Engineering topics
Publications and source records attributed to Stern, R..
The design of the electronics control and data system for the extreme environment seen by a 1.3 Kg, 1666 cubic cm nanorover is presented.
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The major scientific objective of the EUV Imaging Telescope (EIT) is to study the evolution of coronal structure over a wide range of spatial and temporal scales and temperatures. A second strategic objective is to provide full disk synoptic maps of the global corona to aid in unifying SOHO (Solar and Heliospheric Observatory)/Cluster investigations. EIT will also provide images to support the planning of detailed spectroscopic investigations by the CDS (Coronal Diagnostic Spectrometer) and SUMER spectrometers in SOHO. EIT observations will be made in four narrow spectral bands, centered at 171 A (Fe 9), 195 A(Fe 12), 284 A (Fe 15), and 304 A (He 2) representing restricted temperature domains within a wide temperature range from 40,000 to 3,000,000 K. The results will be images of the solar atmosphere from the upper chromosphere and transition region to the active region corona. These maps, made at appropriate time intervals, will be used to study the fine structures in the solar corona and to relate their dynamic properties to the underlying chromosphere and photosphere. Dynamic events in the inner corona will be related to white light transients in the outer corona, and observations of the internal structure of coronal holes will be used to investigate origins of the solar wind.
The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and heliospheric observatory) will provide full disk images in emission lines formed at temperatures that map solar structures ranging from the chromospheric network to the hot magnetically confined plasma in the corona. Images in four narrow bandpasses will be obtained using normal incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. The EIT is capable of providing a uniform one arc second resolution over its entire 50 by 50 arc min field of view. Data from the EIT will be extremely valuable for identifying and interpreting the spatial and temperature fine structures of the solar atmosphere. Temporal analysis will provide information on the stability of these structures and identify dynamical processes. EIT images, issued daily, will provide the global corona context for aid in unifying the investigations and in forming the observing plans for SOHO coronal instruments.
An electron-free plasma consisting of negative ions /SF6(-)/ and positive ions /Ar(+)/, and negligible neutral-ion collision frequencies has been created in the laboratory. This plasma has a mass ratio of approximately 3.5-similar to many computer particle-in-cell simulated systems. A fluid description of this positive and negative ion confinement (PANIC) plasma is given and compared to experimental measurements of a beam-plasma instability for both beam species and a wide range of beam energies. The fluid dispersion relation and most growing modes are predicted to be insensitive to many parameters of the PANIC beam-plasma system, and found to the consistent with the data.
The first observation of a time-resolved X-ray flare in an RS CVn binary is reported. The X-ray flare was detected from the RS CVn binary Sigma CrB on August 17, 1980 during the course of a long pointed-mode observation with the Monitor Proportional Counter on the Einstein Observatory. The flare commenced at about 11:12 UT and lasted for about 205 minutes. During the flare the count rate increased by a factor of five from a quiescent state value of 0.3 count/s to a peak value of 1.5 count/s in the 1.2-10.2-keV energy band. The source spectrum during the flare was found to be considerably harder than that observed in the quiescent state. Details of the various characteristics of the X-ray flare are described.
To date 11 of the brightest X-Ray stars (F-K dwarfs) in the Hyades have been observed with the IUE satellite with the short wavelength spectrograph. The IUE results and the X-Ray observations from the Hyades survey with the Einstein Observatory were combined. The differential emission measure function was estimated for each of the 7 stars which showed evidence of emission lines. Constraints on stellar atmospheric parameters (chromospheric pressure, coronal temperature and filling factor were derived. The implications of these results in the context of loop models for the corona and transition region (TR) of these stars are discussed.
The Apollo-Soyuz data and data reported by Cash et al. (1976) have been reanalyzed in terms of both isothermal models and temperature distribution models. In the latter case, a power-law form is assumed for the relation between emission measure and temperature. A new upper limit on diffuse flux in the 20-73 eV band derived from Apollo-Soyuz observations made in the earth's shadow has been incorporated in the calculation. In the considered investigation the results of the new analysis are presented and the implications for the physical properties of the hot component of the interstellar medium are discussed. The analysis of the Berkeley extreme ultraviolet (EUV) diffuse background measurements using either isothermal or power law temperature distribution models for the emitting plasma indicates excellent qualitative agreement with hard X-ray data that suggest the sun to be immersed in a hot plasma that pervades most of space out to approximately 100 pc.
The effect of the differential rotation of the disk of the galaxy on magnetic field which penetrates the disk is considered. The magnetic field will be progressively distorted from a potential (current-free) form and will at some stage become unstable. We expect, from knowledge of solar flares, that an MHD instability, a resistive instability, or a combination of the two, will result in the release of the excess magnetic energy, and that part of the released energy will be converted into heat. By estimating the energy release and the rate at which this process will occur and by assuming that this energy input is balanced by radiation, we obtain estimates of the parameters of the resulting plasma. It appears that this process alone can heat a galactic corona to temperatures of order one-million K.
