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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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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Transit Rider/Travel Behavior Inventory Survey - Minneapolis-St. Paul Metro - 2010

The Metropolitan Council administered a system-wide transit on-board survey between September and November 2010 as part of the 2010 Travel Behavior Inventory to provide detailed transit usage patterns and rider information to support modeling and planning efforts. The study’s focus was to capture only the most current and reliable data necessary to determine future public transportation needs in the Minneapolis region. The study was structured to collect detailed transit ridership data for different routes during different times of day to develop a disaggregate transit trip table that will support advanced travel demand modeling. The study was designed to leverage existing data sources, such as the 2005 on-board survey, to provide the best quality data to update the Travel Behavior Inventory in the Minneapolis-Saint Paul metropolitan area.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

Long Beach Transit Battery Electric Bus Evaluation (Final Report)

Beginning in March 2017, Long Beach Transit began operating a fleet of 10 battery electric buses (BEBs) in its service area in Southern California. These electric buses, produced by BYD, are 40-foot buses that are typically charged overnight. Long Beach Transit is collaborating with the California Air Resources Board (CARB) and the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) to evaluate the buses in revenue service. NREL evaluated the first year of Long Beach Transit’s BEB fleet under Federal Transit Administration funding and published a report covering results from January 2018 through December 2018. CARB provided funding to cover a second year of evaluation. This report provides an update to the previous reports and is focused on the second year of operation from January 2019 through December 2019. Data are provided on a selection of compressed natural gas (CNG) buses as a baseline comparison.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

Fuel Cell Buses in U.S. Transit Fleets: Current Status 2020

This report summarizes the progress of fuel cell electric bus (FCEB) development in the United States and discusses the achievements and challenges of introducing fuel cell propulsion in transit. The report provides a summary of results from evaluations performed by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL). The 2020 summary results primarily focus on the most recent data on these FCEBs, from January 2020 through July 2020. The primary results presented in the report are from 25 FCEBs deployed at three agencies: Alameda-Contra Costa Transit District (AC Transit) in Oakland, California (10 FCEBs); Orange County Transportation Authority (OCTA) in Santa Ana, California (10 FCEBs); SunLine Transit Agency in Thousand Palms, California (5 FCEBs).

08 HYDROGEN↗
DOE OSTI2021

Foothill Transit Battery Electric Bus Evaluation (Final Report)

This report summarizes results of a battery electric bus (BEB) evaluation at Foothill Transit, located in Southern California. Foothill Transit began a demonstration of three Proterra BEBs in October 2010 to evaluate the battery technology and determine if the BEBs could meet Foothill Transit’s service requirements. Since that pilot project, the agency has added 31 BEBs to its fleet. Foothill Transit is collaborating with the California Air Resources Board (CARB) and the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) to evaluate the buses in revenue service. The focus of the evaluation is to compare performance and cost of the BEBs to that of conventional technology in similar service and track progress over time. This report summarizes the results of the BEB and baseline fleets through December 2020.

25 ENERGY STORAGE↗
DOE OSTI2026

On-Demand Transit: Features, Benefits, Challenges, Costs, and Evaluation

The U.S. Department of Energy's National Laboratory of the Rockies works in partnership with communities and transit agencies across North America to support and evaluate customized on-demand transit (ODT) systems. ODT, also known as on-demand mobility or microtransit, is a flexible form of public mobility. Unlike traditional fixed-route transit, ODT adjusts where and when service is provided rather than following predetermined schedules and routes. Having evolved from commercial ride-hailing business models, ODT leverages smartphone connectivity and real-time route optimization to provide highly responsive and dynamic service. ODT trips, which are usually shared, can function as a standalone service or as a first-/last-mile service connecting riders to other types of transit.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2022

Tuning Spin-Orbit Torques Across the Phase Transition in VO 2 /NiFe Heterostructure

