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DOE OSTI2021

A Synoptic VLBI Technique for Localizing Nonrepeating Fast Radio Bursts with CHIME/FRB

We demonstrate the blind interferometric detection and localization of two fast radio bursts (FRBs) with subarcminute precision on the 400 m baseline between the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the CHIME Pathfinder. In the same spirit as Very Long Baseline Interferometry (VLBI), the telescopes were synchronized to separate clocks, and the channelized voltage (herein referred to as baseband) data were saved to a disk with correlation performed offline. The simultaneous wide field of view and high sensitivity required for blind FRB searches implies a high data rate—6.5 terabits per second (Tb/s) for CHIME and 0.8 Tb s{sup −1} for the Pathfinder. Since such high data rates cannot be continuously saved, we buffer data from both telescopes locally in memory for ≈40 s, and write to the disk upon receipt of a low-latency trigger from the CHIME Fast Radio Burst Instrument (CHIME/FRB). The ≈200 deg{sup 2} field of view of the two telescopes allows us to use in-field calibrators to synchronize the two telescopes without needing either separate calibrator observations or an atomic timing standard. In addition to our FRB observations, we analyze bright single pulses from the pulsars B0329+54 and B0355+54 to characterize systematic localization errors. Our results demonstrate the successful implementation of key software, triggering, and calibration challenges for CHIME/FRB Outriggers: cylindrical VLBI outrigger telescopes which, along with the CHIME telescope, will localize thousands of single FRB events with sufficient precision to unambiguously associate a host galaxy with each burst.

47 OTHER INSTRUMENTATION↗

DOE OSTI2022

Localized Corrosion of Chromium-Containing Conventional and Multiprincipal Element Alloys in Methanol and Aqueous Chloride Environments

The localized corrosion behavior of Type 304L stainless steel (UNS S30400), Alloy 625 (UNS N06625), and three experimental NiCoCrMo multiprincipal element alloys (MPEA), exposed to methanol/lithium chloride solutions with different water contents, is examined in this paper. Cyclic potentiodynamic polarization tests indicated that water increased the pitting and repassivation potentials and the critical temperature at which localized corrosion occurred in chloride solutions. The effect of water on repassivation potential in methanol-chloride solution depended on the chloride concentration and alloy content. At lower chloride concentration and higher alloy content, water had a greater inhibiting effect on repassivation potential, suggesting a competitive reaction between chloride and water on the metal surface in the pit. The localized corrosion resistance of the MPEAs followed the same trend as that of commercial stainless steels and Ni-base alloys in terms of the effect of alloying elements. The implications of these results on the mechanisms of localized corrosion are discussed.

Materials Science↗

DOE OSTI2022

Automated identification of local contamination in remote atmospheric composition time series

Abstract. Atmospheric observations in remote locations offer a possibility of exploring trace gas and particle concentrations in pristine environments. However, data from remote areas are often contaminated by pollution from local sources. Detecting this contamination is thus a central and frequently encountered issue. Consequently, many different methods exist today to identify local contamination in atmospheric composition measurement time series, but no single method has been widely accepted. In this study, we present a new method to identify primary pollution in remote atmospheric datasets, e.g., from ship campaigns or stations with a low background signal compared to the contaminated signal. The pollution detection algorithm (PDA) identifies and flags periods of polluted data in five steps. The first and most important step identifies polluted periods based on the derivative (time derivative) of a concentration over time. If this derivative exceeds a given threshold, data are flagged as polluted. Further pollution identification steps are a simple concentration threshold filter, a neighboring points filter (optional), a median, and a sparse data filter (optional). The PDA only relies on the target dataset itself and is independent of ancillary datasets such as meteorological variables. All parameters of each step are adjustable so that the PDA can be “tuned” to be more or less stringent (e.g., flag more or fewer data points as contaminated). The PDA was developed and tested with a particle number concentration dataset collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the central Arctic. Using strict settings, we identified 62 % of the data as influenced by local contamination. Using a second independent particle number concentration dataset also collected during MOSAiC, we evaluated the performance of the PDA against the same dataset cleaned by visual inspection. The two methods agreed in 94 % of the cases. Additionally, the PDA was successfully applied to a trace gas dataset (CO2), also collected during MOSAiC, and to another particle number concentration dataset, collected at the high-altitude background station Jungfraujoch, Switzerland. Thus, the PDA proves to be a useful and flexible tool to identify periods affected by local contamination in atmospheric composition datasets without the need for ancillary measurements. It is best applied to data representing primary pollution. The user-friendly and open-access code enables reproducible application to a wide suite of different datasets. It is available at https://doi.org/10.5281/zenodo.5761101 (Beck et al., 2021).

