Multiple Mirror Research Articles

Measurement of CO2 in Water from an Ultraviolet Oxidizer for a Space-Worthy Wastewater Recovery System Using Raman Spectroscopy.

NASA has been developing and testing a water recovery system for over two decades to minimize the amount of water required for long duration human space missions. A key system component is the total organic carbon analyzer (TOCA) that determines if the recovered water is below the toxicology-defined health limit of 5 mg/L TOC and is safe to drink. The TOCA is composed of a liquid phase loop and a gas phase loop. The TOCA employs an oxidizer to convert the organics in the liquid phase to carbon dioxide (CO2) and a liquid-gas separator to isolate the CO2 for measurement in the gas phase by infrared spectroscopy. In an effort to reduce the consumables, mass, volume, and power of the system, we investigated the ability of surface-enhanced Raman spectroscopy (SERS), and Raman spectroscopy to measure 5 mg/L carbon in water. The SERS measurement employed silver colloids to increase sensitivity, while the Raman measurements used multiple mirrors to increase sensitivity. Here, we present SERS measurements of carbonate (CO3=) at 3 mg/L carbon and Raman measurements of CO2 at 9 mg/L carbon in the effluent water of a new oxidizer being developed for a future TOCA. Both SERS and Raman techniques can determine TOC in the liquid phase, eliminating the need for the gas phase loop and associated supplies and replacement components, which could effectively decrease the size and weight of the current TOCA by as much as 50%.

Multiple mirrors and the JKLMR conjecture

Multiple mirrors and the JKLMR conjecture

Three Pairs of Mirror Aneurysms and Then Some: A Case Report

Multiple mirror aneurysms have been rarely reported in the literature. To the best of our knowledge, 3 pairs of mirror aneurysms in a single patient have not been reported prior. We present a case of 3 pairs of mirror aneurysms. One pair in the bifurcations of bilateral middle cerebral arteries and 2 pairs in the distal anterior cerebral arteries. The patient also had 2 unpaired aneurysms in the anterior communicating artery and left M1-anterior temporal junction, respectively. We have effectively treated these aneurysms with primary endovascular coiling.

VLBI observations of GRB 201015A, a relatively faint GRB with a hint of very high-energy gamma-ray emission

Context. A total of four long-duration gamma-ray bursts (GRBs) have been confirmed at very high-energy (≥100GeV) with high significance, and any possible peculiarities of these bursts will become clearer as the number of detected events increases. Multi-wavelength follow-up campaigns are required to extract information on the physical conditions within the jets that lead to the very high-energy counterpart, hence they are crucial to reveal the properties of this class of bursts. Aims. GRB 201015A is a long-duration GRB detected using the MAGIC telescopes from ~40 s after the burst. If confirmed, this would be the fifth and least luminous GRB ever detected at these energies. The goal of this work is to constrain the global and microphysical parameters of its afterglow phase, and to discuss the main properties of this burst in a broader context. Methods. Since the radio band, together with frequent optical and X-ray observations, proved to be a fundamental tool for overcoming the degeneracy in the afterglow modelling, we performed a radio follow-up of GRB 201015A over 12 different epochs, from 1.4 days (2020 October 17) to 117 days (2021 February 9) post-burst, with the Karl G. Jansky Very Large Array, e-MERLIN, and the European VLBI Network. We include optical and X-ray observations, performed respectively with the Multiple Mirror Telescope and the Chandra X-ray Observatory, together with publicly available data, in order to build multi-wavelength light curves and to compare them with the standard fireball model. Results. We detected a point-like transient, consistent with the position of GRB 201015A until 23 and 47 days post-burst at 1.5 and 5 GHz, respectively. No emission was detected in subsequent radio observations. The source was also detected in optical (1.4 and 2.2 days post-burst) and in X-ray (8.4 and 13.6 days post-burst) observations. Conclusions. The multi-wavelength afterglow light curves can be explained with the standard model for a GRB seen on-axis, which expands and decelerates into a medium with a homogeneous density. A circumburst medium with a wind-like profile is disfavoured. Notwithstanding the high resolution provided by the VLBI, we could not pinpoint any expansion or centroid displacement of the outflow. If the GRB is seen at the viewing angle θ that maximises the apparent velocity βapp (i.e. θ ~ βapp-1), we estimate that the Lorentz factor for the possible proper motion is Гα ≤ 40 in right ascension and Гδ ≤ 61 in declination. On the other hand, if the GRB is seen on-axis, the size of the afterglow is ≤5pc and ≤16pc at 25 and 47 days. Finally, the early peak in the optical light curve suggests the presence of a reverse shock component before 0.01 days from the burst.

