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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Linear Seismic Source Equivalents in 3D Nonlinear Models: Effects of Embedded Small-Scale, Near-Source Structures

Gaining a proper understanding of how Earth structure and other near-source properties affect estimates of explosion yield is important to the nonproliferation mission. The yields of explosion sources are often based on seismic moment or waveform amplitudes. Quantifying how the seismic waveforms or estimates of the source characteristics derived from those waveforms are influenced by natural or man-made structures within the near-source region, where the wavefield behaves nonlinearly, is required to understand the full range of uncertainty in those yield estimates. We simulate tamped chemical explosions using a nonlinear, shock physics code and couple the ground motions beyond the elastic radius to a linear elastic, full waveform seismic simulation algorithm through 3D media. In order to isolate the effects of simple small-scale 3D structures on the seismic wavefield and linear seismic source estimates, we embed spheres and cylinders close to the fully- tamped source location within an otherwise homogenous half-space. The 3 m diameters spheres, given their small size compared to the predominate wavelengths investigated, not surprisingly are virtually invisible with only negligible perturbations to the far-field waveforms and resultant seismic source time functions. Similarly, the 11 m diameter basalt sphere has a larger, but still relatively minor impact on the wavefield. However, the 11 m diameter air-filled sphere has the largest impact on both waveforms and the estimated seismic moment of any of the investigated cases with a reduction of ~25% compared to the tamped moment. This significant reduction is likely due in large part to the cavity collapsing from the shock instead of being solely due to diffraction effects . Although the cylinders have the same diameters as the 3 m spheres, their length of interaction with the wavefield produces noticeable changes to the seismic waveforms and estimated source terms with reductions in the peak seismic moment on the order of 10%. Both the cylinders and 11 m diameter spheres generate strong shear waves that appear to emanate from body force sources.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
NASA NTRSDate not supplied

Operational Modal Analysis of the Space Launch System Mobile Launcher on the Crawler Transporter ISVV-010 Rollout

NASA is developing an expendable heavy lift launch vehicle capability, the Space Launch System, to support lunar and deep space exploration. To support this capability, an updated ground infrastructure is required including modifying an existing Mobile Launcher system. The Mobile Launcher is a very large heavy beam/truss steel structure designed to support the Space Launch System during its buildup and integration in the Vehicle Assembly Building, transportation between the Vehicle Assembly Building and launch pad 39B by the Crawler Transporter, and provides the launch platform at the launch pad. As part of the Verification and Validation of the Mobile Launcher and Crawler Transporter, two rollouts of the Mobile Launcher transported by the Crawler Transporter, Integrated System Verification and Validation (ISVV) 005 and 010, have been performed to demonstrate the Crawler Transporter’s ability to transport the Mobile Launcher. ISVV-005 occurred in September 2018 and ISVV-010 occurred in late June 2019. ISVV-005 and ISVV-010 also provided the opportunity to gather data that can be used identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics and refine the estimates of the Artemis I integrated launch vehicle rollout forcing functions. While the rollout environment has historically produced relatively small launch vehicle structural loads for the Saturn/Apollo and Space Shuttle programs in comparison to launch and ascent loads, these relatively small structural loads are inputs to structural fatigue analyses. The same holds true for the Space Launch System. Because the rollout forces acting on the Mobile Launcher and the Crawler Transporter are not directly measurable, Operational Modal Analysis techniques, instead of traditional Experimental Modal Analysis techniques, provide an empirical means to identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics. The ISVV-010 rollout modal characteristics provide important supplemental modal information, which along with the Mobile Launcher modal test that was performed in June 2019 immediately prior to ISVV-010 rollout, combine to reduce uncertainty in the test correlated Mobile Launcher on the Crawler Transporter finite element model. A well test correlated finite element model will play a key role in the Building Block approach the Space Launch System program has implemented as part of its certification process for the Artemis I flight and in refining the Artemis I rollout forcing functions. At the time of the ISVV-005 rollout in September 2018, the Mobile Launcher was still undergoing construction, and therefore its modal characteristics are not directly comparable to those of the Mobile Launcher during the June 2019 Mobile Launcher modal test and subsequent ISVV-010 rollout. Hence the ISVV-005 rollout modal characteristics will not be looked at in this paper. This paper will briefly describe the Mobile Launcher and Crawler Transporter physical characteristics, ISVV-010 rollout data collection, the challenges in implementing Operational Modal Analysis techniques due in part to the Crawler Transporter harmonics, and how these challenges were overcome to obtain the ISVV-010 Mobile Launcher on the Crawler Transporter rollout modal characteristics.

