Multiple Ray Research Articles

Spatial detection and localisation of multiple laser beams in optical measuring systems

Abstract Optical instruments are used in a broad range of applications in different fields of research and industry like microscopy, material science, metrology and fabrication. There, the optical adjustment of laser beams, optical rays and optical axes to a certain position is crucial for the correct function of the overall system. Often, multiple axes have to be adjusted, which requires the monitoring of multiple rays, preferably simultaneously. In this paper, a method for the spatial localisation of multiple laser beams is presented and demonstrated for an application in precision dimensional metrology. There, the position of seven spatially distributed laser beams can be detected with an uncertainty of <10 μm, enhancing the accuracy of the overall system. The underlying method is flexible in its approach and can be adapted to other optical systems.

CrystalNet: Texture‐Aware Neural Refraction Baking for Global Illumination

AbstractNeural rendering bakes global illumination and other computationally costly effects into the weights of a neural network, allowing to efficiently synthesize photorealistic images without relying on path tracing. In neural rendering approaches, G‐buffers obtained from rasterization through direct rendering provide information regarding the scene such as position, normal, and textures to the neural network, achieving accurate and stable rendering quality in real‐time. However, due to the use of G‐buffers, existing methods struggle to accurately render transparency and refraction effects, as G‐buffers do not capture any ray information from multiple light ray bounces. This limitation results in blurriness, distortions, and loss of detail in rendered images that contain transparency and refraction, and is particularly notable in scenes with refracted objects that have high‐frequency textures. In this work, we propose a neural network architecture to encode critical rendering information, including texture coordinates from refracted rays, and enable reconstruction of high‐frequency textures in areas with refraction. Our approach is able to achieve accurate refraction rendering in challenging scenes with a diversity of overlapping transparent objects. Experimental results demonstrate that our method can interactively render high quality refraction effects with global illumination, unlike existing neural rendering approaches. Our code can be found at https://github.com/ziyangz5/CrystalNet

Binary Opacity Grids: Capturing Fine Geometric Detail for Mesh-Based View Synthesis

While surface-based view synthesis algorithms are appealing due to their low computational requirements, they often struggle to reproduce thin structures. In contrast, more expensive methods that model the scene's geometry as a volumetric density field (e.g. NeRF) excel at reconstructing fine geometric detail. However, density fields often represent geometry in a "fuzzy" manner, which hinders exact localization of the surface. In this work, we modify density fields to encourage them to converge towards surfaces, without compromising their ability to reconstruct thin structures. First, we employ a discrete opacity grid representation instead of a continuous density field, which allows opacity values to discontinuously transition from zero to one at the surface. Second, we anti-alias by casting multiple rays per pixel, which allows occlusion boundaries and subpixel structures to be modelled without using semi-transparent voxels. Third, we minimize the binary entropy of the opacity values, which facilitates the extraction of surface geometry by encouraging opacity values to binarize towards the end of training. Lastly, we develop a fusion-based meshing strategy followed by mesh simplification and appearance model fitting. The compact meshes produced by our model can be rendered in real-time on mobile devices and achieve significantly higher view synthesis quality compared to existing mesh-based approaches. Our interactive webdemo is available at https://binary-opacity-grid.github.io.

Observation of sunlight diffraction through tree twigs and leaves

This work reports the observation of sunlight diffraction through empty spaces in between twigs and leaves in tree crowns. The diffraction patterns are dominated by red wavelength on front followed by the trail of rest of spectral bands of white light rainbow bursts. Tree crowns act as obstacles and apertures causing diffraction/ interference of solar rays. Separation between leaves and twigs (d) is a few inches and distance between crown and camera (D) is in range of a few meters. Empty spaces in tree crown are much longer than red to violet wavelengths in sunlight therefore scattering, dispersion, reflection, diffraction and interference effects cannot be ruled out. Tree crown deflects solar rays into narrow angles all around to enable interference inside camera lens to create grating structure diffracting light into regular patterns. Diffraction pattern look like red petunia flower having 3 × 3 rose petals. Motorola mobile phone camera was used to record the sunlight diffraction patterns. Mobile camera consists of small focal length (≈5 mm) lens, a fixed opening aperture and an image sensor. Lens consists of few plastic or glass elements and sensor consists of charge coupled device (CCD) or CMOS technology. These diffraction/ interference patterns have potential to increase efficiency of Next Gen solar cells. This paper describes possible theoretical background of light diffraction and multiple ray interference through tree twigs and leaves.

