Chromatographic determination of metallic impurities in reversed-phase HPLC columns

A new test procedure is proposed for the characterization of packed RP columns with respect to their metal content. It is based on the peak asymmetry of 2,2'-bipyridyl, which can be directly correlated to the metal content of the stationary phase. Since an unbuffered eluent (methanol/water, 49:51 w/w) is used, the influence of the simultaneously present silanol groups on peak asymmetry is assessed via 4,4'-bipyridyl, which exhibits no chelating activity. A metal factor, MF, is introduced, which is the ratio of the peak asymmetries of 2,2'-bipyridyl and 4,4'-bipyridyl multiplied by 100. The superiority of this test compared to others is demonstrated via various commercially available columns. It is also demonstrated that columns continuously collect metal ions from the column components and the instrument hardware. Stainless steel nets and frits are the principal source of the metallic contamination. But even in totally metal-free LC systems, the stationary phase collects metal ions from the HPLC grade eluent components.     

Determination of impurities in high-purity germanium dioxide using atomic emission spectrometry

A technique for the determination of the impurity composition of soluble germanium dioxide and one containing up to 0.1% insoluble in 12 M HCl is described. The technique offers the possibility to control the content of 31 impurities simultaneously after preconcentration with detection limits of about 10⁻⁶ to 10⁻⁸ wt % and with an intralaboratory precision not exceeding 20 rel. %.     

On properties of superconducting alloys containing Kondo impurities

The phase transition temperature T _c and the specific heat discontinuity C of a superconductor containing Kondo impurities are expressed self-consistently in terms of the t-matrix for Kondo scattering, which has been calculated within the Tomonaga approximation, thereby taking care of the infrared singularities. The approximation contains the Abrikosov-Gor'kov theory and the exact result for the classical spin as limiting cases. The initial slopes of T _c and C as a function of antiferromagnetic exchange coupling have a maximum, and the zero-temperature transition concentration has a minimum, showing that the impurity undergoes a magnetic-nonmagnetic transition when the coupling is increased. This agrees with previous results for the impurity spin susceptibility. The condition for a reentrant phase boundary is discussed in connection with its implications for the specific heat jump. The results are compared quantitatively with experimental data for LaAl₂ containing Ce and Gd impurities and qualitatively with recent data for the (La _1-x Th _x )Ce system.     

Low-temperature properties of anisotropic superconductors with kondo impurities

We present a self-consistent theory of superconductors in the presence of Kondo impurities, using large-N slave-boson methods to treat the impurity dynamics. The technique is tested on the s-wave case and shown to give good results compared to other methods forT _K >T _c . We calculate low temperature thermodynamic and transport properties for various superconducting states, including isotropic s-wave and representative anisotropic model states with line and point nodes on the Fermi surface.     

Nanocrystalline silicon as the light emitting material of a field emission display device

A nanocrystalline Si-based paste was successfully tested as the light emitting material in a field emission display test device that employed a film of carbon nanofibers as the electron source. Stable emission in the 550-850?nm range was obtained at 16?V?μm(-1). This relatively low field required for intense cathodoluminescence (CL) from the PSi paste may lead to longer term reliability of both the electron emitting and the light emitting materials, and to lower power consumption. Here we describe the synthesis, characterization, and analyses of the light emitting nanostructured Si paste and the electron emitting C nanofibers used for building the device, including x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The corresponding spectra and field emission curves are also shown and discussed.     

多声源定位的关联模糊消除方法研究EI北大核心CSCD

基于到达时差(Time Difference of Arrival,TDOA)的多声源定位中,由于麦克风阵列对测量的TDOA值无法与目标声源进行关联,声源定位过程会产生关联模糊,从而影响多声源定位结果的精度。针对这一问题,提出基于阵列重构的多声源关联模糊消除方法。通过广义互相关(Generialized Cross⁃Correlation,GCC)算法估计麦克风阵列的TDOA值,再利用排序算法获得定位麦克风阵列所有可能的TDOAs序列,并基于Chan算法估计所有可能的声源。通过轮换定位麦克风阵列的参考麦克风,构造多组校验子阵列,利用真实声源与阵列麦克风的相对位置关系来滤除虚假声源。对于不同校验子阵列筛选出的所有声源位置,以出现频数最大化原则再次进行冗余校验,从而提升最终筛选真实声源的准确性。仿真及实验结果表明,该方法能够以最少数量常规麦克风有效消除多声源定位中的虚假声源。在同等麦克风数量的情况下,该方法的定位精度及定位鲁棒性高于对比方法。     

Determination of impurities in aluminum isopropoxide by inductively coupled plasma atomic emission spectrometry

A procedure has been developed for the determination of impurities in aluminum isopropoxide by inductively coupled plasma atomic emission spectrometry. The matrix effect has been compensated by adding a Bi internal standard. The detection limits of impurities are 10⁻⁷ to 10⁻⁵ wt %.     

