Comment coule une pâte granulaire? Etudes des composantes primaire et secondaire et des fluctuations de l'écoulement

Une " boue " est constituée de particules submillimétriques immergées dans un fluide. Nous étudions des boues concentrées (ou " pâtes granulaires "), où la concentration en particules est proche du maximum réalisable. Les particules peuvent être plus denses que le fluide, et sédimenter, ou être équilibrées en densité. Ces deux cas sont examinés, à l'aide d'une boue modèle. Nous étudions les écoulements de ces boues dans une cellule de Couette. Les expériences utilisent des méthodes innovantes, permettant de mesurer les vitesses des grains individuellement et collectivement, et les profils de concentration sous cisaillement. Les expériences apportent des informations nouvelles sur les écoulements, comme l'existence de courants de re-circulation. Les résultats sur les vitesses azimutales et concentrations sont en accord avec la théorie de Morris et Boulay d'équilibre des forces normales, pour un rapport convenable des coefficients viscométriques des forces tangentielle et normales.Wet granular materials are made of solid particles in high concentration, immersed in a viscous fluid. We investigated particle dynamics in a model granular suspension in Couette geometry, at low Reynolds/Taylor numbers for density and non density matched suspension. We used innovated techniques such as: Single Particle Tracking (SPT), Multi Particles Video Trajectography (MPVT) and Concentration Photometry (CP). These experiments allow us to provide information about single and collective motion of grains as well as particle repartition (local volume fraction). We investigated fully 3D velocity profiles in concentrated suspensions, diffusion coefficients, particle fluctuations and recirculation motion, also differential flows. We observe that the flow of non density matched suspensions is localized near the inner cylinder in the low shear rate regime, resulting in a sheared layer only a few particle diameters in thickness, in a way very similar to sheared dry granular materials. At high enough angular velocity, the initially localized flow crosses over to full fluidization: in this regime the granular suspension nearly behaves as a density-matched suspension. Dependence between particles' velocity and associated fluctuation amplitude is evidenced. Experiments as velocity and concentration profiles were compared with theoretical prediction based on the force balance model and different viscometric laws were investigated for normal and shear forces

Comment coule une pâte granulaire ? : études des composantes primaire et secondaire et des fluctuations de l’écoulement

Une « boue » est constituée de particules submillimétriques immergées dans un fluide. Nous étudions des boues concentrées (ou « pâtes granulaires »), où la concentration en particules est proche du maximum réalisable. Les particules peuvent être plus denses que le fluide, et sédimenter, ou être équilibrées en densité. Ces deux cas sont examinés, à l’aide d’une boue modèle. Nous étudions les écoulements de ces boues dans une cellule de Couette. Les expériences utilisent des méthodes innovantes, permettant de mesurer les vitesses des grains individuellement et collectivement, et les profils de concentration sous cisaillement. Les expériences apportent des informations nouvelles sur les écoulements, comme l’existence de courants de re-circulation. Les résultats sur les vitesses azimutales et concentrations sont en accord avec la théorie de Morris et Boulay d’équilibre des forces normales, pour un rapport convenable des coefficients viscométriques des forces tangentielle et normales.Wet granular materials are made of solid particles in high concentration, immersed in a viscous fluid. We investigated particle dynamics in a model granular suspension in Couette geometry, at low Reynolds/Taylor numbers for density and non density matched suspension. We used innovated techniques such as: Single Particle Tracking (SPT), Multi Particles Video Trajectography (MPVT) and Concentration Photometry (CP). These experiments allow us to provide information about single and collective motion of grains as well as particle repartition (local volume fraction). We investigated fully 3D velocity profiles in concentrated suspensions, diffusion coefficients, particle fluctuations and recirculation motion, also differential flows. We observe that the flow of non density matched suspensions is localized near the inner cylinder in the low shear rate regime, resulting in a sheared layer only a few particle diameters in thickness, in a way very similar to sheared dry granular materials. At high enough angular velocity, the initially localized flow crosses over to full fluidization: in this regime the granular suspension nearly behaves as a density-matched suspension. Dependence between particles’ velocity and associated fluctuation amplitude is evidenced. Experiments as velocity and concentration profiles were compared with theoretical prediction based on the force balance model and different viscometric laws were investigated for normal and shear forces

