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Showing papers on "Point source published in 1976"


Journal ArticleDOI
TL;DR: In this article, the authors extended their earlier work to cover the possibility that 9 is a singular generalized function, so that s can be discontinuous or singular, even when s is smooth, generalized functions simplify the notation.
Abstract: Summary. In most seismic calculations the real physical stress tensor S is replaced by a linearized isentropic elastic model stress tensor 9. Backus & Mulcahy showed how the stress glut r = 9- S gives rise to all the usual phenomenological descriptions of earthquake sources, the equivalent forces, the moment tensor densities, the stress-free strain and the seismic moment tensors of various types and degrees. In our earlier paper the displacement field s was supposed to be continuously differentiable, so discontinuous faulting could not be discussed. The present work extends our earlier paper to cover the possibility that 9 is a singular generalized function, so that s can be discontinuous or singular. Even when s is smooth, generalized functions simplify the notation. Surface and volume forces, real or equivalent, can be combined in a single distribution; boundary conditions are automatically included in the field equations; and representing a localized source by certain moment tensors of low degree amounts to approximating the source by a point source with the same moments of low degree. It is shown that all the results in our earlier paper can be extended to discontinuous s and singular 9. New results, not obtainable in our earlier paper, include these: a simple description of the most general seismic point source; a proof that every tensor with the obvious appropriate index symmetries is a forcemoment or glut-moment tensor of a seismic point source; a catalogue of point sources with no seismic effects; a new, direct derivation of the classical phenomenological descriptions of ideal fault sources which Burridge & Knopoff, Dahlen and Walton obtained from the reciprocity theorem and the impulse response; a discussion of how, unlike ideal faults, a real fault might have a seismic moment tensor with non-zero trace; and a description of a source type, the simple surface source, which may be a more accurate phenomenological description of real faults than are the classical ideal fault descriptions. It can be shown that a simple surface source with fault surface Z is uniquely determined by the motion it produces if it is developable or if the Gaussian curvature of Z never vanishes, but not if Z contains a piece of a plane.

320 citations


Journal ArticleDOI
TL;DR: In this article, a laboratory model of the convective planetary boundary layer has provided information concerning the evolution of concentration distributions downwind from a simulated continuous point source located near the ground.
Abstract: A laboratory model of the convective planetary boundary layer has provided information concerning the evolution of concentration distributions downwind from a simulated continuous point source located near the ground Results indicate that a Gaussian plume formulation adequately describes the model γ-concentration distributions, but is useful in predicting the z-concentration distributions only to a distance downstream of about x = 05zi/(w*/U), where zi is the mixed layer depth and w*/U is a dimensionless stability parameter Near this distance an elevated concentration maximum appears at a height above the source release height The elevated maximum rises to a height of about 08zi at x = 17zi/(w*/U) and retains its identity until the pollutants become vertically well mixed farther downstream Use of the stability parameter w*/U permits the model results to be applied to a range of atmospheric conditions encompassing the Pasquill-Gifford stability classes A and B Close agreement is found between the laboratory data and the atmospheric observations of ground-level lateral spread of Islitzer (1961) and Islitzer and Dumbauld (1963), where the latter measurements extended out to x≃ 3 km

231 citations


01 Aug 1976
TL;DR: In this paper, a high energy Gamma ray data from the direction of the galactic anticenter was analyzed and it was shown that this region is characterized by: a diffuse emission from the galactic plane which has a maximum along b=0 deg and an enhancement toward negative latitudes associated with Gould's Belt, a strong point source in the directions of the Crab nebula, and a second intense localized source near galactic coordinates 195 deg, + 5 deg Gamma ray emissions from the Crab source is dominated by a pulsed flux from PSR 0531+21 The total flux above 100Me
Abstract: Analysis of SAS-2 high energy Gamma ray data from the direction of the galactic anticenter shows that this region is characterized by: a diffuse emission from the galactic plane which has a maximum along b=0 deg and an enhancement toward negative latitudes associated with Gould's Belt, a strong point source in the direction of the Crab nebula, and a second intense localized source near galactic coordinates 195 deg, +5 deg Gamma ray emission from the Crab source is dominated by a pulsed flux from PSR 0531+21 The total flux above 100MeV is 37 + or - 08 million/sq cm s The source near 195 deg, + 5 deg has a flux above 100 MeV of 43 + or - 09 million/sq cm s Its spectrum appears flatter than that of the Crab The diffuse galactic plane emission at negative lattitudes shows a general correlation with the local matter distribution associated with Gould's Belt The calculated Gamma ray intensity agrees well with the SAS-2 observations

