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At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Shape memory effect in metallic glasses

Shape memory effect (SME), mainly present in crystalline Ti-Ni alloys, is basically missing in metallic glasses (MGs) that lack the long-range periodic order of crystals. In this work, we report experimental results of SME in annealed MGs, in which the low-energy configuration state recovery is observed by both differential scanning calorimetry and X-ray photon correlation spectroscopy. We elucidate the origin of SME in MGs under the potential energy landscape framework, i.e., after annealing, the energy of MGs enters into a deep basin and atoms are located in the low-energy configuration state. Albeit deviating from their relative stable configurations by temperature changes, atoms in the annealed MGs tend to return to the low-energy atomic configurations along certain trajectories as pre-annealing temperature is approached, These results could extend the application of MGs as functional materials by directionally manipulating their energy states via annealing and rejuvenation.

36 MATERIALS SCIENCE↗

NASA NTRS2000

Aerobraking at Venus and Mars: A Comparison of the Magellan and Mars Global Surveyor Aerobraking Phases

On February 4, 1999 the Mars Global Surveyor spacecraft became the second spacecraft to successfully aerobrake into a nearly circular orbit about another planet. This paper will highlight some of the similarities and differences between the aerobraking phases of this mission and the first mission to use aerobraking, the Magellan mission to Venus. Although the Mars Global Surveyor (MGS) spacecraft was designed for aerobraking and the Magellan spacecraft was not, aerobraking MGS was a much more challenging task than aerobraking Magellan, primarily because the spacecraft was damaged during the initial deployment of the solar panels. The MGS aerobraking phase had to be completely redesigned to minimize the bending moment acting on a broken yoke connecting one of the solar panels to the spacecraft. Even if the MGS spacecraft was undamaged, aerobraking at Mars was more challenging than aerobraking at Venus for several reasons. First, Mars is subject to dust storms, which can significantly change the temperature of the atmosphere due to increased solar heating in the low and middle altitudes (below 50 km), which in turn can significantly increase the density at the aerobraking altitudes (above 100 km). During the first part of the MGS aerobraking phase, a regional dust storm was observed to have a significant and very rapid effect on the entire atmosphere of Mars. Computer simulations of global dust storms on Mars indicate that even larger density increases are possible than those observed during the MGS aerobraking phases. For many aerobraking missions, the duration of the aerobraking phase must be kept as short as possible to minimize the total mission cost. For Mars missions, a short aerobraking phase means that there will be less margin to accommodate atmospheric variability, so the operations team must be ready to propulsively raise periapsis by tens of kilometers on very short notice. This issue was less of a concern on Venus, where the thick lower atmosphere and the slow planet rotation resulted in more predictable atmospheric densities from one orbit to the next.

Lyons, Daniel T.↗

DOE OSTI2023

Uncovering metallic glasses hidden vacancy-like motifs using machine learning

Vacancies are a ubiquitous type of defect in crystalline materials that can affect their properties and behavior, including atomic diffusivity, deformation processes, thermal conductivity, and electrical conductivity. While well-defined in crystals, it is challenging to identify such topological footprints in the amorphous structure of metallic glasses (MGs). Here, we uncover an unforeseen vacancy-like structural motif named Q7, which refers to an atomic Voronoi polyhedron with seven quadrangular faces, by investigating MG local atomic configurations with the help of machine learning. The Q7 motif exhibits characteristics similar to crystalline vacancies and plays a significant role in short-range structural disorder in MGs. The atoms at the center of the Q7 motif display larger local entropy, atomic volume, and local tension. Additionally, its concentration follows an Arrhenius-like relationship with temperature, accurately indicating the glass transition temperature, and is strongly correlated with the yield and failure of MGs during mechanical deformation. The discovery of the Q7 motif provides new insights into understanding the intricate relationship between local disorder and structural relaxation in MGs, offering a remarkable ability to predict their thermal and mechanical behavior. This potentially paves the way for enhancements in the design and manufacturing processes of MGs and other amorphous materials.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Effects of rejuvenation modes on the microstructures and mechanical properties of metallic glasses

