Showing papers on "Point source published in 1975"
TL;DR: In this article, the sound field due to a point source above a plane boundary with a constant normal impedance was obtained by a double saddle point method of integration, which is similar to the one used in this paper.
193 citations
TL;DR: In this article, a steady-state, three-dimensional turbulent diffusion equation describing the concentration distribution of an air pollutant from an elevated point source in the lower atmosphere is solved analytically.
Abstract: A steady-state, three-dimensional turbulent diffusion equation describing the concentration distribution of an air pollutant from an elevated point source in the lower atmosphere is solved analytically. The same formulation can be used to obtain solutions from line, area or other kinds of sources. The solution is developed for the cases in which the velocity, vertical and lateral diffusivities are given by the power law. The model preserves the beauty of analytical solution without sacrificing much on the accuracy of approximating the velocity and eddy diffusivities. Methods of evaluating the parameters, which are required for the model applications, are discussed. Results indicate that the ratio of the plume width to the plume length increases with decreasing stability and with increasing source height. These consequences are in response to the variations of the size of eddies in the vertical direction.
61 citations
TL;DR: In this paper, the generalized ray technique was used to study the SH impulse response of layered medium resulting from the application of a point source shear dislocation, and a comparison of synthetic seismograms with observations from a central California earthquake of magnitude 4.6 indicates a moment of 2.1×1022 ergs with a faulting duration of 0.5 s.
Abstract: The SH impulse response of layered medium resulting from the application of a point source shear dislocation is studied by the generalized ray technique. Numerical seismograms of ground displacement in the range 10–100 km are constructed for a number of different crustal models and source descriptions. The results for shallow events show severe wave form modifications at epicentral distances as small as twice the source depth when models contain soft surface layers. A comparison of synthetic seismograms with observations from a central California earthquake of magnitude 4.6 indicates a moment of 2.1×1022 ergs with a faulting duration of 0.5 s. This moment is noticeably smaller than that estimated from the low frequency level of the whole seismogram spectrum assuming the usual homogeneous half-space model. This occurs because the energy arriving with the surface waves and deep crustal reflections boosts the long period portion of the spectrum, giving the impression of an anomalously large moment when calculated in the conventional manner. The close agreement between synthetic results and the actual data both in the time and in the Fourier transform domain suggests that our deterministic approach can be quite useful in understanding the complexity of seismograms recorded in the local field.
61 citations
TL;DR: In this article, the power spectrum of a turbulence-degraded image of a point source as a function of exposure time is derived based on the near-field Rytov-Kolmogorov approximations and the Taylor hypothesis.
Abstract: Mathematical expressions are obtained for the power spectrum of a turbulence-degraded image of a point source as a function of exposure time. Calculations are based on the near-field Rytov–Kolmogorov approximations and the Taylor hypothesis. Comparisons with available data are satisfactory.
39 citations
TL;DR: In this article, the authors used a rotation modulation collimator to measure the positions of X-ray sources, which was built by the Mullard Space Science Laboratory and used to respond to X rays in the quantum energy range 3.1-9.3 keV.
Abstract: THE satellite Ariel V, launched on October 15, 1974, as part of the US-UK collaborative space programme, contains a rotation modulation collimator experiment designed to measure the positions of X-ray sources, which was built by the Mullard Space Science Laboratory. The experiment responds to X rays in the quantum energy range 3.1–9.3 keV, the area of the proportional counters being 256 cm2 which, allowing for grid transmission, counter efficiency and so on, leads to an effective area of 102 cm2 at 6.0 keV. The pitch-to-separation ratio of the collimator grids is 112, corresponding to a full width at half maximum (FWHM) of the image of a point source of 15′ (ref. 1). The spin axis was manoeuvred to point towards a number of sources in succession in the Centaurus region, including the important binary source Cen X-3, from December 17, 1974 to January 31, 1975, to carry out position and spectrum determinations. Soon after arriving at the first pointing direction in the sequence, a correlation map produced by overlaying data from orbits obtained on December 17–19 showed the presence of a new source not listed in the Uhuru (3U) catalogue, which we have designated A1118-61 from the position given below. The field of view of the experiment is 17° FWHM, so that the light curve could be followed over an interval of 46 d. The light curve is given in Fig. 1 in units of counting rate in our detector, which can be converted approximately to Uhuru counts by multiplication by 8. In the initial and final periods of observation, the source was rather weak, and could be detected at a satisfactory significance only by overlaying orbits, with a consequent reduction in time resolution. The latter improved to one orbit (101 min) when the source was near its maximum brightness. We have, for clarity, averaged the intensity over 12 h in this period, but significant intensity variations, exceeding those attributable to counting statistics, were observed in the one-orbit averages. Where an upper limit only is given, it corresponds to three standard deviations of the background level.