Apollo↗
NASA NTRS2021

Operational Modal Analysis of the Space Launch System Mobile Launcher on the Crawler Transporter ISVV-010 Rollout

NASA is developing an expendable heavy lift launch vehicle capability, the Space Launch System, to support lunar and deep space exploration. To support this capability, an updated ground infrastructure is required including modifying an existing Mobile Launcher system. The Mobile Launcher is a very large heavy beam/truss steel structure designed to support the Space Launch System during its buildup and integration in the Vehicle Assembly Building, transportation between the Vehicle Assembly Building and launch pad 39B by the Crawler Transporter, and provides the launch platform at the launch pad. As part of the Verification and Validation of the Mobile Launcher and Crawler Transporter, two rollouts of the Mobile Launcher transported by the Crawler Transporter, Integrated System Verification and Validation (ISVV) 005 and 010, have been performed to demonstrate the Crawler Transporter’s ability to transport the Mobile Launcher. ISVV-005 occurred in September 2018 and ISVV-010 occurred in late June 2019. ISVV-005 and ISVV-010 also provided the opportunity to gather data that can be used identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics and refine the estimates of the Artemis I integrated launch vehicle rollout forcing functions. While the rollout environment has historically produced relatively small launch vehicle structural loads for the Saturn/Apollo and Space Shuttle programs in comparison to launch and ascent loads, these relatively small structural loads are inputs to structural fatigue analyses. The same holds true for the Space Launch System. Because the rollout forces acting on the Mobile Launcher and the Crawler Transporter are not directly measurable, Operational Modal Analysis techniques, instead of traditional Experimental Modal Analysis techniques, provide an empirical means to identify the Mobile Launcher on the Crawler Transporter rollout modal characteristics. The ISVV-010 rollout modal characteristics provide important supplemental modal information, which along with the Mobile Launcher modal test that was performed in June 2019 immediately prior to ISVV-010 rollout, combine to reduce uncertainty in the test correlated Mobile Launcher on the Crawler Transporter finite element model. A well test correlated finite element model will play a key role in the Building Block approach the Space Launch System program has implemented as part of its certification process for the Artemis I flight and in refining the Artemis I rollout forcing functions. At the time of the ISVV-005 rollout in September 2018, the Mobile Launcher was still undergoing construction, and therefore its modal characteristics are not directly comparable to those of the Mobile Launcher during the June 2019 Mobile Launcher modal test and subsequent ISVV-010 rollout. Hence the ISVV-005 rollout modal characteristics will not be looked at in this paper. This paper will briefly describe the Mobile Launcher and Crawler Transporter physical characteristics, ISVV-010 rollout data collection, the challenges in implementing Operational Modal Analysis techniques due in part to the Crawler Transporter harmonics, and how these challenges were overcome to obtain the ISVV-010 Mobile Launcher on the Crawler Transporter rollout modal characteristics.