Evaluation of Reconfigurable Intelligent Surface-Assisted Underwater Wireless Optical Communication System

Reconfigurable intelligent surfaces (RISs) are an emerging technology aimed to enhance the energy and spectrum efficiency of wireless communication links by reconfiguring the propagation environment of radio-frequency (RF)/optical waves. Planar phased meta-material surfaces or reflect-arrays for RF RIS and multiple smart mirrors have been used for activating optical RIS. In this article, we analyze the underwater optical wireless communication (UWOC) system performance in terms of bit error rate (BER), outage probability (OP) and channel capacity (CC) under the influence of underwater turbulence, beam attenuation, pointing errors and occlusion or blockage due to obstacles. A RIS-assisted UWOC proposed to mitigate the effects obstacles, pointing errors and turbulence and improve the system performances. The probability density function and cumulative distribution functions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> RIS elements based UWOC system are evaluated over the underwater turbulence, pointing errors and blockage due to obstacles. The novel closed-form expressions for BER under binary phase shift keying and binary frequency shift keying modulation schemes using with and without coherent detection, OP, and CC for intensity modulation-direct detection and heterodyne detection cases are obtained and plotted according to the number of RIS elements with respect to the average signal-to-noise ratio. The numerical BER results are validated with the Monte-Carlo simulations.

Indigenous Sand Drawings as Predictors of the Cell Response to Nanoparticle Therapy

A technique for predicting the response of cells and tissues to a physicochemical stimulus without the use of expensive molecular markers and at time points before any morphological changes can be visibly spotted would be a meaningful addendum to the current set of bioimaging tools. One such method was developed here based on correlating transformed distance matrices of populations of cultured cells and digital checkerboard patterns derived from traditional central African drawings in the sand. Similarity measurements were made at an early time point in the therapy administered to bone cancer cells in the form of composite magnetic nanoparticles. At this early of a time point, the cell viability was mildly reduced, but no gross alterations to the cell morphology or density were visible yet. Similarity score evaluation demonstrated a significantly higher degree of similarity between the patterns derived from the sand drawings and the cells subjected to the treatment than between the former patterns and the untreated cell controls. The treated cells produced more ordered and symmetric patterns than the control ones after the processing of their pairwise distant matrices, explaining their better geometric correlation with the ancestral sand arabesques, which were monolinear and commonly comprised multiple mirror planes and rotational symmetry axes. This has suggested that the course of the therapy could be predicted by a relatively simple comparison between raw optical images of cells and indigenous ideographs using the metrics postulated here. The interdisciplinary method developed in this study may prove applicable for in situ monitoring of the response of cells and tissues to various therapies, allowing for the early indications of adverse effects to be noticed based on the simple optical observations of cells and acted upon before the progression toward nonviable states becomes irreversible. The method elaborated here may also provide an impetus for a broader search for solutions to problems plaguing the modern medicine outside of the scope of its mainstream analytical frameworks and in the ancestral heritage of relatively obscure ethnic traditions.

Optical design of Lissajous pattern multipass cells with multiple spherical mirrors based on particle swarm optimization.

We propose a method to intelligently design and optimize a multiple-spherical-mirror-based multipass cell (MPC) with Lissajous patterns. The MPC consists of at least three spherical mirrors, which are placed in a rotationally symmetric arrangement. Particle swarm optimization (PSO) is performed to optimize the parameters of the MPC configurations and accelerate the design process. Two Lissajous patterned MPCs with three and five mirrors are built and tested experimentally. We further develop an open-path gas sensor based on a five-mirror-based MPC to detect methane concentrations in ambient laboratory air, and a detection precision of 1.1 ppb with a 123 s averaging time is realized. The PSO algorithm is efficient for optimizing the proposed MPC, which has superior proprieties of symmetry configuration, cost-effectiveness and high detection sensitivity and is well suited for trace gas sensing applications.

Designing reflective imaging systems with multiple-surfaces-integrated elements using a Gaussian function freeform surface.

We propose a design scheme and method of a freeform off-axis reflective imaging system with multiple mirrors integrated into one element. The use of a multiple-surfaces-integrated element, described by the Gaussian basis functions freeform surface with local and nonsymmetric properties, significantly decreases the system complexity, as well as reduces the assembly and fabrication difficulty, and achieves high imaging performance. The design theory and process including the initial system design, surface conversion, and system optimization are demonstrated in detail. Three design examples are demonstrated to validate the effect and feasibility of the proposed method, and good imaging performance is obtained.

