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Artykuły w czasopismach na temat "Complex Inter-particle Interactions"
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Kahan, Alan, Thomás Fogarty, Jing Li i Thomas Busch. "Driving Interactions Efficiently in a Composite Few-Body System". Universe 5, nr 10 (7.10.2019): 207. http://dx.doi.org/10.3390/universe5100207.
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We study how to efficiently control an interacting few-body system consisting of three harmonically trapped bosons. Specifically, we investigate the process of modulating the inter-particle interactions to drive an initially non-interacting state to a strongly interacting one, which is an eigenstate of a chosen Hamiltonian. We also show that for unbalanced subsystems, where one can individually control the different inter- and intra-species interactions, complex dynamics originate when the symmetry of the ground state is broken by phase separation. However, as driving the dynamics too quickly can result in unwanted excitations of the final state, we optimize the driven processes using shortcuts to adiabaticity, which are designed to reduce these excitations at the end of the interaction ramp, ensuring that the target eigenstate is reached.
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Barcelos, Erika I., Shaghayegh Khani, Mônica F. Naccache i Joao Maia. "Supervised learning for accurate mesoscale simulations of suspension flow in wall-bounded geometries". Physics of Fluids 34, nr 5 (maj 2022): 053110. http://dx.doi.org/10.1063/5.0086759.
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Herein, we have employed a supervised learning approach combined with Core-Modified Dissipative Particle Dynamics Simulations (CM-DPD) in order to develop and design a reliable physics-based computational model that will be used in studying confined flow of suspensions. CM-DPD was recently developed and has shown promising performance in capturing rheological behavior of colloidal suspensions; however, the model becomes problematic when the flow of the material is confined between two walls. Wall-penetration by the particles is an unphysical phenomenon that occurs in coarse-grained simulations such as Dissipative Particle Dynamics (DPD) that mostly rely on soft inter-particle interactions. Different solutions to this problem have been proposed in the literature; however, no reports have been given on how to deal with walls using CM-DPD. Due to complexity of interactions and system parameters, designing a realistic simulation model is not a trivial task. Therefore, in this work we have trained a Random Forest (RF) for predicting wall penetration as we vary input parameters such as interaction potentials, flow rate, volume fraction of colloidal particles, and confinement ratio. The RF predictions were compared against simulation tests, and a sufficiently high accuracy and low errors were obtained. This study shows the viability and potentiality of ML combined with DPD to perform parametric studies in complex fluids.
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Hubbe, Martin A., Pegah Tayeb, Michael Joyce, Preeti Tyagi, Margaret Kehoe, Katarina Dimic-Misic i Lokendra Pal. "Rheology of nanocellulose-rich aqueous suspensions: A Review". BioResources 12, nr 4 (2017): 9556–661. http://dx.doi.org/10.15376/biores.12.4.hubbe.
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The flow characteristics of dilute aqueous suspensions of cellulose nanocrystals (CNC), nanofibrillated cellulose (NFC), and related products in dilute aqueous suspensions could be of great importance for many emerging applications. This review article considers publications dealing with the rheology of nanocellulose aqueous suspensions in the absence of matrix materials. In other words, the focus is on systems in which the cellulosic particles themselves – dependent on their morphology and the interactive forces between them – largely govern the observed rheological effects. Substantial progress in understanding rheological phenomena is evident in the large volume of recent publications dealing with such issues including the effects of flow history, stratification of solid and fluid layers during testing, entanglement of nanocellulose particles, and the variation of inter-particle forces by changing the pH or salt concentrations, among other factors. Better quantification of particle shape and particle-to-particle interactions may provide advances in future understanding. Despite the very complex morphology of highly fibrillated cellulosic nanomaterials, progress is being made in understanding their rheology, which supports their usage in applications such as coating, thickening, and 3D printing.
