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排序方式: 共有132条查询结果,搜索用时 375 毫秒
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52.
《Wave Motion》2018
Hammack & Segur (1978) conducted a series of surface water-wave experiments in which the evolution of long waves of depression was measured and studied. This present work compares time series from these experiments with predictions from numerical simulations of the KdV, Serre, and five unidirectional and bidirectional Whitham-type equations. These comparisons show that the most accurate predictions come from models that contain accurate reproductions of the Euler phase velocity, sufficient nonlinearity, and surface tension effects. The main goal of this paper is to determine how accurately the bidirectional Whitham equations can model data from real-world experiments of waves on shallow water. Most interestingly, the unidirectional Whitham equation including surface tension provides the most accurate predictions for these experiments. If the initial horizontal velocities are assumed to be zero (the velocities were not measured in the experiments), the three bidirectional Whitham systems examined herein provide approximations that are significantly more accurate than the KdV and Serre equations. However, they are not as accurate as predictions obtained from the unidirectional Whitham equation. 相似文献
53.
《Physics Reports》2002,362(4):193-301
We review the subject of QCD inequalities, using both a Hamiltonian variational approach, and a rigorous Euclidean path integral approach. 相似文献
54.
《Tetrahedron: Asymmetry》2001,12(8):1121-1124
The first enantioselective synthesis of (S)-5-bromo-3-(1-methyl-2-pyrrolidinyl)pyridine is described via intramolecular hydroboration–cycloalkylation of an azido-olefin intermediate. The chiral homoallylic alcohol was efficiently synthesized by enantioselective reduction of the corresponding ketone using (+)-diisopinocamphenylchloroborane as the key reaction. The total synthesis of (S)-SIB-1508Y was achieved with an enantiomeric excess (e.e.) of 94% in ten steps and in 18% overall yield from the commercially available 5-bromo-3-pyridinecarboxylic acid. 相似文献
55.
《Electrochemistry communications》1999,1(1):22-25
Alternating films constructed upon successive deposition of redox polymer Os(bpy)2ClPyCH2NHpoly(allylamine) and antibiotin IgG were developed for amperometric immunosensor design. Cyclic voltammetric measurements were used to verify charge transport between redox sites and the redox surface concentration was estimated upon voltammetric peak integration. Biotin–antibiotin complex formation was evaluated using horseradish peroxidase as an enzyme label. Redox mediation between the modified electrode surface and the redox site in the enzyme was verified after substrate addition. Multilayer modified gold electrodes with biologically active antibiotin IgG molecules were employed for the development of a competitive immunoassay with electrochemical label detection. 相似文献
56.
本文报道了一种共价有机大环化合物的高效合成方法。利用双咪唑鎓盐H2-L1(BF4)2(L1=A1,B1)和氧化银反应,生成双核银卡宾大环化合物[Ag2(L1)2](BF4)2(L1=A1,B1),其中连接在2个卡宾配体上的端烯取代基分别排列在环的两侧。随后,通过金属卡宾模板导向的烯烃复分解反应进行关环,制备得到闭环的双核银卡宾大环化合物[Ag2(L2)](BF4)2(L2=A2,B2)。最后,移除模板银离子即可得到拥有空腔结构的共价有机大环化合物H4-L2(BF4)4(L2=A2,B2)。此类多咪唑鎓盐大环的尺寸和形状可以通过改变氮杂环卡宾前驱体连接单元的长度或者宽度进行精细调节。初步研究表明,该大环受体在碘离子的传感、检测和识别方面具有潜在的应用前景。 相似文献
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The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is determined by combining both experimental and theoretical aspects. In modeling the process, an optical model is used to determine how the laser beam is attenuated by the first material and to obtain the laser beam profile at the interface. Using this information as the input data to a thermal model, the evolution of the temperature field within the two components can be estimated. The thermal model is based on the first principles of heat transfer and utilizes the temperature variation laws of material properties. Corroborating the numerical results with the experimental results, some important insights concerning the fundamental phenomena that govern the process could be extracted. This approach proved to be an efficient tool in determining the weldability of polimeric materials and assures a significant reduction of time and costs with the experimental exploration. 相似文献
59.
我国钢铁行业上市公司竞争力实证研究 总被引:7,自引:0,他引:7
钢铁行业是我国的传统行业,在国民经济中具有举足轻重的地位。本文采用主成分分析法,分别从盈利能力、偿债能力、运营能力以及成长能力等方面对我国34家钢铁类上市公司的10项财务指标进行了竞争力综合评价;通过对各个上市公司的分类比较,发现了我国钢铁行业存在的一些问题;最后指出产业整合是提高我国钢铁行业整体竞争力的必要途径。 相似文献
60.