Showing papers by "Technion – Israel Institute of Technology published in 2001"

Why people stay: using job embeddedness to predict voluntary turnover

Abstract: A new construct, entitled “job embeddedness,” is introduced. It includes individuals' (1) links to other people, teams, and groups, (2) perceptions of their fit with job, organization, and community, and (3) what they say they would have to sacrifice if they left their jobs. We developed a measure of job embeddedness with two samples. The results show that job embeddedness predicts the key outcomes of both intent to leave and 'voluntary turnover' and explains significant incremental variance over and above job satisfaction, organizational commitment, job alternatives, and job search.

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.

Human embryonic stem cells can differentiate into myocytes with structural and functional properties of cardiomyocytes.

Abstract: The study of human cardiac tissue development is hampered by the lack of a suitable in vitro model. We describe the phenotypic properties of cardiomyocytes derived from human embryonic stem (ES) cells. Human ES cells were cultivated in suspension and plated to form aggregates termed embryoid bodies (EBs). Spontaneously contracting areas appeared in 8.1% of the EBs. Cells from the spontaneously contracting areas within EBs were stained positively with anti-cardiac myosin heavy chain, anti--alpha-actinin, anti-desmin, anti--cardiac troponin I (anti-cTnI), and anti-ANP antibodies. Electron microscopy revealed varying degrees of myofibrillar organization, consistent with early-stage cardiomyocytes. RT-PCR studies demonstrated the expression of several cardiac-specific genes and transcription factors. Extracellular electrograms were characterized by a sharp component lasting 30 +/- 25 milliseconds, followed by a slow component of 347 +/- 120 milliseconds. Intracellular Ca(2+) transients displayed a sharp rise lasting 130 +/- 27 milliseconds and a relaxation component lasting 200--300 milliseconds. Positive and negative chronotropic effects were induced by application of isoproterenol and carbamylcholine, respectively. In conclusion, the human ES cell--derived cardiomyocytes displayed structural and functional properties of early-stage cardiomyocytes. Establishment of this unique differentiation system may have significant impact on the study of early human cardiac differentiation, functional genomics, pharmacological testing, cell therapy, and tissue engineering.

Analysis of Key-Exchange Protocols and Their Use for Building Secure Channels

Abstract: We present a formalism for the analysis of key-exchange protocols that combines previous definitional approaches and results in a definition of security that enjoys some important analytical benefits: (i) any key-exchange protocol that satisfies the security definition can be composed with symmetric encryption and authentication functions to provide provably secure communication channels (as defined here); and (ii) the definition allows for simple modular proofs of security: one can design and prove security of key-exchange protocols in an idealized model where the communication links are perfectly authenticated, and then translate them using general tools to obtain security in the realistic setting of adversary-controlled links. We exemplify the usability of our results by applying them to obtain the proof of two classes of key-exchange protocols, Diffie-Hellman and key-transport, authenticated via symmetric or asymmetric techniques.

Insulin production by human embryonic stem cells.

Abstract: Type 1 diabetes generally results from autoimmune destruction of pancreatic islet β-cells, with consequent absolute insulin deficiency and complete dependence on exogenous insulin treatment. The relative paucity of donations for pancreas or islet allograft transplantation has prompted the search for alternative sources for β-cell replacement therapy. In the current study, we used pluripotent undifferentiated human embryonic stem (hES) cells as a model system for lineage-specific differentiation. Using hES cells in both adherent and suspension culture conditions, we observed spontaneous in vitro differentiation that included the generation of cells with characteristics of insulin-producing β-cells. Immunohistochemical staining for insulin was observed in a surprisingly high percentage of cells. Secretion of insulin into the medium was observed in a differentiation-dependent manner and was associated with the appearance of other β-cell markers. These findings validate the hES cell model system as a potential basis for enrichment of human β-cells or their precursors, as a possible future source for cell replacement therapy in diabetes.

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.

Granular flow down an inclined plane: Bagnold scaling and rheology

Abstract: We have performed a systematic, large-scale simulation study of granular media in two and three dimensions, investigating the rheology of cohesionless granular particles in inclined plane geometries, i.e., chute flows. We find that over a wide range of parameter space of interaction coefficients and inclination angles, a steady-state flow regime exists in which the energy input from gravity balances that dissipated from friction and inelastic collisions. In this regime, the bulk packing fraction (away from the top free surface and the bottom plate boundary) remains constant as a function of depth z, of the pile. The velocity profile in the direction of flow vx(z) scales with height of the pile H, according to vx(z) proportional to H(alpha), with alpha=1.52+/-0.05. However, the behavior of the normal stresses indicates that existing simple theories of granular flow do not capture all of the features evidenced in the simulations.