The results of the Apollo-Soyuz extreme ultraviolet (EUV)/soft X-ray diffuse background survey are analyzed to assess the contribution of discrete-sources with blackbody or coronal plasma spectra. Blackbody emitters in the EUV must be less luminous and more numerous than hot white dwarfs in order to produce the bulk of the diffuse flux. Significant contributions to the EUV background appear likely only if sufficient numbers of white dwarfs possess low temperature coronae similar to the one suggested for Sirius B.
The effect of the differential rotation of the disk of the Galaxy on magnetic field which penetrates the disk is considered. The magnetic field will be progressively distorted from a potential (current-free) form and will at some stage become unstable. It is expected that an MHD instability, a resistive instability, or a combination of the two, will result in the release of the excess magnetic energy and that part of the released energy will be converted into heat. By estimating the energy release and the rate at which this process will occur and by assuming that this energy input is balanced by radiation, estimates were obtained of the parameters of the resulting plasma. It appears that this process alone can heat a galactic corona to temperatures of order 10 to the 6th power K.
The paper reports results of the most extensive survey to date of the EUV/soft X-ray background, obtained with an EUV telescope on the Apollo-Soyuz mission. The principal results may be summarized as follows: (1) an intense background flux exists down to energies of 100 eV (4.0 plus or minus 1.3 photons/sq cm/sec/sr/eV average diffuse flux); (2) the Apollo-Soyuz data alone places lower and upper limits on single-temperature models for EUV-emitting interstellar gas for the log T range of 5.1-6.0; and (3) the allowed range would have to be restricted to log T of 5.1-5.6 for the Cash, Malina, and Stern (1976), Burstein et al. (1977), and Apollo-Soyuz data sets to satisfy a single-temperature model for the background at not greater than 280 eV.
The EUV (100-1000 A) spectrum of an optically thin plasma over the temperature range 100,000-10 million K is calculated, and the effects of free-free, free-bound, and two-photon continuum radiation are considered. The resulting spectra are presented in graphical form, with a separate tabulation of intensities for the emission lines. Results in the 100-200 A region are compared with those of other workers, and the major sources of uncertainty in this type of calculation are discussed. The applicability of the results to EUV observations of the interstellar medium are also mentioned.
Human peripheral blood and HeLa cells were irradiated in vitro at the ultrasonic frequency of 65 kHz. The whole blood and HeLa cell suspensions were exposed to continuous and pulsed ultrasonic power levels of 0.12, 0.16, 0.72, 1.12 and 2.24 W for a period of one minute. The method of ultrasonic irradiation was carried out with the whole blood or HeLa cell suspensions coupled directly to a cylindrical transducer while heating of the cell suspensions in excess of 41 C was avoided. Irradiated and unirradiated peripheral blood lymphocyte chromosome cultures were prepared and scored for selected numerical and morphological aberrations. There was no significant difference in the frequency of chromosomal aberrations between irradiated and unirradiated cells.
During the Apollo-Soyuz Test Project, an extreme-ultraviolet telescope observed the region of the sky from which the interstellar medium approaches the sun. The instrument had a tin filter whose bandpass included the 584-A line of neutral helium. The observations set an upper bound for the number density of neutral helium in the local interstellar medium of 0.004 + or - 0.0022 per cu cm, which is significantly lower than previously reported. The stated error is dominated by the present uncertainty in the solar 584-A flux, which is taken to be approximately 200 million photons/sq cm per sec at earth's orbit. The result is not consistent with previous resonant-scattering Ly-alpha observations of interstellar hydrogen passing through the solar system, which generally yield a hydrogen number density of about 0.1 per cu cm, unless interstellar helium is locally depleted below its cosmic abundance. The result is consistent with cosmic abundances if the much lower average hydrogen densities inferred from recent column-density measurements to nearby hot stars are in fact representative of the immediate solar neighborhood.
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The letter reports an observation of Sirius in the extreme-ultraviolet (100-1000 A) band, using a grazing-incidence telescope flown aboard the Apollo-Soyuz mission. No positive flux is detected; under the arbitrary assumption of flat incident spectrum, an upper limit to the flux in the 170-620 A band is 5 billion erg/sq cm per sec. A detailed model-atmosphere analysis, when combined with the EUV limits, places severe constraints on models which attribute the previously reported soft X-ray (44-60 A) flux to thermal radiation from deep layers of the atmosphere of the white dwarf Sirius B. EUV radiation should be detectable from Sirius B just below the sensitivity threshold of the current data, or a thermal origin for the X-ray flux is untenable. If the X-ray flux is thermal, the present results provide extremely sensitive constraints on the temperature and helium abundance of Sirius B: the white dwarf has an effective temperature of 32,000 K to 32,500 K and a helium abundance (relative to hydrogen) of 0.0001 to 0.0002.
Results are presented for extreme ultraviolet (100-1000 A) observations of radio pulsars. Using an EUV telescope carried aboard the Apollo-Soyuz mission, data were acquired on the nearby pulsars PSR 1133 + 16, 1451 - 68, and 1929 + 10. None of the objects was detected, with typical upper limits of 6 by 10 to the -26th power erg/sq cm/sec per Hz in the 170-620-A band set on flux incident at earth. The data are interpreted to set limits on the effective temperatures of the neutron stars, yielding values of less than 160,000 K in the best cases, and the limits compared with theoretical predictions.