DEM modeling of rockfall rebound on protective embankments

Design of Rockfall Protection Embankments and estimation of their capacity to control the trajectory of rock boulders are complex issues, which give considerable room for research and improvement. A lack of detailed models for the simulation of block rebound in the embankment vicinity is mainly due to the large number of parameters that influences the phenomenon. Therefore, the evaluation of the embankment efficiency in satisfactorily acting on the block trajectory, as a function of the site characteristics and boulder kinematics, is still precluded to design engineers. In the present paper, the open-source code YADE, based on a discrete element method (DEM), is used to model the bouncing of a rock block on the embankment face, while taking into account a certain number of parameters with influence on the impact. By contrast with previously developed models (DEM, FEM or coupled approaches), the aim is here to propose a model with limited computation cost. In this purpose, the embankment is modelled as a membrane interacting with the rock block. The embankment body is not represented because it would require a large number of particles, and, consequently, a high computational time. Various elements implemented in YADE are used to model the embankment surface, with the aim of mimicking the mechanisms involved during the rock boulder rebound. The validity of the approach is addressed comparing simulation results with the few experimental data available from the literature. The influence of characteristics of the impacting block (radius and weight) and kinematic parameters (impact angle and velocity) on the restitution coefficients is explored. In particular, the normal (Rn), tangential (Rt) and energetic (RTE) coefficients of restitution are monitored. The goal of defining an efficient model in a realistic range of these parameters is pursued

DEM MODELING OF ROCKFALL REBOUND ON PROTECTIVE EMBANKMENTS

Design of Rockfall Protection Embankments and estimation of their capacity to control the trajectory of rock boulders are complex issues, which give considerable room for research and improvement. A lack of detailed models for the simulation of block rebound in the embankment vicinity is mainly due to the large number of parameters that influences the phenomenon. Therefore, the evaluation of the embankment efficiency in satisfactorily acting on the block trajectory, as a function of the site characteristics and boulder kinematics, is still precluded to design engineers.In the present paper, the open-source code YADE, based on a discrete element method (DEM), is used to model the bouncing of a rock block on the embankment face, while taking into account a certain number of parameters with influence on the impact.By contrast with previously developed models (DEM, FEM or coupled approaches), the aim is here to propose a model with limited computation cost. In this purpose, the embankment is modelled as a membrane interacting with the rock block. The embankment body is not represented because it would require a large number of particles, and, consequently, a high computational time. Various elements implemented in YADE are used to model the embankment surface, with the aim of mimicking the mechanisms involved during the rock boulder rebound. The validity of the approach is addressed comparing simulation results with the few experimental data available from the literature. The influence of characteristics of the impacting block (radius and weight) and kinematic parameters (impact angle and velocity) on the restitution coefficients is explored. In particular, the normal (R-n), tangential (R-t) and energetic (R-TE) coefficients of restitution are monitored. The goal of defining an efficient model in a realistic range of these parameters is pursued

The Mass, Normalization and Late Time behavior of the Tachyon Field

We study the dynamics of the tachyon field $T$. We derive the mass of the tachyon as the pole of the propagator which does not coincide with the standard mass given in the literature in terms of the second derivative of $V(T)$ or $Log[V(T)]$. We determine the transformation of the tachyon in order to have a canonical scalar field $\phi$. This transformation reduces to the one obtained for small $\dot T$ but it is also valid for large values of $\dot T$. This is specially interesting for the study of dark energy where $\dot T\simeq 1$. We also show that the normalized tachyon field $\phi$ is constrained to the interval $T_2\leq T \leq T_1$ where $T_1,T_2$ are zeros of the original potential $V(T)$. This results shows that the field $\phi$ does not know of the unboundedness of $V(T)$, as suggested for bosonic open string tachyons. Finally we study the late time behavior of tachyon field using the L'H\^{o}pital rule.Comment: 9 pages, 10 figure

Assessing the operational feasibility and acceptability of an inhalable formulation of oxytocin for improving community-based prevention of postpartum haemorrhage in Myanmar: a qualitative inquiry

