Reactivity of OH and CH3OH between 22 and 64 K: Modelling the gas phase production of CH3O in Barnard 1b

In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CH3OH, which has been recently found to be accelerated at low temperatures yielding CH3O as main product. This finding opened the question of whether the CH3O observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CH3OH and OH. Several chemical models including this reaction and grain-surface processes have been developed to explain the observed abundance of CH$_3$O with little success. Here we report for the first time rate coefficients for the gas-phase reaction of OH and CH3OH down to a temperature of 22 K, very close to those in cold interstellar clouds. Two independent experimental set-ups based on the supersonic gas expansion technique coupled to the pulsed laser photolysis-laser induced fluorescence technique were used to determine rate coefficients in the temperature range 22-64 K. The temperature dependence obtained in this work can be expressed as k(22-64 K) = (3.6+/-0.1)e-12 (T/ 300)^(-1.0+/-0.2) cm3 molecule-1 s-1. Implementing this expression in a chemical model of a cold dense cloud results in CH3O/CH3OH abundance ratios similar or slightly lower than the value of 3e-3 observed in Barnard 1b. This finding confirms that the gas-phase reaction between OH and CH3OH is an important contributor to the formation of interstellar CH3O. The role of grain-surface processes in the formation of CH3O, although it cannot be fully neglected, remains controversial.Comment: Accepted for publication in The Astrophysical Journa

UV-visible Spectra and Gas-Phase Rate Coefficients for the Reaction of 2,3 pentanedione and 2,4-pentanedione with OH Radicals

International audienceThe UV absorption cross-sections of 2,3-pentanedione and 2,4-pentanedione were measured and their reactions with OH were investigated in the gas-phase using a relative rate method. A temperature dependence of the rate coefficients was observed for both reactions over the temperature range 298–338 K. This work provides the first UV cross-section in the gas phase for 2,4-pentanedione and the first kinetic data for the reaction of 2,3-pentanedione with OH radicals as a function of temperature. The tropospheric lifetimes obtained in this work suggest that once emitted into the atmosphere, these species could be quickly degraded close to their emission sources

Pressure Dependent Low Temperature Kinetics for CN + CH3CN: Competition between Chemical Reaction and van der Waals Complex Formation

International audienceThe gas phase reaction between the CN radical and acetonitrile CH3CN was investigated experimentally, at low temperatures, with the CRESU apparatus and a slow flow reactor to explore the temperature dependence of its rate coefficient from 354 K down to 23 K. Whereas a standard Arrhenius behavior was found at T > 200 K, indicating the presence of an activation barrier, a dramatic increase in the rate coefficient by a factor of 130 was observed when the temperature was decreased from 168 to 123 K. The reaction was found to be pressure independent at 297 K unlike the experiments carried out at 52 and 132 K. The work was complemented by ab initio transition state theory based master equation calculations using reaction pathways investigated with highly accurate thermochemical protocols. The role of collisional stabilization of a CN⋯CH3CN van der Waals complex and of tunneling induced H atom abstractions were also considered. The experimental pressure dependence at 52 and 132 K is well reproduced by the theoretical calculations provided that an anharmonic state density is considered for the van der Waals complex CH3CN⋯CN and its Lennard-Jones radius is adjusted. Furthermore, these calculations indicate that the experimental observations correspond to the fall-off regime and that tunneling remains small in the low-pressure regime. Hence, the studied reaction is essentially an association process at very low temperature. Implications for the chemistry of interstellar clouds and Titan are discussed

Reactivity of 3-hydroxy-3-methyl-2-butanone: Photolysis and \OH\ reaction kinetics

International audienceHydroxycarbonyl compounds are important secondary reaction products in the oxidation of Volatile Organic Compounds (VOCs) in the atmosphere. The atmospheric fate of these oxygenated \VOCs\ is however poorly understood, especially the relevance of the photolytic pathway. In this work, a combined investigation of the photolysis and temperature-dependent \OH\ radical reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) is presented. A photolysis lifetime of about 4-5 days was estimated with a global quantum yield of 0.10. The \OH\ reaction rate coefficient follows the Arrhenius trend (298-356 K) and could be modelled through the following expression: k3H3M2B(T) = (5.12 ± 0.07) × 10−12 exp(−563 ± 119/T) in cm3 molecule−1 s−1. A 3H3M2B atmospheric lifetime of 15 days towards the \OH\ radical was evaluated. Our results showed that the photolysis pathway is the major degradation channel for 3H3M2B. Photolysis products were identified and quantified in the present work with a carbon balance of around 80% enabling a reaction mechanism to be proposed. The present work underlines the need for further studies on the atmospheric chemistry of oxygenated VOCs