The emergence of spin-orbit torques as a promising approach to energy-efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin-orbit torques. We report current-induced spin-orbit torques in VO 2 /NiFe heterostructures are investigated using spin-torque ferromagnetic resonance, where the VO 2 layer undergoes a prominent insulator-metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO 2 /NiFe interface spin absorption across the VO 2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current-induced spin-orbit torque across the VO 2 phase transition suggest two competing spin-orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO 2 , corroborated by the first-principles calculation of the spin Hall conductivity σ SH ≈ -10 4 ($\frac{\hbar}{e}$) Ω -1 m -1 , is verified as the main source of the spin-orbit torque in the metallic phase. The self-induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO 2 , can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin-orbit torques of materials that undergo phase transitions for new device functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Direct Imaging of Antiferromagnet-Ferromagnet Phase Transition in van der Waals Antiferromagnet CrSBr

The advent of van der Waals (vdW) ferromagnetic (FM) and antiferromagnetic (AFM) materials offers unprecedented opportunities for spintronics and magneto-optic devices. Combining magnetic Kerr microscopy and density functional theory calculations, the AFM-FM transition is investigated and a surprising abnormal magneto-optic anisotropy in vdW CrSBr associated with different magnetic phases (FM, AFM, or paramagnetic state) is discovered. This unique magneto-optic property leads to different anisotropic optical reflectivity from different magnetic states, permitting direct imaging of the AFM Néel vector orientation and the dynamic process of the AFM-FM transition within a magnetic field. Using Kerr microscopy, not only the domain nucleation and propagation process is imaged but also the intermediate spin-flop state in the AFM-FM transition is identified. In conclusion, the unique magneto-optic property and clear identification of the dynamics process of the AFM-FM phase transition in CrSBr demonstrate the promise of vdW magnetic materials for future spintronic technology.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural Evolution and Transition Dynamics in Lithium Ion Battery under Fast Charging: An Operando Neutron Diffraction Investigation

Abstract Fast charging (<15 min) of lithium‐ion batteries (LIBs) for electrical vehicles (EVs) is widely seen as the key factor that will greatly stimulate the EV markets, and its realization is mainly hindered by the sluggish diffusion of Li + . To have a mechanistic understanding of Li + diffusion within LIBs, in this study, structural evolutions of electrodes for a Ni‐rich LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) || graphite cylindrical cell with high areal loading (2.78 mAh cm −2 ) are developed for operando neutron powder diffraction study at different charging rates. Via sequential Rietveld refinements, changes in structures of NMC622 and Li x C 6 are obtained during moderate and fast charging (from 0.27 C to 4.4 C). NMC622 exhibits the same structural evolution regardless of C‐rates. For phase transitions of Li x C 6 , the stage I (LiC 6 ) phase emerges earlier during the stepwise intercalation at a lower state of charge when charging rate is increased. It is also found that the stage II (LiC 12 ) → stage I (LiC 6 ) transition is the rate‐limiting step during fast charging. The LiC 12 → LiC 6 transition mechanism is further analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. It is concluded as a diffusion‐controlled, 1D phase transition with decreasing nucleation kinetics under increasing chargingrates.

25 ENERGY STORAGE↗
DOE OSTI2022

Gravitational waves from an inflation triggered first-order phase transition

Large excursion of the inflaton field can trigger interesting dynamics. One important example is a first-order phase transition in a spectator sector which couples to the inflaton. Gravitational waves (GWs) from such a first-order phase transition during inflation, an example of an instantaneous source, have an oscillatory feature. In this work, we show that this feature is generic for a source in an era of accelerated expansion. We also demonstrate that the shape of the GW signal contains information about the evolution of the early universe following the phase transition. In particular, the slope of the infrared part of the GW spectrum is sensitive to the evolution of the Hubble parameter when the GW modes reenter the horizon after inflation. The slope of the profile of the intermediate oscillatory part and the ultraviolet part of the GW spectrum depend on the evolution of the Hubble parameter when the modes exit horizon during the inflation and when they reenter the horizon during the reheating. The ultraviolet spectrum also depends on the details of the dynamics of the phase transition. We consider the GW signal in several models of evolution during and after inflation, and compare them with the minimal scenario of quasi- de Sitter inflation followed by radiation domination after a fast reheating, and demonstrate that the shape of the GW can be used to distinguish them. In this way, the GW signal considered in this paper offers a powerful probe to the dynamics of the early universe which is otherwise difficult to explore directly through CMB, large scale structure, big bang nucleosynthesis (BBN), and other well-studied cosmological observables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Pressure engineering of intertwined phase transitions in lanthanide monopnictide NdSb

