Rigidity of closed submanifolds in a locally symmetric Riemannian manifold

Let M~n(n ≥ 4) be an oriented closed submanifold with parallel mean curvature in an(n + p)-dimensional locally symmetric Riemannian manifold N~(n+p). We prove that if the sectional curvature of N is positively pinched in [δ, 1], and the Ricci curvature of M satisfies a pinching condition, then M is either a totally umbilical submanifold, or δ = 1, and N is of constant curvature. This result generalizes the geometric rigidity theorem due to Xu and Gu[15].     

Synthetic and X-ray structural and reactivity studies of Cp*RuIV complexes containing bidentate dithiocarbonate, xanthate, carbonate, and phosphinate ligands (Cp* = eta5-C5Me5)

The reaction of [Cp*RuCl2]2 (1; Cp* = eta5-C5Me5) with tetraalkyldithiuram disulfides (R2NC(S)SS(S)CNR2, R = Me, Et), isopropylxanthic disulfide ([iPrOC(S)S]2), and bis(thiophosphoryl) disulfide ([(iPrO)2P(S)S]2) led to the isolation of dark-red crystalline solids of Cp*RuIVCl2(eta2-dithiolate) complexes [dithiolate = S2CNR2, DTCR (2a, R = Me; 2b, R = Et), S2COiPr (3), and S2P(iPrO)2 (4)]. Dichlorido substitution in 2 and 3 with DTCEt and S2COiPr anions yielded RuIV derivatives containing bis(DTC) and mixed DTC-dithiocarbonate ligands. These are the first organoruthenium complexes of such ligands. The reaction of monophosphines with 2a resulted in monochlorido substitution, whereas the analogous reaction with 3 resulted in displacement of both chlorido ligands and reduction of the metal center to RuII. Reduction at Ru was also observed in the reaction of 2a with [CpCr(CO)3]2. Of these complexes, only 2 and 3 are air-stable in the solid state for an extended period. All of the complexes have been spectrally characterized, and selected compounds are also crystallographically characterized.     

Molecular dynamics simulations of stretched gold nanowires: the relative utility of different semiempirical potentials

The mechanical elongation of a finite gold nanowire has been studied by molecular dynamics simulations using different semiempirical potentials for transition metals. These potentials have been widely used to study the mechanical properties of finite metal clusters. Combining with density functional theory calculations along several atomic-configuration trajectories predicted by different semiempirical potentials, the authors conclude that the second-moment approximation of the tight-binding scheme (TB-SMA) potential is the most suitable one to describe the energetics of finite Au clusters. They find that for the selected geometries of Au wires studied in this work, the ductile elongation of Au nanowires along the [001] direction predicted by the TB-SMA potential is largely independent of temperature in the range of 0.01-298 K. The elongation leads to the formation of monatomic chains, as has been observed experimentally. The calculated force-versus-elongation curve is remarkably consistent with available experimental results.     

Hyper-Rayleigh and hyper-Raman scatterings with intermediate and two-photon resonances

The normally weak process of hyper-Raman scattering can be greatly enhanced when the excitation is two photon resonant with an electronic transition that is both one and two photon allowed. It might be expected to be further enhanced when a one-photon allowed transition provides an intermediate state resonance in the two-photon excitation step. The theory of this triply resonant process is developed for organic nonlinear chromophores. Experimental results are obtained for one donor-acceptor substituted push-pull chromophore in which the energy of the strongly allowed lowest-lying one-photon state may be tuned by varying the solvent without substantially affecting the two-photon resonant transition. Surprisingly, bringing the one-photon allowed state into resonance does not significantly increase the hyper-Rayleigh or hyper-Raman hyperpolarizabilities. Analysis of the resonance Raman, hyper-Rayleigh, and hyper-Raman profiles suggests that the triply resonant path does not make the dominant contribution to the hyperpolarizability in this system.     

