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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

TU-H-207A-01: Development of Conversion Factors to Account for Different CTDI Phantom Setups On a Wide-Beam CT Scanner

Purpose: A fundamental measure performed during an annual physics CT evaluation confirms that system displayed CTDIvol nearly matches the independently measured value in phantom. For wide-beam (z-direction) CT scanners, AAPM Report 111 defined an ideal measurement method; however, the method often lacks practicality. The purpose of this preliminary study is to develop a set of conversion factors for a wide-beam CT scanner, relating the CTDIvol measured with a conventional setup (single CTDI phantom) versus the AAPM Report 111 approach (three abutting CTDI phantoms). Methods: For both the body CTDI and head CTDI, two acquisition setups were used: A) conventional single phantom and B) triple phantom. Of primary concern were the larger nominal beam widths for which a standard CTDI phantom setup would not provide adequate scatter conditions. Nominal beam width (160 or 120 mm) and kVp (100, 120, 140) were modulated based on the underlying clinical protocol. Exposure measurements were taken using a CT pencil ion chamber in the center and 12 o’clock position, and CTDIvol was calculated with ‘nT’ limited to 100 mm. A conversion factor (CF) was calculated as the ratio of CTDIvol measured in setup B versus setup A. Results: For body CTDI, the CF ranged from 1.04 up to 1.10, indicating a 4–10% difference between usage of one and three phantoms. For a nominal beam width of 160 mm, the CF did vary with selected kVp. For head CTDI at nominal beam widths of 120 and 160 mm, the CF was 1.00 and 1.05, respectively, independent of the kVp used (100, 120, and 140). Conclusions: A clear understanding of the manufacturer method of estimating the displayed CTDIvol is important when interpreting annual test results, as the acquisition setup may lead to an error of up to 10%. With appropriately defined CF, single phantom use is feasible.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

WE-H-202-03: Accounting for Large Geometric Changes During Radiotherapy

Deformable image registration has now been commercially available for several years, with solid performance in a number of sites and for several applications including contour and dose mapping. However, more complex applications have arisen, such as assessing response to radiation therapy over time, registering images pre- and post-surgery, and auto-segmentation from atlases. These applications require innovative registration algorithms to achieve accurate alignment. The goal of this session is to highlight emerging registration technology and these new applications. The state of the art in image registration will be presented from an engineering perspective. Translational clinical applications will also be discussed to tie these new registration approaches together with imaging and radiation therapy applications in specific diseases such as cervical and lung cancers. Learning Objectives: To understand developing techniques and algorithms in deformable image registration that are likely to translate into clinical tools in the near future. To understand emerging imaging and radiation therapy clinical applications that require such new registration algorithms. Research supported in part by the National Institutes of Health under award numbers P01CA059827, R01CA166119, and R01CA166703. Disclosures: Phillips Medical systems (Hugo), Roger Koch (Christensen) support, Varian Medical Systems (Brock), licensing agreements from Raysearch (Brock) and Varian (Hugo).; K. Brock, Licensing Agreement - RaySearch Laboratories. Research Funding - Varian Medical Systems; G. Hugo, Research grant from National Institutes of Health, award number R01CA166119.; G. Christensen, Research support from NIH grants CA166119 and CA166703 and a gift from Roger Koch. There are no conflicts of interest.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TH-CD-209-04: Fuzzy Robust Optimization in Intensity-Modulated Proton Therapy Planning to Account for Range and Patient Setup Uncertainties

Purpose: We propose to apply a robust optimization model based on fuzzy-logic constraints in the intensity-modulated proton therapy (IMPT) planning subject to range and patient setup uncertainties. The purpose is to ensure the plan robustness under uncertainty and obtain the best trade-off between tumor dose coverage and organ-at-risk(OAR) sparing. Methods: Two IMPT plans were generated for 3 head-and-neck cancer patients: one used the planning target volume(PTV) method; the other used the fuzzy robust optimization method. In the latter method, nine dose distributions were computed - the nominal one and one each for ±3mm setup uncertainties along three cardinal axes and for ±3.5% range uncertainty. For tumors, these nine dose distributions were explicitly controlled by adding hard constraints with adjustable parameters. For OARs, fuzzy constraints that allow the dose to vary within a certain range were used so that the tumor dose distribution was guaranteed by minimum compromise of that of OARs. We rendered this model tractable by converting the fuzzy constraints to linear constraints. The plan quality was evaluated using dose-volume histogram(DVH) indices such as tumor dose coverage(D95%), homogeneity(D5%-D95%), plan robustness(DVH band at D95%), and OAR sparing like D1% of brain and D1% of brainstem. Results: Our model could yield clinically acceptable plans. The fuzzy-logic robust optimization method produced IMPT plans with comparable target dose coverage and homogeneity compared to the PTV method(unit: Gy[RBE]; average[min, max])(CTV D95%: 59 [52.7, 63.5] vs 53.5[46.4, 60.1], CTV D5% - D95%: 11.1[5.3, 18.6] vs 14.4[9.2, 21.5]). It also generated more robust plans(CTV DVH band at D95%: 3.8[1.2, 5.6] vs 11.5[6.2, 16.7]). The parameters of tumor constraints could be adjusted to control the tradeoff between tumor coverage and OAR sparing. Conclusion: The fuzzy-logic robust optimization generates superior IMPT with minimum compromise of OAR sparing. This research was supported by the National Cancer Institute Career Developmental Award K25CA168984, by the Fraternal Order of Eagles Cancer Research Fund Career Development Award, by The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, by Mayo Arizona State University Seed Grant, and by The Kemper Marley Foundation. eRA Person ID(s) for the Principal Investigator: 11017970 (Research Supported by National Institutes of Health)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Algorithm and program for precise determination of unit-cell parameters of single crystal taking into account the sample eccentricity

