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Documentos disponibles de esta editorial (118)
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Let M denote a p-fold, branched, cyclic, covering space of S3, and suppose that the three-dimensional Smith conjecture is true for p-periodic autohomeomorphisms of S3. J. S. Birman and H. M. Hilden have constructed an algorithm for deciding whet[...]texto impreso
It is shown that a PL, orientable 4-manifold with no 3- or 4-handles is a 3-fold irregular cover of the 4-ball, branched over a ribbon 2-manifold. The author also studies 2-fold branched cyclic covers and finds examples of surfaces in S4 whose 2[...]texto impreso
A set which can be defined by systems of polynomial inequalities is called semialgebraic. When such a scription is possible locally around every point, by means of analytic inequalities varying with the point, the set; is called semianalytic. If[...]texto impreso
Montesinos Amilibia, José María ; Hilden, Hugh Michael ; Lozano Imízcoz, María Teresa | American Mathematical Society | 1983-10This paper establishes two new ways of representing all closed orientable 3-manifolds. (1) Let F,N be a pair of disjoint bounded orientable surfaces in the 3-sphere S3. Let (Sk,Fk,Nk), k=1,2,3, be 3 copies of the triplet (S,F,N). Split S1 along [...]texto impreso
Melle Hernández, Alejandro ; Gusein-Zade, Sabir Medgidovich ; Luengo Velasco, Ignacio | American Mathematical Society | 2008We offer an equivariant version of the classical monodromy zeta function of a singularity as a series with coefficients from the Grothendieck ring of finite G-sets tensored by the field of rational numbers. Main two ingredients of the definition[...]texto impreso
We give in this paper a description of the shape category of compacta in terms of multivalued maps. We introduce the notion of a multi-net and prove that the shape category of compacta is isomorphic to the category HN whose objects are metric co[...]texto impreso
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This paper discusses the construction of asymptotically holomorphic embeddings of a (2n?1) -dimensional contact manifold into the projective space CP 2n+1 such that the image is weakly dominated by the symplectic form. The proof follows the s[...]texto impreso
Parabolic Higgs bundles on a Riemann surface are of interest for many reasons, one of them being their importance in the study of representations of the fundamental group of the punctured surface in the complex general linear group. In this pape[...]texto impreso
In this work we answer a question stated by Loi and Zaharia concerning trivialization of definable functions off the bifurcation set: we prove that definable functions are trivial off the bifurcation set, and the trivialization can be chosen def[...]texto impreso
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It is shown that, in contrast to the complex case, every paracompact finite-dimensional real-analytic manifold can be embedded as a bounded and closed real-analytic submanifold of every infinite-dimensional real Banach space.texto impreso
Cuchillo Ibáñez, Eduardo ; Dydak, J. ; Koyama, A. ; Morón, Manuel A. | American Mathematical Society | 2008-10-10Motivated by the Chapman Complement Theorem, we construct an isomorphism between the topological category of compact Z-sets in the Hilbert cube Q and the C0-coarse category of their complements. The C0-coarse morphisms are, in this particular ca[...]texto impreso
In this paper we characterize the finite dimensionality of a compact Z-set in the Hilbert cube in terms of the existence of a particular canonical cover in its complement.texto impreso
Ciesielski, Krzysztof Chris ; Gámez Merino, José Luis ; Mazza, L. ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2017We investigate the additivity A and lineability L cardinal coeffiients for the following classes of functions: ES\SES of everywhere surjective functions that are not strongly everywhere surjective, Darboux-like, Sierpinski-Zygmund, surjective, a[...]texto impreso
Jaramillo Aguado, Jesús Ángel ; Jiménez Sevilla, María del Mar ; Sánchez González, L. | American Mathematical Society | 2014-03In this note we give sufficient conditions to ensure that the weak Finsler structure of a complete C-k Finsler manifold M is determined by the normed algebra C-b(k)(M) of all real-valued, bounded and C-k smooth functions with bounded derivative [...]texto impreso
Hilbert's 17th Problem asked the following. Let f(x1,?,xn) be a real polynomial which for all real values ?1,?,?n satisfies f(?1,?,?n)?0. Is it true that f=?(gi/hi)2 for polynomials gi,hi?R[x1,?,xn]? (It was known that f=?(gi)2, gi?R[x1,?,xn], i[...]texto impreso
