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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
DOE OSTI2026

Hacking Kilometer-Scale Models: A Participative Model for Climate Information

In May 2025, nearly 700 participants from all around the world coalesced at 10 regional nodes and a few satellite nodes to take part in a global hackathon of kilometer-scale (horizontal grid spacing < 10 km) regional and global Earth system models. Exciting science is emerging from these efforts, ranging across novel model analysis, new ways of integrating with satellite data, and emulation with machine learning. New technologies were trialed that enable the community to work in new and complementary ways to democratize access to global information at a local scale from a set of the world’s highest-resolution climate models. The hackathon demonstrated how exascale data can be organized to be accessible to anyone. Fundamentally, the community could apply these techniques and technologies to move toward more participative models for coproduction and delivery of diverse sources of climate information for climate scientists and citizens alike.

Climate models↗
DOE OSTI2023

Statistical Study of the Nonthermal Continuum Radiation Beaming Angle Measured by the High Frequency Receiver on Van Allen Probes-A

The nonthermal continuum (NTC) radiation beaming angle is computed over the entire Van Allen Probes-A mission when the spacecraft was in the dawn sector. The conditions in the dawn sector are favorable for the wave vector to lie near/in the spacecraft's spin plane allowing a favorable estimate of the beaming angle, and the dawn sector is also advantageous in that previous studies show NTC occurrence to peak in this sector. We found that scatter plots, over the entire mission, of beaming angle versus magnetic latitude form a distinct inverted-V pattern, with the apex at/near the magnetic equator. This pattern was sharpest for frequencies ( f ) ≲ 100 kHz. Using the NTC beaming formula from the linear mode conversion theory (LMCT), we show that such an inverted-V pattern is expected due to the large variation in the plasmapause location over the entire mission. The theoretical derived pattern qualitatively reproduces the observed pattern but not quantitatively. The lack of quantitative agreement is discussed and is attributed to several factors, one factor is off-centered emissions from the radio window. The qualitative agreement strongly supports LMCT as being the dominant mechanism generating NTC for f ≲ 100 kHz. For f ≳ 100 kHz, the inverted-V pattern becomes less distinct, and strong near-equatorial beaming is observed. Finally, after considering contamination of our selections by left-handed polarized AKR, our study suggests that besides LMCT another unidentified NTC generation mechanism becomes important for f ≳ 100 kHz.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2023

Statistical Study of the Non-Thermal Continuum Radiation Beaming Angle Measured By the High Frequency Receiver on Van Allen Probes-A

The nonthermal continuum (NTC) radiation beaming angle is computed over the entire Van Allen Probes-A mission when the spacecraft was in the dawn sector. The conditions in the dawn sector are favorable for the wave vector to lie near/in the spacecraft's spin plane allowing a favorable estimate of the beaming angle, and the dawn sector is also advantageous in that previous studies show NTC occurrence to peak in this sector. We found that scatter plots, over the entire mission, of beaming angle versus magnetic latitude form a distinct inverted-V pattern, with the apex at/near the magnetic equator. This pattern was sharpest for frequencies (f) ≲ 100 kHz. Using the NTC beaming formula from the linear mode conversion theory (LMCT), we show that such an inverted-V pattern is expected due to the large variation in the plasmapause location over the entire mission. The theoretical derived pattern qualitatively reproduces the observed pattern but not quantitatively. The lack of quantitative agreement is discussed and is attributed to several factors, one factor is off-centered emissions from the radio window. The qualitative agreement strongly supports LMCT as being the dominant mechanism generating NTC for f ≲ 100 kHz. For f ≳ 100 kHz, the inverted-V pattern becomes less distinct, and strong near-equatorial beaming is observed. After considering contamination of our selections by left-handed polarized AKR, our study suggests that besides LMCT another unidentified NTC generation mechanism becomes important for f ≳ 100 kHz.

