First performance evaluation of a Multi-layer Thick Gaseous Electron Multiplier with in-built electrode meshes - MM-THGEM

We describe a new micro-pattern gas detector structure comprising a multi-layer hole-type multiplier (M-THGEM) combined with two in-built electrode meshes: the Multi-Mesh THGEM-type multiplier (MM-THGEM). Suitable potential differences applied between the various electrodes provide an efficient collection of ionization electrons within the MM-THGEM holes and a large charge avalanche multiplication between the meshes. Different from conventional hole-type multipliers (e.g. Gas Electron Multipliers - GEMs, Thick Gas Electron Multipliers - THGEMs, etc.), which are characterized by a variable (dipole-like) field strength inside the avalanche gap, electrons in MM-THGEMs are largely multiplied by a strong uniform field established between the two meshes, like in the parallel-plate avalanche geometry. The presence of the two meshes within the holes allows for the trapping of a large fraction of the positive ions that stream back to the drift region. A gas gain above 10^5 has been achieved for single photo-electron detection with a single MM-THGEM in Ar/(10%)CH4 and He/(10%)CO2, at standard conditions for temperature and pressure. When the MM-THGEM is coupled to a conventional THGEM and used as first cascade element, the maximum achievable gains reach values above 10^6 in He/(10%)CO2, while the IBF approaches of 1.5% in the case of optimum detector-bias configuration. This IBF value is several times lower compared to the one obtained by a double GEM/THGEM detector (5-10%), and equivalent to the performance attained by a Micromegas detector.Comment: 11 pages, 8 figures. Submitted to JINS

Finite-temperature properties of frustrated classical spins coupled to the lattice

We present extensive Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice coupled to the lattice degrees of freedom. The Ising-like phase transition, that appears for $J_2/J_1>1/2$ in the pure spin model, is strengthened by the spin-lattice coupling, and is accompanied by a lattice deformation from a tetragonal symmetry to an orthorhombic one. Evidences that the universality class of the transition does not change with the inclusion of the spin-lattice coupling are reported. Implications for ${\rm Li_2VOSiO_4}$, the prototype for a layered $J_1{-}J_2$ model in the collinear regime, are also discussed.Comment: 6 pages and 8 figure

Ising transition driven by frustration in a 2D classical model with SU(2) symmetry

We study the thermal properties of the classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice by extensive Monte Carlo simulations. We show that, for $J_2/J_1 > 1/2$, thermal fluctuations give rise to an effective $Z_2$ symmetry leading to a {\it finite-temperature} phase transition. We provide strong numerical evidence that this transition is in the 2D Ising universality class, and that $T_c\to 0$ with an infinite slope when $J_2/J_1\to 1/2$.Comment: 4 pages with 4 figure

Aportaciones de la Etología Humana a los estudios lingüísticos: el caso de la Fraseología

En este texto se reflexiona sobre los vínculos existentes entre la Etología Humana, a partir de algunos de los supuestos teóricos desarrollados por Eibl-Eibesfeldt, y la Lingüística. Se busca establecer una relación entre estos supuestos y una parcela de los estudios lingüísticos, la Fraseología (especialmente, las fórmulas rutinarias). A fin de cumplir este objetivo, se describen, someramente, los principios básicos de la Etología Humana; se considera, asimismo, la atención que ha consagrado esta ciencia a la comunicación humana, el lenguaje y la Lingüística, y de la posibilidad de aplicar la Etolingüística al estudio de la Fraseología. Se defiende la idea de que la Etología Humana puede apoyar la reflexión sobre las bases innatas y culturales que subyacen a diferentes tipos de fraseologismos.In this paper I analyse the connections between Human Ethology and Linguistics. I start out by considering some of the theoretical principles developed by Eibl-Eibesfeldt 1979a, 1979b and 1993 and I try to relate them with a branch of linguistic studies, Phraseology, and more specifically, the routine formulas. In order to achieve this goal, I first describe, briefly, the fundamentals of Human Ethology. Secondly, I show how this science dealt with human communication, language and Linguistics and I also consider the possibility of applying Etholinguistics to the study of Phraseology. I defend the idea that the ethological studies offer different paths that might turn useful to the phraseological research, especially to unravel the innate and cultural bases ruling the construction and use of formulae.Dans ce texte, nous réfléchissons sur les liens entre Éthologie Humaine et Linguistique, à partir de certaines des hypothèses théoriques développés par Eibl-Eibesfeldt (1979a, 1979b, 1993). Nous cherchons à établir une relation entre ces hypothèses et une partie d’études linguistiques, la Phraséologie (et spécifiquement, les formules de routine). Pour atteindre cet objectif, nous décrivons succinctement, les principes de base de l'Éthologie Humaine. Nous parlons alors des efforts que cette science a consacré à la communication humaine, au langage et la Linguistique, et la possibilité d'appliquer l'Etolinguistique à l'étude de la Phraséologie. Nous défendons l'idée que l'Éthologie Humaine peut favoriser une réflexion sur les fondements innés et culturels qui sous-tendent différents types d'unités phraséologiques

Alternatives for programming a low-cost UAV in robotics

The aim of this paper are to present different alternatives to program a commercially available ffying platform, and to discuss what we consider more convenient to be used by our under-graduate students in a regular robotics course to teach them basic vision based control. Due to the background of our students, we will focus more on the description of the software application interface, than on the hardware, although we will describe also both. We also will describ

Morphometric differentiation and sexual dimorphism in Limnomedusa macroglossa (Duméril & Bibron, 1841) (Anura: Alsodidae) from Uruguay

Intersexual morphological differences within a species occur in many traits, including body size and shape. Many processes that cause geographic variability in morphology have been proposed: population structure, phenotypic plasticity (environmental effects on development), and natural and/or sexual selection. Several hypotheses can explain patterns of sexual dimorphism in anurans, including natural or intra/inter-sexual selection, and differences in life history strategies between sexes. Limnomedusa macroglossa is considered a habitat specialist restricted to rocky outcrops in Brazil, Argentina, Paraguay, and Uruguay. We evaluated the extent of sexual (size and shape) dimorphism in L. macroglossa from Uruguay based on morphometrics and secondary sexual characteristics, while taking into account geographic variation. Sexual dimorphism in body size of adults was found, but multivariate analyses did not demonstrate the existence of significant differences in shape. There were also significant differences in body size and hind leg measurements among six hydrographic basins as a result from the phenotypic plasticity correlated with local temperature, representing a clinal variation along the latitudinal gradient of Uruguay. The sexual dimorphism found in body size is probably the consequence of higher growth rates and/or late sexual maturity in females, which favors larger body size for accommodating larger ovaries, and thus, higher reproductive output