# Events

## Workshops and Conferences

SOS 17 Conference
March 25-28

Successful workshop on Big Data and High Performance Computing hosted by ORNL in Jekyll Island Georgia

SOS is an invitation-only 2 1/2 day meeting held each year by Sandia labs, Oak Ridge National Laboratory, and Swiss Technical institute. This year it was hosted by ORNL in Jekyll Island Georgia on March 25-28, 2013.

The theme this year was "The intersection of High Performance Computing and Big Data." There were 40 speakers and panelists from around the world representing views from industry, academia, and national laboratories. The first day focused on the gaps between big computing and big data and the challenges of turning science data into knowledge. On the second day the talks and panels focused on where HPC and big data intersect and the state of big-data analysis software. The morning of the third day focused on the politics of big data including the issues of data ownership.

Findings of the meeting include the fact that large experimental facilities such as CERNs Large Hadron Collider, and the new telescopes coming online already generate prodigious amounts of scientific data. The volume and speed that data is generated requires that the data be analyzed on the fly and only a tiny fraction be kept. The amount kept still amounts to many petabytes. The attendees stressed how important provenance is to the use of the archived data by other researchers around the world. The majority of today's scientific data is only of value to the original researcher, because the data lacks the meta-data required for others to use it. The talks and panels clearly showed the intersection of high performance computing and big data. They also showed that the converse is not necessarily true, i.e. big data (as defined by Google and Amazon) does not require high performance computing. These vendors and their customers are able to get their work done on large, distributed networks of independent PCs. The meeting was filled with lively discussion, and provocative questions.

For those wanting to know more, the agenda and talks are posted on the SOS17 website: http://www.csm.ornl.gov/workshops/SOS17/

SIAM SEAS 2013 Annual Meeting
March 22-24

On March 22-24, Oak Ridge National Laboratory and the University of Tennessee hosted the 37th annual meeting of the SIAM Southeastern Atlantic Section. The meeting included approximately 160 registered participants, of which roughly 60 were students and 20 were from ORNL. There were 4 plenary talks, 24 mini-symposium sessions, seven contributed sessions, and a poster session. Awards were given to students for Best Paper and Best Poster presentations. Attendees were also given guided tours of the Graphite Reactor, the Spallation Neutron Source, and the National Center for Computational Science. The meeting was organized by Chris Baker (ORNL), Cory Hauck (ORNL), Jillian Trask (UT), Lora Wolfe (ORNL), and Yulong Xing (ORNL/UT).

Durmstrang-2
March 18-19

The semi-annual review for the Durmstrang-2 project was held on March 18-19 in Maryland. Durmstrang-2 is a DoD/ORNL collaboration in extreme scale high performance computing. The long term goal of the project is to support the achievement of sustained exascale processing on applications and architectures of interest to both partners. The Durmstrand-2 project is managed from the Extreme Scale Systems Center (ESSC) of CCSD.

Steve Poole, Chief Scientist of CSMD, presented the overview and general status update at the March review. Benchmarks R&D discussion was facilitated by Josh Lothian, Matthew Baker, Jonathan Schrock, and Sarah Powers of ORNL; Languages and Compilers R&D discussion was facilitated by Matthew Baker, Oscar Hernandez, Pavel Shamis, and Manju Venkata of ORNL; I/O and FileSystems R&D discussion was facilitated by Brad Settlemyer of ORNL; Networking R&D discussion was facilitated by Nagi Rao, Susan Hicks, Paul Newman, and Steve Poole of ORNL; Power Aware Computing R&D discussion was facilitated by Chung-Hsing Shu of ORNL; System Schedulers R&D discussion was facilitated by Greg Koenig and Sarah Powers of ORNL. The topics of discussion during the executive session of the review included continued funding/growth of the program and development of performance metrics for the project.

APS 2013 March Meeting
March 18-22

The American Physical Society (APS) March Meeting is the largest physics meeting in the world, focusing on research from industry, universities, and major labs. Participation in this years' meeting held in Baltimore, MD (March 18-22, 2013) by staff members of the Computational Chemical and Materials Sciences (CCMS) Group included 24 different talks (bold names are from CCMS).

Monojoy Goswami, Bobby G. Sumpter, "Morphology and Dynamics of Ion Containing Polymers using Coarse Grain Molecular Dynamics Simulation", Talk in Session T32: Charged and Ion Containing Polymers (March 21, 2013) APS National Meeting, Baltimore.

Debapriya Banerjee, Kenneth S. Schweizer, Bobby G. Sumpter, Mark D. Dadmun, "Dispersion of small nanoparticles in random copolymer melts", Talk in Session F32: Polymer Nanocomposites II (March 19, 2013) APS National Meeting, Baltimore.

Rajeev Kumar, Bobby G. Sumpter, S. Michael Kilbey II, "00003 Charge regulation and local dielectric function in planar polyelectrolyte brushes", Talk in Session U32: Charged Polymers and Ionic Liquids (March 21, 2013) APS National Meeting, Baltimore.

Alamgir Karim, David Bucknall, Dharmaraj Raghavan, Bobby Sumpter, Scott Sides, "In-situ Neutron Scattering Determination of 3D Phase-Morphology Correlations in Fullerene -Polymer Organic Photovoltaic Thin Films", Talk in Session Y33: Organic Electronics and Photonics-Morphology and Structure I (March 22, 2013) APS National Meeting, Baltimore.

Geoffrey Rojas, P. Ganesh, Simon Kelly, Bobby G. Sumpter, John Schlueter, Petro Maksymovych," Molecule/Surface Interactions and the Control of Electronic Structure In Epitaxial Charge Transfer Salts", Talk in Session U35: Search for New Superconductors III (March 21, 2013) APS National Meeting, Baltimore.

Geoffrey A. Rojas, P. Ganesh, Simon Kelly, Bobby G. Sumpter, John A. Schlueter, Petro Maksymovich, "Density Functional Theory studies of Epitaxial Charge Transfer Salts", Talk in Session N35: Search for New Superconductors III (March 20, 2013) APS National Meeting, Baltimore.

Arthur P. Baddorf, Qing Li, Chengbo Han, J. Bernholc, Humberto Terrones, Bobby G. Sumpter, Miguel Fuentes-Cabrera, Jieyu Yi, Zheng Gai, Peter Maksymovych, Minghu Pan," Electron Injection to Control Self-Assembly and Disassembly of Phenylacetylene on Gold", Talk in Session C33: Organic Electronics and Photonics - Interfaces and Contacts (March 18, 2013) APS National Meeting, Baltimore.

Mina Yoon, Kai Xiao, Kendal W. Clark, An-Ping Li, David Geohegan, Bobby G. Sumpter, Sean Smith, "Understanding the growth of nanoscale organic semiconductors: the role of substrates", Talk in Session Z33: Organic Electronics and Photonics - Morphology and Structure II (March 22, 2013) APS National Meeting, Baltimore.

Chengbo Han, Wenchang Lu, Jerry Bernholc, Miguel Fuentes-Cabrera, Humberto Terrones, Bobby G. Sumpter, Jieyu Yi, Zheng Gai, Arthur P. Baddorf, Qing Li,. Peter Maksymovych, Minghu Pan, "Computational Study of Phenylacetylene Self-Assembly on Au(111) Surface", Talk in Session C33: Organic Electronics and Photonics - Interfaces and Contacts (March 18, 2013) APS National Meeting, Baltimore.

