Experimental and theoretical investigation of BCl_3 decomposition in H_2

International audienceA combined experimental and theoretical study of the homogeneous decomposition of BCl3 in a H2 carrier gas is presented. A detailed description of the B/Cl/H thermodynamic equilibrium is first obtained from ab-initio calculations from which a restricted low energy chemical mechanism is identified to model the decomposition of BCl3. Transition state theory is then invoked to obtain reaction rates and the resulting kinetic mechanism is incorporated in a 1D model of a CVD reactor. Comparison of calculated steady state concentrations with in-situ FT-IR measurements shows a good agreement at low temperatures, thus validating the kinetic model. The divergence observed at higher temperatures is attributed to boron deposition

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Etudes théorique et expérimentale du dépôt CVD de carbures

L’élaboration par CVD (dépôt chimique en phase vapeur ou Chemical Vapor Deposition) de composites à matrices céramiques met en jeu de nombreux mécanismes physico chimiques en interaction les uns avec les autres. La maîtrise du procédé et son optimisation nécessitent une description précise de ces derniers et de leurs couplages, qui peut être réalisé dans un cadre de modélisation suffisamment global. Dans le cas des matériaux déposés dans un réacteur à parois chaudes, qui permet un bon contrôle de la qualité des matériaux, la décomposition des gaz précurseurs en phase gaz joue un rôle extrêmement important. Nous avons entrepris dans cette thèse la modélisation thermodynamique et cinétique de la phase gaz associée aux dépôts des carbures B-C et Si-B-C, systèmes encore mal maîtrisés. En se basant sur des calculs de chimie théorique, nous avons déterminé et caractérisé un ensemble de réactions chimiques d’importance cruciale dans ces systèmes. Nous sommes les premiers à étudier certaines d’entre elles. Un mécanisme réactionnel du système B-C-Cl-H (dépôt de carbure de bore) a été proposé puis utilisé avec un modèle de réacteur unidimensionnel. Des mesures IRTF, également réalisées au cours de cette thèse, permettent une validation du mécanisme réactionnel à différents niveaux. En particulier, la formation de l’espèce BCl2CH3 comme principal produit gazeux carboné a été clairement mise en évidence, ainsi que la température à laquelle BCl3 se décompose pour former BHCl2 et HCl. Les concentrations des espèces en zone chaude ont finalement été mises en relation avec les vitesses de prise de masse et une loi de dépôt a été proposée pour ce système. Dans le cas du système Si-B-C nous avons caractérisé certaines réactions de couplage entre les sous systèmes B-Cl-H et Si-C-Cl-H. Une modélisation globale de la cinétique homogène associée au dépôt de carbures Si-B-C est une perspective à court terme de ce travail. Enfin, l’étude rigoureuse de certaines réactions nous a amené à invoquer et/ou développer des méthodes théoriques spécifiques - et pour certaines non standard - telles que la théorie de l’état de transition, la théorie variationnelle de l’état de transition, la théorie variationnelle de l’état de transition à coordonnée de réaction variable et la théorie RRKM. En particulier, une approche unidimensionnelle du calcul des états propres des modes de vibration lâches a été développée. Sa validité a été confirmée par comparaison à d’autres modèles (oscillateur harmonique, rotation libre, etc …), valables dans des situations plus restreintes.The Chemical Vapour Deposition of ceramics matrix composites involves many coupling physico-chemical mechanisms. The process control and optimization are allowed by precise description of these mechanisms and their interactions, witch can be realized through a global modelisation. In the case of hot wall reactors, witch allowed a good control of deposit properties, homogeneous gas phase decomposition play a crucial function. We have undertaken in this thesis a gas phase thermodynamic and kinetic studies associated to B-C and Si-B-C carbides elaboration, witch remains hard to control. By theoretical chemical calculations, we proposed a set containing crucial reactions for theses systems. We are the first to study some of them. A reaction mechanism of the B-C-Cl-H system (for the boron carbide deposition) have been proprosed and utilised with a one dimensional reactor model. Experimental IRTF spectrum, also investigated in our works, allow different validations of the reactional mechanism. In particular, BCl2CH3 is showed to be the main carbon product in the gas phase, and prediction of activation temperature of BCl3 to BHCl2 and HCl transformation is very good. Finally, hot zone concentration species have been related to the experimental deposition rate and a kinetic deposition law has been proposed for this system. In the case of Si-B-C system, some important coupling reactions between B-Cl-H and Si-C-Cl-H systems have been characterized. A global modelisation of the homogeneous gas phase kinetic for Si-B-C carbides is short-term perspective. At least, the rigorous study for some reactions have needed the use or the development of specific theoretical methodology – no standard for some of them – as the Transition State Theory (TST), the Variationnal Transition State Theory (VTST), the Variationnal Transition State Theory with Variable Reaction Coordinate (VTST-VRC) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. In particular, we have developed a convenient way to compute the eigenvalues of low hindered one dimensional vibration modes. Validity of the approach has been assessed by comparisons with more specific model (harmonic oscillator, free and hindered rotation, etc …

