The morphogenesis of feathers

Feathers are highly ordered, hierarchical branched structures that confer birds with the ability of flight. Discoveries of fossilized dinosaurs in China bearing 'feather-like' structures have prompted interest in the origin and evolution of feathers. However, there is uncertainty about whether the irregularly branched integumentary fibres on dinosaurs such as Sinornithosaurus are truly feathers, and whether an integumentary appendage with a major central shaft and notched edges is a non-avian feather or a proto-feather. Here, we use a developmental approach to analyse molecular mechanisms in feather-branching morphogenesis. We have used the replication-competent avian sarcoma retrovirus to deliver exogenous genes to regenerating flight feather follicles of chickens. We show that the antagonistic balance between noggin and bone morphogenetic protein 4 (BMP4) has a critical role in feather branching, with BMP4 promoting rachis formation and barb fusion, and noggin enhancing rachis and barb branching. Furthermore, we show that sonic hedgehog (Shh) is essential for inducing apoptosis of the marginal plate epithelia, which results in spaces between barbs. Our analyses identify the molecular pathways underlying the topological transformation of feathers from cylindrical epithelia to the hierarchical branched structures, and provide insights on the possible developmental mechanisms in the evolution of feather forms.     

Metal-insulator-semiconductor optoelectronic fibres

The combination of conductors, semiconductors and insulators with well-defined geometries and at prescribed length scales, while forming intimate interfaces, is essential in most functional electronic and optoelectronic devices. These are typically produced using a variety of elaborate wafer-based processes, which allow for small features, but are restricted to planar geometries and limited coverage area. In contrast, the technique of fibre drawing from a preformed reel or tube is simpler and yields extended lengths of highly uniform fibres with well-controlled geometries and good optical transport characteristics. So far, this technique has been restricted to particular materials and larger features. Here we report on the design, fabrication and characterization of fibres made of conducting, semiconducting and insulating materials in intimate contact and in a variety of geometries. We demonstrate that this approach can be used to construct a tunable fibre photodetector comprising an amorphous semiconductor core contacted by metallic microwires, and surrounded by a cylindrical-shell resonant optical cavity. Such a fibre is sensitive to illumination along its entire length (tens of meters), thus forming a photodetecting element of dimensionality one. We also construct a grid of such fibres that can identify the location of an illumination point. The advantage of this type of photodetector array is that it needs a number of elements of only order N, in contrast to the conventional order N2 for detector arrays made of photodetecting elements of dimensionality zero.     

液滴图片数字化引起的超疏表面接触角测量误差模拟研究

液滴在表面上的接触角是衡量表面润湿性能的一个重要指标,近年来在超疏水表面研究领域得到广泛应用。目前接触角测试主要采用座滴法在获取液滴数字图片的基础上对液滴轮廓进行直接测量或拟合得到;数字图片的离散性决定了接触角测试结果具有一定误差这一误差在液滴偏离球冠形状的情况下(例如:超疏水/油表面接触角测量)会变得较为严重。拟采用数值模拟分析方法研究由液滴数字图片决定的超疏水/油表面接触角测量误差随液滴参数和表面性能的变化规律。通过模拟发现,接触角测量误差随着接触角的增大而增大;采用大体积液滴进行测量会带来较大的接触角误差;而密度大或表面张力小的液体带来的误差较太。为实现接触角误差的控制,在采用小体积液滴的同时,可以通过悬滴法进行测试,此时误差可控制在仪器误差限范围之内。     

Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission

Conventional solid-core optical fibres require highly transparent materials. Such materials have been difficult to identify owing to the fundamental limitations associated with the propagation of light through solids, such as absorption, scattering and nonlinear effects. Hollow optical fibres offer the potential to minimize the dependence of light transmission on fibre material transparency. Here we report on the design and drawing of a hollow optical fibre lined with an interior omnidirectional dielectric mirror. Confinement of light in the hollow core is provided by the large photonic bandgaps established by the multiple alternating submicrometre-thick layers of a high-refractive-index glass and a low-refractive-index polymer. The fundamental and high-order transmission windows are determined by the layer dimensions and can be scaled from 0.75 to 10.6 micro m in wavelength. Tens of metres of hollow photonic bandgap fibres for transmission of carbon dioxide laser light at 10.6 micro m wavelength were drawn. The transmission losses are found to be less than 1.0 dB m(-1), orders of magnitude lower than those of the intrinsic fibre material, thus demonstrating that low attenuation can be achieved through structural design rather than high-transparency material selection.     

