Showing papers on "Point source published in 1972"
TL;DR: In this article, the apparent position and energy flux of the brightest images as seen by certain distant observers are calculated as functions of time, taking into account the changing surface brightness of the image and its changing angular size.
Abstract: Geometrical optics is used to analyze the propagation of high-frequency radiation emitted by a point source in a circular orbit in the equatorial plane of an extreme Kerr metric black hole. Both the apparent position and the energy flux of the brightest images as seen by certain distant observers are calculated as functions of time, taking into account the changing surface brightness of the image and its changing angular size. When the star's orbit is close to the black hole and the observer is close to the equatorial plane, the energy flux is sharply peaked in time. The correlation between direction of emission in the frame comoving with the source and the asymptotic direction of a beam of radiation gives the time-averaged energy flux as a function of polar angle. When the orbit of the source is close to the horizon in coordinate radius, most of the radiation comes out near the equatorial plane. (auth)
310 citations
TL;DR: In this paper, sound rays are traced numerically from a point source on the axis of a jet flow with realistically chosen velocity profiles, and directivity patterns computed from the ray paths have no cone of absolute silence, in contrast with analytic results for nonspreading jets.
Abstract: Sound rays are traced numerically from a point source on the axis of a jet flow with realistically chosen velocity profiles. The directivity patterns computed from the ray paths have no cone of absolute silence, in contrast with analytic results for nonspreading jets. A related observation is that the surfaces of constant phase are ultimately spherical. Nevertheless, the computed axial refraction valleys are much deeper than those observed in jet noise studies. The difference is due to diffraction, which tends to offset refraction effects at all but the highest (ray‐acoustic) frequencies.
60 citations
TL;DR: In this paper, the total power and power spectrum due to a point source convecting at a uniform subsonic velocity along the axis of a round jet is calculated, where the source is a discrete frequency source in its own frame of reference.
58 citations
TL;DR: In this paper, a simple spherically symmetric model with an electron point-source at the centre is considered and the equations are explicitly solved for the energy distribution of relativistic electrons in which electrons generated within the source diffuse and decay through synchrotron or Compton radiation.
Abstract: The general solution for the energy distribution of relativistic electrons in which electrons generated within the source diffuse and decay through synchrotron or Compton radiation is given for the case in which the magnetic field and the diffusion coefficient are constant. A very simple spherically symmetric model with an electron point-source at the centre is considered and the equations are explicitly solved. It is shown that notwithstanding its great simplicity this model gives a fair representation of the continuous emission of the Crab nebula from the radio to the X-ray region, with the simple assumption that it is due only to ordinary synchrotron radiation. If the central point source is identified with the pulsar there appears to be an upper limit of about 107 MeV to the energy of the electrons accelerated by the pulsar mechanism.
29 citations
TL;DR: In this paper, an earth-flattening transformation is developed for wave propagation problems that can be formulated in terms of uncoupled scalar Helmholtz equations. But the transformation is exact for homogeneous (no source) problems and is useful for normal mode studies.
Abstract: An earth-flattening transformation is developed for wave-propagation problems that can be formulated in terms of uncoupled scalar Helmholtz equations. Through the transformation, wave problems in isotropic, spherically symmetric media with a specified radial heterogeneity can be expressed in terms of a flat geometry with a suitably vertical heterogeneity. The transformation is exact for homogeneous (no source) problems and is useful for normal mode studies. When a point source of waves is present, the earth-flattening transformation together with the Watson transform converts the reflected wave field from a sum over discrete, spherical eigenfunctions to an integral over continuous wave numbers in a flat geometry. The far-field form of this integral shares many properties with the Weyl integral and is useful for body-wave studies in a spherical earth.
19 citations
TL;DR: In this article, the authors report the observation of a weak point source at the X-ray position, which is not associated with the supernova remnant Milne 56, and argue that an identification with such an extended radio source is unlikely.
Abstract: PREVIOUS attempts to identify the X-ray source GX5-1 have been unsuccessful. An optical search of the 1.2 arc min MIT error circle1 down to 17 mag yielded no clear candidate2, and in radio observations at 4.6 and 11.1 cm no point source was detected down to a limit of 0.1 and 0.005 f.u., respectively3,4. Although Milne and Dickel5 claimed that GX5-1 might be associated with the supernova remnant Milne 56, Ilovaisky and Ryter6 argue that an identification with such an extended radio source is unlikely. We report here the observation of a weak point source at the X-ray position.
16 citations
TL;DR: In this article, it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady-state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium.
Abstract: In this paper it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady-state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium.
The potential generated by the induced polarization is calculated at any point in a layered earth by the same procedure as used for calculating the potential due to a point source of direct current.
On the basis of the definition of the apparent chargeability ma, the expressions of ma for different stratigraphie situations are obtained, provided the IP measurements are carried out on surface with an appropriate AMNB array. These expressions may be used to plot master curves for IP vertical soundings.
