Small-angle neutron scattering investigation of creep damage in type 304 stainless steel and alloy 800

Creep damage accumulation in fully precipitated type 304 stainless steel and alloy 800 was investigated using small-angle neutron scattering. The small-angle scattering decreased initially and then slowly increased during the intermediate stages of creep. The scattering is thought to be dominated by stress assisted coarsening of carbide precipitates during the early stages of creep. This result and the direct observation of cavities by transmission electron microscopy indicate that at least two damage mechanisms, precipitate coarsening and cavitation, were occurring simultaneously. Coarsening dominates the small-angle scattering measurements during the early stages of creep, but cavitation appears to be detectable during the intermediate stages.     

Development of Microstructures of Long-Period Stacking Ordered Structures in Mg85Y9Zn6 Alloys Annealed at 673 K (400 °C) Examined by Small-Angle X-Ray Scattering

Development of LPSO structure and in-plane ordering during annealing the Mg85Y9Zn ternary alloy sample at 673 K (400 °C) was examined by synchrotron radiation small-angle scattering/diffraction measurements. By examining the first diffraction peaks for 18R, 10H, and in-plane order spot, the growth kinetics of in-plane order domain and the transition from 10H into 18R were discussed. The domain growth of in-plane order was characterized by small domain with little correlation between neighboring segregation layers.     

Small-angle X-ray scattering from mitochondria

X-ray (CuKalpha) scattering curves of rat liver mitochondria are characterized by continuously decreasing intensity from 0.5 to 5 mrad and a broad maximum centered near 20 mrad. The condensed-to-orthodox morphological transition of the inner membranes of intact mitochondria causes a dramatic decrease in scattering at very small angle and a marked shift of the 20 mrad maximum to smaller angle. A similar small-angle scattering maximum is observed with inner mitochondrial membrane fractions prepared by digitonin treatment and osmotic shock/step gradient centrifugation procedures. However, the small-angle X-ray scattering curves of mitochondria after acetone treatment and osmoticlysis/sonication are essentially continuous. These characteristics of mitochondrial X-ray scattering are discussed in terms of known structural features of the organelle.     

Growth and coarsening of g. p. Zones in Al- Zn alloys

The structural changes during the precipitation of G. P. zones in Al-Zn binary alloys have been investigated by means of anin situ small-angle scattering technique using synchrotron radiation. Defining a specific time, normalized by the half-completion time, the time-dependent evolution of the precipitation process can be divided into three periods, independent of alloy composition and quench-ing conditions. The structural and kinetic features of the first two periods have been analyzed in detail. The first stage represents a growing process of clusters with diffuse interface into the well-defined G. P. zones. The average size of these clusters increases, and the density decreases. The second stage corresponds to the Ostwald ripening process. This mechanism is described by utilizing a modified Lifshitz-Slyozov-Wagner theory.     

Investigation of the structure of thylakoid membranes (spinach) by means of small-angle neutron scattering

This paper presents experimental data on the determination of the thickness of thylakoid membranes by small-angle neutron scattering. The thylakoids were isolated from spinach chloroplasts. The partial volume of proteins and lipids in the "washed" and "unwashed" membranes was estimated. It is shown that the thickness of thylakoid membranes, measured with this techniques depends on the way the membranes were separated. When isolated thylakoids by the standard method, the membrane thickness amounted to 75 A but if the extracted thylakoids were additionally washed with the isolation medium, the measured thickness was 50 A. In this case a significant decrease in the protein partial volume of the membrane was observed. The obtained results make it possible to explain numerous data on X-ray and small-angle neutron scattering by thylakoid membranes of different origins, proceeding from the assumption that all these membranes have a unified structure and consist of a stable core with a thickness of about 50 A, and layers of peripheral, weakly bound proteins with a thickness which may depends on the nature of the object under investigation and extracting conditions.     