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Local-thermal-gradient and large-scale-circulation impacts on turbine-height wind speed forecasting over the Columbia River Basin

Abstract. We investigate the sensitivity of turbine-height wind speed forecast to initial condition (IC) uncertainties over the Columbia River Gorge (CRG) and Columbia River Basin (CRB) for two typical weather phenomena, i.e., local-thermal-gradient-induced marine air intrusion and a cold frontal passage. Four types of turbine-height wind forecast anomalies and their associated IC uncertainties related to local thermal gradients and large-scale circulations are identified using the self-organizing map (SOM) technique. The four SOM types are categorized into two patterns, each accounting for half of the ensemble members. The first pattern corresponds to IC uncertainties that alter the wind forecast through a modulating weather system, which produces the strongest wind anomalies in the CRG and CRB. In the second pattern, the moderate uncertainties in local thermal gradient and large-scale circulation jointly contribute to wind forecast anomaly. We analyze the cross section of wind and temperature anomalies through the gorge to explore the evolution of vertical features of each SOM type. The turbine-height wind anomalies induced by large-scale IC uncertainties are more concentrated near the front. In contrast, turbine-height wind anomalies induced by the local IC thermal uncertainties are found above the surface thermal anomalies. Moreover, the wind forecast accuracy in the CRG and CRB is limited by IC uncertainties in a few specific regions, e.g., the 2 m temperature within the basin and large-scale circulation over the northeast Pacific around 140∘ W.

17 WIND ENERGY↗

DOE OSTI2026

Local Tractor Activity at S2 (Mt. Airy) Site

This dataset documents local tractor activity at the S2 (Mt. Airy) site during CoURAGE. It identifies periods where local tractor activity impacted aerosol measurements using both PM10/PM2.5 ratios and ARM camera data for visual confirmation of tractor. Data flags are as follows: 1 = confirmed no local tractor influence on aerosol measurements 2 = one data indicator is present (extreme PM10/PM2.5 ratio OR visual confirmation of tractor sighting), but not both 3 = both data indicators confirm local tractor influence on aerosol 0 = missing data, no determination possible

Tractor Activity using ARM camera photos and PM10/↗

NASA NTRS1972

Latitude and local time dependence of precipitated low energy electrons at high latitudes

Data from particle detectors on board the satellite OGO-4 were used to study the precipitation of electrons in the energy range 0.7 to 24 keV. The latitude dependence of these particles in the local time region from midnight to dawn was investigated in detail. The analysis shows that the precipitation of particles of energies 2.3 to 24 keV is centered at an invariant latitude of about 68 deg at midnight with a clear shift in latitude with increasing local time and this shift is more pronounced for lower energies. The highest fluxes of particles in this energy interval are measured at midnight and they decrease rapidly with local time. The data in the energy range 2.3 to 24 keV support a theory where particles are injected in the midnight region from the tail gaining energy due to a betatron process and then drift eastwards in a combined electric and magnetic field. The main part of the electrons at 0.7 keV show a different behavior. They seem to undergo an acceleration process which is rather local, sometimes giving field aligned fluxes which may be super-imposed on the background precipitation.

Gustafsson, G.↗

NASA NTRS1972

Local-time survey of plasma at low altitudes over the auroral zones.

