[Audio] PRISM Seminar Series
http://nanohub.org/resources/5699
Sat, 30 Aug 2014 19:20:48 +0000HUBzero - The open source platform for scientific and educational collaborationnanoHUB.orgsupport@nanohub.orgnodevices, nano electro-mechanical systems, reliability, rf memsJayathi Murthyen-gbCopyright 2014 nanoHUB.orgResourcesEmerging Opportunities, Challenges, and Applications in Exascale Computing
http://nanohub.org/resources/10981
The move towards exascale computing platforms (capable of 10^18 floating point operations) poses tremendous challenges, while presenting opportunities for foundational advances in a variety of application domains. In this talk, I will describe various technical issues that must be overcome to realize the potential of exascale computing platformsThe move towards exascale computing platforms (capable of 10^18 floating point operations) poses tremendous challenges, while presenting opportunities for foundational advances in a variety of application domains. In this talk, I will describe various technical issues that must be overcome to realize the potential of exascale computing platformsnoAMD, high performance computing, Intel, Parallel and distributerd computing, Parallel Processing, research seminarAnanth GramaAnanth GramaOnline PresentationsFri, 11 Mar 2011 03:11:23 +0000/http://nanohub.org/site/resources/2011/03/10989/2011.02.18-Grama-PRISM.mp3From density functional theory to defect level in silicon: Does the “band gap problem” matter?
http://nanohub.org/resources/5495
Modeling the electrical effects of radiation damage in semiconductor devices requires a detailed description of the properties of point defects generated during and subsequent to irradiation. Such modeling requires physical parameters, such as defect electronic levels, to describe carrier recombination. Density functional theory (DFT) is the method of choice for first-principles simulations of defects. However, DFT typically hugely underestimates the fundamental band gap in semiconductors, and the band gap is the energy scale of interest for defect levels. Moreover, boundary conditions in the supercell approximation used in DFT calculations of defects also can inject large errors and uncertainties. I describe a new, more rigorous methodology for supercell calculations, implemented in the SeqQuest DFT code, that incorporates a proper treatment of electrostatic boundary conditions, locates a fixed chemical potential for the net defect electron charge, includes the bulk dielectric response, and creates a robust computational model of isolated defects. Using this methodology, the computed DFT defect level spectrum for a wide variety of Si defects spans the experimental Si gap, i.e., exhibits no band gap problem, and the DFT results agree remarkably well with experiment for those values that are experimentally known. The new scheme adds rigor to computing defect properties, and has important implications for density functional theory development.Modeling the electrical effects of radiation damage in semiconductor devices requires a detailed description of the properties of point defects generated during and subsequent to irradiation. Such modeling requires physical parameters, such as defect electronic levels, to describe carrier recombination. Density functional theory (DFT) is the method of choice for first-principles simulations of defects. However, DFT typically hugely underestimates the fundamental band gap in semiconductors, and the band gap is the energy scale of interest for defect levels. Moreover, boundary conditions in the supercell approximation used in DFT calculations of defects also can inject large errors and uncertainties. I describe a new, more rigorous methodology for supercell calculations, implemented in the SeqQuest DFT code, that incorporates a proper treatment of electrostatic boundary conditions, locates a fixed chemical potential for the net defect electron charge, includes the bulk dielectric response, and creates a robust computational model of isolated defects. Using this methodology, the computed DFT defect level spectrum for a wide variety of Si defects spans the experimental Si gap, i.e., exhibits no band gap problem, and the DFT results agree remarkably well with experiment for those values that are experimentally known. The new scheme adds rigor to computing defect properties, and has important implications for density functional theory development.nodensity functional theory, device simulations, devices, nanoelectronics, radiation damage, radiation effects, reliability, research seminarPeter A. SchultzPeter A. SchultzOnline PresentationsThu, 02 Oct 2008 00:05:56 +0000/http://nanohub.org/site/resources/2008/09/05499/2008.08.21-schultz-nt501.mp3Nanotribology, Nanomechanics and Materials Characterization Studies