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Zhang, Tao, Michelle C. Miller, Yi Zheng, Zhongyu Zhang, Huiting Xue, Dongyang Zhao, Jiyong Su, Kevin H. Mayo, Yifa Zhou i Guihua Tai. "Macromolecular assemblies of complex polysaccharides with galectin-3 and their synergistic effects on function". Biochemical Journal 474, nr 22 (9.11.2017): 3849–68. http://dx.doi.org/10.1042/bcj20170143.
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Although pectin-derived polysaccharides can antagonize galectin function in various pathological disorders, the nature of their binding interactions needs to be better defined for developing them as drugs. Moreover, given their relatively large size and complexity, pectin-derived polysaccharides are also useful as model systems to assess inter-polysaccharide and protein–polysaccharide interactions. Here, we investigated interactions between galectin-3 (Gal-3) and pectin-derived polysaccharides: a rhamnogalacturonan (RG) and two homogalacturonans (HGs). BioLayer Interferometry and fluorescence-linked immunosorbent assays indicate that these polysaccharides bind Gal-3 with macroscopic or apparent KD values of 49 nM, 46 µM, and 138 µM, respectively. 15N-1H heteronuclear single quantum coherence (HSQC) NMR studies reveal that these polysaccharides interact primarily with the F-face of the Gal-3 carbohydrate recognition domain. Even though their binding to Gal-3 does not inhibit Gal-3-mediated T-cell apoptosis and only weakly attenuates hemagglutination, their combination in specific proportions increases activity synergistically along with avidity for Gal-3. This suggests that RG and HG polysaccharides act in concert, a proposal supported by polysaccharide particle size measurements and 13C-1H HSQC data. Our model has HG interacting with RG to promote increased avidity of RG for Gal-3, likely by exposing additional lectin-binding sites on the RG. Overall, the present study contributes to our understanding of how complex HG and RG polysaccharides interact with Gal-3.
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Maity, Tuhin Subhra, Howard M. Fried i Kevin M. Weeks. "Anti-cooperative assembly of the SRP19 and SRP68/72 components of the signal recognition particle". Biochemical Journal 415, nr 3 (15.10.2008): 429–37. http://dx.doi.org/10.1042/bj20080569.
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The mammalian SRP (signal recognition particle) represents an important model for the assembly and role of inter-domain interactions in complex RNPs (ribonucleoproteins). In the present study we analysed the interdependent interactions between the SRP19, SRP68 and SRP72 proteins and the SRP RNA. SRP72 binds the SRP RNA largely via non-specific electrostatic interactions and enhances the affinity of SRP68 for the RNA. SRP19 and SRP68 both bind directly and specifically to the same two RNA helices, but on opposite faces and at opposite ends. SRP19 binds at the apices of helices 6 and 8, whereas the SRP68/72 heterodimer binds at the three-way junction involving RNA helices 5, 6 and 8. Even though both SRP19 and SRP68/72 stabilize a similar parallel orientation for RNA helices 6 and 8, these two proteins bind to the RNA with moderate anti-cooperativity. Long-range anti-cooperative binding by SRP19 and SRP68/72 appears to arise from stabilization of distinct conformations in the stiff intervening RNA scaffold. Assembly of large RNPs is generally thought to involve either co-operative or energetically neutral interactions among components. By contrast, our findings emphasize that antagonistic interactions can play significant roles in assembly of multi-subunit RNPs.
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Goehring, Lucas, Joaquim Li i Pree-Cha Kiatkirakajorn. "Drying paint: from micro-scale dynamics to mechanical instabilities". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2093 (3.04.2017): 20160161. http://dx.doi.org/10.1098/rsta.2016.0161.
