A vibrational study of the activation sequence of C–H and C–C bonds of isobutene and 1-butene on Mo(110) and (4 × 4)-C/Mo(110) surfaces

The thermal decomposition pathways of isobutene and 1-butene on both Mo(110) and 4 × 4-C/Mo(110) surfaces have been studied using high-resolution electron energy loss spectroscopy (HREELS) in order to highlight the substantially different activities of these two surfaces towards the cleavage of C–H and C–C bonds. On clean Mo(110), the CH₂ group of isobutene decomposes upon heating to 150 K, producing either a /-bonded isobutenylidene [(CH₃)₂CCH] species or a 1,1-di-/-bonded isobutenyl [(CH₃)₂CC] species. Upon further heating, extensive C–H bond scission occurs to form hydrocarbon fragments which do not contain CH₃ or CH₂ groups, but appear to have largely intact carbon skeletons. By contrast, isobutene is molecularly adsorbed on the carbide-modified surface at 150 K. Further heating produces isobutylidyne [(CH₃)₂HCC] by 300 K, which subsequently decomposes via C–C bond scission to generate surface methyl groups. The different activation sequence of the C–H and C–C bonds of isobutene on clean and carbide-modified Mo(110) surfaces is also qualitatively confirmed by comparative studies of 1-butene on the two surfaces.     

Streamflow alteration and habitat ramifications for a threatened fish species in the Central United States

In the Central United States, the Arkansas darter (Etheostoma cragini) is listed as a threatened fish species by the State of Kansas. Survival of the darter is threatened by loss of habitat caused by changing streamflow conditions, in particular flow depletion. Future management of darter populations and habitats requires an understanding of streamflow conditions and how those conditions may have changed over time in response to natural and anthropogenic factors. In Kansas, streamflow alteration was assessed at 9 U.S. Geological Survey streamgages in 6 priority basins with no pronounced long‐term trends in precipitation. The assessment was based on a comparison of observed (O) and predicted expected (E) reference conditions for 29 flow metrics. The O/E results indicated a likely or possible diminished flow condition in 2 basins; the primary cause of which is groundwater‐level declines resulting from groundwater pumping for irrigated agriculture. In these 2 basins, habitat characteristics adversely affected by flow depletion may include stream connectivity, pools, and water temperature. The other 4 basins were minimally affected, or unaffected, by flow depletion and therefore may provide the best opportunity for preservation of darter habitat. Through the O/E analysis, anthropogenic streamflow alteration was quantified and the results will enable better‐informed decisions pertaining to the future management of darters in Kansas.     

一种改进的共面波导馈电圆极化天线阵

针对传统平面阵列天线圆极化轴比带宽窄的不足,将顺序旋转馈电技术与共面波导馈电相结合,对一种共面波导馈电的圆极化天线阵进行了改进,适当选择天线单元的旋转角度并对馈线进行相应的相位补偿,就可以增加圆极化天线阵的轴比带宽.仿真结果表明,改进后的阵列天线轴比带宽由传统的0.9%增加到3.7%,同时阵列天线的阻抗带宽也由传统的3.2%增加到6.9%.     

积层多层板用UV油墨的合成研究

采用丙烯酸改性环氧树脂E－44的方法，合成了环氧丙烯酸酯预聚物，并将其用在UV光固化油墨的配方中。在树脂合成过程中，研究了反应温度，催化剂，阻聚剂等因素对合 产品的影响。通过L9(3^4)正交试验，得到了优化的工艺参数：反应温度为90℃，催化剂为N，N－二甲苯胺，用量1％；阻聚剂对苯二酚，用量0．5％，投料环氧树脂和丙烯酸的摩尔比为1：1．08。     

Hybrid control of graphite cast iron structure by partial melt treatment process

The Modified Inmould Process, which forms a cast iron-graphite hybrid alloy with a spheroidal/flake graphite structure (SG/FG), has been developed by the author.^1-3 Though this process can easily control the transitional structure of SG/FG, there are some mild restrictions caused by rapid collision during the mixing of molten metals in the mould on pouring. In this study, a new experimental process was designed to solve this difficulty. The plate-like mould cavity was separated into a reaction chamber (RC) and a product cavity by a thin dam. An alloy of FeSiMg for spheroidization of base molten metal was prepared in the reaction chamber. Molten metal was poured up from the bottom of the product cavity and a part of it flowed over the dam into the reaction chamber. After being spheroidized in the reaction chamber, spheroidal graphite (SG) iron melt flowed backward into the product cavity. The density of SG molten iron with a higher carbon equivalent value is generally lower than that of flake graphite (FG) molten metal. Thus SG molten metal moved into the upper end of the product cavity by replacement of the base metal, while the base metal remained stationary at the lower end of the cavity. As a result of the phenomena of flow, movement and replacement between mutual melts, a SG/FG transitional layer structure was formed, downward, throughout the cast product.     

Small to medium size wind turbines: Local use of a local resource : Paper prepared for the World Renewable Energy Congress-V Florence, 20–25 September 1998

At a time when wind turbines are getting larger, and the electricity injected into the grid from turbines is becoming more competitive, VERGNET has chosen the small scale wind turbine side of the wind energy market to develop its business.     

Editorial

Ozone applications in Canada began in 1954 and have shown continuous growth with the largest installation at the Charles des Baillets drinking water plant in the city of Montreal. Many systems have been installed for treatment of swimming pools, odor control and, in particular, cooling towers. One of the world's largest cooling tower applications is at the Alberta Natural Gas Plant. The use of ozone is expected to continue to grow.     

Plasma etching optimization of oxide/nitride/oxide interpolydielectric breakdown time in flash memory devices

The breakdown time of flash memory oxide/nitride/oxide (ONO) layer t_bd under positive constant current stressing has been found to be closely related to the cumulative extent of (over)etch of the tungsten silicide, control polysilicon, and ONO layers, i.e., Σ(ΛOE). An empirical first-order relation between t_bd and Σ(ΛOE) has been derived to facilitate the plasma etch recipe optimization. This has led to a four-fold increase in the average t_bd across a 200-mm wafer to 208 s. More importantly, the spread in t_bd has been tightened to ~5%, which is down from ~54%     

A Study on the mathematical modeling of turbulent recirculating flows in gas-stirred ladles

Computed results are presented describing the velocity field and the map of the turbulent kinetic energy in a water model of an argon-stirred ladle. The theoretical predictions agree well with the measurements, when an experimentally determined void fraction distribution is used in computing the body force driving the flow. The agreement is somewhat less satisfactory, particularly regarding the maps of the turbulent kinetic energy, when the no-slip or the drift flux models are used to predict the void fraction of the gas.