This study systematically investigates the effects of three rejuvenation modes, namely biaxial loading, thermal pressure loading, and cryogenic thermal cycling, on the microstructures and mechanical properties of Cu 64 Zr 36 metallic glasses (MGs) using molecular dynamics (MD) simulations. The simulation results demonstrate that biaxial tension application during loading results in a rejuvenated glassy state with high strength. Specifically, we find that the yield stress, Young's modulus, and shear modulus of the rejuvenated glass obtained by biaxial tensile loading decreased by 2.8%, 2.1%, and 2.7%, respectively, compared to an as-cast MG reference. We also find that MGs achieve the greatest degree of rejuvenation, at the expense of strength, with the use of thermal pressure loading. Interestingly, the application of cryogenic thermal cycling results in a rejuvenated state with a lower strength drop compared to thermal pressure loading. Furthermore, analysis of the potential energy and medium-range-order (MRO) size indicates that the microstructures of MGs achieves a high-energy ordered glass state after thermal pressure loading, but a high-energy disordered glass state after biaxial tensile loading and cryogenic thermal cycling. Furthermore, these findings provide meaningful insights into the effect of rejuvenation modes on the microstructures and mechanical properties of MGs, as well as useful guidelines for designing MGs with high strength and superior plasticity for prospective applications in industry.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Composition-dependent fracture energy in metallic glasses

The interplay between metallic glasses (MGs) mechanical properties, fracture energy (G), and glass-forming ability (GFA) and their dependence on alloy composition remain poorly understood. Here, we perform molecular dynamics simulations to investigate the intrinsic composition-dependence of G in Cu x Zr 100-x MGs (x = 20, 30, 40, 50, 64). The results indicate that the value of G increases with Cu content. In addition, it is revealed that MGs with higher G values display higher Poisson’s ratio (ν) and GFA, suggesting a close correlation between fracture toughness, mechanical properties, and GFA. This correlation between G, ν and GFA can be understood based on the fragility (m) of supercooled liquids, which is directly related to the structural heterogeneity in MGs. Larger m values are related to dynamic slowdown and supercooled liquid stabilization, which enhance GFA and the formation of pronounced structural heterogeneity, comprised of loosely packed regions that favor β-relaxation and the activation of shear transformation zones. Those concurrently promote the expansion of the plastic zone at the crack tip, enhancing the observed value of G. Furthermore, these simulation results shed light on the intrinsic relationship between fracture toughness, mechanical properties, and alloy composition in MGs.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Tracing the Origin of Moving Groups. III. Detecting Moving Groups in LAMOST DR7

We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91,969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at $V$ ≃ -130 KM s -1 are detected simultaneously in $V$ - $\sqrt{U^2 + 2V^2}$ space. Taking into account the other known MGs, we conclude that MGs in the Galactic disk are spaced by approximately 15–25 km s -1 along $V$ velocity. Furthermore, the origin of detected MGs is analyzed through the distributions of [Fe/H]-[Mg/Fe] and ages. Our results support attributing the origin to the continuous resonant mechanisms probably induced by the bar or spiral arms of the Milky Way.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1984

Spectral Characteristics of Dust in Planetary Nebulae

Some carbon-rich planetary nebulae exhibit a strong broad emission feature beginning at Lambda which is approximately 24 microns and extending to Lambda greater than 30 microns. Thirty to 55 micron spectrophotometry of Ic 418 and NGC 6572, both of which have the strong broad emission feature, allow the wavelength dependence of the emissivity of the dust responsible for the feature to be defined. Comparison with laboratory spectra of candidate materials which are likely to condense in a carbon-rich environment suggests that the feature arises from MgS. The implications of such a strong feature arising from a relatively minor dust constituent are discussed. The environment in which MgS may be found is considered. It is speculated that MgS will be seen in objects with C/O ratios only slightly greater than one, but not in extremely carbon rich objects. In objects with much higher carbon abundances, the formation of CS consumes S so that insufficient MgS can form to exhibit the strong feature. These observations imply that the emergent far infrared spectrum of carbon-rich objects are very different depending on the abundance of the low temperature condensate MgS.