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Charged colloidal dispersions make up the basis of a broad range of industrial and commercial products, from paints to coatings and additives in cosmetics. During drying, an initially liquid dispersion of such particles is slowly concentrated into a solid, displaying a range of mechanical instabilities in response to highly variable internal pressures. Here we summarize the current appreciation of this process by pairing an advection-diffusion model of particle motion with a Poisson–Boltzmann cell model of inter-particle interactions, to predict the concentration gradients in a drying colloidal film. We then test these predictions with osmotic compression experiments on colloidal silica, and small-angle X-ray scattering experiments on silica dispersions drying in Hele–Shaw cells. Finally, we use the details of the microscopic physics at play in these dispersions to explore how two macroscopic mechanical instabilities—shear-banding and fracture—can be controlled. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’
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Daumas, F., N. Destainville, C. Millot, A. Lopez, D. Dean i L. Salomé. "Interprotein interactions are responsible for the confined diffusion of a G-protein-coupled receptor at the cell surface". Biochemical Society Transactions 31, nr 5 (1.10.2003): 1001–5. http://dx.doi.org/10.1042/bst0311001.
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The monitoring of the movements of membrane proteins (or lipids) by single-particle tracking enables one to obtain reliable insights into the complex dynamic organization of the plasma membrane constituents. Using this technique, we investigated the diffusional behaviour of a G-protein-coupled receptor. The trajectories of the receptors revealed a diffusion mode combining a short-term rapid confined diffusion with a long-term slow diffusion. A detailed statistical analysis shows that the receptors have a diffusion confined to a domain which itself diffuses, the confinement being due to long-range attractive inter-protein interactions. The existing models of the dynamic organization of the cell membrane cannot explain our results. We propose a theoretical Brownian model of interacting proteins that is consistent with the experimental observations and accounts for the variations found as a function of the domain size of the short-term and long-term diffusion coefficients.
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KOURAKIS, IOANNIS, i PADMA KANT SHUKLA. "NONLINEAR EXCITATIONS IN STRONGLY-COUPLED PLASMA LATTICES: ENVELOPE SOLITONS, KINKS AND INTRINSIC LOCALIZED MODES". International Journal of Bifurcation and Chaos 16, nr 06 (czerwiec 2006): 1711–25. http://dx.doi.org/10.1142/s0218127406015623.
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Ensembles of charged particles (plasmas) are a highly complex form of matter, most often modeled as a many-body system characterized by weak inter-particle interactions (electrostatic coupling). However, strongly-coupled plasma configurations have recently been produced in laboratory, either by creating ultra-cold plasmas confined in a trap or by manipulating dusty plasmas in discharge experiments. In this paper, the nonlinear aspects involved in the motion of charged dust grains in a one-dimensional plasma monolayer (crystal) are discussed. Different types of collective excitations are reviewed, and characteristics and conditions for their occurrence in dusty plasma crystals are discussed, in a quasi-continuum approximation. Dust crystals are shown to support nonlinear kink-shaped supersonic solitary longitudinal excitations, as well as modulated envelope localized modes associated with longitudinal and transverse vibrations. Furthermore, the possibility for intrinsic localized modes (ILMs) — Discrete Breathers (DBs) — to occur is investigated, from first principles. The effect of mode-coupling is also briefly considered. The relation to previous results on atomic chains, and also to experimental results on strongly-coupled dust layers in gas discharge plasmas, is briefly discussed.
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Sanchez-Mondragon, Joel, i Alberto Omar Vazquez-Hernandez. "Solitary wave collisions by double-dam-broken simulations with the MPS method". Engineering Computations 35, nr 1 (5.03.2018): 53–70. http://dx.doi.org/10.1108/ec-04-2016-0142.
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Purpose The paper aims to apply a modified version of the MPS method to a double-dam-breaking test in which high dispersion zones and high natural clusterization zones are present, such as when the water column collapses into two sides and the two solitary waves collide, respectively. Design/methodology/approach The work takes advantage of the mixed source term from the cheaper computational version of the moving particle semi-implicit (MPS) method to reduce one step from the MPS classical algorithm. The proposed test can be successfully simulated by applying modifications to the variance parameter in the Laplacian operator and gradient model. Findings The results show stable behavior in dispersion and clusterization zones. Also, the collision and merging produced by solitary waves was successfully simulated. Research limitations/implications The main limitation in this work was the development of a comparison between the obtained results and the simulations with the original cheaper computational version of the MPS, this limitation is due to the overestimation of inter particle repulsive forces from its gradient model. Practical implications The application of solitary waves is of paramount importance in a number of applications, and this stems from the fact that the interaction of solitary waves with ships and other floating structures could generate highly deformed and complex free surface flows. Social implications For future work, the modified version of the MPS method can be applied in flow over sill base simulations, in close and open channels, and in simulating breaking waves to determine impact pressures by using solitary wave propagation. Originality/value The simulation of interaction of large groups of particles as in the case when two solitary waves collide could cause severe instability problems in pressure, causing the computer analysis to stop. MPS classical algorithm takes into account an explicit step that, in this case, may provoke the problem. For this reason, the cheaper version of MPS method is used to correctly simulate solitary wave interactions.
