The influence of oxidation reduction potential and water treatment processes on quartz lamp sleeve fouling in ultraviolet disinfection reactors

Ultraviolet (UV) disinfection systems are incorporated into drinking water production facilities because of their broad-spectrum antimicrobial capabilities, and the minimal disinfection by-product formation that generally accompanies their use. Selection of an optimal location for a UV system within a drinking water treatment facility depends on many factors; a potentially important consideration is the effect of system location on operation and maintenance issues, including the potential for fouling of quartz surfaces. To examine the effect of system location on fouling, experiments were conducted at a groundwater treatment facility, wherein aeration, chlorination, and sand filtration were applied sequentially for treatment. In this facility, access to the water stream was available prior to and following each of the treatment steps. Therefore, it was possible to examine the effects of each of these unit operations on fouling dynamics within a UV system. Results indicated zero-order formation kinetics for the fouling reactions at all locations. Increases in oxidation reduction potential, caused by water treatment steps such as aeration and chlorination, increased the rate of sleeve fouling and the rate of irradiance loss within the reactor. Analysis of metals in the sleeve foulant showed that calcium and iron predominate, and relative comparisons of foulant composition to water chemistry highlighted a high affinity for incorporation into the foulant matrix for both iron and manganese, particularly after oxidizing treatment steps. Fouling behavior was observed to be in qualitative agreement with representations of the degree of saturation, relative to the metal:ligand combinations that are believed to comprise a large fraction of the foulants that accumulate on the surfaces of quartz jackets in UV systems used to treat water.     

伊斯坦布尔之路:"人居Ⅱ"大会对规划师和建筑师的挑战

本文第一部分首先回顾了"人居Ⅱ"大会的成果--<人居议程>(The Habitat Agenda)以及联合国人居中心(The UNCentre for Human Settlements)进一步的行动计划并讨论引向这一高峰的背景.第二部分概述了"人居Ⅱ"的成果,分析其出现的前因后果.第三部分研究"人居Ⅱ"之后各界的反应,介绍了一些组织的相应举措.最后一部分阐明了人居会议对于规划和建筑领域的实践、研究和教育的启发意义,提出急需对教育和实践进行鉴定研究和重新定位.     

England's Town Development Act: 1952: PART I: Background of the Act

The land use model recasts an unsuccessful urban form of the past. Concentric rings of declining land value begin at the intense, historic center and grade down through concentric rings to become the city plan. Little planning remains after such a model is accepted. The new freedom of the auto-age city is lost to the principle of a falling body. Further, the land use model plan restricts mobility of resident and employer by type, each to his ring Urban land value patterns are sustained by public action or inaction. A true city plan musters this power to form the best possible city.     

苏格兰小城镇：面临威胁的遗产

作为英国的一部分,苏格兰拥有其地方议会以及大量小城镇。在国际经济形势变化的冲击下,由于缺乏国家和地方政府的持续关注以及自身的某些局限性,苏格兰小城镇正面临重大挑战。尤其是那些位于偏远地区并失去传统产业支柱的小城镇,表现出较高的脆弱性。小城镇遗产保护是环境更加可持续发展的重要组成部分。创新性再定位,以及苏格兰建筑环境论坛提出的＂小城镇体检＂,为小城镇保护提供了新的思路和方法。     

Low Complexity Rake Receivers in Ultra-Wideband Channels

One of the major issues for the design of ultra-wideband (UWB) receivers is the need to recover the signal energy dispersed over many multipath components, while keeping the receiver complexity low. To this aim we consider two schemes for reduced-complexity UWB Rake receivers, both of which combine a subset of the available resolved multipath components. The first method, called partial Rake (PRake), combines theirs/ arriving multipath components. The second is known as selective Rake (SRake) and combines the instantaneously strongest multipath components. We evaluate and compare the link performance of these Rake receivers in different UWB channels, whose models are based on extensive propagation measurements. We quantify the effect of the channel characteristics on the receiver performance, analyzing in particular the influence of small-scale fading statistics. We find that for dense channels the performance of the simpler PRake receiver is almost as good as that of the SRake receiver, even for a small number of fingers. In sparse channels, however, the SRake outperforms the PRake significantly. We also show that for a fixed transmitted energy there is an optimum transmission bandwidth     

Multipath Aided Rapid Acquisition: Optimal Search Strategies

In this paper, we propose a search technique that takes advantage of multipath, which has long been considered deleterious for efficient communication, to aid the sequence acquisition in dense multipath channels. We consider a class of serial-search strategies and use optimization and convexity theories to determine fundamental limits of achievable mean acquisition times (MATs). In particular, we derive closed-form expressions for both the minimum and maximum MATs and the conditions for achieving these limits. We prove that a fixed-step serial search, a form of nonconsecutive serial search, achieves a near-optimal MAT. We also prove that the conventional serial search, in which consecutive cells are tested serially, should be avoided as it results in the maximum MAT. Our results are valid for all signal-to-noise ratio (SNR) values, regardless of the specifics of the detection layer and the fading distributions