Comment coule une pâte granulaire? Etudes des composantes primaire et secondaire et des fluctuations de l'écoulement

Wet granular materials are made of solid particles in high concentration, immersed in a viscous fluid. We investigated particle dynamics in a model granular suspension in Couette geometry, at low Reynolds/Taylor numbers for density and non density matched suspension. We used innovated techniques such as: Single Particle Tracking (SPT), Multi Particles Video Trajectography (MPVT) and Concentration Photometry (CP). These experiments allow us to provide information about single and collective motion of grains as well as particle repartition (local volume fraction). We investigated fully 3D velocity profiles in concentrated suspensions, diffusion coefficients, particle fluctuations and recirculation motion, also differential flows. We observe that the flow of non density matched suspensions is localized near the inner cylinder in the low shear rate regime, resulting in a sheared layer only a few particle diameters in thickness, in a way very similar to sheared dry granular materials. At high enough angular velocity, the initially localized flow crosses over to full fluidization: in this regime the granular suspension nearly behaves as a density-matched suspension. Dependence between particles' velocity and associated fluctuation amplitude is evidenced. Experiments as velocity and concentration profiles were compared with theoretical prediction based on the force balance model and different viscometric laws were investigated for normal and shear forces.Une " boue " est constituée de particules submillimétriques immergées dans un fluide. Nous étudions des boues concentrées (ou " pâtes granulaires "), où la concentration en particules est proche du maximum réalisable. Les particules peuvent être plus denses que le fluide, et sédimenter, ou être équilibrées en densité. Ces deux cas sont examinés, à l'aide d'une boue modèle. Nous étudions les écoulements de ces boues dans une cellule de Couette. Les expériences utilisent des méthodes innovantes, permettant de mesurer les vitesses des grains individuellement et collectivement, et les profils de concentration sous cisaillement. Les expériences apportent des informations nouvelles sur les écoulements, comme l'existence de courants de re-circulation. Les résultats sur les vitesses azimutales et concentrations sont en accord avec la théorie de Morris et Boulay d'équilibre des forces normales, pour un rapport convenable des coefficients viscométriques des forces tangentielle et normales

Écoulement et resuspension visqueuse d'une pâte granulaire modèle en cellule de Couette à large entrefer

Le sable mouillé, certaines boues ou le béton frais sont constitués de grains dans un fluide visqueux. Les grains sont assez gros pour ne pas être browniens, et en grande concentration, ce qui procure au matériau les propriétés mécaniques d’une pâte (on parle de « pâte granulaire »). Décrire les façons dont ce genre de matériau peut couler est un enjeu important, du point de vue académique et pour de nombreuses applications. L’écoulement implique un cisaillement, dont l’effet est de disperser les grains, concurremment à la gravité qui a tendance à les entasser, et par là bloquer l’écoulement. On appelle « resuspension visqueuse » la compétition entre les deux effets. Les nombreux travaux déjà consacrés à ces questions, concernent en général des suspensions adaptées en densité, c'est à dire dans la limite où l’effet de la gravité est négligeable (geff ≈ 0). Nous présentons une étude comparative des cas sans et avec gravité, sur la base d’expériences réalisées avec une pâte granulaire modèle dans un écoulement de Couette à large entrefer. Les données sont ensuite analysées dans le cadre du modèle d’équilibre de contraintes normales de Morris et Boulay. Les expériences sont réalisées avec une pâte modèle transparente et mettent en œuvre des méthodes optiques et d’analyse d’images innovantes, qui nous permettent de mesurer les vitesses azimuthales des particules et les fluctuations de position angulaire, ainsi que le champ de concentration des particules dans l’entrefer. Pour le système isodense, l’accord théorie-expérience est excellent, pour un choix convenable des formes des fonctions viscométriques. En revanche, la même théorie ne rend compte que qualitativement du cas général geff ≠ 0. Les figures calculées reproduisent qualitativement la localisation de l’écoulement observée dans les expériences, mais un désaccord subsiste dans la description des zones de très fortes concentrations