We give a classification of minimal algebras generated in degree 1, defined over any field k of characteristic different from 2, up to dimension 6. This recovers the classification of nilpotent Lie algebras over k up to dimension 6. In the case [...]texto impreso
Gallego Rodrigo, Francisco Javier ; Purnaprajna, Bangere P. | American Mathematical Society | 2008-10In this article we classify quadruple Galois canonical covers of smooth surfaces of minimal degree. The classification shows that they are either non-simple cyclic covers or bi-double covers. If they are bi-double, then they are all fiber produc[...]texto impreso
We provide a criterion for the existence of a residual set of common hypercyclic vectors for an uncountable family of hypercyclic operators which is based on a previous one given by Costakis and Sambarino. As an application, we get common hyperc[...]texto impreso
Let E, F be real Banach spaces, U subset-or-equal-to E and V subset-equal-to F non-void open subsets and C(k)(U) the algebra of real-valued k-times continuously Frechet differentiable functions on U, endowed with the compact open topology of ord[...]texto impreso
Gallardo Gutiérrez, Eva A. ; González, María J. ; Nicolau, Arthur | American Mathematical Society | 2008For any simply connected domain., we prove that a Littlewood type inequality is necessary for boundedness of composition operators on H-p(Omega), 1texto impreso
In this paper the authors review some work relating the topology to algebraic invariants. Three cases are considered: hypersurfaces, vector fields and vector fields tangent to hypersurfaces. An example is the case of "real Milnor fibres". Let f[...]texto impreso
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In this paper we give a characterization of pointwise and uniform convergence of sequences of homogeneous polynomials on a Banach space by means of the convergence of their level sets. Results are obtained both in the real and the complex cases[...]texto impreso
Let (?,?,?) be any measure space, X a Banach space and for 1?ptexto impreso
Let M denote a p-fold, branched, cyclic, covering space of S3, and suppose that the three-dimensional Smith conjecture is true for p-periodic autohomeomorphisms of S3. J. S. Birman and H. M. Hilden have constructed an algorithm for deciding whet[...]texto impreso
Crystal defects such as dislocations are the basis of macroscopic properties such as the strength of materials and control their mechanical, optical and electronic properties. In recent times, advances in electronic microscopy have allowed imagi[...]texto impreso
Gallego Rodrigo, Francisco Javier ; Purnaprajna, Bangere P. | American Mathematical Society | 1997-06A K3 carpet S is a double structure on a rational normal scroll such that its dualizing sheaf is trivial and h1(OS) = 0. In this note the authors show that every K3 carpet S can be smoothed, i.e. there exists a flat family over a smooth curve w[...]texto impreso
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We prove that each positive operator from a Banach lattice E to a Banach lattice F with a disjointly strictly singular majorant is itself disjointly strictly singular provided the norm on F is order continuous. We prove as well that if S : E -->[...]texto impreso
For a variety X?PN, its mth order dual variety is the variety X?m?(PN)? consisting of hyperplanes containing an mth osculating space of X. The strict dual variety X? is the smallest nonempty X?m. All these dual varieties were described by Piene [...]texto impreso
We investigate dual spaces of interpolation spaces defined by means of polygons. We first show that dual spaces may fail to be intermediate spaces with respect to the dual N-tuple, and then we prove that dual spaces of J-spaces can be identified[...]texto impreso
Artal Bartolo, Enrique ; Carmona Ruber, Jorge ; Cogolludo Agustín, José Ignacio | American Mathematical Society | 2007In this paper we construct new invariants of algebraic curves based on (not necessarily generic) braid monodromies. Such invariants are effective in the sense that their computation allows for the study of Zariski pairs of plane curves. Moreover[...]texto impreso
We give an explicit description of some pleating varieties (sets with a fixed set of bending lines in the convex hull boundary) in the quasi-Fuchsian space of the twice punctured torus. In accordance with a conjecture of the second author, we sh[...]texto impreso
Castillo, Jesús M.F. ; García, R. ; Jaramillo Aguado, Jesús Ángel | American Mathematical Society | 2001We study the extension of bilinear and multilinear forms from a given subspace of a Banach space to the whole space. Precisely, an isomorphic embedding j : E --> X is said to be (linearly) N-exact if N-linear forms on E can be (linear and conti[...]texto impreso
