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  • 1
    Publication Date: 1958-01-01
    Print ISSN: 0028-1042
    Electronic ISSN: 1432-1904
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Published by Springer
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  • 2
    Publication Date: 2019-07-12
    Description: The purpose of the work was to determine minimum atmospheric electric fields required for lightning initiation from an airborne vehicle at various altitudes up to 10 km. The problem was reduced to the determination of a condition for initiation of a viable positive leader from a conductive object in an ambient electric field. It was shown that, depending on air density and shape and dimensions of the object, critical atmospheric fields are governed by the condition for leader viability or that for corona onset. To establish quantitative criteria for reduced air densities, available observations of spark discharges in long laboratory gaps were analyzed, the effect of air density on leader velocity was discussed and evolution in time of the properties of plasma in the leader channel was numerically simulated. The results obtained were used to evaluate the effect of pressure on the quantitative relationships between the potential difference near the leader tip, leader current and its velocity; based on these relationships, criteria for steady development of a leader were determined for various air pressures. Atmospheric electric fields required for lightning initiation from rods and ellipsoidal objects of various dimensions were calculated at different air densities. It was shown that there is no simple way to extend critical ambient fields obtained for some given objects and pressures to other objects and pressures.
    Keywords: Meteorology and Climatology
    Type: KSC-2006-173
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-12
    Description: The F-15 Advanced Controls Technology for Integrated Vehicles (ACTIVE) airplane (see figure) was the test bed for a flight test of an intelligent flight control system (IFCS). This IFCS utilizes a neural network to determine critical stability and control derivatives for a control law, the real-time gains of which are computed by an algorithm that solves the Riccati equation. These derivatives are also used to identify the parameters of a dynamic model of the airplane. The model is used in a model-following portion of the control law, in order to provide specific vehicle handling characteristics. The flight test of the IFCS marks the initiation of the Intelligent Flight Control System Advanced Concept Program (IFCS ACP), which is a collaboration between NASA and Boeing Phantom Works. The goals of the IFCS ACP are to (1) develop the concept of a flight-control system that uses neural-network technology to identify aircraft characteristics to provide optimal aircraft performance, (2) develop a self-training neural network to update estimates of aircraft properties in flight, and (3) demonstrate the aforementioned concepts on the F-15 ACTIVE airplane in flight. The activities of the initial IFCS ACP were divided into three Phases, each devoted to the attainment of a different objective. The objective of Phase I was to develop a pre-trained neural network to store and recall the wind-tunnel-based stability and control derivatives of the vehicle. The objective of Phase II was to develop a neural network that can learn how to adjust the stability and control derivatives to account for failures or modeling deficiencies. The objective of Phase III was to develop a flight control system that uses the neural network outputs as a basis for controlling the aircraft. The flight test of the IFCS was performed in stages. In the first stage, the Phase I version of the pre-trained neural network was flown in a passive mode. The neural network software was running using flight data inputs with the outputs provided to instrumentation only. The IFCS was not used to control the airplane. In another stage of the flight test, the Phase I pre-trained neural network was integrated into a Phase III version of the flight control system. The Phase I pretrained neural network provided realtime stability and control derivatives to a Phase III controller that was based on a stochastic optimal feedforward and feedback technique (SOFFT). This combined Phase I/III system was operated together with the research flight-control system (RFCS) of the F-15 ACTIVE during the flight test. The RFCS enables the pilot to switch quickly from the experimental- research flight mode back to the safe conventional mode. These initial IFCS ACP flight tests were completed in April 1999. The Phase I/III flight test milestone was to demonstrate, across a range of subsonic and supersonic flight conditions, that the pre-trained neural network could be used to supply real-time aerodynamic stability and control derivatives to the closed-loop optimal SOFFT flight controller. Additional objectives attained in the flight test included (1) flight qualification of a neural-network-based control system; (2) the use of a combined neural-network/closed-loop optimal flight-control system to obtain level-one handling qualities; and (3) demonstration, through variation of control gains, that different handling qualities can be achieved by setting new target parameters. In addition, data for the Phase-II (on-line-learning) neural network were collected, during the use of stacked-frequency- sweep excitation, for post-flight analysis. Initial analysis of these data showed the potential for future flight tests that will incorporate the real-time identification and on-line learning aspects of the IFCS.