A technique has been developed to refine the unit-cell parameters of single crystals with minimization of the influence of instrumental errors on the result. The corresponding computational procedure HuberUB is added to the software package of Huber-5042 diffractometer with a point detector and closedcycle helium cryostat Displex DE-202. The parameters of unit cell, its orientation, the goniometer zero angles, the sample eccentricity, the distances in the goniometer, and the radiation wavelength were refined by the nonlinear least-squares method, which allows imposition of constraints on the unit-cell parameters, depending on the crystal symmetry. The technique is approved on a LuB{sub 12} single crystal. The unit-cell parameters are determined in a temperature range of 20–295 K, with an absolute error not larger than 0.0004 Å (the relative error is of ~5 × 10{sup –5}). The estimates of the unit-cell parameters obtained by the proposed method are evidenced to be unbiased. Some specific features of the behavior of parameters in the ranges of 120–140 and 20–50 K are revealed, which correlate with the anomalies of the physical properties of the crystal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

On the Problem of Thermonuclear Ignition and Burning in the NIF Laser: Ignition with Capsules Taking into Account the Influence of the Hohlraum Radiation on Implosion

One of the significant problems of modern physics is the creation and use of new energy sources. The decisive step in this direction is the realization of a positive yield in thermonuclear energy on a laboratory scale with the facilities that create and retain plasma. Between 2010 and 2017, a large series of experiments were performed at the National Ignition Facility laser at the Livermore Laboratory in the United States with the aim of achieving such a positive outcome. Until now, however, the ignition has not been reached. In this paper, for the first time the influence of the hohlraum radiation on capsule layers including a deuterium–tritium layer is discussed. It is shown that the negative influence of the ablator transparency can be compensated for by the selection of a capsule design with a greater optical thickness of the part of the ablator. This part of the ablator is not evaporated upon heating by an X-ray pulse. The design of such a capsule is proposed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Theoretical Analysis of the EPR Spectrum Saturation Effect with Account for Spectral Diffusion in a System with a Gaussian Distribution of Spin Resonance Frequencies

We have analyzed the effect of saturation of the EPR spectrum for the model situation when a set of resonance frequencies of spin packets is described by a Gaussian distribution and spectral diffusion, which is a random process without correlation, exists. We have obtained the form of the spectrum for arbitrary values of magnetic–resonant parameters: relaxation times for the longitudinal and transverse components of the magnetization vector of the system, the spectral diffusion rate, the dispersion of the Gaussian distribution of resonance frequency, and the magnetic induction of the microwave field. We have derived an analytic expression for the saturation curve of the EPR spectrum. Detailed analysis of the dependence of the spectrum saturation curve on the spin system parameters is performed for the optimal case when the microwave field frequency coincides with the average frequency of the Gaussian distribution for resonance frequencies. The value of the microwave field induction at which the peak of the saturation curve is attained has been determined for arbitrary values of the paramagnetic relaxation time, spectral diffusion rate, and dispersion of the Gaussian spin frequency distribution. We have formulated the algorithm for determining the spin–lattice relaxation time using the experimentally determined microwave field induction for which the saturation curve passes through the peak. It should be noted that numerical calculations have been performed for parameters typical of EPR spectroscopy. The general analytic expression derived for the shape of the spectrum in the saturation conditions and qualitative conclusions concerning the effect of spectral diffusion on the saturation of stationary spectra obtained in this study can also be used in other fields of spectroscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Analysis of the dispersion relation for resistive wall modes in tokamaks with account of the skin effect

