Showing papers by "École Normale Supérieure published in 2000"

Online and off-line handwriting recognition: a comprehensive survey

Abstract: Handwriting has continued to persist as a means of communication and recording information in day-to-day life even with the introduction of new technologies. Given its ubiquity in human transactions, machine recognition of handwriting has practical significance, as in reading handwritten notes in a PDA, in postal addresses on envelopes, in amounts in bank checks, in handwritten fields in forms, etc. This overview describes the nature of handwritten language, how it is transduced into electronic data, and the basic concepts behind written language recognition algorithms. Both the online case (which pertains to the availability of trajectory data during writing) and the off-line case (which pertains to scanned images) are considered. Algorithms for preprocessing, character and word recognition, and performance with practical systems are indicated. Other fields of application, like signature verification, writer authentification, handwriting learning tools are also considered.

Security Arguments for Digital Signatures and Blind Signatures

Abstract: Since the appearance of public-key cryptography in the seminal Diffie--Hellman paper, many new schemes have been proposed and many have been broken. Thus, the simple fact that a cryptographic algorithm withstands cryptanalytic attacks for several years is often considered as a kind of validation procedure. A much more convincing line of research has tried to provide ``provable'' security for cryptographic protocols. Unfortunately, in many cases, provable security is at the cost of a considerable loss in terms of efficiency. Another way to achieve some kind of provable security is to identify concrete cryptographic objects, such as hash functions, with ideal random objects and to use arguments from relativized complexity theory. The model underlying this approach is often called the ``random oracle model.'' We use the word ``arguments'' for security results proved in this model. As usual, these arguments are relative to well-established hard algorithmic problems such as factorization or the discrete logarithm. In this paper we offer security arguments for a large class of known signature schemes. Moreover, we give for the first time an argument for a very slight variation of the well-known El Gamal signature scheme. In spite of the existential forgery of the original scheme, we prove that our variant resists existential forgeries even against an adaptively chosen-message attack. This is provided that the discrete logarithm problem is hard to solve. Next, we study the security of blind signatures which are the most important ingredient for anonymity in off-line electronic cash systems. We first define an appropriate notion of security related to the setting of electronic cash. We then propose new schemes for which one can provide security arguments.

Mixing beliefs among interacting agents

Abstract: We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions towards an average opinion, whereas low thresholds result in several opinion clusters: members of the same cluster share the same opinion but are no longer influenced by members of other clusters.

Dynamics of sparsely connected networks of excitatory and inhibitory spiking neurons.

Abstract: The dynamics of networks of sparsely connected excitatory and inhibitory integrate-and-fire neurons are studied analytically. The analysis reveals a rich repertoire of states, including synchronous states in which neurons fire regularly; asynchronous states with stationary global activity and very irregular individual cell activity; and states in which the global activity oscillates but individual cells fire irregularly, typically at rates lower than the global oscillation frequency. The network can switch between these states, provided the external frequency, or the balance between excitation and inhibition, is varied. Two types of network oscillations are observed. In the fast oscillatory state, the network frequency is almost fully controlled by the synaptic time scale. In the slow oscillatory state, the network frequency depends mostly on the membrane time constant. Finite size effects in the asynchronous state are also discussed.

Systematic XPS studies of metal oxides, hydroxides and peroxides

Abstract: The results of a systematic XPS study, under high controlled conditions, of different basic oxides of transition metals, alkali and alkaline-earth metals are presented; the XPS data of some hydroxides and peroxides are also reported. Variations of the O 1s binding energies are analysed and one point of interest is the large binding energy scale obtained for O 1s peaks all associated with a ‘‘2− ’’ formal charge. Through extended Huckel theory-tight binding (EHT-TB) calculations, attempts are made to rationalize the observed variations. The results illustrate the significant differences between real charges on oxygen atoms in transition metal and alkaline-earth oxides.

Vortex formation in a stirred Bose-Einstein condensate

Abstract: Summary form only given. We report on an experiment performed with a gaseous Bose-Einstein condensate, which is analogous to the rotating bucket experiment performed with liquid He. The atoms are confined in a static, cylindrically symmetric Ioffe-Pritchard magnetic trap upon which we superimpose a nonaxisymmetric, attractive dipole potential created by a stirring laser beam. The combined potential leads to a cigar-shaped harmonic trap with a slightly anisotropic transverse profile. The transverse anisotropy is rotated as the gas is evaporatively cooled to Bose-Einstein condensation, and it plays the role of the bucket wall roughness. Pictures taken at various rotation frequencies, after a ballistic expansion of the condensate, clearly show that for fast enough rotation frequencies, we can generate one or several "holes" in the transverse density distribution corresponding to vortices. We discuss our determination of the critical frequency for the single and multiple vortex formation, and we report measurements of the nucleation time and the lifetime of the vortex state.