http://nanohub.org/resources/6573
Fundamental nanotribological studies provide insight to molecular origins of interfacial phenomena including adhesion, friction, wear and lubrication. Friction and wear of lightly loaded micro/nano components are highly dependent on the surface interactions (few atomic layers). Nanotribological and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures to provide a bridge between science and engineering. This talk will present an overview of nanotribological and nanomechanics studies and their applications.Fundamental nanotribological studies provide insight to molecular origins of interfacial phenomena including adhesion, friction, wear and lubrication. Friction and wear of lightly loaded micro/nano components are highly dependent on the surface interactions (few atomic layers). Nanotribological and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures to provide a bridge between science and engineering. This talk will present an overview of nanotribological and nanomechanics studies and their applications.noatomic force microscopy, carbon nanotubes, friction force microscopy, Magnetic, material properties, materials, materials science, microscopy, multi-walled carbon nanotubes, nano electro-mechanical systems, nano/bio, nanotribology, nanotubes,...Bharat BhushanBharat BhushanOnline PresentationsMon, 08 Jun 2009 20:14:05 +0000/http://nanohub.org/site/resources/2009/03/06577/2009.03.06-Bhushan-PRISM.mp3Peanuts vs. Pyramids: Two Perspectives on MEMS
http://nanohub.org/resources/7868
MEMS, the acronym for Micro-electromechanical Systems, also known simply as “Micro-systems,” come in two main types: commodity products (the peanuts) and MEMS-enabled products (the pyramids, or, more correctly, the inverted pyramids). The economics of scale greatly affect how these two classes of products are designed, built, manufactured, and sold. The contrast is illustrated with two real-world examples: The Knowles SiSonic&tm; silicon cell-phone microphone, and the Polychromix PhazIR&tm;, a fully portable battery-operated hand-held near-infrared spectrometer.MEMS, the acronym for Micro-electromechanical Systems, also known simply as “Micro-systems,” come in two main types: commodity products (the peanuts) and MEMS-enabled products (the pyramids, or, more correctly, the inverted pyramids). The economics of scale greatly affect how these two classes of products are designed, built, manufactured, and sold. The contrast is illustrated with two real-world examples: The Knowles SiSonic&tm; silicon cell-phone microphone, and the Polychromix PhazIR&tm;, a fully portable battery-operated hand-held near-infrared spectrometer.nonano electro-mechanical systems, optics, research seminar, sensors, SpectroscopyStephen D. SenturiaStephen D. SenturiaOnline PresentationsWed, 30 Dec 2009 02:26:24 +0000/http://nanohub.org/site/resources/2009/11/07872/2009.11.12-Senturia-NT501.mp3Gas Damping of Microcantilevers at Low Ambient Pressures
http://nanohub.org/resources/5683
This seminar will present a theoretical model for predicting the gas damping of long, rectangular silicon microcantilevers, which are oscillating in an unbounded gaseous medium with the ambient pressures varying over 5 orders of magnitude (1000 > Kn > 0.03). The work is the result of a collaboration with Prof. Alina Alexeenko (AAE). The surrounding gas flow is modeled using a sub—continuum, quasisteady Boltzmann equation with a simplified ellipsoidal statistical Bhatnagar—Gross—Krook (ES—BGK) collision operator. The computational results of the model are used to present a closed—form correlation for gas damping of different microcantilever vibration modes. The correlation is uniformly valid over 5 orders of magnitude of Kn numbers easily spanning the range over the free—molecular, the transition, and the low—pressure slip flow regimes. This presentation, will also compare the predictions of this theoretical model with the detailed experimental data acquired by Ryan Tung through controlled pressure vacuum chamber experiments with silicon microcantilevers vibrating in the fundamental and higher vibration modes. The experiments were recently performed by Ryan Tung in collaboration with Dr. H. Sumali at the Sandia National Laboratories, New Mexico. The agreement between theory and experiments is excellent.This seminar will present a theoretical model for predicting the gas damping of long, rectangular silicon microcantilevers, which are oscillating in an unbounded gaseous medium with the ambient pressures varying over 5 orders of magnitude (1000 > Kn > 0.03). The work is the result of a collaboration with Prof. Alina Alexeenko (AAE). The surrounding