Linear Mode Conversion Theory↗
DOE OSTI2025

Object detection with deep learning for rare event search in the GADGET II TPC

In the pursuit of identifying rare two-particle events within the GADGET II Time Projection Chamber (TPC), this paper presents a comprehensive approach for leveraging Convolutional Neural Networks (CNNs) and various data processing methods. To address the inherent complexities of 3D TPC track reconstructions, the data is expressed in 2D projections and 1D quantities. This approach capitalizes on the diverse data modalities of the TPC, allowing for the efficient representation of the distinct features of the 3D events, with no loss in topology uniqueness. Additionally, it leverages the computational efficiency of 2D CNNs and benefits from the extensive availability of pre-trained models. Given the scarcity of real training data for the rare events of interest, simulated events are used to train the models to detect real events. To account for potential distribution shifts when predominantly depending on simulations, significant perturbations are embedded within the simulations. This produces a broad parameter space that works to account for potential physics parameter and detector response variations and uncertainties. These parameter-varied simulations are used to train sensitive 2D CNN object detectors. When combined with 1D histogram peak detection algorithms, this multi-modal detection framework is highly adept at identifying rare, two-particle events in data taken during experiment 21072 at the Facility for Rare Isotope Beams (FRIB), demonstrating a 100% recall for events of interest. Here, we present the methods and outcomes of our investigation and discuss the potential future applications of these techniques.

Convolutional neural network↗
DOE OSTI2017

Panels of HIV-1 Subtype C Env Reference Strains for Standardized Neutralization Assessments

In the search for effective immunologic interventions to prevent and treat HIV-1 infection, standardized reference reagents are a cost-effective way to maintain robustness and reproducibility among immunological assays. To support planned and ongoing studies where clade C predominates, here we describe three virus panels, chosen from 200 well-characterized clade C envelope (Env)-pseudotyped viruses from early infection. All 200 Envs were expressed as a single round of replication pseudoviruses and were tested to quantify neutralization titers by 16 broadly neutralizing antibodies (bnAbs) and sera from 30 subjects with chronic clade C infections. We selected large panels of 50 and 100 Envs either to characterize cross-reactive breadth for sera identified as having potent neutralization activity based on initial screening or to evaluate neutralization magnitude-breadth distributions of newly isolated antibodies. We identified these panels by downselection after hierarchical clustering of bnAb neutralization titers. The resulting panels represent the diversity of neutralization profiles throughout the range of virus sensitivities identified in the original panel of 200 viruses. A small 12-Env panel was chosen to screen sera from vaccine trials or natural-infection studies for neutralization responses. We considered panels selected by previously described methods but favored a computationally informed method that enabled selection of viruses representing diverse neutralization sensitivity patterns, given that we do not a priori know what the neutralization-response profile of vaccine sera will be relative to that of sera from infected individuals. The resulting 12-Env panel complements existing panels. Use of standardized panels enables direct comparisons of data from different trials and study sites testing HIV-1 clade C-specific products. HIV-1 group M includes nine clades and many recombinants. Clade C is the most common lineage, responsible for roughly half of current HIV-1 infections, and is a focus for vaccine design and testing. Standard reference reagents, particularly virus panels to study neutralization by antibodies, are crucial for developing cost-effective and yet rigorous and reproducible assays against diverse examples of this variable virus. We developed clade C-specific panels for use as standardized reagents to monitor complex polyclonal sera for neutralization activity and to characterize the potency and breadth of cross-reactive neutralization by monoclonal antibodies, whether engineered or isolated from infected individuals. We chose from 200 southern African, clade C envelope-pseudotyped viruses with neutralization titers against 16 broadly neutralizing antibodies and 30 sera from chronic clade C infections. We selected panels to represent the diversity of bnAb neutralization profiles and Env neutralization sensitivities. Finally, use of standard virus panels can facilitate comparison of results across studies and sites.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Utilizing genome-scale models to optimize nutrient supply for sustained algal growth and lipid productivity