Etudes théorique et expérimentale du dépôt CVD de carbures

The Chemical Vapour Deposition of ceramics matrix composites involves many coupling physico-chemical mechanisms. The process control and optimization are allowed by precise description of these mechanisms and their interactions, witch can be realized through a global modelisation. In the case of hot wall reactors, witch allowed a good control of deposit properties, homogeneous gas phase decomposition play a crucial function. We have undertaken in this thesis a gas phase thermodynamic and kinetic studies associated to B-C and Si-B-C carbides elaboration, witch remains hard to control. By theoretical chemical calculations, we proposed a set containing crucial reactions for theses systems. We are the first to study some of them. A reaction mechanism of the B-C-Cl-H system (for the boron carbide deposition) have been proprosed and utilised with a one dimensional reactor model. Experimental IRTF spectrum, also investigated in our works, allow different validations of the reactional mechanism. In particular, BCl2CH3 is showed to be the main carbon product in the gas phase, and prediction of activation temperature of BCl3 to BHCl2 and HCl transformation is very good. Finally, hot zone concentration species have been related to the experimental deposition rate and a kinetic deposition law has been proposed for this system. In the case of Si-B-C system, some important coupling reactions between B-Cl-H and Si-C-Cl-H systems have been characterized. A global modelisation of the homogeneous gas phase kinetic for Si-B-C carbides is short-term perspective. At least, the rigorous study for some reactions have needed the use or the development of specific theoretical methodology – no standard for some of them – as the Transition State Theory (TST), the Variationnal Transition State Theory (VTST), the Variationnal Transition State Theory with Variable Reaction Coordinate (VTST-VRC) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. In particular, we have developed a convenient way to compute the eigenvalues of low hindered one dimensional vibration modes. Validity of the approach has been assessed by comparisons with more specific model (harmonic oscillator, free and hindered rotation, etc …).L’élaboration par CVD (dépôt chimique en phase vapeur ou Chemical Vapor Deposition) de composites à matrices céramiques met en jeu de nombreux mécanismes physico chimiques en interaction les uns avec les autres. La maîtrise du procédé et son optimisation nécessitent une description précise de ces derniers et de leurs couplages, qui peut être réalisé dans un cadre de modélisation suffisamment global. Dans le cas des matériaux déposés dans un réacteur à parois chaudes, qui permet un bon contrôle de la qualité des matériaux, la décomposition des gaz précurseurs en phase gaz joue un rôle extrêmement important. Nous avons entrepris dans cette thèse la modélisation thermodynamique et cinétique de la phase gaz associée aux dépôts des carbures B-C et Si-B-C, systèmes encore mal maîtrisés. En se basant sur des calculs de chimie théorique, nous avons déterminé et caractérisé un ensemble de réactions chimiques d’importance cruciale dans ces systèmes. Nous sommes les premiers à étudier certaines d’entre elles. Un mécanisme réactionnel du système B-C-Cl-H (dépôt de carbure de bore) a été proposé puis utilisé avec un modèle de réacteur unidimensionnel. Des mesures IRTF, également réalisées au cours de cette thèse, permettent une validation du mécanisme réactionnel à différents niveaux. En particulier, la formation de l’espèce BCl2CH3 comme principal produit gazeux carboné a été clairement mise en évidence, ainsi que la température à laquelle BCl3 se décompose pour former BHCl2 et HCl. Les concentrations des espèces en zone chaude ont finalement été mises en relation avec les vitesses de prise de masse et une loi de dépôt a été proposée pour ce système. Dans le cas du système Si-B-C nous avons caractérisé certaines réactions de couplage entre les sous systèmes B-Cl-H et Si-C-Cl-H. Une modélisation globale de la cinétique homogène associée au dépôt de carbures Si-B-C est une perspective à court terme de ce travail. Enfin, l’étude rigoureuse de certaines réactions nous a amené à invoquer et/ou développer des méthodes théoriques spécifiques - et pour certaines non standard - telles que la théorie de l’état de transition, la théorie variationnelle de l’état de transition, la théorie variationnelle de l’état de transition à coordonnée de réaction variable et la théorie RRKM. En particulier, une approche unidimensionnelle du calcul des états propres des modes de vibration lâches a été développée. Sa validité a été confirmée par comparaison à d’autres modèles (oscillateur harmonique, rotation libre, etc …), valables dans des situations plus restreintes