Jaron Krogel, Jeongnim Kim, David Ceperley "Prospects for efficient QMC defect calculations: the energy density applied to Ge self-interstitials", Talk in Session J24: Quantum Many-Body Systems and Methods I (March 19, 2013) APS National Meeting, Baltimore.

Kendal Clark, Xiaoguang Zhang, Ivan Vlassiouk, Guowei He,Gong Gu, Randall Feenstra, An-Ping Li, "Mapping the Electron Transport of Graphene Boundaries Using Scanning Tunneling Potentiometry", Talk in Session G6: CVD Graphene - Doping and Defects (March 19, 2013) APS National Meeting, Baltimore.

Gregory Brown, Donald M. Nicholson, Markus Eisenbach, Kh. Odbadrakh "Wang-Landau or Statistical Mechanics", Talk in Session G6: Equilibrium Statistical Mechanics, Followed by GSNP Student Speaker Award (March 18, 2013) APS National Meeting, Baltimore.

Don Nicholson, Kh. Odbadrakh, German Samolyuk, G. Malcolm Stocks," Calculated magnetic structure of mobile defects in Fe", Session Y16: Magnetic Theory II (March 22, 2013) APS National Meeting, Baltimore.

Khorgolkhuu Odbadrakh, Don Nicholson, Aurelian Rusanu, German Samolyuk, Yang Wang, Roger Stoller, Xiaoguang Zhang, George Stocks, "Coarse graining approach to First principles modeling of structural materials", Session A43: Multiscale modeling--Coarse-graining in Space and Time I (March 18, 2013) APS National Meeting, Baltimore.

M. G. Reuter & P. D. Williams, "The Information Content of Conductance Histogram Peaks: Transport Mechanisms, Level Alignments, and Coupling Strengths" Talk in Session R43: Electron Transfer, Charge Transfer and Transport Session, (March 20,2013) APS National Meeting, Baltimore.

Paul R. C. Kent, Panchapakesan Ganesh, Jeongnim Kim, Mina Yoon, Fernando Reboredo, "Binding and Diffusion of Li in Graphite: Quantum Monte Carlo Benchmarks and validation of Van der Waals DFT" Talk in Session A5: Van der Waals Bonding in Advanced Materials – Materials Behavior, (March 18, 2013) APS National Meeting, Baltimore.

Peter Staar, Thomas Maier, Thomas Schulthess, "DCA+: Incorporating self-consistently a continuous momentum self-energy in the Dynamical Cluster Approximation" Talk in Session N24, APS National Meeting, Baltimore.

Thomas Maier, Peter Hirschfeld, Douglas Scalapino, Yan Wang, Andreas Kreisel, "Pairing strength and gap functions in multiband superconductors: 3D effects" Talk in Session G37: Electronic Structute Methods II,(March 20, 2013) APS National Meeting, Baltimore.

Thomas Maier, Yan Wang, Andreas Kreisel, Peter Hirschfeld, Douglas Scalapino, "Spin fluctuation theory of pairing in AFe2As2" Talk in Session G37: Electronic Structure Methods II,(March 20, 2013), APS National Meeting, Baltimore.

Peter Hirschfeld, Andreas Kreisel, Yan Wang, Milan Tomic, Harald Jeschke, Anthony Jacko, Roser Valenti, Thomas Maier, Douglas Scalapino, "Pressure dependence of critical temperature of bulk FeSe from spin fluctuation theory" Talk in Session G37: Electronic Structure Methods II (March 20, 2013), APS National Meeting, Baltimore.

Markus Eisenbach, Junqi Yin, Don M. Nicholson, Ying Wai Li, "First principles calculation of finite temperature magnetism in Ni", Talk in Session C17: Magnetic Theory I (March 18, 2013), APS National Meeting, Baltimore.

Madhusudan Ojha, Don M. Nicholson, Takeshi Egami, "Ab-initio atomic level stresses in Cu-Zr crystal, liquid and glass phases", Talk in Session G42: Focus Session: Physics of Glasses and Viscous Liquids I (March 19, 2013), APS National Meeting, Baltimore.

Junqi Yin, Markus Eisenbach, Don Nicholson, "Spin-lattice coupling in BCC iron", Talk in Session T39: Metals Alloys and Metallic Structures (March 21, 2013), APS National Meeting, Baltimore.

German Samolyuk, Yuri Osetsky, Roger Stoller, Don Nicholson, George Malcolm Stocks, "The modification of core structure and Peierls barrier of 1/2$<111>$ screw dislocation in bcc Fe in presence of Cr solute atoms", Talk in Session T39: Metals Alloys and Metallic Structures (March 21, 2013), APS National Meeting, Baltimore.

SIAM-CSE13
February 25 - March 1

The CSMD had a strong showing at SIAM-CSE13 with over 25 presentations from staff members from the division.  This conference is a leading conference in computer science and mathematics, drawing thousands of researchers from across the globe and supported jointly by NSF and DOE.  Division scientist organized eight different mini-symposiums with close to a hundred invited speakers in areas of modern libraries (Christopher Baker), climate (Kate Evans), nuclear simulations (Bobby Philip), kinetic theory (Cory Hauck), hybrid architecture linear algebra (Ed D'Azevedo), UQ and stochastic inverse problems (Clayton Webster), and Structural Graph Theory, Sparse Linear Algebra, and Graphical Models (Blair Sullivan).

## Seminars

May 31, 2013 - Pablo Seleson: Multiscale Material Modeling with Peridynamics

Multiscale modeling has been recognized in recent years as an important research field to achieve feasible and accurate predictions of complex systems. Peridynamics, a nonlocal reformulation of continuum mechanics based on integral equations, is able to resolve microscale phenomena at the continuum level. As a nonlocal model, peridynamics possesses a length scale which can be controlled for multiscale modeling. For instance, classical elasticity has been presented as a limiting case of a peridynamic model. In this talk, I will introduce the peridynamics theory and show analytical and numerical connections of peridynamics to molecular dynamics and classical elasticity. I will also present multiscale methods to concurrently couple peridynamics and classical elasticity, demonstrating the capabilities of peridynamics towards multiscale material modeling.

Dr. Seleson is a Postdoctoral Fellow in the Institute for Computational Engineering and Sciences at The University of Texas at Austin. He has obtained his Ph.D. in Computational Science from Florida State University in 2010. He holds a M.S. degree in Physics from the Hebrew University of Jerusalem (2006), and a double B.S. degree in Physics and Philosophy also from the Hebrew University of Jerusalem (2002).

May 17, 2013 - Jon Mietling and Tony McCrary: Bling3D: a new game development toolset from l33t Labs

Bling3D is a forthcoming game development toolset from l33t labs.

The fusion of Eclipse 4 with game development technologies, Bling allows both programmers and designers to create compelling interactive experiences from within one powerful tool.

In this talk, you will be introduced to some of Bling's exciting features, including:

• GPU Powered UI - A revolutionary new user interface for Eclipse, which uses shader programs to render widgets directly on the GPU.
• BYOE (Bring Your Own Engine) - Bling is designed as a universal tools platform for game technologies. You can use our game engine or integrate your own!
• Ultimate Toolset - Use the power of Bling's interface and Eclipse's extensibility to create mind blowing tools and plugins.
• Designers Love It - Intuitive visual tools that allow you to create new worlds and artificial realities with ease.
• Transform Your Assets - Easily create new ways to process raw assets (geometry, images, etc) into materials suitable for runtime use.

