Showing papers by "École normale supérieure de Cachan published in 2007"

"Experimental realization of Wheeler's delayed-choice Gedanken Experiment"

Abstract: We report an almost ideal realization of wheeler's "delayed-choice" experiment where the light pulses are true single photons, allowing unambiguous which-way measurements. The clock-triggered single-photon source at the heart of the experiment, previously developed for quantum key distribution, is based on the pulsed, optically excited photoluminescence of a single N-V colour centre in a diamond nanocrystal. This system, which consists in a substitutional nitrogen atom (N) associated to a vacancy (V) in an adjacent lattice site of the diamond crystalline matrix, has an unsurpassed efficiency and photostability at room temperature.

Ribonucleotide reductase and the regulation of DNA replication: an old story and an ancient heritage.

Abstract: All organisms that synthesize their own DNA have evolved mechanisms for maintaining a constant DNA/cell mass ratio independent of growth rate. The DNA/cell mass ratio is a central parameter in the processes controlling the cell cycle. The co-ordination of DNA replication with cell growth involves multiple levels of regulation. DNA synthesis is initiated at specific sites on the chromosome termed origins of replication, and proceeds bidirectionally to elongate and duplicate the chromosome. These two processes, initiation and elongation, therefore determine the total rate of DNA synthesis in the cell. In Escherichia coli, initiation depends on the DnaA protein while elongation depends on a multiprotein replication factory that incorporates deoxyribonucleotides (dNTPs) into the growing DNA chain. The enzyme ribonucleotide reductase (RNR) is universally responsible for synthesizing the necessary dNTPs. In this review we examine the role RNR plays in regulating the total rate of DNA synthesis in E. coli and, hence, in maintaining constant DNA/cell mass ratios during normal growth and under conditions of DNA stress.

Luminescence properties of hexagonal boron nitride: Cathodoluminescence and photoluminescence spectroscopy measurements

Abstract: M. G. Silly,1,2 P. Jaffrennou,1,2,4 J. Barjon,3 J.-S. Lauret,4 F. Ducastelle,1,* A. Loiseau,1 E. Obraztsova,5 B. Attal-Tretout,2 and E. Rosencher2 1Laboratoire d’Etude des Microstructures, ONERA-CNRS, Boite Postale 72, 92322 Châtillon Cedex, France 2Departement de Mesures Physiques, ONERA, Chemin de la Huniere, 91761 Palaiseau Cedex, France 3Groupe d’Etude de la Matiere Condensee, Universite de Versailles St. Quentin, CNRS Bellevue, 1 place Aristide Briand, 92195 Meudon Cedex, France 4Laboratoire de Photonique Quantique et Moleculaire, Institut d’Alembert, Ecole Normale Superieure de Cachan, 61 Avenue du President Wilson, 94235 Cachan Cedex, France 5A. M. Prokhorov General Physics Institute of Russian Academy of Sciences, 38 Vavilov Street, 119991 Moscow, Russia Received 27 July 2006; revised manuscript received 21 December 2006; published 12 February 2007

Probabilistic QoS and soft contracts for transaction based Web services

Abstract: Web services orchestrations and choreographies require establishing quality of service (QoS) contracts with the user. This is achieved by performing QoS composition, based on contracts established between the orchestration and the called Web services. These contracts are typically stated in the form of hard guarantees (e.g., response time always less than 5 msec). In this paper we propose using soft contracts instead. Soft contracts are characterized by means of probability distributions for QoS parameters. We show how to compose such contracts, to yield a global contract (probabilistic) for the orchestration. Our approach is implemented by the TOrQuE tool. Experiments on TOrQuE show that overly pessimistic contracts can be avoided and significant room for safe overbooking exists.

Development of a renal microchip for in vitro distal tubule models.

