Quantitative and Spatially Resolved Measurement of Atomic Potassium in Combustion Using Diode Laser

A compact optical setup for quantitative and spatially resolved measurement of atomic alkali concentration in combustion is demonstrated.Tunable diode laser absorption spectroscopy and laser-induced fluorescence are combined using a single continuous wave diode laser to measure the line-integration concentration and the relative distribution simultaneously,thereby obtaining the absolute concentration distribution along the laser beam.The results indicate the good performance of this method for one-dimensional quantitative measurement.     

我国几种地带性土壤中磷素形态的研究

探明土壤磷素的存在形态,有助于揭示其在环境中的累积、迁移和转化过程及生物有效性。目前,在大尺度样带上开展土壤磷素形态空间变异规律的研究较少。本研究中,沿纬度方向采集了我国东部不同气候带分布的7种地带性林地土壤（包括寒温带的棕色针叶林土、中温带的暗棕壤、暖温带的棕壤、北亚热带的黄棕壤、中亚热带的黄壤、南亚热带的赤红壤和热带的砖红壤）,将化学浸提法与溶液磷-31核磁共振（31P NMR）波谱法相结合,分析了土壤中磷素形态以及与其他土壤性质之间的关系,以期为阐明土壤磷素形态的空间变异性及其驱动因素提供基础资料。结果表明：供试土壤中,全磷、有效磷、无机磷和有机磷的含量范围分别为179.8～825.2,2.41～15.3,92.6～351.2和14.7～474.4 mg·kg-1,其中活性、中等活性、中等稳定性和高稳定性有机磷组分的含量范围分别为1.38～30.9,8.63～213.7,3.01～32.2和1.73～199.2 mg·kg-1。根据溶液31P NMR波谱,鉴定出供试土壤中含有无机形态的磷素即正磷酸盐和焦磷酸盐,同时也鉴定出了磷酸单酯、磷酸二酯和膦酸盐等有机形态磷素的存在,其中磷酸单酯中又鉴定出了新-肌醇六磷酸、D-手性-肌醇六磷酸、RNA单核苷酸、α-磷酸甘油、肌-肌醇六磷酸、β-磷酸甘油和鲨-肌醇六磷酸,磷酸二酯中又鉴定出了DNA的存在;所有土壤中均未检测出多聚磷酸盐的存在,除棕色针叶林土和暗棕壤外的其他土壤中未检测出膦酸盐的存在,而赤红壤中未检测出DNA的存在;无机形态的磷素以正磷酸盐为主,而有机形态的磷素则以磷酸单酯为主。总体来看,无论化学浸提法还是溶液31P NMR波谱法,从寒温带的棕色针叶林土到热带的砖红壤,全磷、有效磷、无机磷、有机磷及其组分的含量均呈现下降趋势。溶液31P NMR波谱与化学浸提法鉴定的磷素形态之间存在相关关系,其中正磷酸盐与活性有机磷的关系最为密切,磷酸单酯和膦酸盐与中等活性有机磷的关系最为密切,而焦磷酸盐和磷酸二酯与中等稳定性有机磷的关系最为密切。与化学浸提法相比,溶液31P NMR波谱法能从详细的分子水平上揭示土壤磷素形态的空间变异规律。     

平面粘弹性问题的辛求解方法

将弹性力学辛对偶求解方法与Laplace变换相结合,提出了一个求解粘弹性平面问题的新方法。首先利用Laplace变换,将粘弹性平面问题转化为一个准弹性问题,在辛弹性力学的框架下,利用分离变量和辛本征展开法对其进行求解,然后由逆变换得到原问题的解。为证明方法的有效性,求解分析了矩形域平面粘弹性圣维南问题,得到了令人满意的结果。     

Duhamel项的精细积分方法在非线性微分方程数值求解中的应用

基于Duhamel项的精细积分方法,构造了几种求解非线性微分方程的数值算法。首先将非线性微分方程在形式上划分为线性部分和非线性部分,对非线性部分进行多项式近似,利用Duhamel积分矩阵,导出了非线性方程求解的一般格式。然后结合传统的数值积分技术,例如Adams线性多步法等,构造了基于精细积分方法的相应算法。本文算法利用了精细积分方法对线性部分求解高度精确的优点,大大提高了传统算法的数值精度和稳定性,尤其是对于刚性问题。本文构造的算法不需要对线性系统矩阵求逆,可以方便的考察不同的线性系统矩阵对算法性能的影响。数值算例验证了本文算法的有效性,并表明非线性系统的线性化矩阵作为线性部分是比较合理的选择。     