剪切流场中液滴形变模型的理论研究

从力学的角度出发,在由两个同心圆筒形成的旋转剪切流场中,分析油水乳化液中分散相液滴的受力及形变,推导出分散相液滴受力与液滴形变的相互关系。提出了剪切流场中液滴形变的三维力学模型,初步建立了拉伸率、收缩系数和剪切应力之间的关系。结果表明,如果测得液滴破裂的临界拉伸率,就很容易求得液滴破裂的临界剪切应力,从而可以应用分散相液滴的拉伸率或收缩系数来分析剪切对油水分离特性的影响。     

Biomimetic self-templating supramolecular structures

In nature, helical macromolecules such as collagen, chitin and cellulose are critical to the morphogenesis and functionality of various hierarchically structured materials. During tissue formation, these chiral macromolecules are secreted and undergo self-templating assembly, a process whereby multiple kinetic factors influence the assembly of the incoming building blocks to produce non-equilibrium structures. A single macromolecule can form diverse functional structures when self-templated under different conditions. Collagen type I, for instance, forms transparent corneal tissues from orthogonally aligned nematic fibres, distinctively coloured skin tissues from cholesteric phase fibre bundles, and mineralized tissues from hierarchically organized fibres. Nature's self-templated materials surpass the functional and structural complexity achievable by current top-down and bottom-up fabrication methods. However, self-templating has not been thoroughly explored for engineering synthetic materials. Here we demonstrate the biomimetic, self-templating assembly of chiral colloidal particles (M13 phage) into functional materials. A single-step process produces long-range-ordered, supramolecular films showing multiple levels of hierarchical organization and helical twist. Three distinct supramolecular structures are created by this approach: nematic orthogonal twists, cholesteric helical ribbons and smectic helicolidal nanofilaments. Both chiral liquid crystalline phase transitions and competing interfacial forces at the interface are found to be critical factors in determining the morphology of the templated structures during assembly. The resulting materials show distinctive optical and photonic properties, functioning as chiral reflector/filters and structural colour matrices. In addition, M13 phages with genetically incorporated bioactive peptide ligands direct both soft and hard tissue growth in a hierarchically organized manner. Our assembly approach provides insight into the complexities of hierarchical assembly in nature and could be expanded to other chiral molecules to engineer sophisticated functional helical-twisted structures.     

AN INVESTIGATION OF THE BENDING FATIGUE OF MODIFIED PPTA FIBRE

PPTA fibres have high axial tensile strength,but the transverse links at the macromolecularlevel of the fibres are low.The high orientation and crystallization of the PPTA fibres leads to alow resistance to bending fatigue.A comparative study on fatigue behaviour of PPTA fibres and modified PPTA fibres weremade by rotating fibre over a pin.The resistant properties of the PPTA fibre to the bending fa-tigue are low,but can be improved by modification.The morphological differences of the deformation processes of the PPTA fibres and modi-fied PPTA fibres as they are tensioned in a monofilament from after being knotted are shown.The properties of resistance to bending fatigue of the different PPTA fibres can be evaluatedby comparing the morphologies of the tensile broken ends of these fibres after knotting.     

SMA路面中各种纤维应用现状及发展趋势

制造SMA一般都采用纤维作为稳定剂，使用的纤维主要有木质素纤维、矿物纤维、聚合物化学纤维3大类．纤维具有加筋、分散、吸附沥青、稳定、增粘等作用，对防止SMA沥青析漏的功效较好．从施工性能、使用性能、成本等方面阐述了以上3种纤维的应用现状及发展趋势．     

液晶中间相的流变性与高性能碳素材料的制造

沥青中间相的液晶特性和流变性对沥青碳纤维、Ｃ／Ｃ复合材料等高性能材料的制造,性能和结构有重要意义,强调了在玻璃相变温度附近的粘度变化,流动取向和塑性形变对这些制造工艺的影响。     

