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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The Submillimeter Wave Astronomy Satellite

The Submillimeter Wave Astronomy Satellite (SWAS) mission is dedicated to the study of star formation and interstellar chemistry. To carry out this mission, SWAS will survey dense (n(sub H2) greater than 10(exp 3) cm(exp -3)) molecular clouds within our galaxy in either the ground-state of a low-lying transition of five astrophysically important species: H2O, H2O-18, O2, CI, and CO-13. By observing these lines SWAS will: (1) test long-standing theories that predict that these species are the dominant coolants of molecular clouds during the early stages of their collapse to form stars and planets, and (2) supply heretofore missing information about the abundanceof key species central to the chemical models of dense interstellar gas. SWAS will employ two independent Schottky barrier diode mixers, passively cooled to approx. 150 K, coupled to a highly efficient 54 x 68 cm off-axis Cassegrain antenna. During its two year mission, SWAS will observe giant and dark cloud cores with the goal of detecting or setting an upper limit on the water abundance of 3 x 10(exp -6) and on th molecular oxygen abundances of 2 x 10(exp -6), both relative to H2. In addition, advantage will be taken of SWAS's relatively large beamsize of 3.2 x 4.0 arcminutes at 551 GHz and 3.6 x 4.5 arcminutes at 492 GHz to obtain large-area (approx. 1 deg x 1 deg) maps of giant and dark clouds in the CO-13 and CI lines. SWAS is scheduled for launch in mid-1995.

Melnick, Gary J.↗
DOE OSTI2015

SU-E-P-55: The Reaserch of Cervical Cancer Delivered with Constant Dose Rate and Gantry Speed Arc Therapy(CDR-CAS-IMAT) On Conventional Linac

Purpose: Postoperative cervical cancer patients with large target volume and the target shape is concave, treatmented with static intensity-modulated radiotherapy (IMRT) is time consuming. The purpose of this study is to investigate using constant dose rate and gantry speed arc therapy(CDR-CAS-IMAT) on conventional linear accelrator, by comparing with the IMRT technology to evaluate the performance of CDR-CAS-IMAT on postoperative cervical cancer patients. Methods: 18 cervical cancer patients treated with IMRT on Varian 23IX were replanted using CDR-CAS-IMAT. The plans were generated on Oncentra v4.1 planning system, PTV was prescribed to 50.4 Gy in 28 fractions. Plans were evaluated based on the ability to meet the dose volume histogram. The homogeneity index (HI), conformity index (CI) of target volume, the dose of organs at risk, radiation delivery time and monitor units were also compared. SPSS 19.0 software paired T-test analysis was carried out on the two sets of data. Results: Compared with the IMRT plans PTV’s CI (t= 3.85, P =0.001), CTV’s CI, HI, D90, D95, D98, V95, V98, V100 (t=4.21, −3.18, 2.13, 4.65, 7.79, 2.29, 6.00, 2.13, p=0.001, 0.005, 0.049, 0.000, 0.000, 0.035, 0.000, 0.049), and cord D2 and rectum V40 (t=−2.65, −2.47, p= P =0.017, 0.025), and treatment time and MU (t=−36.0, −6.26, P =0.000, 0.000) were better than that of IMRT group. But the IMRT plans in terms of decreasing bladder V50, bowel V30 (t=2.14, 3.00, P =0.048, 0.008) and low dose irradiation volume were superior to that of CDR-CAS-IMAT plans. There were no significant differences in other statistical index. Conclusion: Cervical cancer patients with CDR-CAS-IMAT on Varian Clinical 23IX can get equivalent or superior dose distribution compared with the IMRT technology. IMAT have much less treatment time and MU can reduce the uncertainty factor and patient discomfort in treatment. This work was supported by the Medical Science Foundation of the health department of Hebei Province (No. 20130253)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Rapidly Viable Sustained Grid