Analytic ray tracer on GPU for central receiver systems

An accurate ray tracer is essential to calculate the efficiency of central receiver systems. Furthermore, its runtime has a direct influence on the applicable optimization method for finding optimal layouts of heliostat fields. Developing a ray tracer that achieves both objectives is the main focus of this study. There exist several different ray tracing techniques, starting from the classical Monte Carlo method to analytical convolution methods. Within this work, we introduce a new analytical ray tracer with high accuracy at low runtime. This is achieved by integrating over the bivariate Gaussian distributions used in our convolution ray tracer. In such a way the raytracer is capable of including the effect of multiple solar rays without the need of simulating each ray. Besides the overall efficiency, the new ray tracer can also compute accurate flux maps with thousand times fewer rays than the Monte Carlo method. To further improve the overall model accuracy, a new equation to convolute the sun, slope and tracking error is derived. We show that it perfectly matches the results of a separate accounting for these errors. The newly integrated convolution ray tracer is developed on the same platform as a bidirectional Monte Carlo ray tracer and a convolution method. Besides a large cross-validation of the results, this allows for a reasonable direct run time comparison. With extensive case studies, the quality of the solution, the run time, and various other aspects are investigated. Furthermore, all ray tracers are also implemented on the GPU improving the run time compared to the CPU version by a factor of 50. We show that the integrated convolution ray tracer running on the GPU achieves an accuracy of 99.95% for an annual simulation in 0.7 s for the PS10 and in 1.8 s for the Gemasolar.

An Experimental Study of GPR Near-Field Problem in Depth Ranging of Buried Objects

We evaluate the often neglected ranging (or cover depth) error of an object located within the Fresnel Region (or called radiating near-field) and reactive near-field region in ground penetrating radar (GPR). The experiments were conducted in concrete specimens with various rebar cover depths from 10 to 80 mm, which imitates any object imaged by GPR from reactive near-field, Fresnel region to far-field region. Velocities of each individual data point of the hyperbolic reflections of the embedded reinforcement in radargram are calculated by developed algorithms based on common offset antenna and multiple trilaterated ray paths. Two different velocity algorithms, based on semi- and full-trilaterated ray paths, were applied to estimate the wave travelling velocity as a prerequisite of cover depth measurement. The algorithms were firstly validated using a high-frequency 2-GHz antenna to verify the travelling speed of radar waves in air, which is equal to the speed of light. Then, the same antenna was used to estimate the cover depth by measuring the time of flight and velocity based on the two velocity algorithms. The results reveal that the ranging accuracy is highly in doubt in reactive near-field and Fresnel regions but is largely improved when the object locates in far-field region where GPR wave propagation becomes plane-type. The measurements, riding on accurate modelling of ray-path’s trilateration models, provide evidence that the normal linear scale of GPR time-to-depth conversion overlooks the effects of near-field/Fresnel region. We therefore suggest that the GPR near-field/Fresnel region and far-field boundary must be taken into account before any attempt of time-to-depth conversion and depth estimation of objects by GPR are carried out.

LESS LiDAR: A Full-Waveform and Discrete-Return Multispectral LiDAR Simulator Based on Ray Tracing Algorithm

