Reflection Off Research Articles

National Park visitors perceive benefits for themselves and wildlife under blended red-white outdoor lighting

Visitors to Colter Bay Village in Grand Teton National Park were surveyed to elicit their evaluations of experimental outdoor lighting conditions. Luminaires capable of dimming and switching between two LED modules (white, blended red-white) were installed in street and parking areas. The blended red-white lamps consisted of 30 narrowband LED with a peak wavelength 623 nm and two 3000 K white LEDs. Similar “red” lamps were previously shown to reduce impacts to bats and insects. The white and red lamps were closely matched for luminance. Measured horizontal illuminance at survey locations had an interquartile range from 0.63 to 3.82 lx. The red lamps produced lower perceived brightness (VB2(λ)), even after reflection off asphalt, yet survey participants expressed higher ratings for visual comfort and safety under red lighting. Surveys conducted earlier in the evening, with higher levels of predicted solar and measured horizontal illuminance, rated higher on visual comfort and safety, though these correlations were not as strong as the effect of lamp color. Streetlight ratings and support for lighting that protected natural resources were not contingent upon age or gender. Survey participants assessed red lighting as more protective of the environment. These results demonstrate that outdoor lighting designed to reduce ecological impacts can yield superior nocturnal experience for pedestrians.

Microphysics of shock-grain interaction for inertial confinement fusion ablators in a fluid approach.

Ablator materials used for inertial confinement fusion, such as high-density carbon (HDC) and beryllium, have grain structure which may lead to small-scale density nonuniformity and the generation of perturbations when the materials are shocked and compressed. Here, we use a combination of a linear theory of shock interaction with density nonuniformity [Velikovich et al., Phys. Plasmas 14, 072706 (2007)10.1063/1.2745809] and numerical simulations to study shock interaction with a model representation of HDC grains. While the shock-grain interaction is nonlinear, the linear theory shows some key features of the shock-grain interaction, which also hold for the (nonlinear) simulations. The postshock perturbations are made up of sonic reflections off of grain boundaries and vorticity deposition along them, with the latter dominating the perturbed energy content. The mean (per mass) postshock perturbed kinetic energy decreases with increasing grain size, but energy will be deposited at increasing spatial scale. From the perspective of the postshock perturbed energy, the detailed linear theory largely supports a proposed method [S. Davidovits et al., Phys. Plasmas 29, 112708 (2022)1070-664X10.1063/5.0107534] for deresolving the grains (in a similar grains model) that treats the grains statistically. Our simulation results highlight the influence of thermal conduction on the perturbation dynamics at grain scales.

Friction tensor for an ellipsoid enclosed in a rarefied gas

This research renders calculations of rotranslational friction and diffusion tensors in a rarefied gas, considering both specular and diffuse reflection off ellipsoidal particles. Calculations were conducted in a spherical polar coordinate system, revealing the dynamic nature of these off-diagonal tensors. The tensor elements were determined analytically, intending to compute the surface integrals. All diagrams, and pictures of two-dimensional surfaces were obtained by the numerical integration process in MATLAB. Additionally, we performed calculations without using the time parameter and time derivatives in the relevant relations. Deviations from the state of spherical symmetry were observed in the results for an ellipsoid and show that the tensors are dynamic quantities. Therefore, it is necessary to provide average values. We established that the non-zero elements of the friction tensor for an ellipsoid represent the directions of linear momentum transfer. Also, the non-zero components of the diffusion tensor signify the extent of fluctuations in relevant momentum transfers in corresponding directions.

