Room temperature ferromagnetic-like behavior in Mn-implanted and post-annealed InAs layers deposited by Molecular Beam Epitaxy

We report on the magnetic and structural properties of Ar and Mn implanted InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs lattice, like in a diluted magnetic semiconductor (DMS). All of these samples show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments were performed with As as implantation ion all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagnetic-like behavior in the Mn-InAs-RTA layer is not related to lattice disorder produce during implantation, but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns (XRD) and Rutherford Back Scattering (RBS) measurements evidence the segregation of an oxygen deficient-MnO2 phase (nominally MnO1.94) in the Mn-InAs-RTA epitaxial layers which might be on the origin of room temperature ferromagnetic-like response observed.Comment: 16 pages, 5 figures. Acepted in J. Appl. Phy

First order formulation of unimodular gravity

First order Lagrangians for the Weyl invariant formulation of unimodular gravity are proposed. Several alternatives are examined; in some of them, first and second order are equivalent in a certain gauge onlyThis work has been partially supported by the European Union FP7 ITN INVISIBLES (Marie Curie Actions, PITN- GA-2011- 289442) and (HPRN-CT-200-00148), COST action MP1405 (Quantum Structure of Spacetime), COST action MP1210 (The String Theory Universe) as well as by FPA2012-31880 (MINECO, Spain) and S2009ESP-1473 (CA Madrid). The authors acknowledge the support of the Spanish MINECO Centro de Excelencia Severo Ochoa Programme under grant SEV-2012-024

Covariation between variables in a modelling process: The ACODESA (collaborative learning, scientific debate and self-reflection) method

Semiotic representations have been an important topic of study in mathematics education. Previous research implicitly placed more importance on the development of institutional representations of mathematical concepts in students rather than other types of representations. In the context of an extensive research project, in progress since 2005, related to modelling mathematical situations in Québec secondary schools (grades 8 and 9), we have addressed the problem of constructing a specific mathematical concept: covariation between variables as a prerequisite for the concept of function and its graphical representation. However, our research differs from previous studies as we attempt to take into consideration, in a cultural semiotic perspective, the spontaneous non-institutional representations that students produce when solving a problem situation in mathematics. We report our results with a group of students in grade 9, discussing the evolution of the representations the students produced to solve a problem situation, and the key role that the concept of covariation seems to play in helping students grasp the graphical representation of functions. We also discuss the different stages of the teaching method used, based upon collaborative learning, scientific debate and self-reflection (the ACODESA method of teaching) which aims to help the students acquire a cultural semiotic system.Conseil de Recherche en Sciences Humaines du Canada (No. 410-2008-1836, CID 130 252)

The central parsecs of M87: jet emission and an elusive accretion disc

We present the first simultaneous spectral energy distribution (SED) of M87 core at a scale of 0.4 arcsec ($\sim 32\, \rm{pc}$) across the electromagnetic spectrum. Two separate, quiescent, and active states are sampled that are characterized by a similar featureless SED of power-law form, and that are thus remarkably different from that of a canonical active galactic nuclei (AGN) or a radiatively inefficient accretion source. We show that the emission from a jet gives an excellent representation of the core of M87 core covering ten orders of magnitude in frequency for both the active and the quiescent phases. The inferred total jet power is, however, one to two orders of magnitude lower than the jet mechanical power reported in the literature. The maximum luminosity of a thin accretion disc allowed by the data yields an accretion rate of $< 6 \times 10^{-5}\, \rm{M_\odot \, yr^{-1}}$, assuming 10% efficiency. This power suffices to explain M87 radiative luminosity at the jet-frame, it is however two to three order of magnitude below that required to account for the jet's kinetic power. The simplest explanation is variability, which requires the core power of M87 to have been two to three orders of magnitude higher in the last 200 yr. Alternatively, an extra source of power may derive from black hole spin. Based on the strict upper limit on the accretion rate, such spin power extraction requires an efficiency an order of magnitude higher than predicted from magnetohydrodynamic simulations, currently in the few hundred per cent range.Comment: 18 pages, 6 figures. Accepted for publication in MNRA