Objective: This study assessed the potential operational feasibility and acceptability of a heat-stable, inhaled oxytocin (IOT) product for community-based prevention of postpartum haemorrhage in Myanmar. Methods: A qualitative inquiry was conducted between June 2015 and February 2016 through focus group discussions and in-depth interviews. Research was conducted in South Dagon township (urban setting) and in Ngape and Thanlyin townships (rural settings) in Myanmar. Eleven focus group discussions and 16 in-depth interviews were conducted with mothers, healthcare providers and other key informants. All audio recordings were transcribed verbatim in Myanmar language and were translated into English. Thematic content analysis was done using NVivo software. Results: Future introduction of an IOT product for community-based services was found to be acceptable among mothers and healthcare providers and would be feasible for use by lower cadres of healthcare providers, even in remote settings. Responses from healthcare providers and community members highlighted that midwives and volunteer auxiliary midwives would be key advocates for promoting community acceptance of the product. Healthcare providers perceived the ease of use and lack of dependence on cold storage as the main enablers for IOT compared with the current gold standard oxytocin injection. A single-use disposable device with clear pictorial instructions and a price that would be affordable by the poorest communities was suggested. Appropriate training was also said to be essential for the future induction of the product into community settings. Conclusion: In Myanmar, where home births are common, access to cold storage and skilled personnel who are able to deliver injectable oxytocin is limited. Among community members and healthcare providers, IOT was perceived to be an acceptable and feasible intervention for use by lower cadres of healthcare workers, and thus may be an alternative solution for the prevention of postpartum haemorrhage in community-based settings in the future

Oligomerization of amyloid Abeta peptides using hydrogen bonds and hydrophobicity forces

The 16-22 amino acid fragment of the beta-amyloid peptide associated with the Alzheimer's disease, Abeta, is capable of forming amyloid fibrils. Here we study the aggregation mechanism of Abeta(16-22) peptides by unbiased thermodynamic simulations at the atomic level for systems of one, three and six Abeta(16-22) peptides. We find that the isolated Abeta(16-22) peptide is mainly a random coil in the sense that both the alpha-helix and beta-strand contents are low, whereas the three- and six-chain systems form aggregated structures with a high beta-sheet content. Furthermore, in agreement with experiments on Abeta(16-22) fibrils, we find that large parallel beta-sheets are unlikely to form. For the six-chain system, the aggregated structures can have many different shapes, but certain particularly stable shapes can be identified.Comment: 19 pages, 7 figures (to appear in Biophys. J.

Patterns of primary care and mortality among patients with schizophrenia or diabetes: a cluster analysis approach to the retrospective study of healthcare utilization

Abstract Background Patients with schizophrenia have difficulty managing their medical healthcare needs, possibly resulting in delayed treatment and poor outcomes. We analyzed whether patients reduced primary care use over time, differentially by diagnosis with schizophrenia, diabetes, or both schizophrenia and diabetes. We also assessed whether such patterns of primary care use were a significant predictor of mortality over a 4-year period. Methods The Veterans Healthcare Administration (VA) is the largest integrated healthcare system in the United States. Administrative extracts of the VA's all-electronic medical records were studied. Patients over age 50 and diagnosed with schizophrenia in 2002 were age-matched 1:4 to diabetes patients. All patients were followed through 2005. Cluster analysis explored trajectories of primary care use. Proportional hazards regression modelled the impact of these primary care utilization trajectories on survival, controlling for demographic and clinical covariates. Results Patients comprised three diagnostic groups: diabetes only (n = 188,332), schizophrenia only (n = 40,109), and schizophrenia with diabetes (Scz-DM, n = 13,025). Cluster analysis revealed four distinct trajectories of primary care use: consistent over time, increasing over time, high and decreasing, low and decreasing. Patients with schizophrenia only were likely to have low-decreasing use (73% schizophrenia-only vs 54% Scz-DM vs 52% diabetes). Increasing use was least common among schizophrenia patients (4% vs 8% Scz-DM vs 7% diabetes) and was associated with improved survival. Low-decreasing primary care, compared to consistent use, was associated with shorter survival controlling for demographics and case-mix. The observational study was limited by reliance on administrative data. Conclusion Regular primary care and high levels of primary care were associated with better survival for patients with chronic illness, whether psychiatric or medical. For schizophrenia patients, with or without comorbid diabetes, primary care offers a survival benefit, suggesting that innovations in treatment retention targeting at-risk groups can offer significant promise of improving outcomes.http://deepblue.lib.umich.edu/bitstream/2027.42/78274/1/1472-6963-9-127.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78274/2/1472-6963-9-127.pdfPeer Reviewe