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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

High density associative memory

A multi-layered, thin-film, digital memory having associative recall. There is a first memory matrix and a second memory matrix. Each memory matrix comprises, a first layer comprising a plurality of electrically separated row conductors; a second layer comprising a plurality of electrically separated column conductors intersecting but electrically separated from the row conductors; and, a plurality of resistance elements electrically connected between the row condutors and the column conductors at respective intersections of the row conductors and the column conductors, each resistance element comprising, in series, a first resistor of sufficiently high ohmage to conduct a sensible element current therethrough with virtually no heat-generating power consumption when a low voltage as employed in thin-film applications is applied thereacross and a second resistor of sufficiently high ohmage to conduct no sensible current therethrough when a low voltage as employed in thin-film applications is applied thereacross, the second resistor having the quality of breaking down to create a short therethrough upon the application of a breakdown level voltage across the first and second resistors.

Moopenn, Alexander W.↗
NASA NTRS1994

Particle sensor array

A particle sensor array which in a preferred embodiment comprises a static random access memory having a plurality of ion-sensitive memory cells, each such cell comprising at least one pull-down field effect transistor having a sensitive drain surface area (such as by bloating) and at least one pull-up field effect transistor having a source connected to an offset voltage. The sensitive drain surface area and the offset voltage are selected for memory cell upset by incident ions such as alpha-particles. The static random access memory of the present invention provides a means for selectively biasing the memory cells into the same state in which each of the sensitive drain surface areas is reverse biased and then selectively reducing the reversed bias on these sensitive drain surface areas for increasing the upset sensitivity of the cells to ions. The resulting selectively sensitive memory cells can be used in a number of applications. By way of example, the present invention can be used for measuring the linear energy transfer of ion particles, as well as a device for assessing the resistance of CMOS latches to Cosmic Ray induced single event upsets. The sensor of the present invention can also be used to determine the uniformity of an ion beam.

Buehler, Martin G.↗
DOE OSTI2019

Microstructure Anisotropy Effects on Fracture and Fatigue Mechanisms in Shape Memory Alloy Martensites

The chief scientific object was to investigate the fatigue and fracture mechanisms in NiTi shape memory alloys, in the presence of stress concentrating factors such as micro-pores and notches. In particular, the interactions between structure (factors related to the geometry of the specimen, such as holes, pores and notches) and microstructure (related to properties of the material such as grains, secondary phases, twins) in influencing the inelastic deformation, leading up to fracture in NiTi was examined. Primarily, there were two major thrusts. The first thrust focused on fracture behavior in Shape Memory Alloys where the high crystal symmetry cubic phase transformed into the low symmetry phase during deformation and propagation of cracks. This thrust revealed the interplay between size of micro-pores, size of grains and grain orientations in determining the resistance to crack growth, during cyclic tensile deformation of porous-like NiTi specimens. The role of secondary phases (impurities of Ti, often formed during fabrication) were also shown to induce local inelastic deformation gradients during tensile deformation and reduce overall extent of deformation. The second thrust focused on the fatigue and fracture behavior in the low crystal symmetry martensite phase. Unlike high symmetry phases, characterization of deformation in low symmetry phases such as martensitic NiTi has been challenging, due to a hierarchical microstructure spanning from nanoscale twins to the macroscale, a highly anisotropic microstructure stemming from the low crystal symmetry and a multitude of inelastic mechanisms for deformation. Thus, advanced X-ray techniques such as 3D high-energy diffraction microscopy and x-ray micro-Laue diffraction and spectroscopy were used in conjunction with traditional techniques such as SEM and TEM to understand the inelastic deformation in the martensite phase in NiTi, in the presence of notches. This thrust revealed a stark difference in deformation mechanisms based on the nature of stress: regions near the notch experience a highly triaxial stress while those far away experience a uniaxial stress. Additionally, while regions close to the notch were shown to deform locally by amorphization/nanocrystallization, ultimately leading to fracture, regions far away from the notch deformed in a more traditional manner, with detwinning and twin reorientation the primary mechanisms of deformation. More importantly, this thrust revealed that in the presence of structural factors such as notches, the traditional picture of reorientation (coalescence) of nanoscale martensite twins into increasingly larger domains with increased loading does not hold true, even up to fracture of the specimen. These conclusions will inform the modeling and understanding of deformation behavior of specimens, where structure and microstructure coexist and interact.

