Facteur de couplage phase-amplitude des diodes lasers avec absorbant saturable

The phase-amplitude coupling factor (α-factor) is one of the fundamental parameters of semiconductor lasers. We show that this factor can be evaluated by time-resolved spectroscopic measurements in pulsed regime. Experiments are carried out with injectionseeded single-mode GaAs lasers whose active stripe includes regions of saturable absorption made by ion implantation. We show that the measured pulse downchirp is proportional to pulse energy. The downchirp amplitude is found to approach four laser cavity intermode spacings at the highest energies. Correspondingly, the ±-values can be five times higher than those reported to date in litterature. High a-values are confirmed in pulse compression experiments. Several mechanisms are proposed to interprete these new results.     

Design and architecture of a new space priority mechanism for ATM network nodes

This paper presents the architecture of a new space priority mechanism intended to control cell loss in ATM switches. Our mechanism is a new generic concept called: the multiple pushout. It is based on the utilization of both AAL and ATM features and on a particular definition of the priority bit. Whenever one cell of a message overflows the buffer of an ATM switch, the algorithm causes the switch to discard other cells of the message (including later arrivals). Such discarding frees buffer spaces for cells of other messages that have a chance of arriving at their destination intact. Our objective is to emphasize that in case of overload, with most of proposed mechanisms, cells are discarded without any semantic information about the type of cells. Therefore, at the destination, all the fragments of the corrupted messages will be discarded anyway. Finally, we present simulation results comparing cell loss rates and message loss rates of several space priority mechanisms.     

Part II: An example of the use of the comsis software: simulation of an optical network which uses wavelength multiplexing,fsk modulation format and direct detection

This second article deals with using the Comsis software for a particular application. Simulation is used to determine the maximum channel density in presence of crosstalk. In a first part, the modelling of the system is described. The simulation parameters of different optical elements are given. The results show that in the case of channels modulated at 500 Mbitls using fsk modulation format, and a direct detection operation at 1,5 μm, a minimum spacing of 6 GHz can be obtained with a 2 dB penalty. Thus if only the bandwidth of the erbium doped fibre amplifier is taken into account, the maximum number of channels which can be used is 250. However if the fsr (free spectral range) of optical filter is taken into account, the maximun number of channels is limited to 30.     

Supported Lipid Bilayer Assembly on PEDOT:PSS Films and Transistors

Lipid bilayers are widely employed as a model system to investigate interactions between cells and their environment. Supported lipid bilayers (SLB) with integrated transmembrane proteins are emerging as a preferred platform for sensing applications. Challenges lie in the generation of SLB on surfaces which allow transduction of signals for characterization of lipid bilayer and incorporated transmembrane proteins. For the first time, the formation of SLBs is shown on films of the conducting polymer, poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), using traditional methods for characterizing lipid bilayer quality and function (QCM‐D, FRAP) combined with impedance spectroscopy. Further, partial formation of SLBs on PEDOT:PSS based organic electrochemical transistors (OECTs) is successfully demonstrated, as well as the ability to integrate and sense the ion pore α‐hemolysin, confirming the sensitivity of the OECT as a transducer of biological membrane function. This work represents a highly promising first step toward the use of such OECTs for functional readout of transmembrane proteins in their native environment.     

Alterations of phospholipids in ischemic canine myocardium during acute arrhythmia

Myocardial ischemia was produced in the left ventricle of the canine heart by a Harris two-stage occlusion of the left anterior descending coronary artery. The lipid content in the ischemic myocardium was analyzed and compared with the control tissue. No significant change in total phospholipid and cholesterol was detected. A 2-fold elevation in the levels of the major lysophospholipids was observed during acute ventricular arrhythmias at 24hr after the onset of ischemia. Such increases were not caused by preferential hydrolysis of phospholipid plasmalogens from the parent phospholipids.     

Thermomechcmical processing of Inconel 718 by shock-wave deformation

The response of Inconel 718 nickel-base alloy to thermomechanical processing (TMP) utilizing a 510 Kbar planar shock wave was evaluated. The results were compared with those of conventional TMP by cold rolling to 19.1 pct reduction in thickness; this provided a generalized (or effective) strain equivalent to the transient shock strain. Instead of deformation in the solution treated condition, the inclusion of a predeformation, partial aging step in an optimized TMP schedule led to the greatest improvements in strength, stress-rupture life, and low-cycle fatigue life. The mechanical behavior was correlated with substructure and microstructure. Predeformation aging inhibits thermal recovery during final aging and produces a uniform dispersion of γ′’ precipitates. On a generalized (or effective) strain basis, conventional TMP by cold rolling produces higher strengths than shock TMP due to a higher dislocation density in the former. This suggests that maximum shear strain is a better basis of comparison. Since dislocation substructure is the primary contributor to property modification of Inconel 718 by TMP, the effective service temperature of thermomechanically processed material is limited to 1200°F (649°C), irrespective of the method of working.     

Hydrogenation of brown coal. 2. Iron-based catalysis

Some of the inherent cations of Victorian brown coals have been exchanged for iron by treatment with solutions of iron salts. Coals with various iron contents are obtained by variation of the pH of the solutions used. Hydrogenation of coals treated in this way at 395 °C, and an initial hydrogen pressure of 10 MPa, give product yields similar to those obtained using commercial cobalt molybdate on alumina catalysts, and greater than those obtained using red mud as a catalyst. The increase in yields compared with non-catalysed experiments results mainly from increased production of asphaltenes. The amount and composition of gas (80–90 wt% C0₂, resulting from decarboxylation) remains constant. Despite the similar conversions, the hydrogen consumption and tetralin/naphthalene ratios for iron-catalysed experiments are less than for cobalt—molybdate-catalysed experiments.     

Fungal pretreatment of wheat straw: Effects on the biodegradability of cell walls,structural polysaccharides,lignin and phenolic acids by rumen microorganisms

Disappearance of cell wall components of untreated straw and straw treated with the ligninolytic white-rot fungi Phanerochaete chrysosporium, Dichomitus squalens and Cyathus stercoreus were determined during the course of rumen digestion of samples in nylon bags. The first fungus degraded hemicelluloses and cellulose non-selectively, adversely affecting the digestion rate of crude cell walls. Dichomitus squalens and C. stercoreus preferentially degraded hemicelluloses and lignin, affording cell wall degradation rates 1.5 times higher than in native straw. Furthermore, the extent of cell wall digestion was also significantly enhanced. Both strains improved the extent of cellulose digestion, whereas the potentially degradable xylan fraction remained unchanged. Polysaccharide digestion rates were influenced in different ways depending on the strain tested: straw degraded by C. stercoreus showed an increase in cellulose digestion rate by 50%, whereas residual arabinose units were slowly degraded. Xylan was degraded 1.8 times faster in straw decayed' by D. squalens, while cellulose digestion remained unchanged. Phanerochaete chrysosporium depressed both xylan and cellulose digestion rates. Fungal-treated lignins were solubilised in the rumen faster than in untreated straw, whereas only treatment by C. stercoreus resulted in higher lignin losses. Esterified phenolic acids were extensively degraded by all three fungi. Residual ferulic and p-coumaric acids accumulated during rumen digestion, although only the former decreased in the original straw.     

A proof technique for communicating sequential processes

Summary Proof rules are presented for an extension of Hoare's Communicating Sequential Processes. The rules deal with total correctness; all programs terminate in the absence of deadlock. The commands send and receive are treated symmetrically, simplifying the rules and allowing send to appear in guards. Also given are sufficient conditions for showing that a program is deadlock-free. An extended example illustrates the use of the technique.This research was supported in part by the National Science Foundation under grant MCS-7622360.