Étude de l’impact de la pression pulsée sur la réactivité cérébrovasculaire

In vivo, la pression artérielle au niveau des artères cérébrales est pulsée, alors que ex vivo, l’étude de la fonction cérébrovasculaire est majoritairement mesurée en pression statique. L’impact de la pression pulsée sur la régulation du tonus myogénique et sur la fonction endothéliale cérébrale est inconnu. Nous avons posé l’hypothèse selon laquelle en présence d'une pression pulsée physiologique, la dilatation dépendante de l’endothélium induite par le flux et le tonus myogénique seraient optimisés. L’objectif de notre étude est d’étudier ex vivo l’impact de la pression pulsée sur le tonus myogénique et la dilatation induite par le flux dans les artères cérébrales de souris. Nous avons utilisé un artériographe pressurisé couplé à un système générant une onde pulsée de fréquence et d’amplitude réglables. Les artères cérébrales moyennes (≈160 μm de diamètre) ont été isolées de souris C57BL6 âgées de 3 mois et pressurisées à 60 mm Hg, en pression statique ou en pression pulsée. En pression statique, le tonus myogénique est faible mais est potentialisé par le L-NNA (un inhibiteur de la eNOS) et la PEG-catalase (qui dégrade le H2O2), suggérant une influence des produits dilatateurs dérivés de la eNOS sur le tonus myogénique. En présence de pression pulsée (pulse de 30 mm Hg, pression moyenne de 60 mm Hg, 550 bpm), le tonus myogénique est significativement augmenté, indépendamment du L-NNA et de la PEG-catalase, suggérant que la pression pulsée lève l’impact de la eNOS. En pression statique ou pulsée, les artères pré-contractées se dilatent de façon similaire jusqu’à une force de cisaillement de 15 dyn/cm2. Cette dilatation, dépendante de l’endothélium et de la eNOS, est augmentée en condition pulsée à une force de cisaillement de 20 dyn/cm2. En présence de PEG-catalase, la dilatation induite par le flux est diminuée en pression statique mais pas en pression pulsée, suggérant que la pression statique, mais pas la pression pulsée, favorise la production de O2 -/H2O2. En effet, la dilatation induite par le flux est associée à une production de O2 -/H2O2 par la eNOS, mesurable en pression statique, alors que la dilatation induite par le flux en pression pulsée est associée à la production de NO. Les différences de sensibilité à la dilatation induite par le flux ont été abolies après inhibition de Nox2, en condition statique ou pulsée. La pression pulsée physiologique régule donc l’activité de la eNOS cérébrale, en augmentant le tonus myogénique et, en présence de flux, permet la relâche de NO via la eNOS.

Understanding mixing efficiency in the oceans. Do the nonlinearities of the equation of state matter?

There exist two central measures of turbulent mixing in turbulent stratified fluids that are both caused by molecular diffusion: 1) the dissipation rate D(APE) of available potential energy APE; 2) the turbulent rate of change Wr, turbulent of background gravitational potential energy GPEr. So far, these two quantities have often been regarded as the same energy conversion, namely the irreversible conversion of APE into GPEr, owing to the well known exact equality D(APE)=Wr, turbulent for a Boussinesq fluid with a linear equation of state. Recently, however, Tailleux (2009) pointed out that the above equality no longer holds for a thermally-stratified compressible, with the ratio ξ=Wr, turbulent/D(APE) being generally lower than unity and sometimes even negative for water or seawater, and argued that D(APE) and Wr, turbulent actually represent two distinct types of energy conversion, respectively the dissipation of APE into one particular subcomponent of internal energy called the "dead" internal energy IE0, and the conversion between GPEr and a different subcomponent of internal energy called "exergy" IEexergy. In this paper, the behaviour of the ratio ξ is examined for different stratifications having all the same buoyancy frequency N vertical profile, but different vertical profiles of the parameter Υ=α P/(ρCp), where α is the thermal expansion coefficient, P the hydrostatic pressure, ρ the density, and Cp the specific heat capacity at constant pressure, the equation of state being that for seawater for different particular constant values of salinity. It is found that ξ and Wr, turbulent depend critically on the sign and magnitude of dΥ/dz, in contrast with D(APE), which appears largely unaffected by the latter. These results have important consequences for how the mixing efficiency should be defined and measured in practice, which are discussed.