Adsorption of carbon dioxide of 1-site and 3-site models in pillared clays: a Gibbs ensemble Monte Carlo simulation

Adsorption behavior of carbon dioxide confined in pillared clays is analyzed by using constant pressure Gibbs ensemble Monte Carlo (GEMC) method. In our simulation, 1-site and 3-site models are used to represent carbon dioxide. At the 1-site model, carbon dioxide is described as a Lennard-Jones (LJ) sphere, while at the 3-site model, carbon dioxide is modeled as a three-sites linear chain represented by EPM2 potential considering the quadrapolar effect. The potential model from Yi et al. for pillared clays is used to emphasize its quasi two-dimensional structure. Comparing the calculated results from the 1-site and the 3-site models at T=228.15 and 258.15 K, we observe that the adsorption amount from the two models is the same basically. However, the local density presents a significant difference, because the shoulder in the main peak near the wall from 3-site model can reflect the orientation of carbon dioxide. Accordingly, in the systematical investigation to explore the effect of porosity and pore width on the adsorption of carbon dioxide in pillared clays, the 3-site model was only used. We observe that for a narrow pore of H=1.02 nm, each isotherm shape displays type I curve, suggesting that it is not inflected by the porosity. However, for the larger pores of H=1.70 and H=2.38 nm, the increase of the porosity alters the shape of adsorption isotherms from a simple linear relation to the first order jump, indicating that the porosity is of very important factor to affect adsorption and phase behavior of fluids confined in pillared clays. The excess adsorptions of carbon dioxide at supercritical temperatures of T=323.15 and 348.15 K are also investigated. We find that the maximum exists for each excess isotherm, and the optimal pressure corresponding to the maximum increases with the pore width. However, the porosity has no significant effect on the optimal pressure.     

Cross -sections of star bodies and dual mixed volumes

In this paper, we establish an extension of Funk's section theorem. Our result has the following corollary: If is a star body in whose central -slices have the same volume (with appropriate dimension) as the central -slices of a centered body , then the dual quermassintegrals satisfy , for any , with equality if and only if . The case that is a centered body implies Funk's section theorem.

     

磷钼酸和磷钼钒酸及其盐的氧化还原特性

本文以硫酸为支持电解质,在水-1,4-二氧六环混合溶剂中,用电化学方法研究了Keggin结构的H₃PMo₁₂O₄₀、M₃PMo₁₂O₄₀(M=NH₄,Na,K)、H₄PMo₁₁VO₄₀及M_nH_4-nPMo₁₁VO₄₀(M=Na,La,K,Eu;对于Na和La,n=1～4,对于K,n=4;对于Eu,n=2)的氧化还原特性。还分析了钼和钒的氧化还原顺序及其可逆性。     

聚苯胺修饰电极酸碱示波电位滴定法——Ⅰ.水溶液中的酸碱滴定

示波电位滴定具有终点直观、仪器便宜、操作简便、快速、准确等特点。本文将对氢离子响应敏锐、使用寿命长、制备简单的聚苯胺修饰电极(PAME)^[4,5]应用于酸碱示波电位滴定中,使电位突跃更加明显,化学计量点更易判断(与双铂电极体系比较),可滴定多元弱酸、弱碱、混合酸和混合碱.与pH玻璃电极比较,具有阻抗低,响应灵敏、迅速,终点电位突跃大,不易损坏,不需预处理,制备简单等特点.     

轻稀土金属β-二酮络合物催化丙烯二聚的研究

本文对以轻稀土金属β-二酮络合物为基础的催化丙烯二聚体系进行了探索性研究。找出了Pr(acac)₃。H₂O/Et₃Al₂Cl₃/PPh₃体系,在Al/Pr为30—50、P/Pr为3—6、温度为60—80℃范围内有较高二聚活性1200—1300molC₃^-/mol Pr·h和二聚转化率50—60%。在RE(ac-ac)₃/Et₃Al₂Cl₃/PPh₃和Pr(β-二酮)₃/Et₃Al₂Cl₃/PPh₃体系中,活性顺序分别为Ce～Pr>La>Nd>Sm和六氟乙酰丙酮>乙酰丙酮>二苯二甲酰甲烷,其二聚物的组成分布为:甲基戊烯64～66%,线性烯烃24.1—26.4%。二聚选择性在77—93.3%之间。     

含ER流体板结构的振动特性研究

本文制作了含电流变体夹层梁和模拟飞机蒙皮结构的含电流变体加筋层合板,采用响应幅频法,测试了在不同电场强度梁和层合加筋板结构各阶固有频率和振幅的变化;并着重测试了加筋层合板结构在改变板材料、电流变体作用面积等条件时各阶频响特性的变化。实验结果表明,随着电场强度的增加,夹层梁的频响特性有很大变化;而层合板的固有频率变化不大,但振幅却有显著变化,其中铝－层合加筋板的频响幅值的变化率达到５０．１％。