Light detection and ranging (LiDAR) is a widely used technology for the acquisition of three-dimensional (3D) information about a wide variety of physical objects and environments. However, before conducting a campaign, a test is typically conducted to assess the potential of the utilized algorithm for information retrieval. It might not be a real campaign but rather a simulation to save time and costs. Here, a multi-platform LiDAR simulation model considering the location, direction, and wavelength of each emitted laser pulse was developed based on the large-scale remote sensing (RS) data and image simulation framework (LESS) model, which is a 3D radiative transfer model for simulating passive optical remote sensing signals using the ray tracing algorithm. The LESS LiDAR simulator took footprint size, returned energy, multiple scattering, and multispectrum LiDAR into account. The waveform and point similarity were assessed with the LiDAR module of the discrete anisotropic radiative transfer (DART) model. Abstract and realistic scenes were designed to assess the simulated LiDAR waveforms and point clouds. A waveform comparison in the abstract scene with the DART LiDAR module showed that the relative error was lower than 1%. In the realistic scene, airborne and terrestrial laser scanning were simulated by LESS and DART LiDAR modules. Their coefficients of determination ranged from 0.9108 to 0.9984. Their mean was 0.9698. The number of discrete returns fitted well and the coefficient of determination was 0.9986. A terrestrial point cloud comparison in the realistic scene showed that the coefficient of determination between the two sets of data could reach 0.9849. The performance of the LESS LiDAR simulator was also compared with the DART LiDAR module and HELIOS++. The results showed that the LESS LiDAR simulator is over three times faster than the DART LiDAR module and HELIOS++ when simulating terrestrial point clouds in a realistic scene. The proposed LiDAR simulator offers two modes for simulating point clouds: single-ray and multi-ray modes. The findings demonstrate that utilizing a single-ray simulation approach can significantly reduce the simulation time, by over 28 times, without substantially affecting the overall point number or ground pointswhen compared to employing multiple rays for simulations. This new LESS model integrating a LiDAR simulator has great potential in terms of simultaneously simulating LiDAR data and optical images based on the same 3D scene and parameters. As a proof of concept, the normalized difference vegetation index (NDVI) results from multispectral images and the vertical profiles from multispectral LiDAR waveforms were simulated and analyzed. The results showed that the proposed LESS LiDAR simulator can fulfill its design goals.

Retinoic Acid Influences connexin43 Expression During Joint Formation in the Regenerating Zebrafish Fin.

The regenerating zebrafish fin skeleton is comprised of multiple bony fin rays, each made of alternating bony segments and fin ray joints. This pattern is regulated by the gap junction protein Connexin43 (Cx43), which provides instructional cues to skeletal precursor cells (SPCs). Elevated Cx43 favors osteoblast differentiation and disfavors joint forming cell differentiation. The goal of this article is to test if retinoic acid (RA) contributes to the regulation of cx43 expression. Functional studies inhibiting the RA-synthesizing enzyme Adh1a2 were evaluated using in situ hybridization to monitor gene expression and with measurements of the length of fin ray segments to monitor impacts on SPC differentiation and joint formation. Aldh1a2-knockdown leads to reduced expression of cx43 and increased expression of evx1, a gene required for joint formation. Additionally, inhibition of Aldh1a2 function leads to short fin ray segments. We also find evidence for synergy between aldh1a2 and cx43, suggesting that these genes function in a common molecular pathway to regulate joint formation. The role of RA is to promote cx43 expression in the regenerating fin to regulate joint formation and the length of bony fin ray segments. We suggest that RA signaling must coordinate with additional pathways that also regulate cx43 transcription.

Production of live offspring following unilateral (left) ovariectomized Potamotrygon rays (Potamotrygon castexi, Potamotrygon leopoldi, and Potamotrygon motoro).

To evaluate the surgical technique and subsequent clinical observations (reproductive and ultrasound findings) of left unilateral ovariectomy in 3 species of Potamotrygon rays-Potamotrygon castexi, Potamotrygon leopoldi, and Potamotrygon motoro-for reproductive management. Between 2018 and 2019, multiple Potamotrygon rays (P castexi, n = 1; P leopoldi, 1; P motoro, 6) underwent left ovariectomies to evaluate this technique for reproductive management. At time of surgery, patient age ranged from juvenile to adult. Rays were anesthetized with MS222 buffered with sodium bicarbonate, and a left craniodorsal surgical approach was made to isolate and excise the left ovary. All rays had uneventful recoveries. Eight unilateral ovariectomized females and 6 males were combined in a mixed-species freshwater touch pool of Potamotrygon rays and teleost species. In December 2020, 3 live and 1 premature autolyzed pup were noted in the habitat. The following day, the adult females were examined via ultrasound and separated from the males. Four dams were identified that produced 8 viable offspring and 4 premature abortions. A large right ovary was observed in all females, with no evidence of left ovarian tissue present via ultrasound. Previous histologic evaluation of freshwater ray ovarian tissue suggests both ovaries may be functionally active yet maintain left dominance like some other elasmobranch species. This manuscript provides proof the right ovary alone can produce live offspring. Furthermore, the enlarged right ovary observed in these females suggests that removal of the left ovary may result in compensatory enlargement of the right ovary.