Jon Mietling and Tony McCrary are representatives of l33t labs LLC, technology startup from the Detroit, Michigan region.

May 10, 2013 - Xiao Chen: A Modular Uncertainty Quantification Framework for Multi-physics Systems

This talk presents a modular uncertainty quantification (UQ) methodology for multi-physics applications in which each physics module can be independently embedded with its internal UQ method (intrusive or non-intrusive). This methodology offers the advantage of "plug-and-play" flexibility (i.e., UQ enhancements to one module do not require updates to the other modules) without losing the "global" uncertainty propagation property. (This means that, by performing UQ in this modular manner, all inter-module uncertainty and sensitivity information is preserved.) In addition, using this methodology one can also track the evolution of global uncertainties and sensitivities at the grid point level, which may be useful for model improvement. We demonstrate the utility of such a framework for error management and Bayesian inference on a practical application involving a multi-species flow and reactive transport in randomly heterogeneous porous media.

May 2, 2013 - Kenley Pelzer: Quantum Biology: Elucidating Design Principles from Photosynthesis

Recent experiments suggest that quantum mechanical effects may play a role in the efficiency of photosynthetic light harvesting. However, much controversy exists about the interpretation of these experiments, in which light harvesting complexes are excited by a fem to second laser pulse. The coherence in such laser pulses raises the important question of whether these quantum mechanical effects are significant in biological systems excited by incoherent light from the sun. In our work, we apply frequency-domain Green's function analysis to model a light-harvesting complex excited by incoherent light. By modeling incoherent excitation, we demonstrate that the evidence of long-lived quantum mechanical effects is not purely an artifact of peculiarities of the spectroscopy. This data provides a new perspective on the role of noisy biological environments in promoting or destroying quantum transport in photosynthesis.

April 23, 2013 - Kirk W. Cameron: Power-Performance Modeling, Analyses and Challenges

The power consumption of supercomputers ultimately limits their performance. The current challenge is not whether we will can build an exaflop system by 2018, but whether we can do it in less than 20 megawatts. The SCAPE Laboratory at Virginia Tech has been studying the tradeoffs between performance and power for over a decade. We've developed an extensive tool chain for monitoring and managing power and performance in supercomputers. We will discuss our power-performance modeling efforts and the implications of our findings for exascale systems as well as some research directions ripe for innovation.

April 23, 2013 - Jordan Deyton: Tor Bridge Distribution Powered by Threshold RSA

Since its inception, Tor has offered anonymity for internet users around the world. Tor now offers bridges to help users evade internet censorship, but the primary distribution schemes that provide bridges to users in need have come under attack. This talk explores how threshold RSA can help strengthen Tor's infrastructure while also enabling more powerful bridge distribution schemes. We implement a basic threshold RSA signature system for the bridge authority and a reputation-based social network design for bridge distribution. Experimental results are obtained showing the possibility of quick responses to requests from honest users while maintaining both the secrecy and the anonymity of registered clients and bridges.

April 19, 2013 - Maria Avramova and Kostadin Ivanov: OECD LWR UAM and PSBT/BFBT benchmarks and their relation to Advanced LWR Simulations

From 1987 to 1995, Nuclear Power Engineering Corporation (NUPEC) in Japan performed a series of void measurement tests using full-size mock-up tests for both BWRs and PWRs. Void fraction measurements and departure from nucleate boiling (DNB) tests were performed at NUPEC under steady-state and transient conditions. The workshop will provide overview of the OECD/NEA/NRC PWR Subchannel and Bundle Tests (PSBT) and OECD/NEA/NRC BWR Full-size Fine-mesh Bundle Tests (BFBT) benchmarks based on the NUPEC data. The benchmarks were designed to provide a data set for evaluation of the abilities of existing subchannel, system, and computational fluid dynamics (CFD) thermal-hydraulics codes to predict void distribution and departure from nucleate boiling (DNB) in LWRs under steady-state and transient conditions. The first part of the seminar summarizes the description of PSBT and BFBT benchmark databases, specifications, definition of benchmark exercises and comparative analysis of obtained results and makes the case on how these benchmarks can be used for verification, validation and uncertainty quantification of thermal-hydraulic tools developed for advanced LWR simulations.

The second part of the seminar will provide overview of the OECD/NEA benchmark for LWR Uncertainty Analysis in Modeling (UAM) with emphasis on the Exercises of Phase I and Phase II of the benchmark and discussion of the Phase III, which is directly related to coupled multi-physics advanced LWR simulations. Series of well-defined problems with complete sets of input specifications and reference experimental data will be introduced with an objective is to determine the uncertainty in LWR calculations at all stages of coupled reactor physics/thermal hydraulics calculation. The full chain of uncertainty propagation will be discussed starting form from basic data and engineering uncertainties, across different scales (multi-scale), and physics phenomena (multi-physics) as well as how this propagation is tested on a number of benchmark exercises. Input, output and assumptions for each Exercise will be given as well as the procedures to calculate the output and propagated uncertainties in each step will be described supplemented by results of benchmark participants.

Bio of Dr. Maria Avramova
Dr. Maria Avramova is an Assistant Professor in the Mechanical and Nuclear Engineering Department at the Pennsylvania State University. She is currently the Director of Reactor Dynamics and Fuel Management Group (RDFMG). Her expertise and experience is in the area of developing methods and computer codes for multi-dimensional reactor core analysis. Her background includes development, verification, and validation of thermal-hydraulics sub-channel, porous media, and CFD models and codes for reactor core design, transient, and safety computational analysis. She has led and coordinated the OECD/NRC BFBT and PSBT benchmarks and currently is coordinating Phase II of the OECD LWR UAM benchmark. Her latest research efforts have been focused on high-fidelity multi-physics simulations (involving coupling of reactor physics, thermal-hydraulics and fuel performance models) as well as on uncertainty and sensitivity analysis of reactor design and safety calculations. Dr. Avramova has published over 15 refereed journal papers and over 40 refereed conference proceedings articles.

Dr. Kostadin Ivanov is Distinguished Professor in the Mechanical and Nuclear Engineering Department at the Pennsylvania State University. He is currently Graduate Coordinator of Nuclear Engineering Program. His research developments include computational methods, numerical algorithms and iterative techniques, nuclear fuel management and reloading optimization techniques, reactor kinetics and core dynamics methods, cross-section generation and modeling algorithms for multi-dimensional steady-state and transient reactor calculations, and coupling three-dimensional (3-D) kinetics models with thermal-hydraulic codes. He has also led the development of multi-dimensional neutronics, in-core fuel management and coupled 3-D kinetics/thermal-hydraulic computer code benchmarks, multi-dimensional reactor transient and safety analysis methodologies as well as integrated analysis of safety-related parameters, system transient modeling of power plants, and in-core fuel management analyses.
Examples of such benchmarks are OECD/NRC PWR MSLB benchmark, OECD/NRC BWR TT benchmark and OECD/DOE/CEA VVER-1000 CT benchmark. He is currently a chair and coordinator of the Scientific Board and Technical Program Committee of OECD LWR UAM benchmark.