Let ?:P?M be a principal G-bundle. One denotes by J1P the 1-jet bundle of local sections of ?, by autP the Lie algebra of G-invariant vector fields of P and by gauP the ideal of ?-vertical vector fields in autP. A differential form ? on J1P is s[...]texto impreso
We prove the existence of families of germs of holomorphic vector fields in Cm without a separatrix, in every complex dimension m bigger than or equal to 4.texto impreso
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We prove new adjunction inequalities for embedded surfaces in four-manifolds with non-negative self-intersection number using the Donaldson invariants. These formulas are completely analogous to the ones obtained by Ozsvath and Szabo using the S[...]texto impreso
We show that to each inner function, there corresponds at least one interpolating Blaschke product whose angular derivatives have precisely the same behavior as the given inner function. We characterize the Blaschke products invertible in the cl[...]texto impreso
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A bordered Klein surface of algebraic genus p has at most 12(p-1) automorphisms and this is attained for infinitely many values of p. Furthermore, for an infinity of values of p, the largest group of automorphisms of such a surface is $4(p+1)$ o[...]texto impreso
Let T and V be complex analytic spaces, with T reduced and locally irreducible and ?:T×V?T the projection map to the first factor. Let K ? be a complex 0?K n ? X n K n?1 ? X n?1 …? X 2 K 1 ? X 1 K 0 ?0 of O T×V coherent sheaves, whe[...]texto impreso
The author presents various ideas, proofs, constructions and tricks connected with branched coverings of 3-manifolds. After an introductory section on 2-fold branched coverings of S3 the main theme of 3-fold irregular coverings is introduced. [...]texto impreso
Long ago J. W. Alexander showed that any closed, orientable, triangulated n-manifold can be expressed as a branched covering of the n-sphere [Bull. Amer. Math. Soc. 26 (1919/20), 370–372; Jbuch 47, 529]. In general, the branch set is not a manif[...]texto impreso
Bernal González, Luis ; Pellegrino, Daniel ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2014For the last decade there has been a generalized trend in mathematics on the search for large algebraic structures (linear spaces, closed subspaces, or infinitely generated algebras) composed of mathematical objects enjoying certain special prop[...]texto impreso
Luengo Velasco, Ignacio ; Melle Hernández, Alejandro ; Némethi, A. | American Mathematical Society | 2005Using superisolated singularities we present examples and counterexamples to some of the most important conjectures regarding invariants of normal surface singularities. More precisely, we show that the ``Seiberg-Witten invariant conjecture''(of[...]texto impreso
This paper is a study of some vanishing properties of weak solutions to nonlinear elliptic and parabolic equations. Instead of using monotonicity arguments, the method of proof is based on an energy method.texto impreso
González Pérez, Pedro Daniel ; González Villa, Manuel ; Budur, Nero | American Mathematical Society | 2012The log canonical thresholds of irreducible quasi-ordinary hypersurface singularities are computed, using an explicit list of pole candidates for the motivic zeta function found by the last two authors.texto impreso
Buder, Nero ; González Pérez, Pedro Daniel ; Gozález Villa, Manuel | American Mathematical Society | 2012The log canonical thresholds of irreducible quasi-ordinary hypersurface singularities are computed using an explicit list of pole candidates for the motivic zeta function found by the last two authors.texto impreso
Diniz, D. ; Muñoz-Fernández, Gustavo A. ; Pellegrino, D. ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2014-02The Bohnenblust-Hille inequality was obtained in 1931 and ( in the case of real scalars) asserts that for every positive integer m there is a constant Cm so that ((N)Sigma(i1 , . . . , im=1)vertical bar T(e(i1) (,...,) e(im))vertical bar(2m/m+[...]texto impreso
The literature devoted to degree theory and its applications is abundant, but the richness of the topics is such that it is not surprising to see regularly the publication of new books in this area. The emphasis of the present one is on Brouwer[...]texto impreso
If F and G are disjoint compact surfaces with boundary in S3=?D4, let F? and G? be the result of pushing F and G into the interior of D4, keeping ?F and ?G fixed. The authors give an explicit cut and paste description of an irregular 3-fold bran[...]texto impreso
The geometric motivic Poincare series of a variety, which was introduced by Denef and Loeser, takes into account the classes in the Grothendieck ring of the sequence of jets of arcs in the variety. Denef and Loeser proved that this series has a [...]texto impreso
