Weyl transverse gravity (WTDiff) and the cosmological constant

Scale invariant (transverse) gravitational theories are introduced. They are invariant under pure metric rescalings (i.e. the matter fields are inert under those). This symmetry forbids the presence of a cosmological constant. Those theories are not invariant under the full set of diffeomorphisms, but only with respect to those locally characterized by the fact that their generator is transverse \pd_\a \xi^\a=0.Comment: 11 page

Advances in Handwritten Keyword Indexing and Search Technologies

Many extensive manuscript collections are available in archives and libraries all over the world, but their textual contents remain practically inaccessible, buried under thousands of terabytes worth of high-resolution images. If perfect or sufficiently accurate text-image transcripts were available, textual content could be indexed directly for plaintext access using conventional information retrieval systems. But the results of fully automated transcriptions generally lack the level of accuracy needed for reliable text indexing and search purposes. Additionally, manual or even computer-assited transcription is entierely unsustainable when dealing with the extensive image collections typically considered for indexing. This paper explains how accurate indexing and search commands can be implemented directly on the digital images themselves without the need to explicitly resort to image transcripts. Results obtained using the proposed techniques on several relevant historical data sets are presented, clearly supporting the considerable potential of these technologies

Finite time vacuum survival amplitude and vacuum energy decay

The problem of the vacuum energy decay is studied for both signs of the cosmological constant, through the analysis of the vacuum survival amplitude, defined in terms of the conformal time, z, by A(z,z′)≡ {vacz|vacz′}. Transition amplitudes are computed for finite time span, Z ≡ z′ - z, and their late time behavior (directly related to the putative decay width of the state), and the transients are discussed up to first order in the coupling constant, λThis work has been partially supported by the European Commission (HPRN-CT-200-00148) as well as by FPA2009-09017 (DGI del MCyT, Spain) and S2009ESP-1473 (CA Madrid). R.V. is supported by MEC Grant No. AP2006-0187

Implicit IDA-PBC Design and Implementation for a Portal Crane System

Interconnection and damping assignment passivity-based control (IDA-PBC) is a wellknown technique which regulates the behavior of nonlinear systems, assigning a target port-Hamiltonian (pH) structure to the closed-loop. In underactuated mechanical systems (UMSs) its application requires the satisfaction of matching conditions, which in many cases demands to solve partial differential equations (PDEs). Only recently, the IDA-PBC has been extended to UMSs modeled implicitly, where the system dynamics in pH representation are described by a set of differential-algebraic equations (DAEs). In some system classes this implicit approach allows to circumvent the PDE problem and also to design an output-feedback law. The present thesis deals with the design and implementation of the total energy shaping implicit IDA-PBC on a portal crane system located at the laboratory of the Control Engineering Group at TU-Ilmenau. The implicit controller is additionally compared with a simplified (explicit) IDA-PBC [1]. This algorithm shapes the total energy and avoids the PDE problem. However, this thesis reveales a significant implementation flaw in the algorithm, which then could be solved.Interconnection and damping assignment passivity-based control (IDA-PBC) ist eine wohlbekannte Methode zur Regelung von nichtlinearen Systemen, die im geschlossenen Regelkreis eine gewünschte Port-Hamiltonian-Struktur (pH) haben. Die Anwendung auf unteraktuierte mechanische Systeme (UMS) erfordert die Erfüllung von sogenannten Matching Conditions, die meistens die Lösung partieller Differentialgleichungen (PDE) benötigt. Erst kürzlich wurde die IDA-PBC auf implizit modellierte UMS erweitert, bei denen die Systemdynamik in pH-Darstellungen durch Differentialalgebraische Gleichungen (DAE) beschrieben wird. Dieser implizite Ansatz ermöglicht bei einigen Systemklassen, das PDE-Problem zu umgehen und auch eine Ausgangsrückführung zu entwerfen. Die vorliegende Masterarbeit beschäftigt sich mit dem Entwurf und der Implementierung des impliziten IDA-PBC zur Gesamtenergievorgabe auf einem Portalkransystem im Labor des Fachgebiets Regelungstechnik der TU-Ilmenau. Der implizite Regler wird mit einem vereinfachten (expliziten) IDA-PBC verglichen [1]. Dieser Algorithmus gibt ebenso die Gesamtenergie vor und vermeidet das PDE-Problem. In der Masterarbeit wird in diesem Algorithmus ein wesentlicher Implementierungsfehler offengelegt und behoben.Tesi

Very Special (de Sitter) Relativity

The effects of a non-vanishing value for the cosmological constant in the scenario of Lorentz symmetry breaking recently proposed by Cohen and Glashow (which they denote as Very Special Relativity) are explored and observable consequences are pointed out.Comment: LaTex, 14 page