Moseley, H.↗

NASA NTRS1986

Spectral characteristics of dust in planetary nebulae

Moseley, H.↗

NASA NTRS1998

Martian Meteorology: Determination of Large Scale Weather Patterns from Surface Measurements

We employed numerical modelling of the martian atmosphere, and our expertise in understanding martian atmospheric processes, to better understand the coupling between lower and upper atmosphere processes. One practical application of this work has been our involvement with the ongoing atmospheric aerobraking which the Mars Global Surveyor (MGS) spacecraft is currently undergoing at Mars. Dr. Murphy is currently a member of the Mars Global Surveyor (MGS) Aerobraking Atmospheric Advisory Group (AAG). He was asked to participate in this activity based upon his knowledge of martian atmospheric dynamical processes. Aerobraking is a process whereby a spacecraft, in an elliptical orbit, passes through the upper layers of the atmosphere (in this instance Mars). This passage through the atmosphere 'drags' upon the spacecraft, gradually reducing its orbital velocity. This has the effect, over time, of converting the elliptical orbit to a circular orbit, which is the desired mapping orbit for MGS. Carrying out aerobraking eliminates the need for carrying large amounts of fuel on the spacecraft to execute an engine burn to achieve the desired orbit. Eliminating the mass of the fuel reduces the cost of launch. Damage to one of MGS's solar panels shortly after launch has resulted in a less aggressive extended in time aerobraking phase which will not end until March, 1999. Phase 1 extended from Sept. 1997 through March 1998. During this time period, Dr. Murphy participated almost daily in the AAG meetings, and beginning in December 1997 lead the meeting several times per week. The leader of each of the daily AAG meetings took the results of that meeting current state of the atmosphere, identification of any time trends or spatial patterns in upper atmosphere densities, etc.) forward to the Aerobraking Planning Group (APG) meeting, at which time the decision was made to not chance MGS orbit, to lower the orbit to reach higher densities (greater 'drag'), or raise the orbit to avoid experiencing excessive, possibly damaging densities.

Murphy, James R.↗

NASA NTRS1998

Martian Meteorology: Determination of Large Scale Weather Patterns from Surface Measurements

We employed numerical modelling of the martian atmosphere, and our expertise in understanding martian atmospheric processes, to better understand the coupling between lower and upper atmosphere processes. One practical application of this work has been our involvement with the ongoing atmospheric aerobraking which the Mars Global Surveyor (MGS) spacecraft is currently undergoing at Mars. Dr. Murphy is currently a member of the Mars Global Surveyor (MGS) Aerobraking Atmospheric Advisory Group (AAG). He was asked to participate in this activity based upon his knowledge of martian atmospheric dynamical processes. Aerobraking is a process whereby a spacecraft, in an elliptical orbit, passes through the upper layers of the atmosphere (in this instance Mars). This passage through the atmosphere 'drags'upon the spacecraft, gradually reducing its orbital velocity. This has the effect, over time, of converting the elliptical orbit to a circular orbit, which is the desired mapping orbit for MGS. Carrying out aerobraking eliminates the need for carrying large amounts of fuel on the spacecraft to execute an engine burn to achieve the desired orbit. Eliminating the mass of the fuel reduces the cost of launch. Damage to one of MGS's solar panels shortly after launch has resulted in a less aggressive extended in time aerobraking phase which will not end until March, 1999. Phase I extended from Sept. 1997 through March 1998. During this time period, Dr. Murphy participated almost daily in the AAG meetings, and beginning in December 1997 lead the meeting several times per week. The leader of each of the daily AAG meetings took the results of that meeting (current state of the atmosphere, identification of any time trends or spatial patterns in upper atmosphere densities, etc.) forward to the Aerobraking Planning Group (APG) meeting, at which time the decision was made to not change MGS orbit, to lower the orbit to reach higher densities (greater 'drag'), or raise the orbit to avoid experiencing excessive, possibly damaging densities.

Murphy, James R.↗

NASA NTRS2000

An Overview of the Topography of Mars from the Mars Orbiter Laser Altimeter (MOLA)

The Mars Global Surveyor (MGS) spacecraft has now completed more than half of its one-Mars-year mission to globally map Mars. During the MGS elliptical and circular orbit mapping phases, the Mars Orbiter Laser Altimeter (MOLA), an instrument on the MGS payload, has collected over 300 million precise elevation measurements. MOLA measures the range from the MGS spacecraft to the Martian surface and to atmospheric reflections. Range is converted to topography through knowledge of the MGS spacecraft orbit. Ranges from MOLA have resulted in a precise global topographic map of Mars. The instrument has also provided measurements of the width of the backscattered optical pulse and of the 1064 nm reflectivity of the Martian surface and atmosphere. The range resolution of the MOLA instrument is 37.5 cm and the along-track resolution of MOLA ground shots is approx. 300 m; the across-track spacing depends on latitude and time in the mapping orbit. The best current topographic grid has a spatial resolution of approx. 1/16 deg and vertical accuracy of approx. one meter. Additional information is contained in the original extended abstract.

