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Varga  O. 《Archiv der Mathematik》1954,5(1-3):128-131
Ohne Zusammenfassung Alexander Ostrowski zum 60. Geburtstag gewidmet  相似文献   

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Let ℱ: x=x(u1, u2) be a C3-surface in the euclidean space E3, n the unit normal vector of ℱ and let . We consider the vector of ℝ6 and we denote with μ the rank of the matrix (a, a1, a2, a1, 1, a1, 2, a2, 2). We then prove the Theorem: ℱ is a W-surface if and only if μ≦5. Further, μ is 4 resp. 3 if and only if the surface ℱ is part of a cylinder of revolution resp. part of a sphere or a plane.   相似文献   

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Ohne Zusammenfassung Hellmuth Kneser zum 60. Geburtstag gewidmet  相似文献   

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Any solution of the system $$f\left( x \right) = \frac{1}{k} \sum\limits_{i = 0}^{k - 1} { f (\frac{{x + i}}{k}) (k = 1, 2, 3, \ldots ) } $$ of functional equations which is continuous on (0,1) is of the form f(x)=a·cot(πx)+b. The result contains a new characterization of the cotangent function by means of simple properties. The proof is elementary.  相似文献   

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In the present article there is given a characterization of power series spaces of finite type by linear topological invariants. This is used to give a complete characterization of the classes of subspaces and quotient spaces of any nuclear stable power series space 1(). It is further used for the investigation of exact sequences of the form Or()E()O. They are known to split for =+. It is shown that for r<+, p<+, but the sequence need not split. There are examples for for r=+, p<+. At last the characterization is used to determine the structure of certain systems of linear equations in infinitely many variables (ct. Mityagin [10], Probl. 4.6). At the end of the article we give conditions on a space E for the existence of a 1() such that E is a subspace or a quotient space of E and we give an example of an isomorphy proof using the previous results.  相似文献   

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Summary Types of boundary value problems of partial differential equations for infinite domains are discussed which can easily be transformed in such a manner as to allow estimations of error (for approximate solutions) similar to the boundary maximum principle. First, second und third boundary value problems for the outer domain of linear elliptic and certain linear and nonlinear parabolic differential equations are examined. For elliptic differential equations one of the results is that the secound boundary value problem for more than two dimensions can be included. The estimates of the paper can thus be applied to problems of flow around some object, not in the case of two but of three dimensions. This is in a certain sense a counterpart to the conformal mappings method which is successful for two but not for three dimensions. Numerical examples show that estimations of error can easily be carried out.  相似文献   

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The categorySob of sober spaces is a full isomorphismclosed reflective subcategory of the categoryT o of To-spaces (and continuous maps).SobT o is characterized by: (i) every universal morphism of the adjunction is aT o-epic embedding, and (ii) everyT o-epic embedding, whose domain is sober, is a homeomorphism.Sob is the epi-reflective hull of the Sierpinski space D inT o. A subspace of a sober space is sober, iff it is b-closed. A space is sober, iff it is a b-closed subspace of a power of D.  相似文献   

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Für eine groe Klasse von Limitierungsverfahren charakterisieren wir diejenigen cn, für die a n = O(c n) eine Tauber-Bedingung ist. Damit verallgemeinern wir, unter Verwendung adäquater Begriffe, zwei Resultate von Lorentz [13] und Stieglitz [20].  相似文献   

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Zusammenfassung Eilon undHall interessierten sich für optimale Zeitabstände beim Justieren von Maschinen. Die Eigenschaft des Output läßt sich durch eine reelle Zahl messen. Diese wird als normalverteilt angenommen, wobei der Mittelwert linear von der Zeit, die seit der letzten Einstellung vergangen ist, abhängt und die Streuung gegeben ist. Im folgenden wird der Fall betrachtet, daß Mittelwert und Streuung Funktionen der Zeit und eines Einstellungsparameters sind, die gewissen Differenzierbarkeitseigenschaften genügen. Der allgemeinere Fall, daß die Eigenschaften des Ausstoßes durch mehrere reelle Zahlen charakterisiert werden, läßt sich ebenfalls behandeln.
Summary Eilon andHall are interested in the optimal time difference between the adjustment of machines. The quality of the output may be characterized by one real number. This is assumed to be a normally distributed random variable; the expected value is a linear function of the time elapsed since the last adjustment; the variance is given. There follows the case where the expected value and the variance are functions of time and a parameter of the adjustment; these functions may have some properties with respect to their differentiability. The general case is also examined in which the quality of the output is characterized by several real numbers.
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