gas flow is modeled using a sub—continuum, quasisteady Boltzmann equation with a simplified ellipsoidal statistical Bhatnagar—Gross—Krook (ES—BGK) collision operator. The computational results of the model are used to present a closed—form correlation for gas damping of different microcantilever vibration modes. The correlation is uniformly valid over 5 orders of magnitude of Kn numbers easily spanning the range over the free—molecular, the transition, and the low—pressure slip flow regimes. This presentation, will also compare the predictions of this theoretical model with the detailed experimental data acquired by Ryan Tung through controlled pressure vacuum chamber experiments with silicon microcantilevers vibrating in the fundamental and higher vibration modes. The experiments were recently performed by Ryan Tung in collaboration with Dr. H. Sumali at the Sandia National Laboratories, New Mexico. The agreement between theory and experiments is excellent.noatomic force microscopy, experiments, nano electro-mechanical systems, nanocantilevers, research seminarRahul Anil BidkarRahul Anil BidkarOnline PresentationsTue, 04 Nov 2008 00:46:36 +0000/http://nanohub.org/site/resources/2008/10/05687/2008.10.17-bidkar-prism.mp3Molecular Sensors for MEMS
http://nanohub.org/resources/7998
This seminar will cover the issues involved in using molecular sensors in MEMS and their application to microchannels, supersonic micronozzles, microjet impingement, microturbines and unsteady fluidic actuators.This seminar will cover the issues involved in using molecular sensors in MEMS and their application to microchannels, supersonic micronozzles, microjet impingement, microturbines and unsteady fluidic actuators.nodevices, nano electro-mechanical systems, nanofluidics, research seminar, sensors, thermal transport, thermodynamicsJohn P. SullivanJohn P. SullivanOnline PresentationsThu, 10 Dec 2009 21:22:56 +0000/http://nanohub.org/site/resources/2009/12/08002/2009.11.20-Sullivan-PRISM.mp3Experiences with nonintrusive polynomial Chaos and stochastic collocation methods for uncertainty analysis and design
http://nanohub.org/resources/5910
Non—intrusive polynomial chaos expansion (PCE) and stochastic collocation (SC) methods are attractive techniques for uncertainty quantification due to their abilities to produce functional representations of stochastic variability and to achieve exponential convergence rates in statistics of interest. Whereas PCE estimates coefficients for known orthogonal polynomial basis functions, SC forms Lagrange interpolants for known coefficients. The latest results in comparing PCE and SC and embedding these methods within design under uncertainty will be presented.Non—intrusive polynomial chaos expansion (PCE) and stochastic collocation (SC) methods are attractive techniques for uncertainty quantification due to their abilities to produce functional representations of stochastic variability and to achieve exponential convergence rates in statistics of interest. Whereas PCE estimates coefficients for known orthogonal polynomial basis functions, SC forms Lagrange interpolants for known coefficients. The latest results in comparing PCE and SC and embedding these methods within design under uncertainty will be presented.noalgorithms, nano electro-mechanical systems, reliabilityMichael S. EldredMichael S. EldredOnline PresentationsSat, 14 Mar 2009 00:37:12 +0000/http://nanohub.org/site/resources/2008/11/05914/2008.10.31-eldred-prism.mp3The Challenges of Micro-System Product Development
http://nanohub.org/resources/6848
This talk will discuss the historical development of micro‐system technology, the products that have been developed and the challenges to development of a reliable product.This talk will discuss the historical development of micro‐system technology, the products that have been developed and the challenges to development of a reliable product.noinnovation, nano electro-mechanical systems, reliability, research seminarJames J. AllenJames J. AllenOnline PresentationsFri, 05 Jun 2009 18:35:20 +0000/http://nanohub.org/site/resources/2009/06/06852/2008.09.19-Allen-PRISM.mp3Near-field radiative heat transfer and Casimir Force Measurement
http://nanohub.org/resources/8052
