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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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Metabolic engineering of Saccharomyces cerevisiae for overproduction of triacylglycerols
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Improving Solar Cell Performance Using Quantum Dot Triad Charge-Separation Engines
Here, we use kinetic modeling to explore the current–voltage, power–voltage, and power conversion efficiency characteristics of quantum dot dyads and triads as possible light absorption and charge separation engines in quantum dot, bulk heterojunction solar cells. The external and internal power conversion quantum efficiencies are significantly enhanced by introducing a third quantum dot between the donor and acceptor quantum dots. Given the constraint of comparable charge-recombination and charge-separation rates, open-circuit voltages for triads are predicted to be about 10%–17% larger than those for dyads, and short-circuit currents for triads are about 400% larger than those for dyads. These improvements in the efficiencies can be further enhanced by tuning the band-edge energy offset of the middle-position quantum dot from its neighbors. The band-edge energies of the middle quantum dot should be tuned so that they form a cascading band-edge energy alignment from the band-edge energies of the left CdTe QD to the right CdSe QD. To produce the most favorable solar cell performance, the middle quantum dot’s conduction (valence) band edge should be closer to the right quantum dot’s band edge when the charge recombination rates are low (high) and near the conduction (valence) band edge of the left quantum dot when the charge recombination rates are high (low). This analysis identifies prime strategies to design multi-QD assemblies for solar energy harvesting and conversion.
Engineering Organization of DNA Nano-Chambers through Dimensionally Controlled and Multi-Sequence Encoded Differentiated Bonds
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Lattice engineering enables definition of molecular features allowing for potent small-molecule inhibition of HIV-1 entry
Diverse entry inhibitors targeting the gp120 subunit of the HIV-1 envelope (Env) trimer have been developed including BMS-626529, also called temsavir, a prodrug version of which is currently in phase III clinical trials. Here we report the characterization of a panel of small molecule inhibitors including BMS-818251, which we show to be >10-fold more potent than temsavir on a cross-clade panel of 208-HIV-1 strains, as well as the engineering of a crystal lattice to enable structure determination of the interaction between these inhibitors and the HIV-1 Env trimer at higher resolution. By altering crystallization lattice chaperones, we identify a lattice with both improved diffraction and robust co-crystallization of HIV-1 Env trimers from different clades complexed to entry inhibitors with a range of binding affinities. The improved diffraction reveals BMS-818251 to utilize functional groups that interact with gp120 residues from the conserved β20-β21 hairpin to improve potency.
Engineering catalyst supports to stabilize PdO x two-dimensional rafts for water-tolerant methane oxidation
The treatment of emissions from natural gas engines is an important area of research since methane is a potent greenhouse gas. The benchmark catalysts, based on Pd, still face challenges such as water poisoning and long-term stability. In this work, we report an approach for catalyst synthesis that relies on the trapping of metal single atoms on the support surface, in thermally stable form, to modify the nature of further deposited metal/metal oxide. By anchoring Pt ions on a catalyst support we can tailor the morphology of the deposited phase. In particular, two-dimensional (2D) rafts of PdO x are formed, resulting in higher reaction rates and improved water tolerance during methane oxidation. The results show that modifying the support by trapping single atoms could provide an important addition to the toolkit of catalyst designers for controlling the nucleation and growth of metal and metal oxide clusters in heterogeneous catalysts.
Dynamic Behavior of Engineered Lattice Materials
Additive manufacturing (AM) is enabling the fabrication of materials with engineered lattice structures at the micron scale. These mesoscopic structures fall between the length scale associated with the organization of atoms and the scale at which macroscopic structures are constructed. Dynamic compression experiments were performed to study the emergence of behavior owing to the lattice periodicity in AM materials on length scales that approach a single unit cell. For the lattice structures, both bend and stretch dominated, elastic deflection of the structure was observed ahead of the compaction of the lattice, while no elastic deformation was observed to precede the compaction in a stochastic, random structure. The material showed lattice characteristics in the elastic response of the material, while the compaction was consistent with a model for compression of porous media. Here, the experimental observations made on arrays of 4 x 4 x 6 lattice unit cells show excellent agreement with elastic wave velocity calculations for an infinite periodic lattice, as determined by Bloch wave analysis, and finite element simulations.
