Edge Rays Download [UPDATED]
Dimple Demay
Many of the threats sharks and rays face include targeted fisheries and being unintentionally caught (bycatch). Due to the lack of proper management in many fisheries, many shark and ray species have suffered steep declines in the past decades. Habitat degradation, resulting from coastal development, deforestation, pollution and trawling, has also contributed to the bleak status of sharks and rays.
The top 50 EDGE Sharks and Rays includes 11 of the 13 living orders of sharks and rays. It also holds two species which are the only extant representatives of their families, the Whale shark (Rhincodon typus) and the Zebra shark (Stegostoma fasciatum). The top EDGE Sharks and Rays List reflects the dire situation of the family Pristidae, the sawfish, as all 5 species appear among the top 10 on the list.
I ve been somewhat through this before on here with Mitch but never really felt fond of the thinking behind "undersizing" the secondary by letting the "edge rays" go by it to fit a smaller secondary. Intuitively I want to think thats like not making use of your primary mirrors full aperture. I just cant get my head around that.
Having said that, you can surely get away with the 4.5". It isn't absolutely necessary to fit every ray all the way through the system. As it is now, the front end of the Paracorr body blocks the edge rays from the secondary, meaning that the 5" is slightly oversized. With the 4.5", you can move the Paracorr in so that it only slightly intrudes into the light path and adjust the primary to focus. The secondary may miss the very outermost rays (the ones that hit the Paracorr, both coming past it and ones that would have hit the outer edge coming in) and your fully illuminated circle is slightly smaller. But the size of your fully illuminated field looks like it may be limited by your f/# anyway.
I m curious to know if the secondary offset is correctly displayed/derrived. I simply had to slide the secondary away from the focuser and downwards towards the primary to align it s edges with the edges of the "light cone". Does that maneouver put it into the correct offset by default? The offset in the illustration is 7.726 mm.
How do you determine an instruments maximum illuminated image field/circle from the the f-ratio? I m looking at my illustration for the secondary light path and the "rays" diverge going from teh secondary to the instruments natural focalplane. Is that significant of what, if anything? Hm.
As for field diameter, I don't know the mathematical solution. But you have the drawing skills. Just move the primary back, the secondary smaller and the Paracorr in a little. Try to balance everything till the edge rays just touch the inner edge of the front of the tube, the edge of the secondary and the inner edge of the Paracorr body. Then measure the field size. Then you'll know you're getting the maximum fully illuminated field. What you won't truly know is exactly how big the field is after going through the Paracorr glass or how rapidly or slowly the illumination falls off outside that circle.
Although we are securely tied to a marina in Long Beach, CA, the memory of the jumping rays we saw in Los Frailes, Mexico is still fresh and vibrant. As we headed south toward La Paz, we stopped one afternoon to anchor in Los Frailes and were greeted by the distinct sound of belly flops.
Regardless of how the rays are classified, they were an excellent source of entertainment that day in Los Frailes. Every once in a while the slapping sound would stop and the bay would quiet. But soon enough the rays would begin their jump and flop once more and the sound alone would bring a smile to my face.
Purpose: In photon counting (PC) x-ray imaging and computed tomography (CT), the broad x-ray spectrum can be split into two parts using an x-ray filter with appropriate K-edge energy, which can improve material decomposition. Recent experimental study has demonstrated substantial improvement in material decomposition with PC CT when K-edge filtered x-rays were used. The purpose of the current work was to conduct further investigations of the K-edge filtration method using comprehensive simulation studies.
Methods: The study was performed in the following aspects: (1) optimization of the K-edge filter for a particular imaging configuration, (2) effects of the K-edge filter parameters on material decomposition, (3) trade-off between the energy bin separation, tube load, and beam quality with K-edge filter, (4) image quality of general (unsubtracted) images when a K-edge filter is used to improve dual energy (DE) subtracted images, and (5) improvements with K-edge filtered x-rays when PC detector has limited energy resolution. The PC x-ray images of soft tissue phantoms with 15 and 30 cm thicknesses including iodine, CaCO3, and soft tissue contrast materials, were simulated. The signal to noise ratio (SNR) of the contrast elements was determined in general and material-decomposed images using K-edge filters with different atomic numbers and thicknesses. The effect of the filter atomic number and filter thickness on energy separation factor and SNR was determined. The boundary conditions for the tube load and halfvalue layer were determined when the K-edge filters are used. The material-decomposed images were also simulated using PC detector with limited energy resolution, and improvements with K-edge filtered x-rays were quantified.