Smith, David E.↗

NASA NTRS2001

The Mars Orbiter Altimeter (MOLA) Investigation of the Shape and Topography of Mars

The Mars Orbiter Laser Altimeter (MOLA) is an instrument on the Mars Global Surveyor (MGS) spacecraft that has been orbiting Mars since September 1997. After some preliminary observations in Sept/Oct, 1997 and in the spring and summer of 1998, the MGS spacecraft entered its mapping orbit of 400 km above the surface of Mars in February 1999. MGS began a 2 year program of systematically mapping the planet with a camera (MOC), thermal emission spectrometer (TES), magnetometer (MAG), laser altimeter (MOLA), and a radio science investigation for gravity and radio occultations. MOLA has a 48mJ, 1064 nrn ND:YAG, diode pumped laser with a 8 nanosecond pulse width, a pulse rate of 10 Hz, and a range precision of less than 40 cm. MOLA has been operating almost continuously for over two years and obtained over 600 million measurements of the radius of Mars. Using very precise orbits for the MGS spacecraft derived from the Doppler and range tracking of MGS by the Deep Space Network a topographical map of Mars has been developed with an average radial accuracy of a meter and a horizontal accuracy of 100 meters. This topographical map has revealed a new Mars, a planet with some of the flattest areas in the solar system and one of the largest impact basins. MOLA has revealed clear evidence of the effect of past fluid action on the surface and found icecaps that contain as much water ice today as the icecap of Greenland.

Smith, David E.↗

DOE OSTI2023

Hierarchical Data-Driven Protection for Microgrid with 100% Renewable Penetration: Preprint

The accurate detection and isolation of faults is critical for the reliable operation of microgrids (MGs). Traditional protection approaches are even more challenged for 100% renewable MGs because inverter-based resources (IBRs) are the only sources for fault current which are usually low and unpredictable/non-uniform. This calls for new protection scheme that can identify IBR fault responses and detect faults in MGs. Data-driven based protection can learn the pattern of IBR fault responses and make the correct decision to identify faults. Therefore, this paper presents a data-driven approach for fault localization in island MGs. The approach builds a training dataset of comprehensive fault scenarios that can be used to learn fault characteristics from processed measurements. The localization task is modeled as a binary classification problem at each relay, which simplifies the learning process. Then, a hierarchical decision mechanism is used to identify the fault location. The proposed approach is assessed using an exemplary MG with several grid-forming (GFM) and grid-following (GFL) inverters, where accurate estimation of fault location is achieved. The data-driven based protection approach developed in this paper provides a generic framework and useful guidance for power system protection engineers to achieve reliable protection for MGs with 100% renewables.

artificial intelligence↗

NASA NTRS2007

Cartographic Mapping of Mars Landing Sites: A Historical Perspective

Initial mapping of Mars began with the early Mariner 4, 6 and 7 flybys in the 1960's. Mariner 9 obtained the first global coverage of Mars in 1971. Viking Orbiters 1 and 2 added new and higher resolution global coverage. The US Geological Survey produced the first digital global cartographic map products in black and white and in color, the mosaicked digital image models (MDIMs). In 1989, the Phobos 88 mission added imaging as well as multispectral mapping of Mars in the equatorial region. The Mars Global Surveyor (MGS) added to the black and white and color global coverage. The most important development for Mars cartography occurred on MGS with its global coverage of Mars using the Mars Observer Laser Altimeter (MOL A) producing precision ground control in latitude, longitude and radius. The next version of the MDIM was produced at 230 m spatial resolution using MOLA precision cartographic control. The Mars Odyssey mission THEMIS instrument has completed its global infrared mapping of Mars at 100 m spatial resolution. The Mars Express mission is completing its global coverage of Mars in stereo at 100 m spatial resolution or better. MGS, Odyssey and Mars Express continue to provide limited surface coverage at the 1 to 20 m resolution. Currently the new Mars Reconnaissance Orbiter is producing images at the 10's of cm level. All of these datasets provide a rich and historic perspective of Mars covering nearly five decades and allow global cartographic map products to be produced in visual and infrared at the 100 m level with specialized cartographic maps being produced for landing sites at the meter or sub-meter spatial resolution level. This work was produced at the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration, NAS 7-7120.5d, within the NASA Mars Data Analysis Program and the MGS, Odyssey, Mars Express and MRO Participating Scientist Programs.

