乙型肝炎病毒促进肝细胞PD-L1蛋白表达机理

为了研究乙型肝炎病毒(Hepatitis B virus,HBV)能否借助肿瘤细胞的抗免疫机制来逃逸机体免疫,利用HBV感染去肝细胞,研究受感染后的肝细胞对宿主免疫应答的变化.通过实时荧光定量PCR的方法分析HBV感染后的肝细胞内Axin和PD-L1的转录水平,发现HBV不影响Axin和PD-L1的转录水平,采用蛋白免疫印迹技术发现HBV能下调肝细胞内Axin蛋白水平,同时上调PD-L1蛋白水平.进一步在细胞内转染表达HBV的组成蛋白的质粒,通过蛋白免疫印迹技术发现HBV的组成蛋白HBx能下调细胞内Axin蛋白的表达.通过数据相关性分析以及泛素化实验发现,Axin能通过增加PD-L1的E3泛素连接酶SPOP的表达,促进PD-L1泛素蛋白酶体降解.进一步对PD-L1的泛素化方式进行探讨,发现Axin促进PD-L1的K48依赖的泛素化降解作用.结果表明,HBV可能通过HBx下调Axin和SPOP蛋白水平,抑制PD-L1泛素化降解,进而逃逸宿主免疫应答.本研究揭示了HBV免疫逃逸新机制,为治疗HBV奠定了新的基础,在一定程度上推动了抗HBV药物开发.     

电导率张量测量及仪器设计

岩石电各向异性以电导率张量表征,实验室中多采用四极法与六极法测得岩石电导率,但难以一次实验完全获得电导率张量的9个分量,若多次实验易造成较大的测量误差.为此本文基于文献研究成果,针对方样岩芯设计电导率张量测量仪,该方案也适用于柱塞岩芯.通过氮气驱替完全水饱的岩芯,温控系统和围压控制系统控制岩芯夹持器内部的温度和压力,可运用上位机控制电极测量不同含水饱和度时岩芯电导率张量的9个分量.该仪器亦可用于柱塞岩芯的岩电实验,通过测得的电导率数据,确定阿尔奇公式的未知系数.通过理论与实验数据分析,验证了该电导率张量测量仪设计方案的可行性.     

基于RF和KNN的地下采场开挖稳定性评估

针对传统地下采场开挖稳定评估方法存在的局限性,引入机器学习方法,提出基于随机森林算法(Random forest,RF)和K-最近邻算法(K-nearest neighbor,KNN)的地下采场开挖稳定性预测模型.以加拿大8个采场为例,首先,获取并分析399组观测数据,其中涵盖了相应的岩石质量分级(Rock Mass Rating,RMR)值、跨度以及对应的稳定、潜在不稳定或不稳定状态.然后将地下采场的稳定性程度进行三分类及二分类,采用10折交叉验证方法进行模型超参数优化,在不作任何假设的前提下,捕捉地下采场开挖稳定性与RMR值、跨度之间的复杂关系.研究表明:二分类结果准确性高于三分类预测结果;在二分类方式下,两种算法的准确率及召回率均高于90％,其中KNN算法的表现优于RF算法;提出的两种方法较先前研究的正确率有很大提升,为开挖稳定性评估提供了可靠途径.     

高海拔隧道出渣过程CO分布分析及需风量研究

为解决高海拔施工隧道出渣过程的排气排放物污染,改善通风排污效果,基于海拔环境参数变化和紊流扩散理论,构建了高海拔隧道气体扩散模型.以海拔3200 m的川藏铁路某隧道为研究背景,对洞内的环境参数和CO分布进行测定,利用SolidWorks和ANSYS建立施工隧道掌子面出渣模型,采用Fluent中的组分输运方程,对不同海拔高度的有害气体运移规律和质量分数分布进行动态模拟.结果表明,隧道中内燃机械作业时,在靠近工作面迎头位置,CO分布不均匀,极差值较大.在靠近隧道出口方向,CO分布逐渐趋于平稳.CO质量分数随海拔的升高而增加,而CO质量浓度却呈相反的变化趋势.从0 m到6 km,CO质量分数上升了96％;由于环境参数变化对CO质量浓度影响的权重大于CO排放量,导致CO质量浓度下降了18％.在保证隧道内CO质量分数不变的条件下,需风量随海拔高度呈非线性增加.根据得到的需风量计算模型,在海拔3200 m时,需风量约为4.95 m3/(kW·min).     

考虑剪力墙剪切变形影响的框架-剪力墙结构分析的传递矩阵法

考虑剪力墙剪切变形影响、连梁固结连接条件,利用变分原理,建立框架-剪力墙结构分析模型的微分方程。推导微分方程的初参数解,进而建立适应变刚度结构分析的传递矩阵法,给出均布荷载和倒三角形分布荷载作用的传递矩阵荷载附加项的计算公式,导出顶部集中荷载、顶部集中弯矩、沿高度方向均布荷载和倒三角形分布荷载作用下的挠度、转角、剪力墙弯矩、剪力的计算公式。以2个铰结体系框架-剪力墙为例,对计算公式进行验证。研究结果表明:当连梁等效抗弯刚度为0 k N·m/m时固结体系可退化成铰结体系,当剪力墙抗剪刚度趋于无穷大时,弯剪型剪力墙可退化为不考虑剪切变形的弯曲型剪力墙,因此,本文微分方程可适应于多种模型的计算;采用传递矩阵法分析变刚度框架-剪力墙结构,其计算结果与采用平均刚度法的理论解析解结果较吻合,证明传递矩阵法与平均刚度法都具有可行性,但若提高计算精度,则应采用能考虑变刚度特征的传递矩阵法或有限元法;考虑剪力墙剪切变形影响的本文计算公式所得计算结果与其他公式所得结果有一定差别。     