Rapid recovery of power flow, possibly after a blackout, is a crucial need arising in scenarios that are increasingly becoming more frequent; here, solutions for rapid viability of power while the grid is being restored are urgently needed to keep critical infrastructure (CI) online. Increasingly, after the initial recovery phase, sustenance of reliable power requires assistive services to the grid for long periods of time. Even though the need is urgent, there is only sparse effort present toward a comprehensive framework/strategy for making power rapidly viable with an emphasis on sustained grid ancillary services; which is the focus of this proposal. The proposed concept envisions four phases. In the first phase, when a large portion of power is disrupted (see Figure 1(a)), emphasis is on bringing CI online with the objective of maximizing the time horizon of power viability using resources available at the CI. In the second phase (Figure 1(b)), neighborhood resources are tightly coordinated that forms the CI’s central-core (CC) to provide guaranteed viability of CI over a longer horizon. In the third phase, self-organizing power networks are expanded in a distributed layer supporting the central-core (Figure 1(c)). In the fourth phase, separate CI-networks coalesce and are controlled in a coordinated fashion to provide grid ancillary services (AS), such as primary frequency control and enhancing grid resiliency. With time, system efficiencies and penetration of renewables increase, while the time-horizon of guaranteed sustenance of CI is maximized. Under proposed work, the concept will be instantiated with a focus on medical centers as CI. Comprehensive power hardware in the loop strategies and emulated field tests will guide and validate devised solutions. A strong T2M effort to commercialize resulting technology is outlined. The proposed technology will be transformative for the grid. It will fundamentally change the way large contingencies are managed where power systems and critical infrastructure transition from being fragile to being robust using intelligent, self-organizing control for coordinating resources, enhanced resiliency and use of sustainable energy sources.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS2013

Investigation of Sideband Index Response to Prototype Gear Tooth Damage

The objective of this analysis was to evaluate the ability of gear condition indicators (CI) to detect contact fatigue damage on spiral bevel gear teeth. Tests were performed in the NASA Glenn Spiral Bevel Gear Fatigue Rig on eight prototype gear sets (pinion/gear). Damage was initiated and progressed on the gear and pinion teeth. Vibration data was measured during damage progression at varying torque values while varying damage modes to the gear teeth were observed and documented with inspection photos. Sideband indexes (SI) and root mean square (RMS) CIs were calculated from the time synchronous averaged vibration data. Results found that both CIs respond differently to varying torque levels, damage levels and damage modes

health monitoring↗
DOE OSTI2014

An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster–configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2{sup ′}-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

SU-E-T-355: A Comparative Study of Robotic and Linac-Based Stereotactitc Body Radiation Therapy for Lumbar Spinal Tumors

Purpose: Dosimetrically compare CyberKnife (CK) and linac-based (LB) stereotactic body radiotherapy (SBRT) plans for lumbar spine. Methods: Ten patient plans with lumbar spine tumors treated with CK were selected and retrospectively optimized using three techniques: CK, volumetric modulated arc (VMAT, three arcs), and 9-field-intensity modulated radiotherapy (IMRT). For the LB plans, the target volume was expanded by 1mm to accommodate additional uncertainty in patient positioning. All plans were optimized to a prescription dose of 27Gy in 3 fractions covering 90% of the PTV. If the dose constraints to the cauda equina (cauda) were not met, the prescription dose was lowered to 24Gy. Parameters evaluated included Paddick Conformity-Index (CI) and Gradient-Index (GI). A two-tailed paired t-test was used to establish statistically significant differences in cauda doses. Results: Target volumes for LB plans were on average 38% larger. In terms of the indices, the closer the index values to unity the steeper the dose falloff and the higher the dose conformity to the target. The results showed that LB plans were in general statistically superior to CK plans. The IMRT plan showed the best average gradient index of 2.995, with VMAT and CK GI values of 3.699 and 5.476, respectively. Similarly, the same trend occurs with the average CI results: 0.821, 0.814, and 0.758, corresponding to IMRT, VMAT, and CK. Notably, in one CK plan the target dose was reduced to 24Gy to meet cauda constraints. Additionally, there was a statistically significant dose difference for the cauda between the CK and LB plans. Conclusion: This study demonstrates that LB plans for lumbar spine SBRT can be as effective or even better than CK plans. Despite the expansion of the target volume, the LB plans did not demonstrate dosimetric inferiority. The LB plans Resultin 2-to-3 fold decrease of treatment time.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Field-in-field plan does not improve the dosimetric outcome compared with the wedged beams plan for breast cancer radiotherapy