Electron dose calculation using multiple-scattering theory: a new theory of multiple scattering

Starting from the Boltzmann-Fokker-Planck transport equation, we have developed a new theory of multiple scattering which incorporates the advances already made with our Gaussian multiple-scattering theory for electron dose calculation. This incorporation has been accomplished in a natural way, by modifying the scattering power T and by adding a convolution term to the distribution-function equation of the Gaussian theory. Our previous results concerning increasing the accuracy of the small-angle approximation used and dealing with localized tissue inhomogeneities have thus been maintained, and we have arrived at a complete distribution function in both transverse spatial and angular variables. When integrated over the transverse angular variables, for a first-order small-angle approximation this distribution function for a pencil beam is essentially the same as the Moliere multiple-scattering distribution, which includes large-angle single scattering. For a water phantom, we have used comparisons with EGS4 Monte Carlo calculations to demonstrate the greatly increased accuracy of our new multiple-scattering theory over the Gaussian theory, which includes the usual Fermi-Eyges theory. We have also presented a fairly accurate Gaussian approximation to the pencil-beam dose profiles given by our new theory, which can be used in order to maintain the mathematical simplicity of the predictions of the Fermi-Eyges theory.     

Prospects for adoptive T cell therapy

Recent advances in neutron and X-ray sources and instrumentation, new and improved scattering techniques, and molecular biology techniques, which have permitted facile preparation of samples, have each led to new opportunities in using small-angle scattering to study the conformations and interactions of biological macromolecules in solution as a function of their properties. For example, new instrumentation on synchrotron sources has facilitated time-resolved studies that yield insights into protein folding. More powerful neutron sources, combined with molecular biology tools that isotopically label samples, have facilitated studies of biomolecular interactions, including those involving active enzymes.     

Measurement of smoothed Wigner phase-space distributions for small-angle scattering in a turbid medium

We study Wigner phase-space distributions W (x, p) in position (x) and momentum (p) for light undergoing multiple small-angle scattering in a turbid medium. Smoothed Wigner phase-space distributions are measured by using a heterodyne technique that achieves position and momentum resolution determined by the width and the diffraction angle of the local oscillator beam. The sample consists of 5.7-micron-radius polystyrene spheres suspended in a water-glycerol mixture. The momentum distribution of the transmitted light is found to contain a ballistic peak, a narrow diffractive pedestal, and a broad background. The narrow diffractive pedestal is found to decay more slowly than the ballistic peak as the concentration of scatterers is increased. The data are in excellent agreement with a simple theoretical model that explains the behavior of the narrow pedestal by including multiple diffractive scattering and treating large-angle scattering as a loss.     

超细粉末粒度分布的X光小角散射分析(Ⅲ)——分割分布函数法求解的稳定性

分割分布函数法是以x光小角散射数据计算超细粉末粒度分布的方法之一。本文通过优化系数矩阵、另加阻尼因子以及最小二乘法处理,对分割分布函数法求解稳定性进行了研究。全部演算在计算机上完成。结果表明,当满足相应条件时,所求粒度分布的平均偏差不大于所测散射强度的误差。     

Characterization of 9Cr-1MoVNb steel by anomalous small-angle X-ray scattering

The size distribution and volume fraction of Cr₂₃C₆ precipitates in 9Cr-1MoVNb steel have been isolated from the distributions of all other precipitates by the technique of anomalous small-angle X-ray scattering. Three X-ray wavelengths near the Cr K absorption edge were used to vary the scattering contrast of Cr₂₃C₆ while that of the other precipitates was left unchanged. Size distributions calculated from each scattering curve using a maximum entropy method were combined by a scattering contrast gradient analysis to isolate the volume-fraction size distribution of the chromium carbides. Behavior of these carbides was studied as a function of isothermal aging temperature. Mean diameter is smallest and Cr₂₃C₆ number density is highest after aging at 811 K. Above 811 K, the mean diameter of the chromium carbides increases with increasing aging temperature.     

