基体改性对C/C复合材料性能影响的研究(一)

本文从C/C复合材料的基体入手,研究了基体沥青、焦炭中添加氧化物的工艺条件及其在复合材料中的作用.结果表明,添加氧化物对基体改性,不仅能提高C/C复合材料的高温抗氧化性,也能对其它性能带来很大影响.只要控制适当的工艺条件,就可以得到高性能的C/C复合材料.     

Genetic evidence for the role of isocytochrome c2 in photosynthetic growth of Rhodobacter sphaeroides Spd mutants

In Rhodobacter sphaeroides, cytochrome c2 (cyt c2)-deficient mutants are photosynthetically incompetent (PS-). However, mutations which suppress the photosynthetic deficiency (spd mutations) of cyt c2 mutants increase the levels of a cyt c2 isoform, isocyt c2. To determine whether isocyt c2 was required for photosynthetic growth of Spd mutants, we used Tn5 mutagenesis to generate a PS- mutant (TP39) that lacks both cyt c2 and isocyt c2. DNA sequence analysis of wild-type DNA that restores isocyt c2 production and photosynthetic growth to TP39 indicates that it encodes the isocyt c2 structural gene, cycI. The Tn5 insertion in TP39 is approximately 1.5 kb upstream of cycI, and our results show that it is polar onto cycI. The cycI gene has been physically mapped to a region of chromosome I that is approximately 700 kb from the R. sphaeroides photosynthetic gene cluster. Construction of a defined cycI null mutant and complementation of several mutants with the cycI gene under the control of the cyt c2 promoter region indicate that an increase in the levels of isocyt c2 alone is necessary and sufficient for photosynthetic growth in the absence of cyt c2. The data are discussed in terms of the obligate role of isocyt c2 in cyt c2-independent photosynthesis of R. sphaeroides.     

Interactions between normal and tumoral tissues at the boundary of human anterior pituitary adenomas. An immunohistochemical study

Previously, the species complex Oncomelania hupensis, individuals of which act as intermediate hosts for the human bloodfluke Schistosoma japonicum, has been characterised by morphological and isoenzyme criteria. We have examined genetic variation between and within three subspecies of Oncomelania hupensis, i.e. O. h. hupensis (China), O. h. quadrasi (Philippines) and O. h. nosophora (Japan), by direct means using a PCR-based RFLP method. The subspecies of O. hupensis were readily distinguished by their characteristic restriction patterns, supporting isoenzyme data which suggests these may warrant species-specific status. No genetic variation was observed between O. h. quadrasi from different islands within the Philippines. In contrast, geographical isolates of O. h. hupensis differed markedly by this method indicating several genetically distinct populations of O. h. hupensis occur in China.     

Spatial distribution of femoral bone mineral in dual energy X-ray absorptiometry images: a possible technique to improve discrimination between normal and osteoporotic patients

The measurement of bone mineral density (BMD) using dual energy X-ray absorptiometry (DXA) provides an indicator of subsequent risk of hip fracture, but because of the significant overlap of measurements obtained from osteoporotic and control groups its predictive power is limited. The radiographic technique of Singh grading for the assessment of femoral osteoporosis utilizes information about the distribution of trabecular bundles, but the morphological information available in the DXA image has not previously been analysed. In this study of DXA images from 64 individuals (32 controls and 32 classified as osteoporotic) a subjective grading technique analogous to Singh grading is proposed, and quantitative measurements are made of image features corresponding to two of the categories. Discrimination was assessed using receiver operating characteristic (ROC) curves: the best discrimination was by spinal BMD (Az = 0.85 +/- 0.05) a performance equalled by one of the new parameters; the subjective grading method (Az = 0.79 +/- 0.07) performed as well as measurements of BMD in the femur. These results suggest that although the alternative measures do not improve on the discrimination possible using spinal BMD, morphological information from the hip itself may in the future have a place in the assessment of bone quality.     

厚膜导体的金属迁移研究

金属迁移能导致混合微电路发生灾难性失效。本文介绍一种简单易行的测试方法－水滴试验法，来测量厚膜电路的实际金属迁移率。用引方法测量时，发现Ｐｄ－Ａｇ导体的迁移率最大，Ｐｔ－Ａｕ导体的金属迁移率最小。     

瞬态光的光电摄谱测量

“光电摄谱法”是一种辐射光谱计量参数的测量方法,此法解决了单次脉冲闪光灯辐射光谱相对能量分布的精确测量问题。本文介绍了这种方法的测量原理、方法和特点,同时阐述了对接收器件、光路系统和时控电器系统的要求,并以自行研制的闪光光谱测定仪为例,对其计量参数波长和相对能量的标定与校正给予了必要的讨论,最后以实测结果证实了该方法的可靠性。     

Intermodulation analysis of the collector-up InGaAs/InAlAs/InP HBTusing Volterra series

The intermodulation (IM) distortion of the collector-up InGaAs/InAlAs/InP heterojunction bipolar transistor (HBT) is analyzed using Volterra-series theory. A T-equivalent circuit is used for this analysis. The contribution and interaction of four nonlinear elements: base-emitter resistance, base-emitter capacitance, base-collector capacitance, and common base-current gain are analyzed. For the particular device under investigation, it is found that the cancellation effect is not significant and the base-emitter resistance nonlinearity dominates the third-order IM