To evaluate and compare the dosimetry of field-in-field (FIF) and wedged beams (WB) techniques for patients with breast cancer receiving adjuvant radiotherapy after conservative surgery. A total of 89 patients with breast cancer participated in this study. Each patient received a computed tomography–based treatment plan with opposed tangential fields. Two planning techniques (FIF and WB) were generated for each patient by using the Pinnacle treatment-planning system. Three indices, the homogeneity index (HI), conformity index (CI), and uniformity index (UI), as well as maximum dose (D{sub max}), median dose (D{sub 50}), number of portals, monitor unit (MU), and lung volume at 20 Gy (lung{sub 20}) were used for comparison. The mean values tested using a t-test indicated that the WB technique had a significantly lower HI (p < 0.0001), a significantly higher CI (p < 0.0001), and a significantly higher D{sub 50} (p = 0.0002) than did the FIF technique. The FIF technique had a significantly higher D{sub max} compared with the WB technique, but lung{sub 20} did not exhibit a significant difference. By contrast, the FIF technique had a significantly higher UI and a significantly lower MU compared with the WB technique, but a significantly higher number of portals were found in the FIF technique. The FIF technique did not demonstrate superior dosimetric results. The WB technique had a significantly lower HI, higher CI, lower D{sub max}, and lower number of portals; but the FIF technique had a significantly higher UI and lower MU.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Validation testing of radioactive Cesium measurement in Decontaminated waste with the Scattering Gamma Equivalent Method - 17238

Canberra Industries, Inc. [CI], Now Mirion Technologies (Canberra) Inc. [MTC], has developed and validated a new Flexible Container Bag or Feed Roll Assay System 'FRAS' for Interim Storage Facilities [ISF] etc. There is an estimated 22 million cubic meters of soil and vegetation from the decontamination efforts around Fukushima. Removed soil and vegetation waste was put into flexible containers called Super Sacks [SS]. These SSs will be transported to ISF by trucks. These SSs will be divided into three categories according to total Cs radioactivity level (RL). This level is 'higher than 100,000 Bq/kg', '100,000>RL>8,000 Bq/kg' and '8,000 > RL >3,000 Bq/kg', respectively. The main uncertainty for SS measuring is internal inhomogeneity and heterogeneous source distribution. Japan Atomic Energy Agency [JAEA] has developed the Scattering Gamma Equivalent Model [SGE model] for decreasing uncertainty derived from these factors. This method was validated by Mirion Technologies (Canberra) KK [MCKK] and JAEA. According to the validation test, the SGE model can reduce the uncertainty of SS measurement from ± 25% to ± less than 15%. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2012

Internal Structure and Mineralogy of Differentiated Asteroids Assuming Chondritic Bulk Composition: The Case of Vesta

Bulk composition (including oxygen content) is a primary control on the internal structure and mineralogy of differentiated asteroids. For example, oxidation state will affect core size, as well as Mg# and pyroxene content of the silicate mantle. The Howardite-Eucrite-Diogenite class of meteorites (HED) provide an interesting test-case of this idea, in particular in light of results of the Dawn mission which provide information on the size, density and differentiation state of Vesta, the parent body of the HED's. In this work we explore plausible bulk compositions of Vesta and use mass-balance and geochemical modelling to predict possible internal structures and crust/mantle compositions and mineralogies. Models are constrained to be consistent with known HED samples, but the approach has the potential to extend predictions to thermodynamically plausible rock types that are not necessarily present in the HED collection. Nine chondritic bulk compositions are considered (CI, CV, CO, CM, H, L, LL, EH, EL). For each, relative proportions and densities of the core, mantle, and crust are quantified. Considering that the basaltic crust has the composition of the primitive eucrite Juvinas and assuming that this crust is in thermodynamic equilibrium with the residual mantle, it is possible to calculate how much iron is in metallic form (in the core) and how much in oxidized form (in the mantle and crust) for a given bulk composition. Of the nine bulk compositions tested, solutions corresponding to CI and LL groups predicted a negative metal fraction and were not considered further. Solutions for enstatite chondrites imply significant oxidation relative to the starting materials and these solutions too are considered unlikely. For the remaining bulk compositions, the relative proportion of crust to bulk silicate is typically in the range 15 to 20% corresponding to crustal thicknesses of 15 to 20 km for a porosity-free Vesta-sized body. The mantle is predicted to be largely dominated by olivine (>85%) for carbonaceous chondrites, but to be a roughly equal mixture of olivine and pyroxene for ordinary chondrite precursors. All bulk compositions have a significant core, but the relative proportions of metal and sulphide can be widely different. Using these data, total core size (metal+ sulphide) and average core densities can be calculated, providing a useful reference frame within which to consider geophysical/gravity data of the Dawn mission.