Rapid synthesis of carbohydrate derivatives, including mimetics of c-linked disaccharides and c-Linked aza disaccharides, using the Hetero-Diels−Alder Reaction

In this work we demonstrate the value of performing a Hetero Diels-Alder reaction (HDAR) between Danishefsky’s diene and a range of aldehydes or imines, under microwave irradiation. By using a range of aldehydes and imines, including those derived from carbohydrates, access to functionalised 2,3-dihydro-4H-pyran-4-ones or 2,3-dihydro-4-pyridinones in good to excellent synthetic yields is possible. A particular strength of the methodology is its ability to access mimetics of C-linked disaccharides and C-linked aza disaccharides, targets of current therapeutic interest, in a rapid, convenient and diastereoselective manner. The effect of high pressure on the HDARs involving carbohydrate derived aldehydes and imines is also explored, with enhancement in yields occurring for the aldehyde substrates. Finally, HDARs using carbohydrate derived ketones, enones and enals are described under a range of conditions. Optimum results were obtained under high pressure conditions, with highly functionalized carbohydrate derivatives being afforded, in good yields, in this way.

In vitro cumulative gas production techniques: History, methodological considerations and challenges

Methodology used to measure in vitro gas production is reviewed to determine impacts of sources of variation on resultant gas production profiles (GPP). Current methods include measurement of gas production at constant pressure (e.g., use of gas tight syringes), a system that is inexpensive, but may be less sensitive than others thereby affecting its suitability in some situations. Automated systems that measure gas production at constant volume allow pressure to accumulate in the bottle, which is recorded at different times to produce a GPP, and may result in sufficiently high pressure that solubility of evolved gases in the medium is affected, thereby resulting in a recorded volume of gas that is lower than that predicted from stoichiometric calculations. Several other methods measure gas production at constant pressure and volume with either pressure transducers or sensors, and these may be manual, semi-automated or fully automated in operation. In these systems, gas is released as pressure increases, and vented gas is recorded. Agitating the medium does not consistently produce more gas with automated systems, and little or no effect of agitation was observed with manual systems. The apparatus affects GPP, but mathematical manipulation may enable effects of apparatus to be removed. The amount of substrate affects the volume of gas produced, but not rate of gas production, provided there is sufficient buffering capacity in the medium. Systems that use a very small amount of substrate are prone to experimental error in sample weighing. Effect of sample preparation on GPP has been found to be important, but further research is required to determine the optimum preparation that mimics animal chewing. Inoculum is the single largest source of variation in measuring GPP, as rumen fluid is variable and sampling schedules, diets fed to donor animals and ratios of rumen fluid/medium must be selected such that microbial activity is sufficiently high that it does not affect rate and extent of fermentation. Species of donor animal may also cause differences in GPP. End point measures can be mathematically manipulated to account for species differences, but rates of fermentation are not related. Other sources of inocula that have been used include caecal fluid (primarily for investigating hindgut fermentation in monogastrics), effluent from simulated rumen fermentation (e.g., 'Rusitec', which was as variable as rumen fluid), faeces, and frozen or freeze-dried rumen fluid (which were both less active than fresh rumen fluid). Use of mixtures of cell-free enzymes, or pure cultures of bacteria, may be a way of increasing GPP reproducibility, while reducing reliance on surgically modified animals. However, more research is required to develop these inocula. A number of media have been developed which buffer the incubation and provide relevant micro-nutrients to the microorganisms. To date, little research has been completed on relationships between the composition of the medium and measured GPP. However, comparing GPP from media either rich in N or N-free, allows assessment of contributions of N containing compounds in the sample. (c) 2005 Published by Elsevier B.V.

