共查询到20条相似文献，搜索用时 30 毫秒

1.

C. T. Nguyen 《Applied Categorical Structures》1997,5(2):143-154

A category PAlg() of partial algebras of a given type will be introduced. Then we will present a categorical concept in order to characterize those subcategories of PAlg(), which are closed under the formation of various kinds of subobjects. We will also give a characterization for bireflective subcategories of PAlg(), which enables us to show, that the subcategory Alg() consisting of all total algebras of type is the smallest bireflective subcategory of PAlg(). 相似文献

2.

A. Yu. Shevlyakov 《Journal of Mathematical Sciences》1993,67(4):3237-3243

*Let w(x, y), x 0 and y 0 be a Wiener field on the plane; be a curve given parametrically x=x() and y=y(), [0, 1], where x() is a positive, continuous, nondecreasing function; y() is a positive, continuous, nonincreasing function. A best estimate in the mean-square sense is constructed for w(u, v)(u, v) , based on the values w(x, y), (x, y) and its error is found*.Translated from Teoriya Sluchainykh Protsessov, No. 16, pp. 87–93, 1988. 相似文献

3.

We introduce and describe the characteristic class of a difference operator over the difference field (k((t)),). Here k is an algebraically closed field of characteristic zero and is the k-linear automorphism of k((t)) defined by (t)=t/(1+t). The approach is based on the characterization of simple difference operators in terms of their eigenvalues. 相似文献

4.

I. Sh. o. Aliev 《Mathematical Notes》1968,3(4):252-256

Manifolds of algebras with the operation xyz defined by the following identities: 1) xyz yz=x; 2) xxyz z=y; 3) xyxyz =z; 4) xxz =z, which correspond to Steiner quadruplets [3], like manifolds of structures, have a unique equationally complete submanifold [4]. It is proved that in the class of all algebras defined only by the identities 1), 2), and 3) the set of all equationally complete submanifolds has the power of a continuum.Translated from Matematicheskie Zametki, Vol. 3, No. 4, pp. 395–402, April, 1968. 相似文献

5.

On Idempotent Ranks of Semigroups of Partial Transformations

**总被引：2，自引：0，他引：2**A subset U of a semigroup S is a generating set for S
if every element of S may be written as a finite product of
elements of U. The rank of S is the size of a minimal
generating set of S, and the idempotent rank of S is
the size of a minimal generating set of S consisting of
idempotents in S. A partition of a q-element subset of the set X

_{n}={1,2,..., n} is said to be of type if the sizes of its classes form the partition of q n. A non-trivial partition of a positive integer q consists of k < q elements. For a non-trivial partition of q n, the semigroup S(), generated by all the transformations with kernels of type , is idempotent-generated. It is known that if is a non-trivial partition of n, that is, S() consists of total many-to-one transformations, then the rank and the idempotent rank of S() are both equal to max{^{n}_{d}, N()}, where N() is the number of partitions of X_{n}of type . We extend this result to semigroups of partial transformations, and prove that if is a non-trivial partition of q < n, then the rank and the idempotent rank of S() are both equal to N(). 相似文献6.

A. Haghany 《Periodica Mathematica Hungarica》1996,32(3):193-197

We generalize the well-known fact that for a pair of Morita equivalent rings

*R*and*S*their maximal rings of quotients are again Morita equivalent: If_{ n }(*M*) denotes the torsion theory cogenerated by the direct sum of the first*n*+1 injective modules forming part of the minimal injective resolution of*M*then_{ n }(*R*)=_{ n }(*S*) where is the category equivalence*R*-Mod*S*-Mod. Consequently the localized rings*R*_{n }_{(R)}and*S*_{}*n*_{(S)}are Morita equivalent. 相似文献7.

Norbert Kuhlmann 《manuscripta mathematica》1969,1(2):147-189

In this paper we study spaces of level sets of holomorphic mappings. We give an elementary (i.e. we are using elementary means) proof of a theorem a special case of which is the following statement: Let : XY be a holomorphic mapping of the irreducible normal complex space into the reduced complex space Y, which degenerates nowhere; the last condition means in the present case all -level sets having the same dimension; a -level set is a connected component of a fibre

^{–1}(Q), Q (X). Then the space Z of -level sets is a quasicomplex space and the natural mapping : XZ which maps each P X onto the -level set to which P belongs is open. If we substitute the assumption degenerating nowhere by the assumption having compact level sets, we get a space Z of level sets, which is a complex space. - The first part of this statement is a generalisation of a theorem of K. Stein, the second part is a special case of a theorem of H. Cartan and a well known theorem of H. Grauert on proper mappings. We will use our theorem in order to give a new proof of Grauert's theorem in a subsequent paper. 相似文献8.

