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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

THE EFFECTS OF PATCHY REIONIZATION ON SATELLITE GALAXIES OF THE MILKY WAY

We combine the high-resolution Aquarius simulations with three-dimensional models of reionization based on the initial density field of the Aquarius parent simulation, Millennium-II, to study the impact of patchy reionization on the faint satellite population of Milky Way halos. Because the Aquarius suite consists of zoom-in simulations of halos in the Millennium-II volume, we follow the formation of substructure and the growth of reionization bubbles due to the larger environment simultaneously, and thereby determine the reionization redshifts of satellite candidates. We do this for four different reionization models and also compare results to instantaneous reionization. Using a simple procedure for selecting satellites and assigning luminosities in the simulations, we compare the resulting satellite populations. We find that the overall number of satellites depends sensitively on the reionization model, with a factor of 3-4 variation between the four models for a given host halo, although the difference is entirely in the population of faint satellites (M{sub V} > -10). In addition, we find that for a given reionization model the total number of satellites differs by 10%-20% between the patchy and homogeneous scenarios, provided that the redshift is chosen appropriately for the instantaneous case. However, the halo-halo scatter from the six Aquarius halos is large, up to a factor of 2-3, and so is comparable to the difference between reionization scenarios. In order to use the population of faint dwarf galaxies around the Milky Way as a probe of the local reionization history, it is necessary to first better understand the general distribution of substructure around Milky Way-mass halos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EXPLORING MAGNETIC FIELD STRUCTURE IN STAR-FORMING CORES WITH POLARIZATION OF THERMAL DUST EMISSION

The configuration and evolution of the magnetic field in star-forming cores are investigated in order to directly compare simulations and observations. We prepare four different initial clouds having different magnetic field strengths and rotation rates, in which magnetic field lines are aligned/misaligned with the rotation axis. First, we calculate the evolution of such clouds from the prestellar stage until long after protostar formation. Then, we calculate the polarization of thermal dust emission expected from the simulation data. We create polarization maps with arbitrary viewing angles and compare them with observations. Using this procedure, we confirmed that the polarization distribution projected on the celestial plane strongly depends on the viewing angle of the cloud. Thus, by comparing the observations with the polarization map predicted by the simulations, we can roughly determine the angle between the direction of the global magnetic field and the line of sight. The configuration of the polarization vectors also depends on the viewing angle. We find that an hourglass configuration of magnetic field lines is not always realized in a collapsing cloud when the global magnetic field is misaligned with the cloud rotation axis. Depending on the viewing angle, an S-shaped configuration of the magnetic field (or the polarization vectors) appears early in the protostellar accretion phase. This indicates that not only the magnetic field but also the cloud rotation affects the dynamical evolution of such a cloud. In addition, by comparing the simulated polarization with actual observations, we can estimate properties of the host cloud such as the evolutionary stage, magnetic field strength, and rotation rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Outcome Following a Negative CT Angiogram for Gastrointestinal Hemorrhage

ObjectiveThis study was designed to evaluate the role of a negative computed tomography angiogram (CTA) in patients who present with gastrointestinal (GI) hemorrhage.MethodsA review of all patients who had CTAs for GI hemorrhage over an 8-year period from January 2005 to December 2012 was performed. Data for patient demographics, location of hemorrhage, hemodynamic stability, and details of angiograms and/or the embolization procedure were obtained from the CRIS/PACS database, interventional radiology database, secure electronic medical records, and patient’s clinical notes.ResultsA total of 180 patients had 202 CTAs during the 8-year period: 87 CTAs were performed for upper GI hemorrhage (18 positive for active bleeding, 69 negative) and 115 for lower GI hemorrhage (37 positive for active bleeding, 78 negative); 58.7 % (37/63) of patients with upper GI bleed and 77.4 % (48/62) of patients with lower GI bleed who had an initial negative CTA did not rebleed without the need for radiological or surgical intervention. This difference was statistically significant (p = 0.04). The relative risk of rebleeding, following a negative CTA, in lower GI bleeding versus upper GI bleeding patients is 0.55 (95 % confidence interval 0.32–0.95).ConclusionsPatients with upper GI bleed who had negative CTAs usually require further intervention to stop the bleeding. In contrast, most patients presenting with lower GI hemorrhage who had a negative first CTA were less likely to rebleed.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Brought to Light. I. Quantification of Disk Substructure in Dwarf Early-type Galaxies

