Physical Sciences and Mathematics Commons^™

Boundary Approximations For Implicit Schemes For .One-Dimensional Inviscid Equations Of Gasdynamics, Helen Yee, R. M. Beam, R. F. Warming

United States National Aeronautics and Space Administration: Publications

The applicability to practical calculations of recent theoretical developments in the stability analysis of difference approximations is examined for initial boundary-value problems of the hyperbolic type. For the numerical experiments the one-dimensional inviscid gasdynamic equations in conservation law form are selected. A class of implicit schemes based on linear multistep methods for ordinary differential equations is chosen and the use of space or space-time extrapolations as implicit or explicit boundary schemes is emphasized. Some numerical examples with various inflow-outflow conditions highlight the commonly discussed issues: explicit vs implicit boundary schemes, and unconditionally stable schemes.

Environmental Impact Of Solar Variability, Richard G. Hodgson

Pro Rege

No abstract provided.

Civilian Space Policy And Applications, U.S. Office Of Technology Assessment

Space Law Documents

The United States orbited its first satellite in 1958, nearly a quarter century ago. In the intervening years, the United States has made great strides in developing peaceful and practical uses of space technology. However, in spite of the dramatic successes of the space program, among which are the recent flights of the Columbia shuttle orbiter, many informed observers express considerable unease about the future of our civilian efforts in space, particularly in light of increased foreign competition and stringent fiscal restraints.

Because of these uncertainties and also because of emerging new prospects for using the space environment, this assessment …

On The Application And Extension Of Harten's High-Resolution Scheme, Helen C. Yee, R. F. Warming, Amiran Harten

United States National Aeronautics and Space Administration: Publications

Xost first-order upstream conservative differencing methods can capture shocks quite well for one-dimensional problems. A direct application of these first-order methods to two-dimensional problems does not necessarily produce the same type of accuracy unless the shocks are locally aligned with the mesh. Harten has recently developed a second-order high-resolution explicit method for the numerical computation of weak solutions of one-dimensional hyperbolic conservation laws. The main objectives of this paper are (a) to examine the shock resolution of Harten's method for a two-dimensional shock reflection problem, (b) to study the use of a high-resolution scheme as a post-processor to an approximate …

Classroom Demonstration Of Sunspots, Thomas O. Callaway, Harry D. Downing, Glen T. Clayton

Faculty Publications

No abstract provided.

Observations And Analysis Of The Aquarii Jet, Menas Kafatos, Andrew G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

Ultraviolet, optical and radio observations of the symbiotic star R Aquarii are discussed in the light of the discovery of a bright radio and optical jet from this star. The star is probably a binary with a period of 44 years. The VLA maps of the jet reveal a protruding structure extending-10 arc sec from the central radio source with a position angle virtually identical to that of the optical jet observed at Lick. We interpret the observations of R Aqr as indicating the existence of an accretion disk around an unseen companion. The hot subdwarf has effective temperature ,(65,000 …

Uv Emission From The M1 Supergiant Tv Gem, Andrew G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

Low and high dispersion ultraviolet spectra were obtained of the Ml supergiant TV Gem with IUE. Previous IUE observations of this late type supergiant revealed unexpected W continuum emission, perhaps arising from an early B companion. Low resolution spectra obtained approximately one year apart suggest that the strong Si I11 in-combination perhaps with 0 I at wavelengths % A1300 A varies considerably with time. Large variation the column density is required to explain these changes. Sporadic mass expulsion with mass loss rates dM/dt * 10-5 S y r - l from the M supergiant could lead to a dense circumstellar …

Ci Cygni Since The 1980 Eclipse, R. E. Stencel, Andrew G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

Following the 1980 eclipse of the 855 day period symbiotic binary CI Cyg, we were confronted with a data set showing high excitation resonance lines which were largely uneclipsed but brightening on an orbital timescale, and intercombination lines exhibiting pronounced but nontotal eclipses and which were fading on an orbital timescale. Our model invoked a low density dissipating nebula surrounding the hot companion to explain the intercombination lines, and a shock between stellar winds to interpret the resonance lines. Subsequent synoptic observations have revealed continuing changes in the W emission line fluxes, consistent with those described above, except for the …

Iue Observations Of The Peculiar Star Rx Puppis, Menas Kafatos, A. G. Michalitsianos, W. A. Feibelman

