波音梦幻飞机的奋斗历程:大吃一惊还是意料之中?

当一家航空航天公司不得不取消首飞这样的重大计划时,事情的原因可能很复杂     

与BI过招

企业BI何时才能发挥其最大价值？答案很简单：当它与公司业务融合被一线员工和经理所用，并且有可能协力那些与客户及重要合作伙伴接触的人，帮助他们做出最优决策时。     

如何解决锁模不均

有一个简单的方法，可以确保两个半模在分模线处得到正确匹配，即调平注塑机以及使模板保持平行。调平注塑机的方法是：首先，找到机器基座上的所有调平螺栓，调节它们，使它们的扭矩大小一致。然后，在定模板附近的拉杆或模板支座处放置一个水平仪，在机器后端的拉杆或模板支座处放置另一个水平仪，并将第三个水平仪沿纵向放置在拉杆或模板楚座上。     

直线电机取代滚珠丝杠？

最近,有位Control Engineering杂志的读者提问说：＂每当我听到数控铣床系统中预示着滚珠丝杆即将损坏的声音时,就会情不自禁想到,     

英国国家电网公司在电力系统状态估计器及安全分析方面的经验

本文叙述了由安装在英国国家电网公司新国调中心的新型能量管理系统所提供的实时网络分析的应用，并介绍了第一年的运行经验．对经常出现的某些状态估计问题的解决方法和作者所作的尝试的结论进行了讨论，以对安全估计器的结果与现有的离线研究方法的结果进行比较．文章还对应用实时网络分析时遇到的一些原始缺陷的观察结果和在短时段及较长时段内解决这些问题的方法进行了讨论．     

Specific UV absorbance of Aldrich humic acid: changes during transport in aquifer sediment

This study examined the transport behavior of Aldrich humic acid (AHA) in low natural organic carbon content sediment contaminated with tetrachloroethene (PCE), for comparison to a nonionic surfactant mixture previously examined in the same system. Tracking of individual molecular weight (MW) fractions of AHA was attempted by UV absorbance, followed by conversion to mass of carbon using specific ultraviolet absorbance (SUVA) (UV absorbance per mass of carbon) measurements. The analysis required determination of variations of SUVA with MW, which showed a maximum at 10 000 Daltons. Furthermore, SUVAs of AHA MW fractions greater than about 10 000 Daltons increased following AHA interaction with sediment in batch experiments, and this was associated with AHA-driven leaching of cations from the sediment. AHA transport was examined in a series of three columns representing the up-gradient, residual-zone, and down-gradient portions of a DNAPL contaminated site. SUVAs of larger MW AHA fractions cycled through decreased, increased, and eventual return to influent values during the early, intermediate, and final stages of breakthrough, respectively. These variations were attributable to a combination of preferential adsorption of low MW fractions of the AHA during early breakthrough and AHA-driven leaching of sediment cations during intermediate breakthrough, with eventual exhaustion of sediment cation complexation during the final stage of breakthrough. The complex variations in SUVA precluded accurate conversion of measured UV absorbance to carbon mass. However, the effect of AHA loss to sediment on the solubilizing capacity of the AHA solution was indicated by the breakthrough behavior of AHA-solubilized PCE, which showed that AHA loss from the aqueous phase during transport in this system did not decrease the solubilizing capacity of the AHA mixture.     

Synthesis of nanoparticles of barium lanthanum hafnium oxide by a modified combustion process

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba2LaHfO5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO3, La2O3, and HfO2 that had been heated at 1200 degrees C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba2LaHfO5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba2LaHfO5.5 synthesized by the present combustion technique could be sintered to > 97% of the theoretical density at a relatively low temperature of 1425 degrees C. Scanning electron microscopic studies on the sintered Ba2LaHfO5.5 samples showed that the final grain size of the sintered specimen was < 500 nm.     

Determination of bacterial activity by use of an evanescent-wave fiber-optic sensor

A novel technique based on fiber-optic evanescent-wave spectroscopy is proposed for the detection of bacterial activity in human saliva. The sensor determines th e specific concentration of Streptococcus mutans in saliva, which is a major causative factor in dental caries. In this design, one prepares the fiber-optic bacterial sensor by replacing a portion of the cladding region of a multimode fiber with a dye-encapsulated xerogel, using the solgel technique. The exponential decay of the evanescent wave at the core-cladding interface of a multimode fiber is utilized for the determination of bacterial activity in saliva. The acidogenic profile of Streptococcus mutans is estimated by use of evanescent-waveabsorption spectra at various levels of bacterial activity.     

Non-curated distributed databases for experimental data and models in neuroscience

Neuroscience is generating vast amounts of highly diverse data which is of potential interest to researchers beyond the laboratories in which it is collected. In particular, quantitative neuroanatomical data is relevant to a wide variety of areas, including studies of development, aging, pathology and in biophysically oriented computational modelling. Moreover, the relatively discrete and well-defined nature of the data make it an ideal application for developing systems designed to facilitate data archiving, sharing and reuse. At present, the only widely used forms of dissemination are figures and tables in published papers which suffer from inaccessibility and the loss of machine readability. They may also present only an averaged or otherwise selected subset of the available data. Numerous database projects are in progress to address these shortcomings. They employ a variety of architectures and philosophies, each with its own merits and disadvantages. One axis on which they may be distinguished is the degree of top-down control, or curation, involved in data entry. Here we consider one extreme of this scale in which there is no curation, minimal standardization and a wide degree of freedom in the form of records used to document data. Such a scheme has advantages in the ease of database creation and in the equitable assignment of perceived intellectual property by keeping the control of data in the hands of the experts who collected it. It does, however, require a more sophisticated infrastructure than conventional databases since the software must be capable of organizing diverse and differently documented data sets in an effective way. Several components of a software system to provide this infrastructure are now in place. Examples are presented, showing how these tools can be used to archive and publish neuronal morphology data, and how they can give an integrated view of data stored at many different sites.     

认证方式是时候和用户名密码认证说“再见”了吗？

记得从在学校开始接触计算机时，第一个操作就是输入用户名和密码。如今从单机到网络，每个人都要记住许多的用户名和密码，众所周知，这种基本的认证方式虽然有问题，也有了一些替代的认证方式，但是好像用户名和密码还没有到能够被抛弃的时候。[编者按]