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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 703 records · Page 39

Sign reversal of transformation entropy change in Co{sub 2}Cr(Ga,Si) shape memory alloys

In situ X-ray diffraction (XRD) measurements and compression tests were performed on Co{sub 2}Cr(Ga,Si) shape memory alloys. The reentrant martensitic transformation behavior was directly observed during the in situ XRD measurements. The high-temperature parent phase and low-temperature reentrant parent phase were found to have a continuous temperature dependence of lattice parameter, therefore suggesting that they are the same phase in nature. Moreover, compression tests were performed on a parent-phase single crystal sample; an evolution from normal to inverse temperature dependence of critical stress for martensitic transformation was directly observed. Based on the Clausius-Clapeyron analysis, a sign reversal of entropy change can be expected on the same alloy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

High-Throughput, Adaptive FFT Architecture for FPGA-Based Spaceborne Data Processors

Exponential growth in microelectronics technology such as field-programmable gate arrays (FPGAs) has enabled high-performance spaceborne instruments with increasing onboard data processing capabilities. As a commonly used digital signal processing (DSP) building block, fast Fourier transform (FFT) has been of great interest in onboard data processing applications, which needs to strike a reasonable balance between high-performance (throughput, block size, etc.) and low resource usage (power, silicon footprint, etc.). It is also desirable to be designed so that a single design can be reused and adapted into instruments with different requirements. The Multi-Pass Wide Kernel FFT (MPWK-FFT) architecture was developed, in which the high-throughput benefits of the parallel FFT structure and the low resource usage of Singleton s single butterfly method is exploited. The result is a wide-kernel, multipass, adaptive FFT architecture. The 32K-point MPWK-FFT architecture includes 32 radix-2 butterflies, 64 FIFOs to store the real inputs, 64 FIFOs to store the imaginary inputs, complex twiddle factor storage, and FIFO logic to route the outputs to the correct FIFO. The inputs are stored in sequential fashion into the FIFOs, and the outputs of each butterfly are sequentially written first into the even FIFO, then the odd FIFO. Because of the order of the outputs written into the FIFOs, the depth of the even FIFOs, which are 768 each, are 1.5 times larger than the odd FIFOs, which are 512 each. The total memory needed for data storage, assuming that each sample is 36 bits, is 2.95 Mbits. The twiddle factors are stored in internal ROM inside the FPGA for fast access time. The total memory size to store the twiddle factors is 589.9Kbits. This FFT structure combines the benefits of high throughput from the parallel FFT kernels and low resource usage from the multi-pass FFT kernels with desired adaptability. Space instrument missions that need onboard FFT capabilities such as the proposed DESDynl, SWOT (Surface Water Ocean Topography), and Europa sounding radar missions would greatly benefit from this technology with significant reductions in non-recurring cost and risk.

NguyenKobayashi, Kayla↗

Fragile-to-strong transition in liquid As 2 S 3 under pressure: The effect of melt metallization

The well-known classification of glass-forming melts into fragile and strong liquids has several notable exceptions, including water, silica, and certain phase-change materials (PCMs). These exceptional fluid systems exhibit a fragile-to-strong transition (FST) upon cooling: a transformation from a high-temperature liquid with fast atomic dynamics, low viscosity, and low flow activation energy, to a viscous supercooled melt with high energy barriers near the glass transition temperature T g . This behavior is critically important for non-volatile memories, photonic tensor cores, reconfigurable metamaterials, and other devices, that use PCMs, enabling nanosecond-scale crystallization in the fragile regime and long data retention in the strong regime near or below T g . A significant structural transformation is expected between these two viscosity regimes, along with a semiconductor-metal (SC-M) transition upon heating, driven by high internal pressure and associated density increase. By applying high external pressure to the canonical low-conducting chalcogenide melt As 2 S 3 , we observed both the FST and the SC-M transition, occurring simultaneously within the same domain of the P, T−phase space. These findings suggest that the FST is not limited to a few exceptional liquids but is a common phenomenon, at least in systems that exhibit melt metallization within specific regions of their P, T−phase diagrams.

first-principles molecular dynamics↗

Bulk Glassy GeTe 2 : A Missing Member of the Tetrahedral GeX 2 Family and a Precursor for the Next Generation of Phase-Change Materials