April 18, 2013 - Sparsh Mittal: MASTER: A Technique for Improving Energy Efficiency of Caches in Multicore Processors

Large power consumption of modern processors has been identified as the most severe constraint in scaling their performance. Further, in recent CMOS technology generations, leakage energy has been dramatically increasing and hence, the leakage energy consumption of large last-level caches (LLCs) has become a significant source of the processor power consumption.

This talk first highlights the need of power management in LLCs in the modern multi-core processors and then presents MASTER, a micro-architectural cache leakage energy saving technique using dynamic cache reconfiguration. MASTER uses dynamic profiling of LLCs to predict energy consumption of running programs at multiple LLC sizes. Using these estimates, suitable cache quotas are allocated to different programs using cache-coloring scheme and the unused LLC space is turned off to save energy. The implementation overhead of MASTER is small and even for 4 core systems; its overhead is only 0.8% of L2 cache size. Simulations have been performed using an out-of-order x86-64 simulator and 2-core and 4-core multi-programmed workloads from SPEC2006 suite. Further, MASTER has been compared with two energy saving techniques, namely decay cache and way-adaptable cache. The results show that MASTER gives the highest saving in energy and does not harm performance or cause unfairness.

Finally, this talk briefly shows an extension of MASTER for multicore QoS systems. Simulation results confirm that a large amount of energy is saved while meeting the QoS requirement of most of the workloads.

April 17, 2013 - Okwan Kwon: Automatic Scaling of OpenMP Applications Beyond Shared Memory

We present the first fully automated compiler-runtime system that successfully translates and executes OpenMP shared-address-space programs on laboratory-size clusters, for the complete set of regular, repetitive applications in the NAS Parallel Benchmarks. We introduce a hybrid compiler-runtime translation scheme. This scheme features a novel runtime data flow analysis and compiler techniques for improving data affinity and reducing communication costs. We present and discuss the performance of our translated programs, and compare them with the performance of the MPI, HPF and UPC versions of the benchmarks. The results show that our translated programs achieve 75% of the hand-coded MPI programs, on average.

April 17, 2013 - Michael S. Murillo: Molecular Dynamics Simulations of Charged Particle Transport in High Energy-Density Matter

High energy-density matter is now routinely produced at large laser facilities. Producing fusion energy at such facilities challenges our ability to model collisional plasma processes that transport energy among the plasma species and across spatial scales. While the most accurate computational method for describing collisional processes is molecular dynamics, there are numerous challenges associated with using molecular dynamics to model very hot plasmas. However, recent advances in high performance computing have allowed us to develop methods for simulating a wide variety of processes in hot, dense plasmas. I will review these developments and describe our recent results that involve simulating fast particle stopping in dense plasmas. Using the simulation results, implications for theoretical modeling of charged-particle stopping will be given.

April 12, 2013 - Vivek K. Pallipuram: Exploring Multiple Levels Of Performance Modeling For Heterogeneous Systems

One of the major challenges faced by the High-Performance Computing (HPC) community today is user-friendly and accurate heterogeneous performance modeling. Although performance prediction models exist to fine-tune applications, they are seldom easy-to-use and do not address multiple levels of design space abstraction. Our research aims to bridge the gap between reliable performance model selection and user-friendly analysis. We propose a straightforward and accurate multi-level performance modeling suite for multi-GPGPU systems that addresses multiple levels of design space abstraction. The multi-level performance modeling suite primarily targets synchronous iterative algorithms (SIAs) using our synchronous iterative GPGPU execution (SIGE) model and addresses two levels of design space abstraction: 1) low-level where partial details of the implementation are present along with system specifications and 2) high-level where implementation details are minimum and only high-level system specifications are known. The low-level abstraction of the modeling suite employs statistical techniques for runtime prediction, whereas the high-level abstraction utilizes existing analytical and quantitative modeling tools to predict the application runtime. Our initial validation efforts for the low-level abstraction yield high runtime prediction accuracy with less than 10% error rate for several tested GPGPU cluster configurations and case studies. The development of high-level abstraction models is underway. The end goal of our research is to offer the scientific community, a reliable and user-friendly performance prediction framework that allows them to optimally select a performance prediction strategy for the given design goals and system architecture characteristics.

Current Top 500 systems like Titan, Stampede, and Tianhe-1A have started to embrace the use of off-chip accelerators, such as GPUs and x86 coprocessors, to dramatically improve their overall performance and efficiency numbers. At the same time, these systems also make very specific assumptions about the availability of highly optimized interconnects and software stacks that are used to mitigate the effects of running large applications across multiple nodes and their accelerators. This talk focuses on the gap in networking between high-performance computing clusters and data centers and proposes that future clusters should be built around commodity-based networks and managed global address spaces to improve the performance of data movement between host memory and accelerator memory. This thesis is supported by previous research into converged commodity interconnects and ongoing research on the Oncilla managed GAS runtime to support aggregated memory for data warehousing applications. In addition, we will speculate on how commodity-based networks and memory management for clusters of accelerators might be affected by the advent of 3D stacking and fused CPU/GPU architectures.

April 9, 2013 - Cong Liu: Towards Efficient Real-Time Multicore Computing Systems

Current trends in multicore computing are towards building more powerful, intelligent, yet space- and power-efficient systems. A key requirement in correctly building such intelligent systems is to ensure real-time performance, i.e., "make the right move at the right time in a predictable manner." Current research on real-time multicore computing has been limited to simple systems for which complex application runtime behaviors are ignored; this limits the practical applicability of such research. In practice, complex but realistic application runtime behaviors often exist, such as I/O operations, data communications, parallel execution segments, critical sections etc. Such runtime behaviors are currently dealt with by over-provisioning systems, which is an economically wasteful practice. I will present predictable real-time multicore computing system design, analysis, and implementation methods that can efficiently support common types of application runtime behaviors. I will show that the proposed methods are able to avoid over-provisioning systems and to reduce the number of needed hardware components to the extent possible while providing timing correctness guarantees.

In the second part of the talk, I will present energy-efficient workload mapping techniques for heterogeneous multicore CPU/GPU systems. Through both algorithmic analysis and prototype system implementation, I will show that the proposed techniques are able to achieve better energy efficiency while guaranteeing response time performance.

April 9, 2013 - Frank Mueller: On Determining a Viable Path to Resilience at Exascale

Exascale computing is projected to feature billion core parallelism. At such large processor counts, faults will become more common place. Current techniques to tolerate faults focus on reactive schemes for recovery and generally rely on a simple checkpoint/restart mechanism. Yet, they have a number of shortcomings. (1) They do not scale and require complete job restarts. (2) Projections indicate that the mean-time-between-failures is approaching the overhead required for checkpointing. (3) Existing approaches are application-centric, which increases the burden on application programmers and reduces portability.

To address these problems, we discuss a number of techniques and their level of maturity (or lack thereof) to address these problems. These include (a) scalable network overlays, (b) on-the-fly process recovery, (c) proactive process-level fault tolerance, (d) redundant execution, (e) the effort of SDCs on IEEE floating point arithmetic and (f) resilience modeling. In combination, these methods are aimed to pave the path to exascale computing.

