Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

Evaluation of glueball masses from supergravity

Abstract: In the framework of the conjectured duality relation between large N gauge theory and supergravity the spectra of masses in large N gauge theory can be determined by solving certain eigenvalue problems in supergravity. In this paper we study the eigenmass problem given by Witten as a possible approximation for masses in QCD without supersymmetry. We place a particular emphasis on the treatment of the horizon and related boundary conditions. We construct exact expressions for the analytic expansions of the wave functions both at the horizon and at infinity and show that requiring smoothness at the horizon and normalizability gives a well defined eigenvalue problem. We show, for example, that there are no smooth solutions with a vanishing derivative at the horizon. The mass eigenvalues up to ${m}^{2}=1000$ corresponding to smooth normalizable wave functions are presented. We comment on the relation of our work with the results found in a recent paper by C. Cs\'aki et al., hep-th/9806021, which addresses the same problem.

Role of the Alkyl−Alkoxide Precursor on the Structure and Catalytic Properties of Hybrid Sol−Gel Catalysts

Abstract: Detailed diffuse-reflectance infrared Fourier transform structural analysis of a series of organically modified silicates (ORMOSIL)-entrapped catalysts, varying the molar percentage and the alkyl c...

Variational principles and mixed multifractal spectra

Abstract: We establish a \" conditional \" variational principle, which unifies and extends many results in the multifractal analysis of dynam-ical systems. Namely, instead of considering several quantities of local nature and studying separately their multifractal spectra we develop a unified approach which allows us to obtain all spectra from a new mul-tifractal spectrum. Using the variational principle we are able to study the regularity of the spectra and the full dimensionality of their irregular sets for several classes of dynamical systems, including the class of maps with upper semi-continuous metric entropy. Another application of the variational principle is the following. The multifractal analysis of dynamical systems studies multifractal spectra such as the dimension spectrum for pointwise dimensions and the en-tropy spectrum for local entropies. It has been a standing open problem to effect a similar study for the \" mixed \" multifractal spectra, such as the dimension spectrum for local entropies and the entropy spectrum for pointwise dimensions. We show that they are analytic for several classes of hyperbolic maps. We also show that these spectra are not necessarily convex, in strong contrast with the \" non-mixed \" multifractal spectra.

Turbo Parsers: Dependency Parsing by Approximate Variational Inference

Abstract: We present a unified view of two state-of-the-art non-projective dependency parsers, both approximate: the loopy belief propagation parser of Smith and Eisner (2008) and the relaxed linear program of Martins et al. (2009). By representing the model assumptions with a factor graph, we shed light on the optimization problems tackled in each method. We also propose a new aggressive online algorithm to learn the model parameters, which makes use of the underlying variational representation. The algorithm does not require a learning rate parameter and provides a single framework for a wide family of convex loss functions, including CRFs and structured SVMs. Experiments show state-of-the-art performance for 14 languages.

Content Adaptive Wyner-ZIV Video Coding Driven by Motion Activity

Abstract: In distributed video coding (DVC), the video statistics are exploited, partially or totally at the decoder. A particular case of DVC, Wyner-Ziv video coding deals with lossy source coding with side information at the decoder and allows moving part or the entire motion estimation task to the decoder. In this context, it is the decoder responsibility to obtain the side information, a guess of the encoded Wyner-Ziv frame and the encoder only sends parity bits to improve its quality. In this paper, a technique targeting the improvement of the quality of the side information, and thus of the rate-distortion performance of the Wyner-Ziv codec is proposed. This is achieved by adaptively adjusting the size of the motion interpolation structure (or GOP length) according to the motion activity along the sequence. Experimentally, this allows to achieve gains up to 0.8 dB without performing any motion estimation or complex mode decision at the encoder.