Spatial dependence of gain nonlinearities in InGaAs semiconductor optical amplifier

Counter-propagating sub-picosecond pulses are used to monitor gain saturation along the waveguide of an InGaAs superlattice semiconductor optical amplifier at 1550 nm wavelength. The functional form of the spatial dependence of gain saturation is found to depend on pulse energy. These observations are interpreted by combining the optical nonlinearities associated with interband carrier dynamics and carrier heating together and their respective time constants. We show that the results are consistent with the predictions of a propagation model. Implications for all-optical switching, particularly in the limit of full saturation across the whole amplifier, are discussed. (c) 2005 American Institute of Physics.</p

Ultrafast electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3 mu m

The authors report a direct measurement of the absorption dynamics in an InAs p-i-n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28 mu m. The absorption change recovers with characteristic times ranging from 62 ps (0 V) to similar to 700 fs (-10 V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism. (c) 2006 American Institute of Physics.</p

Preparation and degradation of rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols

Rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols have been prepared, and their degradation has been investigated, during the study of the reactivity of the dimers [M(µ-Cl)(I4-C8H12)]2 (M = Rh (1), Ir (2)) and [M(µ-OH)(I4-C8H12)]2 (M = Rh (3), Ir (4)) with 1, 3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex 1 reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of 1, the mononuclear derivative RhCl(I4-C8H12){¿1-Npy-(HBMePHI)} (5), and the binuclear species [RhCl(I4-C8H12)]2{µ-Npy, Npy-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(I4-C8H12){¿1-Npy-(HBMePHI)} (7) and [IrCl(I4-C8H12)]2{µ-Npy, Npy-(HBMePHI)} (8). In contrast to chloride, one of the hydroxide groups of 3 and 4 promotes the deprotonation of HBMePHI to give [M(I4-C8H12)]2(µ-OH){µ-Npy, Niso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KOtBu, the [BMePHI]- ligand undergoes three different degradations: Alcoholysis of an exocyclic isoindoline-N double bond, alcoholysis of a pyridyl-N bond, and opening of the five-membered ring of the isoindoline core.

Characterization of Domiphen Bromide as a New Fast-Acting Antiplasmodial Agent Inhibiting the Apicoplastidic Methyl Erythritol Phosphate Pathway

The evolution of resistance by the malaria parasite to artemisinin, the key component of the combination therapy strategies that are at the core of current antimalarial treatments, calls for the urgent identification of new fast-acting antimalarials. The apicoplast organelle is a preferred target of antimalarial drugs because it contains biochemical processes absent from the human host. Fosmidomycin is the only drug in clinical trials targeting the apicoplast, where it inhibits the methyl erythritol phosphate (MEP) pathway. Here, we characterized the antiplasmodial activity of domiphen bromide (DB), another MEP pathway inhibitor with a rapid mode of action that arrests the in vitro growth of Plasmodium falciparum at the early trophozoite stage. Metabolomic analysis of the MEP pathway and Krebs cycle intermediates in 20 mu M DB-treated parasites suggested a rapid activation of glycolysis with a concomitant decrease in mitochondrial activity, consistent with a rapid killing of the pathogen. These results present DB as a model compound for the development of new, potentially interesting drugs for future antimalarial combination therapies

Starch Synthesis in Ostreococcus tauri: The Starch-Binding Domains of Starch Synthase III-B Are Essential for Catalytic Activity

Starch is the major energy storage carbohydrate in photosynthetic eukaryotes. Several enzymes are involved in building highly organized semi-crystalline starch granules, including starch-synthase III (SSIII), which is widely conserved in photosynthetic organisms. This enzyme catalyzes the extension of the α-1,4 glucan chain and plays a regulatory role in the synthesis of starch. Interestingly, unlike most plants, the unicellular green alga Ostreococcus tauri has three SSIII isoforms. In the present study, we describe the structure and function of OsttaSSIII-B, which has a similar modular organization to SSIII in higher plants, comprising three putative starch-binding domains (SBDs) at the N-terminal region and a C-terminal catalytic domain (CD). Purified recombinant OsttaSSIII-B displayed a high affinity toward branched polysaccharides such as glycogen and amylopectin, and to ADP-glucose. Lower catalytic activity was detected for the CD lacking the associated SBDs, suggesting that they are necessary for enzyme function. Moreover, analysis of enzyme kinetic and polysaccharide-binding parameters of site-directed mutants with modified conserved aromatic amino acid residues W122, Y124, F138, Y147, W279, and W304, belonging to the SBDs, revealed their importance for polysaccharide binding and SS activity. Our results suggest that OT_ostta13g01200 encodes a functional SSIII comprising three SBD domains that are critical for enzyme function