Thermal stability of invar FeNi alloys above 500°C

The high-temperature thermal stability of three FeNi alloys (with 35.0, 40.1 or 43.8 at. % Ni) was investigated by aging samples for 230 days at 625°C. Anomalous small-angle X-ray scattering, analytical transmission electron-microscopy and magneto-thermogravimetric Curie temperature measurements were used for this purpose. The wave-length dependence of the anomalous scattering effect was found to be opposite to what would be expected from a decomposed solid solution. The absence of concentration fluctuations was further confirmed by the other two techniques. Taking into account previous aging results, it is concluded that, in the investigated composition range, FeNi alloys are thermally stable above 500°C.     

Glassy Carbon as an Absolute Intensity Calibration Standard for Small-Angle Scattering

Absolute calibration of small-angle scattering (SAS) intensity data (measured in terms of the differential scattering cross section per unit sample volume per unit solid angle) is essential for many important aspects of quantitative SAS analysis, such as obtaining the number density, volume fraction, and specific surface area of the scatterers. It also enables scattering data from different instruments (light, X-ray, or neutron scattering) to be combined, and it can even be useful to detect the existence of artifacts in the experimental data. Different primary or secondary calibration methods are available. In the latter case, absolute intensity calibration requires a stable artifact with the necessary scattering profile. Glassy carbon has sometimes been selected as this intensity calibration standard. Here we review the spatial homogeneity and temporal stability of one type of commercially available glassy carbon that is being used as an intensity calibration standard at a number of SAS facilities. We demonstrate that glassy carbon is sufficiently homogeneous and stable during routine use to be relied upon as a suitable standard for absolute intensity calibration of SAS data.     

多孔材料孔径及孔径分布的测定方法

孔径及其分布显著影响着多孔体的透过性、渗透速率、过滤性等一系列性能。本文介绍多孔材料孔径及其分布的常用测定方法，包括断面直接观测法、气泡法、透过法、压汞法、气体吸附法、液．液法、悬浮液过滤法、X射线小角度散射法等，并对几种测量方法进行了比较。     

Characterization of SPEEK/Y2O3 proton exchange membrane treated with high magnetic field

The membranes of sulfonated poly(etheretherketone) of 48.3% sulfonation degree doped with Y2O3 were prepared, and then treated with parallel high magnetic field of 6 and 12 T at 120 oC for 4 h, respectively. The small-angle X-ray scattering revealed that the struc- ture of the composite membranes would be changed by high magnetic field treatment. The cross-section morphology of the composite membranes by a scanning electron microscope showed that the Y2O3 could be dispersed evenly in the composite membranes which were relatively smooth and compact but formed small conglomeration with increasing Y2O3 content and treating high magnetic field. The water uptake of membranes would be reduced with Y2O3 content increasing, but not be modified by the treatment of high magnetic field. The proton conductivity of membranes would be increased with temperature rising from 20 to 60 oC, and improved under high magnetic field, which could all exceed 10-2 S/cm at 75% relative humidity, but decrease with doping content of Y2O3 from 2 wt.% to 8 wt.%. The methanol permeability of the composite membranes would be decreased with Y2O3 content increasing and slightly reduced after high magnetic field treatment.     

X-ray diffraction study of in vitro calcification of tendon collagen

Decalcified samples of turkey leg tendon were submitted to in vitro calcification in the presence of metastable solutions of calcium phosphate at different concentrations. The structural relationship between apatitic deposits and collagen fibrils was examined by high- and small-angle X-ray diffraction using conventional and synchrotron radiation sources. At high supersaturation the apatitic crystallites were deposited on the collagen fibrils with their crystallographic c-axis preferentially oriented parallel to the fibril axis. At lower supersaturation, a fraction of the apatitic crystallites also grew with the c-axis preferentially oriented parallel to the collagen fibril axis, whereas other exhibited a preferential orientation perpendicular to the fibril axis. The analysis of the small-angle X-ray diffraction data indicates that the deposition of the apatitic phase in the sample stored in solution at lower supersaturation induced modifications of the collagen electron density distribution in the axial direction, which can be attributed to the deposition of the inorganic crystallites inside the gap region of the collagen structure.     