Electrostatic field-assisted alignment of electrospun nanofibres

Abstract: This paper describes an electrostatic field-assisted assembly technique combined with an electrospinning process used to position and align individual nanofibres (NFs) on a tapered and grounded wheel-like bobbin. The bobbin is able to wind a continuously as-spun nanofibre at its tip-like edge. The alignment approach has resulted in polyethylene oxide-based NFs with diameters ranging from 100-300 nm and lengths of up to hundreds of microns. The results demonstrate the effectiveness of this new approach for assembling NFs in parallel arrays while being able to control the average separation between the fibres.

Group communication specifications: a comprehensive study

Abstract: View-oriented group communication is an important and widely used building block for many distributed applications. Much current research has been dedicated to specifying the semantics and services of view-oriented group communication systems (GCSs). However, the guarantees of different GCSs are formulated using varying terminologies and modeling techniques, and the specifications vary in their rigor. This makes it difficult to analyze and compare the different systems. This survey provides a comprehensive set of clear and rigorous specifications, which may be combined to represent the guarantees of most existing GCSs. In the light of these specifications, over 30 published GCS specifications are surveyed. Thus, the specifications serve as a unifying framework for the classification, analysis, and comparison of group communication systems. The survey also discusses over a dozen different applications of group communication systems, shedding light on the usefulness of the presented specifications. This survey is aimed at both system builders and theoretical researchers. The specification framework presented in this article will help builders of group communication systems understand and specify their service semantics; the extensive survey will allow them to compare their service to others. Application builders will find a guide here to the services provided by a large variety of GCSs, which could help them choose the GCS appropriate for their needs. The formal framework may provide a basis for interesting theoretical work, for example, analyzing relative strengths of different properties and the costs of implementing them.

Green tea polyphenol (-)-epigallocatechin-3-gallate prevents N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration.

Abstract: In the present study we demonstrate neuroprotective property of green tea extract and (-)-epigallocatechin-3-gallate in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice model of Parkinson's disease. N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxin caused dopamine neuron loss in substantia nigra concomitant with a depletion in striatal dopamine and tyrosine hydroxylase protein levels. Pretreatment of mice with either green tea extract (0.5 and 1 mg/kg) or (-)-epigallocatechin-3-gallate (2 and 10 mg/kg) prevented these effects. In addition, the neurotoxin caused an elevation in striatal antioxidant enzymes superoxide dismutase (240%) and catalase (165%) activities, both effects being prevented by (-)-epigallocatechin-3-gallate. (-)-Epigallocatechin-3-gallate itself also increased the activities of both enzymes in the brain. The neuroprotective effects are not likely to be caused by inhibition of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine conversion to its active metabolite 1-methyl-4-phenylpyridinium by monoamine oxidase-B, as both green tea and (-)-epigallocatechin-3-gallate are very poor inhibitors of this enzyme in vitro (770 microg/mL and 660 microM, respectively). Brain penetrating property of polyphenols, as well as their antioxidant and iron-chelating properties may make such compounds an important class of drugs to be developed for treatment of neurodegenerative diseases where oxidative stress has been implicated.

The deoxyguanosine kinase gene is mutated in individuals with depleted hepatocerebral mitochondrial DNA.

Abstract: Mitochondrial DNA (mtDNA)-depletion syndromes (MDS; OMIM 251880) are phenotypically heterogeneous, autosomal-recessive disorders characterized by tissue-specific reduction in mtDNA copy number. Affected individuals with the hepatocerebral form of MDS have early progressive liver failure and neurological abnormalities, hypoglycemia and increased lactate in body fluids. Affected tissues show both decreased activity of the mtDNA-encoded respiratory chain complexes (I, III, IV, V) and mtDNA depletion. We used homozygosity mapping in three kindreds of Druze origin to map the gene causing hepatocerebral MDS to a region of 6.1 cM on chromosome 2p13, between markers D2S291 and D2S2116. This interval encompasses the gene (DGUOK) encoding the mitochondrial deoxyguanosine kinase (dGK). We identified a single-nucleotide deletion (204delA) within the coding region of DGUOK that segregates with the disease in the three kindreds studied. Western-blot analysis did not detect dGK protein in the liver of affected individuals. The main supply of deoxyribonucleotides (dNTPs) for mtDNA synthesis comes from the salvage pathway initiated by dGK and thymidine kinase-2 (TK2). The association of mtDNA depletion with mutated DGUOK suggests that the salvage-pathway enzymes are involved in the maintenance of balanced mitochondrial dNTP pools.