37 citations
TL;DR: In this paper, an analytical expression for the illuminance over a receiver surface and an equation for the caustic surface are derived for rays which have passed through a multi-interface optical system.
Abstract: An analytical expression for the illuminance over a receiver surface and an equation for the caustic surface are derived for rays which have passed through a multi-interface optical system. The results are expressed in terms of the intrinsic geometry of the deflector surface, that is, the Gaussian, mean, and normal curvatures, and the derivative of the incident ray vector over the deflector surface. The original source may be a plane wave, a point source, or an extended source. As a numerical example of this technique, the caustic surface and the line-spread function on different image planes are plotted for an off-axis point source of light whose rays are refracted by a thick double convex lens.
37 citations
TL;DR: In this article, a general perturbation theory for small surface waveheights and for acoustic wavelengths of the order of the ocean surface correlation length is presented and formal solutions for the perturbed field are given and specialized, to the second order of approximation, for the case of a random ocean surface.
Abstract: A general perturbation theory is presented which is valid for small surface waveheights and for acoustic wavelengths of the order of the ocean‐surface correlation length. Formal solutions for the perturbed field are given and are specialized, to the second order of approximation, for the case of a random ocean surface. The scattering reduces the intensity of the carrier (source) signal and creates signal sidebands that are not in general symmetric in amplitude about the carrier. A pair of system functions for the signal sidebands is defined.Subject Classification: 30.40, 30.30, 30.25; 20.15.
24 citations
TL;DR: In this paper, the theoretical surface displacements due to various types of propagating faults located in a semi-infinite medium are obtained and compared with those for an infinite medium.
Abstract: Integrating a point source solution derived in the preceding paper by KAWASAKI et al. (1973), theoretical surface displacements due to various types of propagating faults located in a semi-infinite medium are obtained and compared with those for an infinite medium. General features of wave forms are summarized as follows; (1) Except for SP wave and Rayleigh wave portions, horizontal components Ur and Uφ of free surface displacement are approximately given by doubling the corresponding displacements for an infinite medium. The vertical component Uz is much disturbed by the free surface. (2) The SP wave has an appreciable amplitude comparable to that of P wave as pointed out for a point source case by KAWASAKI et al. (1973). Especially in such cases as shallow sources propagate upward, the SP wave becomes a remarkably marked phase. Hence, careful examinations for SP wave are required on analysing the near-field seismograms, especially for shallow focus earthquakes.
24 citations
TL;DR: In this paper, an analytic solution is constructed for arbitrary Prandtl number and arbitrary direction of the unperturbed flow in the case of a plume produced by a point source, and a Stokes-type paradox occurs: it is found that a line-source solution that vanishes at infinity does not exist.
Abstract: When the buoyancy forces are small compared with the inertia forces, heated plumes in laminar flows which are uniform at upstream infinity approximately satisfy a linearized version of the Boussinesq equations, here called the Oseen–Boussinesq equations. An analytic solution is constructed for arbitrary Prandtl number and arbitrary direction of the unperturbed flow in the case of a plume produced by a point source. The two-dimensional case of the plume from a line source is considered briefly. A Stokes-type paradox occurs: it is found that a line-source solution that vanishes at infinity does not exist.
17 citations
TL;DR: In this paper, a perturbation procedure is applied, through the second order approximation, to the three-dimensional problem of scattering of sound from a point source by a rough surface progressing in the wind direction over an isovelocity ocean.
