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At least 991 records · Page 55
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NASA NTRS1985

On the numerical computation of nonlinear force-free magnetic fields

An algorithm has been developed to extrapolate nonlinear force-free magnetic fields from a source surface, given the proper boundary conditions. The results of this work; describing the mathematical formalism that was developed, the numerical techniques employed, and the stability criteria developed for these numerical schemes are presented. An analytical solution is used for a test case; the results show that the computational accuracy for the case of a nonlinear force-free magnetic field was on the order of a few percent ( 5%).

Wu, S. T.↗
NASA NTRS1985

Turbine blade-tip clearance excitation forces

The results of an effort to assess the existing knowledge and plan the required experimentation in the area of turbine blade tip excitation forces is summarized. The work was carried out in three phases. The first was a literature search and evaluation, which served to highlight the state of the art and to expose the need for an articulated theoretical experimental effort to provide not only design data, but also a rational framework for their extrapolation to new configurations and regimes. The second phase was a start in this direction, in which several of the explicit or implicit assumptions contained in the usual formulations of the Alford force effect were removed and a rigorous linearized flow analysis of the behavior of a nonsymmetric actuator disc was carried out. In the third phase a preliminary design of a turbine test facility that would be used to measure both the excitation forces themselves and the flow patterns responsible for them were conducted and do so over a realistic range of dimensionless parameters.

Martinez-Sanchez, M.↗
NASA NTRS1985

Magnetic probing of the solar interior

The magnetic field patterns in the region beneath the solar photosphere is determined. An approximate method for downward extrapolation of line of sight magnetic field measurements taken at the solar photosphere was developed. It utilizes the mean field theory of electromagnetism in a form thought to be appropriate for the solar convection zone. A way to test that theory is proposed. The straightforward application of the lowest order theory with the complete model fit to these data does not indicate the existence of any reasonable depth at which flux conservation is achieved.

Benton, E. R.↗
NASA NTRS1985

Use of the synoptic view: Examples from Earth and other planets

Space technology has added the synoptic view to other techniques used in geomorphology. Synoptic views are provided by spacecraft images or by application of space technology to time-honored information systems. Examples of spacecraft images of Earth are LANDSAT, SEASAT, and the SIR (Shuttle Imaging Radar) series. Examples of applied space technologies include the digital conversion of topographic maps to shaded relief maps and digital correlation methods. From the study of other planets we have learned that synoptic views enable the deciphering of a planet's history: large features are identified and mapped before small ones; studies proceed from the general to the specific. On Earth, we generally recognize smaller features and study specific processes first, then extrapolate toward larger features and a general synthesis. With the advent of space images of Earth, perhaps the time is ripe to employ the methods used for other planets to the study of terrestrial geology and geomorphology. The following examples illustrate the use of regional-scale studies on Earth: the application of synoptic-view images in Antarctica, the use of digital methods and correlations of multiple data sets in regional studies, and some benefits to our understanding of terrestrial geology that have been obtained from analyses of other planets.

Lucchitta, B. K.↗
NASA NTRS1984

Predicting photothermal field performance

Photothermal field performance in flat plate solar collectors was predicted. An analytical model which incorporates the measured dependency between transmittance loss and UV and temperature exposure levels was developed. The model uses SOLMET weather data extrapolated to 30 years for various sites and module mounting configurations. It is concluded that the temperature is the key to photothermally induced transmittance loss. The sensitivity of transmittance loss to UV level is nonlinear with minimum in curve near one sun. The ethylene vinyl acetate (EVA) results are consistent with 30 year life allocation.

Gonzalez, C. C.↗
NASA NTRS1985

Planetary Dynamos

The MAGSAT-program has added significantly to our knowledge of planetary magnetism. The accuracy of observations has been improved such that a reliable extrapolation of the magnetic field to the core surface is now much more feasible than it has been before, and the prospect of further MAGSAT missions raises the expectation that the time dependence of the geomagnetic field will be known with similar accuracy in the future. In the research support it has been attempted to develop dynamo theory with these applications in mind.

