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  • ASTROPHYSICS  (432)
  • COMMUNICATIONS AND RADAR  (237)
  • Fisheries
  • 2020-2024
  • 1975-1979  (670)
  • 1977  (670)
  • 1
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    Different approaches of spectral analysis (1977)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Several approaches to the problem of the calculation of spectral power density of a random function from an estimate of the autocorrelation function were studied. A comparative study was presented of these different methods. The principles on which they are based and the hypothesis implied were pointed out. Some indications on the optimization of the length of the estimated correlation function was given. An example of application of the different methods discussed in this paper was included.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-75224
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  • 2
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    NASA teleconferencing pilot project - An evaluation of teleconferencing as a substitute for travel (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: NASA conducted a Pilot Project during 1975-1976 to determine the extent to which teleconferencing could replace travel to meetings. The network consisted of approximately 34 teleconference rooms and 50 fast facsimile machines, all interconnected on private lines to a master switchboard in Huntsville, Alabama. In addition, portable conference telephones augmented the voice network and experimental video conferences were attempted. Evaluations showed that the teleconferences saved travel costs approximating 21% of the travel budget at a communications cost of 3% of this budget.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: International Telemetering Conference; Oct 18, 1977 - Oct 20, 1977; Los Angeles, CA
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  • 3
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    The Soviet-American Conference on Cosmochemistry of the Moon and Planets, Part 2 (1977)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The origin and evolution of the solar system is discussed based on ground and satellite observations.
    Keywords: ASTROPHYSICS
    Type: NASA-SP-370-PT-2 , LC-75-600013 , Soviet-American Conference on Cosmochemistry of the Moon and Planets; Jun 04, 1974 - Jun 08, 1974; Moscow; Russia
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  • 4
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    X-ray bursts - The maximum mass of a neutron star (1977)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A review of the great variety of observed properties of X-ray burst sources is presented, including the MXB 1730-355, called the rapid burster. Hypotheses regarding the sources of bursts are discussed, and two models for the rapid burster are described. The first postulates that they are caused by a collapsed object with a mass of approximately 10 solar masses surrounded by a disk of gas spiralling inward. The second posits a neutron star with a strong magnetic field. Theoretical questions regarding the mass of neutron stars are discussed, and prerequisites for such research are identified. Various research projects investigating these questions are described.
    Keywords: ASTROPHYSICS
    Type: Mercury; 6; July-Aug
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  • 5
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    Contraction of the Orion Nebula cluster-molecular cloud A complex (1977)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Observational evidence is presented in support of the view that the width of the molecular lines in Orion is produced by a contraction of the cloud with a velocity directly proportional to the distance from the cloud center. The main support is provided by close agreement between the motions of the cloud and that of the stars embedded in it. A further implication of this agreement is that star formation occurred throughout the Orion cloud, rather than only in the dense center as predicted by the conventional picture of star formation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 217
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  • 6
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    Analysis of economics of a TV broadcasting satellite for additional nationwide TV programs (1977)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The influence of a TV broadcasting satellite, transmitting four additional TV networks was analyzed. It is assumed that the cost of the satellite systems will be financed by the cable TV system operators. The additional TV programs increase income by attracting additional subscribers. Two economic models were established: (1) each local network is regarded as an independent economic unit with individual fees (cost price model) and (2) all networks are part of one public cable TV company with uniform fees (uniform price model). Assumptions are made for penetration as a function of subscription rates. Main results of the study are: the installation of a TV broadcasting satellite improves the economics of CTV-networks in both models; the overall coverage achievable by the uniform price model is significantly higher than that achievable by the cost price model.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-75128 , BMFT-FB-T-76-5 , BMFT-NT-581
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  • 7
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    Evolution of the moon: The 1974 model (1977)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: The interpretive evolution of the moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows: (1) The Beginning: 4.6 billion years ago, (2) The Melted Shell: 4.6 to 4.4 billion years ago, (3) The Cratered Highlands: 4.4 to 4.1 billion years ago, (4) The Large Basins: 4.1 to 3.9 billion years ago, (5) The Light-colored Plains: 3.9 to 3.8 billion years ago, (6) The Basaltic Maria: 3.8 to 3.0(?) billion years ago, and (7) The Quiet Crust: 3.0(?) billion years ago to the present. The contributions of the Apollo and Luna exploration toward the study of those stages of evolution are reviewed.
    Keywords: ASTROPHYSICS
    Type: The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 63-80
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  • 8
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    On the emission of neutrinos and gravitational waves in the formation of neutron stars (1977)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The various modes in which the energy generated by the formation of a neutron star or black hole due to collapse of a stellar core can appear are investigated, and physical constraints are placed on this energy distribution by noting that neutron stars appear to have been found in at least six X-ray binaries and one binary pulsar. The energy generated by a supernova during the collapse of a stellar core to a neutron star is considered along with the manner in which this energy is distributed in the different modes. It is shown that the gravitational binding energy of a neutron star is converted mostly into kinetic energy of rotation or is emitted as neutrinos, gravitational waves, or both. The energy release through mass ejection and cosmic rays is suggested to be no more than a few percent of the total energy involved. A possible scenario is outlined for the case where the initial rotation velocity of the collapsing core exceeds some critical limit. It is concluded that gravitational radiation will be the ultimate outlet for most of the binding energy in this case.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science; 51; 1, Se; Sept
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  • 9
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    Results of special mechanical analyses of Luna 16 material (1977)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: The studies carried out on the Luna 16 regolith have confirmed the data that were already published internationally. By means of activation analysis under irradiation in the reactor, activation analysis with a 14 MeV U-generator, and mass spectroscopy on samples of 10 or 20 mg, six main and 63 trace elements were quantitatively determined and compared with known data.
    Keywords: ASTROPHYSICS
    Type: The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, Pt. 2; p 697-702
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  • 10
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    Metal abundance in the Praesepe and Hyades clusters (1977)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Calcium K-line photometry is reported for 27 A-type stars in the Praesepe cluster, and the data obtained are compared with previous K-line observations of Hyades stars. It is found that calcium and other metals are generally overabundant in Praesepe relative to field stars and that there is a considerable scatter in metal-abundance indices. Comparison with the Hyades results indicates that the Praesepe stars are as metal-enriched as the Hyades stars. These results are taken as evidence favoring Eggen's (1960) proposal that the Hyades and Praesepe clusters should be regarded as a single group having, on the average, about a factor-of-two higher metal abundance than solar-neighborhood field stars as well as a high internal dispersion in metal-line strengths. The questions of where and how the Praesepe-Hyades stars acquired their high average metal abundances, K-line strengths, and associated dispersions are briefly considered.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 214
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  • 11
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    Exploding stars, pulsars and black holes in space (1977)
    In:  CASI
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    Publication Date: 2019-08-13
    Description: Brief factual reviews are provided for supernovae, pulsars and neutron stars, and black holes. Also discussed in general terms are red giants, white dwarfs, quasars and radio galaxies.
    Keywords: ASTROPHYSICS
    Type: NASA-NEWS-RELEASE-77-243 , P77-10242
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  • 12
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    ATS-6 ascending: Near horizon measurements over water at 30 GHz (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The return of the ATS 6 satellite to a western longitude during the fall of 1976 presented a unique opportunity to perform low angle of elevation measurements at 30 GHz. For this purpose a receiver using a 1.5 m antenna was set up at Port Aransas, Texas, resulting in a propagation path entirely over water. The 30 GHz beacon was monitored daily for at least one hour from 8 September 1976 to 21 September 1976. During the time the elevation angle changed from 1.5 deg to 17.3 deg, the mean attenuation decreased from 20 dB to 2 dB and the standard deviation from over 6 dB to less than .2 dB. The deep fades at angles below 4 deg show significantly sharper nulls than peaks on a log scale. Spectra of the log amplitude fluctuations vary as the (-8/3) power of the spectral frequency in the limit. A flattening is noticeable at the low frequencies. A precipitation event at 8.5 deg elevation produced a 16 dB fade and significantly increased the variance.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-159966 , URSI Comm. of Open Symp. on Propagation in Nonionized Media; Apr 28, 1977 - May 06, 1977; LaBaule; France
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  • 13
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    Arguments and evidence concerning non-cosmological redshifts - A partial summary (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Theories which imply an unconventional interpretation of the redshifts are examined, taking into account a new theory of cosmology reported by Segal, scenarios in which the redshifts do not arise from the expansion, and studies concerning a possible existence of systematic effects in the distribution of redshifts. Attention is given to rapidly varying QSOs and BL Lac objects, VLBI studies of a number of QSOs and related objects, and physical associations between objects with very different redshifts. It appears that observational evidence concerning these physical associations is the strongest evidence that objects with large noncosmological redshift components exist. On the other hand, there are a number of cases of QSOs close to galaxies at the same redshifts.
