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American Mathematical Society |
Documentos disponibles de esta editorial (118)
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Let A be an analytic ring. We show:(1) A has finite Pythagoras number if and only if its real dimension is 2, and (2) if every positive semidefinite element of A is a sum of squares, then A is real and has real dimension 2.![]()
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Fernando Galván, José Francisco ; Ruiz Sancho, Jesús María ; Scheiderer, Claus | American Mathematical Society | 2004Let A be an excellent ring. We show that if the real dimension of A is at least three then A has in finite Pythagoras number, and there exists a positive semidefinite element in A which is not a sum of squares in A.![]()
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Gamboa, J. M. ; Broughton, SA ; Bujalance, E. ; Costa, F.A. ; Gromadzki, G. | American Mathematical Society | 1999For all g 2 there is a Riemann surface of genus g whose automorphism group has order 8g+8, establishing a lower bound for the possible orders of automorphism groups of Riemann surfaces. Accola and Maclachlan established the existence of such sur[...]![]()
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Nhu, Nguyen Tho ; Rodríguez Sanjurjo, José Manuel ; Van An, Tran | American Mathematical Society | 1997-10In this second part of our paper, we apply the result of Part 1 to show that the compact convex set with no extreme points, constructed by Roberts (1977), is an AR.![]()
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This paper deals with the Cauchy problem for the nonlinear diffusion equation ?u/?t - ? (u|u|m+1) = 0 on (0, ?) x RN,u(0, .) = u0 when 0![]()
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In this paper we prove that if E is a Banach space with separable dual, then the space C(K, E) of all continuous E-valued functions on a compact Haus-dorff topological space K has the Dieudonnep roperty.![]()
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A Banach Space E Is Said To Be Hereditarily Dunford-Pettis If All Of Its Closed Subspaces Have The Dunford-Pettis Property. In This Note We Prove That The Banach Space 11 (E), Of All Absolutely Summing Sequences In E With The Usual Norm, Is Here[...]![]()
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Muñoz-Fernández, Gustavo A. ; Sarantopoulos, Y ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2010K. Ball has proved the "complex plank problem": if (x(k))(k=1)(n) is a sequence of norm I vectors in a complex Hilbert space (H, (., .)), then there exists a unit vector x for which | | > = 1/root n, k = 1,...,n. In general, this resul[...]![]()
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In this paper, we study some problems related to the Corson theorem. In particular we prove that co does not fulfil such a theorem; hence this theorem is not valid for all infinite-dimensional Banach spaces. We give also generalizations of Corso[...]![]()
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We present a simple and elementary procedure to sketch the tropical conic given by a degree-two homogeneous tropical polynomial. These conics are trees of a very particular kind. Given such a tree, we explain how to compute a defining polynomial[...]![]()
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Radiotherapy consists in the delivery of ionizing radiation with curative goals. It represents a major modality for treating solid malignancies in any anatomical site. It requires extremely precise dosimetry and delivery to control the lesion wh[...]![]()
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An important open question about 3-manifolds is whether or not there exists an algorithm for recognizing S3. The author poses two questions about Heegaard diagrams of S3, appropriate answers to either of which would give such an algorithm. If[...]![]()
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Let (u(t, x), v(t, x)) and (uBAR(t, x), vBAR(t, x)) be two nonnegative classical solutions of (S)[GRAPHICS:{ut=?u+vp, p> 0 ; vt=?v+uq, q> 0] in some strip S(T) = (0, T) x R(N), where 0![]()
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Montesinos Amilibia, José María ; Hilden, Hugh Michael ; Lozano Imízcoz, María Teresa | American Mathematical Society | 1983In an unpublished preprint W. Thurston showed the existence of a six component link in the 3-sphere such that every three-manifold can be expressed as a branched cover of the 3-sphere branched over this link. He called links with this property "[...]![]()
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For a symplectic manifold, the harmonic cohomology of symplectic divisors (introduced by Donaldson, 1996) and of the more general symplectic zero loci (introduced by Auroux, 1997) are compared with that of its ambient space. We also study symple[...]