Behaviour of a puff of resuspended sediment: a conceptual model

The particulate matter concentration above the seabed is usually assumed to decrease with height, following an exponential or Rouse profile. Many particulate matter concentration profiles with a peak were found on the North Mediterranean bottom water at a few tens of metres above the bottom. A particle size signal at the same altitude was found in this area and on the New York Eight shelf. It is assumed that this unexpected shape is due to a cloud of resuspended cohesive sediments originating from an impulse resuspension process. A simplified three-dimensional numerical model is proposed to describe the behaviour of resuspended particulate matter that originates from a sediment impulse vertically injected in the bottom water. This model reproduces the concentration profile shape observed, and it gives indications concerning the length and time characteristics of such a cloud, depending on the water velocity and bottom boundary layer properties.

Scaling, Dimensional Analysis, and Indentation Measurements

We provide an overview of the basic concepts of scaling and dimensional analysis, followed by a review of some of the recent work on applying these concepts to modeling instrumented indentation measurements. Specifically, we examine conical and pyramidal indentation in elastic-plastic solids with power-law work-hardening, in power-law creep solids, and in linear viscoelastic materials. We show that the scaling approach to indentation modeling provides new insights into several basic questions in instrumented indentation, including, what information is contained in the indentation load-displacement curves? How does hardness depend on the mechanical properties and indenter geometry? What are the factors determining piling-up and sinking-in of surface profiles around indents? Can stress-strain relationships be obtained from indentation load-displacement curves? How to measure time dependent mechanical properties from indentation? How to detect or confirm indentation size effects? The scaling approach also helps organize knowledge and provides a framework for bridging micro- and macroscales. We hope that this review will accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to materials scientists and engineers, and (2) providing a better understanding of instrumented indentation measurements.

基于光弹调制技术的波片相位延迟量测量方法

提出了一种基于光弹调制技术的波片相位延迟量测量方法，利用米勒矩阵对其进行了理论推导和误差分析。测量光路包括激光器、起偏器、光弹调制器、被测波片、检偏器和光电探测器，利用探测信号的归一化基频分量和二次谐波分量精确计算出被测波片的相位延迟量。该方法能测量紫外到红外光谱范围内任意相位延迟量的波片，误差分析表明其误差小于0．05°。实验验证了该测量方法的有效性，波片相位延迟量的重复测量精度为0．0048°．

Multicolor luminescence in oxygen-deficient Tb3+;doped calcium aluminogermanate glasses

In this paper, we report on the multicolor luminescence in oxygen-deficient Tb3+-doped calcium aluminogermanate glasses. A simple method was proposed to control oxygen-deficient defects in glasses by adding metal Al instead of the corresponding oxide (Al2O3), resulting in efficient blue and red emissions from Tb3+-undoped glasses with 300 and 380 nm excitation wavelengths, respectively. Moreover, in Tb3+-doped oxygen-deficient glasses, bright three-color (sky-blue, green or yellow, and red) luminescence was observed with 300, 380, and 395 nm excitation wavelengths, respectively. These glasses are useful for the fabrication of white light-emitting diode (LED) lighting.

新书《克隆园》简介

这是一本科幻童话故事. 《克隆园》以科普、科幻童话的形式重点介绍了当今世界最为关注的科技热点——“生物克隆”. 并详细描述了一些世界濒危动物的生活习性, 强调了保护地球生态环境的重要性. 书中叙述了一只身怀绝技——一哭就能让周围人大笑不止的, 名字叫做“小鼠王”的小老鼠在寻找妈妈的路途中意外地闯入克隆园的奇遇。

小麦交联淀粉的制备工艺研究

采用环氧氯丙烷为交联剂 ,以小麦淀粉为原料制备小麦交联淀粉。探讨了环氧氯丙烷用量 ,氢氧化钠用量 ,反应温度 ,反应时间对交联度的影响并利用design -expert 6 .0 .3软件响应面中心组合实验优化得出制备不同交联淀粉的最佳工艺条件 ,分析了双因素间的交互效应。

