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discrete element method

Gili Greenbaum, Nina H Fefferman
In populations occupying discrete habitat patches, gene flow between habitat patches may form an intricate population structure. In such structures, the evolutionary dynamics resulting from interaction of gene flow patterns with other evolutionary forces may be exceedingly complex. Several models describing gene flow between discrete habitat patches have been presented in the population genetics literature; however, these models have usually addressed relatively simple settings of habitable patches, and have stopped short of providing general methodologies for addressing non-trivial gene flow patterns...
February 16, 2017: Molecular Ecology
I A Renteria Marquez, V Bolborici
This manuscript presents a method to model in detail the piezoelectric traveling wave rotary ultrasonic motor (PTRUSM) stator response under the action of DC and AC voltages. The stator is modeled with a discrete two dimensional system of equations using the finite volume method (FVM). In order to obtain accurate results, a model of the stator bridge is included into the stator model. The model of the stator under the action of DC voltage is presented first, and the results of the model are compared versus a similar model using the commercial finite element software COMSOL Multiphysics...
January 31, 2017: Ultrasonics
Seog-Jin Jeon, Adam W Hauser, Ryan C Hayward
The formation of well-defined and functional three-dimensional (3D) structures by buckling of thin sheets subjected to spatially nonuniform stresses is common in biological morphogenesis and has become a subject of great interest in synthetic systems, as such programmable shape-morphing materials hold promise in areas including drug delivery, biomedical devices, soft robotics, and biomimetic systems. Given their ability to undergo large changes in swelling in response to a wide variety of stimuli, hydrogels have naturally emerged as a key type of material in this field...
February 9, 2017: Accounts of Chemical Research
Peter C St John, Michael F Crowley, Yannick J Bomble
BACKGROUND: Production of chemicals from engineered organisms in a batch culture involves an inherent trade-off between productivity, yield, and titer. Existing strategies for strain design typically focus on designing mutations that achieve the highest yield possible while maintaining growth viability. While these methods are computationally tractable, an optimum productivity could be achieved by a dynamic strategy in which the intracellular division of resources is permitted to change with time...
2017: Biotechnology for Biofuels
Jie Zhao, Qiang Cheng, Tian Qi Wang, Wei Yuan, Tie Jun Cui
A method for fast design of broadband terahertz diffusion metasurface is presented. The proposed metasurface is composed by three kinds of simply patterned elements with different resonant properties. To obtain the best broadband performance with the lowest backward reflections, a genetic algorithm is developed to manipulate the resonances for the fast determination of element geometries. An inverse discrete Fourier transform method is used to predict the scattering pattern of the metasurface with high accuracy and low time consumption, significantly enhancing the efficiency of the array-pattern design...
January 23, 2017: Optics Express
Hasitha-Nayanajith Polwaththe-Gallage, Suvash C Saha, Emilie Sauret, Robert Flower, Wijitha Senadeera, YuanTong Gu
BACKGROUND: Blood continuously flows through the blood vessels in the human body. When blood flows through the smallest blood vessels, red blood cells (RBCs) in the blood exhibit various types of motion and deformed shapes. Computational modelling techniques can be used to successfully predict the behaviour of the RBCs in capillaries. In this study, we report the application of a meshfree particle approach to model and predict the motion and deformation of three-dimensional RBCs in capillaries...
December 28, 2016: Biomedical Engineering Online
Mahmoud Karimi, Paul Croaker, Nicole Kessissoglou
An efficient boundary element formulation is proposed to solve three-dimensional exterior acoustic scattering problems with multi-directional periodicity. The multi-directional periodic acoustic problem is represented as a multilevel block Toeplitz matrix. By exploiting the Toeplitz structure, the computational time and storage requirements to construct and to solve the linear system of equations arising from the boundary element formulation are significantly reduced. The generalized minimal residual method is implemented to solve the linear system of equations...
January 2017: Journal of the Acoustical Society of America
Bettina Suhr, Klaus Six
In the discrete element simulation of granular materials, the modelling of contacts is crucial for the prediction of the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb's law of friction is state of the art in modelling particle-particle contacts. Usually in Coulomb's law, for all contacts only one constant coefficient of friction is used, which needs to reflect all tribological effects...
2017: Comput Part Mech
Ryoichi Furukawa, Kazunori Kadota, Tetsuro Noguchi, Atsuko Shimosaka, Yoshiyuki Shirakawa
The closed-die compaction behaviour of D-mannitol granules has been simulated by the discrete element method (DEM) to investigate the granule rearrangement and fracture behaviour during compaction which affects the compactibility of the tablet. The D-mannitol granules produced in a fluidized bed were modelled as agglomerates of primary particles connected by linear spring bonds. The validity of the model granule used in the DEM simulation was demonstrated by comparing to the experimental results of a uniaxial compression test...
January 26, 2017: AAPS PharmSciTech
Yimin Jiang, Mario Liu
Two approaches exist to account for granular dynamics: The athermal one takes grains as elementary, the thermal one considers the total entropy that includes microscopic degrees of freedom such as phonons and electrons. Discrete element method (DEM), granular kinetic theory and athermal statistical mechanics (ASM) belong to the first, granular solid hydrodynamics (GSH) to the second one. A discussion of the conceptual differences between both is given here, leading, among others, to the following insights: 1) While DEM and granular kinetic theory are well justified to take grains as athermal, any entropic consideration is far less likely to succeed...