Vitreous germanium disulfide GeS 2 and diselenide GeSe 2 belong to canonical chalcogenide glasses extensively studied over the past half century. Their high-temperature orthorhombic polymorphs are congruently melting compounds, and the tetrahedral crystal and glass structure is largely preserved in the melt. In contrast, the ditelluride counterpart is absent in the Ge-Te phase diagram, which shows only a single compound, monotelluride GeTe. Phase-change materials based on GeTe have become a technologically important class of solids, and their structure and properties are also widely studied. Surprisingly, very scarce information is available for alloys having GeTe 2 stoichiometry. Using a fast quenching procedure in silica capillaries, high-energy X-ray diffraction, and Raman spectroscopy supported by first-principles simulations, we show that bulk glassy GeTe 2 differs substantially from the lighter GeX 2 members, revealing 46% of trigonal germanium, 31% of three-fold coordinated tellurium, and only 20% of edge-sharing tetrahedra or pyramids. The fraction of homopolar Ge-Ge bonds is low; however, the population of dominant Te-Te dimers and Te n oligomers, n <= 10, appears to be significant. The complex structural and chemical topology of g-GeTe 2 is directly related to the thermodynamic metastability of germanium ditelluride, schematically represented by the following reaction: GeTe 2 $\rightleftarrows$ GeTe + Te. Disproportionation is complete above liquidus in the temperature range of semiconductor-metal transition, and the dense metallic GeTe 2 liquid, mostly consisting of five-fold coordinated Ge species, exhibits high fluidity, strong fragility (m = 99 ± 5), and presumably a fast structural transformation rate combined with low atomic mobility in the vicinity of the glass transition temperature, favorable for reliable long-term data retention in nonvolatile memories. The observed and predicted characteristic features make GeTe 2 a promising precursor for the next generation of phase-change materials, especially coupled with additional metal doping, depolymerizing the tetrahedral interconnected glass network and accelerating (sub)nanosecond crystallization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Spiers Memorial Lecture: Next generation chalcogenide-based absorbers for thin-film solar cells

Inorganic-based thin-film photovoltaics (TFPV) represents an important component of the growing low-carbon energy market and plays a vital role in the drive toward lower cost and increased penetration of solar energy. Yet, commercialized thin-film absorber technologies suffer from some non-ideal characteristics, such as toxic or non-abundant element use (e.g., CdTe and Cu(In,Ga)(S,Se) 2 , which bring into question their suitability for terawatt deployment. Numerous promising chalcogenide, halide, pnictide and oxide semiconductors are being pursued to bridge these concerns for TFPV and several promising paths have emerged, both as prospective replacements for the entrenched technologies, and to serve as partner (i.e., higher bandgap) absorbers for tandem junction devices—e.g., to be used with a lower bandgap Si bottom cell. The current perspective will primarily focus on emerging chalcogenide-based technologies and provide both an overview of absorber candidates that have been of recent interest and a deeper dive into an exemplary Cu 2 BaSnS 4 -related family. Altogether, considering the combined needs of high-performance, low-cost, and operational stability, as well as the experiences gained from existing commercialized thin-film absorber technologies, chalcogenide-based semiconductors represent a promising direction for future PV development and also serve to highlight common themes and needs among the broader TFPV materials family.

14 SOLAR ENERGY↗

Correlation of film density and wet etch rate in hydrofluoric acid of plasma enhanced atomic layer deposited silicon nitride

The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposition (ALD) of silicon nitride (SiN{sub x}), particularly for use a low k dielectric spacer. One of the key material properties needed for SiN{sub x} films is a low wet etch rate (WER) in hydrofluoric (HF) acid. In this work, we report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiN{sub x} and evaluate the film’s WER in 100:1 dilutions of HF in H{sub 2}O. The remote plasma capability available in PEALD, enabled controlling the density of the SiN{sub x} film. Namely, prolonged plasma exposure made films denser which corresponded to lower WER in a systematic fashion. We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions. Limiting all steps in the deposition to a maximum temperature of 350 °C, it was shown to be possible to achieve a WER in PEALD SiN{sub x} of 6.1 Å/min, which is similar to WER of SiN{sub x} from LPCVD reactions at 850 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Integrated circuit random-access memory decoder

Decoder circuit with complementary-symmetry circuit configuration composed of MOS and n-p-n bipolar devices minimizes power consumption. Emitter-follower drive scheme results in low power dissipation and high speed operation.

Katz, S.↗

Digital input is buffered to real-time analog display

Buffering technique utilizes nine-bit binary counter and holding register of eight flip-flops. These flip-flops form the memory device that allows precise asynchronous conversion of the digital source data. Counter generates a waveform which is passed through a low pass filter to recover data in analog form.

Bower, K. F.↗

Ovonic switching in tin selenide thin films

Amorphous tin selenide thin films which possess Ovonic switching properties were fabricated using vacuum deposition techniques. Results obtained indicate that memory type Ovonic switching does occur in these films the energy density required for switching from a high impedance to a low impedance state is dependent on the spacing between the electrodes of the device. The switching is also function of the magnitude of the applied voltage pulse. A completely automated computer controlled testing procedure was developed which allows precise control over the shape of the applied voltage switching pulse. A survey of previous experimental and theoretical work in the area of Ovonic switching is also presented.

