Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “coordination state”

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.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Challenges of COVID-19 Case Forecasting in the US, 2020–2021

During the COVID-19 pandemic, forecasting COVID-19 trends to support planning and response was a priority for scientists and decision makers alike. In the United States, COVID-19 forecasting was coordinated by a large group of universities, companies, and government entities led by the Centers for Disease Control and Prevention and the US COVID-19 Forecast Hub ( https://covid19forecasthub.org ). We evaluated approximately 9.7 million forecasts of weekly state-level COVID-19 cases for predictions 1–4 weeks into the future submitted by 24 teams from August 2020 to December 2021. We assessed coverage of central prediction intervals and weighted interval scores (WIS), adjusting for missing forecasts relative to a baseline forecast, and used a Gaussian generalized estimating equation (GEE) model to evaluate differences in skill across epidemic phases that were defined by the effective reproduction number. Overall, we found high variation in skill across individual models, with ensemble-based forecasts outperforming other approaches. Forecast skill relative to the baseline was generally higher for larger jurisdictions (e.g., states compared to counties). Over time, forecasts generally performed worst in periods of rapid changes in reported cases (either in increasing or decreasing epidemic phases) with 95% prediction interval coverage dropping below 50% during the growth phases of the winter 2020, Delta, and Omicron waves. Ideally, case forecasts could serve as a leading indicator of changes in transmission dynamics. However, while most COVID-19 case forecasts outperformed a naïve baseline model, even the most accurate case forecasts were unreliable in key phases. Further research could improve forecasts of leading indicators, like COVID-19 cases, by leveraging additional real-time data, addressing performance across phases, improving the characterization of forecast confidence, and ensuring that forecasts were coherent across spatial scales. In the meantime, it is critical for forecast users to appreciate current limitations and use a broad set of indicators to inform pandemic-related decision making.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Influence of Polymorphism on the Electronic Structure of Ga 2 O 3

The search for new wide-band-gap materials is intensifying to satisfy the need for more advanced and energy-efficient power electronic devices. Ga 2 O 3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga 2 O 3 , α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theoretical approaches to gain insights into their structure–electronic structure relationships. Valence and conduction electronic structure as well as semicore and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron density functional theory and many-body perturbation theory, provides detailed understanding of the spectroscopic results. The calculated spectra provide very accurate descriptions of all experimental spectra and additionally illuminate the origin of observed spectral features. This paper provides a strong basis for the exploration of the Ga 2 O 3 polymorphs as materials at the heart of future electronic device generations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Synthesis and decomposition of a novel carboxylate precursor to indium oxide

Reaction of metallic indium with benzoyl peroxide in 4-1 methylpyridine (4-Mepy) at 25 C produces an eight-coordinate mononuclear indium(III) benzoate, In(eta(sup 2)-O2CC6H5)3(4-Mepy)2 4H2O (I), in yields of up to 60 percent. The indium(III) benzoate was fully characterized by elemental analysis, spectroscopy, and X-ray crystallography; (I) exists in the crystalline state as discrete eight-coordinate molecules; the coordination sphere around the central indium atom is best described as pseudo-square pyramidal. Thermogravimetric analysis of (I) and X-ray diffraction powder studies on the resulting pyrolysate demonstrate that this new benzoate is an inorganic precursor to indium oxide. Decomposition of (I) occurs first by loss of 4-methylpyridine ligands (100 deg-200 deg C), then loss of benzoates with formation of In2O3 at 450 C. We discuss both use of carboxylates as precursors and our approach to their preparation.

Hepp, Aloysius F.↗
DOE OSTI2022

Quantifying Energetic and Entropic Pathways in Molecular Systems

When examining dynamics occurring at nonzero temperatures, both energy and entropy must be taken into account to describe activated barrier crossing events. Furthermore, good reaction coordinates need to be constructed to describe different metastable states and the transition mechanisms between them. Here we use a physics-based machine learning method called state predictive information bottleneck (SPIB) to find nonlinear reaction coordinates for three systems of varying complexity. SPIB is able to correctly predict an entropic bottleneck for an analytical flat-energy double-well system and identify the entropy- and energy-dominated pathways for an analytical four-well system. Lastly, for a simulation of benzoic acid permeation through a lipid bilayer, SPIB is able to discover the entropic and energetic barriers to the permeation process. Given these results, we thus establish that SPIB is a reasonable and robust method for finding the important entropy, energy, and enthalpy barriers in physical systems, which can then be used to enhance the understanding and sampling of different activated mechanisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Real-time collision avoidance manipulator transfer movements