January 2017: European Physical Journal. E, Soft Matter
Shengjie Yan, Xiaomei Wu, Weiqi Wang
PURPOSE: Radiofrequency (RF) energy is often used to create a linear lesion or discrete lesions for blocking the accessory conduction pathways for treating atrial fibrillation. By using finite element analysis, we study the ablation effect of amplitude control ablation mode (AcM) and bipolar ablation mode (BiM) in creating a linear lesion and discrete lesions in a 5-mm-thick atrial wall; particularly, the characteristic of lesion shape has been investigated in amplitude control ablation...
January 23, 2017: International Journal of Hyperthermia
Ronald W Falta, Wenwen Wang
A semi-analytical approximation for transient matrix diffusion is developed for use in numerical contaminant transport simulators. This method is an adaptation and extension of the heat conduction method of Vinsome and Westerveld (1980) used to simulate heat losses during thermally enhanced oil recovery. The semi-analytical method is used in place of discretization of the low permeability materials, and it represents the concentration profile in the low permeability materials with a fitting function that is adjusted in each element at each time-step...
January 11, 2017: Journal of Contaminant Hydrology
Gwanwoo Park, Sunggu Kang, Howon Lee, Wonjoon Choi
Thermal metamaterials, designed by transformation thermodynamics are artificial structures that can actively control heat flux at a continuum scale. However, fabrication of them is very challenging because it requires a continuous change of thermal properties in materials, for one specific function. Herein, we introduce tunable thermal metamaterials that use the assembly of unit-cell thermal shifters for a remarkable enhancement in multifunctionality as well as manufacturability. Similar to the digitization of a two-dimensional image, designed thermal metamaterials by transformation thermodynamics are disassembled as unit-cells thermal shifters in tiny areas, representing discretized heat flux lines in local spots...
January 20, 2017: Scientific Reports
Kristina Pickl, Jayant Pande, Harald Köstler, Ulrich Rüde, Ana-Sunčana Smith
Propulsion at low Reynolds numbers is often studied by defining artificial microswimmers which exhibit a particular stroke. The disadvantage of such an approach is that the stroke does not adjust to the environment, in particular the fluid flow, which can diminish the effect of hydrodynamic interactions. To overcome this limitation, we simulate a microswimmer consisting of three beads connected by springs and dampers, using the self-developed waLBerla and [Formula: see text] framework based on the lattice Boltzmann method and the discrete element method...
March 29, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Patricia Larkin, Cecily M Begley, Declan Devane
BACKGROUND: How women experience childbirth is acknowledged as critical to the postnatal wellbeing of mother and baby. However there is a knowledge deficit in identifying the important elements of these experiences in order to enhance care. This study elicits women's preferences for the most important elements of their childbirth experiences. METHODS: A mixed methods design was used. An initial qualitative phase (reported previously) was followed by a second quantitative one using a discrete choice experiment (DCE), which is reported on here...
January 10, 2017: BMC Pregnancy and Childbirth
M Aima, W Culberson, C Hammer, J Micka, L DeWerd
PURPOSE: The aim of this work is to determine the TG-43 dose-rate constant analog for a new directional low-dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called "CivaDots". Given the directional nature and non-conventional design of the source, modifications to the AAPM TG-43 protocol for dosimetry are required...
June 2016: Medical Physics
O Zelyak, B Fallone, J St Aubin
PURPOSE: To determine the iterative deterministic solution stability of the Linear Boltzmann Transport Equation (LBTE) in the presence of magnetic fields. METHODS: The LBTE with magnetic fields under investigation is derived using a discrete ordinates approach. The stability analysis is performed using analytical and numerical methods. Analytically, the spectral Fourier analysis is used to obtain the convergence rate of the source iteration procedures based on finding the largest eigenvalue of the iterative operator...
June 2016: Medical Physics
X Hong, G Chen, H Gao
PURPOSE: As a deterministic method for dose calculation, the linear Boltzmann transport equation (LBTE) can reach the same accuracy as the Monte Carlo method (MC). In terms of speed, LBTE can be significantly accelerated through various state-of-art numerical techniques. The angular discretization is crucial since the accuracy of LBTE highly depends on it and the computational time of LBTE is quadratic with respect to number of discretized angles. This work proposes a new angular discretization scheme that synergizes spherical harmonics method and finite element method...
June 2016: Medical Physics
M Mille, C Lee, G Failla
PURPOSE: To use the Attila deterministic solver as a supplement to Monte Carlo for calculating out-of-field organ dose in support of epidemiological studies looking at the risks of second cancers. Supplemental dosimetry tools are needed to speed up dose calculations for studies involving large-scale patient cohorts. METHODS: Attila is a multi-group discrete ordinates code which can solve the 3D photon-electron coupled linear Boltzmann radiation transport equation on a finite-element mesh...
June 2016: Medical Physics
R Yang, B Fallone, J St Aubin
PURPOSE: To develop a Graphic Processor Unit (GPU) accelerated deterministic solution to the Linear Boltzmann Transport Equation (LBTE) for accurate dose calculations in radiotherapy (RT). A deterministic solution yields the potential for major speed improvements due to the sparse matrix-vector and vector-vector multiplications and would thus be of benefit to RT. METHODS: In order to leverage the massively parallel architecture of GPUs, the first order LBTE was reformulated as a second order self-adjoint equation using the Least Squares Finite Element Method (LSFEM)...
June 2016: Medical Physics
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