珍珠层基本结构单元——文石板片的研究进展

珍珠层很久以来就是生物矿化及仿生材料领域的经典研究对象之一,然而关于其基本单元——文石板片的形貌、纳米结构及形成机理仍未取得一致意见,故对其形貌、纳米结构及形成机理进行综述。目前,珍珠层的形成机理均是基于成熟板片结构间接推断出来的,因此观察珍珠层板片的整个形成过程,尤其是对不成熟板片的观察,从而探讨其形成机理是今后的研究方向。另外,穹顶状板片这一类新型文石板片的研究还处于初步阶段,尚有较大的研究空间。     

贝壳珍珠层及其仿生应用

综述了贝壳珍珠层结构及其文石晶体的结晶学取向特征，并概述了珍珠层中参与调控生物矿化的有机基质的结构和功能方面的最新研究进展。从裂纹偏转、纤维拔出、有机基质桥连及矿物桥的作用等方面对珍珠层的高韧性机制进行了讨论。同时介绍了珍珠层的微结构特征及其特殊的组装方式在仿生材料制备方面的应用。     

鲍鱼壳珍珠层无机文石片的层状微结构研究

贝壳珍珠层是软体动物壳的最内层,经过若干世纪的自然进化,贝壳珍珠层形成了优良的微结构,并使贝壳具有了相当高的强度、刚度及断裂韧性.本文利用扫描电镜(SEM)观察了鲍鱼贝壳珍珠层的主要微结构特征,发现其是由层状的无机文石片和有机胶原蛋白质组成的生物陶瓷复合材料.根据发现的贝壳珍珠层层状微结构特征,建立贝壳珍珠层三维有限元模型,并用此模型分析了珍珠层的拉伸屈服极限与无机文石片拉伸屈服极限及其厚度的关系,研究表明珍珠层的屈服极限随无机文石片屈服极限的增加和无机文石片厚度的减小而增加.     

淡水珍珠的生物矿化机理研究进展

碳酸钙广泛存在于生物矿物中, 是地球上最普遍的生物矿物之一。贝壳和珍珠的主要组成部分为碳酸钙无机相。我国淡水养殖珍珠多数品质优异, 具有良好的珍珠光泽。该种珍珠以文石晶型碳酸钙为无机相, 称为文石珍珠。近年来, 在我国淡水养殖珍珠中发现了球文石的存在, 球文石的出现是导致珍珠失去光泽、降低质量的主要原因。本文对比阐述了淡水文石珍珠和球文石珍珠的微观结构与性能, 总结了与珍珠层有关的体外模拟碳酸钙生物矿化的实验结果, 提出了珍珠层生物矿化机理未来的研究方向。     

珍珠的成分、微结构及成因研究

综述了现有珍珠中无机成分、有机质、微量元素、珍珠层仿生学等相关研究领域的进展,重点探讨了结晶多型与无机相转变、有机质作用、微环境影响等问题。珍珠微结构成因理论包括"隔室"说、矿物桥说、模板说、多模板成因说等,在研究珍珠层形成机制时应综合考虑微环境、有机质及无机成分在无机晶体成核、结晶、长大各个阶段所起的作用。     

淡水三角帆蚌贝壳珍珠质的同步辐射XRD研究

利用同步辐射XRD研究淡水三角帆蚌贝壳珍珠质的内应力和珍珠质中单个文石板片的微结构, 发现淡水三角帆蚌贝壳珍珠质中单个文石板片内存在晶内有机物, 且该晶内有机物导致珍珠质层中产生拉应力. 这一拉应力沿不同晶向呈现强烈的各向异性, 表明晶内有机物在文石板片内很可能以某一特定的方式排列. 同步辐射XRD图谱的线形分析进一步证实淡水三角帆蚌贝壳珍珠质中的晶内有机物吸附于文石板片的(002)晶面. 这些研究结果将促进珍珠质矿化及强韧化机制的研究, 为设计高性能无机-有机复合材料及培育珍珠提供科学的根据.     

