Design of a Resonant-Cavity-Enhanced p-i-n GaN/AlxGa1-xN Photodetector

A resonant-cavity-enhanced p-i-n photodetector has been designed and analyzed to operate at a wavelength of 360 nm based on the Al_xGa_1-xN material system. The novel approach has been adopted of using epitaxial AlN/Al_xGa_1-xN quarter-wave stacks as the distributed Bragg reflector that serves as the front mirror. An Al_xGa_1-xN absorptive filter layer is incorporated to suppress all but one resonant mode to ensure single, narrow-band operation. This device structure is projected to achieve wavelength selective, high speed, and high quantum efficiency operation in the ultraviolet. MOCVD-grown 6 1/2-pair AlN/Al_xGa_1-x     

Optical isolator using two tandem phase modulators

We propose and demonstrate an integrated optical isolator in InP using two phase modulators in series. The phase modulators are driven with a single-frequency signal in quadrature. Theoretically there is no effect on the forward signal, and the carrier of the backward signal can be eliminated, the energy distributed to other frequencies. We achieve a carrier isolation of 11?dB and an excess insertion loss of 2.3?dB. Such an isolator can be monolithically integrated with a laser without extra materials or magnetic fields.     

A Skorokhod Problem formulation and large deviation analysis of a processor sharing model

Generalized processor sharing has been proposed as a policy for distributing processing in a fair manner between different data classes in high-speed networks. In this paper we show how recent results on the Skorokhod Problem can be used to construct and analyze the mapping that takes the input processes into the buffer content. More precisely, we show how to represent the map in terms of a Skorokhod Problem, and from this infer that the mapping is well defined (existence and uniqueness) and well behaved (Lipschitz continuity). As an elementary application we present some large deviation estimates for a many data source model. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rheological studies of the gelation of aqueous solutions of acrylamide-acrylic acid copolymers in the presence of chromium chloride

The gelation kinetics of aqueous solutions of acrylamideacrylic acid copolymers in the presence of chromium ions was studied with different rheometers. The gel time is found to vary with the principle of the apparatus because of a low shear dependence of the elongation of the macromolecules. The variations of the gel time with the experimental conditions of the gel preparation were investigated and we conclude that the gelation is governed by the oligornerization kinetics of the chromium ions which are instantaneously, complexated by the carboxylate groups of the polymer. The variation laws of the gel time and of the elastic modulus with chromium and polymer concentrations, temperature and ionic strength are in qualitative agreement with the structure of the temporary network of the semi-dilute solutions of these copolymers.     

Aging, rejuvenation and memory phenomena in spin glasses

In this paper, we review several important features of the out-of-equilibrium dynamics of spin glasses. Starting with the simplest experiments, we discuss the scaling laws used to describe the isothermal aging observed in spin glasses after a quench down to the low-temperature phase. We report in particular new results on the sub-aging behaviour of spin glasses. We then discuss the rejuvenation and memory effects observed when a spin glass is submitted to temperature variations during aging, from the point of view of both energy landscape pictures and real-space pictures. We highlight the fact that both approaches point out the necessity of hierarchical processes involved in aging. Finally, we report an investigation of the effect of small temperature variations on aging in spin glass samples with various anisotropies which indicates that this hierarchy depends on the spin anisotropy.     

Negtive thixotropy of solutions of partially hydrolyzed polyacrylamide. Part I: The influence of shear rate on time changes of flow characteristics

A strongly negative thixotropic behavior of solutions of partially hydrolyzed polyacrylamide in a glycerol-water mixture has been observed at high dilution. Using a Couette viscometer, time changes of viscosity at various shear rates were studied in detail.     

Etude de la structure des hydroxydes de gallium et d'indium par thermogravimétrie et absorption infrarouge

Zusammenfassung Der Vergleich der Absorptionsspektren von GaOOH und In(OH)₃ im IR zwischen 1 und 30 mit Spektren von Kristallen des gleichen Typus läßt die Valenz- und Deformationsschwingungen der Hydroxylgruppen erkennen.

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Summary Comparison of the infrared absorption spectra, between 1 and 30, of GaOOH and In(OH)₃ with those of crystals of the same type gave evidence of valence vibrations and deformation of the OH groups.

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Résumé La comparaison des spectres d'absorption infrarouge entre 1 et 30 de GaOOH et de In(OH)₃ avec ceux de cristaux de même type, met en évidence les vibrations de valence et de déformation des groupements OH.

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En l'honneur du Prof.A. A. Benedetti-Pichler, respectueusement.     

Etudes sur la nature des «pinks» par thermogravimétrie et spectrograpnie infrarouge. I

Résumé L'étude thermogravimétrique des 2 réactions à l'état solide SnCl₂+ +CrO₃ et SnCl₂+K₂Cr₂O₇ pour différentes proportions des constituants, montre que le «pink» formé pour un rapport Sn/Cr supérieur à 5 n'est pas une combinaison de chrome et d'étain.Le spectre d'absorption infrarouge de la poudre violette recueillie à partir de 600 ne présente aucune bande d'absorption en dehors de celles de SnO₂ et de Cr₂O₃. Il s'agit essentiellement d'oxyde d'étain dans lequel se trouve finement dispersé de 2 à 8% d'oxyde Cr₂O₃.

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Summary The thermogravimetric study of two reactions in the solid state, namely SnCl₂+CrO₃ and SnCl₂+ K₂Cr₂O₇ with different proportions of the reactants show that the pink produced by a ratio of Sn/Cr above 5 is not a compound of chromium and tin.The infra red absorption spectrum of the violet powder collected from 600 on shows no absorption band except those of SnO₂ and Cr₂O₃. We are dealing here essentially with a tin oxide containing 2 to 8% of finely dispersed oxide Cr₂O₃.

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Zusammenfassung Die thermogravimetrische Untersuchung der beiden Festkörperreaktionen zwischen Zinn(II)-chlorid und Chromsäureanhydrid bzw. Zinn(II)-ohlorid und Kaliumbichromat bei verschiedenen Gewichtsverhältnissen ergab, daß das bei einem Sn/Cr-Verhältnis > 5 entstehende Pink keine Verbindung aus Chrom und Zinn ist.Das IR-Absorptionsspektrum des über 600 erhaltenen violetten Pulvers enthält keinerlei Absorptionsbande außer denen des SnO₂ und des Cr₂O₃. Es handelt sich im wesentlichen um Zinnoxyd, in dem sich 2 bis 8% Cr₂O₃ in feiner Verteilung finden.

     

G-CSF protects motoneurons against axotomy-induced apoptotic death in neonatal mice

Background  

Granulocyte colony stimulating factor (G-CSF) is a growth factor essential for generation of neutrophilic granulocytes. Apart from this hematopoietic function, we have recently uncovered potent neuroprotective and regenerative properties of G-CSF in the central nervous system (CNS). The G-CSF receptor and G-CSF itself are expressed in α motoneurons, G-CSF protects motoneurons, and improves outcome in the SOD1(G93A) transgenic mouse model for amyotrophic lateral sclerosis (ALS). In vitro, G-CSF acts anti-apoptotically on motoneuronal cells. Due to the pleiotrophic effects of G-CSF and the complexity of the SOD1 transgenic ALS models it was however not possible to clearly distinguish between directly mediated anti-apoptotic and indirectly protective effects on motoneurons. Here we studied whether G-CSF is able to protect motoneurons from purely apoptotic cell death induced by a monocausal paradigm, neonatal sciatic nerve axotomy.