SEARCH · Engineering Papers
Results for “matrices”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Tracking Excited States in Wave Function Optimization Using Density Matrices and Variational Principles
We introduce an approach for finding individual excited states' energy stationary points in complete active space self-consistent field theory that is compatible with standard optimization methods and highly effective at overcoming difficulties due to root flipping and near-degeneracies. Inspired by both the maximum overlap method and recent progress in excited-state variational principles, our approach combines these ideas in order to track individual excited states throughout the orbital optimization process. In a series of tests involving root flipping, near-degeneracies, charge transfers, and double excitations, we show that this approach is more effective for state-specific optimization than either the naive selection of roots on the basis of energy ordering or a more direct generalization of the maximum overlap method. We offer evidence that this state-specific approach improves the performance of complete active space perturbation theory for vertical excitation energies. Furthermore, we find that the state-specific optimization can help avoid state-averaging-induced discontinuities on potential energy surfaces. With a simple implementation, a low cost, and compatibility with large active space methods, the approach is designed to be useful in a wide range of excited-state investigations.
The Representation and Parametrization of Orthogonal Matrices
Explore the source record for details and available documents.
Photodegradable Hydrogel Matrices for Spatiotemporal Control of Bacteria Transport and Delivery
Not provided.
Application of Crystalline Matrices for the Structural Determination of Organic Molecules
Explore the source record for details and available documents.
Embedding PbS Quantum Dots (QDs) in Pb-Halide Perovskite Matrices: QD Surface Chemistry and Antisolvent Effects on QD Dispersion and Confinement Properties
Hybrid materials of metal chalcogenide colloidal quantum dots (QDs) embedded in metal halide perovskites (MHPs) have led to composites with synergistic properties. Here, we investigate how QD size, surface chemistry, and MHP film formation methods affect the resulting optoelectronic properties of QD/MHP “dot-in-matrix” systems. We monitor the QD absorption and photoluminescence throughout synthesis, ligand exchange, and transfer into the MHP ink, and we characterize the final QD/MHP films via electron microscopy and transient absorption. In addition, we are the first to globally map how PbS QDs are distributed on the micrometer scale within these dot-in-matrix systems, using three-dimensional (3D) tomography time-of-flight secondary ion mass spectrometry. The surface chemistry imparted during synthesis directly affects the optical properties of the dot-in-matrix composites. Pb-halide passivation leads to QD/MHP dot-in-matrix samples with optical properties that are well-described by a theoretical model, based on a Type I finite-barrier heterostructure between the PbS QD and the MHP matrix. Samples without Pb-halide passivation show complicated size-dependent behavior, indicating a transition from a Type I heterostructure between the PbS QD wells and MHP barriers for small-sized QDs to PbS QDs that are electronically decoupled from the MHP matrix for larger QDs. Furthermore, the choice in perovskite antisolvent crystallization method leads to a difference in the spatial QD distribution within the perovskite matrix, differences in carrier lifetime, and photoluminescence shifts of up to 180 meV for PbS in methylammonium lead iodide. This work establishes an understanding of such emerging synergistic systems relevant for technologies such as photovoltaics, infrared emitters and detectors, and other unexplored technological applications.
What We Can Learn from the Norms of One-Particle Density Matrices, and What We Can’t: Some Results for Interstate Properties in Model Singlet Fission Systems
Explore the source record for details and available documents.
3D calcite heterostructures for dynamic and deformable mineralized matrices
Scales are rooted in soft tissues, and are regenerated by specialized cells. The realization of dynamic synthetic analogues with inorganic materials has been a significant challenge, because the abiological regeneration sites that could yield deterministic growth behavior are hard to form. Here we overcome this fundamental hurdle by constructing a mutable and deformable array of three-dimensional calcite heterostructures that are partially locked in silicone. Individual calcite crystals exhibit asymmetrical dumbbell shapes and are prepared by a parallel tectonic approach under ambient conditions. Furthermore, the silicone matrix immobilizes the epitaxial nucleation sites through self-templated cavities, which enables symmetry breaking in reaction dynamics and scalable manipulation of the mineral ensembles. With this platform, we devise several mineral-enabled dynamic surfaces and interfaces. For example, we show that the induced growth of minerals yields localized inorganic adhesion for biological tissue and reversible focal encapsulation for sensitive components in flexible electronics.
