Multiple Refraction Research Articles

Specular manifold sampling for rendering high-frequency caustics and glints

Scattering from specular surfaces produces complex optical effects that are frequently encountered in realistic scenes: intricate caustics due to focused reflection, multiple refraction, and high-frequency glints from specular microstructure. Yet, despite their importance and considerable research to this end, sampling of light paths that cause these effects remains a formidable challenge. In this article, we propose a surprisingly simple and general sampling strategy for specular light paths including the above examples, unifying the previously disjoint areas of caustic and glint rendering into a single framework. Given two path vertices, our algorithm stochastically finds a specular subpath connecting the endpoints. In contrast to prior work, our method supports high-frequency normal- or displacement-mapped geometry, samples specular-diffuse-specular ("SDS") paths, and is compatible with standard Monte Carlo methods including unidirectional path tracing. Both unbiased and biased variants of our approach can be constructed, the latter often significantly reducing variance, which may be appealing in applied settings (e.g. visual effects). We demonstrate our method on a range of challenging scenes and evaluate it against state-of-the-art methods for rendering caustics and glints.

Subsurface Weathering Revealed in Hillslope‐Integrated Porosity Distributions

AbstractSubsurface weathering has traditionally been measured using cores and boreholes to quantify vertical variations in weathered material properties. However, these measurements are typically available at only a few, potentially unrepresentative points on hillslopes. Geophysical surveys, conversely, span many more points and, as shown here, can be used to obtain a representative, site‐integrated perspective on subsurface weathering. Our approach aggregates data from multiple seismic refraction surveys into a single frequency distribution of porosity and depth for the surveyed area. We calibrated the porosities at a site where cores are coincident with seismic refraction surveys. Modeled porosities from the survey data match measurements at the core locations but reveal a frequency distribution of porosity and depth that differs markedly from the cores. Our results highlight the value of using the site‐integrated perspective obtained from the geophysical data to quantify subsurface weathering and water‐holding capacity.

Efficient photocatalytic hydrogen production using an NH4TiOF3/TiO2/g-C3N4 composite with a 3D camellia-like Z-scheme heterojunction structure

Photocatalysis is one of the most promising ways to realize artificial photosynthesis. The biologically inspired photocatalysts with 3D flower-like structures have attracted much attention. In this study, an effective method for the synthesis of composite photocatalytic material, NH4TiOF3/TiO2/g-C3N4, with a 3D camellia-like structure, was developed. The 3D hierarchical structure of the composite material enabled multiple refractions and reflections of light within the catalyst, which greatly improved the efficiency of the sunlight harvesting. The combination of NH4TiOF3 and TiO2 also effectively reduced the electron-hole recombination in the g-C3N4. To evaluate its photocatalytic performance, the prepared nanostructured composite materials were tested for the water-splitting with simulated sunlight. It showed the hydrogen evolution at the rate of 3.6 mmol/g/h, which is 4.0 times faster than that from the pure g-C3N4. The composite materials exhibited excellent cycling stability. The detailed mechanism of the Z-scheme heterojunction was also discussed. The proposed synthesis route for the creation of 3D flower-like hierarchical composites provides a new effective technique for developing efficient, active, and stable composite photocatalysts for hydrogen production.

Acoustic spin-1 Weyl semimetal

Topological semimetal, hosting spin-1 Weyl point beyond Dirac and Weyl points, has attracted a great deal of attention. However, the spin-1 Weyl semimetal, which possesses exclusively the spin-1 Weyl points in a clean frequency window, without shadowed by any other nodal points, is yet to be discovered. Here, we report for the first time a spin-1 Weyl semimetal in a phononic crystal. Its spin-1 Weyl points, touched by two linear dispersions and an additional flat band, carry monopole charges (-2,0,2) or (2,0,-2) for the three bands from bottom to top, and result in double Fermi arcs existing both between the 1st and 2nd bands, as well as between the 2nd and 3rd bands. We further observe robust propagation against the multiple joints and topological negative refraction of acoustic surface arc wave. Our results pave the way to explore on the macroscopic scale the exotic properties of the spin-1 Weyl physics.

Multi-Field Interference Simultaneously Imaging on Single Image for Dynamic Surface Measurement.