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Leinonen, Ville, Harri Kokkola, Taina Yli-Juuti, Tero Mielonen, Thomas Kühn, Tuomo Nieminen, Simo Heikkinen i in. "Comparison of particle number size distribution trends in ground measurements and climate models". Atmospheric Chemistry and Physics 22, nr 19 (6.10.2022): 12873–905. http://dx.doi.org/10.5194/acp-22-12873-2022.
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Abstract. Despite a large number of studies, out of all drivers of radiative forcing, the effect of aerosols has the largest uncertainty in global climate model radiative forcing estimates. There have been studies of aerosol optical properties in climate models, but the effects of particle number size distribution need a more thorough inspection. We investigated the trends and seasonality of particle number concentrations in nucleation, Aitken, and accumulation modes at 21 measurement sites in Europe and the Arctic. For 13 of those sites, with longer measurement time series, we compared the field observations with the results from five climate models, namely EC-Earth3, ECHAM-M7, ECHAM-SALSA, NorESM1.2, and UKESM1. This is the first extensive comparison of detailed aerosol size distribution trends between in situ observations from Europe and five earth system models (ESMs). We found that the trends of particle number concentrations were mostly consistent and decreasing in both measurements and models. However, for many sites, climate models showed weaker decreasing trends than the measurements. Seasonal variability in measured number concentrations, quantified by the ratio between maximum and minimum monthly number concentration, was typically stronger at northern measurement sites compared to other locations. Models had large differences in their seasonal representation, and they can be roughly divided into two categories: for EC-Earth and NorESM, the seasonal cycle was relatively similar for all sites, and for other models the pattern of seasonality varied between northern and southern sites. In addition, the variability in concentrations across sites varied between models, some having relatively similar concentrations for all sites, whereas others showed clear differences in concentrations between remote and urban sites. To conclude, although all of the model simulations had identical input data to describe anthropogenic mass emissions, trends in differently sized particles vary among the models due to assumptions in emission sizes and differences in how models treat size-dependent aerosol processes. The inter-model variability was largest in the accumulation mode, i.e. sizes which have implications for aerosol–cloud interactions. Our analysis also indicates that between models there is a large variation in efficiency of long-range transportation of aerosols to remote locations. The differences in model results are most likely due to the more complex effect of different processes instead of one specific feature (e.g. the representation of aerosol or emission size distributions). Hence, a more detailed characterization of microphysical processes and deposition processes affecting the long-range transport is needed to understand the model variability.
Streszczenia konferencji na temat "Complex Inter-particle Interactions"
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Narayanan, Chidambaram, i Djamel Lakehal. "Four-Way Coupling of Dense Particle Beds of Black Powder in Turbulent Pipe Flows". W ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30137.
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The modeling of particle deposition and transport in pipes is one of the most challenging problems in multiphase flow, because the underlying physics is multi-faceted and complex, including turbulence of the carrier phase, particle-turbulence interaction, particle-wall interactions, particle-particle interactions, two-way and four-way couplings, particle agglomeration, deposition and re-suspension. We will discuss these issues and present new routes for the modeling of particle collision stress. Practical examples like black powder deposition and transport in gas pipelines will be presented and discussed. The model employed is based on dense-particle formulation accounting for particle-turbulence interaction, particle-wall interactions, particle-particle interactions via a collision stress. The model solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Inter-particle interactions for dense particle flows with high volume fractions (from 1% to close packing ∼60%) have been accounted for by mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions. Turbulence within the continuum gas field was simulated using the V-LES (Very Large-Eddy Simulation) and full LES, which provides sufficient flow unsteadiness needed to disperse the particles and move the deposited bed.