Baxter, C. R.↗

Research on materials for advanced electronic and aerospace application

Development and understanding of materials most suitable for use in compact magnetic and optical memory systems are discussed. Suppression of metal deterioration by hydrogen is studied. Improvement of mechanical properties of polymers is considered, emphasizing low temperature ductility and compatibility with high modulus fiber materials.

Source record↗

Technical description of space ultra reliable modular computer (SUMC), model 2 B

The design features of the SUMC-2B computer, also called the IBM-HTC are described. It is general purpose digital computer implemented with flexible hardware elements and microprograming to enable low cost customizing to a wide range of applications. It executes the S/360 standard instruction set to maintain problem state compability. Memory technology, extended instruction sets, and I/O channel variations are among the available options.

Source record↗

SEDSAT-1 Technology Development

The Students for the Exploration and Development of Space Satellite (SEDSAT-1) is an ambitious project to design, build, and fly a generally-accessible low-cost satellite which will 1) act as a technology demonstration to verify the suitability of novel optical, battery, microprocessor, and memory hardware for space flight environments, (2) to advance the understanding of tether dynamics and environmental science through the development of advanced imaging experiments, (3) to act as a communication link for radio amateurs, and (4) to provide graduate and undergraduate students with a unique multi-disciplinary experience in designing complex real-world hardware/software. This report highlights the progress made on this project during the time period from January 2, 1996 to June 1, 1996 at the end of which time the SEASIS 0.7 version software was completed and integrated on the SEASIS breadboard, a functional prototype of the Panoramic Annual Lenses (PAL) camera was developed, the preferred image compression technique was selected, the layout of the SEASIS board was begun, porting of the SCOS operating system to the command data system (CDS) board was begun, a new design for a tether release mechanism was developed, safety circuitry to inhibit tether cutting was developed and prototyped, material was prepared to support a comprehensive safety review of the project which was held at Johnson Space Center (JSC) (which was personally attended by one of the Principal Investigators), and prototype ground software was developed.

Maier, Mark W.↗

Assessing application vulnerability to radiation-induced SEUs in memory

One of the goals of the Remote Exploration and Experimentation (REE) project at JPL is to determine how vulnerable applications are to single event upsets (SEUs) when run in low radiation space environments using commercial-off-the-shelf (COTS) components.

radiation SEU software vulnerability↗

Mechanical Components from Highly Recoverable, Low Apparent Modulus Materials

A material for use as a mechanical component is formed of a superelastic intermetallic material having a low apparent modulus and a high hardness. The superelastic intermetallic material is conditioned to be dimensionally stable, devoid of any shape memory effect and have a stable superelastic response without irrecoverable deformation while exhibiting strains of at least 3%. The method of conditioning the superelastic intermetallic material is described. Another embodiment relates to lightweight materials known as ordered intermetallics that perform well in sliding wear applications using conventional liquid lubricants and are therefore suitable for resilient, high performance mechanical components such as gears and bearings.

Padula, Santo, II↗

Harnessing ferro-valleytricity in pentalayer rhombohedral graphene for memory and compute

Two-dimensional materials with multiple degrees of freedom, including spin, valleys, and orbitals, open up an exciting avenue for engineering multifunctional devices. Beyond spintronics, these degrees of freedom can lead to novel quantum effects such as valley-dependent Hall effects and orbital magnetism, which could revolutionize next-generation electronics. However, achieving independent control over valley polarization and orbital magnetism has been a challenge due to the need for large electric fields. A recent breakthrough involving pentalayer rhombohedral graphene has demonstrated the ability to individually manipulate anomalous Hall signals and orbital magnetic hysteresis, forming what is known as a valley-magnetic quartet. Here, we leverage the electrically tunable ferro-valleytricity of pentalayer rhombohedral graphene to develop nonvolatile memory and in-memory computation applications. We propose an architecture for a dense, scalable, and selector-less nonvolatile memory array that harnesses the electrically tunable ferro-valleytricity. In our designed array architecture, nondestructive read and write operations are conducted by sensing the valley state through two different pairs of terminals, allowing for independent optimization of read/write peripheral circuits. The power consumption of our PRG-based array is remarkably low, with only ∼6 nW required per write operation and ∼2.3 nW per read operation per cell. This consumption is orders of magnitude lower than that of the majority of state-of-the-art cryogenic memories. Additionally, we engineer in-memory computation by implementing majority logic operations within our proposed nonvolatile memory array without modifying the peripheral circuitry. In conclusion, our framework presents a promising pathway toward achieving ultra-dense cryogenic memory and in-memory computation capabilities.