Apollo↗
DOE OSTI2016

ON THE COMMONALITY OF 10–30 AU SIZED AXISYMMETRIC DUST STRUCTURES IN PROTOPLANETARY DISKS

An unsolved problem in step-wise core-accretion planet formation is that rapid radial drift in gas-rich protoplanetary disks should drive millimeter-/meter-sized particles inward to the central star before large bodies can form. One promising solution is to confine solids within small-scale structures. Here, we investigate dust structures in the (sub)millimeter continuum emission of four disks (TW Hya, HL Tau, HD 163296, and DM Tau), a sample of disks with the highest spatial resolution Atacama Large Millimeter/submillimeter Array observations to date. We retrieve the surface brightness distributions using synthesized images and fitting visibilities with analytical functions. We find that the continuum emission of the four disks is ∼axisymmetric but rich in 10–30 AU-sized radial structures, possibly due to physical gaps, surface density enhancements, or localized dust opacity variations within the disks. These results suggest that small-scale axisymmetric dust structures are likely to be common, as a result of ubiquitous processes in disk evolution and planet formation. Compared with recent spatially resolved observations of CO snow lines in these same disks, all four systems show enhanced continuum emission from regions just beyond the CO condensation fronts, potentially suggesting a causal relationship between dust growth/trapping and snow lines.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Structure functions from renormalization group improved small x evolution

Abstract We perform the fit to the structure function $$F_2$$ F 2 data from HERA including terms due to the resummation at small x . The equation for the unintegrated gluon density is solved, previously established within the renormalization group improved small x framework. We find very good description of the structure function $$F_2$$ F 2 and its charm component $$F_2^c$$ F 2 c . The resulting unintegrated gluon density is found to be consistent with the calculations based on similar approaches available in the literature, with only slightly higher intercept value.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

LIGHT SCATTERING BY FRACTAL DUST AGGREGATES. I. ANGULAR DEPENDENCE OF SCATTERING

In protoplanetary disks, micron-sized dust grains coagulate to form highly porous dust aggregates. Because the optical properties of these aggregates are not completely understood, it is important to investigate how porous dust aggregates scatter light. In this study, the light scattering properties of porous dust aggregates were calculated using a rigorous method, the T -matrix method, and the results were then compared with those obtained using the Rayleigh–Gans–Debye (RGD) theory and Mie theory with the effective medium approximation (EMT). The RGD theory is applicable to moderately large aggregates made of nearly transparent monomers. This study considered two types of porous dust aggregates—ballistic cluster–cluster agglomerates (BCCAs) and ballistic particle–cluster agglomerates. First, the angular dependence of the scattered intensity was shown to reflect the hierarchical structure of dust aggregates; the large-scale structure of the aggregates is responsible for the intensity at small scattering angles, and their small-scale structure determines the intensity at large scattering angles. Second, it was determined that the EMT underestimates the backward scattering intensity by multiple orders of magnitude, especially in BCCAs, because the EMT averages the structure within the size of the aggregates. It was concluded that the RGD theory is a very useful method for calculating the optical properties of BCCAs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Reconnection in two dimensions - Localization of vorticity and current near magnetic X-points

Simulations of reconnection utilizing spectral methods show that the 'reconnection zone' exhibits internal structure in the form of a current filament and a 'quadrupole' of kinetic vorticity. A qualitative model of the dynamical role of these local structures is presented. It is suggested that the effect of small scale structures near the X-point is to increase the rate of reconnection.

Matthaeus, W. H.↗
NASA NTRS2004

Further Progress in Noise Source Identification in High Speed Jets via Causality Principle

To locate noise sources in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental noise floor. Among all correlations < puu; p/> showed the highest values. Interestingly, , in all respects, were very similar to . The and correlations with 90deg microphone fell below the noise floor. By moving the laser probe at various locations in the jet it was found that the strongest noise source lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the noise floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the noise floor.

Panda, J.↗
NASA NTRS2011

View-Angle Dependent AIRS Cloud Radiances: Implication for Tropical Gravity Waves and Anvil Structures

Tropical anvil clouds play important roles in redistributing energy, water in the troposphere. Interacting with dynamics at a wide range of spatial and temporal scales, they can become organized internally and form structured cells, transporting momentum vertically and laterally. To quantify small-scale structures inside cirrus and anvils, we study view-dependence of the cloud-induced radiance from Atmospheric Infrared Sounder (AIRS) using channels near CO2 absorption line. The analysis of tropical eight-year (30degS-30degN, 2003-2010) data suggests that AIRS east-views observe 10% more anvil clouds than westviews during day (13:30 LST), whereas east-views and westviews observe equally amount of clouds at midnight (1 :30 LST). For entire tropical averages, AIRS oblique views observe more anvils than the nadir views, while the opposite is true for deep convective clouds. The dominance of cloudiness in the east-view cannot be explained by AIRS sampling and cloud microphysical differences. Tilted and banded anvil structures from convective scale to mesoscale are likely the cause of the observed view-dependent cloudiness, and gravity wave-cloud interaction is a plausible explanation for the observed structures. Effects of the tilted and banded cloud features need to be further evaluated and taken into account potentially in large-scale model parameterizations because of the vertical momentum transport through cloud wave breaking.