Hydrogen-enabled microstructure and fatigue strength engineering of titanium alloys
Traditionally, titanium alloys with satisfactory mechanical properties can only be produced via energy-intensive and costly wrought processes, while titanium alloys produced using low-cost powder metallurgy methods consistently result in inferior mechanical properties, especially low fatigue strength. Herein, we demonstrate a new microstructural engineering approach for producing low-cost titanium alloys with exceptional fatigue strength via the hydrogen sintering and phase transformation (HSPT) process. The high fatigue strength presented in this work is achieved by creating wroughtlike microstructures without resorting to wrought processing. This is accomplished by generating an ultrafine-grained as-sintered microstructure through hydrogen-enabled phase transformations, facilitating the subsequent creation of fatigue-resistant microstructures via simple heat treatments. Finally, the exceptional strength, ductility, and fatigue performance reported in this paper are a breakthrough in the field of low-cost titanium processing.
Interfacial engineering of phthalocyanine molecules on graphitic and metal substrates
Metal porphyrin and phthalocyanine have found variety of applications in catalysis, electronic and spintronic devices and photovoltaic cells, many of which rely on accurate position of the molecules and alignment of their electronic levels with respect to the substrate. The substrate and local environment affect significantly the electronic properties of these macrocyclic molecules. Computational simulations provide valuable insights for engineering the molecule–metal, molecule–molecule and molecule–ligand interfaces. In this review, we focus on adsorption of metal phthalocyanine, particularly iron phthalocyanine, on graphite, epitaxial graphene, and metal substrates. Furthermore, these systems show varied interfacial binding strength and chameleon-like molecular electronic structures. Spin of the molecules can be controlled by small ligands, and the ground state can be tuned between S = 1, S = 1/2 and S = 0. Inclusion of van der Waals interaction in the first-principles calculations is shown to be essential for accurate description of the interfaces.
Overview of the physics and engineering design of NSTX upgrade
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Two-Dimensional Electron Gases at LaAlO 3 /SrTiO 3 Interfaces: Orbital Symmetry and Hierarchy Engineered by Crystal Orientation
Recent findings show the emergence of two-dimensional electron gases (2DEGs) at LaAlO 3 /SrTiO 3 interfaces along different orientations; yet details on band reconstructions have remained so far unknown. In this study, via x-ray linear dichroism spectroscopy, we demonstrate that crystal symmetry imposes distinctive 2DEG orbital hierarchies on (001)-and (110)-oriented quantum wells, allowing selective occupancy of states of different symmetry. Such orientational tuning expands the possibilities for electronic engineering of 2DEGs and opens up enticing opportunities to understand the link between orbital symmetry and complex correlated states at LaAlO 3 /SrTiO 3 quantum wells.
Climate-resilient agroforestry: physiological responses to climate change and engineering of crassulacean acid metabolism (CAM) as a mitigation strategy: CAM engineering in trees
We know that global climate change threatens the sustainability of agriculture and agroforestry worldwide through increased heat, drought, surface evaporation and associated soil drying. Exposure of crops and forests to warmer and drier environments will increase leaf:air water vapour–pressure deficits (VPD), and will result in increased drought susceptibility and reduced productivity, not only in arid regions but also in tropical regions with seasonal dry periods. Fast-growing, short-rotation forestry (SRF) bioenergy crops such as poplar (Populus spp.) and willow (Salix spp.) are particularly susceptible to hydraulic failure following drought stress due to their isohydric nature and relatively high stomatal conductance. One approach to sustaining plant productivity is to improve water-use efficiency (WUE) by engineering crassulacean acid metabolism (CAM) into C3 crops. CAM improves WUE by shifting stomatal opening and primary CO 2 uptake and fixation to the night-time when leaf:air VPD is low. CAMmembers of the tree genus Clusia exemplify the compatibility of CAM performance within tree species and highlight CAM as a mechanism to conserve water and maintain carbon uptake during drought conditions. Moreover, the introduction of bioengineered CAM into SRF bioenergy trees is a potentially viable path to sustaining agroforestry production systems in the face of a globally changing climate.
Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain
Epitaxy forms the basis of modern electronics and optoelectronics. We report coherent atomically thin superlattices in which different transition metal dichalcogenide monolayers—despite large lattice mismatches—are repeated and laterally integrated without dislocations within the monolayer plane. Grown by an omnidirectional epitaxy, these superlattices display fully matched lattice constants across heterointerfaces while maintaining an isotropic lattice structure and triangular symmetry. This strong epitaxial strain is precisely engineered via the nanoscale supercell dimensions, thereby enabling broad tuning of the optical properties and producing photoluminescence peak shifts as large as 250 millielectron volts. We present theoretical models to explain this coherent growth and the energetic interplay governing the ripple formation in these strained monolayers. Such coherent superlattices provide building blocks with targeted functionalities at the atomically thin limit.
Isolating the effects of reactivity stratification in reactivity-controlled compression ignition with iso-octane and n -heptane on a light-duty multi-cylinder engine
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Performance Engineering Research Center and RECOVERY. Performance Engineering Research Institution SciDAC-e Augmentation. Performance enhancement
This project concentrated on various ways to improve the measurement and tuning large-scale parallel applications. This project was supplement to the project DE-FC0206ER25763 (“Performance Engineering Research Center”). The research conducted during this project is summarized in this report. The complete details of the work are available in the ten publications listed at the end of the report. It also supported the Ph.D. studies of three students and one research scientist.
Lubricant Formulations to Enhance Engine Efficiency in Modern Internal Combustion Engines
The research program presented aimed to investigate, develop, and demonstrate low-friction, environmentally-friendly and commercially-feasible lubricant formulations that would significantly improve the mechanical efficiency of modern engines without incurring increased wear, emissions or deterioration of the emission-aftertreatment system.
Individual Wave Detection and Tracking within a Rotating Detonation Engine through Computer Vision Object Detection applied to High-Speed Images
Known for their simplistic design and continuous detonation, rotating detonation engines (RDEs) constitute a majority of current pressure gain combustion (PGC) research efforts. Experimental RDE operation times have been continuously extended through the use of rig cooling techniques. As the window of observable behavior is expanded, and as the technology matures toward eventual integration within gas turbines, monitoring techniques must evolve to better match industrial diagnostics. High-speed image analysis techniques prove useful to capture and evaluate the unsteady detonation behavior within the RDE. Traditional image analysis techniques, however, require extensive processing times which prohibit simultaneous monitoring. To better address this problem, a computer vision object detection methodology is proposed to quickly detect individual detonation waves within a single down-axis image. Detonation waves are detected in individual images by the implemented computer vision method You Only Look Once (YOLO) object detection network. In order to detect detonation waves, the network must first be trained using RDE images of interest, for which each required phase of network development is outlined. Detection of waves is improved through proper treatment of the collected image set, variation of Intersection over Union (IoU) and confidence thresholding, and through a parametric study of annotation dimensions. Each detected wave is described by its location and rotational direction, and locations are tracked to calculate wave velocity across each frame, leading to a timestep resolution of 20 µs. Wave velocities are also calculated through a series of frames, leading to a suitable average velocity estimation using as few as 10 frames. Uncertainty analysis accounting for variation in camera framerate, pixel width and annotation centroid locations estimates a total uncertainty of ±4.3% for velocity calculations, using the smallest annotation boxes. This method offers great reductions in processing times, as a step toward real-time monitoring of detonation waves within an RDE. Improving on previous studies, this technique is impartial to wave modes not included in the original training set and calculates wave velocities independent of high-speed pressure data. The ability to isolate waves within predicted bounding boxes will likely facilitate analysis of pixel intensity variation as an estimation of wave strength in future work.