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Hydrodynamic performance study of manta ray gliding in groups

To investigate the effect of group gliding formation on the hydrodynamic performance of manta rays, numerical simulations were used to investigate the drag, the lift and pressure distribution of multiple manta rays in tandem, triangular and diamond-shaped arrangements. The simulation results show that the leader manta ray at the head of the group always suffers the least drag, and in most cases, the companion manta ray at the tail of the group suffers the most drag. The pressure distribution in the flow field shows that the drag reduction effect mainly comes from the distribution of high pressure and low pressure zones among the individual rays in the cluster, the high pressure zone is beneficial to the manta rays at the front of the group, and under certain circumstances, the presence of low pressure zone generates forward suction to reduce the drag of the manta rays at the end of the group. It is found that when manta rays glide in "two in front and one at the back", four-body diamond, six-body tandem and six-body diamond arrangement, the average drag of the system can be reduced, which provides theoretical guidance for the formation of bionic vehicle groups.

On Dynamic Ray Tracing and Anticipative Channel Prediction for Dynamic Environments

Ray tracing algorithms, that can simulate multipath radio propagation in presence of geometric obstacles such as buildings, objects or vehicles, are becoming quite popular, due to the increasing availability of digital environment databases and high-performance computation platforms, such as multi-core computers and cloud computing services. When objects or vehicles are moving, which is the case of industrial or vehicular environments, multiple successive representations of the environment ("snapshots") and multiple ray tracing runs are often necessary, which require a great human effort and a great deal of computation resources. Recently, the Dynamic Ray Tracing (DRT) approach has been proposed to predict the multipath evolution within a given time lapse on the base of the current multipath geometry, assuming constant speeds and/or accelerations for moving objects, using analytical extrapolation formulas. This is done without re-running a full ray tracing for every "snapshot" of the environment, therefore with a great reduction in both human labour and computation time. When DRT is embedded in a mobile radio system and used in real-time, ahead-of-time (or anticipative) field prediction is possible that opens the way to interesting applications. In the present work, a full-3D DRT algorithm is presented that allows to account for multiple reflections, edge diffraction and diffuse scattering for the general case where moving objects can translate and rotate. For the purpose of validation, the model is first applied to some ideal cases and then to realistic cases where results are compared with conventional ray tracing simulation and measurements available in the literature.

A machine-learning digital-twin for rapid large-scale solar-thermal energy system design

In many industrialized regions of the world, large-scale photovoltaic systems now contribute a significant part to the energy portfolio during daylight operation. However, as energy demands peak shortly before sunset and persist for several hours afterwards, the integration of solar-thermal systems is extremely advantageous as a green “bridge” energy source. Accordingly, this work develops a digital-twin model to track and optimize the flow of incoming solar power through a complex solar-thermal storage system, consisting of a large array of adaptable mirrors, an optical-receiver and a power distribution system for customers to extract energy. Specifically, the solar power flow is rapidly computed with a reduced order model of Maxwell’s equations, based on a high-frequency decomposition of the irradiance into multiple rays that experience mirror reflections, losses and ultimately receiver absorption and customer delivery. The method allows for rapid testing (in microseconds) of the performance of large numbers of mirror-receiver layout configurations in design space, over extremely long time periods, such as weeks, months and years, using a genetic-based machine-learning digital-twin framework, which integrates submodels for: •optics and tracking of the Fresnel multi-mirror system,•thermal absorption of the optical energy by the receiver and•optimal operating temperatures balancing radiative losses with heat storage. The overall machine-learning digital-twin optimizes the configuration layout to balance meeting customer demands and operational efficiency. Numerical examples are provided to illustrate the approach. Finally, a deep-learning algorithm is developed and applied to the create an Artificial Neural-Net representation, which allows for even further simulation speedup.