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Mahadevan, T. S., M. Milosevic, M. Kojic, F. Hussain, N. Kojic, M. Ferrari i A. Ziemys. "Nanoparticle Transport Through Boundaries of Nanoporous Structures". W ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85775.
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In transport phenomena involving colloidal nanoparticle (NP) suspensions in complex environments, the inter particle interactions play an important role especially when the sizes of the confining environments approaches the particle sizes. Specific examples of such systems are encountered in NP transport through nanochannels used in drug delivery and nanofluidic cooling[1–5]. In ionic colloidal suspensions like the ones encountered in the above applications, the NPs acquire characteristic surface charges which results in a surface potential and a double layer of co- and counter-ions from the solution. DLVO theory predicts the interaction energy resulting from the double layer to be [6]:(1)Wr=64πkBTRρ∞γ2κ2exp-κr where r is the separation between NP surfaces, and R is the radius of the NP, ρ∞ is the concentration of ions in the suspension, κ−1 is the Debye screening length (characteristic size of the double layer) and kB and T are the Boltzmann constant and the temperature. As κ−1 approaches the size range of the particles, the interactions amongst the particles may span several times the particle size and contributes to particle diffusion.
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Goh, H. J., M. Damodaran i Q. Y. Ng. "Modeling Airflow and Particle Trajectories Near the Head/Disk Interface Region of a Small Form Factor Hard Disk Drive Enclosure". W World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63633.
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Airflow characteristics and particle trajectories inside a small form factor hard disk drive (HDD) enclosure is modeled by creating a complex unstructured mesh around the various geometrical artifacts in the HDD enclosure using a commercial flow-solver which solves the incompressible Navier-Stokes Equations. From this model insight on the airflow characteristics in the vicinity of the slider could be obtained. The effect of the read/write head on the global flow field is also addressed for typical disk operation conditions. The computed airflow patterns are then used to predict particle trajectories in the vicinity of head/disk interface (HDI), the knowledge of which has relevance for tribological aspects connected with the HDI region. The effects of gravity and thermal gradients on the airflow characteristics within the HDD enclosure are also considered. Knowledge of particle trajectories and interaction provide useful guidelines for HDD design and filter locations. Depending on the types of particles, these are likely to be subjected to gravitational and thermophoretic forces, or inter particle interactions. Particles of different materials and sizes are used to evaluate the effects of these forces, which influence the particle trajectories.
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Endicott, Derick, Samir Tambe i San-Mou Jeng. "Aerodynamic Investigation of Multi-Swirler Array Utilizing Low and High Swirl Swirler Combinations for a Lean Direct Injection Combustor". W ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42494.
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An experimental study has been carried out to investigate the isothermal aerodynamic behavior and to discern the effects on the flow-field resulting from interactions between low and high-swirl counter-rotating radial-radial air swirlers in three Lean Direct Injection configurations utilizing a 3 × 3 array of radial-radial swirlers. Configurations consisted of varying combinations of two swirlers featuring high and low swirl intensity. Two-dimensional velocity data is presented from the measurement of 37 planes spanning the width of the LDI array. Particle Image Velocimetry (PIV) was used to take velocity field measurements and to study the inter-swirler interactions. Three test cases were studied which utilized a combination of a low and high Swirl Number swirlers: the baseline case utilized 9 low swirl (SN about 0.6) swirlers, the second case used one high swirl (SN about 1.0) swirler in the center of the array, and the third case used 3 high swirl swirlers in a row within the array. The flow field developed by the three experimental cases differed significantly and inter-swirler interaction proved significant and highly complex. The velocity fields developed from swirlers in an array varied from that of the individual swirler, and as such, it should not be expected that the array have the same characteristics of the individual swirler. Placing a high-swirl swirler in a low-swirl array increased swirler interaction and led to substantial favorable changes in velocity fields and the recirculation zones developed downstream of each swirler in comparison to the baseline configuration including the development of a large CTRZ with weakened intensity for increased flame anchoring potential.
