Radiative isotropic cosmologies with extra dimensions

We solve Einsteins equations in an n-dimensional vacuum with the simplest ansatz leading to a Friedmann-Robertson-Walker (FRW) four-dimensional space time. We show that the FRW model must be of radiation. For the open models the extra dimensions contract as a result of cosmological evolution. For flat and closed models they contract only when there is one extra dimension.

Expansió accelerada de l’univers i teories de gravetat modificada a grans escales

Estudi realitzat a partir d’una estada al Physics Department de la New York University, United States, Estats Units, entre 2006 i 2008. Una de les observacions de més impacte en la cosmologia moderna ha estat la determinació empírica que l’Univers es troba actualment en una fase d’Expansió Accelerada (EA). Aquest fenòmen implica que o bé l’Univers està dominat per un nou sector de matèria/energia, o bé la Relativitat General deixa de tenir validesa a escales cosmològiques. La primera possibilitat comprèn els models d’Energia Fosca (EF), i el seu principal problema és que l’EF ha de tenir propietats tan especials que es fan difícils de justificar teòricament. La segona possibilitat requereix la construcció de teories consistents de Gravetat Modificada a Grans Distàncies (GMGD), que són una generalització dels models de gravetat massiva. L’interès fenomenològic per aquestes teories també va resorgir amb l’aparició dels primers exemples de models de GMGD, com ara el model de Dvali, Gabadadze i Porrati (DGP), que consisteix en un tipus de brana en una dimensió extra. Malauradament, però, aquest model no permet explicar de forma consistent l’EA de l’Univers. Un dels objectius d’aquest projecte ha estat establir la viabilitat interna i fenomenològica dels models de GMGD. Des del punt de vista fenomenològic, ens hem centrat en la questió més important a la pràctica: trobar signatures observacionals que permetin distingir els models de GMGD dels d’EF. A nivell més teòric, també hem investigat el significat de les inestabilitats del model DGP.L’altre gran objectiu que ens vam proposar va ser la construcció de noves teories de GMGD. En la segona part d’aquest projecte, hem elaborat i mostrat la consistència del model “DGP en Cascada”, que generalitza el model DGP a més dimensions extra, i representa el segon model consistent i invariant-Lorentz a l’espai pla conegut. L’existència d’altres models de GMGD més enllà de DGP és de gran interès atès que podria permetre obtenir l’EA de l’Univers de forma purament geomètrica.

Cosmic strings in extra dimensions

The Einstein equations coupled with a cloud of geometric strings for a five-dimensional Bianchi type-I cosmological model are studied. The cosmological consequences of having strings along the fifth dimension are examined. Particular solutions with dynamical compactifications of the extra dimensions and compatibility with expanding three-dimensional spaces are presented.

Does absorptive capacity determine collaborative research returns to innovation? A geographical dimension

This paper aims to estimate the impact of research collaboration with partners in different geographical areas on innovative performance. By using the Spanish Technological Innovation Panel, this study provides evidence that the benefits of research collaboration differ across different dimensions of the geography. We find that the impact of extra-European cooperation on innovation performance is larger than that of national and European cooperation, indicating that firms tend to benefit more from interaction with international partners as a way to access new technologies or specialized and novel knowledge that they are unable to find locally. We also find evidence of the positive role played by absorptive capacity, concluding that it implies a higher premium on the innovation returns to cooperation in the international case and mainly in the European one.

Hopf bifurcation for degenerate singular points of multiplicity 2n-1 in dimension 3

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The Cuntz semigroup, the Elliott conjecture, and dimension functions on C*-Algebras

We prove that the Cuntz semigroup is recovered functorially from the Elliott invariant for a large class of C¤-algebras. In particular, our results apply to the largest class of simple C¤-algebras for which K-theoretic classification can be hoped for. This work has three significant consequences. First, it provides new conceptual insight into Elliott's classification program, proving that the usual form of the Elliott conjecture is equivalent, among Z-stable algebras, to a conjecture which is in general substantially weaker and for which there are no known counterexamples. Second and third, it resolves, for the class of algebras above, two conjectures of Blackadar and Handelman concerning the basic structure of dimension functions on C¤-algebras. We also prove in passing that the Kuntz-Pedersen semigroup is recovered functorially from the Elliott invariant for all simple unital C¤-algebras of interest.

The ‘Global Dimension’ of Contemporary Politics. An Argument for Taking ‘Global’ Seriously

Recent years have seen a striking proliferation of the term ‘global’ in public and political discourse. The popularity of the term is a manifestation of the fact that there is a widespread notion that contemporary social reality is ‘global’. The acknowledgment of this notion has important political implications and raises questions about the role played by the idea of the ‘global’ in policy making. These questions, in turn, expose even more fundamental issues about whether the term ‘global’ indicates a difference in kind, even an ontological shift, and, if so, how to approach it. This paper argues that the notion of ‘global’, in other words the ‘global dimension’, is a significant aspect of contemporary politics that needs to be investigated. The paper argues that in the globalization discourse of International Studies ‘global’ is ‘naturalized’, which means that it is taken for granted and assumed to be self-evident. The term ‘global’ is used mainly in a descriptive way and subsumed under the rubric of ‘globalization’. ‘Global’ tends to be equated with transnational and/or world-wide; hence, it addresses quantitative differences in degree but not (alleged) differences in kind. In order to advance our understanding of contemporary politics, ‘global’ needs to be taken seriously. This means, firstly, to understand and to conceptualize ‘global’ as a social category; and, secondly, to uncover ‘global’ as a ‘naturalized’ concept in the Political and International Studies strand of the globalization discourse in order to rescue it for innovative new approaches in the investigation of contemporary politics. In order to do so, the paper suggests adopting a strong linguistic approach starting with the analysis of the word ‘global’. Based on insights from post-structuralism as well as cognitive and general constructivist perspectives it argues that a frame-based corpus linguistic analysis offers the possibility of investigating the collective/social meaning(s) of global in order to operationalize them for the analysis of the ‘global dimension’ of contemporary politics.

