X-ray spectral variability of Seyfert 2 galaxies

Variability across the electromagnetic spectrum is a property of AGN that can help constraining the physical properties of these galaxies. This is the third of a serie of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern in a sample of optically selected type 2 Seyfert galaxies. We use the 26 Seyferts in the Veron-Cetty and Veron catalogue with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source are simultaneously fitted and we let different parameters to vary in the model. Whenever possible, short-term variations and/or long-term UV flux variations are studied. We divide the sample in Compton-thick, Compton-thin, and changing-look candidates. Short-term variability at X-rays is not found. From the 25 analyzed sources, 11 show long-term variations; eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related with absorbers at hard X-rays are less common, and in many cases these variations are accompained with variations of the nuclear continuum. At UV frequencies nuclear variations are nor found. We report for the first time two changing-look candidates, MARK273 and NGC7319. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results; the Compton-thick candidates are dominated by reflection, which supresses their continuum making them seem fainter, and not showing variations, while the Compton-thin and changing-look candidates show variations.Comment: Accepted for publication in A&

X-ray spectral variability of seven LINER nuclei with XMM-Newton and Chandra data

One of the most important features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on time scales from hours to years. Among the AGN family and according to theoretical studies, Low-Ionization Nuclear Emission Line Region (LINER) nuclei would be variable objects on long time scales. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these kinds of objects, as well as their accretion mechanism. Chandra and XMM-Newton public archives were used to compile X-ray spectra of seven LINER nuclei at different epochs with time scales of years. To search for variability we fit all the spectra from the same object with a set of models, in order to identify the parameters responsible for the variability pattern. We also analyzed the light curves in order to search for short time scale (from hours to days) variability. Whenever possible, UV variability was also studied. We found spectral variability in four objects, with variations mostly related to hard energies (2-10 keV). These variations are due to changes in the soft excess, and/or changes in the absorber, and/or intrinsic variations of the source. Another two galaxies seem not to vary. Short time scale variations during individual observations were not found. Our analysis confirms the previously reported anticorrelation between the X-ray spectral index and the Eddington ratio, and also the correlation between the X-ray to UV flux ratio and the Eddington ratio. These results support an Advection Dominated Accretion Flow (ADAF) as the accretion mechanism in LINERs.Comment: 35 pages, 53 figures, recently accepted pape

X-ray spectral variability of LINERs selected from the Palomar sample

Variability is a general property of active galactic nuclei (AGN). At X-rays, the way in which these changes occur is not yet clear. In the particular case of low ionisation nuclear emission line region (LINER) nuclei, variations on months/years timescales have been found for some objects, but the main driver of these changes is still an open question. The main purpose of this work is to investigate the X-ray variability in LINERs, including the main driver of such variations, and to search for eventual differences between type 1 and 2 objects. We use the 18 LINERs in the Palomar sample with data retrieved from Chandra and/or XMM-Newton archives corresponding to observations gathered at different epochs. All the spectra for the same object are simultaneously fitted in order to study long term variations. The nature of the variability patterns are studied allowing different parameters to vary during the spectral fit. Whenever possible, short term variations from the analysis of the light curves and UV variability are studied.Comment: 49 pages, accepted. arXiv admin note: text overlap with arXiv:1305.222

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

Conformational Control of Tetrahydropyran-based Hybrid Dipeptide Catalysts Improves Activity and Stereoselectivity

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Herein, we introduce and demonstrate how carbohydrates can be used as conformational control units of organocatalysts to tune their catalytic properties. New hybrid dipeptide-like organocatalysts based on ζ-sugar aminoacids and proline were prepared and tested for the asymmetric Michael addition of aldehydes to β-nitrostyrenes. Taking full advantage of the modular nature of the carbohydrate motif, both reactivity and stereoselectivity were significantly improved. By simple structural changes, such as the elimination of the methoxy group in the C4 position of the tetrahydropyran ring, we obtained two complementary catalysts that allow access to both enantiomers of the γ-nitroaldehydes with excellent yields, diastereoselectivity, and enantiomeric excesses between 97 and 99%, using a catalytic load even below 1 mol%

¿Es posible la clasificación de individuos perinatales a partir de caracteres objetivos?