Association-induced folding of globular proteins

It has generally been assumed that the aggregation of partially folded intermediates during protein refolding results in the termination of further protein folding. We show here, however, that under some conditions the association of partially folded intermediates can induce additional structure leading to soluble aggregates with many native-like properties. The amount of secondary structure in a monomeric, partially folded intermediate of staphylococcal nuclease was found to double on formation of soluble aggregates at high protein or salt concentrations. In addition, more globularity, as determined from Kratky plots of small-angle x-ray scattering data, was also noted in the associated states.     

赛博空间中的天线散射特性研究

5G网络技术可以满足赛博空间（Cyberspace）发展对通信平台性能提出的高要求,大规模MIMO（Multiple-input multiple-output）天线阵列是5G核心技术之一。实际中大规模MIMO天线阵列的互耦效应会大大降低香农容量,在未来5G天线系统中,面临的最大挑战是如何有效消除阵列中单元天线间的互耦。针对大规模阵列天线互耦问题,应进行天线单元的散射特性研究。本文在开路状态下“不可见”的最小散射天线基础上,推导了最小散射天线串联四分之一波长透明网络的散射矩阵,证明该状态即为短路状态下的最小散射天线。对一种X波段波纹喇叭天线分别进行短路、开路、匹配三种负载状态下的散射测量,根据最小散射天线理论分离出了天线的额外散射、伴随散射和失配散射。用分离获得的散射分量,推算了波纹喇叭天线的散射最大值和最小值,其中推算出的最小值远低于天线匹配时的散射。用滑动短路器作为可变负载,进行预设负载状态下波纹喇叭天线的散射测量,实测获得了推算出的散射最大值和最小值,验证了单元天线散射特性研究的正确性。结果说明,在进行大规模阵列的单元天线设计时,除了考虑单元天线的辐射特性之外,也要考虑天线的散射特性,以降低天线的互耦效应。      

The susceptibility of pure tubulin to high magnetic fields: a magnetic birefringence and x-ray fiber diffraction study

The orientational behavior of microtubules assembled in strong magnetic fields has been studied. It is shown that when microtubules are assembled in a magnetic field, they align with their long axis parallel to the magnetic field. The effect of several parameters known to affect the microtubule assembly are investigated with respect to their effect on the final degree of alignment. Aligned samples of hydrated microtubules suitable for low-resolution x-ray fiber diffraction experiments have been produced, and the results obtained from the fiber diffraction experiments have been compared with the magnetic birefringence experiments. Comparisons with earlier fiber diffraction work and small-angle x-ray solution scattering experiments have been made.     

Determination of dispersoid size distributions in Inconel MA 754 by small-angle X-ray scattering

The dispersoid size frequency distribution and volume fraction of the nickel based oxide dispersion strengthened alloy Inconel MA 754 have been determined using small-angle X-ray scattering (SAXS). Two methods of determining dispersoid size distributions from the SAXS spectra are utilized. One method involves a calculation of log-normal distribution parameters from the integrated intensity, forward scattering and the Porod radius. A second method employs an integral transform of the data to calculate the size distribution. Dispersoid size distributions from the transform method exhibit close agreement with histograms obtained from thin foil transmission electron microscopy. Measurement of dispersoid volume fractions from the integrated intensity, coupled with dispersoid size frequency distributions allow a calculation of the average planar separation distance of the dispersoids. The results for two heats of MA 754 lead to predicted dislocation creep strengths which are in reasonable agreement with short time creep data at 1000 and 1093°C. The effect of the presence of mixed aluminum-yttrium oxides in MA 754 is considered.