April 5, 2013 - Sarat Sreepathi: Optimus: A Parallel Metaheuristic Optimization Framework With Environmental Engineering Applications

Optimus (Optimization Methods for Universal Simulators) is a parallel optimization framework for coupling computational intelligence methods with a target scientific application. Optimus includes a parallel middleware component, PRIME (Parallel Reconfigurable Iterative Middleware Engine) for scalable deployment on emergent supercomputing architectures. PRIME provides a lightweight communication layer to facilitate periodic inter-optimizer data exchanges. A parallel search method, COMSO (Cooperative Multi-Swarm Optimization) was designed and tested on various high dimensional mathematical benchmark problems. Additionally, this work presents a novel technique, TAPSO (Topology Aware Particle Swarm Optimization) for network based optimization problems. Empirical studies demonstrate that TAPSO achieves better convergence than standard PSO for Water Distribution Systems (WDS) applications. Scalability analysis of Optimus was performed on the Cray XK6 supercomputer (Jaguar) at Oak Ridge Leadership Computing Facility for the leak detection problem in WDS. For a weak scaling scenario, we achieved 84.82% of baseline at 200,000 cores relative to performance at 1000 cores.

March 20, 2013 - J.W. Banks: Stable Partitioned Solvers for Compresible Uid-structure Interaction Problems

In this talk, we discuss recent work concerning the developing and analysis of stable, partitioned solvers for uid-structure interaction problems. In a partitioned approach, the solvers for each uid or solid domain are isolated from each other and coupled only through the interface. This is in contrast to fully-coupled monolithic schemes where the entire system is advanced by a single unied solver, typically by an implicit method. Added-mass instabilities, common to partitioned schemes, are addressed through the use of a newly developed interface projection technique. The overall approach is based on imposing the exact solution to local uid-solid Riemann problems directly in the numerical method. Stability of the FSI coupling is discussed using normal-mode stability theory, and the new scheme is shown to be stable for a wide range of material parameters. For the rigid body case, the approach is shown to be stable even for bodies of no mass or rotational inertia. This dicult limiting case exposes interesting subtleties concerning the notion of added mass in uid-structure problems at the continuous level.

March 13, 2013 - Travis Thompson: Navier-Stokes equations to Describe the Motion of Fluid Substances

The Navier-Stokes equations describe the motion of fluid substances; the equations are widely utilized to model many physical phenomena such as weather patterns, ocean currents, turbulent fluid flow and magneto-hydrodynamics. Despite their wide utilization a comprehensive theoretical understanding remains an open question; the equations offer a venue for challenges at the forefront of both theoretical and computational knowledge. My work at Texas A&M has focused, primarily, on two topics: aspects of hyperbolic conservation laws, specifically mass conservation for incompressible Navier-Stokes, and computational investigation of an LES model based on a new eddy-viscosity; both embody appeal to highly-parallel scientific computing albeit in differing ways.

With respect to hyperbolic conservation laws: on the computational side I have implemented a one-step artificial compression term in a numerical code which counteracts an entropy-viscosity regularization term. This is an innovative approach; canonical methods for interface tracking are two-step or adaptive procedures. In addition the implementation utilizes a splitting approach, originally designed for use in a highly-parallel momentum equation variant, as an approximation operator in the time-stepping scheme; this approach imbues the algorithm with additional parallelism. On the theoretical side a distinct approach towards the analysis of dispersion error, utilizing a commutator expression, has been investigated for particular finite element spaces; the approach offers a computational segue into investigating consistency error and moves away from the canonical, tedious, expansion-based methodology of analysis.

With respect to large eddy simulations (LES): Computational investigations of an eddy-viscosity model based on the entropy-viscosity of Guermond & Popov has been underway for the last six months; in collaboration with Dr. Larios, a post-doc here at Texas A&M, an analysis of the qualitative and statistical attributes of high Reynolds number, turbulent flow is being conducted. We will compare our results to the Smagorinsky-Lilly turbulence model and attempt to verify basic tenets of isotropic turbulence theory; namely the Kolmogorov – 5/3 law and predictions regarding the uncorrelated nature of velocity structure functions.

March 1, 2013 - Bob Salko: Development, Improvement, and Validation of Reactor Thermal-Hydraulic Analysis Tools

As a result of the need for continual development, qualification, and application of computational tools relating to the modeling of nuclear systems, the Reactor Dynamics and Fuel Management Group (RDFMG) at the Pennsylvania State University has maintained an active involvement in this area. This presentation will highlight recent RDFMG work relating to thermal-hydraulic modeling tools. One such tool is the COolant Boiling in Rod Arrays - Two Fluids (COBRA-TF) computer code, capable of modeling the independent behavior of continuous liquid, vapor, and droplets using the sub-channel methodology. Work has been done to expand the modeling capabilities from the in-vessel region only, which COBRA-TF has been developed for, to the coolant-line region by developing a dedicated coolant-line-analysis package that serves as an add-on to COBRA-TF. Additional COBRA-TF work includes development of a pre-processing tool for faster, more user-friendly creation of COBRA-TF input decks, implementation of post-processing capabilities for visualization of simulation results, and optimization of the source code for significant improvements in simulation speed and memory management. Of equal importance to these development activities is the validation of the resulting tools for their intended applications. The code capability to capture rod-bundle thermal-hydraulic behavior during prototypical PWR operating conditions will be demonstrated through comparison of predicted and experimental results for the New Experimental Studies of Thermal-Hydraulics of Rod Bundles (NESTOR) tests. Due to the growing usage of Computational Fluids Dynamics (CFD) tools in this area, modeling results predicted by the STAR-CCM+ CFD tool will also be presented for these tests.

In this talk I will discuss a convergence framework for directly approximating the viscosity solutions of fully nonlinear second order PDE problems. The main focus will be the introduction of a set of sufficient conditions for constructing convergent finite difference (FD) methods. The conditions given are meant to be easier to realize and implement than those found in the current literature. The given FD methodology will then be shown to generalize to a class of discontinuous Galerkin (DG) methods. The proposed DG methods are high order and allow for increased flexibility when choosing a computational mesh. Numerical experiments will be presented to gauge the performance of the proposed DG methods. An overview of the PDE theory of viscosity solutions will also be given. The presented ideas are part of a larger project concerned with efficiently and accurately approximating the Hamilton-Jacobi-Bellman equation from stochastic optimal control.

February 22, 2013 - Charles K. Garrett: Numerical Integration of Matrix Riccati Differential Equations with Solution Singularities

A matrix Riccati differential equation (MRDE) is a quadratic ODE of the form

X' = A21 + A22X – XA11 – XA12X.

It is well known that MRDEs may have singularities in their solution. In this presentation, both the theory and practice of numerically integrating MRDEs past solution singularities will be analyzed. In particular, it will be shown how to create a black box numerical MRDE solver, which accurately solves an MRDE with or without singularities.

