Influence de la taille et de la gradation des particules sur la résistance au cisaillement et le comportement dilatant des matériaux granulaires

Résumé : Cette étude examine l'impact de la taille et de la gradation de particules sur les corrélations théoriques et empiriques existantes les plus connues entre la résistance au cisaillement et le comportement dilatatant des matériaux granulaires en condition de déformation plane et en compression triaxiale drainée. À cette fin, 276 tests de cisaillements symétriques directs et 35 tests de compressions triaxiales drainées ont été menés sur des échantillons composés de billes de basalte (particules rondes), et de sables constitués de particules angulaires (sable de Péribonka et sable d'Eastmain) sur une échelle de 63 µm à 2000 µm afin d'évaluer leur résistance au cisaillement et leur comportement de dilatance sur une vaste échelle de pressions normales et de densités relatives initiales. Premièrement, la fiabilité et l'applicabilité des limites de mesure à l’aide de tests physiques de cisaillements symétriques directs dans l'interprétation de la résistance au cisaillement frictionnel en déformation plane des matériaux granulaires ont été discutées et confirmées par l'usage du code informatique DEM, SiGran. L'accent a été particulièrement mis sur la validation du modèle DEM au moyen de comparaison des résultats des simulations DEM avec leurs équivalents physiques à une échelle macro. Les résultats virtuels DSA sont abordés du point de vue de la coaxialité entre les principales tensions et les principales directions des paliers de pression ainsi que de la déviation de la direction d'extension nulle à partir de la direction horizontale. Les résultats numériques fournissent également des données quantitatives sur les différentes formes d'énergie consommées durant le cisaillement confirmées par d'autres résultats physiques et numériques publiés. Sur la base des postulats précédents, un examen minutieux des résultats des essais de cisaillements directs et de données issues de la littérature a été accompli afin d'évaluer la fiabilité des formules empiriques bien connues de Bolton et Collins et al. avec leurs constantes couramment employées en condition de déformation plane. L'étude montre qu'une application des relations empiriques de force-dilatation de cisaillement avec les constantes proposées par Bolton (1986) et Collins et al. (1992) aux sables ayant une distribution de taille de particules différente peut conduire à surestimer leurs valeurs en terme de force de cisaillement. Dans cette étude, les coefficients des équations de Bolton et Collins et al. ont donc été ajustée afin de prendre en compte les caractéristiques des particules, en particulier le diamètre médian, D50. De manière analogue, les effets microstructuraux imposés par la géométrie interne des particules (par exemple la taille, la forme et la gradation des particules) sur la relation tension-dilatation très connue, celle de Rowe (1962), et son ajustement empirique en condition triaxiale drainée ont été examinés dans cette étude. Une comparaison des prédictions des formules proposées avec les données de force de cisaillement issues de la littérature fournit de nombreuses preuves en faveur des contraintes mises en place au sein des relations existantes de force-dilatation de cisaillement en condition de déformation plane et triaxiale. Ces comparaisons prouvent également que la prise en compte de la taille des grains conduit à des résultats plus tangibles que lorsque la taille de la particule n'est pas considérée. Les formules de force-dilatation ajustées peuvent se révéler avantageuses pour évaluer indépendamment la cohérence des forces de cisaillement déterminées expérimentalement et pour introduire des lois d’écoulement plus précises dans les analyses géotechniques analytiques et numériques.

Dos visiones un conflicto: los intereses de Noruega e India en sus mediaciones en el conflicto esrilanqués. Periodo (1987-1990 & 2002-2008)

El objetivo de este estudio de caso es describir y analizar los intereses nacionales desde la concepción de India y Noruega durante el contexto histórico del conflicto en Sri Lanka, además examinar cómo estos intereses influenciaron la consolidación de las estrategias y tácticas de negociación. La hipótesis aprobar es que las mediaciones de India y Noruega se desarrollan de forma distinta debido a sus intereses, sin embargo, ambas lograron formas de entendimiento entre el Gobierno de esrilanqués y el Grupo Insurgente Tigres de Liberación de la Tierra Tamil (LTTE). Para esto, se revisan los límites de las mediaciones conforme a los intereses. Siguiendo distintas perspectivas académicas del realismo, neorrealismo y cientificismo se utilizan distintos conceptos desarrollados por Hans Morgentau, Robert Osgood, Johan Galtung, Oliver Ramsbothan, Saddia Touval e Isak Svensson. Desde el método descriptivo histórico y análisis cuantitativo se describen los intereses nacionales y su influencia en las mediaciones que se llevaron a cabo en Sri Lanka.