Constraints on the e± pair injection of pulsar halos: Implications from the Galactic diffuse multi-TeV gamma-ray emission

Diffuse gamma-ray emission (DGE) has been discovered over the Galactic disk in the energy range from sub-GeV to sub-PeV. While it is believed to be dominated by the pionic emission of cosmic ray hadrons via interactions with interstellar medium, unresolved gamma-ray sources may also be potential contributors. TeV gamma-ray halos around middle-aged pulsars have been proposed as such sources. Their contribution to DGE, however, highly depends on the injection rate of electrons and the injection spectral shape, which are not well determined based on current observations. The measured fluxes of DGE can thus provide constraints on the ${e}^{\ifmmode\pm\else\textpm\fi{}}$ injection of the pulsar halo population in turn. In this paper, we estimate the contribution of pulsar halos to DGE based on the Australia Telescope National Facility pulsar samples with taking into account the off-beam pulsars. The recent measurement on DGE by Tibet $\mathrm{AS}\ensuremath{\gamma}$ and an early measurement by Multiple Institution Los Alamos Gamma Ray Observatory (MILAGRO) are used to constrain the pair injection parameters of the pulsar halo population. Our result may be used to distinguish different models for pulsar halos.

Strontium-Cobaltite-Based Perovskite (SrCoO3) for Solar-Driven Interfacial Evaporation Systems for Clean Water Generation.

Solar-driven evaporation technology is often used in areas with limited access to clean water, as it provides a low-cost and sustainable method of water purification. Avoiding salt accumulation is still a substantial challenge for continuous desalination. Here, an efficient solar-driven water harvester that consists of strontium-cobaltite-based perovskite (SrCoO3) anchored on nickel foam (SrCoO3@NF) is reported. Synced waterways and thermal insulation are provided by a superhydrophilic polyurethane substrate combined with a photothermal layer. The structural photothermal properties of SrCoO3 perovskite have been extensively investigated through state-of-the-art experimental investigations. Multiple incident rays are induced inside the diffuse surface, permitting wideband solar absorption (91%) and heat localization (42.01 °C @ 1 sun). Under 1 kW m-2 solar intensity, the integrated SrCoO3@NF solar evaporator has an outstanding evaporation rate (1.45 kg/m2 h) and solar-to-vapor conversion efficiency (86.45% excluding heat losses). In addition, long-term evaporation measurements demonstrate small variance under sea water, illustrating the system's working capacity for salt rejection (1.3 g NaCl/210 min), which is excellent for an efficient solar-driven evaporation application compared to other carbon-based solar evaporators. According to the findings of this research, this system offers significant potential for producing fresh water devoid of salt accumulation for use in industrial applications.

Measurement of angular correlation changes in double-photon emission nuclides using ultrasound irradiation

Our group has been developing DPECT (Double Photon Emission CT) to enhance nuclear medicine diagnostics using cascade nuclides that emit multiple gamma rays simultaneously. It is possible to detect the local environment around the nuclide by examining the angular correlation of the emitted cascade gamma-rays. In this study, with the goal of developing a new imaging method combining ultrasound and nuclear medicine, we investigated the effect of ultrasound on cascade gamma-ray emission and found that the angular correlation could be changed by a micro-electric field around 111In in an aqueous solution caused by ultrasound irradiation. Using 8 × 8 array of GAGG scintillators as a detector and Hamamatsu Photonics 8 × 8 MPPCs as a photomultiplier, eight detectors were used and arranged in a ring shape to surround the point source 111In from 360° direction. For the readout system, using a dynamic ToT board, read out its channel information, energy information as ToT signal, and detection time information simultaneously and independently concerning gamma-ray detection. We measured the angular correlation change with four types of ultrasound intensities of 0.05 V, 0.10 V, 0.15 V, and 0.20 V input voltage, and found that the gamma-ray emission angle distribution decreased by about up to 5% around the 90° direction and increased by about up to 5% around 0° and 180° for an ultrasound with an input voltage of 0.15 V or higher.

