下一代通信技术对广播电视业务发展的影响(下)

(接上期第43页) 3 下一代通信接入对广播电视业务发展的影响 3.1 突破用户接入的瓶颈 随着宽带业务的发展,网络接入部分(最后1 km)的带宽瓶颈问题显露出来.目前,接入部分两侧都已跨入吉比特级以上的速率,如用户端广泛使用的PC,其内部传送速率已达到32 Gb/s,城域网或长途网的每波长速率也已达到2.5～10 Gb/s,两者都比接入部分高出至少3个数量级.可见,尽快打通接入部分的带宽瓶颈,各种宽带服务与应用才能开展起来,网络容量的潜力才能真正发挥.     

昆钢高炉铁水脱碳实验研究

研究了不同铁矿粉氧化剂以及矿粉加入量、铁水初始成分、铁水温度等因素对铁水碳、硅、锰氧化的影响.实验表明巴西粉与滇滩矿具有较好的脱碳效果,在高炉出铁温度范围内,用巴西粉或滇滩矿加入量为2%时,可平均脱去3.3%的碳、50%的硅和30%的锰.对铁水进行氧化脱碳处理后进行冷却,没有发现片状石墨析出.     

A retrograde fluorescent-labeling study of direct relationship between the limbic (anterodorsal and anteroventral thalamic nuclei) and the visual system in the albino rat

Case-control methodology was used to assess lung cancer risk from exposure to arsenic in air, employing data from former workers in different units at the Chuquicamata copper mine and smelter complex. Thirty two workers from this complex were identified among the lung cancer deaths that occurred in the Northern region of Chile between 1987 and 1991. Each case was matched on age and sex, with controls that had a similar date of enrolment in the company. Available data on arsenic concentrations in air for six work sites were compiled from 1952 to 1991 and these were used to categorize the workplaces: Administrative area (1.6 micrograms/m3), Mine (2.3 micrograms/m3), Oxid Plant (3.1 micrograms/m3), Workshop and Services (9.8 micrograms/m3), Sulphur Plant (8.4 micrograms/m3) and Smelter (201.7 micrograms/m3). The results indicate an Odds Ratio of 5.7 (Fisher's p = 0.016) of dying from lung cancer among workers of the smelter compared with the rest of the workers.     

强弱起伏下电离层电波闪烁特性

基于随机媒质电波传播理论,采用Rytov近似和Markov过程近似,得到了强、弱起伏下,电离层电波传播的强度闪烁指数.结合电离层电子密度不均匀体起伏的Shkarofsky功率谱函数,对电离层强、弱起伏下的电波闪烁进行数值模拟和讨论.结果表明,不同的电波频率,电离层电子密度不均匀体不同的厚度,电子密度不均匀体的内、外尺度,谱指数以及电子密度不同的起伏方差,均对电离层电波闪烁产生一定的影响.     

Sm(Co_(0.74)Cu_(0.12)Fe_(0.1)Zr_(0.04)_(7.5)纳米晶烧结磁体的结构和磁性能

采用放电等离子烧结技术制备了致密纳米晶SmCoCuFeZr烧结磁体,研究了磁体的结构和磁性能.X衍射结果表明,烧结磁体具有TbCu_7结构.TEM观察显示,烧结磁体平均晶粒尺寸为35nm.室温时磁体的剩磁为0.49T,矫顽力高达1.42T,而剩磁比Mr/Ms为0.63,表明在纳米晶之间存在晶间交换耦合作用.     

In situ localization and chromosomal mapping of the AG1 (Dmp1) gene

Dentinogenesis is being used as a model for understanding the biomineralization process. The odontoblasts synthesize a structural matrix comprised of Type I collagen fibrils which define the basic architecture of the tissue. The odontoblasts also synthesize and deliver a number of dentin-specific acidic macromolecules into the extracellular compartment. These acidic macromolecules may be involved in regulating the ordered deposition of hydroxyapatite crystals within the matrix. AG1 is the first tooth-specific acidic macromolecule to have been cloned and sequenced. To identify which cells of the rat incisor pulp/odontoblast complex were responsible for synthesis of AG1, in situ hybridization was used. Digoxigenin labeled sense and anti-sense AG1 riboprobes were prepared. The AG1 mRNA was found to be expressed in the mature secretory odontoblasts. Neither pulp cells nor pre-odontoblasts showed any staining with the anti-sense probes. Chromosomal localization studies placed the AG1 gene on mouse chromosome 5q21, in tight linkage with Fgf5. AG1 has been renamed Dmp1 (dentin matrix protein 1) in accordance with present chromosomal nomenclature. Mouse 5q21 corresponds to the 4q21 locus in humans. This is the locus for the human tooth mineralization disorder dentinogenesis imperfecta Type II (DI-II). These data suggest that the Dmp1 gene is involved in mineralization and is a candidate gene for DI-II.     

500kV线路带电作业方法及工器具的应用

500kV线路电压等级高,杆塔类型多,各塔型塔头尺寸较通常情况复杂．造成带电作业过程中塔头承力工器具的通用性不好,不仅增加了工作难度和成本,同时也限制了带电作业的实践应用。为此,对进入强电场的绝缘工器具及作业方法进行摸索、改进和现场应用．包括更换ZM塔型直线绝缘子串的工器具改进、单柱绝缘爬梯的现场应用、500kV线路带电作业的现场应用等。     

分组投切电容器装置的不平衡故障分析及保护计算

在工程应用中,存在一套电容器装置包含多个电容器组并共用中性点的情况。文章以采用开口三角电压保护的装置为例分析了此类电容器装置的不平衡故障状态,建立了相应的计算模型,给出了不平衡电压保护的计算方法。结合实例与具有相同分组形式并与独立开关投切的电容器装置进行了比较,为今后工程实施提出了建议。