Showing papers by "Tel Aviv University published in 1997"

University Versus Corporate Patents: A Window On The Basicness Of Invention

Abstract: This paper is an attempt to quantify key aspects of innovations, ‘basicness’ and appropriability, and explore the linkages between them. We rely on detailed patent data. particularly on patent citations, thus awarding the proposed measures a very wide coverage. Relying on the prior that universities perform more basic research than corporations, we find that forward-looking measures of ‘importance’ and ‘generality’ capture aspects of the basicness of innovations. Similarly, measures of the degree of reliance on scientific sources. and of the closeness to the origins of innovational paths, appear to reflect the basicness of research. As measures of appropriability we use the fraction of citations coming from patents awarded to the sarne inventor, and in fact these measures are much higher for corporations than fbr universities. An examination of a small number of patents that are universally recognized as ‘basic’ provides further support for these measures. We find also evidence of the existence of ‘techno...

Software transactional memory

Abstract: As we learn from the literature, flexibility in choosing synchronization operations greatly simplifies the task of designing highly concurrent programs. Unfortunately, existing hardware is inflexible and is at best on the level of a Load–Linked/Store–Conditional operation on a single word. Building on the hardware based transactional synchronization methodology of Herlihy and Moss, we offer software transactional memory (STM), a novel software method for supporting flexible transactional programming of synchronization operations. STM is non-blocking, and can be implemented on existing machines using only a Load–Linked/Store–Conditional operation. We use STM to provide a general highly concurrent method for translating sequential object implementations to non-blocking ones based on implementing a k-word compare&swap STM-transaction. Empirical evidence collected on simulated multiprocessor architectures shows that our method always outperforms the non-blocking translation methods in the style of Barnes, and outperforms Herlihy’s translation method for sufficiently large numbers of processors. The key to the efficiency of our software-transactional approach is that unlike Barnes style methods, it is not based on a costly “recursive helping” policy.

A sub-constant error-probability low-degree test, and a sub-constant error-probability PCP characterization of NP

