Composite Mirror Research Articles

Gossip-based asynchronous algorithms for distributed composite optimization

The distributed composite optimization problem associated a multi-agent network is investigated in this paper. Different from conventional optimization issues, the cost function of composite optimization consists of a convex function and a regularization function (possibly nonsmooth). The gossip protocol is also introduced to enhance the robustness of the network, and a gossip-based distributed composite mirror descent algorithm is presented to deal with the previous problem, which adopts the asynchronous communication method. Moreover, the algorithm performance is analyzed and the theoretical results on the corresponding error bounds are obtained. Finally, the distributed logistic regression is provided as an example to validate the practicability of the proposed algorithm.

Bryophyte-Bioinspired Nanoporous AAO/C/MgO Composite for Enhanced CO2 Capture: The Role of MgO.

A composite material composed of anodized aluminum oxide (AAO), carbon (C), and magnesium oxide (MgO) was developed for CO2 capture applications. Inspired by the bryophyte organism, the AAO/C/MgO composite mirrors two primary features of these species-(1) morphological characteristics and (2) elemental composition-specifically carbon, oxygen, and magnesium. The synthesis process involved two sequential steps: electroanodization of aluminum foil followed by a hydrothermal method using a mixture of glucose and magnesium chloride (MgCl2). The concentration of MgCl2 was systematically varied as the sole experimental variable across five levels-1 mM, 2 mM, 3 mM, 4 mM, and 5 mM-to investigate the impact of MgO formation on the samples' chemical and physical properties, and consequently, their CO2 capture efficiency. Thus, scanning electron microscopy analysis revealed the AAO substrate's porous structure, with pore diameters measuring 250 ± 30 nm. The growth of MgO on the AAO substrate resulted in spherical structures, whose diameter expanded from 15 nm ± 3 nm to 1000 nm ± 250 nm with increasing MgCl2 concentration from the minor to major concentrations explored, respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that carbon serves as a linking agent between AAO and MgO within the composite. Notably, the composite synthesized with a 4 mM MgCl2 concentration exhibited the highest CO2 capture efficiency, as determined by UV-Vis absorbance studies using a sodium carbonate solution as the CO2 source. This efficiency was quantified with a 'k' constant of 0.10531, significantly higher than those of other studied samples. The superior performance of the 4 mM MgCl2 sample in CO2 capture is likely due to the optimal density of MgO structures formed on the sample's surface, enhancing its adsorptive capabilities as suggested by the XPS results.

The large-area hybrid-optics CLAS12 RICH: First years of data-taking

The CLAS12 deep-inelastic scattering experiment at the upgraded 12 GeV continuous electron beam accelerator facility of Jefferson Lab conjugates luminosity and wide acceptance to study the 3D nucleon structure in the yet poorly explored valence region, and to perform precision measurements in hadron spectroscopy. A large area ring-imaging Cherenkov detector has been designed to achieve the required hadron identification in the momentum range from 3 GeV/c to 8 GeV/c, with the kaon rate about one order of magnitude lower than the rate of pions and protons. The adopted solution comprises aerogel radiator and composite mirrors in a novel hybrid optics design, where either direct or reflected light could be imaged in a high-packed and high-segmented photon detector. The first RICH module was assembled during the second half of 2017 and installed at the beginning of January 2018, in time for the start of the experiment. The second RICH module, planned with the goal to be ready for the beginning of the operation with polarized targets, has been timely built despite the complications caused by the pandemic crisis and successfully installed in June 2022. The detector performance is here discussed with emphasis on the operation and stability during the data-taking, calibration and alignment procedures, reconstruction and pattern recognition algorithms, and particle identification.

Distributed Stochastic Constrained Composite Optimization Over Time-Varying Network With a Class of Communication Noise.

This article is concerned with the distributed stochastic multiagent-constrained optimization problem over a time-varying network with a class of communication noise. This article considers the problem in composite optimization setting, which is more general in the literature of noisy network optimization. It is noteworthy that the mainstream existing methods for noisy network optimization are Euclidean projection based. Based on the Bregman projection-based mirror descent scheme, we present a non-Euclidean method and investigate their convergence behavior. This method is the distributed stochastic composite mirror descent type method (DSCMD-N), which provides a more general algorithm framework. Some new error bounds for DSCMD-N are obtained. To the best of our knowledge, this is the first work to analyze and derive convergence rates of optimization algorithm in noisy network optimization. We also show that an optimal rate of O(1/√T) in nonsmooth convex optimization can be obtained for the proposed method under appropriate communication noise condition. Moveover, novel convergence results are comprehensively derived in expectation convergence, high probability convergence, and almost surely sense.