SEROPREVALENȚA MARKERILOR HEPATITELOR VIRALE A, B, C ȘI E LA BOLNAVII UROLOGICI

Obiective. Sublinierea importanței testării periodice la markerii hepatitelor virale pentru pacienții  urologici, ca măsură crucială pentru gestionarea adecvată a infecțiilor. Metode. A fost efectuat un studiu epidemiologic descriptiv transversal (cross-secțional). De la bolnavii secției de urologie a Spitalului Clinic Republican ”Timofei Moșneaga” au fost prelevate probe de sânge pentru examinarea acestora prin metoda imuno-enzimatică (ELISA) la markerii hepatitelor virale: anti-HAV, anti-HAV IgM, AgHBs, anti-HBcor, anti-HBs, anti-HCV, anti-HEV IgG și anti-HEV IgM. În total au fost examinați 234 bolnavi, fiind efectuate 1638 investigații de laborator. Rezultate. La bolnavii din secția de urologie a Spitalului Clinic Republican ”Timofei Moșneaga” au fost identificate următoarele nivele de seroprevalență a markerilor hepatitelor virale: AgHBs – 9,0±1,9%; anti-HBcor – 47,9±3,3%; anti-HBs – 41,0±3,2%; anti-HCV – 7,7±1,7%; anti-HAV – 95,3±1,4%; anti-HAV IgM – 0%; anti-HEV IgG – 17,5±2,5%; anti-HEV IgM – 27,4±2,9%. Cele mai afectate grupuri pentru hepatitele B și C au fost persoanele de gen feminin din zona de Centru a țării, iar pentru hepatita E – persoanele de gen masculin provenite din zona de Nord. Concluzii. Rezultatele obținute denotă faptul, că pacienții urologici pot fi considerați ca un grup la risc sporit de infectare cu virusurile hepatitelor B, C și E

SEROPREVALENȚA MARKERILOR HEPATITELOR VIRALE A, B, C ȘI E LA LUCRĂTORII MEDICALI DIN DOMENIUL UROLOGIEI

Obiective. Stabilirea nivelului seroprevalenței markerilor hepatitelor virale A, B, C și E la lucrătorii medicali din secția de urologie a Spitalului Clinic Republican în vederea ajustării măsurilor de profilaxie a acestor infecții la ei. Metode. A fost realizat un studiu epidemiologic descriptiv transversal în baza probelor de sânge prelevate de la lucrătorii medicali, care au fost testate prin metoda imuno-enzimatică la markerii hepatitelor virale: anti-HAV, anti-HAV IgM, AgHBs, anti-HBcor, anti-HBs, anti-HCV, anti-HEV IgG și anti-HEV IgM. În total, au fost examinați 49 lucrători medicali, efectuându-se 392 de investigații de laborator. Rezultate. În cadrul lucrătorilor din secția de urologie, s-au identificat următoarele seroprevalențe pentru markerii virali: AgHBs - 2,0±2,0%; anti-HBcor - 38,8±7,0%; anti-HBs - 51,0±7,1%; anti-HCV - 4,1±2,8%; anti-HAV - 100%; anti-HAV IgM - 0%; anti-HEV IgG - 12,2±4,7%; anti-HEV IgM - 12,2±4,7%. Grupurile cele mai afectate au fost persoanele de gen feminin, asistentele medicale sau personalul auxiliar și cei cu o experiență de muncă de ≥30 ani. Concluzii. Rezultatele obținute indică faptul că lucrătorii medicali din secția de urologie pot fi considerați un grup cu risc crescut de infectare cu virusurile hepatitelor B, C și E

