平面应力条件下闭合断续节理岩体力学特性试验研究

通过平面应力条件下闭合断续节理岩体的破坏试验,采用自行研制的高压柔性加载装置施加垂向和侧向荷载,用千分表和激光散斑照相技术量测试体位移场,用应变花量测试体平面应力场． 结果表明,激光散斑法用于测定闭合断续节理岩体的位移场效果良好,其测值比对应点千分表测值偏小１４％ 左右．据所测得的位移场和应力场,研究了裂纹尖端应力场的演变及裂纹扩展的路径,分析了试体的变形和破坏特征,测定了翼裂纹初裂角,探讨了试体的破坏机理．     

Interactions between metal ions and carbohydrates. Coordination behavior of neutral erythritol to Ca(II) and lanthanide ions

The study of the sugar-metal ion interactions remains one of the main objectives of carbohydrate coordination chemistry because the interactions between metal ions and carbohydrates are involved in many biochemical processes. This paper presents a comparison of coordination structures of erythritol with alkaline-earth-metal and lanthanide chloride and nitrate in the solid state using FT-IR and X-ray diffraction. Neutral, nondeprotonated erythritol (E) reacts with CaCl(2) to give three CaCl(2)(-)erythritol (CaE(I), CaE(II), CaE(III)) complexes, showing that three of the five general features of calcium-carbohydrate complexes deduced in the reference encounter contrary examples. Different coordination structures have been observed for calcium and lanthanide chloride and nitrates. The coordination of carbohydrates to metal ions is complicated, and erythritol, chloride ions, nitrates, water molecules, and ethanol (crystallization medium and reaction solvents) have the chance to coordinate to metal ions. IR spectral results show that different lanthanide ions, from LaCl(3) to TbCl(3), have similar coordination structures with erythritol. The results show that erythritol can act as two bidentate neutral ligands (CaE(I), CaE(II), CaE(III), CaEN, PrE, NdE) or as a three-hydroxyl donor (NdEN). The IR results are consistent with the crystal structures.     

Effects of copper and oxygen vacancies on the ferromagnetism of Mn- and Co-doped Cu2O

The ferromagnetic properties of Mn- and Co-doped Cu₂O with copper and oxygen vacancies (V_Cu and V_O) are studied by first-principles calculations. The results indicate that Mn-doped Cu₂O has an antiferromagnetic state in the near configuration, while it has a ferromagnetic state for the far configuration. On the contrary, Co-doped Cu₂O possess a ferromagnetic state regardless of the distance between the two Co atoms. The observed ferromagnetism can be attributed to the 90° ferromagnetic super-exchange mechanism. The presence of V_O can enhance the ferromagnetism, whereas V_Cudepresses it.     

一种基于荧光猝灭原理的光纤氧气传感器

用钌 (Ⅱ ) 邻菲咯啉配合物作为指示剂 ,研制成功一种基于荧光猝灭原理的光纤氧气传感器。采用锁相放大技术 ,实现了对弱荧光信号的检测。该传感器的检测下限为 5× 10 -6,检测精度为 5× 10 -7,响应时间T≤ 10s,并具有较强的抗干扰能力、较好的重复性和稳定性。     

基于最小Csiszár’s I-散度的高精度深度定位方法*

模态波束形成技术可用于水下目标定位,在深度定位方面,其定位精度(百米量级)往往不能满足实际需求;因此,高精度的深度定位方法需要被探索。传统高精度估计方法,如最小方差无畸变响应,面临着许多问题,如需要大量的快拍样本数等。最小Csiszár’s I-散度的迭代算法可以解决线性系统的求逆问题,但需满足系统的非负性条件,在图像的去模糊领域已得到广泛应用。该文将此算法和模态波束形成技术相结合,提出了一种新的高精度深度定位方法。基于SWellEx-96实验的海洋环境参数,分别用仿真和实验数据验证了该方法的以下性能：实现深度的高精度定位且抑制旁瓣能量;在小快拍数的情况下,深度定位性能良好。     

碱法纳米纤维素模板剂合成介孔TiO2及其性能

以生物可再生资源碱法纳米纤维素为模板剂,TiCl4为钛源,采用液相水解-沉淀法合成了具有介孔结构的TiO2光催化剂,采用透射电镜、X射线衍射、热重差热、低温N2物理吸附-脱附等技术对催化剂进行了表征,并以苯酚为模型物,考察了介孔TiO2的光催化活性.结果表明,所得TiO2催化剂具有良好的孔隙结构,平均孔径6.17nm、比表面积176.3m2/g、平均晶粒尺寸13.5nm.碱法纳米纤维素的加入在一定程度上提高了锐钛矿相向金红石相转变的温度.该TiO2晶粒小、孔隙较多、比表面积大、吸附性能强,因此表现出较高的光催化活性.     

Superconductivity at 27 K in Nb-1222 cuprate: NbSr2(GdCe)2Cu2Oy

Samples of NbSr₂Gd_2−xCe_xCu₂O_y have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49<x<0.51 that has TaSr₂ (NdCe)₂Cu₂O_y structure [1], the cell parameters being a=3.8669±0.0046 Å and c=28.742±0.0048 Å. Superconductivity was found by resistance measurements in the sample of NbSr₂Gd_1.5Ce_0.5Cu₂O_y: the onset transition temperature is 27.4 K, and zero resistance appears at approximately 13 K.     

常微分方程近似解的LS-SVM改进求法

提出一种基于最小二乘支持向量机(LS-SVMs)的求解常微分方程近似解的改进方法.该方法首先通过离散计算域,将常微分方程转换为有约束条件的目标优化问题,然后利用径向基(RBF)核函数可导的性质,用带有导数形式的LS-SVM模型将此优化问题转化为LS-SVM回归问题,进而进行求解.最终得到的闭式近似解具有精度高、连续可微、结构简单且形式固定的特点.该方法适用于任意阶非刚性和奇异的线性常微分方程初值问题和边值问题,以及一阶非线性常微分方程问题.仿真结果验证了该方法具有良好的有效性.     

Electrochemically fabricated nanovolcano arrays for SERS applications

Nanovolcano arrays were fabricated by electrodepositing Ni/Cu alloys into a monolayer of self‐assembled nanospheres and then electrochemically etching the deposited alloy film. The fabricated nanovolcano arrays feature highly ordered hexagonally arranged concave nanobowls decorated with triangular nanopores at their interstices. After coated with Ag, the nanovolcano arrays serve as high‐performance substrates for surface enhancement Raman spectroscopy (SERS) measurements. The experimental study shows that the structural features of the nanovolcano arrays, including concave nanobowls, nanopores, and their long‐range orders, all contribute to the observed strong SERS enhancement in a synergetic manner, which is further confirmed by the simulation results obtained using the finite‐difference time‐domain method. Copyright © 2012 John Wiley & Sons, Ltd.     

Hartree-Fock ground state of the three-dimensional electron gas

In 1962, Overhauser showed that within Hartree-Fock (HF) the electron gas is unstable to a spin-density wave state. Determining the true HF ground state has remained a challenge. Using numerical calculations for finite systems and analytic techniques, we study the unrestricted HF ground state of the three-dimensional electron gas. At high density, we find broken spin symmetry states with a nearly constant charge density. Unlike previously discussed spin wave states, the observed wave vector of the spin-density wave is smaller than 2k(F). The broken-symmetry state originates from pairing instabilities at the Fermi surface, a model for which is proposed.