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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Using predictions of outcomes of cache memory access requests for controlling whether a request generator sends memory access requests to a memory in parallel with cache memory access requests

An electronic device handles memory access requests for data in a memory. The electronic device includes a memory controller for the memory, a last-level cache memory, a request generator, and a predictor. The predictor determines a likelihood that a cache memory access request for data at a given address will hit in the last-level cache memory. Based on the likelihood, the predictor determines: whether a memory access request is to be sent by the request generator to the memory controller for the data in parallel with the cache memory access request being resolved in the last-level cache memory, and, when the memory access request is to be sent, a type of memory access request that is to be sent. When the memory access request is to be sent, the predictor causes the request generator to send a memory request of the type to the memory controller.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Projections of H-mode access and edge pedestal in the SPARC tokamak

In order to inform core performance projections and divertor design, the baseline SPARC tokamak plasma discharge is evaluated for its expected H-mode access, pedestal pressure and edge-localized mode (ELM) characteristics. A clear window for H-mode access is predicted for full field DT plasmas, with the available 25 MW of design auxiliary power. Additional alpha heating is likely needed for H-mode sustainment. Pressure pedestal predictions in the developed H-mode are surveyed using the EPED model. The projected SPARC pedestal would be limited dominantly by peeling modes and may achieve pressures in excess of 0.3 MPa at a density of approximately 3 × 10 20 m -3 . High pedestal pressure is partially enabled by strong equilibrium shaping, which has been increased as part of recent design iterations. Edge-localized modes (ELMs) with >1 MJ of energy are projected, and approaches for reducing the ELM size, and thus the peak energy fluence to divertor surfaces, are under consideration. The high pedestal predicted for SPARC provides ample margin to satisfy its high fusion gain (Q) mission, so that even if ELM mitigation techniques result in a 2x reduction of the pedestal pressure, Q > 2 is still predicted.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Access Patterns and Performance Behaviors of Multi-layer Supercomputer I/O Subsystems under Production Load

Scientific computing workloads at HPC facilities have been shifting from traditional numerical simulations to AI/ML applications for training and inference while processing and producing ever-increasing amounts of scientific data. To address the growing need for increased storage capacity, lower access latency, and higher bandwidth, emerging technologies such as non-volatile memory are integrated into supercomputer I/O subsystems. With these emerging trends, we need a better understanding of the multilayer supercomputer I/O systems and ways to use these subsystems efficiently. In this work, we study the I/O access patterns and performance characteristics of two representative supercomputer I/O subsystems. Through an extensive analysis of year-long I/O logs on each system, we report new observations in I/O reads and writes, unbalanced use of storage system layers, and new trends in user behaviors at the HPC I/O middleware stack.

Bez, JL↗
NASA NTRS1999

Advanced Cosmic-Ray Composition Experiment for Space Station (ACCESS): ACCESS Accommodation Study Report

In 1994 NASA Administrator selected the first high-energy particle physics experiment for the Space Station, the Alpha Magnetic Spectrometer (AMS), to place a magnetic spectrometer in Earth orbit and search for cosmic antimatter. A natural consequence of this decision was that NASA would begin to explore cost-effective ways through which the design and implementation of AMS might benefit other promising payload experiments. The first such experiment to come forward was Advanced Cosmic-Ray Composition Experiment for Space Station (ACCESS) in 1996. It was proposed as a new mission concept in space physics to attach a cosmic-ray experiment of weight, volume, and geometry similar to the AMS on the International Space Station (ISS), and replace the latter as its successor when the AMS is returned to Earth. This was to be an extension of NASA's suborbital balloon program, with balloon payloads serving as the precursor flights and heritage for ACCESS. The balloon programs have always been a cost-effective NASA resource since the particle physics instrumentation for balloon and space applications are directly related. The next step was to expand the process, pooling together expertise from various NASA centers and universities while opening up definition of the ACCESS science goals to the international community through the standard practice of peer review. This process is still ongoing, and the accommodation study presented here will discuss the baseline definition of ACCESS as we understand it today.

