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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Dynamic Modeling and Soil Mechanics for Path Planning of the Mars Exploration Rovers

To help minimize risk of high sinkage and slippage during drives and to better understand soil properties and rover terramechanics from drive data, a multidisciplinary team was formed under the Mars Exploration Rover project to develop and utilize dynamic computer-based models for rover drives over realistic terrains. The resulting system, named ARTEMIS (Adams-based Rover Terramechanics and Mobility Interaction System), consists of the dynamic model, a library of terramechanics subroutines, and the high-resolution digital elevation maps of the Mars surface. A 200-element model of the rovers was developed and validated for drop tests before launch, using Adams dynamic modeling software. The external library was built in Fortran and called by Adams to model the wheel-soil interactions include the rut-formation effect of deformable soils, lateral and longitudinal forces, bull-dozing effects, and applied wheel torque. The paper presents the details and implementation of the system. To validate the developed system, one study case is presented from a realistic drive on Mars of the Opportunity rover. The simulation results match well from the measurement of on-board telemetry data. In its final form, ARTEMIS will be used in a predictive manner to assess terrain navigability and will become part of the overall effort in path planning and navigation for both Martian and lunar rovers.

rover↗
NASA NTRS2011

Dynamic Modeling and Soil Mechanics for Path Planning of the Mars Exploration Rovers

To help minimize risk of high sinkage and slippage during drives and to better understand soil properties and rover terramechanics from drive data, a multidisciplinary team was formed under the Mars Exploration Rover (MER) project to develop and utilize dynamic computer-based models for rover drives over realistic terrains. The resulting tool, named ARTEMIS (Adams-based Rover Terramechanics and Mobility Interaction Simulator), consists of the dynamic model, a library of terramechanics subroutines, and the high-resolution digital elevation maps of the Mars surface. A 200-element model of the rovers was developed and validated for drop tests before launch, using MSC-Adams dynamic modeling software. Newly modeled terrain-rover interactions include the rut-formation effect of deformable soils, using the classical Bekker-Wong implementation of compaction resistances and bull-dozing effects. The paper presents the details and implementation of the model with two case studies based on actual MER telemetry data. In its final form, ARTEMIS will be used in a predictive manner to assess terrain navigability and will become part of the overall effort in path planning and navigation for both Martian and lunar rovers.

terramechanics↗
DOE OSTI2023

Effect of Framework Composition and NH 3 on the Diffusion of Cu + in Cu-CHA Catalysts Predicted by Machine-Learning Accelerated Molecular Dynamics

Cu-exchanged zeolites rely on mobile solvated Cu + cations for their catalytic activity, but the role of the framework composition in transport is not fully understood. Ab initio molecular dynamics simulations can provide quantitative atomistic insight but are too computationally expensive to explore large length and time scales or diverse compositions. We report a machine-learning interatomic potential that accurately reproduces ab initio results and effectively generalizes to allow multinanosecond simulations of large supercells and diverse chemical compositions. Biased and unbiased simulations of [Cu(NH 3 ) 2 ] + mobility show that aluminum pairing in eight-membered rings accelerates local hopping and demonstrate that increased NH 3 concentration enhances long-range diffusion. The probability of finding two [Cu(NH 3 ) 2 ] + complexes in the same cage, which is key for SCR-NOx reaction, increases with Cu content and Al content but does not correlate with the long-range mobility of Cu + . Supporting experimental evidence was obtained from reactivity tests of Cu-CHA catalysts with a controlled chemical composition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

