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882. A note on infinite aS-groups
- Creator:
- Nikandish, Reza and Miraftab, Babak
- Format:
- print, bez média, and svazek
- Type:
- model:article and TEXT
- Subject:
- matematika, mathematics, infinite aS-group, supplemented subgroup, nilpotent group, 13, and 51
- Language:
- English
- Description:
- Let G be a group. If every nontrivial subgroup of G has a proper supplement, then G is called an aS-group. We study some properties of aS-groups. For instance, it is shown that a nilpotent group G is an aS-group if and only if G is a subdirect product of cyclic groups of prime orders. We prove that if G is an aS-group which satisfies the descending chain condition on subgroups, then G is finite. Among other results, we characterize all abelian groups for which every nontrivial quotient group is an aS-group. Finally, it is shown that if G is an aS-group and |G| ≠ pq, p, where p and q are primes, then G has a triple factorization., Reza Nikandish, Babak Miraftab., and Obsahuje seznam literatury
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
883. A note on integral vortex strength
- Creator:
- Kolář, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- circulation, unsteady Taylor vortex, vortex intensity, vortex strength, vorticity, vorticity decomposition, cirkulace, nestacionární Taylorův vír, intenzita víru, síla víru, vířivost, and rozklad vířivosti
- Language:
- Slovak
- Description:
- Controversial aspects of the conventional and widely used concept of the integral vortex strength are briefly discussed. The strength of a vortex is usually calculated as the circulation along the vortex boundary, or equivalently due to Green’s theorem, as the surface integral of vorticity over the planar vortex cross section. However, the local effect of an arbitrary ''superimposed shear'' is fully absorbed by vorticity what makes the circulation a shear-biased vortex characteristic. The present paper shows that different vortexstrength models can be derived on the basis of different local vortex intensities proposed in the literature. The outcome of these models naturally differs, even for an ideally axisymmetric vortex. Three different vortex-strength models are compared and discussed by examining the unsteady Taylor vortex. and V práci jsou stručně diskutovány sporné stránky konvenčního a široce užívaného pojetí integrální síly víru. Síla víru je obvykle počítána jako cirkulace podél hranice víru nebo ekvivalentně podle Greenovy věty jako plošný integrál vířivosti přes příčný rovinný řez vírem. Lokální efekt libovolného ''superponovaného smyku'' je však plně absorbován vířivostí, což činí z cirkulace smykově zkreslenou vírovou charakteristiku. Tento článek ukazuje, že lze odvodit různé modely síly víru na základě různých lokálních intenzit víru navržených v odborné literatuře. Výsledky těchto modelů se přirozeně liší, dokonce i pro ideálně osově symetrický vír. Na podkladě zkoumání nestacionárního Taylorova víru jsou porovnány a diskutovány tři různé modely síly víru.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
884. A note on integration by parts for abstract Perron-Stieltjes integrals
- Creator:
- Schwabik, Štefan
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- integration by parts, Kurzweil-Stieltjes integral, and Perron-Stieltjes integral
- Language:
- English
- Description:
- Integration by parts results concerning Stieltjes integrals for functions with values in Banach spaces are presented. The background of the theory is the Kurzweil approach to integration based on Riemann type integral sums, which leads to the Perron integral.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
885. A note on k-c-semistratifiable spaces and strong β-spaces
- Creator:
- Wang, Li-Xia and Peng, Liang-Xue
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- c-semistratifiable space, k-c-semistratifiable space, submesocompact space, g function, and strong β-space
- Language:
- English
- Description:
- Recall that a space X is a c-semistratifiable (CSS) space, if the compact sets of X are Gδ-sets in a uniform way. In this note, we introduce another class of spaces, denoting it by k-c-semistratifiable (k-CSS), which generalizes the concept of c-semistratifiable. We discuss some properties of k-c-semistratifiable spaces. We prove that a T2-space X is a k-c-semistratifiable space if and only if X has a g function which satisfies the following conditions: (1) For each x ∈ X, {x} = ∩ {g(x, n): n ∈ ℕ} and g(x, n + 1) ⊆ g(x, n) for each n ∈ N. (2) If a sequence {xn}n∈N of X converges to a point x ∈ X and yn ∈ g(xn, n) for each n ∈ N, then for any convergent subsequence {ynk }k∈N of {yn}n∈N we have that {ynk }k∈N converges to x. By the above characterization, we show that if X is a submesocompact locally k-csemistratifiable space, then X is a k-c-semistratifible space, and the countable product of k-c-semistratifiable spaces is a k-c-semistratifiable space. If X = ∪ {Int(Xn): n ∈ N} and Xn is a closed k-c-semistratifiable space for each n, then X is a k-c-semistratifiable space. In the last part of this note, we show that if X = ∪ {Xn : n ∈ N} and Xn is a closed strong β-space for each n ∈ ℕ, then X is a strong β-space.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
886. A note on Lemaître´s model for third order resonance
- Creator:
- Pauwels, Thierry
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- space research and third order resonance
- Language:
- Czech
- Description:
- In recent papers Henrard and Lemaître have studied what they call "The Second Fundamental Model for Resonance" and higher order generalizations of it. The action integral ("area index") was computed analytically, but the phase space and the action integral as a function of the parameter δ were only plotted on scale by a computer. By using properties of quartic equations, however, the mathematically special values of δ were found. For third order resonances, one of these turned out to correspond to a minimum in the value of the "area index" A2, but since it is very shallow and very close to the starting point of the function, this feature was invisible in Lemaître's plots, This has some theoretical implications for the process of capture into a third order resonance, although numerically the effect will be small due to the shallowness of the minimum. A similar exercise on first and second order resonances revealed no new features.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
887. A note on local automorphisms
- Creator:
- Fošner, Ajda
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- automorphism, local automorphism, and algebra of operators on a Hilbert space
- Language:
- English
- Description:
- Let $H$ be an infinite-dimensional almost separable Hilbert space. We show that every local automorphism of $\mathcal B(H)$, the algebra of all bounded linear operators on a Hilbert space $H$, is an automorphism.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
888. A note on maximal estimates for stochastic convolutions
- Creator:
- Veraar, Mark and Weis, Lutz
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- stochastic convolutions, maximal inequalities, path-continuity, stochastic partial differential equations, $H^\infty $-calculus, $\gamma $-radonifying operators, and exponential tail estimates
- Language:
- English
- Description:
- In stochastic partial differential equations it is important to have pathwise regularity properties of stochastic convolutions. In this note we present a new sufficient condition for the pathwise continuity of stochastic convolutions in Banach spaces.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
889. A note on maximal inequality for stochastic convolutions
- Creator:
- Hausenblas, Erika and Seidler, Jan
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- infinite-dimensional Wiener process, stochastic convolution, and maximal inequality
- Language:
- English
- Description:
- Using unitary dilations we give a very simple proof of the maximal inequality for a stochastic convolution \[ \int ^t_0 S(t-s)\psi (s)\mathrm{d}W(s) \] driven by a Wiener process $W$ in a Hilbert space in the case when the semigroup $S(t)$ is of contraction type.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
890. A note on model structures on arbitrary Frobenius categories
- Creator:
- Li, Zhi-Wei
- Format:
- print, bez média, and svazek
- Type:
- model:article and TEXT
- Subject:
- matematika, mathematics, Frobenius categorie, triangulated categories, model structure, 13, and 51
- Language:
- English
- Description:
- We show that there is a model structure in the sense of Quillen on an arbitrary Frobenius category F such that the homotopy category of this model structure is equivalent to the stable category F as triangulated categories. This seems to be well-accepted by experts but we were unable to find a complete proof for it in the literature. When F is a weakly idempotent complete (i.e., every split monomorphism is an inflation) Frobenius category, the model structure we constructed is an exact (closed) model structure in the sense of Gillespie (2011)., Zhi-Wei Li., and Seznam literatury
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public