Synthesis and optical properties of europium-doped ZnS: Long-lasting phosphorescence from aligned nanowires

Quasi-aligned Eu2+-doped wurtzite ZnS nanowires on Au-coated Si wafers have been successfully synthesized by a vapor deposition method under a weakly reducing atmosphere. Compared with the undoped counterpart, incorporation of the dopant gives a modulated composition and crystal structure, which leads to a preferred growth of the nanowires along the [0110] direction and a high density of defects in the nanowire hosts. The ion doping causes intense fluorescence and persistent phosphorescence in ZnS nanowires. The dopant Eu2+ ions form an isoelectronic acceptor level and yield a high density of bound excitions, which contribute to the appearance of the radiative recombination emission of the bound excitons and resonant Raman scattering at higher pumping intensity. Co-dopant Cl- ions can serve not only as donors, producing a donor-acceptor pair transition with the Eu2+ acceptor level, but can also form trap levels together with other defects, capture the photoionization electrons of Eu2+, and yield long-lasting (about 4 min), green phosphorescence. With decreasing synthesis time, the existence of more surface states in the nanowires forms a higher density of trap centers and changes the crystal-field strength around Eu2+. As a result, not only have an enhanced Eu2+ -4f(6)5d(1)-4f(7) intra-ion transition and a prolonged afterglow time been more effectively observed (by decreasing the nanowires' diameters), but also the Eu2+ related emissions are shifted to shorter wavelengths.

Study on growth mechanism of low-temperature prepared microcrystalline Si thin films

Microcrystalline silicon thin films at different growth stages were prepared by hot wire chemical vapor deposition. Atomic force microscopy has been applied to investigate the evolution of surface topography of these films. According to the fractal analysis I it was found that, the growth of Si film deposited on glass substrate is the zero-diffused stochastic deposition; while for the film on Si substrate, it is the finite diffused deposition on the initial growth stage, and transforms to the zero-diffused stochastic deposition when the film thickness reaches a certain value. The film thickness dependence of island density shows that a maximum of island density appears at the critical film thickness for both substrates. The data of Raman spectra approve that, on the glass substrate, the a-Si: H/mu c-Si:H transition is related to the critical film thickness. Different substrate materials directly affect the surface diffusion ability of radicals, resulting in the difference of growth modes on the earlier growth stage.

基于贝叶斯网络近似推理的网络脆弱性评估方法

针对大规模计算机网络的脆弱性评估,提出了一种基于贝叶斯网络近似推理的评估方法,对网络各组件和影响网络安全的因素进行建模,采用模型检测工具生成攻击状态转移图,描述网络脆弱性的利用过程,通过采用随机采样的方法对网络的攻击状态转移图进行近似推理,经过对采样样本的统计分析得到网络脆弱性评估的量化结果,为提升网络的安全性能提供理论依据。