Busse, F. H.↗
NASA NTRS1985

Spectra and positions of galactic gamma-ray sources

The UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment aboard HEAO-1 scanned the galactic center region during three epochs in 1977 and 1978 from 13 to 180 keV. The results are presented from the scanning epoch of 1978 September. Twenty-two known 2 to 10 keV source positions were necessary for an acceptable fit to the data. The spectra of the 16 strongest, least confused sources are all consistent with power laws with photon spectral indices ranging from 2.1 to 7.2. Acceptable fits to thermal bremsstrahlung models are also possible for most sources. No one source in this survey can be extrapolated to higher energy to match the intensity of the gamma-ray continuum as measured by HEAO-1 large field of view detectors, which implies that the continuum is a composite of contributions from a number of sources.

Knight, F. K.↗
NASA NTRS1985

Composition of primary cosmic rays at energies 10(15) to approximately 10(16) eV

The sigma epsilon gamma spectrum in 1 approx. 5 x 1000 TV observed at Mt. Fuji suggests that the flux of primary protons 10 to the 15 approx 10th eV is lower by a factor of 2 approx. 3 than a simple extrapolation from lower energies; the integral proton spectrum tends to be steeper than around to the power V and the spectral index tends to be steeper than Epsilon to the -17th power around 10 to the 14th power eV and the spectral index becomes approx. 2.0 around 10 to the 15th power eV. If the total flux of primary particles has no steepening up to approx 10 to the 15th power eV, than the fraction of primary protons to the total flux should be approx 20% in contrast to approx 45% at lower energies.

Amenomori, M.↗
NASA NTRS1985

Electron and muon parameters of EAS and the composition of primary cosmic rays in 10(15) to approximately 10(16) eV

Estimation of the relative intensities of protons and heavy nuclei in primary cosmic rays in the energy region 10 to the 15th power approx. 10 to the 17th power eV, was done by a systematic comparison between all available observed data on various parameters of extensive air showers (EAS) and the results of simulation. The interaction model used is an extrapolation of scaling violation indicated by recent pp collider results. A composition consisting of various percentages of Fe in an otherwise pure proton beam was assumed. Greatest overall consistency between the data and the simulation is found when the Fe fraction is in the region of 25%.

Cheung, T.↗
NASA NTRS1985

Search for bursts in air shower data

There have been reports in recent years of the possible observation of bursts in air shower data. If such events are truly of an astrophysical nature then, they represent an important new class of phemonenon since no other bursts have been observed above the MeV level. The spectra of conventional gamma ray bursts are unknown at higher energies but their observed spectra at MeV energies appear generally to exhibit a steepening in the higher MeV range and are thus unlikely to extrapolate to measurable fluxes at air shower energies. An attempt has been made to look for deviations from randomness in the arrival times of air showers above approx. 10 to the 14th power eV with a number of systems and results so far are presented here. This work will be continued for a substantial period of ime with a system capable of recording bursts with multiple events down to a spacing of 4 microns. Earlier data have also been searched for the possible association of air shower events with a glitch of the Vela pulsar.

Bruce, T. E. G.↗
NASA NTRS1985

Cosmic rays in the 10(16) to 10(19) eV range from pulsars

The flux is calculated of cosmic rays (CRs) produced by a distribution of pulsars that are: (1) born with rapid rotation rates, (2) slow down as they evolve, and (3) produce energetic nuclei with a characteristic energy proportional to their rotation rates. It is found that, for energy independent escape from the disk of the galaxy, the predicted spectrum will be essentially what is observed between approx 10 to the 16th power to 10 to the 19 power eV if the slow down law as inferred for radio pulsars can be extrapolated to young pulsars with shorter periods.

Wandel, A.↗
NASA NTRS1985

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays from an early design study employing Monte Carlo calculations. The response to 50 to 600 MeV solar neutrons was estimated from a simple model which did not consider secondary charged particles escaping into the veto shields. In view of numerous detections by the GRS of solar flares emitting high energy gamma rays, including at least two emitting directly detectable neutrons, the calibration of the high energy mode in the flight model has been recalculated by the use of more sophisticated Monte Carlo computer codes. New results presented show that the GRS response to gamma rays above 20 MeV and to neutrons above 100 MeV is significantly lower than the earlier estimates.