First-principles study of electron transport in ScN

We investigate the conduction-band structure and electron mobility in rocksalt ScN based on density functional theory. The first-principles band structure allows us to obtain band velocities and effective masses as a function of energy. Electron-phonon scattering is assessed by explicitly computing the q-dependent electron-phonon matrix elements, with the inclusion of the long-range electrostatic interaction. The influence of free-carrier screening on the electron transport is assessed using the random phase approximation. We find a notable enhancement of electron mobility when the carrier concentration exceeds 10 20 cm -3 . We calculate the room-temperature electron mobility in ScN to be 587 cm2 /Vs at low carrier concentrations. When the carrier concentration is increased, the electron mobility starts to decrease significantly around n = 10 19 cm -3 , and drops to 240 cm 2 /Vs at n = 10 21 cm -3 . We also explore the influence of strain in (111)- and (100)-oriented ScN films. For (111) films, we find that a 1.0% compressive epitaxial strain increases the in-plane mobility by 72 cm 2 /Vs and the out-of-plane mobility by 50 cm 2 /Vs. For (100) films, a 1.0% compressive epitaxial strain increases the out-of-plane mobility by as much as 172 cm2 /Vs, but has a weak impact on the in-plane mobility. Our study sheds light on electron transport in ScN at different electron concentrations and shows how strain engineering could increase the electron mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We then used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also found that impurity scattering dominates cyclotron resonance decay in the 2DHG, in contrast with the dominance of superradiant damping in two-dimensional electron gases. Our results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interlayer-Decoupled Sc-Based Mxene with High Carrier Mobility and Strong Light-Harvesting Ability

Two-dimensional (2D) van der Waals (vdW) layered materials offer a unique combination of electronic and structural properties attractive for technological applications. Most of them show strong vdW interactions, which lead to interlayer-coupled optoelectronic properties due to quantum confinement. Here we present a systematic computational study of one Mxene, 2D double-metal-layered scandium chloride carbides (Sc 2 CCl 2 ). Unlike conventional quantum-confined nanosystems, 2D Sc 2 CCl 2 exhibits weak vdW interactions with robust interlayer-decoupled optoelectronic properties and extremely high and anisotropic carrier mobilities of about 1–4.5 × 10 4 cm 2 V –1 s –1 that consequently produce comparatively large drain currents. Specifically, the 2D Sc 2 CCl 2 family has strong light-harvesting ability and could be utilized as efficient donor materials in excitonic solar cells. Overall, in combination with high structural stability against ambient conditions, interlayer-decoupled robust optoelectronic properties potentially relax the requirements for the fabrication of high-quality monolayers and for selection of suitable substrates and suggest promising next-generation optoelectronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

K-band mobile propagation measurements using ACTS

An overview of two planned propagation campaigns employing land-mobile scenarios with ACTS is presented. The campaigns will be undertaken through a joint effort involving the Johns Hopkins University, Applied Physics Laboratory (APL), The University of Texas at Austin, Electrical Engineering Research Laboratory (EERL), and the NASA Lewis Research Center (NASA LeRC). Propagation campaigns are planned in Central Maryland in November 1993 (elevation angle approx. equals 40 deg.) and in Fairbanks, Alaska in June 1994 (elevation angle approx. equals 8 deg.) employing a computer controlled antenna tracking system located atop a van containing a receiver/data acquisition system. The antenna will track (in azimuth) downlink transmissions at 19.914 GHz from ACTS during the mobile propagation measurements. The major objectives of the campaigns are to measure the fade and multipath effects of trees and terrain at 20 GHz for rural and suburban scenarios and to extend existing models which were previously validated at UHF to S-Band.

Goldhirsh, Julius↗
DOE OSTI2016

Communication: Polymer entanglement dynamics: Role of attractive interactions

The coupled dynamics of entangled polymers, which span broad time and length scales, govern their unique viscoelastic properties. To follow chain mobility by numerical simulations from the intermediate Rouse and reptation regimes to the late time diffusive regime, highly coarse grained models with purely repulsive interactions between monomers are widely used since they are computationally the most efficient. In this paper, using large scale molecular dynamics simulations, the effect of including the attractive interaction between monomers on the dynamics of entangled polymer melts is explored for the first time over a wide temperature range. Attractive interactions have little effect on the local packing for all temperatures T and on the chain mobility for T higher than about twice the glass transition T g . Finally, these results, across a broad range of molecular weight, show that to study the dynamics of entangled polymer melts, the interactions can be treated as pure repulsive, confirming a posteriori the validity of previous studies and opening the way to new large scale numerical simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Estimating traffic volumes for signalized intersections using connected vehicle data