Behavioral responses of free-flying Drosophila melanogaster to shiny, reflecting surfaces

Active locomotion plays an important role in the life of many animals, permitting them to explore the environment, find vital resources, and escape predators. Most insect species rely on a combination of visual cues such as celestial bodies, landmarks, or linearly polarized light to navigate or orient themselves in their surroundings. In nature, linearly polarized light can arise either from atmospheric scattering or from reflections off shiny non-metallic surfaces like water. Multiple reports have described different behavioral responses of various insects to such shiny surfaces. Our goal was to test whether free-flying Drosophila melanogaster, a molecular genetic model organism and behavioral generalist, also manifests specific behavioral responses when confronted with such polarized reflections. Fruit flies were placed in a custom-built arena with controlled environmental parameters (temperature, humidity, and light intensity). Flight detections and landings were quantified for three different stimuli: a diffusely reflecting matt plate, a small patch of shiny acetate film, and real water. We compared hydrated and dehydrated fly populations, since the state of hydration may change the motivation of flies to seek or avoid water. Our analysis reveals for the first time that flying fruit flies indeed use vision to avoid flying over shiny surfaces.

Quantum atomic matter near two-dimensional materials in microgravity

Novel two-dimensional atomically flat materials, such as graphene and transition-metal dichalcogenides, exhibit unconventional Dirac electronic spectra. We propose to effectively engineer their interactions with cold atoms in microgravity, leading to a synergy between complex electronic and atomic collective quantum phases and phenomena. Dirac materials are susceptible to manipulation and quantum engineering via changes in their electronic properties by application of strain, doping with carriers, adjustment of their dielectric environment, etc. Consequently the interaction of atoms with such materials, namely the van der Waals/Casimir–Polder interaction, can be effectively manipulated, leading to the potential observation of physical effects such as quantum reflection off atomically thin materials and confined Bose–Einstein condensate frequency shifts.

Polarization-dependent beam shifts upon metallic reflection in high-contrast imagers and telescopes

Context. To directly image rocky exoplanets in reflected (polarized) light, future space- and ground-based high-contrast imagers and telescopes aim to reach extreme contrasts at close separations from the star. However, the achievable contrast will be limited by reflection-induced polarization aberrations. While polarization aberrations can be modeled with numerical codes, these computations provide little insight into the full range of effects, their origin and characteristics, and possible ways to mitigate them. Aims. We aim to understand polarization aberrations produced by reflection off flat metallic mirrors at the fundamental level. Methods. We used polarization ray tracing to numerically compute polarization aberrations and interpret the results in terms of the polarization-dependent spatial and angular Goos-Hänchen and Imbert-Federov shifts of the beam of light as described with closed-form mathematical expressions in the physics literature. Results. We find that all four beam shifts are fully reproduced by polarization ray tracing. We study the origin and characteristics of the shifts as well as the dependence of their size and direction on the beam intensity profile, incident polarization state, angle of incidence, mirror material, and wavelength. Of the four beam shifts, only the spatial Goos-Hänchen and Imbert-Federov shifts are relevant for high-contrast imagers and telescopes because these shifts are visible in the focal plane and create a polarization structure in the point-spread function that reduces the performance of coronagraphs and the polarimetric speckle suppression close to the star. Conclusions. Our study provides a fundamental understanding of the polarization aberrations resulting from reflection off flat metallic mirrors in terms of beam shifts and lays out the analytical and numerical tools to describe these shifts. The beam shifts in an optical system can be mitigated by keeping the f-numbers large and angles of incidence small. Most importantly, mirror coatings should not be optimized for maximum reflectivity, but should be designed to have a retardance close to 180°. The insights from our study can be applied to improve the performance of SPHERE-ZIMPOL at the VLT and future telescopes and instruments such as the Roman Space Telescope, the Habitable Worlds Observatory, GMagAO-X at the GMT, PSI at the TMT, and PCS (or EPICS) at the ELT.

Wide-Aperture MIMO via Reflection off a Smooth Surface

This paper provides a deterministic channel model for a scenario where wireless connectivity is established through a reflection off a smooth planar surface of an infinite extent. The developed model is rigorously built upon the physics of wave propagation and is as precise as tight are the unboundedness and smoothness assumptions on the surface. This model allows establishing how line-of-sight multiantenna communication is altered by a reflection off an electrically large surface, a situation of high interest for mmWave and terahertz frequencies.