Advances in cycloaddition polymerizations

Cycloaddition reactions have been employed in polymer synthesis since the mid-nineteen sixties. This critical review will highlight recent notable advances in this field. For example, [2 + 2] cycloaddition reactions have been utilized in numerous polymerizations to enable the construction of strained polymer systems such as poly(2-azetidinone)s that can, in turn, afford polyfunctional beta-amino acid derived polymers. Polymers have also been synthesized successfully via (3 + 2) cycloaddition methods utilizing both thermal and high-pressure conditions. 'Click chemistry'-a process involving the reaction of azides with olefins, has also been adopted to generate linear and hyperbranched polymer architectures in a very efficient manner. [4 + 2] Cycloadditions have also been utilized under thermal and high-pressure conditions to produce rigid polymers such as polyimides and polyphenylenes. These cycloaddition polymerization methods afford polymers with potential for use in high performance polymers applications such as high temperature resistant coatings and polymeric organic light emitting diodes.

Fractionation of oligosaccharides by nanofiltration

Two loose nanofiltration membranes (NF-CA-50 and NF-TFC-50) and one dense ultrafiltration membrane (UF-CA-1) were used to fractionate commercial oligosaccharide mixtures by applying diafiltration in a 'dead-end' filtration cell at 40bar constant pressure with a maximum volume concentration ratio (VCR) of 6 at each fractionation. The rejections of a monosaccharide (glucose) and a disaccharide (lactose) were determined for each membrane; the results indicated that fractionation between these two sugars was possible using the two nanofiltration membranes. During the nanofiltration purification of a commercial oligosaccharide mixture, yields of 19% (w/w) for monosaccharides and 88% (w/w) for di- and oligosaccharides were obtained with the NF-TFC-50 membrane after four filtration steps, indicating that removal of the monosaccharides is possible with only minor losses of the oligosaccharide content of the mixture. The ultrafiltration membrane, at the same time, gave purification levels similar to the NF-TFC-50 membrane with fewer diafiltration steps but with higher losses of di- and oligosaccharides (12% (w/w) for monosaccharides and 53% (w/w) for di- and oligosaccharides on the third run). (C) 2003 Society of Chemical Industry.

Cloud-resolving simulations of deep convection over a heated mountain

Cloud-resolving numerical simulations of airflow over a diurnally heated mountain ridge are conducted to explore the mechanisms and sensitivities of convective initiation under high pressure conditions. The simulations are based on a well-observed convection event from the Convective and Orographically Induced Precipitation Study (COPS) during summer 2007, where an isolated afternoon thunderstorm developed over the Black Forest mountains of central Europe, but they are idealized to facilitate understanding and reduce computational expense. In the conditionally unstable but strongly inhibited flow under consideration, sharp horizontal convergence over the mountain acts to locally weaken the inhibition and moisten the dry midtroposphere through shallow cumulus detrainment. The onset of deep convection occurs not through the deep ascent of a single updraft but rather through a rapid succession of thermals that are vented through the mountain convergence zone into the deepening cloud mass. Emerging thermals rise through the saturated wakes of their predecessors, which diminishes the suppressive effects of entrainment and allows for rapid glaciation above the freezing level as supercooled cloud drops rime onto preexisting ice particles. These effects strongly enhance the midlevel cloud buoyancy and enable rapid ascent to the tropopause. The existence and vigor of the convection is highly sensitive to small changes in background wind speed U0, which controls the strength of the mountain convergence and the ability of midlevel moisture to accumulate above the mountain. Whereas vigorous deep convection develops for U0 = 0 m s−1, deep convection is completely eliminated for U0 = 3 m s−1. Although deep convection is able to develop under intermediate winds (U0 = 1.5 m s−1), its formation is highly sensitive to small-amplitude perturbations in the initial flow.

Incorporating HACCP into national food control systems - Analyzing progress in the United Arab Emirates

Today governments and other parties involved in food control are under constant pressure to find more efficient and effective mechanisms to carry out their mandates for food control. This has led to international recognition of the importance of the HACCP system as a food control tool and guidance on the role of government agencies in the application of such a system has been developed. Based on this international guidance, four main elements identified as key activities have been used in this study to evaluate the progress of HACCP implementation in the UAE. The internal Strengths and Weaknesses, as well as the external Opportunities and Threats that the government is facing towards the implementation of a HACCP-based food control system have been identified. The analysis shows that the government’s dedicated role has been an essential driving force to encourage the implementation of a HACCP-based food control system. Some areas of difficulty, including the dependence on high levels of food imports, are highlighted.