Nutrient availability is critical for growth of algae and other microbes used for generating valuable biochemical products. Determining the optimal levels of nutrient supplies to cultures can eliminate feeding of excess nutrients, lowering production costs and reducing nutrient pollution into the environment. With the advent of omics and bioinformatics methods, it is now possible to construct genome-scale models that accurately describe the metabolism of microorganisms. In this study, a genome-scale model of the green alga Chlorella vulgaris (iCZ946) was applied to predict feeding of multiple nutrients, including nitrate and glucose, under both autotrophic and heterotrophic conditions. The objective function was changed from optimizing growth to instead minimizing nitrate and glucose uptake rates, enabling predictions of feed rates for these nutrients. The metabolic model control (MMC) algorithm was validated for autotrophic growth, saving 18% nitrate while sustaining algal growth. Additionally, we obtained similar growth profiles by simultaneously controlling glucose and nitrate supplies under heterotrophic conditions for both high and low levels of glucose and nitrate. Finally, the nitrate supply was controlled in order to retain protein and chlorophyll synthesis, albeit at a lower rate, under nitrogen-limiting conditions. This model-driven cultivation strategy doubled the total volumetric yield of biomass, increased fatty acid methyl ester (FAME) yield by 61%, and enhanced lutein yield nearly 3 fold compared to nitrogen starvation. This study introduces a control methodology that integrates omics data and genome-scale models in order to optimize nutrient supplies based on the metabolic state of algal cells in different nutrient environments. This approach could transform bioprocessing control into a systems biology-based paradigm suitable for a wide range of species in order to limit nutrient inputs, reduce processing costs, and optimize biomanufacturing for the next generation of desirable biotechnology products.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Sodium Ion Expansion Power Block for Distributed CSP

The Sodium Ion Expansion Power Block for Distributed CSP was a three-plus-one-year effort under the Concentrating Solar Power: Advanced Projects Offering Low LCOE Opportunities (CSP: APOLLO) funding program within the U.S. Department of Energy Solar Energy Technologies Office. The primary objective of this project is to develop a dual-stage modular sodium thermal electrochemical converter (Na-TEC) heat engine power block, which can be potentially integrated with either a small-scale dish solar or large-scale heliostats and parabolic trough CSP. Na-TEC is a heat engine that generates electricity through the isothermal expansion of sodium ions. The Na-TEC is a closed system that can theoretically achieve conversion efficiencies above 45% when operating between thermal reservoirs at 1150 K and 550 K. However, thermal designs have confined previous single-stage devices to thermal efficiencies below 20%. To mitigate some of these limitations, we consider dividing the isothermal expansion into two stages; one at the evaporator temperature (1150 K) and another at an intermediate temperature (650 K –1050 K). This dual-stage Na-TEC takes advantage of regeneration and reheating, and could be amenable to better thermal management. In light of this, we first designed and developed a thermo-electrochemical model, and thermodynamically demonstrated how the dual-stage device can improve the efficiency by up to 8% points over the best performing single-stage device. We also established an application regime map for the single- and dual-stage Na-TEC in terms of the power density and the total thermal parasitic loss. Moreover, a thermal design of an axisymmetric dual-stage Na-TEC is developed to guide the scale-up and fabrication of sub-components of prototype module. A reduced-order finite-element model is used in conjunction with a Na-TEC thermodynamic model that was developed to determine the total parasitic heat loss of this dual-stage design. A number of simplifications are applied in the reduced-order model to decrease the computational time while maintaining acceptable accuracy. According to this analysis, a maximum efficiency of 29% and a maximum power output of 125 W can be achieved. Ultimately, we were able to demonstrate thermal efficiency improvements of the Na-TEC heat engine from 19% up to 40.3%, in a dual-stage (non-optimized) prototype module that we designed, fabricated, and tested with high temperature stage at 923 K. Furthermore, a cost-performance analysis for this improved dual-stage design was carried out for distributed-CSP systems. A high-level techno-economic analysis (TEA) explores four scenarios where a Na-TEC is used as the heat engine for a distributed-CSP system. Overnight capital cost and levelized cost of electricity (LCOE) are estimated for a system lifetime of 30 years, revealing that overnight capital costs in a range from $3.57 to $17.71 per We are feasible, which equate to LCOEs from 6.9 to 17.2 cents/kWh e -1 . This analysis makes a significant contribution by concurrently quantifying the efficiency and unit costs for a range of multistage configurations, and demonstrating that a Na-TEC may be a promising alternative to Stirling engines for distributed-CSP systems at residential scale of 1–5 kW e .

