电解分离-ICP-AES测定铜-银-磷钎料中的磷

采用电解法分离铜后,电感耦合等离子体-原子发射光谱法直接测定了铜-银-磷钎料中磷的含量。实验表明,在1.0moI·L^-1硝酸电解液中可以使铜基本电离完全,对磷的测定不产生干扰。在最佳的测定条件下,该法用于铜-银-磷钎料中磷的测定,回收率在98.3%—102.4%之间,相对标准偏差2.28%。     

Study on the ground state of NiO: The LSDA (GGA)+U method

The ground-state properties of NiO have been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) and the so-called LSDA (GGA)+U (LSDA—local-spin-density approximation; GGA—generalized gradient approximation) method. The calculated result indicates that our estimation of U is in good agreement with experimental data. It is also found that none of the LSDA (GGA) methods is able to provide, at the same time, accurate electronic and structural properties of NiO. Although the GGA+U method can properly predict the electronic band gap, it overestimates the lattice constant and underestimates the bulk modulus. Then only the LSDA+U method accurately reports the electronic and structural properties of NiO. The calculated band gap and the density of states (DOS) show that the material NiO is the charge-transfer insulator, which agrees with the spectroscopy data. The comparison between the charge density of LSDA (not considering U) and that of LSDA+U (considering U) demonstrates that the trend of ionic crystal for NiO is obvious.     

一种新型Ca3Mg3Si4O14:Eu2+绿色荧光粉的制备及其性能研究

采用CaCO3,MgO,SiO2,Eu2O3原料,通过高温固相法制备了Ca3Mg3Si4O14:Eu2+荧光粉.通过XRD图谱和PL光谱图,研究了Eu的掺杂浓度与助溶剂(NH4Cl,BaF2)对Ca3Mg3Si4O14:Eu2+荧光粉结构、发光性能和热稳定的影响.XRD图谱对比结果表明,制备的Ca3Mg3Si4O14:Eu2+荧光粉XRD图与理论计算得到的图谱几乎一致.Ca3Mg3Si4O14:Eu2+荧光粉在360～450 nm有很强的激发强度,并且在440 nm激发下发射峰值波长为530 nm的发射光.随着Eu2+离子浓度的增加,发射光谱出现了红移,且在Eu2+离子浓度约为6％时发生了浓度猝灭现象.当添加NH4Cl和BaF2作为助溶剂,Ca3Mg3Si4O14:Eu2+荧光粉的发光强度有一定提高.与未添加助溶剂的Ca3Mg3Si4O14:Eu2+荧光粉的发光强度相比,添加NH4Cl助溶剂后发光强度增加了70％.此外,当温度升高至150 ℃时,Ca3Mg3Si4O14:Eu2+荧光粉和商用绿色荧光粉的发光强度分别降低了7.6％和14％,表明Ca3Mg3Si4O14:Eu2+荧光粉具有良好的热稳定性.这些发光性能均表明Ca3Mg3Si4O14:Eu2+荧光粉是是一种可应用于固态照明的有前景的绿色荧光粉.     

担载纳米硅的锂-碳复合微球作为锂二次电池负极

金属锂由于其极高的理论比容量(3860mAh·g~(-1),2061mAh·cm~(-3))和低的还原电势(相对于标准氢电极(SHE)为-3.04 V)等特点,成为了高能量密度锂电池负极材料的极佳选择之一。从上个世纪七十年代开始,科研工作者便开始了金属锂负极的研究,然而,由于金属锂与电解液反应严重,镀锂过程体积膨胀大,且在循环中易生成枝晶,以金属锂为负极的电池循环稳定性差,而且容易短路从而带来安全隐患。因此金属锂做为锂电池负极的商业化推广最终没有成功。在本工作中,我们在前期设计的锂-碳纳米管复合微球(Li-CNT)中引入了纳米硅颗粒制备了硅颗粒担载的锂-碳复合球(LiCNT-Si)。实验发现,纳米硅颗粒的加入不仅提高了锂-碳复合微球的载锂量(10%(质量百分含量)的硅添加量使得比容量从2000 mAh·g~(-1)提高到2600 mAh·g~(-1)),降低了锂的沉积/溶解过电势,有利于引导锂离子回到复合微球内部沉积,大大提高了材料的循环稳定性。同时,担载了纳米硅颗粒的锂-碳复合球也继承了锂-碳复合微球循环过程中体积膨胀小,不长枝晶的优点。而且添加的纳米硅颗粒还填充了Li-CNT微球中的孔隙,减少了电解液渗入复合微球内部腐蚀里面的金属锂,进一步提高了材料的库仑效率。以添加10%硅的锂碳复合材料作为负极,与商用磷酸铁锂正极组成全电池,在常规酯类电解液中1C (0.7 mA·cm~(-2))条件下能稳定循环900圈以上,库仑效率为96.7%,大大高于同样条件下测得的Li-CNT复合材料(90.1%)和金属锂片(79.3%)的库仑效率。因此,这种通过简单的熔融浸渍法即可制备的,具有高的比容量和长的循环稳定性的锂硅-碳复合材料具有较大的潜能成为高能量密度电池的负极材料,尤其适用于锂硫、锂氧这种正极不含锂源的电池体系。     

