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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 1,315 records · Page 73

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NASA NTRS1981

A new method for focusing and imaging X-rays and gamma-rays with diffraction crystals

Bent diffraction crystals in which the intercrystalline-plane spacing is varied as a function of position in the crystal are used to focus monochromatic radiation from a point source or parallel beam down to a point image. Conversely, radiation from a point source can be focused into an outgoing parallel beam. The Bragg angle for diffraction of monochromatic radiation will now vary as a function of position in the crystal and this new degree of freedom is used to obtain focusing and imaging of the diffracted beam. This approach to focusing and imaging is applied to the design of a large-area, high resolution X-ray telescope that is also a high resolution monochromator with the unique feature that the width of the energy increment that is diffracted can be controlled and varied during the operation of the instrument. The field can be scanned with a wide energy increment and then switched to a narrow energy increment for the high resolution work. Both transmission and reflection type diffraction crystals can be used.

Smither, R. K.↗

NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the ascent thrust vector control actuator subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results for the Ascent Thrust Vector Control (ATVC) Actuator hardware are documented. The function of the Ascent Thrust Vector Control Actuators (ATVC) is to gimbal the main engines to provide for attitude and flight path control during ascent. During first stage flight, the SRB nozzles provide nearly all the steering. After SRB separation, the Orbiter is steered by gimbaling of its main engines. There are six electrohydraulic servoactuators, one pitch and one yaw for each of the three main engines. Each servoactuator is composed of four electrohydraulic servovalve assemblies, one second stage power spool valve assembly, one primary piston assembly and a switching valve. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Critical failures resulting in loss of ATVC were mainly due to loss of hydraulic fluid, fluid contamination and mechanical failures.

Wilson, R. E.↗

DOE OSTI2019

Temperature Dependence of Self-diffusion in Cr2O3 from First Principles

Understanding and predicting the dominant diffusion processes in Cr2O3 is essen- tial to its optimization for anti-corrosion coatings, spintronics, and other applications. Despite significant theoretical effort in modeling defect mediated diffusion in Cr2O3 the correlation with experimentally measured diffusivities remains poor partly due to the insufficient accuracy of the theoretical approaches. Here an attempt to resolve these discrepancies is made through high accuracy density functional theory simulations cou- pled with grand canonical formalism of defect thermochemistry. In this approach, point defect formation energies were computed using hybrid exchange correlation functional. This level of theory proved to be essential for achieving the agreement with experi- mental self-diffusion coefficients. The analysis of the resulting self-diffusion coefficients indicate that chromium has higher mobility at low temperatures and high oxygen partial pressures, in particular at standard temperature and pressure conditions. At high vacuum, high temperature conditions, oxygen diffusion becomes dominant. At Cr/Cr2O3 interfaces O vacancies were found to be more mobile than Cr vacancies at all temperatures. Cr diffuses preferentially along the c-axis at low temperatures but switches to basal plane at higher temperatures. O diffusion is primarily bound to basal plane at all temperatures.

Medasani, Bharat K.↗

NASA NTRS2004

Mechanisms for Antagonistic Regulation of AMPA and NMDA-D1 Receptor Complexes at Postsynaptic Sites

From the analysis of these pathways we conclude that postsynaptic processes that regulate synaptic transmission undergo significant cross-talk with respect to glutamatergic and neuromodulatory (dopamine) signals. The main hypothesis is that of a compensatory regulation, a competitive switch between the induction of increased AMPA conductance by CaMKII-dependent phosphorylation and reduced expression of PP2A, and increased D1 receptor sensitivity and expression by increased PKA, PP2A and decreased PP-1/calcineurin expression. Both types of plasticity are induced by NMDA receptor activation and increased internal calcium, they require different internal conditions to become expressed. Specifically we propose that AMPA regulation and D1 regulation are inversely coupled;The net result may be a bifurcation of synaptic state into predominantly AMPA or NMDA-D1 synapses. This could have functional consequences: stable connections for AMPA and conditional gating for NMDA-D1 synapses.