Collision free robot manipulator maneuvers for transferring a payload from one location to another in the presence of obstacles are discussed. Such maneuvers are executed by means of two algorithms running in parallel. The first algorithm performs an on-line, one step ahead acceleration optimization, with an adaptive N-step ahead precaution measure to prevent overshooting the specified forbidden joint coordinates. The second algorithm, an on-line planning algorithm, at the same time, selects the current target state and the current forbidden joint coordinates for the first algorithm. Since the task is a point to point transfer movement, the problem is dealt in robot joint space directly and the kinematic problem can be bypassed completely. A simulation example using a 2 degree-of-freedom planner robot is given.

Chen, N.↗
NASA NTRS2020

Terrain Relative Navigation for Guided Descent on Titan

Titan’s dense atmosphere, low gravity, and high winds at high altitudes create descent times of >90 minutes with standard entry/descent/landing (EDL) architectures and result in large unguided landing ellipses, with 99% values of 110x110 km and 149x72 km in recent Titan lander proposals. Enabling precision landing on Titan could increase science return for the types of missions proposed to date and make additional types of landing sites accessible, opening up new possibilities for science investigations. Precision landing on Titan has unique challenges, because the hazy atmosphere makes it difficult to see the surface and because it requires guided descent with divert ranges that are one to two orders of magnitude larger than needed for other target bodies, i.e. up to on the order of 100 km. It is conceivable that such a divert capability could be provided economically by a parafoil or other steerable aerodynamic decelerator deployed several 10s of km above the surface. The long descent times lead to large inertial navigation errors, hence a need for terrain relative navigation (TRN). This would require a TRN capability that can operate at such altitudes, despite challenges of seeing the surface sufficiently clearly and of depending on map products that are two orders of magnitude lower in spatial resolution than those for Mars and airless bodies. We then develop algorithms for map matching and feature tracking with descent images and test these with synthetic images created from Cassini/Huygens data sets and our radiative transfer model. We also introduce new possibilities for TRN based on the potential to discriminate some specific types of terrain onboard in descent imagery, such as lake vs adjacent ground and dune vs interdune. We use sensor measurement noise models in simulations of state estimation with an extended Kalman filter that includes coordinates of a set of tracked features in the state vector. Case studies were done for two notional landing sites, one in a site with only dry ground and one in a Titan lake district. In both cases, the filter error model shows 3 position error at touchdown on the order of 2 km. More work is needed to validate these results with higher fidelity camera models and larger data sets, but this is very promising.

Matthies, Larry↗
DOE OSTI2021

Atlantic Offshore Wind Transmission Literature Review and Gaps Analysis

In support of the national goal to deploy 30 gigawatts of offshore wind by 2030, DOE’s Wind Energy Technologies Office has published an Atlantic Offshore Wind Transmission Literature Review and Gaps Analysis. Transmission constraints— including both land-based transmission interconnections and offshore transmission—are expected to be one of the central challenges to meeting offshore wind deployment goals. Given current trends in offshore wind development, available technology, and state-level procurement goals, most of the first 30 GW of offshore wind are anticipated to be developed along the East Coast. This report summarizes current publicly available transmission analyses along the Atlantic Coast, as well as gaps in existing analyses. Improving understanding of offshore wind transmission options, establishing coordination and aligning processes among states and regions, and quantifying the long-term impacts of offshore wind transmission options will catalyze offshore wind energy’s growth and ensure adequate transmission and a reliable grid.

17 WIND ENERGY↗
DOE OSTI2025

The inorganic chemist's guide to actinide radiation chemistry: a review

This review aims to provide an overview of the current state of radiation chemistry with respect to the actinide elements, thorium through californium. Despite the inherent radioactivity of the actinides, only a few studies explore the effects of ionizing radiation on their redox chemistry and surrounding environment. This fundamental knowledge gap, coupled with the current renaissance in actinide-based technologies such as nuclear power, space exploration, and medicine, underscores the importance of research in this interdisciplinary area. This review will focus on the interactions between reactive species formed by radiolysis with actinides and their complexes, offering an inorganic chemist's perspective on research in radiation chemistry. In addition, a thorough discussion of our current understanding of radiation-induced changes in actinide speciation in both aqueous solution and the solid-state will be provided, focusing on changes in oxidation state distribution, complexation, and secondary coordination effects within inorganic materials. Finally, this review will discuss challenges and opportunities for inorganic chemists to explore this unique intersection of fields.

