水面油污染物差分偏振光谱信号预处理算法研究

采用差分偏振光谱法在3～5μm波段对水面溢油污染物进行被动遥感时,所测差分偏振光谱是含有强大气吸收光谱信号与油污染物目标弱光谱信号的混合谱,这给油污染物光谱特征识别带来了困难。另外,受环境因素以及油膜自身张力影响,水面油膜厚度分布以及油膜表面粗糙度在测量过程中发生变化,从而使得连续测量的差分偏振光谱中油污染物光谱信息含量存在不同。利用这一特点,基于固定点迭代的快速主成分分析算法FastPCA设计了水面溢油污染物差分偏振光谱信号预处理算法。实验结果表明,该算法可以有效地将水面油污染物目标光谱特征信息从具有强大气吸收的混合差分偏振光谱信号中提取出来,通过光谱重构得到油污染物光谱特征信号,可用于进一步的定性、定量分析。     

Magnetic characterization of dual phase FeZrB soft magnetic alloy

The magnetic properties and the annealing process of Fe₇₈Zr₇B₁₅ amorphous ribbons are investigated by X-ray diffraction (XRD), differential scanning calorimetry, and vibrating sample magnetometer. The fully amorphous structure of the as-quenched ribbons is confirmed by the XRD pattern. The Curie temperature and the saturation magnetization M_s of the ribbons are 305 °C and 124.3 emu/g, respectively. Annealing at 550 °C can result in an increase in M_s with annealing time due to the increasing crystallized volume fraction of α-Fe phase. The optimized annealing process is established at 550 °C for 20-30 min with maximum M_s of 146.6 emu/g. The morphology of the ribbons annealed at 550 °C is observed by scanning electron microscopy, showing that nanocrystalline α-Fe grains are dispersed in an amorphous matrix.     

The electronic transport properties in C60 molecular devices with different contact distances

By applying non-equilibrium Green?s functions in combination with the density-functional theory, we investigate the transport behavior of molecular devices composed by metal electrode-C₆₀ molecule-metal electrode. Our results show that the electronic transport properties are affected obviously by the different contact distances between the electrodes, and the tunneling current decreases approximately exponentially at a certain bias with the increasing of contact distances. The negative differential resistance is observed and the peak-to-valley ratio can be tuned by different contact distances. The mechanisms of the contact distance effect and the negative differential resistance behavior are proposed.     

The Existence of Weak Solutions to Non-homogeneous A-Dirac Equations with Dirichlet Boundary Data

This paper is concerned with the weak solutions to a class of non-homogeneous A-Dirac equations DA(x, u, Du) + B(x, u, Du) = 0 with the Dirichlet boundary data. By means of the Poincaré inequalities of the Clifford valued function and some assumptions on operators A and B, we obtain the existence and uniqueness of solution to the scalar part of ${{\int_{\Omega}}{\overline{A(x, u, Du)}}D{\varphi}\,dx + {\int_{\Omega}}{\overline{B(x, u, Du)}}{\varphi}\,dx = 0}$ . for each ${\varphi \in W^{1,p}_0 (\Omega, C\ell_n^k)}$ .     

Ultraviolet detection of amino acids based on their on-column conjugation with cupric cation using a disposable electrophoresis microdevice

A method for fast sensitive ultraviolet detection of amino acids was developed with a disposable electrophoresis microdevice. The microdevice was conveniently constructed by fixing a fused-silica capillary with a sampling fracture to a printed circuit board. During the separation process, the on-column conjugation of amino acids with cupric cation led to the ultraviolet absorption at 232 nm that could be directly used for fast analysis of amino acids. Using 20 mM boric acid (pH 5.3) containing 5 mM cupric cation and 0.015% Tween 20 as running buffer, this method could completely separate lysine, glutamine and serine at a sampling time of 2 s at +210 V and a separation voltage of +1800 V (240 V/cm). The theoretical plate numbers were from 140,000 to 205,000 plates/m. The linear ranges were from 10 to 500 μM for lysine, 20-1000 μM for glutamine and serine. The novel protocol had been successfully used to detect amino acids in beverage samples with recovery more than 85.0%, indicating its advantages and potential analytical application in different fields.     

The dielectric and leakage current behavior of CoFe2O4-BaTiO3 composite films prepared by combining method of sol-gel and electrophoretic deposition

Composite CoFe₂O₄-BaTiO₃ films were prepared by combining method of sol-gel and electrophoretic deposition. CoFe₂O₄ thick films were prepared by electrophoretic deposition method and then BaTiO₃ precursor solution was spin-coated on these thick films to obtain dense structure. X-ray diffraction indicated that the films consisted of both spinel CoFe₂O₄ and perovskite BaTiO₃ phase. Dielectric properties and leakage current conduction of the films were studied. Leakage current characterization of the films exhibits an Ohmic conduction behavior at lower electric field and space charge limited conduction behavior at higher electric field, respectively.     

Breakdown-quenching characteristics and mechanisms for silicon photomultipliers

Some deviant breakdown-quenching characteristics of silicon photomultipliers are demonstrated and their physical mechanisms are explored. “Twice breakdown” phenomenon, “flat-topped” avalanche pulses and the determination method of the real breakdown voltage of the detector are analyzed. These characteristics are explained by the integration model in terms of avalanche threshold current based on the Haitz's equivalent circuit model. The reasoning results show that the maximum over-voltage for a normal operating silicon photomultiplier equals the product of the avalanche threshold current and the quenching resistor of the avalanche photo-diode (APD) pixel, approximately. Moreover, the model and results can be extended to other small avalanche junctions with quenching resistor.