Investigation of silicon on insulator fabricated by two-step O+ implantation

In this paper, we investigated the dose window of forming a continuous buried oxide (BOX) layer by single implantation at the implantation energy of 200 keV. Then, an improved two-step implantation process with second implantation dose of 3×10¹⁵ cm^?2 was developed to fabricate high quality separation by implanted oxygen (SIMOX) silicon on insulator (SOI) wafers. Compared with traditional single implantation, the implantation dose is reduced by 18.2%. In addition, the thickness and uniformity of the BOX layers were evaluated by spectroscopic ellipsometry. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces were observed by transmission electron microscopy, indicating a high crystal quality and a perfect structure of the SOI fabricated by two step implantation. The top Si/BOX interface morphology of the SOI wafers fabricated by single or two-step implantation was also investigated by atomic force microscopy.     

AlMgB_（14）三元超硬硼化物的实验制备与理论研究

三元硼化物AlMgB14材料具有高硬度,高韧性,低密度,低摩擦系数以及抗高温氧化腐蚀等众多优异性能,在工具、模具、微机械制造及航空航天关键零部件等领域具有重要的应用前景.本文采用多靶射频磁控共溅射技术,以高纯度Al（99.99%）,Mg（99.95%）,B（99.9%）材料为溅射靶源,在单晶Si（100）衬底上溅射沉积得到了表面均匀致密,不同化学组分的Al-Mg-B三元非晶态薄膜,通过调控溅射参数,可以实现原子比接近Al：Mg：B=1：1：14.对于所制备的薄膜样品,在三元相图上沿Al-Mg等含量线,Al-Mg-B材料的硬度,随着B元素含量增加由13GPa增大到32GPa,其中AlMgB14附近成分点的硬度达到25~32GPa.同时,采用第一性原理计算,得到AlMgB14晶体的维氏硬度为27.6GPa,与实验值接近.通过电子结构分析,我们进一步探讨了AlMgB14晶体和其他相似结构富B三元化合物硬度的起源,发现他们共同具有的B12二十面体骨架是决定硬度的主要因素.Al,Mg等金属元素主要通过向B12的电荷转移对材料硬度进行微调,Al-B之间形成了弱的共价键而Mg-B之间形成离子键,这点同时也为XPS实验谱图所证实.采用准简谐近似德拜模型,我们还研究了AlMgB14晶体的热学性质以及温度对体弹性模量的影响,发现体模量随温度增加明显的减小,同实验上提高衬底温度对硬度的增强呈现了相反的变化趋势.这从侧面说明了衬底温度提高导致的硬度增强并不是改变了材料的本征硬度,而可能由于加强了薄膜同衬底间附着力.     

Generation of transgenic cucumbers with expression of a ten-tandem repeat long-acting GLP-1 analogue and their biological function on diabetic rats

Glucagon-like peptide-1 （GLP-1） is a 30-amino acid peptide hormone, which has the regulatory function of stimulating the secretion of insulin to balance blood glucose levels. In this study, marker-free expression vector pX6 with a fusion gene of ten tandem repeated GLP-1 analog （[Ser8, Gln26 and Asp34]-GLP-1） genes was constructed and transformed into cucumbers by Agrobacterium tumefaciens-mediated transformation method. Four transgenic lines were obtained by PCR and Southern blotting analysis and two transgenic lines successfully expressed the fusion protein （named GLP-T）, which was revealed by Western blotting analysis. The biological activity test results showed that the serum glucose level of diabetic rats was significantly decreased after oral administration of the fusion protein GLP-T extracted from the transgenic cucumber fruitage. These results suggest that this may provide a brand-new strategy to prevent and cure the diabetes with no pain.     

Nightside field-aligned current during the April 6, 2000 superstorm

Using the east-west geomagnetic disturbance fields observed from stations at mid-latitudes, we investigate the characteristics of field-aligned currents on the nightside during the April 6, 2000 superstorm. The results indicate that there is an eastward disturbance on the nightside of Northern Hemisphere during the main phase of magnetic storm, while the interplanetary magnetic field (IMF) is continued southward. The positive disturbances in the postmidnight are larger than that in the premidnight. This suggests that upward field-aligned currents develop on the nightside, when the IMF is directed southward. The peak of upward field- aligned currents is located in postmidnight, and it will be more obvious at substorm expansion. We get the conclusion that both partial ring current and region-2 field-aligned current shift to dusk sector. The upward region-2 current is decreased at substorm onset, and intensified after it. We also investigate the relationship between the upward field-aligned currents on the nightside and the auroral electrojets at high latitudes. It shows a good correspondence between region-2 current and the westward electrojet in the postmidnight. We suppose that they are both associated with the convection electric field.     