Surface form error measurement for rough surfaces using an infrared lateral shearing interferometry

The fabrication of a large monolithic mirror or a segmented mirror requires a high throughput that satisfies the time-cost requirement. Particularly, the rough surface properties of grinding pose a challenge for accurate measurement of the surface figure error (SFE). If the SFE during grinding is as small as possible, the material removal volume in the figuring process gets reduced, and the total required time of the fabrication is greatly minimized. In this paper, we propose a new metrology tool called intermediate surface figure error measurement (ISFEM) that can be applied to measurement of SFE for rough surfaces. It consists of a CO2 laser of wavelength 10.6 µm as a light source, a lateral shearing interferometer as a wavefront sensor, and several optical components for beam shaping and imaging. The ISFEM demonstrated its ability to measure the microns to sub-micron rms SFE of the ground surface by testing the samples with a 0.59 µm -1.56 µm rms of surface roughness and a large SFE of about 3 µm rms. The system was applied to the fabrication of an off-axis parabolic mirror of diameter 1.1 m, where it successfully performed as an intermediate metrology between laser tracker measurement for the rough surface and interferometric measurement for the polished surface. The ISFEM obtained measurements from 3.88 µm rms SFE during the fine grinding process and down to 0.38 µm rms during the polishing process. Therefore, we confirmed that the ISFEM provides a unique solution for high throughput for the fabrication of large or multiple segmented mirrors.

Underground Object Classification Using Deep 3-D Convolutional Networks and Multiple Mirror Encoding for GPR Data

Ground-penetrating radar (GPR) is an effective tool for underground object detection, but its data interpretation remains a great challenge. In this letter, we propose a novel underground object classification algorithm using deep 3-D convolutional networks (C3D) and multiple mirror encoding (MME) for 3-D GPR data. Although deep learning technique has been applied to interpret the GPR data, most of the existing methods are based on GPR B-scans and have a relatively low accuracy since the reflections from various subsurface targets present similar hyperbolic patterns in B-scans. To improve the classification accuracy, we use 3-D GPR data as training data for C3D to capture the spatio-temporal features between parallel B-scans. Since 3-D GPR data including single object has different sizes in consideration of actual sizes of objects, they are rearranged by the MME method to enhance spatio-temporal features, as well as to satisfy the requirement of the network input. Experimental results demonstrate that the proposed method outperforms the state-of-the-art B-scan-based methods.

Computation of aberration coefficients for plane-symmetric reflective optical systems using Lie algebraic methods

The Lie algebraic method offers a systematic way to find aberration coefficients of any order for plane-symmetric reflective optical systems. The coefficients derived from the Lie method are in closed form and solely depend on the geometry of the optical system. We investigate and verify the results for a single reflector. The concatenation of multiple mirrors follows from the mathematical framework.

Kaleidoscopic structured light

Full surround 3D imaging for shape acquisition is essential for generating digital replicas of real-world objects. Surrounding an object we seek to scan with a kaleidoscope, that is, a configuration of multiple planar mirrors, produces an image of the object that encodes information from a combinatorially large number of virtual viewpoints. This information is practically useful for the full surround 3D reconstruction of the object, but cannot be used directly, as we do not know what virtual viewpoint each image pixel corresponds---the pixel label. We introduce a structured light system that combines a projector and a camera with a kaleidoscope. We then prove that we can accurately determine the labels of projector and camera pixels, for arbitrary kaleidoscope configurations, using the projector-camera epipolar geometry. We use this result to show that our system can serve as a multi-view structured light system with hundreds of virtual projectors and cameras. This makes our system capable of scanning complex shapes precisely and with full coverage. We demonstrate the advantages of the kaleidoscopic structured light system by scanning objects that exhibit a large range of shapes and reflectances.

Rate equations model for multiple magnetic mirrors in various thermodynamic scenarios

Axial particle loss is one of the main challenges for fusion aimed, linear magnetic mirror plasma configurations. One way to mitigate this disadvantage and increase the confinement time is to use a multiple mirrors setup. The idea is to reduce the outgoing flux by collisions in the outer magnetic cells. Here, we develop a semi-kinetic rate equation model for the ions' density dynamics, including scattering within the magnetic cell and the transmission between neighboring cells. The dominant parameter is the ions' mean free path, which depends on the temperature and density in each cell. The steady-state flow is studied analytically and numerically for three thermodynamic scenarios: isothermal plasma, adiabatic expansion, and constant diffusion. It is found that the confinement time varies about fivefold over the different scenarios, where the adiabatic cooling is the best confining scenario.