Actinides↗
NASA NTRS2021

Context and future directions for integrating forest carbon into sub-national climate mitigation planning in the RGGI region of the U.S.

International frameworks for climate mitigation that build from national actions have been developed under the United National Framework Convention on Climate Change and advanced most recently through the Paris Climate Agreement. In parallel, sub-national actors have set greenhouse gas (GHG) reduction goals and developed corresponding climate mitigation plans. Within the U.S., multi-state coalitions have formed to facilitate coordination of related science and policy. Here, utilizing the forum of the NASA Carbon Monitoring System’s Multi-State Working Group, we collected and reviewed climate mitigation plans for 11 states in the Regional Greenhouse Gas Initiative region of the Eastern U.S. For each state we reviewed the (a) policy framework for climate mitigation, (b) GHG reduction goals, (c) inclusion of forest activities in the state’s climate action plan, (d) existing science used to quantify forest carbon estimates, and (e) stated needs for forest carbon monitoring science. Across the region, we found important differences across all categories. While all states have GHG reduction goals and framework documents, nearly three-quarters of all states do not account for forest carbon when planning GHG reductions; those that do account for forest carbon use a variety of scientific methods with various levels of planning detail and guidance. We suggest that a common, efficient, standardized forest carbon monitoring system would provide important benefits to states and the geographic region as a whole. In addition, such a system would allow for more effective transparency and progress tracking to support state, national, and international efforts to increase ambition and implementation of climate goals.

Rachel L Lamb↗
DOE OSTI2023

Joint X-ray/neutron structure of Lentinus similis AA9_A at room temperature

Lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes which cleave polysaccharides oxidatively and are important in pathogen biology, carbon cycling and biotechnology. The Lentinus similis family AA9 isoform A (LsAA9_A) has been extensively studied as a model system because its activity towards smaller soluble saccharide substrates has allowed detailed structural characterization of its interaction with a variety of substrates by X-ray crystallography at high resolution. Here, the joint X-ray/neutron room-temperature crystallographic structure of carbohydrate-free LsAA9_A in the copper(II) resting state refined against X-ray and neutron data at 2.1 and 2.8 Å resolution, respectively, is presented. The results provide an experimental determination of the protonation states of the copper(II)-coordinating residues and second-shell residues in LsAA9_A, paving the way for future neutron crystallographic studies of LPMO–carbohydrate complexes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Assessment and Commissioning of Electrical Substation Grid Testbed with a Real-Time Simulator and Protective Relays/Power Meters in the Loop

Electrical utility substations are wired with intelligent electronic devices (IEDs), such as protective relays, power meters, and communication switches. Substation engineers commission these IEDs to assess the appropriate measurements for monitoring, control, power system protection, and communication applications. Like real electrical utility substations, complex electrical substation grid testbeds (ESGTs) need to be assessed for measuring current and voltage signals in monitoring, power system protection, control (synchro check), and communication applications that are limited by small measurement percentage errors. In the process of setting an ESGT with real-time simulators and IEDs in the loop, protective relays, power meters, and communication devices must be commissioned before running experiments. In this study, an ESGT with IEDs and distributed ledger technology was developed. The ESGT with a real-time simulator and IEDs in the loop was satisfactorily assessed and commissioned. The commissioning and problem-solving tasks of the testbed are described to define a method with flowcharts to assess possible trouble-shooting in ESGTs. This method was based on comparing the simulations versus IED measurements for the phase current and voltage magnitudes, three-phase phasor diagrams, breaker states, protective relay times with selectivity coordination at electrical faults, communication data points, and time-stamp sources.