MMsRT: A Hardware Architecture for Ray Tracing in the Mobile Domain

Today’s desktop rendering platforms typically use GPUs, which have become the most powerful computing chip to meet the growing visual needs, especially in ray tracing. However, ray tracing is challenging for mobile platforms because mobile GPUs need to accommodate insufficient computing power, hardware resources, and memory bandwidth. This paper presents a novel architecture for the mobile domain called Mobile Multiple stacks Ray Tracing (MMsRT). The most complicated calculations in ray tracing are completed through lightweight embedded design. MMsRT has three key features: First, we set multiple stacks to ensure multiple rays are parallel in the system. Second, it sets a stack cache to store the data in stacks when the storage space of multiple stacks is insufficient. Third, we adopt the data prefetching mechanism to set caches to improve the cache hit rate and performance. An accurate simulator test proves that our design can be applied to mobile devices. We calculate the performance of about 82.9 Million Rays Per Second (MRPS), the chip area is about 0.856[Formula: see text]mm2, and 96.85[Formula: see text]MRPS/mm2.

Raytracing in Galerkin Boundary Integral form

Raytracing is an established method for computing the late-time part of room impulse responses. But it has the drawback that only very crude Monte Carlo models of boundary scattering and diffraction are possible to include without losing its attractive computational cost scaling. This happens because higher-resolution models of these processes output multiple child rays for every parent ray received, making the number of rays grow with reflection order. An emerging solution is so-called 'Surface-Based' Geometrical Acoustics. Here the distribution of rays arriving at a boundary is mapped onto a predefined set of spatial elements and angular interpolation functions, producing a vector of coefficients. Re-radiation of subsequent reflections is then a matrix multiplication, with the steady state solution being solvable via a Neumann series. Since rays only every propagate one reflection order before being collected, diffraction and scattering process that cause them to multiply can be included without issue. Here we present a new formulation based on a Galerkin Boundary Element Method (BEM). A unique feature is its ability to readily change interpolation functions, so their effect on accuracy and convergence can be assessed. In this preliminary work, it is verified against an Image Source Model for a rectangular room.

Rapid Near-Field Attenuation of Ground Motion from Shallow Induced Earthquakes, Case Study: Preston New Road, United Kingdom

Abstract Ground motions from shallow induced earthquakes and tectonic seismicity were investigated in this study by directly modeling the seismic attenuation quality factor (Q) using spectral fitting and coda envelope decay methods. We use data from the Preston New Road (PNR) shale gas induced seismicity sequences near Blackpool, United Kingdom, in 2018 and 2019, in addition to regional tectonic events in the United Kingdom. Our results show that the local Q obtained from the induced seismic sequences at PNR, attributed to shallower layers in the crust, leads to a rapid rate of near-field decay (sudden loss in amplitude of earthquake signal over a short distances), with significantly stronger attenuation than observed for regional events. We furthermore find that estimates of Q are nonunique to a given record, differing both with the method and the analysis windows used, particularly at high frequency. These differences can be attributed to the different modeling methodologies (e.g., different assumptions) or to fundamental differences in physical attenuation processes within the seismic wavefield itself, which traverses multiple ray paths and comprises various phases. Our results indicate that to model ground motions for shallow earthquakes, it is important to consider the composite Q along a specific path rather than an average regional Q. To this extent, a depth-dependent attenuation model is considered crucial to bridge the gap between shallow induced earthquakes and tectonic seismicity.

Registration and evaluation of micrometeorod parameters using the effect of micrometeoroids interrupting a light curtain of multiple re-reflected optical rays

A mathematical model and a block diagram of an information-measuring system based on the effect of interruption by micrometeoroids of a light curtain of multiple re-reflected optical rays formed by a line of LEDs are presented. The description of options for the formation of a light curtain at different angles of the optical beam is given. The maximum allowable distance between the source and receiver of optical radiation is determined, taking into account the distance between the planes, the reflection coefficient of mirror surfaces, the parameters of the recorded micrometeoroids and external destabilizing factors.