Almost sure convergence of stochastic composite objective mirror descent for non-convex non-smooth optimization

Almost sure convergence of stochastic composite objective mirror descent for non-convex non-smooth optimization

Evaluation of a composite nickel mirror as a back mirror of a flashlamp-pumped Nd:YAG laser system in free running regime

Evaluation of a composite nickel mirror as a back mirror of a flashlamp-pumped Nd:YAG laser system in free running regime

Alleviation of honeycomb print-through of NiP/Cu coated carbon fiber composite mirror via robot-arm wheel polishing

In order to realize higher lightweight rate, CFRP (Carbon Fiber Reinforced Polymer) composites were applied to fabricate mirror. A NiP coating was prepared on the surface, meanwhile honeycomb print through was discussed in the paper. Before NiP alloy coating plating, a Cu film was prepared through magnetron sputtering to reinforce the adherence with CFRP mirror. The NiP coating contained 10.9% P and exhibited an amorphous structure. Obvious “honeycomb print-through” was found in the classical polish, the final surface accuracy was just 0.048λ (RMS, λ = 632.8 nm). However, the print-through can be alleviated through Robot-arm wheel polishing. 0.015λ (RMS) of surface accuracy was realized on a Ф100mm CFRP mirror.

Effect of Electric Field Regulation on Laser Damage of Composite Low-Dispersion Mirrors

Low dispersion mirrors are important because of their potential use in petawatt (PW) laser systems. The following two methods are known to increase the laser-induced damage threshold of low dispersion optical components: use of a wide-bandgap-material protective layer and control of electric field distribution. By controlling the electric field distribution of composite low-dispersion mirrors (CLDM), we shift the electric field peaks from the material interface into the wide-bandgap material. However, the damage threshold of modified-electric-field composite low dispersion mirror (E-CLDM) does not increase. Damage morphology shows that the initial damaged layer is Ta2O5. An immediate cause is the enhancement of the electric field in internal layers caused by surface electric field regulation. Theoretical calculations show that the damage threshold of CLDM or E-CLDM is determined by the competition results of bandgap and the electric field of layer materials. The CLDM with different materials or different protective layer periods can be optimally designed according to the electric field competition effect in the future.

Combining analytical chemistry and traceology: An innovative approach applied to Mesoamerican mirrors found at the Sojo site (Costa Rica)

An innovative approach based on the combination of spectroscopy and traceology was used in order to analyse iron ore mirrors excavated at the Sojo site (Chibcha area, present-day Costa Rica) in the northern Pacific region of Costa Rica (AD 300 to AD 500–600). Such mirrors were prestigious artefacts related to power, shamanism and divination during the Classic Period in the Maya area. Stone bases, adhesives and tesserae were characterised using FT-IR, SEM/EDX and Raman Spectroscopy, as well as X-Ray Fluorescence (XRF) and the techniques used in their manufacture were elucidated using traceology. Similar materials were found to have been used for all the bases, tesserae, adhesives and coatings of the different mirrors. Furthermore, two tessera-shaped fragments were most probably part of a composite mirror, manufactured by sticking hematite nodules onto stone tesserae using a clay mixed with an organic binder. Chert and obsidian tools were used to make, respectively, perforations and edges on all mirror bases, and the two main types of abrasion of the base surfaces were found to have been made with basalt or limestone. These analyses indicate a probable Maya origin as their manufacturing traces distinguish them from Teotihuacan mirrors.

Effect of photoinitiator concentration on hygroscopic stability of UV cured precision replicated composite optics.

Replicated composite optics is a promising technique to fabricate high-quality mirrors with reduced weight and processing time compared to conventional glass mirrors; however, the optical layer is organic and susceptible to environmentally-induced dimensional changes, specifically to moisture exposures. Generally, to enhance polymer stability, thermal curing is necessary to maximize the cure state. Because replications are bonded, thermal exposures generate residual stresses that degrade optical quality. In this paper, the cure state of a UV-cured epoxy with RT processing was varied by changing the photoinitiator (PI) concentration, and the replication stability was evaluated in different humidity environments by laser interferometry. Increasing the PI concentration transformed the epoxy microstructure from homogenous to a more phasic network, as evidenced by both DMA and AFM, resulting in significant changes to the Tg, modulus, and moisture absorption. When replications were exposed to moisture, they experienced initial swelling followed by stress relaxation to net-zero regardless of initial processing stress. Reduced PI concentrations exhibited higher moduli and shorter swelling periods, with dimensional changes as small as 35 nm and complete stress relaxation in days. TTS master curves describing stress relaxation behavior correlated well with the observed behavior in replicated mirror samples. Furthermore, it was shown that the relieved stress persisted through multiple humidity cycles between 100% to 0% RH. These results show that high-humidity conditioning treatments can be utilized to eliminate residual stress in as-fabricated replicated mirrors over just a few days, providing a viable manufacturing and processing route for highly precise and stable replicated composite mirrors.