To obtain the dynamic surface of high-frequency vibrating mirrors (VMs), a novel method involving multi-field interference (MFI) pattern imaging on a single image is proposed in this paper. Using multiple reflections and refractions, the proposed method generates three interference patterns at the same time, which improves the traditional time-series methods where a single interference pattern can be obtained at one time. Experimental results show that a series of MFI patterns can be obtained on a single image, with the laser repetition frequency (LRF) ranging from 200 Hz to 10 Hz, and the frame rate of the camera at 10 Hz. Particularly if the LRF (10 Hz) is equal to the frame rate of image, crosstalk is avoided completely, which is particularly desirable in dynamic surface measurement. In summary, the MFI imaging method provides an effective way for VM dynamic surface measurement.

Detection of Fermi arcs in Weyl semimetals through surface negative refraction

One of the main features of Weyl semimetals is the existence of Fermi arc surface states at their surface, which cannot be realized in pure two-dimensional systems in the absence of many-body interactions. Due to the gapless bulk of the semimetal, it is, however, challenging to observe clear signatures from the Fermi arc surface states. Here, we propose to detect such novel surface states via perfect negative refraction that occurs between two adjacent open surfaces with properly orientated Fermi arcs. Specifically, this phenomenon visibly manifests in non-local transport measurement, where the negative refraction generates a return peak in the real-space conductance. This provides a unique signature of the Fermi arc surface states. We discuss the appearance of this peak both in inversion and time-reversal symmetric Weyl semimetals, where the latter exhibits conductance oscillations due to multiple negative refraction scattering events.

Scattering of aerosol by a high-order Bessel vortex beam for multimedia information transmission in atmosphere

The essence of wireless communication and multimedia information transmission is the propagation of electromagnetic waves in the atmosphere. Within the framework of Generalized Lorenz Mie theory, and combining the vector wave theory with the generalized multi-spheres Mie theory, the analytical solution to the scattering of the high-order Bessel vortex beam (HOBVB) by aerosol aggregation in atmosphere is investigated. The angle distributions of the scattered field of soot, silicate and nitrate aerosol cluster particles illuminated by a HOBVB are numerically discussed. The examples are selected to illustrate the effects of aggregation configuration, mean value, particle number, topological charge and half-cone angle of the beam on the angle distribution of scattered field. It is noticed that the angle distribution of scattered field is sensitive to the configuration of the cluster for the multiple refraction and interactive scattering. The variation of the mean value of radius of the aerosol aggregation will result in different scattering characteristics and different transmission efficiency. The integration of the scattering algorithm and deep learning can be used in inversion of the shape and components of the aerosol clusters and in the improvement of transmission efficiency of multimedia information in atmosphere.

Analytical study of surface wave multiple refraction in boundary of a scalar impedance surface with a tensor impedance surface

In this paper, the multiple refraction phenomenon is investigated on the boundary of a scalar impedance surface (SIS) and a tensor impedance surface (TIS). When a surface wave (SW) propagates on the SIS and radiates to the boundary of the TIS, the propagation direction of it is changed and the refraction phenomenon is accrued. The method that is proposed in this paper can predict the multiple refraction for the SW. Moreover, another analytical method is introduced for designing the proposed structure which the double refraction (DR) occurs at arbitrary angles on it. Using it, a sample of the structure is designed by printed circuits in 15.2GHz and the results are verified by the full-wave simulation and measurement. The results are shown that in the structure, DR is occurred in 2° and 22° as predicted. The proposed method can provide many applications such as design of SW power dividers based on the TISs, impedance surface based waveguides, holographic antennas, and feeding of array antennas.

Structure and pigment make the eyed elater’s eyespots black

Surface structures that trap light leading to near complete structural absorption creates an appearance of “super black.” Well known in the natural world from bird feathers and butterfly scales, super black has evolved independently from various anatomical structures. Due to an exceptional ability to reduce specular reflection, these biological materials have garnered interest from optical industries. Here we describe the false eyes of the eyed elater click beetle, which, while not classified as super black, still attains near complete absorption of light partly due to an array of vertically-aligned microtubules. These cone-shaped microtubules are modified hairs (setae) that are localized to eyespots on the dorsum of the beetle, and absorb 96.1% of incident light (at a 24.8° collection angle) in the spectrum between 300–700 nm. Filled with melanin, the setae combine structure and pigment to generate multiple reflections and refractions causing light to travel a greater distance. This light-capturing architecture leaves little light available to receivers and the false eyes appear as deep black making them appear more conspicuous to predators.

