How granular materials deform in quasistatic conditions

Based on numerical simulations of quasistatic deformation of model granular materials, two rheological regimes are distinguished, according to whether macroscopic strains merely reflect microscopic material strains within the grains in their contact regions (type I strains), or result from instabilities and contact network rearrangements at the microscopic level (type II strains). We discuss the occurrence of regimes I and II in simulations of model materials made of disks (2D) or spheres (3D). The transition from regime I to regime II in monotonic tests such as triaxial compression is different from both the elastic limit and from the yield threshold. The distinction between both types of response is shown to be crucial for the sensitivity to contact-level mechanics, the relevant variables and scales to be considered in micromechanical approaches, the energy balance and the possible occurrence of macroscopic instabilitie

Discrete numerical simulation, quasistatic deformation and the origins of strain in granular materials.

International audienceSystematic numerical simulations of model dense granular materials in monotonous, quasistatic deformation reveal the existence of two different régimes. In the first one, the macroscopic strains stem from the deformation of contacts. The motion can be calculated by purely static means, without inertia, stress controlled or strain rate controlled simulations yield identical smooth rheological curves for a same sample. In the second régime, strains are essentially due to instabilities of the contact network, the approach to the limits of large samples and of small strain rates is considerably slower and the material is more sensitive to perturbations. These results are discussed and related to experiments : measurements of elastic moduli with very small strain increments, and slow deformation (creep) under constant stress

Quasistatic rheology and the origins of strain

Published in special issue of "Comptes-Rendus Physique" on granular materialsInternational audienceFeatures of rheological laws applied to solid-like granular materials are recalled and confronted to microscopic approaches via discrete numerical simulations. We give examples of model systems with very similar equilibrium stress transport properties -- the much-studied force chains and force distribution -- but qualitatively different strain responses to stress increments. Results on the stability of elastoplastic contact networks lead to the definition of two different rheological regimes, according to whether a macroscopic fragility property (propensity to rearrange under arbitrary small stress increments in the thermodynamic limit) applies. Possible consequences are discussed

Discrete numerical simulation, quasistatic deformation and the origins of strain in granular materials

Systematic numerical simulations of model dense granular materials in monotonous, quasistatic deformation reveal the existence of two different r\'egimes. In the first one, the macroscopic strains stem from the deformation of contacts. The motion can be calculated by purely static means, without inertia, stress controlled or strain rate controlled simulations yield identical smooth rheological curves for a same sample. In the second r\'egime, strains are essentially due to instabilities of the contact network, the approach to the limits of large samples and of small strain rates is considerably slower and the material is more sensitive to perturbations. These results are discussed and related to experiments : measurements of elastic moduli with very small strain increments, and slow deformation (creep) under constant stress.Comment: Third international symposium on deformation characteristics of geomaterials, Lyon : France (2003

Kinetics of shape equilibration for two-dimensional islands

We study the relaxation to equilibrium of two dimensional islands containing up to 20000 atoms by Kinetic Monte Carlo simulations. We find that the commonly assumed relaxation mechanism - curvature-driven relaxation via atom diffusion - cannot explain the results obtained at low temperatures, where the island edges consist in large facets. Specifically, our simulations show that the exponent characterizing the dependence of the equilibration time on the island size is different at high and low temperatures, in contradiction with the above cited assumptions. Instead, we propose that - at low temperatures - the relaxation is limited by the nucleation of new atomic rows on the large facets : this allows us to explain both the activation energy and the island size dependence of the equilibration time.Comment: 9 pages, revte

Surface Loving and Surface Avoiding modes

We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focussing on periodic modes in the vicinity of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared to its surface is a key parameter. We exhibit two kind of modes: Surface Avoiding and Surface Loving Modes whose envelope functions have their minima and respectively maxima in the vicinity of the surface. We finally consider the observability of such modes. While Surface avoiding modes have experimentally been observed (Phys. Rev. Lett. 97, 1224301 (2006)), we show that Surface Loving Modes are likely to be observable and we discuss the achievement of such experiments. The proposed approach could be easily transposed to other types of wave propagation in unidimensional semi-infinite periodic structures as photonic Bragg mirror.Comment: 12 pages, 9 figure

Quasistatic rheology and the origins of strain

Features of rheological laws applied to solid-like granular materials are recalled and confronted to microscopic approaches via discrete numerical simulations. We give examples of model systems with very similar equilibrium stress transport properties -- the much-studied force chains and force distribution -- but qualitatively different strain responses to stress increments. Results on the stability of elastoplastic contact networks lead to the definition of two different rheological regimes, according to whether a macroscopic fragility property (propensity to rearrange under arbitrary small stress increments in the thermodynamic limit) applies. Possible consequences are discussed.Comment: Published in special issue of "Comptes-Rendus Physique" on granular material