Schumann, Johann↗

NASA NTRS2003

Comparison of two weighted integration models for the cueing task: linear and likelihood

In a task in which the observer must detect a signal at two locations, presenting a precue that predicts the location of a signal leads to improved performance with a valid cue (signal location matches the cue), compared to an invalid cue (signal location does not match the cue). The cue validity effect has often been explained with a limited capacity attentional mechanism improving the perceptual quality at the cued location. Alternatively, the cueing effect can also be explained by unlimited capacity models that assume a weighted combination of noisy responses across the two locations. We compare two weighted integration models, a linear model and a sum of weighted likelihoods model based on a Bayesian observer. While qualitatively these models are similar, quantitatively they predict different cue validity effects as the signal-to-noise ratios (SNR) increase. To test these models, 3 observers performed in a cued discrimination task of Gaussian targets with an 80% valid precue across a broad range of SNR's. Analysis of a limited capacity attentional switching model was also included and rejected. The sum of weighted likelihoods model best described the psychophysical results, suggesting that human observers approximate a weighted combination of likelihoods, and not a weighted linear combination.

NASA Program Biomedical Research and Countermeasur↗

NASA NTRS2006

Single Phase Passive Rectification Versus Active Rectification Applied to High Power Stirling Engines

Stirling engine converters are being considered as potential candidates for high power energy conversion systems required by future NASA explorations missions. These types of engines typically contain two major moving parts, the displacer and the piston, in which a linear alternator is attached to the piston to produce a single phase sinusoidal waveform at a specific electric frequency. Since all Stirling engines perform at low electrical frequencies (less or equal to 100 Hz), space explorations missions that will employ these engines will be required to use DC power management and distribution (PMAD) system instead of an AC PMAD system to save on space and weight. Therefore, to supply such DC power an AC to DC converter is connected to the Stirling engine. There are two types of AC to DC converters that can be employed, a passive full bridge diode rectifier and an active switching full bridge rectifier. Due to the inherent line inductance of the Stirling Engine-Linear Alternator (SE-LA), their sinusoidal voltage and current will be phase shifted producing a power factor below 1. In order to keep power the factor close to unity, both AC to DC converters topologies will implement power factor correction. This paper discusses these power factor correction methods as well as their impact on overall mass for exploration applications. Simulation results on both AC to DC converters topologies with power factor correction as a function of output power and SE-LA line inductance impedance are presented and compared.

Santiago, Walter↗

DOE OSTI2017

Switch-off slow shock/rotational discontinuity structures in collisionless magnetic reconnection: What to look for in satellite observations: SWITCH-OFF STRUCTURES IN RECONNECTION

In Innocenti et al. (2015) we have observed and characterized for the first time Petschek-like switch-off slow shock/rotational discontinuity (SO-SS/RD) compound structures in a 2-D fully kinetic simulation of collisionless magnetic reconnection. Observing these structures in the solar wind or in the magnetotail would corroborate the possibility that Petschek exhausts develop in collisionless media as a result of single X point collisionless reconnection. Here we highlight their signatures in simulations with the aim of easing their identification in observations. The most notable signatures include a four-peaked ion current profile in the out-of-plane direction, associated ion distribution functions, increased electron and ion anisotropy downstream the SS, and increased electron agyrotropy downstream the RDs.

58 GEOSCIENCES↗

DOE OSTI2020

Comprehensive Electrical Control of Metamagnetic Transition of a Quasi-2D Antiferromagnet by In Situ Anisotropic Strain

Effective nonmagnetic control of the spin structure is at the forefront of the study for functional quantum materials. This study demonstrates that, by applying an anisotropic strain up to only 0.05%, the metamagnetic transition field of spin–orbit-coupled Mott insulator Sr 2 IrO 4 can be in situ modulated by almost 300%. Simultaneous measurements of resonant X-ray scattering and transport reveal that this drastic response originates from the complete strain-tuning of the transition between the spin-flop and spin-flip limits, and is always accompanied by large elastoconductance and magnetoconductance. This enables electrically controllable and electronically detectable metamagnetic switching, despite the antiferromagnetic insulating state. The obtained strain-magnetic field phase diagram reveals that C 4 -symmetry-breaking anisotropy is introduced by strain via pseudospin-lattice coupling, directly demonstrating the pseudo-Jahn–Teller effect of spin–orbit-coupled complex oxides. The extracted coupling strength is much weaker than the superexchange interactions, yet crucial for the spontaneous symmetry-breaking, affording the remarkably efficient strain-control.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Ionic Control over Ferroelectricity in 2D Layered van der Waals Capacitors