贝壳珍珠层的研究现状

贝壳中的珍珠层是由占壳重95%的CaCO3晶体和占壳重仅5%的有机体构成的一种优异的天然纳米复合材料.对珍珠层的研究现状和最新进展进行了评述.重点介绍了珍珠层形成机制中的隔室说、矿物桥说、模板说和多模板二步成因假说等4种学说,及裂纹的偏转、纤维的拔出、有机质的桥连、矿物桥机制和凹凸镶嵌结构等5种增韧机理,简述了珍珠层的组成和微结构,指出了珍珠层研究中有待解决的问题.     

SC铸片微结构对烧结NdFeB结构与磁性能的影响

研究了铸片工艺SC(StripCasting)制备的合金铸片的微结构对烧结钕铁硼磁体微结构与磁性能的影响。结果表明:冷却速度过高时铸片厚度变薄,同时在急冷面产生细小的等轴晶,使烧结磁体容易出现固固烧结现象和主相晶粒的反常长大,降低了磁体的永磁性能;采用合适的冷却速度制备的铸片几乎全部由厚度3～5μm片状晶组成,且被富钕相薄层均匀隔开,采用该类铸片可以获得高永磁性能的烧结磁体,其永磁性能达到:Br=1.44T,jHc=877KA/m,(BH)max=398kJ/m3(50MGOe)。     

双壳纲三角帆蚌贝壳的三维微结构及其化学组成研究

通过场发射扫描电镜(FE-SEM)、傅里叶变换红外(FTIR)光谱、X射线粉晶衍射(XRD)对淡水三角帆蚌贝壳各壳层的微结构特征及化学组成进行较系统的对比研究。结果表明:在贝壳的垂直生长层方向,最外层的角质层可细化为外角质层与矿化区,其中在贝壳的不同区域中该角质层的厚度存在明显差异;棱柱层中的棱柱与外层的角质层及内层的珍珠层文石板片呈近垂直交接,棱柱层的厚度在贝壳的不同位置同样存在差异;首次发现珍珠层中文石板片的厚度从接近棱柱层一端至珍珠层内侧面逐渐变厚,该结论与前人的文献报道恰好相反。基于本研究的结论,推测贝壳中复合的微纳米结构与化学组成共同决定了软体动物贝壳优异的力学性能。     

贝壳珍珠层生物矿化及其对仿生材料的启示

贝壳珍珠层作为一种典型的生物矿化材料而备受关注. 本文综述了贝壳珍珠层结构及其文石晶体的结晶学取向, 概述了贝壳珍珠层成因的生物矿化机理. 同时介绍了贝壳珍珠层特殊的组装方式在仿生材料方面近年来的研究进展, 认为选择合适的有机物,使其自组装成各种超分子结构作为无机物沉积的模板, 是仿生合成的关键.     

在线工业镀层及涂层厚度分析仪

产品和金属元件表面镀层或防腐层厚度是与产品质量与性能相关的重要指标。为满足分析要求,介绍了自行研制的同位素X射线荧光分析仪的主要技术方法及具体应用。实际应用效果表明该分析仪在对工业镀层和汽车涂层厚度进行在线测量时其测量精度可达2%～4%,是一种具有快速、简便、无损等优点的新型分析方法。     

Daily oscillation of gene expression associated with nacreous layer formation

Three major organic matrix components, nacrein, MSI60 and N16 have been reported from the nacreous layer of Japanese pearl oyster, Pinctada fucata. Though several in vitro experiments have been carried out to elucidate the functions of these molecules details have not yet been clarified. In this report, we tempt to clarify the gene expression levels encoding the above three proteins between samples of 1) summer and winter seasons and 2) ocean and aquarium environments by using real-time polymerase chain reaction (PCR). It was confirmed that the biomineralization process of P. fucata is mainly influenced by the circatidal rhythm of the ocean environment. The gene expressions coding for N16 and MSI60 increased at the time of high tide, while that of nacrein increased at the time of low tide. The similar tendency observed in N16 and MSI60 showed the possibility that both components are secreted simultaneously, supporting a hypothesis that N16 forms cross-linkage with MSI60 to form the membrane. The expressions of MSI60, N16 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were remarkable in winter season, while no variation was found in the expression level of the nacrein gene in summer and winter season. The study is the first attempt regarding the seasonal and circadian rhythms observed on gene expressions incorporated into molluscan shell formation. The results will give a new insight into the relationship between molluscan physiology and the mechanism of shell formation.     