Sobre la comprensión en estudiantes de matemáticas del concepto de integral impropia : algunas dificultades, obstáculos y errores

En el presente trabajo mostramos algunas de las dificultades, obstáculos y errores que los alumnos universitarios encuentran al aprender los conceptos relativos a la integración impropia; algunos de ellos parecen inherentes al propio concepto de integral impropia y otros vienen relacionados con ausencia de significado o con otros conceptos del cálculo. Con el objetivo de analizar estas dificultades, obstáculos y errores construimos un marco teórico basado, principalmente, en la teoría de Duval sobre los registros semióticos de representación y construimos un modelo de competencia para evaluar la comprensión de nuestros alumnos.In this paper we present some difficulties, obstacles and errors university students face when learning the concepts relative to improper integration. Some of them seem to be inherent to the improper integral concept itself and some others are related to lack of meaning or to other concepts of calculus. With the aim of analysing these difficulties, obstacles and errors we built up a theoretical framework based, fundamentally, on Duval's theory of semiotic registers of representation and we designed a competence model to assess our students' comprehension

Diseño de Metodologías Activas para Másteres

El objetivo de la Universidad de Burgos desde el Máster en Inspección, Restauración, Rehabilitación y Eficiencia Energética de Edificación (MIREE), es la implementación de metodologías docentes activas con el fin de la formación del alumnado, a través de casos concretos y reales que adicionalmente reportarán un beneficio social. Alguno de estos métodos pueden ser el estudio de casos, la resolución de ejercicios y problemas, el aprendizaje basado en problemas y orientado a proyectos, el aprendizaje cooperativo, etc. Lo que pretendemos con las metodologías activas de aprendizaje es, que los alumnos adquieran las competencias propuestas en el programa docente, desarrollando un aprendizaje profundo en cada una de ellas. Para ello debemos evitar que el profesorado monopolice la docencia, y es necesario comunicarles tanto al alumnado como al profesorado, que la docencia es una inversión en beneficio mutuo. La realización de este tipo de proyectos favorece notablemente a los alumnos ya que desarrollan la motivación de aprendizaje o puesta en práctica de las enseñanzas recibidas, pero lo que sin duda es motivador para ellos es el reconocimiento social al trabajo realizado. Esto se ve reflejado en la Estrategia Europea 2020 a nivel universitario que habla de reforzar la cooperación entre la Universidad, Investigación y Empresa

Chemotherapy-free treatments: are we ready for prime time?

Epithelial ovarian cancer (EOC) is most frequently diagnosed at an advanced stage and, despite high response rates to initial taxane-platinum-based chemotherapy, more than 70% of patients will develop recurrent disease and will receive several chemotherapy treatments. At present, the 5-year overall survival (OS) for women diagnosed with stage III–IV disease is 46% and patients with genetic impairments of DNA repair pathways [BRCA mutations and in general homologous recombination deficiency (HRD)] live longer and possibly will receive even more lines of chemotherapy

The introduction of real numbers in secondary education. An institutional analysis of textbooks

In this paper we analyse the introduction of irrational and real numbers in secondary textbooks, and specifically the propositions on how these should be taught, in a sample of Brazilian textbooks used in state schools and approved by the Ministry of Education. The analyses discussed in this paper follow an institutional perspective (using Chevallard's Anthropological Theory of Didactics). Our results indicate that the notion of irrational number is generally introduced on the basis of the decimal representation of numbers, and that the mathematical need for the construction of the field of real numbers remains unclear in the textbooks. It seems that textbooks used in secondary teaching institutions develop mathematical organisations which focus on the practical block

A dark energy multiverse

We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunchs or big rips singularities. Classicaly these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe

Alteraciones de la superficie del cuerpo vertebral en una población medieval de Logroño (s. XI y XII)

X Congreso Nacional de Paleopatología. Univesidad Autónoma de Madrid, septiembre de 200