Developing a Design of a Composite Linear Fresnel Mirror Concentrating System

The study is aimed at developing a solar power plant module based on flat Fresnel mirrors for use in autonomous solar installations of sufficient capacity in order for individual consumers to obtain thermal, mechanical, or electrical energy. A simpler design technology of manufacturing a composite compact linear Fresnel mirror concentrating system (LFMCS) is presented. A module of a solar installation consisting of an LFMCS with linear flat elements of optimal size, coordinated with the optimal size of the receiver that is installed in the focal zone and converts the energy of concentrated solar radiation flows to thermal energy to generate high-pressure steam. A distinct feature of the new design is that it uses a number of optimally sized linear flat mirrors. The approach to determining the optimal dimensions of flat mirrors is validated. These mirrors are used instead of their parabolic counterparts. The simplest technology of manufacturing a concentrator is proposed. That said, the task of making the radiant flux denser for a more efficient conversion of solar energy to electricity is fulfilled by coordinating the optimal receiver size with the optimal size of flat elements. The specific optimal sizes of linear elements of a 10 × 10 m2 LFMCS are determined by optical-geometric modeling with regard to the optimal size of the receiver located in the focal zone. The optimal process solutions for manufacturing a 10 × 10 m2 LFMCS design with a receiver of dopt = 0.11 m are established that have the highest efficiency at Lopt = 0.072 m of the unified linear elements of the LFMCS.

Imaging Atmospheric Cherenkov Telescope for the TAIGA Observatory—JINR Participation

IACTs are one of the key parts of the TAIGA observatory and designed for study of gamma rays and charged cosmic rays in the energy range of 10 $${}^{13}{-}10^{18}$$ eV. The first IACT was designed and fabricated at the JINR workshop and has been operating since 2016 in the Tunka valley. The second one has been assembled there at September 2018 and the production of the third one is in progress to be transported to the Tunka valley in August 2019. The R&D to fabricate focusing glass mirrors directly in JINR is underway. The report presents the TAIGA IACT main characteristics and the results of the comparison between the JINR glass mirrors and composite mirrors (Media Lario company, Italy).

Numerical and experimental investigation on dynamics of deployable space telescope experiencing deployment and attitude adjustment motions coupled with laminated composite shell

Nonlinear dynamic modeling methods for a flower-like clustered deployable space telescope (DST) with laminated composite material experiencing large deployment and attitude adjustment motions is proposed in present work. The flexible mirrors are discretized into shell elements in absolute node coordinate formulation (ANCF) considering nonlinear structures instead of using conventional shell elements in hybrid coordinate formulation (HCF). Meanwhile the stress–strain relations of laminated composite mirrors with considering nonlinear material and geometric properties are respectively deduced by high order shear deformation theory and continuum mechanics. Then, the accuracy of dynamic behavior is investigated by comparison of the results obtained by using ANCF and HCF, and it is indicated that ANCF shell elements are suitable for solving large deformation and deployment dynamic analysis of DST with high accuracy and strong convergence by numerical simulations. Further, the experiments for evaluating the dynamic behavior of surrounding mirrors with simultaneous deployment in different deployment strategies are conducted. Numerical results are in good agreement with those obtained from experiments to validate the correctness of the present nonlinear modeling formulation. And, the experiment and numerical simulation of the primary mirror experiencing attitude adjustment motions are also carried out. Those results illustrate the performance of the dynamic properties of DST with different deployment strategies and laminated composite structures in the present modeling method. These conclusions will have significant theory and engineering practice values for predicting surface accuracy, pointing accuracy and vibration performance of DST mechanism.

Numerical Simulation of the Adaptive Control System of the Composite Primary Mirror of a Large-Size Space Telescope

We describe a mathematical model developed for the adaptive control system of the composite primary mirror of a telescope similar in characteristics to the international project of the Millimetron space telescope. Results of numerical simulation of the adaptive control system with allowance for restrictions of the hardware–software implementation are presented. According to results of the simulation, the error of maintaining the shape of the composite primary mirror is estimated. The estimate corroborates the applicability of the mathematical model.

