Scudder J.D.,University of Iowa |
Karimabadi H.,SciberQuest, Inc.
Astrophysical Journal | Year: 2013
This paper outlines the rather narrow conditions on a radiatively decoupled plasma where a Maxwell-Boltzmann (MB) distribution can be assumed with confidence. The complementary non-thermal distribution with non-perturbative kurtosis is argued to have a much broader purview than has previously been accepted. These conditions are expressed in terms of the electron Knudsen number, Ke , the ratio of the electron mean free path to the scale length of electron pressure. Rather generally, f(v < v 2(K e )) will be Gaussian, so that MB atomic or wave particle effects controlled by speeds v < v 2 ≡ w(15/8Ke ) 1/4 will remain defensible, where w is the most probable speed. The sufficient condition for Spitzer-Braginskii plasma fluid closure at the energy equation requires globally Ke (s) ≤ 0.01; this global condition pertains to the maximum value of Ke along the arc length s of the magnetic field (to its extremities) provided that contiguous plasma remains uncoupled from the radiation field. The non-thermal regime Ke > 0.01 is common in all main-sequence stellar atmospheres above approximately 0.05 stellar radii from the surface. The entire solar corona and wind are included in this regime where non-thermal distributions with kurtosis are shown to be ubiquitous, heat flux is not well modeled by Spitzer-Braginskii closure, and fluid modeling is qualitative at best. © 2013. The American Astronomical Society. All rights reserved..
Agency: NSF | Branch: Standard Grant | Program: | Phase: MAGNETOSPHERIC PHYSICS | Award Amount: 80.00K | Year: 2011
This project will investigate the possibility that a new approach to deriving a linear theory of the tearing mode instability in space plasmas can be successfully developed. Such a linear theory would then form the basis of a full non-linear theory of magnetic reconnection in a collisonless plasma. Previous analytical work on the linear tearing mode relied on using an asymptotic approach to make the equations tractable. However, fullly kinetic, particle simulations have indicated that the asymptotic approach breakes down in most realistic geometries. The purpose of this exploratory resarch is threefold:
1) Determine why the asymptotic appoach breaks down and develop a new approach using an exact linear Vlasov solver to determine the conditions where a direct transition from linear theory to non-linear turbulence occurs; 2) Determine whether or not the formation of secondary tearing island formation is due to a linear instability; 3) Examine the controversial question of whether linear mode properties have a significant influence on the resulting reconnection rate in large systems.
This is a project that has the potential to transform the way magnetic reconnection is treated in plasma theory and simulations. It could affect our understanding of phenomena on the sun, in the solar wind, in planetary magnetospheres and in astrophysical plasmas.
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 148.66K | Year: 2012
DESCRIPTION (provided by applicant): Adverse events and medical errors result in thousands of accidental deaths and over one million excess injuries each year. To avoid medical errors in radiation cancer treatment, careful attention needs to be made to ensure accurate implementation of the intended treatment plan. We propose a SmartTool to automatically detect and highlight potential errors in a radiotherapy treatment plan, in real time and before its execution. SmartTool will double check all the treatment parameters in the background against a previously built Predictive Model of a Medical Error (PMME) and flag the operator, [post human QA,] if there is a discrepancy in the treatment plan, by stopping execution, highlighting the outlier treatment parameter and prompting human intervention. To build the PMME we will mine the dataset of previously treated cancer patients, by clustering the data in the groups based on treatment parameter similarity, labeling the clusters and using an innovative algorithm to build a highly accurate anomaly detection tool. PMME will also be dynamically updated [to include new treatment data instances coming in to the system, and updating the model should any treatment flags be identified as false positive or false negative]. Thevastly innovative aspect of SmartTool is in the novel use of machine learning techniques to automatically build an anomaly prediction model on unlabeled data (customarily a labeled data is required to build a predictive model) and provide an automatic, real time and unobtrusive intelligent computational treatment checking algorithm. Moreover, having an analytical model of an outlier/anomaly offers the capability to describe the conditions of the outlier being created and is the essential in gaining investigative (and medical) insight in what went wrong and how to improve the process in the future. SmartTool can also be applied in a variety of other medical areas (e.g. predicting errors in pharmacy, laboratory data, and treatment procedure data), to detect anomalies and describe them, offering potential novel medical discoveries and a prospect of saving thousands more lives, with a vast commercialization aspect. PUBLIC HEALTH RELEVANCE: The proposal is aimed at promoting research and development in biomedical computational science and technology that is consistent with the objective of the NIH and NCI to support rapid progress in areas of scientific opportunity in biomedical research, and enhancing the public health. If the project is successfully completed, this proof of concept study will result in a valuable health information technology tool for automatic detection of catastrophic errors in cancer radiotherapy, which adds another safeguard for patient safety.
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 599.45K | Year: 2009
Existing scientific visualization tools have specific limitations for large scale scientific data sets. Of these four limitations can be seen as paramount: (i) memory management, (ii) remote visualization, (iii) interactivity, and (iv) specificity. In Phase I, we proposed and successfully developed a prototype of a collection of computer tools and libraries called SciViz that overcome these limitations and enable researchers to visualize large scale data sets (greater than 200 gigabytes) on HPC resources remotely from their workstations at interactive rates. A key element of our technology is the stack oriented rather than a framework driven approach which allows it to interoperate with common existing scientific visualization software thereby eliminating the need for the user to switch and learn new software. The result is a versatile 3D visualization capability that will significantly decrease the time to knowledge discovery from large, complex data sets. Typical visualization activity can be organized into a simple stack of steps that leads to the visualization result. These steps can broadly be classified into data retrieval, data analysis, visual representation, and rendering. Our approach will be to continue with the technique selected in Phase I of utilizing existing visualization tools at each point in the visualization stack and to develop specific tools that address the core limitations identified and seamlessly integrate them into the visualization stack. Specifically, we intend to complete technical objectives in four areas that will complete the development of visualization tools for interactive visualization of very large data sets in each layer of the visualization stack. These four areas are: Feature Objectives, C++ Conversion and Optimization, Testing Objectives, and Domain Specifics and Integration. The technology will be developed and tested at NASA and the San Diego Supercomputer Center.
Omelchenko Y.A.,SciberQuest, Inc. |
Karimabadi H.,SciberQuest, Inc.
Physical Review Letters | Year: 2012
By conducting two-dimensional hybrid simulations of an infinitely long field-reversed θ-pinch discharge we discover a new type of plasma rotation, which rapidly develops at the plasma edge in the ion diamagnetic direction due to the self-consistent generation of a Hall-driven radial electric field. This effect is different from the previously identified end-shorting and particle-loss mechanisms. We also demonstrate flutelike perturbations frequently inferred in experiments and show that in the absence of axial contraction effects they may quickly alter the toroidal symmetry of the plasma. © 2012 American Physical Society.