Finally some field experiments over sedimentary formations and the quantitative interpretation procedure are reported.
16 citations
TL;DR: In this article, the Thomson-Haskell matrix device is used to solve the problem of the static deformation of a multilayered spherical Earth model by buried sources, which consists of p-1 concentric spherical shells plus an inner core; each shell as well as the core being homogeneous, isotropic and perfectly elastic.
Abstract: Summary
The Thomson-Haskell matrix device is used to solve the problem of the static deformation of a multilayered spherical Earth model by buried sources. The model consists of p-1 concentric spherical shells plus an inner core; each shell as well as the core being homogeneous, isotropic and perfectly elastic. The point source is represented as a discontinuity in the motion-stress vector across the spherical surface passing through the source. Explicit series expressions in terms of layer matrices are obtained for the displacements and stresses at any point in the medium for three sources: a vertical strike-slip fault, a vertical dip-slip fault and a centre of explosion. The singular case corresponding to the Legendre polynomial of the first degree (n= 1) has been discussed in detail.
16 citations
TL;DR: Fast neutron absorbed dose rates near 252Cf finite line sources in several infinite tissue compositions have been calculated and kerma from a point source was obtained from the flux, using recently calculated kerma-fluence factors.
Abstract: Fast neutron absorbed dose rates near 252Cf finite line sources in several infinite tissue compositions have been calculated. The neutron flux produced by a point source was calculated using the one-dimensional energy-dependent discrete ordinates computer code, DTF-IV. The calculations utilized an S-16 angular quadrature approximation, 21 energy groups and anisotropic scattering up to the third order in the cosine of the scattering angle. The kerma from a point source was obtained from the flux, using recently calculated kerma-fluence factors. The absorbed dose rates for line sources were obtained by using the point source kerma as a kernel and integrating over the length of the source, assuming charged particle equilibrium.
14 citations
Patent•
11 May 1972TL;DR: In this paper, several heterodyne microscopes are illustrated in which light from a point source is directed to interfere with light scattered from an object to provide a large area interference pattern representing a point on that object.
Abstract: Several heterodyne microscopes are illustrated herein in which light from a point source is directed to interfere with light scattered from an object to provide a large area interference pattern representing a point on that object. Scanning apparatus varies the interference pattern to represent different object points. Conventional heterodyne signal processing apparatus processes light from the interference pattern to provide an image. The resolution of the image is determined by the size of the point source and by the percentage of the area of the interference pattern from which the processing apparatus receives signals. A high resolution image is obtained by using a small pinhole aperture to provide the point source and by using a diffusive surface to receive and scatter light from the interference pattern to the signal processing apparatus.
9 citations
TL;DR: In this article, the flow due to a point source of oscillatory strength in an inviscid, rotating, stratified liquid is deduced as a limit, and the solutions do not exhibit any spherical symmetry.
Abstract: In this paper solutions are presented in closed form for the flow due to a point source of oscillatory strength in an inviscid, rotating, stratified liquid. The solutions do not exhibit any spherical symmetry. The flow due to a steady source is deduced as a limit.
TL;DR: In this article, a Monte Carlo model for the surface gamma density gauge has been set up based on the principle of similitude, which takes the finite extension of the detector area into account in a consistent manner.
TL;DR: Photographed edge response of a quadrant target made through atmospheric turbulence was found to fit an error function form quite accurately and a theoretical estimate of the intensity point spread function based upon a parabolic approximation to the wave structure function for a point source is consistent with the data.
Abstract: Photographed edge response of a quadrant target made through atmospheric turbulence at a range of 1.6 km 10.7 m above water was found to fit an error function form quite accurately. A theoretical estimate of the intensity point spread function based upon a parabolic approximation to the wave structure function for a point source is consistent with the data. Assuming the validity of the approximation, thermal values of Cn give turbulence inner scales in the millimeter range.
TL;DR: A mathematical analysis of the application of moiré fringe contouring to fluid film thickness measurement is made and the fringe patterns viewed by an observer near the grid when there is a point source of light are analyzed.
Abstract: A mathematical analysis of the application of moire fringe contouring to fluid film thickness measurement is made. Two special cases are treated. The first considers the generation of contours with a collimated light source and distant observer. The second analyzes the fringe patterns viewed by an observer near the grid when there is a point source of light. Geometrical restrictions imposed on the experimental setup are detailed. Experimental results are included.
TL;DR: In this article, wave fields of quasi-longitudinal and quasitransverse elastic vibrations from a point source of an instantaneous pulse type are studied in an anisotropic medium with four elastic constants.
TL;DR: In this paper, a solution for the coherence function governing the propagation of radiation from a finite incoherent source in a statistically homogeneous random medium is presented in the form of the product of the free space coherence of the source and the resulting from a point source of radiation in a random medium.