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features such as bars and spiral arms, that lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components: the bright, dominant, diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2% and 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, as well as the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al., in which we investigate the origins of the substructure in such dwarf systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Percutaneous Irreversible Electroporation (IRE) of Hepatic Malignancy: A Bi-institutional Analysis of Safety and Outcomes

Aim: Irreversible electroporation (IRE) is a non-thermal ablative option in patients unsuitable for standard thermal ablation, due to its potential to preserve collagenous structures (vessels and ducts) and a reduced susceptibility to heat sink effects. In this series from two large tertiary referral hepatobiliary centres, we aim to assess the safety/outcomes of hepatic IRE. Materials and Methods: Bi-institutional retrospective, longitudinal follow-up series of IRE for primary hepatic malignancy; [hepatocellular carcinoma (n = 20), cholangiocarcinoma (n = 3)] and secondary metastatic disease; colorectal (n = 28), neuroendocrine (n = 1), pancreatic (n = 1), breast (n = 1), gastrointestinal stromal tumour (GIST, n = 1) and malignant thymoma (n = 1). Outcome measures included procedural safety/effectiveness, time to progression and time to death. Results: Between 2013 and 2017, 52 patients underwent percutaneous IRE of 59 liver tumours in 53 sessions. All tumours were deemed unsuitable for thermal ablation. Cases were performed using ultrasound (US) or computed tomography (CT) guidance. A complete ablation was achieved in n = 44, (75%) of cases with an overall complication rate of 17% (n = 9). Of the complete ablation group, median time to progression was 8 months. At 12 months, 44% were progression-free (95% CI 30–66%). The data suggest that larger lesion size (> 2 cm) is associated with shorter time to progression and there is highly significant difference with faster time to progression in mCRC compared with HCC. Median survival time was 38 months. Conclusion: This bi-institutional review is the largest UK series of IRE and suggests this ablative technology can be a useful tool, but appears to mainly induce local tumour control rather than cure with HCC having better outcomes than mCRC.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Implementation of a hybrid particle code with a PIC description in r–z and a gridless description in ϕ into OSIRIS

For many plasma physics problems, three-dimensional and kinetic effects are very important. However, such simulations are very computationally intensive. Fortunately, there is a class of problems for which there is nearly azimuthal symmetry and the dominant three-dimensional physics is captured by the inclusion of only a few azimuthal harmonics. Recently, it was proposed [1] to model one such problem, laser wakefield acceleration, by expanding the fields and currents in azimuthal harmonics and truncating the expansion. The complex amplitudes of the fundamental and first harmonic for the fields were solved on an r–z grid and a procedure for calculating the complex current amplitudes for each particle based on its motion in Cartesian geometry was presented using a Marder's correction to maintain the validity of Gauss's law. In this paper, we describe an implementation of this algorithm into OSIRIS using a rigorous charge conserving current deposition method to maintain the validity of Gauss's law. We show that this algorithm is a hybrid method which uses a particles-in-cell description in r–z and a gridless description in ϕ. We include the ability to keep an arbitrary number of harmonics and higher order particle shapes. Examples for laser wakefield acceleration, plasma wakefield acceleration, and beam loading are also presented and directions for future work are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Perforation of the IVC: Rule Rather Than Exception After Longer Indwelling Times for the Guenther Tulip and Celect Retrievable Filters