DDT run-up distance in an obstructed tube

Self-luminous high-speed photography was used to study flame acceleration and deflagration-to-detonation transition (DDT) in a clear polycarbonate round tube equipped with orifice plates. The 288 cm long, 7.6 cm inner-diameter tube was equipped with equally spaced 50% and 75% area-blockage orifice plates. The primary test mixture was stoichiometric ethylene–oxygen diluted with varying amounts of nitrogen, and the initial pressure was varied between 5 and 90 kPa. Tests were also performed with stoichiometric hydrogen–oxygen with large argon dilution to study the effect of detonation cell structure regularity. High-speed video showed that the initial DDT always occurred following shock reflection off an obstacle, allowing an accurate determination of the DDT run-up distance. Soot foils were used to measure cell size at the end of the obstacle-free tube. A correlation for flame acceleration to one-half the Chapman–Jouguet detonation velocity (VCJ) predicted the measured DDT run-up distance successfully for the most reactive mixture conditions. However, the measured DDT run-up distance increasingly deviated from the correlation with decreasing initial pressure, significantly under predicting the run-up distance at the DDT limit. A correlation for the DDT run-up distance was proposed based on the concept of flame acceleration to one-half VCJ followed by an induction phase that ends with the transition to detonation. For a given tube and obstacle configuration, the flame acceleration distance depends on the flame properties, and the DDT induction distance depends on the properties that quantify the detonation length-scale and stability.

Acoustic Wave Reflection in Water Affects Underwater Wireless Sensor Networks.

The phenomenon of acoustic wave reflection off fluid-solid surfaces is the focus of this research. This research aims to measure the effect of material physical qualities on oblique incidence acoustic attenuation across a large frequency range. To construct the extensive comparison shown in the supporting documentation, reflection coefficient curves were generated by carefully adjusting the porousness and permeability of the poroelastic solid. The next stage in determining its acoustic response is to determine the pseudo-Brewster angle shift and the reflection coefficient minimum dip for the previously indicated attenuation permutations. This circumstance is made possible by modeling and studying the reflection and absorption of acoustic plane waves encountering half-space and two-layer surfaces. For this purpose, both viscous and thermal losses are taken into account. According to the research findings, the propagation medium has a significant impact on the form of the curve that represents the reflection coefficient, whereas the effects of permeability, porosity, and driving frequency are relatively less significant to the pseudo-Brewster angle and curve minima, respectively. This research additionally found that as permeability and porosity increase, the pseudo-Brewster angle shifts to the left (proportionally to porosity increase) until it reaches a limiting value of 73.4 degrees, and that the reflection coefficient curves for each level of porosity exhibit a greater angular dependence, with an overall decrease in magnitude at all incident angles. These findings are given within the framework of the investigation (in proportion to the increase in porosity). The study concluded that when permeability declined, the angular dependence of frequency-dependent attenuation reduced, resulting in iso-porous curves. The study also discovered that the matrix porosity largely affected the angular dependency of the viscous losses in the range of 1.4 × 10-14 m2 permeability.

Acoustic cavitation localization during histotripsy using transmit-receive capable arrays

The nucleation and collapse of cavitation generated during histotripsy results in point-like emissions of shockwaves. Owing to the short duration acoustic pulses utilized during histotripsy the acoustic background from pulse reflections off intervening tissues is minimal and temporally isolated. This allows acoustic cavitation emission (ACE) shockwaves to be differentiated from the background in measured signals using simplified approaches such as peak detection and time gating, even in signals acquired using narrow bandwidth receivers such as the transmitting elements of the histotripsy array. The array elements allow acquisitions from across the array's entire aperture, which in turn allows cavitation to be localized in 3D. Here we describe multiple methods for localizing cavitation and evaluating induced tissue damage based on ACE signals measured using transmit-receive capable histotripsy arrays. The speed and accuracy of the methods were evaluated in ex vivo and in vitro experiments. Cavitation could be localized in 3D at rates >100Hz. Mean localization errors, with respect to measurements from optical images, were <2 mm (approximately the diameter of the generated bubbles). Cavitation lifespans could be assessed concurrently with the bubbles' 3D locations and correlated well with histological observations of induced damage, allowing 3D assessments of damage.

