also discussed.

Fees Versus Royalties and the Private Value of a Patent

Abstract: We compare how much profit an owner of a patented cost-reducing invention can realize by licensing it to an oligopolistic industry producing a homogeneous product, by means of a fixed fee or a per unit royalty. Our analysis is conducted in terms of a noncooperative game involving n + 1 players: the inventor and the n firms. In this game the inventor acts as a Stackelberg leader, and it has a unique subgame perfect equilibrium in pure strategies. It is shown that licensing by means of a fixed fee is superior to licensing by means of a royalty for both the inventor and consumers. Only a "drastic" innovation is licensed to a single producer.

Efficient algorithms for finding minimum spanning trees in undirected and directed graphs

Abstract: Recently, Fredman and Tarjan invented a new, especially efficient form of heap (priority queue). Their data structure, theFibonacci heap (or F-heap) supports arbitrary deletion inO(logn) amortized time and other heap operations inO(1) amortized time. In this paper we use F-heaps to obtain fast algorithms for finding minimum spanning trees in undirected and directed graphs. For an undirected graph containingn vertices andm edges, our minimum spanning tree algorithm runs inO(m logβ (m, n)) time, improved fromO(mβ(m, n)) time, whereβ(m, n)=min {i|log(i) n ≦m/n}. Our minimum spanning tree algorithm for directed graphs runs inO(n logn + m) time, improved fromO(n log n +m log log log(m/n+2) n). Both algorithms can be extended to allow a degree constraint at one vertex.

Statistical Theory of Groundwater Flow and Transport: Pore to Laboratory, Laboratory to Formation, and Formation to Regional Scale

Abstract: The statistical approach has been applied increasingly to groundwater flow problems in the last decade, as is illustrated in Figure 3 by the cumulative number of articles published in this field in Water Resources Reseach. This development has been motivated by the recognition of the fact that porous formations are heterogeneous, i.e., with properties which vary in an irregular manner in space. Flow domains are characterized by the length scale L of their spatial extent and three such scales of a fundamental nature are introduced: the laboratory, the local, and the regional scale. Heterogeneity is characterized by the spatial correlation scale I of the property of interest, the three scales corresponding to the above ones being the pore scale, the log hydraulic conductivity, and the log transmissivity integral scales. The medium properties and related flow variables are regarded as random space functions which satisfy two basic requirements: they enjoy some type of stationarity and I ≪ L. An additional scale D is the measurement or computational scale, characterizing the size of the measurement device of a flow variable or the element over which the variable is averaged for computational purposes. In both cases, the interest resides in the space average of the flow variable over a volume or area of length scale D. The primary aim of the theory of flow and transport through porous media is to determine the statistical moments of the space-averaged variables, given the statistical structure of the spatially variable property. The main objective of the study is to show that flow and transport problems at the three fundamental scales can be treated by a unified statistical approach, along this line. The specific aspects of each scale are examined separately, and areas of interest for future research are indicated. In the concluding remarks it is submitted that the statistical approach to groundwater flow has become a comprehensive theory, beyond the stage of an ad hoc modeling technique.

Multichannel Landauer formula for thermoelectric transport with application to thermopower near the mobility edge

Abstract: Various thermoelectric linear transport coefficients are defined and calculated for two reservoirs connected with ideal multichannel leads and a segment of an arbitrary disordered system. The reservoirs have different temperatures and chemical potentials. All of the inelastic scattering (and, thus, the dissipation) is assumed to occur only in the reservoirs. The definitions of the chemical potentials and temperature differences across the sample itself (mostly due to elastic scattering) are presented. Subtleties of the thermoelectric effects across the sample are discussed. The associated transport coefficients display deviations from the Onsager relations and from the Cutler-Mott formula for the thermopower (although the deviations vanish for a large number of channels and/or high resistance). The expression obtained is used to predict the critical behavior of the electronic thermopower near the mobility edge. It is shown to satisfy a scaling form in the temperature and separation from the mobility edge.

