Point source

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

Analysis of the diffuse near-IR emission from 2MASS deep integration data: foregrounds vs the cosmic infrared background

Abstract: This is one of two papers in which we report the detection of structure in the cosmic infrared background (CIB) between 1.25 - 2.2 micron through the use of data from the Two Micron Sky Survey (2MASS). This paper concentrates on data assembly, analysis and the estimate of the various foreground contributions; the companion paper (Kashlinsky, Odenwald, Mather, Skrutskie, Cutri 2002, hereafter KOMSC) presents the cosmological results for the CIB fluctuations and their implications. By using repeated observations of a specific calibration star field, we were able to achieve integration times in excess of 3900 seconds compared to the 7.8 seconds in the standard 2MASS data product. This yielded a point source detection limit (3 \sigma) of +18.5^m in K_s band. The resulting co-added images were processed to remove point sources to a limiting surface brightness of +20^m/arcsec$^2 or 40 nW/m^2/sr. The remaining maps contained over 90% of the pixels and were Fourier transformed to study the spatial structure of the diffuse background light. After removing resolved sources and other artifacts, we find that the power spectrum of the final images has a power-law distribution consistent with clustering by distant galaxies. We estimate here the contributions to this signal from Galactic foregrounds, atmospheric OH-glow, zodiacal light and instrument noise, all of which are small and of different slopes. Hence, this supports the KOMSC identification of the signal as coming from the CIB fluctuations produced by distant clustered galaxies.

Seismic waves due to a shear fault in a semi-infinite medium

Abstract: In order to clarify basic characteristics of seismic waves in the near-field as well as in the far-field, exact solutions for free surface displacements generated from a shear fault with an arbitrary orientation in a semi-infinite medium are obtained in a cylindrical coordinate system. First, taking the free surface effects into account, expressions for Laplace transforms of displacements with respect to time are derived, and secondly exact transient solutions are obtained by using the Cagniard's method which gives the inverse Laplace transforms in a very ingenious manner when the source time function is of the ramp type. In sections 2, 3 and 4, mathematical expressions are derived, and the results and interpretations of numerical computations for a point source are presented in section 5. Basic characteristics of each phase are summarized as follows: P pulse has basically a rectangular form. The initial pulse amplitudes in a semi-infinite medium are, even in rather near-field, close to those in an infinite medium with correction of surface effects due to plane wave incidence. SP pulse, which radiates from the source as S phase, is incident onto the free surface with a critical angle and then is propagated along the surface with the speed of P-wave velocity, has a relatively large amplitude in the near-field and cannot be neglected when the wave form on the free surface is discussed. This pulse is observed when the epicentral distance is greater than the critical distance. S pulse forms are quite different at epicentral distances less than and greater than the critical distance. S pulse beyond the critical distance has logarithmic infinities at the arrival time of S phase, tS, and tS+t0, t0 being the rise time of the source function. Therefore a plane-wave correction can-not be applied successfully as in the case of an onset of the P pulse. The Rayleigh pulse is well developed when the epicentral distance is about five to ten times as large as the focal depth and its form is not very much affected by the rise time of the source function. For surface focus, S pulse has no logarithmic infinity but the Rayleigh pulse has infinities at the arrival time tR and tR+t0. It is shown that the solutions for a moving source can be obtained by numerical integrations of the solutions for the point source. This case will be dealt with in a subsequent paper.

Airborne remote sensing and in situ measurements of atmospheric CO 2 to quantify point source emissions

Abstract: . Reliable techniques to infer greenhouse gas emission rates from localised sources require accurate measurement and inversion approaches. In this study airborne remote sensing observations of CO2 by the MAMAP instrument and airborne in situ measurements are used to infer emission estimates of carbon dioxide released from a cluster of coal-fired power plants. The study area is complex due to sources being located in close proximity and overlapping associated carbon dioxide plumes. For the analysis of in situ data, a mass balance approach is described and applied, whereas for the remote sensing observations an inverse Gaussian plume model is used in addition to a mass balance technique. A comparison between methods shows that results for all methods agree within 10 % or better with uncertainties of 10 to 30 % for cases in which in situ measurements were made for the complete vertical plume extent. The computed emissions for individual power plants are in agreement with results derived from emission factors and energy production data for the time of the overflight.