Temporal-Frequency Attention-Based Human Activity Recognition Using Commercial WiFi Devices

Human activity recognition has been growing for decades in a variety of technological disciplines. However, in the existing WiFi-based human activity recognition systems, there are the following problems: Firstly, in the processing of channel state information (CSI) data, mainly for the removal of noise in the superimposed signal, there is no effective removal of useless multipath signals; Secondly, the data segmentation algorithm based on the empirical threshold requires manual adjustment of the threshold in different environments, resulting in poor robustness and unstable segmentation; Thirdly, simple learning classification is applied without specific design for CSI data structure and sufficiently abstracting information features. In this paper, a device-free human activity recognition system with a temporal-frequency attention mechanism is proposed, which can be deployed on commercial WiFi devices to identify human's daily activities. Firstly, the multipath signal affected by the channel change is extracted by using the difference of the propagation delay of different multipath, thereby eliminating the delay and invalid multipath signals that have undergone multiple reflections and refractions. Secondly, a neural network model based on attention mechanism is proposed, which assigns different weights to different characteristics and sequences by imitating the human brain to dedicate more attention to important information. Then, the long short-term memory (LSTM) model is used to learn the correlation features of different dimensions to realize human activity recognition. Finally, the system performance is evaluated in different environments, and the experimental results show that our syetem holds a better performance in both line-of-sight (LOS) and non-line-of-sight (NLOS) than the existing human activity recognition systems.

Lights Out! Nano-Scale Topography Imaging of Sample Surface in Opaque Liquid Environments with Coated Active Cantilever Probes.

Atomic force microscopy is a powerful topography imaging method used widely in nanoscale metrology and manipulation. A conventional Atomic Force Microscope (AFM) utilizes an optical lever system typically composed of a laser source, lenses and a four quadrant photodetector to amplify and measure the deflection of the cantilever probe. This optical method for deflection sensing limits the capability of AFM to obtaining images in transparent environments only. In addition, tapping mode imaging in liquid environments with transparent sample chamber can be difficult for laser-probe alignment due to multiple different refraction indices of materials. Spurious structure resonance can be excited from piezo actuator excitation. Photothermal actuation resolves the resonance confusion but makes optical setup more complicated. In this paper, we present the design and fabrication method of coated active scanning probes with piezoresistive deflection sensing, thermomechanical actuation and thin photoresist polymer surface coating. The newly developed probes are capable of conducting topography imaging in opaque liquids without the need of an optical system. The selected coating can withstand harsh chemical environments with high acidity (e.g., 35% sulfuric acid). The probes are operated in various opaque liquid environments with a custom designed AFM system to demonstrate the imaging performance. The development of coated active probes opens up possibilities for observing samples in their native environments.

Borehole interface converted electromagnetic wave of double cylindrical formation

In recent years, electrokinetic effect has received wide attention. The electrokinetic effect refers to the coupling and conversion of acoustic waves and electromagnetic waves in a porous medium. Due to the electric double layer structure of porous medium, electromagnetic waves are generated during acoustic waves propagation in the liquid-containing porous medium. Based on this phenomenon, one proposes a method for electrokinetic effect logging.The electrokinetic effect has great application prospects in earthquake prediction and engineering exploration. The generation mechanism and propagation law of acoustic-electric coupling wave in electrokinetic effect logging of double-cylindrical-layer porous medium are explored in this paper. By calculating the vertical secant integral of the electric field branch point, the total response of the interface converted electromagnetic wave can be obtained. Previously, in the cylindrical layered medium, the secant integral corresponding to the borehole fluid and the inner layer medium branch point is zero. So the examples in this paper are calculated from the vertical secant integral of branch point <i>k</i><sub>em2</sub>, which corresponds to the outermost infinite medium. It is found that when each time the longitudinal and transverse waves of the formation propagate to the interface, the interface converted electromagnetic waves are generated. These converted electromagnetic waves constitute the total response of the interface converted electromagnetic wave. At the same time, the influence of porous medium fluid salinity on interface converted electromagnetic wave is investigated. It is found that when only the inner layer porous medium fluid salinity changes, the amplitude of the interface converted electromagnetic wave response of the two interfaces is affected. When only the salinity of the outermost porous medium fluid changes, only the amplitude of the interface converted electromagnetic wave generated at the second interface is affected, but the interface electromagnetic waves generated at the internal interface are not influenced. When the difference in pore fluid salinity between both sides of the medium interface is larger, the amplitude of the interface converted electromagnetic wave is greater and the electromagnetic waves generated from the two interfaces are independent of each other.The case where fluid intrusion zone in porous medium is investigated, and the generation mechanism of interface converted electromagnetic wave is also studied when only a mineralization interface exists. It is found that the converted electric field is also generated when the acoustic waves propagates to the salinity interface. Since there exists neither multiple refraction of acoustic wave nor reflection of acoustic wave in the porous medium, the interface electromagnetic wave has only two wave packets, which are interface converted electromagnetic waves generated respectively at the borehole wall and at the electrochemical interface.The interface converted electromagnetic wave can be used to detect the location of the medium interface and the salinity interface. It can also clearly reflect the refraction and reflection law of wave propagating in stratified porous medium, which is of great significance for understanding the interface response mechanism of double-cylindrical-layer porous medium in electrokinetic effect logging.