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have obtained the first high-dispersion observations of RX Pup in the wavelength region 1200-2000 A with the International Ultraviolet Explorer. RX Pup has been classified a symbiotic star and has been compared to slow novae as well as to 11 Carinae. The anomalies that we observed in high-excitation lines in RX Pup such as He II, 0 III], C III], C IV, and Si IIIl that show split line profiles, Doppler displaced multiple components, and possible inverse P Cygni profiles inN III] and N IV J suggest dynamic activity in circumstellar material that probably has the form of rings …

Ultraviolet Spectrum Of The Crab Nebula, K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, R. A. Fesen, R. A. Parise, C. A. Harvel, Menas Kafatos, V. L. Trimble

Mathematics, Physics, and Computer Science Faculty Articles and Research

Data from 65 hours of observation of the Crab Nebula with the International Ultraviolet Explorer are reported, together with new ground-based spectrophotometry. We have measured the important C IV λ1549, He II λ1640, and C III] λ1908 emission line intensities and placed upper limits on other ultraviolet features for the brightest filamentary region in the nebula. We have also measured some ultraviolet continuum surface brightnesses at two places in the Crab. The emission lines imply an average ionic abundance ratio n(C^+2)/n(O^+2 ) in the range from 0.4 to 1.5 in the observed gaseous condensations. The elemental abundance ratio of carbon …

Ultraviolet Observations Of Four Symbiotic Stars, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

Observations were obtained with the International Ultraviolet Explorer (IUE) of four symbiotic stars. The UV spectra of YY Her, SY Mus, CL Sco, and BX Mon are characterized by varying degrees of thermal excitation. We have analyzed these low resolution spectra in terms of line-blanketed model atmospheres of early A, B, and F type stars in order to identify the nature of the hot companion in these systems. The expected emission from early main sequence stars does not fully explain the observed distribution of UV continuum energy over the entire IUE spectral range (1200-3200 A). More likely the observed continuum …

Radio And Optical Observations Of The R Aquarii Jet, R. J. Sopka, G. Herbig, Menas Kafatos, A. G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Articles and Research

VLA observations at 6 cm and Lick Observatory optical plates of R Aquarii indicate the existence of a jetlike feature extending 7" -10" from the central star. A wide field map at 6 cm shows an unresolved compact radio source which lies close to the axis defined by the jet at a distance of ~ 3' from R Aqr. Episodic mass transfer in this symbiotic variable could explain the erratic outbursts that R Aqr is known to undergo. Formation of an accretion disk and the accompanying radio-optical jet may characterize the observed outbursts in this system.

International Ultraviolet Explorer Observations Of The Aquarii Jet, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet spectra were obtained with the International Ultraviolet Explorer of the newly discovered optical-radio jet feature in the symbiotic variable R Aquarii. The far-UV continuum of the jet is characterized by strong continuum which rises with decreasing wavelength in the 1200-2000 A wavelength range and is considerably different in appearance from the relatively flat continuum exhibited by ionized nebulosity in the central star. Prominent Si III] and Si II emission lines seen in the central region are virtually absent in the jet. This could reflect the depletion of silicon in the feature, the result of grain formation in material that …

A Brightening Of The Symbiotic Variable Sy Muscae, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, G. Wallerstein

Mathematics, Physics, and Computer Science Faculty Articles and Research

The symbiotic variable SY Muscae has been observed with IUE in September 1980 and June 1981 and in the photographic region in May 1981. The entire ultraviolet spectrum brightened between September and June by about a factor of 5. The spectrum shows high excitation including emission from N v and high electron density, about 10^10 cm^-3 as determined from various line ratios in the ultraviolet. The optical spectrum is dominated by permitted lines; even [0 m] is very weak again indicating high density in the ionized region. The increase in ultraviolet continuum and line emission may be due to enhanced …

Ultraviolet Observations Of The 1980 Eclipse Of The Symbiotic Star Ci Cygni, R. E. Stencel, A. G. Michalitsianos, Menas Kafatos, A. A. Boyarchuk

Mathematics, Physics, and Computer Science Faculty Articles and Research

Secular and eclipse variations of UV lines and continua during the course of nearly a full orbit of the symbiotic binary CI Cygni are presented. High-excitation resonance lines have brightened on an orbital time scale and show minimal effects of eclipse, while intercombination lines have faded and show pronounced but nontotal eclipse effects. The data are discussed in terms of mass transfer from the extended cool envelope of the red giant to a compact secondary. The formation of an accretion disk is a transitory phenomenon in which viscosity eventually dissipates the disk over orbital time scales. A large-scale low-density nebula …

Landau Free Energy Form At The F Point Of The Roverline3 Structure, Dorian M. Hatch, Daniel L. Decker

Faculty Publications

A free energy form compatible with the F point of the trigonal D63d(Roverline3c) symmetry is constructed. It is a function of the order parameter, elastic strain, and the stress. The resulting free energy exhibits a close formalistic analogy to the stressed cubic perovskite structures and their associated multicriticality.

