Numerical simulations of sand behaviour using DEM with two different descriptions of grain roughness

A quasi-static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three-dimensional DEM model. Grain roughness was modelled by two different approaches: first with contact moments applied to rigid spheres and second with clusters of rigid spheres imitating irregular particle shapes. The effect of the grain roughness (shape) on shear strength, dilatancy, energy and dissipation was analyzed using both models. Numerical results were directly compared with experimental results on Karlsruhe sand

Investigations of quasi-static vortex-structures in 3D sand specimens based on DEM and Helmholtz-Hodge vector field decomposition

The paper presents some three-dimensional simulation results of granular vortex-structures in cohesionless initially dense sand during quasi-static plane strain compression. The sand behaviour was simulated using the discrete element method (DEM). Sand grains were modelled by spheres with contact moments to approximately capture the irregular grain shape. The Helmholtz-Hodge decomposition (HHD) of the displacement vector field from DEM calculations was used. The variational discrete multiscale vector field decomposition allowed for separating a vector field into the sum of three uniquely defined components: curl free, divergence free and harmonic. Vortex-structures were strongly connected to shear localization. They slightly changed along the specimen depth. They localized in locations where shear zones ultimately developed

Electronic structure and rovibrational predissociation of the 2sPi state in KLi

Adiabatic potential energy curves of the 3sSigma+, 3tSigma+, 2sPi and 2tPi states correlating for large internuclear distance with the K(4s) + Li(2p) atomic asymptote were calculated. Very good agreement between the calculated and the experimental curve of the 2sPi state allowed for a reliable description of the dissociation process through a small (20 cm-1 for J = 0) potential energy barrier. The barrier supports several rovibrational quasi-bound states and explicit time evolution of these states via the time-dependent nuclear Schroedinger equation, showed that the state populations decay exponentially in time. We were able to precisely describe the time-dependent dissociation process of several rovibrational levels and found that our calculated spectrum match very well with the assigned experimental spectrum. Moreover, our approach is able to predict the positions of previously unassigned lines despite their low intensit

Investigations of micro-structure evolution in granular shear zones using DEM

The evolution of shear zones in initially medium dense cohesionless sand for quasistatic earth pressure problems of a retaining wall was analysed with a 3D discrete element method DEM using spheres with contact moments. The passive sand failure for a very rough retaining wall undergoing horizontal translation was discussed. Attention was laid on some micro-structural events appearing in shear zones (force chains, vortex structures, local density fluctuations). The calculated geometry of shear zones was compared with experimental results of laboratory model tests and finite element calculations

From Flow to Jamming: Lattice Gas Automaton Simulations in Granular Materials

We introduce the first extension of a Lattice Gas Automaton (LGA) model to accurately replicate observed emergent phenomena in granular materials with a special focus on previously unexplored jamming transitions by incorporating gravitational effects, energy dissipation in particle collisions, and wall friction. We successfully reproduce flow rate evolution, density wave formation, and jamming transition observed in experiments. We also explore the critical density at which jamming becomes probable. This research advances our understanding of granular dynamics and offers insights into the jamming behavior of granular materials

Reversible migration of silver on memorized pathways in Ag-Ge<inf>40</inf>S<inf>60</inf> films

Reversible and reproducible formation and dissolution of silver conductive filaments are studied in Ag-photodoped thin-film Ge40S60 subjected to electric fields. A tip-planar geometry is employed, where a conductive-atomic-force microscopy tip is the tip electrode and a silver patch is the planar electrode. We highlight an inherent “memory” effect in the amorphous chalcogenide solid-state electrolyte, in which particular silver-ion migration pathways are preserved “memorized” during writing and erasing cycles. The “memorized” pathways reflect structural changes in the photodoped chalcogenide film. Structural changes due to silver photodoping, and electrically-induced structural changes arising from silver migration, are elucidated using Raman spectroscopy. Conductive filament formation, dissolution, and electron (reduction) efficiency in a lateral device geometry are related to operation of the nano-ionic Programmable Metallization Cell memory and to newly emerging chalcogenide-based lateral geometry MEMS technologies. The methods in this work can also be used for qualitative multi-parameter sampling of metal/amorphous-chalcogenide combinations, characterizing the growth/dissolution rates, retention and endurance of fractal conductive filaments, with the aim of optimizing devices.This work was supported by World Premier International Research Center Initiative (WPI), MEXT, Japan. J.O. and A.L.G. acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC, UK).This is the final version of the article. It first appeared from AIP via http://dx.doi.org/10.1063/1.492700