Purpose: This study was designed to assess the incidence, magnitude, and impact upon retrievability of vena caval perforation by Guenther Tulip and Celect conical inferior vena cava (IVC) filters on computed tomographic (CT) imaging. Methods: Guenther Tulip and Celect IVC filters placed between July 2007 and May 2009 were identified from medical records. Of 272 IVC filters placed, 50 (23 Guenther Tulip, 46%; 27 Celect, 54%) were retrospectively assessed on follow-up abdominal CT scans performed for reasons unrelated to the filter. Computed tomography scans were examined for evidence of filter perforation through the vena caval wall, tilt, or pericaval tissue injury. Procedure records were reviewed to determine whether IVC filter retrieval was attempted and successful. Results: Perforation of at least one filter component through the IVC was observed in 43 of 50 (86%) filters on CT scans obtained between 1 and 880 days after filter placement. All filters imaged after 71 days showed some degree of vena caval perforation, often as a progressive process. Filter tilt was seen in 20 of 50 (40%) filters, and all tilted filters also demonstrated vena caval perforation. Transjugular removal was attempted in 12 of 50 (24%) filters and was successful in 11 of 12 (92%). Conclusions: Longer indwelling times usually result in vena caval perforation by retrievable Guenther Tulip and Celect IVC filters. Although infrequently reported in the literature, clinical sequelae from IVC filter components breaching the vena cava can be significant. We advocate filter retrieval as early as clinically indicated and increased attention to the appearance of IVC filters on all follow-up imaging studies.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Systematic calibration of an integrated x-ray and optical tomography system for preclinical radiation research

Purpose: The cone beam computed tomography (CBCT) guided small animal radiation research platform (SARRP) has been developed for focal tumor irradiation, allowing laboratory researchers to test basic biological hypotheses that can modify radiotherapy outcomes in ways that were not feasible previously. CBCT provides excellent bone to soft tissue contrast, but is incapable of differentiating tumors from surrounding soft tissue. Bioluminescence tomography (BLT), in contrast, allows direct visualization of even subpalpable tumors and quantitative evaluation of tumor response. Integration of BLT with CBCT offers complementary image information, with CBCT delineating anatomic structures and BLT differentiating luminescent tumors. This study is to develop a systematic method to calibrate an integrated CBCT and BLT imaging system which can be adopted onboard the SARRP to guide focal tumor irradiation. Methods: The integrated imaging system consists of CBCT, diffuse optical tomography (DOT), and BLT. The anatomy acquired from CBCT and optical properties acquired from DOT serve as a priori information for the subsequent BLT reconstruction. Phantoms were designed and procedures were developed to calibrate the CBCT, DOT/BLT, and the entire integrated system. Geometrical calibration was performed to calibrate the CBCT system. Flat field correction was performed to correct the nonuniform response of the optical imaging system. Absolute emittance calibration was performed to convert the camera readout to the emittance at the phantom or animal surface, which enabled the direct reconstruction of the bioluminescence source strength. Phantom and mouse imaging were performed to validate the calibration. Results: All calibration procedures were successfully performed. Both CBCT of a thin wire and a euthanized mouse revealed no spatial artifact, validating the accuracy of the CBCT calibration. The absolute emittance calibration was validated with a 650 nm laser source, resulting in a 3.0% difference between simulated and measured signal. The calibration of the entire system was confirmed through the CBCT and BLT reconstruction of a bioluminescence source placed inside a tissue-simulating optical phantom. Using a spatial region constraint, the source position was reconstructed with less than 1 mm error and the source strength reconstructed with less than 24% error. Conclusions: A practical and systematic method has been developed to calibrate an integrated x-ray and optical tomography imaging system, including the respective CBCT and optical tomography system calibration and the geometrical calibration of the entire system. The method can be modified and adopted to calibrate CBCT and optical tomography systems that are operated independently or hybrid x-ray and optical tomography imaging systems.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Edema and Seed Displacements Affect Intraoperative Permanent Prostate Brachytherapy Dosimetry

