Temperature and junction-type dependency of Andreev reflection in MgB2

We studied the voltage and temperature dependency of the dynamic conductance of normal metal-MgB₂ junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of MgB₂ samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Δ/k_BT_c=3.3. In out-of-plane, high-pressure point-contacts we obtained almost ideal Andreev reflection characteristics showing a single small s-wave gap Δ=2.6±0.2 meV (clean limit).     

In situ neutron diffraction study (300-1273 K) of non-stoichiometric strontium ferrite SrFeOx

The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeO_x (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeO_x changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeO_x is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeO_x to be described in terms of a solid solution of the composition end members. Cubic SrFeO_x at high temperature is found to closely obey Vegard's law. The density of cubic SrFeO_x is also found to exhibit a linear relationship with composition.     

人体胆结石成分及无机元素的分析探讨

本文运用三种仪器对胆结石中无机元素含量和成分进行测定,对照标准谱图分析.四个样品的主要成分均为胆固醇,含有较多的元素依次为Ca、Na、P、K和Mg.通过所得结果对胆固醇的成因、无机元素含量变化的作用进行了讨论.     

观赏南瓜色素的提取及性质研究

对观赏南瓜色素的提取及性质进行了初步的探索,研究了光、温度、pH、氧化剂、还原剂、常用的食品添加剂对色素的影响.结果表明:观赏南瓜色素对光和热都比较稳定;适宜在pH值4-12之间使用;耐氧化性和耐还原性均较好;Vc对色素有一定的消色作用;柠檬酸三钠对色素有增色作用;色素对常用的食品添加剂有较强稳定性.     

一种在弱酸性介质中有电化学发光性能的鲁米诺衍生物

报道了一种鲁米诺的衍生物-3-(1-乙酰丙酮偶氮)苯二甲酰肼在酸性介质中的电化学发光行为,该化合物与鲁米诺类似,发生两步电化学氧化反应,但其氧化电位较鲁米诺低约0.5V,在氧化铟锡玻璃电极上具有良好的电化学发光性能,有效地避免了氧化铟锡玻璃电极本身的发光干扰.不仅在碱性介质中具有较高的电化学发光效率,而且在酸性介质中也产生较稳定的电化学发光,在1.0×10-6mol/L以上浓度,电化学发光强度与浓度有良好的线性关系.     

Laguerre expansion on the Heisenberg group and Fourier-Bessel transform on C~n Dedicated to Professor Sheng GONG on the occasion of his 75th birthday

Given a principal value convolution on the Heisenberg group Hn = Cn×R, we study the relation between its Laguerre expansion and the Fourier-Bessel expansion of its limit on Cn. We also calculate the Dirichlet kernel for the Laguerre expansion on the group Hn.     

Surface morphology for ion-beam sputtered Al layer with varying sputtering conditions

We study the growth morphology of thin macrostructure films which is known to be largely affected by the deposition conditions as thin film nucleation and formation is dependent on the kinetic energy and chemical free energy of the atoms. The ion-beam sputtering technique used for depositing thin layers is due to the advantage over other techniques, e.g. the independent control of many process parameters, such as the pressure and/or the energy of the ion-beam and the substrate temperature. Therefore, the dependence of various sputtering parameters such as: (i) sputtering pressure and/or the rate of deposition and (ii) the effect of substrate temperature on the growth has been studied by depositing a single layer of Al. The variations show some interesting dependencies on the structural parameters for the Al layer deposited which has been understood in terms of thin film growth and nucleation theory.     

关于一类具有相同非负群逆和M-P逆的非负矩阵的进一步研究

1引言设A是n阶非负方阵．设矩阵方程(1)AXA=A,(2)XAX=X,(3)(AX)~T= AX,(4)(XA)~T=XA,(5)AX=XA．A具有非负广义逆是指存在非负方阵X满足方程(1)～(4),并记为A~(?)．A具有非负群逆是指存在非负方阵X满足方程(1),(2),(5),并记为A~#．在A~(?)存在的前提下,两者相同的充分必要条件有(a)AA~(?)=A~(?)A；(b)A~(?)=p(A),其     

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Infrared (IR) spectroscopy of chemisorbed C₆₀ on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm^-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C₆₀/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules. Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C₆₀ molecules, which results in rather small values (∼2×10⁹ s^-1 for Ag and Au, and ∼1.6×10⁹ s^-1for Cu), consistent with a marked metallic character of the adsorbed molecules. Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C₆₀ deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron–phonon coupling with induced surface states. Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

An optodynamic method for the real-time determination of the depth of a laser-drilled hole

An experimental method for determining the real-time depth of laser-drilled holes is presented. The proposed method involves detecting the laser-induced optoacoustic waves generated during the interaction of the laser beam with the material. Our optodynamic study involved measuring the propagation times of these waves as they traveled through the material and analyzing their temporal behavior during the drilling process. The experimental observations revealed an exponential relationship between the propagation time of the longitudinal stress wave and the number of consecutive laser pulses. Received: 25 October 2001 / Accepted: 27 October 2001 / Published online: 20 December 2001