    Keywords: ASTROPHYSICS
    Type: International Conference on the evolution of the galaxies and its cosmological implications; Sep 08, 1976 - Sep 09, 1976; Paris; France
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  • 14
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    Temperature of solid particles in colloidal plasmas in space (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Lehnert (1970) has investigated the question of the relationship between the kinetic temperature and the internal temperature at which a solid coexists with a plasma in a thermal steady state. The reported investigation is a more refined version of Lehnert's preliminary analysis of this relationship. The electric potential of grains is considered along with the ambient radiation field and the grain temperatures in the thermal steady state. An illustrative calculation is conducted of the grain temperatures in the dense regions of the primordial circumsolar colloidal plasma envelope such as envisioned in the Alfven-Arrhenius model (1976) of the origin of the solar system. It is shown that under certain conditions the solid grains can coexist with the plasma phase up to fairly high plasma densities and temperatures.
    Keywords: ASTROPHYSICS
    Type: Lunar Science Conference; Mar 14, 1977 - Mar 18, 1977; Houston, TX
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  • 15
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    Aircraft measurement of radio frequency noise at 121.5 MHz, 243MHz and 406MHz (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An airborne survey measurement of terrestrial radio-frequency noise over U.S. metropolitan areas has been made at 121.5, 243 and 406 MHz with horizontal-polarization monopole antennas. Flights were at 25,000 feet altitude during the period from December 30, 1976 to January 8, 1977. Radio-noise measurements, expressed in equivalent antenna-noise temperature, indicate a steady-background noise temperature of 572,000 K, at 121.5 MHz, during daylight over New York City. This data is helpful in compiling radio-noise temperature maps; in turn useful for designing satellite-aided, emergency-distress search and rescue communication systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Symposium and Technical Exhibition; Jun 28, 1977 - Jun 30, 1977; Montreux; Switzerland
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  • 16
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    The proposed coding standard at GSFC (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: As part of the continuing effort to introduce standardization of spacecraft and ground equipment in satellite systems, NASA's Goddard Space Flight Center and other NASA facilities have supported the development of a set of standards for the use of error control coding in telemetry subsystems. These standards are intended to ensure compatibility between spacecraft and ground encoding equipment, while allowing sufficient flexibility to meet all anticipated mission requirements. The standards which have been developed to date cover the application of block codes in error detection and error correction modes, as well as short and long constraint length convolutional codes decoded via the Viterbi and sequential decoding algorithms, respectively. Included are detailed specifications of the codes, and their implementation. Current effort is directed toward the development of standards covering channels with burst noise characteristics, channels with feedback, and code concatenation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: EASCON-77; Electronics and Aerospace Systems Convention; Sep 26, 1977 - Sep 28, 1977; Arlington, VA
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  • 17
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    Public Service Communication Satellite Program (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The proposed NASA Public Service Communication Satellite Program consists of four different activities designed to fulfill the needs of public service sector. These are: interaction with the users, experimentation with existing satellites, development of a limited capability satellite for the earliest possible launch, and initiation of an R&D program to develop the greatly increased capability that future systems will require. This paper will discuss NASA efforts in each of these areas.
    Keywords: COMMUNICATIONS AND RADAR
    Type: EASCON-77; Electronics and Aerospace Systems Convention; Sep 26, 1977 - Sep 28, 1977; Arlington, VA
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  • 18
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    Communication satellite services for special purpose users (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The present study identifies potential satellite services, examines the technology necessary for efficient implementation of these services, and determines minimum service cost versus user network size. The generic satellite services evaluated comprise TV and radio distribution (for retransmission), video teleconferencing (interactive), audio/facsimile teleconferencing (interactive), multiplexed data/voice (point-to-point), and satellite-supported land mobile. Satellite costs are based on extrapolations from ongoing commercial satellite programs. Production methods, new technology, and effect of production quantities on present and future production costs are examined to provide information on earth station equipment cost versus the variable 'buy'. Six different launch vehicles from a Delta 2914 to a dedicated Shuttle and three frequency bands and both broadcast (no eclipse capability) and fixed service satellites are considered to assess the effect of satellite size on cost and performance. It is assumed that the user pays only for his prorata share of the space segment costs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intelcom ''77 Symposium; Oct 09, 1977 - Oct 15, 1977; Atlanta, GA
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  • 19
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    Low cost Ku-band earth terminals for voice/data/facsimile (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A Ku-band satellite earth terminal capable of providing two way voice/facsimile teleconferencing, 128 Kbps data, telephone, and high-speed imagery services is proposed. Optimized terminal cost and configuration are presented as a function of FDMA and TDMA approaches to multiple access. The entire terminal from the antenna to microphones, speakers and facsimile equipment is considered. Component cost versus performance has been projected as a function of size of the procurement and predicted hardware innovations and production techniques through 1985. The lowest cost combinations of components has been determined in a computer optimization algorithm. The system requirements including terminal EIRP and G/T, satellite size, power per spacecraft transponder, satellite antenna characteristics, and link propagation outage were selected using a computerized system cost/performance optimization algorithm. System cost and terminal cost and performance requirements are presented as a function of the size of a nationwide U.S. network. Service costs are compared with typical conference travel costs to show the viability of the proposed terminal.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intelcom ''77 Symposium; Oct 09, 1977 - Oct 15, 1977; Atlanta, GA
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  • 20
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    Multiple-access channels without synchronization (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper discusses models for multiple-access communications which take into account the fact that the channel users may not be able to synchronize their transmissions. It is shown that for a broad class of such channels, the capacity region is the same as it would be with user synchronization. Some open problems are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 12, 1977 - Jun 15, 1977; Chicago, IL
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  • 21
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    Carrier synchronization techniques for unbalanced QPSK signals. I (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper uses MAP estimation techniques to obtain carrier reconstruction circuits for unbalanced QPSK signals. In addition, the performance analysis of these circuits is carried out to the extent that a loop design can proceed. Numerical results are presented in order to demonstrate the utility of the theory developed. This signal design will be used in the development of the Tracking and Data Relay Satellite System (TDRSS) and the Navigation Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS).
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 12, 1977 - Jun 15, 1977; Chicago, IL
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  • 22
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    Spectrally efficient modulation (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Spectrally efficient modulation, involving the maximization of the transmitted data rate through a specified bandwidth, may aid in alleviating the problem of spectral congestion in the electromagnetic spectrum. Attention is given to pulse-shaping and nonbinary modulation, and particularly to combined amplitude- and phase-modulation. Theoretical performance limits, such as Shannon's bound, are used to assess the effectiveness of the systems described. Consideration is also allotted to spectrally efficient modulation for terrestrial microwave systems, required to provide 1000 voice channels in the 4- and 6-GHz band.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 12, 1977 - Jun 15, 1977; Chicago, IL
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  • 23
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    System design for the digitally implemented communications experiment /DICE/ (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Full-duplex digital television providing a teleconference capability is to be evaluated in an experimental program utilizing the Communications Technology Satellite. The digitally implemented communications experiment employs a QPSK modulator-demodulator capable of operation over a wide range of bit rates. In addition to simultaneous data transmission (used for digital high-speed facsimiles and remote computer terminals), voice transmission through four-to-one compression will be studied.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 12, 1977 - Jun 15, 1977; Chicago, IL
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  • 24
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    Interaction of electromagnetic and acoustic waves in a stochastic atmosphere (1977)
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    Publication Date: 2019-07-13