Abstract: We introduce a new low-degree-test, one that uses the restriction of low-degree polynomials to planes (i. e., afine sub-spaces of dimension 2), rather than the restriction to lines (i. e., afine sub-spaces of dimension 1). We prove the new test to be of a very small emorprobability (in particular, much smaller than constant). The new test enables us to prove a low-error characterization of NP in terms of PCP. Specifically, OUT theorem states that, for any given c > 0, membership in any NP language can be verijied with 0(1) accesses, each r’eading logarithmic number of bits, and such that the error-probability is 2‘“~’-’ n. Our results are in fact stronger, as stated below. One application of the new characterization of NP is that approximating SETCOVER to within a logarithmic factors is NP-hard. Previous analysis for low-degree-tests, as well as previous characten”zations of NP in terms of PCP, have managed to achieve, with constant number of accesses, error-probability of, at best, a constant. The proof for the smail err-or-probability of our new low-degree-test is, nevertheless, significantly simpler than previous proofs. In particular, it is combinatorial and geometrical in nature, rather than algebraic. 1 Characterizations of NP in terms of PCP Characterizing the class NP, by itself or with respect to other computational-complexity clssses, is perhaps one *URL http: //www.math.tau. ac.il/school/courses/PCP tWejzmm ~st., ISRAEL. ~-a@wj~dom.wej--$ ac,J 1Tel-Aviv University, ISRAEL. Permissionto nmhcdigiiol/hmi copies ol’iill w poti ,d’hs motcrizl Ibr personal or claswoom use is grmltd without fee provided Ih:)t the copies ‘are nof m.adt or disirihutcd I“or pI-o~II or ccrmmcrc. ial :Id\’Jm:Igt. Ilw L’OPV right notice. the Iil!c ot’lhc puhiimlion nnd iLs tiate nppcm’, imd uotice is given that copyright is by pcnniwi(m oflhe AChl, 10C. To copyolherwise. 10rcpuhlish. 10 POM m swvws or In redis(rilul!c In lists. requires specilic permission amikrr I’te .STOC ‘ 97 El ]>;lSO. ‘] ’~XSS [ IS.A Copyrighl1997 ACM O-8979 I-XNL61’9705 ,$3.50 of the most fundamental avenues of research in theory of computer-science. Since the early days, when the classes P and NP were defined, and the question was posed as to whether they are the same or do they differ, many problems were shown to be NP-complete, thereby increasing the weight on finding stricter characterization for the class NP. NP has since been given a few alternative characterizations. The one most commonly applied being Cook’s [CO071], which characterizes NP in terms of efficient verification of proofs (or nondeterministic computations). A new perspective, by which improved characterizations of NP can be obtained, has been recently proposed. The motivation for which stems from questions regarding the hardness of approximation versions, for problems whose exact computation is known to be NP-hard. This avenue of research was initiated by [FGL+91], which introduced a new methodology for proving hardness results for approximation problems. The method takes advantage of results in a seemingly unrelated area — that of interactive proofs [GMR89, Bab85, BGKW88, LFKN92, Sha92, BFL91] — however interprets those results with quite a different perspective in mind. Much effort has been invested since towards a better understanding of this methodology, and the class NP has consequently gained stricter characterizations [AS92, ALM+92, BGS95], which are referred to as characterizations of NP in terms of PCP (or, in short, PCP characterizations of NP). The PCP characterization of NP — though has taken around 20 years to be formulated — seems now as the most natural extension of the old characterization of NP [CO071], if one has in mind proving hardness results for approximation problems. This characterization has already been used to obtain quite a few hardness results for approximation problems [FGL+91, AS92, ALM+ 92, PY91, LY94, BGLR93, KLS93, BGS95, Hiis96a, H5a96b, H5s97]. The previous characterization of NP in terms of the PCP hierarchy [AS92, ALM+ 92], seemed at first ss the best possible up to constant factors. A stronger characterization was later conjectured in [BGLR93]; one that, as an outcome, implies NP-hardness of approximating SET-COVER to within logarithmic factors [LY94, BGLR93]. The conjecture itself, more-

Steric Effects in Electrolytes: A Modified Poisson-Boltzmann Equation

Abstract: The adsorption of large ions from solution to a charged surface is investigated theoretically. A generalized Poisson-Boltzmann equation which takes into account the finite size of the ions is presented. We obtain analytical expressions for the electrostatic potential and ion concentrations at the surface, leading to a modified Grahame equation. At high surface charge densities the ionic concentration saturates to its maximum value. Our results are in agreement with recent experiments.

An introduction to infinite ergodic theory

Abstract: Non-singular transformations General ergodic and spectral theorems Transformations with infinite invariant measures Markov maps Recurrent events and similarity of Markov shifts Inner functions Hyperbolic geodesic flows Cocycles and skew products Bibliography Index.

Advanced Model for Solid Electrolyte Interphase Electrodes in Liquid and Polymer Electrolytes

Abstract: Recent studies show that the SEI on lithium and on anodes in liquid nonaqueous solutions consists of many different materials including , LiF, LiCl, , alkoxides, and nonconducting polymers. The equivalent circuit for such a mosaic‐type SEI electrode is extremely complex. It is shown that near room temperature the grain‐boundary resistance (Rgb) for polyparticle solid electrolytes is larger than the bulk ionic resistance. Up to now, all models of SEI electrodes ignored the contribution of Rgb to the overall SEI resistance. We show here that this neglect has no justification. On the basis of recent results, we propose here for SEI electrodes equivalent circuits which take into account the contribution of grain‐boundary and other interfacial impedance terms. This model accounts for a variety of different types of Nyquist plots reported for lithium and electrodes in liquid nonaqueous and polymer electrolytes.

The effects of hours of work on health: A meta-analytic review.

