Composite biasing in Monte Carlo radiative transfer

Biasing or importance sampling is a powerful technique in Monte Carlo radiative transfer, and can be applied in different forms to increase the accuracy and efficiency of simulations. One of the drawbacks of the use of biasing is the potential introduction of large weight factors. We discuss a general strategy, composite biasing, to suppress the appearance of large weight factors. We use this composite biasing approach for two different problems faced by current state-of-the-art Monte Carlo radiative transfer codes: the generation of photon packages from multiple components, and the penetration of radiation through high optical depth barriers. In both cases, the implementation of the relevant algorithms is trivial and does not interfere with any other optimisation techniques. Through simple test models, we demonstrate the general applicability, accuracy and efficiency of the composite biasing approach. In particular, for the penetration of high optical depths, the gain in efficiency is spectacular for the specific problems that we consider: in simulations with composite path length stretching, high accuracy results are obtained even for simulations with modest numbers of photon packages, while simulations without biasing cannot reach convergence, even with a huge number of photon packages.Comment: 12 pages, accepted for publication in A&

Antimagnets: Controlling magnetic fields with superconductor-metamaterial hybrids

Magnetism is very important in science and technology, from magnetic recording to energy generation to trapping cold atoms. Physicists have managed to master magnetism - to create and manipulate magnetic fields- almost at will. Surprisingly, there is at least one property which until now has been elusive: how to 'switch off' the magnetic interaction of a magnetic material with existing magnetic fields without modifying them. Here we introduce the antimagnet, a design to conceal the magnetic response of a given volume from its exterior, without altering the external magnetic fields, somehow analogous to the recent theoretical proposals for cloaking electromagnetic waves with metamaterials. However, different from these devices requiring extreme material properties, our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials. Antimagnets may have applications in magnetic-based medical techniques such as MRI or in reducing the magnetic signature of vessels or planes.Comment: 14 pages, 4 figure

Black Branes in a Box: Hydrodynamics, Stability, and Criticality

We study the effective hydrodynamics of neutral black branes enclosed in a finite cylindrical cavity with Dirichlet boundary conditions. We focus on how the Gregory-Laflamme instability changes as we vary the cavity radius R. Fixing the metric at the cavity wall increases the rigidity of the black brane by hindering gradients of the redshift on the wall. In the effective fluid, this is reflected in the growth of the squared speed of sound. As a consequence, when the cavity is smaller than a critical radius the black brane becomes dynamically stable. The correlation with the change in thermodynamic stability is transparent in our approach. We compute the bulk and shear viscosities of the black brane and find that they do not run with R. We find mean-field theory critical exponents near the critical point.Comment: 23 pages, 3 figures. v2: added comments on first-order phase transitio

A multi-agent system to manage users and spaces in a adaptive environment system

This paper, deals with the actual problem of manage user preferences and local specifications on an IoT adaptive system, namely using a multi agent system to achieve a Smart Environment System. On a new era of interaction between persons and physical spaces, users want those spaces smartly adapt to their preferences in a transparent way. To achieve that, new approaches are needed. In this project we develop a multi agent system architecture with different layers to achieve a solution that entails all the proposed objectives.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019

Using jason framework to develop a multi-agent system to manage users and spaces in an adaptive environment system

Manage user preferences and local specifications on an IoT adaptive system is a actual problem. This paper uses Jason framework to develop a multi agent system to achieve a Smart Environment System, and supports interaction between persons and physical spaces, that users want to smartly adapt to their preferences in a transparent way. This work proposes a new approach, that has been developed using a multi agent system architecture with different layers to achieve a solution that entails all the proposed objectives.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019

Synthesis of large low-redundancy linear arrays

Aperture synthesis interferometric radiometers can overcome mass, weight and mechanical scan limitations of present-day radiometers. A full antenna array is “thinned” by eliminating selected antennas, while keeping all possible antenna separations. This brief describes a new technique for the direct synthesis of low-redundancy large arrays, consisting in growing small arrays by inserting a seed repeatedly. This technique has achieved the largest thinned arrays with the least redundancy reported in the literature.Peer Reviewe

(El-) Mekta

Gisement princeps du Capsien s’étalant à mi-pente d’une colline située en Tunisie à une vingtaine de kilomètres au Nord de Gafsa. Découvert en 1908 par P. Boudy et signalé pour la première fois par J. de Morgan, il a été fouillé vers 1932 par R. Vaufrey et ensuite par le Dr Gobert qui en publia une monographie en 1952. La proximité de Gafsa (Capsa dans l’antiquité) a fait donner le nom de capsien à l’industrie reconnue dans ce site. Les capsiens se sont installés sur une plate-forme dominée p..

Entropy of the self-dual string soliton

We compute the entropy and the corresponding central charge of the self-dual string soliton in the supergravity regime using the blackfold description of the fully localized M2-M5 intersection.Comment: 15 pages, 1 figure, harvma