Bulk and Surface Nucleation Processes in Ag2S Conductance Switches

We studied metallic Ag formation inside and on the surface of Ag2S thin films, induced by the electric field created with a STM tip. Two clear regimes were observed: cluster formation on the surface at low bias voltages, and full conductance switching at higher bias voltages (V > 70mV). The bias voltage at which this transition is observed is in agreement with the known threshold voltage for conductance switching at room temperature. We propose a model for the cluster formation at low bias voltage. Scaling of the measured data with the proposed model indicates that the process takes place near steady state, but depends on the STM tip geometry. The growth of the clusters is confirmed by tip retraction measurements and topography scans. This study provides improved understanding of the physical mechanisms that drive conductance switching in solid electrolyte memristive devices.Comment: In press for PR

Implementation of Remedial Measures to Contain a PCB Spill

A large spill of Polychlorinated Biphenols (PCB\u27s) occurred at Federal Pioneer Limited\u27s Regina Plant in 1976. The City of Regina is underlain by a relatively shallow aquifer which supplies a significant proportion of its drinking water. A remedial measures plan was developed to contain this spill within the boundaries of the site and clean up any contamination which had spread to adjacent property. The remedial measures plan developed involved limiting or reversing the normal downward hydraulic gradient. The three principle measures introduced to accomplish this reversal included the construction of a cutoff wall around the site, installation of a thick surface seal over the entire surface and active dewatering. The performance of these measures was monitored by an extensive network of piezometers and sampling well. Monitoring over the past seven years has produced no evidence of further downward migration of PCB\u27s

INSEMINAÇÃO ARTIFICIAL INTRAUTERINA E CERVICAL EM OVELHAS UTILIZANDO SÊMEN REFRIGERADO

O presente trabalho objetivou verificar a prenhez de ovelhas inseminadas por via intrauterina ou cervical com sêmen refrigerado a 5ºC durante 8 horas nos diluentes citrato-gema e Cornell University Extender (CUE). Foram utilizados 4 carneiros da raça Suffolk. Em cada inseminação era colhido sêmen de 2 animais e após a avaliação seminal as amostras eram homogeneizadas, divididas em 2 alíquotas e diluídas na proporção de uma parte de sêmen para três de diluente em citrato-gema e CUE. A diluição ocorria a 30ºC e o abaixamento progressivo da temperatura se dava em 2 horas em caixa de isopor contendo gelo. As amostras permaneceram nesta temperatura durante 8 horas. Foram inseminadas 91 ovelhas mestiças da raça Suffolk, as quais tiveram o estro sincronizado com pessários vaginais impregnados com 50 mg de acetato de medroxiprogesterona, permanecendo por 14 dias, quando se administrou 500 UI de Gonadotrofina Coriônica (eCG) via intramuscular. Todas as ovelhas foram inseminadas independente do aparecimento do estro. A aplicação do sêmen foi realizada pela via cervical e intra-uterina por laparoscopia. A dose mínima inseminante foi de 250 milhões de espermatozóides, em volume de 0,4 ml, por ovelha. A utilização do diluente CUE resultou em 69,56% (n=23) e 8,33% (n=24) de prenhez para as vias intra-uterina e cervical, respectivamente contra 85,71% (n=21) e 21,74% (n=23) para o diluente citrato-gema. O sêmen diluído em citrato-gema forneceu índices de prenhez superiores, porém não significativos (P>0,05), nas duas vias estudadas em relação ao CUE. A fertilidade foi superior quando se utilizou a via intra-uterina (P0.05) has been found between values of pregnancy attained with suspensions of spermatozoa either in CUE or in citrate-york extender, in spite of the fact that the latter one gave higher pregnancy rates. Intrauterine insemination gave higher values of fertility (