86 citations


Journal ArticleDOI
TL;DR: In this paper, a set of orthonormal functions closely related to the Zernike polynomials were used to determine the respective power spectra of the time dependent expansion coefficients.
Abstract: The wavefronts of a point source of radiation that is immersed in a turbulent atmosphere become distorted and deformed as they propagate outward. The phase surfaces incident on an unobscured collecting aperture therefore will not be perfectly spherical, but instead will be aberrated in some way. We have expanded this phase profile in a set of orthonormal functions closely related to the Zernike polynomials and then determined the respective power spectra of the time dependent expansion coefficients. The results show, for all spectra, a sharp cutoff of f^{-11/3} for frequencies f > ( u/2R) , where u is the wind velocity transverse to the point source and the receiver, and R is the aperture radius. In particular, for the tilt component expansion coefficients, this result differs from the usual phase difference power spectra previously used by many workers.

84 citations


Journal ArticleDOI
TL;DR: In this article, an approximate solution for the transfer of radiation through spherically symmetric gas clouds surrounding a point source of X-rays is presented, which is similar to that of Tarter and Salpeter (1969) except that heating by Compton scattering and the Auger effect is included.
Abstract: Approximate solutions are presented for the transfer of radiation through spherically symmetric gas clouds surrounding a point source of X-rays. The approach is similar to that of Tarter and Salpeter (1969) except that heating by Compton scattering and the Auger effect is included. The temperature and ionization structure are sensitive to the source spectrum, and the solutions are not unique if soft X-rays are deficient. The emergent spectrum is rich in optical, ultraviolet, and X-ray emission lines. The radiation force due to photoelectric absorption of X-rays may exceed the force due to Compton scattering by a factor of order 10 for the radiation fields and densities likely to be encountered in galactic binary X-ray sources.

62 citations


Journal ArticleDOI
TL;DR: Modification of the Pasquill atmospheric diffusion equations for estimating viable microbial airborne cell concentrations downwind form a continuous point source and a graphical method to estimate the ground level cell concentration are presented.
Abstract: Modification of the Pasquill atmospheric diffusion equations for estimating viable microbial airborne cell concentrations downwind form a continuous point source is presented. A graphical method is given to estimate the ground level cell concentration given (i) microbial death rate, (ii) mean wind speed, (iii) atmospheric stability class, (iv) downwind sample distance from the source, and (v) source height.

61 citations


Journal ArticleDOI
TL;DR: In this paper, a linear combination of moment tensor elements is proposed for the propagation of Love and Rayleigh wave from a point source in a layered elastic half-space. But the expansion is not complete.
Abstract: Summary The equations representing Love and Rayleigh waves due to point sources are derived as linear combinations of the moment tensor elements. Using an analogy in free oscillation excitation, exact expressions for the wavenumber transform of the expansion coefficients are obtained in the case of a step function source time history. The solution to the well-known problem of Love and Rayleigh wave propagation from a point source in a layered elastic half-space can be expressed as a linear combination of the moment tensor elements. The advantages to such an approach are: (1) that the expansion is linear and therefore amenable to the stochastic least-squares estimation procedure (Foster 1961) and (2) that the expansion is complete consisting of monopole, dipole and quadrupole terms (Knopoff & Randall 1970) which ensures reliability in the estimated source parameters. An easy way to demonstrate this expansion is to merge the moment tensor formalism of Gilbert (1 970) with the vector harmonic expressions given by Saito (1967). The Love and Rayleigh wave problems separate out onto vector components when written in terms of the vector cylindrical harmonics. These are:

45 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of the propagation of sound from a point source over a locally reacting complex impedance boundary is made using complex angles of incidence as the variable in steepest descents integration.
Abstract: An analysis, using complex angles of incidence as the variable in a steepest descents integration, is made of the propagation of sound from a point source over a locally reacting complex impedance boundary. The integration process contains more terms than are normally used in the analysis, and the solution is valid over a large range of horizontal distances. Conditions for the existence of surface waves are discussed in some detail. A comparison is made of measured and calculated values of pressure on the boundary.Subject Classification: [43]28.40; [43]20.15, [43]20.30.

44 citations


Patent
04 Mar 1976
TL;DR: In this article, a radiation detector is mounted on a probe suitable for insertion into internal regions of a living body or into recesses in mechanical structure to be examined, where the output of the detector controls electron beam intensity within a cathode ray type display tube wherein the raster pattern is synchronized with that of the X-ray source to produce an image of internal structure of the subject.
Abstract: Radiographic images of high definition and clarity are produced quickly and with reduced radiation exposure of the subject by utilizing a scanning X-ray source in which a moving point source of X-rays is created by sweeping an electron beam in a raster pattern on a broad anode. A radiation detector having a very small radiation sensitive area is situated on the opposite side of the subject from the source. The output of the detector controls electron beam intensity within a cathode ray type display tube wherein the raster pattern is synchronized with that of the X-ray source to produce an image of internal structure of the subject. In some embodiments of the invention, the small radiation detector is mounted on a probe suitable for insertion into internal regions of a living body or into recesses in mechanical structure to be examined. Stereo images may be produced by employing two spaced apart detectors controlling two separate images which are directed to separate eyes of the observer or by using a single detector alternately controlling each of the two images while the raster pattern at the source is alternately shifted between two at least partially separate areas of the anode. As the detector output is an electronic signal, the image data may be stored on magnetic tape or the like and may also be readily processed by electronic techniques for such purposes as image enhancement, and addition, subtraction or superimposition of images. Automatic brightness control may also be provided to produce uniform contrast in different areas of the image where the corresponding different regions of the subject have different average densities.

39 citations


ReportDOI
01 Oct 1976
TL;DR: In this article, a numerical technique was developed to solve the three-dimensional potential distribution about a point source of current located in or on the surface of a half-space containing arbitrary two-dimensional conductivity distribution.
Abstract: A numerical technique was developed to solve the three-dimensional potential distribution about a point source of current located in or on the surface of a half-space containing arbitrary two-dimensional conductivity distribution. Finite difference equations are obtained for Poisson's equations, making point as well as area discretization, of the subsurface. Potential distribution at all points in the set defining the half-space are simultaneously obtained for multiple point sources of current injection. The solution is obtained with direct, explicit, matrix inversion techniques. An empirical mixed boundary condition is used at the ''infinitely distant'' edges of the lower half-space. Accurate solutions using area discretization method were obtained with significantly less attendant computational costs than with the relaxation, finite-element or network solution techniques, for models of comparable dimensions.

34 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical simulation of automatic welding as a moving point source of heat with conduction as the dominant mode of transfer is refined to incorporate change of state across the melt boundary.

Journal ArticleDOI
TL;DR: This paper takes up the case of an extended source and follows Steel et al.'s method of calculation, but has used an intensity distribution which is shown to be valid in the central region and experimental results are presented that confirm these theoretical predictions.
Abstract: The diffraction corrections associated with a circular aperture in the case of an extended source and a detector located in the fully illuminated region have been calculated in 1972 by Steel, De, and Bell. We have shown recently that the intensity distribution formula that they have used is not accurate in the central region of the diffraction pattern and greatly underestimates the diffraction corrections associated with a point source. In this paper, we take up the case of an extended source; we have followed Steel et al.’s method of calculation, but have used an intensity distribution which we have shown to be valid in the central region. We show that in the case of complex radiation, the variation of the diffraction correction with the source radius ρ takes a very simple form: the diffraction correction remains approximately constant as ρ increases, until the source and detector subtend equal angles at the center of the aperture; if ρ is increased further, the diffraction correction decreases linearly with 1/ρ over a certain range of ρ. Experimental results are presented that confirm these theoretical predictions.