Abstract: Current developments in tissue engineering and microtechnology fields have allowed the proposal of pertinent tools, microchips, to investigate in vitro toxicity. In the framework of the proposed REACH European directive and the 3R recommendations, the purpose of these microtools is to mimic organs in vitro to refine in vitro culture models and to ultimately reduce animal testing. The microchip consists of functional living cell microchambers interconnected by a microfluidic network that allows continuous cell feeding and waste removal controls by fluid microflow. To validate this approach, Madin Darby Canine Kidney (MDCK) cells were cultivated inside a polydimethylsiloxane microchip. To assess the cell proliferation and feeding, the number of inoculated cells varied from 5 to 10 x 10(5) cells/microchip (corresponding roughly to 2.5 to 5 x 10(5) cells/cm2) and from four flow rates 0, 10, 25, and 50 microL/min were tested. Morphological observations have shown successful cell attachment and proliferation inside the microchips. The best flow rate appears to be 10 microL/min with which the cell population was multiplied by about 2.2 +/- 0.1 after 4 days of culture, including 3 days of perfusion (in comparison to 1.7 +/- 0.2 at 25 microL/min). At 10 microL/min flow rate, maximal cell population reached about 2.1 +/- 0.2 x 10(6) (corresponding to 7 +/- 0.7 x 10(7) cells/cm(3)). The viability, assessed by trypan blue and lactate deshydrogenase measurements, was found to be above 90% in all experiments. At 10 microL/min, glucose monitoring indicated a cell consumption of 16 +/- 2 microg/h/10(6) cells, whereas the glutamine metabolism was demonstrated with the production of NH3 by the cells about 0.8 +/- 0.4 micromol/day/10(6) cells. Augmentation of the flow rate appeared to increase the glucose consumption and the NH3 production by about 1.5- to 2-fold, in agreement with the tendencies reported in the literature. As a basic chronic toxicity assessment in the microchips, 5 mM and 10 mM ammonium chloride loadings, supplemented in the culture media, at 0, 10, and 25 micaroL/min flow rates were performed. At 10 microL/min, a reduction of 35% of the growth ratio with 5 mM and of 50% at 10 mM was found, whereas at 25 microL/min, a reduction of 10% with 5 mM and of 30% at 10 mM was obtained. Ammonium chloride contributed to increase the glucose consumption and to reduce the NH3 production. The microchip advantages, high surface/volume ratio, and dynamic loadings, coupled with the concordance between the present and literature results dealing with ammonia/ammonium effects on MDCK illustrate the potential of our microchip for wider in vitro chronic toxicity investigations.

Supporting groups in sorting decisions: Methodology and use of a multi-criteria aggregation/disaggregation DSS

Abstract: This paper addresses the situation where a group wishes to cooperatively develop a common multicriteria evaluation model to sort actions (projects, candidates) into classes. It is based on an aggregation/disaggregation approach for the ELECTRE TRI method, implemented on the Decision Support System IRIS. We provide a methodology in which the group discusses how to sort some exemplary actions (possibly fictitious ones), instead of discussing what values the model parameters should take. This paper shows how IRIS may be used to help the group to iteratively reach an agreement on how to sort one or a few actions at a time, preserving the consistency of these sorting examples both at the individual level and at the collective level. The computation of information that may guide the discussion among the group members is also suggested. We provide an illustrative example and discuss some paths for future research motivated by this work.

Global existence for quadratic systems of reaction-diffusion

Abstract: We prove global existence in time of weak solutions to a class of quadratic reaction-diffusion systems for which a Lyapounov structure of LlogL-entropy type holds. The approach relies on an a priori dimension-independent L-2-estimate, valid for a wider class of systems includingalso some classical Lotka-Volterra systems, and which provides an L-1-bound on the nonlinearities, at least for not too degenerate diffusions. In the more degenerate case, some global existence may be stated with the use of a weaker notion of renormalized solution with defect measure, arising in the theory of kinetic equations.

Room temperature triggered single-photon source in the near infrared

Abstract: We report the realization of a solid-state triggered single-photon source with narrow emission in the near infrared at room temperature. It is based on the photoluminescence of a single nickel–nitrogen NE8 colour centre in a chemical vapour deposited diamond nanocrystal. Stable single-photon emission has been observed in the photoluminescence under both continuous-wave and pulsed excitations. The realization of this source represents a step forward in the application of diamond-based single-photon sources to quantum key distribution (QKD) under practical operating conditions.

Blind estimation of timing and carrier frequency offsets in OFDM systems

Abstract: Information fusion refers to the reconciliation of evidence presented by multiple sources of information in order to generate a decision. In the context of biometrics, evidence reconciliation plays a pivotal role in enhancing the recognition accuracy of human authentication systems and is referred to as multibiometrics. Multibiometric systems combine the information presented by multiple biometric sensors, algorithms, samples, units, or traits. Besides enhancing matching performance, these systems are expected to improve population coverage, deter spoofing and impart fault-tolerance to biometric applications. This introductory paper enumerates the various sources of biometric information that can be consolidated as well as the different levels of fusion in a biometric system. The role of using ancillary information such as biometric data quality and soft biometric traits (e.g., height) to enhance the performance of these systems is also discussed. It is becoming increasingly apparent that multibiometric systems will play a pivotal role in establishing identity in the 21st century.