Light absorption coefficients of ionic liquids under electric field**Project supported by the National Natural Science Foundation of China (Grant Nos. 51576054 and 51705210).

Ionic liquids have attracted a lot of research attention for their applications in novel optoelectronic structures and devices as an optical means of regulating electricity. Although the electro-optic effect of ionic liquids is mentioned in some literature, quantitative testing and analysis are hardly found in light absorption coefficients of ionic liquids under an electric field. In the present study, an experimental apparatus is designed to measure the absorption coefficients of ionic liquids under different electric fields. Five groups of imidazole ionic liquids are experimentally investigated and an inversion is performed to determine the spectral absorption coefficients of the imidazole ionic liquids under the electric fields. Different intensities with multiple interface refractions and reflections are also considered, and the various measurement errors are analyzed through uncertainties propagation analysis. Spectral absorptions of ionic liquids from 300 nm to 2500 nm are obtained and the absorption coefficients are retrieved. It is found that the absorption behavior of ionic liquids changes in some frequency bands under an applied electric field. The experimental results show that the absorption coefficient of the ionic liquid increases with the voltage increasing at 1520 nm and 1920 nm. The change rate is affected by the types of anions and cations in the ionic liquid and the diffusion rate of the ions therein. This study provides illustrations for the ionic liquid-based electro-optical regulation in terms of physical property parameters and the testing technique.

Physically-Based Rendering of Particle-Based Fluids with Light Transport Effects

Recent interactive rendering approaches aim to efficiently produce images. However, time constraints deeply affect their output accuracy and realism (many light phenomena are poorly or not supported at all). To remedy this issue, in this paper, we propose a physically-based fluid rendering approach. First, while state-of-the-art methods focus on isosurface rendering with only two refractions, our proposal (1) considers the fluid as a heterogeneous participating medium with refractive boundaries, and (2) supports both multiple refractions and scattering. Second, the proposed solution is fully particle-based in the sense that no particles transformation into a grid is required. This interesting feature makes it able to handle many particle types (water, bubble, foam, and sand). On top of that, a medium with different fluids (color, phase function, etc.) can also be rendered.

The propagation of longitudinal stress waves in an infinite rod with a viscoelastic region

The problem of propagation of longitudinal stress waves in an infinite piece-wise homogeneous rod with a viscoelastic region of finite size is solved. A mathematical formulation of the problem and its analytical solution in stresses are obtained. The solution uses the method of the Laplace integral transformation with respect to time. The expressions obtained allow one to determine the stresses in an arbitrary cross-section of the rod at any time. The structure of the solution reflects the process of transformation of the incoming wave with its multiple refraction and reflection at the boundaries of the sections. The solution obtained makes it possible to quantitatively investigate the damping effect of the viscoelastic region and can serve as the basis for selecting the parameters of the insert material when it is used to extinguish the dynamic effects.

Quijobytes: reflejos especulares del mito quijotesco en el ocio electrónico

Desde su publicación en 1605, Don Quijote se ha ido convirtiendo en parte de una cultura global colectiva, al ser traducido y adaptado a numerosas lenguas y contextos sociales. El más reciente paso en la tradición quijotesca es la aparición de videojuegos que supuestamente encuentran inspiración en el clásico cervantino. Estas nuevas remediaciones proporcionan una percepción de los múltiples reflejos del hipotexto, a veces ocultos en el crossover narrativo, o reducidos al uso del nombre del protagonista. Ya estén cerca o lejos del texto seminal, estas nuevas adaptaciones demuestran que el mito quijotesco tiene todavía una fuertepresencia en nuestra cultural global.

