Surprising strength of silkworm silk

Commercial silkworm silk is presumed to be much weaker and less extensible than spider dragline silk, which has been hailed as a 'super-fibre'. But we show here that the mechanical properties of silkworm silks can approach those of spider dragline silk when reeled under controlled conditions. We suggest that silkworms might be able to produce threads that compare well with spider silk by changing their spinning habits, rather than by having their silk genes altered.     

纳米化学——太阳能电池发展的加速剂

论文5与论文8的研究内容分别是硅和二氧化钛纳米材料在太阳能电池领域中的应用,研究结果表明,二者均能有效提高太阳能电池的性能。     

Surprising dissimilarities in a newly formed pair of 'identical twin' stars

The mass and chemical composition of a star are the primary determinants of its basic physical properties-radius, temperature and luminosity-and how those properties evolve with time. Accordingly, two stars born at the same time, from the same natal material and with the same mass, are 'identical twins,' and as such might be expected to possess identical physical attributes. We have discovered in the Orion nebula a pair of stellar twins in a newborn binary star system. Each star in the binary has a mass of 0.41 +/- 0.01 solar masses, identical to within 2 per cent. Here we report that these twin stars have surface temperatures differing by approximately 300 K ( approximately 10 per cent) and luminosities differing by approximately 50 per cent, both at high confidence level. Preliminary results indicate that the stars' radii also differ, by 5-10 per cent. These surprising dissimilarities suggest that one of the twins may have been delayed by several hundred thousand years in its formation relative to its sibling. Such a delay could only have been detected in a very young, definitively equal-mass binary system. Our findings reveal cosmic limits on the age synchronization of young binary stars, often used as tests for the age calibrations of star-formation models.     

Friction enhances elasticity in granular solids

For years, engineers have used elastic and plastic models to describe the properties of granular solids, such as sand piles and grains in silos. However, there are theoretical and experimental results that challenge this approach. Specifically, it has been claimed that stress in granular solids propagates in a manner described by wave-like (hyperbolic) equations, rather than the elliptic equations of static elasticity. Here we report numerical simulations of the response of a two-dimensional granular slab to an external load, revealing that both approaches are valid--albeit on different length scales. For small systems that can be considered mesoscopic on the scale of the grains, a hyperbolic-like, strongly anisotropic response is expected. However, in large systems (those typically considered by engineers), the response is closer to that predicted by traditional isotropic elasticity models. Static friction, often ignored in simple models, plays a key role: it increases the elastic range and renders the response more isotropic, even beyond this range.     

137 Cs在土壤中淋溶迁移的模拟试验

~(137)Cs作为示踪元素广泛应用于土壤侵蚀及泥沙沉积研究中,其在土壤中的稳定性是决定其能否用于示踪土壤沉积与侵蚀的前提条件.但也有学者对应用~(137)Cs示踪技术的重要假设提出质疑,认为被土壤颗粒吸附的~(137)Cs易解吸成Cs+离子,随水流失或被植物吸收.本文利用双层土柱模拟淋溶装置研究了~(137)Cs和土壤粒径组成在不同雨量条件下的淋失和垂直迁移特征.结果表明,在600~3 000mm降雨量内,土壤中~(137)Cs平均质量活度为10.9Bq·kg-1,略小于试验前的11.5Bq·kg~(-1),与雨量并无显著相关性,土壤中的~(137)Cs有向下垂直迁移现象,但并不显著;土壤中~(137)Cs质量活度与土壤中的黏粒含量有很好的正相关性,决定系数R2达到0.73;有待于增加模拟雨量,作进一步研究.     

Liquid-like movements in crystalline insulin

Diffuse X-ray scattering from protein crystals provides information about molecular flexibility and packing irregularities. Here we analyse diffraction patterns from insulin crystals that show two types of scattering related to disorder: very diffuse, liquid-like diffraction, and haloes around the Bragg reflections. The haloes are due to coupled displacements of neighbouring molecules in the lattice, and the very diffuse scattering results from variations in atomic positions that are only locally correlated within each molecule. The measured intensity was digitally separated into three components: the Bragg reflections and associated haloes; the water and Compton scattering; and the scattering attributed to internal protein movements. We extend methods used to analyse disorder in membrane structures to simulate the diffuse scattering from crystalline insulin in terms of (1) the Patterson (autocorrelation) function of the ideal, ordered crystal structure, (2) the root-mean-square (r.m.s.) amplitude of the atomic movements, and (3) the mean distance over which these displacements are coupled. Movements of the atoms within the molecules, with r.m.s. amplitudes of 0.4-0.45 A, appear to be coupled over a range of approximately 6 A, as in a liquid. These locally coupled movements account for most of the disorder in the crystal. Also, the protein molecules, as a whole, jiggle in the lattice with r.m.s. amplitudes of approximately 0.25 A that appear to be significantly correlated only between nearest neighbours.     