This presentation first makes a simple introduction on how the charge fluctuations give rises to these effects that are nowadays most effectively detected using MEMS or AFM technologies. This will lead to question the relevance of these effects in the use of MEMS. After description of our quantitative measurement of the Casimir force and comparison with theory, I shall report on our experimental data on the thermal flux spatial dependence. Theory based on the Derjaguin approximation, successfully used here for the first time to describe radiative heat transfer from the far field to the near field regimes, reproduces the measured dependence.This presentation first makes a simple introduction on how the charge fluctuations give rises to these effects that are nowadays most effectively detected using MEMS or AFM technologies. This will lead to question the relevance of these effects in the use of MEMS. After description of our quantitative measurement of the Casimir force and comparison with theory, I shall report on our experimental data on the thermal flux spatial dependence. Theory based on the Derjaguin approximation, successfully used here for the first time to describe radiative heat transfer from the far field to the near field regimes, reproduces the measured dependence.noAFM, Casimir forces, MEMSJoel ChevrierJoel ChevrierOnline PresentationsThu, 31 May 2012 06:26:04 +0000/http://nanohub.org/site/resources/2009/12/08056/2009.10.23-Chevrier-PRISM.mp3Development of the ReaxFF reactive force fields and applications to combustion, catalysis and material failure
http://nanohub.org/resources/11774
This lecture will describe how the traditional, non-reactive FF-concept can be extended for application including reactive events by introducing bond order/bond distance concepts. Furthermore, it will address how these reactive force fields can be trained against QM-data, thus greatly enhancing their reliability and transferability.This lecture will describe how the traditional, non-reactive FF-concept can be extended for application including reactive events by introducing bond order/bond distance concepts. Furthermore, it will address how these reactive force fields can be trained against QM-data, thus greatly enhancing their reliability and transferability.no1st principles, materials science, molecular dynamics, quantum mechanicsAdri van DuinAdri van DuinOnline PresentationsTue, 13 Sep 2011 00:24:51 +0000/http://nanohub.org/site/resources/2011/07/11779/2011.06.10-Duin-PRISM.mp3Mesoscopic Simulations of Nitromethane
http://nanohub.org/resources/12037
We present recent developments on the dissipative particle model that allow simulating the physico-chemical behavior of a molecular material at the mesoscale level. Several ingredients have been added to the previous model, in particular concerning the intermolecular force field and the contributions of the internal degree's of freedom.We present recent developments on the dissipative particle model that allow simulating the physico-chemical behavior of a molecular material at the mesoscale level. Several ingredients have been added to the previous model, in particular concerning the intermolecular force field and the contributions of the internal degree's of freedom.no1st principles, atomic simulation, materials science, Monte Carlo simulationJean-Bernard MailletJean-Bernard MailletOnline PresentationsThu, 22 Sep 2011 23:29:31 +0000/http://nanohub.org/site/resources/2011/09/12119/2011.07.06-Maillet-PRISM.mp3Experiments and Models Regarding Strain Dependent Thermal Conductivity and Strength at the Nanoscale and Microscale
http://nanohub.org/resources/11603
Silicon micro- and nano-structures are essential in today’s integrated circuits and sensors. The functioning and performance of such devices are highly affected by thermal properties. Due to the size effect, the thermal properties of bulk silicon cannot represent those of silicon micro-structures. Furthermore, stress/strain inside the silicon structures can have a significant effect on their thermal properties. ...Silicon micro- and nano-structures are essential in today’s integrated circuits and sensors. The functioning and performance of such devices are highly affected by thermal properties. Due to the size effect, the thermal properties of bulk silicon cannot represent those of silicon micro-structures. Furthermore, stress/strain inside the silicon structures can have a significant effect on their thermal properties. ...noexperiments, material properties, materials science, nanocomposites, Si, strain, supperlattices, thermal conductivityVikas TomarVikas TomarOnline PresentationsFri, 23 Sep 2011 00:14:55 +0000/http://nanohub.org/site/resources/2011/07/11606/2011.04.29-Tomar-PRISM.mp3Verification and Validation in Simulations of Complex Engineered Systems
http://nanohub.org/resources/12525
