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51.
七里北地区钻井工程地质特征及提高钻速的技术途径 总被引:2,自引:1,他引:1
七里北潜伏构造南邻渡口河、北邻铁山坡,这些构造均在飞仙关鲕滩钻获良好的天然气,具有很好的勘探前景。七里北1井钻探表明,该井在飞仙关地层获天然气80×104m3,但储层埋藏深度达5600m,且侏罗系地层的钻井工程地质条件与相邻构造有显著差异,钻井速度低和钻具事故多这两大问题突出,严重制约了探井钻井速度。认真分析了七里北1井的钻井工程地质特征,有针对性地提出提高飞仙关探井钻井速度的技术途径,有利于解决钻井工程面临的突出问题,对加快该地区飞仙关鲕滩气藏的勘探速度有着重要意义。 相似文献
52.
Prediction of brittle-to-ductile transitions in polystyrene 总被引:1,自引:0,他引:1
In this study it is attempted to predict brittle-to-ductile transitions (BDTs) in polystyrene blends, induced either by an increase in temperature or by a decrease in inter-particle distance. A representative, two-dimensional volume element (RVE) of a polystyrene matrix with 20% circular voids, is deformed in tension. During deformation a hydrostatic-stress based craze-nucleation criterion [1] is evaluated. The simulations demonstrate that crazes initiate at low temperatures while a transition from crazing to shear yielding (BDT) is found around 75 °C. The numerical results correlate well with tensile tests on similar heterogeneous polystyrene. The presence of an absolute length, as experimentally found, is more difficult to explain. Near a free surface a Tg-depression is measured for polystyrene and also the resistance to indentation in polystyrene is lower than expected from bulk properties. Both observations are rationalised by an enhanced segmental mobility of chains near a free surface. As a consequence of these findings, an absolute length-scale could be incorporated in the numerical simulations. For simplicity, the length-scale is modelled by taking a temperature gradient over a thin layer near the internal free surfaces of the RVE. Deformation of the RVE with different absolute length-scales shows that indeed also the experimentally found brittle-to-ductile transition can be predicted if the ligament thickness between the inclusions (‘voids’) in polystyrene is below a critical value of ca. 15 nm. 相似文献
53.
层序单元体系域划分及勘探意义 总被引:3,自引:3,他引:0
体系域是层序地层学理论体系中的重要概念,在隐蔽油气藏的勘探中,勘探家们极为重视低位体系域。但体系域的成因意义、是否有不同级别层序的体系域以及如何划分,在实际工作中认识不一致。结合勃海湾盆地的勘探实例,分析体系域的成因机制、组合特征和勘探规律,认为:体系域是基准面变化等因素作用的产物,不同级别的层序都发育着与其对应的体系域:一般情况下,三级层序对应的体系域单元与含油气层的规模相匹配,但四级层序对应的体系域才是隐蔽油气藏赋存的有利部位。图5参6。 相似文献
54.
Ouzounov S. Hegt H. van Roermund A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(5):399-403
A new type of sigma-delta modulator that operates in a special mode named limit-cycle mode (LCM) is proposed. In this mode, most of the SDM building blocks operate at a frequency that is an integer fraction of the applied sampling frequency. That brings several very attractive advantages: a reduction of the required power consumption per converted bandwidth, an immunity to excessive loop delays and to digital-analog converter waveform asymmetry and a higher tolerance to clock imperfections. The LCMs are studied via a graphical application of the describing function theory. A second-order continuous time SDM with 5 MHz conversion bandwidth, 1 GHz sampling frequency and 125 MHz limit-cycle frequency is used as a test case for the evaluation of the performance of the proposed type of modulators. High level and transistor simulations are presented and compared with the traditional SDM designs. 相似文献
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56.
概述了电磁干扰(EMI)和电磁兼容(EMC)的基本知识,对DC/DC电源中的电磁干扰进行了综合分析,并给出了各自的解决方案。 相似文献
57.
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59.
van Schoor G. van Wyk J.D. Shaw I.S. 《Industrial Electronics, IEEE Transactions on》2003,50(3):546-553
A hybrid power compensator (HPC) consisting of a static VAr compensator and a dynamic compensator needs to be optimally controlled during the compensation of nonlinear loads. The HPC must be controlled to meet minimum requirements in terms of power factor and harmonic distortion, while at the same time minimizing its total cost. An artificial neural network (ANN) is used to control the HPC amidst a very dynamic power system environment. The performance of a reference ANN is evaluated while controlling an HPC connected to a typical nonlinear industrial load. The training and performance of the ANN is then optimized in terms of training set size, training set packing and ANN topology and the performance compared to the reference ANN. This paper highlights the importance of optimising the mentioned ANN parameters to achieve optimum ANN training and modeling accuracy. The results obtained reveals that the application of an ANN in controlling an HPC is feasible given that the ANN parameters are chosen appropriately. 相似文献
60.
A review of the literature on the impact of sexual contacts between adults and boys reveals the existence of two principal outcomes: 1) some participants develop various disorders once in adulthood, such as behavioural problems, sexual disorders, or personality problems; 2) some participants do not present with any major disorders in the long run. These different outcomes may be associated with several moderating variables related to the sexual contacts, such as the level of coercion at the time of these contacts, the bond between the child and the adult, or the context of the sexual relation. However, the conclusions relating to the relations between early sexual contacts with adults and subsequent problems of adaptation in adulthood are difficult to determine. This is because of various methodological problems associated with relevant studies (i.e., definition of these contacts, nature of the sample, method evaluation, statistical analyses). In this article, we propose certain avenues of research that may help clarify this problem. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献