Abstract: A perturbation procedure is applied, through the second order of approximation, to the three‐dimensional problem of scattering of sound from a point source by a rough surface progressing in the wind direction over an isovelocity ocean. The results satisfy conservation of energy, in a ray‐theoretic sense, and are uniformly valid throughout the field. At points in the region of surface‐image interference (Lloyd’s‐mirror region), the signal is shown to be strongly modulated. Results are presented which depict the power in the carrier and signal sidebands. The latter are not, in general, symmetric in amplitude about the carrier. However, it is demonstrated analytically that, on two specific planes in the field, the signal power spectrum is symmetric about the carrier.Subject Classification: 30.40, 30.20, 30.25.
16 citations
TL;DR: A theoretical analysis is presented which shows that the depth distribution of activity is not correct for a dual opposed detector system, because of self-attenuation of the photons by the organ (or source).
Abstract: Most methods used to estimate the absolute organ content of a gamma-emitting radionuclide from external counting measurements assume that the depth distribution of activity is equivalent to a point source of the same activity located at an 'effective' depth. A theoretical analysis is presented which shows that this assumption is not correct of a dual opposed detector system, because of self-attenuation of the photons by the organ (or source). Experimental verification is also given, and it indicates that the error caused by this assumption is normally less than 10%, although it can be very large in special cases.
Patent•
09 Jul 1975
TL;DR: The laser target simulator of as discussed by the authors comprises two point sources of light energy (LEDs) aimed at a section of concave spherical mirror which collimates the light energy and projects it across the full aperture of a laser seeker.
Abstract: The laser target simulator of the invention comprises two point sources of light energy (LEDs) aimed at a section of concave spherical mirror which collimates the light energy and projects it across the full aperture of a laser seeker. One of the point sources of light energy is positioned on the laser seeker boresight at the mirror focal point. The other is positioned in spaced adjacent relationship to it and is rotatable about the laser seeker boresight. A CW light source is positioned coaxially to the boresight point source of light. The simulator also includes light source control circuits that make it possible to test the various operational modes of the laser seeker including tracking rates and accuracies, acquisition logic, laser pulse coding, and false target rejection.
TL;DR: The diffraction losses associated with absolute radiometers were calculated using Blevin's treatment, which assumes a point source and a single diffracting aperture, and it is shown that this treatment is sufficiently accurate for a typical absolute radiometer configuration.
Abstract: The diffraction losses associated with absolute radiometers were calculated for the case where the source is a tungsten lamp used with a long wavelength suppressing filter. The calculations were done using Blevin’s treatment, which assumes a point source and a single diffracting aperture. We have shown that this treatment is sufficiently accurate for a typical absolute radiometer configuration. The calculations were done for color temperatures in the 1600–3200 K range for three typical glass filters.
TL;DR: In this article, an exact expression for the surface displacement in an elastic half space due to a buried moving point source has been derived and compared with those of a stationary point source.
Abstract: Summary Exact expression for the surface displacement in an elastic half space due to a buried moving point source has been derived. The disturbance is generated by a point source moving along a line inclined to the free surface with a constant velocity. Both the supersonic and subsonic cases are considered. Effect of the moving source on the surface displacement is discussed in detail. Theoretical seismograms for both supersonic and subsonic sources are constructed and compared with those of the stationary source. Results show that surface displacements for a subsonic source differ only in the relative amplitude from those for a stationary source. In case of a supersonic source additional conical phases appear on the surface and surface displacements are significantIy different from those of the stationary source. A moving source is a more realistic model of the mechanism of earthquakes than a stationary source. Ben-Menahem (1 962) proposed an approximate method for taking into account the effect of moving sources on theoretical seismograms as far as body waves are concerned. Most of the exact theory for moving sources to date is concerned with moving line loads. Payton (1967) used Betti’s reciprocal theorem to obtain surface displacements due to a buried line load. Mention can also be made of the works of Mandel & Avramesco (1961), Eason (1964), Cole & Huth (1958), Ang (1960). Papadopoulos (1963) considered in brief the effect of the motion of a point source on the response of an elastic half space. However, his method is open to question (Longman 1965). Gakenheimer & Miklowitz (1969) first showed that the CagniardDe Hoop technique can be applied to obtain displacements inside an elastic half space due to a point source moving along the surface. In this paper we extend their results to a more realistic buried source problem. We represent the disturbance at the focus of an earthquake by a point source moving with uniform velocity along a straight line inclined to the surface. The model of the earth is taken to be an elastic half space. For explaining the characteristics of initial pulses in an actual seismogram, an elastic half space is an adequate model of the real earth, the layering effect being prominent only in case of later pulses. Thus the results of the present paper can be used fruitfully for the exact calculation of the theoretical pulse, so as to give an additional check in obtaining the velocity of fracture propagation and other parameters associated with earthquake foci.