Towards a Multi-Perspective Time of Flight Laser Ranging Device Based on Mirrors and Prisms

This paper investigates the feasibility of redirecting the field of view (FOV) of a light-based time-of-flight (ToF) ranging device, commonly known as a pulsed lidar, using fixed mirrors and prisms for possible future use in robotics. The emphasis is on configurations where the FOV redirection element is positioned beyond the ranging device’s dead zone. A custom made direct ToF ranging device with time-over-threshold (TOT)-based walk error compensation was used to evaluate the effects of the FOV redirecting optics on range measurement accuracy and precision. The tests include redirecting the FOV with a clean prism with anti-reflective (AR) coating on its legs, as well as with a regular and a first surface mirror in both a clean and dusted state. The study finds the prism to be unsuitable due to parasitic reflections, which ruin the ranging data. The clean mirrors were found to have no noticeable effect on ranging accuracy. When they are dusty, mirrors introduce a negative measurement error. This effect is the most pronounced when a mirror is positioned toward the end of the partial dead zone of the ToF rangefinder, but loses influence as the mirror is moved farther away. The error is attributed to the parasitic reflection off dust on the mirror, which reduces the time of detection of the pulse reflected off the real target, and interferes with the walk error compensation by widening the detected pulse.

Kinetic effects on the 660-km-phase transition in mantle upstreams and seismological implications

Summary The effects of reaction kinetics of bridgmanite and ferropericlase transforming to ringwoodite on elastic properties in upwelling mantle are investigated using data of kinetic experiments and internally self-consistent thermodynamic modelling of density and seismic velocities. The kinetic experiments show inhibited grain growth of ringwoodite. At the initiation of ringwoodite growth, bridgmanite completely transforms to a metastable pyrope-bearing garnet. Ringwoodite then gradually grows from the metastable assemblage of ferropericlase and garnet. The changes in mineralogy result in a low-velocity zone directly above the 660 km seismic discontinuity due to the lower seismic velocities and densities of ferropericlase and garnet compared to ringwoodite and bridgmanite. The modelling of the effects of reaction kinetics and its effect on seismic structure at ∼660 km depth shows more sensitivity to grain size than to temperature and upwelling rate. Modelling 1-D synthetic seismograms of PP (SS) underside reflections off the kinetically inhibited backward reaction to ringwoodite shows advanced traveltimes of underside reflections off ∼660 km depth of 0.2–0.8 s (1.2–1.6 s) for upwelling rates of 50 cm yr–1 and initial grain sizes between 5 and 20 cm due to the low-velocity zone above the 660 km discontinuity. The finite width of the low-velocity layer results in frequency-dependent behaviour of PP and SS underside reflection amplitudes, with higher amplitudes towards shorter periods. The effect on the traveltimes of P-to-s conversions used for receiver function is small (<0.7 s) but the inhibited backward reaction leads to strong amplitude changes and significant waveform variations. The effects of reaction kinetics in mantle upwellings might serve as an additional means to map regions of large-scale upwellings and to constrain grain size in the lower mantle.

Topological reflection matrix

While periodically-driven phases offer a unique insight into non-equilibrium topology that is richer than its static counterpart, their experimental realization is often hindered by ubiquitous decoherence effects. Recently, we have proposed a decoherence-free approach of realizing these Floquet phases. The central insight is that the reflection matrix, being unitary for a bulk insulator, plays the role of a Floquet time-evolution operator. We have shown that reflection processes off the boundaries of systems supporting higher-order topological phases (HOTPs) simulate non-trivial Floquet phases. So far, this method was shown to work for one-dimensional Floquet topological phases protected by local symmetries. Here, we extend the range of applicability by studying reflection off three-dimensional HOTPs with corner and hinge modes. We show that the reflection processes can simulate both first-order and second-order Floquet phases, protected by a combination of local and spatial symmetries. For every phase, we discuss appropriate topological invariants calculated with the nested scattering matrix method.