On the union of Jordan regions and collision-free translational motion amidst polygonal obstacles

Abstract: Let ?1,..., ?m bem simple Jordan curves in the plane, and letK1,...,Km be their respective interior regions. It is shown that if each pair of curves ?i, ?j,i ?j, intersect one another in at most two points, then the boundary ofK=?i=1mKi contains at most max(2,6m ? 12) intersection points of the curves?1, and this bound cannot be improved. As a corollary, we obtain a similar upper bound for the number of points of local nonconvexity in the union ofm Minkowski sums of planar convex sets. Following a basic approach suggested by Lozano Perez and Wesley, this can be applied to planning a collision-free translational motion of a convex polygonB amidst several (convex) polygonal obstaclesA1,...,Am. Assuming that the number of corners ofB is fixed, the algorithm presented here runs in timeO (n log2n), wheren is the total number of corners of theAi's.

Hydrophobic interactions: role in bacterial adhesion

Abstract: The last decade has seen a dramatic rise in scientific interest in the field of bacterial adhesion and related subjects. Much of this interest has been directed in search of “specific interactions” between bacterium and substratum, such as those that are inhibited by specific sugar moieties. A second avenue of research has been the study of the role of less specific, hydrophobic interactions. Since it appears that this second avenue of research is being increasingly followed, reviews dealing with bacterial hydrophobicity and adhesion should be of use. The aims of the present chapter are to (1) present some relevant aspects of hydrophobic interactions; (2) describe the methodology available for measurements related to bacterial cell-surface hydrophobicity and the parameters they may measure; (3) discuss investigations dealing with surface components that promote or reduce bacterial hydrophobicity; and (4) survey studies related to the role of hydrophobic interactions in mediating bacterial adhesion to interfaces, traversing areas of environmental and medical interest.

Too Many Words: Length of Utterance and Pragmatic Failure

Abstract: This paper investigates the theoretical and applied domains of pragmatic failure. With respect to theory, it further clarifies pragmatic failure both in native and non-native speech, and with respect to the applied domain compares request realizations of native and non-native speakers in terms of length of utterance. In discussing the results of this comparison, a number of hypotheses are put forward concerning the ways in which deviation from native norms of utterance length might be a potential cause for pragmatic failure.The data were collected within the CCSARP (Cross-Cultural Speech Act Realization Pattern) project involving seven different languages and dialects (Blum-Kulka & Olshtain, 1984). The data were collected from both native and non-native speakers of each of the languages. The analysis of responses across several languages revealed a systematic difference in length of utterance used to realize speech acts by non-native speakers as compared to native speakers. The types of pragmatic failure that might be linked to being a non-native speaker are examined, thus continuing a line of research focusing on the pragmatic aspects of interlanguage (Blum-Kulka, 1982; Thomas, 1983; Edmondson et al., 1984).

Systematic risk, total risk and size as determinants of stock market returns*

Abstract: This paper studies the historical relationship for the period 1962–1981 between stock market returns and the following variables: beta, residual standard deviation (or total variance), and size. We conclude that neither the traditional measure of risk (beta) nor the alternative risk measures (variance or residual standard deviation) can explain the cross-sectional variation in returns; only size seems to matter. When January returns are eliminated, even the size variable loses its statistical significance.

The Lognormal Fit to Raindrop Spectra from Frontal Convective Clouds in Israel

Abstract: Measurements of rain drop size spectra in Israel were carried out over a period of two years. It is shown that the size distribution can be best described by a lognormal distribution. With its parameters weighted by a certain choice of moments, this distribution has a better squared-error fit to the observed data than the gamma or the exponential distributions. Furthermore, this distribution is well suited for explaining drop size distribution effects in the dual-parameter remote measurement of rainfall. The lognormal distribution has the advantage that all its moments are also lognormally distributed. Its parameters, in their form presented here, have physical meaning (NT=drop concentration, Dg=the geometric mean diameter, and σ=standard geometric deviation). This facilitates direct interpretation of variations in the drop size spectrum. The different moments can easily be integrated to obtain simple expressions for the various rainfall parameters. The observed values of Dg and NT are found to d...

