月尘的性质及危害评述

月尘一直以来都是阻碍人类探索月球的一大问题,月尘颗粒锋利、细微和带静电等特性可对各类机械结构、密封结构、功能表面、空间仪器载荷以至宇航员产生巨大危害。文章总结了目前月尘防护技术的研究进展,包括月尘的全流程防护及大空间月尘防护研究;以电磁法为代表的主动防护技术,如电帘、静电场、等离子体束、电喷雾和磁辊等除尘技术;以表面改性技术为主的被动防护技术,如减弱范德瓦耳斯力的低表面能、高粗糙度的纳米尺度涂层和减弱静电力的功函数匹配涂层等。聚焦中国探月工程水冰探测计划的月尘防护,综述了针对采掘、加热和分析三个环节所使用的过滤和密封的防尘手段,包括采掘钻杆使用螺旋槽和间隙密封;加热和分析容器采用金属刀口主密封和O型圈辅助密封;在分析仪器前设置烧结金属过滤器、高效空气过滤器（HEPA）和多级永磁月尘过滤器（LAF-PMS）;在连接管道处设置双层O型圈密封;在外接出口处设置迷宫密封和HEPA等。最后,给出一种“水冰探测仪月尘防护的方案设计”。

     

Flowability of lunar soil simulant JSC-1a

We have done a complete flowability characterization of the lunar soil simulant, JSC-1a, following closely the ASTM-6773 standard for the Shulze ring shear test. The measurements, which involve pre-shearing the material before each yield point, show JSC-1a to be cohesionless, with an angle of internal friction near 40°. We also measured yield loci after consolidating the material in a vibration table which show it to have significant cohesion (≈ 1 kPa) and an internal friction angle of about 60°. Hopper designs based on each type of flowability test differ significantly. These differences highlight the need to discern the condition of the lunar soil in the specific process where flowability is an issue. We close with a list—not necessarily comprehensive—of engineering rules of thumb that apply to powder flow in hoppers.     

Using a multi-agent system to optimise resource utilisation in multi-site manufacturing facilities

Due to cost economies and better serving the global market, many enterprises expanded their manufacturing environment from a localised, single-site facility to more globalised, multi-site facilities. In order to take advantage of operating multi-site facilities, it is vital to make optimisation decisions of resource utilisation as if these facilities situated across different geographical locations are one integrated facility and take into account of the extended multi-site constraints and variables. This paper proposes a multi-agent system, using its characteristics of autonomy and intelligence, to integrate process planning and production scheduling across different facilities, so as to secure the most efficient and cost-effective plan and schedule to meet the demand. A currency-based agent iterative bidding mechanism is developed to facilitate the co-ordination of agents to achieve the goal. A genetic algorithm is employed to tune the currency values for agent bidding. In this paper, a case study is used for simulation in order to demonstrate the effectiveness and performance of the proposed agent system.     

Temperature and wavelength dependent transmission of optically transparent glass fibre poly (methyl methacrylate) composites

The temperature and wavelength dependent transmission was measured for glass fibre reinforced transparent composites prepared by sheet lamination and pressure curing processes. A mathematical model using fibre volume content, glass fibre diameter, refractive index of the fibre and matrix, non-wet fibre content and thickness of the composites was used to predict the transmission of the composite as a function of temperature and wavelength. The transmission calculated from the model for 20–70 °C and between 500 to 800 nm agreed well with the measured optical transmission for a thin composite containing < 10 vol % of 17 m glass fibres. A small amount of non-wet fibre (e.g. 2.0% of total fibre) was predicted to reduce the maximum transmission by up to 17% for a composite containing 7.2 vol % fibres and a thickness of 0.5 mm.     

