共查询到20条相似文献,搜索用时 31 毫秒
1.
Thomas Nordahl 《Semigroup Forum》1974,8(1):332-346
In this paper we characterize Archimedean semigroups with idempotents satisfying (xy)m = xmym as exactly those semigroups which are a retract extension of a completely simple semigroup satisfying (xy)m = xmym by a nil semigroup satisfying (xy)m = xmym. Regular semigroups satisfying (xy)2 = x2y2 are exactly those semigroups which are a spined product of a band and a semigroup which is a semilattice of Abelian groups. A semigroup which is a nil extension of a regular semigroup satisfies (xy)2 = x2y2 if and only if it is a retract extension of a regular semigroup satisfying (xy)2 = x2y2 by a nil semigroup satisfying (xy)2 = x2y2 相似文献
2.
Giulio Caviglia 《Journal of Algebraic Combinatorics》2009,30(4):539-548
In this paper we prove that the coordinate ring of the pinched Veronese, k[X
3,X
2
Y,XY
2,Y
3,X
2
Z,Y
2
Z,XZ
2,YZ
2,Z
3], is Koszul. The result is obtained by combining the use of a flat deformation induced by a distinguished weight together
with a generalization of the notion of Koszul filtrations. 相似文献
3.
A cyclic coloring of a plane graph is a vertex coloring such that vertices incident with the same face have distinct colors. The minimum number of colors in a cyclic coloring of a graph is its cyclic chromatic number χc. Let Δ* be the maximum face degree of a graph. There exist plane graphs with χc = ?3/2 Δ*?. Ore and Plummer [ 5 ] proved that χc ≤ 2, Δ*, which bound was improved to ?9/5, Δ*? by Borodin, Sanders, and Zhao [ 1 ], and to ?5/3,Δ*? by Sanders and Zhao [ 7 ]. We introduce a new parameter k*, which is the maximum number of vertices that two faces of a graph can have in common, and prove that χc ≤ max {Δ* + 3,k* + 2, Δ* + 14, 3, k* + 6, 18}, and if Δ* ≥ 4 and k* ≥ 4, then χc ≤ Δ* + 3,k* + 2. © 2006 Wiley Periodicals, Inc. J Graph Theory 相似文献
4.
Yury Nikolayevsky 《Results in Mathematics》1999,36(3-4):313-330
A non-totally-geodesic submanifold of relative nullity n — 1 in a symmetric space M is a cylinder over one of the following submanifolds: a surface F 2 of nullity 1 in a totally geodesic submanifold N3 ? M locally isometric to S 2(c) × ? or H 2(c) × ?; a submanifold F k+1 spanned by a totally geodesic submanifold F k(c) of constant curvature moving by a special curve in the isometry group of M; a submanifold F k+l of nullity k in a flat totally geodesic submanifold of M; a curve. 相似文献
5.
James E. Baumgartner 《Israel Journal of Mathematics》1975,21(4):296-307
Partition relations of the form α→(α,m)2, where α is an ordinal andm is a positive integer, are considered. Let κ be a cardinal. The following are proved: If κ is singular and 2K=K + then (K+)2?((K+)2,3)2. If κ is a strong limit cardinal, then2, iff ((cfκ)2→((cfκ)2,m)2. If κ is regular and K2→(K2,3)2, then the κ-Souslin hypothesis holds. If Kω<α+ and cfα=cfκ>ω, then α?(α,3)2. 相似文献
6.
An explicit expression is obtained for a pair of generalized inverses (B?,A?) such that B?A?=(AB)+MN, and a class of pairs (B?,A? of this property is shown. A necessary and sufficient condition for (AB)? to have the expression B?A? is also given. 相似文献
7.
The question of which C1-algebras have only inner derivations has been considered by a number of authors for 25 years. The separable case is completely solved, so this paper deals only with the non-separable case. In particular, we show that the C1-tensor product of a von Neumann algebra and an abelian C1-algebra has only inner derivations. Other special types of C1-algebras are shown to have only inner derivations as well such as the C1-tensor product of L(H) (all bounded operators on separable Hilbert space) and any separable C1-algebra having only inner derivations. Derivations from a smaller C1-algebra into a larger one are also considered, and this concept is generalized to include derivations between C1-algebras connected by a 1-homomorphism. Finally, we consider the general problem of a sequence of linear functionals on a C1-algebra which converges to zero (in norm) when restricted to any abelian C1-subalgebra. Does such a sequence converge to zero in norm? The answer is “yes” for normal functionals on L(H), but unknown in general. 相似文献
8.