Valor diagnóstico del pepsinógeno i/ii como biomarcador de lesiones pre-malignas y malignas gástricas: revisión sistemática

Antecedentes: El cáncer gástrico se diagnostica tardíamente. Sólo en países como Corea y Japón existen políticas de tamizaje, que se justificarían en cualquier país con alta prevalencia de cáncer gástrico como Colombia o Chile. El análisis del pepsinógeno sérico se ha propuesto para el diagnóstico de lesiones premalignas y malignas gástricas, por lo cual se pretende revisar sistemáticamente en la literatura el valor diagnóstico del cociente pepsinógeno I/II como marcador de lesiones premalignas y malignas gástricas. Metodología: Se revisó la literatura hasta septiembre del 2016 con palabras claves lesiones malignas, premalignas gástricas y pepsinógeno en las bases de datos PubMed, OVID, EMBASE, EBSCO, LILACS, OPENGRAY y Dialnet, artículos de prueba diagnóstica que evaluaran el cociente pepsinógeno I/II en relación con los hallazgos histológicos. Resultados: Se incluyeron 21 artículos conun total de 20601 pacientes, que demuestranuna sensibilidad entre13.7% - 91.2%, una especificidad entre 38.5% - 100%, un Valor Predictivo Positivo entre 6.3% - 100% y un Valor Predictivo Negativo entre 33.3% - 98.8%del cociente pepsinógeno I/II en relación con el diagnósticode lesiones premalignas y malignas gástricas. Conclusiones: Los valores del cociente pepsinógeno I/II disminuidos se relacionan con la presencia delesiones premalignas y malignas gástricas.Dado que tiene mejor especificidad que sensibilidad, en cuanto prueba para tamizaje, sería útil para la selección de pacientes que se beneficiaríande la EVDA. Se requieren más estudios de prueba diagnóstica para validar un punto de corte específico que pueda ser utilizado como valor estándar.

Percepción de los trabajadores acerca de la seguridad en el trabajo en una empresa del sector de gas natural en Casanare

Introducción: La percepción puede ser considerada principalmente como un grupo de procesos internos en las personas que genera en los observadores una representación mental del entorno. Percibir es adelantarse al suceso, a lo que puede llegar a suceder, determinando lo que puede ser un peligro a nuestra seguridad y salud. Objetivo: El presente estudio tiene como objetivo determinar la percepción de los trabajadores acerca de la seguridad en el trabajo en áreas de procesos automatizados y mecánicas en una empresa del sector de gas natural en el departamento de Casanare, Colombia 2016. Metodología: Se llevó a cabo un estudio de corte transversal en 50 trabajadores de una empresa del sector de gas natural en Casanare. Se uttilizó el Cuestionario nórdico NOSACQ-50-Spanish, instrumento validado para evaluar la percepción acerca de la seguridad y salud en el lugar de trabajo. Se incluyeron variables sociodemográficas, laborales y las relacionadas con la percepción de la seguridad en el lugar del trabajo. Para el análsiis estadistico se calcularon medidas de tendencia central y de dispersión. El estudio de la percepción de seguridad tuvo como puntos de corte: < 2,5 mala percepción y > 2,5 buena percepción. Se emplearon pruebas de asociación X2 o test exacto de Fisher (valores esperados <5) y medidas de asociación OR con sus intervalos de confianza del 95% y se usaron modelos de regresión lineal. Resultados: El total de trabajadores fue de 50 personas, el 76% correspondió al sexo masculino y la mayor distribución se presentó en áreas mecánicas con 52% frente al 48% que se encontró en áreas automatizadas. Se halló asociación estadísticamente significativa entre las variables sociodemográficas área/sexo (Pr = 0,016), indicando que a los trabajadores de sexo femenino se les ubican en el área mecánica mientras que los de sexo masculino, laboran en todas las áreas sin darle relevancia al género. También se encontró asociación con las variables área/año de nacimiento (Pr =0.022), indicando que en el área automatizada se dejan profesionales con promedio de edad de 32 años, por el tipo de requisitos en competencias que exigen para ejecutar las labores. Para las demás variables ocupacionales que evaluaron la percepción de seguridad frente al trabajo, no se encontró asociación significativa. Conclusión: Los resultados permiten realizar acciones en pro de mejorar la percepción de los trabajadores dentro de la organización. Se podrán desarrollar programas de seguridad y salud en el trabajo, que respondan de manera efectiva a los peligros laborales detectados.