Monopoles in arbitrary dimension

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Els refranys: estudi i equivalències

Treball de recerca realitzat per una alumna d'ensenyament secundari i guardonat amb un Premi CIRIT per fomentar l'esperit científic del Jovent l'any 2009. El treball es divideix en tres grans blocs temàtics, seguint una seqüència lògica: teoria dels refranys, recull de refranys catalans i els seus equivalents (inclou la creació d un diccionari) i l’aplicació pràctica del treball en un lloc web. Dins del bloc teòric es tracten amb profunditat àmbits de la fraseologia i la paremiologia (ciència dels refranys i les unitats fraseològiques) com ara la formació dels refranys, la seva estructura, el seu significat i el seu ús. També s’hi inclou un criteri de comparació de refranys de llengües diferents, tenint en compte aspectes com el seu grau d idiomaticitat (possibilitat d’establir el significat d’una unitat pel seu sentit figurat i a la vegada pel seu sentit literal). Cal destacar que l’estudi teòric dels refranys és gairebé inexistent en llengua catalana, i que en conseqüència l’elaboració d’aquesta part del projecte ha requerit un esforç suplementari. En el segon bloc, partint d’un recull de refranys pertanyent al besavi de l’alumna, on hi constaven refranys catalans amb els seus equivalents en francès i castellà, s’elabora un diccionari de refranys, explicant el significat d’aquests i afegint-hi l’equivalent en anglès, i en alguns casos, fins i tot es comenta l’antecedent llatí del refrany. Per tal de trobar una dimensió pràctica al nou recull, es procedeix a la creació d’un lloc web, amb la intenció de difondre el contingut del diccionari. Aquest seria el tercer bloc que conforma el treball.

Blow-up, concentration phenomenon and global existence for the Keller-Segel model in high dimension

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Gaussian estimates for the density of the non-linear stochastic heat equation in any space dimension

In this paper, we establish lower and upper Gaussian bounds for the probability density of the mild solution to the stochastic heat equation with multiplicative noise and in any space dimension. The driving perturbation is a Gaussian noise which is white in time with some spatially homogeneous covariance. These estimates are obtained using tools of the Malliavin calculus. The most challenging part is the lower bound, which is obtained by adapting a general method developed by Kohatsu-Higa to the underlying spatially homogeneous Gaussian setting. Both lower and upper estimates have the same form: a Gaussian density with a variance which is equal to that of the mild solution of the corresponding linear equation with additive noise.

Temperamental Dimension and Anxiety Problems in a Clinical Sample of Three- to Six-year old Children: A Study of Variables

In the last few years, many researchers have studied the presence of common dimensions of temperament in subjects with symptoms of anxiety. The aim of this study is to examine the association between temperamental dimensions (high negative affect and activity level) and anxiety problems in clinicalpreschool children. A total of 38 children, ages 3 to 6 years, from the Infant and Adolescent Mental Health Center of Girona and the Center of Diagnosis and Early Attention of Sabadell and Olot were evaluated by parents and psychologists. Their parents completed several screening scales and, subsequently, clinical child psychopathology professionals carried out diagnostic interviews with children from the sample who presented signs of anxiety. Findings showed that children with high levels of negative affect and low activity level have pronounced symptoms of anxiety. However, children with anxiety disorders do not present different temperament styles from their peers without these pathologies

Some hypothesis tests for the covariance matrix when the dimension is large compared to the sample size

This paper analyzes whether standard covariance matrix tests work whendimensionality is large, and in particular larger than sample size. Inthe latter case, the singularity of the sample covariance matrix makeslikelihood ratio tests degenerate, but other tests based on quadraticforms of sample covariance matrix eigenvalues remain well-defined. Westudy the consistency property and limiting distribution of these testsas dimensionality and sample size go to infinity together, with theirratio converging to a finite non-zero limit. We find that the existingtest for sphericity is robust against high dimensionality, but not thetest for equality of the covariance matrix to a given matrix. For thelatter test, we develop a new correction to the existing test statisticthat makes it robust against high dimensionality.

The left-right dimension in Latin America

We present voters' self-placement and 68 political party locations on the left-right dimension in 17 Latin American countries. Innovative calculations are based on data from Latinobarometer annual surveys from 1995 to 2002. Our preliminary analysis of the results suggests that most Latin American voters are relatively highly ideological and rather consistently located on the left-right dimension, but they have very high levels of political alienation regarding the party system. Both voters' self-placement and the corresponding party locations are presently highly polarized between the center and the right, with a significant weakness of leftist or broadly appealing 'populist' positions.

A data-dependent skeleton estimate and a scale-sensitive dimension for classification

The classical binary classification problem is investigatedwhen it is known in advance that the posterior probability function(or regression function) belongs to some class of functions. We introduceand analyze a method which effectively exploits this knowledge. The methodis based on minimizing the empirical risk over a carefully selected``skeleton'' of the class of regression functions. The skeleton is acovering of the class based on a data--dependent metric, especiallyfitted for classification. A new scale--sensitive dimension isintroduced which is more useful for the studied classification problemthan other, previously defined, dimension measures. This fact isdemonstrated by performance bounds for the skeleton estimate in termsof the new dimension.