A new H-2-linked class I gene whose expression depends on a maternally inherited factor

The maternally transmitted antigen (Mta) is expressed on the cells of most strains of mice. It is a medial histocompatibility antigen, that is, it is recognized by unrestricted cytotoxic T lymphocytes as are major H antigens, but unlike these it is a weak transplantation antigen and does not itself restrict the T-cell recognition of minor H antigens. All other medial H antigens are encoded by genes closely linked to the major histocompatibility complex, H-2 in the mouse. By contrast, Mta appeared to follow extrachromosomal, maternal inheritance. Several substrains of NZB, NZO and non-inbred European NMRI mice are Mta-negative. Females of these strains bear only Mta- offspring, while females of the inbred Mta+ strains bear only Mta+ offspring. Repeated backcrossing from Mta+ females to NZB or NMRI males has shown that, given the right cytoplasmic genes, the chromosomal genes of these Mta- strains permit expression of Mta2. As the Mta type of a mouse cannot be influenced by embryo transfer or foster nursing, we concluded that it was determined by a cytoplasmic factor (Mtf), transmitted through the egg. We now show that a gene, Hmt, closely linked to the H-2 complex, is also required for expression of Mta.     

Cell lineage-specific undermethylation of mouse repetitive DNA

Several distinct cell lineages are established during mouse embryogenesis. The trophectoderm and primitive endoderm give rise to extraembryonic structures alone, while the primitive ectoderm becomes the fetus proper. Recent studies suggest that the levels of DNA modification are lower in inactive X chromosomes from extraembryonic tissues than in embryonic and adult somatic tissues. Using HpaII/MspI isoschizomers, Southern blots and cloned probes, we show here that repetitive DNA sequences from all derivatives of the two extraembryonic lineages, trophectoderm and primitive endoderm, are substantially undermethylated compared with primitive ectoderm derivatives. This contrasts with the highly methylated state of these repetitive elements observed in adult somatic tissues. Specific demethylation or inhibition of de novo methylation, or a combination of both mechanisms, may be involved. These findings suggest that elements of gene regulation dependent on DNA modification may be different in extraembryonic cell lineages.     

基于小波分析的过零点滤波器与地震降噪

为解决地震勘探中的面波压制问题,该文基于小波分析理论处理单分量地震资料,根据面波频率低、能量强的特征设计了过零点滤波器,在小波分解后的逼近系数中识别并压制了面波,在细节系数中进行了有效波补偿。实际资料处理表明,该方法能剔除95%以上的面波,并且在压制面波的同时减少反射波的损失,较之传统方法有显著改善。     

垃圾热解中PVC组分HCl的析出特性

以垃圾中的PVC组分为试验物料,在外热式固定床热解试验台上,研究了PVC热解过程中HCl的析出特性·通过改变加热方式、热解终温、加热温度、加热时间等参数研究了HCl的析出过程、析出量和质量分数·试验表明,加热方式对HCl析出有很大的影响,快加热方式析出的HCl量几乎是慢加热方式的2倍;HCl析出过程可分为三个阶段,325℃时开始有HCl析出;热解终温对HCl析出过程有较大的影响,并决定着HCl的析出量,本试验在550℃左右析出的HCl量最多,这说明存在一个HCl析出量最大的峰值温度·并依据试验结果,从理论上进行了初步探讨     

桩承载力反向自平衡试桩法数值模拟分析

为推动反向自平衡试桩法在实践中的应用,采用有限元分析方法对反向自平衡试桩法进行了数值模拟分析。以管桩为例,运用ABAQUS有限元软件建立反向自平衡试桩法数值模型,分别采用位移控制法和荷载控制法进行桩身和桩顶加载模拟,得到了基桩抗压极限承载力,进行了桩身轴力和桩侧摩阻力分析;对建立的数值模型进行了位移控制法下的静载试验模拟,并与反向自平衡试桩法模拟得到的极限承载力进行了对比分析。模拟结果表明,反向自平衡试桩法确定的基桩极限承载力与静载试桩法结果较为接近,不需要进行正、负摩阻力转换,但也存在平衡点位置的确定问题。     

涡旋压缩机的变基圆型线研究

研究了具有内、外起始角的变基圆涡旋型线,根据展开角是否在x轴起始,给出两种形式的变基圆外型线方程,并明确给出相对应的内型线方程,推导出偏心距的表达式,分析了两种形式的变基圆涡旋型线方程的关系.对两种形式的变基圆涡旋型线进行双圆弧齿头修正,给出双圆弧修正型线方程,分析两种情况下修正型线方程的关系,并探究修正展角对修正齿头几何形状与压缩比的影响,为变基圆涡旋型线的研究提供了一定的理论基础和应用参考.     

射频负偏压等离子体鞘层流体动力学模拟

采用流体动力学方法建立了一种自洽的无碰撞射频直流偏压等离子体鞘层动力学模型.模型中考虑了极板直流负偏压对离子运动的影响,模拟了在不同偏压条件下射频等离子体鞘层内各参量的时空演化特性.在该模型中,认为鞘层厚度是与时间有关的函数,并采用等效电路模型建立了鞘层瞬时厚度与鞘层电位降的关系.模拟结果表明,极板上电势呈非正弦周期性变化;鞘层厚度变化与极板电势变化周期相同,趋势相反,且略滞后于射频周期.     

超支化聚酯的合成及表征

以双酚酸[4,4-双(4-羟基苯基)戊酸]为主要原料,采取熔融缩聚的方法制得了超支化聚酯,利用傅立叶变换红外、端基分析法、乌氏黏度计及热重分析对产物等测试技术进行了初步表征, 结果表明,超支化聚酯表现为较低的特性黏度、良好的溶解性和热稳定性.     

Na0.5Bi0．5TiO3纳米线的制备及其光致发光特性研究

采用溶胶-凝胶-水热合成技术,以钛酸四丁酯、醋酸钠和五水硝酸铋为原料,NaOH为矿化剂,合成了直径约10～20 nm,长度达到微米量级的钙钛矿结构钛酸铋钠纳米线单晶. 通过X射线衍射仪,透射电子显微镜,X射线光电子能谱等技术对纳米线的形貌和成分进行了表征,并研究了Na0.5Bi0.5TiO3纳米线的光致发光特性.