Molecular Interaction and Energy Transfer between Human Serum Albumin and Polyoxometalates

Abstract: As a step toward the elucidation of the mechanistic pathways governing the known bioactivity of polyoxometalates (POMs), two representative molecules of this class of chemicals, the wheel-shaped [NaP5W30O110]14- (P5W30) and the Keggin-type anion [H2W12O40]6- (H2W12), are shown, by two independent techniques, to interact with the fatty-acid-free human serum albumin (HSA). The excited-state lifetime of the single tryptophan molecule of this protein is dramatically decreased by the binding. The quenching mechanism is found to constitute the first example of energy transfer between HSA and POMs. Such molecular recognition is believed to be a key step for subsequent evolution of the systems. Circular dichroism (CD) was used to assess the structural effects of POM binding on HSA and to confirm the interaction revealed by fluorescence studies. CD experiments showed that the two POMs have different effects on the secondary structure of the protein. Binding P5W30 partially unfolds the protein whereas H2W12 has no ...

Fluorescence Quenching upon Binding of Copper Ions in Dye‐Doped and Ligand‐Capped Polymer Nanoparticles: A Simple Way to Probe the Dye Accessibility in Nano‐Sized Templates

Abstract: The synthesis and properties of well-defined core–shell type fluorescent metal-chelating polymer nanoparticles NP, in the 15 nm diameter range, with a fluorophore (9,10-diphenylanthracene: DPA) entrapped in the particle core and a selective ligand (1,4,8,11-tetraazacyclotetradecane: Cyclam), grafted onto the surface are presented NPs with different number of dye-per-particle are readily obtained by entrapment of the fluorophore within the polymer core The ligand-coated NPs exhibit a high affinity for Cu2+ ions in aqueous solution and quenching of the DPA fluorescence is observed upon binding of copper The quenching of fluorescence arises through energy transfer (FRET) from the dye to the copper-cyclam complexes that form at the NP surface with an operating distance (d) in the 2 nm range A simple core–shell model accounts for the steady-state and time-resolved fluorescence titration experiments: dye molecules located in the outer sphere (thickness d) of the NPs are quenched while the fluorescence of dyes embedded more deeply is not affected by the binding of copper ions The observed high quenching efficiency (60–65 %), which is tightly correlated to the volumic and microstructural features of the NPs, shed light on the enhanced accessibility inherent in nano-sized templates The response towards different metal ions was investigated and this confirmed the selectivity of the nanoparticle template-assembled sensor for cupric ions

Model order selection for short data: an exponential fitting test (EFT)

Abstract: High-resolution methods for estimating signal processing parameters such as bearing angles in array processing or frequencies in spectral analysis may be hampered by the model order if poorly selected. As classical model order selection methods fail when the number of snapshots available is small, this paper proposes a method for noncoherent sources, which continues to work under such conditions, while maintaining low computational complexity. For white Gaussian noise and short data we show that the profile of the ordered noise eigenvalues is seen to approximately fit an exponential law. This fact is used to provide a recursive algorithm which detects a mismatch between the observed eigenvalue profile and the theoretical noise-only eigenvalue profile, as such a mismatch indicates the presence of a source. Moreover this proposed method allows the probability of false alarm to be controlled and predefined, which is a crucial point for systems such as RADARs. Results of simulations are provided in order to show the capabilities of the algorithm.

Embedded discontinuity finite element method for modeling of localized failure in heterogeneous materials with structured mesh: an alternative to extended finite element method

Abstract: In this work we discuss the finite element model using the embedded discontinuity of the strain and displacement field, for dealing with a problem of localized failure in heterogeneous materials by using a structured finite element mesh. On the chosen 1D model problem we develop all the pertinent details of such a finite element approximation. We demonstrate the presented model capabilities for representing not only failure states typical of a slender structure, with crack-induced failure in an elastic structure, but also the failure state of a massive structure, with combined diffuse (process zone) and localized cracking. A robust operator split solution procedure is developed for the present model taking into account the subtle difference between the types of discontinuities, where the strain discontinuity iteration is handled within global loop for computing the nodal displacement, while the displacement discontinuity iteration is carried out within a local, element-wise computation, carried out in parallel with the Gauss-point computations of the plastic strains and hardening variables. The robust performance of the proposed solution procedure is illustrated by a couple of numerical examples. Concluding remarks are stated regarding the class of problems where embedded discontinuity finite element method (ED-FEM) can be used as a favorite choice with respect to extended FEM (X-FEM).

Water waves generated by a moving bottom

Abstract: Waves at the surface of a liquid can be generated by various mechanisms: wind blowing on the free surface, wavemaker, moving disturbance on the bottom or the surface, or even inside the liquid, fall of an object into the liquid, liquid inside a moving container, etc. In this paper, we concentrate on the case where the waves are created by a given motion of the bottom. One example is the generation of tsunamis by a sudden seafloor deformation.

Inferring periodic orbits from spectra of simply shaped microlasers

Abstract: Dielectric microcavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate microlasers of simple shapes (Fabry-Perot, square, pentagon, and disk). Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with microdisks.