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Electronics for processing random event trains may contain some elements which are paralyzable in combination with others which are nonparalyzable. An expression is derived which gives the counting efficiency or live time of such a system when its input is a Poisson random arrival process.
An ideal seeding device is proposed generating particles that exactly follow the flow out are still a major source of error, i.e., with a particle counting bias wherein the probability of measuring velocity is a function of velocity. The error in the measured mean can be as much as 25%. Many schemes have been put forward to correct for this error, but there is not universal agreement as to the acceptability of any one method. In particular it is sometimes difficult to know if the assumptions required in the analysis are fulfilled by any particular flow measurement system. To check various correction mechanisms in an ideal way and to gain some insight into how to correct with the fewest initial assumptions, a computer simulation is constructed to simulate laser anemometer measurements in a turbulent flow. That simulator and the results of its use are discussed.
The MIT-Green Bank (MG) radio survey (reported by Bennett and colleagues in 1984 and 1985) is the largest 5 GHz survey to date. In this paper the source counts from the MG survey are examined. They are consistent with past measurements, but due to the large size of the MG survey the Poisson errors have been reduced. Radio source evolution models (such as that reported by Condon in 1984) are consistent with these new measurements.
It has recently been argued that the break in the galaxy correlation function observed in the Lick counts of Shane and Wirtanen may be an artifact of plate variations in limiting magnitude. This has stimulated us to generalize our analysis of the effect of errors in the plate depths to include a possible systematic term, and to develop tests for the random and systematic errors. The tests show that neither can have appreciably affected the distinctive feature found in the galaxy two-point correlation function for the Lick sample.
Ostriker and Heisler (1984) suggested that optically thick dust in galaxies could reduce the number of high-redshift quasars without reddening the observed quasars, because the only observed quasars would be those seen through no intervening galaxies. However, Ostriker and Heisler assumed that galaxies were hard-edged uniform disks, and the fuzzy edges of real galaxies significantly change this conclusion. The quasar distribution observed through more realistic galaxy models is calculated, and it is found that dust cannot significantly reduce the high-redshift quasar counts without also reddening the observed sample. But this reddening could be consistent with past studies of quasar reddening; improved studies of quasar reddening using new UV and IR data are needed.
EUV and far UV applications of wedge and strip anodes in photon-counting microchannel plate detector systems are discussed in light of performance data obtained as a result of EUV Explorer spacecraft open face detector and FAUST-Spacelab far UV sealed tube sensor calibrations. CsI quantum detection efficiencies of about 80 percent at 114 A and about 40 percent at 600 and 1300 A have been achieved; a position sensitivity of less than 10 microns is demonstrated, and the position resolution, image linearity, background rate, and flat-field characteristics are discussed.
The development of a new microchannel plate photon-counting detector with an analog readout method based on a resistive anode is reported. This detector exhibits extremely high, stable electron gains of 10 to the 8th. At this gain, the spatial resolution is no longer primarily limited by the noise of the resistive anode, so that digital methods of readout, such as discrete conductors, lose their advantage. These detectors can be readily scaled to 40 mm and 70 mm formats to match plate scales of 2-m (and larger) telescopes. New, high speed digital electronics fully exploit the high spatial and time resolution made possible by gains of this level. Analysis of the theoretical performance of this detector shows that the major limitation to the spatial resolution is the proximity focus of the photocathode and the first microchannel plate. The detector has been mated to an echelle spectrograph developed.
The calibration of photon counting imaging detectors for satellite based EUV astronomy is a complex process designed to ensure the validity of the data received 'in orbit'. The methods developed to accomplish calibration of microchannel plate detectors for the Extreme Ultraviolet Explorer are described and illustrated. The characterization of these detectors can be subdivided into three categories: stabilization, performance tests, and environmental tests.
An explicit test of the ability of the galaxy two-point correlation function to be recovered from the Lick counts of galaxies (Shane and Wirtanen, 1967) is reported. High-fidelity simulations are created, starting with the distribution of galaxies in space. These distributions are projected onto a set of simulated Lick plates which are reduced to a uniform limiting magnitude with the method of Seldner et al. (1977). The simulated catalogs are then analyzed with the methods of Groth and Peebles (1977). The resulting correlation functions are found to reproduce accurately the correlation functions that were built in during the first step of the simulations.
Rockwell International's Solid State Photomultiplier (SSPM) is an impurity-band avalanche device which can count individual photons with wavelengths between 0.4 and 28 micrometers. Its response to a photon is a pulse of between 10(exp 4) and 10(exp 5) conduction electrons, making it an important device for use in phenomenology. The characteristics of the SSPM make it a potentially important device for use in astronomical applications. Contract NAS2-12400 was initiated in June 1986 to conduct modeling and characterization studies of the SSPM to provide a basis for assessing its use in astronomical systems. Some SSPM models and results of measurements which characterize the group of SSPMs recently fabricated on this contract are discussed.