MOLA↗

DOE OSTI2022

Discovering exceptionally hard and wear-resistant metallic glasses by combining machine-learning with high throughput experimentation

Lack of crystalline order in amorphous alloys, commonly called metallic glasses (MGs), tends to make them harder and more wear-resistant than their crystalline counterparts. However, finding inexpensive MGs is daunting; finding one with enhanced wear resistance is a further challenge. Relying on machine learning (ML) predictions of MGs alone requires a highly precise model; however, incorporating high-throughput (HiTp) experiments into the search rapidly leads to higher performing materials even from moderately accurate models. Here, we exploit this synergy between ML predictions and HiTp experimentation to discover new hard and wear-resistant MGs in the Fe–Nb–B ternary material system. Several of the new alloys exhibit hardness greater than 25 GPa, which is over three times harder than hardened stainless steel and only surpassed by diamond and diamond-like carbon. This ability to use less than perfect ML predictions to successfully guide HiTp experiments, demonstrated here, is especially important for searching the vast Multi-Principal-Element-Alloy combinatorial space, which is still poorly understood theoretically and sparsely explored experimentally.

36 MATERIALS SCIENCE↗

DOE OSTI2020

A Learning-based Power Management Method for Networked Microgrids Under Incomplete Information

In this paper, we present a model-free reinforcement learning (RL)-based technique to solve the power management problem of networked microgrids (MGs), when the utility has only limited or no detailed knowledge of the MG asset models.The proposed method consists of two levels: at the first level, using an approximate RL strategy and aggregated data, a utility agent determines the locational price signals to maximize its profit under incomplete information on the MGs’ private data behind their points of common coupling (PCC). The proposed RL strategy enables the utility to adapt to changing system conditions and learn from previous experiences, while respecting the data ownership of the MGs. At the second level, the MGs receive the price signals to dispatch their generation/storage assets individually over look-ahead decision time window, while considering power flow constraints. The performance of the proposed RL technique has been verified under realistic operational scenarios.

Zhang, Qianzhi↗

DOE OSTI2025

Distribution System Blackstart and Restoration Using DERs and Dynamically Formed Microgrids

Extreme weather events have led to long-duration outages in the distribution system (DS), necessitating novel approaches to blackstart and restore the system. Existing blackstart solutions utilize blackstart units to establish multiple microgrids (MGs), sequentially energize non-blackstart units, and restore loads. However, these approaches often result in isolated MGs. In DERs-aided blackstart, the continuous operation of these MGs is limited by the finite energy capacity of commonly used blackstart units like battery energy storage (BES)-based gridforming inverters (GFMIs). To address this issue, this article proposes a holistic blackstart and restoration framework that incorporates synchronization between dynamic MGs and the entire DS with the transmission grid (TG). To support synchronization, we leveraged virtual synchronous generator-based control for GFMIs to estimate their frequency response to load pick-up events using only initial/final quasi-steady-state points. Subsequently, a synchronization switching condition is developed to model synchronizing switches, aligning them seamlessly with a linearized branch flow problem. Finally, we designed a bottomup blackstart and restoration framework that considers the switching structure of the DS, energizing/synchronizing switches, DERs with grid-following inverters, and BES-based GFMIs with frequency security constraints. In conclusion, the proposed framework is validated in IEEE-123-bus system, considering cases with two and four GFMIs under various TG recovery instants.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2020

Multiscale modeling of shear banding in metallic glasses (Final report)

Metallic glasses (MGs) possess remarkably high strength but suffer from minimal tensile ductility due to the formation of catastrophic shear bands. The goal of this research project is to develop an understanding of the microstructures and deformation mechanisms that control shear banding in MGs, which will enable the development of MGs with enhanced plasticity. Two scientific objectives have been pursued. (1) Understand the underlying mechanisms of shear banding phenomena in presence of nanoscale heterogeneities in MGs. (2) Understand the evolution of MG heterogenous structure upon thermomechanical stimuli for plasticity enhancement through controlling and distributing multiple shear bands.

36 MATERIALS SCIENCE↗