A Reappraisal of the Solar Photospheric C/O Ratio

Accurate determination of photospheric solar abundances requires detailed modeling of the solar granulation and accounting for departures from local thermodynamical equilibrium (LTE). We argue that the forbidden C I line at 8727 A is largely immune to departures from LTE, and can be realistically modeled using LTE radiative transfer in a time-dependent three-dimensional simulation of solar surface convection. We analyze the [C I] line in the solar flux spectrum to derive the abundance log epsilon(C)= 8.39 +/- 0.04 dex. Combining this result with our parallel analysis of the [O I] 6300 A line, we find C/O=0.50 +/- 0.07, in agreement with the ratios measured in the solar corona from gamma-ray spectroscopy and solar energetic particles.Comment: 5 pages, 2 figures, to appear in ApJL July 1

Seeing, Wind and Outer Scale Effects on Image Quality at the Magellan Telescopes

We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind conditions (>10 m/s), we find that the Magellan telescopes still significantly outperform the DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also report on the first detection of a negative bias in DIMM data. This is found to occur, as predicted, when the DIMM is affected by certain optical aberrations and the turbulence profile is dominated by the upper layers of the atmosphere.Comment: Accepted for publication in PASP. 10 pages, 12 figures

Socioeconomic segregation of students

School segregation may be questioning the equity of the Spanish educational system. In this research, we analyse the school segregation by socioeconomic status using the Hutchens Index. Specifically, we decompose the effect of attending public vs semiprivate schools in terms of segregation. The analyses is based on data collecting information from the population of Andalusian students attending 5th grade. We found significant differences in the level of segregation between both schools types. Particularly, the results show that students from high socioeconomic and cultural status are more segregated in public schools, while students from a low socioeconomic and cultural status are more segregated in semiprivate schools. These differences provide evidence of the inequity of the education policy, which should rethink funding mechanisms as a means to fight against inequality.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The data used in this research has been provided by the Consejería de Educación de la Junta de Andalucía. This work has been partly supported by the Ministerio de Economía y Competitividad under Research Project ECO2017-88883-R; Consejería de Innovación, Ciencia y Empresa de la Junta de Andalucía under PAI group SEJ-532. Claudia Prieto Latorre acknowledges the scholarship FPU2017 00432 of the Ministry of Education, Culture and Sports [Ministerio de Educación, Cultura y Deporte] and the training received from the University of Malaga PhD Program in Economics and Business [Programa de Doctorado en Economía y Empresa de la Universidad de Malaga]

Elemental Abundance Survey of The Galactic Thick Disk

[Abridged abstract] We have performed an abundance analysis for 176 F- and G- dwarfs of the Galactic thick disk component. Using accurate radial velocities combined with $Hipparcos$ astrometry, kinematics (U, V, and W) and Galactic orbital parameters were computed. We estimate the probability for a star to belong to the thin disk, the thick disk or the halo. Abundances of C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, Ce, Nd, and Eu have been obtained. The abundances for thick disk stars are compared with those for thin disk members from Reddy et al. (2003). The ratios of $\alpha$-elements (O, Mg, Si, Ca and Ti) to iron for thick disk disk stars show a clear enhancement compared to thin disk members in the range $-0.3 <$ [Fe/H] $< -1.2$. There are also other elements -- Al, Sc, V, Co, and possibly Zn -- which show enhanced ratios to iron in the thick disk relative to the thin disk. The abundances of Na, Cr, Mn, Ni, and Cu (relative to Fe) are very similar for thin and thick disk stars. The dispersion in abundance ratios [X/Fe] at given [Fe/H] for thick disk stars is consistent with the expected scatter due to measurement errors, suggesting a lack of `cosmic' scatter. The observed compositions of the thin and thick disks seem to be consistent with models of galaxy formation by hierarchical clustering in a $\Lambda$CDM universe. In particular, the distinct abundance patterns observed in the thin and thick disks, and the chemical homogeneity of the thick disk at different galactocentric distances favor a scenario in which the majority of thick-disk stars were formed {\it in situ}, from gas rich merging blocks.Comment: 57 pages (text: 27 pages in MNRAS format + 27 figures) Accepted for publication in MNRA