    Keywords: Man/System Technology and Life Support
    Type: DRC-01-35 , NASA Tech Briefs, October 2003; 5-6
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-12
    Description: We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich (SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope (ACT) collaboration discovered ACT-CL J0102-4915 as the most significant Sunyaev-Zeldovich (SZ) decrement in a sky survey area of 755 square degrees. Our VLT/FORS2 spectra of 89 member galaxies yield a cluster redshift, z = 0.870, and velocity dispersion, sigma(gal) +/- 1321 106 km s-1. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of T(X) = 14:5 +/- 0:1 keV and 0.5 2.0 keV band luminosity of L(X) = (2:19 0:11) 1045 h(exp -2)70erg s-1. We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Y(X) , and integrated SZ distortion, we estimate a cluster mass of M(200) = (2:16 +/- 0:32) 10(exp 15) h(exp-1) 70M compared to the Sun. We constrain the stellar content of the cluster to be less than 1% of the total mass, using Spitzer IRAC and optical imaging. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102-4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6:6 +/- 0:7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22 +/- 6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other from which we estimate a merger speed of around 1300 km s(exp -1) for an assumed merger timescale of 1 Gyr. ACTCL J0102-4915 is possibly a high-redshift analog of the famous Bullet Cluster. Such a massive cluster at this redshift is rare, although consistent with the standard CDM cosmology in the lower part of its allowed mass range. Massive, high-redshift mergers like ACT-CL J0102-4915 are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.
    Keywords: Astronomy
    Type: GSFC.JA.5672.2011
    Format: application/pdf
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  • 5
    Publication Date: 2015-11-18
    Description: Binding of extracellular ligands to G protein-coupled receptors (GPCRs) initiates transmembrane signaling by inducing conformational changes on the cytoplasmic receptor surface. Knowledge of this process provides a platform for the development of GPCR-targeting drugs. Here, using a site-specific Cy3 fluorescence probe in the human β2-adrenergic receptor (β2AR), we observed that...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 6
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉South Africa is a mineral rich country with a diverse geology and a long history of mining. Historical mining records have not been accurately recorded, or lost with time. This has resulted in significant geohazard risk during infrastructure development, especially in and around historical mining towns, e.g. Johannesburg and Ermelo. These geohazard risks require careful appraisal and quantification prior to any infrastructure design or construction.This case study aims to set out the development aspects of the Multi-Faceted Geophysical Modelling Systems approach used by the South African National Roads Agency SOC Ltd (SANRAL), in an investigation of undermined ground for the historical mining town of Ermelo for the N11/N2 ring road.The systems approach used a combination of airborne geophysics (Versatile Time Domain Electromagnetic System (VTEM〈sup〉TM〈/sup〉 and magnetics), generally used in mining exploration, land-based and borehole geophysics, borehole water testing, and ground-truthing.The systems approach developed used a continuous, iterative approach, building on the data at hand, thus reducing unnecessary investigations while eliminating the possibility of anomalies being missed, as in the case of the conventional discrete drilling.The investigation ensured that 100% of the route was comprehensively investigated with a high confidence in the geological and geophysical data, and concomitant mitigation of infrastructure risk.The Multi-Faceted Geophysical Modelling Systems approach was successfully used to identify a previously unknown 1mx1m mining stope cavity at 90m depth and a 3mx5m access tunnel at 24m depth in a timely and cost-effective manner. Seven RC percussion boreholes carried out confirmed the structural integrity of these underground cavities, as well as the structural geology along the centreline.Based on the great success achieved in identifying shallow anomalies, this Multi-Faceted Geophysical Modelling Systems approach is now being considered for field trails on the Dolomitic formations and the Wild Coast greenfields road project where there are large historical slumps and many fault lines.South Africa's rich history of mining activities includes the extraction of coal from the Ecca Group Sediments of the Karoo Supergroup (250 Ma), gold and uranium from the Witwatersrand Supergroup (2900Ma), as well as platinum, uranium, tin and lead from the layered Bushveld Igneous Complex (BIC)(2150 Ma).The extraction of gold, copper, tin, lead and rare earth minerals also took place in the Archaean Rocks of Swazium Age (3000-3500 Ma).In this case study, SANRAL planned a ring road around the coal-mining town of Ermelo (South Africa), to ensure mobility between major routes, whilst maintaining town access.〈/span〉