    Description: This paper considers the interaction of electromagnetic and acoustic waves where a Radio Acoustic Sounding System (RASS) is operated in a stochastic environment characterized by turbulence, winds and mean-temperature gradients. It has been shown that for a RASS operating at acoustic frequencies below a few kilohertz propagating under typical atmospheric conditions, turbulence has little effect on the strength of the received radio signal scattered from the pulse at heights up to a few kilometers. This result implies that the received RF signal level (power) is primarily a function of sound intensity which decreases as x exp minus 2 where x is the altitude.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Union Radio Scientifique Internationale Open Symposium; Apr 28, 1977 - May 06, 1977; Loire-Atlantique; France
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  • 25
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    Rain depolarization and attenuation measurements at 11.7, 19.04, and 28.56 GHz - A description of the experiment and some preliminary results (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The considered investigation made use of the Communications Technology Satellite (CTS) downlink and the beacons carried by the Comstar satellites. The general behavior of rain attenuation and depolarization is illustrated with the aid of data from a storm which took place on July 15, 1976. The effect of the rain on the copolarized signal is indicated in a graph. Another graph shows the behavior of the cross-polarized signal component. Phase effects are also considered together with statistical curves for attenuation. The considered data from CTS indicate that, at least during summer convective storms, attenuation at 11.7 GHz is much more severe than anticipated. Attenuation may be a more serious impediment to dual polarized satellite links at this frequency than is depolarization.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Union Radio Scientifique Internationale Open Symposium; Apr 28, 1977 - May 06, 1977; Loire-Atlantique; France
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  • 26
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    CTS /Hermes/ - United States experiments and operations summary (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The U.S. experiments conducted with the Communications Technology Satellite, a joint Canadian-U.S. venture launched in 1976, are discussed. The 14/12 GHz frequencies employed by the 200-W transmitter on board the satellite provide two-way television and voice communications. Applications of the satellite in the categories of health care, community services and education are considered; experiments have also made use of the special properties of the super-high frequency band (e.g. link characterization and digital communications). Time-sharing of the 14/12 GHz communication between the U.S. and Canada has functioned well.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Symposium on Hermes (Communications Technology Satellite): Its Performance and Applications; Nov 29, 1977 - Dec 01, 1977; Ottawa; Canada
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  • 27
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    A digitally implemented communications experiment utilizing the Hermes /CTS/ satellite (1977)
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    Publication Date: 2019-07-13
    Description: Attention is given to an investigation being conducted by NASA-Lewis and Comsat Laboratories which uses the Hermes (CTS) satellite to explain digital link implementation and the advantages it provides over conventional analog systems. The experiment concentrates on developing several video, audio, and data digital communications techniques.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Symposium on Hermes (Communications Technology Satellite): Its Performance and Applications; Nov 29, 1977 - Dec 01, 1977; Ottawa; Canada
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  • 28
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    Utilization of NASA Lewis mobile terminals for the Hermes satellite (1977)
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    Publication Date: 2019-07-13
    Description: The paper describes the portable earth terminal (PET) and the transportable earth terminal (TET) which enable two-way television and voice communication. Both terminals were developed by NASA and utilize the high power of the Hermes satellite. PET is a bus-type vehicle which has receiving equipment for full duplex color television and which can transmit programs originating in either the on-board PET studio or in nearby buildings. PET has a collapsible 2.4-m diameter parabolic antenna interfacing with a 500-watt 14-GHz wideband TV transmitter and a 12-GHz wideband TV receiver system. TET uses two parabolic reflector antennas, 3 m and 1.2 m in diameter, mounted on a flat trailer towed by a truck. TET can receive and relay color TV signals, and its narrowband transmitter can serve as a return audio link permitting a question-and-answer format. Also described are uplink and downlink performance characteristics, operation procedures, and field demonstrations which enabled personnel at several hospitals to participate in a distant medical conference.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Symposium on Hermes (Communications Technology Satellite): Its Performance and Applications; Nov 29, 1977 - Dec 01, 1977; Ottawa; Canada
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  • 29
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    Extreme ultraviolet observations of white dwarfs (1977)
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    Publication Date: 2019-07-13
    Description: Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme-ultraviolet band (100-1000 A). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme-ultraviolet telescope; both stars are copious EUV emitters, with four billionths and three billionths erg/sq cm sec in the 170-620-A band, respectively. The EUV data, combined with optical spectrophotometry, allow their temperatures to be estimated as 80,000 and 60,000 K, respectively. The corresponding interstellar neutral hydrogen column densities are about 4 by 10 to the 18th power per sq cm.
    Keywords: ASTROPHYSICS
    Type: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 30
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    Hot gas in clusters of galaxies (1977)
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    Publication Date: 2019-07-13
    Description: Radio and X-ray observations are discussed which seem to favor the presence of a hot intracluster gas in rich clusters of galaxies. On the assumption that the X-rays are produced by thermal bremsstrahlung, a temperature of the order of 100 million K and a density of a few thousandths per cu cm are computed for the intracluster gas. Theories on the origin and dynamics of this gas are reviewed, and the discovery of an iron line in the spectrum of the Perseus cluster is taken as strong evidence for thermal emission from a hot intracluster gas. Effects of and on the intracluster gas are considered, particularly the formation of radio-tail galaxies due to ram pressure on the galaxies in rich clusters, stripping of interstellar gas from the galaxies, and heating of the intracluster gas by the galaxies. It is concluded that the intracluster gas: (1) originated partially in primordial matter that collapsed into the clusters and partially in gas lost from the galaxies, (2) is in static or almost static equilibrium in the clusters, and (3) either is tightly bound or has an equation of state corresponding to a gamma value of less than 5/3.
    Keywords: ASTROPHYSICS
    Type: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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    OSO-8 X-ray polarimeter and Bragg crystal spectrometer observations (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results are discussed for observations of the Crab Nebula, Cyg X-1, and Cyg X-2 with the focusing mosaic graphite crystal X-ray polarimeter aboard OSO-8 as well as for observations of A0620-00 with the Bragg crystal spectrometer aboard the same satellite. The observed X-ray polarization of the Crab Nebula is shown to be in agreement with a previous measurement of the optical polarization and to confirm with very high confidence the earlier conclusion that the X-ray emission occurs by the synchrotron process. No evidence is found for polarization of X-rays from Cyg X-1, but a preliminary result of 4.8% + or 1.0% polarization at an energy of 2.6 keV and a position angle of 141.7 + or - 6.6 deg is reported for Cyg X-2. It is noted that this value is within the range expected for accretion disks. The spectrometry of A0620-00 yielded a continuous spectrum that can be accurately fitted with a thermal bremsstrahlung spectrum at a temperature of 15 million K.
    Keywords: ASTROPHYSICS
    Type: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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    The origin of comets (1977)
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    Publication Date: 2019-07-13
    Description: Empirical data related to questions regarding the origin of comets are examined, taking into account the primitive temperature and its evolution, the cometary C-12/C-13 isotope ratio, the chemistry of comets, and the solar-system related orbits of the comets. The theories of cometary origin considered are related to a condensation of comets from the solar nebula and a later ejection into Oort's cloud, a recent condensation of comets in situ, a capture of interstellar comets, and a reversal of the arrow of time in the traditional evolution of comets. The only hypothesis which seems to survive an evaluation of the theories on the basis of the existing data is that the comets were condensed some five billion years ago in the vicinity of the giant planets or beyond, at the outer edge of the solar nebula.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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    Isotopic abundances in interstellar clouds (1977)
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    Publication Date: 2019-07-13
    Description: Results of microwave measurements in dense interstellar clouds are discussed which pertain to determinations of relative isotopic abundances. Difficulties in deriving relative abundances from observations of the relative intensities of isotopic lines are examined, and measures available for coping with these complications are outlined. Results are presented concerning the relative abundances of C-13, O-17, O-18, N-15, Si-30, S-33, S-34, and D in a variety of interstellar clouds; the consistency of these results is evaluated. It is concluded that: (1) the relative abundances of C-13 and O-17 in interstellar clouds are generally higher than those in the solar system; (2) the abundances of N-15 and D are lower than the solar-system values; (3) the O-18 abundance is possibly higher than in the solar system; and (4) there are substantial variations in the isotopic abundances between different large interstellar clouds, with some of these variations not dependent on distance from the galactic center alone.
