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61.
In an earlier article, Willem H. Haemers has determined the minimum number of parallel classes in a resolvable 2‐(qk,k,1) covering for all k ≥ 2 and q = 2 or 3. Here, we complete the case q = 4, by construction of the desired coverings using the method of simulated annealing. Secondly, we look at equitable resolvable 2‐(qk,k,1) coverings. These are resolvable coverings which have the additional property that every pair of points is covered at most twice. We show that these coverings satisfy k < 2q ? , and we give several examples. In one of these examples, k > q. © 2003 Wiley Periodicals, Inc. J Combin Designs 11: 113–123, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10024 相似文献
62.
Controlled Wild Algebras 总被引:1,自引:0,他引:1
The controlled wild algebra is introduced, a covering criterionfor a finite-dimensional algebra to be controlled wild is given,and this criterion is applied to the algebras with radical squarezero, algebras with zero relations, local algebras and finitep-group algebras. 2000 Mathematical Subject Classification:16G20, 16G60. 相似文献
63.
Robert Myers 《Proceedings of the American Mathematical Society》2000,128(5):1507-1513
In this paper it is proven that if the group of covering translations of the covering space of a compact, connected, -irreducible 3-manifold corresponding to a non-trivial, finitely-generated subgroup of its fundamental group is infinite, then either the covering space is almost compact or the subgroup is infinite cyclic and has normalizer a non-finitely-generated subgroup of the rational numbers. In the first case additional information is obtained which is then used to relate Thurston's hyperbolization and virtual bundle conjectures to some algebraic conjectures about certain 3-manifold groups. 相似文献
64.
Edgar E. Enochs J. R. Garcí a Rozas Luis Oyonarte 《Proceedings of the American Mathematical Society》2000,128(10):2863-2868
We prove that for certain classes of modules such that direct sums of -covers ( -envelopes) are -covers ( -envelopes), -covering ( -enveloping) homomorphisms are always right (left) minimal. As a particular case we see that over noetherian rings, essential monomorphisms are left minimal. The same type of results are given when direct products of -covers are -covers. Finally we prove that over commutative noetherian rings, any direct product of flat covers of modules of finite length is a flat cover. 相似文献
65.
地面覆盖物对交通噪声衰减量的研究 总被引:1,自引:0,他引:1
肖红兵 《达县师范高等专科学校学报》2007,17(2):43-45
就地面覆盖物(包括农作物、草地、裸露的土壤等)对交通噪声衰减量的影响进行了深入研究。通过大量现场测试、数据处理与分析,重新确定了衰减因子的取值,建立了由地面覆盖物所引起的交通噪声附加衰减量与水平距离之间更为合理的关系式,最后,对回归方程的精度进行了检验。 相似文献
66.
设S为有单位元的可消半群.引入半群S对C-Mod的作用及半群S分次C-模范畴的概念,证明了当C为B的Galois盖时,B-模范畴与C的不动点满子范畴是一致的.对半群S分次B-模范畴,Smash积C#S-模范畴与半群S分次B-模范畴是一致的;同时还讨论了半群S分次模的Smash积,刻画了Smash积函子#与(-)*之间的关系. 相似文献
67.
This paper investigates the semi-online scheduling problem with the known largest size on two uniform machines. The objective is to maximize the minimum machine completion time. Both lower bounds and algorithms are given. Algorithms are optimal for the majority values of s≥1, where s is the speed ratio of the two machines. The largest gap between the competitive ratio and the lower bound is about 0.064. Moreover, the overall competitive ratio 2 matches the overall lower bound. 相似文献
68.
69.
In this paper, the concept of covering domain is introduced to develop a general expression for the Fredholm Integral Equations
Method, by which elasticity problems of arbitrarily shaped bodies loaded by external forces can be solved. Some special expressions
are given for a body with non-zero remote stresses, or subjected to some concentrated forces on its boundary. The relationship
between the loading forces and solutions are also discussed. Some analytical solutions can be obtained for simple cases. When
numerical computations are needed for the solution, the method proves to have high precision and fast convergency. 相似文献
70.
利用太赫兹时域光谱技术测量了聚乙烯、聚丙烯、聚氯乙烯、聚四氟乙烯和丙烯腈-丁二烯-苯乙烯的太赫兹透射谱,研究其在0.2~2.6 THz频段的光谱特性,得到了在室温氮气环境下这些材料的太赫兹吸收谱和折射率色散特性.发现这五种塑料在太赫兹波段的折射率和吸收系数差异显著,折射率分别在1.35~1.85之间,聚乙烯、聚丙烯、聚四氟乙烯吸收很小,相比之下聚氯乙烯、丙烯腈-丁二烯-苯乙烯吸收很大,这为塑料种类的鉴别及高太赫兹透过率塑料衬底选择提供了依据. 相似文献