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1.
 根据行波管内微波信号在输能装置和切断衰减器处两个不连续性之间来回反射的物理现象,建立行波管输出段的简易网络串模型,并对行波管输出段传输特性参数的幅频特性、相频特性进行计算分析。结果表明:输能装置和切断衰减器的不连续性是造成幅相一致性行波管相位不可补偿的重要因素之一。  相似文献   
2.
《Physica A》2006,362(1):204-209
We present a numerical comparison between two Lagrangian techniques for the simulation of fluids, smoothed dissipative particle dynamics (SDPD) and Voronoi fluid particle model. These methods reproduce the movement of the fluid with extensive particles. The main differences between these techniques are the volume definition and the implementation of the second derivatives. The Voronoi model is computationally more efficient than SDPD. For quasi-regular meshes, the Voronoi method is more accurate than SDPD but for arbitrary configurations its precision degrades. This means that the SDPD discrete versions of the second derivative operators are better than the ones used in the Voronoi method.  相似文献   
3.
《Tetrahedron: Asymmetry》2006,17(14):2054-2058
The catalytic enantioselective addition of different organozinc reagents, such as diethylzinc, or in situ generated phenylzinc derivatives to simple ketones was accomplished using titanium tetraisopropoxide and supported chiral ligands derived from trans-1-phenylsulfonylamino-2-isoborneolsulfonylamidocyclohexane, to give the corresponding tertiary alcohols with enantioselectivities up to >99%. A simple and efficient procedure for the synthesis of the disulfonamide monomeric ligand and the corresponding polymerization is described.  相似文献   
4.
The zero-field splittings of sites I and II for Mn2+ in guanidinium aluminum sulfate hexahydrate (GASH) are calculated from the superposition model by using the normal intrinsic parameter 2(R0) obtained from Mn2+ ions in many oxygen octahedra. The results are in good agreement with the experimental findings. Based on this, the local compressibilities and local thermal expansion coefficients in the vicinity of the impurity ion Mn2+ have been studied from the stress and temperature dependence of zero-field splitting and are found to be half of the host ones. The reasonableness of these local values is discussed.  相似文献   
5.
The characteristics of analytical and reference signals (RS) were studied in laser-enhanced ionization (LEI) spectrometry combined with laser ablation of solid samples into a flame. Optoacoustic (OA) and atomic emission (AE) signals have been considered as possible RS. An algorithm of RS selection has been developed. Correlations between LEI signals and RS, which carry information on sample evaporation processes, have been explored. OA (the 1st minimum) and AE (AlI, λ = 396.1 nm) signals were found to be useful as RS (the correlation coefficients were 0.992 and 0.993, respectively). Both RS did not depend on the analyte (Li) content in the sample. It has been shown that the slope of the correlation plots (LEI vs. RS) depends on the Li content in the solid sample. This slope may be used as a novel type of normalized analytical signal, which does not depend on the ablation pulse energy. The influence of both ablating laser radiation characteristics and sample matrix composition on the analytical signal is eliminated (or at least diminished) when using this normalization.  相似文献   
6.
<正> 研究聚合物的结晶动力学,过去大多采用膨胀计法和解偏振光法。曾有文献报道采用反气相色谱法测得聚乙烯等温结晶线。通过实验可知,测定聚丙烯结晶度时,试样热历史和测定前陈化温度的选择均影响测定结果。此外在测定聚丙烯试样的熔点时,保留图中出现了两个转折,经反复实验证实:此两转折对应于聚丙烯中不同晶形(α-、β-形)的熔点。  相似文献   
7.
《Tetrahedron: Asymmetry》2005,16(6):1183-1187
The asymmetric palladium-catalyzed benzylic reaction of 1-(2-naphthyl)ethyl acetate and its 6-methoxy substituted analogue with dimethyl malonate anion led to substitution products with up to 90% ee when the iPr-DUPHOS chiral ligand was used.  相似文献   
8.
《Tetrahedron: Asymmetry》2006,17(16):2328-2333
Chiral dinuclear titanium(IV) complexes (generated in situ from hexadentate Schiff bases and titanium tetra-isopropoxide) have been found to be more effective catalysts for the asymmetric addition of trimethylsilyl cyanide to aldehydes and the ring opening of cyclohexene oxide than their mononuclear analogues. The best results were obtained for benzaldehyde (86% enantiomeric excess) and cyclohexene oxide (89% enantiomeric excess).  相似文献   
9.
分别在静态和动态条件下研究了Friedel—Crafs后交联型聚苯乙烯-二乙烯基苯(St-DVB)大孔吸附树脂对水溶液中多种低级一元醇的吸附性能,测定静态吸附等温线和动态吸附曲线,并分别按照Langmuir和Freundlich模型进行拟合.结果显示,树脂对水中低浓度低级一元醇的吸附过程属于放热的物理吸附过程,树脂吸附能力随着一元醇碳原子数的增加,即分子内疏水基团质量的增加而增加;树脂对直链醇的吸附能力稍强于同分异构的支链醇.  相似文献   
10.

As an important research direction, operational research (OR) has always attracted scholars worldwide. We study the structure, trend and prospect in the OR field by conducting a bibliometric analysis of publications in the period of 1952–2020, which are included in the Web of Science (WoS) database. Using three effective bibliometric tools, namely, VOS viewer, CiteSpace, and Bibliometrix, a total of 5,353 publications were retrieved to show clear visual results using a series of scientific analyses. First, a performance analysis revealed the basic characteristics of publications considering the type distribution, annual trend, quantity and quality. Then, a cooperation analysis presented the influential countries/regions and showed the relationships among countries/regions, institutions and authors during different periods based on bibliometric indicators and co-authorship networks. Moreover, a keyword analysis was conducted to investigate the hot topics and development of the OR field, using co-occurrence analysis, timeline view analysis and evolution analysis. Finally, we discussed the implications and limitations, and summarized the main findings. This study hopes to provide important and valuable references for future research on the OR field.

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