    Keywords: ASTROPHYSICS
    Type: Topics in interstellar matter; Commission 34 Session, General Assembly; Aug 25, 1976; Grenoble; France
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    A comparison of the composition of new and evolved comets (1977)
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    Publication Date: 2019-07-13
    Description: The continuum to molecular emission intensity ratio in cometary spectra is examined as an indicator of initial composition of the comets. This ratio presumably measures the dust to gas ratio in comets, or the component of gas yielding visible emissions. The spectral relationships and compositions of new comets and more evolved ones are compared. No significant difference in the continuum to emission ratio was noted between new and more evolved comets, which is in contradiction to Oort's conclusion. This suggests that no systematic change occurs in the continuum to emission ratio as comets evolve from new to periodic. Perihelion passage does not seem to produce a general weakening of the continuum, although it occurs in individual cases.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 35
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    The pristine nature of comets (1977)
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    Publication Date: 2019-07-13
    Description: Abundance considerations suggest that comets are likely to be the most pristine minor bodies in the solar system. In proportion to solar abundances, the present scanty data suggest that cometary oxygen is not depleted, whereas carbon is by a factor of 4 and hydrogen, by a factor of 2000. This implies that comets are less depleted in H, C, N, O than CI chondrites, namely 10:1 in hydrogen, 4:1 in carbon and 3:1 in oxygen. These results have been obtained by using dust-to-gas ratios in comets to measure the relative abundance of silicon and metals to volatile material, and the spectra of atomic lines, mainly from the vacuum ultraviolet, to determine the H/O and C/O ratios of the mixture of volatile molecules.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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    A compendium of millimeter wave propagation studies performed by NASA (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Key millimeter wave propagation experiments and analytical results were summarized. The experiments were performed with the Ats-5, Ats-6 and Comstar satellites, radars, radiometers and rain gage networks. Analytic models were developed for extrapolation of experimental results to frequencies, locations, and communications systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156781
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    CTS attenuation and cross-polarization measurements at 11.7 GHz (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The results of data obtained 80 days preceding the solar eclipse shutdown of the CTS 11.7 GHz righthand circularly polarized beacon transmitter are presented. Attenuation and cross polarization isolation were measured. It was determined that depolarization presents a serious limitation to satellite system reliability when frequency reuse by polarization diversity is employed. A 27 db isolation margin would reduce reliability below 99.95%. For the same percentage the required fade margin was below 3 db.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156771
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    Design and demonstration of an advanced data collection/position location system (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The final report on a breadboard evaluation and demonstration program is reported concerning the applicability of MSK modulation and chirp-z transformer technology in Advanced Data Collection/Position Location (ADC/PL) systems. The program effort consisted of three phases - design, testing, and evaluation. Section 2 describes the breadboard hardware built during the design phase of the program, Section 3 describes the tests conducted on the breadboard and the results of the tests, and Section 4 presents a brief analysis and summary of the findings of the breadboard tests and develops a sample ADC/PL system which incorporates both MSK modulation and a chirp-z transformer.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156748
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    Analysis of synthetic aperture radar imagery (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Some problems faced in applications of radar measurements in hydrology are: (1) adequate calibration of the radar systems and direct digital data will be required in order that repeatable data can be acquired for hydrologic applications; (2) quantitative hydrologic research on a large scale will be prohibitive with aircraft mounted synthetic aperture radar systems due to the system geometry; (3) spacecraft platforms appear to be the best platforms for radar systems when conducting research over watersheds larger than a few square kilometers; (4) experimental radar systems should be designed to avoid use of radomes; and (5) cross polarized X and L band data seem to discriminate between good and poor hydrologic cover better than like polarized data.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156743 , RSC-3359-2
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    Electromagnetic plasma wave emissions from the auroral field lines (1977)
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    Publication Date: 2019-07-13
    Description: The most important types of auroral radio emissions are reviewed, both from a historical perspective as well as considering the latest results. Particular emphasis is placed on four types of electromagnetic emissions which are directly associated with the plasma on the auroral field lines. These emissions are (1) auroral hiss, (2) saucers, (3) ELF noise bands, and (4) auroral kilometric radiation. Ray tracing and radio direction finding measurements indicate that both the auroral hiss and auroral kilometric radiation are generated along the auroral field lines relatively close to the earth, at radial distances from about 2.5 to 5 R sub e. For the auroral hiss the favored mechanism appears to be amplified Cerenkov radiation. For the auroral kilometric radiation several mechanisms have been proposed, usually involving the intermediate generation of electrostatic waves by the precipitating electrons.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-155172 , U-OF-IOWA-77-36 , Gen. Sci. Assembly of the Intern. Assoc. of Geomagnetism and Aeronomy; Jan 01, 1977; Seattle
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    Communication system analysis for manned space flight (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: One- and two-dimensional adaptive delta modulator (ADM) algorithms are discussed and compared. Results are shown for bit rates of two bits/pixel, one bit/pixel and 0.5 bits/pixel. Pictures showing the difference between the encoded-decoded pictures and the original pictures are presented. The effect of channel errors on the reconstructed picture is illustrated. A two-dimensional ADM using interframe encoding is also presented. This system operates at the rate of two bits/pixel and produces excellent quality pictures when there is little motion. The effect of large amounts of motion on the reconstructed picture is described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-151508
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    Solid state Ku-band spacecraft transmitters (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A transmitter is considered that consists of GaAs IMPATT and Read diodes operating in a microstrip circuit environment to provide amplification with a minimum of 63 db small signal gain and a minimum compressed gain at 5 W output of 57 db. Reported are Schottky-Read diode design and fabrication, microstrip and circulator optimization, preamplifier development, power amplifier development, dc-to-dc converter design, and integration of the breadboard transmitter modules. A four-stage power amplifier in cascade with a three-stage preamplifier had an overall gain of 56.5 db at 13.5 GHz with a power output of 4.5 W. A single-stage Read amplifier delivered 5.9 W with 4 db gain at 22% efficiency.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152590 , TI-08-77-11
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    Final report on technical work accomplished under contract NASw-2953 (1977)
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    Publication Date: 2019-07-13
    Description: A report is given on the technical work accomplished in the area of plasma physics. The subjects covered are: (1) oblique whistler instabilities, (2) current-limited electron beam injection, (3) three-dimensional ion sound turbulence, (4) theoretical aspects of sounder antenna operation and (5) whistler modes in bow shock structures.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-153294 , TRW-29697-6002-RU-00
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    Research in millimeter wave techniques (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The following is investigated; (1) the design of a 183 GHz single ended fundamental mixer to serve as a back up mixer to the subharmonic mixer for airborne applications, (2) attainment of 6 db single sideband conversion loss with the 6 GHz subharmonic mixer model, together with initial tests to determine the feasibility of pumping the mixer at w sub s/4, (3) additional ground based radiometric measurements, and (4) derivation of equations for power transmission of wire grid interferometers, and initial tests to verify these equations.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-156762 , SATR-6
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    A depolarization and attenuation experiment using the CTS satellite (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Rain attenuation and depolarization data collected on the communications technology satellite 11.7 GHz downlink, and changes made in equipment following rain leak damage to the parametric amplifier are discussed. A 15 GHz radar system is described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152535 , QTPR-1
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    Aircraft measurement of radio frequency noise at 121.5 MHz, 243 MHz and 406 MHz (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: An airborne survey measurement of terrestrial radio-frequency noise over U.S. metropolitan areas was carried out at 121.5, 243 and 406 MHz with horizontal-polarization monopole antennas. Flights were at 25,000 feet altitude. Radio-noise measurements, expressed in equivalent antenna-noise temperature, indicate a steady-background noise temperature of 572,000 K, at 121.5 MHz, during daylight over New York City. This data is helpful in compiling radio-noise temperature maps; in turn useful for designing satellite-aided, emergency-distress search and rescue communication systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-X-71283 , X-952-77-11 , Symp. and Technical Exhibition on Electromagnetic Compatibility; Jun 28, 1977 - Jun 30, 1977; Montreux; Switzerland
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    A depolarization and attenuation experiment using the CTS satellite. Volume 2: Data (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: An experiment for measuring precipitation attenuation and depolarization on the CTS 11.7 GHz downlink is described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152482
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    Symposium on Recent Results in Infrared Astrophysics (1977)
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    Publication Date: 2019-07-13
    Description: Abstracts of papers presented at a symposium titled Recent Results in Infrared Astrophysics are set forth. The abstracts emphasize photometric, spectroscopic, polarization, and theoretical results on a broad range of current topics in infrared astrophysics.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-X-73190 , A-6856 , Jan 01, 1977; Moffett Field, CA; United States
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    Repeater in the sky (1977)
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    Publication Date: 2019-07-13
    Description: The Public Service Communications Satellite (PSCS) program is intended to develop and demonstrate a space system aimed at stimulating future commercial markets in fixed and mobile applications. The services are envisioned for rural areas, regions beyond access to terrestrial systems, or for continuous cross-country applications. The system incorporates a UHF repeater for mobile voice and data experiments; 8 MHz of spectrum is specified for serving 70 channels. This paper describes the PSCS program and discusses some demonstration experiments. A future concept based on large structure multibeam antennas is also discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: National Electronics Conference; Oct 10, 1977 - Oct 12, 1977; Chicago, IL
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  • 50
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    Carrier synchronization techniques for unbalanced QPSK signals. II (1977)
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    Description: This paper develops a theory for assessing the tracking performance and designing carrier synchronization loops which are to be matched to an unbalanced QPSK signal design. It is assumed that the power split and the I and Q channel data rates are arbitrary. Bit synchronization is assumed to be unavailable for both carrier reconstruction techniques which have been suggested via MAP estimation theory. Numerical results are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Bit timing with pulse distortion and intersymbol interference (1977)