Synthesis of few layer single crystal graphene grains on platinum by chemical vapour deposition

The present competition of graphene electronics demands an ef fi cient route which produces high quality and large area graphene. Chemical vapour deposition technique, where hydrocarbons dissociate in to active carbon species and form graphene layer on the desired metal catalyst via nucleation is considered as the most suitable method. In this study, single layer graphene with the presence of few layer single crystal graphene grains were grown on Pt foil via chemical vapour deposition. The higher growth temperature changes the surface morphology of the Pt foil so a delicate process of hydrogen bubbling was used to peel off graphene from Pt foil samples with the mechanical support of photoresist and further transferred to Si O2/Si substrates for analysis. Optical microscopy of the graphene transferred samples showed the regions of single layer along with different oriented graphene domains. Two type of interlayer stacking sequences, Bernal and twisted, were observed in the graphene grains.The presence of different stacking sequences in the graphene layers in fl uence the electronic and optical properties; in Bernal stacking the band gap can be tunable and in twisted stacking the overall sheet resistance can be reduced. Grain boundaries of Pt provides low energy sites to the carbon species, therefore the nucleation of grains are more at the boundaries. The stacking order and the number of layers in grains were seen more clearly with scanning electron microscopy. Raman spectroscopy showed high quality graphene samples due to very small D peak. 2D Raman peak for single layer graphene showed full width half maximum(FWHM) value of 30 cm-1. At points A, B and C, Bernal stacked grain showed FWHM values of 51.22, 58.45 and 64.72 cm-1, while twisted stacked grain showed the FWHM values of 27.26, 28.83 and 20.99 cm-1,respectively. FWHM values of 2D peak of Bernal stacked grain showed an increase of 20–30 cm-1 as compare to single layer graphene which showed its dispersive nature and con fi rmed Bernal sequence. On the other hand, the slightest decrease in FWHM values of 2D peak in twisted grain comparing to single layer con fi rmed the twisted sequence of grains. Atomic force microscopy analysis showed an increasing trend in grain height pro fi le with an increase in the number of layers.     

DSC analyses of static and dynamic precipitation of an Al–Mg–Si–Cu aluminum alloy

In the present investigation, both static and dynamic precipitations of an Al–Mg–Si–Cu aluminum alloy after solid-solution treatment(SST)were comparatively analyzed using differential scanning calorimetry(DSC). Dynamic aging was performed in the SST alloy through equal channel angular pressing(ECAP) at different temperatures of room temperature, 110, 170, 191 and 300 1C. For comparison, static artificial aging was conducted in the SST alloy at 191 1C with two aging times of 4 and 10 h. The DSC analyses reveal that the dynamic precipitation has occurred in the ECAPed samples, while the activation energies associated with the strengthening precipitates in the dynamic samples are considerably higher than the energies in the SST and static aged samples. The higher activation energies are probably attributed to the smaller grains and higher dislocation density developed after ECAP. The results in the present investigation allow the prediction of the type of the dynamic precipitates to influence the strength of the ultrafine grained alloy during ECAP at various temperatures.     

Plant microremains provide direct evidence for the functions of stone knives from the Lajia site,northwestern China

A large number of stone knives have been recovered from Neolithic archaeological sites in East Asia. However, direct evidence regarding the functions of the stone knives has been scarce, and hence, their functions have remained controversial. In this study, we recovered and analysed ancient starch grains and phytoliths from residues adhering to stone knives excavated from the Lajia site, Qinghai Province, northwest China, thus providing direct evidence for the functions of the knives. Our anal- yses were based on the following： （1） an assemblage of 278 identifiable starch grains, representing grains from the stems of foxtail millet （Setaria italica） and broomcorn millet （Panicum miliaceum） （65.1% of the total） and the stems of Hordeum and Triticum species （3.6 % of the total）, and （2） an assemblage of 361 identifiable phytoliths, the majority of which were from the stems and leaves of plants such as Panicoideae and related taxa （96 % of the total）. Our study demonstrates that one of the functions of the stone knives was the harvesting crops. In addition, a few starch grains from food legumes and roots （3.4 % of the total） indicate that the stone knives were also likely used to process, peel and cut some foods.     

A molecular cryptography model based on structures of DNA self-assembly

With the progress of DNA computing, DNA- based cryptography becomes an emerging interdisciplinary research field. In this paper, we present a novel DNA cryptography that takes advantage of DNA self assembled structure. Making use of the toehold strands recognition and strand displacement, the bit-wise exclusive-or （XOR） operation is carried out to fulfill the information encryption and decryption in the form of a one-time-pad. The security of this system mainly comes from the physical isolation and specificity of DNA molecules. The system is con- structed by using complex DNA self-assembly, in which technique of fluorescent detection is utilized to implement the signal processing. In the proposed DNA cryptography, the XOR operation at each bit is carried out individually, thus the encryption and decryption process could be con- ducted in a massive, parallel way. This work may dem- onstrate that DNA cryptography has the great potential applications in the field of inRwmation security.