Local-time survey of the low-energy proton and electron intensities precipitated into the earth's atmosphere over the auroral zones during periods of magnetic quiescence. This survey was constructed by selecting a typical individual satellite crossing of this region in each of eight local-time sectors from a large library of similar observations with the polar-orbiting satellite Injun 5. The trapping boundary for more-energetic electron intensities, E greater than 45 keV, was found to be a 'natural coordinate' for delineating the boundary between the two major types of lower-energy, 50 less than or equal to E less than or equal to 15,000 eV, electron precipitation commonly observed over the auroral zones at low altitudes. Poleward of this trapping boundary inverted 'V' electron precipitation bands are observed in all local-time sectors. These inverted 'V' electron bands in the evening and midnight sectors are typically more energetic and have greater latitudinal widths than their counterparts in the noon and morning sectors. In general, the main contributors to the electron energy influx into the earth's atmosphere over the auroral zones are the electron inverted 'V' precipitation poleward of the trapping boundary in late evening, the plasma-sheet electron intensities equatorward of this boundary in early morning, and both of these precipitation events near local midnight.

Frank, L. A.↗

NASA NTRS1973

An association of magnetospheric whistler dispersion characteristics with changes in local plasma density.

We use OGO 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large-scale field-aligned variations. The results are then compared with ray refraction estimates appropriate for low-frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform medium.

Scarf, F. L.↗

NASA NTRS1979

A theory of local and global processes which affect solar wind electrons. 2: Experimental support

The microscopic characteristics of the Coulomb cross section show that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E kT sub c; the transthermals with kT sub c E 7 kT sub c and the extrathermals E 7 kT sub c. Data from three experimental groups on three different spacecraft in the interplanetary medium over a radial range are presented to support the five interrelations projected between solar wind electron properties and changes in the interplanetary medium: (1) subthermals respond primarily to local changes (compression and rarefactions) in stream dynamics; (2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; (3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; (4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and (5) the extrathermal differential 'temperature' should be nearly independent of radius within 1 AU.

Scudder, J. D.↗

NASA NTRS1979

A theory of local and global processes which affect solar wind electrons. II - Experimental support

Strong observational support from data obtained on three different satellites and reported by three independent experimental groups is presented for all of the theoretically predicted correlations of a previous paper concerning local and global processes that affect solar-wind electrons. Specifically, it is shown that: (1) subthermal electrons behave most nearly as a classical gas; (2) the solar-wind extrathermal fraction of the electron density is anticorrelated within steady-state stream patterns with the local bulk speed; (3) the extrathermal electrons form a spectrally distinguishable subpopulation whose differential 'temperature' is anticorrelated with the local bulk speed; (4) the heat flux carried by electrons is anticorrelated with the bulk speed; and (5) the extrathermal 'temperature' is nearly independent of radius in the inner heliosphere. It is concluded that the previously discussed global and local Coulomb collisional effects are essential aspects of the solar-wind plasma as it is observed.

Scudder, J. D.↗

NASA NTRS1981

An extension of the local momentum theory to a distorted wake model of a hovering rotor

The local momentum theory is based on the instantaneous balance between the fluid momentum and the blade elemental lift at a local station in the rotor rotational plane. Therefore, the theory has the capability of evaluating time wise variations of air loading and induced velocity distributions along a helicopter blade span. Unlike a complex vortex theory, this theory was developed to analyze the instantaneous induced velocity distribution effectively. The boundaries of this theory and a computer program using this theory are discussed. A concept introduced into the theory is the effect of the rotor wake contraction in hovering flight. A comparison of this extended local momentum theory with a prescribed wake vortex theory is also presented. The results indicate that the extended local momentum theory has the capability of achieving a level of accuracy similar to that of the prescribed wake vortex theory over wide range variations of rotor geometrical parameters. It is also shown that the analytical results obtained using either theory are in reasonable agreement with experimental data.

Kawachi, K.↗

NASA NTRS1954

Variation of Local Liquid-Water Concentration About and Ellipsoid of Fineness Ratio 5 Moving in a Droplet Field

Trajectories of water droplets about an ellipsoid of revolution with a fineness ratio of 5 (which often approximates the shape of an aircraft fuselage or missile) were computed with the aid of a differential analyzer. Analyses of these trajectories indicate that the local concentration of liquid water at various points about an ellipsoid in flight through a droplet field varies considerably and under some conditions may be several times the free-stream concentration. Curves of the local concentration factor as a function of spatial position were obtained and are presented in terms of dimensionless parameters Re(sub 0) (free-stream Reynolds number) and K (inertia), which contain flight and atmospheric conditions. These curves show that the local concentration factor at any point is very sensitive to change in the dimensionless parameters Re(sub 0) and K. These data indicate that the expected local concentration factors should be considered when choosing the location of, or when determining antiicing heat requirements for, water- or ice-sensitive devices that protrude into the stream from an aircraft fuselage or missile. Similarly, the concentration factor should be considered when choosing the location on an aircraft of instruments that measure liquid-water content or droplet-size distribution in the atmosphere.

