12,079 research outputs found
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
Computational thinking and robotics in education
After the computational thinking sessions in the previous 2016-2018 editions of TEEM Conference, the fourth edition of this track has been organized in the current 2019 edition. Computational thinking is still a very significant topic, especially, but not only, in pre-university education. In this edition, the robotic has a special role in the track, with a strength relationship with the STEM and
STEAM education of children at the pre-university levels, seeding the future of our society
Generation of rotationally dominated galaxies by mergers of pressure-supported progenitors
Through the analysis of a set of numerical simulations of major mergers
between initially non-rotating, pressure supported progenitor galaxies with a
range of central mass concentrations, we have shown that: (1) it is possible to
generate elliptical-like galaxies, with v/sigma > 1 outside one effective
radius, as a result of the conversion of orbital- into internal-angular
momentum; (2) the outer regions acquire part of the angular momentum first; (3)
both the baryonic and the dark matter components of the remnant galaxy acquire
part of the angular momentum, the relative fractions depend on the initial
concentration of the merging galaxies. For this conversion to occur the initial
baryonic component must be sufficiently dense and/or the encounter should take
place on a orbit with high angular momentum. Systems with these hybrid
properties have been recently observed through a combination of stellar
absorption lines and planetary nebulae for kinematic studies of early-type
galaxies. Our results are in qualitative agreement with such observations and
demonstrate that even mergers composed of non-rotating, pressure-supported
progenitor galaxies can produce early-type galaxies with significant rotation
at large radii.Comment: 5 pages, 6 figures, 2 tables. Accepted for publication in A&A Letter
3D MODELLING OF THE NEGRO TOWER FOR ITS COMPREHENSIVE ANALYSIS AND A CONSERVATION PROPOSAL
Abstract. The Negro Tower, in El Algar, Cartagena (Region of Murcia, Spain), is a building which dates to 1585. It is a tower built in a rural environment, inland from the coast, to alert and protect the population from pirate attacks. It was part of the network of watchtowers and defense posts along the coast of Murcia built between the sixteenth and seventeenth centuries. The tower is protected as a historical monument, but its state of conservation is very poor. For this reason, a comprehensive study has been carried out to ensure its correct restoration and future conservation. Historical and constructive analysis has allowed us to discover the social, cultural and architectural characteristics of the tower. Digital photogrammetry and 3D laser scanning compatible with classic topography have been used for the graphic survey of the tower. All this information has permitted the elaboration of thorough three-dimensional modelling and the proposal of a volumetric recomposition of the tower. The presentation will set out the working methodology followed as well as the important results achieved. This research work aims to contribute to the recognition and correct conservation of the Tower. The graphic survey and the three-dimensional model obtained will allow the recovery of the tower and its integration into the natural environment
Development of a calibration satellite for a CMB telescope flying in formation about L2 libration point
Trabajo presentado a la 8th European Conference for aeronautics and aerospace sciences (EUCASS), celebrada en Madrid (España) del 1 al 4 de julio de 2019.The new generation of cosmic microwave background (CMB) telescopes have reached unprecedented levels of sensitivity. These telescopes measure several cosmological parameters with different levels of accuracy. In particular, considerable effort has been made to measure the B-mode polarization, which is
related to the inflationary process of the universe. The power spectrum of this signal is about four orders of magnitude fainter than the CMB temperature power spectrum. Due to the signal weakness, the instruments must be subjected to calibration processes before and after launching. Additionally, data from the same sky area is gathered repeatedly to mitigate during data analysis the systematic errors induced by instruments. Celestial sources are often used as an external reference for calibration after launch, but these sources are not perfectly characterized. In this paper we study the concept of using a calibration satellite (CalSat) flying in formation with a CMB telescope in an orbit located at the second Lagrange point (L2). The CalSat is conceived as a micro satellite (10-100 kg) and serves as a perfectly known source of a reference signal to reduce the polarization angle measurement uncertainty. According to the scanning law followed
by the telescope, the influence of the relative position between the spacecrafts in the calibration process is studied. The relative motion of the spacecrafts is considered with a simplified dynamic model. Based on the mission requirements, the different subsystems are sized and a preliminary design to evaluate the
feasibility is obtained. The design has been carried out under the principle of reducing at minimum the impact on the telescope architecture. It would require to be launched along with the telescope to reach L2 at the same time and being able to communicate with the telescope. This new calibration element could
have a huge impact on the performance of this kind of missions, providing a significant improvement in the measurements accuracy without requiring new and costly technological developments.The authors would like to thank Spanish Ministry for Economy and Competitiveness (currently Ministry of Science,innovation and Universities) for the financial support provided under the projects with references ESP2017-92135-EXP all co-financed with EU FEDER funds
High-pressure eo-Hercynian metamorphism and development of an inverted metamorphic gradient in the schists from the Santiago Unit (Ordenes Complex, NW Iberian Massif, Spain)
[Resumen] La evolución tectonotermal de la Unidad de Santiago, situada en el margen occidental del Complejo de Ordenes, está caracterizada por el desarrollo de un episodio de metamorfismo eo-hercínico de alta -P y baja a intermedia -T. Las condiciones P-T para las paragénesis del evento de alta presión (que se conservan esencialmente como una Si = SI muy fina incluida en porfidoblastos de albita de esquistos semipelíticos) han sido estimadas en 493 ± 9°C y 14,7 ± 0.7 kbar (presión
mínima). El desarrollo del metamorfismo de alta presión y la ausencia de reequilibrios significativos en su mineralogía característica, sugiere que la unidad (probablemente un fragmento del margen continental de Gondwana) ha sido elevada inmediatamente después de su subducción en el comienzo de la Orogenia Hercínica. El ascenso sin-F2 de la Unidad de Santiago induce una trayectoria P-T marcadamente descompresiva y ligeramente prograda. Esta trayectoria sugiere muy probablemente que la mayor parte de la historia ascensional de la unidad tuvo lugar en un contexto de extensión dúctil, relacionada con la subducción progresiva del margen continental de Gondwana y el desarrollo contemporáneo de extensión compensatoria por encima. La disposición actual de las zonas metamórficas sin-F2 es inversa, con la zona de la estaurolita (que representa el pico térmico) ocupando el techo de la unidad.[Abstract] A high-pressure-Iow to intermediate-temperature eo-Hercynian metamorphic event characterizes the tectonothermal evolution of the Santiago Unit, in the western margin of the Ordenes Complexo P-T conditions for the mineral assemblages of the high-pressure event (wich is essentially preserved as a very thin Si =SI included in albite porphyroblasts from semipelitic schists) have been estimated
at 493 ± 9°C and 14.7 ± 0.7 kbar (minimum pressure). The development of the high-pressure metamorphism and the lacking of significative reequilibrium of their characteristic mineralogy, suggests that the unit (probably a fragment of the continental margin of Gondwana) has been uplifted inmediately after undergoing subduction in the beginning of the Hercynian Orogeny. The syn-D2 uplift of the Santiago Unit cause a markedly decompressive-slightly prograde P-T path. This path very likely suggests that the majority of the rising history of the unit took place in a context of ductile extensión, related to the continued underplating of the continental margin of Gondwana and compensating extension aboye. The actual disposition of the syn-D2 metamorphic zones is inverse, with the staurolite zone (which represents the thermal peak) occupying the top of the uni
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