The van der Waals layered material CuInP 2 S 6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the buildup of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Tension-free Dirac strings and steered magnetic charges in 3D artificial spin ice

3D nano-architectures presents a new paradigm in modern condensed matter physics with numerous applications in photonics, biomedicine, and spintronics. They are promising for the realization of 3D magnetic nano-networks for ultra-fast and low-energy data storage. Frustration in these systems can lead to magnetic charges or magnetic monopoles, which can function as mobile, binary information carriers. However, Dirac strings in 2D artificial spin ices bind magnetic charges, while 3D dipolar counterparts require cryogenic temperatures for their stability. Here, we present a micromagnetic study of a highly frustrated 3D artificial spin ice harboring tension-free Dirac strings with unbound magnetic charges at room temperature. We use micromagnetic simulations to demonstrate that the mobility threshold for magnetic charges is by 2 eV lower than their unbinding energy. By applying global magnetic fields, we steer magnetic charges in a given direction omitting unintended switchings. The introduced system paves the way toward 3D magnetic networks for data transport and storage.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Temperature dependence of field;#8208;responsive mechanisms in lead zirconate titanate

Abstract not provided

Chung, Ching↗

NASA NTRS1981

Manned geosynchronous mission requirements and system analysis study extension. Manned Orbital Transfer Vehicle (MOTV) capabilities handbook and user guide

The primary change in crew capsule definition is a smaller MOTV crew capsule, switching from a 3-man capsule to a 2-man capsule. A second change permitted crew accommodations for sleeping and privacy to be combined with the flight station. The current baseline DRM, ER1, requires 2 men for 3 to 4 days to repair a multi-disciplined GOE Platform and a modest amount of mission dedicated hardware. A 2-man MOTV crew capsule to be used as a design reference point for the OTV, and its interfaces between the STS and other associated equipment or facilities are described in detail. The functional capabilities of the 2-man capsule, as well as its application to a wide range of generic missions, is also presented. The MOTV turnaround is addressed and significant requirements for both space based and ground based scenarios are summarized.

Source record↗

DOE OSTI2020

Control of magnetic properties of MnBi 2 Te 4 using a van der Waals ferroelectric III 2 -VI 3 film and biaxial strain

Using the first-principles calculations, we systematically investigated magnetic properties of a MnBi 2 Te 4 (MBT) monolayer in contact with III 2 -VI 3 two-dimensional ferroelectric substrates. As the electric polarization in the ferroelectric films is switched, a semiconductor to half-metal transition occurs in MBT, and its magnetic easy axis in several cases reorients. As an example, the Curie temperature of MBT/In 2 Se 3 can be enhanced to 21.5 or 32 K under the influence of electric polarization and biaxial strain, much higher than that of the pristine MBT monolayer, which is 14.5 K in our calculations. Our results in this work suggest effective ways to tune magnetic properties of MBT and provide useful insights for the further development of these important van der Waals functional materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1982

Simultaneous stabilization and simultaneous pole placement by nonswitching dynamic compensation

The 'simultaneous stabilization problem' is defined and theorems are proposed for its solution. The problem consists in answering the question: given an r-tuple G sub 1(s), G sub r(s) of p x m proper transfer functions, does there exist a compensator K(s) such that the closed loop systems G sub 1(s) (I+K(s)G sub 1(s)) (-1), G sub r(s) (I+K(s) G sub r(s)) (-1) are (internally) stable. This question arises in reliability theory, where G sub 2(s), G sub r(s) represents a plant G sub 1(s) operating in various modes of failure and K(s) is a nonswitching stabilizing compensator. It is important in the stability analysis and design of a plant which can be switched into various operating modes. The simultaneous stabilization problem can also apply to the stabilization of a nonlinear system which is linearized at several equilibria. Conditions are defined for pole placement and the generalized Sylvestor matrix is discussed.

