Molecular cloning and nucleotide sequencing of a novel aminoglycoside 6'-N-acetyltransferase gene from an R-plasmid of Salmonella typhimurium S24 isolated in Taiwan

A conjugative aminoglycoside resistance plasmid pST2 has been isolated from Escherichia coli K-12 14R525, which was mated with a clinical isolate of Salmonella typhimurium S24. A novel resistance gene of aminoglycoside 6'-N-acetyltransferase[AAC(6')] was cloned from plasmid pST2 on a 1,393 kilobase (kb) of SphI-SalI fragment into vector pACYC184 and pUC18. This novel AAC(6') gene in plasmid pST2 acetylated kanamycin, amikacin, dibekacin, tobramycin, gentamicin, netilmicin, and sisomicin. The complete nucleotide sequence of the novel AAC(6') gene and its neighboring sequences were also determined. Minicell experiments detected only one protein of 24.7 kilodaltons (kDa) translated from an open reading frame of the 618 base pairs (bp) gene.     

改性膨润土对天然橡胶的力学性能影响研究

本文讨论了改性膨润土对天然橡胶的力学性能的影响，并同未改性膨润土及白炭黑作了比较。用Ｘ光衍射仪和红外光谱分析了膨润土改性前后的结构变化。     

Control of circulating current in two parallel three-phase boost rectifiers

One unique feature in parallel three-phase converters is a potential zero-sequence circulating current. To avoid the circulating current, most present technology uses an isolation approach, such as transformers or separate power supplies. This paper proposes a parallel system where individual converters connect both AC and DC sides directly without additional passive components to reduce size and cost of the overall parallel system. In this case, the control of the circulating current becomes an important objective in the converter design. This paper: (1) develops an averaged model of the parallel converters based on a phase-leg averaging technique; (2) a zero-sequence model is then developed to predict the dynamics of the zero-sequence current; (3) based on the zero-sequence model, this paper introduces a new control variable, which is associated with space-vector modulation; (4) a strong zero-sequence current control loop is designed to suppress the circulating current; and (5) simulation and experimental results validate the developed model and the proposed control scheme.     

死髓变色前牙的激光漂白治疗临床评价

本文的研究目的是探讨激光冠内漂白治疗死髓牙变色的治疗作用。材料与方法 :漂白基本操作同激光活髓牙变色的漂白操作程序。先将牙龈及口唇有效防护 ,将漂白药物放在唇舌两面并同时封入根冠内。结果 :所有牙齿的灰暗变色均有 3- 5级的色度提高。平均治疗次数为 3.4± 0 .75 ,脱色 85 %以上的占 89%。结论 :牙齿创伤和牙髓分解是冠内变色的常见原因 ,激光冠内漂白是治疗这种变色的有效手段 ,可以完全恢复患者的自信。     

通讯网的演进

在光纤高速传输技术、光交换与智能光网等与宽带接入、多媒体、3G等网络应用技术的推动下，建设基于IPv6协议的IP基础电信网成为可能。现在IP网正在朝着有序的、可管理的、有QoS保障的、可以支持各类业务的综合业务基础网演进。电信网也正在从网络接入层上、从长途网络层面上、从本地网络层面上、从固定网向含3G在内的移动网络等方面向支持IP技术及其综合业务的方面全面推进。     

振动采油工艺在稠油区的实验研究与应用

在天然地震的影响下,油井产量发生波动,使人们受到启示,从而引进了振动采油工艺技术。本文对振动增产的机理进行了探讨,指出振动增油机理在于加快地层中流体的流速;改变储集层内油、气、水的重新分布;改变岩石表面润湿性,有利于清除油层堵塞,提高渗透率。通过分析两个试验区的振动采油效果,总结出在不同扰动力、不同激振频率、不同振动周期下的增产效果和规律,对振动采油的实施具有一定的指导意义。     

论创新素质

江泽民同志曾多次强调:"创新是一个民族进步的灵魂,是国家兴旺发达的不竭动力."科学的生命力在于创新,教育科学的生命力同样在于创新.时代呼唤创新教育,呼唤创新型人才,而创新人才必须具有较高的创新素质.在创造性活动中,先进、强大的物质技术手段具有突出的作用和意义,但是最重要的工具始终是人的创造性的大脑,这也就是说,从事创造活动需要具备良好的创造性的主观素质和修养.     

Matrix morphology and fibre pull-out strength of T700/PPS and T700/PET thermoplastic composites

The main objective of this fundamental study was to investigate effects of processing conditions and resulting matrix morphology on interfacial bond strength of fibre reinforced thermoplastic composites. Using a hot stage microscope, single fibre pull-out samples were produced with T700S high strength carbon fibre and two semicrystalline thermoplastic matrices, polyphenylene sulphide (PPS) and polyethylene terephthalate (PET), respectively. Processing temperatures and cooling histories were the major variables in sample preparation. The T700S fibre had no clear effect on the surrounding PPS and PET matrix morphology, as long as direct cooling at constant rates was selected. A transcrystalline phase around the fibres could be induced in the T700S/PPS system, if isothermal crystallization was carried out at 227°C. Fibre pull-out tests were conducted at room temperature and two basic failure paths were observed, i.e. debonding at the fibre-matrix interface and cohesive failure of the matrix close to the fibre surface. The results indicate that slow cooling rate and a resulting coarse spherulitic morphology around the fibres correlate with high interfacial shear strength. In fact somewhat higher strength values were obtained for samples with transcrystalline layers around the fibres.     

Calendar maintenance of arbitrarily structured systems

A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics and an optimal term of maintenance work are determined for the system. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006.