14 SOLAR ENERGY↗
DOE OSTI2020

Analysis of diagonal G and subspace W approximations within fully self-consistent GW calculations for bulk semiconducting systems

Fully self-consistent GW (sc-GW) methods are now available to evaluate quasiparticle and spectral properties of various molecular and bulk systems. However, such techniques based on the full matrix of G and W are computationally demanding. Additionally, the routinely used single-shot GW approximation (G 0 W 0 ) has an undesirable dependency on the choice of initial exchange-correlation functional. In the literature, many so-called self-consistent GW methods are based on diagonal approximation of G and low-ranking approximation of W. It is thus worth checking how good such approximations are in comparison with the full matrix method. In this work, we consider AlAs, AlP, GaP, and ZnS as the prototype systems to perform sc-GW calculations by expressing the full G matrix using a plane-wave basis set. We compared our sc-GW results with the diagonal G and subspace W approximated sc-GW results (sc-GW-diagG and sc-GW-subW methods). In the sc-GW-diagG method, interacting G is expanded in the eigenvectors of noninteracting G such that only diagonal elements are retained, whereas the number of eigenmodes is truncated in sc-GW-subW calculations. A systematic analysis of the results obtained from the above techniques is presented. The differences in the quasiparticle band gap between the approximated and the full matrix sc-GW approaches are mostly less than 1.7%, which validates such widely adopted approximations, and also shows how such low-ranking approximation can be used to include higher-order terms such as the vertex correction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

A Bayesian Machine Learning Model for Estimating Building Occupancy from Open Source Data

Understanding building occupancy is critical to a wide array of applications including natural hazards loss analysis, green building technologies, and population distribution modeling. Due to the expense of directly monitoring buildings, scientists rely in addition on a wide and disparate array of ancillary and open source information including subject matter expertise, survey data, and remote sensing information. These data are fused using data harmonization methods which refer to a loose collection of formal and informal techniques for fusing data together to create viable content for building occupancy estimation. In this paper, we add to the current state of the art by introducing the Population Data Tables (PDT), a Bayesian based informatics system for systematically arranging data and harmonization techniques into a consistent, transparent, knowledge learning framework that retains in the final estimation uncertainty emerging from data, expert judgment, and model parameterization. PDT probabilistically estimates ambient occupancy in units of people/1000ft2 for over 50 building types at the national and sub-national level with the goal of providing global coverage. The challenge of global coverage led to the development of an interdisciplinary geospatial informatics system tool that provides the framework for capturing, storing, and managing open source data, handling subject matter expertise, carrying out Bayesian analytics as well as visualizing and exporting occupancy estimation results. We present the PDT project, situate the work within the larger community, and report on the progress of this multi-year project.Understanding building occupancy is critical to a wide array of applications including natural hazards loss analysis, green building technologies, and population distribution modeling. Due to the expense of directly monitoring buildings, scientists rely in addition on a wide and disparate array of ancillary and open source information including subject matter expertise, survey data, and remote sensing information. These data are fused using data harmonization methods which refer to a loose collection of formal and informal techniques for fusing data together to create viable content for building occupancy estimation. In this paper, we add to the current state of the art by introducing the Population Data Tables (PDT), a Bayesian model and informatics system for systematically arranging data and harmonization techniques into a consistent, transparent, knowledge learning framework that retains in the final estimation uncertainty emerging from data, expert judgment, and model parameterization. PDT probabilistically estimates ambient occupancy in units of people/1000 ft 2 for over 50 building types at the national and sub-national level with the goal of providing global coverage. The challenge of global coverage led to the development of an interdisciplinary geospatial informatics system tool that provides the framework for capturing, storing, and managing open source data, handling subject matter expertise, carrying out Bayesian analytics as well as visualizing and exporting occupancy estimation results. We present the PDT project, situate the work within the larger community, and report on the progress of this multi-year project.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS2001

