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1.
In the note, it is proved that, under natural conditions, any infinite-dimensional unitary representation T of a direct product of groups G = K × N, where K is a compact group and N is a locally compact Abelian group, is imaged by a representation of the nonstandard analog \(\tilde G\) of the group G in the group of nonstandard matrices of a fixed nonstandard size. 相似文献
2.
A. Vera-López J. M. Arregi Leyre Ormaetxea F. J. Vera-López Olga Basova 《Israel Journal of Mathematics》2016,214(2):675-697
We denote by Gn the group of the upper unitriangular matrices over Fq, the finite field with q = pt elements, and r(Gn) the number of conjugacy classes of Gn. In this paper, we obtain the value of r(Gn) modulo (q2 -1)(q -1). We prove the following equalities 相似文献
3.
Let G be a finite group. A normal subgroup N of G is a union of several G-conjugacy classes, and it is called n-decomposable in G if it is a union of n distinct G-conjugacy classes. In this paper, we first classify finite non-perfect groups satisfying the condition that the numbers of conjugacy classes contained in its non-trivial normal subgroups are two consecutive positive integers, and we later prove that there is no non-perfect group such that the numbers of conjugacy classes contained in its non-trivial normal subgroups are 2, 3, 4 and 5. 相似文献
4.
Suppose that G is a finite group and K is a non-trivial conjugacy class of G such that KK?1 = 1 ∪ D ∪ D?1 with D a conjugacy class of G. We prove that G is not a non-abelian simple group and we give arithmetical conditions on the class sizes determining the solvability and the structure of 〈K〉 and 〈D〉. 相似文献
5.
Letm be a fixed non-negative integer. In this work we try to answer the following question: What can be said about a (finite) groupG if all of its irreducible (complex) characters vanish on at mostm conjugacy classes? The classical result of Burnside about zeros of characters says thatG is abelian ifm=0, so it is reasonable to expect that the structure ofG will somehow reflect the fact that the irreducible characters vanish on a bounded number of classes. The same question can also be posed under the weaker hypothesis thatsome irreducible character ofG hasm classes of zeros. For nilpotent groups we shall prove that the order is bounded by a function ofm in the first case but only the derived length can be bounded in general under the weaker condition. For solvable groups the situation is not so well understood although we shall prove that the Fitting height can be bounded by a double logarithmic function ofm, improving a recent result by G. Qian. 相似文献
6.
S. M. Robati 《Acta Mathematica Hungarica》2016,148(1):109-116
A digraph \({\overrightarrow{\mathcal{Pc}}(G)}\) is said to be the directed power graph on the conjugacy classes of a group G, if its vertices are the non-trivial conjugacy classes of G, and there is an arc from vertex C to C′ if and only if \({C \neq C'}\) and \({C \subseteqq {C'}^{m}}\) for some positive integer \({m > 0}\). Moreover, the simple graph \({\mathcal{Pc}(G)}\) is said to be the (undirected) power graph on the conjugacy classes of a group G if its vertices are the conjugacy classes of G and two distinct vertices C and C′ are adjacent in \({\mathcal{Pc}(G)}\) if one is a subset of a power of the other. In this paper, we find some connections between algebraic properties of some groups and properties of the associated graph. 相似文献
7.
I. B. Gorshkov 《Proceedings of the Steklov Institute of Mathematics》2016,293(1):58-65
Let G be a finite group G, and let N(G) be the set of sizes of its conjugacy classes. It is shown that, if N(G) equals N(Alt n ) or N(Sym n ), where n > 1361, then G has a composition factor isomorphic to an alternating group Altm with m ≤ n and the interval (m, n] contains no primes. 相似文献
8.
Robert M. Guralnick 《Proceedings of the Steklov Institute of Mathematics》2016,292(1):112-117
Let G be a permutation group acting transitively on a finite set Ω. We classify all such (G, Ω) when G contains a single conjugacy class of derangements. This was done under the assumption that G acts primitively by Burness and Tong-Viet. It turns out that there are no imprimitive examples. We also discuss some results on the proportion of conjugacy classes which consist of derangements. 相似文献
9.
