Measurement of terrestrial radio noise.
Terrestrial radio noise from lightning discharges measured by Ariel 3 satellite to deduce sources distribution
Bent, R. B.↗
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The potential calculation and some applications
Potential calculation from given source distribution, including direct and iterative methods, error analysis, convergence, computer programs and applications in plasma physics
Hockney, R. W.↗
Radio Astronomy Explorer (RAE) 1 observations of terrestrial radio noise
Radio Astonomy Explorer (RAE) 1 data are analyzed to establish characteristics of HF terrestrial radio noise at an altitude of about 6000 km. Time and frequency variations in amplitude of the observed noise well above cosmic noise background are explained on the basis of temporal and spatial variations in ionospheric critical frequency coupled with those in noise source distributions. It is shown that terrestrial noise regularly breaks through the ionosphere and reaches RAE with magnitudes 15 or more db higher than cosmic noise background. Maximum terrestrial noise is observed when RAE is over the dark side of the Earth in the neighborhood of equatorial continental land masses where thunderstorms occur most frequently. The observed noise level is 30-40 db lower with RAE over oceans.
Herman, J. R.↗
A generalized theory on the noise generation from supersonic shear layers.
A generalization is presented of Phillips' (1960) theory of noise generation by supersonic turbulent shear layers. Both Mach wave radiation and non-Mach wave noise radiation mechanisms are considered. The range of validity of Phillips' theory has been expanded to include the low supersonic and transonic ranges. These generalizations are important not only for their analytical rigor, but also for their prospective applications to practical problems in jet noise prediction and control. The noise generation mechanisms in a supersonic jet are found to differ from those in a subsonic jet. The theory is considered to offer some prospects of answering important questions in supersonic jet noise, such as noise source distribution, mean flow refraction effects, directivity, spectrum, and efficiency of noise radiation.
Pao, S. P.↗
Aeroacoustic characteristics of jet flap type exhausts.
This work which is intended to shed more light on the acoustic and fluid dynamic characteristics of jet flap type exhaust flows, reports and discusses some typical experimental results obtained with cold model air jets in a reverberation chamber. Acoustic data on the total sound power output and the overall noise spectrum of various jet flap configurations are given and compared with data from conventional circular jets. In addition various flow data for the same jets resulting from hot wire measurements are reported and general conclusions are obtained regarding the expected noise source distribution. The results indicate the dependence of the acoustic and flow characteristics on the major nozzle parameters. For the jet flaps the total radiated sound power is found to follow a 3 to 6 power of the exhaust velocity while for the circular jets the 8 power law is confirmed. The noise produced in the secondary mixing region downstream of the flap trailing edge tends to exceed the noise issuing from the primary mixing region.
Gruschka, H. D.↗
Production and propagation of particles with A greater than 81 in the Galaxy.
A detailed mathematical model is developed to describe the transformation of the charge composition of superheavy (A greater than 81) cosmic rays by spallation on interstellar hydrogen in the Galaxy. If one takes a single source which suddenly injects particles with an r-process charge spectrum t years in the past, the calculated relative abundance ratios in four atomic mass groups are consistent with measured values for t equal to 250,000 years. We further conclude that for any initial source distribution the upper limit on t is 1 m.y.
Kaiser, T. B.↗
Transmitter and receiver antenna gain analysis for laser radar and communication systems
A comprehensive and fairly self-contained study of centrally obscured optical transmitting and receiving antennas is presented and is intended for use by the laser radar and communication systems designer. The material is presented in a format which allows the rapid and accurate evaluation of antenna gain. The Fresnel approximation to scalar wave theory is reviewed and the antenna analysis proceeds in terms of the power gain. Conventional range equations may then be used to calculate the power budget. The transmitter calculations, resulting in near and far field antenna gain patterns, assumes the antenna is illuminated by a laser operating in the fundamental cavity mode. A simple equation is derived for matching the incident source distribution to a general antenna configuration for maximum on-axis gain. An interpretation of the resultant gain curves allows a number of auxiliary design curves to be drawn which display the losses in antenna gain due to pointing errors and the cone angle of the outgoing beam as a function of antenna size and central obscuration. The use of telescope defocusing as an approach to spreading the beam for target acquisition is compared to some alternate methods.
Klein, B. J.↗
Characteristics of the lunar photoelectron layer in the geomagnetic tail.
The charged particle lunar environment experiment, a part of the Apollo 14 lunar surface package, is an ion-electron spectrometer capable of measuring ions and electrons with energies between 40 eV and 50 keV. The instrument, with apertures 26 cm above the surface, has detected a photoelectron gas layer above the sunlit lunar surface. No detectable flux above 200 eV has been observed. Experimental data for periods while the moon was in the earth's magnetotail for electrons with energies 40 eV less than or equal to 200 eV follow a power-law spectrum. In the absence of photoelectrons with E greater than 200, we assume that the surface potential is at least 200 V. The modulation of this potential in the presence of intense plasma-sheet fluxes has been observed. Also, a detailed history of the Feb. 10, 1971, total lunar eclipse, to determine the source distribution of high-energy solar photons, is presented.
Reasoner, D. L.↗
Anisotropy of the neutron fluence from a plasma focus.
The fluence of neutrons from a plasma focus was measured by gamma spectrometry of an activated silver target. This method results in a significant increase in accuracy over the beta-counting method. Multiple detectors were used in order to measure the anisotropy of the fluence of neutrons. The fluence was found to be concentrated in a cone with a half-angle of 30 deg about the axis, and to drop off rapidly outside of this cone; the anisotropy was found to depend upon the total yield of neutrons. This dependence was strongest on the axis. Neither the axial concentration of the fluence of neutrons nor its dependence on the total yield of neutrons is explained by any of the currently proposed models. Some other explanations, including the possibility of an axially distributed source, are considered.
