Stress Corrosion Cracking of an Austenitic Stainless Steel in Nitrite-Containing Chloride Solutions
This article describes the susceptibility of 316L stainless steel to stress corrosion cracking (SCC) in a nitrite-containing chloride solution. Slow strain rate testing (SSRT) in 30 wt. % MgCl2 solution established SCC susceptibility, as evidenced by post-SSRT fractography. Addition of nitrite to the chloride solution, which is reported to have inhibitive influence on corrosion of stainless steels, was found to increase SCC susceptibility. The susceptibility was also found to increase with nitrite concentration. This behaviour is explained on the basis of the passivation and pitting characteristics of 316L steel in chloride solution.
Time-multiscale methods for the simulation of slow transport problems in atomistic systems
En esta tesis presentamos una teoria adaptada a la simulacion de fenomenos lentos de transporte en sistemas atomisticos. En primer lugar, desarrollamos el marco teorico para modelizar colectividades estadisticas de equilibrio. A continuacion, lo adaptamos para construir modelos de colectividades estadisticas fuera de equilibrio. Esta teoria reposa sobre los principios de la mecanica estadistica, en particular el principio de maxima entropia de Jaynes, utilizado tanto para sistemas en equilibrio como fuera de equilibrio, y la teoria de las aproximaciones del campo medio. Expresamos matematicamente el problema como un principio variacional en el que maximizamos una entropia libre, en lugar de una energia libre. La formulacion propuesta permite definir equivalentes atomisticos de variables macroscopicas como la temperatura y la fraccion molar. De esta forma podemos considerar campos macroscopicos no uniformes. Completamos el marco teorico con reglas de cuadratura de Monte Carlo, gracias a las cuales obtenemos modelos computables. A continuacion, desarrollamos el conjunto completo de ecuaciones que gobiernan procesos de transporte. Deducimos la desigualdad de disipacion entropica a partir de fuerzas y flujos termodinamicos discretos. Esta desigualdad nos permite identificar la estructura que deben cumplir los potenciales cineticos discretos. Dichos potenciales acoplan las tasas de variacion en el tiempo de las variables microscopicas con las fuerzas correspondientes. Estos potenciales cineticos deben ser completados con una relacion fenomenologica, del tipo definido por la teoria de Onsanger. Por ultimo, aportamos validaciones numericas. Con ellas ilustramos la capacidad de la teoria presentada para simular propiedades de equilibrio y segregacion superficial en aleaciones metalicas. Primero, simulamos propiedades termodinamicas de equilibrio en el sistema atomistico. A continuacion evaluamos la habilidad del modelo para reproducir procesos de transporte en sistemas complejos que duran tiempos largos con respecto a los tiempos caracteristicos a escala atomica. ABSTRACT In this work, we formulate a theory to address simulations of slow time transport effects in atomic systems. We first develop this theoretical framework in the context of equilibrium of atomic ensembles, based on statistical mechanics. We then adapt it to model ensembles away from equilibrium. The theory stands on Jaynes' maximum entropy principle, valid for the treatment of both, systems in equilibrium and away from equilibrium and on meanfield approximation theory. It is expressed in the entropy formulation as a variational principle. We interpret atomistic equivalents of macroscopic variables such as the temperature and the molar fractions, wich are not required to be uniform, but can vary from particle to particle. We complement this theory with Monte Carlo summation rules for further approximation. In addition, we provide a framework for studying transport processes with the full set of equations driving the evolution of the system. We first derive a dissipation inequality for the entropic production involving discrete thermodynamic forces and fluxes. This discrete dissipation inequality identifies the adequate structure for discrete kinetic potentials which couple the microscopic field rates to the corresponding driving forces. Those kinetic potentials must finally be expressed as a phenomenological rule of the Onsanger Type. We present several validation cases, illustrating equilibrium properties and surface segregation of metallic alloys. We first assess the ability of a simple meanfield model to reproduce thermodynamic equilibrium properties in systems with atomic resolution. Then, we evaluate the ability of the model to reproduce a long-term transport process in complex systems.
The uprising of the marginalised: a socio-economic perspective of the Syrian uprising
More than three years after the outbreak of protests in a number of Arab countries, the role of socio-economic factors in these events is attracting more attention. One of the cases that needs more research is Syria. More than three years into the Syrian uprising, the socio-economic roots of the protest movement that became one of the bloodiest civil conflicts in the history of the Middle East need to be examined. While it has been observed that the Syrian uprising, contrary to some ‘Arab Spring’ countries, has been an uprising of more marginalised social groups with a strong role played by poorer segments in the society, particularly rural and rural-to-urban migrants, the socio-economic explanation for this is still underdeveloped. This paper aims at contributing to a better understanding of this issue by examining the political and socio-economic compromise that underlined the rule of the Ba’th party in Syria for four decades and unpacking how a combination of internal and external shifts that started in the 1990s and intensified in the 2000s led to the erosion of this compromise, providing the background to the events that began in 2011.