Patent•
13 Jan 1975
TL;DR: In this paper, the authors proposed a method to determine spectral and positional information of a point source of optical radiation in a relatively wide field of view by using a narrow bandpass filter for enabling approximately monochromatic energy of the source to impinge on a second detector means displaced from the first detector means.
Abstract: A scanner having an instantaneous narrow field of view determines spectral and positional information of a point source of optical radiation in a relatively wide field of view. A first optical path includes the scanning means, a dispersion means, and a first detector means so that different wavelengths of the source are convoluted to impinge on the first detector means at different times during a scan of the field of view. A second optical path includes the scanning means, the second detector means, and a narrow bandpass filter for enabling approximately monochromatic energy of the source to impinge on a second detector means displaced from the first detector means. Thereby, a predetermined wavelength is imaged on the second detector means at a time during a scan that differs from the time when that wavelength is imaged on the first detector means, even though the source angular position in the field of view is substantially the same for both of the optical paths. To enable the system to be responsive only to point sources, to the exclusion of nonpoint sources, each of the first and second detector means is divided into a multiplicity of separate, spaced detector elements. Each of the detector elements has a length in the direction of scan no greater than the length of the point source imaged on the first and second detector means. In response to the amplitude of energy impinging on the elements of the second detector means, a signal replica of the convoluted spectral energy impinging on one of the elements of the first detector means is coupled to a signal processing network that recognizes point sources having a predetermined spectral signature and enables the position of the recognized sources to be determined.
TL;DR: In this article, the theoretical attenuation of traffic noise by long barriers has been studied, by using a Monte Carlo snapshot technique for description of individual vehicle contributions, and the results compared with those obtained when line and point source approximations are used for the traffic noise source.
01 Mar 1975
TL;DR: In this article, a theoretical analysis of the acoustic wave field radiated by a time-harmonic point source in a homogeneous, isotropic turbulent medium is presented, where the smoothing method is used to study the incoherent, or randomly fluctuating, component of the wave field.
Abstract: A theoretical analysis of the acoustic wave field radiated by a time-harmonic point source in a homogeneous, isotropic turbulent medium is presented. The smoothing method is used to study the incoherent, or randomly fluctuating, component of the wave field. The analysis considers the effect on the wave of the velocity fluctuations, as well as the index-of-refraction fluctuations, of the medium. An approximate expression for the second moment of the incoherent wave is obtained for the case in which the wavelenght is much less than the minimum correlation length of the medium. This expression shows that the fluctuations of the wave increase initially in proportion to the propagation distance, but that at larger distances they tend to a limiting, or saturation, value. These results agree with observations of waves propagating in real media. It is also found that the mean square of the total (i.e., coherent plus incoherent) acoustic pressure is unaffected by the randomness of the medium.
TL;DR: In this paper, the Westerbork Synthesis Radio Telescope (WSRT) at 1.415 GHz was used to detect an arc-shaped source partially encircling a point source centred on NGC7319.
Abstract: RADIO observations have been reported for several apparently interacting astronomical systems1,4. These observations do not provide conclusive data as to the frequency of occurrence of radio emission from multiple systems compared with that for normal galaxies. Although the detected radio fluxes do not generally fall in the ‘radio galaxy’ range, there is evidence that for some interacting systems at least, there is a statistical excess of the number of radio sources in their vicinity5,6. The aperture synthesis observations mostly show sources coincident with member galaxies; a few show emission from regions between the galaxies. In the case of Stephan's Quintet, observations7 with the Westerbork Synthesis Radio Telescope (WSRT) at 1.415 GHz suggest an arc-shaped source partially encircling a point source centred on NGC7319.