Lee, J. H.↗
On the isotropy of the X-ray background radiation.
The spatial fluctuations expected for various models of the X-ray background radiation are examined. The constraints that observations place on the source distribution and radiation mechanisms are then presented. Most models are at present consistent with the lack of observed small scale anisotropy. Future measurements of the beam-to-beam fluctuations could offer a positive test of the inverse Compton explanation for the origin of the X-ray background radiation.
Brecher, K.↗
Radio Astronomy Explorer /RAE/. I - Observations of terrestrial radio noise.
Radio Astronomy Explorer (RAE) I data are analyzed to establish characteristics of HF terrestrial radio noise at an altitude of about 6000 km. Time and frequency variations in amplitude of the observed noise well above cosmic noise background are explained on the basis of temporal and spatial variations in ionospheric critical frequency coupled with those in noise source distributions. It is shown that terrestrial radio noise regularly breaks through the ionosphere and reaches RAE with magnitudes 15 dB and more above cosmic noise background, on frequencies above the F-layer critical frequency.
Herman, J. R.↗
Some recent developments in cometary physics.
Recent observations and associated theoretical developments bearing on the composition and structure of comets are briefly reviewed. The physical and dynamical processes in cometary atmospheres and ionospheres are discussed, and detailed hydrodynamic models of expanding multiconstituent cometary atmospheres corresponding both to a central nucleus as well as a central nucleus surrounded by a distributed source are presented for comparison with observation. It is argued that observed 'slow' speed for the neutral hydrogen is not incompatible with a purely H2O 'parent' source for that species.
Mendis, D. A.↗
Sound measurements within and in the radiated field of an annular duct with flow.
Recent theory on sound propagation for flow ducts initiated a research program (sponsored by NASA-Langley, Contract NAS1-10472) which has the objective of comparing detailed acoustical measurements with the analytical predictions for sound propagation in a duct with sheared flow. The effects considered experimentally mean flow, shear, wall impedance, and source distribution on sound propagation within and radiation from finite lenght annular ducts. Results reported here are confined to acoustic distribution in hard annular ducts with and without mean flow and radiated field patterns for the same conditions. The acoustic distributions are shown for single and multi-mode excitation. The flow duct facility is also described.
Plumblee, H. E.↗
An Analytical Investigation of Wing-Jet Interaction
The aerodynamic interaction between the wing and an inviscid jet with Mach number nonuniformity is formulated by using a two-vortex-sheet model for the jet. One of the vortex sheets accounts for the induced jet flow and the other the induced outer flow. No additional source distribution is needed for the jet at an angle of attack. The above problem is solved by satisfying the jet and wing tangency and the jet pressure-continuity conditions and using a quasi vortex lattice method for computing the induced flow field. The latter method is derived through theoretical consideration by properly accounting for singularities present in the equations and possesses the same simplicity and generality as the conventional vortex lattice method but has a better rate of numerical convergence. The resulting system of algebraic equations is solved by Purcell's vector method. The numerical formulation is first applied to the wing-slipstream interaction problem. Results for one centered-jet configuration are compared with those predicted by some existing theories.
Lan, E. C.↗
An analytical study of the effects of jets located more than one jet diameter above a wing at subsonic speeds
A procedure has been developed to calculate the effects of blowing two jets over a swept tapered wing at low subsonic speeds. The algorithm used is based on a vortex lattice representation of the wing lifting surface and a line sink-source distribution to simulate the effects of the jet exhaust on the wing lift and drag. The method is limited to those cases where the jet exhaust does not intersect or wash the wing. The predictions of this relatively simple procedure are in remarkably good agreement with experimentally measured interference lift and interference induced drag.
Putnam, L. E.↗
An analytical study of the effects of jets located more than one jet diameter above a wing at subsonic speeds
A procedure has been developed for calculating the effects of blowing two jets over a swept tapered wing at low subsonic speeds. The algorithm used is based on a vortex-lattice representation of the wing lifting surface and a line sink-source distribution to simulate the effects of the jet exhaust on the wing lift and drag. The method is limited to those cases in which the jet exhaust does not intersect or wash the wing. The predictions of this relatively simple procedure are in remarkably good agreement with experimentally measured interference lift and interference induced drag.
Putnam, L. E.↗
Magnetisation of comets
Construction of a model explaining the means by which the interplanetary magnetic field could mix with the plasma of a comet tail. It is suggested that the magnetic fields in comet tails derive from the hydromagnetic conversion of kinetic energy into magnetic energy in the nuclear region of the comet. In particular, it is shown that, if the nuclear region consists of a supplementary distributed source for the coma gases, a turbulent flow with maximum velocities of the order of thermal velocity may be expected in this region, with the necessary ordering in the turbulent velocity field provided by the rotation of the nuclear region. It is concluded that a comet, when sufficiently close to the sun, may be able to generate an appreciable magnetic field and that the magnetic fields observed in the tail may then result from processes analogous to those producing the earth's magnetotail.
Mendis, A.↗
The third Uhuru catalog of X-ray sources
A new edition of the catalog of X-ray sources observed with Uhuru is presented. About 125 days of data have been analyzed for the 3U catalog, yielding a total of 161 X-ray sources. The distribution of sources is similar to that obtained for earlier editions of this catalog. Location error regions for many of the sources previously listed in the 2U catalog have been significantly reduced in size.
Giacconi, R.↗