Computational simulation is a ubiquitous tool in engineering. Further, the explosion of computational capabilities over the last several decades has resulted in the use of computational models of unprecedented complexity to make critical design and operation decisions. One potential benefit should be to improve reliability of the engineered system while reducing margins, due to the more accurate predictions such models could produce.Computational simulation is a ubiquitous tool in engineering. Further, the explosion of computational capabilities over the last several decades has resulted in the use of computational models of unprecedented complexity to make critical design and operation decisions. One potential benefit should be to improve reliability of the engineered system while reducing margins, due to the more accurate predictions such models could produce.nonanofluidics, reliability, Simulation, simulation and modeling, uncertainty quantificationRobert MoserRobert MoserOnline PresentationsWed, 04 Jan 2012 00:42:14 +0000/http://nanohub.org/site/resources/2011/11/12545/2011.10.19-Moser.mp3Quantifying Uncertainties from the Grid in CFD Solutions
http://nanohub.org/resources/12548
This talk begins with a study on grid-quality measures that assume grid-induced errors in a CFD solution at a cell is a function of the cell size and shape, the grid distribution around that cell, and the solution computed in the neighborhood of that cell. This talk begins with a study on grid-quality measures that assume grid-induced errors in a CFD solution at a cell is a function of the cell size and shape, the grid distribution around that cell, and the solution computed in the neighborhood of that cell. noCFD, multigrid, uncertainty quantificationTom I-P. ShihTom I-P. ShihOnline PresentationsWed, 04 Jan 2012 01:05:34 +0000/http://nanohub.org/site/resources/2011/11/12550/2011.10.07-Shih-PRISM.mp3Multiscale Considerations in DNS Studies of Multiphase Flows
http://nanohub.org/resources/14130
Here we discuss such simulations from a multi-scale perspective, focusing on two aspects: First of all, DNS results can help with the development of closure relations of unresolved processes in simulations of large-scale “industrial” systems. As an example we discuss recent results for deformable bubbles in weakly turbulent channel flows. The lift induced lateral migration of the bubbles controls the flow, but the lift is very different for nearly spherical and more deformable bubbles, resulting in different flow configuration and flow ratesHere we discuss such simulations from a multi-scale perspective, focusing on two aspects: First of all, DNS results can help with the development of closure relations of unresolved processes in simulations of large-scale “industrial” systems. As an example we discuss recent results for deformable bubbles in weakly turbulent channel flows. The lift induced lateral migration of the bubbles controls the flow, but the lift is very different for nearly spherical and more deformable bubbles, resulting in different flow configuration and flow ratesnomultiscaleGretar TryggvasonGretar TryggvasonOnline PresentationsFri, 01 Jun 2012 00:56:42 +0000/http://nanohub.org/site/resources/2012/05/14142/2012.02.03-Tryggvason-PRISM.mp3Micromechanics of Polycrystals: Full-field Computations and Second-order Homogenization Approaches
http://nanohub.org/resources/14131
In the first part of this talk we will present a spectral formulation based on crystal plasticity and Fast Fourier Transforms (FFT) for the determination of micromechanical fields in plastically-deformed 3-D polycrystals. This formulation, pioneered by Suquet and coworkers as a fast algorithm to compute the response of composites using as input a digital image of the microstructure, has been in turn adapted to deal with polycrystals deforming by dislocation glide.Next, the FFT-based formulation will be used to assess the accuracy of different available nonlinear homogenization approaches for the prediction of the viscoplastic behavior of polycrystalline aggregates. We will show that Ponte Castañeda’s second-order formulation, which explicitly uses information on average intragranular field fluctuations, implemented within the widely-used ViscoPlastic Self-Consistent (VPSC) code, yields the most accurate results.In the first part of this talk we will present a spectral formulation based on crystal plasticity and Fast Fourier Transforms (FFT) for the determination of micromechanical fields in plastically-deformed 3-D polycrystals. This formulation, pioneered by Suquet and coworkers as a fast algorithm to compute the response of composites using as input a digital image of the microstructure, has been in turn adapted to deal with polycrystals deforming by dislocation glide.Next, the FFT-based formulation will be used to assess the accuracy of different available nonlinear homogenization approaches for the prediction of the viscoplastic behavior of polycrystalline aggregates. We will show that Ponte Castañeda’s second-order formulation, which explicitly uses information on average intragranular field fluctuations, implemented within the widely-used ViscoPlastic Self-Consistent (VPSC) code, yields the most accurate results.nocomputational engineering, crystals, fast fourier transforms, materials scienceRicardo LebensohnRicardo LebensohnOnline PresentationsThu, 31 May 2012 07:26:19 +0000/http://nanohub.org/site/resources/2012/05/14145/2012.01.27-Lebensohn-PRISM.mp3Exascale Co-design for Materials in Extreme Environments: Heterogeneous Algorithms for Heterogeneous Architectures
