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21.
22.
In this paper we study three-color Ramsey numbers. Let K
i,j
denote a complete i by j bipartite graph. We shall show that (i) for any connected graphs G
1, G
2 and G
3, if r(G
1, G
2)≥s(G
3), then r(G
1, G
2, G
3)≥(r(G
1, G
2)−1)(χ(G
3)−1)+s(G
3), where s(G
3) is the chromatic surplus of G
3; (ii) (k+m−2)(n−1)+1≤r(K
1,k
, K
1,m
, K
n
)≤ (k+m−1)(n−1)+1, and if k or m is odd, the second inequality becomes an equality; (iii) for any fixed m≥k≥2, there is a constant c such that r(K
k,m
, K
k,m
, K
n
)≤c(n/logn), and r(C
2m
, C
2m
, K
n
)≤c(n/logn)
m/(m−1)
for sufficiently large n.
Received: July 25, 2000 Final version received: July 30, 2002
RID="*"
ID="*" Partially supported by RGC, Hong Kong; FRG, Hong Kong Baptist University; and by NSFC, the scientific foundations of
education ministry of China, and the foundations of Jiangsu Province
Acknowledgments. The authors are grateful to the referee for his valuable comments.
AMS 2000 MSC: 05C55 相似文献
23.
Hongwei Lu Yusheng Qin Xianhong Wang Xiangguang Yang Suobo Zhang Fosong Wang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(17):3797-3804
Recently, rare earth ternary coordination catalyst represented as Y(CCl3OO)3‐Glycerin‐ZnEt2 has been used for producing poly(propylene carbonate) (PPC, an alternating copolymer of carbon dioxide and propylene oxide) in industry scale, but its catalytic activity needs further improvement. One reason for the relatively low catalytic activity lied in that only 11.7% of active center was efficient due to possible embedding of active center in the heterogeneous catalyst. In this report, supporting strategy was developed, where Y(CCl3OO)3‐Glycerin‐ZnEt2 was supported on various inorganic oxides. Two supporting methods were carried out. One way was to mix Y(CCl3OO)3‐Glycerin with inorganic oxide first and then ZnEt2 was dropped to form the supported catalyst, and the other was to make Y(CCl3OO)3‐Glycerin‐ZnEt2 at first and then mixing with inorganic oxides. The former showed decreasing catalytic activity compared with corresponding unsupported rare earth ternary catalyst, while an improvement of 16–36% in catalytic activity was realized in the latter. PPC with an average number molecular weight (Mn) of over 100 kg/mol and carbonate unit (CU) content of higher than 96% was prepared by both supported catalysts. The catalytic activity of the supported catalyst depended significantly on the supports, which increased in the following order: α‐Al2O3 < MgO < ZnO ≈ SiO2 <γ‐Al2O3. γ‐Al2O3 was the best support for rare earth ternary catalyst, which showed a remarkable 36% increase in catalytic activity, corresponding to the utilization of 17% of active center. Although MgO supported catalyst gave only an 8% increase in catalytic activity, the Mn and CU content of PPC were raised to about 143 kg/mol and 99%, whereas the PPC from common rare earth ternary catalyst was about 108 kg/mol and 97%, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
24.
25.
Yusheng Qin Xianhong Wang Suobo Zhang Xiaojiang Zhao Fosong Wang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(17):5959-5967
Cobalt porphyrin complex (TPPCoIIIX) (TPP = 5, 10, 15, 20‐Tetraphenyl‐ porphyrin; X = halide) in combination with ionic organic ammonium salt was used for the regio‐specific copolymerization of propylene oxide and carbon dioxide. A turnover frequency of 188 h?1 was achieved after 5 h, and the byproduct propylene carbonate was successfully controlled to below 1%, where the obtained poly(propylene carbonate) (PPC) showed number average molecular weight (Mn) of 48 kg/mol, head‐to‐tail content of 93%, and carbonate linkage of over 99%. When the polymerization time was prolonged to 24 h, PPC with Mn over 115 kg/mol and head‐to‐tail linkage maintaining 90% was prepared, whose glass transition temperature reached 44.5 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5959–5967, 2008 相似文献
26.
Shengqiang Wang Hongtao Lu Jingya Li Dapeng Zou Yusheng Wu Yangjie Wu 《Tetrahedron letters》2017,58(12):1107-1111
An efficient and general protocol for the decarboxylative cross-coupling of pyridazine-3-carboxylic acids with aryl-bromides has been described. This method provides a new avenue for the synthesis of 3-arylpyridazines via decarboxylative cross-coupling strategy by employing the dual-catalyst system of Pd(PPh3)4/Cu2O in the presence of Li2CO3 at 160 °C in DMA. 相似文献
27.
本文用有限解析差分格式研究在多孔介质中化学输运问题的数值模型,系统地计算结果表明:1.有限解析差分格式能够消除数值弥散和伪振荡; 2.随着弥散数(Peclct数)的减小(增加),浓度突破曲线将延迟到达和形状变陡,最终趋近浓度对流曲线;3.当流速数增加后,非稳态吸附对浓度分布的影响趋近稳态吸附的影响。 相似文献
28.
Lijin Qin Hongmeng Cui Dapeng Zou Jingya Li Zhiwu Zhu Yusheng Wu 《Tetrahedron letters》2010,51(33):4445-11097
Pd-catalyzed cross-coupling reaction of tert-butyl carbamate with various aryl(Het) halides with Cs2CO3 as base in 1,4-dioxane as solvent was investigated, which resulted in the formation of the desired compounds in moderate to excellent yields. 相似文献
29.
Yibo Lei Bingbing Suo Yusheng Dou Yubin Wang Zhenyi Wen 《Journal of computational chemistry》2010,31(8):1752-1758
Multireference configuration interaction with single and double excitations (MRCISD) as well as its analytic CI gradients has been implemented in the semiempirical framework. The hole‐particle symmetry and a mixed driven model for computing coupling coefficients have been used in the new code that allows us to perform MRCI and gradient calculations with higher efficiency and less storage requirements. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
30.
断层破碎带中的透镜体及透镜体力学效应研究在文献中不多见。但是许多断层尤其是扭性断层中的透镜体非常发育,这些透镜体往往控制断层破碎带的强度大小和变形破坏机理,是工程岩体中必须重视的工程地质力学问题。作者经研究认为:(1)透镜体类型多种;(2)透镜体周边一般具断层泥线或泥膜分布;(3)透镜体内具有节理裂隙系统;(4)透镜体周边可以当作结构面或软弱结构面看待;(5)透镜体本身可以作为一个复合结构体看待。在原位力学试验中也揭示了断层泥透镜体在原位剪切试验和单轴压缩试验中的若干力学行为,其表现是:(1)透镜体周边具有结构面力学效应;(2)断层泥透镜体控制着强度大小、变形破坏机理。 相似文献