Partial Classification of Lorenz Knots: Syllable Permutations of Torus Knots Words

We define families of aperiodic words associated to Lorenz knots that arise naturally as syllable permutations of symbolic words corresponding to torus knots. An algorithm to construct symbolic words of satellite Lorenz knots is defined. We prove, subject to the validity of a previous conjecture, that Lorenz knots coded by some of these families of words are hyperbolic, by showing that they are neither satellites nor torus knots and making use of Thurston's theorem. Infinite families of hyperbolic Lorenz knots are generated in this way, to our knowledge, for the first time. The techniques used can be generalized to study other families of Lorenz knots

Consuming durable goods when stock markets jump: a strategic asset allocation approach

Agents derive their utilities from consumption over time. In this paper we consider an agent that invests in thefinancial market and in consumption goods. The agent has an infinite time horizon and a utility that depends on consumption at each point in time, consuming both a durable good and a perishable good. There are costs for transacting the durable good. We show that an agent who does not consider the impact of jumps in the return process of risky assets will make suboptimal decisions, not only regarding the fraction of wealth invested in the stock market, but also with respect to the timing for trading on the durable good.Optimal asset allocation, durable consumption good, transaction costs.

To Be or Not To Be in Office Again: Political Business Cycles with Local Governments

Most opportunistic-type models of political business cycles tend to posit a given objective for incumbents: maximisation of re-election chances. Though taking an opportunistic view too, we suggest a new explanation for a fiscal policy cycle: the incumbent’s concern with her own welfare in cases of victory and defeat. This rationale addresses local policy-making in particular. An equilibrium perfect-foresight model is designed which totally dispenses with any form of irrationality (namely, on the part of voters) or the common objective functions (re- election chances). Being well grounded in basic microeconomic theory (welfare maximisation by the individual agent), our model provides another foundation for the emergence of political business cycles at the local level. The empirical plausibility of theoretical predictions is then tested on Portuguese municipal data. The estimation of an error- components econometric framework finds evidence in favour of the proposed explanation during the period 1986 to 1993, and enlightens the role played by several politico-economic determinants of local governments’ investment outlays, such as electoral calendar, re- candidacy decisions, political cohesion and intergovernmental capital transfers.local public finance; public choice; political business cycle; elections; Portugal

To Be or Not To Be in Office Again, That is the Question: Political Business Cycles with Local Governments

Most opportunistic -type models of political business cycles tend to posit a given objective for incumbents: maximisation of re-election chances. Though taking an opportunistic view too, we suggest a new explanation for a fiscal policy cycle: the incumbents concern with her own welfare in cases of victory and defeat. This rationale addresses local policy-making in particular. An equilibrium perfectforesight model is designed which totally dispenses with any form of irrationality (namely, on the part of voters) or the common objective functions (re-election chances). Being well grounded in basic microeconomic theory (welfare maximisation by the individual agent), our model provides another foundation for the emergence of political business cycles at the local level. The empirical plausibility of theoretical predictions is then tested on Portuguese municipal data ranging from 1977 to 1993. The estimation of an error-components econometric framework finds evidence in favour of the proposed explanation and enlightens the role played by several politicoeconomic determinants of local governments investment outlays, such as electoral calendar, re-candidacy decisions, political cohesion and intergovernmental capital transfers.local public finance; public choice; political business cycles; elections; Portugal

Three-dimensional modelling and inversion of controlled source electromagnetic data

The marine Controlled Source Electromagnetic (CSEM) method is an important and almost self-contained discipline in the toolkit of methods used by geophysicists for probing the earth. It has increasingly attracted attention from industry during the past decade due to its potential in detecting valuable natural resources such as oil and gas. A method for three-dimensional CSEM modelling in the frequency domain is presented. The electric field is decomposed in primary and secondary components, as this leads to a more stable solution near the source position. The primary field is computed using a resistivity model for which a closed form of solution exists, for example a homogeneous or layered resistivity model. The secondary electric field is computed by discretizing a second order partial differential equation for the electric field, also referred in the literature as the vector Helmholtz equation, using the edge finite element method. A range of methods for the solution of the linear system derived from the edge finite element discretization are investigated. The magnetic field is computed subsequently, from the solution for the electric field, using a local finite difference approximation of Faraday’s law and an interpolation method. Tests, that compare the solution obtained using the presented method with the solution computed using alternative codes for 1D and 3D synthetic models, show that the implemented approach is suitable for CSEM forward modelling and is an alternative to existing codes. An algorithm for 3D inversion of CSEM data in the frequency domain was developed and implemented. The inverse problem is solved using the L-BFGS method and is regularized with a smoothing constraint. The inversion algorithm uses the presented forward modelling scheme for the computation of the field responses and the adjoint field for the computation of the gradient of the misfit function. The presented algorithm was tested for a synthetic example, showing that it is capable of reconstructing a resistivity model which fits the synthetic data and is close to the original resistivity model in the least-squares sense. Inversion of CSEM data is known to lead to images with low spatial resolution. It is well known that integration with complementary data sets mitigates this problem. It is presented an algorithm for the integration of an acoustic velocity model, which is known a priori, in the inversion scheme. The algorithm was tested in a synthetic example and the results demonstrate that the presented methodology is promising for the improvement of resistivity models obtained from CSEM data

Landau Gauge Fixing on GPUs and String Tension

We explore the performance of CUDA in performing Landau gauge fixing in Lattice QCD, using the steepest descent method with Fourier acceleration. The code performance was tested in a Tesla C2070, Fermi architecture. We also present a study of the string tension at finite temperature in the confined phase. The string tension is extracted from the color averaged free energy and from the color singlet using Landau gauge fixing.Comment: 7 pages, 4 figures, 1 table. Contribution to the International Meeting "Excited QCD", Peniche, Portugal, 06 - 12 May 201

Landau gauge fixing on the lattice using GPU's

In this work, we consider the GPU implementation of the steepest descent method with Fourier acceleration for Laudau gauge fixing, using CUDA. The performance of the code in a Tesla C2070 GPU is compared with a parallel CPU implementation.Comment: 3 pages, 1 figure, Proceedings of the Xth Quark Confinement and the Hadron Spectrum, 8-12 October 2012, TUM Campus Garching, Munich, German