Time-resolved gas-phase kinetic, quantum chemical, and RRKM studies of reactions of silylene with alcohols

Time-resolved kinetic studies of silylene, SiH2, generated by laser flash photolysis of 1-silacyclopent-3-ene and phenylsilane, have been carried out to obtain rate constants for its bimolecular reactions with methanol, ethanol, 1-propanol, 1-butanol and 2-methyl-1-butanol. The reactions were studied in the gas phase over the pressure range 1-100 Torr in SF6 bath gas, at room temperature. In the study with methanol several buffer gases were used. All five reactions showed pressure dependences characteristic of third body assisted association reactions. The rate constant pressure dependences were modelled using RRKM theory, based on Eo values of the association complexes obtained by ab initio calculation (G3 level). Transition state models were adjusted to fit experimental fall-off curves and extrapolated to obtain k∞ values in the range 1.9 to 4.5 × 10-10 cm3 molecule-1 s-1. These numbers, corresponding to the true bimolecular rate constants, indicate efficiencies of between 16 and 67% of the collision rates for these reactions. In the reaction of SiH2 + MeOH there is a small kinetic component to the rate which is second order in MeOH (at low total pressures). This suggests an additional catalysed reaction pathway, which is supported by the ab initio calculations. These calculations have been used to define specific MeOH-for-H2O substitution effects on this catalytic pathway. Where possible our experimental and theoretical results are compared with those of previous studies.

Radiative forcing and global warming potentials of 11 halogenated compounds

Radiative forcing values have been calculated for 11 halogenated compounds which are in current use or which have been suggested as possible replacements for the chlorofluorocarbons. Absorption cross-sections measured over a range of atmospheric temperature and pressure conditions as part of a multi-laboratory programme have been used together with a narrow band radiative transfer model. We provide a “best estimate” radiative forcing taking into account the likely vertical profile of the gas in each case. The Global Warming Potential over a variety of time horizons has also been calculated where the lifetime is available. We present the first such information for 1,2-dichloroethane. For chloroform our radiative forcing is 5 times higher than the value used in previous assessments, possibly because these ignored the effect of absorption outside the 800–1200 cm−1 “window”. For several of the other compounds considered here, our forcing is between 10 and 30% lower than previous assessments. The perfluorocarbons have been found to have large global warming potentials, many times that of CFC-11, due to both strong absorption and long lifetimes. The importance of absorption features at wavenumbers below 800 cm−1 and the effect of temperature variations in absorption cross-section on the radiative forcing are also investigated.

Unraveling an antique subduction process from metamorphic basement around Medellin city, Central Cordillera of Colombian Andes

In the surroundings of Caldas and El Retiro cities (Colombia) metamorphic rocks derived from basic and pelitic protoliths comprise the Caldas amphibole schist and the Ancon schist respectively. Subordinated metamorphosed granite bodies (La Miel gneiss) are associated to these units, and The El Retiro amphibolites, migmatites and granulites crops out eastwards of these units, separated by shear zones. The Caldas amphibole schist and the Ancon schist protoliths could have been formed in a distal marine reduced environment and amalgamated to the South American continent in an apparent Triassic subduction event. The El Retiro rocks are akin to a continental basement and possible include impure metasediments of continental margin, whose metamorphism originated granulite facies rocks and migmatites as a result of the anatexis of quartz-feldspathic rocks. The metamorphism was accompanied by intense deformation, which has juxtaposed both migmatites and granulite blocks. Afterward, heat and fluid circulation associated with the emplacement of minor igneous intrusions resulted in intense fluid-rock interaction, variations in the grain size of the minerals and, especially, intense retrograde metamorphic re-equilibrium. Thermobarometric estimations for the Caldas amphibole schist indicate metamorphism in the Barrovian amphibolite fades. The metamorphic path is counter-clockwise, but retrograde evolution could not be precisely defined. The pressures of the metamorphism in these rocks range from 6.3 to 13.5 kbar, with narrow temperature ranging from 550 to 630 degrees C. For the Ancon schist metapelites the P-T path is also counter-clockwise, with a temperature increase evidenced by the occurrence of sillimanite and the cooling by later kyanite. The progressive metamorphism event occurred at pressures of 7.6-7.2 kbar and temperatures of 645-635 degrees C for one sample and temperature between 500 and 600 degrees C under constant pressure of 6 kbar. The temperature estimated for these rocks varies between 400 and 555 degrees C at pressures of 5-6 kbar in the retrograde metamorphic path. The El Retiro rocks evidence strong decompression with narrow variation in temperature, showing pressure values between 8.7 and 2.7 kbar at temperatures of 740-633 degrees C. These metamorphic fragments of the basement in the Central Cordillera of the Colombian Andes could represent a close relationship with an antique subduction zone. (C) 2011 Elsevier Ltd. All rights reserved.

