当纽约作为世界首都

<正>2001年9月11日上午,站在曼哈顿第五大道的起点华盛顿广场那个凯旋门不远处,眼看着纽约世界贸易中心两栋塔楼相继垮掉,周围人山人海。第一栋塔楼倒下,一位老太太腿软倒地时嗓子里发出奇怪的声音,几个小年轻嘴里蹦出那个音节很短的脏字动词,然后鸦雀无声。看惯了双塔并立的景致,突然没了一栋,仿佛某种构图被破坏。剩下一     

Capteur de resine chelatante pour le prelevement la preconcentration et la determination de metaux traces toxiques (Zn, Cd, Hg, Pb) dans les eaux

The subject of this article is the elaboration of a catcher of toxic metals (Zn, Cd, Hg, Pb) which enables them to be determined at μg 1⁻¹ level.It is known that, at these low concentrations, it is advisable to prevent the sample from being altered in any way between the time of taking and the time of analysis; moreover, it is necessary to proceed, on the one hand, to the pre-concentration of the wanted elements and, on the other hand, to the elimination of the main elements present in water and likely to interfere at the time of analytical determination.We therefore made a catcher which makes it possible to achieve these two desired effects by chromatographic separation and to carry out the conditioning of the sample, in the field, in a well-defined, chemical form, stable in time as a small volume in a solid state, easy to carry and to store.The catcher is in the shape of a small, cylindrical capsule (diameter = 29 mm, thickness = 10 mm) in Makrolon (Lexan) whose bases are made of a nylon cloth and which contains a chelating resin load (Chelex-100, 100–200 mesh).At the time of use, the catcher is put into a dismountable filtering-apparatus which permits percolation of the solution containing the wanted metal traces.Then, to proceed to the analytical determination of the elements it is possible to use two methods: analysis in solution after elution;X-ray fluorescence spectrometry, or else activation analysis on the catcher dried and then pelletized when hot in an hydraulic press.The experimentation has included the following points:

1. 1. Determination of the conditions of chromatographic separation on Chelex-100 resin which permits optimal fixation of Zn, Cd, Hg and Pb and the elution of the main elements Ca, Mg and Fe. We chose soda-citrate medium 7.1 · 10⁻² M at pH = 7.00;

2. 2. Determination of the conditions of use of the catcher and its efficiency according to the main elements in the sample of water.

The process we chose involves a sample of 1 l. of water which is acidified at pH 1 by concentrated HNO₃ and then filtered through a membrane (0.45 μm).The solid residue is examined by X-ray fluorescence spectrometry.To the filtrate are added 100 ml of soda-citrate buffer 7.1 · 10⁻¹ M and the pH is set to seven by addition of NaOH. Then the filtrate is percolated through the Chelex-100 resin catcher (flux = 1.5 ml min⁻¹).Then, it is possible to proceed: either to the elution of toxic metals by HNO₂ 2M to determine them in solution (atomic absorption spectrophotometry, anodic stripping voltammetry); or to pelletizing of the catcher and to the analytical determination by X-ray fluorescence spectromy or activation analysis.The results of these methods are compared with different water: (1) spring warer: (2) over waters and (3) sea-water. The elution method as well as direct analysis of the pelletized catcher gave satisfactory agreement.     

Biodegradability and ecotoxicity of commercially available geothermal heat transfer fluids

Commercially available heat transfer fluids used in borehole heat exchangers were investigated for their composition, their biodegradability as well as their ecotoxicity. The main components of the fluids are organic compounds (often glycols) for freezing protection. Biodegradation of the fluids in laboratory studies caused high oxygen depletion as well as nitrate/iron(III) reduction under anaerobic conditions. Additives such as benzotriazoles for corrosion protection were persistent. Ecotoxicity data show that the commercially available fluids caused much higher ecotoxicity than their main organic constituents. Consequently, with regard to groundwater protection pure water as heat transfer medium is recommended. The second best choice is the usage of glycols without any additives. Effects on groundwater quality should be considered during ecological-economical cost-benefit-analyses of further geothermal energy strategies. The protection of groundwater as the most important drinking water resource must take priority over the energy gain from aquifers.     

埃因霍温Frits Philips音乐厅

知名设计双人组Van Eijk&Van der Lubbe携手Philips Ambient Experience Design合作完成了Frits Philips音乐厅的室内设计。在这里,灯光     

Notes for a Substantive Theory of Rural Planning: Evidence from the US Experience

Rural areas are the locus of many pressing planning issues, pointing to the need for and possibility of a substantive theory of rural planning. In this article we develop a framework for such a theory. We begin by outlining the emergence of planning and the marginalization of ‘the rural,’ by investigating aspects of existing planning theory. Then we explain the framework and apply it to a small set of critical cases in deep rural areas of the U.S. To conclude, we summarize our findings and propose future directions for theory in rural planning.     

Load/unload measurements using laser doppler vibrometry and acoustic emission

The dynamics of the load/unload process are studied using a so-called ‘periscope approach’ which allows us to follow the slider motion during load/unload (L/UL) with the beam of a Laser Doppler Vibrometer (LDV). LDV signals and acoustic emission signals are obtained for three different slider airbearing designs and for load/unload conditions with different vertical velocities and spindle speeds. The load process is investigated statistically using the acoustic emission signal in order to determine the effect of vertical load speed and spindle speed on the probability of contacts between slider and disk.The results indicate that small vertical load speeds decrease the number of head/disk contacts, and that slider designs with a cavity centered close to the trailing edge enable a smooth unloading process.     

Contact force measurement using acoustic emission analysis and system identification methods

Acoustic emission (AE) signals were used to investigate the contact force occurring at the head/disk interface of a computer hard drive. The AE sensor was calibrated directly using the “ball drop method” and indirectly using system identification. For the indirect calibration, a high bandwidth laser Doppler vibrometer (LDV) was used. The transfer function was established from the harmonic response derived at different vibration modes and frequencies. A finite element method based transient response simulation of impact was used to estimate the velocity and stress response of the slider. In our experiments, contact forces were found to be in the range of 5–25 mN for nano sliders and 2–10 mN for pico sliders.     

Investigations of nano- and macro-wear of magnetic tape head materials

The nano- and macro-wear characteristics of calcium titanate, single crystal ferrite and polycrystalline ferrite were investigated using nano-scratch testing and wear bar testing. Nano- and micro-indentations were made to determine nano- and micro-hardness, and nano-scratch testing was used to evaluate relative wear rates on the nano-scale. The macro-wear characteristics of the various head materials against metal particle tapes was investigated as a function of tape speed using wear bars mounted in a DLT tape drive. The micro-indentation method was used to investigate wear of the head/tape interface in a linear tape drive. The results from nano- and macro-wear tests were analysed and correlated with the microstructure of the materials.