Unraveling iron oxides as abiotic catalysts of organic phosphorus recycling in soil and sediment matrices
In biogeochemical phosphorus cycling, iron oxide minerals are acknowledged as strong adsorbents of inorganic and organic phosphorus. Dephosphorylation of organic phosphorus is attributed only to biological processes, but iron oxides could also catalyze this reaction. Evidence of this abiotic catalysis has relied on monitoring products in solution, thereby ignoring iron oxides as both catalysts and adsorbents. Here we apply high-resolution mass spectrometry and X-ray absorption spectroscopy to characterize dissolved and particulate phosphorus species, respectively. In soil and sediment samples reacted with ribonucleotides, we uncover the abiotic production of particulate inorganic phosphate associated specifically with iron oxides. Reactions of various organic phosphorus compounds with the different minerals identified in the environmental samples reveal up to twenty-fold greater catalytic reactivities with iron oxides than with silicate and aluminosilicate minerals. Importantly, accounting for inorganic phosphate both in solution and mineral-bound, the dephosphorylation rates of iron oxides were within reported enzymatic rates in soils. Our findings thus imply a missing abiotic axiom for organic phosphorus mineralization in phosphorus cycling.
Reply to: How much does corrosion of nuclear waste matrices matter
No abstract provided.
In-flight positional and energy use data set of a DJI Matrice 100 quadcopter for small package delivery
Abstract We autonomously directed a small quadcopter package delivery Uncrewed Aerial Vehicle (UAV) or “drone” to take off, fly a specified route, and land for a total of 209 flights while varying a set of operational parameters. The vehicle was equipped with onboard sensors, including GPS, IMU, voltage and current sensors, and an ultrasonic anemometer, to collect high-resolution data on the inertial states, wind speed, and power consumption. Operational parameters, such as commanded ground speed, payload, and cruise altitude, were varied for each flight. This large data set has a total flight time of 10 hours and 45 minutes and was collected from April to October of 2019 covering a total distance of approximately 65 kilometers. The data collected were validated by comparing flights with similar operational parameters. We believe these data will be of great interest to the research and industrial communities, who can use the data to improve UAV designs, safety, and energy efficiency, as well as advance the physical understanding of in-flight operations for package delivery drones.
Sol-Generating Chemical Vapor into Liquid (SG-CViL) deposition – a facile method for encapsulation of diverse cell types in silica matrices
In nature, cells perform a variety of complex functions such as sensing, catalysis, and energy conversion which hold great potential for biotechnological device construction. However, cellular sensitivity to ex vivo environments necessitates development of bio–nano interfaces which allow integration of cells into devices and maintain their desired functionality. In order to develop such an interface, the use of a novel Sol-Generating Chemical Vapor into Liquid (SG-CViL) deposition process for whole cell encapsulation in silica was explored. In SG-CViL, the high vapor pressure of tetramethyl orthosilicate (TMOS) is utilized to deliver silica into an aqueous medium, creating a silica sol. Cells are then mixed with the resulting silica sol, facilitating encapsulation of cells in silica while minimizing cell contact with the cytotoxic products of silica generating reactions (i.e. methanol), and reduce exposure of cells to compressive stresses induced from silica condensation reactions. Using SG-CVIL, Saccharomyces cerevisiae (S. cerevisiae) engineered with an inducible beta galactosidase system were encapsulated in silica solids and remained both viable and responsive 29 days post encapsulation. By tuning SG-CViL parameters, thin layer silica deposition on mammalian HeLa and U87 human cancer cells was also achieved. Thus, the ability to encapsulate various cell types in either a multi cell (S. cerevisiae) or a thin layer (HeLa and U87 cells) fashion shows the promise of SG-CViL as an encapsulation strategy for generating cell–silica constructs with diverse functions for incorporation into devices for sensing, bioelectronics, biocatalysis, and biofuel applications.
Heating and cooling of ligand-coated colloidal nanocrystals in solid films and solvent matrices
Ligand-to-nanocrystal heating and subsequent cooling to the environmental medium is investigated with infrared pump, electronic probe (IPEP) spectroscopy. Compared to solid films, solvated nanocrystals show faster ligand-to-nanocrystal heat equilibration (c. 11 ps versus c. 17 ps). Solvated nanocrystals also display more cooling of the hot ligand–nanocrystal complex on the experimentally measured time-scale, emphasizing the thermally insulating nature of semiconductor nanocrystal solids. Although heating transfer rates among solvents are all between 150 ps and 330 ps, cooling of the nanocrystal–ligand complex is slower, on average, in chlorinated solvents (c. 315 ps) compared to deuterated hydrocarbon solvents (c. 215 ps). Differences between chlorinated and hydrocarbon solvents show the importance of matching the vibrational energies of the solvent and the ligands for increasing the rate of heat transfer. Increases in the cooling time for poorer hydrocarbon solvents, in which nanocrystals aggregated, such as toluene, compared to better solvents, like methylcyclohexane, indicate that penetration of solvent into the ligand layer facilitates improved heat transfer to the matrix.
Zirconium metal–organic frameworks incorporating tetrathiafulvalene linkers: robust and redox-active matrices for in situ confinement of metal nanoparticles
Stable and redox active metal–organic frameworks were constructed by incorporating Zr 6 clusters and redox-active TTF-based linkers, which allow in situ generation and stabilization of ultra-small noble metal nanoparticles for heterogenous catalysis.