纤维弱节的力学特征与判定

纤维弱节是造成纤维力学性能退化和纤维品质下降的主要原因。这里采用单纤维拉伸和形态轮廓观察结合的方法，对羊电纤维弱节的力学行为进行表征。提出了用纤维细节处的平均断裂应力σ^-和断裂应变ε^-，作为纤维弱节的判断的依据。并对羊电的细节断裂、弱节断裂，非弱节(正常)断裂的概率作了实到和理论计算，其结果分别为印％、奶％和印％。这征明作者采用的单纤维性能分析仪(SIFAN)法和显微图像加单纤维强力仪(OM XQ)法的实用性与有效性。     

Contact time of a bouncing drop

When a liquid drop lands on a solid surface without wetting it, it bounces with remarkable elasticity. Here we measure how long the drop remains in contact with the solid during the shock, a problem that was considered by Hertz for a bouncing ball. Our findings could help to quantify the efficiency of water-repellent surfaces (super-hydrophobic solids) and to improve water-cooling of hot solids, which is limited by the rebounding of drops as well as by temperature effects.     

Nanoscale chemical tomography of buried organic-inorganic interfaces in the chiton tooth

Biological organisms possess an unparalleled ability to control the structure and properties of mineralized tissues. They are able, for example, to guide the formation of smoothly curving single crystals or tough, lightweight, self-repairing skeletal elements. In many biominerals, an organic matrix interacts with the mineral as it forms, controls its morphology and polymorph, and is occluded during mineralization. The remarkable functional properties of the resulting composites-such as outstanding fracture toughness and wear resistance-can be attributed to buried organic-inorganic interfaces at multiple hierarchical levels. Analysing and controlling such interfaces at the nanometre length scale is critical also in emerging organic electronic and photovoltaic hybrid materials. However, elucidating the structural and chemical complexity of buried organic-inorganic interfaces presents a challenge to state-of-the-art imaging techniques. Here we show that pulsed-laser atom-probe tomography reveals three-dimensional chemical maps of organic fibres with a diameter of 5-10?nm in the surrounding nano-crystalline magnetite (Fe(3)O(4)) mineral in the tooth of a marine mollusc, the chiton Chaetopleura apiculata. Remarkably, most fibres co-localize with either sodium or magnesium. Furthermore, clustering of these cations in the fibre indicates a structural level of hierarchy previously undetected. Our results demonstrate that in the chiton tooth, individual organic fibres have different chemical compositions, and therefore probably different functional roles in controlling fibre formation and matrix-mineral interactions. Atom-probe tomography is able to detect this chemical/structural heterogeneity by virtue of its high three-dimensional spatial resolution and sensitivity across the periodic table. We anticipate that the quantitative analysis and visualization of nanometre-scale interfaces by laser-pulsed atom-probe tomography will contribute greatly to our understanding not only of biominerals (such as bone, dentine and enamel), but also of synthetic organic-inorganic composites.     

Electronic and structural transitions in dense liquid sodium

At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure. It was predicted from theory--and later confirmed by experiment--that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states--an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well.     

考虑孔隙比影响的堆石料湿化试验及湿化模型

对某堆石坝的坝壳料进行了不同密实状态下的单线法三轴湿化试验,分析了湿化变形随围压、应力水平以及初始孔隙比的变化规律。结果表明：在围压和应力水平相同条件下,随着初始孔隙比的减小,堆石料湿化轴向应变和体积应变均明显降低;初始孔隙比对湿化应力剪胀规律影响不大,采用对数形式的湿化剪胀方程可对不同初始孔隙比条件下的湿化应力剪胀关系进行统一描述。对指数形式的湿化轴向应变经验模型进行修正,构建了考虑初始孔隙比及应力状态影响的湿化轴向应变计算模型,并联立湿化剪胀方程推导了湿化体积应变的计算公式,通过对三轴湿化试验结果进行模拟验证了该公式的合理性。     

磁性纤维混合媒质等效磁导率的确定

从等效介质理论出发,推导出微波频率下磁性纤 维混合媒质磁导率的理论计算公式,在此基础上,对铁纤维混合媒质磁导率进行了计算,计 算结果与实验符合得较好.并给出了铁纤维体积填充系数为0.3时混合媒质磁导率的预估曲线 .     