Gas-Phase Rate Coefficients for the Reaction of 3-hydroxy-2-butanone and 4-hydroxy-2-butanone with OH and Cl

International audienceThe reactions of the OH radicals and the Cl atoms with 3-hydroxy 2-butanone (3H2B) and 4-hydroxy 2-butanone (4H2B) were investigated in the gas-phase using relative rate method. The kinetic study on the OH-reactions was carried out using a Pyrex atmospheric chamber at 600-760 Torr of purified air. The temperature ranges were 298-338 K for 3H2B and 278-333 K for 4H2B. A slight negative dependence of the rate coefficients behavior was observed and the Arrhenius expressions obtained are (in cm3 molecule-1 s-1): k3H2B(OH) = (1.25±0.20)×10-12exp(612±50/T) and k4HB (OH) = (7.50± 2.0) ×10-12exp(196±20/T). Rate coefficients for the gas-phase reactions of Cl atoms with 3H2B and 4H2B were measured using an atmospheric simulation chamber made of Teflon at 298 ± 3 K and 760 Torr. The obtained rate coefficients (in cm3 molecule-1 s-1) were (4.90± 0.45) ×10-11 and (1.45± 0.15) ×10-10 for 3H2B and 4H2B, respectively. The obtained data are presented, compared to those reported in the literature and the reactivity trends discussed. The estimated tropospheric lifetimes obtained in this work suggest that once emitted into the atmosphere, 3H2B and 4H2B will be oxidized near the emission sources

Evaluación del uso de collar cervical de inmovilización después de la descompresión y fusion cervical por acceso anterior: Revisión sistemática

This study aims to evaluate safety and effectiveness of the use of orthesis in postoperative degenerative disorders of the cervical spine. Although widely used, there are not defined criteria for the use of cervical collars, and their importance on cervical arthrodesis. A systematic literature review was undertaken and a multicentre controlled clinical trial comprising 32 specialized services, with a total of 257 patients who met the inclusion criteria of the review. Clinical and radiographic outcomes were compared in post surgical patients that used or not rigid cervical collar during 6 to 12 weeks after surgery. The evidence available on literature, although weak, suggests that cervical collar decreases the clinical scores in first weeks after surgery. Furthermore, it does not alter the rate of fusion when used concomitantly with plaque and screws through anterior access in cervical degenerative diseases on a single anatomical level.Este estudio tiene como objetivo evaluar la eficacia y seguridad de la utilización de ortesis después de la cirugía de trastornos degenerativos de la columna cervical. Aunque ampliamente utilizado, no existen criterios para la aplicación de collares cervicales y su importancia en la artrodesis cervical. Se realizó una revisión sistemática de la literatura y un estudio multicéntrico controlado, compuesto de 32 departamentos, con un total de 257 pacientes que cumplieron los criterios de inclusión de la revisión. Se compararon los resultados clínicos y radiográficos de pacientes, en un solo nivel anatómico, que usaron o no el collar cervical duro durante 6 a 12 semanas después de la cirugía. La evidencia disponible en la literatura, aunque débil, sugiere que el uso del collar cervical reduce las puntuaciones clínicas en las primeras semanas después de la cirugía. Además, no altera la tasa de fusión cuando se utiliza de forma concomitante con la placa y tornillos colocados por acceso anterior en la enfermedad degenerativa cervical en un solo nivel anatómico.Este estudo tem como objetivo avaliar a efetividade e a segurança do uso de órteses no pós-operatório de afecções degenerativas da coluna cervical. Apesar de amplamente utilizados, não existem critérios definidos para a aplicação de colares cervicais e sua relevância na artrodese cervical. Foi realizada uma revisão sistemática da literatura, além de um estudo multicêntrico controlado, composto por 32 serviços, com um total de 257 pacientes que satisfizeram os critérios de inclusão da revisão. Foram comparados desfechos clínicos e radiográficos de pacientes operados em um único nível anatômico que fizeram uso ou não de colar cervical rígido por 6 a 12 semanas após a cirurgia. As evidências disponíveis na literatura, apesar de fracas, sugerem que o uso do colar cervical diminui os escores clínicos nas primeiras semanas após o procedimento cirúrgico. Além disto, não altera a taxa de fusão quando utilizado concomitantemente à placa e aos parafusos por acesso anterior, em doenças degenerativas cervicais em um único nível anatômico.Santa Casa da Misericórdia de SantosUniversidade Estadual PaulistaHospital do Servidor Público Estadual Francisco Morato de OliveiraUniversidade Federal de São Paulo (UNIFESP)UNIFESP, ISS, SantosSciEL