Fano-like line shape of spontaneous emission spectrum in a weakly driven two-level atom

It has been shown that the Fano-like profile of spontaneous emission spectrum can be obtained in a weakly driven two-level atom under certain conditions. Coherent control of the spectral ‘hole’ or dark line generated in the asymmetric line shape can also be achieved by varying those conditions.     

Method of selective doping of silicon by segregating impurities

An original method for the controlled doping of silicon by segregating donor impurities is proposed. The approach is based on a rapid variation of the growth temperature during the molecular beam epitaxy between the regimes of kinetically limited segregation and maximum segregation of the dopant. By example of antimony, it is demonstrated that the proposed method can be used to obtain several-nanometer-thick selectively Sb-doped Si epilayers, in which a tenfold change in the volume concentration of the dopant is achieved on a 2–3 nm scale.     

C基薄膜电子场发射的一般特性及发射模型

介绍了几种碳基材料的场发射特性及其发射模型.金刚石表面具有较低的或负的电子亲和势,因无法实现N型掺杂,难以用作电子发射材料.类金刚石膜及非晶碳膜材料经过"激活"后在表面形成具有较大场增强因子的熔坑,在几～几十V/μm的低阈值电场下得到非本征的电子发射,纳米结构的碳和碳纳米管本身具有较大的场增强因子,是较有前途的平面阴极场发射材料.碳基材料的导电性不同,遵循的发射模型不同.     

阿哌沙班中8种已知杂质的HPLC法定量检测

建立高效液相色谱法测定阿哌沙班中的8个已知杂质。色谱柱为Waters Xbridge Shield RP18(150mm×4.6mm,5μm);以乙腈-醋酸铵溶液为流动相,柱温:40℃,流量:1.0 m L/min,检测波长280 nm。阿哌沙班中8种杂质分离较好,与主峰均能有效分离,线性范围为0.01~11μg/m L;8种杂质的平均回收率分别为98.7%,105.3%,100.7%,111.4%,97.4%,103.4%,98.9%,97.6%,RSD分别为2.8%,4.3%,3.3%,4.5%,3.1%,4.0%,2.7%,3.1%。该法简便、准确、重复性好,可为阿哌沙班质量标准的制定提供参考。     

电去离子净水设备脱除弱电解质的机理及能力

电去离子(EDI)净水设备能否从其进水中彻底除去弱电解质,是使用EDI净水设备所碰到的关键问题.文章提出了EDI净水设备脱盐能力的概念,并给出估算脱盐能力的经验公式,可用它作为衡量EDI净水设备正常工作的判据.讨论了EDI净水设备脱除弱电解质的机理和能力,及与脱除强电解质的区别,同时,还用提出的电去离子过程的反应叠加模型,通过离子交换层谱给以形象化的解释.     

The residual resistivity of very dilute iron impurities in copper,and their precipitation by oxidation

The residual resistance of high-purity copper can be greatly reduced if the metal is annealed in oxygen at a temperature just below its melting point. The effect is well known and has been used in many low-temperature investigations of the electronic properties of pure copper. We have carried out electrical and magnetic measurements which confirm that the effect is due to oxidation of residual Fe impurities in the copper, but in addition the formation of macroscopic particles of Fe₃O₄ is a necessary condition for success of the method. The macroscopic precipitation was discovered at Fe impurity levels down to 1 ppm. As a result of freezing out the contribution of Fe to the residual resistance, a minimum figure can be deduced for the resistivity contribution of free Fe impurities, and this figure is not in agreement with values deduced in earlier works. Resistance measurements were made with a superconducting galvanometer and magnetic measurements by the Faraday method.Submitted in partial fulfillment of the requirements for the D.Sc. degree of the Technion-Israel Institute of Technology.     

Field emission properties of AIN nanostructures

AIN with different morphologies, including thin film, nanowires, nanoneedles and nanochilies, depending on the controlled growth parameters, have been successfully synthesized by chemical vapor deposition technique. Field emission properties have been systematically studied. The experimental results show that all AIN nanostructures have good field emission properties. In comparison, AIN nano-chilies possess the best field emission properties with a low turn-on and threshold fields of 1.8 V/microm and 3.1 V/microm, respectively. The results suggest that the morphological modulation is an effective way to optimize field emission performance of nanostructures.     

Efficient and directed Nano-LED emission by a complete elimination of transverse-electric guided modes

A key to the success of solid-state lighting is an ultraefficient light extraction, ～90%. Recent advances in nanotechnology, particularly in creating nanorods, present an unprecedented opportunity to manipulate optical modes at nanometer scales. Here, we report an optically pumped nanorod light-emitting diode (LED) with an ultrahigh extraction efficiency of 79% at λ = 460 nm without the use of either a back reflector or thin film technology. We demonstrated experimentally three key mechanisms for achieving high efficiency: guided mode-reduction, embedded quantum wells, and ultraefficient light out-coupling by the fundamental HE(11) mode. Furthermore, we show that size reduction at nanoscale represents a new degree-of-freedom for alternating and achieving a more directed LED emission.