X-Ray Survey Of The Small Magellanic Cloud, F. D. Seward, Melanie Mitchell

Computer Science Faculty Publications and Presentations

A region of over 40 square degrees centered on the Small Magellanic Cloud (SMC) has been surveyed with the imaging instruments of the Einstein Observatory. The survey is approximately complete to L_x = 1036 ergs s^-1, and the faintest source detected in the SMC, has L_x ≈ 3 x 1035 ergs s^-1. Twenty-six sources were clearly seen. Five are identified with objects not associated with the SMC. The only previously known source detected was SMC X-1 which, when in a high state, is the brightest source in the SMC. The second brightest source observed, …

O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor

Physics Faculty Publications

It is shown that the revised photochemical theory for O⁺⁺ in the earth's ionopshere, where double photoionization of O is the dominant source, is consistent with recent O⁺⁺ measurements on Venus. A rate coefficient of 1.5 × 10⁻¹⁰ cm³ s⁻¹ for O⁺⁺ + O is obtained, and the possible importance of O⁺⁺ chemistry on minor atomic ions and airglow emissions is explored.

Iue Observations And Interpretation Of The Symbiotic Star Rw Hya, Menas Kafatos, Andrew G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

IUE observations of the high excitation symbiotic star RW Hya (gM2 + pec) have been obtained. Analysis of the intense UV continuum observed between II00 A to 2000 A suggests this star is a binary system in which the secondary is identified as a hot subdwarf with T _. _I0 D K. We deduce a distance to the system of ~1000 pc. The UV spectrum consists of mainly semi-forbidden and allowed transition lines of which the ClV (1548 A, 1550 A) emission lines are particularly strong, and UV continuum at both shorter and longer wavelengths. Strong forbidden lines seem to …

Iue Observations Of Circumstellar Emission From The Late Type Variable R Aqr (M7 + Pec), R. W. Hobbs, Andrew G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

As part of a program to observe circumstellar emission from late type stars, IUE observations of R Aqr (M7 + pec) have been obtained in low dispersion. Strong permitted, semi-forbidden and forbidden emission lines are seen, superimposed on a bright ultraviolet continuum. We deduce that the strong emission line spectrum that involves C III], C IV, Si III], [0 II] and [0 lll] probably arises from a dense compact nebula the size of which is comparable to the orbital radius of the binary system of which R Aqr is the primary star. The low excitation emission lines of Fe II, …

Superbubbles, T. R. Gull, F. C. Bruhweiler, Menas Kafatos, S. Sofia

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

Individual massive stars with Mbol < -6 have huge stellar winds that create interstellar bubbles. Stars with masses greater than 8Mo (4Mo?) are considered supernova progenitors. These massive stars are numerous in OB associations where few supernova remnants are detected. Model calculations describing the evolution of an association show: i) that large, hot cavities are formed by pushing the ambient gas into neutral shells; 2) that the shell radii change with galactocentric radius, 3) that only thirty percent of the interstellar medium is in the form of supercavities and 4) that a consequence is that only a small fraction of supernovae form supernova remnants. These results have strong bearing on interpretation of interstellar studies being done by IUE and by HEAO-B.

Oh Emission In The Direction Of Tv Gem And Bi Cyg, L. W. Brown, R. W. Hobbs, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

OH maser main-line emission at 1665 MHz has been detected in the direction of two late-type supergiants, TV Gem (Mllab) and BI Cyg (M3Iab), with the 43-m telescope and 18-cm receiver at NRAO-Green Bank. Detection of two new OH maser sources here is particularly interesting in view of the relatively small number of late-type supergiants that are known as molecular radio sources or associated in close proximity with OH emission clouds. The infrared, ultraviolet, and radio properties of these stars are discussed briefly.

