Self-force via Green functions and worldline integration

A compact object moving in curved spacetime interacts with its own gravitational field. This leads to both dissipative and conservative corrections to the motion, which can be interpreted as a self-force acting on the object. The original formalism describing this self-force relied heavily on the Green function of the linear differential operator that governs gravitational perturbations. However, because the global calculation of Green functions in non-trivial black hole spacetimes has been an open problem until recently, alternative methods were established to calculate self-force effects using sophisticated regularization techniques that avoid the computation of the global Green function. We present a method for calculating the self-force that employs the global Green function and is therefore closely modeled after the original self-force expressions. Our quantitative method involves two stages: (i) numerical approximation of the retarded Green function in the background spacetime; (ii) evaluation of convolution integrals along the worldline of the object. This novel approach can be used along arbitrary worldlines, including those currently inaccessible to more established computational techniques. Furthermore, it yields geometrical insight into the contributions to self-interaction from curved geometry (back-scattering) and trapping of null geodesics. We demonstrate the method on the motion of a scalar charge in Schwarzschild spacetime. This toy model retains the physical history-dependence of the self-force but avoids gauge issues and allows us to focus on basic principles. We compute the self-field and self-force for many worldlines including accelerated circular orbits, eccentric orbits at the separatrix, and radial infall. This method, closely modeled after the original formalism, provides a promising complementary approach to the self-force problem.Comment: 18 pages, 9 figure

Integral equation mei applied to three-dimensional arbitrary surfaces

The authors present a new formulation of the integral equation of the measured equation of invariance (MEI) as a confined field integral equation discretised by the method of moments, in which the use of numerically derived testing functions results in an approximately sparse linear system with storage memory requirements and a CPU time for computing the matrix coefficients proportional to the number of unknowns.Peer ReviewedPostprint (published version

Analysis of microstrip antennas by multilevel matrix decomposition algorithm

Integral equation methods (IE) are widely used in conjunction with Method of Moments (MoM) discretization for the numerical analysis of microstrip antennas. However, their application to large antenna arrays is difficult due to the fact that the computational requirements increase rapidly with the number of unknowns N. Several techniques have been proposed to reduce the computational cost of IE-MoM. The Multilevel Matrix Decomposition Algorithm (MLMDA) has been implemented in 3D for arbitrary perfectly conducting surfaces discretized in Rao, Wilton and Glisson linear triangle basis functions . This algorithm requires an operation count that is proportional to N·log2N. The performance of the algorithm is much better for planar or piece-wise planar objects than for general 3D problems, which makes the algorithm particularly well-suited for the analysis of microstrip antennas. The memory requirements are proportional to N·logN and very low. The main advantage of the MLMDA compared with other efficient techniques to solve integral equations is that it does not rely on specific mathematical properties of the Green's functions being used. Thus, we can apply the method to interesting configurations governed by special Green's functions like multilayered media. In fact, the MDA-MLMDA method can be used at the top of any existing MoM code. In this paper we present the application to the analysis of large printed antenna arrays.Peer ReviewedPostprint (published version

Robustness of the European power grids under intentional attack

The power grid defines one of the most important technological networks of our times and sustains our complex society. It has evolved for more than a century into an extremely huge and seemingly robust and well understood system. But it becomes extremely fragile as well, when unexpected, usually minimal, failures turn into unknown dynamical behaviours leading, for example, to sudden and massive blackouts. Here we explore the fragility of the European power grid under the effect of selective node removal. A mean field analysis of fragility against attacks is presented together with the observed patterns. Deviations from the theoretical conditions for network percolation (and fragmentation) under attacks are analysed and correlated with non topological reliability measures.Comment: 7 pages, 4 figure

Meshless Simulation of Multi-site Radio Frequency Catheter Ablation through the Fragile Points Method

Computational models for radio frequency catheter ablation (RFCA) of cardiac arrhythmia have been developed and tested in conditions where a single ablation site is considered. However, in reality arrhythmic events are generated at multiple sites which are ablated during treatment. Under such conditions, heat accumulation from several ablations is expected and models should take this effect into account. Moreover, such models are solved using the Finite Element Method which requires a good quality mesh to ensure numerical accuracy. Therefore, clinical application is limited since heat accumulation effects are neglected and numerical accuracy depends on mesh quality. In this work, we propose a novel meshless computational model where tissue heat accumulation from previously ablated sites is taken into account. In this way, we aim to overcome the mesh quality restriction of the Finite Element Method and enable realistic multi-site ablation simulation. We consider a two ablation sites protocol where tissue temperature at the end of the first ablation is used as initial condition for the second ablation. The effect of the time interval between the ablation of the two sites is evaluated. The proposed method demonstrates that previous models that do not account for heat accumulation between ablations may underestimate the tissue heat distribution

