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991.
为了适应当前大力开展矿产资源地质勘探和深部找矿的需要,进一步提升金刚石钻头设计制造水平,研制高效率、长寿命新型钻头,促进金刚石钻头产品的产业化,规模化生产,结合从事金刚石锯片等其它工具研制的经验,提出一些新的钻头设计制造思路,供业内同行参考,共同提高。 相似文献
992.
993.
994.
超薄金刚石切割片,由于具有超薄切割槽宽,切割断口平滑,废品率低,切割效率高等优点,已逐步得到人们的重视。文章综述了近10年来超薄金刚石切割片的主要制作方法的研究进展及应用现状,介绍了超薄金刚石切割片的制备方法,包括电镀法和固化树脂法,其中电镀法以其设备简单、绿色环保、可循环生产等优点成为最有可能大规模工业应用的制备方法,文章最后指出了其发展方向。 相似文献
995.
996.
文章系统论述了广东天然气发展的基础和机遇,同时以广东的社会经济发展目标为依据,分析了广东天然气需求和发展设想,并从保障能源供应安全、满足天然气发展需求、实现能源安全和社会稳定,促进广东社会经济又好又快发展等方面研究了加快建立统一长输管网的意义。 相似文献
997.
传统的镀铬工艺,由于其本身的特点,在电镀大型工件和形状复杂零件时,镀层容易产生缺陷,成品率不高.通过对较大零件内孔镀硬铬的工艺过程及产生的缺陷进行考察,分析了产生缺陷的可能原因,提出了避免硬铬镀层产生缺陷的解决措施.实施结果证明:产生原因分析正确,所提改进措施科学合理,实施后硬铬镀层质量有较大的提高. 相似文献
998.
Abstract. We show that tests for a break in the persistence of a time series in the classical I (0)/ I (1) framework have serious size distortions when the actual data-generating process (DGP) exhibits long-range dependencies. We prove that the limiting distribution of a CUSUM of squares-based test depends on the true memory parameter if the DGP exhibits long memory. We propose adjusted critical values for the test and give finite sample response curves that allow easy implementation of the test by the practitioner and also ease in computing the relevant critical values. We furthermore prove the consistency of the test for a simple breakpoint estimator also under long memory. We show that the test has satisfying power properties when the correct critical values are used. 相似文献
999.
大口径长距离顶管施工技术 总被引:1,自引:0,他引:1
根据长距离顶管施工的技术特点,结合无锡市污水排海工程超长距离顶管施工实例,分析了大口径长距离顶管施工中的泥浆减阻、中继间设置、轴线控制等关键施工技术,提出了切实可行的具体技术措施,取得了良好的工程效果。 相似文献
1000.
Use of angle resolved PIV to estimate local specific energy dissipation rates for up- and down-pumping pitched blade agitators in a stirred tank 总被引:1,自引:0,他引:1
A. Gabriele 《Chemical engineering science》2009,64(1):126-5874
Up-pumping pitched blade turbines (and similar impellers) have recently been shown to be particularly effective for achieving a variety of mixing duties. Here, their turbulent flow characteristics are analysed by angle-resolved particle image velocimetry (PIV) for the first time and compared with their down-pumping equivalent, the usual time-averaged parameters also being determined for each. The work was conducted in 0.15 m diameter vessel (T) with a 45° impeller of diameter D (=0.45T) in water. The angle-resolved PIV enables a number of novel features to be identified. Firstly, the two pumping directions are shown to give very different vortex structures, even though the flow numbers, Fl, are the same (=0.79). In addition, the ‘spottiness’ of the normalized kinetic energy along a radius as the trailing vortex moved away from each impeller can be identified, which is not shown from time-averaged data. Often, the most important parameter for processing is the local normalized specific energy dissipation rate, and this is estimated using three methodologies: by measurement of the components of the stress tensor directly, ; by dimensional analysis, , with measured integral length scales (ILS); and by the Smagorinsky closure method, , to model unresolved scales (with a Smagorinsky constant used in the literature on stirred vessels). Again, only the angle-resolved results show the spottiness of and also higher values than the time-averaged. Differences in the values obtained by the three methods are discussed and compared with the existing literature. Most importantly, for the first time, the power input in the PIV-interrogated region is calculated from the three methods and compared to the input based on the impeller torque. Both DA and SGS methods are shown to overestimate the true power by a factor of 5 and 2, respectively, whilst the DE method provided a significant underestimate (1/5th) due to the limitation of the resolved length scales. The SGS method shows the greatest promise and by changing the value of the Smagorinsky constant in accordance with recent recommendations, good agreement is obtained. Nevertheless, it is concluded that there is still a need for improved methods for determining the important mixing parameter, . 相似文献