February 21, 2013 - Giacomo Dimarco: Asymptotic Preserving Implicit-Explicit Runge-Kutta Methods For Non-Linear Kinetic Equations

In this talk, we will discuss Implicit-Explicit (IMEX) Runge Kutta methods which are particularly adapted to stiff kinetic equations of Boltzmann type. We will consider both the case of easy invertible collision operators and the challenging case of Boltzmann collision operators. We give sufficient conditions in order that such methods are asymptotic preserving and asymptotically accurate. Their monotonicity properties are also studied. In the case of the Boltzmann operator the methods are based on the introduction of a penalization technique for the collision integral. This reformulation of the collision operator permits to construct penalized IMEX schemes which work uniformly for a wide range of relaxation times avoiding the expensive implicit resolution of the collision operator. Finally we show some numerical results which confirm the theoretical analysis.

February 20, 2013 - Tom Berlijn: Effects of Disorder on the Electronic Structure of Functional Materials

Doping is one of the most powerful ways to tune the properties of functional materials such as thermoelectrics, photovoltaics and superconductors. Besides carriers and chemical pressure, the dopants insert disorder into the materials. In this talk I will present two case studies of doped Fe based superconductors: Fe vacancies in KxFeySe2 [1] and Ru substitutions in Ba(Fe1-xRux)2As2 [2]. With the use of a recently developed first principles method [3], non-trivial disorder effects are found that are not only interesting scientifically, but also have potential implications for materials technology. Open questions for further research will be discussed.

[1] TB, P.j. Hirschfeld, W. Ku, PRL 109 (2012)
[2] L. Wang, TB, C.-H. Lin, Y. Wang, P.j. Hirschfeld, W. Ku, PRL 110 (2013)
[3] TB, D. Volja, W. Ku, PRL 106 (2011)

February 19, 2013 - Joshua D. Carmichael: Seismic Monitoring of the Western Greenland Ice Sheet: Response to Early Lake Drainage

In 2006, the drainage of a supraglacial lake through hydrofracture on the Greenland Ice-sheet was directly observed for the first time. This event demonstrated that surface-to-bed hydrological connections can be established through 1km of cold ice and thereby allow surficial forcing of a developed subglacial drainage system by surface meltwater. In a climate changing scenario, supraglacial lakes on the Western Greenland Ice Sheet are expected to drain earlier each summer and form new lakes at higher elevations. The ice sheet response to these earlier drainages in the near future is of glaciological concern. We address the response of the Western Greenland Ice Sheet to an observed early lake drainage using a synthesis of seismic and GPS monitoring near an actively draining lake. This experiment demonstrates that (1) seismic activity precedes the drainage event by several days and is likely coincident with crack coalescence, that (2) seismic multiplet locations are coincident with the uplift of the ice during drainage and (3) a diurnal seismic response of the ice sheet follows after the ice surface settles to pre-drainage elevation a week later. These observations are consistent with a model in which the subglacial drainage system is likely distributed, highly pressurized and with low hydraulic conductivity at drainage initiation. It also demonstrates that an early lake drainage likely reduces basal normal stress for order-week time scales by storing water subglacially. We conclude with recommendations for future long-range lake drainage detection.

February 18, 2013 - Mili Shah: Calculating a Symmetry Preserving Singular Value Decomposition

The symmetry preserving singular value decomposition (SPSVD) produces the best symmetric (low rank) approximation to a set of data. These symmetric approximations are characterized via an invariance under the action of a symmetry group on the set of data. The symmetry groups of interest consist of all the non-spherical symmetry groups in three dimensions. This set includes the rotational, reflectional, dihedral, and inversion symmetry groups. In order to calculate the best symmetric (low rank) approximation, the symmetry of the data set must be determined. Therefore, matrix representations for each of the non-spherical symmetry groups have been formulated. These new matrix representations lead directly to a novel reweighting iterative method to determine the symmetry of a given data set by solving a series of minimization problems. Once the symmetry of the data set is found, the best symmetric (low rank) approximation can be established by using the SPSVD. Applications of the SPSVD to protein dynamics problems as well as facial recognition will be presented.

February 14, 2013 - Zheng (Cynthia) Gu: Efficient and Robust Message Passing Schemes for Remote Direct Memory Access (RDMA)-Enabled Clusters

While significant effort has been made in improving Message Passing Interface (MPI) performance, existing work has mainly focused on eliminating software overhead in the library and delivering raw network performance to applications. The current MPI implementations such as MPICH2, MVAPICH2, and Open MPI still suffer from performance issues such as unnecessary synchronizations, communication progress problems, and lack of communication-computation overlaps. The root cause of these problems is the mis-match between the communication protocols/algorithms and the communication scenarios. In my PhD research, I will develop efficient and robust message passing schemes for both point-to-point and collective communications for RDMA-enabled clusters. Unlike existing approaches for optimizing MPI performance, our approach will allow different communication protocols/algorithms for different communication scenarios. The idea is to use the most appropriate communication scheme for each communication so as to remove the mis-matches, which will eliminate unnecessary synchronizations, improve communication progress, and maximize communication-computation overlaps during a communication operation. This prospectus will describe the background of this research, present our preliminary research, and summarize the proposed future work.

February 8, 2013 - Taylor Patterson: Simulation of Complex Nonlinear Elastic Bodies Using Lattice Deformers

Lattice deformers are a popular option in computer graphics for modeling the behavior of elastic bodies as they avoid the need for conforming mesh generation, and their regular structure offers significant opportunities for performance optimizations. This talk will present work that expands the scope of current grid-based elastic deformers, adding support for a number of important simulation features. The approach to be described accommodates complex nonlinear, optionally anisotropic materials while using an economical one-point quadrature scheme. The formulation fully accommodates near-incompressibility by enforcing accurate nonlinear constraints, supports implicit integration for large time steps, and is not susceptible to locking or poor conditioning of the discrete equations. Additionally, this technique increases the solver accuracy by employing a novel high-order quadrature scheme on lattice cells overlapping with the embedded model boundary, which are treated at sub-cell precision. This accurate boundary treatment can be implemented at a minimal computational premium over the cost of a voxel-accurate discretization. Finally, this talk will present part of the expanding feature set of this approach that is currently under development.

February 6, 2013 - Makhan Virdi: Modeling High-resolution Soil Moisture to Estimate Recharge Timing and Experiences with Geospatial Analyses

Estimating the time of groundwater recharge after a rainfall event is poorly understood because of it's dependence on non-linear soil characteristics and variability in antecedent soil conditions. Movement of water in variably saturated soil can be described by Richards' equation - a non-linear partial differential equation without a closed-form analytical solution, which is difficult to approximate. To develop a simple recharge model using minimum number of soil parameters, high resolution soil moisture data from a soil column in controlled laboratory conditions were analysed to understand the wetting front propagation at a finer temporal scale. Findings from a series of simulations using an existing Finite Element model by varying soil properties and depth to water table were used to propose a simple model that uses only the most significant representative soil properties and antecedent soil matrix state. In other separate geospatial analyses, satellite imagery was used for determining landslide risk cost to develop an algorithm for safest and shortest route planning in hilly areas susceptible to landslide; effects of decadal climate extremes was studied on lake-groundwater exchanges; Effects of Phosphate mining on a regional scale were studied using hydrological models and geospatial analysis LiDAR derived DEM and watershed.