    Print ISSN: 1470-9236
    Electronic ISSN: 2041-4803
    Topics: Geosciences
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  • 7
  • 8
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉A few, thin, Mississippian siliciclastic limestone beds, interbedded with ammonoid (uppermost 〈span〉Eumorphoceras〈/span〉 Zone)-bearing shales within the South Syncline Ridge section on the Nuclear Test Site in southern Nevada, contain an abundant, low-diversity assemblage of late Serpukhovian/late Chesterian calcareous foraminifers dominated by the archaediscaceans 〈span〉Neoarchaediscus altiluminis〈/span〉, 〈span〉Brenckleina rugosa〈/span〉, 〈span〉Eosigmoilina robertsoni〈/span〉, and 〈span〉Betpakodiscus〈/span〉 of the group 〈span〉B〈/span〉. 〈span〉attenuatus〈/span〉. These limestone beds were deposited in a shallow-water, clastic facies of the Scotty Wash Formation and, based on common conodont occurrences, correlate southeast to the Bird Spring Formation below the Mississippian-Pennsylvanian GSSP at Arrow Canyon, Nevada. The South Syncline Ridge foraminifers are comparable to those found in coeval beds at Arrow Canyon and represent the only other known foraminiferal assemblage to exist in association with uppermost 〈span〉Eumorphoceras〈/span〉 Zone ammonoids in North America outside of Arkansas in the southern Midcontinent. Reconciliation of regional conodont and ammonoid zonations shows that the range of eosigmoiline foraminifers (〈span〉E〈/span〉. 〈span〉robertsoni〈/span〉 and 〈span〉B〈/span〉. 〈span〉rugosa〈/span〉), now generally considered an upper Serpukhovian index, extends from a position either just below or at the lower-upper boundary of the Serpukhovian Stage into the lower part of the Bashkirian Stage in North America; their upper range falls within the lower part of the 〈span〉Homoceras〈/span〉 ammonoid zone beginning in the upper part of the Serpukhovian Stage. Discussion of the foraminiferal taxa includes support for retaining the genus 〈span〉Betpakodiscus〈/span〉 rather than synonymizing it under 〈span〉Tubispirodiscus〈/span〉, as proposed by some specialists during the past few years.〈/span〉
    Print ISSN: 0096-1191
    Electronic ISSN: 1943-264X
    Topics: Geosciences
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  • 9
    Publication Date: 2017-09-28
    Description: The radiation risk radiometer-dosimeter (R3D)-R2 solid-state detector performed radiation measurements at the European Space Agency EXPOSE-R2 platform outside of the Russian “Zvezda” module at the International Space Station (ISS) from 24 October 2014-11 January 2016. The ISS orbital parameters were: average altitude of 415 km and 51.6° inclination. We developed special software and used experimentally-obtained formulas to determine the radiation flux-to-dose ratio from the R3DR2 Liulin-type deposited-energy spectrometer. We provide for the first time simultaneous, long-term estimates of radiation dose external to the ISS for four source categories: (i) galactic cosmic ray particles and their secondary products; (ii) protons in the South Atlantic Anomaly region of the inner radiation belt (IRB); (iii) relativistic electrons and/or bremsstrahlung in the outer radiation belt (ORB); and (iv) solar energetic particle (SEP) events. The latter category is new in this study. Additionally, in this study, secondary particles (SP) resulting from energetic particle interaction with the detector and nearby materials are identified. These are observed continuously at high latitudes. The detected SPs are identified using the same sorting requirements as SEP protons. The IRB protons provide the highest consistent hourly dose, while the ORB electrons and SEPs provide the most extreme hourly doses. SEPs were observed 11 times during the study interval. The R3DR2 data support calculation of average equivalent doses. The 30-day and 1-year average equivalent doses are much smaller than the skin and eyes doses recommendations by the National Council on Radiation Protection (Report 132), which provides radiation protection guidance for Low Earth Orbit.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2001-01-01
    Print ISSN: 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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