"Lesion journey" nell'idrosadenite suppurativa: correlazione clinica e ultrasonografica

Introduzione: L'idrosadenite suppurativa (HS) è una malattia immuno-mediata che colpisce i follicoli piliferi situati principalmente nelle aree ricche di ghiandole apocrine. Materiali e metodi: È stato condotto uno studio osservazionale prospettico monocentrico finalizzato a correlare i parametri clinici ed ecografici con: l'evoluzione delle lesioni, la probabilità di riacutizzazione o di andare incontro ad un trattamento chirurgico/laser-CO2. Risultati: Sono stati reclutati sessantuno pazienti con un'età media pari a 29,5 ± 7,5 anni che presentavano un numero basale di 127 noduli infiammatori, 43 ascessi e 62 fistole. Dopo un tempo medio di 77,9 settimane, rispettivamente il 40%, 14%, 8% di noduli, ascessi e fistole erano guariti, il 5%, 30%, 29% persistevano privi di infiammazione, il 47%, 33%, 63 % presentava uno stato infiammatorio, e l'8% e il 23% dei noduli e degli ascessi erano evoluti in fistole. Sono stati registrati 137 episodi di flare nelle lesioni acute (noduli + ascessi) e 54 nelle lesioni croniche (fistole), mentre il numero di interventi procedurali è stato rispettivamente pari a 59 e 50. I fattori predittivi associati ad un'evoluzione sfavorevole (stato infiammatorio o cronicizzazione) per ascessi e noduli sono stati: evidenza ecografica di frammenti piliferi intralesionali, elevato segnale Power Doppler (PD) ed edema all'ecografia, profondità della localizzazione ed interessamento genitale; i predittori associati alle fistole sono stati: profondità della localizzazione, edema e dimensioni della lesione. La probabilità che una lesione acuta venisse sottoposta ad un intervento procedurale è stata correlata a: età, presenza di frammenti piliferi, segnale PD, edema e profondità della localizzazione; per le fistole l'unico predittore indipendente è stato la dimensione. I predittori di riacutizzazione della patologia per ascessi e noduli sono stati: giovane età all'esordio, segnale PD, evidenza ecografica di frammenti follicolari, profondità della localizzazione e dimensioni; per le fistole i predittori sono stati: localizzazione ascellare, profondità della localizzazione, edema e dimensione.

Sviluppo di un metodo termoanalitico per la quantificazione di microplastiche in matrici complesse

Microplastics (MPs) are highly debated emerging contaminants that are widespread on Earth. Nowadays, assessment of the risk that MPs pose on human health and environment were not developed yet, and standardized analytical methods for their quantification in complex matrices do not exist. Therefore, the formulation of standards which regulating MPs emission in the environment is not possible. The purpose of this study was to develop and apply a method for the analysis of MPs in sewage sludges and water from a wastewater treatment plant (WWTP), due to the relevance of those matrices as important pathway for MPs to enter the environment. Seven polymers were selected, because of their relevance on market production and their frequency of occurrence in such plants: polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC), and nylon 6 (PA-6). In the study, a pre-treatment procedure was optimised using Fenton’s reagent and analyses carried out by combining thermochemolysis with Py-GC-MS after sample filtration on quartz (0.3 µm). Polymer quantification was performed with solid polymer mixture in silica and good correlations were obtained with internal calibration. As main results, Fenton's reagent negatively affected the recovery of some polymers (PP, PE, PS, PA-6) and a possible matrix interference was noticed, especially for PET and PVC. The WWTP allowed a good abatement of PS, PE, PP and PVC (on average 90 %) and comparable results were hypothesised for the other polymers. Polymer concentrations is sewage sludges ranged between < 2 μg/gdry and 3.5 mg/ gdry, for PC and PVC, respectively. Possible overestimations for PET and PVC, due to matrix interreferences, were taken into account and discussed.