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    Description: Pulse distortion and intersymbol interference due to insufficient filtering in PCM and PSK channels cause performance degradation in terms of both bit error probabilities and timing errors. This paper reports the results of a study analyzing these effects on bit timing subsystems. Consideration is given to both the filter-rectifier and transition tracking type of timing subsystem. Although both these systems perform similarly in high SNR and ideal pulse models, pulse distortion and intersymbol affects each differently. The primary effects in both systems is to cause the presence of an irreducible mean squared timing error due to the intersymbol which limits the ultimate performance. Design procedures to minimize the anomalies of both systems are presented, and indicate modifications of the standard timing subsystems. It is found that specific design directions depend on whether the intersymbol or the receiver noise tends to dominate.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Non-parametric PCM to ADM conversion (1977)
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    Publication Date: 2019-07-13
    Description: An all-digital technique to convert pulse code modulated (PCM) signals into adaptive delta modulation (ADM) format is presented. The converter developed is shown to be independent of the statistical parameters of the encoded signal and can be constructed with only standard digital hardware. The structure of the converter is simple enough to be fabricated on a large scale integrated circuit where the advantages of reliability and cost can be optimized. A concise evaluation of this PCM to ADM translation technique is presented and several converters are simulated on a digital computer. A family of performance curves is given which displays the signal-to-noise ratio for sinusoidal test signals subjected to the conversion process, as a function of input signal power for several ratios of ADM rate to Nyquist rate.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Minimax decoding of cyclic block codes (1977)
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    Description: A minimax decoding algorithm utilizing soft bit detection of an (n,k) cyclic block code is described which will permit the correction of up to n-k bit errors interspersed at random locations throughout the block. The decoding solution consists of: (1) identifying the ordered soft bit set and, (2) finding the minimum order solution to the resulting syndrome equations where the nonzero error vector components are constrained to be a subset of the soft bit set. An efficient implementation of the decoding operation is described. In essence, this algorithm focuses the correction capability of the code on those bit positions which have the lowest a posteriori probabilities of correct detection.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    On signal design by the R/0/ criterion for non-white Gaussian noise channels (1977)
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    Description: The use of the cut-off rate criterion for modulation system design is investigated for channels with non-white Gaussian noise. A signal space representation of the waveform channel is developed, and the cut-off rate for vector channels with additive non-white Gaussian noise and unquantized demodulation is derived. When the signal input to the channel is a continuous random vector, maximization of the cut-off rate with constrained average signal energy leads to a water-filling interpretation of optimal energy distribution in signal space. The necessary condition for a finite signal set to maximize the cut-off rate with constrained energy and an equally likely probability assignment of signal vectors is presented, and an algorithm is outlined for numerically computing the optimum signal set. As an example, the rectangular signal set which has the water-filling average energy distribution and the optimum rectangular set are compared.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Comparison of convolutional and block code performance on the Rician channel (1977)
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    Description: The paper is concerned with the relative performance of short constraint length convolutional codes vis-a-vis block codes when used in conjunction with either BPSK or DPSK modulation on the classical Rician fading channel. A variety of soft-decision decoding algorithms is considered for block codes while the Viterbi algorithm is used exclusively for decoding convolutional codes. Results indicate a substantial performance/complexity advantage in favor of short constraint length convolutional codes and Viterbi decoding which increases with fading severity. The work reported here extends the well-known performance advantage of convolutional codes on the AWGN channel to representative fading channels.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Measured results of polarization crosstalk cancellation using LMS control (1977)
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    Description: This paper discusses the use of wideband decoupling networks for the cancellation of polarization crosstalk in dual-polarized communication links. Measured cancellation performance for an all-electronic IF network and an RF electro-mechanical waveguide network are presented. Each of these networks utilizes LMS-type adaptive control techniques to adjust the cancellation network.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
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    Antenna bias rigging for performance objective (1977)
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    Description: An optimum bias rigging for a paraboloidal antenna can be used to minimize the expected average mean-square half-pathlength surface deviations. Statistics of deep space planetary missions are employed to develop weighting factors for antenna elevation angles during these missions. A procedure is shown to compute the optimum rigging angle from these weights.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Mechanical Engineering in Radar Symposium; Nov 08, 1977 - Nov 10, 1977; Arlington, VA
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    Evaluating computed distortions of parabolic reflectors (1977)
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    Description: Distortion outputs from structural analysis of a 64-m paraboloidal reflector are analyzed by two computer programs for their radio-frequency performance characteristics. The computed and field measured values are compared.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Mechanical Engineering in Radar Symposium; Nov 08, 1977 - Nov 10, 1977; Arlington, VA
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    Acceleration and modulation of electrons and ions by propagating interplanetary shocks (1977)
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    Description: The theory and observation of shock spikes are reviewed. Models of the orbits of charged particles and their energization during interaction with discontinuities under various geometries are studied. In situ observations of shock spikes are discussed. These have shown that sharp spikes are found sometimes ahead of and sometimes behind the shock, with the highest energies being ahead. One generally observes larger, field-aligned ion anisotropies ahead of shocks rather than behind. Intensity modulation of protons, alpha particles, medium nuclei, and iron have been observed.
    Keywords: ASTROPHYSICS
    Type: L. D. de Feiter Memorial Symposium; Jun 07, 1977 - Jun 10, 1977; Tel Aviv; Israel
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    The comet-solar wind interaction (1977)
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    Publication Date: 2019-07-13
    Description: The important roles of comets as natural probes of the solar wind, particularly at high heliographic latitudes and small heliocentric distances, unattained thus far by artificial space probes, is stressed. It is becoming clear the solar wind is not merely responsible for shaping and maintaining the cometary plasma tail, but is also indirectly responsible for the rapid ionization processes in the coma. Despite this, however, the detailed interaction of the solar wind with comets, which is underlined by the complex and time-varying morphology observed in the cometary head and the tail, constitutes a formidable problem, and is only very imperfectly understood at present. The current views are critically reviewed and an attempt is made to identify the dominant physical mechanisms that are involved.
    Keywords: ASTROPHYSICS
    Type: L. D. de Feiter Memorial Symposium; Jun 07, 1977 - Jun 10, 1977; Tel Aviv; Israel
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    Recent high energy gamma-ray results from SAS-2 (1977)
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    Publication Date: 2019-07-13
    Description: Recent developments in gamma-ray astronomy due to the results from SAS-2 have focused on two areas. First, the emission from the plane of the Galaxy is the dominant feature in the gamma-ray sky. The galactic latitude and longitude distributions are consistent with the concept that the high-energy radiation originates from cosmic rays interacting with interstellar matter, and the measurements support a galactic origin for cosmic rays. Second, searches of the SAS-2 data for emission from localized sources have shown three strong discrete gamma-ray sources: the Crab nebula and PSR 0531 + 21, the Vela supernova remnant and PSR 0833-45, and a source near galactic coordinates 193 deg longitude, +3 deg latitude, which does not appear to be associated with other known celestial objects. Evidence has also been found for pulsed gamma-ray emission from two other radio pulsars, PSR 1818-04 and PSR 1747-46. A localized source near longitudes 76-80 deg may be associated with the X-ray source Cyg X-3.
    Keywords: ASTROPHYSICS
    Type: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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    An upper limit for the flux of interstellar dust grains in the solar system (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Data from the LEAM (Lunar Ejecta and Meteorite experiment, a micrometeorite detector at the Apollo 17 landing site) have been examined for evidence of interstellar (IS) dust grains traversing the solar system. The analysis technique considers IS grains approaching the solar system from the local solar apex. A model calculates the grains' hyperbolic orbits into the solar system and predicts the impact directions on the moon. The observations are then compared with the predicted impact directions to measure the IS dust flux. No evidence has been found (at the 97.5% confidence level) for a flux greater than about 6 hundred-thousandths per sq m/sec for particles of at least 2 by 10 to the -14th power g.
    Keywords: ASTROPHYSICS
    Type: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 63
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    Approximations to microwave attenuation in precipitation (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A three-term approximation and a discrete drop-size distribution have been used to obtain an analytical expression for the microwave attenuation coefficient for precipitation. Results compared to an exact calculation using the same drop size distribution showed a relative difference of 50% or less over a broad range of rainrates (5-150 mm/hr) and wavelengths (2-5 cm). Since the use of a discrete drop-size distribution is computationally complex, the exponential size distribution formulated by Marshall and Palmer (1948) was studied. This distribution resulted in an overprediction of the attenuation coefficient of as much as 100% at a 2 cm wavelength and a 150 mm/hr rainrate, although the prediction was much closer at lower rainrates and different wavelengths.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Conference on Radar Meteorology; Oct 26, 1976 - Oct 29, 1976; Seattle, WA
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  • 64
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    K-band attenuation by rain at constant reflectivity (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The paper considers a radar method of determining rain intensity which uses a dual wavelength system to measure both reflectivity Z and attenuation A and solving for the constants in an assumed exponential drop size distribution. Calculations are confined to the K-band, relations between A and the rain intensity R being determined for different values of Z for wavelengths of 0.86 and 1.24 cm. It is shown that measurements of reflectivity and attenuation by a dual wavelength radar can provide separate derivations of rain intensity. Available data on errors in an A-R relation indicate that the derivation from the attenuation measurement will be no better than from the Z-R relation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Conference on Radar Meteorology; Oct 26, 1976 - Oct 29, 1976; Seattle, WA
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  • 65
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    Accretion flows in binary X-ray systems (1977)
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    Publication Date: 2019-07-13
    Description: Recent developments in the study of accretion flows in binary X-ray systems are reviewed, concentrating on issues concerning the gas flows rather than the radiation mechanisms. A model for Her X-1 is presented which illustrates the main structures expected to exist in the case where mass transfer is by Roche-lobe overflow and the X-ray source is a rotating magnetized neutron star. A model for Cyg X-1 is given which shows the accretion-flow structures to be expected if the compact object is a black hole, including an accretion wake and a very small accretion disk around the black hole. Physical parameters of the accretion flows in these two instances are examined along with some scale lengths that may be derived from these parameters by dimensional analysis. Detailed attention is given to neutron-star magnetospheres (for slow, intermediate, and fast rotators), accretion-disk structure, accretion from stellar winds, and the relationship between X-rays and the gas dynamics of accretion flows. It is suggested that accretion flows in binary X-ray systems be observed directly by means of high-resolution UV and X-ray spectroscopy.