Authenticated key exchange secure against dictionary attacks

Abstract: Password-based protocols for authenticated key exchange (AKE) are designed to work despite the use of passwords drawn from a space so small that an adversary might well enumerate, off line, all possible passwords. While several such protocols have been suggested, the underlying theory has been lagging. We begin by defining a model for this problem, one rich enough to deal with password guessing, forward secrecy, server compromise, and loss of session keys. The one model can be used to define various goals. We take AKE (with "implicit" authentication) as the "basic" goal, and we give definitions for it, and for entity-authentication goals as well. Then we prove correctness for the idea at the center of the Encrypted Key-Exchange (EKE) protocol of Bellovin and Merritt: we prove security, in an ideal-cipher model, of the two-flow protocol at the core of EKE.

Synaptic Mechanisms and Network Dynamics Underlying Spatial Working Memory in a Cortical Network Model

Abstract: Single-neuron recordings from behaving primates have established a link between working memory processes and information-specific neuronal persistent activity in the prefrontal cortex. Using a network model endowed with a columnar architecture and based on the physiological properties of cortical neurons and synapses, we have examined the synaptic mechanisms of selective persistent activity underlying spatial working memory in the prefrontal cortex. Our model reproduces the phenomenology of the oculomotor delayed-response experiment of Funahashi et al. (S. Funahashi, C.J. Bruce and P.S. Goldman-Rakic, Mnemonic coding of visual space in the monkey's dorsolateral prefrontal cortex. J Neurophysiol 61:331-349, 1989). To observe stable spontaneous and persistent activity, we find that recurrent synaptic excitation should be primarily mediated by NMDA receptors, and that overall recurrent synaptic interactions should be dominated by inhibition. Isodirectional tuning of adjacent pyramidal cells and interneurons can be accounted for by a structured pyramid-to-interneuron connectivity. Robust memory storage against random drift of the tuned persistent activity and against distractors (intervening stimuli during the delay period) may be enhanced by neuromodulation of recurrent synapses. Experimentally testable predictions concerning the neural basis of working memory are discussed.

Generating solitons by phase engineering of a bose-einstein condensate

Abstract: Quantum phase engineering is demonstrated with two techniques that allow the spatial phase distribution of a Bose-Einstein condensate (BEC) to be written and read out. A quantum state was designed and produced by optically imprinting a phase pattern onto a BEC of sodium atoms, and matter-wave interferometry with spatially resolved imaging was used to analyze the resultant phase distribution. An appropriate phase imprint created solitons, the first experimental realization of this nonlinear phenomenon in a BEC. The subsequent evolution of these excitations was investigated both experimentally and theoretically.

Parameter-Free Elicitation of Utility and Probability Weighting Functions

Abstract: This paper proposes a two-step method to successively elicit utility functions and decision weights under rank-dependent expected utility theory and its "more descriptive" version: cumulative prospect theory. The novelty of the method is that it is parameter-free, and thus elicits the whole individual preference functional without imposing any prior restriction. This method is used in an experimental study to elicit individual utility and probability weighting functions for monetary outcomes in the gain and loss domains. Concave utility functions are obtained for gains and convex utility functions for losses. The elicited weighting functions satisfy upper and lower subadditivity and are consistent with previous parametric estimations. The data also show that the probability weighting function for losses is more "elevated" than for gains.

Anionic Pd(0) and Pd(II) intermediates in palladium-catalyzed Heck and cross-coupling reactions.

Abstract: The anions of PdCl(2)L(2) and Pd(OAc)(2), precursors of palladium(0) used in cross-coupling and Heck reactions, play a crucial role in these reactions. Tricoordinated anionic complexes Pd(0)L(2)Cl(-) and Pd(0)L(2)(OAc)(-) are the effective catalysts instead of the usually postulated Pd(0)L(2) complex. The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as well as the structure and reactivity of the arylpalladium(II) complexes produced in this reaction. Thus, pentacoordinated anionic complexes are formed, ArPdI(Cl)L(2)(-) or ArPdI(OAc)L(2)(-), the precursor of neutral trans-ArPd(OAc)L(2), instead of the usually postulated trans-ArPdIL(2) complex (L = PPh(3)).