Let G = SpecA be an affine K-group scheme and à = {w ∈ A*: dim K A*·w < ∞, dim K w· A* < ∞}. Let 〈?,?〉: A* × Ã → K, 〈w, \(\tilde w\)〉:=tr(w~w), be the trace form. We prove that G is linearly reductive if and only if the trace form is non-degenerate on A*. 相似文献
10.
The well-known Landau’s theorem states that, for any positive integer k, there are finitely many isomorphism classes of finite groups with exactly k (conjugacy) classes. We study variations of this theorem for p-regular classes as well as p-singular classes. We prove several results showing that the structure of a finite group is strongly restricted by the number of p-regular classes or the number of p-singular classes of the group. In particular, if G is a finite group with Op(G) = 1 then |G/F(G)|p' is bounded in terms of the number of p-regular classes of G. However, it is not possible to prove that there are finitely many groups with no nontrivial normal p-subgroup and kp-regular classes without solving some extremely difficult number-theoretic problems (for instance, we would need to show that the number of Fermat primes is finite). 相似文献
11.
Given the ring of integers O K of an algebraic number field K, for which natural numbers n there exists a finite group G???GL(n, O K ) such that O K G, the O K -span of G, coincides with M(n, O K ), the ring of (n?×?n)-matrices over O K ? The answer is known if n is an odd prime. In this paper we study the case n?=?2; in the cases when the answer is positive for n?=?2, for n?=?2m there is also a finite group G???GL(2m, O K ) such that O K G?=?M(2m, O K ). 相似文献
12.
Let G be a finite group and N a normal subgroup of G. We determine the structure of N when the graph \(\Gamma _{G}(N)\), which is the graph associated to the conjugacy classes of G contained in N, has no triangles and when the graph consists in exactly one triangle. 相似文献
13.
Classical Clifford theory studies the decomposition of simple G-modules into simple H-modules for some normal subgroup H ? G. In this paper we deal with chains of normal subgroups 1?G 1?· · ·?G d = G, which allow to consider fragments and in particular glider representations. These are given by a descending chain of vector spaces over some field K and relate different representations of the groups appearing in the chain. Picking some normal subgroup H ? G one obtains a normal subchain and one can construct an induced fragment structure. Moreover, a notion of irreducibility of fragments is introduced, which completes the list of ingredients to perform a Clifford theory. 相似文献
14.
Let α be an automorphism of a finite group G. For a positive integer n, let E G,n (α) be the subgroup generated by all commutators [...[[x,α],α],…,α] in the semidirect product G 〈α〉 over x ∈ G, where α is repeated n times. By Baer’s theorem, if E G,n (α)=1, then the commutator subgroup [G,α] is nilpotent. We generalize this theorem in terms of certain length parameters of E G,n (α). For soluble G we prove that if, for some n, the Fitting height of E G,n (α) is equal to k, then the Fitting height of [G,α] is at most k + 1. For nonsoluble G the results are in terms of the nonsoluble length and generalized Fitting height. The generalized Fitting height h*(H) of a finite group H is the least number h such that F h* (H) = H, where F 0* (H) = 1, and F i+1* (H) is the inverse image of the generalized Fitting subgroup F*(H/F i *(H)). Let m be the number of prime factors of the order |α| counting multiplicities. It is proved that if, for some n, the generalized Fitting height E G,n (α) of is equal to k, then the generalized Fitting height of [G,α] is bounded in terms of k and m. The nonsoluble length λ(H) of a finite group H is defined as the minimum number of nonsoluble factors in a normal series each of whose factors either is soluble or is a direct product of nonabelian simple groups. It is proved that if λE G,n (α)= k, then the nonsoluble length of [G,α] is bounded in terms of k and m. We also state conjectures of stronger results independent of m and show that these conjectures reduce to a certain question about automorphisms of direct products of finite simple groups. 相似文献
15.
Let G be a finite group and NA(G) denote the number of conjugacy classes of all nonabelian subgroups of non-prime-power order of G. The Symbol π(G) denote the set of the prime divisors of |G|. In this paper we establish lower bounds on NA(G). In fact, we show that if G is a finite solvable group, then NA(G) = 0 or NA(G) ≥ 2|π(G)|?2, and if G is non-solvable, then NA(G) ≥ |π(G)| + 1. Both lower bounds are best possible. 相似文献
16.