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Zhang, X., S. Kanuparthi, G. Subbarayan, B. Sammakia i S. Tonapi. "Hierarchical Modeling and Trade-Off Studies in Design of Thermal Interface Materials". W ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/ipack2005-73259.
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Particle laden polymer composites are widely used as thermal interface materials in the electronics cooling industry. The projected small chip-sizes and high power applications in the near future demand higher values of effective thermal conductivity of the thermal interface materials (TIMs) used between the chip and the heat-spreader and the heat-spreader and heat-sink. However, over two decades of research has not yielded materials with significantly improved effective thermal conductivities. A critical need in developing these TIMs is apriori modeling using fundamental physical principles to predict the effect of particle volume fraction and arrangements on effective behavior. Such a model will enable one to optimize the structure and arrangement of the material. The existing analytical descriptions of thermal transport in particulate systems under predict (as compared to the experimentally observed values) the effective thermal conductivity since these models do not accurately account for the effect of inter-particle interactions, especially when particle volume fractions approach the percolation limits of approximately 60%. Most existing theories are observed to be accurate when filler material volume fractions are less than 30–35%. In this paper, we present a hierarchical, meshless, computational procedure for creating complex microstructures, explicitly analyzing their effective thermal behavior, and mathematically optimizing particle sizes and arrangements. A newly developed object-oriented symbolic, java language framework termed jNURBS implementing the developed procedure is used to generate and analyze representative random microstructures of the TIMs.
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Alam, Manjurul, i Jeff Darabi. "Dipole-Dipole Interaction Between Particle Complexes in a Magnetophoretic Bioseparation Chip". W ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icnmm2016-8030.
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Particle-particle interaction is an important phenomenon in the analysis of particle transport in a microfluidic device. This paper presents a computational study to predict the interaction force between particle complexes in a magnetophoretic bio-separation chip. Magnetic flux gradients are simulated in OpenFOAM CFD software and imported to Matlab to obtain the particle trajectories. The interaction force is approximated using a dipole based model and implemented to track the particle motion in a microfluidic device in the presence of an applied magnetic field. The analysis of particle trajectories is performed for cases where the applied magnetic field is parallel or perpendicular to the inter-particle distance of the particle complexes by solving a system of coupled ordinary differential equations.
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Jayakumar, Paramsothy, Dave Mechergui i Tamer M. Wasfy. "Understanding the Effects of Soil Characteristics on Mobility". W ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-68314.
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The Army’s mission is to develop, integrate, and sustain the right technology solutions for all manned and unmanned ground vehicles, and mobility is a key requirement for all ground vehicles. Mobility focuses on ground vehicles’ capabilities that enable them to be deployable worldwide, operationally mobile in all environments, and protected from symmetrical and asymmetrical threats. In order for military ground vehicles to operate in any combat zone, mobility on off-road terrains should be extensively investigated. Mobility on off-road terrains is poorly understood because of the empirical and semi-empirical methods used in predicting the mobility map. These methods do not capture the soil deformation as well as its non-linear behavior. The discrete element method (DEM) was identified as a high-fidelity method that can capture the deformation of the soil and its non-linear behavior. The DEM method allows to simulate the vehicle on any off-road terrain and to generate an accurate mobility map. In this paper, a simulation study was undertaken to understand the influence of soil characteristics on mobility parameters such as wheel sinkage, wheel slip, vehicle speed, and tractive force. The interaction of the vehicle wheels with soft soil is poorly understood, this study helps understand this interaction. A nominal wheeled vehicle model was built in the DIS/IVRESS software and simulated over different cohesive and non-cohesive soils modeled using DEM. Some characteristics of these soils were varied namely, the soil inter-particle cohesion, the soil inter-particle friction, the soil particle size, and the soil density. The mobility parameters were measured and correlated to the soil characteristics. This study showed that the vehicle speed increased with cohesion, friction, soil density, and particle size, while wheel sinkage and wheel slip decreased with those parameters. The influence of these characteristics combined is more complex; extensive studies of other soil characteristics need to be carried out in the future to understand their effect on vehicle mobility.