Abstract: A quantitative and qualitative review of existing literature on working hours and health was carried out. Meta-analyses were performed on 21 study samples. Results indicated small, but significant positive mean correlations between overall health symptoms, physiological and psychological health symptoms, and hours of work. Qualitative analysis of 12 other studies supported these findings of a positive relationship between hours of work and ill-health. Different factors which may obscure the relationship between health and hours of work are discussed, together with other moderating influences. Taking these into account it is proposed that the results of the meta-analyses together with the qualitative analysis offer support for a link between hours of work and ill-health.

Finding and counting given length cycles

Abstract: We present an assortment of methods for finding and counting simple cycles of a given length in directed and undirected graphs. Most of the bounds obtained depend solely on the number of edges in the graph in question, and not on the number of vertices. The bounds obtained improve upon various previously known results.

Geometric hashing: an overview

Abstract: Geometric hashing, a technique originally developed in computer vision for matching geometric features against a database of such features, finds use in a number of other areas. Matching is possible even when the recognizable database objects have undergone transformations or when only partial information is present. The technique is highly efficient and of low polynomial complexity.

Factorization for hard exclusive electroproduction of mesons in QCD

Abstract: We formulate and prove a QCD factorization theorem for hard exclusive electroproduction of mesons in QCD. The proof is valid for the leading power in Q and all logarithms. This generalizes previous work on vector meson production in the diffractive region of small x. The amplitude is expressed in terms of off-diagonal generalizations of the usual parton densities. The full theorem applies to all kinds of meson and not just to vector mesons. The parton densities used include not only the ordinary parton density, but also ! ,

Optimal Quantum Cloning Machines

Abstract: We present quantum cloning machines that transform $N$ identical qubits into $MgN$ identical copies and we prove that the fidelity (quality) of these copies is optimal. The connection between cloning and measurement is discussed in detail. When the number of clones $M$ tends towards infinity, the fidelity of each clone tends towards the optimal fidelity that can be obtained by a measurement on the input qubits. More generally, quantum cloning machines are universal devices to translate quantum information into classical information.

Prospective and retrospective duration judgments: A meta-analytic review

Abstract: Most theorists propose that when a person is aware that a duration judgment must be made (prospective paradigm), experienced duration depends on attention to temporal information, which competes with attention to nontemporal information. When a person is not aware that a duration judgment must be made until later (retrospective paradigm), remembered duration depends on incidental memory for temporal information. In the present article we describe two experiments in which durations involved with high-level, executive-control functions were judged either prospectively or retrospectively. In one experiment, the executive function involved resolving syntactic ambiguity in reading. In another experiment, it involved controlling the switching between tasks. In both experiments, there was a unique cost to the operation of control high-level, executive functions which was manifested by prospective reproductions shortening a finding that supports an attentional model of prospective timing. In addition, activation of executive functions produced contextual changes that were encoded in memory and resulted in longer retrospective reproductions, a finding that supports a contextual-change model of retrospective timing. Thus, different cognitive processes underlie prospective and retrospective timing. Recent findings obtained by some brain researchers also support these conclusions.

Disaggregation of Alzheimer β-amyloid by site-directed mAb

Abstract: In Alzheimer disease, β-amyloid peptide accumulates in the brain as insoluble amyloid plaques. Amyloid filaments, similar to those found in amyloid plaques, can be assembled in vitro from chemically synthesized β-peptides. In this study, we report that antibodies raised against the N-terminal region (1–28) of the β-amyloid peptide bind to the in vitro-formed β-amyloid assemblies, leading to disaggregation of the fibrils and partial restoration of the peptide’s solubility. The concomitant addition of fibrillar β-amyloid with these antibodies to PC 12 cells leads to the inhibition of the neurotoxic effects of β-amyloid. Some of the mAbs raised against soluble β-peptide (1–28) have been found to prevent in vitro fibrillar aggregation of β-amyloid peptide. These experimental data suggest that site-directed mAbs interfere with the aggregation of β-amyloid and trigger reversal to its nontoxic, normal components. The above findings give hints on how to convert in vivo senile plaques into nontoxic, diffuse components and may have therapeutic interest for those studying Alzheimer disease and other human diseases related to amyloidogenic properties of physiological peptides and proteins.

