Comments on the scalar propagator in AdS x S and the BMN plane wave

We discuss the scalar propagator on generic AdS_{d+1} x S^{d'+1} backgrounds. For the conformally flat situations and masses corresponding to Weyl invariant actions the propagator is powerlike in the sum of the chordal distances with respect to AdS_{d+1} and S^{d'+1}. In all other cases the propagator depends on both chordal distances separately. We discuss the KK mode summation to construct the propagator in brief. For AdS_5 x S^5 we relate our propagator to the expression in the BMN plane wave limit and find a geometric interpretation of the variables occurring in the known explicit construction on the plane wave.Comment: 7 pages, Fortsch.Phys. style, Talk given at 36th International Symposium Ahrenshoop on the Theory of Elementary Particles: Recent Developments in String/M- Theory and Field Theory, Wernsdorf, Germany, 26-30 Aug 200

D-branes in overcritical electric fields

We collect some arguments for treating a D-brane with overcritical electric field as a well-posed initial condition for a D-brane decay. Within the field theoretical toy model of Minahan and Zwiebach we give an estimate for the condensates of the related infinite tower of tachyonic excitations.Comment: 11 pages, 2 figures; references and comments added, version to appear in PR

An upper bound for the solving degree in terms of the degree of regularity

The solving degree is an important parameter for estimating the complexity of solving a system of polynomial equations. In this paper, we provide an upper bound for the solving degree in terms of the degree of regularity. We also show that this bound is optimal. As a direct consequence, we prove an upper bound for the last fall degree and a Macaulay bound.Comment: 7 page

Challenges for Landscape Architecture: Designed Urban Ecosystems and Social Acceptance

The creation of new ecosystems within urban contexts has undeniable benefits for city dwellers in terms of increased urban biodiversity and related provisioning of ecosystem services. However, designing new ecosystems in areas with a high population density or which are subject to intensive use may also generate negative impacts on the anthropic dimension and cause social conflicts that, in turn, can undermine the project’s effectiveness. This article focuses on the quite unexplored issue of anthropic “costs” that new urban ecosystems can generate, and on design and management challenges that they open up in terms of social acceptance. Landscape architecture, as a synthesis of ecological, aesthetic, and ethical aspects, seems to be the most appropriate framework for adopting a holistic approach to the design of new urban ecosystems. The article analyzes three Italian landscape architecture projects. All projects adopted spatial measures oriented at fostering perception, understanding, and acceptance of the recreated ecosystems, while preserving them from anthropic impacts. However, these efforts are sometimes jeopardized by a lack of concomitant operational measures, such as stakeholder involvement and site maintenance. Co-existence of delicate habitats and urban functions is thus not utopic but asks that projects effectively integrate ecological sciences, landscape design and management, as well as social-oriented practices

Imágenes que administran el tiempo

Los sujetos de la cultura de masas viven una condición omnipresente de repetición, donde nunca pasa nada “por primera vez”. La sociología ha reconocido esta actitud como “nostalgia del presente”. Ésta es el resultado de una política de las imágenes que tiene por objeto el control social a través de la neutralización del presente. Similares resultados han sido obtenidos en la Unión Soviética por medio de la propaganda estalinista, la cual puede, por tanto, considerarse como una avanzada experimentación en el uso político de las imágenes mediáticas.The subjects of mass culture live an omnipresent condition of repetitions, where nothing ever happens “for the first time”. Sociology has recognized this attitude as “longing for the present”. This is the result of a policy of images which aims at a social control through the neutralization of the present. Similar results have been obtained in the Soviet Union by the Stalin propaganda, which may therefore be considered as an advanced experimentation in the political use of media images

MacWilliams' Extension Theorem for rank-metric codes

The MacWilliams' Extension Theorem is a classical result by Florence Jessie MacWilliams. It shows that every linear isometry between linear block-codes endowed with the Hamming distance can be extended to a linear isometry of the ambient space. Such an extension fails to exist in general for rank-metric codes, that is, one can easily find examples of linear isometries between rank-metric codes which cannot be extended to linear isometries of the ambient space. In this paper, we explore to what extent a MacWilliams' Extension Theorem may hold for rank-metric codes. We provide an extensive list of examples of obstructions to the existence of an extension, as well as a positive result.Comment: 12 page

Renormalization of noncommutative U(N) gauge theories

We give an explicit proof that the noncommutative U(N) gauge theories are one-loop renormalizableComment: 12 pages, Latex. v3: calculations redone, conclusions reversed. v4, v5: minor change