Compte rendu La rêve: Sa nature, sa fonction et une méthode d'analyse.

Reviews the book, La rêve: Sa nature, sa fonction et une méthode d'analyse by George W. Baylor and Daniel Deslauriers (1987). This book consists of 85 pages, notes and bibliography included. The work is divided in four chapters. The motif of the title is evident in the first chapter. The three other chapters expose a method of analysis advanced by the authors. On the whole, a method interesting for research but a exercise at the very least harassing in practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High speed, high capacity ATM optical switches for futuretelecommunication transport networks

This paper describes the work carried out in the RACE Project R2039 ATMOS (asynchronous transfer mode optical switching). The project is briefly illustrated, together with its main goal: to develop and assess concepts and technology suitable for optical fast packet switching. The project's technical approach consisted in the exploitation of the space and wavelength domains for fast routing and buffering: The major achievements are then reported. Four different switch architecture concepts have been proposed, investigated and developed, all based on a high speed optical routing matrix electrically controlled at lower speed. The basic optical key components and subsystems (wavelength converters, space switches and optical buffers) are described in detail, with the outstanding results obtained and the corresponding projected performance. In particular, system demonstration of wavelength conversion at 10 and 20 Gb/s has been realized, to show the usefulness of the ATMOS technology both to implement optimized high performance optical packet-switching fabrics as well as transparent optical circuit-routing nodes. Four rack-mounted, reduced size demonstrators of basic switching matrices have been designed and implemented scalable to real system sizes. The obtained good results in terms of bit error rate and hardware integration are reported, showing that ATM switches are feasible with state of-the-art optical technology     

30 GHz bandwidth, 1.55 μm MQW-DFB laser diode based on a newmodulation scheme

The authors present a new concept of modulation for a 1.55 μm DFB MQW laser diode allowing generation of millimetre waves. The method consists in modulating the saturable absorber of a two-section laser. The improvements brought by the new concept are evaluated theoretically and have been verified experimentally for the first time. In particular, a 30 GHz cutoff frequency has been measured     

Monolithic photoreceiver integrating GaInAs PIN/JFET with diffused junctions

A new integrated PIN/JFET using an original three-layer GalnAs structure has been developed in order to optimise both devices separately. Thanks to the good performances and high reliability of individual components, the sensitivity of such monolithic photoreceivers is ? 33.7 dBm for a 10?9 bit error rate at 140 Mbit/s.     

Dynamic in vivo (31)P nuclear magnetic resonance study of Saccharomyces cerevisiae in glucose-limited chemostat culture during the aerobic-anaerobic shift

The purpose of this work was to analyse in vivo the influence of sudden oxygen depletion on Saccharomyces cerevisiae, grown in glucose-limited chemostat culture, using a recently developed cyclone reactor coupled with (31)P NMR spectroscopy. Before, during and after the transition, intracellular and extracellular phosphorylated metabolites as well as the pHs in the different cellular compartments were monitored with a time resolution of 2.5 min. The employed integrated NMR bioreactor system allowed the defined glucose-limited continuous cultivation of yeast at a density of 75 g DW/l and a p(O(2)) of 30% air saturation. A purely oxidative metabolism was maintained at all times. In vivo (31)P NMR spectra obtained were of excellent quality and even allowed the detection of phosphoenolpyruvate (PEP). During the switch from aerobic to anaerobic conditions, a rapid, significant decrease of intracellular ATP and PEP levels was observed and the cytoplasmic pH decreased from 7.5 to 6.8. This change, which was accompanied by a transient influx of extracellular inorganic phosphate (P(i)), appeared to correlate linearly with the decrease of the ATP concentration, suggesting that the cause of the partial collapse of the plasma membrane pH gradient was a reduced availability of ATP. The complete phosphorous balance established from our measurement data showed that polyphosphate was not the source of the increased intracellular P(i). The derived intracellular P(i), ATP and ADP concentration data confirmed that the glycolytic flux at the level of glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and enolase enzymes is mainly controlled by thermodynamic constraints.     