Correlation and prediction of mixing thermodynamic properties of ester-containing systems Ester+alkane and ester+ester binary systems and the ternary dodecane+ethyl pentonoate+ethyl ethanoate

[EN]Excess thermodynamic properties VE m and HE m, have been measured for the ternary mixture dodecane + ethyl pentanoate + ethyl ethanoate and for the corresponding binaries dodecane + ethyl pentanoate, dodecane + ethyl ethanoate, ethyl pentanoate + ethyl ethanoate at 298.15 K. All mixtures show endothermic and expansive effects. Experimental results are correlated with a suitable equation whose final form for the excess ternary quantity ME contains the particular contributions of the three binaries (i–j) and a last term corresponding to the ternary, all of them obtained considering fourth-order interactions.

Measurements and correlations of the isobaric vapor-liquid equilibria of binary mixtures and excess properties for mixtures containing and alkyl (Methyl, Ethyl) butanoate with an alkane (Heptane, Nonane) at 101.32 kPa.

[EN]In this work, the measurements of the isobaric vapor−liquid equilibrium (VLE) data at 101.32 kPa and the excess molar volumes (vE), obtained at 10 K intervals of temperature in the range (288.15 to 328.15) K, for four binary systems comprised of methyl or ethyl butanoate with two alkanes (heptane and nonane) are presented.

Azimuthal correlations of electrons from heavy-flavor decay with hadrons in p plus p and Au plus Au collisions at root s(NN)=200 GeV

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modification of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side-jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at root s(NN) = 200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.

Thermodynamic and topological instability approaches for forecasting glass-forming ability in the ternary Al-Ni-Y system

A thermodynamic approach to predict bulk glass-forming compositions in binary metallic systems was recently proposed. In this approach. the parameter gamma* = Delta H-amor/(Delta H-inter - Delta H-amor) indicates the glass-forming ability (GFA) from the standpoint of the driving force to form different competing phases, and Delta H-amor and Delta H-inter are the enthalpies for-lass and intermetallic formation, respectively. Good glass-forming compositions should have a large negative enthalpy for glass formation and a very small difference for intermetallic formation, thus making the glassy phase easily reachable even under low cooling rates. The gamma* parameter showed a good correlation with GFA experimental data in the Ni-Nb binary system. In this work, a simple extension of the gamma* parameter is applied in the ternary Al-Ni-Y system. The calculated gamma* isocontours in the ternary diagram are compared with experimental results of glass formation in that system. Despite sonic misfitting, the best glass formers are found quite close to the highest gamma* values, leading to the conclusion that this thermodynamic approach can lie extended to ternary systems, serving as a useful tool for the development of new glass-forming compositions. Finally the thermodynamic approach is compared with the topological instability criteria used to predict the thermal behavior of glassy Al alloys. (C) 2007 Elsevier B. V. All rights reserved.

Phase Equilibrium and Optimization Tools: Application for Enhanced Structured Lipids for Foods

Solid-liquid phase equilibrium modeling of triacylglycerol mixtures is essential for lipids design. Considering the alpha polymorphism and liquid phase as ideal, the Margules 2-suffix excess Gibbs energy model with predictive binary parameter correlations describes the non ideal beta and beta` solid polymorphs. Solving by direct optimization of the Gibbs free energy enables one to predict from a bulk mixture composition the phases composition at a given temperature and thus the SFC curve, the melting profile and the Differential Scanning Calorimetry (DSC) curve that are related to end-user lipid properties. Phase diagram, SFC and DSC curve experimental data are qualitatively and quantitatively well predicted for the binary mixture 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) and 1,2,3-tripalmitoyl-sn-glycerol (PPP), the ternary mixture 1,3-dimyristoyl-2-palmitoyl-sn-glycerol (MPM), 1,2-distearoyl-3-oleoyl-sn-glycerol (SSO) and 1,2,3-trioleoyl-sn-glycerol (OOO), for palm oil and cocoa butter. Then, addition to palm oil of Medium-Long-Medium type structured lipids is evaluated, using caprylic acid as medium chain and long chain fatty acids (EPA-eicosapentaenoic acid, DHA-docosahexaenoic acid, gamma-linolenic-octadecatrienoic acid and AA-arachidonic acid), as sn-2 substitutes. EPA, DHA and AA increase the melting range on both the fusion and crystallization side. gamma-linolenic shifts the melting range upwards. This predictive tool is useful for the pre-screening of lipids matching desired properties set a priori.

