Effect of ZnO on Cu/ZnO/Al_2O_3 catalysts for methanol synthesis

[中文文摘]用高速碰撞共沉淀法制备m(CuO) /m(ZnO) /m(Al2 O3 )比分别为 60 /3 0 /1 0和 3 0 /60 /1 0的 1 #和 2 #催化剂 ,结果表明高ZnO的 2 #催化剂活性较好 ,分散度较大。XPS测试表明 2 #催化剂表面ZnO吸附的中间体 (CHx 或CHxO)较多且表面的Cu+1浓度较高 ,从而促进CO加氢合成甲醇的活性。[英文文摘]Cu/ZnO/Al_2O_3 catalysts with ratios of 60/30/10 and 30/60/10 have been prepared by high speed collision coprecipitation method. The performance of the catalyst with the higher ZnO content shows the higher activity in methanol synthesis. The characterization results indicated that the catalyst with the higher ZnO content has higher dispersion. On the surface of the higher ZnO content catalyst, there was more Cu+1 and more intermediate (CH_x and CH_xO) adsorpted. It is beneficial for the CO hydrogenating to produce methanol

Enumerating tree-like polyphenyl isomers

NSFC [10831001]Enumeration of molecules is one of the fundamental problems in bioinformatics and plays an important role in drug discovery, experimental structure elucidation (e.g., by using NMR or mass spectrometry), molecular design and virtual library construction. We consider the enumeration of tree-like polyphenyls (C(6)nH(4n+2)). For this purpose, we de fine two generating functions T (x) and R (x) involving the numbers t(n) and r(n) of tree-like polyphenyls (TL-polyphenyls) and monosubstituted tree-like polyphenyls (MTL-polyphenyls), respectively. By characterizing the symmetry groups with respect to TL-polyphenyls and MTL-polyphenyls, we establish two functional equations for these two generating functions. This yields for the first time an efficient recursion formula for calculating the numbers t(n) and r(n). The two functional equations are also the fundamentals for analyzing their asymptotic behaviors, from which we derive the precise asymptotic values for both r(n) and t(n). The resulting asymptotic values are shown to fit well to the numerical results obtained by using our recursion formula. Finally, we give an explicit enumerating expression for TL-polyphenyls of a particular type: the linear polyphenyls

Dimer coverings on random multiple chains of planar honeycomb lattices

We study dimer coverings on random multiple chains. A multiple chain is a planar honeycomb lattice constructed by successively fusing copies of a 'straight' condensed hexagonal chain at the bottom of the previous one in two possible ways. A random multiple chain is then generated by admitting the Bernoulli distribution on the two types of fusing, which describes a zeroth-order Markov process. We determine the expectation of the number of the pure dimer coverings (perfect matchings) over the ensemble of random multiple chains by the transfer matrix approach. Our result shows that, with only two exceptions, the average of the logarithm of this expectation (i.e., the annealed entropy per dimer) is asymptotically nonzero when the fusing process goes to infinity and the length of the hexagonal chain is fixed, though it is zero when the fusing process and the length of the hexagonal chain go to infinity simultaneously. Some numerical results are provided to support our conclusion, from which we can see that the asymptotic behavior fits well to the theoretical results. We also apply the transfer matrix approach to the quenched entropy and reveal that the quenched entropy of random multiple chains has a close connection with the well-known Lyapunov exponent of random matrices. Using the theory of Lyapunov exponents we show that, for some random multiple chains, the quenched entropy per dimer is strictly smaller than the annealed one when the fusing process goes to infinity. Finally, we determine the expectation of the free energy per dimer over the ensemble of the random multiple chains in which the three types of dimers in different orientations are distinguished, and specify a series of non-random multiple chains whose free energy per dimer is asymptotically equal to this expectation.NSFC [10831001, 11061027

Design and Fabrication of Al_2O_3/SiO_2 Double-Layer Antireflection Coatings on 4H-SiC Substrate

在4H-SiC基底上设计并制备了Al2O3/SiO2紫外双层减反射膜,通过扫描电镜(SEM)和实测反射率谱来验证理论设计的正确性。利用编程计算得到Al2O3和SiO2的最优物理膜厚分别为42.0nm和96.1nm以及参考波长λ=280nm处最小反射率为0.09%。由误差分析可知,实际镀膜时保持双层膜厚度之和与理论值一致有利于降低膜系反射率。实验中应当准确控制SiO2折射率并使Al2O3折射率接近1.715。用电子束蒸发法在4H-SiC基底上淀积Al2O3/SiO2双层膜,厚度分别为42nm和96nm。SEM截面图表明淀积的薄膜和基底间具有较强的附着力。实测反射率极小值为0.33%,对应λ=276nm,与理论结果吻合较好。与传统SiO2单层膜相比,Al2O3/SiO2双层膜具有反射率小,波长选择性好等优点,从而论证了其在4H-SiC基紫外光电器件减反射膜上具有较好的应用前景。Al2O3/SiO2 double-layer UV antireflection coatings were designed and fabricated on 4H-SiC substrate,and the validity of theoretical design was further verified by scanning electron microscope (SEM) and reflection spectrum. The optimal physical thickness of Al2O3 and SiO2 is 42.0 nm and 96.1 nm respectively by programming calculation. And then the minimum reflectance of 0.09% is obtained at reference wavelength λ=280 nm. According to error analysis,keeping the sum of double-layer thickness consistent with theoretical value is helpful to reduce the reflectance. In addition,the refractive index of SiO2 should more accurate and the refractive index of Al2O3 should be controlled close to 1.715 in the experiment. Al2O3/SiO2 double-layer coatings were deposited on 4H-SiC substrate by electron beam evaporation and the physical thickness is 42 nm and 96 nm respectively. SEM images show that the deposited layers and the substrate perform good adhesion to each other. The practical minimum reflectance is 0.33% at λ=276 nm which is close to theoretical value. Compared with conventional SiO2 single layer,Al2O3/SiO2 double-layer coatings show low reflectance and better wavelength selectivity. These results make the possibility for 4H-SiC based UV optoelectronic devices with Al2O3/SiO2 films as antireflection coatings