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

The Digital Competence of Pre-Service Educators: The Influence of Personal Variables

[EN] Currently, 21st century students need competences that enable them to adapt to a new type of individual information and individual knowledge relationship, and, therefore, the education system should contemplate new ways for learners to develop in accordance with this so-called information and knowledge society. One of special importance is so-called digital competency. This article presents the results of a research study to determine the influence that the variables of gender, age, and academic degree have on the acquisition of digital competence by pre-service educators, with a sample of 370 students from different education degrees from the University of Salamanca (Spain). A quantitative methodology was used, employing a non-experimental method and the electronic survey technique to collect information on the dimensions of knowledge, as well as the management of and attitude towards information and communication technologies (ICTs). Data were analyzed inferentially from a comparison of means using nonparametric tests. This analysis was completed with the incorporation of Receiver Operating Characteristic (ROC) curves, which allowed us to graphically verify the differences between the subsamples and thus compare the different groups in relation to the proposed dimensions. The main conclusion was that the three variables studied can be considered as influential, though not determinant, in the acquisition of digital competency

The Digital Competence of Pre-Service Educators: The Influence of Personal Variables

[EN]Currently, 21st century students need competences that enable them to adapt to a new type of individual information and individual knowledge relationship, and, therefore, the education system should contemplate new ways for learners to develop in accordance with this so-called information and knowledge society. One of special importance is so-called digital competency. This article presents the results of a research study to determine the influence that the variables of gender, age, and academic degree have on the acquisition of digital competence by pre-service educators, with a sample of 370 students from different education degrees from the University of Salamanca (Spain). A quantitative methodology was used, employing a non-experimental method and the electronic survey technique to collect information on the dimensions of knowledge, as well as the management of and attitude towards information and communication technologies (ICTs). Data were analyzed inferentially from a comparison of means using nonparametric tests. This analysis was completed with the incorporation of Receiver Operating Characteristic (ROC) curves, which allowed us to graphically verify the differences between the subsamples and thus compare the different groups in relation to the proposed dimensions. The main conclusion was that the three variables studied can be considered as influential, though not determinant, in the acquisition of digital competency

Digital competence of early childhood education teachers: attitude, knowledge and use of ICT

[EN] The main objective of the research described here was to learn how young learners self-evaluate their digital competence. A nonexperimental and descriptive quantitative methodology was employed, an electronic survey being used to collect the data. Among the main results, we can highlight that these learners selfevaluate their attitude towards Information and Communication Technologies (ICT) as favourable, their handling of them as moderate and their knowledge of them as scarce. It became clear that they do not have a level of digital competence suitable for being called ‘digital natives’, nor sufficient ability to use ICT in their academic life or in their professional future

Attosecond photoionization delays in the vicinity of molecular Feshbach resonances

Temporal delays extracted from photoionization phases are currently determined with attosecond resolution by using interferometric methods. Such methods require special care when photoionization occurs near Feshbach resonances due to the interference between direct ionization and autoionization. Although theory can accurately handle these interferences in atoms, in molecules, it has to face an additional, so far insurmountable problem: Autoionization is slow, and nuclei move substantially while it happens, i.e., electronic and nuclear motions are coupled. Here, we present a theoretical framework to account for this effect and apply it to evaluate time-resolved and vibrationally resolved photoelectron spectra and photoionization phases of N2 irradiated by a combination of an extreme ultraviolet (XUV) attosecond pulse train and an infrared pulse. We show that Feshbach resonances lead to unusual non-Franck-Condon vibrational progressions and to ionization phases that strongly vary with photoelectron energy irrespective of the vibrational state of the remaining molecular cationThis work was supported by European COST Action CA18222 AttoChem; the Synergy Grant of the European Research Council TOMATTO (ref. 951224); the projects PDC2021-121073-I00, PID2019-105458RB-I00, and PID2019-106732GB-I00 funded by MCIN/AEI /10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTRMICINN programs; the Comunidad de Madrid project FULMATEN (ref. Y2018NMT-5028); the “Severo Ochoa” Programme for Centres of Excellence in R&D (CEX2020-001039-S); and the “Maria de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M). L.A. acknowledges the DOE CAREER grant no. DE-SC0020311V and the NSF grant PHY-1912507. V.J.B. thanks the MICINN for the FPI grant (BES-2017-081521) related to the project FIS2016-77889-