Gravitational Lensing and Wormhole Shadows

The problem of bending and scattering of light rays passing outside the entrance of a wormhole with zero gravitational mass is considered. The process of ray capture by a wormhole, as well as the formation process of a shadow when illuminated by a standard screen, is investigated. These mechanisms are also compared to the case of light ray motion in the vicinity of the Schwarzschild black hole.

Light-driven dynamic surface wrinkles for adaptive visible camouflage

Camouflage is widespread in nature, engineering, and the military. Dynamic surface wrinkles enable a material the on-demand control of the reflected optical signal and may provide an alternative to achieve adaptive camouflage. Here, we demonstrate a feasible strategy for adaptive visible camouflage based on light-driven dynamic surface wrinkles using a bilayer system comprising an anthracene-containing copolymer (PAN) and pigment-containing poly (dimethylsiloxane) (pigment-PDMS). In this system, the photothermal effect–induced thermal expansion of pigment-PDMS could eliminate the wrinkles. The multiwavelength light–driven dynamic surface wrinkles could tune the scattering of light and the visibility of the PAN film interference color. Consequently, the color captured by the observer could switch between the exposure state that is distinguished from the background and the camouflage state that is similar to the surroundings. The bilayer wrinkling system toward adaptive visible camouflage is simple to configure, easy to operate, versatile, and exhibits in situ dynamic characteristics without any external sensors and extra stimuli.

A NOVEL METHOD BASED ON THE OTSU THRESHOLD FOR INSTANTANEOUS ELIMINATION OF LIGHT REFLECTION IN PIV IMAGES

The base of particle image velocimetry (PIV) is the maximization of the correlation between the distribution of particle images in an interrogation window or a volume separated by an instant of time. In real images, the unwanted reflection of light on fixed walls or moving objects can directly interfere with the correlation, deteriorating the PIV quality. In this work, a new method for automatically generating instantaneous masks based on the Otsu threshold for instantaneous elimination of light reflection in PIV images is proposed. This method separates the saturated image caused by the unwanted scattering of light from the tracer particles images through the Otsu threshold combined with the Gauss filter and Wiener adaptive local filter. This new method, called Otsu-Gauss-Wiener (OGW), was first tested using synthetic PIV images. In these tests, the authors analyzed the reflection caused by an object regarding different sizes, shapes, and intensities to evaluate the performance of the proposed method. Later, the OGW method was tested in PIV experimental cases with real adversities, for example, scattering of light on a fixed wall in a channel with periodic hills (Case B – 4th PIV Challenge), strong reflection in a centrifugal impeller (Case C – 1st PIV Challenge) and light scattering caused by an out-of-plane motion of the diaphragm of a pulsatile pediatric ventricular assist device. The results shown that the method can remove the reflections by static and moving objects using an automatic mask generated for each instantaneous image.

An Explanation of Subsurface Optical Pathways through Food Myosystems and their Effect on Colorimetry

Light may pass along and across the long axes of muscle fibers in any food myosystem. Thus, incident light may be scattered in several ways before some of it reappears at the surface as diffuse reflectance. Pathways may be short if scattering is strong, or long if scattering is weak. Short pathways minimize selective absorbance by chromophores such as myoglobin, while long pathways maximize selective absorbance. Many food myosystems exhibit a post-mortem decrease in pH caused by anaerobic glycolysis with a series of microstructural changes – glycogen granules between myofibrils are lost, myofibrils shrink laterally as myofilaments move closer together, water moves from within myofibrils to the space between them, muscle fiber membranes leak and lose their electrical capacitance, and myoglobin is flushed into the fluid filled spaces between muscle fibers. These changes increase scattering of light passing across the long axes of muscle fibers. Scattering of light along muscle fibers is caused by sarcomere discs (A-bands). Interference from one or a small number of sarcomere discs may cause iridescence, but in most cases interference from numerous discs causes achromatic diffuse reflectance. Commission International de l’Éclairage (CIE) chromaticity coordinates were calculated for various subsurface optical pathways. Pathways across versus along muscle fibers had a strong effect on CIE y (r = 0.84, P < 0.01) and an even stronger effect on CIE Y% (r = 0.95, P < 0.005).