36 MATERIALS SCIENCE↗
NASA NTRS2012

I-V Characteristics of a Static Random Access Memory Cell Utilizing Ferroelectric Transistors

I-V characteristics for FeFET different than that of MOSFET Ferroelectric layer features hysteresis trend whereas MOSFET behaves same for both increasing and decreasing VGS FeFET I-V characteristics doesn't show dependence on VDS A Transistor with different channel length and width as well as various resistance and input voltages give different results As resistance values increased, the magnitude of the drain current decreased.

Laws, Crystal↗
DOE OSTI2025

The Effects of Compounded Model Size Reductions on Adversarial Robustness

Recent advances in Edge AI and Tiny Machine Learning (TinyML) have enabled the deployment of machine learning models on resource-constrained environments. However, deploying these models on edge devices, such as micro-controllers, requires significant model footprint reduction through a variety of techniques such as quantization, pruning, and clustering. While these optimization methods offer considerable advantages, they potentially introduce AI-related security vulnerabilities, particularly concerning model robustness with respect to adversarial AI attacks. Prior research has extensively examined the impact of quantization on adversarial robustness; however, the effects of alternative reduction techniques and their combinations remain understudied. This paper investigates the impact of model size reduction techniques on adversarial robustness, when applied individually and combined. We utilized Fast Gradient Sign Method (FGSM) and Projected Gradient Descent (PGD) attacks to generate adversarial perturbations for both training and testing data, and then evaluated the models' accuracy under adversarial training conditions. Our findings revealed that reduction techniques generally diminished robustness; although, combining techniques was not found to make robustness any worse than when applied individually. Moreover, specific techniques can potentially enhance resistance to small size perturbations. This research provides insights into the trade-offs between model size reduction and security, establishing a foundation for future investigations into improving adversarial training techniques and methodologies for maintaining robustness while preserving memory footprint benefits.

Austria, Phillipe [ORNL] (ORCID:0000000236223973)↗
DOE OSTI2020

Self-assembly for electronics

Self-assembly, a process in which molecules, polymers, and particles are driven by local interactions to organize into patterns and functional structures, is being exploited in advancing silicon electronics and in emerging, unconventional electronics. Additionally, silicon electronics has relied on lithographic patterning of polymer resists at progressively smaller lengths to scale down device dimensions. Yet, this has become increasingly difficult and costly. Assembly of block copolymers and colloidal nanoparticles allows resolution enhancement and the definition of essential shapes to pattern circuits and memory devices. As we look to a future in which electronics are integrated at large numbers and in new forms for the Internet of Things and wearable and implantable technologies, we also explore a broader material set. Semiconductor nanoparticles and biomolecules are prized for their size-, shape-, and composition-dependent properties and for their solution-based assembly and integration into devices that are enabling unconventional manufacturing and new device functions.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Transformation temperatures of martensite in beta-phase nickel aluminide.

Resistivity and thermal arrest measurements determined that the compositional dependence of M sub s temperatures for NiAl martensite was linear between 60 and 69 at. % Ni, with M sub s = (124 Ni - 7410)K. Resistivity and surface relief experiments for selected alloys indicated the presence of thermoelastic martensite. Some aspects of the transformation were studied by hot-stage microscopy and related to the behavior observed for alloys exhibiting the shape-memory effect.

Smialek, J. L.↗
DOE OSTI2025

Unconventional unidirectional magnetoresistance in heterostructures of a topological semimetal and a ferromagnet

Unidirectional magnetoresistance (UMR) in a bilayer heterostructure, consisting of a spin-source material and a magnetic layer, refers to a change in the longitudinal resistance on the reversal of magnetization and originates from the interaction of non-equilibrium spin accumulation and magnetization at the interface. Since the spin polarization of an electric-field-induced non-equilibrium spin accumulation in conventional spin-source materials is restricted to be in the film plane, the ensuing UMR can only respond to the in-plane component of magnetization. However, magnets with perpendicular magnetic anisotropy are highly desired for magnetic memory and spin-logic devices, whereas the electrical read-out of perpendicular magnetic anisotropy magnets through UMR is critically missing. Here, in this study, we report the discovery of an unconventional UMR in the heterostructures of a topological semimetal (WTe 2 ) and a perpendicular magnetic anisotropy ferromagnetic insulator (Cr 2 Ge 2 Te 6 ), which allows to electrically read the up and down magnetic states of the Cr 2 Ge 2 Te 6 layer through longitudinal resistance measurements.

