Number of results to display per page
Search Results
27522. On non-periodic groups whose finitely generated subgroups are either permutable or pronormal
- Creator:
- Kurdachenko, L. A., Subbotin, I. Ya., and Ermolkevich, T. I.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- pronormal subgroup, permutable subgroup, finitely generated subgroup, and abnormal subgroup
- Language:
- English
- Description:
- The current article considers some infinite groups whose finitely generated subgroups are either permutable or pronormal. A group G is called a generalized radical, if G has an ascending series whose factors are locally nilpotent or locally finite. The class of locally generalized radical groups is quite wide. For instance, it includes all locally finite, locally soluble, and almost locally soluble groups. The main result of this paper is the following Theorem. Let G be a locally generalized radical group whose finitely generated subgroups are either pronormal or permutable. If G is non-periodic then every subgroup of G is permutable.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27523. On nonmeasurable images
- Creator:
- Rałowski, Robert and Żeberski, Szymon
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- nonmeasurable set, Bernstein set, and Polish ideal space
- Language:
- English
- Description:
- Let $(X,\mathbb I)$ be a Polish ideal space and let $T$ be any set. We show that under some conditions on a relation $R\subseteq T^2\times X$ it is possible to find a set $A\subseteq T$ such that $R(A^2)$ is completely $\mathbb I $-nonmeasurable, i.e, it is $\mathbb I$-nonmeasurable in every positive Borel set. We also obtain such a set $A\subseteq T$ simultaneously for continuum many relations $(R_\alpha )_{\alpha <2^\omega }.$ Our results generalize those from the papers of K. Ciesielski, H. Fejzić, C. Freiling and M. Kysiak.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27524. On nonoscillation of canonical or noncanonical disconjugate functional equations
- Creator:
- Singh, Bhagat
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- canonical, noncanonical, oscillatory, nonoscillatory, and principal system
- Language:
- English
- Description:
- Qualitative comparison of the nonoscillatory behavior of the equations \[ L_ny(t) + H(t,y(t)) = 0 \] and \[ L_ny(t) + H(t,y(g(t))) = 0 \] is sought by way of finding different nonoscillation criteria for the above equations. $L_n$ is a disconjugate operator of the form \[ L_n = \frac{1}{p_n(t)} \frac{\mathrm{d}{}}{\mathrm{d}t} \frac{1}{p_{n-1}(t)} \frac{\mathrm{d}{}}{\mathrm{d}t} \ldots \frac{\mathrm{d}{}}{\mathrm{d}t} \frac{\cdot }{p_0(t)}. \] Both canonical and noncanonical forms of $L_n$ have been studied.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27525. On nonregular ideals and $z^\circ$-ideals in $C(X)$
- Creator:
- Azarpanah, F. and Karavan, M.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- $z^\circ $-ideal, prime $z$-ideal, nonregular ideal, almost ${P}$-space, $\partial $-space, and $m$-space
- Language:
- English
- Description:
- The spaces $X$ in which every prime $z^\circ $-ideal of $C(X)$ is either minimal or maximal are characterized. By this characterization, it turns out that for a large class of topological spaces $X$, such as metric spaces, basically disconnected spaces and one-point compactifications of discrete spaces, every prime $z^\circ $-ideal in $C(X)$ is either minimal or maximal. We will also answer the following questions: When is every nonregular prime ideal in $C(X)$ a $z^\circ $-ideal? When is every nonregular (prime) $z$-ideal in $C(X)$ a $z^\circ $-ideal? For instance, we show that every nonregular prime ideal of $C(X)$ is a $z^\circ $-ideal if and only if $X$ is a $\partial $-space (a space in which the boundary of any zeroset is contained in a zeroset with empty interior).