Daily oscillation of gene expression associated with nacreous layer formation

Three major organic matrix components, nacrein, MSI60 and N16 have been reported from the nacreous layer of Japanese pearl oyster, Pinctada fucata. Though several in vitro experiments have been carried out to elucidate the functions of these molecules details have not yet been clarified. In this report, we tempt to clarify the gene expression levels encoding the above three proteins between samples of 1) summer and winter seasons and 2) ocean and aquarium environments by using real-time polymerase chain reaction (PCR).It was confirmed that the biomineralization process of P. fucata is mainly influenced by the circatidal rhythm of the ocean environment. The gene expressions coding for N16 and MSI60 increased at the time of high tide, while that of nacrein increased at the time of low tide. The similar tendency observed in N16 and MSI60 showed the possibility that both components are secreted simultaneously, supporting a hypothesis that N16 forms cross-linkage with MSI60 to form the membrane. The expressions of MSI60, N16 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were remarkable in winter season, while no variation was found in the expression level of the nacrein gene in summer and winter season.The study is the first attempt regarding the seasonal and circadian rhythms observed on gene expressions incorporated into molluscan shell formation. The results will give a new insight into the relationship between molluscan physiology and the mechanism of shell formation.     

Dynamic effective thickness in laminated-glass beams and plates

In recent years, several equations have been proposed to calculate deflections and stresses in laminated-glass beams and plates under static loading using the concept of effective thickness, which consists of calculating the thickness of a monolithic element with equivalent bending properties to a laminated element. Recently, an effective thickness for the dynamic behavior of laminated-glass beams has been proposed to enable the modal parameters (natural frequencies, loss factors and mode shapes) to be determined using an equivalent monolithic model. In the present paper, the technique has been extended to the two-dimensional case of rectangular laminated-glass plates and the steps needed to estimate the modal parameters of laminated-glass elements using this methodology are presented. The dynamic effective thickness concept has been validated by experimental tests made on a laminated-glass beam and a laminated-glass plate. The results show that good accuracy is achieved in the natural frequencies and mode shapes but high scatter is encountered in the loss factors.     

Fracture of plates with variable thickness

We study the mechanics of fracture of plates with variable thickness weakened by rectilinear through cracks and propose a method for the solution of problems of the theory of elasticity for plates of this kind. We also generalize theoretical results of the investigation of crack propagation in deformable elastoplastic plates to plates with variable thickness and present solutions of new problems in the mechanics of structural arrest of propagating through cracks by local changes in the thickness of platelike structural members near the crack tip. Azerbaijan Technical University, Baku, Azerbaijan. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 3, pp. 46–54, May–June, 1996.     

TEM investigation of self-organized PbSe quantum dots as a function of spacer layer thickness and growth temperature

PbSe quantum dot/PbEuTe superlattices were grown on PbTe/BaF₂(111) using molecular beam epitaxy. The spacer thickness was varied from 32.4 to 312 nm and the growth temperature was 335 or 380°C. Three different dot stacking sequences form with either vertical, face-centered cubic like or disordered stacking sequence along the [111] growth direction. The different stacking sequence can be controlled by the thickness of the spacer layer and the growth temperature. The dots are fully strained and the shape of the dots is either triangular pyramids or dome like depending on the spacer layer thickness. An analysis of the lateral and vertical correlation of the dots as well as the size and shape of the buried dots with respect to spacer thickness and growth temperature is presented.     

Temperature fields and displacement of plates of linearly variable thickness

The problem of thermoelastic bending of plates of linearly variable thickness is solved by the method of a small parameter.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 833–839, November, 1985.     

含吸声层和阻尼层叠层板的动力学建模研究

基于基板和吸声层的一阶微分控制方程,考虑阻尼层的自重,并借助黏弹性理论和层间连续性条件将阻尼层的剪应力及偏心力矩写为基板和吸声层状态向量的形式,该研究建立了含吸声层和阻尼层叠层板的整合动力学控制方程.结合边界条件和齐次扩容精细积分方法提出了一种求解此类叠层板力学特性的半数值半解析方法.为了验证该方法的正确性,采用有限元...