Journal ArticleDOI
TL;DR: In this article, a soft, weak X-ray source close to or within the Crab Nebula has been found, which can be interpreted as a weak point source in the field of view, an extended source associated with the expanding filaments of the Crab, or the scattering of X-rays by interstellar dust between the Earth and the Crab.
Abstract: Data from a recent lunar occultation show the existence of a soft, weak X-ray source close to or within the Crab Nebula. The interpretations of the data include a weak point source in the field of view, an extended source associated with the expanding filaments of the Crab, or the scattering of X-rays by interstellar dust between the Earth and the Crab. If these X-rays are associated with the ejected material from the Crab, then the X-ray nebular emission can be divided into two parts. One part is a strong source of approximately 2' diameter associated with and surrounding the pulsar and being decidedly nonthermal in nature, and a second part where a few percent of the Crab X-rays come from a larger region and are perhaps thermal. The luminosity and spectrum of this second ''thermal'' source is compatible with that of other young supernova remnants. This and the alternate interpretations of the data are considered, and useful information is derived. (AIP)

Journal ArticleDOI
TL;DR: In this article, a single horizontally polarized seismometer can be used to find the six independent elements of the seismic moment tensor of a buried point source, provided that the instrument is neither longitudinally nor transversely polarized.
Abstract: Summary In theory, a single horizontally polarized seismometer can be used to find the six independent elements of the seismic moment tensor of a buried point source, provided that the instrument is neither longitudinally nor transversely polarized. Also, two vertically polarized seismometers can be used, provided that the epicentre does not lie on the great circle through the two instruments. These results form the theoretical basis for a procedure for retrieving the source mechanism from a sparse seismographic network.

Journal ArticleDOI
TL;DR: In this paper, it is shown experimentally and theoretically that artificially produced ions form a plume rather similar to a smoke plume and that the ion plume can be used successfully as a tracer in short range atmospheric diffusion studies.

Journal ArticleDOI
TL;DR: In this paper, the highest possible ground-level ambient air concentrations due to an elevated point source diffusing over flat terrain are obtained from the Gaussian Plume Model for power law forms of the dispersion coefficients.

Journal ArticleDOI
TL;DR: The linear response of a cold anisotropic plasma to a point source under impulse excitation displays a frequency spectrum having maxima at the two frequencies determined by the resonance cone condition and at the upper hybrid frequency as mentioned in this paper.
Abstract: The linear response of a cold anisotropic plasma to a point source under impulse excitation displays a frequency spectrum having maxima at the two frequencies determined by the resonance cone condition and at the upper hybrid frequency. A laboratory demonstration is reported.

Journal ArticleDOI
TL;DR: In this paper, an approximate method has been given to determine the total, the full energy peak, the intrinsic, intrinsic, and the intrinsic full-energy peak efficiencies of Ge(Li) and NaI(Tl) detectors for the gamma rays coming from a point source placed on the detector axis at a distance D from the detector surface.

Book ChapterDOI
TL;DR: In this paper, the authors provide an overview of the use of the occultation technique for radio sources with continuous spectra and the time scale of a point source's occultation curve.
Abstract: Publisher Summary This chapter provides an overview of lunar occultation measurements. The occultation technique is concerned only with sources that contain angular structure much smaller than the size of the Moon. The variation in received power when a source passes behind the Moon depends on the size of the source relative to the size of a Fresnel zone at the Moon's distance, which, over the range of frequencies of interest, ranges from a few seconds of arc to a maximum of about 20 arc sec. Provided the source size is much greater than the size of the Fresnel zone, diffraction effects can be neglected, and the shape of the occultation curve represents the strip integral of the brightness distribution in a direction perpendicular to the limb at the point of occultation. The true strip brightness distribution can then be recovered simply by differentiating the observed occultation curve. A discussion on the use of occultation technique in measurement of the positions and structures of small angular size radio sources with continuous spectra is presented and time scale of the occultation curve of a point source is also analyzed in the chapter.

