Point source

About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.

An X-ray pulsar in SNR G109.1–1.0

Abstract: The unusual extended X-ray source G109.1–1.0 (ref. 1), discovered with the Einstein Observatory2, looks like a supernova remnant (SNR) and is of particular interest because it contains a point source 1E2259+586, from which a long curving arc of emission appears to extend, joining smoothly with the outer edge of the diffuse emission. We have now analysed the photon arrival times for the point source. (The point source was previously1,3 designated as GF2259+586; here we will use the 1E designation adopted by Tuohy and Garmire4.) We conclude that the point source is an X-ray pulsar.

The dynamics of plume-ridge interaction: 2. Off-ridge plumes

Abstract: A variety of geophysical and geochemical evidence indicates that ascending mantle plumes can interact with ocean ridges located up to 1400 km away. I investigate the dynamics of this interaction using a simple model in which a point source with volume flux Q (analogous to a plume “stem”) releases buoyant fluid into a viscous corner flow driven by the divergence of rigid surface plates with thickness ∼(kx/U)1/2, where U is the half spreading rate. The point source is located at a distance xp from the ridge, and ridge migration is neglected. The buoyant fluid forms a thin sublithospheric layer whose thickness S(x, y) satisfies a nonlinear advection-diffusion equation describing the balance of advection by the corner flow, buoyancy-driven “self-spreading,” flow toward the ridge along the sloping base of the lithosphere, and continuous accretion into the lithosphere. Numerical solutions of this equation yield scaling laws for the lateral extent W (“waist width”) of plume material along the ridge, the fraction R of the plume flux that crosses the ridge, and the maximum value of xp beyond which interaction ceases. The sloping base of the lithosphere has only a minor (few tens of percent) influence on these quantities, which are determined principally by the balance of advection and self-spreading. An extension of the model to include plume-induced lithospheric thinning shows that this process increases the waist width by an amount of order 10%. Finally, the model provides a new explanation for the observation that plumes interact primarily with ridges that are migrating away from them, rather than toward them.

Spatial audio processing method and apparatus for context switching between telephony applications

Abstract: Multiple audio streams are spatially separated with a context switching system to allow a listener to mentally focus on individual point sources of auditory information in the presence of other sound sources. The switching system simultaneously directs incoming sound sources to different spatial processors. Each spatial processor moves the received sound sources to different audibly perceived point sources. The outputs from the spatial processors are mixed into a stereo signal with left and right outputs and then output to the listener. Important sound sources are moved to a foreground point source for increased intelligibility while less important source sources are moved to a background point source.

Monte Carlo dosimetry of a new 192Ir pulsed dose rate brachytherapy source.

Abstract: A new microSelectron pulsed dose rate source has been designed, containing two active pellets instead of one inactive and one active pellet contained in the old design, to facilitate the incorporation of higher activity up to 74 GBq (2 Ci). In this work, Monte Carlo simulation is used to derive full dosimetric data following the AAPM TG-43 formalism, as well as the dose rate per unit air kerma strength data in Cartesian, "away and along" coordinates for both source designs. The calculated dose rate constant of the new PDR source design was found equal to lambda=(1.121 +/- 0.006) cGy h(-1) U(-1) compared to lambda = (1.124 +/- 0.006) cGy h(-1) U(-1) for the old design. Radial dose functions of the two sources calculated using the point source approximated geometry factors were found in close agreement (within 1%) except for radial distances under 2 mm. At polar angles close to the longitudinal source axis at the sources' distal end, the new design presents increased anisotropy (up to 10%) compared to the old one due to its longer active core. At polar angles close to the longitudinal source axis at the sources' drive wire end however, the old design presents increased anisotropy (up to 18%) due to attenuation of emitted photons through the inactive Ir pellet. These differences, also present in "away and along" dose rate results, necessitate the replacement of treatment planning input data for the new microSelectron pulsed dose rate source.

The Propagation of an Acoustic Wave along a Boundary

Abstract: The sound field of a point source near the boundary of two media cannot be obtained by an acoustic‐ray approach. In fact, such an approach which utilizes the reflection coefficient for plane waves leads to completely contradictory results at grazing incidence. A more rigorous solution is obtained, the procedure followed being exactly similar to that initiated by Sommerfeld to derive the electromagnetic field of a vertical dipole situated near a conducting plane. The results of such an analysis as applied to an acoustic point source are presented. As pointed out by Van Der Pol, the resultant solution may be regarded as that due to the point source and a diffuse image. The discussion of the solution is restricted to cases in which the sound source is at the boundary although it is given for all source heights. The solution shows that when the boundary medium has a high real specific acoustic impedance, non‐zero fields are obtained at all points along the boundary. For bounding media adequately described by simple porosity theory, the acoustic pressure at the boundary is inversely proportional to the square of the distance and the square of the frequency, at reasonably large distances and low frequencies. Also there appears to be decreased phase velocities along the boundary. Some calculations of the sound pressure as a function of height above Quietone show, among other things, the presence of a minimum occurring some distance above the boundary. At large distances from the source there are very large decreases in amplitude as the receiver height is increased in the region above this minimum.