Wu, Dong L.↗
NASA NTRS2024

SiC Charged Particle Telescope GRC Independent Research and Development (IRAD) Program End of Project Final Report

In an advancement over the state-of-the art, NASA Glenn Research Center (GRC) has developed a large area silicon carbide (SiC)-based charged particle telescope through an Independent Research and Development (IRAD) project. The telescope has been demonstrated to have improved noise characteristics and resolution than previous SiC detectors. This improvement will meet the challenges of compact multidirectional robust radiation detector systems to study a wide range of elementary particle mass and energies. In order to provide a complete understanding of how energetic processes internal and external to the solar system shape magnetospheres, atmospheres, and surfaces, in situ particle observations should include measurements of Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR), along with solar wind and plasma. The potential temperature stability, tolerance to high radiation environments, and low noise characteristics expected in SiC-based detectors can have advantages over the state-of-the-art silicon detectors. These advantages will allow the detectors to be deployed in small compact systems on a variety of platforms, enabling compact structures for small satellite platforms with improved data quality.

Field and particle detectors↗
DOE OSTI2016

NARROW-LINE-WIDTH UV BURSTS IN THE TRANSITION REGION ABOVE SUNSPOTS OBSERVED BY IRIS

Various small-scale structures abound in the solar atmosphere above active regions, playing an important role in the dynamics and evolution therein. We report on a new class of small-scale transition region structures in active regions, characterized by strong emissions but extremely narrow Si iv line profiles as found in observations taken with the Interface Region Imaging Spectrograph (IRIS). Tentatively named as narrow-line-width UV bursts (NUBs), these structures are located above sunspots and comprise one or multiple compact bright cores at sub-arcsecond scales. We found six NUBs in two data sets (a raster and a sit-and-stare data set). Among these, four events are short-lived with a duration of ∼10 minutes, while two last for more than 36 minutes. All NUBs have Doppler shifts of 15–18 km s{sup −1}, while the NUB found in sit-and-stare data possesses an additional component at ∼50 km s{sup −1} found only in the C ii and Mg ii lines. Given that these events are found to play a role in the local dynamics, it is important to further investigate the physical mechanisms that generate these phenomena and their role in the mass transport in sunspots.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Inhomogeneity in electronic phase and flat band in magnetic kagome metal Co 3 Sn 2 S 2

Co 3 Sn 2 S 2 has been reported to be a Weyl semimetal with c-axis ferromagnetism below a Curie temperature of 177 K. Despite the large interest in Co 3 Sn 2 S 2 , the magnetic structure is still unclear. Recent studies have challenged the magnetic phase diagram of Co 3 Sn 2 S 2 by reporting unusual magnetic phases including the presence of exchange bias. Here we show, using X-ray Magnetic Circular Dichroism, a shift in the magnetization hysteresis loop, reminiscent of exchange bias and establish that the magnetic moment in Co arises from the spin, with negligible orbital moment. At 6 K, using spatially-resolved angle-resolved photoemission spectroscopy, we detect a butterfly-shaped electronic band structure at small regions of the sample distinct from the known ferromagnetic band structure. Our density functional theory calculations suggest that the butterfly bands correspond to an antiferromagnetic phase. Separately, we detect a sharp flat band at the Fermi level at some regions in the sample, which we attribute to a surface state. These different electronic states found in a stoichiometric intermetallic invite further efforts to explore the origin and nature of the electronic inhomogeneity associated to magnetism on the mesoscale.