Fabrication of optically transparent cotton fiber composite

In this study, we fabricated optically transparent cotton fibers composite by resin impregnation without having to prepare cellulose nanofibers. Although the surface acetylation of the cotton microfibrils aided the resin impregnation process, excess acetylation resulted in the gradual breakdown of the cellulose crystal structure, with the resulting composite showing a high coefficient of thermal expansion (CTE). To prevent this, a swelling pretreatment, namely surface carboxylation by TEMPO-mediated oxidation, was performed to facilitate the surface acetylation of the microfibrils and hence the resin impregnation process. After the swelling pretreatment and the subsequent surface acetylation process, an optically transparent cotton fiber composite with a high regular light transmittance (83.23% at 600 nm) and a low CTE (19.5 ppm/K) was obtained. Finally, when this technique was used with a commercial cotton cloth, a transparent composite with a high total transmittance (88.5% at 600 nm) could be obtained.     

Minimax design of optically transparent and reflective coatings

We consider the design problem of creating coatings that are either highly reflective or highly transparent. The goal is to create an optical element, consisting of planar dielectric layers, that reflects (or transmits) energy over a given range of wavelengths and angles of incidence. The approach that we take is to formulate the problem as a minimax optimization problem. We demonstrate that the approach can be effective in producing coatings of a few layers with desirable properties.     

Mechanical properties of optically transparent,multi-layered laminates

The objective of this investigation was to study how the mechanical properties of an optically transparent composite varied with the geometrical arrangement, stacking sequence, of polymethylmethacrylate (PMMA) (designated as P) and composite (designated as C) layers. The multi-layered composites (about 6.63 mm thick) were highly transparent between 22 to 46°C in the visible region. As expected, the sandwich structure, (CCPP)s had the highest Young's modulus while (PCCP)s and (PPCC)s composites had the highest flexural strength and work of fracture, respectively. The flexural strength of these laminated composites, which contained only 0.8 vol % fibre without any coupling agent, was up to 21% higher than that of pure PMMA.The stress distribution through the thickness at the midpoint of a sample loaded in three-point bending was computed by the finite element method (FEM). The computed stress distribution allowed the expected point of failure to be established. The relationship between the stacking sequence, stress level under a given load, and strength was also investigated. The observed fracture modes were complex and the maximum stress failure criterion did not fit these composites. The fracture was always complex (tensile and shear), starting with tensile failure followed by shear mode (delamination) and another tensile mode. The first crack always commenced at a PMMA layer adjoining the composite layer which contained the highest stress. The optimum stacking sequence when such composites are used as a window is concluded to be (PCCP)s, since this sequence had the highest flexural strength (141 MPa) and a moderate work of fracture (37 kJ m^–2).     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

卷簧式可伸缩月壤取样臂的设计与分析

针对目前月壤取样器不能同时满足功耗、体积、重量及反复、精确取样的要求的问题,提出了一种新型卷簧式可伸缩月壤取样臂(CSRA).介绍了该取样臂的力学模型,并对其进行有限元分析,以研究薄壳杆几何参数对其最大推力的影响,且给出了最大推力数学估计公式.对比分析表明,用最大推力数学估计公式计算的结果与有限元分析结果吻合得较好.该...     

Linnik tomographic microscope for investigation of optically transparent objects

The Linnik tomographic (sectional X-ray diffraction analysis) microscope for measurement of the spatial distribution of the index of refraction within optically transparent (phase) objects is described. The microscope is constructed on the base of the MII-4 microinterferometer with a laser lighting source and constitutes a fully automated integrated system that incorporates a CCD camera, frame grabber, a computer-controlled PZT mirror, and a two-coordinate micrometer stage. The measurement system and performance characteristics of the microscope are presented. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 18–22, October, 1998.     

Fabrication of transparent continuous oxynitride glass fiber-reinforced glass matrix composite

Unidirectional-aligned continuous SiCaAlON fiber-reinforced glass matrix composites have been fabricated and their light transmittance was measured. Optically transparent composites with the fiber volume fraction from 0.03 to 0.10 were fabricated by a hot-pressing method. The light transmittance of the composite perpendicular to the fiber axis in the wavelength range from 200 to 700 nm was measured, and found to decrease with the increase of the fiber volume fraction. This decrease is explained by the theory proposed by the authors (Hl and YK). The major source of a light transmittance loss of the composite originates from a phase change of transmitted light in the composite.     