Toplis, M. J.↗
DOE OSTI2019

Palliative Prostate Artery Embolization for Prostate Cancer: A Case Series

Introduction: Prostate artery embolization (PAE) is recognized as a treatment for lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia. LUTS and urinary retention are common in men with prostate cancer (PCa). The purpose of this study was to estimate the efficacy and safety of palliative PAE on LUTS or urinary retention in men with advanced PCa. Materials and methods: This prospective, single-center trial was conducted from March 2017 to November 2018. The trial protocol was registered online (ClinicalTrials.gov Identifier: NCT03104907). Only men with advanced PCa suffering from LUTS or urinary retention were included. The primary outcome was the ability to void without a catheter and International Prostate Symptom Score (IPSS) in non-catheter-dependent patients. The paired t test was used to analyze changes from baseline with 95% confidence intervals (CI). A p value < 0.05 was considered statistically significant. Results: Seventeen patients were assessed for eligibility, and 15 patients with a mean age of 73.8 years were enrolled. Four men did not complete follow-up: cancer-related death (n = 2), lost to follow-up (n = 1), and unsuccessful embolization due to severe atherosclerosis (n = 1). Bilateral embolization was achieved in ten cases, and urinary retention resolved in one of six patients. LUTS improved in the remaining (n = 5) patients by a mean 12.2-point reduction in IPSS (95% CI − 23.53; − 0.87). According to the CIRSE classification, two grade 1 and two grade 3 complications occurred. Conclusion: In this study, palliative PAE was safe and efficient for treatment for LUTS associated with PCa. Level of Evidence: Level 4, Case Series. Trial registration ClinicalTrials.gov Identifier: NCT03104907.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS2010

Correlate Life Predictions and Condition Indicators in Helicopter Tail Gearbox Bearings

Research to correlate bearing remaining useful life (RUL) predictions with Helicopter Health Usage Monitoring Systems (HUMS) condition indicators (CI) to indicate the damage state of a transmission component has been developed. Condition indicators were monitored and recorded on UH-60M (Black Hawk) tail gearbox output shaft thrust bearings, which had been removed from helicopters and installed in a bearing spall propagation test rig. Condition indicators monitoring the tail gearbox output shaft thrust bearings in UH-60M helicopters were also recorded from an on-board HUMS. The spal-lpropagation data collected in the test rig was used to generate condition indicators for bearing fault detection. A damage progression model was also developed from this data. Determining the RUL of this component in a helicopter requires the CI response to be mapped to the damage state. The data from helicopters and a test rig were analyzed to determine if bearing remaining useful life predictions could be correlated with HUMS condition indicators (CI). Results indicate data fusion analysis techniques can be used to map the CI response to the damage levels.

Dempsey, Paula J.↗
DOE OSTI2023

Evaluation of the excitation spectra with diffusion Monte Carlo on an auxiliary bosonic ground state

We aim to improve upon the variational Monte Carlo (VMC) approach for excitations replacing the Jastrow factor by an auxiliary bosonic (AB) ground state and multiplying it by a fermionic component factor. The instantaneous change in imaginary time of an arbitrary excitation in the original interacting fermionic system is obtained by measuring observables via the ground-state distribution of walkers of an AB system that is subject to an auxiliary effective potential. The effective potential is used to (i) drive the AB system’s ground-state configuration space toward the configuration space of the excitations of the original fermionic system and (ii) subtract from a diffusion Monte Carlo (DMC) calculation contributions that can be included in conventional approximations, such as mean-field and configuration interaction (CI) methods. In this novel approach, the AB ground state is treated statistically in DMC, whereas the fermionic component of the original system is expanded in a basis. The excitation energies of the fermionic eigenstates are obtained by sampling a fermion–boson coupling term on the AB ground state. We show that this approach can take advantage of and correct for approximate eigenstates obtained via mean-field calculations or truncated interactions. We demonstrate that the AB ground-state factor incorporates the correlations missed by standard Jastrow factors, further reducing basis truncation errors. Relevant parts of the theory have been tested in soluble model systems and exhibit excellent agreement with exact analytical data and CI and VMC approaches. In particular, for limited basis set expansions and sufficient statistics, AB approaches outperform CI and VMC in terms of basis size for the same systems. The implementation of this method in current codes, despite being demanding, will be facilitated by reusing procedures already developed for calculating ground-state properties with DMC and excitations with VMC.

