CiteULike: Author Fort

SOM's mathematics

JC Fort — 2008-08-03T16:09:29-00:00

Neural Networks, Vol. 19, No. 6-7. ( 2006), pp. 812-816.

Since the discovery of the SOM's by T. Kohonen, many results that provide a better description of their behaviour have been found. Most of them are very convincing, but from a mathematical point of view, only a few are actually proved. In this paper, we make a review of some results that are still to be proved and give some framework to formulate various questions.

Anderson localization of a non-interacting Bose–Einstein condensate

Giacomo Roati — 2008-06-12T04:36:16-00:00

Nature, Vol. 453, No. 7197., pp. 895-898.

Convergence of the Monte Carlo Expectation Maximization for Curved Exponential Families

Gersende Fort — 2008-06-27T14:24:56-00:00

The Annals of Statistics, Vol. 31, No. 4. (2003), pp. 1220-1259.

The Monte Carlo expectation maximization (MCEM) algorithm is a versatile tool for inference in incomplete data models, especially when used in combination with Markov chain Monte Carlo simulation methods. In this contribution, the almost-sure convergence of the MCEM algorithm is established. It is shown, using uniform versions of ergodic theorems for Markov chains, that MCEM converges under weak conditions on the simulation kernel. Practical illustrations are presented, using a hybrid random walk Metropolis Hastings sampler and an independence sampler. The rate of convergence is studied, showing the impact of the simulation schedule on the fluctuation of the parameter estimate at the convergence. A novel averaging procedure is then proposed to reduce the simulation variance and increase the rate of convergence.

An Agonist of Toll-Like Receptor 5 Has Radioprotective Activity in Mouse and Primate Models

Lyudmila Burdelya — 2008-05-10T12:08:46-00:00

Science, Vol. 320, No. 5873. (11 April 2008), pp. 226-230.

The toxicity of ionizing radiation is associated with massive apoptosis in radiosensitive organs. Here, we investigate whether a drug that activates a signaling mechanism used by tumor cells to suppress apoptosis can protect healthy cells from the harmful effects of radiation. We studied CBLB502, a polypeptide drug derived from Salmonella flagellin that binds to Toll-like receptor 5 (TLR5) and activates nuclear factor-kappaB signaling. A single injection of CBLB502 before lethal total-body irradiation protected mice from both gastrointestinal and hematopoietic acute radiation syndromes and resulted in improved survival. CBLB502 injected after irradiation also enhanced survival, but at lower radiation doses. It is noteworthy that the drug did not decrease tumor radiosensitivity in mouse models. CBLB502 also showed radioprotective activity in lethally irradiated rhesus monkeys. Thus, TLR5 agonists could potentially improve the therapeutic index of cancer radiotherapy and serve as biological protectants in radiation emergencies. 10.1126/science.1154986

Anderson localization of a non-interacting Bose-Einstein condensate

G Roati — 2008-04-17T07:32:09-00:00

(16 Apr 2008)

One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by Anderson, fifty years ago, in the context of transport of electrons in crystals. Anderson localization is actually a much more general phenomenon, and it has been observed in a large variety of systems, including light waves. However, it has never been observed directly for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to high degree of control of most of the system parameters, including interaction. Here we employ for the first time a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed with a onedimensional quasi-periodic lattice, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. Localization is clearly demonstrated by investigating transport properties, spatial and momentum distributions. We characterize the crossover, finding that the critical disorder strength scales with the tunnelling energy of the atoms in the lattice. Since the interaction in the condensate can be controlled at will, this system might be employed to solve open questions on the interplay of disorder and interaction and to explore exotic quantum phases.

A simple scaling approach to Mott conductivity

D Jana — 2004-12-28T16:09:47-00:00

Physica B, Vol. 344, No. 1. (15 February 2004), pp. 62-65.

Transfer Hydrogenation of Imines Catalyzed by a Nickel(0)/NHC Complex

S Kuhl — 2008-03-29T02:02:11-00:00

Organometallics, Vol. 22, No. 21. (13 October 2003), pp. 4184-4186.

Abstract: Transfer hydrogenation of imines to the corresponding amines by Et2CHONa catalyzed by the monocoordinate Ni(0)/N-heterocyclic carbene species Ni(0)/IMes has been studied. Using this catalyst, a variety of aldimines and ketimines were reduced in good to excellent yields under mild conditions.

