Ga1-xInxAs/InAsyP1-y/InP异质结的MOCVD生长及表征

Ga1-xInxAs(x>0.53)材料是未来长距离低损耗光纤通信的理想光源材料和探测器材料之一.我们采用水平常压MOCVD系统,在InP衬底上成功地生长了Ga1-xInxAs(x>0.53)/InAsyP1-y/Inp异质结材料.其中InAs1-yPy为组份阶梯变化的多层结构.由样品的(400)面X光衍射结果测定了各层组份.由二次离子质谱(SIMS)得到了样品剖面组份变化结果,证明InAs1-yPy层组份为阶梯状变化的.通过对光致发光结果和X光衍射结果比较,可以看到,InAsyP1-y层通过位错和弹性畸变二种方式来释放或积累Ga1-xInxAs与InP间的失配应力,从而减少了Ga1-xInxAs中的失配位错.有效地改善了Ga1-xInxAs的质量.已获得了x高达0.94表面光亮的Ga1-xInxAs/InAs1-yPy/InP异质结材料.     

Magnetic resonance imaging and pulsed Doppler sonography of poststenotic jets: Correlation between signal void and flow velocity distribution

To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography.     

牙齿化石中由辐照产生的陷阱电子的热稳定性研究

本文对周口店北京猿人遗址的动物牙齿化石进行了辐照产生的陷阱捕获电子的热稳定性研究和釉质样品及牙质样品的热稳定性对比实验。得到釉质样品中g=2.0016 ESR峰的寿命为7.1×10⁶年(20℃)。说明了取该峰进行ESR年代测定的可信性和用釉质样品进行ESR年代测定的必要性。     

Emission and sputtering characteristics of Ne-Ar mixed gas glow discharge plasmas.

The emission characteristics of several Cu lines emitted from a Ne-Ar mixed gas glow discharge plasma were investigated. The addition of small amounts of Ar to a Ne plasma increases the sputtering rate of a Cu sample because Ar ions, which work as the impinging ions for cathode sputtering, are predominantly produced through Penning ionization collisions between Ne metastables and Ar atoms. Ar addition also elevates the number density of electrons in the plasma. These changes occurring in the Ne-Ar mixed gas plasma result in enhanced emission intensities of the Cu lines. The Cu II 270.10-nm and the Cu II 224.70-nm lines yield different intensity dependence on the Ar partial pressure added. This phenomenon is because these Cu II lines are excited principally through different charge transfer processes: collisions with Ne ions for the Cu II 270.10-nm line and collisions with Ar ions for the Cu II 224.70-nm line. The shape of sputtered craters in the Ne-Ar glow discharge plasma was measured. The depth resolution was improved when Ar was added to a Ne plasma because the crater bottoms were flatter with larger Ar partial pressures.     

The application of spectral distribution of product of two random matrices in the factor analysis

In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted.     

In situ observation of NaBi(WO4)2 dendrite growth and the study on microstructure of solidification

The dendrite growth process of transparent NaBi(WO₄)₂ with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS data of solidification structure of quenched NaBi(WO₄)₂ melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface during the growth process. Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623)     

Generalized 3G theorem and application to relativistic stable process on non-smooth open sets

Let G(x,y) and GD(x,y) be the Green functions of rotationally invariant symmetric α-stable process in Rd and in an open set D, respectively, where 0<α<2. The inequality GD(x,y)GD(y,z)/GD(x,z)?c(G(x,y)+G(y,z)) is a very useful tool in studying (local) Schrödinger operators. When the above inequality is true with c=c(D)∈(0,∞), then we say that the 3G theorem holds in D. In this paper, we establish a generalized version of 3G theorem when D is a bounded κ-fat open set, which includes a bounded John domain. The 3G we consider is of the form GD(x,y)GD(z,w)/GD(x,w), where y may be different from z. When y=z, we recover the usual 3G. The 3G form GD(x,y)GD(z,w)/GD(x,w) appears in non-local Schrödinger operator theory. Using our generalized 3G theorem, we give a concrete class of functions belonging to the non-local Kato class, introduced by Chen and Song, on κ-fat open sets. As an application, we discuss relativistic α-stable processes (relativistic Hamiltonian when α=1) in κ-fat open sets. We identify the Martin boundary and the minimal Martin boundary with the Euclidean boundary for relativistic α-stable processes in κ-fat open sets. Furthermore, we show that relative Fatou type theorem is true for relativistic stable processes in κ-fat open sets. The main results of this paper hold for a large class of symmetric Markov processes, as are illustrated in the last section of this paper. We also discuss the generalized 3G theorem for a large class of symmetric stable Lévy processes.     

高能闪光照相对电子束参数的要求

对高能闪光机光源性能用Monte-Carlo方法模拟研究发现：并非击靶电子束半径越小、发射度越低, 闪光机的照相性能就会越好. 研究结果表明：为了使闪光照相图像视面上照射量分布比较均匀, 对束半径与电子束归一发射度有一个联合限制, 对于20MeV闪光机, 如果击靶电子束有效半径是0.12cm, 那么仅当束归一发射度≥550cm.mrad时,在2°内的照射量不均匀性才小于5%.     

The effect of surface crystalline layers on asymmetric off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using a pick-up coil wound around the sample. One side of a ribbon was etched in hydrofluoric acid solution during various times in order to change the thickness of the surface crystalline layer appearing after annealing. The asymmetric two-peak field dependence of the off-diagonal impedance was observed for all samples. The evolution of the off-diagonal magnetoimpedance with the change in the ribbon thickness is analyzed.     

Photoemission studies of oxygen adsorbed on a LiAl(1 1 0) alloy surface: Role of Li segregation

We investigated that the effect of the number of segregated Li atoms on the rate of oxidation on a LiAl alloy surface. Oxygen molecules adsorbed on the LiAl alloy react with the surface atoms to form stable oxides. The segregated Li atoms at reconstructed surfaces (c(2×2) and (2×1)) enhance the oxidation rate and form stable LiAlO_x and Li₂O. The degree of enhancement of oxidation by segregated Li atoms varies as a function of O₂ exposure and annealing temperature, where the latter is directly related to the mode of surface reconstruction by Li segregation.