2D materials↗

High-Performance, Radiation-Hardened Electronics for Space Environments

The Radiation Hardened Electronics for Space Environments (RHESE) project endeavors to advance the current state-of-the-art in high-performance, radiation-hardened electronics and processors, ensuring successful performance of space systems required to operate within extreme radiation and temperature environments. Because RHESE is a project within the Exploration Technology Development Program (ETDP), RHESE's primary customers will be the human and robotic missions being developed by NASA's Exploration Systems Mission Directorate (ESMD) in partial fulfillment of the Vision for Space Exploration. Benefits are also anticipated for NASA's science missions to planetary and deep-space destinations. As a technology development effort, RHESE provides a broad-scoped, full spectrum of approaches to environmentally harden space electronics, including new materials, advanced design processes, reconfigurable hardware techniques, and software modeling of the radiation environment. The RHESE sub-project tasks are: SelfReconfigurable Electronics for Extreme Environments, Radiation Effects Predictive Modeling, Radiation Hardened Memory, Single Event Effects (SEE) Immune Reconfigurable Field Programmable Gate Array (FPGA) (SIRF), Radiation Hardening by Software, Radiation Hardened High Performance Processors (HPP), Reconfigurable Computing, Low Temperature Tolerant MEMS by Design, and Silicon-Germanium (SiGe) Integrated Electronics for Extreme Environments. These nine sub-project tasks are managed by technical leads as located across five different NASA field centers, including Ames Research Center, Goddard Space Flight Center, the Jet Propulsion Laboratory, Langley Research Center, and Marshall Space Flight Center. The overall RHESE integrated project management responsibility resides with NASA's Marshall Space Flight Center (MSFC). Initial technology development emphasis within RHESE focuses on the hardening of Field Programmable Gate Arrays (FPGA)s and Field Programmable Analog Arrays (FPAA)s for use in reconfigurable architectures. As these component/chip level technologies mature, the RHESE project emphasis shifts to focus on efforts encompassing total processor hardening techniques and board-level electronic reconfiguration techniques featuring spare and interface modularity. This phased approach to distributing emphasis between technology developments provides hardened FPGA/FPAAs for early mission infusion, then migrates to hardened, board-level, high speed processors with associated memory elements and high density storage for the longer duration missions encountered for Lunar Outpost and Mars Exploration occurring later in the Constellation schedule.

Keys, Andrew S.↗

Neurogenic Effects of Low-Dose Whole-Body HZE (Fe) Ion and Gamma Irradiation

Understanding the dose-toxicity profile of radiation is critical when evaluating potential health risks associated with natural and man-made sources in our environment. This study was done to evaluate the effects of low-dose whole-body high-energy charged (HZE) iron (Fe) ions and low-energy gamma exposure on proliferation and differentiation of adult-born neurons within the dentate gyrus of the hippocampus, cells deemed to play a critical role in memory regulation. To determine the dose-response characteristics of the brain to whole-body Fe-ion vs. gamma-radiation exposure, C57BL/6J mice were irradiated with 1 GeV/n Fe ions or a static 137 Cs source (0.662 MeV) at doses ranging from 0 to 300 cGy. The neurogenesis was analyzed at 48 h and one month postirradiation. These experiments revealed that whole-body exposure to either Fe ions or gamma radiation leads to: 1. An acute decrease in cell division within the dentate gyrus of the hippocampus, detected at doses as low as 30 and 100 cGy for Fe ions and gamma radiation, respectively; and 2. A reduction in newly differentiated neurons (DCX immunoreactivity) at one month postirradiation, with significant decreases detected at doses as low as 100 cGy for both Fe ions and gamma rays. The data presented here contribute to our understanding of brain responses to whole-body Fe ions and gamma rays and may help inform health-risk evaluations related to systemic exposure during a medical or radiologic/nuclear event or as a result of prolonged space travel.

61 RADIATION PROTECTION AND DOSIMETRY↗

RTSJ Memory Areas and Their Affects on the Performance of a Flight-Like Attitude Control System

The two most important factors in improving performance in any software system, but especially a real-time, embedded system, are knowing which components are the low performers and knowing what can be done to improve their performance. The word performance with respect to a real-time, embedded system does not necessarily mean fast execution, which is the common definition when discussing non real-time systems. It also includes meeting all of the specified execution dead-lines and executing at the correct time without sacrificing non real-time performance. Using a Java prototype of an existing control system used on Deep Space 1[1], the effects from adding memory areas are measured and evaluated with respect to improving performance.

Real-time Specification for Java2 (RTSJ)↗