Fluorescence strobo-stereoscopy for specular reflection-suppressed full field of view imaging

This paper introduces fluorescence strobo-stereoscopy (FSS) to suppress strong specular reflection and enable the full field of view (FFOV) 3D surface imaging while the part is rotating. Specular reflection off the target surface significantly degrades the image quality and becomes critical for highly reflective surface measurements. In FSS, the fluorescent dye-doped fluid applied on the machined surface is excited upon incident ultra-violet light and becomes a new light source by Stokes' Law. Thus, specular reflection off of smooth surface can be suppressed by separating the fluorescent light from the excitation light. The developed FSS comprises a pair of imaging cameras, spatial filters, and an excitation light source. As a result, FSS effectively rejected the specular reflection and improved the FFOV 3D surface image quality of the machined part by enhancing contrast in the rotating target surface. Such enhancements in 3D imaging allowed to identify manufacturing tolerance of the part and to detect the surface features. The axial and lateral accuracy errors of FSS were 2.3% and 1.4% with the target size of 4.07 mm and 0.215 mm, respectively. A whole view reconstruction of the cylindrical target sample was performed, and the corresponding cylindricity and diameter deviation were assessed. The fluid media effect and the target surface quality effect were discussed.

Near-Range Multipath Mitigation Methodology for Multistatic SAR Applications Using Matched-Adaptive Filters

This article presents a methodology based on matched-adaptive filters, which is used to mitigate the effect of near-range multipath in multistatic SAR systems and transponders. It is challenging to physically construct a bistatic receiver such that the reference signal is not leaked into the received signal, either via coupling in the circuitry or via reflections off objects in the vicinity of the receiver. Due to its much larger amplitude, the reference signal can easily mask near-range targets with its sidelobes. A similar signal degradation is observed in active transponders that are used for calibrating radar systems, when objects exist in their vicinity. In this article, we address these two issues: the coupling between the reference channel and the imaging channel, and the parasitic echoes present in the transponder response. A novel methodology is proposed that is capable of time-domain filtering the undesired components in real time. The novelty consists in combining matched and adaptive filters as a means of boosting performance and resolution estimation, resulting in an extremely accurate multipath elimination method. The proposed methodology is experimentally evaluated and optimized for each of the two aforementioned problems.

SRG/eROSITA view of X-ray reflection in the Central Molecular Zone: a snapshot in September–October 2019

ABSTRACT X-ray reflection off dense molecular clouds in the Galactic Centre region has established itself as a powerful probe for the past activity record of the supermassive black hole Sgr A* on a time-scale of a few hundred years. Detailed studies of the reflection signal from individual clouds allow us to estimate parameters of the brightest flare(s) and explore properties of the dense gas distribution inside and around them. On the other hand, wide-area surveys covering the full Central Molecular Zone (CMZ) are crucial to spot the brightening of the new clouds and long-term decay of the flux from the once bright ones. Here, we present and discuss the data obtained by the SRG/eROSITA telescope in the course of its commissioning observations in late 2019 in regard to the X-ray reflection off CMZ clouds located to the East of Sgr A*. We measure the hard X-ray (4–8 keV) flux from the currently brightest (in reflected emission) molecular complex, Sgr A, and derive upper limits for other molecular complexes. We confirm that the Sgr A complex keeps being bright at the level of $4\times 10^{-13}\,{\rm erg\, s^{-1}\,cm^{-2}\,arcmin^{-2}}$, making it an excellent candidate for the deep forthcoming high-resolution imaging and polarimetric observations. We also discuss distinct features of the reflected emission from the clouds for which the primary illumination front has already passed away and the signal is dominated by multiply scattered radiation.