    Keywords: ASTROPHYSICS
    Type: General Assembly of the International Astronomical Union; Aug 24, 1976 - Sep 02, 1976; Grenoble; France
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  • 66
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    Meteor streams in the making (1977)
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    Publication Date: 2019-07-13
    Description: The well-known associations of meteor streams with periodic comets and the probable cometary origin of the zodiacal dust cloud point to the importance, in the cometary debris, of particles with masses exceeding roughly 10 to the -6th gram. It is shown that these large particles dominate in the sunward-oriented anomalous tails of comets. Their study is essential for meaningful estimates of the mass of meteor streams and of the injection rate of the cometary debris that contributes to the zodiacal cloud. Favorable conditions for the detection of anomalous tails can be recognized in advance, as demonstrated by the successful predictions for comets Kohoutek (1973 XII) and Bradfield (1975p). To answer the question as to whether short-period comets can support the zodiacal cloud, a study of anomalous tails at future returns of these comets is considered indispensable.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 67
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    Radiation pressure and Poynting-Robertson drag for small spherical particles (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Robertson's expression for the velocity-dependent effect of solar radiation on the motion of small particles is difficult because of its dependence on relativistic considerations, and it is also deficient in that it assumes perfectly absorbing particles. The present paper gives a heuristic derivation of the Poynting-Robertson effect. Robertson's expression for perfectly absorbing particles is obtained but on a much simpler physical basis, and an expression is also obtained for a particle that in general scatters, transmits, and absorbs light. Some numerical results on the solar radiation forces felt by small particles of cosmochemically important compositions are given.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 68
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    The constitution of cometary nuclei (1977)
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    Publication Date: 2019-07-13
    Description: The nongravitational term in the expression for the total force acting on a comet is calculated, and an upper limit is obtained for the product of the radial nongravitational term times the radius times the square root of the albedo. This condition is satisfied for ten periodic comets with q no greater than 1.5 AU, and the activity of these comets is consistent with control by H2O ice. Some of the comets must be spotty to account for their low albedo values. The effect of cosmic rays on comets, leading to frosting of their surface, is discussed.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 69
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    A digitally implemented communications experiment utilizing the Hermes (CTS) satellite (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The Hermes (CTS) experiment program made possible a significant effort directed toward new developments which will reduce the costs associated with the distribution of satellite services. Advanced satellite transponder technology and small inexpensive earth terminals were demonstrated as part of the Hermes program. Another system element that holds promise for reduced transmission cost is associated with the communication link implementation. An experiment is described which uses CTS to demonstrate digital link implementation and its advantages over conventional analog systems. A Digitally Implemented Communications experiment which demonstrates the flexibility and efficiency of digital transmission of television video and audio, telephone voice and high-bit-rate data is also described. Presentation of the experiment concept which concentrates on the evaluation of full-duplex digital television in the teleconferencing environment is followed by a description of unique equipment that was developed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-73827 , Symp. on Hermes (Comm. Technol. Satellite) its Performance and Appl.; Nov 29, 1977 - Dec 01, 1977; Ottawa, Ontario; Canada
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  • 70
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    New lidar concept for measuring the slant range transmission in aircraft landing approaches (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The single-scatter, single-wavelength, scalar-backscatter lidar equation is investigated to determine the transmission along a line from a point on the ground to what is known as the decision point on the 3 degree aircraft glide slope. It may be applied in aircraft landing approaches for measuring the slant range transmission.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Laser Radar Conference on Laser Atmospheric Studies; Jun 06, 1977 - Jun 09, 1977; Philadelphia, PA; US
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  • 71
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    A measurement of the interstellar C-12/C-13 isotopic abundance ratio toward Zeta Oph from observations of the 3957-A line of CH/+/ (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: ASTROPHYSICS
    Type: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 72
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    Isotope ratios and chemical fractionation of CO in Lynds 134 (1977)
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    Publication Date: 2019-07-13
    Description: A radio observation of (C-12)(O-17) in the dust cloud Lynds 134 is reported, and the question of the (C-13)(O-16)/(C-12)(O-18) ratio across this cloud is considered. A value of approximately 0.28 is obtained for the (C-12)(O-17) column-density ratio, and it is shown that the (C-13)(O-16)/(C-12)(O-18) ratio is very different at two positions in the cloud separated by about 3.75 arcmin. (C-13)(O-16)/(C-12)(O-18) column-density ratios are calculated on the assumption of LTE and found to have a mean value of 4.8 at six positions in the most obscured part of the cloud; the same ratio is determined to be much larger and variable outside the cloud core. It is suggested that chemical fractionation of CO is occurring in this cloud, that (C-13)(O-16) is considerably enriched in its outer regions, and that the cloud's C-12/C-13 ratio is approximately 104.
    Keywords: ASTROPHYSICS
    Type: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 73
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    CNO nucleosynthesis and the nova outburst (1977)
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    Publication Date: 2019-07-13
    Description: Predictions for CNO nucleosynthesis by the classical nova outburst are presented. Properties of the nova phenomenon pertinent to the production of CNO isotopes are discussed, the effect of beta(+) unstable nuclei on outburst evolution is examined, and the need for enhanced CNO nuclei in the envelope is described. Possible mechanisms for producing such enhancement are considered, and recent observations of enhanced CNO nuclei in nova ejecta are reviewed. Results of model evolutionary calculations are outlined which show that a thermonuclear runaway in the hydrogen envelope of a carbon-oxygen white dwarf can reproduce the gross features of the classical nova outburst, that the behavior of the outburst depends at least on the hydrogen-envelope mass and the degree of CNO enhancement, and that all degrees of isotopic enhancement result in an outburst that may be compared with observed events. Two enhancement mechanisms are identified, both of which involve mixing in the envelope.
    Keywords: ASTROPHYSICS
    Type: General Assembly, Special Session no CNO isotopes in astrophysics; Aug 30, 1976; Grenoble; France
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  • 74
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    Spectrum and isotropy of the submillimeter background radiation (1977)
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    Publication Date: 2019-07-13
    Description: Infrared evidence referable to the spectrum and isotropy of the background radiation of the universe is considered, along with theoretical implications. Difficulties in the submillimeter region are indicated. Two types of anisotropy are treated: small-scale granularity (attributable to discrete sources such as galaxies or to condensation in the primordial plasma) and large-scale anisotropies; the anisotropies are discussed as possible indicators of the early history of the universe, and in relation to future possible generalized Michelson-Morley experiments (to detect effects on local physics of the existence of a universal rest frame). A complete blackbody spectrum is seen as the clear signature of the primordial fireball, and slight deviations from a perfect thermal spectrum (or perfect isotropy) are to be sought and scrutinized.
    Keywords: ASTROPHYSICS
    Type: Symposium on Infrared and submillimeter astronomy; Jun 08, 1976 - Jun 10, 1976; Philadelphia, PA
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    A review of the thermonuclear runaway model of a nova outburst (1977)
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    Publication Date: 2019-07-13
    Description: Kraft's (1963) model for a nova outburst caused by a thermonuclear runaway in the hydrogen-rich matter accreted onto the white dwarf in a binary system is reviewed. Hydrostatic and hydrodynamic studies of this phenomenon are summarized, analyses of shock ejection based on hydrodynamic computer codes are discussed, and one specific hydrodynamic code is outlined. Results obtained with this code are presented and evaluated for an initial model containing a white dwarf with a hydrogen-rich envelope of 0.0001 to 0.001 solar mass in hydrostatic and thermal equilibrium. It is shown that an implicit hydrodynamic computer code is required in order to study the thermonuclear-runaway phenomenon. The early evolution of three models with different intrinsic luminosities is illustrated, and enhancement of CNO nuclei at the bottom of the hydrogen-rich envelope is investigated. It is suggested that the concentration of C-13, N-15, and O-17 should be greatly enhanced in nova ejecta.