Educación del Serenazgo en gestión del riesgo de desastres y su impacto en la atención al vecino surcano

Universidad Nacional Agraria La Molina. Escuela de Posgrado. Maestría en AdministraciónLa investigación presente “Educación del Serenazgo en Gestión del Riesgo de Desastres y su impacto en la atención al vecino surcano”, tiene como objetivo, efectuar el análisis y el efecto de la educación del Serenazgo en la Gestión del Riesgo de Desastres del distrito de Santiago de Surco, para motivar, incrementar las potencialidades y mejorar las capacidades del personal de Serenazgo del Municipio distrital de Santiago de Surco en lo que respecta a los procesos para la estimación, procesos de prevención y reducción, procesos de preparación, respuesta y recuperación, y finalmente, reconstrucción ante el riesgo de que se produzcan desastres; impactando en la atención del vecino surcano. La metodología se tradujo en diagnosticar el nivel de educación del Serenazgo y su impacto en la Gestión del Riesgo de Desastres dentro del radio de alcance del Municipio distrital de Santiago de Surco, cuyos actores son la Subgerencia de Defensa Civil, así como en la Gerencia de Desarrollo Urbano y en la Subgerencia de Seguridad Ciudadana. Se utilizaron estadísticas y estudios previos con las áreas involucradas, documentación digital como papers y documentos web. El resultado principal de esta investigación fue la necesidad de capacitar al personal de Serenazgo para lograr conocimiento en la gestión que pueda permitir afrontar los riesgos y aplicarlo en la gestión ante los desastres, orientados a reducir los daños psicológicos y físicos de los vecinos del distrito. La conclusión general es entonces capacitar al personal de Serenazgo en la Estimación de riesgo ante los desastres, para desarrollar herramientas que permitan en primer lugar la detección y luego la estimación del riesgo, así como el de orientar a la población en la prevención a fin de lograr la reducción del riesgo, identificando aliados de carácter estratégico, que fortalezcan la capacitación y difusión.The present research "Education of the Serenazgo in disaster risk management and its impact on the attention to the surcano neighbor", has as purpose, to carry out the analysis and the effect of the education of the Serenazgo in the Disaster risk management of the district of Santiago of Surco, to motivate, increase the potentialities and improve the capabilities of the Serenazgo personnel of the District Municipality of Santiago de Surco regarding the processes for estimation, prevention and reduction processes, preparation, response and recovery processes, and finally, reconstruction in the face of the risk of disasters; impacting the attention of the surcano neighbor. The methodology was translated into diagnosing the level of education of the Serenazgo and its impact on the management of the risk of occurrence of disastrous events within the range of the District Municipality of Santiago de Surco, whose actors are the Civil Defense Sub-Department, as well as in the Department of Urban Development and the Deputy Manager of Citizen Security. Statistics and previous studies were used with the areas involved, digital documentation such as papers and web documents. The main result of this research was the need to train Serenazgo personnel to gain knowledge in management that could allow them to face the risks and apply it in disaster management, aimed at reducing the psychological and physical damage of the residents of the district. The general conclusion is then to train the personnel of Serenazgo in the Estimation of risk in the face of disasters, to develop tools that allow first of all the detection and then the estimation of the risk, as well as that of orienting the population in the prevention in order to achieve risk reduction, identifying strategic allies that strengthen training and dissemination

Myths and lessons of liberal intervention: The British campaign for the abolition of the Atlantic slave trade to Brazil

This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 Martinus NijhoffThis article takes issue with recent references to the British nineteenth century campaign for the abolition of the trans-Atlantic slave trade to Brazil that serve to bolster interventionist or imperialist agendas. In particular, such accounts reproduce two and a half myths about the campaign: that it can serve as a model for the present age; that the success of the campaign can be explained through the actions of the intervening party alone (with a corresponding neglect of those of the ‘target’ state); and the half-myth that the campaign’s success was due to military action (at the expense of institutional (legal) and normative factors and the capacity of the target state). I argue instead that this case – and interventions more generally – would benefit from an analysis that considers the role of force in relation to a series of residual institutional and cultural constraints within the liberal state and to political conditions in the target state. In light of the complexities and contingencies that these factors present the underlying lesson is that military force should be used sparingly, if at all