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Voigt, Christian, i Graham Ashcroft. "On the Extension of a Harmonic Balance Method for the Simulation of Compressor Casing Treatments". W ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56990.
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In recent years both linear and nonlinear frequency domain methods have become increasingly popular in the simulation and investigation of time-periodic flows in turbomachinery. In this work the extension of an alternating frequency/time domain Harmonic Balance method to support arbitrary inter-domain block interfaces, with possibly different frames of reference, is described in detail. The approach outlined is based on the time-domain, area-based interpolation algorithm originally developed for the investigation of casing treatments. In this paper, it is shown that by solving the domain coupling problem in the time-domain it is possible to accurately and efficiently capture the flow physics of such complex, nonlinear problems as blade tip interaction with casing treatments in transonic compressors. To demonstrate and verify the basic algorithm the advection of a simple entropy disturbance in a subsonic duct flow is first computed. Secondly, unsteady flow due to rotor-stator interaction in a transonic compressor stage is simulated and the data compared with reference numerical methods. Finally, to validate the method a single stage transonic axial compressor with casing treatments is simulated and the results are compared with previously published time-domain simulations as well as experimental data based on particle image velocimetry measurements in the blade tip region.
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Hadavand, Mahshid, Aydin Nabovati i Antonio C. M. Sousa. "Two-Dimensional Simulation of Magnetohydrodynamic Two-Phase Flow in Random Porous Media Using the Lattice Boltzmann Method". W 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22983.
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The present work employs the single relaxation time lattice Boltzmann method along with the pseudo potential model for the two-phase flow simulation of a ferrofluid in a random two-dimensional medium under the influence of a spatially variable external magnetic field. The magnetic field is created and controlled by placing a permanent magnet at the outlet end of the channel filled with a porous medium. The magnitude of the magnetic force acting on the ferrofluid is controlled by changing the distance of the magnet from the channel outlet. The spatially variable magnetic field strength was analytically calculated inside the channel using the available relations in the literature. The main goal of the present work is to qualitatively study the applicability of the single relaxation time (SRT) lattice Boltzmann method (LBM) to modelling flow of a ferrofluid and its steering into porous media. Penetration of the ferrofluid into the porous medium, which is initially filled with a fluid with no magnetic properties, was simulated in time. The simulation results for the flow front are presented and the effect of the magnetic field strength on the rate of flow penetration and front advancement was studied qualitatively. The LBM has proved to be a powerful tool for modelling flows, which involve multi-physics in complex geometries, when mesoscopic inter-particle forces and interaction with external complex forces have to be determined.
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Kulander, Kenneth C. "Time Dependent Hartree Fock Theory of Multiphoton Ionization". W Multiple Excitations of Atoms. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/mea.1986.tub3.
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The theory of multiphoton ionization for single electron atoms (or pseudo-one electron atoms such as sodium and cesium) is relatively well established from the standpoint of the knowing the relevant equations to be solved and interpreting the results. There is still some debate about the above threshold effects, but ionization rates have been calculated for high order processes, and the results agree well with experiment. This is not the case for multi-electron systems. In the limit of laser fields which are very strong compared to the Coulombic interactions, collective motion should be expected. At lower laser intensities, linear response theory or perturbation theory has proven to be adequate to model the absorption processes. In this regime, the inter-electronic forces are stronger than the photon-electron interaction so that the perturbation series is convergent. For the intermediate regime, say >1014W/cm2, these two kinds of interactions should be treated on the same footing. A complete, exact, many body calculation for this problem is not possible so that several approximations have been considered. Independent particle models seem to be the most reasonable, with time dependent Hartree Fock being able to include most of the important physical effects, particularly as the number of electrons increases. The major approximation of this approach is that the state of the system is represented by a single, determinantal wave function for all time. This constraint limits the kinds of information which can be obtained from the calculations to averaged quantities. It has the merit, however, of including the effects of the time evolution of the electronic charge density on the absorption process. The redistribution of absorbed energy between all the system's electrons, and the rate at which this occurs is part and parcel of the calculations. This energy exchange is done self consistently so that an understanding of the total absorption dynamics is possible. This seems a minimum requirement in order to investigate any collective effects.