Effective spectral index properties for Fermi blazars

Blazars are a special subclass of active galactic nuclei with extreme observation properties. This subclass can be divided into two further subclasses of flat spectrum radio quasars(FSRQs) and BL Lacertae objects(BL Lacs) according to their emission line features. To compare the spectral properties of FSRQs and BL Lacs, the 1.4 GHz radio, optical R-band, 1 keV X-ray, and 1 GeVy-ray flux densities for 1108 Fermi blazars are calculated to discuss the properties of the six effective spectral indices of radio to optical(α_(RO)), radio to X-ray(α_(RX)), radio to y ray(α_(Ry)), optical to X-ray(α_(OX)), optical to y ray(α_(Oy)), and X-ray to y ray(α_(Xy)).The main results are as follows: For the averaged effective spectral indices, α_(OX_ α_(Oy) α_(Xy) α_(Ry) α_(RX) α_(RO) for samples of whole blazars and BL Lacs; α_(Xy)≈α_(Ry)≈α_(RX) for FSRQs and low-frequency-peaked BL Lacs(LBLs); and α_(OX)≈α_(Oy)≈α_(Xy) for high-synchrotron-frequency-peaked BL Lacs(HBLs). The distributions of the effective spectral indices involving optical emission(α_(RO), α_(OX), and α_(Oy)) for LBLs are different from those for FSRQs, but if the effective spectral index does not involve optical emission(α_(RX), α_(Ry), and α_(Xy)), the distributions for LBLs and FSRQs almost come from the same parent population. X-ray emissions from blazars include both synchrotron and inverse Compton (IC) components; the IC component for FSRQs and LBLs accounts for a larger proportion than that for HBLs; and the radiation mechanism for LBLs is similar to that for FSRQs, but the radiation mechanism for HBLs is different from that for both FSRQs and LBLs in X-ray bands. The tendency of α_(Ry) decreasing from LBLs to HBLs suggests that the synchrotron self-Compton model explains the main process for highly energetic y rays in BL Lacs.     

数值模拟高阶色散和非线性对光孤子传输的影响

光孤子传输中的高阶色散以及高次非线性效应是光纤通讯发展的重要制约因素。从光孤子在光纤中的一般传输方程出发, 在较大的入纤功率的前提下, 综合考虑了高阶色散、五次非线性和损耗因素, 得到其具体传输方程, 并据此从理论上分析了高阶色散和非线性对光孤子传输性能的影响。本文采用分步傅里叶方法, 以MATLAB为实现工具, 实现高阶色散和非线性对光孤子传输影响的模拟计算, 并深入分析了高阶色散和非线性导致的孤子脉冲频移现象。计算结果表明: 在入射功率较大的时候, 高阶色散效应不可忽略。当五次非线性γ2>0时,孤子脉冲主峰发生微小频移; 而当五次非线性γ2<0时, 孤子脉冲主峰基座产生微小频移; 当高阶色散β3>0时频率出现红移, 而当β3<0时, 频率出现蓝移。     

基于六角氮化硼二维薄膜的忆阻器

报道了一种基于多层六角氮化硼(h-BN)二维薄膜的忆阻器件.该器件不需要电预处理过程,且具有自限流的双极性阻变行为;具有较好的抗疲劳性和较长的数据保持时间.该器件在脉冲编程条件下具有模拟转变特性,即在连续的电压脉冲下器件的电阻态能被连续地调控,使得该器件能够模仿神经网络系统中的神经突触权重变化行为.综上所述,基于多层h-BN的忆阻器具有应用在非易失性存储和神经计算中的潜力.     

3D Nanostructured Polypyrrole/Sodium Alginate Conducting Hydrogel from self-assembly with High Supercapacitor Performance

Due to their possible ideal three dimensional (3D) nanostructures and excellent electrochemical properties, conducting hydrogels have attracted much attention in recent years. Herein, pyrrole monomer was directly dissolved in an aqueous solution of sodium alginate (SA), and was allowed to undergo in-situ polymerization to form polypyrrole (Ppy), resulting in formation of Ppy/SA, a conducting hydrogel, via self-assembly between the polymers. Observation by SEM indicated that the microstructure of the Ppy/SA hydrogel was a typical 3D nano-cylinder network, with the cylinders formed by entanglements of the Ppy and SA molecular chains (cylinder diameter was ～100 nm). The electrochemical measurements of cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy indicated that the Ppy/SA hydrogel possessed typical pseudocapacitance, good charging and discharging rate performance, and favorable capacitive behavior; the specific capacity reached up to 249 F/g at the current density of 0.2 A/g. We suggest it has great potential in the field of high-performance electrode materials for supercapacitors.     

A Scheme for Spin Manipulation in a Quantum Dot with Both Charge and Spin Bias

We propose a scheme for the effective polarization and manipulation of electron spin by using a quantum dot with both charge and spin bias. Using the equation of motion for Keldysh nonequilibrium Green function, we study the spin accumulation and polarization for the system. Through analytical analysis and a few numerical examples, it is demonstrated that fairly large spin accumulation and polarization can be produced due to the breakingsymmetry of the chemical potential for different electron spin in the leads. Moreover, the direction and the strength of the spin polarization can be conveniently controlled and tuned by varying the charge bias or the gate voltage.     

基于最小二乘支持向量机算法的三维荧光光谱技术在中国白酒分类中的应用

为了对白酒的鉴别分类方法进行创新研究,文章对近百种白酒的荧光光谱进行了测定,并合成其三维荧光光谱图。经对比研究和反复仿真实验发现,通过所提取的白酒三维荧光光谱的3个特定参数,可以实现对白酒种类的准确分类。分类的准确率可达87%以上。为了证明所选参数对白酒分类的有效性,把最小二乘支持向量机应用到白酒的鉴别分类中,并通过计算机模拟进行验证。同时还应用经典支持向量机、概率神经网络对所提取的相同数据进行分类和仿真,并将其仿真结果与使用最小二乘支持向量机仿真的结果进行比较。结果发现,使用最小二乘支持向量机可以取得更为准确的分类结果。