退火温度对低温生长MgxZn1－xO薄膜光学性质的影响

用射频磁控溅射法在80℃衬底温度下制备出Mg_xZn_1-xO(x=0.16)薄膜，用X射线衍射(XRD)、光致发光(PL)和透射谱研究了退火温度对Mg_xZn_1-xO薄膜结构和光学性质的影响.测量结果显示，Mg_xZn_1-xO薄膜为单相六角纤锌矿结构，并且具有沿c轴的择优取向；随着退火温度的升高，(002)XRD峰强度、平均晶粒尺寸和紫外PL峰强度增大，(002)XRD峰半高宽(F 关键词： xZn_1-xO薄膜')" href="#">Mg_xZn_1-xO薄膜 射频磁控溅射 退火     

Upconversion luminescence of Tm^3＋/Yb^3＋ codoped oxyfluoride glasses

Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - （4.9 - x） AlF3（x=0, 0.5, 1.0, 1.5, 2.0） in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3＋： ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3＋ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3＋ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.     

The analysis of thermal stresses in thermopiezoelastic semi-infinite body with an edge crack

Summary  Thermopiezoelastic materials have recently attracted considerable attention because of their potential use in intelligent or smart structural systems. The governing equations of a thermopiezoelastic medium are more complex due to the intrinsic coupling effects that take place among mechanical, electrical and thermal fields. In this analysis, we deal with the problem of a crack in a semi-infinite, transversely isotropic, thermopiezoelastic material by means of potential functions and Fourier transforms under steady heat-flux loading conditions. The problem is reduced to a singular integral equation that is solved. The thermal stress intensity factor for a crack situated in a cadmium selenide material is calculated. Received 20 March 2001; accepted for publication 18 October 2001     

Theoretical STM images of alkaline-earth metal adsorbed Si(1 1 1)3 × 2 surfaces

We have performed total-energy calculations to study theoretical scanning tunneling microscopy (STM) images of the Si(1 1 1)3 × 2 surfaces induced by the adsorption of alkaline-earth metals (AEMs). Previously, in a series of works on Ba/Si(1 1 1) system, we have found that the observed Si(1 1 1)3 × 1-Ba LEED phase indeed has a 3 × 2 periodicity with a Ba coverage of 1/6 ML and the HCC substrate structure. Based on results of the Ba case, we proposed that the HCC structure is also adopted for other AEM atoms, which was confirmed by our recent work. In this paper, we mainly report the STM simulations for different AEM systems to compare with existing experimental data. We discuss the difference in the detailed STM images for different AEM adsorbates. Especially, the difference in filled-state images between Mg and other AEM atoms is attributed to the strong Mg-Si interaction.     

Au/SiO2纳米多层薄膜的制备及其性质表征

利用多靶磁控溅射技术制备了Au/SiO₂纳米颗粒分散氧化物多层复合薄膜.研究了在保持Au单层颗粒膜沉积时间一定时薄膜厚度一定、变化SiO₂的沉积时间及SiO₂的沉积时间一定而改变薄膜厚度时，多层薄膜在薄膜厚度方向的微观结构对吸收光谱的影响.研究结果表明：具有纳米层状结构的Au/SiO₂多层薄膜在560 nm波长附近有明显的表面等离子共振吸收峰，吸收峰的强度随Au颗粒的浓度增加而增强，在Au颗粒浓度相同的情况下，复合薄膜 关键词： 2纳米复合薄膜')" href="#">Au/SiO₂纳米复合薄膜 多靶磁控溅射 吸收光谱 有效介质理论     

Mesorbitolina (Cretaceous larger foraminifera) from the Yezo Group in Hokkaido,Japan and its stratigraphic and paleobiogeographic significance

In this paper, we describe an Aptian (Early Cretaceous) larger foraminiferal species Orbitolina (Mesorbitolina) parva from the limestone olistoliths in the lower part of the Yezo Group in the Yubari–Ashibetsu area, central Hokkaido and from limestone pebbles in the lowermost part of the Yezo Group in the Nakagawa area, northern Hokkaido. This is the first report of this species from the circum-North Pacific regions. Based on its occurrences, the shallow-marine carbonates, re-deposited in the lower part of the Yezo Group, are precisely assigned in age to the Late Aptian. Comparison of the lower part of the Yezo Group in central and northern Hokkaido indicates differences of the Aptian–Albian depositional history between the two areas. This study reveals that after Late Aptian, Mesogean key taxa (typical Cretaceous Tethyan biota) demised in the Northwest Pacific.     

The structure of monolayer SiO2 on Mo(1 1 2): A 2-D [Si-O-Si] network or isolated [SiO4] units?

In this letter, atomically resolved scanning tunneling microscopic (STM) images obtained from monolayer SiO₂/Mo(1 1 2) are presented. The results are consistent with a previously proposed structural model of isolated [SiO₄] units based on vibrational features observed by high-resolution electron energy loss spectroscopy (HREELS) and infrared reflection-absorption spectroscopy (IRAS), and oxygen species identified by ultra-violet photoemission spectroscopy (UPS). These results are inconsistent with a structural model that assumes a two-dimensional (2-D) [Si-O-Si] network. These data illustrate that a metal substrate, although coated with an oxide thin layer, can be directly imaged at the atomic-scale with STM.     

基于内生信息的股票发售机制比较研究

本文在内生信息成本的基础上，通过引入投资银行的信息成本函数，考察了国际上主要股票发售机制的内在机理，并用一个统一的框架比较了各种发售机制的差异及演进趋势。本研究表明，在投资银行和投资者信息成本相同的情况下，由于固定价格发售机制须用额外的折价去解决投资者之间的信息问题，因而相对于累计投标询价制是一种处于劣势的机制选择。同时指出，具有信息成本优势的机构投资者的出现和发展，是固定价格发行向询价发行过渡的一个必要条件。     

Approximate and Exact Small Signal Analysis for Single-Mode Fiber Near Zero Dispersion Wavelength with Higher Order Dispersion

This article presents the comparison of approximate and exact small-signal theories for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero dispersion wavelength for linear single-mode fiber. For the approximate theory, the generalized conversion matrix has been reported and gives the transfer function of intensity and phase from the fiber input to fiber output for a laser source including the influence of any higher-order dispersion term. In addition, expressions for the small-signal frequency response and the relative intensity noise (RIN) response of an ultrafast laser diode including noises are derived. However, it is observed that the approximation assumed for the second-order dispersion term for the approximate analysis is not valid. From the approximate theory, the exact generalized conversion matrix and exact expressions for small-signal frequency response and relative intensity noise (RIN) are obtained. We show that for the exact theory, the second-order dispersion term has no effect on intensity and frequency response even at large modulating frequencies and large propagation distances contrary to the approximate theory as reported by other authors. But we show that third-order dispersion term certainly has some minute impact on the frequency and RIN response for long distance links at high modulating frequencies.     

A posteriori error estimators for the Stokes equations

Summary We present two a posteriori error estimators for the mini-element discretization of the Stokes equations. One is based on a suitable evaluation of the residual of the finite element solution. The other one is based on the solution of suitable local Stokes problems involving the residual of the finite element solution. Both estimators are globally upper and locally lower bounds for the error of the finite element discretization. Numerical examples show their efficiency both in estimating the error and in controlling an automatic, self-adaptive mesh-refinement process. The methods presented here can easily be generalized to the Navier-Stokes equations and to other discretization schemes.This work was accomplished at the Universität Heidelberg with the support of the Deutsche Forschungsgemeinschaft