Purpose: We sought to identify the intraoperative displacement patterns of seeds and to evaluate the correlation of intraoperative dosimetry with day 30 for permanent prostate brachytherapy. Methods and Materials: We analyzed the data from 699 patients. Intraoperative dosimetry was acquired using transrectal ultrasonography (TRUS) and C-arm cone beam computed tomography (CBCT). Intraoperative dosimetry (minimal dose to 40%-95% of the volume [D{sub 40}-D{sub 95}]) was compared with the day 30 dosimetry for both modalities. An additional edema-compensating comparison was performed for D{sub 90}. Stranded seeds were linked between TRUS and CBCT using an automatic and fast linking procedure. Displacement patterns were analyzed for each seed implantation location. Results: On average, an intraoperative (TRUS to CBCT) D{sub 90} decline of 10.6% ± 7.4% was observed. Intraoperative CBCT D{sub 90} showed a greater correlation (R{sup 2} = 0.33) with respect to Day 30 than did TRUS (R{sup 2} = 0.17). Compensating for edema, the correlation increased to 0.41 for CBCT and 0.38 for TRUS. The mean absolute intraoperative seed displacement was 3.9 ± 2.0 mm. The largest seed displacements were observed near the rectal wall. The central and posterior seeds showed less caudal displacement than lateral and anterior seeds. Seeds that were implanted closer to the base showed more divergence than seeds close to the apex. Conclusions: Intraoperative CBCT D{sub 90} showed a greater correlation with the day 30 dosimetry than intraoperative TRUS. Edema seemed to cause most of the systematic difference between the intraoperative and day 30 dosimetry. Seeds near the rectal wall showed the most displacement, comparing TRUS and CBCT, probably because of TRUS probe–induced prostate deformation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Low Cerebral Blood Volume Identifies Poor Outcome in Stent Retriever Thrombectomy

BackgroundMechanical thrombectomy (MT) is an efficient treatment of acute stroke caused by large-vessel occlusion. We evaluated the factors predicting poor clinical outcome (3-month modified Rankin Scale, mRS >2) although MT performed with modern stent retrievers.MethodsWe prospectively collected the clinical and imaging data of 105 consecutive anterior circulation stroke patients who underwent MT after multimodal CT imaging. Patients with occlusion of the internal carotid artery and/or middle cerebral artery up to the M2 segment were included. We recorded baseline clinical, procedural and imaging variables, technical outcome, 24-h imaging outcome and the clinical outcome. Differences between the groups were studied with appropriate statistical tests and binary logistic regression analysis.ResultsLow cerebral blood volume Alberta stroke program early CT score (CBV-ASPECTS) was associated with poor clinical outcome (median 7 vs. 9, p = 0.01). Lower collateral score (CS) significantly predicted poor outcome in regression modelling with CS = 0 increasing the odds of poor outcome 4.4-fold compared to CS = 3 (95% CI 1.27–15.5, p = 0.02). Lower CBV-ASPECTS significantly predicted poor clinical outcome among those with moderate or severe stroke (OR 0.82, 95% CI 0.68–1, p = 0.05) or poor collateral circulation (CS 0–1, OR 0.66, 95% CI 0.48–0.90, p = 0.009) but not among those with mild strokes or good collaterals.ConclusionsCBV-ASPECTS estimating infarct core is a significant predictor of poor clinical outcome among anterior circulation stroke patients treated with MT, especially in the setting of poor collateral circulation and/or moderate or severe stroke.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Percutaneous ureteral biopsy: safety and diagnostic yield

