空间分辨漫反射的一阶散射参量灵敏度

以输运理论的P3近似为基础,推导了空间分辨漫反射的一阶散射参量灵敏度的解析表示,并进行了数值分析,比较了散射参量对P3近似和漫射近似漫反射的影响.结果表明:在距光源两个输运平均自由程以内,该灵敏度与相应于漫射近似的灵敏度差别较为明显;距离光源约四个输运平均自由程附近,该灵敏度等于零,并且与光源之距与相应于漫射近似情况也...     

Recent advances in DWS-based micro-rheology

We have reviewed recent developments in diffusing wave spectroscopy (DWS) that have facilitated micro-rheological studies of soft solids and complex liquids. In particular, we have focussed on two novel ensemble-averaging methods, two-cell DWS and charged-coupled device DWS (CCD-DWS), that directly address problems of non-ergodicity and broken time–translation invariance in these materials. The applications of these methods to the study of slow evolutionary dynamics, mechanical aging and transient phenomena are also discussed.     

St-DVB微凝胶星型两性接枝共聚物的单分子膜性质研究

用自由基引发苯乙烯-二乙烯基苯(St-DVB)共聚合成了带有大量乙烯基的活性微凝胶,再将此活性胶核与甲基丙烯酸(MMA)共聚制得微凝胶星型两性聚合物,并成功地制备了LB膜,此微凝胶星型两性聚合物LB膜与-般典型LB膜的区别在于它的疏水部分不是长脂链,而是分子量比较大的苯乙烯-二乙烯基苯微凝胶;此疏水的微凝胶核与亲水的聚甲基丙烯酸链在气-液界面上形成类似"浮萍"结构的单分子膜,因而在诸多方面表现出特异性质。     

Diffusing wave spectroscopy investigations of acid milk gels containing pectin

The influence of the polysaccharide pectin on the gelation of acidified milk is studied in concentrated, undiluted, quiescent systems, primarily using diffusing wave spectroscopy. For pectins with a low degree of methylesterification (DM), interactions with milk-serum calcium yielded precipitated polysaccharide aggregates, even without acidification, that subsequently did not interact with casein micelles. However, high DM fine structures do not interact significantly with serum-calcium and absorb onto casein micelles as the pH is reduced below 5. A limited surface coverage of high DM pectin facilitates efficient bridging which enhances the rate of micelle aggregation and subsequent gelation and produces a clear signature in the shape of the measured MSD. The work highlights the fact that the behaviour of pectin in milk systems depends not only on the interaction of different polymeric fine structures with casein micelles, but also to a large extent on the interactions with calcium.     

Light Scattering Probes of Viscoelastic Fluids and Solids

In this article, we discuss recent advances in static and dynamic light scattering applied to soft materials. Special emphasis is given to light scattering methods that allow access to turbid and solid‐like systems, such as colloidal suspensions, emulsions, glasses, or gels. Based on a combination of single‐ and multispeckle detection schemes, it is now possible to cover an extended range of relaxation times from a few nanoseconds to minutes or hours and length scales below 1 nm up to several microns. The corresponding elastic properties of viscoelastic fluids or solid materials range roughly from below 1 Pa to several 100 kPa. Different applications are discussed such as light scattering from suspensions of highly charged colloidal particles, colloid and protein gels, as well as dense surfactant solutions.     

Remarks on ergodicity and invariant occupation measure in branching diffusions with immigration

We give a necessary and sufficient condition for ergodicity with finite invariant occupation measure for branching diffusions with immigration. We do not assume uniformly subcritial reproduction means. We discuss the structure of the invariant occupation measure and of its density.     

Si(001)表面分子束外延生长的小尺寸Ge量子点

通过调节生长参数, 在Si(001)衬底表面利用分子束外延(MBE)方法生长得到尺寸小于10 nm的高密度Ge量子点. 扩展的X射线吸收精细结构(EXAFS)的研究结果表明, 在500 ℃和550 ℃制备的小尺寸量子点内, GeSi合金的含量分别为75%和80%. 经热力学分析, 在量子点生长完成后的退火过程中, 可能存在Si原子从衬底表面向量子点表面扩散, 并和Ge原子通过表面偏析发生混合的过程. 另一方面, 小尺寸量子点较高的高宽比, 也会导致形成较高含量的GeSi合金.     

Experimental study of the potential use of diffusing wave spectroscopy to investigate the structural characteristics of blood under multiple scattering

The extension of the photon correlation spectroscopy (PCS) in multiple scattering regime, so-called diffusing wave spectroscopy (DWS) was employed to the study of blood samples. Multiple scattered light from a helium-neon (He-Ne) laser beam incident on the blood samples was detected by a photomultiplier, and both the temporal autocorrelation intensity functions g 2(tau) and power spectra S(omega) were measured by a spectrum analyzer. The potentials of using DWS for the qualitative and quantitative determination of the structural characteristics of the blood elements were studied experimentally. The experimental studies made, permits the use of DWS for blood cells monitoring in a multiple scattering regime. This paper describes our initial attempts at applying DWS to the study of the discrete blood samples of both healthy donors and patients with the cardiac ischemia. The subsequent experiments provide a verification of DWS of blood cells shape monitoring under multiple scattering.     

A diffusing wave spectroscopy study of the kinetics of Ostwald ripening in protein-stabilised oil/water emulsions

Diffusing wave spectroscopy (DWS) has been used to study the kinetics of ageing processes in n-decane/water emulsions, stabilised by the milk protein _S1-casein. A particular advantage of this particle size measuring technique is its direct applicability to the concentrated emulsion, avoiding the necessity for dilution to single scattering levels demanded by traditional dynamic light scattering methods. The observed droplet growth rates were found to conform to the kinetic law of Ostwald ripening. Monotonic increases in coarsening rates have been observed with increasing oil volume fraction and these results are compared with theoretical predictions. The effect of excess protein has also been measured but no evidence for depletion flocculation due to free _S1-casein was detectable.