Recently connected vehicle (CV) technology has received significant attention thanks to active pilot deployments supported by the US Department of Transportation (USDOT). At signalized intersections, CVs may serve as mobile sensors, providing opportunities of reducing dependencies on conventional vehicle detectors for signal operation. However, most of the existing studies mainly focus on scenarios that penetration rates of CVs reach certain level, e.g., 25%, which may not be feasible in the near future. How to utilize data from a small number of CVs to improve traffic signal operation remains an open question. In this work, we develop an approach to estimate traffic volume, a key input to many signal optimization algorithms, using GPS trajectory data from CV or navigation devices under low market penetration rates. To estimate traffic volumes, we model in this paper vehicle arrivals at signalized intersections as a time-dependent Poisson process, which can account for signal coordination. The estimation problem is formulated as a maximum likelihood problem given multiple observed trajectories from CVs approaching to the intersection. An expectation maximization (EM) procedure is derived to solve the estimation problem. Two case studies were conducted to validate our estimation algorithm. One uses the CV data from the Safety Pilot Model Deployment (SPMD) project, in which around 2800 CVs were deployed in the City of Ann Arbor, MI. The other uses vehicle trajectory data from users of a commercial navigation service in China. Mean absolute percentage error (MAPE) of the estimation is found to be 9–12%, based on benchmark data manually collected and data from loop detectors. Finally, considering the existing scale of CV deployments, the proposed approach could be of significant help to traffic management agencies for evaluating and operating traffic signals, paving the way of using CVs for detector-free signal operation in the future.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

First-principles design of nanostructured hybrid photovoltaics based on layered transition metal phosphates

The performance of bulk organic and hybrid organic-inorganic heterojunction photovoltaics is often limited by high carrier recombination arising from strongly bound excitons and low carrier mobility. Structuring materials to minimize the length scales required for exciton separation and carrier collection is therefore a promising approach for improving efficiency. In this work, first-principles computations are employed to design and characterize a new class of photovoltaic materials composed of layered transition metal phosphates (TMPs) covalently bound to organic absorber molecules to form nanostructured superlattices. Using a combination of transition metal substitution and organic functionalization, the electronic structure of these materials is systematically tuned to design a new hybrid photovoltaic material predicted to exhibit very low recombination due to the presence of a local electric field and spatially isolated, high mobility, two-dimensional electron and hole conducting channels. Furthermore, this material is predicted to have a large open-circuit voltage of 1.7 V. Here, this work suggests that hybrid TMPs constitute an interesting class of materials for further investigation in the search for achieving high efficiency, high power, and low cost photo Zirconium phosphate was chosen, in part, due to previous experiment voltaics.

14 SOLAR ENERGY↗
DOE OSTI2014

Ultrafast Bulk Diffusion of AlHxin High-Entropy Dehydrogenation Intermediates of NaAlH4

Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in γ-NaAlH4, a recently proposed high-entropy polymorph of NaAlH4. For charged AlH4– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the α phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of γ-NaAlH4, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the α phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4 are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Infrastructure Perception and Control Laboratory [ITS Research Lab]

U.S. Department of Energy national laboratories host world-class advanced computing and modeling capabilities. The National Renewable Energy Labowratory (NREL) inaugurated the Infrastructure Perception and Control Laboratory (IPC Lab) to advance mobility reach into real-world applications.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2016

NVL-C: Static Analysis Techniques for Efficient, Correct Programming of Non-Volatile Main Memory Systems

Computer architecture experts expect that non-volatile memory (NVM) hierarchies will play a more significant role in future systems including mobile, enterprise, and HPC architectures. With this expectation in mind, we present NVL-C: a novel programming system that facilitates the efficient and correct programming of NVM main memory systems. The NVL-C programming abstraction extends C with a small set of intuitive language features that target NVM main memory, and can be combined directly with traditional C memory model features for DRAM. We have designed these new features to enable compiler analyses and run-time checks that can improve performance and guard against a number of subtle programming errors, which, when left uncorrected, can corrupt NVM-stored data. Moreover, to enable recovery of data across application or system failures, these NVL-C features include a flexible directive for specifying NVM transactions. So that our implementation might be extended to other compiler front ends and languages, the majority of our compiler analyses are implemented in an extended version of LLVM's intermediate representation (LLVM IR). We evaluate NVL-C on a number of applications to show its flexibility, performance, and correctness.

Denny, Joel↗
DOE OSTI2017

Structures and transitions in tungsten grain boundaries

The objective of this study is to develop a computational methodology to predict structure, energies of tungsten grain boundaries as a function of misorientation and inclination. The energies and the mobilities are the necessary input for thermomechanical model of recrystallization of tungsten for magnetic fusion applications being developed by the Marian Group at UCLA.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

In-plane g factor of low-density two-dimensional holes in a Ge quantum well.