Spreading of nanofluids on solids

Suspensions of nanometre-sized particles (nanofluids) are used in a variety of technological contexts. For example, their spreading and adhesion behaviour on solid surfaces can yield materials with desirable structural and optical properties. Similarly, the spreading behaviour of nanofluids containing surfactant micelles has implications for soil remediation, oily soil removal, lubrication and enhanced oil recovery. But the well-established concepts of spreading and adhesion of simple liquids do not apply to nanofluids. Theoretical investigations have suggested that a solid-like ordering of suspended spheres will occur in the confined three-phase contact region at the edge of the spreading fluid, becoming more disordered and fluid-like towards the bulk phase. Calculations have also suggested that the pressure arising from such colloidal ordering in the confined region will enhance the spreading behaviour of nanofluids. Here we use video microscopy to demonstrate both the two-dimensional crystal-like ordering of charged nanometre-sized polystyrene spheres in water, and the enhanced spreading dynamics of a micellar fluid, at the three-phase contact region. Our findings suggest a new mechanism for oily soil removal--detergency.     

Dislocation-driven surface dynamics on solids

Dislocations are line defects that bound plastically deformed regions in crystalline solids. Dislocations terminating on the surface of materials can strongly influence nanostructural and interfacial stability, mechanical properties, chemical reactions, transport phenomena, and other surface processes. While most theoretical and experimental studies have focused on dislocation motion in bulk solids under applied stress and step formation due to dislocations at surfaces during crystal growth, very little is known about the effects of dislocations on surface dynamics and morphological evolution. Here we investigate the near-equilibrium dynamics of surface-terminated dislocations using low-energy electron microscopy. We observe, in real time, the thermally driven nucleation and shape-preserving growth of spiral steps rotating at constant temperature-dependent angular velocities around cores of dislocations terminating on the (111) surface of TiN in the absence of applied external stress or net mass change. We attribute this phenomenon to point-defect migration from the bulk to the surface along dislocation lines. Our results demonstrate that dislocation-mediated surface roughening can occur even in the absence of deposition or evaporation, and provide fundamental insights into mechanisms controlling nanostructural stability.     

多孔有机硅固体材料的制备

研究了以聚硅氧烷、硅树脂和硅橡胶为基体制备多孔有机硅固体材料的制备原理及泡体膨胀机理,并对多孔固体材料进行结构表征和性能测试.结果表明:聚硅氧烷体系在季铵碱的催化下可发生交联及发泡反应,借助内发泡剂氢气使泡体自由膨胀,制得的多孔固体材料密度较小且无发泡剂残留;黏度为760Pa.s的羟基硅树脂体系的交联固化速率与发泡体系的分解速率匹配,能得到泡孔细密、分布均匀、低密度的海绵状多孔固体材料;向甲基乙烯基硅橡胶中加入含氢硅油和硫化剂,通过加成硫化,提高了泡体硫化速率与硫化程度,可制备高拉伸强度和高断裂伸长率的弹性体多孔固体材料.     

Observations of nonlinear oscillation phenomena in metallic solids

A great number of in situ observations proved that at normal temperature and pressure there exists a nonlinear oscillation phenomenon in the solid alloys. This kind of oscillation phenomenon exhibits fluid-like character in localized areas, fluctuating with crystal rotation, cell's moving, expansion and contraction.     

Vacancies in solids and the stability of surface morphology

Determining how thermal vacancies are created and destroyed in solids is crucial for understanding many of their physical properties, such as solid-state diffusion. Surfaces are known to be good sources and sinks for bulk vacancies, but directly determining where the exchange between the surface and the bulk occurs is difficult. Here we show that vacancy generation (and annihilation) on the (110) surface of an ordered nickel-aluminium intermetallic alloy does not occur over the entire surface, but only near atomic step edges. This has been determined by oscillating the sample's temperature and observing in real time the response of the surface structure as a function of frequency (a version of Angstr?m's method of measuring thermal conductivity) using low-energy electron microscopy. Although the surface-exchange process is slow compared with bulk diffusion, the vacancy-generation rate nevertheless controls the dynamics of the alloy surface morphology. These observations, demonstrating that surface smoothing can occur through bulk vacancy transport rather than surface diffusion, should have important implications for the stability of fabricated nanoscale structures.     

小尺寸固体变形中的表面效应

固体的表面性质不同于内部.这种差异的影响对于大尺寸固体的变形可以忽略,而对于纳米尺度的小尺寸固体则相当显著.我们综述了近年来关于小尺寸变形固体表面效应研究的若干进展,特别是表面应力导致的弹性变形的尺度相关性.