New directions in oxidant by-product research: identification and significance

Exciting new research in the field of oxidant by-products in drinking water and wastewater is progressing along three main lines: 1) investigation into the mechanism of the aquatic humic/aqueous chlorine reaction, 2) correlation of by-product identity and yield with mutagenic activity, and 3) analysis of previously intractable organic by-products such as high molecular weight polar substances and N-chloroorganic compounds. Just as earlier research was stimulated by the development of the combined gas chromatograph/mass spectrometer, these new investigations have been fostered by the development of new analytical methods such as solid state C-13 nuclear magnetic resonance spectroscopy, extended mass range mass spectrometry, new ionization techniques such as fast atom bombardment and combined liquid chromatography/mass spectrometry. Application of these new techniques is allowing these and many other important public health questions to be addressed.     

笔记本电脑声卡HD音效测试

许多家庭媒体中心使用PC．甚至是笔记本电脑负责整个系统的内容播放．因此Microsoft Vista对音频的要求就成了电脑声卡及其它相关外设的重要指标,其需要达到HD音频的输出品质。此外．对于空间较小的居住环境,如学生公寓等,笔记本电脑就成了其HD欣赏体验的核心设备。     

AM broadcast antennas with elevated radials: varying the number ofradials and their height above ground

Previous computer-modeling studies indicated that four elevated radials may be used in conjunction with an elevated vertical monopole (tower) to produce radiated field strength which is equivalent to that emitted by a similar monopole using 120 buried radials. Inquiries have been received concerning the effect of increasing the number of elevated radials, and/or changing the height of the radials above ground. Analysis shows that there seems to be an optimum number of elevated radials for each height and soil type. Surprisingly, the continued addition of more and more elevated radials eventually produces a reduction in performance. The computer code used for this work was NEC, a “method of moments” program developed at Lawrence Livermore National Laboratory     

Impedance stability and bandwidth considerations forelevated-radial antenna systems

An examination is made of the variations in feed-point impedance that occur in an elevated antenna system due to changes in the electrical characteristics of the underlying soil. The bandwidth of such antennas is also investigated by looking at deviations in the input impedance as the operating frequency is varied about its nominal value. In all cases, results for the elevated antenna are compared with those of the conventional ground-mounted system. The computer program used for this work was NEC (Numerical Electromagnetics Code), a method-of-moments software package     

Elevated vertical monopole antennas: effects of changes in radiatorheight and radial length

Computer analysis and field tests indicate that an elevated vertical monopole with elevated horizontal radials can provide ground-wave field intensities which are comparable to those generated by a conventional ground-mounted monopole with 120 buried radials. Computer modeling was used to investigate the effects of changes in monopole height and radial length on the transmitted field intensity. The tower height was varied in 45-degree increments from 45° to 225° as was the length of the four elevated horizontal radials. Born the direct and isolated feed methods were utilized, and elevation heights of 5 m and 10 m were modeled. The results show that 90° radials generally give the strongest field strength, irrespective of the radiator height or the feed method. Isolated feed was usually somewhat better than direct feed, and an elevation height of 10 m was slightly superior to a height of 5 m in most cases. Taller towers always produced higher maximum values of electric field strength. Conventional antenna systems with various heights and radial lengths were also modeled to serve as a baseline reference