Performance Evaluation of Elliptical and Multi-part Mirrors for Concentrating Diffused Light onto Collector Surface from Half Celestial Sphere

An elliptical mirror has a mirror surface at the first focal point on a plane perpendicular to its central axis, which, in turn, passes through the first and second focal points. It can collect diffused light from a half celestial sphere, which extends 360◦ in the axial rotation direction and 180◦ in the axial direction at the second focal point. An elliptical mirror allows only the light incident on the first focal point to be concentrated on only the second focal point. A single elliptical mirror consists of only one elliptical mirror. A multi-part mirror is composed of multiple elliptical mirrors. In a multi-part elliptical mirror, the first focal point lies on its surface, and the second focal point is so positioned that it is aligned with the top of the multi-part mirror. A multipart mirror can concentrate diffused light from a wider area than a single elliptical mirror because its first focal points are dispersed. Furthermore, in a single elliptical mirror, only the light incident on the first focal point isconcentrated on only the second focal point; therefore, the light-concentrating efficiency is low. In this study, we installed a collector surface on the second focal point of an elliptical mirror to increase its light-concentrating efficiency. Subsequently, we evaluated single elliptical and multi-part mirrors that capture the diffused light from a half celestial sphere not incident on the first focal point and concentrate it on the collector surface as well as the second focal point. We configured a coordinate system for the design of single elliptical and multi-part mirrors and subsequently analyzed the mechanism by which the light will strike these designed mirrors and concentrate on their collector surfaces. Based on the design values, we manufactured actual single elliptical and multi-part mirrors, which were illuminated with diffused light, and measured the illuminance of the light concentrated on their collector surfaces. Finally, we evaluated the light-concentrating performance of these mirrors based on the analysis results and measured illumination.

Single‐station radar‐based UAV position estimation in complex urban environments

In the complex electromagnetic environment of cities, detection and positioning of slow and small unmanned aerial vehicles (UAVs) have always been a very challenging research topic. Usually, multiple radar observation stations are required to detect and track targets. Moreover, each radar observation station requires strict synchronisation, and the system is complex and costly. In view of this, under the condition of known prior information of urban geography, this study proposes a method to locate UAVs in complex electromagnetic environments, which use multiple virtual mirror synchronous radars constructed by multipaths and created by the complex buildings in urban environments. First, the simulation model is constructed, and the corresponding simulation parameters are given. Then, the algorithm for solving the single-station radar location is proposed, and the algorithm is verified by the simulation of a ray propagation model. Finally, the proposed algorithm is further verified based on the measured data captured by the radar system in Section 2. The results show that the proposed algorithm based on the single-station radar is able to locate the UAV in both line-of-sight and non-line-of-sight site, and its positioning accuracy is better than 1 m.

Simons Observatory HoloSim-ML: machine learning applied to the efficient analysis of radio holography measurements of complex optical systems.

Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.

Toward the Autonomous Assembly of Large Telescopes Using CubeSat Rendezvous and Docking

This paper describes the results of a system study for the in-space assembly of large optical telescopes using a building block approach involving multiple mirror segments. Such an approach is enabled by CubeSat rendezvous and docking and mirror steering technologies for compensating misalignment of the assembly. This concept thus removes the constraints imposed by the limited volume of launchers’ fairing, and hence larger telescope dimensions can be envisaged, leading to new observation capabilities. Each mirror segment is mounted on top of a small satellite, containing the miniaturized subsystems to achieve autonomous docking to either the service module containing the science instruments or other segments to build up the primary mirror. A systems’ design of all the elements constituting the assembly is provided, including tradeoffs, optimization, as well as mass and power budgets. The proposed solution scales with the size of the telescope and can be used to build primary mirrors as large as 20 m in diameter. The critical guidance, navigation, and control function is introduced, and related docking performances are presented. The results indicate that the in-space assembly of such large telescopes is feasible once these two key technologies are demonstrated in flight in the coming years.