Synthesis and characterization of ternary hybrid material based on poly-o-methoxyaniline and poly(ethylene oxide) in mesostructured V(2)O(5)

New hybrid composites based on mesostructured V(2)O(5) containing intercalated poly(ethylene oxide), poly-o-methoxyaniline and poly(ethylene oxide)/poly-o-methoxyaniline were prepared. The results suggest that the polymers were intercalated into the layers of the mesostructured V(2)O(5). Electrochemical studies showed that the presence of both polymers in the mesostructured V(2)O(5) (ternary hybrid) leads to an increase in total charge and stability after several cycles compared with binary hybrid composites. This fact makes this material a potential component as cathode for lithium ion intercalation and further, a promising candidate for applications in batteries.

The influence of nitrogen and oxygen additions on the thermal characteristics of aluminium-based thin films

The ternary aluminium oxynitride (AlNxOy) system offers the possibility to obtain a wide range of properties by tailoring the ratio between pure Al, AlNx and AlOy and therefore opening a significant number of possible applications. In this work the thermal behaviour of AlNxOy thin films was analysed by modulated infrared radiometry (MIRR), taking as reference the binary AlOy and AlNx systems. MIRR is a non-contact and non-destructive thermal wave measurement technique based on the excitation, propagation and detection of temperature oscillations of very small amplitudes. The intended change of the partial pressure of the reactive gas (N2 and/or O2) influenced the target condition and hence the deposition characteristics which, altogether, affected the composition and microstructure of the films. Based on the MIRR measurements and their qualitative and quantitative interpretation, some correlations between the thermal transport properties of the films and their chemical/physical properties have been found. Furthermore, the potential of such technique applied in this oxynitride system, which present a wide range of different physical responses, is also discussed. The experimental results obtained are consistent with those reported in previous works and show a high potential to fulfil the demands needed for the possible applications of the systems studied. They are clearly indicative of an adequate thermal response if this particular thin film system is aimed to be applied in small sensor devices or in electrodes for biosignal acquisition, such as those for electroencephalography or electromyography as it is the case of the main research area that is being developed in the group.

On the binary nature of the γ-ray sources AGL J2241+4454 (= MWC 656) and HESS J0632+057 (= MWC 148)

We present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the gamma-ray sources AGL J2241+4454 and HESS J0632+0 57, respectively. The main parameters of the Halpha emission line (EW, FWHM and centroid velocity) in these stars are modulated on the proposed orbital periods of 60.37 and 321 days, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two gamma-ray sources thus confirming their binary nature. Our orbital solution support eccentricities e~0.4 and 0.83+-0.08 for MWC 656 and MWC 148, respectively. Further, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ~0.3 orbital phases after periastron passage, similarly to the case of LS I +61 303. In addition, the optical photometric light curve maxima in AGL J2241+4454/MWC 656 occur ~0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with orbital period for the known gamma-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of VHE radiation. Another correlation between the EW of Halpha and orbital period is also observed, similarly to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters Porb and e from the Halpha line in future Be gamma-ray binary candidates.

Self and cross-velocity correlation functions and diffusion coefficients in liquids: a molecular dynamics study of binary mixtures of soft spheres

Molecular dynamics simulation is applied to the study of the diffusion properties in binary liquid mixtures made up of soft-sphere particles with different sizes and masses. Self- and distinct velocity correlation functions and related diffusion coefficients have been calculated. Special attention has been paid to the dynamic cross correlations which have been computed through recently introduced relative mean molecular velocity correlation functions which are independent on the reference frame. The differences between the distinct velocity correlations and diffusion coefficients in different reference frames (mass-fixed, number-fixed, and solvent-fixed) are discussed.