    Keywords: ASTROPHYSICS
    Type: International Conference on Novae and related stars; Sep 07, 1976 - Sep 09, 1976; Paris; France
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    A Technique for Measuring Rotocraft Dynamic Stability in the 40 by 80 Foot Wind Tunnel (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: An on-line technique is described for the measurement of tilt rotor aircraft dynamic stability in the Ames 40- by 80-Foot Wind Tunnel. The technique is based on advanced system identification methodology and uses the instrumental variables approach. It is particulary applicable to real time estimation problems with limited amounts of noise-contaminated data. Several simulations are used to evaluate the algorithm. Estimated natural frequencies and damping ratios are compared with simulation values. The algorithm is also applied to wind tunnel data in an off-line mode. The results are used to develop preliminary guidelines for effective use of the algorithm.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-151955
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    Meteorological radar facility (MRF) slot conductance investigations (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: A preliminary meteorological radar facility (MRF) array design was completed in support of the slot conductance measurement program. Three different slot measurement techniques were evaluated. The selection of the probe comparison measurement technique was selected as the principal experimental method with the impedance measurement technique chosen to measure a few higher conductance slots to be used as reference slots. The impedance of 43 slots in 0.9 x 0.4 inch standard waveguide and of 40 slots in 0.835 x 0.4 inch waveguide was measured. Also, impedance measurements were made of a few slots using image planes to simulate mutual coupling effects. The measured and theoretical conductance, susceptance, and radiation phase data are presented in graphic form as a function of slot displacement for constant slot length, and of slot length for constant slot displacement. It is concluded that the proposed MRF array design approach is a feasible one.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152465 , P77-20 , HAC-REF-D7036
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  • 78
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    Proceedings: Voice Technology for Interactive Real-Time Command/Control Systems Application (1977)
    In:  CASI
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    Description: Speech understanding among researchers and managers, current developments in voice technology, and an exchange of information concerning government voice technology efforts are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152283 , NAS 1.26:152283 , Voice Technology for Interactive Real-Time Command/Control Systems Application; Dec 06, 1977 - Dec 08, 1977; Moffett Field, CA; United States
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  • 79
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    Surface brightness, standard candles and q/0/ (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The most direct way to determine the deceleration parameter, q(0), of the universe is through the study of the redshift-magnitude relation of extragalactic sources. Progress has been slow because the necessary sources for this study must be standard candles, which have identical absolute total luminosity (balometric or monochromatic). The present paper shows, first of all, that, although necessary, this is not a sufficient condition for nonpoint-like (or resolved) sources. A modification of the redshift-magnitude relation is then described for a certain class of nonstandard candles using measurements of isophotal surface brightness. It is noted that such measurements can be used to standardize the central surface brightness of galaxies, but the standardization of the scale parameter remains beyond observations.
    Keywords: ASTROPHYSICS
    Type: Conference on Redshifts and the expansion of the universe; Sep 06, 1976 - Sep 07, 1976; Paris; France
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  • 80
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    Dust evolution from comets (1977)
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    Publication Date: 2019-07-13
    Description: The studies of the evolution of cometary debris are reviewed. The subject is divided into three major sections: (1) the developments in the immediate vicinity of the cometary nucleus, which is the source of the dust; (2) the formation of the dust tail; and (3) the blending of the debris with the dust component of interplanetary matter. The importance of the physical theory of comets is emphasized for the understanding of the early phase of the evolution of cometary dust. A physico-dynamical model designed to analyze the particle-emission mechanism from the distribution of light in the dust tails is described and the results are presented. Increased attention is paid to large particles because of their importance for the evolution of the zodiacal cloud. Finally, implications are discussed for the future in situ investigations of comets.
    Keywords: ASTROPHYSICS
    Type: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 81
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    A forecast of broadcast satellite communications (1977)
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    Publication Date: 2019-07-13
    Description: This paper presents forecasts of likely changes in broadcast satellite technology, the technology of ground terminals, and the technology of terrestrial communications competitive with satellites. The impacts of these changes in technology are then assessed, using a cross-impact model of U.S. domestic telecommunications, to determine the consequences of various possible changes in communications satellite technology. These consequences are discussed in terms of various possible services, for households, businesses, and specialized customers, which might become economically viable as a result of improvements in satellite technology.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NAECON ''77: National Aerospace and Electronics Conference; May 17, 1977 - May 19, 1977; Dayton, OH
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  • 82
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    Molecular clouds (1977)
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    Description: An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.
    Keywords: ASTROPHYSICS
    Type: Symposium on Star Formation; Sep 06, 1976 - Sep 10, 1976; Geneva; Switzerland
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  • 83
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    Low-temperature condensates in comets (1977)
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    Publication Date: 2019-07-13
    Description: Recent observational data on the volatile fraction of comets are confronted with a model based on the fractional condensation, in the 80-100 K range, of a higher-temperature equilibrium obtained from a solar mixture, more or less depleted in oxygen and in hydrogen. It is possible to almost duplicate the observational data, only by assuming that the solar ratio of C/O is at least as large as 0.66 and that the hydrogen was drastically depleted by an unknown process in the primitive solar nebula. Although none of these two assumptions is at variance with present knowledge, the latter is sufficiently exotic to propose a simpler explanation, namely that comets could be made of interstellar grains relatively unprocessed by heat.
    Keywords: ASTROPHYSICS
    Type: International Colloquium; Aug 17, 1976 - Aug 20, 1976; Lyons; France
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  • 84
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    Experiments in data collection technology using satellites (1977)
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    Publication Date: 2019-07-13
    Description: A variety of techniques potentially useful to data collection have been tested. An automatic data collection platform with a minicomputer collects and preprocesses data, then sends desired information when interrogated through a communication satellite. Position surveillance by tone-code ranging through communication satellites is automatic, real time and accurate. Emergency medical data transmissions from ambulances to hospitals can be extended to rural and remote areas by direct satellite links. A small platform can send emergency-related data through a satellite while the satellite is routinely relaying powerful communication signals. A low orbit satellite provides means to locate existing emergency locator beacons.
    Keywords: COMMUNICATIONS AND RADAR
    Type: AIAA PAPER 77-1563 , Conference on Satellite applications to marine technology; Nov 15, 1977 - Nov 17, 1977; New Orleans, LA
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  • 85
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    Observations of O VI (1977)
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    Publication Date: 2019-07-13
    Description: A useful spectroscopic tracer for a hot phase of interstellar gas is the O VI ion, which reaches its maximum concentration in collisional ionization between 100,000 and 1 million K. Presently, over 70 stars have been observed for O VI absorption by the Copernicus satellite. Nearly all of the stars show broad weak lines, but no evidence favoring a circumstellar origin for the gas can be found. An overall average for the electron density of the hot gas in the galactic plane is of the order of 0.001 per cu cm. The relative volume in space occupied by the hot-gas regions (and hence their internal density) is uncertain, but a filling factor in the range from 0.02 to 0.2 seems most plausible. Fluctuations in radial velocities and column densities suggest there are roughly 6 regions per kpc, each with an O VI column density of approximately 10 trillion per sq cm. The observed rms dispersion of radial velocities for these regions is 26 km/s.
    Keywords: ASTROPHYSICS
    Type: Topics in interstellar matter; Commission 34 Session, General Assembly; Aug 25, 1976; Grenoble; France
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  • 86
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    Effect of interference on delta modulator encoded video signals (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-154523
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  • 87
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    Utilization of NASA Lewis mobile terminals for the Hermes satellite (1977)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The high power of the Hermes satellite enables two-way television and voice communication with small ground terminals. The Portable Earth Terminal (PET) and the Transportable Earth Terminal (TET) were developed and built by NASA-Lewis to provide communications capability to short-term users. The NASA-Lewis mobile terminals are described in terms of vehicles and onboard equipment, as well as operation aspects, including use in the field. The section on demonstrations divides the uses into categories of medicine, education, technology and government. Applications of special interest within each category are briefly described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-73859 , E-9448 , Symp. of Hermes, Commun. Technol. Satellite: Its Performance and Appl.; Nov 29, 1977 - Dec 01, 1977; Ottawa
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  • 88
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    Radial distribution of Beta meteoroids from the Pioneers 8 and 9 cosmic dust experiments (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: ASTROPHYSICS
    Type: Symposium on Minor Constituents and Excited Species; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA; US|Symposium on Minor Constituents and Excited Species; Jun 09, 1976 - Jun 10, 1976
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  • 89
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    Interpretation of cosmological information on radio sources (1977)
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    Description: The question of whether any cosmological information can be obtained from radio astronomy is considered. Specific attention is given to the discovery and cosmological interpretation of the microwave background radiation, attempts to derive a Hubble relation for the optical objects identified with radio sources, searches for relations between the angular diameters of radio sources and the redshifts of their optically identified counterparts as well as between angular diameter and radio flux, construction of log N - log S curves, and luminosity volume tests. A brief outline is given of the situation that might prevail if a significant population of radio sources is not at great distances and is associated with QSOs that have been ejected from relatively nearby galaxies. It is concluded that: (1) some types of cosmological investigations have been premature; (2) much of the discussion in this area still depends on the distances of QSOs; and (3) there is no conclusive proof that the population of radio sources is changing with epoch.