In this paper we prove that two N-compact spaces are homeomorphic if and only if they have the same shape. We also obtain a result concerning shape domination, and finally we give an answer to the problem of components in shape theory.texto impreso
We study the formality of the mapping torus of an orientation-preserving diffeomorphism of a manifold. In particular, we give conditions under which a mapping torus has a non-zero Massey product. As an application we prove that there are non-for[...]texto impreso
We consider normal (possibly) branched, finite-sheeted coverings $ \pi:X\rightarrow X'$ between hyperelliptic real algebraic curves. We are interested in the topology of such coverings and also in describing them in terms of algebraic equations.[...]texto impreso
Given a 3-fold simple (i.e. generic branched) covering p:M?S3, a standard modification (called "move C'' in this paper and due to the author and the reviewer in their theses in 1972) permits one to change the branch set but not the covering mani[...]texto impreso
We are concerned in this paper with the density of functionals which do not attain their norms in Banach spaces. Some earlier results given for separable spaces are extended to the nonseparable case. We obtain that a Banach space X is reflexive [...]texto impreso
Applied to a knot K of S1 in S3, Zeeman's n-twist-spinning construction produces a knot Kn of S2 in S4 [ E. C. Zeeman , Trans. Amer. Math. Soc. 115 (1965), 471–495;]. Here the author gives an explicit "movie presentation'' of Kn, that is, a desc[...]texto impreso
We give a different proof of the result of M. Sakuma [Math. Sem. Notes Kobe Univ. 9 (1981), no. 1, 159–180] that every closed, oriented 3-manifold M has a 2-fold branched covering space N which is a surface bundle over S1. We also give a new pro[...]texto impreso
We give conditions on the nonlinearities of a reaction-diffusion equation with nonlinear boundary conditions that guarantee that any solution starting at bounded initial data is bounded locally around a certain point x0 of the boundary, uniforml[...]texto impreso
We shall prove the following: ( 1) Let r : X --> Y be a refinable map between paracompact spaces. Then X is finitistic if and only if Y is finitistic. ( 2) Let f : X --> Y be a hereditary shape equivalence between metric spaces. Then if X is f[...]texto impreso
“Let A be the coordinate ring of the real plane, i.e., A = R[X, Y ], where X, Y are algebraically independent over the field of real numbers R. The purpose of this paper is to describe all the valuation rings of A which are compatible with some [...]texto impreso
The main application of the results of this paper is to prove the existence of real valuation rings of the quotient field K of an excellent domain A having prescribed centers, ranks, rational ranks and residue dimensions. The major part of the p[...]texto impreso
In this work we study how open and closed semialgebraic maps between two semialgebraic sets extend, via the corresponding spectral maps,to the Zariski and maximal spectra of their respective rings of semialgebraic and bounded semialgebraic functions.texto impreso
It is proved that if p is a prime ideal in the ring S{M) of semialgebraic functions on a semialgebraic set M, the quotient field of S(M)/p is real closed. We also prove that in the case where M is locally closed, the rings S(M) and P(M)—polynomi[...]texto impreso
Artal Bartolo, Enrique ; Cassou-Noguès, Pierrette ; Luengo Velasco, Ignacio ; Melle Hernández, Alejandro | American Mathematical Society | 2011The concept of ?-quasi-ordinary power series, which is a generalization of quasi-ordinary power series, was first introduced by H. Hironaka. In the paper under review, the authors study ?-quasi-ordinary power series and give a factorization theo[...]texto impreso
Gallego Rodrigo, Francisco Javier ; Purnaprajna, Bangere P. | American Mathematical Society | 2011-03-07I In this article we study the bicanonical map ?2 of quadruple Galois canonical covers X of surfaces of minimal degree. We show that ?2 has diverse behavior and exhibits most of the complexities that are possible for a bicanonical map of surface[...]texto impreso
Gallego Rodrigo, Francisco Javier ; Purnaprajna, Bangere P | American Mathematical Society | 2003-03-19Let S be a regular surface of general type with at worst canonical singularities and with basepoint-free canonical system. Let X be its canonical image. It is well known that X must be a canonical surface or a minimal degree surface. The main re[...]texto impreso
The authors study the Cauchy problem for the degenerate parabolic equation ut = div(|Du| p?2 Du)(ptexto impreso
