Assessing organo-clay dispersion in polymer layered silicate nanocomposites: A SAXS approach

A SAXS method for the quantitative assessment of the morphology of polymer layered silicate nanocomposites is proposed. Fitting the SAXS patterns, the number of clay layers, the periodicity of the layers in the tactoids, the thickness of the regions interposed between the clay platelets and their distributions can be measured. A good agreement with TEM data was obtained, avoiding the inconsistencies with microscopical observations often reported in the literature.     

A small-angle X-ray scattering study of powder compaction

This work demonstrated a novel and potentially important application of two-dimensional small-angle X-ray scattering (2D-SAXS) to investigate powder compaction. SAXS from powder compacts of three materials commonly used for pharmaceutical tabletting exhibited azimuthal variations, with stronger intensity in the direction of the applied compaction force, relative to the transverse direction. This implied that compaction of a (macroscopic) powder could also produce changes on the molecular (nanometre) scale, which can be probed by 2D-SAXS. Two possible explanations for this effect were suggested. A combination of anisometric (i.e. elongated or flattened) granules with anisotropic morphologies could result in azimuthal variation in X-ray scattering due to granule orientation. It is expected that this mechanism would require relatively low packing density, so may operate during die filling. Granule re-orientation appeared less likely at higher packing densities and compaction pressures, however. Under these conditions, the changes in the 2D-SAXS patterns would be consistent with the powder granules becoming relatively flattened in the compression direction, with corresponding changes in their nano-scale morphology. The magnitude of this effect was found to vary between the materials used and increased with compaction pressure. This suggested that 2D-SAXS studies could provide useful information on force-transmission within a compressed powder. Further analysis of the data also suggested differences in the compaction mechanisms (i.e. granule re-orientation, deformation or fragmentation) between the materials studied.     

一种改进的图像域SAR目标散射中心特征提取方法

散射中心是SAR图像目标识别的重要特征。本文基于属性散射中心模型，在文献[6]的基础上，提出了一种改进的图像域SAR目标散射中心特征提取方法。在该方法中，通过引入参数规则化处理步骤，解决了属性散射中心特征提取方法的收敛问题，提高了属性散射中心特征参数估计的精度和效率；提出了一种能同时实现散射中心数目确定和结构判别的方法，实现了散射中心类型的可靠判别。仿真数据和MSTAR实测SAR图像数据的实验结果，验证了本文改进的图像域SAR目标散射中心特征提取方法的有效性。     

Distributed Optical Fiber Sensor for Multi-point Temperature Measurement

The distributed optical fiber sensing technology is overviewed, which is based on Raman scattering light theory. Basic operation principle, structure, system characteristics and signal processing are discussed. This structure and method of the signal processing possess of certain spatial resolution, hence will ensure the practicability of system.     

Surface segregation studied by low-energy ion scattering: experiment and numerical simulation

The changes in surface composition of metallic alloys caused by segregation can be very efficiently studied by low-energy ion scattering (LEIS) due to the specific surface sensitivity of this technique. Investigations of single-crystal surfaces of ordered alloys are of particular interest because they provide the possibility to investigate the interplay between segregation effects and the order-disorder phase transition when passing through the transition temperature. Exemplifying these effects for bimetallic alloys we consider in particular the CuAu-system.For the quantitative interpretation of energy and angle resolved LEIS intensity distributions we compare experimental results with those from numerical simulations using the MARLOWE code which we extended with a detailed trajectory analysis. This allows us to apply various discrimination criteria, such as number of collisions, distance of closest approach, identification of the scattering crystal layer, total path length, etc. On this basis structural effects, ion survival probabilities and the influence of thermal vibrations can be studied.We demonstrate this potential by using CuAu(1 0 0) as a special example. The scattering potential parameters were calibrated with elemental single crystals of known structures and the anisotropic Debye temperatures taken from the literature showed good agreement, neutralization was of minor importance in this case. Our procedure could be successfully used for the quantitative analysis of the composition of the first and second layer as a function of temperature. These results are in good agreement with theoretical predictions.     

Intermediate order in tetrahedrally coordinated silicon: evidence for chainlike objects

In this report, we describe the nature of intermediate order in silicon as determined by recent measurements on thin films using transmission electron microscopy (TEM) and Raman scattering. The TEM images show in addition to the expected continuous random network (CRN), the presence of highly ordered quasi-one-dimensional “chain-like objects” (CLO's) that are 1–2 nm wide and tens of nm long that meander and show some evidence of cross-linking with each other. The presence of these objects correlate to a Raman feature centered at 490 cm⁻¹ whose width is 35–40 cm⁻¹, and is used to quantify the heterogeneity in terms of the CLO and CRN (=475 cm⁻¹ scattering) concentrations. The 490 and 35 cm⁻¹ values are consistent with bond angle deviations approaching 0°, and thus reinforces an association with the CLOs. We find that in reference quality a-Si:H (made using pure SiH₄), the CLO concentration is about 5 vol%, while in state-of-the-art material using high H₂ levels of dilution during processing, it increases to about 15%. Increased stability of such material to light-soaking is thus not mediated by a direct volumetric replacement of poor with high-quality components. Rather, an important characteristic of intermediate order in silicon is the low-dimensional aspect of its order, which allows it to influence more total volume than which it is itself composed. Consistent with these and other recent findings, we propose a tensegrity model of amorphous silicon.     

Determination of the width of the transition layer between the crystalline and amorphous zones in nylon 1010 by SAXS

The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity.     

电离层时域探测方法

给出了各向同性分层半空间等离子体对时域电磁脉冲后向散射的有关公式，得出了反抛物层时域响应的解析表达式，并利用时频分析方法演出了电子密度分布。     

基于布里渊散射的分布式光纤传感器的进展

目的 介绍了基于布里渊散射的分布式光纤传感器的当前进展及趋势。方法 给出了基于布里渊散射的分布式光纤传感器的原理，介绍了基于光纤时域反射的BOTDR和BOTDA的分布式光纤传感器，以及基于自发布里渊散的同时测试应变和温度分布多光纤传感器，并指出了遇到的问题。结果 使读者详细了解基于布里渊散射的分布式光纤传感器当前进展及发展趋势。结论 基于布里渊散射的分布式光纤传感器继承了分布式光纤传感器的优点，并使测试的范围增大，可测信息种类增多，精度更高。