http://nanohub.org/resources/14132
Computational materials scientists have been among the earliest and heaviest users of leadership-class supercomputers. The codes and algorithms which have been developed span a wide range of physical scales and have been useful not only for gaining scientific insight, but also as testbeds for exploring new approaches for tacking evolving challenges, including massive (nearly million-way) concurrency, an increased need for fault and power management, and data bottlenecks. Multiscale, or …Computational materials scientists have been among the earliest and heaviest users of leadership-class supercomputers. The codes and algorithms which have been developed span a wide range of physical scales and have been useful not only for gaining scientific insight, but also as testbeds for exploring new approaches for tacking evolving challenges, including massive (nearly million-way) concurrency, an increased need for fault and power management, and data bottlenecks. Multiscale, or …noexascale, exascale computing, materials, Materials EngineeringTimothy C. GermannTimothy C. GermannOnline PresentationsThu, 31 May 2012 07:38:53 +0000/http://nanohub.org/site/resources/2012/05/14148/2012.02.07-Germann-PRISM.mp3MD Simulations of Gas Flows in Nano-Channels and Interface Thermal Resistance Between Simple Liquids and Solids
http://nanohub.org/resources/14133
This talk focuses on our group’s recent research on molecular dynamics simulations of gas flows in nano-scale confined geometries, and interface thermal resistance between simple liquids and solids. Gas flow research demonstrates the importance of wall force field effects that penetrate approximately 1 nm from each surface. Gas density, viscous and normal stress distributions and the velocity profiles within this region show deviations from the Boltzmann equation solutions. Presence of this near wall sub-layer indicates the breakdown of similitude between the rarefied and nano-scale confined gas flows, solely based on the Knudsen number. In addition, MD simulations performed in a wide Knudsen range enable prediction of the Tangential Momentum Accommodation Coefficient for argon gas in contact with FCC surfaces. The second half of the talk summarizes our research on MD simulations of heat transfer in nano-channels, and our efforts to determine a phenomenological model for the interface thermal resistance (Kapitza resistance) between liquid argon and FCC surfaces. We utilize MD results to extract a model for the Kapitza length as a function of the molecular properties and temperature of the wall, and wall-fluid interaction strength. Specific results for the Kapitza length at argon-silver and argon-graphite interfaces are given; and onset of continuum behavior for liquid argon confined in nano-channels as small as 5 nm is demonstrated.This talk focuses on our group’s recent research on molecular dynamics simulations of gas flows in nano-scale confined geometries, and interface thermal resistance between simple liquids and solids. Gas flow research demonstrates the importance of wall force field effects that penetrate approximately 1 nm from each surface. Gas density, viscous and normal stress distributions and the velocity profiles within this region show deviations from the Boltzmann equation solutions. Presence of this near wall sub-layer indicates the breakdown of similitude between the rarefied and nano-scale confined gas flows, solely based on the Knudsen number. In addition, MD simulations performed in a wide Knudsen range enable prediction of the Tangential Momentum Accommodation Coefficient for argon gas in contact with FCC surfaces. The second half of the talk summarizes our research on MD simulations of heat transfer in nano-channels, and our efforts to determine a phenomenological model for the interface thermal resistance (Kapitza resistance) between liquid argon and FCC surfaces. We utilize MD results to extract a model for the Kapitza length as a function of the molecular properties and temperature of the wall, and wall-fluid interaction strength. Specific results for the Kapitza length at argon-silver and argon-graphite interfaces are given; and onset of continuum behavior for liquid argon confined in nano-channels as small as 5 nm is demonstrated.noBoltzmann equation, molecular dynamics, thermal resistanceAli BeskokAli BeskokOnline PresentationsFri, 01 Jun 2012 01:16:56 +0000/http://nanohub.org/site/resources/2012/05/14156/2011.12.02-Beskok-PRISM.mp3Particle Simulations of Ion Generation and Transport in Microelectromechanical Systems and Micropropulsion