Enhancing the cellular downlink capacity via co-processing at the transmitting end

Abstract: A linear pre-processing plus encoding scheme is proposed, which significantly enhances cellular downlink performance, while putting the complexity burden on the transmitting end. The approach is based on LQ factorization of the channel transfer matrix combined with the "writing on dirty paper" approach (Caire, G. and Shamai, S., Proc. 38th Annual Allerton Conference on Communication, Control and Computing, 2000) for eliminating the effect of uncorrelated interference, which is fully known at the transmitter but unknown at the receiver. The attainable average rates with the proposed scheme approach those of optimum joint processing at the high SNR region.

A fast super-resolution reconstruction algorithm for pure translational motion and common space-invariant blur

Abstract: This paper addresses the problem of recovering a super-resolved image from a set of warped blurred and decimated versions thereof. Several algorithms have already been proposed for the solution of this general problem. In this paper, we concentrate on a special case where the warps are pure translations, the blur is space invariant and the same for all the images, and the noise is white. We exploit previous results to develop a new highly efficient super-resolution reconstruction algorithm for this case, which separates the treatment into de-blurring and measurements fusion. The fusion part is shown to be a very simple non-iterative algorithm, preserving the optimality of the entire reconstruction process, in the maximum-likelihood sense. Simulations demonstrate the capabilities of the proposed algorithm.

The cell-cycle regulatory protein Cks1 is required for SCF Skp2 -mediated ubiquitinylation of p27

Abstract: The cell-cycle regulatory protein Cks1 is required for SCF Skp2 -mediated ubiquitinylation of p27

Friction-Reducing Surface-Texturing in Reciprocating Automotive Components

Abstract: A model is presented to study the potential use of micro-surface structure in the form of micro pores to improve tribological properties of reciprocating automotive components. The Reynolds equation and the equation of motion are solved simultaneously for a simplified “piston/cylinder” system with surface texturing. The solution provides the time behavior of both the clearance and the friction force between the “piston ring” and “cylinder liner” surfaces. It is shown that surface texturing can efficiently be used to maintain hydrodynamic effects even with nominally parallel surfaces. It is also shown that optimum surface texturing may substantially reduce the friction losses in reciprocating automotive components. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001

The Order of Encryption and Authentication for Protecting Communications (or: How Secure Is SSL?)

Abstract: We study the question of how to generically compose symmetric encryption and authentication when building "secure channels" for the protection of communications over insecure networks. We show that any secure channels protocol designed to work with any combination of secure encryption (against chosen plaintext attacks) and secure MAC must use the encrypt-then-authenticate method. We demonstrate this by showing that the other common methods of composing encryption and authentication, including the authenticate-then-encrypt method used in SSL, are not generically secure. We show an example of an encryption function that provides (Shannon's) perfect secrecy but when combined with any MAC function under the authenticate-then-encrypt method yields a totally insecure protocol (for example, finding passwords or credit card numbers transmitted under the protection of such protocol becomes an easy task for an active attacker). The same applies to the encrypt-and-authenticate method used in SSH. On the positive side we show that the authenticate-then-encrypt method is secure if the encryption method in use is either CBC mode (with an underlying secure block cipher) or a stream cipher (that xor the data with a random or pseudorandom pad). Thus, while we show the generic security of SSL to be broken, the current practical implementations of the protocol that use the above modes of encryption are safe.

A unified approach to approximating resource allocation and scheduling

Abstract: We present a general framework for solving resource allocation and scheduling problems. Given a resource of fixed size, we present algorithms that approximate the maximum throughput or the minimum loss by a constant factor. Our approximation factors apply to many problems, among which are: (i) real-time scheduling of jobs on parallel machines, (ii) bandwidth allocation for sessions between two endpoints, (iii) general caching, (iv) dynamic storage allocation, and (v) bandwidth allocation on optical line and ring topologies. For some of these problems we provide the first constant factor approximation algorithm. Our algorithms are simple and efficient and are based on the local-ratio technique. We note that they can equivalently be interpreted within the primal-dual schema.

The capacity of discrete-time memoryless Rayleigh-fading channels

Abstract: We consider transmission over a discrete-time Rayleigh fading channel, in which successive symbols face independent fading, and where neither the transmitter nor the receiver has channel state information. Subject to an average power constraint, we study the capacity-achieving distribution of this channel and prove it to be discrete with a finite number of mass points, one of them located at the origin. We numerically compute the capacity and the corresponding optimal distribution as a function of the signal-to-noise ratio (SNR). The behavior of the channel at low SNR is studied and finally a comparison is drawn with the ideal additive white Gaussian noise channel.