Cooper, J. F.↗
NASA NTRS1985

Proton-air and proton-proton cross sections from air shower data

Data on the fluctuations in depth of maximum development of cosmic ray air showers, corrected for the effects of mixed primary composition and shower development fluctuations, yield values of the inelastic proton-air cross section for laboratory energies in the range 10 to the 8th power to 10 to the 10th power GeV. From these values of proton-air cross section, corresponding values of the proton-proton total cross section are derived by means of Glauber theory and geometrical scaling. The resulting values of proton-proton cross section are inconsistent with a well known 1n(2)s extrapolation of ISR data which is consistent with SPS data; they indicate a less rapid rate of increase in the interval 540 sq root of s 100000 GeV.

Linsley, J.↗
NASA NTRS1985

Some remarks about simulation of cosmic ray phenomena with use of nuclear interaction models based on the current SPS proton-antiproton data

The x-y controversy is studied by introducing models with as many features (except for x and y distributions) in common, as possible, to avoid an extrapolation problem, only primary energies of 500 TeV are considered. To prove the point, Monte Carlo simulations are performed of EAS generated by 500 TeV vertical primary protons. Four different nuclear interaction models were used. Two of them are described elsewhere. Two are: (1) Model M-Y00 - with inclusive x and y distributions behaving in a scaling way; and (2) Model M-F00 - at and below ISR energies (1 TeV in Lab) exactly equivalent to the above, then gradually changing to provide the distributions in rapidity at 155 TeV as given by SPS proton-antiproton. This was achieved by gradual decrease in the scale unit in x distributions of produced secondaries, as interaction energy increases. Other modifications to the M-Y00 model were made.

Wrotniak, J. A.↗
NASA NTRS1985

General consequences of the violated Feynman scaling

The problem of scaling of the hadronic production cross sections represents an outstanding question in high energy physics especially for interpretation of cosmic ray data. A comprehensive analysis of the accelerator data leads to the conclusion of the existence of breaked Feynman scaling. It was proposed that the Lorentz invariant inclusive cross sections for secondaries of a given type approaches constant in respect to a breaked scaling variable x sub s. Thus, the differential cross sections measured in accelerator energy can be extrapolated to higher cosmic ray energies. This assumption leads to some important consequences. The distribution of secondary multiplicity that follows from the violated Feynman scaling using a similar method of Koba et al is discussed.

Kamberov, G.↗
NASA NTRS1985

Simulation of EAS properties on the basis of high energy interaction model deduced from the accelerator data

Calculations of extensive air showers in atmosphere were performed using formulae describing p-p and p-air nucleus interactions. The formulae fitted to the accelerator data were extrapolated taking the same trend up to 10 to the 16 eV. Above that energy it was assumed that the degree of scaling violating/alpha-parameter/ is saturating or even decreasing. The latter assumption follows from earlier work where it was found that without this restriction shower maxima at the highest energies are located too high in the atmosphere. Results of calculations have been compared with experimental data. The comparison was made separately for the curves obtained from the so called equal intensity cuts and for the Cerenkov data.

Kubiak, G.↗
NASA NTRS1985

New aspects in nucleon-nucleus collisions and EAS properties around 10(6) GeV

At energies higher than 2 x 10 to the 5 GeV, very little information exists on detailed properties of nucleon-nucleon collision; the rare elements are coming from jets, and, as nondirect improvements from gamma-ray families. The results exhibit some conflicting features, or, at least, very large fluctuations like copious production of gamma-rays in opposition to Centauro-like events, sometimes suggest that phase transition to quark gluon plasma occurs in nucleus-nucleus collisions and even in nucleon-nucleus collision. The multicluster phenomenological model (MPM) extrapolated for extensive air showers EAS simulation up to 5 x 10 to the 6 GeV to put in evidence some significant deviation between experimental data and prediction.

Capdevielle, J. N.↗
NASA NTRS1985

Small air showers and collider physics

At energies lower than 2.5 X 10 to the 5 GeV (in Lab. system), more accurate information on nucleon-nucleon collision (p-p collider and on primary composition now exist. The behavior of those both basic elements in cosmic ray phenomenology from ISR energy suggests some tendencies for reasonable extrapolation in the next decade 2.0x10 to the 5 to 2.0x10 to the 6 GeV. Small showers in altitude, recorded in the decade 2 X 10 to the 4 to 2 X 10 to the 5 GeV offers a good tool to testify the validity of all the Monte-Carlo simulation analysis and appreciate how nucleon-air collision are different from nucleon-nucleon collisions.

Capdevielle, J. N.↗