Journal ArticleDOI
TL;DR: The spectrum of the 2-micron point source at the galactic center is presented over the range from 1.4 to 2.7 microns, confirming that the radiation from this source is due to a cool supergiant star as discussed by the authors.
Abstract: The spectrum of the 2-micron point source at the galactic center is presented over the range from 1.4 to 2.7 microns. The two-level-transition CO band heads are seen near 2.3 microns, confirming that the radiation from this source is due to a cool supergiant star. The heliocentric radial velocity is found to be - 173 (+ or -90) km/s and is consistent with the star being in orbit about a dense galactic nucleus. No evidence is found for Brackett-gamma emission, and no interstellar absorption features are seen. Upper limits for the column densities of interstellar H2, CH4, CO, and NH3 are derived.

Journal ArticleDOI
TL;DR: In this article, it was shown that the cross-correlation function for two points not too far apart approaches that of Cook et al. in the reverberant field of the chamber.

Journal ArticleDOI
TL;DR: In this paper, the view factor calculated by a numerical integration procedure was used to evaluate the error involved by using the view factors obtained by various approximate methods, such as: a) the well known spherical point sources approximation, b) a spherical point source approximation utilizing the reciprocity relationship, and c) the closed form integration over the spherical surface, where the cones from any point subtend the other sphere.

Patent
08 Mar 1976
TL;DR: In this article, a relatively large field of view is scanned to derive an indication of a point source, optical energy emitter, being in the field-of-view, without recognizing relatively large, non-point emitters in the view.
Abstract: A relatively large field of view is scanned to derive an indication of a point source, optical energy emitter being in the field of view, without recognizing relatively large, non-point emitters in the field of view. Each detector in an array of linearly, arranged point source detectors generates an output current in response to the energy irradiating it. The detectors have slightly displaced, narrow fields of view which are scanned so that the field of view of each detector traces a relatively narrow, substantially straight line path across the large field of view. The paths traced by a pair of detectors are substantially parallel and close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at the outputs of the pair of detectors. Each of a plurality of negative feedback differential operational amplifiers, one for each pair of detectors, includes complementary input and output terminals which are connected to the detectors so that a point source target illuminating one of the detectors is indicated by the polarity of a pulse output of the amplifier. The inputs of the amplifier are connected to spatially arranged detectors in the array so that the large targets are subtracted in the amplifier and are not indicated in the amplifier output. In response to the output signal of each amplifier, an indication is derived to indicate which of the detectors is responsive to a point source.

Journal ArticleDOI
TL;DR: In this article, the authors considered the acoustic radiation due to a point source in the close vicinity of a composite medium consisting of different fluid strata in motion and provided a general expression for the reflexion coefficient.

ReportDOI
21 May 1976
TL;DR: The continuous point-source computer code calculates concentrations and surface deposition of radioactive and chemical pollutants at distances from 0.1 to 100 km, assuming a Gaussian plume as mentioned in this paper.
Abstract: The continuous-point-source computer code calculates concentrations and surface deposition of radioactive and chemical pollutants at distances from 0.1 to 100 km, assuming a Gaussian plume. The basic input is atmospheric stability category and wind speed, but a number of refinements are also included.