Abstract: We presenthere first the solution for the coherence function governing the propagation of radiation from a finite incoherent source in a statistically homogeneous random medium. The solution is in the form of the product of the free space coherence of the finite incoherent source and the coherence function resulting from a point source of radiation in a random medium. We next generalize the solution to the case in which the mean statistical parameters vary slowly in the mean propagation direction. Again, the solution is in the product form. Finally, we specialize the solution to consider two problems: (a) propagation from a finite incoherent source located some distance from the random medium, and (b) coherence of the radiation some distance from the random medium after it has propagated through the medium.
TL;DR: In this article, the concentration profile downstream from a source of decaying effluent is described by a solution of the diffusion equation with a source with finite width at the origin and conditions under which the plug flow model may be used are discussed and a set of curves are given for estimating the distance required for lateral mixing from sources of different widths.
TL;DR: In this paper, the shadowing function, defined as the probability that a point on a rough surface will be illuminated by radiation from a source at fixed height above the surface, is considered.
Abstract: The shadowing function, defined as the probability that a point on a rough surface will be illuminated by radiation from a source at fixed height above the surface, is considered. An exact expression for this probability is derived and evaluated approximately when the surface elevation is a normal random process. The effect of surface correlation is considered and shown to be appreciable. Several numerical computations of the shadowing function are presented.
01 Oct 1972
TL;DR: In this article, the behavior of an instantaneous point source, as it disperses in a thick, neutrally stratified, turbulent shear layer, has been examined by a laser light-scattering technique in the Meteorological Wind Tunnel.
Abstract: : The behavior of an instantaneous point source, as it disperses in a thick, neutrally stratified, turbulent shear layer, has been examined by a laser light-scattering technique in the Meteorological Wind Tunnel. An aerosol-filled gas bubble was released in a column of water to subsequently rise and burst at the floor of the wind tunnel. This pseudo-instantaneous gas volume dispersed in the turbulent shear layer. Time dependent concentrations at a point were monitored by measuring the scattered light from a coherent light source by a photomultiplier-fiber optics probe. Data consisted of a series of concentration realizations downstream from the ground level source. The distribution of concentration was described by selecting coefficients empirically in a Gram-Charlier series. Puff dispersion characteristics were compared with prediction of the Lagrangian similarity diffusion theory. (Author Modified Abstract)
Patent•
15 May 1972TL;DR: In this paper, the authors describe a system that provides UNIFORM ILLUMINATION of a plane by means of a COMPACT SOURCE and a CORRECTing OPTICAL System.
Abstract: A COMPACT SYSTEM PROVIDING UNIFORM ILLUMINATION OF A PLANE BY MEANS OF A COMPACT SOURCE AND A CORRECTING OPTICAL SYSTEM. THE ILLUMINATION FROM A POINT SOURCE BY ITSELF IS PROPORTIONAL TO THE COSINE3 OF THE ANGLE WHICH A RAY FROM THE SOURCE MAKES WITH THE NORMAL TO THE PLANE. A WIDE ANGLE LENS REFRACTS RADIATION FROM THE SOURCE INTO A 90* CONE AND REDISTRIBUTES IT WITHIN THE CONE INVERSELY AS THE COSINE3 OF THE ANGLE SO THAT THE EFFEC- TIVE ILLUMINATION ON THE PLANE IS UNIFORM. THE SYSTEM IS PARTICULARLY USEFUL FOR OBTAINING UNIFORM PRINTING EXPOSURE OF PHOTOSENSITIVE PLATES IN OFFSET PRINTING.
Patent•
07 Dec 1972
TL;DR: An improved point light source visual system using a toric lens to concentrate the light from the point source and increase screen brightness is described in this paper, where proper positioning of the elements is also possible to use a line of light rather than a point and further increase brightness.
Abstract: An improved point light source visual system using a toric lens to concentrate the light from the point source and increase screen brightness. By proper positioning of the elements it is also possible to use a line of light rather than a point and further increase brightness.
TL;DR: In this article, the point source effect in the time-averaged spatial cross-correlation and the determination of mean drift velocities by the radio spaced-antenna method are discussed.
TL;DR: In this paper, the diffraction field of an ellipsoidal aperture with an off-axis point source is given by an infinite series of Bessel functions of integral orders and of the first kind.
Abstract: The diffraction field of a circular aperture with an off-axis point source is given by an infinite series of Bessel functions of integral orders and of the first kind. Because each function has a coefficient whose magnitude decreases with increase of the order of the function, the infinite series converges rapidly. The solution is used to study the properties of an ellipsoidal aperture system with an off-axis point source. From the results thus obtained, it is asserted that, with an input wave which is divided into circular zones having appropriate phase differences, the system may give a high irradiance at its principal focus.
