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Point source
About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.
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TL;DR: In this paper, the authors investigate the possibility of characterizing inhomogeneities in the framework of the diffusion approximation of the radiative transfer equation using the factorization method, for purely scattering inclusions, or if the scattering and absorption coefficients interplay in a correct way, if and only if the point source lies inside one of the inclusions.
Abstract: In optical tomography, one tries to determine the spatial absorption and scattering distributions inside a body by using measured pairs of inward and outward fluxes of near-infrared light on the object boundary. In many practically important situations, the scatter and the absorption inside the object are smooth apart from inclusions where at least one of the two optical parameters jumps to a higher or lower value. In this work, we investigate the possibility of characterizing these inhomogeneities in the framework of the diffusion approximation of the radiative transfer equation using the factorization method: for purely scattering inclusions, or if the scattering and absorption coefficients interplay in a correct way, the outcoming flux corresponding to a point source belongs to the range of an operator, determined through boundary measurements, if and only if the point source lies inside one of the inclusions.
26 citations
TL;DR: In this paper, a maximum likelihood test for density evolution is applied to a full-sky redshift survey of 5297 galaxies selected from the IRAS data base and flux-limited at 1.2 Jy.
Abstract: A maximum likelihood test for density evolution is applied to a full-sky redshift survey of 5297 galaxies selected from the IRAS data base and flux-limited at 1.2 Jy. No evidence for evolution is found. Attention is given to important systematic errors which decrease the certainty with which evolution can be measured, namely, limited knowledge of the cosmological model, the unknown intrinsic spectral energy distribution of IRAS galaxies from 16 to 140 microns, the effect of density fluctuations, a Malmquist-like bias arising from flux errors in the IRAS Point Source Catalog, and possible incompleteness of the sample at high redshifts and low Galactic latitudes. It is shown that the Malmquist bias could result in a significant overestimation of the evolution rate, especially if the catalog has a flux limit near the completion limit of the Point Source Catalog.
26 citations
TL;DR: In this paper, the authors analyzed the heat and mass transfer by natural convection in a square cavity with turbulent flow, covering a wide range of Rayleigh number of 104 −⩽−Ra ⩽ −1010 with a constant value of CH −= 3000 −ppm. Governing equations of mass, energy and concentration were solved by the finite volume method.
26 citations
TL;DR: The theoretical analysis and laboratory calibration of a sensor to measure fluid flux in soil or other porous medium shows that a flow velocity of 10−4 cm sec−1 can be readily measured, and that sensor output is uniquely related to flux as mentioned in this paper.
Abstract: The theoretical analysis and laboratory calibration of a sensor to measure fluid flux in soil or other porous medium shows that a flow velocity of 10−4 cm sec−1 can be readily measured, and that sensor output is uniquely related to flux. The flow to be measured causes asymmetry in the temperature field,generated by an approximation to a point source of heat located centrally in the instrument. The temperature difference due to this asymmetry gives rise to the output of the instrument.
26 citations
TL;DR: In this article, the adaptive filter was applied to optimize the detection and extraction of point sources from a one-dimensional array of time-ordered data such as the one that will be produced by the future 30-GHz LFI28 channel of the ESA Planck mission.
Abstract: Wavelet-related techniques have proven useful in the processing and analysis of one- and two-dimensional data sets (spectra in the former case, images in the latter). In this work we apply adaptive filters, introduced in a previous work, to optimize the detection and extraction of point sources from a one-dimensional array of time-ordered data such as the one that will be produced by the future 30-GHz LFI28 channel of the ESA Planck mission. At a 4σ detection level, 224 sources over a flux of 0.88 Jy are detected with a mean relative error (in absolute value) of 21 per cent and a systematic bias of −7.7 per cent. The position of the sources in the sky is determined with errors inferior to the size of the pixel. The catalogue of detected sources is complete at fluxes ≥4.3 Jy. The number of spurious detections is less than 10 per cent of the true detections. We compared the results with the ones obtained by filtering with a Gaussian filter and a Mexican Hat Wavelet of width equal to the scale of the sources. The adaptive filter outperforms the other filters in all considered cases. We conclude that optimal adaptive filters are well suited to detect and extract sources with a given profile embedded in a background of known statistical properties. In the Planck case, they could be useful to obtain a real-time preliminary catalogue of extragalactic sources, which would have a great scientific interest, e.g. for follow-up observations.
26 citations