http://nanohub.org/resources/14112
The first part of the talk deals with use of the PIC method with Monte Carlo collisions (MCC) between electrons and the ambient neutral gas to develop models to predict charge accumulation, breakdown voltage, etc. for various ambient gases, gap sizes, cathode material, and frequency of applied voltage. The second part deals with the modeling of field emission ion thrusters which are low thrust/high specific impulse devices used for in-space propulsion. The thrust is generated by extracting ions from a metallic liquid surface and accelerating them through a few kV potential difference. Particle simulations used to predict performance parameters of these thrusters are validated using experimental data for the current distribution.The first part of the talk deals with use of the PIC method with Monte Carlo collisions (MCC) between electrons and the ambient neutral gas to develop models to predict charge accumulation, breakdown voltage, etc. for various ambient gases, gap sizes, cathode material, and frequency of applied voltage. The second part deals with the modeling of field emission ion thrusters which are low thrust/high specific impulse devices used for in-space propulsion. The thrust is generated by extracting ions from a metallic liquid surface and accelerating them through a few kV potential difference. Particle simulations used to predict performance parameters of these thrusters are validated using experimental data for the current distribution.noelectrostatics, ions, materials science, MEMS, Monte Carlo, particle simulationsVenkattraman AyyaswamyVenkattraman AyyaswamyOnline PresentationsWed, 30 May 2012 07:53:21 +0000/http://nanohub.org/site/resources/2012/05/14116/2012.03.21-Ayyaswamy-PRISM.mp3Application-driven Co-Design: Using Proxy Apps in the ASCR Materials Co-Design Center
http://nanohub.org/resources/14149
Computational materials science is performed with a suite of applications that span the quantum mechanics of interatomic bonding to the continuum mechanics of engineering problems and phenomenon specific models in between. In this talk, we will review this suite and the motifs used in each of the codes with particular emphasis on how the proxy apps are used for exascale co-design.Computational materials science is performed with a suite of applications that span the quantum mechanics of interatomic bonding to the continuum mechanics of engineering problems and phenomenon specific models in between. In this talk, we will review this suite and the motifs used in each of the codes with particular emphasis on how the proxy apps are used for exascale co-design.nocomputational materials, exascale computing, materials science, modeling and simulation, Programming, quantum mechanics, SimulationJim BelakJim BelakOnline PresentationsFri, 01 Jun 2012 00:46:10 +0000/http://nanohub.org/site/resources/2012/05/14153/2012.03.07-Belak-PRISM.mp3Active subspace methods in theory and practice: Or, does your model really have lots of parameters?
http://nanohub.org/resources/20824
Science and engineering models typically contain multiple parameters representing input data---e.g., boundary conditions or material properties. The map from model inputs to model outputs can be viewed as a multivariate function. One may naturally be interested in how the function changes as inputs are varied. However, if computing the model output is expensive given a set of inputs, then exploring the high-dimensional input space is infeasible. Such issues arise in the study of uncertainty quantification, where uncertainty in the inputs begets uncertainty in model predictions....Science and engineering models typically contain multiple parameters representing input data---e.g., boundary conditions or material properties. The map from model inputs to model outputs can be viewed as a multivariate function. One may naturally be interested in how the function changes as inputs are varied. However, if computing the model output is expensive given a set of inputs, then exploring the high-dimensional input space is infeasible. Such issues arise in the study of uncertainty quantification, where uncertainty in the inputs begets uncertainty in model predictions....noPaul G. ConstantinePaul G. ConstantineOnline PresentationsFri, 11 Apr 2014 21:51:48 +0000/http://nanohub.org/site/resources/2014/04/20831/2014.03.11-Constantine-PRISM.mp3