High-mobility two-dimensional (2D) holes residing in a Ge quantum well are a new electronic system with potentials in quantum computing and spintronics. Since for any electronic material, the effective mass and the g factor are two fundamental material parameters that determine the material response to electric and magnetic fields, measuring these two parameters in this material system is thus an important task that needs to be completed urgently. Because of the quantum confinement in the crystal growth direction (z), the biaxial strain of epitaxial Ge on SiGe, and the valance band nature, both the effective mass and the g factor can show very strong anisotropy. In particular, the in-plane g factor (g ip ) can be vanishingly small while the perpendicular g factor (g z ) can be much larger than 2. Here we report the measurement of g ip at very low hole densities using in-plane magneto-resistance measurement performed at the NHMFL.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Emulating the Android Boot Process

Critical vulnerabilities continue to be discovered in the boot process of Android smartphones used around the world. The entire device's security is compromised if boot security is compromised, so any weakness presents undue risk to users. Vulnerabilities persist, in part, because independent security analysts lack access and appropriate tools. In response to this gap, we implemented a procedure for emulating the early phase of the Android boot process. This work demonstrated feasibility and utility of emulation in this space. By using HALucinator, we derived execution context and data flow, as well as incorporated peripheral hardware behavior. While smartphones with shared processors have substantial code overlap regardless of vendor, generational changes can have a significant impact. By applying our approach to older and modern devices, we learned interesting characteristics about the system. Such capabilities introduce new levels of introspection and operation understanding not previously available to mobile researchers.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

Heterogeneous Multi-Domain Dataset Synthesis to Facilitate Privacy and Risk Assessments in Smart City IoT

The emergence of the Smart Cities paradigm and the rapid expansion and integration of Internet of Things (IoT) technologies within this context have created unprecedented opportunities for high-resolution behavioral analytics, urban optimization, and context-aware services. However, this same proliferation intensifies privacy risks, particularly those arising from cross-modal data linkage across heterogeneous sensing platforms. To address these challenges, this paper introduces a comprehensive, statistically grounded framework for generating synthetic, multimodal IoT datasets tailored to Smart City research. The framework produces behaviorally plausible synthetic data suitable for preliminary privacy risk assessment and as a benchmark for future re-identification studies, as well as for evaluating algorithms in mobility modeling, urban informatics, and privacy-enhancing technologies. As part of our approach, we formalize probabilistic methods for synthesizing three heterogeneous and operationally relevant data streams—cellular mobility traces, payment terminal transaction logs, and Smart Retail nutrition records—capturing the behaviors of a large number of synthetically generated urban residents over a 12-week period. The framework integrates spatially explicit merchant selection using K-Dimensional (KD)-tree nearest-neighbor algorithms, temporally correlated anchor-based mobility simulation reflective of daily urban rhythms, and dietary-constraint filtering to preserve ecological validity in consumption patterns. In total, the system generates approximately 116 million mobility pings, 5.4 million transactions, and 1.9 million itemized purchases, yielding a reproducible benchmark for evaluating multimodal analytics, privacy-preserving computation, and secure IoT data-sharing protocols. To show the validity of this dataset, the underlying distributions of these residents were successfully validated against reported distributions in published research. We present preliminary uniqueness and cross-modal linkage indicators; comprehensive re-identification benchmarking against specific attack algorithms is planned as future work. This framework can be easily adapted to various scenarios of interest in Smart Cities and other IoT applications. By aligning methodological rigor with the operational needs of Smart City ecosystems, this work fills critical gaps in synthetic data generation for privacy-sensitive domains, including intelligent transportation systems, urban health informatics, and next-generation digital commerce infrastructures.

IoT↗
NASA NTRS1990

Data-Management Software For PiFEx

UNIX Based Data Management System is collection of computer programs for use in Pilot Field Experiment (PiFEx), which attempts to mimic mobile/satellite-communications (MSAT) scenario. Major purposes to define mobile-communications channels and test workability of new concepts used to design various components of receiver system. Results, large amounts of raw data that must be retrieved according to researcher's needs. Intended to manage PiFEx data in interactive way. Written in either FORTRAN-77 or UNIX shell-scripts.

Kantak, Anil V.↗