酚醛纤维增强纸基摩擦材料的性能研究

采用湿式成型工艺制备出5种不同酚醛纤维含量的纸基摩擦材料,研究了酚醛纤维含量对纸基摩擦材料各项性能的影响.通过力学试验机测试了材料剪切强度和压缩-回弹性能,利用同步热分析仪和湿式摩擦试验机测试了材料热性能及摩擦磨损性能,通过扫描电镜观察材料摩擦表面和剪切断裂面的微观形貌.结果表明:随着酚醛纤维含量的增加,材料层间剪切强度逐渐提高,而压缩率变化较小,回弹率先增大后减小;材料耐热性随酚醛纤维含量的增加而降低;随着酚醛纤维含量的增加,磨损率逐渐降低,同时摩擦系数保持稳定.     

Inequalities for Eigenvalues of the Sub-Laplacian on Strictly Pseudoconvex CR Manifolds

Mathematical Notes - The sub-Laplacian plays a key role in CR geometry. In this paper, we investigate eigenvalues of the sub-Laplacian on bounded domains of strictly pseudoconvex CR manifolds,...     

Lower order eigenvalues of a system of equations of the drifting Laplacian on the metric measure spaces

Let \(\Omega \) be a bounded domain with smooth boundary in an n-dimensional metric measure space \((\mathbb {R}^n, \langle ,\rangle , e^{-\phi }dv)\) and let \(\mathbf {u}=(u^1, \ldots , u^n)\) be a vector-valued function from \(\Omega \) to \(\mathbb {R}^n\). In this paper, we investigate the Dirichlet eigenvalue problem of a system of equations of the drifting Laplacian: \(\mathbb {L}_{\phi } \mathbf {u} + \alpha [ \nabla (\mathrm {div}\mathbf { u}) -\nabla \phi \mathrm {div} \mathbf {u}]= - \widetilde{\sigma } \mathbf {u}\), in \( \Omega \), and \(u|_{\partial \Omega }=0,\) where \(\mathbb {L}_{\phi } = \Delta - \nabla \phi \cdot \nabla \) is the drifting Laplacian and \(\alpha \) is a nonnegative constant. We establish some universal inequalities for lower order eigenvalues of this problem on the metric measure space \((\mathbb {R}^n, \langle ,\rangle , e^{-\phi }dv)\) and the Gaussian shrinking soliton \((\mathbb {R}^n, \langle ,\rangle _{\mathrm {can}}, e^{-\frac{|x|^2}{4}}dv, \frac{1}{2})\). Moreover, we give an estimate for the upper bound of the second eigenvalue of this problem in terms of its first eigenvalue on the gradient product Ricci soliton \((\Sigma \times \mathbb {R}, \langle ,\rangle , e^{-\frac{\kappa t^2}{2}}dv, \kappa )\), where \( \Sigma \) is an Einstein manifold with constant Ricci curvature \(\kappa \).     

A Novel Design of Grating Couplers for Efficient Broadband Coupling between Silicon-on-Insulator Nanophotonic Waveguides and Fibres

A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode-based simulations, showing that the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1dB bandwidth about 23 nm.     

Chaotic electron trajectories in a circular free electron laser

The motion of a relativistic electron is analyzed in the field configuration consisting of a circular wiggler magnetic field, an axial magnetic field, and the equilibrium self-electric and self-magnetic fields produced by the non-neutral electron ring. By generating Poincare surface-of-section maps, it is shown that when the equilibrium self-fields is strong enough, the electron motions become chaotic. Although the realistic circular wiggler magnetic field destroys the integrability of the electron motion as the equilibrium self-fields do, the role the latter plays to make the motions become chaotic is stronger than the former. In addition, the axial magnetic field can restrain the occurrence of the chaoticity.     