The accuracy of the dispersion relations derived earlier analytically for the resistive wall modes (RWMs) in tokamaks is evaluated. Existing models use the expansions in the ratio of the wall thickness d{sub w} to the skin depth s. This parameter is small in the standard theory of 'slow' RWMs, but it is large in the recently developed approach for the 'fast' RWMs. Here, a dispersion relation applicable not only to these extreme cases, but also to the intermediate range is derived in the single-mode cylindrical approximation without restrictions on s/d{sub w}. The derived equation is solved numerically, the result is compared with the predictions of the earlier analytical models with either s Much-Greater-Than d{sub w} or s Much-Less-Than d{sub w}. The applicability limits of the asymptotic expressions for the RWM growth rate are clarified. In particular, the limits are specified in which their error does not exceed 10%. It is shown that these expressions always underestimate the growth rate. The study confirms the necessity of the skin effect incorporation in the description of RWM dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Modeling of the rotational stabilization of tokamak plasmas with account of skin effect in the resistive wall

The influence of the Resistive Wall Mode (RWM) rotation on its stability in tokamaks is analyzed. Recently developed analytical theory [V. D. Pustovitov, Phys. Plasmas 19, 062503 (2012)] predicts that, when the skin depth s becomes much smaller than the wall thickness d{sub w}, the resistive dissipation in the wall in combination with the mode rotation stabilizes the mode up to complete suppression of instability. Here this effect is studied without the restriction on the ratio s/d{sub w}. Thereby the applicability of analytical predictions and accuracy of asymptotic expressions relating the growth rate to the rotation frequency of RWM is clarified. The dispersion relation for the rotating modes is derived in the single-mode cylindrical approximation and solved numerically. It is shown that the rotational stabilization of the plasma, the same as found earlier, is possible even at s/d{sub w} of the order unity if the mode rotation frequency is above a critical level. The dependences of the growth rate on the mode frequency are calculated for different plasma parameters. It is shown that, at a given plasma state with a linear response to external perturbations, the growth rate of the mode is maximal at the mode locking (when the rotation is lost). The relation of the mode minimal rotation frequency at the stability boundary with the growth rate at the mode locking is found. The analysis demonstrates strong influence of dissipation in the wall on the dynamics of rotating and locked RWMs and confirms the necessity to incorporate the skin effect into their description. The obtained estimates allow one to compare these predictions with experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This work applies a multiscale mechanistic damage model developed for brittle ceramics and implemented in commercial finite element (FE) packages via user subroutines to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under normal operating and shutdown conditions including redox effects. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. The volumetric “swelling” that occurs during redox is treated in constitutive modeling similarly to thermal expansion, but swelling strains are irreversible. Furthermore, this damage model was first validated through predictions of strength and stress-strain response for the SOFC electrode materials. Next, it has been applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells. Multicell stack models were simulated in both co-flow and counter-flow configurations. In addition, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the nickel (Ni)-based anode in the anode-supported cells.

25 ENERGY STORAGE↗
DOE OSTI2015

A Full-Core Resonance Self-Shielding Method Using a Continuous-Energy Quasi–One-Dimensional Slowing-Down Solution that Accounts for Temperature-Dependent Fuel Subregions and Resonance Interference

In this paper, a correction-based resonance self-shielding method is developed that allows annular subdivision of the fuel rod. The method performs the conventional iteration of the embedded self-shielding method (ESSM) without subdivision of the fuel to capture the interpin shielding effect. The resultant self-shielded cross sections are modified by correction factors incorporating the intrapin effects of radial variation of the shielded cross section, radial temperature distribution, and resonance interference. A quasi–one-dimensional slowing-down equation is developed to calculate such correction factors. The method is implemented in the DeCART code and compared with the conventional ESSM and subgroup method with benchmark MCNP results. The new method yields substantially improved results for both spatially dependent reaction rates and eigenvalues for typical pressurized water reactor pin cell cases with uniform and nonuniform fuel temperature profiles. Finally, the new method is also proved effective in treating assembly heterogeneity and complex material composition such as mixed oxide fuel, where resonance interference is much more intense.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

Identification of Amino Acids that Account for Long-Range Interactions in Two Triosephosphate Isomerases from Pathogenic Trypanosomes

For a better comprehension of the structure-function relationship in proteins it is necessary to identify the amino acids that are relevant for measurable protein functions. Because of the numerous contacts that amino acids establish within proteins and the cooperative nature of their interactions, it is difficult to achieve this goal. Thus, the study of protein-ligand interactions is usually focused on local environmental structural differences. Here, using a pair of triosephosphate isomerase enzymes with extremely high homology from two different organisms, we demonstrate that the control of a seventy-fold difference in reactivity of the interface cysteine is located in several amino acids from two structurally unrelated regions that do not contact the cysteine sensitive to the sulfhydryl reagent methylmethane sulfonate, nor the residues in its immediate vicinity. The change in reactivity is due to an increase in the apparent pKa of the interface cysteine produced by the mutated residues. Our work, which involved grafting systematically portions of one protein into the other protein, revealed unsuspected and multisite long-range interactions that modulate the properties of the interface cysteines and has general implications for future studies on protein structure-function relationships.

59 BASIC BIOLOGICAL SCIENCES↗