Wilson, Thomas L.↗
DOE OSTI2020

Prioritizing local and remote memory access in a non-uniform memory access architecture

A miss in a cache by a thread in a wavefront is detected. The wavefront includes a plurality of threads that are executing a memory access request concurrently on a corresponding plurality of processor cores. A priority is assigned to the thread based on whether the memory access request is addressed to a local memory or a remote memory. The memory access request for the thread is performed based on the priority. In some cases, the cache is selectively bypassed depending on whether the memory access request is addressed to the local or remote memory. A cache block is requested in response to the miss. The cache block is biased towards a least recently used position in response to requesting the cache block from the local memory and towards a most recently used position in response to requesting the cache block from the remote memory.

Boyer, Michael W.↗
DOE OSTI2020

Acid Erosion of Carbonate Fractures and Accessibility of Arsenic-Bearing Minerals: In Operando Synchrotron-Based Microfluidic Experiment

Underground flows of acidic fluids through fractured rock can create new porosity and increase accessibility to hazardous trace elements such as arsenic. In this study, we developed a custom microfluidic cell for an in operando synchrotron experiment using X-ray attenuation. The experiment mimics reactive fracture flow by passing an acidic fluid over a surface of mineralogically heterogeneous rock from the Eagle Ford shale. Over 48 h, calcite was preferentially dissolved, forming an altered layer 200–500 μm thick with a porosity of 63–68% and surface area >10$\times$ higher than that in the unreacted shale as shown by xCT analyses. Calcite dissolution rate quantified from the attenuation data was 3 $\times$ 10 –4 mol/m 2 s and decreased to 3 $\times$ 10 –5 mol/m 2 s after 24 h because of increasing diffusion limitations. Erosion of the fracture surface increased access to iron-rich minerals, thereby increasing access to toxic metals such as arsenic. Quantification using XRF and XANES microspectroscopy indicated up to 0.5 wt % of As(-I) in arsenopyrite and 1.2 wt % of As(V) associated with ferrihydrite. This study provides valuable contributions for understanding and predicting fracture alteration and changes to the mobilization potential of hazardous metals and metalloids.

58 GEOSCIENCES↗
DOE OSTI2020

High-Level Considerations for Access and Access Controls by Design

Nuclear power plants must be, by design and construction, robust structures and difficult to penetrate. Limiting access with difficult-to-penetrate physical barriers is going to be key for staffing reduction. Ideally, for security, the reactors would be sited underground, beneath a massive solid block, too thick to be penetrated by tools or explosives with all communications and power transfer lines also underground and fortified. Having the minimal possible number of access points and methods to completely block access from these points if a threat is detected will greatly help us justify staffing reduction.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1983

A comparison of Frequency Domain Multiple Access (FDMA) and Time Domain Multiple Access (TDMA) approaches to satellite service for low data rate Earth stations

A technological and economic assessment is made of providing low data rate service to small earth stations by satellite at Ka-band. Various Frequency Domain Multiple Access (FDMA) and Time Domain Multiple Access (TDMA) scenarios are examined and compared on the basis of cost to the end user. Very small stations (1 to 2 meters in diameter) are found not to be viable alternatives to available terrestrial services. However, medium size (3 to 5 meters) earth stations appear to be very competitive if a minimum throughput of about 1.5 Mbs is maintained. This constrains the use of such terminals to large users and shared use by smaller users. No advantage was found to the use of FDMA. TDMA had a slight advantage from a total system viewpoint and a very significant advantage in the space segment (about 1/3 the required payload weight for an equivalent capacity).

Stevens, G.↗
NASA NTRS1985

Evolution of area access safety training required for gaining access to Space Shuttle launch and landing facilities

Assuring personnel and equipment are fully protected during the Space Shuttle launch and landing operations has been a primary concern of NASA and its associated contractors since the inception of the program. A key factor in support of this policy has been the area access safety training requirements for badging of employees assigned to work on Space Shuttle Launch and Facilities. This requirement was targeted for possible cost savings and the transition of physical on-site walkdowns to the use of television tapes has realized program cost savings while continuing to fully satisfy the area access safety training requirements.

