A proper edge coloring of a graph G is called acyclic if there is no 2-colored cycle in G. The acyclic chromatic index of G, denoted by χ'a(G), is the least number of colors such that G has an acyclic edge k-colo...A proper edge coloring of a graph G is called acyclic if there is no 2-colored cycle in G. The acyclic chromatic index of G, denoted by χ'a(G), is the least number of colors such that G has an acyclic edge k-coloring. Let G be a graph with maximum degree Δ and girth g(G), and let 1≤r≤2Δ be an integer. In this paper, it is shown that there exists a constant c > 0 such that if g(G)≥cΔ r log(Δ2/r) then χa(G)≤Δ + r + 1, which generalizes the result of Alon et al. in 2001. When G is restricted to series-parallel graphs, it is proved that χ'a(G) = Δ if Δ≥4 and g(G)≥4; or Δ≥3 and g(G)≥5.展开更多
美国科罗拉多州立大学的PosarenkeE V 和俄罗斯门捷列夫化工大学的PosarenkoV N 研究开发出的一种非循环的天然气制甲醇联合发电的新工艺,可使甲醇生产成本降低25%～30%。该工艺合成气是在动力装置(内燃机、燃气透平)及与之联用的甲烷...美国科罗拉多州立大学的PosarenkeE V 和俄罗斯门捷列夫化工大学的PosarenkoV N 研究开发出的一种非循环的天然气制甲醇联合发电的新工艺,可使甲醇生产成本降低25%～30%。该工艺合成气是在动力装置(内燃机、燃气透平)及与之联用的甲烷蒸汽转化和部分氧化催化反应器中制得的。甲醇合成的催化反应是在有3个或4个反应器的系统内的铜基催化剂上进行的。在第一个反应器之后各反应器都要进行甲醇的脱除和合成气的再压缩。第一个反应器的温度保持为180～250℃,压力保持为3 8～4 2MPa;二、三两个反应器的温度保持为200～250℃,压力保持为7～8MPa。合成气转化成所需产品的总转化率为75%～90%(质量分数)。新压缩型燃气柴油机和燃气透平也已开发出来,效率系数超过56%。新动力装置较为价廉,可长期连续投入运行。展开更多
基金supported by National Natural Science Foundation of China (Grant Nos.11001055,11101086,11101088)National Natural Science Foundation of Fujian Province (Grant Nos.2010J05004,2011J06001,JK2010007)
文摘A proper edge coloring of a graph G is called acyclic if there is no 2-colored cycle in G. The acyclic chromatic index of G, denoted by χ'a(G), is the least number of colors such that G has an acyclic edge k-coloring. Let G be a graph with maximum degree Δ and girth g(G), and let 1≤r≤2Δ be an integer. In this paper, it is shown that there exists a constant c > 0 such that if g(G)≥cΔ r log(Δ2/r) then χa(G)≤Δ + r + 1, which generalizes the result of Alon et al. in 2001. When G is restricted to series-parallel graphs, it is proved that χ'a(G) = Δ if Δ≥4 and g(G)≥4; or Δ≥3 and g(G)≥5.
文摘美国科罗拉多州立大学的PosarenkeE V 和俄罗斯门捷列夫化工大学的PosarenkoV N 研究开发出的一种非循环的天然气制甲醇联合发电的新工艺,可使甲醇生产成本降低25%～30%。该工艺合成气是在动力装置(内燃机、燃气透平)及与之联用的甲烷蒸汽转化和部分氧化催化反应器中制得的。甲醇合成的催化反应是在有3个或4个反应器的系统内的铜基催化剂上进行的。在第一个反应器之后各反应器都要进行甲醇的脱除和合成气的再压缩。第一个反应器的温度保持为180～250℃,压力保持为3 8～4 2MPa;二、三两个反应器的温度保持为200～250℃,压力保持为7～8MPa。合成气转化成所需产品的总转化率为75%～90%(质量分数)。新压缩型燃气柴油机和燃气透平也已开发出来,效率系数超过56%。新动力装置较为价廉,可长期连续投入运行。