Ghosh, B. K.↗

NASA NTRS1983

Simultaneous stabilization and simultaneous pole-placement by nonswitching dynamic compensation

Ghosh, B. K.↗

NASA NTRS1995

Operational characteristics of a 200 C LC parallel resonant circuit

Research efforts are currently underway at the NASA Lewis Research Center to design and demonstrate an inverter capable of operating with a baseplate temperature of 200 C. In support of this project, various electrical components including capacitors, inductors, transformers, cables, and semiconductor switches are being developed or evaluated for integration into the inverter. In this work, a parallel LC resonant circuit was constructed and evaluated under simultaneous electrical and thermal stressing. The tests were performed in the temperature range of 25 to 200 C with an applied voltage of up to 90 V, 20 kHz. The individual components were comprised of high temperature film capacitors and powder core inductors developed in-house. The circuit was characterized in terms of the component currents and case temperatures as well as frequency of resonance as a function of applied bias and temperature. The results obtained, which have indicated good functional stability up to 200 C, are presented and discussed.

Baumann, Eric D.↗

NASA NTRS2010

An Integrated, Evidence-Based Approach to Transitioning to Operations: Specifications for Future Replacement Lights on ISS

The International Space Station (ISS) currently uses General Luminaire Assemblies (GLAs) as its primary light source. These GLAs are composed of fluorescent lighting and are integrated into the electrical system on Station. Seventy seven of these units are distributed throughout the vehicle, and many of the lights, having reached their lifespan, are no longer functional; while backup panels are available on orbit, it is anticipated that the supplies of fluorescents on the station will be exhausted by 2015. The ISS vehicle office is therefore preparing to replace all of the GLAs, with Solid State Light Assemblies (SSLAs) composed of white Light Emitting Diodes (LEDs). In the Spring of 2010, an announcement for the replacement lights was released. The announcement specified that proposed lighting systems should use LED technology, given certain power draw restrictions and no changes to how the lights are currently controlled (a central on/off switch per node, and a dial to turn on/off and increase brightness on each lighting unit). The replacement lights are to follow current specifications for brightness levels (lux) and color temperature (degrees Kelvin, or K). Reportedly, the lighting on orbit is dim and suboptimal. The average brightness of the lights (given all lights within a node are operational) is 291 lux; by comparison, recommended office lighting ranges from 200 to 500 lux, and daylight ranges on a typical overcast day, consists of 10,000 to 25,000 lux. Representatives from NASA Behavioral Health and Performance Element (BHP) and Human Factors and Habitability identified that maintaining current brightness levels limits visual acuity, work space, and the use of light as a countermeasure for improving circadian entrainment, hastening phase shifting, evoking acute alertness and enhancing performance. Revised lighting specifications are therefore needed to optimize the replacement lights for the ISS.

Leveton, Lauren↗

DOE OSTI2017

Development of a Dynamic Lidar Uncertainty Framework

As wind turbine sizes increase and wind energy expands to more complex and remote sites, remote-sensing devices such as lidars are expected to play a key role in wind resource assessment and power performance testing. The switch to remote-sensing devices represents a paradigm shift in the way the wind industry typically obtains and interprets measurement data for wind energy. For example, the measurement techniques and sources of uncertainty for a remote-sensing device are vastly different from those associated with a cup anemometer on a meteorological tower. Current IEC standards for quantifying remote sensing device uncertainty for power performance testing consider uncertainty due to mounting, calibration, and classification of the remote sensing device, among other parameters. Values of the uncertainty are typically given as a function of the mean wind speed measured by a reference device and are generally fixed, leading to climatic uncertainty values that apply to the entire measurement campaign. However, real-world experience and a consideration of the fundamentals of the measurement process have shown that lidar performance is highly dependent on atmospheric conditions, such as wind shear, turbulence, and aerosol content. At present, these conditions are not directly incorporated into the estimated uncertainty of a lidar device. In this presentation, we describe the development of a new dynamic lidar uncertainty framework that adapts to current flow conditions and more accurately represents the actual uncertainty inherent in lidar measurements under different conditions. In this new framework, sources of uncertainty are identified for estimation of the line-of-sight wind speed and reconstruction of the three-dimensional wind field. These sources are then related to physical processes caused by the atmosphere and lidar operating conditions. The framework is applied to lidar data from a field measurement site to assess the ability of the framework to predict errors in lidar-measured wind speed. The results show how uncertainty varies over time and can be used to help select data with different levels of uncertainty for different applications, for example, low uncertainty data for power performance testing versus all data for plant performance monitoring.

17 WIND ENERGY↗