Coexistence of non-trivial band topology and intrinsic magnetic order not only leads to emergent phenomena but also allows for the tunability of the exotic properties from different degrees of freedom. By performing transport measurements at synergetic extreme conditions, here we report on pressure engineering of intertwined structural, magnetic, and topological phase transitions in antiferromagnetic Dirac semimetal NdSb. We show that the original antiferromagnetic state is strengthened in the low pressure region while destabilized upon further compression close to the critical pressure when a structural transition from Fm-3m phase to P4/mmm phase takes place at P C ~ 18 GPa, forming a Ger-shaped evolution in response to magnetic field, pressure and temperature. Concomitant with the structural transition, NdSb simultaneously carries on a magnetic transition to the ferromagnetic state. Further, theoretical calculations unravel that the ferromagnetic tetragonal phase presents nontrivial features of Weyl fermions. These findings offer new important insight into the microscopic interplay among lattice, spin, and relativistic fermions in lanthanide monopnictides.

42 ENGINEERING↗
DOE OSTI2025

Microstructure characteristics of LPBF&HIP fabricated graded composite transition joint between ferritic steel and austenitic stainless steel

Graded composite transition joints (GCTJs) offer a promising alternative to conventional dissimilar metal welds (DMWs) by enabling smooth compositional and microstructural transitions. However, GCTJs fabricated solely through additive manufacturing (AM) face challenges such as heat accumulation, complex parameter control, and elemental segregation. In this study, we propose a novel approach that relies on AM to design a spatially graded structure in one alloy and then employs hot isostatic pressing (HIP) as a diffusion bonding method to join it with a second alloy. Here, this method combines the flexibility of AM with the powder net-shaping advantage of HIP. Specifically, a series of closely packed austenitic stainless steel 304 conical structures were printed using laser powder bed fusion (LPBF) and then combined with ferritic steel P91 powder via HIP. By using electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM) techniques, the microstructure characteristics of the GCTJ of 304&P91, especially the interdiffusion zone (IDZ), have been systematically investigated. The microstructure at the interface transitions from austenite-ferrite (A+F) to austenite-martensite-ferrite (A+M+F), and finally to martensite-ferrite (M+F) due to diffusion. Additionally, the diffusion width between 304 and P91 increases with the volume fraction of P91. This unique design also ensures a gradual transition in both hardness and thermal expansion coefficient from 304 to P91, thereby enabling a smooth gradient in functional properties. Overall, this study proposes a novel approach for fabricating GCTJs and contributes to advancing design concepts in the field of dissimilar metal joining.

Additively manufacturing (AM)↗
DOE OSTI2026

Opportunities for bioenergy crops to support transitions from irrigated agriculture and conserve the U.S. High Plains Aquifer