February 5, 2013 - Roshan J. Vengazhiyil and C. F. Jeff Wu: Experimental Design, Model Calibration, and Uncertainty Quantification

We will start the talk with a newly developed space-filling design, called minimum energy design (MED). The key ideas involved in constructing the MED are the visualization of each design point as a charged particle inside a box, and minimization of the total potential energy of these particles. It is shown through theoretical arguments and simulations, that under regularity conditions and proper choice of the charge function, the MED can asymptotically generate any arbitrary probability density function. This new design technique has important applications in Bayesian computation and uncertainty quantification. The second part of the talk will focus on model calibration. The commonly used Kennedy and O'Hagan's (KO) approach treats the computer model as a black box and therefore, the statistically calibrated models lack physical interpretability. We propose a new framework that opens up the black box and introduces statistical models inside the computer model. This approach leads to simpler models that are physically more interpretable. Then, we will present some theoretical results concerning the convergence properties of calibration parameter estimation in the KO formulation of the model calibration problem. The KO calibration is shown to be asymptotically inconsistent. A new approach, called L2 distance calibration, is shown to be consistent and asymptotically efficient in estimating the calibration parameters.

February 4, 2013 - Li-Shi Luo: Kinetic Methods for CFD

Computational fluid dynamics (CFD) is based on direct discretizations of the Navier-Stokes equations. The traditional approach of CFD is now being challenged as new multi-scale and multi-physics problems have begun to emerge in many fields -- in nanoscale systems, the scale separation assumption does not hold; macroscopic theory is therefore inadequate, yet microscopic theory may be impractical because it requires computational capabilities far beyond our present reach. Methods based on mesoscopic theories, which connect the microscopic and macroscopic descriptions of the dynamics, provide a promising approach. Besides their connection to microscopic physics, kinetic methods also have certain numerical advantages due to the linearity of the advection term in the Boltzmann equation. Dr. Luo will discuss two mesoscopic methods: the lattice Boltzmann equation and the gas-kinetic scheme, their mathematical theory and their applications to simulate various complex flows. Examples include incompressible homogeneous isotropic turbulence, hypersonic flows, and micro-flows.

January 23, 2013 - Tarek Ali El Moselhy: New Tools for Uncertainty Quantification and Data Assimilation in Complex Systems

In this talk, Dr. Tarek Ali El Moselhy will present new tools for forward and inverse uncertainty quantification (UQ) and data assimilation.

In the context of forward UQ, Dr. Moselhy will briefly summarize a new scalable algorithm particularly suited for very high-dimensional stochastic elliptic and parabolic PDEs. The algorithm relies on computing a compact separated representation of the stochastic field of interest. The separated presentation is computed iteratively and adaptively via a greedy optimization algorithm. The algorithm has been successfully applied to problems of flow and transport in stochastic porous media, handling “real world” levels of spatial complexity and providing orders of magnitude reduction in computational time compared to state of the art methods.

In the context of inverse UQ, Dr. Moselhy will present a new algorithm for the Bayesian solution of inverse problems. The algorithm explores the posterior distribution by finding a {\it transport map} from a reference measure to the posterior measure, and therefore does not require any Markov chain Monte Carlo sampling. The map from the reference to the posterior is approximated using polynomial chaos expansion and is computed via stochastic optimization. Existence and uniqueness of the map are guaranteed by results from the optimal transport literature. The map approach is demonstrated on a variety of problems, ranging from inference of permeability fields in elliptic PDEs to benchmark high-dimensional spatial statistics problems such as inference in log-Gaussian cox point processes.

In addition to its computational efficiency and parallelizability, advantages of the map approach include: providing clear convergence criteria and error measures, providing analytical expressions for posterior moments, evaluating at no additional computational cost the marginal likelihood/evidence (thus enabling model selection), the ability to generate independent uniformly-weighted posterior samples without additional model evaluations, and the ability to efficiently propagate posterior information to subsequent computational modules (thus enabling stochastic control).

In the context of data assimilation, Dr. Moselhy will present an optimal map algorithm for filtering of nonlinear chaotic dynamical systems. Such an algorithm is suited for a wide variety of applications including prediction of weather and climate. The main advantage of the algorithm is that it inherently avoids issues of sample impoverishment common to particle filters, since it explicitly represents the posterior as the push forward of a reference measure rather than with a set of samples.

December 13, 2012 - Russell Carden: Automating and Stabilizing the Discrete Empirical Interpolation Method for Nonlinear Model Reduction

The Discrete Empirical Interpolation Method (DEIM) is a technique for model reduction ofnonlinear dynamical systems. It is based upon a modification to proper orthogonal decomposition, which is designed to reduce the computational complexity for evaluating the reduced order nonlinear term. The DEIM approach is based upon an interpolatory projection and only requires evaluation of a few selected components of the original nonlinear term. Thus, implementation of the reduced order nonlinear term requires a new code to be derived from the original code for evaluating the nonlinearity. Dr. Carden will describe a methodology for automatically deriving a code for the reduced order nonlinearity directly from the original nonlinear code. Although DEIM has been effective on some very difficult problems, it can under certain conditions introduce instabilities in the reduced model. Dr. Carden will present a problem that has proved helpful in developing a method for stabilizing DEIM reduced models.

December 12, 2012 - Charlotte Kotas: Bringing Real-Time Array Signal Processing to the NVIDIA Tesla

Underwater acoustic detection of hostile targets at range requires increasingly computationally advanced algorithms as adversaries become quieter. This seminar will discuss the mathematics behind one such algorithm and some of the challenges associated with modifying it to work in a real-time networked environment. The algorithm was modified from a sequential MATLAB formulation to a parallel CUDA FORTRAN formation designed to run on an NVIDIA Tesla C2050 processor. Speedups of greater than 50◊ were observed over comparable computational sections.

December 6, 2012 - Shuaiwen "Leon" Song: Power, Performance and Energy Models and Systems for Emergent Architectures

Massive parallelism combined with complex memory hierarchies and heterogeneity in high-performance computing (HPC) systems form a barrier to efficient application and architecture design. The performance achievements of the past must continue over the next decade to address the needs of scientific simulations. However, building an exascale system by 2022 that uses less than 20 megawatts will require significant innovations in power and performance efficiency. Prior to this work, the fundamental relationships between power and performance were not well understood. Our analytical modeling approach allows users to quantify the relationship between power and performance at scale by enabling study of the effects of machine and application dependent characteristics on system energy efficiency. Our model helps users isolate root causes of energy or performance inefficiencies and develop strategies for scaling systems to maintain or improve efficiency. I will also show how this methodology can be extended and applied to model power and performance in heterogeneous GPU-based architectures.

Shuaiwen "Leon" Song is a PhD candidate in the Computer Science department of Virginia Tech. His primary research interests fall broadly within the area of High Performance Computing (HPC) with a focus on power and performance analysis and modeling for large scale homogeneous and heterogeneous parallel architectures and runtime systems. He is a recipient of the 2011 Paul E. Torgersen Award for Graduate Student Research Excellence and in 2011 was an Institute for Scientific Computing Research (ISCR) Scholar at Lawrence Livermore National Laboratory. His work has been published in conferences and journals including IPDPS, IEEE Cluster, PACT, MASCOTS, IEEE TPDS, and IJHPCA.

December 6, 2012 - Miroslav Stoyanov: Gradient Based Dimension Reduction Approach for Stochastic Partial Differential Equations

Dimension reduction approach is considered for uncertainty quantification, where we use gradient information to partition the uncertainty domain into “active” and “passive” subspaces, where the “passive” subspace is characterized by near zero variance of the quantity of interest. We present a way to project the model onto the low dimensional “active” subspace and solve the resulting problem using conventional techniques. We derive rigorous error bounds for the projection algorithm and show convergence in $L^1$ norm.