A Comprehensive Standardized Model for Ultrawideband Propagation Channels

AF Molisch — 2008-03-14T09:37:18-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 54, No. 11. (2006), pp. 3151-3166.

A comprehensive statistical model is described for ultrawideband (UWB) propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, builtup outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the path gain as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay-dependent cluster decay constants. A separate model is specified for the frequency range below 1 GHz. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a Task Group as standard model for evaluation of UWB system proposals. This paper also presents a critical assessment of the applicability of the model and possible generalizations and improvements

Ultra-wideband channel model for communication around the human body

A Fort — 2008-03-14T09:37:49-00:00

Selected Areas in Communications, IEEE Journal on, Vol. 24, No. 4. (2006), pp. 927-933.

Using ultra-wideband (UWB) wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no detailed models describing the UWB radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have measured radio propagation around the body in a typical indoor environment and incorporated these results into a simple model. We then implemented this model on a computer and compared experimental data with the simulation results. This paper proposes a simple statistical channel model and a practical implementation useful for evaluating UWB body area communication systems.

Noise correlation spectroscopy of the broken order of a Mott insulating phase

V Guarrera — 2008-03-14T02:46:45-00:00

arXiv:0803.2015 (13 Mar 2008)

We use a two-color lattice to break the homogeneous site occupation of an atomic Mott Insulator of bosonic 87Rb. We detect the disruption of the ordered Mott domains via noise correlation analysis of the atomic density distribution after time-of-flight. The appearance of additional correlation peaks evidences the redistribution of the atoms into a strongly inhomogeneous insulating state, in quantitative agreement with the predictions.

On Evolutionary Spatial Heterogeneous Games

H Fort — 2008-01-04T11:30:12-00:00

(20 Dec 2007)

How coperation between self-interested individuals evolve is a crucial problem, both in biology and in social sciences, that is far from being well understood. Evolutionary game theory is a useful approach to this issue. The simplest model to take into account the spatial dimension in evolutionary games is in terms of cellular automata with just a one-parameter payoff matrix. Here, the effects of spatial heterogeneities of the environment and/or asymmetries in the interactions among the individuals are analysed through different extensions of this model. Instead of using the same universal payoff matrix, bimatrix games in which each cell at site (i,j) has its own different `temptation to defect' parameter T(i,j) are considered. Firstly, the case in which these individual payoffs are constant in time is studied. Secondly, an evolving evolutionary spatial game such that T=T(i,j;t), i.e. besides depending on the position evolves (by natural selection), is used to explore the combination of spatial heterogeneity and natural selection of payoff matrices.

Is the auditory sensory memory sensitive to visual information?

J Besle — 2007-10-30T20:46:45-00:00

Exp Brain Res, Vol. 166, No. 3-4. (October 2005), pp. 337-344.

The mismatch negativity (MMN) component of auditory event-related brain potentials can be used as a probe to study the representation of sounds in auditory sensory memory (ASM). Yet it has been shown that an auditory MMN can also be elicited by an illusory auditory deviance induced by visual changes. This suggests that some visual information may be encoded in ASM and is accessible to the auditory MMN process. It is not known, however, whether visual information affects ASM representation for any audiovisual event or whether this phenomenon is limited to specific domains in which strong audiovisual illusions occur. To highlight this issue, we have compared the topographies of MMNs elicited by non-speech audiovisual stimuli deviating from audiovisual standards on the visual, the auditory, or both dimensions. Contrary to what occurs with audiovisual illusions, each unimodal deviant elicited sensory-specific MMNs, and the MMN to audiovisual deviants included both sensory components. The visual MMN was, however, different from a genuine visual MMN obtained in a visual-only control oddball paradigm, suggesting that auditory and visual information interacts before the MMN process occurs. Furthermore, the MMN to audiovisual deviants was significantly different from the sum of the two sensory-specific MMNs, showing that the processes of visual and auditory change detection are not completely independent.

Early auditory-visual interactions in human cortex during nonredundant target identification.

A Fort — 2007-06-13T22:24:08-00:00

Brain Res Cogn Brain Res, Vol. 14, No. 1. (June 2002), pp. 20-30.