Rotating Black Holes at Future Colliders. III. Determination of Black Hole Evolution

TeV scale gravity scenario predicts that the black hole production dominates over all other interactions above the scale and that the Large Hadron Collider will be a black hole factory. Such higher dimensional black holes mainly decay into the standard model fields via the Hawking radiation whose spectrum can be computed from the greybody factor. Here we complete the series of our work by showing the greybody factors and the resultant spectra for the brane localized spinor and vector field emissions for arbitrary frequencies. Combining these results with the previous works, we determine the complete radiation spectra and the subsequent time evolution of the black hole. We find that, for a typical event, well more than half a black hole mass is emitted when the hole is still highly rotating, confirming our previous claim that it is important to take into account the angular momentum of black holes.Comment: typoes in eqs(82)-(84) corrected; version to appear in Phys. Rev. D; references and a footnote added; same manuscript with high resolution embedded figures available on http://www.gakushuin.ac.jp/univ/sci/phys/ida/paper

Lost colours: Photogrammetry, image analysis using the DStretch plugin, and 3-D modelling of post-firing painted pottery from the south west Iberian Peninsula

The main purpose of this project was to verify the use of the DStretch plugin, designed to study rock art, for analysing post-firing painted pottery from the Late Bronze Age and Early Iron Age in the Atlantic façade of the Iberian Peninsula. To do so, a Guadalquivir-type carinated pot was used as a study vessel from the excavations of Portaceli (Medellín, Badajoz, Spain). The study brought together all of the different methods used, from the photogrammetry used to obtain a high-quality image of the piece, analysis with DStretch, and the final 3-D modelling process in order to accurately reproduce the shape and decoration of the vessel. The final goal was to obtain precise documentation on these types of vessels, the handling of which is not recommended due to the fragile nature of the pigments used in their decoration.This work is part of the R&D&I Project entitled “Building Tartessos: Constructive, Spatial, and Territorial Analysis of an Architectural Model in the Central Guadiana Valley” (HAR2015-63788-P)

Guidelines for oral assessment

En este documento se presentan los lineamientos y teoría para la implementación de un sistema de evaluación oral en el Centro de Idiomas de la Universidad Eafit. El texto desarrolla tres temas principales: 1) el enfoque comunicativo para la enseñanza y la evaluación ; 2) la planeación de la evaluación; y 3) el uso de las herramientas de evaluación.This document aims at offering teachers a framework for assessing oral language and some guidelines that will foster the implementation and practice of a homogeneous oral assessment system (OAS) at the EAFIT University Language Center. The document deals with three main topics, namely (1) Communicative Approach to Teaching and Assessment; (2) Planning for Assessment; and (3) Using the Oral Assessment Rubric

Infection risk of Monilinia fructicola on stone fruit during cold storage and immersion in the dump tank

Monilinia spp. is the main pathogen responsible for postharvest losses of stone fruit. Several studies have examined the conditions for Monilinia spp. infection in the field, but very limited information is available about postharvest. Storing fruit for 1 day in the cold room or dumping fruit in a water tank are the most common handling operations during the postharvest of fruit. Then, the aim of this study was to investigate the risk of Monilinia fructicola infection for two peach and one nectarine cultivars during cold storage and water dump operations. A new methodology was performed using a dry inoculum of M. fructicola. A set of fruit was used as control to demonstrated that at 20 °C 60% relative humidity (RH) was not able to infect fruit, however, the disease was developed when was already infected. In addition, M. fructicola was able to infect and develop disease in fruit at 20 °C 100 RH. The storage of fruit with the presence of M. fructicola conidia on their surface for up to 30 days at 0 °C 100% RH or 4 °C 100% RH did not suppose an important risk of infection since only 3.3 and 3.8%, respectively of fruit were already infected. Overall, all treatments tested with the water dump operation gave optimal conditions to M. fructicola to infect fruit when it was superficially dry inoculated or it was immersed with water contaminated with conidia, increasing the need for water disinfection. In addition, when fruit was immersed in water free from M. fructicola conidia, the postharvest operation gave optimal conditions to develop infections already produced.info:eu-repo/semantics/acceptedVersio