Prospective observational cohort study on grading the severity of postoperative complications in global surgery research

Background The Clavien–Dindo classification is perhaps the most widely used approach for reporting postoperative complications in clinical trials. This system classifies complication severity by the treatment provided. However, it is unclear whether the Clavien–Dindo system can be used internationally in studies across differing healthcare systems in high- (HICs) and low- and middle-income countries (LMICs). Methods This was a secondary analysis of the International Surgical Outcomes Study (ISOS), a prospective observational cohort study of elective surgery in adults. Data collection occurred over a 7-day period. Severity of complications was graded using Clavien–Dindo and the simpler ISOS grading (mild, moderate or severe, based on guided investigator judgement). Severity grading was compared using the intraclass correlation coefficient (ICC). Data are presented as frequencies and ICC values (with 95 per cent c.i.). The analysis was stratified by income status of the country, comparing HICs with LMICs. Results A total of 44 814 patients were recruited from 474 hospitals in 27 countries (19 HICs and 8 LMICs). Some 7508 patients (16·8 per cent) experienced at least one postoperative complication, equivalent to 11 664 complications in total. Using the ISOS classification, 5504 of 11 664 complications (47·2 per cent) were graded as mild, 4244 (36·4 per cent) as moderate and 1916 (16·4 per cent) as severe. Using Clavien–Dindo, 6781 of 11 664 complications (58·1 per cent) were graded as I or II, 1740 (14·9 per cent) as III, 2408 (20·6 per cent) as IV and 735 (6·3 per cent) as V. Agreement between classification systems was poor overall (ICC 0·41, 95 per cent c.i. 0·20 to 0·55), and in LMICs (ICC 0·23, 0·05 to 0·38) and HICs (ICC 0·46, 0·25 to 0·59). Conclusion Caution is recommended when using a treatment approach to grade complications in global surgery studies, as this may introduce bias unintentionally

The surgical safety checklist and patient outcomes after surgery: a prospective observational cohort study, systematic review and meta-analysis

© 2017 British Journal of Anaesthesia Background: The surgical safety checklist is widely used to improve the quality of perioperative care. However, clinicians continue to debate the clinical effectiveness of this tool. Methods: Prospective analysis of data from the International Surgical Outcomes Study (ISOS), an international observational study of elective in-patient surgery, accompanied by a systematic review and meta-analysis of published literature. The exposure was surgical safety checklist use. The primary outcome was in-hospital mortality and the secondary outcome was postoperative complications. In the ISOS cohort, a multivariable multi-level generalized linear model was used to test associations. To further contextualise these findings, we included the results from the ISOS cohort in a meta-analysis. Results are reported as odds ratios (OR) with 95% confidence intervals. Results: We included 44 814 patients from 497 hospitals in 27 countries in the ISOS analysis. There were 40 245 (89.8%) patients exposed to the checklist, whilst 7508 (16.8%) sustained ≥1 postoperative complications and 207 (0.5%) died before hospital discharge. Checklist exposure was associated with reduced mortality [odds ratio (OR) 0.49 (0.32–0.77); P\u3c0.01], but no difference in complication rates [OR 1.02 (0.88–1.19); P=0.75]. In a systematic review, we screened 3732 records and identified 11 eligible studies of 453 292 patients including the ISOS cohort. Checklist exposure was associated with both reduced postoperative mortality [OR 0.75 (0.62–0.92); P\u3c0.01; I2=87%] and reduced complication rates [OR 0.73 (0.61–0.88); P\u3c0.01; I2=89%). Conclusions: Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine

Critical care admission following elective surgery was not associated with survival benefit: prospective analysis of data from 27 countries

This was an investigator initiated study funded by Nestle Health Sciences through an unrestricted research grant, and by a National Institute for Health Research (UK) Professorship held by RP. The study was sponsored by Queen Mary University of London