Статьи журнала - Владикавказский математический журнал
Все статьи: 883
Color energy of some cluster graphs
Статья научная
Let G be a simple connected graph. The energy of a graph G is defined as sum of the absolute eigenvalues of an adjacency matrix of the graph G. It represents a proper generalization of a formula valid for the total π-electron energy of a conjugated hydrocarbon as calculated by the Huckel molecular orbital (HMO) method in quantum chemistry. A coloring of a graph G is a coloring of its vertices such that no two adjacent vertices share the same color. The minimum number of colors needed for the coloring of a graph G is called the chromatic number of G and is denoted by χ(G). The color energy of a graph G is defined as the sum of absolute values of the color eigenvalues of G. The graphs with large number of edges are referred as cluster graphs. Cluster graphs are graphs obtained from complete graphs by deleting few edges according to some criteria. It can be obtained on deleting some edges incident on a vertex, deletion of independent edges/triangles/cliques/path P3 etc. Bipartite cluster graphs are obtained by deleting few edges from complete bipartite graphs according to some rule. In this paper, the color energy of cluster graphs and bipartite cluster graphs are studied.
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Conformal Ricci soliton in an indefinite trans-Sasakian manifold
Статья научная
Conformal Ricci solitons are self similar solutions of the conformal Ricci flow equation. A new class of n-dimensional almost contact manifold namely trans-Sasakian manifold was introduced by Oubina in 1985 and further study about the local structures of trans-Sasakian manifolds was carried by several authors. As a natural generalization of both Sasakian and Kenmotsu manifolds, the notion of trans-Sasakian manifolds, which are closely related to the locally conformal Kahler manifolds introduced by Oubina. This paper deals with the study of conformal Ricci solitons within the framework of indefinite trans-Sasakian manifold. Further, we investigate the certain curvature tensor on indefinite trans-Sasakian manifold. Also, we have proved some important results.
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Cyclically compact operators in banach spaces
Статья научная
The Boolean-valued interpretation of compactness gives rise to the new notions of cyclically compact sets and operators which deserves an independent study. A part of the corresponding theory is presented in this work. General form of cyclically compact operators in Kaplansky--Hilbert module as well as a variant of Fredholm Alternative for cyclically compact operators are also given.
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Cлабая непрерывность оператора суперпозиции в пространствах последовательностей
Статья научная
Изучаются условия слабой непрерывности оператора суперпозиции, действующего в некотором пространстве последовательностей. Даны условия, при которых слабая непрерывность оператора суперпозиции равносильна его аффинности. В то же самое время, в пространстве сходящихся к нулю последовательностей любая ограниченная непрерывная функция порождает слабо непрерывный оператор суперпозиции. Приведены примеры, показывающие существенность предположения об ограниченности. Показывается, что в произвольном бесконечномерном пространстве последовательностей всегда существует оператор суперпозиции, являющийся слабо непрерывным и не представимый в виде суммы аффинного оператора и оператора обладающего конечномерной областью значений.
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Derivations on Banach *-ideals in von Neumann algebras
Статья научная
It is known that any derivation δ:M→M on the von Neumann algebra M is an inner, i.e. δ(x):=δa(x)=[a,x]=ax-xa, x∈M, for some a∈M. If H is a separable infinite-dimensional complex Hilbert space and K(H) is a C∗-subalgebra of compact operators in C∗-algebra B(H) of all bounded linear operators acting in H, then any derivation δ:K(H)→K(H) is a spatial derivation, i.e. there exists an operator a∈B(H) such that δ(x)=[x,a] for all x∈K(H). In addition, it has recently been established by Ber A. F., Chilin V. I., Levitina G. B. and Sukochev F. A. (JMAA, 2013) that any derivation δ:E→E on Banach symmetric ideal of compact operators E⊆K(H) is a spatial derivation. We show that the same result is also true for an arbitrary Banach ∗-ideal in every von Neumann algebra M. More precisely: If M is an arbitrary von Neumann algebra, E be a Banach ∗-ideal in M and δ:E→E is a derivation on E, then there exists an element a∈M such that δ(x)=[x,a] for all x∈E, i.e. δ is a spatial derivation.
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Erratum to: "Infinitesimals in ordered vector spaces"
Другой
In this note, Theorem 1 in the article which is cited in the title is corrected.