The Distribution of Human Capital and Economic Growth

Abstract: This paper analyzes the interaction between the distribution of human capital, technological progress, and economic growth. It argues that the composition of human capital is an important factor in the determination of the pattern of economic development. The study demonstrates that the evolutionary pattern of the human capital distribution, the income distribution, and economic growth are determined simultaneously by the interplay between a local home environment externality and a global technological externality. In early stages of development the local home environment externality is the dominating factor and hence the distribution of income becomes polarized; whereas in mature stages of development the global technological externality dominates and the distribution of income ultimately contracts. Polarization, in early stages of development may be a necessary ingredient for future economic growth. An economy that prematurely implements a policy designed to enhance equality may be trapped at a low stage of development. An underdeveloped economy, which values equality as well as prosperity, may confront a trade-off between equality in the short-run followed by equality and stagnation in the long-run, and inequality in the short-run followed by equality and prosperity in the long run.

ATAXIA-TELANGIECTASIA AND THE NIJMEGEN BREAKAGE SYNDROME: Related Disorders But Genes Apart

Abstract: ▪ Abstract Gene mutations provide valuable clues to cellular metabolism. In humans such insights come mainly from genetic disorders. Ataxia-telangiectasia (A-T) and Nijmegen breakage syndrome (NBS) are two distinct, but closely related, single gene disorders that highlight a complex junction of several signal transduction pathways. These pathways appear to control defense mechanisms against specific types of damage to cellular macromolecules, and probably regulate the processing of certain types of DNA damage or normal intermediates of DNA metabolism. A-T is characterized primarily by cerebellar degeneration, immunodeficiency, genome instability, clinical radiosensitivity, and cancer predisposition. NBS shares all these features except cerebellar deterioration. The cellular phenotypes of A-T and NBS are almost indistinguishable, however, and include chromosomal instability, radiosensitivity, and defects in cell cycle checkpoints normally induced by ionizing radiation. The recent identification of the gene...

NOx from lightning 1. Global distribution based on lightning physics

Abstract: This paper begins a study on the role of lightning in maintaining the global distribution of nitrogen oxides (NOx) in the troposphere. It presents the first global and seasonal distributions of lightning-produced NOx (LNOx) based on the observed distribution of electrical storms and the physical properties of lightning strokes. We derive a global rate for cloud-to-ground (CG) flashes of 20–30 flashes/s with a mean energy per flash of 6.7×109 J. Intracloud (IC) flashes are more frequent, 50–70 flashes/s but have 10% of the energy of CG strokes and, consequently, produce significantly less NOx. It appears to us that the majority of previous studies have mistakenly assumed that all lightning flashes produce the same amount of NOx, thus overestimating the NOx production by a factor of 3. On the other hand, we feel these same studies have underestimated the energy released in CG flashes, resulting in two negating assumptions. For CG energies we adopt a production rate of 10×1016 molecules NO/J based on the current literature. Using a method to simulate global lightning frequencies from satellite-observed cloud data, we have calculated the LNOx on various spatial (regional, zonal, meridional, and global) and temporal scales (daily, monthly, seasonal, and interannual). Regionally, the production of LNOx is concentrated over tropical continental regions, predominantly in the summer hemisphere. The annual mean production rate is calculated to be 12.2 Tg N/yr, and we believe it extremely unlikely that this number is less than 5 or more than 20 Tg N/yr. Although most of LNOx, is produced in the lowest 5 km by CG lightning, convective mixing in the thunderstorms is likely to deposit large amounts of NOx, in the upper troposphere where it is important in ozone production. On an annual basis, 64% of the LNOx, is produced in the northern hemisphere, implying that the northern hemisphere should have natural ozone levels as much as 2 times greater than the southern hemisphere, even before anthropogenic influences. The amount of O3 produced from this NOx is expected to exceed the stratospheric source by a factor of 1.5, and thus the hemispheric asymmetry in LNOx would lead to a significant excess of northern hemisphere O3 even in the preindustrial troposphere. (The monthly climatologies for LNOx on a 1°×1° latitude-longitude grid can be obtained by e-mail to cprice@flash.tau.ac.il).