Journal ArticleDOI
TL;DR: In this article, a 0.5-3-keV X-ray map of the Perseus cluster of galaxies is presented, showing a region of strong emission centered near NGC 1275 plus a highly elongated emission region which lies along the line of bright galaxies that dominates the core of the cluster.
Abstract: A 0.5-3-keV X-ray map of the Perseus cluster of galaxies is presented. The map shows a region of strong emission centered near NGC 1275 plus a highly elongated emission region which lies along the line of bright galaxies that dominates the core of the cluster. The data are compared with various models that include point and diffuse sources. One model which adequately represents the data is the superposition of a point source at NGC 1275 and an isothermal ellipsoid resulting from the bremsstrahlung emission of cluster gas. The ellipsoid has a major core radius of 20.5 arcmin and a minor core radius of 5.5 arcmin, consistent with the values obtained from galaxy counts. All acceptable models provide evidence for a compact source (less than 3 arcmin FWHM) at NGC 1275 containing about 25% of the total emission. Since the diffuse X-ray and radio components have radically different morphologies, it is unlikely that the emissions arise from a common source, as proposed in inverse-Compton models.

Journal ArticleDOI
TL;DR: In this paper, a generalized statistical model is proposed to determine the probability density function of the concentration history measured at a fixed point in the wake of a continuous point source in coastal currents.
Abstract: A generalized statistical model is proposed to determine the probability density function of the concentration history measured at a fixed point in the wake of a continuous point source in coastal currents. An application of the model using the experimental data indicates that the log-normal distribution is adequate for many practical problems. Some general statistical characteristics of the concentration field are computed from the model.

Journal ArticleDOI
TL;DR: In this article, the point source flux densities as a function of energy and position were obtained from a discrete-ordinates calculation, and the flux density densities were multiplied by their corresponding kerma factors and added to obtain point source dose rates.
Abstract: Gamma flux density and dose rate distributions have been calculated about implantable californium-252 sources for an infinite tissue medium. Point source flux densities as a function of energy and position were obtained from a discrete-ordinates calculation, and the flux densities were multiplied by their corresponding kerma factors and added to obtain point source dose rates. The point dose rates were integrated over the line source to obtain line source dose rates. Container attenuation was accounted for by evaluating the point dose rate as a function of platinum thickness. Both primary and secondary flux densities and dose rates are presented. The agreement with an independent Monte Carlo calculation was excellent. The data presented should be useful for the design of new source configurations.

Book ChapterDOI
01 Jan 1976
TL;DR: In this paper, the authors describe three different types of point-source imaging systems: mechanical, optical, and electronic scanning, where the phase of the incoming signal as collected by an array is carefully adjusted to synthesize a spherical lens.
Abstract: There are several acoustic imaging systems which are designed to respond to the energy coming from a point source in the form of a spherically diverging wave. The field pattern of a given object can be thought of as a large number of point sources — each with a different amplitude and phase. Thus, if the imaging system can sequentially receive energy from each of these points on the image we can build up the entire pattern. In this chapter we will describe three such systems in order to give the reader some appreciation of the variety of ideas that have evolved. Each system uses a lens to focus on the point source and the scanning is carried out either by mechanical motion of the object through this focal point or by “electronic scanning” wherein the phase of the incoming signal as collected by an array is carefully adjusted to synthesize a spherical lens.

Journal ArticleDOI
TL;DR: In this paper, a contour integration technique accounts for a part time zero condition plus other supplementary hypotheses (e.g. that of stability), leading via the stationary phase technique to an asymptotic solution valid for large time.
Abstract: An isotropic multidimensional medium is propagating dispersive radiation from a suddenly triggered immersed point source. The latter's subsequent action is postulated as being transient. A contour integration technique accounts for a part time zero condition plus other supplementary hypotheses (e.g. that of stability), leading via the stationary phase technique to an asymptotic solution valid for large time. One set of results holds at comparably far range. In the ensuing dispersion, concentrically expanding trains of Kelvin approximated waves get emitted. These wave trains are generally bounded by spherical advancing frontal and/or rear edges near which Airy-type approximations can be made. Several such edges may coincide or almost coincide. Another set of results, involving Hankel or Bessel functions, holds at any given finite range; it indicates slow wave packets and implies, consistent with a transient source, the ultimate attainment of a steady state of silence, possibly within a 'slowest' spherical edge. Applications are illustrated for elastic plate deflexions and Klein-Gordon governed motions.