Kao, I-Hsuan [Carnegie Mellon Univ., Pittsburgh, P↗
DOE OSTI2020

Combinatorial Exploration and Mapping of Phase Transformation in a Ni–Ti–Co Thin Film Library

Combinatorial synthesis and high-throughput characterization of a Ni–Ti–Co thin film materials library are reported for exploration of reversible martensitic transformation. The library was prepared by magnetron co-sputtering, annealed in vacuum at 500 °C without atmospheric exposure, and evaluated for shape memory behavior as an indicator of transformation. Composition, structure, and transformation behavior of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and four-point probe temperature-dependent resistance (R(T)) measurements. A new, expanded composition space having phase transformation with low thermal hysteresis and Co > 10 at. % is found. Unsupervised machine learning methods of hierarchical clustering were employed to streamline data processing of the large XRD and XPS data sets. Through cluster analysis of XRD data, we identified and mapped the constituent structural phases. Finally, composition–structure–property maps for the ternary system are made to correlate the functional properties to the local microstructure and composition of the Ni–Ti–Co thin film library.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

First-principles study and experimental characterization of metal incorporation in germanium telluride

Germanium telluride is a well-known phase change material (PCM) used in non-volatile memory cells and radio frequency switches. Controlling the properties of GeTe for improved PCM device performance has sometimes been achieved by doping and/or alloying with metals, often at concentrations greater than 10 at. % and using non-equilibrium methods. Here, since switching PCMs between the low-resistance crystalline and high-resistance amorphous states requires a heating cycle, the stability of metal-incorporated GeTe (Ge 0.5–x M x Te 0.5 ) films is also critical to practical implementation of these materials in electronic and optoelectronic devices. In this work, we use both density-functional theory and experimental characterization methods to probe the solubility and critical properties of Ge 0.5–x M x Te 0.5 films. Using first-principles calculations, we determine the enthalpy of formation for GeTe with 2.08, 4.17, and 6.25 at. % of Cu, Fe, Mn, Mo, and Ti and show trends between the stability of the Ge 0.5–x M x Te 0.5 systems and the atomic position, composition, and distribution of the metal atoms in the GeTe matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sulfurization Engineering of One–Step Low–Temperature MoS 2 and WS 2 Thin Films for Memristor Device Applications

2D materials have been of considerable interest as new materials for device applications. Non-volatile resistive switching applications of MoS 2 and WS 2 have been previously demonstrated; however, these applications are dramatically limited by high temperatures and extended times needed for the large-area synthesis of 2D materials on crystalline substrates. The experimental results demonstrate a one-step sulfurization method to synthesize MoS 2 and WS 2 at 550 °C in 15 min on sapphire wafers. Furthermore, a large area transfer of the synthesized thin films to SiO 2 /Si substrates is achieved. Following this, MoS 2 and WS 2 memristors are fabricated that exhibit stable non-volatile switching and a satisfactory large on/off current ratio (10 3 –10 5 ) with good uniformity. Tuning the sulfurization parameters (temperature and metal precursor thickness) is found to be a straightforward and effective strategy to improve the performance of the memristors. Furthermore, the demonstration of large-scale MoS 2 and WS 2 memristors with a one-step low-temperature sulfurization method with simple strategy to tuning can lead to potential applications such as flexible memory and neuromorphic computing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Large thermal hysteresis in a single-phase NiTiNb shape memory alloy

Large thermal hysteresis ($T$ hys ) is favorable in shape memory alloys (SMAs) because it renders wide service and storage temperature range of the SMA-made parts. In this letter, we show that large intrinsic $T$ hys up to 100 K is achieved in a low Nb content (2 at.%), β-Nb-free and single-phase NiTiNb SMA fabricated by casting, forging, wire-drawing and annealing. Such a large $T$ hys is comparable to that of the widely used dual-phase NiTiNb SMAs in which high Nb content and β-Nb are required. By exploiting the grain-size-dependence of $T$ hys in our single-phase NiTiNb SMA and that in an equiatomic NiTi SMA, we attribute the large $T$ hys to the enhanced kinetic resistance of transformation by the small grains. In conclusion, the connection between the $T$ hys and the kinetic resistance is demonstrated by a modified dislocation-based kinetic model.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Phase IB study of ziv-aflibercept plus pembrolizumab in patients with advanced solid tumors