Purpose: To evaluate safety and diagnostic yield of percutaneous CT-guided biopsy of extrarenal upper urinary tract lesions. Materials and methods: Retrospective review of our institutional database of image-guided biopsies yielded 44 CT-guided percutaneous biopsies in 44 unique patients that targeted ureteral (30, 68%) or other non-renal upper urinary tract lesions (14, 32%) between January 1, 2000 and May 1, 2017. Indications, pre-biopsy imaging, biopsy technique, peri-procedural antithrombotic use, complications including bleeding defined by Society of Interventional Radiology criteria, pathology results, and subsequent imaging were reviewed up to 3 months after the procedure to evaluate safety and diagnostic yield. Results: Mean patient age was 66 (range 27–88) and 23/44 patients were male. The majority (34/44) of lesions were sampled with an 18-gauge biopsy device via a 17-gauge introducer needle, and the remaining 10/44 lesions were sampled with a 19/20 gauge system. The mean number of core samples obtained was 4 (range 2–10). No major complications occurred. Specifically, no patient developed a urine leak or urinary obstruction. Minor complications occurred in 3/44 (7%) biopsies, all retroperitoneal hemorrhages that did not require transfusion or other intervention. Biopsy was adequate for pathologic examination in 41 of 44 (93%) cases. Among patients undergoing surgical resection, biopsy diagnosis was concordant with surgical pathology in 9/10 (90%) cases and discordant in 1/10 (10%). Conclusion: CT-guided percutaneous biopsy of upper urinary tract lesions can be performed safely, with high diagnostic yield, and with a high rate of concordance on subsequent surgical pathology.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

WE-G-BRA-06: Application of Systems and Control Theory-Based Hazard Analysis to Radiotherapy

Purpose: The process of delivering radiation occurs in a complex socio-technical system heavily reliant on human operators. Furthermore, both humans and software are notoriously challenging to account for in traditional hazard analysis models. High reliability industries such as aviation have approached this problem through using hazard analysis techniques grounded in systems and control theory. The purpose of this work is to apply the Systems Theoretic Accident Model Processes (STAMP) hazard model to radiotherapy. In particular, the System-Theoretic Process Analysis (STPA) approach is used to perform a hazard analysis of a proposed on-line adaptive cranial radiosurgery procedure that omits the CT Simulation step and uses only CBCT for planning, localization, and treatment. Methods: The STPA procedure first requires the definition of high-level accidents and hazards leading to those accidents. From there, hierarchical control structures were created followed by the identification and description of control actions for each control structure. Utilizing these control structures, unsafe states of each control action were created. Scenarios contributing to unsafe control action states were then identified and translated into system requirements to constrain process behavior within safe boundaries. Results: Ten control structures were created for this new CBCT-only process which covered the areas of hospital and department management, treatment design and delivery, and vendor service. Twenty three control actions were identified that contributed to over 80 unsafe states of those control actions resulting in over 220 failure scenarios. Conclusion: The interaction of people, hardware, and software are highlighted through the STPA approach. STPA provides a hierarchical model for understanding the role of management decisions in impacting system safety so that a process design requirement can be traced back to the hazard and accident that it is intended to mitigate. Varian Medical Systems, Inc.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

First-principles Hubbard U approach for small molecule binding in metal-organic frameworks

We apply first-principles approaches with Hubbard U corrections for calculation of small molecule binding energetics to open-shell transition metal atoms in metal-organic frameworks (MOFs). Using density functional theory with van der Waals dispersion-corrected functionals, we determine Hubbard U values ab initio through an established linear response procedure for M-MOF-74, for a number of different metal centers (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). While our ab initio U values differ from those used in previous work, we show that they result in lattice parameters and electronic contributions to CO{sub 2}-MOF binding energies that lead to excellent agreement with experiments and previous results, yielding lattice parameters within 3%. In addition, U-dependent calculations for an example system, Co-MOF-74, suggest that the CO{sub 2} binding energy grows monotonically with the value of Hubbard U, with the binding energy shifting 4 kJ/mol (or 0.041 eV) over the range of U = 0-5.4 eV. These results provide insight into an approximate but computationally efficient means for calculation of small molecule binding energies to open-shell transition metal atoms in MOFs and suggest that the approach can be predictive with good accuracy, independent of the cations used and the availability of experimental data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