Etudes théorique et expérimentale du dépôt CVD de carbures

L élaboration par CVD (dépôt chimique en phase vapeur ou Chemical Vapor Deposition) de composites à matrices céramiques met en jeu de nombreux mécanismes physico chimiques en interaction les uns avec les autres. La maîtrise du procédé et son optimisation nécessitent une description précise de ces derniers et de leurs couplages, qui peut être réalisé dans un cadre de modélisation suffisamment global. Dans le cas des matériaux déposés dans un réacteur à parois chaudes, qui permet un bon contrôle de la qualité des matériaux, la décomposition des gaz précurseurs en phase gaz joue un rôle extrêmement important. Nous avons entrepris dans cette thèse la modélisation thermodynamique et cinétique de la phase gaz associée aux dépôts des carbures B-C et Si-B-C, systèmes encore mal maîtrisés. En se basant sur des calculs de chimie théorique, nous avons déterminé et caractérisé un ensemble de réactions chimiques d importance cruciale dans ces systèmes. Nous sommes les premiers à étudier certaines d entre elles. Un mécanisme réactionnel du système B-C-Cl-H (dépôt de carbure de bore) a été proposé puis utilisé avec un modèle de réacteur unidimensionnel. Des mesures IRTF, également réalisées au cours de cette thèse, permettent une validation du mécanisme réactionnel à différents niveaux. En particulier, la formation de l espèce BCl2CH3 comme principal produit gazeux carboné a été clairement mise en évidence, ainsi que la température à laquelle BCl3 se décompose pour former BHCl2 et HCl. Les concentrations des espèces en zone chaude ont finalement été mises en relation avec les vitesses de prise de masse et une loi de dépôt a été proposée pour ce système. Dans le cas du système Si-B-C nous avons caractérisé certaines réactions de couplage entre les sous systèmes B-Cl-H et Si-C-Cl-H. Une modélisation globale de la cinétique homogène associée au dépôt de carbures Si-B-C est une perspective à court terme de ce travail. Enfin, l étude rigoureuse de certaines réactions nous a amené à invoquer et/ou développer des méthodes théoriques spécifiques - et pour certaines non standard - telles que la théorie de l état de transition, la théorie variationnelle de l état de transition, la théorie variationnelle de l état de transition à coordonnée de réaction variable et la théorie RRKM. En particulier, une approche unidimensionnelle du calcul des états propres des modes de vibration lâches a été développée. Sa validité a été confirmée par comparaison à d autres modèles (oscillateur harmonique, rotation libre, etc ), valables dans des situations plus restreintes.The Chemical Vapour Deposition of ceramics matrix composites involves many coupling physico-chemical mechanisms. The process control and optimization are allowed by precise description of these mechanisms and their interactions, witch can be realized through a global modelisation. In the case of hot wall reactors, witch allowed a good control of deposit properties, homogeneous gas phase decomposition play a crucial function. We have undertaken in this thesis a gas phase thermodynamic and kinetic studies associated to B-C and Si-B-C carbides elaboration, witch remains hard to control. By theoretical chemical calculations, we proposed a set containing crucial reactions for theses systems. We are the first to study some of them. A reaction mechanism of the B-C-Cl-H system (for the boron carbide deposition) have been proprosed and utilised with a one dimensional reactor model. Experimental IRTF spectrum, also investigated in our works, allow different validations of the reactional mechanism. In particular, BCl2CH3 is showed to be the main carbon product in the gas phase, and prediction of activation temperature of BCl3 to BHCl2 and HCl transformation is very good. Finally, hot zone concentration species have been related to the experimental deposition rate and a kinetic deposition law has been proposed for this system. In the case of Si-B-C system, some important coupling reactions between B-Cl-H and Si-C-Cl-H systems have been characterized. A global modelisation of the homogeneous gas phase kinetic for Si-B-C carbides is short-term perspective. At least, the rigorous study for some reactions have needed the use or the development of specific theoretical methodology no standard for some of them as the Transition State Theory (TST), the Variationnal Transition State Theory (VTST), the Variationnal Transition State Theory with Variable Reaction Coordinate (VTST-VRC) and the Rice Ramsperger Kassel Marcus (RRKM) theory. In particular, we have developed a convenient way to compute the eigenvalues of low hindered one dimensional vibration modes. Validity of the approach has been assessed by comparisons with more specific model (harmonic oscillator, free and hindered rotation, etc )BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

