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NASA NTRS2017

Solar Flare Termination Shock and the Synthetic Fe XXI 1354.08 Å Line

Solar flares are one of the most energetic phenomena occurred in the solar system. In the standard solar flare model, a fast mode shock, which is often referred to as the flare termination shock (TS), can exist above the loop-top source of hard X-ray emissions. The existence of the termination shock has been recently related to spectral hardening of flare hard X-ray spectrum at energies > 300 keV. Observations of the Fe XXI 1354.08 Å line during solar flares by the IRIS spacecraft have found significant redshift with >100 km/s, which is consistent with a reconnection downflow. The ability to identify such a redshift by IRIS is made possible by IRIS's high time resolution, high spatial resolution, high sensitivity and cadence spectral observations. The ability to identify such a redshift by IRIS suggests that one may be able to use IRIS observations to identify flare termination shocks. Using a MHD simulation to model magnetic reconnection of a solar flare and assuming the existence of a TS in the downflow of the reconnection plasma, we model the synthetic emission of the Fe XXI 1354.08 Å line in this work. We show that the existence of the TS in the solar flare may manifest itself from the Fe XXI 1354.08 Å line.Plain Language SummaryA solar flare is a brief eruption of intense high-energy radiation from the sun's surface, associated with sunspots and causing electromagnetic disturbances on the earth, as with radio frequency communications and power line transmissions. The standard solar flare model proposes that magnetic reconnection drives solar flares and fast mode shock, which is often referred to as the flare termination shock (TS), can exist at the reconnection outflows. The existence of the termination shock has been recently related to spectral hardening of flare hard X-ray spectrum.

Guo, Lijia↗

NASA NTRS1972

What is KASC ?

The organization and functions of the Knowledge Availability System Center are discussed. The KASC is defined as a nonprofit, computerized information center at the University of Pittsburgh. The KASC provides literature searching and referral services designed to identify useful scientific and technical data to its clients. Two types of service are provided: (1) the retrospective search, in which entire reference files are searched, and (2) the current awareness service which provides information on new developments and work being done in related fields. It is stated that the services provided by KASC will reduce duplication of expensive research and aid the movement of new knowledge across industrial, regional, and disciplinary boundaries.

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NASA NTRS1978

A bibliography on the search for extraterrestrial intelligence

This report presents a uniform compilation of works dealing with the search for extraterrestrial intelligence. Entries are by first author, with cross-reference by topic index and by periodical index. This bibliography updates earlier bibliographies on this general topic while concentrating on research related to listening for signals from extraterrestrial intelligence.

Mallove, E. F.↗

NASA NTRS1979

Fiber optic rotation sensor /FORS/ signal detection and processing

The recent development of low-loss single-mode optical fiber waveguides for light has made possible a new class of inertial reference devices built on the principle of a closed loop interferometer. Light circulating through the loop in both directions experiences a relative phase delay proportional to rotation rate about the loop axis. This paper derives the phase delay and discusses signal detection, signal processing techniques and error sources. It is concluded that synchronous modulation and demodulation and an active gain control at the signal calculation level are required to eliminate drift errors. Potential performance is extraordinarily good; rotation rate sensitivity of a few milli-arc seconds per second and angular position random walk errors of an arc second per square root hour appear feasible.

Goss, W. C.↗

NASA NTRS1979

On-axis velocity component measurement with laser velocimeters

The application of Doppler shifted laser light to the measurement of the two velocity components normal to the optical axis of the system is relatively simple as compared to the measurement of the on-axis velocity component. The present paper deals with the reference-beam (local oscillator) technique and the dual-beam (fringe mode) technique, which have been developed for measuring the on-axis component. Some results obtained for the on-axis component are examined.

Neti, S.↗

NASA NTRS1983

Dynamical evolution of interplanetary magnetic fields and flows between 0.3 AU and 8.5 AU - Entrainment

An analysis is presented of the radial evolution of interplanetary flows and associated magnetic fields between 0.3 AU and 8.5 AU using data from Helios 1 and B Voyager 1, respectively. The results indicate that in moving to 8 AU the largest corotating streams swept up the slower flows and shocks into a relatively thin region in which they coalesced to form a single large-amplitude compression. As a result of this process, referred to as entrainment, memory of the sources and flow configurations near the sun is lost, while small-scale features are erased as the flows move outward and energy is transferred from small scales to large scales.It is concluded that in the outer solar system the structure of the solar wind may be dominated by large scale pressure waves separated by several AU, while beyond several AU most of the compression waves are no longer driven by streams, and the compression waves expand freely. At large distances (greater than 25 AU) these compression waves will have interacted extensively with one another producing another state of the solar wind, with fewer large-scale nonuniformities and more small-scale nonuniformities.

