ISLAND—Inverse Square Law Acceleration Measurement Using iNertial Drift

By using a novel free-flying, rotating, optical bench aboard the International Space Station (ISS) as the basis for a measurement of differential acceleration between two gravitating bodies, in principle the Newtonian inverse-square law and the constant of gravitation, G, can be determined at the parts in 10⁶ level.     

Effect of Low Energy Electron Exposure on Ion Scattering Spectroscopy

The effect of low energy electron (LEE) exposure on ISS, including on the sputter peak and scatter peak as well as on ion neutralization, has been investigated for different samples. Some new results are discussed.     

基于ISS特征点的快速CPD建筑物点云配准算法

针对大规模建筑物点云数据采用CPD（coherent point drift）算法进行配准时,计算复杂度增大的问题,提出了一种基于建筑物点云特征点简化数据的快速配准ISS-CPD算法。该配准算法采用ISS(intrinsic shape signature)算法求得建筑物点云的特征点,可减少建筑物点云的数据量规模,再对所提取的不同视角下建筑物点云的特征点用CPD算法进行配准。实验结果表明,改进的配准算法提高了建筑物点云的配准效率。     

基于无源辨识器的随机非线性系统自适应跟踪模块化设计

运用基于估计的模块化设计思想,研究了受方差不确定Wiener噪声干扰的参数严格反馈非线性系统对已知信号的自适应跟踪问题.构造控制Lyapunov函数,设计了具有鲁棒稳定特性的输入状态稳定控制器,确保系统满足控制器-辨识器分离.对不确定方差采用自适应方式处理.根据无源性理论,设计无源辨识器模块,给出了参数自适应律,确保系统误差的有界性,使跟踪误差在概率意义下收敛.     

农林复合经营工程领域研究热点与前沿分析

【目的】农林复合经营是解决当前资源枯竭、用地矛盾等问题的可持续土地管理模式,在我国继续推行农林复合经营有着重要的意义。分析该领域的研究热点,有助于明确研究现状,找准自身定位和方向,进而提高研究水平。【方法】基于Web of Science 数据库检索平台,应用CiteSpace科学引文分析方法和中国工程院ISS系统对检索到的全球农林复合经营领域研究文献进行全面梳理,并对该领域所涉及的主要研究技术、研究热点等进行分析。【结果】农林复合经营研究的热度随地区的经济水平提高而增加;全球研究主要热词为系统、经营管理、多样性保护和林分生长;农林复合经营的研究前沿为培育研究、多样性研究、空间分布研究、能量流动研究和生物多样性保护等方面。【结论】我国农林复合经营的研究应增进广泛的国际合作,促进全球化的宏观研究;运用低成本、低破坏手段获取高精度林分结构参数,全面理解植物之间的作用机制和化感等互作效应将是未来研究的挑战和机遇;农林复合系统在中国有着广阔的发展前景,必将为缓解全球气候变化做出应有的贡献。     

Influence of compaction and surface roughness on low‐energy ion scattering signals

Investigation of the surface composition of powders often requires compaction. To study the effect of compaction on surface analysis, samples have been compacted at various pressures ranging from 0 Pa (i.e. no compaction) up to 2000 MPa (2 × 10⁴ kg cm^?2) Low‐energy ion scattering (LEIS) was used to determine the composition of the outermost atomic surface layer. Using scanning electron microscopy, changes in the morphology due to compaction have been detected in the SiO₂ test samples. The LEIS yield of a compacted silica powder is found to be independent of the applied pressure during compaction between 2 MPa and 2000 MPa (2 × 10⁴ kg cm^?2). Analysis of a submonolayer of Ta₂O₅ on a silica support shows that the composition of the outermost atomic layer is not changed after compaction up to a pressure of at least 300 MPa. When compaction is applied, the absolute LEIS yield appears to be independent of the specific surface area of silica supports in the range 50–380 m² g^?1. A minor difference in LEIS signals is observed between compacted silica supports and flat quartz samples. In order to determine the surface roughness factor independently, and to study the material dependence of the surface roughness factor, angle‐dependent LEIS measurements have been carried out on oxidized silicon, gallium and gold surfaces. The results on the oxidized silicon confirm the small influence of surface roughness for silica particles, whereas measurements on the more closely packed metallic gallium and gold surfaces indicate a significant surface roughness effect. Copyright © 2004 John Wiley & Sons, Ltd.     

Surface segregation of silicon impurities in organic materials

The present revolution in novel organic materials is driven by the synthesis of new materials exhibiting specific functional properties. Traces of silicon compounds are often present in these materials and, although the bulk concentrations of these impurities may be low, segregation can seriously modify the surface composition. Surfaces and interfaces play an important role in many applications, and the intrinsic properties of the materials are thus often obscured by the presence of segregated impurities. By studying silicon impurity segregation in poly‐dialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules, we demonstrate how low‐energy ion scattering may be used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species. We demonstrate that the performance of PPV‐ based light‐emitting diodes is significantly reduced for submonolayer coverages of siloxanes. We find that the kinetics of the segregation process depend strongly on the materials and the sample preparation conditions. We find that the presence of solvents is needed to enable segregation at room temperature. Heating does enable siloxane impurity segregation in polycarbonate in the solid phase, whereas for polydimethylsiloxane in PPV films we find that segregation in the solid phase does not occur up to 200 °C. The siloxane molecules are found to segregate to preferential sites at the surface, shielding the polar groups. Finally, we demonstrate that purification of the surface is often possible through simple procedures that provide an easy way to study the intrinsic properties of the materials. Copyright © 2004 John Wiley & Sons, Ltd.     

Surface composition of alloys

The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success.