Autonomous Vision-Guided Object Collection From Water Surfaces With a Customized Multirotor

This article presents a multirotor system with an integrated net mechanism for autonomous object detection and collection from water surfaces utilizing only onboard sensors. The task of object collection on water surfaces is challenging due to the following reasons: 1) propeller outwash alters the object's dynamics; 2) unpredictable current flows, 3) extreme reflection and glare off water surfaces affect the object detection; and 4) noisy height measurements over water surface. A two-phase object-detection algorithm is developed with a linearized polarization filter and specularity removal algorithm to eliminate reflections and an edge-based contour detector for detection of objects on water surface. Subsequently, a boundary layer sliding-mode control is implemented to ensure the system is robust to modeling uncertainties. A dynamic sliding surface is designed based on constrained linear model predictive control. The efficacy of the proposed collection system is validated by multiple outdoor tests. Multiple objects of different shapes and sizes are collected with an overall success rate of 91.6%.

Solving the Alhazen–Ptolemy Problem: Determining Specular Points on Spherical Surfaces for Radiative Transfer of Titan’s Seas

Abstract Given a light source, a spherical reflector, and an observer, where on the surface of the sphere will the light be directly reflected to the observer, i.e., where is the specular point? This is known as the Alhazen–Ptolemy problem and finding this specular point for spherical reflectors is useful in applications ranging from computer rendering to atmospheric modeling to GPS communications. Existing solutions rely upon finding the roots of a quartic equation and evaluating numerically which root provides the real specular point. We offer a formulation, and two solutions thereof, for which the correct root is predeterminable, thereby allowing the construction of the fully analytical solutions we present. Being faster to compute, our solutions should prove useful in cases that require repeated calculation of the specular point, such as Monte Carlo radiative transfer, including reflections off of Titan’s hydrocarbon seas.

Study of RSS-Based Indoor Positioning System for Target Using Visible Light Communication

An optical wireless positioning system that uses white light-emitting diodes (LEDs) based on Visible Light Communication (VLC) is presented in this paper. In the proposed system, four LEDs are employed for illumination and communication. The trilateration technique is used for determining the receiver's location and the practical Received Signal Strength (RSS) measurements are used for distance estimation. The impact of ambient light on Signal-to-Noise-Ratio (SNR) is studied by taking into consideration the first-order light reflection off of the ceiling, floor, and walls for channel modeling with both direct and indirect sunlight exposure. A modeling equation from the RSS measurements is proposed. The results show that the illuminance in all of the places in the room can be satisfied. Furthermore, the average positioning error by adopting the derived equation and trilateration technique was an error of less than 3 cm.

Surface conductivity effects during shock wave reflection off curved surfaces

Previous work has shown that heat transfer into a plane conducting surface affects shock wave reflection properties. In the more complex reflection case of a curved surface the situation would be different because of the increased number of reflection patterns, with a rapid change in reflection geometry as the wave propagates up the surface. Test pieces of different thermal conductivities (0.19 W/mK and 401 W/mK) and hydraulically smooth surfaces are used on both convex and concave cylindrical surfaces. The test pieces are placed in identical positions on either side of a plane of symmetry and at the same incident angles in a shock tube. Tests are performed at incident shock Mach numbers of 1.22< M <1.5 and imaged using high-speed shadowgraph photography. The images are analyzed both quantitatively through reflection angle measurements and qualitatively by searching for asymmetry. Both the qualitative and quantitative measurements clearly indicate that the thermal conductivity of the surface affects the reflection patterns due to the complex transient thermal environment. Asymmetry in the reflection patterns is found at all Mach numbers. In contrast to the plane wall case the lack of theory limits comparison, where in that case it was shown that the lower the thermal conductivity the closer the experimental results approached the ideal adiabatic case. Similar comparisons in the relationship of reflection types between different materials are found in the current case. The findings could be refined by using higher imaging frame rates and spatial resolution, and sophisticated numerical modeling.