The impact of frequency-flat fading on the spectral efficiency of CDMA

Abstract: The capacity of the randomly spread synchronous code-division multiple-access (CDMA) channel subject to frequency-flat fading is studied in the wide-band limit of large number of users. We find the spectral efficiency as a function of the number of users per chip, the distribution of the flat fading, and the signal-to-noise ratio (SNR), for the optimum receiver as well as linear receivers (single-user matched filter, decorrelator, and minimum mean-square error (MMSE)). The potential improvements due to both decentralized transmitter power control and multi-antenna receivers are also analyzed.

Learning in Networks of Cortical Neurons

Abstract: The results presented here demonstrate selective learning in a network of real cortical neurons. We focally stimulate the network at a low frequency (0.3–1 Hz) until a desired predefined response is observed 50 ± 10 msec after a stimulus, at which point the stimulus is stopped for 5 min. Repeated cycles of this procedure ultimately lead to the desired response being directly elicited by the stimulus. By plotting the number of stimuli required to achieve the target response in each cycle, we are able to generate learning curves. Presumably, the repetitive stimulation is driving changes in the circuit, and we are selecting for changes consistent with the predefined desired response. To the best of our knowledge, this is the first time learning of arbitrarily chosen tasks, in networks composed of real cortical neurons, is demonstrated outside of the body.

Exogenous ascorbic acid (vitamin c) increases resistance to salt stress and reduces lipid peroxidation

Abstract: The transition from reversible to permanent wilting, in whole tomato seedlings (Lycopersicon esculentum Mill. cv. M82) following severe salt-stress by root exposure to 300 mM NaCl, was investigated. Salinized seedlings wilted rapidly but recovered if returned to non-saline nutrient solution within 6 h. However, after 9 h of salt-treatment 100% of the seedlings remained wilted and died. Remarkably, the addition of an anti-oxidant (0.5 mM ascorbic acid) to the root medium, prior to and during salt-treatment for 9 h, facilitated the subsequent recovery and long-term survival of c .5 0% of the wilted seedlings. Other organic solutes without known anti-oxidant activity were not effective. Salt-stress increased the accumulation in roots, stems and leaves, of lipid peroxidation products produced by interactions with damaging active oxygen species. Additional ascorbic acid partially inhibited this response but did not significantly reduce sodium uptake or plasma membrane leakiness.

SALSA: the stochastic approach for link-structure analysis

Abstract: Today, when searching for information on the WWW, one usually performs a query through a term-based search engine. These engines return, as the query's result, a list of Web pages whose contents matches the query. For broad-topic queries, such searches often result in a huge set of retrieved documents, many of which are irrelevant to the user. However, much information is contained in the link-structure of the WWW. Information such as which pages are linked to others can be used to augment search algorithms. In this context, Jon Kleinberg introduced the notion of two distinct types of Web pages: hubs and authorities. Kleinberg argued that hubs and authorities exhibit a mutually reinforcing relationship: a good hub will point to many authorities, and a good authority will be pointed at by many hubs. In light of this, he dervised an algoirthm aimed at finding authoritative pages. We present SALSA, a new stochastic approach for link-structure analysis, which examines random walks on graphs derived from the link-structure. We show that both SALSA and Kleinberg's Mutual Reinforcement approach employ the same metaalgorithm. We then prove that SALSA is quivalent to a weighted in degree analysis of the link-sturcutre of WWW subgraphs, making it computationally more efficient than the Mutual reinforcement approach. We compare that results of applying SALSA to the results derived through Kleinberg's approach. These comparisions reveal a topological Phenomenon called the TKC effectwhich, in certain cases, prevents the Mutual reinforcement approach from identifying meaningful authorities.

Pancharatnam Berry phase in space-variant polarization-state manipulations with subwavelength gratings

Abstract: We report the appearance of a geometrical phase in space-variant polarization-state manipulations. This phase is related to the classic Pancharatnam–Berry phase. We show a method with which to calculate it and experimentally demonstrate its effect, using subwavelength metal stripe space-variant gratings. The experiment is based on a unique grating for converting circularly polarized light at a wavelength of 10.6 μm into an azimuthally polarized beam. Our experimental evidence relies on analysis of far-field images of the resultant polarization.

Fast geodesic active contours

Abstract: We use an unconditionally stable numerical scheme to implement a fast version of the geodesic active contour model. The proposed scheme is useful for object segmentation in images, like tracking moving objects in a sequence of images. The method is based on the Weickert-Romeney-Viergever (additive operator splitting) AOS scheme. It is applied at small regions, motivated by the Adalsteinsson-Sethian level set narrow band approach, and uses Sethian's (1996) fast marching method for re-initialization. Experimental results demonstrate the power of the new method for tracking in color movies.

Robust Threshold DSS Signatures

Abstract: We present threshold DSS (digital signature standard) signatures where the power to sign is shared by n players such that for a given parameter t