TL;DR: In this paper, the normal mode solution for Love waves from a shear fault in a stratified layer over the half-space is investigated with special attention to the azimuthal behavior of amplitude compared with the radiation pattern of SH waves.
Abstract: The normal mode solution for Love waves from a shear fault in a stratified layer over the half-space is investigated with special attention to the azimuthal behavior of amplitude compared with the radiation pattern of SH waves. It is found that Love waves are denoted by the sum of two terms associated with a particular set of rays of physical significance. For the torsional oscillation of a homogeneous elastic sphere due to the shear fault, a similar relation is recognized between higher radial modes and rays. The mode-ray relations obtained in the above two cases coincide with the ones derived in other literature from quite different considerations that interpret the normal modes by interference phenomena. The radiation patterns of SH waves and of normal modes are found to be
TL;DR: In this paper, the authors used Gifford's fluctuating model to determine the Hay-Pasquill scale parameter which relates the Lagrangian and Eulerian scales of turbulence.
Abstract: Diffusion of helium gas from an instantaneous point source within a neutral boundary layer has been studied. Concentrations from a simulated point source, located at a fixed height of 8 inches above a smooth surface, were measured for several downstream cross-sections of the diffusing cloud. Separation of the total dispersion into two components, spreading and meandering, is obtained on the basis of Gifford's fluctuating model. The results of this analysis are used to determine the Hay-Pasquill scale parameter which relates the Lagrangian and Eulerian scales of turbulence. Meandering is shown to have a significant effect on the scale parameter. DOI: 10.1111/j.2153-3490.1972.tb01549.x
01 Jan 1972
TL;DR: In this paper, the authors discuss three possible techniques for producing optical point images of acoustic field points with a point source of illumination: (1) the desired optical point image is formed directly when the acoustic wavelength equals one half the optical wavelength, and (2) if the optical point source coincides with the acoustic point, the ring image reduces to a point image.
Abstract: Most acoustic imaging by optical Bragg diffraction uses a coherent line source of light to illuminate the acoustic field and cylindrical lenses to form one conventional optical point image for each point in the acoustic field. Likewise it is generally realized that an optical point source of illumination produces an optical ring image for each acoustic field point [Ref. 1]. In general, the diameter of the ring is larger than the theoretical acoustic resolution, thus providing a poor image of the acoustic field. I will discuss three possible techniques for producing optical point images of acoustic field points with a point source of illumination. (1) The desired optical point images are formed directly when the acoustic wavelength equals one half the optical wavelength. (2) If the optical point source coincides with the acoustic point, the ring image reduces to a point image. (3) The optical ring image can be changed into a point image by a second imaging operation through a second acoustic field or a spatial filter.
Journal Article•
TL;DR: In this article, Ray geometry, travel time, and spreading loss are derived for refracted/bottom-reflected rays having an arbitrary initial direction at a bottom-mounted point source and experiencing multiple bottom reflections in a horizontal channel.
Abstract: The sound‐speed gradient is assumed to be a vector of constant magnitude and direction that has both horizontal and vertical components. Ray geometry, travel time, and spreading loss are derived for refracted/bottom‐reflected rays having an arbitrary initial direction at a bottom‐mounted point source and experiencing multiple bottom reflections in a horizontal channel. Rays intercepting a bottom‐mounted receiving point after traversing a given number of lobes are isolated and studied. It is found that the changes in travel time and spreading loss caused by the presence of the horizontal gradient are approximately proportional to the component of the horizontal gradient in the direction of the receiving point. With the receiving point placed in the direction of the horizontal gradient, a calculation is made of the total field due to a CW source as a function of the magnitude of the horizontal gradient. Substantial changes from the values when the gradient is purely vertical are found in both intensity and phase. An approximate formula shows that the change in phase is also proportional to the component of the horizontal gradient in the receiving‐point direction.
01 Mar 1972
TL;DR: In this article, a general formula for the concentration after full or partical reflection from the sides of a straight channel using a series of image sources is derived for diffusion in a valley flow.
Abstract: Given an arbitrary stationary concentration distributionF(x,y,z) from a continuous point source in free space, a general formula is derived for the concentration after full or partical reflection from the sides of a straight channel using a series of image sources. SpecifyingF(x,y,z) as a Gaussian concentration distribution the model is used to obtain numerical estimates for diffusion in a valley flow from a continuous point source.
TL;DR: In this article, the authors examined the transmission of high-frequency radio waves through the ionosphere for a plane-stratified, isotropic ionospheric model and an impulsive point source.
Abstract: The transmission of high-frequency radio waves through the ionosphere is examined for a plane-stratified, isotropic ionospheric model and an impulsive point source. Explicit solutions for the path relations and the signal amplitude for the homogeneous-slab model illustrate the breakdown of straight-line approximations to the ray path. Implicit solutions for the path relations that are useful for iterative evaluation are also found for more general ionospheric profiles.