Exploring a Black Body Source as an Absolute Radiometric Calibration Standard and Comparison with a NIST Traced Lamp Standard

Radiometric calibration of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) is required for the scientific research and application objectives pursued with the spectroscopic measurements. Specifically calibration is required for: inter-comparison of AVIRIS data measured at different locations and at different times; analysis of AVIRIS data with data measured by other instruments; and analysis of AVIRIS data in conjunction with computer models. The primary effect of radiometric calibration is conversion of AVIRIS instrument response values (digitized numbers, or DN) to units of absolute radiance. For example, a figure shows the instrument response spectrum measured by AVIRIS over a portion of Rogers Dry Lake, California, and another figure shows the same spectrum calibrated to radiance. Only the calibrated spectrum may be quantitatively analyzed for science research and application objectives. Since the initial development of the AVIRIS instrument-radiometric calibration has been based upon a 1000-W irradiance lamp with a calibration traced to the National Institute of Standards and Technology (NIST). There are several advantages to this irradiance-lamp calibration approach. First, the considerable effort of NIST backs up the calibration. Second, by changing the distance to the lamp, the output can closely span the radiance levels measured by AVIRIS. Third, this type of standard is widely used. Fourth, these calibrated lamps are comparatively inexpensive. Conversely, there are several disadvantages to this approach as well. First, the lamp is not a primary standard. Second, the lamp output characteristics may change in an unknown manner through time. Third, it is difficult to assess, constrain, or improve the calibration uncertainty delivered with the lamp. In an attempt to explore the effect and potentially address some of these disadvantages a set of analyses and measurements comparing an irradiance lamp with a black-body source have been completed. This research is ongoing, and the current set of measurements, analyses, and results are presented in this paper.

Green, Robert O.↗
DOE OSTI2023

Adjustments to the law of the wall above an Amazon forest explained by a spectral link

Modification to the law of the wall represented by a dimensionless correction function ϕ RSL (z/h) is derived using atmospheric turbulence measurements collected at two sites in the Amazon in near-neutral stratification, where z is the distance from the forest floor and h is the mean canopy height. The sites are the Amazon Tall Tower Observatory for z/h∈ [1,2.3] and the Green Ocean Amazon (GoAmazon) site for z/h∈ [1,1.4]. Here, a link between the vertical velocity spectrum E ww (k) (k is the longitudinal wavenumber) and ϕ RSL is then established using a co-spectral budget (CSB) model interpreted by the moving-equilibrium hypothesis. The key finding is that ϕ RSL is determined by the ratio of two turbulent viscosities and is given as ν t,BL /ν t,RSL, where ν t,RSL = (1/A)∫$^{∞}_{0}$ τ(k)E ww (k)dk, ν t,BL = k v (z−d)u * , τ(k) is a scale-dependent decorrelation time scale between velocity components, A = C R /(1−C I ) = 4.5 is predicted from the Rotta constant C R = 1.8, and the isotropization of production constant C I = 3/5 given by rapid distortion theory, k v is the von Kármán constant, u * is the friction velocity at the canopy top, and d is the zero-plane displacement. Because the transfer of energy across scales is conserved in E ww (k) and is determined by the turbulent kinetic energy dissipation rate (ε), the CSB model also predicts that ϕ RSL scales with L BL /L d , where L BL is the length scale of attached eddies to z = d, and L d = u$_{*}^{3}$/ε is a macro-scale dissipation length.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Identification of broadly neutralizing antibody epitopes in the HIV-1 envelope glycoprotein using evolutionary models