TU-D-209-02: A Backscatter Point Spread Function for Entrance Skin Dose Determination

Purpose: To determine the distribution of backscattered radiation to the skin resulting from a non-uniform distribution of primary radiation through convolution with a backscatter point spread function (PSF). Methods: A backscatter PSF is determined using Monte Carlo simulation of a 1 mm primary beam incident on a 30 × 30 cm × 20 cm thick PMMA phantom using EGSnrc software. A primary profile is similarly obtained without the phantom and the difference from the total provides the backscatter profile. This scatter PSF characterizes the backscatter spread for a “point” primary interaction and can be convolved with the entrance primary dose distribution to obtain the total entrance skin dose. The backscatter PSF was integrated into the skin dose tracking system (DTS), a graphical utility for displaying the color-coded skin dose distribution on a 3D graphic of the patient during interventional fluoroscopic procedures. The backscatter convolution method was validated for the non-uniform beam resulting from the use of an ROI attenuator. The ROI attenuator is a copper sheet with about 20% primary transmission (0.7 mm thick) containing a circular aperture; this attenuator is placed in the beam to reduce dose in the periphery while maintaining full dose in the region of interest. The DTS calculated primary plus backscatter distribution is compared to that measured with GafChromic film and that calculated using EGSnrc Monte-Carlo software. Results: The PSF convolution method used in the DTS software was able to account for the spread of backscatter from the ROI region to the region under the attenuator. The skin dose distribution determined using DTS with the ROI attenuator was in good agreement with the distributions measured with Gafchromic film and determined by Monte Carlo simulation Conclusion: The PSF convolution technique provides an accurate alternative for entrance skin dose determination with non-uniform primary x-ray beams. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Improved Modelling for the Assembly Discontinuity Factors in the APEC Method

Modern reactor analysis of light water reactor depends largely on a two-step procedure based on the simplified equivalence theory (SET). Consequently, the resulting homogenized two-group cross-section (XS) and associated discontinuity factor (DF) are subject to noticeable, intrinsic uncertainties. In our previous study, we introduced the albedo-corrected parameterized equivalence constants (APEC) method, which is a new leakage correction method applicable to the fuel assembly homogenized two-group XS of the standard two-step procedure. In the APEC method, fuel assembly two-group XS is expressed as a simple polynomial function of assembly-wise current-to-flux ratio (CFR), and it was demonstrated that two-group XSs can be well corrected during a nodal calculation and the nodal accuracy is improved a lot. However, since the conventional assembly discontinuity factor (ADF) is still used in the current APEC method, a small but non-negligible error is unavoidable. Therefore, it is necessary to include improved DF model in the APEC method for a higher accuracy. The functionalized discontinuity factor (FDF) using the definition of CFR was investigated by authors before the development of the APEC method, where it was motivated by the boundary perturbation theory by F. Rahnema. However, in our previous study on FDF, lattice calculations were performed only with one-dimensional two-group diffusion equation and could not be applied to actual core analysis. In this paper, feasibility study of DF functionalization is performed based on a 2-D method of characteristics (MOC) lattice code, DeCART2D.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Robust and efficient overset grid assembly for partitioned unstructured meshes

This paper presents a method to perform efficient and automated Overset Grid Assembly (OGA) on a system of overlapping unstructured meshes in a parallel computing environment where all meshes are partitioned into multiple mesh-blocks and processed on multiple cores. The main task of the overset grid assembler is to identify, in parallel, among all points in the overlapping mesh system, at which points the flow solution should be computed (field points), interpolated (receptor points), or ignored (hole points). Point containment search or donor search, an algorithm to efficiently determine the cell that contains a given point, is the core procedure necessary for accomplishing this task. Donor search is particularly challenging for partitioned unstructured meshes because of the complex irregular boundaries that are often created during partitioning. Another challenge arises because of the large variation in the type of mesh-block overlap and the resulting large load imbalance on multiple processors. Desirable traits for the grid assembly method are efficiency (requiring only a small fraction of the solver time), robustness (correct identification of all point types), and full automation (no user input required other than the mesh system). Additionally, the method should be scalable, which is an important challenge due to the inherent load imbalance. This paper describes a fully-automated grid assembly method, which can use two different donor search algorithms. One is based on the use of auxiliary grids and Exact Inverse Maps (EIM), and the other is based on the use of Alternating Digital Trees (ADT). The EIM method is demonstrated to be more efficient than the ADT method, while retaining robustness. An adaptive load re-balance algorithm is also designed and implemented, which considerably improves the scalability of the method.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Integration of Heat Transfer, Stress, and Particle Trajectory Simulation