Dorsch, Robert G.↗

NASA NTRS1982

Fringe localization requirements for three-dimensional flow visualization of shock waves in diffuse-illumination double-pulse holographic interferometry

A theory of fringe localization in rapid-double-exposure, diffuse-illumination holographic interferometry was developed. The theory was then applied to compare holographic measurements with laser anemometer measurements of shock locations in a transonic axial-flow compressor rotor. The computed fringe localization error was found to agree well with the measured localization error. It is shown how the view orientation and the curvature and positional variation of the strength of a shock wave are used to determine the localization error and to minimize it. In particular, it is suggested that the view direction not deviate from tangency at the shock surface by more than 30 degrees.

Decker, A. J.↗

NASA NTRS1982

The local dispersion relation for magneto-atmospheric waves

The local dispersion relation for magneto-atmospheric waves is discussed in terms of the linearized theory of waves in a plane-stratified, inviscid, perfectly conducting atmosphere under uniform gravity. The normally used local dispersion relation is demonstrated to not be unique, depending instead on the order of derivation from the fundamental first-order perturbation equations of continuity, momentum, energy, and induction. Furthermore, it is shown that the local dispersion relation predicts that the cutoff frequency decreases with increasing magnetic field strength, while the WKB approximation method projects an increase in the cutoff frequency with increasing magnetic field strength. A new form of the local dispersion relation is developed, and consideration is given to the special case of a global dispersion relation in conditions of an isothermal atmosphere with a horizontal magnetic field.

Thomas, J. H.↗

NASA NTRS1984

Analysis of local delaminations and their influence on composite laminate behavior

An equation was derived for the strain energy release rate, G, associated with local delamination growth from a matrix ply crack. The critical GC for edge delamination onset in 25/902s graphite epoxy laminates was measured and used in this equation to predict local delamination onset strains in 25/90ns, n = 4, 6, 8 laminates. A simple technique for predicting strain concentrations in the primary load bearing plies near local delaminations was developed. These strain concentrations were responsible for reduced laminate nominal failure strains in laminates containing local delaminations. The influence of edge delamination and matrix crack tip delamination on laminate stiffness and strength was compared.

Obrien, T. K.↗

NASA NTRS1984

Local Interstellar Extinction with an Emphasis on Uvby Beta Results

Some theories concerning the distribution of interstellar dust are surveyed. Average reddening and the distribution of local dust studied by means of ultraviolet photometry are discussed. The existence of local dust in the pole directions, local voids, variations of color excess with distance, and properties of local diffuse dust clouds are among the topics considered.

Knude, J.↗

NASA NTRS1984

Endpoints of stellar evolution - X-ray surveys of the Local Group

The galaxies of the Local Group offer a variety of settings in which to study galactic source populations unhampered by local interstellar-absorption and distance ambiguities. A review of the subject of Local Group X-ray astronomy from the first discovery of a source in the Large Magellanic Cloud 15 years ago to the most recent analysis of the Einstein Observatory data (in which over 200 X-ray sources were detected in Local Group members) is presented. Following a detailed presentation of the latest results, two examples of the constraints these data impose on stellar and galactic evolution are discussed: study of the distribution of properties for the 30 detected supernova remnants in the Large Magellanic Cloud, and a comparison of the populations of classical X-ray binaries in M31, M33, the Magellanic Clouds, and the Galaxy. A prospectus for future research, including a discussion of the contributions which could be made by the next generation of X-ray observatories, is provided.

Helfand, D. J.↗

NASA NTRS1985

Analysis of local delaminations and their influence on composite laminate behavior

Obrien, T. K.↗