Background The combination of antiangiogenic agents with immune checkpoint inhibitors could potentially overcome immune suppression driven by tumor angiogenesis. We report results from a phase IB study of ziv-aflibercept plus pembrolizumab in patients with advanced solid tumors. Methods This is a multicenter phase IB dose-escalation study of the combination of ziv-aflibercept (at 2–4 mg/kg) plus pembrolizumab (at 2 mg/kg) administered intravenously every 2 weeks with expansion cohorts in programmed cell death protein 1 (PD-1)/programmed death-ligand 1(PD-L1)-naïve melanoma, renal cell carcinoma (RCC), microsatellite stable colorectal cancer (CRC), and ovarian cancer. The primary objective was to determine maximum tolerated dose (MTD) and recommended dose of the combination. Secondary endpoints included overall response rate (ORR) and overall survival (OS). Exploratory objectives included correlation of clinical efficacy with tumor and peripheral immune population densities. Results Overall, 33 patients were enrolled during dose escalation (n=3) and dose expansion (n=30). No dose-limiting toxicities were reported in the initial dose level. Ziv-aflibercept 4 mg/kg plus pembrolizumab 2 mg/kg every 2 weeks was established as the MTD. Grade ≥3 adverse events occurred in 19/33 patients (58%), the most common being hypertension (36%) and proteinuria (18%). ORR in the dose-expansion cohort was 16.7% (5/30, 90% CI 7% to 32%). Complete responses occurred in melanoma (n=2); partial responses occurred in RCC (n=1), mesothelioma (n=1), and melanoma (n=1). Median OS was as follows: melanoma, not reached (NR); RCC, 15.7 months (90% CI 2.5 to 15.7); CRC, 3.3 months (90% CI 0.6 to 3.4); ovarian, 12.5 months (90% CI 3.8 to 13.6); other solid tumors, NR. Activated tumor-infiltrating CD8 T cells at baseline (CD8+PD1+), high CD40L expression, and increased peripheral memory CD8 T cells correlated with clinical response. Conclusion The combination of ziv-aflibercept and pembrolizumab demonstrated an acceptable safety profile with antitumor activity in solid tumors. The combination is currently being studied in sarcoma and anti-PD-1-resistant melanoma. Trial registration number NCT02298959 .

Rahma, Osama E.↗
NASA NTRS2014

Analyzing a 35-Year Hourly Data Record: Why So Difficult?

At the Goddard Distributed Active Archive Center, we have recently added a 35-Year record of output data from the North American Land Assimilation System (NLDAS) to the Giovanni web-based analysis and visualization tool. Giovanni (Geospatial Interactive Online Visualization ANd aNalysis Infrastructure) offers a variety of data summarization and visualization to users that operate at the data center, obviating the need for users to download and read the data themselves for exploratory data analysis. However, the NLDAS data has proven surprisingly resistant to application of the summarization algorithms. Algorithms that were perfectly happy analyzing 15 years of daily satellite data encountered limitations both at the algorithm and system level for 35 years of hourly data. Failures arose, sometimes unexpectedly, from command line overflows, memory overflows, internal buffer overflows, and time-outs, among others. These serve as an early warning sign for the problems likely to be encountered by the general user community as they try to scale up to Big Data analytics. Indeed, it is likely that more users will seek to perform remote web-based analysis precisely to avoid the issues, or the need to reprogram around them. We will discuss approaches to mitigating the limitations and the implications for data systems serving the user communities that try to scale up their current techniques to analyze Big Data.

computational performance↗
DOE OSTI2021

Observation of current-induced switching in non-collinear antiferromagnetic IrMn 3 by differential voltage measurements