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Every lateral band is the kernel of an orthogonally additive operator
Статья научная
In this paper we continue a study of relationships between the lateral partial order ⊑ in a vector lattice (the relation x⊑y means that x is a fragment of y) and the theory of orthogonally additive operators on vector lattices. It was shown in [1] that the concepts of lateral ideal and lateral band play the same important role in the theory of orthogonally additive operators as ideals and bands play in the theory for linear operators in vector lattices. We show that, for a vector lattice E and a lateral band G of E, there exists a vector lattice F and a positive, disjointness preserving orthogonally additive operator T:E→F such that kerT=G. As a consequence, we partially resolve the following open problem suggested in [1]: Are there a vector lattice E and a lateral ideal in E which is not equal to the kernel of any positive orthogonally additive operator T:E→F for any vector lattice F?
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Existence and uniqueness theorems for a differential equation with a discontinuous right-hand side
Статья научная
We consider new conditions for existence and uniqueness of a Caratheodory solution for an initial value problem with a discontinuous right-hand side. The method used here is based on: 1) the representation of the solution as a Fourier series in a system of functions orthogonal in Sobolev sense and generated by a classical orthogonal system; 2) the use of a specially constructed operator A acting in l2, the fixed point of which are the coefficients of the Fourier series of the solution. Under conditions given here the operator A is contractive. This property can be employed to construct robust, fast and easy to implement spectral numerical methods of solving an initial value problem with discontinuous right-hand side. Relationship of new conditions with classical ones (Caratheodory conditions with Lipschitz condition) is also studied. Namely, we show that if in classical conditions we replace L1 by L2, then they become equivalent to the conditions given in this article.
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Existence of classical solutions for a class of the Khokhlov-Zabolotskaya-Kuznetsov type equations
Статья научная
In medical sciences, during medical exploration and diagnosis of tissues or in medical imaging, we often use mathematical models to answer questions related to these examinations. Among these models, the nonlinear partial differential equation of the Khokhlov-Zabolotskaya-Kuznetsov type (abbreviated as the KZK equation) is of proven interest in ultrasound acoustics problems. This mathematical model describes the nonlinear propagation of a sound pulse of finite amplitude in a thermo-viscous medium. The equation is obtained by combining the conservation of mass equation, the conservation of momentum equation and the equations of state. It should be noted that for this equation little mathematical analysis is reserved. This equation takes into account three combined effects: the diffraction of the wave, the absorption of energy and the nonlinearity of the medium in which the wave propagates. KZK-type equation introduced in this paper is a modified version of the KZK model known in acoustics. We study a class of the Khokhlov-Zabolotskaya-Kuznetsov type equations for the existence of global classical solutions. We give conditions under which the considered equations have at least one and at least two classical solutions. To prove our main results, we propose a new approach based on recent theoretical results.
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Existence of global classical solutions for the Saint-Venant equations
Статья научная
Nowadays, investigations of the existence of global classical solutions for non linear evolution equations is a topic of active mathematical research. In this article, we are concerned with a classical system of shallow water equations which describes long surface waves in a fluid of variable depth. This system was proposed in 1871 by Adhemar Jean-Claude Barre de Saint-Venant. Namely, we investigate an initial value problem for the one dimensional Saint-Venant equations. We are especially interested in question of what sufficient conditions the initial data and the topography of the bottom must verify in order that the considered system has global classical solutions. In order to prove our main results we use a new topological approach based on the fixed point abstract theory of the sum of two operators in Banach spaces. This basic and new idea yields global existence theorems for many of the interesting equations of mathematical physics.
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Existence results for a Dirichlet boundary value problem involving the p(x)-Laplacian operator
Статья научная
The aim of this paper is to establish the existence of weak solutions, in W1,p(x)0(Ω), for a Dirichlet boundary value problem involving the p(x)-Laplacian operator. Our technical approach is based on the Berkovits topological degree theory for a class of demicontinuous operators of generalized (S+) type. We also use as a necessary tool the properties of variable Lebesgue and Sobolev spaces, and specially properties of p(x)-Laplacian operator. In order to use this theory, we will transform our problem into an abstract Hammerstein equation of the form v+S∘Tv=0 in the reflexive Banach space W-1,p′(x)(Ω) which is the dual space of W1,p(x)0(Ω). Note also that the problem can be seen as a nonlinear eigenvalue problem of the formAu=λu, where Au:=-Div(|∇u|p(x)-2∇u)-f(x,u). When this problem admits a non-zero weak solution u, λ is an eigenvalue of it and u is an associated eigenfunction.