This study investigates potential economic and groundwater driven transitions from irrigated maize production—the dominant irrigated cropping system in the High Plains Aquifer (HPA) region—to alternative crops such as sorghum and switchgrass, two common bioenergy feedstocks. Unsustainable groundwater extraction in the U.S. High Plains presents critical challenges including reduced irrigation capacities, diminished crop yields, lower land values, and escalating energy costs. Using a spatially explicit optimization framework combined with comprehensive economic and hydrogeological data, we evaluate optimal land-use strategies and irrigation system investments over a 30-year planning period. Results indicate significant regional variability in the future economic viability of irrigated agriculture, driven by differences in aquifer recharge rates, groundwater availability, and market conditions. Nebraska and parts of northern Texas can sustain irrigated maize profitability due to relatively favorable groundwater conditions and lower land rents, respectively. In contrast, many portions of Kansas and southern Texas are more likely to transition to dryland agriculture within two decades. Colorado and New Mexico show potential for significant adoption of switchgrass production as an alternative biomass-based energy crop. Overall, over the 30-year horizon, our model implies that approximately 23% of currently irrigated maize area across the HPA region may transition to dryland farming under business-as-usual conditions. This transition is complemented by a threefold increase in non-irrigated sorghum production, from 0.20 to 0.77 Mt yr−1, indicating that groundwater-driven shifts in agricultural production may support a larger regional base for bioenergy feedstocks. The study also reveals opportunities for producers to optimize economic returns and biomass production potential.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Theoretical assessments of CO 2 activation and hydrogenation pathways on transition-metal surfaces

Carbon dioxide (CO 2 ) hydrogenation on transition-metal active sites offers a promising carbon utilization route toward mitigating greenhouse gas emissions. C 1 products are often formed in parallel during CO 2 hydrogenation, prompting investigations into the intrinsic properties of transition metals that drive activity and product selectivity. Here, in this work, close-packed surfaces of a selection of transition-metal catalysts (Ni, Co, Rh, Ru, Pd, and Pt) were studied with density functional theory (DFT) calculations to understand their fundamental reactivities for CO 2 transformation reactions. Results indicate that CO 2 conversion proceeds through CO* formation and hydrogenation to form C 1 products (* denotes an adsorbed species). Ni, Co, Rh, and Ru favor CO/CH 4 formation, while Pd and Pt favor CO/CH 3 OH formation. The ability of a metal to dissociate C-O bonds drives selectivity between CH 4 and CH 3 OH, while competition between CO* desorption and surface hydrogenation describes CO selectivities. The C-O bond dissociation steps often impose the highest barrier along CH 4 formation reaction profiles, suggesting their kinetic relevance for CH 4 formation rates. The provided DFT-derived data sets detail a comprehensive reaction network of elementary steps relevant to C 1 chemistries, ultimately offering a benchmark for insights into design strategies for materials that exploit transition-metal active sites in carbon capture or utilization processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Targeted synthesis, characterization, and electrochemical analysis of transition-metal-oxide catalysts for the oxygen evolution reaction

Hydrogen fuel can be produced through the electrochemical splitting of water, an energy-intensive process that requires the use of electrocatalysts to be more efficient. Whereas current precious-metal-based electrocatalysts might be costly on a larger scale, transition-metal-oxide catalysts are more earth abundant and have shown promising activity. Here, the development and improvement of highly active transition-metal-oxide electrocatalysts is thus an important area of study where different catalyst enhancement strategies are used to drive the field forward. Additionally, transition-metal-oxide catalysts come in various different structures with their own advantages; thus, this review is focused on investigating the continuing field of transition-metal-oxide electrocatalysts of different structures and innovative methods of improving activity. By the end, new and promising paths forward in this field will be highlighted, particularly in the development of rock-salt oxides for the water-splitting system.

08 HYDROGEN↗
DOE OSTI2023

Exploring structural transitions at grain boundaries in Nb using a generalized embedded atom interatomic potential