Interaction between ATM protein and c-Abl in response to DNA damage

Abstract: The gene mutated in the autosomal recessive disorder ataxia telangiectasia (AT), designated ATM (for 'AT mutated'), is a member of a family of phosphatidylinositol-3-kinase-like enzymes that are involved in cell-cycle control, meiotic recombination, telomere length monitoring and DNA-damage response. Previous results have demonstrated that AT cells are hypersensitive to ionizing radiation and are defective at the G1/S checkpoint after radiation damage. Because cells lacking the protein tyrosine kinase c-Abl are also defective in radiation-induced G1 arrest, we investigated the possibility that ATM might interact with c-Abl in response to radiation damage. Here we show that ATM binds c-Abl constitutively in control cells but not in AT cells. Our results demonstrate that the SH3 domain of c-Abl interacts with a DPAPNPPHFP motif (residues 1,373-1,382) of ATM. The results also reveal that radiation-induction of c-Abl tyrosine kinase activity is diminished in AT cells. These findings indicate that ATM is involved in the activation of c-Abl by DNA damage and this interaction may in part mediate radiation-induced G1 arrest.

SCIM--spinal cord independence measure: a new disability scale for patients with spinal cord lesions

Abstract: The Spinal Cord Independence Measure (SCIM) is a new disability scale developed specifically for patients with spinal cord lesions in order to make the functional assessments of patients with paraplegia or tetraplegia more sensitive to changes. The SCIM includes the following areas of function: self-care (subscore (0-20), respiration and sphincter management (0-40) and mobility (0-40). Each area is scored according to its proportional weight in these patients' general activity. The final score ranges from 0 to 100. This study was performed to evaluate the reliability of the SCIM and its sensitivity to functional changes in spinal cord lesion patients compared with the Functional Independence Measure (FIM). Thirty patients were included. Scores were recorded one week after admission and thereafter every month during hospitalization. Each area of function was assessed by a pair of staff members from the relevant discipline. The comparison of scores between each pair of rates revealed a remarkable consistency (r = 0.91-0.99; P < 0.0001; slope approximately 1; constant approximately 0). The total SCIM score (mean = 51, SD = 21) was lower than the total FIM score (mean = 87, SD = 23) owing to the difference in scale range structure and the relatively high cognitive scores of our patients; however, a relationship was noted between the scores of both scales (r = 0.85, P < 0.01). The SCIM was more sensitive than the FIM to changes in function of spinal cord lesion patients: the SCIM detected all the functional changes detected by the FIM total scoring, but the FIM missed 26% of the changes detected by the SCIM total scoring. The mean difference between consecutive scores was higher for the SCIM (P < 0.01). We conclude that the SCIM is a reliable disability scale and is more sensitive to changes in function in spinal cord lesion patients than the FIM. The SCIM when administered by a multidisciplinary team, may be a useful instrument for assessing changes in everyday performance in patients with spinal cord lesion.

Differential expression of two P5CS genes controlling proline accumulation during salt‐stress requires ABA and is regulated by ABA1, ABI1 and AXR2 in Arabidopsis

