催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe MgO、Co MgO和Ni MgO为催化剂 ,CH4 为碳源气 ,H2 为还原气 ,在 873、973和 10 73K制备出碳纳米管 ,通过TEM和拉曼光谱表征 ,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响 .结果表明 :不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异 .其中Fe MgO催化剂制备的碳纳米管管径粗 ,且大小不均匀 ,而Ni MgO催化剂制备的碳纳米管管径较细、较均匀 .碳纳米管的产率随着裂解温度的变化而改变 .Fe MgO催化剂制备碳纳米管的产率随制备温度的升高而提高 ,而Ni MgO催化剂制备碳纳米管的产率随制备温度的升高而降低 .Fe MgO催化剂制备碳纳米管 ,在10 73K甚至更高的制备温度才能达到其最高产率 .Co MgO催化剂制备碳纳米管的产率在 973K左右产率较高 ,而用Ni MgO催化剂制备碳纳米管 ,则在 873K甚至更低的制备温度就能达到最高产率 .反应时间与碳纳米管的产率不成正比 ,有一最佳反应时间 ,如Ni MgO催化剂的最佳反应时间为 2h .     

多重休假的带启动期Geom/G/1排队

本文研究多重休假的带启动期的Geom/G/1离散时间排队。给出稳态队长，等待时间分布的母函数及其随机分解结果，推导出忙期，假期和启动期的母函数等。     

On the Properties of Accretive-Dissipative Matrices

Let A be a complex n × n matrix, and let A = B + iC, B = B*, C = C* be its Toeplitz decomposition. Then A is said to be (strictly) accretive if B > 0 and (strictly) dissipative if C > 0. We study the properties of matrices that satisfy both these conditions, in other words, of accretive-dissipative matrices. In many respects, these matrices behave as numbers in the first quadrant of the complex plane. Some other properties are natural extensions of the corresponding properties of Hermitian positive-definite matrices.__________Translated from Matematicheskie Zametki, vol. 77, no. 6, 2005, pp. 832–843.Original Russian Text Copyright ©2005 by A. George, Kh. D. Ikramov.     

Algebraic and Geometric Properties of Matrix Solutions of Nonlinear Wave Equations

We improve the construction of exact matrix solutions for nonlinear wave equations by using unitary anti-Hermitian and anticommuting matrices. We prove the theorem that constructs the matrix functions u _n satisfying the nonlinear wave equation for a set of special potentials. In this case, the graph of complex solution u ₁ has a soliton-like form with a finite number of coils. Exponential representation of matrix solutions u _n is associated with continuous rotations that can be used for describing intrinsic rotations and state changes of elementary particles. We also prove the theorem on the decomposition of continuous rotation (described by solution u ₂) onto three simultaneous rotations about coordinate vectors. Each of the three constructed matrix solutions u ₃ is also decomposed into the triplet of elementary matrix solutions.     

On string topology of three manifolds

Let M be a closed, oriented and smooth manifold of dimension d. Let LM be the space of smooth loops in M. In [String topology, preprint math.GT/9911159] Chas and Sullivan introduced the loop product, a product of degree -d on the homology of LM. We aim at identifying the three manifolds with “nontrivial” loop product. This is an application of some existing powerful tools in three-dimensional topology such as the prime decomposition, torus decomposition, Seifert fiber space theorem, torus theorem.     

Charge density analysis of some processes involving intramolecular hydrogen transfer

The variations in topology of the electron density along the reaction paths of the keto-enol tautomerism of acetaldehyde, the pinacol rearrangement of protonated 1,2-ethanediol, and the unimolecular decomposition of methanediol, were studied as examples of hydrogen transfer between, respectively, C?O, C?C, and O?O atoms. The evolution of atomic charges, determined using two different atomic partitionings (AIM and Hirshfeld), indicates that the main electronic charge transfer in keto-enol tautomerism takes place between the migrating hydrogen and the carbon of the carbonyl group. The topology of the electron density demonstrates that a hydrogen-bridge structure is never formed along the reaction path of the pinacol rearrangement. The methanediol decomposition follows a concerted mechanism with very small variations in the atomic charges.     

人脸识别中应用小波变换的两个关键问题

由于小波分解在空域和频域上都能提供良好的局部信息,尤其是在小波分解后可以减少图像的分辨率,进而相应地减少计算复杂度,因此小波变换经常被用于图像处理和图像分析中.为探究基于人脸识别的小波变换最佳应用效果,着重讨论了小波变换应用于人脸识别的两个关键问题:小波基的选择和分解层数的确定,并通过实验分析和比较研究得出相应的答案和指导原则.     

Lie-algebraic approach for pricing moving barrier options with time-dependent parameters

In this paper we apply the Lie-algebraic technique for the valuation of moving barrier options with time-dependent parameters. The value of the underlying asset is assumed to follow the constant elasticity of variance (CEV) process. By exploiting the dynamical symmetry of the pricing partial differential equations, the new approach enables us to derive the analytical kernels of the pricing formulae straightforwardly, and thus provides an efficient way for computing the prices of the moving barrier options. The method is also able to provide tight upper and lower bounds for the exact prices of CEV barrier options with fixed barriers. In view of the CEV model being empirically considered to be a better candidate in equity option pricing than the traditional Black-Scholes model, our new approach could facilitate more efficient comparative pricing and precise risk management in equity derivatives with barriers by incorporating term-structures of interest rates, volatility and dividend into the CEV option valuation model.     

Constructing frames for finite dimensional Hilbert spaces

In this paper, we use the characterization of frames, introduced in [W. Rolli, A characterization of frames for finite dimensional Hilbert spaces, preprint], to construct frames for finite dimensional Hilbert spaces. Furthermore this approach allows for the construction of frames with prescribed properties.