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27526. On nonuniform dichotomy for stochastic skew-evolution semiflows in Hilbert spaces
- Creator:
- Stoica, Diana and Megan, Mihail
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- stochastic skew-evolution semiflow and nonuniform exponential dichotomy in mean square
- Language:
- English
- Description:
- In this paper we study a general concept of nonuniform exponential dichotomy in mean square for stochastic skew-evolution semiflows in Hilbert spaces. We obtain a variant for the stochastic case of some well-known results, of the deterministic case, due to R. Datko: Uniform asymptotic stability of evolutionary processes in a Banach space, SIAM J. Math. Anal., 3(1972), 428–445. Our approach is based on the extension of some techniques used in the deterministic case for the study of asymptotic behavior of skew-evolution semiflows in Banach spaces.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27527. On numerical solution of compressible flow in time-dependent domains
- Creator:
- Feistauer, Miloslav, Horáček, Jaromír, Kučera, Václav, and Prokopová, Jaroslava
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- compressible Navier-Stokes equations, arbitrary Lagrangian-Eulerian method, discontinuous Galerkin finite element method, interior and boundary penalty, semi-implicit time discretization, and biomechanics of voice
- Language:
- English
- Description:
- We show that dynamical systems in inverse problems are sometimes foliated if the embedding dimension is greater than the dimension of the manifold on which the system resides. Under this condition, we end up reaching different leaves of the foliation if we start from different initial conditions. For some of these cases we have found a method by which we can asymptotically guide the system to a specific leaf even if we start from an initial condition which corresponds to some other leaf. We demonstrate the method by two examples. In the chosen cases of the harmonic oscillator and Duffing's oscillator we find an alternative set of equations which represent a collapsed foliation, such that no matter what initial conditions we choose, the system would asymptotically reach the same desired sub-manifold of the original system. This process can lead to cases for which a system begins in a chaotic region, but is guided to a periodic region and vice versa. It may also happen that we could move from an orbitThe paper deals with numerical simulation of a compressible flow in time-dependent 2D domains with a special interest in medical applications to airflow in the human vocal tract. The mathematical model of this process is described by the compressible Navier-Stokes equations. For the treatment of the time-dependent domain, the arbitrary Lagrangian-Eulerian (ALE) method is used. The discontinuous Galerkin finite element method (DGFEM) is used for the space semidiscretization of the governing equations in the ALE formulation. The time discretization is carried out with the aid of a linearized semi-implicit method with good stability properties. We present some computational results for the flow in a channel, representing a model of glottis and a part of the vocal tract, with a prescribed motion of the channel walls at the position of vocal folds. of one period to an orbit of another period.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27528. On one approach to local surface smoothing
- Creator:
- Dikoussar, Nikolay and Török, Csaba
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- data smoothing, least squares and related methods, linear regression, approximation by polynomials, interpolation, computer aided design (modeling of curves and surfaces), and surface approximation
- Language:
- English
- Description:
- A bicubic model for local smoothing of surfaces is constructed on the base of pivot points. Such an approach allows reducing the dimension of matrix of normal equations more than twice. The model enables to increase essentially the speed and stability of calculations. The algorithms, constructed by the aid of the offered model, can be used both in applications and the development of global methods for smoothing and approximation of surfaces.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27529. On operators with the same local spectra
- Creator:
- Torgašev, Aleksandar
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- Banach space, spectrum, and local spectrum
- Language:
- English
- Description:
- Let $B(X)$ be the algebra of all bounded linear operators in a complex Banach space $X$. We consider operators $T_1,T_2\in B(X)$ satisfying the relation $\sigma _{T_1}(x) = \sigma _{T_2}(x)$ for any vector $x\in X$, where $\sigma _T(x)$ denotes the local spectrum of $T\in B(X)$ at the point $x\in X$. We say then that $T_1$ and $T_2$ have the same local spectra. We prove that then, under some conditions, $T_1 - T_2$ is a quasinilpotent operator, that is $\Vert (T_1 - T_2)^n\Vert ^{1/n} \rightarrow 0$ as $n \rightarrow \infty $. Without these conditions, we describe the operators with the same local spectra only in some particular cases.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
27530. On optimal decay rates for weak solutions to the Navier-Stokes equations in ℝn
- Creator:
- Miyakawa, Tetsuro and Schonbek, Maria Elena
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- decay rates and Navier-Stokes equations
- Language:
- English
- Description:
- This paper is concerned with optimal lower bounds of decay rates for solutions to the Navier-Stokes equations in Rn. Necessary and sufficient conditions are given such that the corresponding Navier-Stokes solutions are shown to satisfy the algebraic bound ||u(t)|| ≥ (t + 1)− (n+4)⁄2 .
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public