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Статья научная
In this paper, we provide sufficient conditions for the existence of solutions of initial value problem, for perturbed partial functional hyperbolic differential equations of fractional order involving Caputo fractional derivative with state-dependent delay by reducing the research to the search of the existence and the uniqueness of fixed points of appropriate operators. Our main result for this problem is based on a nonlinear alternative fixed point theorem for the sum of a completely continuous operator and a contraction one in Banach spaces due to Burton and Kirk and a fractional version of Gronwall's inequality. We should observe the structure of the space and the properties of the operators to obtain existence results. To our knowledge, there are very few papers devoted to fractional differential equations with finite and/or infinite constant delay on bounded domains. Many other questions and issues can be investigated regarding the existence in the space of weighted continuous functions, the uniqueness, the structure of the solutions set and also whether or not the condition satisfied by the operators are optimal. This paper can be considered as a contribution in this setting case. Examples are given to illustrate this work.
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Exponential stability for a swelling porous-heat system with thermodiffusion effects and delay
Статья научная
In the present work, we consider a one-dimensional swelling porous-heat system with single time-delay in a bounded domain under Dirichlet-Neumann boundary conditions subject to thermodiffusion effects and frictional damping to control the delay term. The coupling gives new contributions to the theory associated with asymptotic behaviors of swelling porous-heat. At first, we state and prove the well-posedness of the solution of the system by the semigroup approach using Lumer-Philips theorem under suitable assumption on the weight of the delay. Then, we show that the considered dissipation in which we depended on are strong enough to guarantee an exponential decay result by using the energy method that consists to construct an appropriate Lyapunov functional based on the multiplier technique, this result is obtained without the equal-speed requirement. Our result is new and an extension of many other works in this area.
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Extension of an almost f-algebra multiplication
Статья научная
It is proved that an almost f-algebra multiplication and a d-algebra multiplication defined on a majorizing vector sublattice of a Dedekind complete vector lattice can be extended to the whole vector lattice by using purely algebraic and order theoretical means.
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Functional calculus and Minkowski duality on vector lattices
Статья научная
The paper extends homogeneous functional calculus on vector lattices. It is shown that the function of elements of a relatively uniformly complete vector lattice can naturally be defined if the positively homogeneous function is defined on some conic set and is continuous on some closed convex subcone. An interplay between Minkowski duality and homogeneous functional calculus leads to the envelope representation of abstract convex elements generated by the linear hull of a finite collection in a uniformly complete vector lattice.
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Functions with uniform sublevel sets on cones
Статья научная
Extended real-valued functions on a real vector space with uniform sublevel sets are important in optimization theory. Weidner studied these functions in [1]. In the present paper, we study the class of these functions, which coincides with the class of Gerstewitz functionals, on cones. These cone are not necessarily embeddable in vector spaces. Almost any Weidner's results are not true on cones without extra conditions. We show that the mentioned conditions are necessary, by nontrivial examples. Specially for element k from the cone P, we define k-directional closed subsets of the cone and prove some properties of them. For a subset A of the cone P, we characterize domain of the φA,k (function with uniform sublevel set) and show that this function is k-transitive. One of the important conditions for satisfying the results, is that k has the symmetric element in the cone. Also, we prove that, under some conditions, the class of Gerstewitz functionals coincides with the class of k-translative functions on P.
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Generalization of Eberlein's and sine's ergodic theorems to lr-nets
Статья научная
The notion of LR-nets provides an appropriate setting for study of various ergodic theorems in Banach spaces. In the present paper, we prove Theorems 2.1, 3.1 which extend Eberlein's and Sine's ergodic theorems to LR-nets. Together with Theorem 1.1, these two theorems form the necessary background for further investigation of strongly convergent LR-nets. Theorem 2.1 is due to F. Rabiger, and was announced without a proof in [1].
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Generalization of the Ostrowski inequalities on time scales
Статья научная
The idea of time scales calculus’ theory was initiated and introduced by Hilger (1988) in his PhD thesis order to unify discret and continuous analysis and to expend the discrete and continous theories to cases ``in between''. Since then, mathematical research in this field has exceeded more than 1000 publications and a lot of applications in the fields of science, i.e., operations research, economics, physics, engineering, statistics, finance and biology. Ostrowski proved an inequality to estimate the absolute deviation of a differentiable function from its integral mean. This result was obtained by applying the Montgomery identity. In the present paper we derive a generalization of the Montgomery identity to the various time scale versions such as discrete case, continuous case and the case of quantum calculus, by obtaining this generalization of Montgomery identity we would prove our results about the generalization of the Ostrowski inequalities (without weighted case) to the several time scales such as discrete case, continuous case and the case of quantum calculus and recapture the several published results of different authors of various papers and thus unify corresponding discrete version and continuous version. Similarly we would also derive our results about the generalization of the Ostrowski inequalities (weighted case) to the different time scales such as discrete case and continuous case and recapture the different published results of several authors of various papers and thus unify corresponding discrete version and continuous version. Moreover, we would use our obtained results (without weighted case) to the case of quantum calculus.
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