Strawberry Hemangioma in Preterm Infants

Abstract: Of 973 preterm infants, strawberry hemangioma was recorded in 124 during the first year of life, giving an overall frequency of 12.7%. Male:female ratio was 1:1.4. In 96 infants with birth weight below 1000 g, hemangioma occurred in 22 (22.9%), and in the group of very low-birth-weight infants (below 1500 g) the rate was 15.6%. Ninety-four infants had a single hemangioma and three had more than 10 lesions each. With one exception, no treatment was needed, as spontaneous involution started at age 5 to 12 months.

The Role of Threat to Self-Esteem and Perceived Control in Recipient Reaction to Help: Theory Development and Empirical Validation

Abstract: Publisher Summary This chapter focuses on one theoretical orientation—the threat to self-esteem model of reactions to aid—with the goal of introducing a conceptual development to it. The chapter discusses the basic postulates of the original Fisher et al. formulation and then examines the implications of it on the models of effective helping and coping. It discusses the way the findings of research on donor recipient similarity support the theoretical postulates. The chapter also describes the applied implications of the research and its place within the context of social psychology. This chapter illustrates that orientation opens the door for a true link between social psychological research and theory on helping and the world of social problems. Knowing recipients' immediate and long-term responses to help are likely to result in an enhanced ability to create helping programs that can truly help the recipient and enable the person to be self-reliant.

The neuroleptic malignant syndrome: agent and host interaction.

Abstract: This review comprises an exhaustive analysis of 120 case reports of neuroleptic malignant syndrome (NMS) representing the majority of published clinical data on this syndrome. Epidemiological, clinical and biological parameters, as well as those concerning the agent and the treatment of the syndrome, are critically evaluated on the basis of this data. The rate of neuroleptic loading is shown to play a cardinal role in the development of NMS. Rechallenge and aftercare of patients who need anti-psychotic treatment after NMS are considered.

Nonlinearity of Daveport:80Schinzel sequences and of generalized path compression schemes

Abstract: Davenport—Schinzel sequences are sequences that do not contain forbidden subsequences of alternating symbols. They arise in the computation of the envelope of a set of functions. We show that the maximal length of a Davenport—Schinzel sequence composed ofn symbols is Θ (nα(n)), where α(n) is the functional inverse of Ackermann’s function, and is thus very slowly increasing to infinity. This is achieved by establishing an equivalence between such sequences and generalized path compression schemes on rooted trees, and then by analyzing these schemes.

On the continuous limit for a system of classical spins

Abstract: The continuum limit of a cubic latice of classical spins processing in the magnetic field created by their closest neighbours is considered. Results concerning existence, uniqueness and (for initially small spin deviation) long time behaviour, are presented.

Stroke Rehabilitation Three Exercise Therapy Approaches

Abstract: The purpose of this study was to compare the therapeutic efficacy of three exercise therapy approaches. Three groups of adult stroke patients (N = 131) participated in the study. The first group received conventional treatment that consisted of traditional exercises and functional activities. The treatment of the second group was based on proprioceptive neuromuscular facilitation techniques. The third group was treated using the Bobath approach. The improvement of each patient was evaluated after six weeks of treatment in terms of functional gains in activities of daily living as measured using the Barthel index, changes in the muscle tone of the involved limbs as measured using a five-point ordinal scale, changes in the isolated motor control of the ankle and wrist as measured by tests of muscle strength and range of motion, and changes in the patients' ambulatory status as measured using a nominal scale of four categories. The therapeutic effects of exercise according to each of the three approaches were compared using descriptive and nonparametric statistical methods. No substantial advantage could be attributed to any one of the three therapeutic approaches.

Effect of pentoxifylline on the phagocytic activity, cAMP levels, and superoxide anion production by monocytes and polymorphonuclear cells.

Abstract: The effect of pentoxifylline (Trental) on the phagocytic capacity, cAMP levels, and superoxide anion production of human peripheral blood monocytes and polymorphonuclears (PMNs) was studied. The drug inhibited the phagocytosis of latex particles by both monocytes and PMNs in a dose-dependent manner. In addition, superoxide anion production during the phagocytic process was also reduced following incubation of the cells with pentoxifylline. It is suggested that this inhibitory effect is due to the increased intracellular levels of cAMP induced by the drug.