Analysis and design of close operations at Phobos

This Thesis presents the analysis of a descent maneuver to the Martian moon Phobos, treated mathematically as a Low-Thrust Optimal Control Problem. In order to increase the accuracy of the problem, the gravity acceleration at each of the trajectory nodes is obtained by applying the Polyhedron method, discussed in Chapter 2. The following document is structured by discussing rst the general aspects of the problem analyzed, focusing then completely on the Optimal Control Problem solved. Firstly, the scienti c aims that a mission to Phobos presents are discussed, together with the uncertainties that are still present when studying a mission to this Martian moon. Then, a theoretical approach to the Polyhedron method is discussed, as well as the reasons by which this method is chosen ahead of others. From that point on, a closer approach to the problem is made; rst, by making a general theoretical discussion about the numerical methods present in the GPOPS program that could be used to solve the problem stated, reasoning then the election made and the aspects that have prevailed for this decision to be taken. Subsequently, a detailed characterization of both the dynamical and path constraints implemented is made, as well as a brief description of the propulsive parameters chosen and the reference frame selected, in the same fashion as other articles [1] that treat a descent maneuver too. Finally, the analysis is centered exclusively on the solving process followed. The computational work carried out is explained rst, detailing the modi cations made in order to overcome the computational resources' problem that arose. The results for the optimization are then presented, making a thorough description of the physical phenomena occurring in the spacecraft dynamics. As concluding remarks, a summary of the results obtained is made, together with their limitations; a roadmap for future work is added too, setting the steps that should be taken in the future for making an even more realistic study, which could be used as a rst pragmatic approach to propose a real mission to Phobos.Ingeniería Aeroespacia

STIP VI - TARGET 9. RADIATION DAMAGE ASSESSMENT BASED ON A MCNPX SIMULATION

The SINQ Target Irradiation Program (STIP) has been developed at Paul Scherrer Institute (PSI) during the last twenty years. It is aimed to analyze the radiation damage induced by spallation reactions in different structural materials. It is also providing relevant data for developing future spallation sources as well as advanced spallation targets. STIP VI was conducted in SINQ Target 9 during 2011/2012 receiving a total proton charge of 13.16 Ah. The Monte Carlo N-Particle eXtended code (MCNPX) is used for implementing the model and performing the simulation to obtain the proton and neutron fluences as well as the energy deposition in the different points of interest. Afterwards, this information is used for calculating the displacement per atom (dpa) plus the Helium and Hydrogen production in atomic parts per million (appm). The results will contribute to understand the irradiation effect in different structural materials. It will also be useful for comparing it with the real radiation damage measurements of the irradiated materials after its cool down period. The target mainly consists of the AlMg3 inverted semi-sphere Beam Entrance Window (BEW) and the cylindrical Rod Container Box (RCB) which keeps inside 306 rods fitting 36 rows. There is also the Safety Hull Tube (SHT), made of AlMg3, which consists of a double cylinder walls surrounding the RCB and linked to the inverted BEW at the bottom. The source definition is implemented in the MCNPX input file from the gamma mapping performed at the irradiated Target 9. The material specification of the specimen rods is implemented by taking its average composition, assuming a uniform distribution. The maximum proton flux obtained at the inverted BEW is 1.75x1014 p/(cm2 ·s·mA). The maximum proton fluence in the target is obtained in Row 0 becoming 8.33x1025 p/m2 . The maximum neutron fluence is obtained in Row 8 with a value of 1.99x1026 n/m2 , which in flux units stands for 4.19x1014 n/(cm2 ·s·mA). Regarding the SHT, the maximum proton flux escaping from the target is obtained above Row 36 with a value of 5.99x1011 p/(cm2 ·s·mA) and the maximum neutron flux is escaping around the middle part of the target with a value of 1.39x1014 n/(cm2 ·s·mA). The maximum energy deposition in Zircaloy-2 cladding tubes is obtained in the center rod placed in Row 2 with a value of 400.32 W/(cm3 ·mA). Page 2 The irradiation parameters have been calculated by multiplying the proton and neutron fluence with its corresponding material cross section data. The results obtained at the center of the inverted BEW are 8.85 dpa, 2447 appm He and 4854 appm H. For the SHT, the maximum values of the irradiation parameters are obtained around the middle part of the target with the following values: 3.14 dpa, 17.63 appm He and 71.64 appm H. Finally, the maximum displacement per atom in the specimen rods is obtained for Zircaloy-2 in Rod 1, placed in Row 2, with a value of 72.07 dpa and the maximum Helium & Hydrogen concentration are obtained for Tantalum in Rod A, placed in Row 1, with the following values: 3629 appm He and 17418 appm H

Is grade retention the solution for failing?

The convenience of grade retention for students’ adequate progression in the education system has been the focus of great debate. However, the characteristics that the grade retention variable presents when explaining students’ academic achievement has prevented most of the research works to delve into the effect of this policy. Because of that, in the present research work we intend to get as close as possible to endogeneity free estimate by the use of rich census and longitudinal data, together with a student fixed-effects within students between-academic years strategy. We find that grade retention affects students’ academic performance. Autores: Luis Alejandro Lopez-Agudo, Claudia Prieto Latorre, Oscar David Marcenaro-Gutierrez Palabras clave: grade retention, repetion, academic performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech