A subgroup A of a finite group G is called {1≤G}-embedded in G if for each two subgroups K≤H of G, where K is a maximal subgroup of H, A either covers the pair (K,H) or avoids it. Moreover, a subgroup H of G is called nearly m-embedded in G if G has a subgroup T and a {1≤G}-embedded subgroup C such that G?=?HT and H∩T≤C≤H. In this paper, we mainly prove that G is solvable if and only if its Sylow 3-subgroups, Sylow 5-subgroups and Sylow 7-subgroups are nearly m-embedded in G. 相似文献
This article is a contribution to the study of the automorphism groups of 3-(v,k,3) designs.Let S =(P,B) be a non-trivial 3-(q+ 1,k,3) design.If a two-dimensional projective linear group PSL(2,q) acts flag-transitively on S,then S is a 3-(q + 1,4,3) or 3-(q + 1,5,3) design. 相似文献
Thermal treatment of CaF2 has a significant influence on the number and intensity of the peaks seen by thermo-luminescence. A combination of ion implants and anneal cycles leads to the conclusion that the 90°C glow peak is derived from a defect of a substitutional trivalent impurity (e.g. Ce+3) linked to an interstitial fluorine ion. Perturbations of this centre by other defects modify the centre and the glow peak temperature is raised to 110°C. The peaks at 180, 220 and 350°C all involve intrinsic defect clusters. The building of models for the different glow peaks was helped by a comparison of impurity and self ion implantations. 相似文献
The aim of this article is to introduce luminescence dating and relate it to luminescence and Raman spectroscopy of minerals. The physical bases of luminescence signals used in dating and their relationships to other radiation-induced luminescence and Raman signals are briefly reviewed. The manner in which these signals are applied to evaluate luminescence ages is described. Archaeological and geological case studies from the author's experience are used to illustrate potentialities and issues related to different contexts, techniques, and materials. 相似文献
Geographic structure can affect patterns of genetic differentiation and speciation rates. In this article, we investigate the dynamics of genetic distances in a geographically structured metapopulation. We model the metapopulation as a weighted directed graph, with vertices corresponding to subpopulations that evolve according to an individual based model. The dynamics of the genetic distances is then controlled by two types of transitions — mutation and migration events. We show that, under a rare mutation–rare migration regime, intra subpopulation diversity can be neglected and our model can be approximated by a population based model. We show that under a large population-large number of loci limit, the genetic distance between two subpopulations converges to a deterministic quantity that can asymptotically be expressed in terms of the hitting time between two random walks in the metapopulation graph. Our result shows that the genetic distance between two subpopulations does not only depend on the direct migration rates between them but on the whole metapopulation structure. 相似文献
Existing black box and other algorithms for explicitly recognising groups of Lie type over have asymptotic running times which are polynomial in , whereas the input size involves only . This has represented a serious obstruction to the efficient recognition of such groups. Recently, Brooksbank and Kantor devised new explicit recognition algorithms for classical groups; these run in time that is polynomial in the size of the input, given an oracle that recognises PSL}(2,q)$"> explicitly.
The present paper, in conjunction with an earlier paper by the first two authors, provides such an oracle. The earlier paper produced an algorithm for explicitly recognising in its natural representation in polynomial time, given a discrete logarithm oracle for . The algorithm presented here takes as input a generating set for a subgroup of that is isomorphic modulo scalars to PSL}(2,q)$">, where is a finite field of the same characteristic as ; it returns the natural representation of modulo scalars. Since a faithful projective representation of PSL}(2,q)$">in cross characteristic, or a faithful permutation representation of this group, is necessarily of size that is polynomial in rather than in , elementary algorithms will recognise PSL} (2,q)$"> explicitly in polynomial time in these cases. Given a discrete logarithm oracle for , our algorithm thus provides the required polynomial time oracle for recognising PSL}(2,q)$"> explicitly in the remaining case, namely for representations in the natural characteristic.
This leads to a partial solution of a question posed by Babai and Shalev: if is a matrix group in characteristic , determine in polynomial time whether or not is trivial.
For a prime p at least 5,let T=PSL(2,p).This paper gives a classification of the connected arc-transitive cubic Cayley graphs on T and a determination of the gener- ated pairs ((?),(?)) of T such that o((?))=2 and o((?))=3. 相似文献