    Keywords: ASTROPHYSICS
    Type: Symposium on Radio astronomy and cosmology; Aug 16, 1976 - Aug 20, 1976; Cambridge
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  • 90
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    Performance of the 12GHz, 200 watt transmitter experiment package for the Hermes satellite (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Performance characteristics from on-orbit tests of the Transmitter Experiment Package (TEP) for the Hermes Satellite are presented. The TEP consists of a Power Processing System (PPS), an Output Stage Tube (OST) and a Variable Conductance Heat Pipe System (VCHPS), all of which are described. The OST is a coupled-cavity Traveling Wave Tube (TWT) with a Multistage Depressed Collector (MDC) and a stepped velocity-tapered slow wave structure for efficiency enhancement. It has an RF output power of 233 watts and overall efficiency of 50.75 percent at a center band frequency of 12.080 GHz. The PPS provides the required operating voltages, regulation, control and protection for the OST. The VCHPS consists of a fin radiator and three dual-artery stainless steel heat pipes using methanol and a mixture of inert gases. Test results presented include efficiencies, RF output power and body current. A discussion of thermal anomalies which occurred is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-73804 , E-9385 , Symp. on Hermes (Communications Technol. Satellite) its Performance and Applications; Nov 29, 1977 - Dec 01, 1977; Ottawa
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  • 91
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    A theoretical investigation of isotopic anomalies of xenon in terrestrial and extra-terrestrial samples (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The abundance and isotopic composition of noble gases in meteorites is discussed in relation to the composition of the early solar system. Carbonaceous chondrites contain a unique Xenon-X, which is rich in heavy and light isotopes. Variations in the occurrence of type-X and type-Y (the normal component) noble gases are of such magnitude that neither the injection of material from a nearby supernova nor presence of presolar grains can account for the anomalies in meteorites. Therefore, it is suggested that the entire solar system may have condensed from the debris of a single local supernova.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-155255
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  • 92
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    Computer simulation of plasma and N-body problems (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Any spiral structure in computer-generated galaxies is generally short lived and the final state is a rotating bar. The bar thus obtained rotates more slowly than the stars. It has been argued that core/halo components have a stabilizing effect on galaxies and result in longer lived spiral structure. However, numerical experiments with large fixed stellar components representing the core/halo component show that multiarmed spiral structure develops and persists for many rotations but only in an evolving manner. That is, the spiral structure is either wound up into a tight pattern or it is wound up and then reappears again. A recent study of the effect of fixed core/halo components does show that the bar instability is indeed inhibited by a sufficiently large fixed component. The present study determines the effect of a self-consistent (rather than fixed) core/halo component in order to show whether there are any instabilities (such as two-stream) or other important interactions present that may be suppressed with a fixed core. Also studied were the effects of finite thickness of the disk and of three-dimensional essentially spherical core/halo components.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-155517 , PGSTR-PH77-66
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  • 93
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    Coherent optical processing of synthetic aperture radar data (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Consideration is given to the data processing algorithm used in synthetic aperture radar (SAR) systems. Examples are presented of radar imagery obtained with the ERIM X-band SAR system and processed with a precision optical processor. An optical recording of the data is the input to the coherent optical processing channel. The encoding technique, spatial format, and quality of the stored data are discussed. Several optical processor configurations are outlined, noting particularly the tilted-plane system. A scanning photodetector serves to convert the optical processor output image data into an electronic signal stream. Solid-state two-dimensional photodetector arrays may provide this function at increased speeds and with greater accuracy.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Effective utilization of optics in radar systems; Symposium; Sep 27, 1977 - Sep 29, 1977; Huntsville, AL
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  • 94
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    Study of large adaptive arrays for space technology applications (1977)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The research in large adaptive antenna arrays for space technology applications is reported. Specifically two tasks were considered. The first was a system design study for accurate determination of the positions and the frequencies of sources radiating from the earth's surface that could be used for the rapid location of people or vehicles in distress. This system design study led to a nonrigid array about 8 km in size with means for locating the array element positions, receiving signals from the earth and determining the source locations and frequencies of the transmitting sources. It is concluded that this system design is feasible, and satisfies the desired objectives. The second task was an experiment to determine the largest earthbound array which could simulate a spaceborne experiment. It was determined that an 800 ft array would perform indistinguishably in both locations and it is estimated that one several times larger also would serve satisfactorily. In addition the power density spectrum of the phase difference fluctuations across a large array was measured. It was found that the spectrum falls off approximately as f to the minus 5/2 power.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-152593 , VFRC-112
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  • 95
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    Contributions of speech science to the technology of man-machine voice interactions (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Research in speech understanding was reviewed. Plans which include prosodics research, phonological rules for speech understanding systems, and continued interdisciplinary phonetics research are discussed. Improved acoustic phonetic analysis capabilities in speech recognizers are suggested.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NADC, Proceedings: Voice Technology for Interactive Real-Time Command(Control Systems Application; p 25-44
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  • 96
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    RF environment survey of Space Shuttle related EEE frequency bands (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Radio frequency assignments within the continental United States in frequency bands between 121 MHz abd 65 GHz were surveyed and analyzed in order to determine current utilization of anticipated frequency bands for the shuttle borne electromagnetic environment experiment. Data from both government and nongovernment files were used. Results are presented in both narrative form and in histograms which show the total number of unclassified assignments versus frequency and total assigned power versus frequency.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-160081 , NSL-21-136
    Format: application/pdf
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  • 97
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    Clutter free synthetic aperture radar correlator (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A synthetic aperture radar correlation system including a moving diffuser located at the image plane of a radar processor is described. The output of the moving diffuser is supplied to a lens whose impulse response is at least as wide as that of the overall processing system. A significant reduction in clutter results is given.
    Keywords: COMMUNICATIONS AND RADAR
    Format: application/pdf
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  • 98
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    The Viking Relativity Experiment (1977)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Measurements of the round-trip time of flight of radio signals transmitted from the earth to the Viking spacecraft are being analyzed to test the predictions of Einstein's theory of general relativity. According to this theory the signals will be delayed by up to approximately 250 microsec owing to the direct effect of solar gravity on the propagation. A very preliminary qualitative analysis of the Viking data obtained near the 1976 superior conjunction of Mars indicates agreement with the predictions to within the estimated uncertainty of 0.5%.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research; 82; 28; 4329-4334
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  • 99
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    The interstellar medium in the direction of the Crab Nebula - Reconciling soft X-ray and radio observations (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The total soft X-ray photoabsorption cross section of the interstellar medium (ISM) in the direction of the Crab Nebula is computed on the basis of a two-phase model of the ISM. This cross section is used to reanalyze Copernicus data on the X-ray spectrum of the Crab between 0.7 and 1.5 keV. The total hydrogen column density along the line of sight to that nebula is found to be approximately 2.6 by 10 to the 21st power H atoms/sq cm. This result is evaluated in light of the two-phase model of the ISM, and the predictions based on the X-ray data are compared with results of radio and UV observations. A discrepancy between the radio and X-ray measurements of the hydrogen column density is resolved by noting that 21-cm absorption measurements sample only the neutral hydrogen in clouds while X-ray measurements are sensitive to all forms of hydrogen in both cloud and intercloud regions. It is suggested that roughly 50% of the hydrogen in the direction of the Crab Nebula is in clouds and that 85% of this hydrogen is neutral and atomic.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 61; 3; Nov. 197
    Format: text
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  • 100
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    Absorption of X-rays in the interstellar medium (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The X-ray photoabsorption cross sections (per hydrogen atom) of interstellar clouds and the intercloud medium are calculated separately, taking into account abundance evolution, self-blanketing by grains, molecule formation, and ionization structure. A reference cross section describing a neutral monatomic gas of elements in solar abundances is computed for purposes of comparison, the cross section of the intercloud medium is calculated by assuming that 15% of the hydrogen is ionized, and the cross section of the clouds is computed for the cases where all hydrogen is in either molecular or atomic form. A comparison of the reference cross section with the others shows that a cross section is increased relative to the reference if abundances are enhanced or if molecular hydrogen exists and is decreased if atoms exist in grains or if hydrogen is ionized. It is noted that the total cross section will be a linear combination of the cross sections of the clouds and the intercloud medium and can reflect the characteristics of a particular line of sight.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 61; 3; Nov. 197
    Format: text
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