TL;DR: In this paper, near-infrared plates of a region in Cygnus show an extremely red nebula, about 25 arc seconds in diameter, which is displaced by about 18 arc seconds from UOA 27, an object with infrared and microwave properties similar to those of the Becklin-Neugebauer point source in Orion.
Abstract: Near-infrared plates of a region in Cygnus show an extremely red nebula, about 25 arc seconds in diameter, which is displaced by about 18 arc seconds from UOA 27, an object with infrared and microwave properties similar to those of the Becklin-Neugebauer point source in Orion. This nebula may be reflecting light from the same obscured star which is the energy source for UOA 27, and could therefore provide a unique, though indirect, means of investigating the nature of stars which heat the BN point source and related objects.
TL;DR: In this article, a two-dimensional isotropic solid is given a static homogeneous deformation, and a point perturbing body force is then superposed on this finite deformation causing anisotropic elastic waves to spread outward from the origin.
TL;DR: In this article, a method for determining the thickness dimensions of a thick, covered, extended source for the purpose of accurately calculating photon-intensity corrections for such a source is presented, and an approximation is developed for obtaining the solid angle subtended by a cylindrical aperture at a point source.
TL;DR: In this article, the propagation of sound from a point source placed in a subsonic jet separated by two plane vortex sheets from two semi-infinite still media is considered and it is found that instability waves arise at particular points on the vortex sheets and that their effect is confined to certain regions.
Abstract: The propagation of sound from a point source placed in a subsonic jet separated by two plane vortex sheets from two semi-infinite still media is considered and it is found that instability waves arise at particular points on the vortex sheets and that their effect is confined to certain regions.
TL;DR: In this paper, a normal mode approach that solves the wave equation governing underwater sound propagation from a point source with directivity expressible as an expansion in spherical multipoles is summarized and extended by the development of a general theory of propagation loss for multipole sources of arbitrary order.
Abstract: A normal‐mode approach that solves the wave equation governing underwater sound propagation from a point source with directivity expressible as an expansion in spherical multipoles is summarized. The theory is extended by the development of a general theory of propagation loss for multipole sources of arbitrary order. Exact long‐range pressure field and propagation loss expressions are developed and presented for the first three multipole orders. Numerical results of the pressure fields and the propagation loss for monopole, dipole, and quadrupole sources are presented for the case of a realistic sound‐speed profile.Subject Classification: 30.20; 20.15, 20.40.
TL;DR: In this paper, infrared photometry at 5, 10, and 20 wavelengths was performed for V1057 Cyg (LkH 190) and the observations extend from 1971 July through 1974 July, during which time the 5 brightness has remained essentially constant and the long-wavelength fluxes have decreased by 0.8.
Abstract: Broadband infrared photometry at 5 , 10 , and 20 is presented for V1057 Cyg (= LkH 190). The observations extend from 1971 July through 1974 July, during which time the 5 brightness has remained essentially constant and the long-wavelength fluxes have decreased by 0"'8. The origin of the flux excess observed at wavelengths between 1 and 5 is uncertain; remnant circumstdlar dust, which is radiatively heated by a central point source of declining luminosity, provides a satisfactory explanation of the 10 and 20 light curves. Key words: circumstellar shells - infrared sources - variable stars
TL;DR: In this paper, the effect of the initial distribution of dispersant is investigated by obtaining solutions corresponding to different initial instantaneous point and plane source distributions, and the governing equations are converted to a tractable system of moment equations which is solved by numerical methods with the aid of a digital computer for the zeroth, first, second, third, and fourth moment of the longitudinal concentration distribution.
Abstract: The effect of the initial distribution of dispersant is investigated by obtaining solutions corresponding to different initial instantaneous point and plane source distributions. The governing equations are converted to a tractable system of moment equations which is solved by numerical methods with the aid of a digital computer for the zeroth, first, second, third, and fourth moment of the longitudinal concentration distribution. The initial instantaneous point source distribution is located at η 0 = 0, 0.25, 0.50, 0.75, and 1.0. During the initial period of dispersion, the convective transport produces a considerable change in the moments of the dispersing cloud as compared with the Gaussian long dispersion time behavior, and the longitudinal dispersion in a turbulent open-channel flow is strongly dependent on the location of the instantaneous point source.
