Engineering topics

Wells, D. C.

Publications and source records attributed to Wells, D. C..

9 records

NASA NTRS1999

Pretreatment methods to improve nerve immunostaining in corneas from long-term fixed embryonic quail eyes

Pretreatment methods were used to improve neurofilament immunostaining in corneas from embryonic day 16 Japanese quail corneas that had been stored in fixative solution for several months. A sequential combination of the following three pretreatments: brief microwave heating in saline, followed by extraction with sodium dodecyl sulfate (SDS) at 37 degrees C, followed by digestion with hyaluronidase at 37 degrees C, produced significantly increased antibody staining of corneal neurofilament proteins, compared with embryonic corneas subjected to no prior pretreatments or to single or two-step protocols. After applying the sequence of all three pretreatments, darkest nerve staining and increased numbers of fine branches were observed, together with lower background staining. Thus, the result of applying the three-step pretreatment sequence is better than that of applying any of its component single pretreatments or even combinations of any two of them. These findings therefore suggest that each of these three pretreatments causes a unique effect, beneficial to immunostaining of neurofilament proteins, and that their individual effects are independent and additive. In addition to embryonic corneas, the three-step procedure also may be useful for immunostaining of nerves in other very delicate, highly-hydrated tissues containing an abundance of extracellular matrix.

NASA Discipline Developmental Biology↗

NASA NTRS1998

Effects of silver ion (Ag+) on a cellular shape change in the absence of microtubules in fertilized eggs of Ilyanassa obsoleta

No abstract available

Non-NASA Center↗

NASA NTRS1992

The VLBA correlator: Real-time in the distributed era

The correlator is the signal processing engine of the Very Long Baseline Array (VLBA). Radio signals are recorded on special wideband (128 Mb/s) digital recorders at the 10 telescopes, with sampling times controlled by hydrogen maser clocks. The magnetic tapes are shipped to the Array Operations Center in Socorro, New Mexico, where they are played back simultaneously into the correlator. Real-time software and firmware controls the playback drives to achieve synchronization, compute models of the wavefront delay, control the numerous modules of the correlator, and record FITS files of the fringe visibilities at the back-end of the correlator. In addition to the more than 3000 custom VLSI chips which handle the massive data flow of the signal processing, the correlator contains a total of more than 100 programmable computers, 8-, 16- and 32-bit CPUs. Code is downloaded into front-end CPU's dependent on operating mode. Low-level code is assembly language, high-level code is C running under a RT OS. We use VxWorks on Motorola MVME147 CPU's. Code development is on a complex of SPARC workstations connected to the RT CPU's by Ethernet. The overall management of the correlation process is dependent on a database management system. We use Ingres running on a Sparcstation-2. We transfer logging information from the database of the VLBA Monitor and Control System to our database using Ingres/NET. Job scripts are computed and are transferred to the real-time computers using NFS, and correlation job execution logs and status flow back by the route. Operator status and control displays use windows on workstations, interfaced to the real-time processes by network protocols. The extensive network protocol support provided by VxWorks is invaluable. The VLBA Correlator's dependence on network protocols is an example of the radical transformation of the real-time world over the past five years. Real-time is becoming more like conventional computing. Paradoxically, 'conventional' computing is also adopting practices from the real-time world: semaphores, shared memory, light-weight threads, and concurrency. This appears to be a convergence of thinking.

Wells, D. C.↗

NASA NTRS1984

Crystal gazing. Part 2: Implications of advanced in digital data storage technology

During the next 5-10 years it is likely that the bit density available in digital mass storage systems (magnetic tapes, optical and magnetic disks) will be increased to such an extent that it will greatly exceed that of the conventional photographic emulsions like IIIaJ which are used in astronomy. These developments imply that it will soon be advantageous for astronomers to use microdensitometers to completely digitize all photographic plates soon after they are developed. Distribution of digital copies of sky surveys and the contents of plate vaults will probably become feasible within ten years. Copies of other astronomical archieves (e.g., Space Telescope) could also be distributed with the same techniques. The implications for designers of future microdensitometers are: (1) there will be a continuing need for precision digitization of large-format photographic imagery, and (2) that the need for real-time analysis of the output of microdensitometers will decrease.

Wells, D. C.↗

NASA NTRS1982

A multiwavelength comparison of Cassiopeia A and Tycho's supernova remnant

A comparison of high resolution radio, optical, and X-ray images of two young supernova remnants (SNR), Cas A and Tycho, shows significant differences between them. Cas A probably broke into many small knots at the time of the initial explosion, whereas Tycho's SNR appears to be a more uniformly expanding blast wave.

Dickel, J. R.↗

NASA NTRS1979

Picture processing analysis of the optical structure of NGC 5128 /Centaurus A/

Results are presented for a detailed study of the peculiar elliptical galaxy NGC 5128 (Cen A), based on computer video analysis of several photographic plates of exceptional quality reduced to the standard UBV system. The picture-processing results and the measured properties of the elliptical and gaseous-disk components of NGC 5128 are examined, along with the distribution, spectral characteristics, and chemical composition of the H II regions in the disk. The data show that NGC 5128 consists of a giant E2 galaxy containing a significant amount of gas and dust situated predominantly in an equatorial disk where vigorous star formation is occurring. Reasons why NGC 5128 is so different from giant ellipticals in clusters are considered.

Dufour, R. J.↗

NASA NTRS1973

A portable millisecond-integration-time photoelectric photometer.

Portable equipment for recording millisecond-integration-time photoelectric photometric data is described. Digital data are reliably recorded on standard 6.35 mm audio grade magnetic tape via a quadradial audio grade tape deck. The system is designed specifically for recording lunar occulations of stars, but the data recording technique is independent of the data source. Recovery of the data is made via minicomputer.

Mcgraw, J. T.↗

NASA NTRS1972

The angular diameter of X Cancri.

Analysis of an occultation reappearance of the semiregular variable X Cancri observed with the 107-inch telescope of McDonald Observatory on 9 November 1971 by the laser group using slightly modified laser equipment. The problem of the effective temperature of this carbon star is discussed, and estimates near 2500 K are derived both from the occultation data and from an integration based on the multicolor photometry reported by Mendoza (1967). This figure is 300-400 K higher than Mendoza's calibration, and it is clear that unsolved problems remain in many areas connected with these stars.

Bartholdi, P.↗

NASA NTRS1972

The occultation of beta Scorpii by Jupiter and Io. I - Jupiter.

Use of computer-controlled one-dimensional area-scanning photometers to observe the occultation of the Beta Scorpii system by Jupiter on May 13, 1971. Six high-quality light curves were obtained; three of the occultations of the brighter component Beta Sco A and three of Beta Sco C. The mean scale height of the Jovian upper atmosphere is 32 plus or minus 6 km near -10 deg zenographic latitude, 31 plus or minus 2 km at -47 deg zenographic latitude, and 24 plus or minus 2 km at -57 deg zenographic latitude. The determination of the atmospheric scale height is highly sensitive to the background level subtracted, providing a possible explanation of an earlier result by Baum and Code (1953) placing the scale height at about 8 km. Correlated departures of the light curve from a theoretical isothermal curve are reproduced in the three bright-star curves, and are thus not due to random density fluctuations in the Jovian atmosphere, but are rather due to global stratification. Details of the stratification, which includes at least a number of warm layers, are examined by deconvolution of the light curves. There is evidence for a high-temperature (T greater than 300 K) thermosphere on two of the bright-star light curves.

Hubbard, W. B.↗