Point source

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

Coherent point source electron beams

Abstract: The concept of a point source for electrons in view of quantum mechanical experiments is described. The engineering of such atomic electron emitters is discussed and recent experiments in holography with low energy electrons are presented.

ROSAT HRI and ASCA Observations of the Spiral Galaxy NGC 6946 and Its Northeast Complex of Luminous SNRs

Abstract: Analysis of 80 ksec ASCA and 60 ksec ROSAT HRI observations of the face-on spiral galaxy NGC 6946 are presented. The ASCA image is the first observation of this galaxy above ∼2 keV. Diffuse emission may be present in the inner ∼4 ′ extending to energies above ∼2–3 keV. In the HRI data, fourteen point-like sources are detected, the brightest two being a source very close to the nucleus and a source to the northeast that corresponds to a luminous complex of interacting supernova remnants (SNRs). We detect a point source that lies ∼30 ′′ west of the SNR complex but with a luminosity ∼1/15 of the SNR complex. None of the point sources shows evidence of strong variability; weak variability would escape our detection. The ASCA spectrum of the SNR complex shows evidence for an emission line at ∼0.9 keV which could be either Ne IX at ∼0.915 keV or a blend of ion stages of Fe L-shell emission if the continuum is fit with a power law. However, a two component, Raymond-Smith thermal spectrum with no lines gives an equally valid continuum fit and may be more physically plausible given the observed spectrum below 3 keV. Adopting this latter model, we derive a density for the SNR complex of 10–35 cm −3 , consistent with estimates inferred from optical emission line ratios. The complex’s extraordinary X-ray luminosity may be related more to the high density of the surrounding medium than to a small but intense interaction region where two of the complex’s SNRs are apparently colliding.

A study of light signals in aviation and navigation

Abstract: Visibility of point sources.—Laboratory experiments have been devised to make measurements of the visibility of light signals under conditions essentially similar to those encountered by the aviator or the navigator. Data have been collected on the direct visibility of flashing point sources of light of different colors, flash lengths and intervals, against different backgrounds; the time it takes to locate a visible beacon was studied as a function of the beacon intensity and frequency of flashing. The threshold candle power C required for visibility of a point source at distance D (cm) against a background of brightness H (candles×cm−2) is given by the empirical equation C/D2=3.5×10−9 H1/2. Colored point sources were not found to be useful except in the case of red lights with background intensities above moonlight. For an airplane approaching a beacon it is advantageous to use frequencies of flashing as high as 12 to 30 per minute, although with exceptionally clear atmosphere, lower frequencies may be ...

Light refocusing with up-scalable resonant waveguide gratings in confocal prolate spheroid arrangements

Abstract: Resonant waveguide gratings (RWGs) are thin-film structures, where coupled modes interfere with the diffracted incoming wave and produce strong angular and spectral filtering The combination of two finite-length and impedance matched RWGs allows the creation of a passive beam steering element, which is compatible with up-scalable fabrication processes Here, we propose a design method to create large patterns of such elements able to filter, steer, and focus the light from one point source to another The method is based on ellipsoidal mirrors to choose a system of confocal prolate spheroids where the two focal points are the source point and observation point, respectively It allows finding the proper orientation and position of each RWG element of the pattern, such that the phase is constructively preserved at the observation point The design techniques presented here could be implemented in a variety of systems, where large-scale patterns are needed, such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays

Extended source effect on microlensing light curves by an Ellis wormhole

Abstract: We can survey an Ellis wormhole which is the simplest Morris-Thorne wormhole in our Galaxy with microlensing. The light curve of a point source microlensed by the Ellis wormhole shows approximately 4% demagnification while the total magnification of images lensed by a Schwarzschild lens is always larger than unity. We investigate an extended source effect on the light curves microlensed by the Ellis wormhole. We show that the depth of the gutter of the light curves of an extended source is smaller than the one of a point source since the magnified part of the extended source cancels the demagnified part out. We can, however, distinguish between the light curves of the extended source microlensed by the Ellis wormhole and the ones by the Schwarzschild lens in their shapes even if the size of the source is a few times larger than the size of an Einstein ring on a source plane. If the relative velocity of a star with the radius of $1{0}^{6}\text{ }\text{ }\mathrm{km}$ at 8 kpc in the bulge of our Galaxy against an observer-lens system is smaller than $10\text{ }\text{ }\mathrm{km}/\mathrm{s}$ on a source plane, we can detect microlensing of the star lensed by the Ellis wormhole with the throat radius of 1 km at 4 kpc.