Uri Yechiali 《The Journal of the Operational Research Society》1977,28(2):325-337
The expected steady-state waiting time, Wq(s), in a GI/M/s system with interarrival-time distribution H(·) is compared with the mean waiting time, Wq, in an "equivalent" system comprised of s separate GI/M/1 queues each fed by an interarrival-time distribution G(·) with mean arrival rate equal to 1/s times that of H(·). For H(·) assumed to be Exponential, Gamma or Deterministic three possible relationships between H(·) and G(·) are considered: G(·) can be of the "same type" as H(·); G(·) can be derived from H(·) by assigning new arrivals to the individual channels in a cyclic order; and G(·) may be obtained from H(·) by assigning customers probabilistically to the different queues. The limiting behaviour of the ratio R = Wq/Wq(s) is studied for the extreme values (1 and 0) of the common traffic intensity, ρ. Closed form results, which depend on the forms of H(·) and G(·) and on the relationships between them, are derived. It is shown that Wq is greater than Wq(s) by a factor of at least (s + 1)/2 when ρ approaches one, and that R is at least s(s!) when ρ tends to zero. In the latter case, however, R goes to infinity (!) in most cases treated. The results may be used to evaluate the effect on the waiting times when, for certain (non-queueing) reasons, it is needed to partition a group of s servers into several small groups. 相似文献
17.
Andreas Arvanitoyeorgos Yu Wang Guosong Zhao 《Annals of Global Analysis and Geometry》2018,54(3):315-328
We investigate homogeneous geodesics in a class of homogeneous spaces called M-spaces, which are defined as follows. Let G / K be a generalized flag manifold with \(K=C(S)=S\times K_1\), where S is a torus in a compact simple Lie group G and \(K_1\) is the semisimple part of K. Then, the associated M-space is the homogeneous space \(G/K_1\). These spaces were introduced and studied by H. C. Wang in 1954. We prove that for various classes of M-spaces the only g.o. metric is the standard metric. For other classes of M-spaces we give either necessary, or necessary and sufficient conditions, so that a G-invariant metric on \(G/K_1\) is a g.o. metric. The analysis is based on properties of the isotropy representation \(\mathfrak {m}=\mathfrak {m}_1\oplus \cdots \oplus \mathfrak {m}_s\) of the flag manifold G / K [as \({{\mathrm{Ad}}}(K)\)-modules]. 相似文献
18.
Michael J. J. Barry 《Archiv der Mathematik》2011,97(6):503-512
If K is a field of finite characteristic p, G is a cyclic group of order q = p α , U and W are indecomposable KG-modules, and p ≥ dim U + dim W ? 1, we describe how to find a generator for each of the indecomposable components of the KG-module \({U \otimes W}\). 相似文献
19.
Finite <Emphasis Type="Italic">p</Emphasis>-groups with a class of complemented normal subgroups
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Assume G is a finite group and H a subgroup of G. If there exists a subgroup K of G such that G = HK and H ∩ K = 1, then K is said to be a complement to H in G. A finite p-group G is called an NC-group if all its proper normal subgroups not contained in Φ(G) have complements. In this paper, some properties of NC-groups are investigated and some classes of NC-groups are classified. 相似文献
20.
In Behravesh (J Lond Math Soc 55(2):251–260, 1997), c(G), q(G) and p(G) are defined for a finite group G. In this paper, we will calculate c(G), q(G) and p(G) for some 2-groups G satisfying the Hasse principle in Fuma and Ninomiya (Math J Okayama Univ 46:31–38, 2004). We will consider where m ≥ 4. By comparing the character tables and Galois conjugacy classes of Irr(G) and Irr(Z(G)), we will show that
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$G=\langle x, y, z: x^{2^{m-2}}=y^{2}=z^2=1, [x, y]=[y, z]=1, x^{z}=xy \rangle$
$c(G)=q(G)=p(G)= 2c(Z(G))=2^{m-2}+4.$