December 5, 2012 - Barbara Chapman: Enabling Exascale Programming:  The Intranode Challenge

As we continue to debate the best way to program emerging generations of leadership-class hardware, it is imperative that we do not ignore the more traditional paths.
Dr. Chapman's presentation considers some of the ways in which today's intranode programming models may help us migrate legacy application code.

December 5, 2012 - Andrew Christlieb: An Implicit Maxwell Solver Based on Method of Lines Transpose

Fast summation methods have been successfully used in a range of plasma applications. However, in the case of moving point charges, direct application of fast summation methods in the time domain requires the use of retarded potentials. In practices, this means that every time a point charge moves in a simulation, it leaves behind an image charge that becomes a source term for all time. Hence, at each time step the number of points in the simulation grows with the number of particles being simulated.

In this talk, Dr. Christlieb will present a new approach to Maxwell's equations based on the method of lines transpose. The method starts by expressing Maxwell’s equations in second order form, and then the time operator is discretized. The resulting implicit system is then solved using integral methods. This process is known as the method of lines transpose. This approach pushes the time history into a volume integral, which does not grow in complexity with time. To efficiently solve the boundary integral, Dr. Christlieb will explain the developed ADI method that is combined with a $O(N)$ solver for the 1D boundary integrals that is competitive with explicit time stepping methods. Because the new method is implicit, this approach does not have a CFL. Further, because the approach is based on an integral formulation, the new method easily encompasses complex geometry with no special modification. Dr. Christlieb will present preliminary results of this method applied to wave propagation and some basic Maxwell examples.

November 27, 2012 - Charles Jackson: Metrics for Climate Model Validation

A “valid” model is a model that has been tested for its intended purpose. In the Bayesian formulation, the “log-likelihood” is a test statistic for selecting, weeding, or weighting climate model ensembles with observational data. Thisstatistic has the potential to synthesize the physical and data constraints on quantities of interest. One of the thorny issues in formulating the log-likelihood is how one should account for biases because not all biases affect predictions of quantities of interest.  Dr. Jackson makes use of a 165-member ensemble CAM3.1/slab ocean climate models with different parameter settings to think through the issues that are involved with predicting eachmodel’s sensitivity to greenhouse gas forcing given what can be observed from the base state. In particular, Dr. Jackson uses multivariate empirical orthogonal functions to decompose the differences that exist among this ensemble to discover what fields and regions matter to the model’s sensitivity. What is found is that the differences that matter can be a small fraction of the total discrepancy. Moreover, weighting members of the ensemble using this knowledge does a relatively poor job of adjusting the ensemble mean toward the known answer. Dr. Jackson will discuss the implications of this result.

November 15, 2012 - Erich Foster: Finite Elements for the Quasi-Geostrophic Equations of the Ocean

Erich Foster will present a conforming finite element (FE) discretization of the stream function formulation of the pure stream function form of the quasi-geostrophic equations (QGE), which are a commonly used model for the large scale wind-driven ocean circulation. The pure stream function form of the QGE is a fourth-order PDE and therefore requires a C^1 FE discretization to be conforming. Thus, the Argyris finite element, a C^1 FE with 21 degrees of freedom, was chosen for the FE discretization of the QGE. Optimal error estimates for the pure stream function form of the QGE will be presented. The QGE is a simplified model of the ocean, however it can be computationally expensive to resolve all scales, therefore numerical methods, such as the two-level method, are indispensable for time sensitive projects. A two-level method and optimal error estimate for a two-level method applied to the conforming FE discretization of the pure stream function form of the QGE will be presented and computational efficiency will be demonstrated.

October 25, 2012 - Shi Jin: Asymptotic-Preserving Schemes for Boltzmann Equation and Relative Problems with Stiff Sources

Dr. Shi Jin will propose a general framework to design asymptotic preserving schemes for the Boltzmann kinetic and related equations. Numerically solving these equations are challenging due to the nonlinear stiff collision (source) terms induced by small mean free or relaxation time. Dr. Jin will propose to penalize the nonlinear collision term by a BGK-type relaxation term, which can be solved explicitly even if discretized implicitly in time. Moreover, the BGK-type relaxation operator helps to drive the density distribution toward the local Maxwellian, thus naturally imposes an asymptotic-preserving scheme in the Euler limit. The scheme so designed does not need any nonlinear iterative solver or the use of Wild Sum. It is uniformly stable in terms of the (possibly small) Knudsen number, and can capture the macroscopic fluid dynamic (Euler) limit even if the small scale determined by the Knudsen number is not numerically resolved. Dr. Jin will show how this idea can be applied to other collision operators; such as the Landau-Fokker-Planck operator, Ullenbeck-Urling model, and in the kinetic-fluid model of disperse multiphase flows.

October 24, 2012 - Shi Jin: Semiclassical Computation of High Frequency Waves in Heterogeneous Media

Dr. Shi Jin will introduce semiclassical Eulerian methods that are efficient in computing high frequency waves through heterogeneous media. The method is based on the classical Liouville equation in phase space, with discontinuous Hamiltonians due to the barriers or material interfaces. Dr. Jin will provide physically relevant interface conditions consistent with the correct transmissions and reflections, and then build the interface conditions into the numerical fluxes. This method allows the resolution of high frequency waves without numerically resolving the small wave lengths, and capture the correct transmissions and reflections at the interface. This method can also be extended to deal with diffraction and quantum barriers. Dr. Jin will also discuss Eulerian Gaussian beam formulation which can compute caustics more accurately.

October 09, 2012 - Christian Ringhofer: Charged Particle Transport in Narrow Geometries under Strong Confinement

Kinetic transport in narrow tubes and thin plates, involving scattering of particles with a background, is modeled by classical and quantum mechanical sub-band type macroscopic equations for the density of particles (ions).  The result are diffusion equation with the projection of the (asymptotically conserved) energy tensor on the confined directions as an additional free variable, on large time scales.  Classical transport of ions through protein channels and quantum transport in thin films are discussed as examples of the application  of this methodology.

October 05, 2012 - Amilcare Porporato: Stochastic soil moisture dynamics: from soil-plant biogeochemistry and land-atmosphere interactions to sustainable use of soil and water

The soil-plant-atmosphere system is characterized by a large number of interacting processes with high degree of unpredictability and nonlinearity. These elements of complexity, while making a full modeling effort extremely daunting, are also responsible for the emergence of characteristic behaviors. Duke University model these processes by mean of minimalist models which describe the main deterministic components of the system and surrogate the high dimensional ones (i.e., hydroclimatic variability and rainfall in particular) with suitable stochastic terms. The solution of the stochastic soil water balance allows us to describe probabilistically several ecohydrological processes, including ecosystem response plant productivity as well as soil organic matter and nutrient cycling dynamics. Dr. Porporato will also discuss how such an approach can be extended to include land atmosphere feedbacks and related impact on convective precipitation. Dr. Porporato will conclude with a brief discussion of how these methods can be employed to address quantitatively the sustainable management of water and soil resources, including optimal irrigation and fertilization, phytoremediation, and soil salinization risk.