采用电滤波方式从20Gbit／s的光信号中提取2.5GHz的电时钟

采用增益开关激光器作光源，利用色散补偿光纤对超短光脉冲进行了压缩。利用光纤延时的办法得到了８×２．５Ｇｂｉｔ／ｓ的ＯＴＤＭ信号。采用高Ｑ电滤器滤波的方式成功地从８×２．５Ｇｂｉｔ／ｓ的光信号中提取出了２．５ＧＨｚ的电时钟信号。提取出的电时钟抖动量小于１％。     

应用于全光网络的取样布拉格光纤光栅Interleaver设计

基于取样光纤布拉格光栅(SFBG)的光Interleaver能将一路光信号解复用为两路奇偶波长信号,具有插入损耗低、各信道反射率均匀和低色散等优点,特别适用于未来全光DWDM中波长复用/解复用、插入/分离。为此介绍了取样光栅Interleaver的基本设计理论,给出了设计实例,对取样光栅Interleaver等光器件的实用化有一定的参考意义。     

单腔双光梳激光器及其应用研究

双光梳技术凭借其超高的频率分辨力与检测精度成为当今科研领域探索的重点。本文分别介绍了利用电光调制、微谐振腔、相位锁定两台独立的锁模激光器、单腔双光梳激光器产生双光梳的方法,重点阐述了基于单腔双波长激光器的双光梳产生方法集成度高、结构较简单、成本低的优势;之后详细介绍了目前单腔双光梳激光器中,双波长腔内运转的脉冲波形复用法、空间复用法、方向复用法、波长复用法和偏振复用法的工作原理及最前沿的研究进展;最后,具体分析了单腔双光梳在光谱学、测距、光纤传感等领域的应用情况,并展望未来单腔双光梳的研究与发展方向,为推动单腔双光梳技术性能的进一步提升和广泛应用提供借鉴。     

有理数谐波锁模SOA光纤环形激光器数值研究

采用自再现理论,对工作在有理数谐波锁模时的半导体光放大器(SOA)光纤环形激光器进行了研究.为了获得振幅均衡的有理数谐波锁模脉冲,必须在原有的实验装置中添加一个掺铒光纤放大器(EDFA)以提高注入调制光信号功率.数值结果表明,调制SOA的偏置电流和注入调制光信号功率对有理数谐波锁模脉冲的振幅均衡度都存在较大影响.合理选择调制SOA的偏置电流和注入调制光信号功率,可获得2～5阶振幅均衡的有理数谐波锁模脉冲序列.     

基于有源光纤环路的光缓存单元

设计了一个低噪声的EDFA,结合0.8nm的窄带光滤波器,采用长为10439m的标准单模光纤,构成了一个有源光纤环路.对其输出特性进行了详细的测试,测试结果表明该系统具有良好的信号复制能力.基于此设计了一个光缓存单元,描述了其存储原理,定义了其单位缓存时间和最大缓存时间,实验表明该光缓存单元实现了光脉冲信号的缓存,单位缓存时间约为50 μs,复制光脉冲个数在500个以上,相应的最大缓存时间约为25 ms.     

一种基于FPGA的压控晶振同步频率控制系统

晶振时钟信号存在长期稳定度差和累积误差的问题。本文是利用GPs提供的1pps秒脉冲信号,在FPGA的基础上利用干扰秒脉冲信号消除和偏差频率平均运算等方法,减少外围电路,既消减了GPS时钟信号的随机干扰误差,又消除了本地晶振时钟信号的累计误差,从而控制本地压控晶振输出频率,提高晶振的长期稳定性。     

基于GPS的目标飞行时间异地高精度测量技术

针对远程目标异地作用的特性以及异地时间测量对时间统一标准的严格要求,提出了一种基于GPS的高精度异地目标光信号时间测量系统.该系统将GPS授时与本地温补晶振时钟结合起来,利用GPS授时秒脉冲1 pps进行时间同步,由本地时钟结合GPS的标准时间测量出飞行目标启动和停止的精确时间及时间间隔;同时设计了高精度的授时方案,对GPS秒脉冲进行监控和补偿,有效提高了系统的可靠性.实验表明,该系统测量在400 s内所产生的累积测量误差小于300μs,等效精度达到7.5×10-7.     

一种数字时钟的校准方法及验证装置

为准确测量数字时钟示值偏差,保障数字时钟溯源的有效性,提出并设计一种数字时钟的校准方法及验证装置。采用PIN结硅光电二极管对数字时钟的数码管进行检测,将多路检测信号运算放大,与阈值电压进行比较后输出逻辑电平,再经过秒脉冲发生电路输出秒脉冲信号与标准时间秒脉冲进行比较测量。实验表明,验证装置延时223.4ns,不确定度为100.1ns(k=1)。     

石油射孔用的爆破系统

爆破系统１０特别适用于地下环境，例如石油开采和生产。爆破装置２里含有装药３，它可由预置频率和功率和激光脉冲束起爆。激光脉冲由激光器６发出，沿发纤５向下传递并通过光分离器４，光分离器４只允许上面提取的预置频率的光脉冲通过，并将所有其它频率的光反射掉。为检测光纤的完整性，第二激光器１１发出一个测试信号沿光纤传输。测试信号的频率不同与起爆信号的频率，功能也远低于起爆信号的功率，因而它能光分离器反射并沿光     

电影与电视技术的结合点——数字化(下)

4、数字化的实现1)A/D(模—数)转换,见图6。 模拟信号就是用电信号的值来模拟被代表图象信号的值,如果传送的图象是由光组成的,模拟信号值就是代表光的强弱;如果是声音,就是代表声音的大小。 模拟信号来了后,就要抽样。要抽样,就要脉冲,这里就需要一个时钟源,当时钟脉冲到来     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.