自由涡尾迹方法中涡核尺寸对风力机气动计算的影响

涡核模型中的涡核尺寸对自由涡尾迹(free vortex wake, FVW)方法准确预估风力机气动特性至关重要,涡核尺寸包括初始涡核半径和由于耗散效应涡核半径在尾迹中的增长. FVW方法中涡线控制方程离散采用三步三阶预估校正格式,涡核模型采用经典Lamb-Oseen模型,并考虑了涡耗散效应和拉伸效应.首先,通过气动载荷和叶尖涡涡量平均值的分析得到初始涡核半径的取值范围;然后,根据叶尖涡耗散特性的分析,确定体现涡黏性耗散效应涡核半径增长的经验常数的取值;最后,分析了涡核尺寸对叶尖涡结构的影响,进一步验证初始涡核半径和涡黏性耗散经验常数的取值对风力机气动计算的影响.结果表明:当初始涡核半径大于50%弦长时,FVW方法收敛稳定且能准确预估风轮气动载荷;综合风轮气动载荷和叶尖涡耗散特性,初始涡核半径取60%到70%弦长为宜,且对应的涡黏性耗散经验常数取值也不同;风轮气动载荷和叶尖涡结构的准确预估主要受初始涡核半径影响,经验常数对其影响不大,而经验常数主要影响风轮下游尾流场叶尖涡的耗散特性.     

天然和培育金刚石品质表征与呈色分析

金刚石是集最高硬度、超宽禁带、最高热导率等优异性能于一体的典型超硬多功能材料,天然金刚石储量低且价格昂贵,其中彩色天然金刚石在自然界中产储量极其稀少且致色机制较为复杂。高温高压法是制备金刚石的有效手段,然而调控金刚石颜色获得可控的彩色金刚石,仍面临极大挑战。本文通过对粉色、绿色天然和高温高压温度梯度法制备的金刚石进行一系列拉曼、荧光、红外和可见光吸收测试,详细地研究其品质、缺陷随温度变化及致色原因,发现彩色金刚石致色与电中性的N₂V缺陷(H₃)、剪切应力、塑性形变和NV⁰/NV^-色心等因素相关。通过各种手段获得不同颜色的金刚石不仅是为了其欣赏及收藏价值,其颜色的调控也有助于人们对金刚石形成机制的进一步了解,为培育彩色金刚石提供新的参考。     

酞菁晶体结构与荧光性质的压力调控

酞菁是一种重要的有机光电材料,关于其晶体结构和光电性质间的内在关联尚存争议.本文利用高压原位拉曼散射光谱及荧光光谱技术对酞菁晶体在高压下的结构转变和光学性质进行了研究.当压力达到12.0 GPa时,酞菁分子本身仍保持稳定,没有发生开环反应.酞菁晶体结构在压力作用下由α相逐渐转变为χ相,这一转变在卸压后恢复到初始α相.酞菁的高压荧光光谱研究表明,荧光强度随压力增高而衰减,至3.0 GPa时消失.高压下酞菁分子间所形成的激基缔合物荧光受抑制,而常压下α相酞菁中观察不到的酞菁分子荧光在高压下出现,这可能与酞菁晶体中呈平行排列的分子之间在压力下重叠程度减小有关.     

First-Principles Studies on Properties of Boron-Related Impurities in c-BN

We investigate, by first-principles calculations, the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities （VB, Cs, NB, and OB） with different charged states in cubic boron nitride （c-BN） using a supercell approach. It is found that the nitrogen atoms surrounding the defect relax inward in the case of CB, while the nitrogen atoms relax outward in the other cases. These boron-related impurities become much more stable and have larger concentration with increasing pressure. The impurity CB^＋1 is found to have the lowest formation enthalpy, make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities. Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.     

一种新型三维配位聚合物的合成以及表征和磁性测定(英文)

通过水热法合成了三维(3D)网状金属有机框架物[Pr(NTA)(H2O)]n(NTA=nitrilotriacetic acid);利用元素分析、红外光谱分析、X射线单晶衍射等表征了产物的结构,利用热重分析和示差热重分析评价了其热稳定性,并测定了其磁性能.结果表明,目标配合物的Pr(Ⅲ)采取九配位模式(N1O8)形成三帽三角棱柱几何构型,配位聚合物通过O-C-O链组装成高度有序的3D结构.此外,合成的配合物具有较高的热稳定性,并因(O2C-C-C-CO2)2桥联而显示反铁磁性.     