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

SU-F-R-53: CT-Based Radiomics Analysis of Non-Small Cell Lung Cancer Patients Treated with Stereotactic Body Radiation Therapy

Purpose: Stereotactic body radiation therapy (SBRT) is the standard of care for medically inoperable non-small cell lung cancer (NSCLC) patients and has demonstrated excellent local control and survival. However, some patients still develop distant metastases and local recurrence, and therefore, there is a clinical need to identify patients at high-risk of disease recurrence. The aim of the current study is to use a radiomics approach to identify imaging biomarkers, based on tumor phenotype, for clinical outcomes in SBRT patients. Methods: Radiomic features were extracted from free breathing computed tomography (CT) images of 113 Stage I-II NSCLC patients treated with SBRT. Their association to and prognostic performance for distant metastasis (DM), locoregional recurrence (LRR) and survival was assessed and compared with conventional features (tumor volume and diameter) and clinical parameters (e.g. performance status, overall stage). The prognostic performance was evaluated using the concordance index (CI). Multivariate model performance was evaluated using cross validation. All p-values were corrected for multiple testing using the false discovery rate. Results: Radiomic features were associated with DM (one feature), LRR (one feature) and survival (four features). Conventional features were only associated with survival and one clinical parameter was associated with LRR and survival. One radiomic feature was significantly prognostic for DM (CI=0.670, p<0.1 from random), while none of the conventional and clinical parameters were significant for DM. The multivariate radiomic model had a higher median CI (0.671) for DM than the conventional (0.618) and clinical models (0.617). Conclusion: Radiomic features have potential to be imaging biomarkers for clinical outcomes that conventional imaging metrics and clinical parameters cannot predict in SBRT patients, such as distant metastasis. Development of a radiomics biomarker that can identify patients at high-risk of recurrence could facilitate personalization of their treatment regimen for an optimized clinical outcome. R.M. had consulting interest with Amgen (ended in 2015).

60 APPLIED LIFE SCIENCES↗
NASA NTRS1992

Time to detection of circulating microbubbles as a risk factor for symptoms of altitude decompression sickness

This study investigated the association between time at onset of circulating microbubbles (CMB) and symptoms of altitude decompression sickness (DCS), using Cox proportional hazard regression models. The study population consisted of 125 individuals who participated in direct ascent, simulated extravehicular activities profiles. Using individual CMB status as a time-dependent variable, we found that the hazard for symptoms increased significantly (at the end of 180 min at altitude) in the presence of CMB (Hazard Ratio = 29.59; 95 percent confidence interval (95 percent CI) = 7.66-114.27), compared to no CMB. Further examination was conducted on the subgroup of individuals who developed microbubbles during the test (n = 49), by using Cox regression. Individuals with late onset of CMB (greater than 60 min at altitude) showed a significantly reduced risk of symptoms (hazard ratio = 0.92; 95 percent CI = 0.89-0.95), compared to those with early onset (equal to or less than 60 min), while controlling for other risk factors. We conclude that time to detection of circulating microbubbles is an independent determinant of symptoms of DCS.

Kumar, K. V.↗
DOE OSTI2025

Understanding the Competition between Alcohol Formation and Dimerization during Electrochemical Reduction of Aromatic Carbonyl Compounds

The electrochemical reductive dimerization of small aromatic carbonyl compounds derived from lignocellulosic biomass is a crucial C−C coupling reaction for upgrading small molecules to longchain hydrocarbons, particularly in the synthesis of drop-in sustainable aviation fuels. Although other electrochemical reduction reactions of these reactants (i.e., hydrogenation and hydrogenolysis) have undergone extensive mechanistic investigation, the understanding of dimerization remains relatively underdeveloped. Most importantly, there is a lack of understanding of the selectivity-determining step between dimerization and monomer reduction and critical factors that can affect this step. In this study, we provide a comprehensive mechanistic model to explain the competition between dimerization and monomer reduction of benzaldehyde under various conditions. Our model proposes that the selectivity between dimerization and monomer reduction depends on the competition between desorption of a ketyl radical from the electrode, necessary for dimerization, and further reduction of the ketyl radical to an alcohol on the electrode by proton-coupled electron transfer (PCET). Computationally comparing the adsorption/desorption energy and PCET activation barrier energy is challenging because conventional DFT calculations substantially underestimate the PCET kinetic barriers. In this study, we employed constrained DFTbased configuration interaction (CDFT-CI) to obtain a reliable comparison of these energies. Our mechanistic model was tested and supported by experimental results obtained with four electrodes (Cu, Pb, Bi, graphite), three pH conditions (acidic, neutral, basic), and three potentials. Our study offers a coherent mechanistic foundation that can explain how each of these conditions impacts the desorption and PCET processes and the selectivities for dimerization and alcohol production.