Results: The K-edge filters with atomic numbers from 56 to 71 and K-edge energies 37.4-63.4 keV, respectively, can be used for tube voltages from 60 to 150 kVp, respectively. For a particular tube voltage of 120 kVp, the Gd and Ho were the optimal filter materials to achieve highest SNR. For a particular K-edge filter of Gd and tube voltage of 120 kVp, the filter thickness 0.6 mm provided maximum SNR for considered imaging applications. While K-edge filtration improved SNR of CaCO3 and iodine by 41% and 36%, respectively, in DE subtracted images, it did not deteriorate SNR in general images. For x-ray imaging with nonideal PC detector, the positive effect of the K-edge filter was increased when FWHM energy resolution was degraded, and maximum improvement was at 60% FWHM.
Conclusions: This study has shown that K-edge filtered x-rays can provide substantial improvements of material selective PC x-ray and CT imaging for nearly all imaging applications using 60-150 kVp tube voltages. Potential limitations such as tube load, beam hardening, and availability of filter material were shown to not be critical.
The analysis of radiation transfer in specular reflector configurations, with multiple or distorted images of an extended radiation source, appears to be so complicated that the need for detailed ray tracing is usually considered inescapable. I show that the number of calculations can be greatly reduced when the source is isotropic. Starting from the fact that the radiation received from an isotropic source depends only on the emissive power of the source and on the angular contour subtended by the source, I show that only edge rays need to be traced, no matter what the curvature of the reflector. Edge rays are rays that pass through the edge of the source or of the reflector. This approach makes it possible to obtain the exact solution for configurations for which the number of reflections is not impractically high. For the solution of general configurations I propose a fast numerical procedure. Based on interpolation between the impact points of a small number of edge rays, it offers high accuracy and unli ted resolution; the convergence is rapid as the number of rays is increased. A test that uses the example of a generalizedcompound parabolic concentrator demonstrates that with this method one can achieve accuracies that are far better than with conventional ray-trace methods while tracing a number of rays that are orders of magnitude smaller.
Conventional algorithms for rejecting cosmic rays in single CCD exposures rely on the contrast between cosmic rays and their surroundings and may produce erroneous results if the point-spread function is smaller than the largest cosmic rays. This paper describes a robust algorithm for cosmic-ray rejection, based on a variation of Laplacian edge detection. The algorithm identifies cosmic rays of arbitrary shapes and sizes by the sharpness of their edges and reliably discriminates between poorly sampled point sources and cosmic rays. Examples of its performance are given for spectroscopic and imaging data, including Hubble Space Telescope Wide Field Planetary Camera 2 images.
A very cheap way might be to just use a pre-blurred texture billboard. Or maybe a few layers of criss-crossing fixed geometry with a blurry texture and additive blending. For additive blending, a bright light colour that fades to black at the edges - alpha is not necessary. Something like this?
I just found this approach too. Static geometry with additive blending again, but with the softer edges you're after. The normal of the cone geometry and distance from the tip is used to guess the thickness. The depth buffer is also used to bound the thickness in the event objects are inside the cone.
Aiming to control chemical reactions via manipulating electron dynamics in molecules with ultrashort laser pulses27, attosecond water window X-rays will also play an important role in the emerging field of attochemistry. Charge migration, a process strongly affecting chemical reactivity, occurs on sub to few femtosecond time scale28, 29. Water window attosecond pulses are unique tools for measuring the charge distribution in molecules containing carbon/oxygen atoms and exploring the possibility to predetermine chemical reaction path by controlling the initial charge migration step27.
Image of unfiltered x rays, apertured by the back-thinned optic (a), simulation of the unfiltered x-ray image (b), horizontal (c), and vertical (d) lineouts of the image and simulation through the center.
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