Realistic Ultrasound Simulation of Complex Surface Models Using Interactive Monte‐Carlo Path Tracing

AbstractRay‐based simulations have been shown to generate impressively realistic ultrasound images in interactive frame rates. Recent efforts used GPU‐based surface raytracing to simulate complex ultrasound interactions such as multiple reflections and refractions. These methods are restricted to perfectly specular reflections (i.e. following only a single reflective/refractive ray), whereas real tissue exhibits roughness of varying degree at tissue interfaces, causing partly diffuse reflections and refractions. Such surface interactions are significantly more complex and can in general not be handled by conventional deterministic raytracing approaches. However, these can be efficiently computed by Monte‐Carlo sampling techniques, where many ray paths are generated with respect to a probability distribution. In this paper, we introduce Monte‐Carlo raytracing for ultrasound simulation. This enables the realistic simulation of ultrasound‐tissue interactions such as soft shadows and fuzzy reflections. We discuss how to properly weight the contribution of each ray path in order to simulate the behaviour of a beamformed ultrasound signal. Tracing many individual rays per transducer element is easily parallelizable on modern GPUs, as opposed to previous approaches based on recursive binary raytracing. We further propose a significant performance optimization based on adaptive sampling.

One- and two-dimensional gap solitons and dynamics in the [formula omitted]-symmetric lattice potential and spatially-periodic momentum modulation

The influence of spatially-periodic momentum modulation on beam dynamics in parity-time (PT) symmetric optical lattice is systematically investigated in the one- and two-dimensional nonlinear Schrödinger equations. In the linear regime, we demonstrate that the momentum modulation can alter the first and second PT thresholds of the classical lattice, periodically or regularly change the shapes of the band structure, rotate and split the diffraction patterns of beams leading to multiple refraction and emissions. In the Kerr-nonlinear regime for one-dimension (1D) case, a large family of fundamental solitons within the semi-infinite gap can be found to be stable, even beyond the second PT threshold; it is shown that the momentum modulation can shrink the existing range of fundamental solitons and not change their stability. For two-dimension (2D) case, most solitons with higher intensities are relatively unstable in their existing regions which are narrower than those in 1D case, but we also find stable fundamental solitons corroborated by linear stability analysis and direct beam propagation. More importantly, the momentum modulation can also utterly change the direction of the transverse power flow and control the energy exchange among gain or loss regions.

Distributed acoustic emission sensing for large complex air structures

The vast majority of existing work on acoustic emission–based structural health monitoring is for geometrically simple structures with uninterrupted propagation path and constant wave speed. Realistic systems such as a full-scale fuselage, however, are built from interconnected pieces of acoustically mismatched parts such as sandwich core panels, stringer stiffened skin, and fastener holes. The geometric complexity and dynamic operating environment of realistic systems mean that the acoustic emission wave undergoes multiple reflections, refractions, and mode changes resulting in overlapped transducer outputs with no clear beginning and end. The objective of this paper is to outline the fundamental limitations of acoustic emission as applied to complex systems and present a new distributed data-centric acoustic emission sensing network for durability health monitoring and damage tolerance applications in large and complex systems. The study considers the case of a full-scale composite rotorcraft fuselage to introduce several new concepts on acoustic emission data acquisition time control for alleviating effects of wave distortion as well as methods for improving event location analysis in large quasi-isotropic materials. Methods for adaptive front-end signal processing and data volume control are presented. Despite the size and complexity of realistic full-scale systems and the acoustic emission data, we show that it is possible to locate damage with acceptable accuracy.

An analytical approach to the light transport in columnar phosphors. Detector Optical Gain, angular distribution and the CsI:Tl paradigm

PurposeAn analytical model has been developed for the light propagation in columnar phosphors, based on the optical photon propagation physical and geometrical principles. MethodsThis model accounts for the multiple reflections on the sides of the crystal column, as well as for the infinite forward and backward reflections of the propagated optical photon beams created in the crystal bulk. Additionally it considers the lateral propagated optical photon beams after multiple refractions from the neighbor columns and the optical photon attenuation inside the scintillator.The model was used to predict the Detector Optical Gain (DOG), and the angular distribution, of the columnar CsI:Tl scintillators, used in medical imaging. ResultsThe model was validated against CsI:Tl optical photon transmission published results and good agreement was observed. It was, also, found that the DOG is affected by the length of the columns, as well as the incident X-ray energy spectrum. The results of the angular distribution are in accordance with the theory that the longer crystal columns have more directional light distribution. ConclusionsThe results of DOG are in accordance with the use of short crystal columns for lower energies (mammography) and the use of long crystal columns for higher energies (general radiology). Angular distribution was found more directive for long crystal columns.