6H-SiC衬底上AlGaN基垂直结构紫外LED的制备

利用金属有机物化学气相沉积方法,在n型6H-SiC衬底上制备了15对Si掺杂Al_(0.19)Ga_(0.81)N/Al_(0.37)Ga_(0.63)N DBR,并采用低温AlN缓冲层有效抑制了DBR结构中裂纹的产生,得到了表面均方根粗糙度仅为0.4 nm且导电性能良好的n型DBR,其在369 nm处峰值反射率为68%,阻带宽度为10 nm。在获得导电DBR的基础上,进一步在n型6H-SiC衬底上构建了有、无DBR的垂直结构紫外LED。对比两者电致发光光谱,发现DBR结构的引入有效增强了LED紫外发光强度。     

某机载红外转塔低温像面抖动的分析与研究

针对某机载红外转塔在低温环境下会产生像面抖动的现象,分析了引起像面抖动的主要因素,通过建立模型、热力学分析和静力分析,得出在低温环境下俯仰支架变形量最大为0.34 mm,承受加速度过载下变形最大为0.46 mm。通过对俯仰支架进行调整、固化形态,使俯仰组件低温转动平滑,应力变形量在0.05 mm以内。同时对旋变布线方式及电机电刷安装位置提出了改进措施并给出了控制数据,解决了某机载红外转塔低温像面抖动问题。     

Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi_2Sr_2CuO_6 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy

By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi_2Sr_2CuO_(6+δ)(Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with T_c covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from holelike Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of ~0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states.Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.     

Detailed electronic structure of three-dimensional Fermi surface and its sensitivity to charge density wave transition in ZrTe_3 revealed by high resolution laser-based angle-resolved photoemission spectroscopy

The detailed information of the electronic structure is the key to understanding the nature of charge density wave(CDW) order and its relationship with superconducting order in the microscopic level. In this paper, we present a high resolution laser-based angle-resolved photoemission spectroscopy(ARPES) study on the three-dimensional(3 D) hole-like Fermi surface around the Brillouin zone center in a prototypical quasi-one-dimensional CDW and superconducting system ZrTe_3. Double Fermi surface sheets are clearly resolved for the 3 D hole-like Fermi surface around the zone center. The3 D Fermi surface shows a pronounced shrinking with increasing temperature. In particular, the quasiparticle scattering rate along the 3 D Fermi surface experiences an anomaly near the charge density wave transition temperature of ZrTe_3(～ 63 K). The signature of electron–phonon coupling is observed with a dispersion kink at ～ 20 me V; the strength of the electron–phonon coupling around the 3 D Fermi surface is rather weak. These results indicate that the 3 D Fermi surface is also closely connected to the charge-density-wave transition and suggest a more global impact on the entire electronic structure induced by the CDW phase transition in ZrTe_3.     

时域自适应精细算法求解对流热传导问题

应用时域自适应精细算法求解对流传热问题.通过展开技术,可更准确地描述变量随时间的变化,同时将时空耦合的初边值问题转化为一系列的空间边值问题,并采用有限元方法递推求解.自适应技术可弥补时间步长不同时可能造成的计算精度损失.并进行了数值检验.     

聚甲苯胺蓝-(多壁碳纳米管/PDDA)n杂化膜修饰电极的制备及其对NADH的催化氧化

导电聚合物修饰电极由于聚合物结构致密,限制了底物在聚合物膜中的渗透,且随着膜厚的增加其导电能力逐渐减弱.碳纳米管在导电聚合物中的掺杂明显改善了导电聚合物的导电性~([1]).但是碳纳米管的水溶性差及纳米尺寸带来的聚集效应,使得通过主体聚合制备杂化膜的过程中容易出现相分离进而影响到杂化膜的性质~([2]).