Raporty organizacyjne na temat "Complex Inter-particle Interactions"
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Shmulevich, Itzhak, Shrini Upadhyaya, Dror Rubinstein, Zvika Asaf i Jeffrey P. Mitchell. Developing Simulation Tool for the Prediction of Cohesive Behavior Agricultural Materials Using Discrete Element Modeling. United States Department of Agriculture, październik 2011. http://dx.doi.org/10.32747/2011.7697108.bard.
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The underlying similarity between soils, grains, fertilizers, concentrated animal feed, pellets, and mixtures is that they are all granular materials used in agriculture. Modeling such materials is a complex process due to the spatial variability of such media, the origin of the material (natural or biological), the nonlinearity of these materials, the contact phenomenon and flow that occur at the interface zone and between these granular materials, as well as the dynamic effect of the interaction process. The lack of a tool for studying such materials has limited the understanding of the phenomena relevant to them, which in turn has led to energy loss and poor quality products. The objective of this study was to develop a reliable prediction simulation tool for cohesive agricultural particle materials using Discrete Element Modeling (DEM). The specific objectives of this study were (1) to develop and verify a 3D cohesionless agricultural soil-tillage tool interaction model that enables the prediction of displacement and flow in the soil media, as well as forces acting on various tillage tools, using the discrete element method; (2) to develop a micro model for the DEM formulation by creating a cohesive contact model based on liquid bridge forces for various agriculture materials; (3) to extend the model to include both plastic and cohesive behavior of various materials, such as grain and soil structures (e.g., compaction level), textures (e.g., clay, loam, several grains), and moisture contents; (4) to develop a method to obtain the parameters for the cohesion contact model to represent specific materials. A DEM model was developed that can represent both plastic and cohesive behavior of soil. Soil cohesive behavior was achieved by considering tensile force between elements. The developed DEM model well represented the effect of wedge shape on soil behavior and reaction force. Laboratory test results showed that wedge penetration resistance in highly compacted soil was two times greater than that in low compacted soil, whereas DEM simulation with parameters obtained from the test of low compacted soil could not simply be extended to that of high compacted soil. The modified model took into account soil failure strength that could be changed with soil compaction. A three dimensional representation composed of normal displacement, shear failure strength and tensile failure strength was proposed to design mechanical properties between elements. The model based on the liquid bridge theory. An inter particle tension force measurement tool was developed and calibrated A comprehensive study of the parameters of the contact model for the DEM taking into account the cohesive/water-bridge was performed on various agricultural grains using this measurement tool. The modified DEM model was compared and validated against the test results. With the newly developed model and procedure for determination of DEM parameters, we could reproduce the high compacted soil behavior and reaction forces both qualitatively and quantitatively for the soil conditions and wedge shapes used in this study. Moreover, the effect of wedge shape on soil behavior and reaction force was well represented with the same parameters. During the research we made use of the commercial PFC3D to analyze soil tillage implements. An investigation was made of three different head drillers. A comparison of three commonly used soil tillage systems was completed, such as moldboard plow, disc plow and chisel plow. It can be concluded that the soil condition after plowing by the specific implement can be predicted by the DEM model. The chisel plow is the most economic tool for increasing soil porosity. The moldboard is the best tool for soil manipulation. It can be concluded that the discrete element simulation can be used as a reliable engineering tool for soil-implement interaction quantitatively and qualitatively.