Contour methods for long-range Ising models: weakening nearest-neighbor interactions and adding decaying fields

We consider ferromagnetic long-range Ising models which display phase transitions. They are long-range one-dimensional Ising ferromagnets, in which the interaction is given by $J_{x,y} = J(|x-y|)\equiv \frac{1}{|x-y|^{2-\alpha}}$ with $\alpha \in [0, 1)$, in particular, $J(1)=1$. For this class of models one way in which one can prove the phase transition is via a kind of Peierls contour argument, using the adaptation of the Fr\"ohlich-Spencer contours for $\alpha \neq 0$, proposed by Cassandro, Ferrari, Merola and Presutti. As proved by Fr\"ohlich and Spencer for $\alpha=0$ and conjectured by Cassandro et al for the region they could treat, $\alpha \in (0,\alpha_{+})$ for $\alpha_+=\log(3)/\log(2)-1$, although in the literature dealing with contour methods for these models it is generally assumed that $J(1)\gg1$, we can show that this condition can be removed in the contour analysis. In addition, combining our theorem with a recent result of Littin and Picco we prove the persistence of the contour proof of the phase transition for any $\alpha \in [0,1)$. Moreover, we show that when we add a magnetic field decaying to zero, given by $h_x= h_*\cdot(1+|x|)^{-\gamma}$ and $\gamma >\max\{1-\alpha, 1-\alpha^* \}$ where $\alpha^*\approx 0.2714$, the transition still persists.Comment: 13 page

Windowed Green function method for the Helmholtz equation in the presence of multiply layered media

This paper presents a new methodology for the solution of problems of two- and three-dimensional acoustic scattering (and, in particular, two-dimensional electromagnetic scattering) by obstacles and defects in the presence of an arbitrary number of penetrable layers. Relying on the use of certain slow-rise windowing functions, the proposed windowed Green function approach efficiently evaluates oscillatory integrals over unbounded domains, with high accuracy, without recourse to the highly expensive Sommerfeld integrals that have typically been used to account for the effect of underlying planar multilayer structures. The proposed methodology, whose theoretical basis was presented in the recent contribution (Bruno et al. 2016 SIAM J. Appl. Math. 76, 1871–1898. (doi:10.1137/15M1033782)), is fast, accurate, flexible and easy to implement. Our numerical experiments demonstrate that the numerical errors resulting from the proposed approach decrease faster than any negative power of the window size. In a number of examples considered in this paper, the proposed method is up to thousands of times faster, for a given accuracy, than corresponding methods based on the use of Sommerfeld integrals

The Electromagnetic Form Factor of the Kaon in the Light-Front Approach

The kaon electromagnetic form factor is calculated within a light-front constituent quark model (LFCQM). The electromagnetic components of the current are extracted from the Feynman triangle diagram within the light-front approach. We also obtain the electroweak decay constant and the charge radius for the kaon in the light-front approach. In this work, the kaon observables are calculated and a fairly good agreement is obtained with a very higher accuracy when compared with the experimental data.Comment: Paper with 4 pages, 1 figure, reference: XII HADRON PHYSICS Conference - to appear in AIP Conference Proceeding

Study of Conformally Flat Initial Data for Highly Spinning Black Holes and their Early Evolutions

We study conformally-flat initial data for an arbitrary number of spinning black holes with exact analytic solutions to the momentum constraints constructed from a linear combination of the classical Bowen-York and conformal Kerr extrinsic curvatures. The solution leading to the largest intrinsic spin, relative to the ADM mass of the spacetime epsilon_S=S/M^2_{ADM}, is a superposition with relative weights of Lambda=0.783 for conformal Kerr and (1-Lambda)=0.217 for Bowen-York. In addition, we measure the spin relative to the initial horizon mass M_{H_0}, and find that the quantity chi=S/M_{H_0}^2 reaches a maximum of \chi^{max}=0.9856 for Lambda=0.753. After equilibration, the final black-hole spin should lie in the interval 0.9324<chi_{final}<0.9856. We perform full numerical evolutions to compute the energy radiated and the final horizon mass and spin. We find that the black hole settles to a final spin of chi_{final}^{max}=0.935 when Lambda=0.783. We also study the evolution of the apparent horizon structure of this "maximal" black hole in detail.Comment: 9 pages, 8 figure