Negociação e liderança: papel da chefia direta na gestão da pressão

Este estudo tem por finalidade identificar perspectiva dos profissionais de Recursos Humanos a correlação entre as competências gerenciais e a relação construída entre líderes de diferentes níveis hierárquicos e suas equipes diretas, bem como o impacto na percepção da pressão e do estresse pelas suas respectivas equipes. Um dos desafios que gerentes e outros líderes encontram é como manter um time motivado e mobilizado em um ambiente de pressão crescente, seja decorrente de uma expansão ou uma retração do seu mercado. No primeiro capítulo e no segundo capítulos fazemos a introdução e a definição do Problema, os objetivos e delimitações do estudo. No terceiro capítulo caminhamos pela história do trabalho, da organização e do homem, buscando fundamentar no tempo a jornada em busca do equilíbrio trabalho e trabalhador, o lugar do homem na construção desta história e alguns importantes pensadores da gestão de pessoas. Este capítulo abre portas para entendermos o capítulo seguinte, no qual estudamos o estresse e, em particular, o estresse ocupacional. Mostramos, ainda, a diferença entre pressão – que está no ambiente externo- e estresse, que deriva da percepção do indivíduo. O interesse neste tema é decorrente da constatação prática de que a pressão aumenta em tempos de retração do mercado, mas também aumenta em períodos em o mercado está aquecido. Logo, se houver uma correlação entre como uma equipe ou um liderado ‘percebe’ o seu líder, essa informação poderá ser útil para a Gestão de Pessoas. Aprofundamos o conceito de Suporte Social, a rede que protege o colaborador nem contextos de alta pressão e demos maior ênfase ao papel do líder como importante fonte deste suporte. No quinto capítulo analisamos o tema conflito por ser um dos temas que mais impactam o estresse ocupacional. As relações de trabalho são, por sua natureza, relações de longo prazo, o que faz do manejo adequado do conflito no ambiente de trabalho um assunto relevante na agenda do gerente. Entretanto, seu manejo adequado depende tanto do diagnóstico correto, bem como da relação de confiança construída pelo líder. Embora cientes de que parte significativa dos conflitos está relacionada às estruturas e estratégias corporativas, propositalmente dirigimos nossa atenção aos gerentes e líderes que compõem a massa de liderança dessas organizações visando provocar idéias que possam contribuir para a melhoria das relações e dos resultados. No sexto capitulo apresentamos a Metodologia e no último capítulo apresentamos e discutimos o resultado da pesquisa realizada com profissionais de Recursos Humanos de grandes empresas, buscando, através do olhar do RH, uma percepção sobre as lideranças de cada empresa e a comparação entre líderes com maior ou menor capacidade de negociação junto à sua equipe. O estudo usou uma grade flexível suportada por um questionário semi-estruturado e os dados foram tratados usando a metodologia da Análise de Conteúdo sem que fosse necessário um tratamento estatístico devido ao tamanho da amostra. O estudo apontou para a necessidade de uma exploração mais profunda do tema uma vez que a literatura e os resultados iniciais demonstraram um importante papel da chefia direta na percepção grupal do estresse e no clima organizacional. Ao concluir o trabalho a pesquisa oferece algumas ponderações sobre o papel das lideranças e o papel das corporações na equalização de equipes que vivem sob pressão constante.

