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1.
《Journal of the European Ceramic Society》2005,25(2-3):129-135
A poly(aminoborazine), precursor for hexagonal boron nitride (h-BN) obtained by reaction of borazine B3N3H6 with ammonia, and its pyrolysis derivatives have been extensively characterised by 15N and 11B MAS NMR. The various B and N sites have been identified according to their first neighbouring atoms, as well as to the second ones in the case of 15N, and have also been quantified. This study demonstrates that a suitable choice of NMR techniques together with the use of isotopic enrichment can lead to a large improvement in spectral resolution, which allows a better understanding of such complex BN preceramic polymer structures and permits to follow the polymer-to-ceramic transformation. 相似文献
2.
反距离加权法流场矢量插值研究 总被引:1,自引:0,他引:1
为解决非结构网格下诸多水流模型计算所得流场(流速、水位和通量等)在后处理图中显示凌乱(不利于反映流场特征)的问题,运用反距离加权法对非结构网格的流场结果进行插值,得到任意目标结构网格下的流场值.该方法应用于实际工程中,插值结果与原计算结果吻合较好,满足工程精度要求. 相似文献
3.
Cadmium in agricultural soils,vegetables and rice and potential health risk in vicinity of Dabaoshan Mine in Shaoguan,China 总被引:6,自引:0,他引:6
Soil cadmium (Cd) contamination resulted from mining and smelting is a major environmental concern,and health risk associated with Cd exposure to multi-media through muti-pathway is increasing.Cd concentrations in soils,vegetables and paddy rice were investigated,and potential non-carcinogenic and carcinogenic health risks exposure to Cd were estimated at six villages around the Dabaoshan Mine,South China.A total of 87 soil samples were found to exceed the China's maximum permission level (MPL) for Cd,while the highest value of 4.42 mg/kg was found near irrigation ditch associated with Hengshi River in Xinyi (XY) Village.Cd contents in vegetables and rice exceeded the maximum permissible concentration by more than five times in every village.Cadmium accumulation in plants is in the order of celery 〉 lactuca sativa L 〉 Chinese cabbage 〉 Romaine lettuce 〉 asparagus lettuce 〉 mustard 〉 cabbage mustard 〉 cabbage.The mean hazard quotient (HQ) of all villages is in the range of [5.29,25.75],and the mean values of cancer risk for investigated areas are more than 10 times greater than the USEPA (2009) threshold limit value of 10-4.Moreover,human non-carcinogenic and carcinogenic risks are mainly attributable to paddy rice intake,followed by vegetables intake,soil ingestion,inhalation,and dermal contact.The results indicate that Cd has a huge potential risk on human health for the local residents. 相似文献
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水库温度分层使水库水动力特性及污染物输移过程异于均温型水库.采用三维非线性RNG浮力流模型对分层水库污染物输移的典型过程进行模拟,分析了水体分层条件对污染物输移的影响,探讨了不同分层条件下污染物在不同密度流流动区域射流区、交换区、潜流区的输移扩散规律.研究结果表明,水库分层条件对污染物输移有显著影响,污染物输移的分离点水深、交换区厚度、无量纲时间参数与水库分层强度成反比.研究结果可为水库水质、水生环境管理与调度、水库应急预警方案的制定提供参考. 相似文献
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Ceria catalysts supported on sulfated zirconia showed a remarkable resistance towards alkali metal poisoning in selective catalytic reduction of NO by NH3. TPD results revealed sulfation treatment of supports produced massive acid sites on the surface of catalysts. Adequate acidity was of importance for the enhanced resistance to alkali metal ions. The introduction of potassium did not affect the crystalline phases and morphology of catalysts, but it could lead to higher surface areas of samples. 相似文献
8.
While domain reduction has been successfully applied in branch-and-bound based global optimization over the last two decades, it has not been systematically studied for decomposition based global optimization, which is usually more efficient for problems with decomposable structures. This paper discusses integration of domain reduction in Benders decomposition based global optimization, specifically, generalized Benders decomposition (GBD) and nonconvex generalized Benders decomposition (NGBD). Revised GBD and NGBD frameworks are proposed to incorporate bound contraction operations or/and range reduction calculations, which can reduce the variable bounds and therefore improve the convergence rate and expedite the solution of nonconvex subproblems. Novel customized bound contraction problems are proposed for GBD and NGBD, and they are easier to solve than the classical bound contraction problems because they are defined on reduced variable spaces. The benefits of the proposed methods are demonstrated through a gas production operation problem and a power distribution system design problem. 相似文献
9.
苯乙烯是一种极易自聚的物质,不加以控制会导致温度持续上升甚至引发储罐爆炸。苯乙烯为可疑致癌物,具刺激性。一旦发生事故,对环境具有严重的危害。本文根据苯乙烯的特性,从设备选型、工艺流程、安全检测等方面对苯乙烯储罐的安全设计进行分析和讨论。 相似文献
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