基于化学反应的膛口温度场孤立波解

膛口流场是由从膛内高速流出的膨胀不足的非定常射流与膛口空气的相互作用而形成的。在这过程中伴随着涡流和冲击波等现象的发生．其中，燃气与空气中氧作用而发生爆燃．形成中心焰和二次焰．由此可见，膛口火焰区是一个极为复杂的带有键式化学反应的区域，必然是一个同时有热传导，扩散，对流及化学反应起作用的区域．火焰的形成与传播同温度和反应物浓度及其分布有关．该文针对膛口温度场的中心焰及二次焰形成与传播机制，考虑到化学反麻、热传导、扩散等，建立了膛口温度场的一维物理模型．从孤立波的角度解释了膛口火焰的形成机理，理论与实验符合得较好。     

Investigation of silicon on insulator fabricated by two-step O~+ implantation

In this paper,we investigated the dose window of forming a continuous buried oxide(BOX) layer by single implantation at the implantation energy of 200 keV. Then,an improved two-step implantation process with second implantation dose of 3×1015 cm-2 was developed to fabricate high quality separation by implanted oxygen(SIMOX) silicon on insulator(SOI) wafers. Compared with traditional single implantation,the implantation dose is reduced by 18.2%. In addition,the thickness and uniformity of the BOX layers were evaluated by spectroscopic ellipsometry. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces were observed by transmission electron microscopy,indicating a high crystal quality and a perfect structure of the SOI fabricated by two step implantation. The top Si/BOX interface morphology of the SOI wafers fabricated by single or two-step implantation was also investigated by atomic force microscopy.     

多媒体数字版权保护系统的研究与实现

在分析目前多媒体数字版权保护现状问题的基础上,提出了一个通用的多媒体数字版权保护架构,并实现了一个多媒体数字版权保护原型系统,具有透明支持多媒体数据的本地回放和在线播放的能力,使用XrML作为权限表达语言,实现了权限表达的标准化,并提出了基于策略的身份认证模型,实现了用户名/密码、USB设备、智能卡、指纹4种身份认证方法,有效地解决了目前多媒体数字版权保护领域的关键问题.实际系统的部署和初步试验结果表明了系统实现了对多媒体数据良好的保护.     

Dynamic changes in flag leaf angle contribute to high photosynthetic capacity

Dynamic changes in flag leaf angle, anatomy, photosynthesis, chlorophyll content, population photosynthesis, and light transmission are investigated in three wheat cultivars： Xiaoyan 81 （Xy 81） in which flag leaf angle changes from erect to draped, Xiaoyan 41 （Xy 41） in which flag leaf angle changes from erect to half draped （middle type）, and Xiaoyan 6 （Xy 6） in which the flag leaf remains erect from the flowering to the grain-filling stage. No obvious differences in leaf thickness, leaf area, mesophyll morphology, granal stacking, photosynthesis, or chlorophyll content are found among the three cultivars. It is of interest to find that the flag leaf angle of Xy 81 changes from erect to draped during the grain - filling stage, but there are no obvious changes in chlorophyll content or photosynthetic capacity during this period, indicating that changes in flag leaf angle do not result from senescence. Moreover, the study shows that levels of population photosynthesis and light transmission in Xy 81 are higher than in Xy 41 and Xy 6. Taken together, these results demonstrate that dynamic changes in Xy 81 flag leaf angle enhance population photosynthesis and thus may improve wheat yield.     

Fabrication and its characteristics of low-temperature polycrystalline silicon thin films

In order to reduce the cost of solar cells or flat-panel display,it is very important to synthesis polycrystalline silicon films on low cost substrate such as glass at low temperature.In this work,electron cyclotron resonance(ECR)plasma enhanced chemical vapor deposition(PECVD)system was successfully applied to synthesize poly-Si thin-film on common glass substrate using H2 as the plasma source and SiH4(Ar:SiH4=19:1)as the precursor gas at low temperature.Since the multicusp cavity-coupling ECR plasma sourc...