A common finding of behavioral studies is that objects characterized by redundant multisensory cues are identified more rapidly than the same objects presented in either unimodal condition. In a previous electrophysiological study in humans, we have described a network of crossmodal interactions that could be associated with this facilitation effect [M.H. Giard, F. Peronnet, J. Cogn. Neurosci. 11(5) (1999) 473-490]. Here, we sought to determine whether the recognition of objects characterized by nonredundant bimodal components may still induce crossmodal neural interactions. Subjects had to identify three objects defined either by auditory or visual features alone, or by the combination of nonredundant auditory and visual features. As expected, behavioral measures showed no sign of facilitation in bimodal processing. Yet, event-related potential analysis revealed the existence of early (<200 ms latency) crossmodal activities in sensory-specific and nonspecific cortical areas, that were partly dependent on the sensory dominance of the subjects to perform the task. Comparative analysis of the interaction patterns involved in redundant and nonredundant cue processing provides evidence for the robustness of the principle of crossmodal neural synergy that applies whatever the stimulus content (redundant or nonredundant information), and for the high flexibility of the neural networks of integration that are sensitive both to the nature of the perceptual task and to the sensory skill of the individual in that particular task.

Ultra-wide-band transmitter for low-power wireless body area networks: design and evaluation

J Ryckaert — 2007-04-11T01:26:06-00:00

Circuits and Systems I: Regular Papers, IEEE Transactions on [Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on], Vol. 52, No. 12. (2005), pp. 2515-2525.

The successful realization of a wireless body area network (WBAN) requires innovative solutions to meet the energy consumption budget of the autonomous sensor nodes. The radio interface is a major challenge, since its power consumption must be reduced below 100 /spl mu/W (energy scavenging limit). The emerging ultra-wide-band (UWB) technology shows strong advantages in reaching this target. First, most of the complexity of an UWB system is in the receiver, which is a perfect scenario in the WBAN context. Second, the very little hardware complexity of a UWB transmitter offers the potential for low-cost and highly integrated solutions. Finally, in a pulse-based UWB scheme, the transmitter can be duty-cycled at the pulse rate, thereby reducing the baseline power consumption. We present a low-power UWB transmitter that can be fully integrated in standard CMOS technology. Measured performances of a fully integrated pulse generator are provided, showing the potential of UWB for low power and low cost implementations. Finally, using a WBAN channel model, we present a comparison between our UWB solution and state-of-the-art low-power narrow-band implementations. This paper shows that UWB performs better in the short range due to a reduced baseline power consumption.

A 13,000-year climate record from western Tibet

F Gasse — 2007-01-28T08:56:38-00:00

Nature, Vol. 353, No. 6346. (24 October 1991), pp. 742-745.

Time Series Forecasting: Obtaining Long Term Trends with Self-Organizing Maps

Geoffroy Simon — 2007-01-11T07:22:37-00:00

(8 Jan 2007)

Kohonen self-organisation maps are a well know classification tool, commonly used in a wide variety of problems, but with limited applications in time series forecasting context. In this paper, we propose a forecasting method specifically designed for multi-dimensional long-term trends prediction, with a double application of the Kohonen algorithm. Practical applications of the method are also presented.

Mixed-Linkage Cellooligosaccharides: A New Class of Glycoside Hydrolase Inhibitors

Sébastien Fort — 2006-09-13T17:54:31-00:00

ChemBioChem, Vol. 2, No. 5. (2001), pp. 319-325.

A new class of inhibitors for ?-d-glycoside hydrolases, in which a single ?-(1?4)-glycosidic bond is incorporated into an otherwise all-?-(1?4)-linked oligosaccharide, is described. Such mixed ?/?-linkage cellooligosaccharides are not transition-state mimics, but instead are capable of utilising binding energy from numerous subsites, spanning either side of the catalytic centre, without the need for substrate distortion. This binding is significant; a mixed ?/?-d-tetrasaccharide acts competitively on a number of cellulases, displaying inhibition constants in the range of 40-300 ?m. Using the Bacillus agaradhaerens enzyme Cel5A as a model system, one such mixed ?/?-cellooligosaccharide, methyl 4II,4III-dithio-?-cellobiosyl-(1?4)-?-cellobioside, displays a Ki value of 100 ?m, an inhibition at least 150 times better than is observed with an equivalent all-?-linked compound. The three-dimensional structure of B. agaradhaerens Cel5A in complex with methyl 4II,4III-dithio-?-cellobiosyl-(1?4)-?-cellobioside has been determined at 1.8 Å resolution. This confirms the expected mode of binding in which the ligand, with all four pyranosides in the 4C1 chair conformation, occupies the -3, -2 and +1 subsites whilst evading the catalytic (-1) subsite. Such ?by-pass? compounds offer great scope for the development of a new class of ?-d-glycoside hydrolase inhibitors.