Electronic properties and materials↗
DOE OSTI2011

Prospect for characterizing interacting soft colloidal structures using spin-echo small angle neutron scattering

Spin-echo small angle neutron scattering (SESANS) presents a new experimental tool for structural investigation. Regarding the material study using neutron scattering it is of particular novel: Due to the action of spin echo encoding, SESANS registers the spatial correlations function in real space, which is distinct from the measurables of conventional elastic neutron scattering techniques. To make viable the use of SESANS in structural characterization, particularly for the interacting colloidal suspensions, we have conducted a theoretical study focusing on understanding the essential features of the SESANS correlation functions obtained from different model systems consisting of particles with uniform density profile (J. Chem. Phys. 132, 174509 (2010)). Within the same framework, we continue to explore the prospect of using SESANS to investigate the structural characteristics of colloid systems consisting of particle with non-uniform intraparticle mass distribution. As an example, a Gaussian model of interacting soft colloids is put forward in our mean-field calculations to investigate the manifestation of structural softness in SESANS measurement. Furthermore, the exploration shows a characteristically different SESANS correlation function for interacting soft colloids, in comparison to that of the referential uniform hard sphere system, due to the Abel transform imbedded in the mathematical formalism bridging the SESANS spectra and the spatial autocorrelation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Determination of bimetallic architectures in nanometer-scale catalysts by combining molecular dynamics simulations with x-ray absorption spectroscopy

In this study, we present an approach for the determination of an atomic structure of small bimetallic nanoparticles by combining extended X-ray absorption fine structure spectroscopy and classical molecular dynamics simulations based on the Sutton-Chen potential. The proposed approach is illustrated in the example of PdAu nanoparticles with ca 100 atoms and narrow size and compositional distributions. Using a direct modeling approach and no adjustable parameters, we were able to reproduce the size and shape of nanoparticles as well as the intra-particle distributions of atoms and metal mixing ratios and to explore the influence of these parameters on the local structure and dynamics in nanoparticles.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

STRUCTURAL VARIATION OF MOLECULAR GAS IN THE SAGITTARIUS ARM AND INTERARM REGIONS

We have carried out survey observations toward the Galactic plane at l Almost-Equal-To 38 Degree-Sign in the {sup 12}CO and {sup 13}CO J = 1-0 lines using the Nobeyama Radio Observatory 45 m telescope. A wide area (0.{sup 0}8 Multiplication-Sign 0.{sup 0}8) was mapped with high spatial resolution (17''). The line of sight samples the gas in both the Sagittarius arm and the interarm regions. The present observations reveal how the structure and physical conditions vary across a spiral arm. We classify the molecular gas in the line of sight into two distinct components based on its appearance: the bright and compact B component and the fainter and diffuse (i.e., more extended) D component. The B component is predominantly seen at the spiral arm velocities, while the D component dominates at the interarm velocities and is also found at the spiral arm velocities. We introduce the brightness distribution function and the brightness distribution index (BDI, which indicates the dominance of the B component) in order to quantify the map's appearance. The radial velocities of BDI peaks coincide with those of high {sup 12}CO J = 3-2/{sup 12}CO J = 1-0 intensity ratio (i.e., warm gas) and H II regions, and tend to be offset from the line brightness peaks at lower velocities (i.e., presumably downstream side of the arm). Our observations reveal that the gas structure at small scales changes across a spiral arm: bright and spatially confined structures develop in a spiral arm, leading to star formation at the downstream side, while extended emission dominates in the interarm region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca 1 - x Sr x Co 2 - y As 2

We report the inference of Ying et al. [Europhys. Lett. 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type antiferromagnetic (AFM) structure at small x to ab-plane alignment in an unknown AFM structure at larger x in Ca 1-x Sr x Co 2-y As 2 with the body-centered tetragonal ThCr 2 Si 2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 ≲ x ≲ 0.3 between these two phases. Also, in this region the magnetic susceptibility vs temperature χ ab (T) measured with magnetic fields H applied in the ab plane exhibit typical AFM behaviors with cusps at the Néel temperatures of ~ 65 K, whereas χ c (T) and the low-temperature isothermal magnetization M c (H) with H aligned along the c axis exhibit extremely soft ferromagneticlike behaviors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