Willams, M. C.↗
NASA NTRS1990

Multiple access capacity trade-offs for a Ka-band personal access satellite system

System capability is critical to the economic viability of a personal satellite communication system. Ka band has significant potential to support a high capacity multiple access system because of the availability of bandwidth. System design tradeoffs are performed and multiple access schemes are compared with the design goal of achieving the highest capacity and efficiency. Conclusions regarding the efficiency of the different schemes and the achievable capacities are given.

Dessouky, Khaled↗
DOE OSTI2022

Accessing and Photo-Accelerating Low-Overpotential Pathways for CO 2 Reduction: A Bis-Carbene Ruthenium Terpyridine Catalyst

A ruthenium catalyst bearing a bidentate bis(carbene) ligand is prepared and studied as a catalyst for CO 2 electroreduction. The catalyst [Ru(tpy)(bis-mim)(MeCN)][PF 6 ] 2 (tpy) is 2,2′,:6′,2″-terpyridine; bis-mim is (methylenebis(N-methylimidazol-2-ylidene)) mediates reduction of CO 2 into CO with a turnover frequency of 630 s –1 and Faradaic efficiency (FE) of 30% at an overpotential of 730 mV. The strongly donating bis(carbene) ligand also enables access to a pathway operating at a lower overpotential of ca. 310 mV. While low-overpotential catalysis is slow in the dark (TOF = 0.01 s –1 ), visible light illumination increases the rate 10-fold (TOF = 0.11 s –1 ). Here, a full mechanistic picture is developed using kinetic analysis from cyclic voltammetry, spectroelectrochemistry, and computational methods, with the bis-mim ligand facilitating rapid CO 2 activation at low overpotentials. Comparisons with other ruthenium catalysts yield insight into the ability to tune the rate of chemical steps (e.g., ligand dissociation and CO 2 nucleophilic attack) and the overpotential by tailoring the primary coordination sphere while retaining the “redox-active” tpy ligand.

CO2 reduction↗
DOE OSTI2020

High-Level Considerations for Access and Access Controls by Design

Nuclear power plants must be, by design and construction, robust structures and difficult to penetrate. Ideally, for security, the reactors would be sited underground, beneath a massive solid block, too thick to be penetrated by tools or explosives with all communications and power transfer lines also underground and fortified. Limiting access with difficult-to-penetrate physical barriers is going to be key for determining response and staffing requirements.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

High-Level Considerations for Access and Access Controls by Design

The design and construction of a nuclear power plant must include robust structures and a security boundary that is difficult to penetrate. For security considerations, the reactors would ideally be sited underground, beneath a massive solid block, which would be too thick to be penetrated by tools or explosives. Additionally, all communications and power transfer lines would also be located underground and would be fortified against any possible design basis threats. Limiting access with difficult-to-penetrate physical barriers is a key aspect for determining response and staffing requirements. Considerations considered in a graded approach to physical protection are described.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

Accessing Microsoft Access Databases Using ODBC and RODBC

ODBC (Open Database Connectivity) is an industry-standard API (Application Program Interface) that provides a standard interface, based on SQL (Structured Query Language) between applications and databases. This insulates applications from specific details of different database management systems (DBMS). Microsoft Windows TM provides an implementation of ODBC, which, along with drivers for various databases, supports the API. Windows also provides a driver for Access databases.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1989

Spacelab system analysis: The modified free access protocol: An access protocol for communication systems with periodic and Poisson traffic

The protocol definition and terminal hardware for the modified free access protocol, a communications protocol similar to Ethernet, are developed. A MFA protocol simulator and a CSMA/CD math model are also developed. The protocol is tailored to communication systems where the total traffic may be divided into scheduled traffic and Poisson traffic. The scheduled traffic should occur on a periodic basis but may occur after a given event such as a request for data from a large number of stations. The Poisson traffic will include alarms and other random traffic. The purpose of the protocol is to guarantee that scheduled packets will be delivered without collision. This is required in many control and data collection systems. The protocol uses standard Ethernet hardware and software requiring minimum modifications to an existing system. The modification to the protocol only affects the Ethernet transmission privileges and does not effect the Ethernet receiver.

Ingels, Frank↗