Abstract: Summary Proline is a common compatible osmolyte in higher plants Proline accumulation in response to water stress and salinity is preceded by a rapid increase of the mRNA level of Δ1-pyrroline-5-carboxylate synthase (P5CS) controlling the rate-limiting step of glutamate-derived proline biosynthesis P5CS is encoded by two differentially regulated genes in Arabidopsis Gene AtP5CS1 mapped to chromosome 2-785 is expressed in most plant organs, but silent in dividing cells Gene AtP5CS2 located close to marker m457 on chromosome 3–1013 contributes 20–40% of total P5CS mRNA in plant tissues, but is solely responsible for the synthesis of abundant P5CS mRNA in rapidly dividing cell cultures Accumulation of AtP5CS transcripts is regulated in a tissue specific manner and inducible by drought, salinity, ABA, and to a lesser extent by auxin Induction of AtP5CS1 mRNA accumulation in salt-treated seedlings involves an immediate early transcriptional response regulated by ABA signalling that is not inhibited by cycloheximide, but abolished by the deficiency of ABA biosynthesis in the aba1 Arabidopsis mutant However, inhibition of protein synthesis by cycloheximide prevents the induction of AtP5CS2 mRNA accumulation, and blocks further increase of AtP5CS1 mRNA levels during the second, slow phase of salt-induction Mutations abi1 and axr2, affecting ABA-perception in Arabidopsis, reduce the accumulation of both AtP5CS mRNAs during salt-stress, whereas ABA-signalling functions defined by the abi2 and abi3 mutations have no effect on salt-induction of the AtP5CS genes

Quantum Manipulations of Small Josephson Junctions

Abstract: Low-capacitance Josephson junction arrays in the parameter range where single charges can be controlled are suggested as possible physical realizations of the elements which have been considered in the context of quantum computers. We discuss single and multiple quantum-bit systems. The systems are controlled by applied gate voltages, which also allow the necessary manipulation of the quantum states. We estimate that the phase-coherence time is sufficiently long for experimental demonstration of the principles of quantum computation.

A construction of a cipher from a single pseudorandom permutation

Abstract: We suggest a scheme for a block cipher which uses only one randomly chosen permutation,F. The key, consisting of two blocks,K 1 andK 2, is used in the following way. The message block is XORed withK 1 before applyingF, and the outcome is XORed withK 2, to produce the cryptogram block. We show that the resulting cipher is secure (when the permutation is random or pseudorandom). This removes the need to store, or generate a multitude of permutations.

Querying the World Wide Web

Abstract: The World Wide Web is a large, heterogeneous, distributed collection of documents connected by hypertext links. The most common technology currently used for searching the Web depends on sending information retrieval requests to "index servers". One problem with this is that these queries cannot exploit the structure and topology of the document network. The authors propose a query language, WebSQL, that takes advantage of multiple index servers without requiring users to know about them, and that integrates textual retrieval with structure and topology-based queries. They give a formal semantics for WebSQL using a calculus based on a novel "virtual graph" model of a document network. They propose a new theory of query cost based on the idea of "query locality," that is, how much of the network must be visited to answer a particular query. Finally, they describe a prototype implementation of WebSQL written in Java.

Scale-sensitive dimensions, uniform convergence, and learnability

Abstract: Learnability in Valiant's PAC learning model has been shown to be strongly related to the existence of uniform laws of large numbers These laws define a distribution-free convergence property of means to expectations uniformly over classes of random variables Classes of real-valued functions enjoying such a property are also known as uniform Glivenko-Cantelli classes In this paper, we prove, through a generalization of Sauer's lemma that may be interesting in its own right, a new characterization of uniform Glivenko-Cantelli classes Our characterization yields Dudley, Gine´, and Zinn's previous characterization as a corollary Furthermore, it is the first based on a Gine´, and Zinn's previous characterization as a corollary Furthermore, it is the first based on a simple combinatorial quantity generalizing the Vapnik-Chervonenkis dimension We apply this result to obtain the weakest combinatorial condition known to imply PAC learnability in the statistical regression (or “agnostic”) framework Furthermore, we find a characterization of learnability in the probabilistic concept model, solving an open problem posed by Kearns and Schapire These results show that the accuracy parameter plays a crucial role in determining the effective complexity of the learner's hypothesis class

Thermodynamics and the measure of entanglement

Abstract: We point out formal correspondences between thermodynamics and entanglement. By applying them to previous work, we show that entropy of entanglement is the unique measure of entanglement for pure states.