09 BIOMASS FUELS↗
DOE OSTI2014

SU-F-BRD-05: Dosimetric Comparison of Protocol-Based SBRT Lung Treatment Modalities: Statistically Significant VMAT Advantages Over Fixed- Beam IMRT

Purpose: The purpose of this study is to inter-compare and find statistically significant differences between flattened field fixed-beam (FB) IMRT with flattening-filter free (FFF) volumetric modulated arc therapy (VMAT) for stereotactic body radiation therapy SBRT. Methods: SBRT plans using FB IMRT and FFF VMAT were generated for fifteen SBRT lung patients using 6 MV beams. For each patient, both IMRT and VMAT plans were created for comparison. Plans were generated utilizing RTOG 0915 (peripheral, 10 patients) and RTOG 0813 (medial, 5 patients) lung protocols. Target dose, critical structure dose, and treatment time were compared and tested for statistical significance. Parameters of interest included prescription isodose surface coverage, target dose heterogeneity, high dose spillage (location and volume), low dose spillage (location and volume), lung dose spillage, and critical structure maximum- and volumetric-dose limits. Results: For all criteria, we found equivalent or higher conformality with VMAT plans as well as reduced critical structure doses. Several differences passed a Student's t-test of significance: VMAT reduced the high dose spillage, evaluated with conformality index (CI), by an average of 9.4%±15.1% (p=0.030) compared to IMRT. VMAT plans reduced the lung volume receiving 20 Gy by 16.2%±15.0% (p=0.016) compared with IMRT. For the RTOG 0915 peripheral lesions, the volumes of lung receiving 12.4 Gy and 11.6 Gy were reduced by 27.0%±13.8% and 27.5%±12.6% (for both, p<0.001) in VMAT plans. Of the 26 protocol pass/fail criteria, VMAT plans were able to achieve an average of 0.2±0.7 (p=0.026) more constraints than the IMRT plans. Conclusions: FFF VMAT has dosimetric advantages over fixed beam IMRT for lung SBRT. Significant advantages included increased dose conformity, and reduced organs-at-risk doses. The overall improvements in terms of protocol pass/fail criteria were more modest and will require more patient data to establish difference trends of more statistical significance.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1982

Theoretical studies of the electronic structure of small metal clusters

Theoretical studies of the electronic structure of metal clusters, in particular clusters of Group IIA and IIB atoms were conducted. Early in the project it became clear that electron correlation involving d orbitals plays a more important role in the binding of these clusters than had been previously anticipated. This necessitated that computer codes for calculating two electron integrals and for constructing the resulting CI Hamiltonions be replaced with newer, more efficient procedures. Program modification, interfacing and testing were performed. Results of both plans are reported.

Jordan, K. D.↗
DOE OSTI2017

An assessment of CFD-based wall heat transfer models in piston engines

The lack of accurate submodels for in-cylinder heat transfer has been identified as a key shortcoming in developing truly predictive, physics-based computational fluid dynamics (CFD) models that can be used to develop combustion systems for advanced high-efficiency, low-emissions engines. Only recently have experimental methods become available that enable accurate near-wall measurements to enhance simulation capability via advancing models. Initial results show crank-angle dependent discrepancies with respect to previously used boundary-layer models of up to 100%. However, available experimental data is quite sparse (only few data points on engine walls) and limited (available measurements are those of heat flux only). Predictive submodels are needed for medium-resolution ("engineering") LES and for unsteady Reynolds-averaged simulations (URANS). Recently, some research groups have performed DNS studies on engine-relevant conditions using simple geometries. These provide very useful data for benchmarking wall heat transfer models under such conditions. Further, a number of new and more sophisticated models have also become available in the literature which account for these engine-like conditions. Some of these have been incorporated while others of a more complex nature, which include solving additional partial differential equations (PDEs) within the thin boundary layer near the wall, are underway. These models will then be tested against the available DNS/experimental data in both SI (spark-ignition) and CI (compression-ignition) engines.

33 ADVANCED PROPULSION SYSTEMS↗