L_n-PIR的粘弹行为及其对分子链结构、分子量和分子量分布的依赖性

本论文应用应力应变和动态力学方法，系统地表征了L_n-PIR的粘弹行为及其对聚合物链结构、分子量和分子量分布的依赖性，建立了有关力学量与分子量和分子量之间的相互作用规律的数学模式。结果表明，聚合物的粘弹力学量可以用有效分子量的概念来描述：P=K{(M-bar)_ηexp[(M-bar)_w/(M-bar)_n-1]}~(-α) <1>不同类型的分子量的K_D值是不同的，其K_D大小顺序为：(M-bar)_n > (M-bar)_w > (M-bar)_k > (M-bar)_z。弹性物理量对分子量分布的依赖性较粘性物理量为小。分子量和分子量分布对屈服行为的影响，可以归结为分子链缠结行为的作用。L_n-PIR的屈服强度与链缠结点数(m-1)之间的关系满足如下指数方程λ_yσ_y=5.99*10~5(m-1)~(0.47)，达因·厘米~(-2) <2>聚合物的屈服活化能与解链缠结活化能等值等效，均是为使分子链开始解缠结，克服缠结间链段的分子间作用力所做的功，是链缠结分子量的函数。对L_n-PIR，ΔEy与Me之间的关系为 ΔEy=-148.0+40.0 logMe，千焦/摩尔 <3>在M-bar=Mc时，ΔEy达最大值，为其流动活化能。L_n-PIR的屈服破坏能等效于解分子链缠结能，是为使缠结点解脱，克服缠结点的单体单元之间的范德华力所做的功。ΔEd是缠结点数(m-1)的函数ΔEd.=1.38*10~4(m-1)，焦耳·摩尔~(-1) <4>单个链缠结点对ΔEd的贡献是相同的，约为0.143er，相当于相互缠结的两分子链段的链节单元之间的距离接近于范德华平衡半径re=2.84A的分子间作用力。另由于L_n-PIR聚合物本体内存在的紧密的分子链缠结结构，导致非牛顿效应，其流变行为和应力松弛行为偏离牛顿线性流动规律。L_n-PIR的本体粘度与分子量和分子量分布的关系为η_0~(100)=8.91*10~(-19) (M-bar)_η~(4.25)exp[-0.30*4.25((M-bar)_w/(M-bar)_n-1)]，达因·厘米~(-2)·秒 <5>正应力系数与分子量和分子量分布之关系为ξ_0~(100)=1.43*10~(-32) (M-bar)_η~(6.86)exp[-1.10((M-bar)_w/(M-bar)_n-1)]，达因·厘米~(-2)·秒<6>由于分子链的热运动状况不同，回复柔量对分子链结构和分子结构的依赖性是随温度而变化的。L_n-PIR在25 ℃和100 ℃时，回复柔量与分子量和分子量分布的关系为25 ℃: Je-o=0.158(M-bar)_η~(-0.75)exp[+0.298((M-bar)_w/(M-bar)_n-1)]，达因~(-1)·厘米~2 <7> 100 ℃: Je-o=1.32*10~6(M-bar)_η~(-1.81)exp[0.704((M-bar)_w/(M-bar)_n-1)]达因~(-1)·厘米~2 <8>最大松弛时间与(M-bar)_η、MWD之关系为Jm=1.19*10~(-6)(M-bar)_η~(1.72)exp[-0.282((M-bar)_w/(M-bar)_n-1)]，秒<9> Rouse松弛时间与(M-bar)_η、MWD之关系为Jr=1.79*10~(-14)(M-bar)_η~(3.46)exp[-0.567((M-bar)_w/(M-bar)_n-1)]，秒 <10>。

低温制备微晶硅薄膜生长机制的研究

采用热丝化学气相沉积技术制备了一系列处于不同生长阶段的薄膜样品,用原子力显微镜系统地研究生长在单晶硅衬底和玻璃衬底上薄膜表面形貌的演化.按照分形理论分析得到:在玻璃衬底上的硅薄膜以零扩散随机生长模式生长;而在单晶硅衬底上,薄膜早期以有限扩散生长模式生长,当膜厚超过某一临界厚度时转变为零扩散随机生长模式.岛面密度与膜厚的依赖关系表明,在临界厚度时硅衬底和玻璃衬底上的岛面密度均出现了极大值.Raman谱的测量证实,玻璃衬底上薄膜临界厚度与非晶/微晶相变之间存在密切的关系.不同的衬底材料直接影响反应基元的表面扩散能力,从而造成薄膜早期生长模式的差异.

湖北省近500年区域干湿序列重建及其比较分析

在历史旱涝记载资料可靠性检验的基础上,重建了湖北省3个区域近500年来的干湿气候变化序列,并比较分析了各区域干湿气候变化的趋势特征、准周期性及跃变现象。结果表明:在3个区域中,鄂东区1570~1770、1890~1950年两个时段偏湿,1470~1520、1790~1830年则偏干;鄂北区偏湿时期主要在1470~1530、1710~1750、1850~1910年三个时段,1470~1530、1770~1830年则偏干;鄂西南区有1550~1610、1650~1710、1830~1890、1930~1990