Background: Identification of the epitopes targeted by antibodies that can neutralize diverse HIV-1 strains can provide important clues for the design of a preventative vaccine. Methods: We have developed a computational approach that can identify key amino acids within the HIV-1 envelope glycoprotein that influence sensitivity to broadly cross-neutralizing antibodies. Given a sequence alignment and neutralization titers for a panel of viruses, the method works by fitting a phylogenetic model that allows the amino acid frequencies at each site to depend on neutralization sensitivities. Sites at which viral evolution influences neutralization sensitivity were identified using Bayes factors (BFs) to compare the fit of this model to that of a null model in which sequences evolved independently of antibody sensitivity. Conformational epitopes were identified with a Metropolis algorithm that searched for a cluster of sites with large Bayes factors on the tertiary structure of the viral envelope. Results: We applied our method to ID 50 neutralization data generated from seven HIV-1 subtype C serum samples with neutralization breadth that had been tested against a multi-clade panel of 225 pseudoviruses for which envelope sequences were also available. For each sample, between two and four sites were identified that were strongly associated with neutralization sensitivity (2ln(BF) > 6), a subset of which were experimentally confirmed using site-directed mutagenesis. Conclusions: Our results provide strong support for the use of evolutionary models applied to cross-sectional viral neutralization data to identify the epitopes of serum antibodies that confer neutralization breadth.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

A method for evaluating image quality of monochrome and color displays based on luminance by use of a commercially available color digital camera

Purpose: The aim of this study is to propose a method for the quantitative evaluation of image quality of both monochrome and color liquid-crystal displays (LCDs) using a commercially available color digital camera. Methods: The intensities of the unprocessed red (R), green (G), and blue (B) signals of a camera vary depending on the spectral sensitivity of the image sensor used in the camera. For consistent evaluation of image quality for both monochrome and color LCDs, the unprocessed RGB signals of the camera were converted into gray scale signals that corresponded to the luminance of the LCD. Gray scale signals for the monochrome LCD were evaluated by using only the green channel signals of the camera. For the color LCD, the RGB signals of the camera were converted into gray scale signals by employing weighting factors (WFs) for each RGB channel. A line image displayed on the color LCD was simulated on the monochrome LCD by using a software application for subpixel driving in order to verify the WF-based conversion method. Furthermore, the results obtained by different types of commercially available color cameras and a photometric camera were compared to examine the consistency of the authors’ method. Finally, image quality for both the monochrome and color LCDs was assessed by measuring modulation transfer functions (MTFs) and Wiener spectra (WS). Results: The authors’ results demonstrated that the proposed method for calibrating the spectral sensitivity of the camera resulted in a consistent and reliable evaluation of the luminance of monochrome and color LCDs. The MTFs and WS showed different characteristics for the two LCD types owing to difference in the subpixel structure. The MTF in the vertical direction of the color LCD was superior to that of the monochrome LCD, although the WS in the vertical direction of the color LCD was inferior to that of the monochrome LCD as a result of luminance fluctuations in RGB subpixels. Conclusions: The authors’ method based on the use of a commercially available color camera is useful to evaluate and understand the display performances of both monochrome and color LCDs in radiology departments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-J-102: Lower Esophagus Margin Implications Based On Rapid Computational Algorithm for SBRT