The advancement in experimental techniques, like the atom probe tomography and high resolution electron microscopy, is fueling interest in studying structural transformations of grain boundaries in metal and alloys to uncover correlations between mechanical properties and solute or impurity segregation to grain boundaries. Atomistic modeling is an important tool that can pinpoint the intricate dynamics of grain boundary phase transitions, but the lack of accurate interatomic potentials needed to simulate the complex dynamics of grain boundary structural transitions and identify different metastable phases has been the bottleneck. To this end, we use niobium as a model body centered cubic (BCC) metal and develop an interatomic potential to study grain boundary phase transitions. The potential for Nb is based on a generalization of the embedded atomic method potential and has sufficient flexibility to learn complex energy landscapes using a small set of training structures. We systematically test and validate the using data from ab initio density functional theory calculations and experiments. Using this potential, we calculate energies of multiple symmetric-tilt grain boundaries spanning a wide range of misorientation angles. Additionally, we explore different metastable structures of the Σ 27(552) [$1\overline{1}0$] grain boundary and use molecular dynamic simulations to study the coexistence of metastable phases and grain boundary transitions at finite temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optically induced quantum transitions in direct probed mesoscopic NbSe 2 for prototypical bolometers

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe 2 , has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe 2 -based sensor within the TES framework remains unexplored. In this work, direct-probed superconducting NbSe 2 absorbers led to a proof-of-concept demonstration for the transduction of incoming light to heat, where a thermodynamic superconducting phase transition in NbSe 2 was evident to switch it to the normal-state, when biased below its superconducting transition temperature. A wavelength-dependent response of its optical absorption properties was observed, based on the incident optical excitation source used. Furthermore, extensive optical characterization studies were conducted using Raman spectroscopy, where the in-plane and out-of-plane thermal conductivity was empirically determined. Our results open new possibilities for the use of NbSe 2 in superconducting radiation detectors, including in a TES framework

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Solid-solid phase transition via the liquid in a Pd 43 Cu 27 Ni 10 P 20 bulk metallic glass under conventional conditions

The microscopic mechanism of solid-solid phase transitions is a long-standing fundamental issue in materials science. Here we directly report the experimental evidence of the existence of an intermediate liquid during the solid-solid phase transition in a bulk Pd 43 Cu 27 Ni 10 P 20 alloy by in situ high temperature high energy X-ray diffraction, combined with the differential scanning calorimetry at slow heating rates down to 5 K/min. We elucidate that this intermediate liquid is attributed to the melting of the low-melting-point crystalline phases, rather than induced by the elastic stress energy along the interface proposed in literatures. This could also be a general feature in multicomponent alloys if a low-melting-point crystalline phase is formed together with other crystalline phases during heating. Furthermore, all results obtained here are scientifically sound and provide new insight into the phase transition theory, which will trigger more studies on the microscopic mechanism of solid-solid phase transition via an intermediate liquid.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetoelastic transition and magnetocaloric effect in induction melted Fe 100-x Rh x bulk alloys with x = 50, 51

Magnetoelastic transitions (METs) in bulk in nearly equiatomic Fe-Rh alloys produced by arc melting may show poor reproducibility related to insufficient chemical homogeneity and presence of impurity phases in variable concentrations. To better understand the synthesis conditions that reliably yield bulk FeRh materials with reproducible MET characteristics, Fe 100-x Rh x alloys with x = 50, 50.5 and 51 at. % were prepared by induction melting and thermal annealing under identical conditions. The fabricated samples were cut into several slices, followed by characterization of METs in each of the slices using isothermal and isofield magnetization measurements, differential scanning calorimetry, and direct measurements of the magnetocaloric effect. All of the slices exhibit METs between the AFM and FM states, but the transitions are abrupt with nearly the same change of magnetization, ΔM, when x = 50.5 and 51, whereas for the x = 50 alloy the transition spreads over a wide temperature interval and ΔM may fluctuate by as much as 10 % from one specimen to another. A comparison of the magnetocaloric responses of x = 50 and 51 materials is presented. The clearly different effect of the magnetic field on the transition in both directions leads to significant differences in the reversibility and maximum values of the magnetic field-induced entropy and adiabatic temperature changes, as well as average hysteresis losses. In terms of reproducibility, our results suggest that induction melting is a more appropriate technique to prepare these binary alloys.

36 MATERIALS SCIENCE↗