Lattice code decoder for space-time codes

Abstract: We explore the lattice sphere packing representation of a multi-antenna system and the algebraic space-time (ST) codes. We apply the sphere decoding (SD) algorithm to the resulted lattice code. For the uncoded system, SD yields, with small increase in complexity, a huge improvement over the well-known V-BLAST detection algorithm. SD of algebraic ST codes exploits the full diversity of the coded multi-antenna system, and makes the proposed scheme very appealing to take advantage of the richness of the multi-antenna environment. The fact that the SD does not depend on the constellation size, gives rise to systems with very high spectral efficiency, maximum-likelihood performance, and low decoding complexity.

Mutations in SPINK5, encoding a serine protease inhibitor, cause Netherton syndrome.

Abstract: We describe here eleven different mutations in SPINK5, encoding the serine protease inhibitor LEKTI, in 13 families with Netherton syndrome (NS, MIM256500). Most of these mutations predict premature termination codons. These results disclose a critical role of SPINK5 in epidermal barrier function and immunity, and suggest a new pathway for high serum IgE levels and atopic manifestations.

Universal quantum computation with the exchange interaction.

Abstract: Various physical implementations of quantum computers are being investigated, although the requirements that must be met to make such devices a reality in the laboratory at present involve capabilities well beyond the state of the art. Recent solid-state approaches have used quantum dots, donor-atom nuclear spins or electron spins; in these architectures, the basic two-qubit quantum gate is generated by a tunable exchange interaction between spins (a Heisenberg interaction), whereas the one-qubit gates require control over a local magnetic field. Compared to the Heisenberg operation, the one-qubit operations are significantly slower, requiring substantially greater materials and device complexity--potentially contributing to a detrimental increase in the decoherence rate. Here we introduced an explicit scheme in which the Heisenberg interaction alone suffices to implement exactly any quantum computer circuit. This capability comes at a price of a factor of three in additional qubits, and about a factor of ten in additional two-qubit operations. Even at this cost, the ability to eliminate the complexity of one-qubit operations should accelerate progress towards solid-state implementations of quantum computation.

A game theoretic framework for bandwidth allocation and pricing in broadband networks

Abstract: In this paper, we present a game theoretic framework for bandwidth allocation for elastic services in high-speed networks. The framework is based on the idea of the Nash bargaining solution from cooperative game theory, which not only provides the rate settings of users that are Pareto optimal from the point of view of the whole system, but are also consistent with the fairness axioms of game theory. We first consider the centralized problem and then show that this procedure can be decentralized so that greedy optimization by users yields the system optimal bandwidth allocations. We propose a distributed algorithm for implementing the optimal and fair bandwidth allocation and provide conditions for its convergence. The paper concludes with the pricing of elastic connections based on users' bandwidth requirements and users' budget. We show that the above bargaining framework can be used to characterize a rate allocation and a pricing policy which takes into account users' budget in a fair way and such that the total network revenue is maximized.

Controlling droplet deposition with polymer additives

Abstract: Controlling the impact of drops onto solid surfaces is important for a wide variey of coating and deposition processes--for example, the treatment of plants with herbicides and pesticides requires precise targeting in order to meet stringent toxicological regulations. However, the outer wax-like layer of the leaves is a non-wetting substrate that causes sprayed droplets to rebound; often less than 50% of the initial spray is retained by the plant. Although the impact and subsequent retraction of non-wetting aqueous drops on a hydrophobic surface have been the subjects of extensive experimental and theoretical work, non-newtonian rheological effects have not been considered in any detail. Here we report that, by adding very small amounts of a flexible polymer to the aqueous phase, we can inhibit droplet rebound on a hydrophobic surface and markedly improve deposition without significantly altering the shear viscosity of the solutions. Our results can be understood by taking into account the non-newtonian elongational viscosity, which provides a large resistance to drop retraction after impact, thereby suppressing droplet rebound.

