Periodic cells for large-scale problem initialization

In geotechnical applications the success of the discrete element method (DEM) in simulating fundamental aspects of soil behaviour has increased the interest in applications for direct simulation of engineering scale boundary value problems (BVP’s). The main problem is that the method remains relatively expensive in terms of computational cost. A non-negligible part of that cost is related to specimen creation and initialization. As the response of soil is strongly dependant on its initial state (stress and porosity), attaining a specified initial state is a crucial part of a DEM model. Different procedures for controlled sample generation are available. However, applying the existing REV-oriented initialization procedures to such models is inefficient in terms of computational cost and challenging in terms of sample homogeneity. In this work a simple but efficient procedure to initialize large-scale DEM models is presented. Periodic cells are first generated with a sufficient number of particles matching a desired particle size distribution (PSD). The cells are then equilibrated at low-level isotropic stress at target porosity. Once the cell is in equilibrium, it is replicated in space in order to fill the model domain. After the domain is thus filled a few mechanical cycles are needed to re-equilibrate the large domain. The result is a large, homogeneous sample, equilibrated under prescribed stress at the desired porosity. The method is applicable to both isotropic and anisotropic initial stress states, with stress magnitude varying in space

An approach to enhance efficiency of DEM modelling of soils with crushable grains

In this study oedometric compression tests of hydrocarbon coke, Fontainebleau sand and silica sand are simulated in three dimensions using breakable particles. The method adapts a rigorous breakage criterion for elasto-brittle spheres to represent failure of grains isolated between platens or within granular masses. The breakage criterion allows for the effect of particle bulk and contact properties to be treated separately. A discrete fragmentation multigenerational approach is applied as a spawning procedure. The number of particles quickly increases during the simulation, but is kept manageable by systematic fine exclusion and upscaling. Fine exclusion leads to mass losses between generations, but that loss is accounted for outside the mechanical model. Sensitivity analysis shows that it is enough to keep 53% of the crushed particle mass within the mechanical model to correctly reproduce experimental macroscopic behaviour. Practical upscaling rules are proposed for (a) contact stiffness, (b) breakage criteria and (c) grain size distribution, and validated simulating the same test, reducing by half the initial number of particles. The results are promising as both the mechanical and grading evolution are well captured with two orders of magnitude savings in computing efficiency

On the progressive nature of grain crushing

In this work acoustic emission (AE) is used as experimental evidence of the progressive nature of grain crushing. Stress controlled high pressure oedometric compression test are carried out on 1.2 mm monodisperse samples of glass beads. It was observed that the granular assembly starts to experience particle breakage at a vertical stress of about 25MPa. When this yield pressure is exceeded the glass beads start to break emitting loud impulsive sound and the vertical displacement increases rapidly. The load was increased beyond the yield stress and at each increment while the vertical stress remained constant the sample continued to emit sound. The emission of sound at a constant vertical stress indicates that crushing is a progressive failure mechanism; once the first crushing event occurs, the structure starts to rearrange causing other crushing events to occur and additional settlement. In particular, two signal processing algorithms are used on the samples of the acoustic signal to obtain two additional metrics of the crushing evolution. The first is the cumulative energy versus time. The second is the number of crushing events versus time, which is based on the automatic detection of the peaks of the sound signal envelope. There is a clear correlation between the cumulative acoustic energy emitted and the observed sample displacement. Using laser scanning, the evolution of the particle size distribution and particle shape are measured in detail so that a link between the acoustic data and the crushing intensity is established. The crushing intensity was controlled using materials with different strengths

Ruxolitinib discontinuation syndrome: incidence, risk factors, and management in 251 patients with myelofibrosis

none36Ruxolitinib discontinuation syndrome: incidence, risk factors, and management in 251 patients with myelofibrosisopenPalandri F.; Palumbo G.A.; Elli E.M.; Polverelli N.; Benevolo G.; Martino B.; Abruzzese E.; Tiribelli M.; Tieghi A.; Latagliata R.; Cavazzini F.; Bergamaschi M.; Binotto G.; Crugnola M.; Isidori A.; Caocci G.; Heidel F.; Pugliese N.; Bosi C.; Bartoletti D.; Auteri G.; Cattaneo D.; Scaffidi L.; Trawinska M.M.; Stella R.; Ciantia F.; Pane F.; Cuneo A.; Krampera M.; Semenzato G.; Lemoli R.M.; Iurlo A.; Vianelli N.; Cavo M.; Breccia M.; Bonifacio M.Palandri, F.; Palumbo, G. A.; Elli, E. M.; Polverelli, N.; Benevolo, G.; Martino, B.; Abruzzese, E.; Tiribelli, M.; Tieghi, A.; Latagliata, R.; Cavazzini, F.; Bergamaschi, M.; Binotto, G.; Crugnola, M.; Isidori, A.; Caocci, G.; Heidel, F.; Pugliese, N.; Bosi, C.; Bartoletti, D.; Auteri, G.; Cattaneo, D.; Scaffidi, L.; Trawinska, M. M.; Stella, R.; Ciantia, F.; Pane, F.; Cuneo, A.; Krampera, M.; Semenzato, G.; Lemoli, R. M.; Iurlo, A.; Vianelli, N.; Cavo, M.; Breccia, M.; Bonifacio, M