BL Lac objects, extracted from the Einstein Extended Medium Sensitivity Survey (EMSS), are examined. X-ray selection proved to be a powerful tool to find new BL Lacs, and allows the creation of complete, well defined and sizable samples. X-ray selected BL Lac objects (XBL) have in general more starlight in the optical spectra than radio selected BL Lacs. Redshifts for a significant fraction of objects in samples of XBL can be determined. It is thus possible to study the cosmological properties of BL Lac objects. Different models of luminosity functions of BL Lacs, including relativistic beaming, are considered and integrated over luminosity and redshift. The results are compared with the observed number-counts. The observed redshift distribution and the models' predictions are analyzed.
A compendium is presented of the ground and inflight scanner and nonscanner offsets and count conversion (gain) coefficients used for the Earth Radiation Budget Experiment (ERBE) production processing of data from the ERBS, NOAA-9, and NOAA-10 satellites for the 1 Nov. 1984 to 31 Dec. 1986.
Extragalactic number counts and diffuse backgrounds at 25, 60, and 100 microns are predicted using new luminosity functions and improved spectral-energy distribution density functions derived from IRAS observations of nearby galaxies. Galaxies at redshifts z less than 3 that are like those in the local universe should produce a minimum diffuse background of 0.0085, 0.038, and 0.13 MJy/sr at 25, 60, and 100 microns, respectively. Models with significant luminosity evolution predict backgrounds about a factor of 4 greater than this minimum.
Two methods, the 2-(4-Iodophenyl) 3-(4-nitrophenyl) 5-phenyltetrazolium chloride (INT) method and the direct viable count (DVC), were tested and compared for their efficiency for the determination of the viability of bacterial populations. Use of the INT method results in the formation of a dark spot within each respiring cell. The DVC method results in elongation or swelling of growing cells that are rendered incapable of cell division. Although both methods are subjective and can result in false positive results, the DVC method is best suited to analysis of waters in which the number of different types of organisms present in the same sample is assumed to be small, such as processed waters. The advantages and disadvantages of each method are discussed.
In EUV and FUV space-astronomy applications, the best contemporary detector designs are based on the use of microchannel plates due to their ability to deliver photon-counting performance with high efficiency. The major unresolved issue is the choice of position-readout system for the individual photoevents. Electrical event-readout systems are divided into two classes: the discrete wire anodes that perform coordinate digitization by wire-group selection, and the continuous centroid-position encoders for which coordinates are digitized in the associated electronics. The centroid-position encoder techniques are discussed in terms of how they overcome the four chief limitations of the discrete-wire readouts - their limited format size, their flat focal surface, their fundamental hex-channel vs squared-pixel moire pattern, and their image undersampling. With these limitations overcome, microchannel based image systems can deliver the performance demanded by the forthcoming generation of applications in space astronomy.
A family of imaging, pulse-counting, photoelectric detector systems, the Multi-Anode Microchannel Arrays (MAMAs), are now under active development for use on a number of space ultraviolet astrophysics missions at far-ultraviolet (FUV) and extreme-ultraviolet wavelengths between about 300 and 28 nm. Specifically, MAMA detectors are being fabricated and tested for use in two instruments on the ESA/NASA Solar and Heliospheric Observatory mission, for the NASA Goddard Space Flight Center's Hubble Space Telescope Imaging Spectrograph, and for the prime FUV spectrograph of the Far Ultraviolet Spectroscopic Explorer FUSE/Lyman mission. The construction and performance characteristics of the different MAMA detector systems are described, and techniques for improving the spatial resolution of each of the detector systems by the use of custom application specific integrated circuits in the electronics are discussed.
The design, implementation, and evaluation of a high-resolution vidicon-based reconfigurable imaging system for integration into a photon-counting streak camera that can be readily coupled to a standard interface and computer have been achieved. Experimental results are reported which demonstrate that the design goals are met, providing the capability to measure differential time to better than 3 picosecond accuracy. Augmented by real-time calibration, the accuracy, linearity, noise levels, and stability of the system are adequate to support dual wavelength laser ranging.
An investigation is conducted to address the questions of whether chimpanzees can count and whether rhesus monkeys can differentiate written numbers. One investigation demonstrates the capacity of a chimpanzee to produce a quantity of responses appropriate to a given Arabic numeral. Rhesus monkeys are shown to have the capability for making fine differentiations between quantities of pellets and Arabic numerals.