高压导致纳米TiO2形变的电子显微研究

α-PbO₂相TiO₂高压相具有适宜的带隙能和可见光范围的光催化能力,是一种适用于可见光、高效且环保的光催化材料.本文使用金刚石对顶压砧对锐钛矿纳米球进行加压-卸压处理得到了α-PbO₂相TiO₂高压相.利用透射电子显微镜对比初始样品和卸压样品,观察结果表明晶粒发生了明显形变,高分辨图显示其晶粒中存在大量[100]方向层错和形变孪晶,其中亚微米级晶粒中形成了透镜形片层结构的形变孪晶带;纳米级晶粒中形成了扇形多重形变孪晶.研究表明高压下锐钛矿TiO₂可以发生明显的形变,其形变的微观机制与金属类似,主要为形变孪晶和层错滑移,形变孪晶的形成存在明显的尺寸效应.这些结果为TiO₂高压相变的尺寸效应研究提供了一个新的切入点,同时还为制备孪晶α-PbO₂相TiO₂高压相提供了方法.     

Controllable preparation and disorder-dependent photoluminescence of morphologically different C60 microcrystals

Different C₆₀ crystals were synthesized by precipitation from a mixture of the good solvent m-xylene and the poor solvent isopropyl alcohol. The samples were characterized by scanning electron microscopy (SEM), Raman spectroscopy, thermogravimetric analysis, and high resolution transmission electron microscope (HRTEM). We found that the morphologies and sizes of the samples could be controlled by adjusting the volume ratio between the good and poor solvents. Especially, an unexpected short flower column-like crystal was synthesized at low ratios (from 1:6 to 1:12). Room temperature photoluminescence (PL) and HRTEM studies of the C₆₀ crystal samples reveal that the PL efficiency of the crystals decreases with increasing crystalline order and that the disordered C₆₀ crystals synthesized at the ratio of 1:2 show 10 times higher PL efficiency than that of pristine C₆₀. The mechanism of the growth process of these C₆₀ crystals was also studied by replacing the good solvents m-xylene with toluene and mesitylene.     

Structural stability and electrical properties of AlB2-type MnB2 under high pressure

The structural stability and electrical properties of AlB2-type MnB2 were studied based on high pressure angledispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell(DAC) and first-principles calculations under high pressure. The x-ray diffraction results show that the structure of AlB2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9±3.7 GPa with a fixed pressure derivative of 4, which indicates that AlB2-type MnB2 is a hard and incompressible material. The electrical resistance undergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure.     

纤锌矿氮化硼及其应用的研究（Ⅱ）——纤锌矿型氮化硼的等温状态方程

 使用两种不同的高压在位X光衍射法，研究了用爆炸法合成的纤锌矿型氮化硼（wBN）在室温下的等温状态方程。一种方法是用转靶X光角色散粉末衍射法，研究了它在0~40 GPa压力范围内的等温压缩行为。结果表明，wBN在0~40 GPa的压力范围内是稳定的，没有发生结构相变。通过p-V数据对Murnaghan方程拟合，得到wBN在p=0时的等温体模量B₀=(335±34) GPa及其对压力的一阶导数B₀'=4.21；另一种是用同步辐射X光能量色散衍射法，研究了它在0~25 GPa压力范围内的等温状态方程。实验中，使用了改进的自动加压的DAC高压装置，此装置保证了实验中衍射角θ₀固定不变。将获得的p-V数据仍用Murnaghan方程拟合，得到wBN在p=0时等温体模量B₀=(280±56) GPa，及其B₀'=4.39。     

聚丙烯酸的单分子应力-应变行为

利用原子力显微镜的一种新方法 单分子力谱技术 研究了聚丙烯酸单链的弹性性质，得到了聚丙烯酸链的拉力与拉伸曲线．其拉力与拉伸曲线可以通过修改的Ｌａｎｇｅｖｉｎ方程进行较好地拟合．结果表明聚丙烯酸链的弹性性质与长度线性成比例，聚丙烯酸链具有相同的Ｋｕｈｎ长度（０６４±００５ｎｍ）和链段弹性系数（１３０００±２０００ｐＮ／ｎｍ），充分表明我们位伸的是聚丙烯酸的单链，所测得的拉力 拉伸行为是聚丙烯酸单链的弹性行为