Entre o cartão-postal e a cidade real: um estudo sobre paisagem e produção imobiliária em Natal/RN

Recent studies concerning the landscape have investigated the most important activities that contribute for its modification and have tried to better understand the society through the marks left by its quotidian. It is understood that singular landscapes constitute the cultural patrimonies of the cities, once they are part of the daily life of the citizens and are present in their social representations. Some contemporary authors defend the preservation of the natural and urban landscape trying, specially, to keep its importance for the local population. Natal is a city where the ambient qualities are well defined and known by the beauty of the area where it is located. Situated just between a river and the sea, the city grew following its geographic characteristics. The Potengi River, the Atlantic Ocean and the vast dunes ecosystem represented natural limits to the urban expansion; at the same time they have favored the development of a landscape pattern marked by the dialectic between the natural elements and the human interventions. However, this relationship changed after the intensification of the high rising development process that took place since the 1960s. The urban legislation tried to preserve the features of the local landscape delimiting Areas for Controlling Building High , destined to protect the scenic value of some parts of the city. On the other hand, the civil construction sector has made constant pressure in sense to abolish or to modify this legal instrument, aiming profits that have increased, in the 1990s, because of the consumption and the qualification of the urban space for tourist activities. It is necessary the raising of new elements to stimulate the quarrel about the landscape preservation, the process of the urban space production and the best way for the legislation implementation. This work tries to raise elements about the subject at local level, in sense to use Natal City experience to contribute for the formulation of indicators to raise the question about the lack of measure for subjective values, for example the cultural and affective value of the landscape. The natural elements inserted in the urban profile, represent strong visual references and supply identity to the town; they are part of the collective imaginary and are detached in the social context of the city. Then, why the preservation of the landscape, that estimates the improvement in the quality of life, is not enough to justify the controlling building high already previewed as part of Natal City Legislation? These questions send us to the approach of the landscape, as a community patrimony, alerting that some of its significant esthetics attributes must be preserved as a legacy for the future generations

Adição de poliuretana em pastas de cimento para poços de petróleo como agente de correção do filtrado

Chemical admixtures, when properly selected and quantified, play an important role in obtaining adequate slurry systems for quality primary cementing operations. They assure the proper operation of a well and reduce costs attributed to corrective cementing jobs. Controlling the amount lost by filtering through the slurry to permeable areas is one of the most important requirements in an operation, commonly controlled by chemical admixtures, such as carboxymethylcellulose (CMC). However, problems related to temperature, salttolerance and the secundary retarding effect are commonly reported in the literature. According to the scenario described above, the use of an aqueous dispersion of non-ionic poliurethane was proposed to control the filter loss, given its low ionic interaction with the free ions present in the slurries in humid state. Therefore, this study aims at assessing the efficiency of poliurethane to reduce filter loss in different temperature and pressure conditions as well as the synergistic effect with other admixtures. The temperatures and pressures used in laboratory tests simulate the same conditions of oil wells with depths of 500 to 1200 m. The poliurethane showed resistance to thermal degradation and stability in the presence of salts. With the increase in the concentration of the polymer there was a considerable decrease in the volume lost by filtration, and this has been effective even with the increase in temperature

Distribution of neutral prilocaine in a phospholipid bilayer: Insights from molecular dynamics simulations

In this work, we report a 20-ns constant pressure molecular dynamics simulation of prilocaine (PLC), in amine-amide local anesthetic, in a hydrated liquid crystal bilayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine. The partition of PLC induces the lateral expansion of the bilayer and a concomitant contraction in its thickness. PLC molecules are preferentially found in the hydrophobic acyl chains region, with a maximum probability at similar to 12 angstrom from the center of the bilayer (between the C(4) and C(5) methylene groups). A decrease in the acyl chain segmental order parameter, vertical bar S-CD vertical bar, compared to neat bilayers, is found, in good agreement with experimental H-2-NMR studies. The decrease in vertical bar S-CD vertical bar induced by PLC is attributed to a larger accessible volume per lipid in the acyl chain region. (C) 2008 Wiley Periodicals, Inc.