以甲苯为前驱体化学液气相沉积法制备碳/碳复合材料

以甲苯为前驱体利用化学液气相沉积法,采用碳布叠层作预制体,于950℃下沉积9h制备了密度为1.63g/cm³的碳/碳复合材料.用金相显微镜、扫描电子显微镜(SEM)和X射线粉末衍射(XRD)等手段对所得的材料进行了组织结构分析,并测定了其力学性能.实验结果表明,以甲苯为前驱体利用该方法可以制备组织结构比较均匀的碳/碳复合材料.用GC/MS气相色谱质谱联用仪对甲苯热分解产物(不挥发成分)进行了成分分析,提出了甲苯裂解制备碳/碳复合材料的初期热裂解机理和热缩聚机理.     

用于高性能锂-硫电池的氮化硼纳米片/碳纤维改性隔膜

通过静电纺丝、热亚胺化和碳化过程,将氮化硼纳米片(BNNSs)负载在碳纤维(CFs)表面,组成用于修饰商业聚丙烯(PP)隔膜的氮化硼纳米片/碳复合纤维(BNNSs/CFs)复合材料。BNNSs和CFs的协同作用为电池提供了额外的导电路径,并将可溶性多硫化锂固定在正极区域。结果表明,采用10BNNSs/CFs-PP隔膜的电池在0.05C下的初始放电容量高达1 295.7 mAh·g^-1,当电流密度增加到1C时,以10BNNSs/CFs-PP为隔膜的电池也具有良好的长期循环稳定性,在400次循环后最终容量高达568.1mAh·g^-1,每次循环容量衰减0.073%。     

热解碳化学气相沉积中的多重定态和非平衡相变的研究

讨论在热解碳化学气相沉积过程中出现的多重定态和非平衡相变这一典型的非平衡物理现象的机理和发展趋势.通过理论分析和实验结果的分析发现热解碳化学气相沉积的化学反应是一个典型的非平衡化学反应,其中在沉积过程中出现的生成碳黑的过程是一个典型的非平衡相变.在这一非平衡化学反应中,自由基的反应模型符合Schlogl模型.在这一非平衡化学反应中,有线性区和非线性区,线性区的产物是热解碳,而非线性区是碳黑.在线性区,反应速率方程是唯一的、线性的,而在非线性区,反应速率方程是多重的、非线性的. 关键词： 非平衡化学反应 非平衡相变 化学气相沉积 Schlogl模型 热解碳     

Inequalities for lower order eigenvalues of second order elliptic operators in divergence form on Riemannian manifolds

In this paper, we investigate the Dirichlet eigenvalue problems of second order elliptic operators in divergence form on bounded domains of complete Riemannian manifolds. We discuss the cases of submanifolds immersed in a Euclidean space, Riemannian manifolds admitting spherical eigenmaps, and Riemannian manifolds which admit l functions ${f_\alpha : M \longrightarrow \mathbb{R}}$ such that ${\langle \nabla f_\alpha, \nabla f_\beta \rangle = \delta_{\alpha \beta}}$ and Δf _α = 0, where ? is the gradient operator. Some inequalities for lower order eigenvalues of these problems are established. As applications of these results, we obtain some universal inequalities for lower order eigenvalues of the Dirichlet Laplacian problem. In particular, the universal inequality for eigenvalues of the Laplacian on a unit sphere is optimal.     

高温退火一步非破坏性纯化碳纳米管

针对催化化学气相法合成的碳纳米管含有金属、金属氧化物和碳杂质, 且缺陷较多进行了非破坏性纯化研究. 基于碳纳米管与碳杂质间结构、性质的微小差异, 1800 ℃使粗制的碳纳米管高温退火3 h, 为避免碳纳米管氧化, 高温退火过程在氩气气氛中完成. 运用扫描电镜、透射电镜观察碳纳米管的形貌和结构, 发现高温退火后, 碳纳米管的端帽大部分被打开. 能谱检测显示, 粗制的碳纳米管中的杂质(Al, Si, Ni, Cu 质量分数w分别为4.67%, 0.27%, 40.12%和1.34%)退火后被除去. 拉曼分析表明, 退火前后石墨D, G峰面积S_D, S_G分别从1314900降至474921, 767157降至566292, 退火不仅有效地去除了样品中的碳杂质, 而且使碳纳米管的缺陷得到一定程度的修复, 石墨化度随之大大提高. 研究提出了一种简单的、非破坏性的、便于规模化的纯化方法.