On the Development of a Space Satellite Mirror with Intrinsic Self-Healing Properties

In the aerospace industry the demand for very strong and light components is a permanent objective and for this matter composite materials began to be used at large scales in construction of space structures. The presence of micrometeoroids and orbital debris in space, particularly in the lower earth orbit, presents a continuous hazard to orbiting satellites, spacecraft, and the International Space Station. Among the 8700 objects larger than 10 cm in Earth Orbits, only about 6% are operational satellites and the remainder is space debris. Likewise, a major challenge for space missions is the material selection due to the fact that in space materials present a higher degradation rate and they are subjected to wear and structural damage, especially when facing extreme environmental conditions. In this paper, a self-healing concept embedded into a Carbon Fiber Reinforced Polymer (CFRP) composite parabolic satellite mirror is under development at COMOTI Research & Development Institute for Gas Turbines. The goal of the research is to provide a material that increases the operational life of satellites in Low Earth Orbit (LEO). The work addresses two different but interconnected fields, material science for developing a multifunctional composite material having an embedded self-healing system and aerospace field for developing a new, lightweight structure. The self-healing system under study consists in a blend of microcapsules containing variations of dicyclopentadiene (DCPD) monomers, 5-Vinyl-2-norbornene (VNB), 5-Ethylidene-2-norbornene (5E2N or ENB) and ethylene glycol dicyclopentenyl ether methacrylate (EGDP).

Lightweight design of high volume SiC/Al composite mirror for remote camera

For the design of mirrors in the use of remote camera, high stiffness and less mass are the most critical facts. In this paper, SiC/Al composite material was selected as the material of the mirror. The precise constrains with six degree of freedom was adopted for optimizing the mirror in the diameter of Φ400mm. Traditional empirical design method was used to determine the initial shape parameters of the mirror. The RMS value of the surface shape error and mass were set as the goal of optimization. The Pareto front of the multi-objective parameters was obtained and the objective function was processed to determine the optimal design of the mirror. The results show that the mirror after optimization achieved better performance. Compared with mirror designed with experience-basedmethod, the lightweight ratio of the mirror is increased by 9.1%. The mass is reduced by 12.9% compared with the mirror in the material of SiC. The optimized design method and results of the mirror in this paper can provide a reference for the application of mirrors of the high volume fraction SiC/Al composite material.

Influence of the Ply Angle Deviation on the Out-of-Plane Deformation of the Composite Space Mirror

In order to discuss the influence of the ply angle deviation, six symmetric quasi-isotropic layup sequences imposed the fixed or random angle deviation were studied based on the numerical analysis, such as Monte Carlo stochastic finite element method and statistic analysis. The out-of-plane deformation was observed in spite of the symmetric quasi-isotropic sequences subjected to a temperature change due to the ply angle deviation in the space mirror. The surface peak-to-valley (PV), which is one kind of out-of-plane deformation, is proportional to the magnitude of the fixed angle deviation, and the mean of PVs is also proportional to the standard deviation of the random angle deviation. The out-of-plane deformation resulting from two-ply angle deviation indirectly satisfies the parallelogram law, and if each ply angle deviation is random independently, the probability density of that satisfies the Rayleigh distribution. In this paper, it is found that the most effective method to improve the surface accuracy of the space mirror is decreasing the standard deviation of the angle deviation, next to decreasing ply thickness and optimizing layup sequence, which is useful for application in the space mirror.

A Sparse Stochastic Method With Optimal Convergence Rate for Optimizing Pseudo-Linear Performance Measures

Optimizing pseudo-linear performance measures has gained increasing interest in recent years. Compared with the existing works focusing on L2-norm, it is more challenging to design the model with L1-norm, especially, when data are of large scale. To address the issue, in this paper, we propose a sparse stochastic method to optimize the pseudo-linear metrics. The algorithm begins by formulating the problem as a cost-sensitive classification with L1 regularization, then composite objective mirror descent (COMID) is adopted for the inner optimization, which can obtain a sparse solution with promising performance. However, the original COMID method only has $\mathcal {O}(log(T)/T)$ convergence rate with the strong convex objective. To this end, a simple yet efficient polynomial-decay average strategy is suggested. We prove that with this strategy, the proposed algorithm can not only achieve the optimal convergence rate of $\mathcal {O}(1/T)$ but also obtain the classifier with higher sparsity. The empirical studies on several public benchmark data sets demonstrate the superior performance of the proposed algorithm in terms of both efficiency and sparsity.

Numerical simulation of the adaptive control system of the composite main mirror of a large-size space telescope

Numerical simulation of the adaptive control system of the composite main mirror of a large-size space telescope

Correction to: Influence of Layup Sequence on the Surface Accuracy of Carbon Fiber Composite Space Mirrors

The original version of this article unfortunately contained mistakes. Below is a list of corrections. The red color font is the final correct text after the modification. Several images in the article that need to be changed are already marked below.