Optimum performances for non-linear finite elements model of 8/6 switched reluctance motor based on intelligent routing algorithms

This paper presents torque ripple reduction with speed control of 8/6 Switched Reluctance Motor (SRM) by the determination of the optimal parameters of the turn on, turn off angles Theta_(on), Theta_(off), and the supply voltage using Particle Swarm Optimization (PSO) algorithm and steady state Genetic Algorithm (ssGA). With SRM model, there is difficulty in the control relapsed into highly non-linear static characteristics. For this, the Finite Elements Method (FEM) has been used because it is a powerful tool to get a model closer to reality. The mechanism used in this kind of machine control consists of a speed controller in order to determine current reference which must be produced to get the desired speed, hence, hysteresis controller is used to compare current reference with current measured up to achieve switching signals needed in the inverter. Depending on this control, the intelligent routing algorithms get the fitness equation from torque ripple and speed response so as to give the optimal parameters for better results. Obtained results from the proposed strategy based on metaheuristic methods are compared with the basic case without considering the adjustment of specific parameters. Optimized results found clearly confirmed the ability and the efficiency of the proposed strategy based on metaheuristic methods in improving the performances of the SRM control considering different torque loads

Giardia intestinalis assemblages among Egyptian symptomatic/asymptomatic cases in Cairo

Giardia intestinalis is frequent enteric protozoa, affecting humans worldwide. Human infections aremainly caused by two genetically different assemblages call A & B. This cross-sectional study characterizedthe Giardia genotypes isolated from the stool of symptomatic and asymptomatic Egyptians inCairo and correlated these genotypes with the demographic and clinical data of the cases. Stool sampleswere collected from 389 individuals (245 complaining of gastrointestinal (GIT) symptoms and144 apparently healthy asymptomatic individuals), and microscopically examined. Positive Samplesfor G. intestinalis were molecularly characterized by Copro-nPCR targeting beta-giardin gene, andthen analyzed by RFLP for assemblage identification. Giardia was detected in 62 samples (15.9%); 53samples in symptomatic cases (21.6%) and 9 samples in asymptomatic individuals (6.25%). DNA ofpositive samples was amplified by nPCR-RFLP assays. There was a significant predominance of assemblageB among symptomatic (82.7%) and asymptomatic (77.8%) groups, while the rest of sampleshad assemblage A. Among the clinical data, only flatulence was significantly associated with Giardiainfection with assemblage B. Assemblage B is the predominant genotype found in Egypt in symptomaticand asymptomatic patients suggesting an anthropologic transmission cycle.Key Words: Giardia; genotyping; Assemblage; nPCR-RFLP; beta-giardin

Arbutus unedo L.: Chemical and Biological Properties

Arbutus unedo L. (strawberry tree) has a circum-Mediterranean distribution, being found in western, central and southern Europe, north-eastern Africa (excluding Egypt and Libya) and the Canary Islands and western Asia. Fruits of the strawberry tree are generally used for preparing alcoholic drinks (wines, liqueurs and brandies), jams, jellies and marmalades, and less frequently eaten as fresh fruit, despite their pleasing appearance. An overview of the chemical composition of different parts of the plant, strawberry tree honey and strawberry tree brandy will be presented. The biological properties of the different parts of A. unedo and strawberry tree honey will be also overviewed