In this paper we characterize those compact Hausdorff spaces such that (and ) have the Dunford-Pettis Property, answering thus in the negative a question posed by Castillo and González who asked if and have this property.texto impreso
Herrero, Miguel A. ; Oleaga Apadula, Gerardo Enrique ; Velázquez, J.J. L. | American Mathematical Society | 2006This work deals with the linear wave equation considered in the whole plane R2 except for a rectilinear moving slit, represented by a curve ? (t) = {(x1, 0) : ??texto impreso
Let X C P-N be an irreducible threefold having a hyperplane section Y that is a smooth Enriques surface and such that X is not a cone over Y. In 1938 Fano claimed a classification of such threefolds; however, due to gaps in his proof, the proble[...]texto impreso
Artal Bartolo, Enrique ; Cassou-Noguès, Pierrette ; Luengo Velasco, Ignacio ; Melle Hernández, Alejandro | American Mathematical Society | 2008In this article we show that for a given, reduced or non reduced, germ of a complex plane curve, there exists a local system of coordinates such that its log-canonical threshold at the singularity can be explicitly computed from the intersection[...]texto impreso
The minimum genus problem consists on determining the minimum algebraic genus of a surface on which a given group G acts. For cyclic groups G this problem on bordered Klein surfaces was solved in 1989. The next step is to fix the number of bound[...]texto impreso
Llavona, José G. ; Linares Briones, Pablo ; Ibort Latre, Luis Alberto | American Mathematical Society | 2010A multilinear generalization of the trigonometric problem of moments is presented and discussed. The moments c(k), k is an element of Z(n) of a regular Borel polymeasure gamma on T(n) are characterized by means of a norm parallel to . parallel t[...]texto impreso
Acquistapace, Francesca ; Broglia, Fabrizio ; Fernando Galván, José Francisco | American Mathematical Society | 2016In this work we prove the real Nullstellensatz for the ring O(X) of analytic functions on a C-analytic set X ? Rn in terms of the saturation of ?ojasiewicz’s radical in O(X): The ideal I(?(a)) of the zero-set ?(a) of an ideal a of O(X) coincides[...]texto impreso
We improve the known results on eigenvalue distributions of weakly singular integral operators having (power) order of the singularity equal to half of the dimension of the underlying domain. Moreover we show that our results are the best possible.texto impreso
In the same vein as the classical Stone–?Cech compactification, we prove in this work that the maximal spectra of the rings of semialgebraic and bounded semialgebraic functions on a semialgebraic set M ? Rn, which are homeomorphic topological sp[...]texto impreso
Sánchez Gabites, Jaime Jorge ; Rodríguez Sanjurjo, José Manuel | American Mathematical Society | 2007Suppose phi : M x R -> M is a continuous flow on a locally compact metrizable space M and K is an ( asymptotically stable) attractor. Let D =partial derivative A( K) be the boundary of the basin of attraction of K. In the present paper it will [...]texto impreso
Let K and S be compact Hausdorff spaces and 8 a continuous function from K onto S. Then for any Banach space E the map / -» / ° 9 isometrically embeds C(S, £) as a closed subspace of C(K, E). In this note we prove that when E' has the Radon-Niko[...]texto impreso
Given a Banach space X and an integer n, the existence of an n-homogeneous polynomial which is not uniformly continuous with respect to the polynomial topology on B-X is investigated. We provide a complete characterization for some classical Ban[...]texto impreso
A mapping between Banach spaces is said to be polynomially continuous if its restriction to any bounded set is uniformly continuous for the weak polynomial topology. A Banach space X has property(RP) if given two bounded sequences (u(j)), (v(j))[...]texto impreso
In this note we use the space ? in order to prove that a result concerning movability and mutational retractions cannot be transferred from the compact to the arbitrary metrizable casetexto impreso
We characterize the double Veronese embedding of P-n as the only variety that, under certain general conditions, can be isomorphically projected from the Grassmannian of lines in P2n+1 to the Grassmannian of lines in Pn+1.texto impreso
The authors classify all topological types of degenerate central fibers appearing in holomorphic families of closed Riemann surfaces of genus g?2 over the unit disc. A degenerating family of genus g is a triple (M,D,?) consisting of a 2-dime[...]texto impreso
Melle Hernández, Alejandro ; Artal Bartolo, Enrique ; Cassou-Noguès, Pierrette ; Luengo Velasco, Ignacio | American Mathematical Society | 2005-11The main objective of this paper is to prove the monodromy conjecture for the local Igusa zeta function of a quasi-ordinary polynomial of arbitrary dimension defined over a number field. In order to do it, we compute the local Denef-Loeser motiv[...]texto impreso