Purpose: To quantify inter-fraction esophagus-variation. Methods: Computed tomography and daily on-treatment 0.3-T MRI data sets for 7 patients were analyzed using a novel Matlab-based (Mathworks, Natick, MA) rapid computational method. Rigid registration was performed from the cricoid to the gastro-esophageal junction. CT and MR-based contours were compared at slice intervals of 3mm. Variation was quantified by “expansion,” defined as additional length in any radial direction from CT contour to MR contour. Expansion computations were performed with 360° of freedom in each axial slice. We partitioned expansions into left anterior, right anterior, right posterior, and left posterior quadrants (LA, RA, RP, and LP, respectively). Sample means were compared by analysis of variance (ANOVA) and Fisher’s Protected Least Significant Difference test. Results: Fifteen fractions and 1121 axial slices from 7 patients undergoing SBRT for primary lung cancer (3) and metastatic lung disease (4) were analyzed, generating 41,970 measurements. Mean LA, RA, RP, and LP expansions were 4.30±0.05 mm, 3.71±0.05mm, 3.17±0.07, and 3.98±0.06mm, respectively. 50.13% of all axial slices showed variation > 5 mm in one or more directions. Variation was greatest in lower esophagus with mean LA, RA, RP, and LP expansion (5.98±0.09 mm, 4.59±0.09 mm, 4.04±0.16 mm, and 5.41±0.16 mm, respectively). The difference was significant compared to mid and upper esophagus (p<.0001). The 95th percentiles of expansion for LA, RA, RP, LP were 13.36 mm, 9.97 mm, 11.29 mm, and 12.19 mm, respectively. Conclusion: Analysis of on-treatment MR imaging of the lower esophagus during thoracic SBRT suggests margin expansions of 13.36 mm LA, 9.97 mm RA, 11.29 mm RP, 12.19 mm LP would account for 95% of measurements. Our novel algorithm for rapid assessment of margin expansion for critical structures with 360° of freedom in each axial slice enables continuously adaptive patient-specific margins which may reduce overlap with high-dose regions.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Chemically Activated Formation of Organic Acids in Reactions of the Criegee Intermediate with Aldehydes and Ketones

Reactions of the Criegee intermediate (CI, .CH2OO.) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between .CH2OO. and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48–51 kcal mol-1 lower in energy, formed via 1,3- cycloaddition of .CH2OO. across the CQO bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O–O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO o CH3CHO o CH3COCH3 (the highest yield being 10-4 times lower than the initial .CH2OO. concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2020

Distinguishing electronic contributions of surface and sub-surface transition metal atoms in Ti-based MXenes

MXenes are a rapidly-expanding family of 2D transition metal carbides and nitrides that have attracted attention due to their excellent performance in applications ranging from energy storage to electromagnetic interference shielding. Numerous other electronic and magnetic properties have been computationally predicted, but not yet realized due to the experimental difficulty in obtaining uniform surface terminations (T x ), necessitating new design approaches for MXenes that are independent of surface groups. In this study, we distinguished the contributions of surface and sub-surface Ti atoms to the electronic structure of four Ti-based MXenes (Ti 2 CT x , Ti 3 C 2 T x , Cr 2 TiC 2 T x , and Mo 2 TiC 2 T x ) using soft x-ray absorption spectroscopy, revealing minimal changes in the spectral features between the parent MAX phase and its MXene when no surface Ti atoms are present in the MXene, such as Mo 2 TiC 2 T x and Cr 2 TiC 2 T x . In contrast, for MXenes with surface Ti atoms, here Ti 3 C 2 T x and Ti 2 CT x , the Ti L-edge spectra are significantly modified compared to their parent MAX phase compounds. First principles calculations provide similar trends in the partial density of states derived from surface and interior Ti atoms, corroborating the spectroscopic measurements. Furthermore, these results reveal that electronic states derived from sub-surface M-site layers are largely unperturbed by the surface groups, indicating a relatively short length scale over which the T x groups alter the nominal electron count associated with Ti atoms and suggesting that desired band features should be hosted by sub-surface M-sites that are electronically more robust than their surface M-site counterparts.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mechanism and dynamics of fatty acid photodecarboxylase