Characterization of microscope objective lenses from 1,400 to 1,650 nm to evaluate performance for long-wavelength nonlinear microscopy applications

We have demonstrated a simple method for characterization of objective lens performance at longer wavelengths for 3PLSM and THG imaging. We investigated a range of air and oil-immersion objective lenses across a wavelength range of 1,400-1,650 nm using a synchronously pumped optical parametric oscillator laser source. In the first instance, we investigated the percentage light transmission across this spectral range. Second, we used a simple second harmonic autocorrelation pulse measurement technique to study the dispersion properties of these lenses at the range of input wavelengths. For the objective lenses investigated, we observed pulse broadening on the order of around 4%-7% for air immersion lenses and 9%-12% for oil immersion lenses. Even for the greater dispersion incurred by the application of the oil immersion lenses, these objectives are suitable for longer wavelength application in conjunction with a suitable light source. The same techniques could easily be applied for a larger range of objective lenses and adapted for alternative spectral windows and pulse durations.     

Calcul de la matrice Jacobienne nécessaire à la commande coordonnée d'un manipulateur

This article deals with the coordination of the movements of a manipulator when the end effector has to follow a series of imposed positions and orientations. At any instant the position is defined by the three Cartesian components x₁, x₂, x₃ of the center of mass of the end effector, and the orientation by the Euler parameters x₄, x₅, x₆; this choice keeps the intrinsic symmetry of the problem. The vectorial relation $\text{f}$ - called the geometrical model of the manipulator - is established between the vector $\text{x}$ whose components are x₁, x₂, …, x₆ and the vector of generalized coordinates $\text{q}$ whose components are q₁, q₂,…, q_n. The calculation of the error δq generated on the generalized coordinates by an error δ$\text{x}$ between the vector $\text{x}$ and an input vector $\text{x}$

(t) requires the matrix expression - called the Jacobian matrix - of the partial derivatives of the function $\text{f}$ relative to the components of the vector $\text{q}$. In particular, the solution given in this article for obtaining the Jacobian matrix simplifies calculations which normally are very complicated. It consists of expressing certain elements of this matrix as a function of those of the generalized transformation matrix between a frame linked to the end effector and one linked to the structure. An example of the calculation of the Jacobian matrix of a manipulator having six degrees of freedom is given.     

Phase retrieval from speckle images

In ground-based astronomy, the inverse problem of phase retrieval from speckle images is a means to calibrate static aberrations for correction by active optics. It can also be used to sense turbulent wavefronts. However, the number of local minima drastically increases with the turbulence strength, mainly because of phase wrapping ambiguities. Multifocal phase diversity has been considered to overcome some ambiguities of the phase retrieval problem. We propose an effective algorithm for phase retrieval from a single focused image. Our algorithm makes use of a global optimization strategy and an automatically tuned smoothness prior to overcome local minima and phase degeneracies. We push the limit of D/r(0)=4 achieved by Irwan and Lane [J. Opt. Soc. Am. A.15, 2302 (1998)] up to D/r(0)=11, which is a major improvement owing to the drastic increase in the problem complexity. We estimate the performances of our approach from consistent simulations for different turbulence strengths and noise levels (down to 1500 photons per image). We also investigate the benefit of temporal correlation.     

Integrated multiscale modeling of the nervous system: predicting changes in hippocampal network activity by a positive AMPA receptor modulator

One of the fundamental characteristics of the brain is its hierarchical organization. Scales in both space and time that must be considered when integrating across hierarchies of the nervous system are sufficiently great as to have impeded the development of routine multilevel modeling methodologies. Complex molecular interactions at the level of receptors and channels regulate activity at the level of neurons; interactions between multiple populations of neurons ultimately give rise to complex neural systems function and behavior. This spatial complexity takes place in the context of a composite temporal integration of multiple, different events unfolding at the millisecond, second, minute, hour, and longer time scales. In this study, we present a multiscale modeling methodology that integrates synaptic models into single neuron, and multineuron, network models. We have applied this approach to the specific problem of how changes at the level of kinetic parameters of a receptor-channel model are translated into changes in the temporal firing pattern of a single neuron, and ultimately, changes in the spatiotemporal activity of a network of neurons. These results demonstrate how this powerful methodology can be applied to understand the effects of a given local process within multiple hierarchical levels of the nervous system.