回收LNG冷能的新型碳二烃两级膨胀朗肯循环

提出了一种新型的回收LNG冷能的两级膨胀朗肯动力循环,可以乙烯或乙烷作为工质。此工艺流程采用多股流低温板翅式换热器(MSCHE)作为主要设备,使工质两级膨胀并采用回热过程,可以使循环的冷能利用效率得到明显提高。针对此工艺分别以乙烯或乙烷为工质,与LNG直接膨胀结合和不结合,共四种方案采用HYSYS软件进行工艺模拟,并对模拟结果进行了比较和分析,可得出无LNG膨胀的乙烯两级膨胀工艺流程最为合理,其冷能和火用的利用率可以分别达到19.67%和21.75%。     

Impacts of air pressure on the evolution of nanosecond pulse discharge products

Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge (NPD) plasma under different air pressures are calculated. The results show that the air pressure has significant impacts on the NPD products and the peak values of particle number density for particles such as O atoms, O3 molecules, N2(A3) molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N2(B3) and N2(C3) molecules in excited states are only slightly affected by the air pressure.     

Role of chelating agent in chemical and fluorescent properties of SnO2 nanoparticles

A modified polyacrylamide gel route is applied to synthesize SnO2 nanoparticles. High-quality SnO2 nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λex = 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.     

785nm便携式光栅外腔可调谐半导体激光器的研制和输出特性

针对移频激发拉曼光谱测试系统的小型化需求,在Littrow结构中,采用商用的785nm大功率激光二极管作为增益器件,构建了一款便携式光栅外腔可调谐半导体激光器。该激光器通过采用一种新型的波长调谐方法,即以改变半导体增益器件相对于准直透镜的水平位置来实现波长的连续调谐,实现了尺寸为140mm×65mm×50mm的小型化结构设计。相比于传统的旋转衍射光栅改变光线在光栅上的入射角来实现波长调谐的方式,该方法有效地缩减了增益器件的平移距离,从而有利于便携式外腔激光器波长的快速宽带调谐。实验结果表明,该激光器具有较宽的波长调谐范围,在340~900mA注入电流下均可实现10nm以上的波长调谐,尤其在900mA大注入电流下,其波长调谐覆盖779.40~791.07nm,调谐范围可达11.67nm,且激射线宽小于0.2nm,单波长输出功率最高可达280mW,放大的自发辐射抑制比大于25dB,呈现出较优异的输出性能,满足移频激发拉曼光谱检测系统对光源的基本要求。此外,该激光器可采用一微型压电陶瓷驱动器来实现波长的电动调谐,实验获得了1.35nm的波长调谐范围,证实了所制785nm便携式光栅外腔可调谐半导体激光器适合作为便携式移频激发拉曼光谱检测系统的光源用于减除原始拉曼光谱中的荧光背景。     

Productions of X(1835) as baryonium with sizable gluon content

X(1835) has been treated as a baryonium with sizable gluon content, and to be almost flavor singlet. This picture allows us to rationally understand X(1835) production in J/ψ radiative decays, and its large couplings with pˉ, η^′ππ. The processes ϒ(1S) → γX(1835) and J/ψ → ωX(1835) have been examined. It has been found that Br(ϒ(1S) → γX(1835))Br(X(1835) → pˉ) < 6.45×10^-7, which is compatible with CLEO's recent experimental result (Phys. Rev. D 73, 032001 (2006) hep-ex/0510015). The branching fractions Br(J/ψ → ωX(1835)), Br(J/ψ → ρX(1835)) with X(1835) → pˉ and X(1835) → η^′π⁺π^- have been estimated by the quark-pair creation model. We show that they are heavily suppressed, so the signal of X(1835) is very difficult, if not impossible, to be observed in these processes. The experimental checks for these estimations are expected. The existence of the baryonium nonet is conjectured, and a model-independent derivation of their production branching fractions is presented.     

Characterization of ceramic PVD thin films on AZ31 magnesium alloys

Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO₂ and Al₂O₃ as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiO_x film as well as the AlO_x film. In the electrochemical corrosion test, the AlO_x coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiO_x coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate.     

Spin-transfer switching in MgO magnetic tunnel junction nanostructures

Spin-transfer driven switching was observed in MgO based magnetic tunnelling junctions (MTJ) with tunnelling magnetoresistance ratio of up to 160% and the average intrinsic switching current density (J_c0) down to 2 MA/cm², which are the best known results reported in spin-transfer switched MTJ nanostructures. Based on a comparison of results both from MgO and AlO_x MTJs, further switching current decrease via MgO dual structures with two pinned layers is discussed.     

Electron attenuation lengths in fullerene and fullerides

Using X-ray photoemission measurements, we have determined the attenuation length of C 1s photoelectrons in C₆₀ film to be 21.5 Å with the incident photon energy of Mg Kα radiation. The inelastic mean free path calculated with the TPP-2M algorithm coincides fairly well with the experimentally determined attenuation length, indicating the validity of the algorithm to fullerene and fullerides. The inelastic mean free paths for some fullerides, i.e. K₃C₆₀, K₆C₆₀, Ba₄C₆₀, Sm_2.75C₆₀ and Sm₆C₆₀ are calculated to help the quantitative analyses of the photoemission spectra for these compounds.     

Synthesis, structure and optical properties of Eu/TiO2 nanocrystals at room temperature

The nanocrystal samples of titanium dioxide doped with europium ion (Eu³⁺/TiO₂ nanocrystal) are synthesized by the sol-gel method with hydrothermal treatment. The Eu³⁺ contents (molar ratio) in the samples are 0, 0.5%, 1%, 2%, 3% and 4%. The X-ray diffraction, UV-Vis spectroscopy data and scanning electron microscope image show that crystallite size is reduced by the doping of Eu³⁺ into TiO₂. Comparing the Raman spectra of TiO₂ with Eu³⁺/TiO₂ (molar ratio Eu³⁺/TiO₂=1%, 2% and 4%) nanocrystals at different annealing temperatures indicates that the anatase-to-rutile phase transformation temperatures of Eu³⁺/TiO₂ nanocrystals are higher than that of TiO₂. This is due to the formation of Eu-O-Ti bonds on the surface of the TiO₂ crystallite, as characterized by the X-ray photoelectron spectroscopy. The photoluminescence spectra of TiO₂ in Eu³⁺/TiO₂ nanocrystals are interpreted by the surface self-trapped and defect-trapped exciton relaxation. The photoluminescence of Eu³⁺ in Eu³⁺/TiO₂ nanocrystals has the strongest emission intensity at 2% of Eu³⁺ concentration.     

More precise determination of thermal lens focal length for end-pumped solid-state lasers

A method of more precise determination of the focal length of equivalent thermal lens (TL) is presented in this paper. The method is based on the diffraction theory of aberrations. By numerically calculating the optical path difference (OPD) distribution and the Strehl ratio, the focal lengths for “top-hat” pumping and Gaussian pumping are obtained and the equations for the focal lengths are presented by curve fitting. Also the equations for average pump radii are presented. The experiment on a fiber-coupled LD pumped Nd:YAG laser is carried out. The experimental results verify the validity of the method.