Castrillón López, Marco ; Ratiu, Tudor S. ; Shkoller, Steve | American Mathematical Society | 1999-11-01In Lagrangian mechanics the simplest example of reduction is the Euler-Poincaré reduction. In this case, the configuration space is a Lie group G and the Lagrangian function L:TG?R is invariant under the natural action of the group on TG by righ[...]texto impreso
Let G be a topological group. The set G? of all characters (i.e., continuous homomorphisms from G to the torus T=R/Z) is an abelian group (with pointwise addition). The sets (C,U)={f?G? : f(C)?U}, where C runs over all compact subsets of G and U[...]texto impreso
In 1920, J. W. Alexander proved that, if M3 is a closed orientable three-dimensional manifold, then there exists a covering M3?S3 that branches over a link [same Bull. 26 (1919/20), 370–372; Jbuch 47, 529]. In the paper under review, the author [...]texto impreso
We introduce the class of everywhere like functions, which helps us to recover some known classes (such as that of everywhere surjective ones). We also study the algebraic genericity of this new class together with the class of fractal functions.texto impreso
Acquistapace, Francesca ; Andradas Heranz, Carlos ; Broglia, Fabrizio | American Mathematical Society | 1999We study the problem of deciding whether two disjoint semialgebraic sets of an algebraic variety over R are separable by a polynomial. For that we isolate a dense subfamily of spaces of orderings, named geometric, which suffice to test separatio[...]texto impreso
Gámez Merino, José Luis ; Muñoz-Fernández, Gustavo A. ; Sánchez, V.M. ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2010-11We find large algebraic structures inside the following sets of pathological functions: (i) perfectly everywhere surjective functions, (ii) differentiable functions with almost nowhere continuous derivatives, (iii) differentiable nowhere monoton[...]texto impreso
Enflo, Per H. ; Gurariy, Vladimir ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2014A subset M of a topological vector space X is called lineable (respectively, spaceable) in X if there exists an infinite dimensional linear space (respectively, an infinite dimensional closed linear space) Y subset of M boolean OR {0}. In this a[...]texto impreso
The spider principle is used for establishing a formula for a finite quadratic sequence which determines the multiplicity sequences of all the sprouts which are founded upon the given finite quadratic sequence. This formula is basic for the theo[...]texto impreso
In this interesting paper, the author gives a stability condition for the fixed point property in terms of K. Borsuk's fundamental metric on a hyperspace of a compact metric space. This condition is equivalent to that originally given by V. L. K[...]texto impreso
Hernández, Francisco L. ; Semenov, Evgeny M. ; Tradacete Pérez, Pedro | American Mathematical Society | 2010-02We study the class Vp of strictly singular non-compact operators on Lp spaces. This allows us to obtain interpolation results for strictly singular operators on Lp spaces. Given 1 ? ptexto impreso
Aron, Richard M. ; Conejero, Jose A. ; Peris, Alfredo ; Seoane-Sepúlveda, Juan B. | American Mathematical Society | 2007We examine the question of whether there are algebras of functions having special properties. The types of functions studied will be everywhere surjective functions, hypercyclic entire functions, and continuous functions that attain their maximu[...]texto impreso
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.texto impreso
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.texto impreso
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[...]texto impreso
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.texto impreso
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 0texto impreso
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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.texto impreso
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[...]texto impreso
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[...]texto impreso
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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[...]texto impreso
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[...]texto impreso
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[...]texto impreso
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[...]texto impreso
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 0texto impreso
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 "[...]texto impreso
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[...]