01 Jan 1975
TL;DR: In this article, the authors show the galactic center source Sgr A to consist of a non-thermal source, SGR A East, an H I[ Region, SGr A West and an unusual point source.
Abstract: Interferometer measurements show the galactic center source Sgr A to consist of a non-thermal source, Sgr A East, an H I[ Region, Sgr A West and an unusual point source The properties of these sources are given below:
TL;DR: In this article, the authors proposed to transform point-source potential data into line-source apparent resistivity data and interpret the transformed apparent resistivities by the master curves provided by the source.
Abstract: Investigations of apparent resistivity due to a point source over an inclined contact have been reported by Aldredge (1937), Unz (1953), Maeda (1955), and Chastenet de Gery and Kunetz (1956). In these investigations either the image or the harmonic method has been utilized. In this note, we propose to solve the same problem as follows: (1) Transform point-source potential data into line-source apparent resistivity data. (2) Interpret transformed apparent resistivities by the master curves provided.
TL;DR: In this paper, the performance of a line array to discriminate between two near-field acoustic point sources from the viewpoint of statistical hypothesis testing was investigated and the optimum binary detectors were presented for noise alone and noise plus point source interference environments.
Abstract: This paper studies the ability of a line array to discriminate between two nearfield acoustic point sources from the viewpoint of statistical hypothesis testing. The optimum binary detectors are presented for noise alone and noise plus point source interference environments. Under a small signal‐to‐noise power ratio assumption, general expressions are presented for the performance of these detectors. For a uniformly spaced line array with a large aperture (compared to the source range) in a spatially white noise environment, the detector performance is shown to be linearly proportional to signal‐to‐noise ratio, inversely proportional to hydrophone spacing and proportional to a factor involving the ratio of the separation of the two sources to the acoustic wavelength. When operating in a noise plus interference environment, the performance of this detector is severely degraded. The optimum detector for noise plus interference is shown to perform significantly better.Subject Classification: 60.20, 60.30.
01 Oct 1975
TL;DR: In this paper, a detailed series of graphs is provided along with accompanying analyses to show cloud overcast effects upon the visible radiation emanating from a point source to a target at the ground, and the appendixed graphs apply to the following set of hypothetical conditions: the medium of propagation is a nonattenuating (no scattering or absorbing) atmosphere, the overlying cloud acts as a 100% diffusely reflecting surface, the ground surface is nonrelecting and The target acts as Lambert-type receiver.
Abstract: : A detailed series of graphs is provided along with accompanying analyses to show cloud overcast effects upon the visible radiation emanating from a point source to a target at the ground. The appendixed graphs apply to the following set of hypothetical conditions: The medium of propagation is a nonattenuating (no scattering or absorbing) atmosphere, The overlying cloud acts as a 100% diffusely reflecting surface, The ground surface is nonrelecting and The target acts as a Lambert-type receiver. Total atmospheric radiation transmission maxima are about 300% of the direct transmission in a nonattenuating atmosphere. This occurs, for example, when a high-altitude source is close to an overcast with the target parallel to the ground and clouds and its horizontal distance is close to ground zero.
TL;DR: In this paper, the surface temperature distribution of thermally polluted water was observed with an infrared radiation thermometer installed on an airplane, and the lateral distribution of temperature can be expressed by the Gaussian function, though it is not symmetrical with respect to the center line.
Abstract: Publisher Summary The diffusion of thermal pollution is more or less affected by air temperature, wind velocity, depth of the sea, current velocity, exhaust velocity of the pollution, and other factors. This chapter discusses and finds clues to the complicated problems of oceanic diffusion. It presents a case study to illustrate diffusion from a continuous point source and the simplest kind of oceanic pollution. The surface temperature distribution of thermally polluted water was observed with an infrared radiation thermometer installed on an airplane, saving manpower and time. The lateral distribution of temperature can be expressed by the Gaussian function, though it is not symmetrical with respect to the center line. The temperature along the centerline near the source decreased linearly with distance, but after some distance, it is likely to become inversely proportional to the distance. The emissivity of the sea surface and attenuation of infrared radiation during passage through the air can also affect the readings of the radiometer. Because the sea-surface temperatures were measured at only a few points in the present study, the data are not enough for analysis, and this problem needs to be solved in the future.