周云华 《数学物理学报(B辑英文版)》2011,31(1):102-108
Let T : X → X be a uniformly continuous homeomorphism on a non-compact metric space (X, d). Denote by X* = X ∪ {x*} the one point compactification of X and T * : X* → X* the homeomorphism on X* satisfying T *|X = T and T *x* = x*. We show that their topological entropies satisfy hd(T, X) ≥ h(T *, X*) if X is locally compact. We also give a note on Katok’s measure theoretic entropy on a compact metric space. 相似文献
9.
Cedric A.B Smith 《Journal of Combinatorial Theory, Series B》1974,16(1):64-76
A matroid M over a set E of elements is semiseparated by a partition {S1, S2} of E iff rank E = rank S1 + rank S2 + 1. Such a semiseparation defines in each Si a pair of matroids or patroid Pi = (Mi, mi); the two patroids P1, P2 weld to form M. The operations of removing and contracting a non-degenerate element of a matroid produce a patroid. The properties of patroids, their bases, and circuits are discussed. 相似文献
10.
The aim of the paper is to study the asymptotic behaviour of solutions of second‐order elliptic and parabolic equations, arising in modelling of flow in cavernous porous media, in a domain Ωε weakly connected by a system of traps ??ε, where ε is the parameter that characterizes the scale of the microstructure. Namely, we consider a strongly perforated domain Ωε ?Ω a bounded open set of ?3 such that Ωε =Ω1ε ∪Ω2ε ∪??ε ∪ Wε, where Ω1ε, Ω2ε are non‐intersecting subdomains strongly connected with respect to Ω, ??ε is a system of traps and meas Wε → 0 as ε → 0. Without any periodicity assumption, for a large range of perforated media and by means of variational homogenization, we find the homogenized models. The effective coefficients are described in terms of local energy characteristics of the domain Ωε associated with the problem under consideration. The resulting homogenized problem in the parabolic case is a vector model with memory terms. An example is presented to illustrate the methodology. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
Kazuyuki Sait 《Journal of Mathematical Analysis and Applications》2009,360(2):369-376
Akemann showed that any von Neumann algebra with a weak* separable dual space has a faithful normal representation on a separable Hilbert space. He posed the question: If a C*-algebra has a weak* separable state space, must it have a faithful representation on a separable Hilbert space? Wright solved this question negatively and showed that a unital C*-algebra has the weak* separable state space if and only if it has a unital completely positive map, into a type I factor on a separable Hilbert space, whose restriction to the self-adjoint part induces an order isomorphism. He called such a C*-algebra almost separably representable. We say that a unital C*-algebra is small if it has a unital complete isometry into a type I factor on a separable Hilbert space. In this paper we show that a unital C*-algebra is small if and only if the state spaces of all n by n matrix algebras over the C*-algebra are weak*-separable. It is natural to ask whether almost separably representable algebras are small or not. We settle this question positively for simple C*-algebras but the general question remains open. 相似文献
12.
设R是有单位元1的结合环,(S,≤)是严格全序Artin幺半群,M_R是右R-模,Att(M_R)与Att([M~(S,≤)]_([[R~(S,≤)]]))分别表示模M_R与广义逆多项式模[M~(S,≤)]_([[R~(S,≤)]])的所有Attached素理想组成的集合.该文主要讨论了广义幂级数环[[R~(S;≤)]]广义逆多项式模[[R~(S;≤)]]的Attached素理想的相关性质,证明了在一定条件下,有Att([M~(S,≤)]_([[R~(S,≤)]])={[[PR~(S;≤)]]P∈Att(M_R)}.这一结论表明广义逆多项式模([M~(S,≤)]_([[R~(S,≤)]])的Attached素理想在一定条件下可以用模M_R的Attached素理想来刻画,推广了Annin S在文献[1]中关于斜多项式环上逆多项式模的Attached素理想的相关结论. 相似文献
13.
Domingo A. Herrero 《Integral Equations and Operator Theory》1983,6(1):515-524
Let T be an injective bilateral weighted shift onl 2 thought as "multiplication by λ" on a space of formal Laurent series L2(β). (a) If L2(β) is contained in a space of quasi-analytic class of functions, then the point spectrum σp(T?) of T? contains a circle and the cyclic invariant subspaceM f of T generated by f is simply invariant (i.e., ∩{(Tk M f)?: k ≥ 0}= {0}) for each f in L2(β); (b) If L2(β) contains a non-quasi-analytic class of functions (defined on a circle г) of a certain type related with the weight sequence of T, then there exists f in L2(ß) such thatM f is a non-trivial doubly invariant subspace (i.e., (TM f)? =M f); furthermore, if г ? σp(T*), then σp (T*) = г and f can be chosen so that σp([T∣M f]*) = г?{α}, for some α ε г. Several examples show that the gap between operators satisfying (a) and operators satisfying (b) is rather small. 相似文献
14.