Tor Helleseth Torleiv Kløve Vladimir I. Levenshtein 《Designs, Codes and Cryptography》2003,28(3):265-282

An ordered orthogonal array OOA(,

*k*,*n*) is a binary 2^{ k }×*n*matrix with the property that for each complete -set of columns, each possible -tuple occurs in exactly 2^{ k–}rows of those columns (for definition of a complete -set, see below). Constructions of OOA(,*k*,*n*) for = 4 and = 5 are given. 相似文献9.

Norbert Polat 《Czechoslovak Mathematical Journal》2001,51(3):477-492

For an end and a tree

*T*of a graph*G*we denote respectively by*m*() and*m*_{ T }() the maximum numbers of pairwise disjoint rays of*G*and*T*belonging to , and we define tm() := min{*m*_{T}():*T*is a spanning tree of*G*}. In this paper we give partial answers — affirmative and negative ones — to the general problem of determining if, for a function*f*mapping every end of*G*to a cardinal*f*() such that tm()*f*()*m*(), there exists a spanning tree*T*of*G*such that*m*_{ T }() =*f*() for every end of*G*. 相似文献10.

J. Płonka 《Southeast Asian Bulletin of Mathematics》2002,25(3):495-502

We consider algebras of a type , without nullary fundamental operation symbols. A structural property

*p*of an identity of type is*hereditary*if for every set*I*of identities of type having the property*p*every consequence of*I*(derived identity) has the property*p*. An algebra of type we call*characteristic*for a hereditary property*p*if for every variety*V*of type we have:*V*if and only if every identity from*Id*(*V*) has the property*p*. In this paper we show minimal characteristic algebras for several hereditary properties, e.g., to be regular, to be normal, etc.1991 Mathematics Subject Classification 08B05 相似文献11.

G. S. Mishuris 《Mechanics of Composite Materials》1998,34(5):439-456

The local stress-strain state in the vicinity of the crack tip in a composite is studied, taking into account the mechanical and geometric features of the nearest interface. The modeling of Mode I and II problems for a semi-infinite crack terminating normally at a nonideal interface in the bimaterial plane is considered. The constituents, of the composite are assumed to be elastic, homogeneous, and isotropic. The intermediate zone between the constituents is modeled by interfacial conditions in the form: [

_{ n }]=0, [*u*]=*r*^{}_{ n }, where [u] and [_{ n }] are jumps of the vectors of displacements and tractions along the interface. The diagonal matrix with nonnegative components and the parameter, 0 are defined by the mechanical and geometric characteristics of the intermediate zone, respectively. Thus, the case =0 corresponds to the usual ideal contact conditions along the interface. Using the method of integral transformations, the corresponding problems are reduced to systems of functional equations, and later to systems of integral equations with fixed point singularities. The solvability of the systems of integral equations is proved and the asymptotics of their solutions is found. Based on these results, the local distributions of the displacements and stresses near the crack tip are obtained. It is shown that the interfacial parameters and greatly influence the stress not only qualitatively (the character of the stress singularity near the crack tip changes), but also quantitatively (number of singular terms in the asymptotics increases). The graphs illustrating these results are presented as the values of the interfacial parameters and , as well as the ratio of the shear moduli_{0}/_{1}of the constituents.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Polytechnical Institute Poland. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 621–642, September–October, 1998. 相似文献12.

Wolfgang Bischoff 《Annals of the Institute of Statistical Mathematics》1992,44(2):229-238

Let

^{*}be an exact*D*-optimal design for a given regression model*Y*_{}=*X*_{}+*Z*_{}. In this paper sufficient conditions are given for sesigning how the covariance matrix of*Z*_{}may be changed so that not only^{*}remains*D*-optimal but also that the best linear unbiased estimator (BLUE) of stays fixed for the design^{*}, although the covariance matrix of*Z*_{}* is changed. Hence under these conditions a best, according to*D*-optimality, BLUE of is known for the model with the changed covariance matrix. The results may also be considered as determination of exact*D*-optimal designs for regression models with special correlated observations where the covariance matrices are not fully known. Various examples are given, especially for regression with intercept term, polynomial regression, and straight-line regression. A real example in electrocardiography is treated shortly. 相似文献13.

Let

_{K}be the worst-case (supremum) ratio of the weight of the minimum degree-K spanning tree to the weight of the minimum spanning tree, over all finite point sets in the Euclidean plane. It is known that_{2}= 2 and_{5}= 1. In STOC 94, Khuller, Raghavachari, and Young established the following inequalities: 1.103 <_{3}\le 1.5 and 1.035 <_{4}\le 1.25. We present the first improved upper bounds:_{3}< 1.402 and_{4}< 1.143. As a result, we obtain better approximation algorithms for Euclidean minimum bounded-degree spanning trees. Let_{K}^{(d)}be the analogous ratio in d-dimensional space. Khuller et al. showed that_{3}^{(d)}< 1.667 for any d. We observe that_{3}^{(d)}< 1.633. 相似文献14.