There is accelerating interest in developing memory devices using antiferromagnetic (AFM) materials, motivated by the possibility for electrically controlling AFM order via spin-orbit torques, and its read-out via magnetoresistive effects. Recent studies have shown, however, that high current densities create non-magnetic contributions to resistive switching signals in AFM/heavy metal (AFM/HM) bilayers, complicating their interpretation. Here we introduce an experimental protocol to unambiguously distinguish current-induced magnetic and nonmagnetic switching signals in AFM/HM structures, and demonstrate it in IrMn 3 /Pt devices. A six-terminal double-cross device is constructed, with an IrMn 3 pillar placed on one cross. The differential voltage is measured between the two crosses with and without IrMn 3 after each switching attempt. For a wide range of current densities, reversible switching is observed only when write currents pass through the cross with the IrMn 3 pillar, eliminating any possibility of non-magnetic switching artifacts. Micromagnetic simulations support our findings, indicating a complex domain-mediated switching process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Nanoscale magnetic Josephson junctions and superconductor/ferromagnet proximity effects for low-power spintronics

Competition between superconducting and ferromagnetic ordering at interfaces between ferromagnets (F) and superconductors (S) gives rise to several proximity effects such as odd-triplet superconductivity and spin-polarized supercurrents. A prominent example of an S/F proximity effect is the spin switch effect observed in S/F/N/F superconducting spin valve multilayers, in which the superconducting transition temperature T c is controlled by the angle Φ between the magnetic moments of the F layers separated by a nonmagnetic metallic spacer N. We carried out an experimental study of spin switch effect in Nb/Co/Cu/Co/CoO x nanowires measured as a function of bias current flowing in the plane of the layers. These measurements reveal an unexpected dependence of T c (Φ) on the bias current: T c (Φ) – T c (0) changes sign with increasing current bias. We attribute the origin of this bias dependence of the spin switch effect to a spin Hall current originating in Nb and flowing perpendicular to the plane of the multilayer, which suppresses T c of the multilayer. The bias dependence of spin switch effect can be important for hybrid F/S devices such as cryogenic memory for superconducting computers when device dimensions are scaled down to the nanometer length scale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Exploring the Adoption Challenges of Post-Quantum Cryptography in EV Charging Infrastructure

The rapid evolution of electric vehicle (EV) technology and the corresponding growth of the Electric Vehicle Charging Infrastructure (EVCI) brings to light significant cybersecurity concerns, notably in the context of emerging post-quantum computing capabilities. This report, prepared by Pacific Northwest National Laboratory (PNNL) under the U.S. Department of Energy contract, delves into the challenges associated with integrating Post-Quantum Cryptography (PQC) into EVCI to safeguard against potential quantum computing threats. Post-quantum computers will eventually be able to invalidate technologies secured through public key cryptography. As part of this effort, the primary gaps and challenges in the EVCI were investigated with a focus on comparing traditional algorithms against PQC algorithms. One of the notable findings was that the P-521 algorithm was frequently surpassed in performance by PQC algorithms. This document provides a thorough examination of the hurdles the industry can expect when transitioning to PQC within the EVCI, such as interoperability concerns, the computational and memory demands of PQC algorithms, and the organizational readiness for such a transition. It emphasizes the necessity of a forward-thinking approach to cybersecurity, advocating for early and strategic engagement among EVCI stakeholders to ensure a seamless and cost-effective migration to quantum-resistant cryptographic standards. Through this report, the authors aim to catalyze awareness and action among policymakers, industry leaders, and cybersecurity professionals towards fortifying the EVCI against emerging quantum threats, thereby securing the infrastructure essential for the future of electric mobility.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2024

Cycle equivalence classes, orthogonal Weingarten calculus, and the mean field theory of memristive systems

Abstract It has been recently noted that for a class of dynamical systems with explicit conservation laws represented via projector operators, the dynamics can be understood in terms of lower dimensional equations. This is the case, for instance, of memristive circuits. Memristive systems are important classes of devices with wide-ranging applications in electronic circuits, artificial neural networks, and memory storage. We show that such mean-field theories can emerge from averages over the group of orthogonal matrices, interpreted as cycle-preserving transformations applied to the projector operator describing Kirchhoff’s laws. Our results provide insights into the fundamental principles underlying the behavior of resistive and memristive circuits and highlight the importance of conservation laws for their mean-field theories. In addition, we argue that our results shed light on the nature of the critical avalanches observed in quasi-two-dimensional nanowires as boundary phenomena.

97 MATHEMATICS AND COMPUTING↗