Step-by-Step Engineered Multiparticle Entanglement

Abstract: After quantum particles have interacted, they generally remain in an entangled state and are correlated at a distance by quantum-mechanical links that can be used to transmit and process information in nonclassical ways. This implies programmable sequences of operations to generate and analyze the entanglement of complex systems. We have demonstrated such a procedure for two atoms and a single-photon cavity mode, engineering and analyzing a three-particle entangled state by a succession of controlled steps that address the particles individually. This entangling procedure can, in principle, operate on larger numbers of particles, opening new perspectives for fundamental tests of quantum theory.

A reliable and valid measurement scale for the perceived service quality of banks

Abstract: Describes a study performed in Canada to develop a reliable and valid scale for the measurement of the perceived service quality of bank services. A sample of retail banking customers was questioned. The proposed scale is called banking service quality (BSQ) and comprises 31 items which span six dimensions: effectiveness and assurance; access; price; tangibles; services portfolio and reliability.

Disruption of Eph/ephrin signaling affects migration and proliferation in the adult subventricular zone

Abstract: The subventricular zone (SVZ) of the lateral ventricles, the largest remaining germinal zone of the adult mammalian brain, contains an extensive network of neuroblasts migrating rostrally to the olfactory bulb Little is known about the endogenous proliferation signals for SVZ neural stem cells or guidance cues along the migration pathway Here we show that the receptor tyrosine kinases EphB1-3 and EphA4 and their transmembrane ligands, ephrins-B2/3, are expressed by cells of the SVZ Electron microscopy revealed ephrin-B ligands associated with SVZ astrocytes, which function as stem cells in this germinal zone A three-day infusion of the ectodomain of either EphB2 or ephrin-B2 into the lateral ventricle disrupted migration of neuroblasts and increased cell proliferation These results suggest that Eph/ephrin signaling is involved in the migration of neuroblasts in the adult SVZ and in either direct or indirect regulation of cell proliferation

Are communities saturated? On the relationship between α, β and γ diversity

Abstract: A popular way to suggest a regional influence on local species diversity has been to plot local versus regional diversity. The form of these curves has been interpreted as evidence for or against “community saturation” due to species interactions. This interpretation, however, is unwarranted. Using the concepts of α, β and γ diversity, I show that local–regional richness curves are determined by the way total diversity is partitioned between its α and β components, which itself is a matter of scale. Changing the scale of the local community amounts to changing the scale at which the heterogeneity of the interactions between organisms and their environment manifests itself, and hence the balance between α and β diversity. Community saturation may occur because of physical limitations, but there are no theoretical grounds for the belief that species interactions set an absolute upper limit to diversity at any scale. A distinction between different meanings of the concept of “saturation” is proposed to clarify this issue. I argue that the challenge now is to understand the relationship between α and β diversity at multiple scales, and the processes that determine it.

Bose-einstein condensation in quasi-2D trapped gases

Abstract: We discuss Bose-Einstein condensation (BEC) in quasi-2D trapped gases and find that well below the transition temperature ${T}_{c}$ the equilibrium state is a true condensate, whereas at intermediate temperatures $Tl{T}_{c}$ one has a quasicondensate (condensate with fluctuating phase). The mean-field interaction in a quasi-2D gas is sensitive to the frequency ${\ensuremath{\omega}}_{0}$ of the (tight) confinement in the ``frozen'' direction, and one can switch the sign of the interaction by changing ${\ensuremath{\omega}}_{0}$. Variation of ${\ensuremath{\omega}}_{0}$ can also reduce the rates of inelastic processes. This offers promising prospects for tunable BEC in trapped quasi-2D gases.

Typing of intimin genes in human and animal enterohemorrhagic and enteropathogenic Escherichia coli: characterization of a new intimin variant.

Abstract: Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) produce the characteristic "attaching and effacing" (A/E) lesion of the brush border. Intimin, an outer membrane protein encoded by eae, is responsible for the tight association of both pathogens with the host cell. Several eae have been cloned from different EPEC and EHEC strains isolated from humans and animals. These sequences are conserved in the N-terminal region but highly variable in the last C-terminal 280 amino acids (aa), where the cell binding activity is localized. Based on these considerations, we developed a panel of specific primers to investigate the eae heterogeneity of the variable 3' region by using PCR amplification. We then investigated the distribution of the known intimin types in a large collection of EPEC and EHEC strains isolated from humans and different animal species. The existence of a yet-unknown family of intimin was suspected because several EHEC strains, isolated from human and cattle, did not react with any of the specific primer pairs, although these strains were eae positive when primers amplifying the conserved 5' end were used. We then cloned and sequenced the eae present in one of these strains (EHEC of serotype O103:H2) and subsequently designed a PCR primer that recognizes in a specific manner the variable 3' region of this new intimin type. This intimin, referred to as "epsilon," was present in human and bovine EHEC strains of serogroups O8, O11, O45, O103, O121, and O165. Intimin epsilon is the largest intimin cloned to date (948 aa) and shares the greatest overall sequence identity with intimin beta, although analysis of the last C-terminal 280 aa suggests a greater similarity with intimins alpha and gamma.