Fibre type composition of single motor units during synapse elimination in neonatal rat soleus muscle

Skeletal motor neurones innervate the specialized 'types' of fibres comprising most mammalian muscles in a characteristic fashion: each motor neurone forms a 'motor unit' by innervating a set of fibres all of the same type. Because the type expression of adult muscle fibres is plastic and apparently controlled by their innervation, each motor neurone is thought to impose a common type differentiation on all the fibres in its motor unit. However, the situation in developing muscles cannot be this simple. Muscle fibres in neonates receive synaptic input from several motor neurones and achieve the adult, single innervation only after a period of 'synapse elimination. Despite this polyneuronal innervation, differentiated fibre types are present in neonatal muscles. This means either that the motor neurones polyneuronally innervate fibres in a random fashion and type expression is not determined by innervation or that the polyneuronal innervation is ordered in such a way that each fibre could receive unambiguous instructions for type differentiation. We have investigated these possibilities here by determining the fibre type composition of motor units in neonatal rat soleus muscle. We find that even during the time of polyneuronal innervation each motor neurone confines its innervation to largely one of two fibre types present in the muscle. Therefore, some mechanism during early development segregates the synapses of two groups of soleus motor neurones onto two separate populations of soleus muscle fibres.     

纸张纤维及填料的X射线取向分析

提出了利用ｘ射线衍射法的分析纸张中纤维取向的简便方法，该方法能定量计算出纸张中纤维取向的角分布函数，基于对纸张原料及纸张的Ｘ射线衍射方位角扫描谱半高宽度的测量。对几种商品纸的填料取向也作了分析，从ｘ射线方位角扫描谱的分析表明：滑石粉、高岭土和硫酸顿在纸张中都存在沿纤维方向的品轴取向，而装饰纸中ＴｉＯ２填料的晶轴取向不明显。     

Synthesis of fast myosin induced by fast ectopic innervation of rat soleus muscle is restricted to the ectopic endplate region

Skeletal muscle fibres, long multinucleated cells, arise by fusion of mononucleated myoblasts to form a myotube that matures into the adult fibre. The two major types of mature fibre, fast and slow fibres, differ physiologically in their rate of isotonic shortening. At the molecular level these type-specific physiological properties are ascribed to different isoforms of myosin, a major protein involved in shortening. Differentiation of fast and slow fibres seems to be under the control of motoneurones, and mature fibres are innervated by only one motoneurone. When rat soleus muscle (SOL, a slow muscle) is dually innervated with a fast nerve, it acquires some properties of a fast muscle, that is, low sensitivity to caffeine and high glycogen content. We report here that in dually innervated soleus muscle the foreign fast nerve induces synthesis of fast isoforms of myosin, but only in the segment of the muscle fibre that is close to the foreign endplate. The localized influence of the nerve endplates suggest that factors controlling the phenotypic expression of the muscle fibre have a short range of activity.     

西域砾岩砂砾料沥青混凝土心墙坝湿化变形数值分析

我国新疆地区广泛使用西域砾岩砂砾料作为筑坝材料,由于西域砾岩砂砾料浸水后易软化、崩解,大坝蓄水后的湿化变形分析成为工程界广泛关注的问题.联合广义塑性模型和西域砾岩砂砾料湿化模型,对某沥青混凝土心墙坝进行了湿化变形有限元分析.结果表明:广义塑性模型和西域砾岩砂砾料湿化模型能够很好地反映大坝湿化变形及应力分布规律;上游蓄水湿化使坝体向上游方向的水平位移和沉降都增大,最大水平位移由竣工时的1.5cm增至22cm左右,最大竖向沉降由竣工时的0.17%坝高增至0.53%坝高,筑坝料的湿陷使心墙的变形也增大;西域砾岩砂砾料的湿化变形明显大于花岗岩堆石料,最大竖向沉降是花岗岩堆石料的近3倍,其湿化造成坝顶上游侧出现局部拉应力区,有可能导致坝顶出现裂缝.因此,在新疆干旱地区采用西域砾岩砂砾料筑坝时考虑蓄水时的湿化影响是十分必要的.