Photoenzymes are rare biocatalysts driven by absorption of a photon at each catalytic cycle; they inspire development of artificial photoenzymes with valuable activities. Fatty acid photodecarboxylase (FAP) is a natural photoenzyme that has potential applications in the bio-based production of hydrocarbons, yet its mechanism is far from fully understood. RATIONALE To elucidate the mechanism of FAP, we studied the wild-type (WT) enzyme from Chlorella variabilis (CvFAP) and variants with altered active-site residues using a wealth of techniques, including static and time-resolved crystallography and spectroscopy, as well as biochemical and computational approaches. RESULTS A 1.8-Å-resolution CvFAP x-ray crystal structure revealed a dense hydrogen-bonding network positioning the fatty acid carboxyl group in the vicinity of the flavin adenine dinucleotide (FAD) cofactor. Structures solved from free electron laser and low-dose synchrotron x-ray crystal data further highlighted an unusual bent shape of the oxidized flavin chromophore, and showed that the bending angle (14°) did not change upon photon absorption (step 1) or throughout the photocycle. Calculations showed that bending substantially affected the energy levels of the flavin. Structural and spectroscopic analysis of WT and mutant proteins targeting two conserved active-site residues, R451 and C432, demonstrated that both residues were crucial for proper positioning of the substrate and water molecules and for oxidation of the fatty acid carboxylate by 1 FAD* (~300 ps in WT FAP) to form FAD ∙– (step 2). Time-resolved infrared spectroscopy demonstrated that decarboxylation occured quasi-instantaneously upon this forward electron transfer, consistent with barrierless bond cleavage predicted by quantum chemistry calculations and with snapshots obtained by time-resolved crystallography. Transient absorption spectroscopy in H 2 O and D 2 O buffers indicated that back electron transfer from FAD ∙– was coupled to and limited by transfer of an exchangeable proton or hydrogen atom (step 3). Unexpectedly, concomitant with FAD ∙– reoxidation (to a red-shifted form FAD RS ) in 100 ns, most of the CO 2 product was converted, most likely into bicarbonate (as inferred from FTIR spectra of the cryotrapped FAD RS intermediate). Calculations indicated that this catalytic transformation involved an active-site water molecule. Cryo-Fourier transform infrared spectroscopy studies suggested that bicarbonate formation (step 4) was preceded by deprotonation of an arginine residue (step 3). At room temperature, the remaining CO 2 left the protein in 1.5 μs (step 4'). The observation of residual electron density close to C432 in electron density maps derived from time-resolved and cryocrystallography data suggests that this residue may play a role in stabilizing CO 2 and/or bicarbonate. Three routes for alkane formation were identified by quantum chemistry calculations; the one shown in the figure is favored by the ensemble of experimental data. CONCLUSION Finally, we provide a detailed and comprehensive characterization of light-driven hydrocarbon formation by FAP, which uses a remarkably complex mechanism including unique catalytic steps. We anticipate that our results will help to expand the green chemistry toolkit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Strategies for Choosing Descent Flight-Path Angles for Small Jets

Three candidate strategies for choosing the descent flight path angle (FPA) for small jets are proposed, analyzed, and compared for fuel efficiency under arrival metering conditions. The strategies vary in operational complexity from a universally fixed FPA, or FPA function that varies with descent speed for improved fuel efficiency, to the minimum-fuel FPA computed for each flight based on winds, route, and speed profile. Methodologies for selecting the parameter for the first two strategies are described. The differences in fuel burn are analyzed over a year s worth of arrival traffic and atmospheric conditions recorded for the Dallas/Fort Worth (DFW) Airport during 2011. The results show that the universally fixed FPA strategy (same FPA for all flights, all year) burns on average 26 lbs more fuel per flight as compared to the minimum-fuel solution. This FPA is adapted to the arrival gate (direction of entry to the terminal) and various timespans (season, month and day) to improve fuel efficiency. Compared to a typical FPA of approximately 3 degrees the adapted FPAs vary significantly, up to 1.3 from one arrival gate to another or up to 1.4 from one day to another. Adapting the universally fixed FPA strategy to the arrival gate or to each day reduces the extra fuel burn relative to the minimum-fuel solution by 27% and 34%, respectively. The adaptations to gate and time combined shows up to 57% reduction of the extra fuel burn. The second strategy, an FPA function, contributes a 17% reduction in the 26 lbs of extra fuel burn over the universally fixed FPA strategy. Compared to the corresponding adaptations of the universally fixed FPA, adaptations of the FPA function reduce the extra fuel burn anywhere from 15-23% depending on the extent of adaptation. The combined effect of the FPA function strategy with both directional and temporal adaptation recovers 67% of the extra fuel relative to the minimum-fuel solution.

Wu, Minghong Gilbert↗