An Efficient and Accurate Formalism for the Treatment of Large Amplitude Intramolecular Motion

International audienceWe propose a general approach to describe Large Amplitude Motions (LAM) with multiple Degrees Of Freedom (DOF) in molecules or reaction intermediates, which is useful for the computation of thermochemical or kinetic data. The kinetic part of the LAM Lagrangian is derived using a Z-matrix internal coordinate representation within a new numerical procedure. This derivation is exact for a classical system, and the uncertainties on the prediction of observable quantities largely arise from uncertainties on the LAM Potential Energy Surface (PES). In order to rigorously account for these uncertainties, we present an approach based on Bayesian theory to infer a parametrized physical model of the PES using ab initio calculations. This framework allows a quantification of uncertainties associated with a PES model, as well as a propagation scheme for the final quantity of interest. A selection and generalization of some treatments accounting for the coupling of the LAM with other internal or external degrees of freedom are also presented. Finally, we discuss and validate the approach with two applications: the calculation of the partition function of the 1,3-butadiene, and the calculation of the high-pressure reaction rate of the CH$_3$ + $H$ → CH$_4$ recombination

An Efficient and Accurate Formalism for the Treatment of Large Amplitude Intramolecular Motion.

We propose a general approach to describe large amplitude motions (LAM) with multiple degrees of freedom (DOF) in molecules or reaction intermediates, which is useful for the computation of thermochemical or kinetic data. The kinetic part of the LAM Lagrangian is derived using a Z-matrix internal coordinate representation within a new numerical procedure. This derivation is exact for a classical system, and the uncertainties on the prediction of observable quantities largely arise from uncertainties on the LAM potential energy surface (PES) itself. In order to rigorously account for these uncertainties, we present an approach based on Bayesian theory to infer a parametrized physical model of the PES using ab initio calculations. This framework allows for quantification of uncertainties associated with a PES model as well as the forward propagation of these uncertainties to the quantity of interest. A selection and generalization of some treatments accounting for the coupling of the LAM with other internal or external DOF are also presented. Finally, we discuss and validate the approach with two applications: the calculation of the partition function of 1,3-butadiene and the calculation of the high-pressure reaction rate of the CH(3) + H → CH(4) recombination