We apply the general theory of -Corson Compact spaces to remove an unnecessary hypothesis of zero-dimensionality from a theorem on polyadic spaces of tightness . In particular, we prove that polyadic spaces of countable tightness are Uniform Eberlein compact spaces. 相似文献

15.

Gerhard Pazderski 《Acta Appl Math》1998,52(1-3):315-323

Let L|K be a finite Galois extension. Using central simple algebras we deal with the crossed representations of G = Gal(L|K) over L which are defined as mappings X

_{}of G into GL_{n}(L) satisfying X_{}= X_{}^{}X_{}. The last equation is the Noetherian equation in case n=1. Furtheron, more general crossed projective representations are considered which obey an equation X_{}^{}X_{}= X_{}f_{,}where f_{,}L. 相似文献16.

Dr.-Ing. P.-Th. Wilrich 《Mathematical Methods of Operations Research》1968,12(1):185-209

Zusammenfassung Die zeitabhängige (instationäre) Lösung für die Zustandswahrscheinlichkeiten und für einige Kenngrößen von Warteschlangensystemen mit einer Bedienungsstation, unendlich vielen Warteplätzen, exponentiellem Zu- und Abgang und beliebigem Anfangszustand wird bestimmt. Die Zustandswahrscheinlichkeiten

Vorgel. v.:J. Nitsche. 相似文献

*P*_{ v }(), d. h. die Wahrscheinlichkeiten für Einheiten im System zur Zeit, ergeben sich als Integrale, in denen modifizierteSessel-Funktionen 1. Art auftreten. Der Erwartungswert*L*() und die Varianz*V*() der Zahl von Einheiten im System lassen sich als Integrale darstellen, in denen nur die Zustandswahrscheinlichkeit*P*_{0}() auftritt.Für<1 und erreichen die Systeme einen stationären Zustand (für den die Lösung bekannt ist); für1 und gilt*P*_{ v }()0 für alle*, L*(),*V*().Ist>1, dann wachsen*L*() und*V*() für große linear mit; ihre Asymptoten werden berechnet. Ist=1, dann wachsen*L*() und die Standardabweichung() für große mit ; einfache Näherungsformeln werden gefunden.Summary The time dependent solution is determined for the state probabilities and for some characteristic values of queuing systems with a single server, an infinite number of waiting places, exponentially distributed inter-arrival and service times, and any initial state. The state probabilitiesP_{ v }(), i.e. the probabilities for units in the system at time, are given in the form of integrals in which modifiedBessel functions of the first kind occur. Integrating the state probalityP_{0}() over leads to the meanL() and the varianceV() of the number of units in the system.For<1 and the systems tend to a steady state (for which the solution is known); for1 and we haveP_{ v }()0 for all, L(),V().If>1 asymptotic expansions for large are found givingL() andV() proportional to. If=1 simple approximate formulas for large are obtained givingL() and the standard deviation() proportional to .

Vorgel. v.:J. Nitsche. 相似文献

17.

In order to treat one-parameter semigroups of linear operators on Banach spaces which are not strongly continuous, we introduce the concept of bi-continuous semigroups defined on Banach spaces with an additional locally convex topology . On such spaces we define bi-continuous semigroups as semigroups consisting of bounded linear operators which are locally bi-equicontinuous for and such that the orbit maps are -continuous. We then apply the result to semigroups induced by flows on a metric space as studied by J. R. Dorroh and J. W. Neuberger. 相似文献

18.

We generalize the notion of (,)-derivation of Nakajima and Bresar. We define the generalized (,)-derivations, generalized Jordan (,)-derivations, and generalized Lie (,)-derivations, We study interrelations between these classes of derivations as well as their homological properties. 相似文献

19.

We consider the problem of extending the notion of -pseudocompactness from spaces to continuous mappings, obtain conditions under which the product of -pseudocompact mappings is -pseudocompact. Since any space

*X*can be considered as a continuous mapping from*X*into a singleton, we obtain consequences of the theorems on multiplicativity of -pseudocompactness for spaces. Thus, we study the notion of -pseudocompact mapping and some its properties similar to those of a pseudocompact space as well as consequences of the obtained assertions for spaces. 相似文献20.

A. F. Vakulenko 《Journal of Mathematical Sciences》1984,27(2):2559-2561

One considers a self-adjoint operator H for which one has a unitary group U

_{}such that the operator H^{}U_{}HU_{}^{–1}is analytic with respect to . Under certain additional restrictions on H, one proves the absence of the singular continuous spectrum of H. In this connection one admits such a behavior of the essential spectrum of H^{}for Im 0 which excludes the application of the method of analytic dilatations. In our analysis, analogies with the method of the inverse scattering problem play an important role.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 127, pp. 3–6, 1983. 相似文献