How to Move the Discs on the Tower of Hanoi

Hanoi塔问题自提出以来已有一百多年的历史．其间，这一问题吸引了许多的研究者．正如H.A.Simon所指出的，Hanoi塔问题对于认知科学就象大肠杆菌对现代基因学那样，是一个无价的研究标本．事实上，它已成为组合数学，人工智能，计算机科学以及规划等中的递归问题的典型例子，并由此产生了各种各样成熟的算法．回顾这些结果，我们提出一个基本问题：能否对Hanoi塔问题给出一个公式解？本文就此给出了一个肯定的回答．在我们的研究中，图论将是一个有力的工具The primary version of the Tower of Hanoi problem (puzzle) was firstly invented by E.Lucas in 1883,and later was numbered by"problem 3918"(with 3 pegs).The general version was introduced by Wood,Gerety and Cull.As pointed out by H.A. Simon,the tower (of Hanoi) was to cognitive science what the bacteria,E.coli,were to modern genetics-an invaluable standard research setting.During the past 100 years or more,this puzzle has attracted more attentions of,not only the mathematicians', but also the computer scientists'. A large number of various (recursive, iterative, cyclic and loopless etc.) algorithms for solving this puzzle were established. Reviewing the previous literatures, it leads naturally to an elementary question: is it possible to find an algebraic formula (non-algorithm) for this problem? Here we show that the answer is "Yes".This work is supported by NSFC(69673042) and XMUF(Y07001)

SLOPE STABILITY ANALYSIS WITH NONLINEAR FAILURE ENVELOPES USING JANBU'S GENERALIZED PROCEDURE OF SLICES

解释了土体强度各向异性、非线性的物理本质,结合常规直剪试验、三轴试验结果,在前人工作基础上建立了边坡稳定性分析中强度各向异性、非线性的描述方法,其中特别提出了一个各向异性函数.基于Janbu普遍条分法(GPS),运用SPREADSHEET模板程序,提出了一个能将各向异性、非线性强度准则逐点等效到Mohr-Coulomb直线强度准则处理上的迭代方法,准确方便地获得了非线性强度下的边坡稳定性分析.最后的算例展示了方法的使用过程

Relationship Between the Selectivity of Ethylene Epoxidation and the Adspecies on Silver Catalysts

用 X P S、 T P d M S等方法研究乙烯环氧化银催化剂表面的吸附态和 Ag 的价态，并关联其选择性.结果表明催化剂表面吸附适量的 C O2-3 和 O H- 物种能促进 Ag 电子输出功的增加，使表面 Ag 原子带部分正电荷，从而抑制带负电荷较多的具有深度氧化和破坏氧化的 Oδ- 的生成和迁移，进而提高乙烯环氧化的选择性.XPS and TPD MS methods have been employed to study the surface adspecies and the valence state of silver on the silver catalysts for ethylene epoxidation.The results indicated that the adsorption of suitable amount of CO 2- 3 and OH - species on the surface of the catalysts brought about promoted an increase in the work function of silver particles and made them partially positively charged.This can suppress the formation and migration of O δ - with partially negative charge and responding for the deep oxidation, thus improve the selectivity for ethylene epoxidation

Enumerating DNA polyhedral links

NSFC [10831001]With the fast-growing of DNA self-assembly techniques, a large number of DNA catenanes or more specifically, DNA polyhedral links were synthesized in the past decade. As a sequel of a recent paper (J. Math. Chem. 50, p. 1693, 2012) by the present authors on the enumeration problem of polyhedral links, this paper considers the enumeration problem of DNA polyhedral links. In contrast to a general molecular link, a DNA polyhedral link has four notable features: 1. the memory of DNA chain direction; 2. the accurate DNA complementary base pairing; 3. the twist patterns of the double-helical strands; 4. the migration in branched junction. These features put forward particular requests for treating the enumeration problem of DNA polyhedral links. In addition to using the standard Plya's counting theory, we here introduce the generating function and edge direction retentivity analysis to the enumeration problem, by which we establish explicit expressions of the numbers of DNA polyhedral links for three typical models. These models have been used as strategies or are potential strategies in the synthesis of DNA polyhedral links