The piston error recognition technique used in the modified Shack–Hartmann sensor

Segmented telescopes and multi-aperture telescopes are effective ways to realize high-resolution observations in astronomy. An important work for the high-resolution observations with segmented telescopes and multi-aperture telescopes is phasing the multiple segmented mirrors or sub-apertures. Modified Shack–Hartmann sensor is proposed for piston error detection. The signal of the modified Shack–Hartmann sensor is the interference pattern created by a lens placed across two adjacent pupils in the exit pupil plane. The information of piston error is encoded in the interference pattern. Many methods are proposed to extract piston error from the interference pattern. In this paper, three existing piston error extraction methods are introduced and reproduced. The influence of the offset of the lens in modified Shack–Hartmann​ sensor on the three methods is analyzed. The offset lens causes the three methods failed in high accuracy piston error detection. We propose a piston error recognition technique based on phase retrieval technology to resolve the problem caused by the offset lens. The proposed piston error recognition technique can recognize not only the piston error but also the offset value of the lens. Therefore, the proposed technique can also be used to debug the modified Shack–Hartmann sensor. By means of simulations we show that the proposed method shows improved performance and it works well in noise and sub-pupil aberration situations.

Spectroscopic Confirmation of Two Extremely Massive Protoclusters, BOSS1244 and BOSS1542, at z = 2.24

Abstract We present spectroscopic confirmation of two new massive galaxy protoclusters at z = 2.24 ± 0.02, BOSS1244 and BOSS1542, traced by groups of Coherently Strong Lyα Absorption (CoSLA) systems imprinted in the absorption spectra of a number of quasars from the Sloan Digital Sky Survey III (SDSS III) and identified as overdensities of narrowband-selected Hα emitters (HAEs). Using Multiple Mirror Telescope/Magellan Infrared Spectrograph and Large Binocular Telescope/LUCI near-infrared (NIR) spectroscopy, we confirm 46 and 36 HAEs in the BOSS1244 (∼55 arcmin2) and BOSS1542 (∼61 arcmin2) fields, respectively. BOSS1244 displays a southwest (SW) component at z = 2.230 ± 0.002 and another northeast (NE) component at z = 2.246 ± 0.001 with the line-of-sight velocity dispersions of 405 ± 202 km s−1 and 377 ± 99 km s−1, respectively. Interestingly, we find that the SW region of BOSS1244 contains two substructures in redshift space, likely merging to form a larger system. In contrast, BOSS1542 exhibits an extended filamentary structure with a low-velocity dispersion of 247 ± 32 km s−1 at z = 2.241 ± 0.001, providing a direct confirmation of a large-scale cosmic web in the early universe. The galaxy overdensities δ g on the scale of 15 cMpc are 22.9 ± 4.9, 10.9 ± 2.5, and 20.5 ± 3.9 for the BOSS1244 SW, BOSS1244 NE, and BOSS1542 filament, respectively. They are the most overdense galaxy protoclusters (δ g &gt; 20) discovered to date at z &gt; 2. These systems are expected to become virialized at z ∼ 0 with a total mass of M SW = (1.59 ± 0.20) × 1015 M ⊙, M NE = (0.83 ± 0.11) × 1015 M ⊙ and M filament = (1.42 ± 0.18) × 1015 M ⊙, respectively. Our results suggest that the dense substructures of BOSS1244 and BOSS1542 will eventually evolve into the Coma-type galaxy clusters or even larger. Together with BOSS1441 described in Cai et al., these extremely massive overdensities at z = 2–3 exhibit different morphologies, indicating that they are in different assembly stages in the formation of early galaxy clusters. Furthermore, there are two quasar pairs in BOSS1441 and one quasar pair in BOSS1244 and BOSS1542; CoSLAs detected in these quasar pairs can be used to trace the extremely massive large-scale structures of the universe.

A design method for optimizing the secondary reflector of a parabolic trough solar concentrator to achieve uniform heat flux distribution

Non-uniform solar flux distribution in a parabolic trough concentrator (PTC) causes large temperature gradients on absorber tube surface, making the PTC inefficient and damaged. To solve the problem, a novel method is proposed for designing the additional secondary reflector (SR) in a PTC to improve uniform heat flux distribution on absorber tube surface. In the design, the heat flux between upper and lower surfaces of absorber tube is well balanced by optimizing the location of absorber. Then, the SR with segmented broken-line type composed of multiple plane mirrors is delicately designed with local heat flux compensation strategy. Two case studies are conducted to compare the performances of the newly designed SRs with other existing SR designs. It is shown that the uniformity of heat flux distribution can be improved to over 90% for present SR design, much higher than those for other existing SR designs. Also, the optical efficiency of the PTC with present SR design is also increased as compared with other designs. The results indicate that this proposed method is competent for designing SR in a PTC with uniform heat flux distribution.