Análisis de la distribución de tráfico en una red inalámbrica semipública

INTRODUCCIÓN:La Administración de Redes IP debe velar por que todos los dispositivos de la red de datos LAN y WAN, aseguren lasprestaciones de los servicios de tecnología hub, switch, router, firewall, Gateway, etc.Uno de los problemas frecuentes para estos dispositivos es la administración del ancho de banda de Internet, BW (Consumo por parte de la red). No sólo se debe evitar la "monopolización" del BW (distribución justa) si no también contribuir a la maximización de su uso, ya que es un recurso costoso que debe usarse en su totalidad durante el mayor tiempo posible.Los procedimientos de prueba de hipótesis se diseñan en problemas en los que se conoce la población o distribución de probabilidad y las hipótesis involucran a los parámetros de la distribución. Otro tipo de hipótesis que se encuentra a menudo es que sabe la distribución subyacente de la población, y se quiere probar la hipótesis que una distribución particular será satisfactoria como un modelo de población. En esta investigación se usó un procedimiento de prueba formal de bondad de ajuste basado en la distribución chi-cuadrado.A partir de la función densidad de probabilidad que gobierna esta situación, calculada desde un punto de vista pragmático, con una casuística abundante, junto con la Prueba de Hipótesis pertinente, se obtiene una guía para la arquitectura del sistema informáticoMETODOLOGIA:Los algoritmos usados para los controladores de BW, requieren que se configuren parámetros que condicionan elcomportamiento de las conexiones de los usuarios, en un ambiente donde no se conozcan a priori, ni el factor desimultaneidad, ni el tipo de dispositivo, ni el uso esperado de los canales. Solamente se conocen los usuarios, lasconexiones que realizan cada uno de ellos, los bytes entrantes, salientes y el tipo de conexión.Para la adquisición de datos se usa el protocolo RADIUS (Remote Access Dial In User Service). Es un protocolo AAA(Authentication, Authorization and Accounting) que provee autenticación, autorización y contabilidad de forma centralizada para los dispositivos que usan un servicio de red. El archivo en formato .xls es posible encontrarlo en http://www.um.edu.ar/math/ con 65536 conexiones a la redinalámbrica de la UM.Los datos con los que se trabaja provienen del funcionamiento de los algoritmos de control de ancho de banda, como el programa TC (Traffic Control) de Linux que utiliza el algoritmo HTB (Hierarchical Token Bucket), o los Delay pools que utilizan SQUID (aplicación proxy). Los parámetros que especifican el comportamiento del ancho de banda son dos: X, "tamaño de la cuba" de BW reservado para ese elemento (Red, host, etc). Y, es la "velocidad de relleno de la cuba" de ancho de banda para dicho elemento.Se ha utilizado Mathcad (® Parametric Technology Corporation) para la adecuación de datos y el análisis estadístico correspondiente, mediante una función creada (“sacamuestras”) para extraer un vector Bw de 2000 elementos aleatoriamente selecciona-dos y se determina el histograma que permite tener una apreciación a "grosso modo" de la forma de la densidad de probabilidad.Una observación aplicable a este ensayo se refiere a la magnitud de frecuencias, el efecto "desflecamiento“ y el uso de intervalos adyacentes dando un nivel de significancia a = 0.01CONCLUSIONES:Se puede inferir que es posible determinar el comportamiento de las conexiones de los usuarios, a través de la función densidad de probabilidad del proceso. Esto permite al diseñador del sistema informático y al experto en comunicaciones tener una previsión del comportamiento global con lo cual quedan habilitados a disponer de los recursos con mayor eficiencia y seguridad.Se dispone de una guía estratégica para relevar un sistema, encontrando los parámetros adecuados que permitan hallar los perfiles que definen los comportamiento

Early Science with the Large Millimeter Telescope: an energy-driven wind revealed by massive molecular and fast X-ray outflows in the Seyfert Galaxy IRAS 17020+4544

We report on the coexistence of powerful gas outflows observed in millimeter and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544. Thanks to the large collecting power of the Large Millimeter Telescope, a prominent line arising from the 12CO(1-0) transition was revealed in recent observations of this source. The complex profile is composed by a narrow double-peak line and a broad wing. While the double-peak structure may be arising in a disk of molecular material, the broad wing is interpreted as the signature of a massive outflow of molecular gas with an approximate bulk velocity of -660 km/s. This molecular wind is likely associated to a multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c and column densities in the range 10^{21-23.9} cm^-2 that was reported in the source prior to the LMT observations. The momentum load estimated in the two gas phases indicates that within the observational uncertainties the outflow is consistent with being propagating through the galaxy and sweeping up the gas while conserving its energy. This scenario, which has been often postulated as a viable mechanism of how AGN feedback takes place, has so far been observed only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary multi-wavelength data recently obtained on this source will allow us to corroborate the proposed hypothesis.Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figure