Piesciorovsky, Emilio↗
DOE OSTI2024

Detection of the BICT State in a Borafluorene with High Stokes Shift Fluorescence

Four-coordinate aryl borafluorenes with boron–oxygen and boron–nitrogen dative bonds can exhibit very large fluorescence Stokes shifts. The large Stokes shifts are hypothesized to arise from cleavage of the boron-donor dative bond in the excited state, via a mechanism called bond-cleavage-induced intramolecular charge transfer (BICT). The primary goal of this current investigation is to directly observe the BICT state by performing transient absorption spectroscopy (TAS) on four-coordinate borafluorenes, which have improved optical stability. A novel four-coordinate aryl borafluorene was synthesized which features a dative B–O bond and two tert-butyl moieties on the aryl ring. TAS of the new borafluorene is consistent with the existence of a single, three-coordinate species in the excited state, as predicted by the BICT hypothesis. In conclusion, the TAS data is supported by fluorescence lifetime measurements and DFT calculations.

Absorption↗
DOE OSTI2021

Exciton-Phonon Coupling and Carrier Relaxation in PbS Quantum Dots: The Case of Carboxylate Ligands

Some ligand-nanocrystal combinations exhibit rapid cooling of highly excited electronic states while other nanocrystal/shell combinations do not appear to have this effect. There remains a need to identify the distinguishing properties of ligand-nanocrystal interactions that avoid such rapid relaxation processes to guide the design of colloidal quantum dots (QDs) that take advantage of multiple exciton generation or hot-carrier extraction processes. Here, we use mid-infrared transient absorption spectroscopy to investigate the influence that carboxylate ligands with distinct excited state surface chemistries has on exciton-phonon coupling and hot exciton relaxation in PbS quantum dot (QD) films. Our findings reveal that despite significant differences in the excited state surface chemistry of oleate (OA) and iodide/mercaptopropionic acid (I-/MPA) ligands, PbS QD films passivated with both ligand types exhibit identical electronic relaxation rates and exciton-phonon coupling strengths within experimental precision. The data suggest that the inorganic lattice is the principal source of exciton-phonon coupling that influences hot exciton relaxation, rather than the vibronic modes of carboxylate ligands. The size-dependent nature of the exciton-phonon coupling strength is consistent with the localization of charge on the QD surfaces, which enhances the mixing of electronic and nuclear coordinates particularly when the electronic states are more quantum confined in smaller nanocrystals.

14 SOLAR ENERGY↗
NASA NTRS1991

Discrete Kalman filtering equations of second-order form for control-structure interaction simulations

A second-order form of discrete Kalman filtering equations is proposed as a candidate state estimator for efficient simulations of control-structure interactions in coupled physical coordinate configurations as opposed to decoupled modal coordinates. The resulting matrix equation of the present state estimator consists of the same symmetric, sparse N x N coupled matrices of the governing structural dynamics equations as opposed to unsymmetric 2N x 2N state space-based estimators. Thus, in addition to substantial computational efficiency improvement, the present estimator can be applied to control-structure design optimization for which the physical coordinates associated with the mass, damping and stiffness matrices of the structure are needed instead of modal coordinates.

Park, K. C.↗
DOE OSTI2023

Tailoring Mid–Gap States of Chalcogenide Glass by Pressure–Induced Hypervalent Bonding Towards the Design of Electrical Switching Materials

Phase change memory (PCM) and ovonic threshold switching (OTS) materials using chalcogenide glass are essential elements in advanced 3D memory chips. The mid–gap states, induced by the disorder and defects in the glass, are the physical mechanisms of the electrical switching behavior, while the origin of these trap states is still under debate and the medium–range clusters that break the global octet rule, such as over–coordinated atoms, are known to be responsible in various glass. Here, it is discovered that a large fraction of over–coordinated clusters fails to generate mid–gap states, which are probably caused by hypervalent bonding, a multi–centered covalent bond participated by delocalized lone–pair electrons. This is confirmed by the pressure–driven simulations of amorphous GeSe models, in which it is found that octahedral motifs and hypervalent bonds prevent the over–coordinated medium–range clusters from providing excessive electrons. In practical applications, compatible dopants can be used to change the number of hypervalent bonds, thus controlling the number of mid–gap states and consequently the performance of PCM and OTS materials. Finally, these results reveal the origin of mid–gap states in chalcogenide glasses, enabling extensive control in the development of pioneering electrical switching materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Photophysics of graphene quantum dot assemblies with axially coordinated cobaloxime catalysts