Vulnerability to high risk sexual behaviour (HRSB) following exposure to war trauma as seen in post-conflict communities in eastern uganda: a qualitative study

<p>Abstract</p> <p>Background</p> <p>Much of the literature on the relationship between conflict-related trauma and high risk sexual behaviour (HRSB) often focuses on refugees and not mass in-country displaced people due to armed conflicts. There is paucity of research about contexts underlying HRSB and HIV/AIDS in conflict and post-conflict communities in Uganda. Understanding factors that underpin vulnerability to HRSB in post-conflict communities is vital in designing HIV/AIDS prevention interventions. We explored the socio-cultural factors, social interactions, socio-cultural practices, social norms and social network structures that underlie war trauma and vulnerability to HRSB in a post-conflict population.</p> <p>Methods</p> <p>We did a cross-sectional qualitative study of 3 sub-counties in <it>Katakwi </it>district and 1 in <it>Amuria </it>in Uganda between March and May 2009. We collected data using 8 FGDs, 32 key informant interviews and 16 in-depth interviews. We tape-recorded and transcribed the data. We followed thematic analysis principles to manage, analyse and interpret the data. We constantly identified and compared themes and sub-themes in the dataset as we read the transcripts. We used illuminating verbatim quotations to illustrate major findings.</p> <p>Results</p> <p>The commonly identified HRSB behaviours include; transactional sex, sexual predation, multiple partners, early marriages and forced marriages. Breakdown of the social structure due to conflict had resulted in economic destruction and a perceived soaring of vulnerable people whose propensity to HRSB is high. Dishonour of sexual sanctity through transactional sex and practices like incest mirrored the consequence of exposure to conflict. HRSB was associated with concentration of people in camps where idleness and unemployment were the norm. Reports of girls and women who had been victims of rape and defilement by men with guns were common. Many people were known to have started to display persistent worries, hopelessness, and suicidal ideas and to abuse alcohol.</p> <p>Conclusions</p> <p>The study demonstrated that conflicts disrupt the socio-cultural set up of communities and destroy sources of people's livelihood. Post-conflict socio-economic reconstruction needs to encompass programmes that restructure people's morals and values through counselling. HIV/AIDS prevention programming in post-conflict communities should deal with socio-cultural disruptions that emerged during conflicts. Some of the disruptions if not dealt with, could become normalized yet they are predisposing factors to HRSB. Socio-economic vulnerability as a consequence of conflict seemed to be associated with HRSB through alterations in sexual morality. To pursue safer sexual health choices, people in post-conflict communities need life skills.</p

An approach to enhance efficiency of dem modelling of soils with crushable grains

In this study oedometric compression tests of hydrocarbon coke, Fontainebleau sand and silica sand are simulated in three dimensions using breakable particles. The method adapts a rigorous breakage criterion for elasto-brittle spheres to represent failure of grains isolated between platens or within granular masses. The breakage criterion allows for the effect of particle bulk and contact properties to be treated separately. A discrete fragmentation multigenerational approach is applied as a spawning procedure. The number of particles quickly increases during the simulation, but is kept manageable by systematic fine exclusion and upscaling. Fine exclusion leads to mass losses between generations, but that loss is accounted for outside the mechanical model. Sensitivity analysis shows that it is enough to keep 53% of the crushed particle mass within the mechanical model to correctly reproduce experimental macroscopic behaviour. Practical upscaling rules are proposed for (a) contact stiffness, (b) breakage criteria and (c) grain size distribution, and validated simulating the same test, reducing by half the initial number of particles. The results are promising as both the mechanical and grading evolution are well captured with two orders of magnitude savings in computing efficiency.Peer ReviewedPostprint (published version