Photodegradation of the aminoazobenzene acid orange 52 by three advanced oxidation processes: UV/H2O2, UV/TiO2 and VIS/TiO2: Comparative mechanistic and kinetic investigations

Abstract: This paper presents the results obtained from the oxidation of the aminoazobenzene dye AO52 by the UV/H2O2, UV/TiO2 and VIS/TiO2 systems. In the former case, we investigated the formation of first by-products by means of GC/MS, HPLC and 1H NMR. spectroscopy. We conclude that hydroxyl radicals are added to aromatic rings in the ipso position with respect to the sulfonate group or to the azo-linkage-bearing carbon. The reaction of the inorganic radical with the N,N-dimethylamino substituent, leading to demethylation, adds to the multiplicity of the possible pathways. Degradation by the UV/TiO2 system is pH dependent. Whereas hydroxyl radicals are the main oxidative agent in neutral and alkaline solutions, positive hole-induced oxidation competes with the reduction of the protonated dye molecules in acid media. Moreover, FTIR spectroscopy of AO52/TiO2 wafers provided an insight to the nature of the photoproducts. This process is very efficient since only ultimate breakdown products, i.e. aliphatic acids and inorganic salts, are detected. Similar results were obtained using visible light as the irradiation source in the case of wafers whereas in heterogeneous solutions, the dye seems to be resistant to degradation.

Managerial Strategies of Domination. Power in Soft Bureaucracies

Abstract: This paper discusses the emergence and reinforcement of organizational political regimes based on domination and centralization in French organizations Domination and power are old concepts in organizational sociology, but the confrontation of two well-known approaches to politics in organizations, that of Weber and that of Crozier, suggests that an `archaic' notion such as domination is still very useful for understanding how business leaders `govern' organizations todayBased on empirical studies, the paper proposes that organizations should be seen as `soft bureaucracies', in which centralization and entrepreneurial forms of governance are combined Thus, choosing a Weberian point of view, this paper simultaneously describes organizations as `structures of domination' and as `structures of legitimacy' It defends the idea that, in spite of the success of the network form utopia, the re-emergence of bureaucracies is a sign that organizations are more and more politically centralized and governed

Photodimerization of anthracenes in fluid solution:structural aspects

Abstract: Owing to their versatile photophysical and photochemical properties, anthracene and its derivatives are being employed in many systems, for instance as energy migration probes in polymers, triplet sensitizers, molecular fluorosensors, electron acceptor or donor chromophores in artificial photosynthesis, photochromic substrates in 3D memory materials, etc. One remarkable feature is their ability to photodimerize under UV irradiation which induces considerable changes in their physical properties. This account reports the preparative and structural aspects of this very useful and protean photocycloaddition.

Efficacy of a cognitive-behavioral treatment for generalized anxiety disorder: evaluation in a controlled clinical trial.

Abstract: Recent advances in the understanding of worry have led to the development of treatments for generalized anxiety disorder (GAD). The present study tested a GAD treatment that targeted intolerance of uncertainty, erroneous beliefs about worry, poor problem orientation, and cognitive avoidance. Twenty-six primary GAD patients were randomly allocated to a treatment condition (n = 14) or a delayed treatment control condition (n = 12). Self-report, clinician, and significant other ratings assessed GAD and associated symptoms. The results show that the treatment led to statistically and clinically significant change at posttest and that gains were maintained at 6- and 12-month follow-ups. Furthermore, 20 of 26 participants (77%) no longer met GAD diagnostic criteria following treatment. With regard to the treatment's underlying model, the results show that intolerance of uncertainty significantly decreased over treatment and that gains were maintained at both follow-ups. Although nonspecific factors were not significant predictors of treatment outcome, their role in the treatment of GAD requires further investigation.