Burlaga, L. F.↗

NASA NTRS1985

Design considerations for high-altitude, long-endurance, microwave-powered aircraft

The sizing and performance analyses have been conducted in the design of long-endurance, high-altitude airplanes. These airplanes receive power either continuously beamed from a phased array transmitter or intermittently beamed from a dish transmitter. Results are presented for the cases of flight in zero wind speed and nonzero wind speed. Sensitivity studies indicate that the vehicle size is relatively insensitive to changes in the transmitter size. Cost estimates were made using models that excluded the airplane cost. Using a reference payload, results obtained from array and dish configurations were compared. Comparisons showed savings in cost as well as smaller vehicle sizes when an array transmitter was used.

Nguyen, H. Q.↗

NASA NTRS1988

Shock analysis - Three useful new relations

The behavior of collisionless hydromagnetic shocks in interplanetary space is considered analytically, with a focus on relations, implicit in the governing Rankine-Hugoniot equations, involving the magnetic field (B) and the plasma velocity (V). A moving reference frame aligned with the shock is employed, and expressions are derived which make it possible (1) to determine the speed of a shock of arbitrary orientation from upstream and downstream measurements of B and V; (2) to characterize the change in flow direction as the plasma crosses the shock in terms of the plasma beta, the Mach number, and the angle between the upstream field and the shock normal; and (3) to infer the third component of the upstream-downstream velocity jump from B and two-dimensional V measurements. These expressions are applied to ISEE-3 data on an interplanetary shock on April 5, 1979, and the results are presented in tables.

Smith, Edward J.↗

NASA NTRS1989

Active galactic nuclei. III - Accretion flow in an externally supplied cluster of black holes

This third paper in the series modeling QSOs and AGNs as clusters of accreting black holes studies the accretion flow within an externally supplied cluster. Significant radiation will be emitted by the cluster core, but the black holes in the outer halo, where the flow is considered spherically symmetric, will not contribute much to the overall luminosity of the source because of their large velocities relative to the infalling gas and therefore their small accretion radii. As a result, the scenario discussed in Paper I will refer to the cluster cores, rather than to entire clusters. This will steepen the high-frequency region of the spectrum unless inverse Compton scattering is effective. In many cases accretion flow in the central part of the cluster will be optically thick to electron scattering, resulting in a spectrum featuring optically thick radiative component in addition to power-law regimes. The fitting of these spectra to QSO and AGN observations is discussed, and application to 3C 273 is worked out as an example.

Pacholczyk, A. G.↗

NASA NTRS1989

Adaptive precompensators for flexible-link manipulator control

The application of input precompensators to flexible manipulators is considered. Frequency domain compensators color the input around the flexible mode locations, resulting in a bandstop or notch filter in cascade with the system. Time domain compensators apply a sequence of impulses at prespecified times related to the modal frequencies. The resulting control corresponds to a feedforward term that convolves in real-time the desired reference input with a sequence of impulses and produces a vibration-free output. An adaptive precompensator can be implemented by combining a frequency domain identification scheme which is used to estimate online the modal frequencies and subsequently update the bandstop interval or the spacing between the impulses. The combined adaptive input preshaping scheme provides the most rapid slew that results in a vibration-free output. Experimental results are presented to verify the results.

Tzes, Anthony P.↗

NASA NTRS1990

Collected software engineering papers, volume 8

A collection of selected technical papers produced by participants in the Software Engineering Laboratory (SEL) during the period November 1989 through October 1990 is presented. The purpose of the document is to make available, in one reference, some results of SEL research that originally appeared in a number of different forums. Although these papers cover several topics related to software engineering, they do not encompass the entire scope of SEL activities and interests. Additional information about the SEL and its research efforts may be obtained from the sources listed in the bibliography. The seven presented papers are grouped into four major categories: (1) experimental research and evaluation of software measurement; (2) studies on models for software reuse; (3) a software tool evaluation; and (4) Ada technology and studies in the areas of reuse and specification.

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NASA NTRS1992

Critical needs of fringe-order accuracies in two-color holographic interferometry

Requirements for the fringe order accuracy in two-color holographic interferometry are discussed with reference to crystal growth. A simple test cell (rectangular parallelepiped) containing a fluid is considered. The temperature and concentration variations are related to the fringe orders from the two interference patterns, and the uncertainties in the fringe orders are related to errors in the temperature and concentration determination. The formulation developed here is applied to the particular case of an aqueous solution of triglycerine sulfate as an example.

Vikram, C. S.↗

NASA NTRS1992

Correlation-based technique for automated tunable diode laser scan stabilization

A software-based method for real-time, active stabilization of tunable diode laser spectral scans is described. The procedure is suitable for use with field and laboratory instrumentation where automated, unattended spectrometer operation is required. An autocorrelation of two high-resolution reference gas infrared spectra is computed at regular intervals, and the location of the maximum value of the autocorrelation provides the relative abscissa shift between the spectra. Small adjustments to the laser scan parameters are thereby made to ensure that drifts in the laser output frequency are tracked and compensated. Calculations required for stabilization of a 512-point spectrum can be completed in under 25 ms using an inexpensive, moderate-speed, array processor installed in a PC.