Nontrivial difference sets in groups of order a power of 2 are part of the family of difference sets called Menon difference sets (or Hadamard), and they have parameters (22d+2, 22d+1±2
d
, 22d
±2
d
). In the abelian case, the group has a difference set if and only if the exponent of the group is less than or equal to 2
d+2. In [14], the authors construct a difference set in a nonabelian group of order 64 and exponent 32. This paper generalizes that result to show that there is a difference set in a nonabelian group of order 22d+2 with exponent 2
d+3. We use representation theory to prove that the group has a difference set, and this shows that representation theory can be used to verify a construction similar to the use of character theory in the abelian case. 相似文献
15.
《Comptes Rendus de l'Academie des Sciences Series IIA Earth and Planetary Science》1999,328(8):663-668
In this Note, we give a new proof of the uniqueness of mild solutions of the Navier-Stokes equation in C([0,T) ; (L3(ℝ3))3). The main tool of the proof is the maximal Lp-regularity of the Laplacian in (L3 (ℝ3))3. 相似文献
16.
Paolo Boggiatto Giuseppe De Donno Alessandro Oliaro 《Mathematische Nachrichten》2009,282(12):1656-1663
We study boundedness and compactness properties for the Weyl quantization with symbols in Lq (?2d ) acting on Lp (?d ). This is shown to be equivalent, in suitable Banach space setting, to that of the Wigner transform. We give a short proof by interpolation of Lieb's sufficient conditions for the boundedness of the Wigner transform, proving furthermore that these conditions are also necessary. This yields a complete characterization of boundedness for Weyl operators in Lp setting; compactness follows by approximation. We extend these results defining two scales of spaces, namely L*q (?2d ) and L?q (R2d ), respectively smaller and larger than the Lq (?2d ),and showing that the Weyl correspondence is bounded on L*q (R2d ) (and yields compact operators), whereas it is not on L?q (R2d ). We conclude with a remark on weak‐type Lp boundedness (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
Summary In this note we use the Hopf map π: S3 → S2 to construct an interesting family of Riemannian metrics hfon the 3-sphere, which are parametrized on the space of positive smooth functions f on the 2-sphere. All these metrics make the Hopf map a Riemannian submersion. The Hopf tube over an immersed curve γ in S2 is the complete lift π-1(γ) of γ, and we prove that any geodesic of this Hopf tube satisfies a Clairaut relation. A Hopf tube plays the role in S3 of the surfaces of revolution in R3. Furthermore, we show a geometric integration method of the Frenet equations for curves in those non-standard S3. Finally, if we consider the sphere S3 equipped with a family hf of Lorentzian metrics, then a new Clairautrelation is also obtained for timelike geodesics of the Lorentzian Hopf tube, and
a geometric integration method for curves is still possible. 相似文献
18.
David E. Dobbs 《International Journal of Mathematical Education in Science & Technology》2013,44(3):358-362
It is proved that if the differential equations y ( n )=f(x, y, y′, …, y ( n ?1 )) and y ( m )=g(x, y, y′, …, y ( n ?1 )) have the same particular solutions in a suitable region where f and g are continuous real-valued functions with continuous partial derivatives (alternatively, continuous functions satisfying the classical Lipschitz condition), then n?=?m and the functions f and g are equal. This note could find classroom use in a course on differential equations as enrichment material for the unit on the existence and uniqueness theorems for solutions of initial value problems. 相似文献
19.
We develop the method introduced previously, to construct infinitesimal generators on locally compact group C
*-algebras and on tensor product of C
*-algebras. It is shown in particular that there is a C
* -algebra A such that the C
*-tensor product of A and an arbitrary C
*-algebra B can have a non-approximately inner strongly one parameter group of *-automorphisms. 相似文献
20.
Let G be a finite group. The prime graph of G is denoted by Γ(G). In this paper, as the main result, we show that if G is a finite group such that Γ(G) = Γ(2 D n (3α)), where n = 4m+ 1 and α is odd, then G has a unique non-Abelian composition factor isomorphic to 2 D n (3α). We also show that if G is a finite group satisfying |G| = |2 D n (3α)|, and Γ(G) = Γ(2 D n (3α)), then G ? 2 D n (3α). As a consequence of our result, we give a new proof for a conjecture of Shi and Bi for 2 D n (3α). Application of this result to the problem of recognition of finite simple groups by the set of element orders are also considered. Specifically, it is proved that 2 D n (3α) is quasirecognizable by the spectrum. 相似文献