Characterization and discrete element simulation of grading and shape-dependent behavior of JSC-1A Martian regolith simulant

Granular regolith simulants have been extensively used in the preparation of space missions to test rovers and scientific instruments. In this work, the physical and mechanical properties of the JSC-1A Martian regolith simulant (MRS) are characterized using conventional and advanced laboratory techniques. Particle images are obtained using X-ray computed tomography, from which particle shapes are characterized through a series of imaging processing techniques and are further used to generate irregularly-shaped numerical particles. The characterized particle size distribution and irregularly-shaped numerical particles are incorporated into a discrete element model to simulate grading and shape-dependent behavior of the JSC-1A MRS. The developed discrete element model is calibrated and validated against laboratory direct shear tests. Simulations without the consideration of particle shapes and simulations with a rolling resistance contact model are also performed to investigate the effect of particle shapes on the behavior of the JSC-1A MRS.     

Fabrication of transparent silica glass by powder sintering

Transparent silica glasses were obtained by sintering a green compact (fabricated by slip-casting methods for high-purity silica glass powder) in diverse atmospheres. The relationships between sintering atmosphere and sintering temperature that result in transparent, sintered silica glass were shown. The results indicate that there are four forming phases for each sintering atmosphere and temperature: (1) nontransparent glass resulting from an overabundance of pores (2) crystal, such as cristobalite or β-quartz, (3) moganite, and (4) transparent glass. Optimum sintering temperature for fabricating transparent silica glass was above 1673 K in a high-vacuum (10⁻⁴ Pa: p(O₂)=10⁻¹⁴) atmosphere. We investigate the fabrication of transparent and hydroxyl-free silica glass by a powder-sintered method. After studying the effect of sintering schedule on residual [OH⁻] concentration for transparent, sintered silica glasses, we sintered a green compact prepared by silica powders with a mean particle size of 1.6 μm, first heating it to 1523 K for dehydration and then to 1873 K for densification. This typical fabricated condition resulted in a transparent, sintered silica glass with <1 ppm [OH⁻] concentration.     

Fabrication of transparent silica glass by powder sintering

Transparent silica glasses were obtained by sintering a green compact (fabricated by slip-casting methods for high-purity silica glass powder) in diverse atmospheres. The relationships between sintering atmosphere and sintering temperature that result in transparent, sintered silica glass were shown. The results indicate that there are four forming phases for each sintering atmosphere and temperature: (1) nontransparent glass resulting from an overabundance of pores (2) crystal, such as cristobalite or β-quartz, (3) moganite, and (4) transparent glass. Optimum sintering temperature for fabricating transparent silica glass was above 1673 K in a high-vacuum (10^–4 Pa: p(O₂) = 10^–14) atmosphere. We investigate the fabrication of transparent and hydroxyl-free silica glass by a powder-sintered method. After studying the effect of sintering schedule on residual [OH^–] concentration for transparent, sintered silica glasses, we sintered a green compact prepared by silica powders with a mean particle size of 1.6 µm, first heating it to 1523 K for dehydration and then to 1873 K for densification. This typical fabricated condition resulted in a transparent, sintered silica glass with <1 ppm [OH^–] concentration.     