Magnetic Anisotropy of Isolated Cobalt Nanoplatelets

Motivated in part by experiments performed by M.H. Pan et al. (nanoletters, v.5, p 83, 2005), we have undertaken a theoretical study of the the magnetic properties of two-monolayer thick Co nanoplatelets with an equilateral triangular shape. The analysis is carried out using a microscopic Slater-Koster tight-binding model with atomic exchange and spin-orbit interactions designed to realistically capture the salient magnetic features of large nanoclusters containing up to 350 atoms. Two different truncations of the FCC lattice are studied, in which the nanoplatelet surface is aligned parallel to the FCC (111) and (001)crystal planes respectively. We find that the higher coordination number in the (111) truncated crystal is more likely to reproduce the perpendicular easy direction found in experiment. Qualitatively, the most important parameter governing the anisotropy of the model is found to be the value of the intra-atomic exchange integral J. If we set the value of J near the bulk value in order to reproduce the experimentally observed magnitude of the magnetic moments, we find both quasi-easy-planes and perpendicular easy directions. At larger values of J we find that the easy-axis of magnetization is perpendicular to the surface, and the value of the magnetic anisotropy energy per atom is larger. The possible role of hybridization with substrate surface states in the experimental systems is discussed.Comment: 15 pages, 13 figure

Forecasting ocean warming impacts on seabird demography: a case study on the European storm petrel

Bottom-up climatic forcing has been shown to be influential for a variety of marine taxa, but evidence on seabird populations is scarce. Seasonal variation in environmental conditions can have an indirect effect on subsequent reproduction, which, given the longevity and single-brooding of seabirds, may affect population dynamics. Our study focuses on linking the effect of oceanographic conditions (from 1991 to 2013) to the fecundity and consequently pop - ulation growth rate of the Mediterranean subspecies of the European storm petrel Hydrobates pelagicus melitensis. In this study, we examined 23 yr of > 5400 capture–mark−recaptures (CMR) and modelled the probability of skipping reproduction as a function of oceanographic variables using CMR models. We demonstrate that a decrease in sea surface temperature in the pre-breeding period negatively influences skipping propensity, and therefore hypothesize that this behaviour would have significant influence on population abundance over time. For this reason, we analysed population growth as a function of skipping probability as affected by oceanographic conditions. We used stochastic demographic models to forecast the fate of the population, and evaluated contrasted environmental condition scenarios. As a result, we found that a decrease in frequency of cold winter events would probably reduce skipping propensity, with a positive effect on the population as a whole

A systematic comparison of supervised classifiers

Pattern recognition techniques have been employed in a myriad of industrial, medical, commercial and academic applications. To tackle such a diversity of data, many techniques have been devised. However, despite the long tradition of pattern recognition research, there is no technique that yields the best classification in all scenarios. Therefore, the consideration of as many as possible techniques presents itself as an fundamental practice in applications aiming at high accuracy. Typical works comparing methods either emphasize the performance of a given algorithm in validation tests or systematically compare various algorithms, assuming that the practical use of these methods is done by experts. In many occasions, however, researchers have to deal with their practical classification tasks without an in-depth knowledge about the underlying mechanisms behind parameters. Actually, the adequate choice of classifiers and parameters alike in such practical circumstances constitutes a long-standing problem and is the subject of the current paper. We carried out a study on the performance of nine well-known classifiers implemented by the Weka framework and compared the dependence of the accuracy with their configuration parameter configurations. The analysis of performance with default parameters revealed that the k-nearest neighbors method exceeds by a large margin the other methods when high dimensional datasets are considered. When other configuration of parameters were allowed, we found that it is possible to improve the quality of SVM in more than 20% even if parameters are set randomly. Taken together, the investigation conducted in this paper suggests that, apart from the SVM implementation, Weka's default configuration of parameters provides an performance close the one achieved with the optimal configuration

Kitchen-Sink Enlightenment: A Review of “Grace for Amateurs”

Excerpt: Here’s an honest admission: Several times while reading Lily Burana’s new book Grace for Amateurs: Field Notes on a Journey Back to Faith, I consulted the copyright page, confirming again that Grace for Amateurs was really published by Thomas Nelson, the notoriously evangelical (and, in my mind, notoriously traditional) press. After all, it wasn’t that long ago that Thomas Nelson asked another writer to remove the word “vagina” from her book, well aware that Christian readers would balk at language so closely associated with women and S-E-X. Would this same publisher be willing to support a memoir as edgy and progressive as Burana’s

Electromagnetic Structure of the Pion

In this work, we analyze the electromagnetic structure of the pion. We calculate its electromagnetic radius and electromagnetic form factor in low and intermediate momentum range. Such observables are determined by means of a theoretical model that takes into account the constituent quark and antiquark of the pion within the formalism of light-front field theory. In particular, we consider a nonsymmetrical vertex in this model, with which we calculate the electromagnetic form factor of the pion in an optimized way, so that we obtain a value closer to the experimental charge radius of the pion. The theoretical calculations are also compared with the most recent experimental data involving the pion electromagnetic form factor and the results show very good agreement.Comment: Paper with 4 pages, 1 figure, presented in XII HADRON PHYSICS Conference - to appear in AIP Conference Proceeding