May, Randy D.↗

NASA NTRS1990

Exercise during long term exposure to space: Value of exercise during space exploration

There appear to be two general physiological reasons why exercise will be beneficial to space travelers who will experience a weightless and isolated environment for many months or a few years: (1) to alleviate or prevent tissue atrophy (principally bone and muscle), to maintain cardiovascular function, and to prevent deleterious changes in extracellular and cellular fluid volumes and plasma constituents, especially electrolytes; and (2) to maintain whole organism functional physical and physiological status with special reference to neuromuscular coordination (physical skill) and physical fitness (muscle strength and power, flexibility, and aerobic endurance). The latter reason also relates well to the ability of the crew members to resist both general and local fatigue and thus ensure consistent physical performance. Various forms of exercise, performed regularly, could help alleviate boredom and assist the travelers in coping with stress, anxiety, and depression. The type, frequency, duration and intensity of exercise and ways of ensuring that crew members engage in it are discussed.

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NASA NTRS1992

Collected Software Engineering Papers, Volume 10

This document is a collection of selected technical papers produced by participants in the Software Engineering Laboratory (SEL) from Oct. 1991 - Nov. 1992. The purpose of the document is to make available, in one reference, some results of SEL research that originally appeared in a number of different forums. Although these papers cover several topics related to software engineering, they do not encompass the entire scope of SEL activities and interests. Additional information about the SEL and its research efforts may be obtained from the sources listed in the bibliography at the end of this document. For the convenience of this presentation, the 11 papers contained here are grouped into 5 major sections: (1) the Software Engineering Laboratory; (2) software tools studies; (3) software models studies; (4) software measurement studies; and (5) Ada technology studies.

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NASA NTRS1997

High Performance Circularly Polarized Microstrip Antenna

A microstrip antenna for radiating circularly polarized electromagnetic waves comprising a cluster array of at least four microstrip radiator elements, each of which is provided with dual orthogonal coplanar feeds in phase quadrature relation achieved by connection to an asymmetric T-junction power divider impedance notched at resonance. The dual fed circularly polarized reference element is positioned with its axis at a 45 deg angle with respect to the unit cell axis. The other three dual fed elements in the unit cell are positioned and fed with a coplanar feed structure with sequential rotation and phasing to enhance the axial ratio and impedance matching performance over a wide bandwidth. The centers of the radiator elements are disposed at the corners of a square with each side of a length d in the range of 0.7 to 0.9 times the free space wavelength of the antenna radiation and the radiator elements reside in a square unit cell area of sides equal to 2d and thereby permit the array to be used as a phased array antenna for electronic scanning and is realizable in a high temperature superconducting thin film material for high efficiency.

Bondyopadhyay, Probir K.↗

NASA NTRS2001

In-Flight Characterization of the Electromagnetic Environment Inside an Airliner

In 1995, the NASA Langley Research Center conducted a series of experimental measurements that characterized the electromagnetic environment (EME) inside a Boeing 757 airliner while in flight, Measurements were made of the electromagnetic energy coupled into a commercially configured aircraft as it was flown in close proximity to ground-based radio frequency (RF) transmitters operating at approximately 26, 173. and 430 MHz. The goal of this experiment was to collect data for the verification of analytical predictions of the internal aircraft response to an external stimulus. This paper describes the experiment, presents the data collected by it, and discusses techniques used to compute both the magnitude of the electric field illuminating the aircraft and its direction of propagation relative to a coordinate system fixed to the aircraft. The latter is determined from Global Positioning System (GPS) and aircraft Inertial Reference Unit (IRU) data. The paper concludes with an examination of the shielding effectiveness of the test aircraft. as determined by comparison of' the measured internal EME and computed external EME.

Moeller, Karl J.↗

NASA NTRS2003

Selection of the Final Four Landing Sites for the Mars Exploration Rovers

Engineering constraints developed for the Mars Exploration Rovers (MER), their translation into ~185 potential landing sites and their downselection to 6 high priority science sites have been described [1, 2]. These 6 sites (Meridiani-previously referred to as Hematite, Gusev, Isidis, Melas, Eos, and Athabasca) were evaluated in detail as to their science potential and safety, relative to specific engineering constraints, at the 3rd MER Landing Site Workshop held March 26-28, 2002 in Pasadena, CA. This abstract describes: (1) the evaluation of these 6 sites, (2) the removal and reprioritization of sites following this workshop, (3) the identification of a low-wind site in Elysium, (4) the final 4 sites being considered for landing the 2 MER and (5) their evaluation at the 4th MER Landing Site Workshop held January 8-10, 2003 in Pasadena, CA [3].

Golombek, M.↗