Iue Observations Of Two Late Type Stars Bx Mon (M4 + Pec) And Tv Gem (M1 Iab), Andrew G. Michalitsianos, R. W. Hobbs, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

IUE observations of two late type stars BX Mon and TV Gem have been obtained that reveal the emission properties in the ultraviolet of subluminous companions. Analysis of the continuum emission observed from BX Mon suggests the companion is a middle A III star. High excitation emission lines observed between 1200 A and 2000 A (C IV, Si Ill], C III ) that generally do not typify emission observed in either late M type variables or A type stars are also detected. It is suggested that these strong high-excitation lines arise in a large volume of gas heated by non-radiation …

Preliminary Report On Iue Spectra Of Crab Nebula, K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, Menas Kafatos, V. L. Trimble

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

The Crab Nebula is marginally observable with the IUE. Observations of the optically brightest filamentary regions, made with IUE in August 1979, show the C IV x1549, He II x1640, and C III] x1909 emission lines. The intensities of these lines have been compared with visual-wavelength data. It appears that carbon is not overabundant in the Crab; carbon/- oxygen is approximately "normal" oxygen is slightly scarcer than "normal" as a fraction of the total mass.

Ingress Observations Of The 1980 Eclipse Of The Symbiotic Star Ci Cygni, R. E. Stencel, Andrew G. Michalitsianos, Menas Kafatos, Alexander A. Boyarchuk

Mathematics, Physics, and Computer Science Faculty Books and Book Chapters

One of the major results from the IUE may prove to be the new knowledge gained by studies of the ultraviolet spectra of symbiotic stars. Symbiotics combine spectral features of a cool M giant-like photosphere with strong high excitation emission lines of nebular origin, superposed. An excellent pre-UV review has been given by Swings (i). The UV spectra are dominated by intense permitted and semi-forbidden emission lines and weak continua indicative of hot compact objects and accretion disks. Two symbiotics, AR Pay and CI Cyg are thought to be eclipsing binaries, and we have begun IUE observations during the predicted …

A Cosmic Clock For The Classroom, Laurence A. Marschall

Physics and Astronomy Faculty Publications

Teachers who watched the first episode of Carl Sagan's Cosmos show on the Public Broadcasting System may have been impressed by his use of the "Cosmic Calendar" to dramatically introduce the evolutionary time scale of the universe. In this calendar, which Sagan first represented in The Dragons of Eden, the 15 billion year history of the universe is compressed into a single year. Each month represents 1.25 billion years, each day 40 billion years, and each second 500 years. At this scale the entire recorded history of mankind flashes by during the final 10 seconds of the cosmic year. [ …

Magnetohydrodynamics In An Open Universe, Oscar Norris

Masters Theses & Specialist Projects

A study of magnetohydrodynamics (MHD) in an open universe is presented. We discuss the data and justification behind our choice of an open universe for investigation in this thesis, as opposed to the closed universe theory, which is more appealing in some ways. We explicitly define all parameters used in the analysis of magnetohydrodynamic Bianchi Type V cosmologies and outline the formulation behind them. We then proceed to present a solution to a Bianchi Type V magnetohydrodynamic cosmology with a diagonal metric. After that, the results are compared with present observations. Lastly, we conclude with an assessment of the model …

Influence Of Nonequilibrium Radiation And Shape Change On The Flowfield Of A Jupiter Probe With Ablation And Mass Injection, Sundaresa Venkata Subramanian

Mechanical & Aerospace Engineering Theses & Dissertations

The influence of nonequilibrium radiative energy transfer and the effect of probe configuration changes on the flow phenomena around a Jovian entry body is investigated. The radiating shock-layer flow is assumed to be axisymmetric, viscous, laminar and in chemical equilibrium. The radiative transfer equations are derived under nonequilibrium conditions which include multi-level energy transitions. The equilibrium radiative transfer is calculated with an existing nongray radiation model which accounts for molecular band, atomic line and continuum transitions. The nonequilibrium results are obtained with and without ablation injection in the shock layer. The nonequilibrium results are found to be influenced greatly by …

150 Ghz Observations Of Three Radio Galaxies, Menas Kafatos, R. W. Hobbs, S. P. Maran, L. W. Brown

Mathematics, Physics, and Computer Science Faculty Articles and Research

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C Ill were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. Each of these three central sources has been previously discussed as the site of the energy supply for the associated distant components. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components …

Iue Observations Of Two Late Type Stars: R Aql And W Hya, Menas Kafatos, A. G. Michalitsianos, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet spectra of two late type M stars R Aql and W Hya were obtained with the International Ultraviolet Explorer (IUE). Spectra were obtained of R Aql near maximum (cf>=0.21) and minimum (cf>=0.65) of the visible light curve. We find that the absolute flux intensity of the Mgn resonance doublet (2796 A, 2803 A) is essentially the same at these phases in the visible light curve. A nebular emission feature at 3133 A is detected at minimum light in R Aql that is possibly due to 0 III. Mg II emission is totally absent in W Hya, which …