Calabazas Creek Research, Inc. developed and currently markets Beam Optics Analyzer (BOA) in the United States and abroad. BOA is a 3D, charged particle optics code that solves the electric and magnetic fields with and without the presence of particles. It includes automatic and adaptive meshing to resolve spatial scales ranging from a few millimeters to meters. It is fully integrated with CAD packages, such as SolidWorks, allowing seamless geometry updates. The code includes iterative procedures for optimization, including a fully functional, graphical user interface. Recently, time dependent, particle in cell capability was added, pushing particles synchronically under quasistatic electromagnetic fields to obtain particle bunching under RF conditions. A heat transfer solver was added during this Phase I program. Completed tasks include: (1) Added a 3D finite element heat transfer solver with adaptivity; (2) Determined the accuracy of the linear heat transfer field solver to provide the basis for development of higher order solvers in Phase II; (3) Provided more accurate and smoother power density fields; and (4) Defined the geometry using the same CAD model, while maintaining different meshes, and interfacing the power density field between the particle simulator and heat transfer solvers. These objectives were achieved using modern programming techniques and algorithms. All programming was in C++ and parallelization in OpenMP, utilizing state-of-the-art multi-core technology. Both x86 and x64 versions are supported. The GUI design and implementation used Microsoft Foundation Class.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

TU-C-17A-01: A Data-Based Development for Pratical Pareto Optimality Assessment and Identification

Purpose: To develop an efficient Pareto optimality assessment scheme to support plan comparison and practical determination of best-achievable practical treatment plan goals. Methods: Pareto efficiency reflects the tradeoffs among competing target coverage and normal tissue sparing in multi-criterion optimization (MCO) based treatment planning. Assessing and understanding Pareto optimality provides insightful guidance for future planning. However, current MCO-driven Pareto estimation makes relaxed assumptions about the Pareto structure and insufficiently account for practical limitations in beam complexity, leading to performance upper bounds that may be unachievable. This work proposed an alternative data-driven approach that implicitly incorporates the practical limitations, and identifies the Pareto frontier subset by eliminating dominated plans incrementally using the Edgeworth Pareto hull (EPH). The exactness of this elimination process also permits the development of a hierarchical procedure for speedup when the plan cohort size is large, by partitioning the cohort and performing elimination in each subset before a final aggregated elimination. The developed algorithm was first tested on 2D and 3D where accuracy can be reliably assessed. As a specific application, the algorithm was applied to compare systematic plan quality for lower head-and-neck, amongst 4 competing treatment modalities. Results: The algorithm agrees exactly with brute-force pairwise comparison and visual inspection in low dimensions. The hierarchical algorithm shows sqrt(k) folds speedup with k being the number of data points in the plan cohort, demonstrating good efficiency enhancement for heavy testing tasks. Application to plan performance comparison showed superiority of tomotherapy plans for the lower head-and-neck, and revealed a potential nonconvex Pareto frontier structure. Conclusion: An accurate and efficient scheme to identify Pareto frontier from a plan cohort has been developed. This implementation would guide generating good yet practically achievable plan quality goals for further planning. The observation of a systematic performance bias and a nonconvex Pareto frontier warrants further investigation.

60 APPLIED LIFE SCIENCES↗