Prediction of manufacturing resource requirements from customer demands in mass-customisation production

Mass-customisation production is a new manufacturing approach to produce customised products based on requirements of individual customers while maintaining the quality and efficiency of mass production. Due to the large variations of customised products, the traditional methods for planning manufacturing resources based on volumes of mass produced products are not effective for mass-customization production. In this research, a new manufacturing resource planning method is developed by studying the relations between customer demands and manufacturing resource requirements based on the true data from a mass-customisation production company—Gienow Windows and Doors. In this research, first the relations between the customer demands, modeled by sales data at levels of whole company, sales branches, and markets in sales branches, and the manufacturing resource requirements, modeled by labour requirements of different production lines are studied. Fuzzy pattern clustering method is employed for classifying the resource requirements into patterns to further understand the relations. Based on this study, linear regression and neural network are used to model the linear and non-linear relations between customer demands and manufacturing resource requirements, and to predict the manufacturing resource requirements from available customer demands. A manufacturing resource planning system was developed to demonstrate the effectiveness of this introduced approach.     

Ultraviolet-visible spectroelectrochemistry of chemisorbed molecular layers on optically transparent carbon electrodes

Pyrolysis of diluted commercial photoresist spun onto quartz slides yields optically transparent graphitic films. Transparent carbon electrodes approximately 6 nm thick can be reproducibly prepared, with a maximum absorbance in the ultraviolet-visible (UV-vis) range of 0.25 at 270 nm. These electrodes are sufficiently conductive for electrochemistry, enabling modification of the surface via diazonium ion reduction and spectroelectrochemistry. Good quality ultraviolet-visible absorption spectra of covalently bonded molecular layers of nitroazobenzene, nitrobiphenyl, and azobenzene, with thicknesses of 1.4-4 nm, were obtained after subtracting the spectrum of the unmodified substrate. The spectra of all three molecules immobilized on the carbon surface showed red shifts of the absorption maxima relative to a solution of free molecules, indicating substantial electronic interactions between chemisorbed molecules and the Pi system of the substrate and/or intermolecular coupling. Spectroelectrochemical measurements show that reduction of free and chemisorbed molecules produce new absorption features in the 500-800 nm range; these spectral changes are partially reversible upon repeated potential cycling. Finally, density functional calculations correlate the new bands to the formation of anion radical or "methide" species that have more extensive electron delocalization than the parent molecules. The results from this work are useful for linking structural transformations in molecular layers "buried" under conductive top contacts in a type of molecular junction to changes in the electronic properties of the junction.     

面向精密制造的光学自由曲面在位偏折测量技术

复杂光学曲面的在位测量是当前精密工程领域面临的重要难题。偏折术对光学曲面的测量精度可与干涉仪相比,而且拥有更高的测量效率、稳定性及动态范围,因此具有广阔的应用前景。但是偏折测量本质上是一个标定问题,其测量精度直接取决于几何标定的可靠性。本文结合单点金刚石切削机床设计了原位偏折测量系统,采用机床中自带的气浮转台安装辅助反射镜,在两个姿态下进行光线追迹,通过数值优化计算各元件之间的相对位置,将标定精度提高一个数量级。根据反向投影偏差的统计规律,可有效分离工件的面形偏差与位姿误差。该方法有效利用了工件的名义面形信息,将传统的位置-面形单向映射转变为双向映射,显著提高了在位测量的灵活性与效率。对于复杂的自由曲面,采用子孔径拼接测量方法,对待测的局部区域发展了精准定位技术,有效保证了迭代重构过程的正确收敛。采用离轴抛物镜等光学曲面进行实验验证,所提出的偏折测量方法的精度优于150 nm RMS。     

Model for continuous-wave laser-induced thermal lens spectrometry of optically transparent surface-absorbing solids

A theoretical model for cw laser-induced thermal lens spectrometry of optically transparent surface-absorbing solids is developed. In the model, the sample is represented as a set of discrete layers with certain thicknesses and light absorptivities. The bloomed thermo-optical element in the sample is described with a summation of heat-flux functions for all the layers. The model employs simple mathematical expressions and can be used for both steady-state and time-resolved thermal lens experiments. Good coincidence of the experimental and theoretically predicted signal dependences is achieved. This model is verified for volume-absorbing samples (colored optical glasses) and used successfully to calculate absorbances and concentrations for various surface-absorbing samples.