Laser Doppler anemometry measurements in an index of refraction matched column in the presence of dispersed beads: Part I

SJ Haam — 2006-09-13T14:22:40-00:00

International Journal of Multiphase Flow, Vol. 26, No. 9. (1 September 2000), pp. 1401-1418.

Laser Doppler anemometry was used to measure axial and radial velocity components in a liquid flow field in the presence of dispersed beads. Index of refraction matching between the fluid (para-cymene) and large, spherical beads, made of polymethyl methacrylate, was essential to extract the turbulence data from the fluid phase because of the high concentration of beads. The match allowed measurements without generating noise from the surface of the beads. The measurements were obtained under transient flow conditions to avoided need for an external solids circulation loop. The resulting data were statistical and ensembled averaged for short periods during the transient experiments where the concentration could be taken as approximately constant. The concentration levels were determined from separate particle tracking velocimetry measurements, to be described in Part II. The bead density was greater than the fluid and thus wakes were created. These local areas of fluid experienced a lowering of the velocity. The turbulent fluctuation results showed that the presence of the beads extracted energy from the mean flow and transferred that energy to the turbulence. The increase of turbulent intensity was impressive along the centerline of the column where the measurements were made. The axial turbulent intensity of the fluid without beads was of the order of 10% and with beads, the level was increased to nearly 70%.

A measurement system for odor classification based on the dynamic response of QCM sensors

C Di Nucci — 2005-12-06T15:16:35-00:00

Instrumentation and Measurement, IEEE Transactions on, Vol. 52, No. 4. (2003), pp. 1079-1086.

[Electronic nose, frequency meter, quartz crystal microbalance (QCM), polymer chemical transients, transient analysis, high-sampling rate, high-frequency detector] In this paper, an innovative measurement system for odor classification, based on quartz crystal microbalances (QCMs), is presented. The application proposed in this paper is the detection of typical wine aroma compounds in mixtures containing ethanol. In QCM sensors, the sensitive layer is, e.g., a polymeric layer deposited on a quartz surface. Chemical mixtures are sorbed in the sensitive layer, inducing a change in the polymer mass and, therefore, in the quartz resonance frequency. In this paper, the frequency shift is measured by a dedicated, fully digital front-end hardware implementing a technique that allows reducing the measurement time while maintaining a high-frequency resolution . The developed system allows, therefore, measuring variations of the QCM resonance frequency shifts during chemical transients obtained with abrupt changes in odor concentration. Hence, the reaction kinetics can be exploited to enhance the sensor selectivity. In this paper, some measurements obtained with an array of four sensors with different polymeric sensitive layers are presented. An exponential fitting of the transient responses is used for feature extraction. Finally, to reduce data dimensionality, principal component analysis is used.

Probing dark matter caustics with weak lensing

Raphael Gavazzi — 2005-07-07T08:44:00-00:00

(2 Jun 2005)

Caustics are high-density structures that form frequently in collisionless media. Under self-gravity, cold dark matter flows focus onto caustics which are yet to be resolved in numerical simulations and or observed in the real world. If detected, caustics would provide a strong evidence for dark matter and would rule out alternative models such as those with modified dynamics. Here, we demonstrate how they might be observed in the weak lensing data. We evaluate the shear distortion and show that its radial profile is marked by a characteristic sawtooth pattern due to the caustics in dark matter haloes that form by selfsimilar accretion. We discuss the observational complications, mainly due to the poor knowledge of the virial radii of the haloes and demonstrate that a superposition of about 600 cluster-size haloes would give a signal-to-noise ratio which is sufficiently large for the detection of caustics with ground-based observations. This number is reduced to 200 for space-based observations. These bounds can be easily achieved by the ongoing wide field optical surveys such as CFHTLS and the future space-based projects SNAP and DUNE which have to be accompanied by a X-ray follow-up of the selected clusters for a precise determination of their virial radii.

A simple scaling approach to Mott conductivity

Debnarayan Jana — 2005-07-01T16:12:54-00:00

Physica B: Condensed Matter, Vol. 344, No. 1-4. (15 February 2004), pp. 62-65.

We present a simple scaling form of Mott's formula of conductivity in case of amorphous materials in an arbitrary dimension d for a density of states which has a soft gap at the Fermi energy. We also indicate the scaling form of the conductivity at a high electric field. Previously known results can be obtained from this generalised form of the conductivity.