We report a study of chromophore-catalyst assemblies composed of light harvesting hexabenzocoronene (HBC) chromophores axially coordinated to two cobaloxime complexes. The chromophore-catalyst assemblies were prepared using bottom-up synthetic methodology and characterized using solid-state NMR, IR, and x-ray absorption spectroscopy. Detailed steady-state and time-resolved laser spectroscopy was utilized to identify the photophysical properties of the assemblies, coupled with time-dependent DFT calculations to characterize the relevant excited states. The HBC chromophores tend to assemble into aggregates that exhibit high exciton diffusion length (D = 18.5 molecule 2 /ps), indicating that over 50 chromophores can be sampled within their excited state lifetime. We find that the axial coordination of cobaloximes leads to a significant reduction in the excited state lifetime of the HBC moiety, and this finding was discussed in terms of possible electron and energy transfer pathways. By comparing the experimental quenching rate constant (1.0 × 10 9 s -1 ) with the rate constant estimates for Marcus electron transfer (5.7 × 10 8 s -1 ) and Förster/Dexter energy transfers (8.1 × 10 6 s -1 and 1.0 × 10 10 s -1 ), we conclude that both Dexter energy and Marcus electron transfer process are possible deactivation pathways in CoQD-A. No charge transfer or energy transfer intermediate was detected in transient absorption spectroscopy, indicating fast, subpicosecond return to the ground state. Finally, these results provide important insights into the factors that control the photophysical properties of photocatalytic chromophore-catalyst assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2014

Comparison of Nickel XANES Spectra and Elemental Maps from a Ureilite, a LL3.8 Ordinary Chondrite, Two Carbonaceous Chondrites and Two Large Cluster IDPs

Nickel in the extraterrestrial world is commonly found in both Fe-Ni sulfide and Fe-Ni met-al forms [1] and in the pure metal state in the interior of iron meteorites where it is not easily oxidized. Ni is also found in olivine, pyroxene and glasses and in some melts the partitioning of Ni between the olivines and glass is controlled by the amount of S in the melt [2]. Its most common valence state is Ni(2+) but Ni also occurs as Ni(0), Ni(+), and Ni(3+) and rarely as Ni(2-), Ni(1-) and Ni(4+) [3]. It's valence state in olivines is Ni(2+) in octa-hedral coordination on the M1 site and rarely on the M2 site.[4]. The chemical sensitivity of X-ray absorp-tion near-edge structure (XANES) spectroscopy is well established and can be used to determine not only va-lence states but also coordination sites [5]. We report here Ni XANES spectroscopy and elemental maps collected from 2 carbonaceous chondrites, 2 large clus-ter IDPs, 1 ureilite and 1 LL3 orginary chondrite.Using XANES it may be possible to find a common trait in the large cluster IDPs that will also be found in mete-orite samples.

Wirick, S.↗
DOE OSTI2025

Watching Polarons Dance: Coherent Carrier–Phonon Coupling in Hematite Revealed by Transient Absorption Spectroscopy

Hematite remains a prominent photoanode candidate for the oxygen evolution reaction in solar water splitting, despite efficiency limitations from rapid trapping of photoexcited electrons and holes. While the formation of polarons, quasiparticles formed by electron–hole interactions with lattice vibrations, is a proposed trapping mechanism, direct evidence of such states has been elusive. Here, we use potential-dependent transient absorption spectroscopy to identify the coherent phonon mode and strong exciton–phonon coupling responsible for exciton–polaron formation after band gap excitation in α-hematite and identify the three underlying d–d transitions that are strongly modulated by this phonon. The equilibrium geometry of exciton–polarons in α-hematite is displaced from the ground state geometry along the vibrational coordinate of an A 1g symmetric Fe–O stretching motion at 225 ± 7 cm –1 , resulting in vibrational coherence with a lifetime of 1.9 ± 0.1 ps. Our comparative ex situ and in situ experiments reveal that the energy and dephasing time of the A 1g mode are remarkably resilient to applied potential and the addition of an Al 2 O 3 overlayer; however, the dephasing time is sensitive to substrate identity. Furthermore, this potential-dependent transient absorption approach establishes a powerful platform for directly probing polaron dynamics in photoelectrochemical systems, opening new pathways to rationally design modified hematite and other transition metal oxide electrodes with enhanced charge transport properties for more efficient solar water splitting.

Hematite↗