Characteristics of InGaN-based superluminescent diodes with one-sided oblique cavity facet

We have fabricated InGaN-based superlumi-nescent diodes （SLDs） with one-sided oblique facet. The characteristics of the SLDs and laser diodes with the same cavity length （800 μm） were compared. The typical peak wavelength and the full width at half maximum of the spectrum in superluminescence regime are 445.3 and 7.7 nm for the SLDs with 800 μm cavity length. The characteristics of the SLDs with different cavity length were also demon-strated in a comparative way. It is found that the gain of the InGaN multi-quantum wells in blue spectral range is a linear function of the current density below gain saturation region. The lasing threshold current turns out to be higher for the shorter SLD （S-SLD） （400 μm）, but the output light intensity of the longer SLD （800 μm） is higher than that of the S-SLD under the same current density. The gain saturation phe-nomenon was observed in S-SLD when it was biased at a current density larger than 27.5 kA/cm^2. The increase of junction temperature was identified as the main reason for gain saturation through spectra analysis.     

一种新颖的跨世纪大型粮仓

最近,我省农业科技考察团到南斯拉夫进行了考察。在考察中,不但发现南斯拉夫农业科研水平较高,科技成果转化效率很高,农业整体实力较强外,还发现一种新型粮仓。这种粮仓造型别致,富有艺术感,容积大、造价低、运行经济,被国际上称为下一世纪世界上最有吸引力的粮食仓库。     

Numerical research on the 3D fiber orientation distribution in arbitrary planar flows

The fiber orientation distribution in a fiber suspension flow was investigated by a finite difference scheme in spherical coordinates. The diffusivity was transformed between Cartesian and spherical coordinates through tensor analysis to obtain efficiency. It is found that under simple shear flow condition the diffusivity in the azimuthal direction, Dr, has greater effect on the orientation distribution than that in the colatitude direction, Drθθ.     

谈英语学习中的负迁移问题

人们在学习英语时，通常会自觉或不自觉地借助母语语言习惯来学习，这种现象就叫迁移。当迁移不当，在目的语中不能接受，影响学习时，就成了负迁移。本文对英语学习者在英语语音、词汇、语法和语用方面的负迁移情况进行一些分析和讨论。     

有关金属表层X射线应力分析的讨论

本提出金属表面附近层区的三维应力的新的测试方法，对于存在应力梯度的金属表面层研究有着特殊的意义。本在Ｘ射线宏观应力测试中采用非线性回归方法，较之常规应力测试的线性回归方法，可以得到更具合理性的应力参数，这些应力参数所表示的是金属表面厚度约（１．１～１．２）Ⅱｏ范围内的平均值。这里，Ⅱｏ＝ｓｉｎθψ·０／μ定义为能够产生Ｘ射线衍射的表面层的有效厚度，μ是Ｘ射线的线衰减系数。分析表明，自由表面附…     

Reinforcing effect of laminate structure on the fracture toughness of Al3Ti intermetallic

Metal/intermetallic laminate composites can improve the mechanical properties of intermetallic materials using metal layers. In recent years, titanium aluminide intermetallics have received increasing attention due to their excellent performance properties, such as high melting point, high specific strength and stiffness, and good corrosion resistance. However, the low fracture toughness of Al3Ti alloys at room temperature has greatly limited their application, and fiber or particle reinforcement has not shown a significant toughening effect. Research into the reinforcing effects of the interface and near-interface zone on the fracture behavior of Al3Ti is lacking. Ti/Al3Ti metal/intermetallic laminate composite was synthesized from titanium and aluminum foils using vacuum hot-pressed sintering technology. The microstructure of the prepared material was analyzed by scanning electron microscope and electron backscattered diffraction. Results illustrate that both Ti and Al3Ti were single-phase and there was a noticeable stress concentration on the interface. To obtain indentation and cracks, loads were applied to different locations of the composite by a microhardness tester. The growth path of the cracks was then observed under microscope, showing that crack propagation was prevented by the interface between the Ti and Al3Ti layers, and the cracks that propagated parallel to the laminate shifted to the interface. Fracture toughness of the different areas, including Al3Ti layers, interface, and near-interface zone, were measured by the indentation fracture method. The fracture toughness at and near the interface was 1.7 and 2 times that of the Al3Ti layers, respectively. Results indicate that crack blunting and crack front convolution by the laminate structure was primarily responsible for increased toughness.     

Negative refraction in two-dimensional photonic crystals

Recent progress made in research on negative refraction in two-dimensional photonic crystals is reviewed. Special attentions are paid to the research results of our group. We explore the underlying mechanism governing the occurrence of negative refraction in periodic and quasiperiodic photonic crystals. These results may be useful references for the application of photonic crystals. The perspectives of future research on negative refraction are briefly predicted．     

Silica nanoparticle is a possible safe carrier for gene therapy

In order to develop a safe and effective gene therapy carrier, some toxicological and biodynamical experiments were carried out on silica nanoparticles （SiNPs）. First we prepared SiNPs with appropriate portions of cyclohexane, deionized water and ethyl silicate, and then transfected the modified SiNPs and GFP plasmid DNA complex into the HT1080 cells to test the effectiveness of transfection for gene therapy. At the same time, we injected the SiNPs into a number of mice through tail vein. Then we made the mice crossed to evaluate the acute, long-term and reproductive toxicity. In vivo distribution analysis and pathological examination were made on both adult mice and their offspring. SiNPs were uniform and had an average diameter of 40 nm, and the modified SiNPs carried exogenous DNA molecules into target cells and the transferred GFP fusion gene was effectively expressed in the cells. The SiNPs injected via tail vein were widely distributed in almost all of tissues, and the injected mice had the ability to reproduce normally. The in vivo and in vitro results of this study clearly show that SiNPs can be used as a safe and effective carrier for gene transfection and gene therapy.