Evidence for precession of the isolated neutron star RX J0720.4-3125

The XMM-Newton spectra of the isolated neutron star RX J0720.4-3125 obtained over 4.5 years can be described by sinusoidal variations in the inferred blackbody temperature, the size of the emitting area and the depth of the absorption line with a period of 7.1 +/- 0.5 years, which we suggest to be the precession period of the neutron star. Precession of a neutron star with two hot spots of different temperature and size, probably not located exactly in antipodal positions, may account for the variations in the X-ray spectra, changes in the pulsed fraction, shape of the light curve and the phase-lag between soft and hard energy bands observed from RX J0720.4-3125. An independent sinusoidal fit to published and new pulse timing residuals from a coherent analysis covering ~12 years yields a consistent period of 7.7 +/- 0.6 years supporting the precession model.Comment: Accepted for publication in A&A Letters, 5 pages, 5 figure

Search for the companions of Galactic SNe Ia

The central regions of the remnants of Galactic SNe Ia have been examined for the presence of companion stars of the exploded supernovae. We present the results of this survey for the historical SN 1572 and SN 1006. The spectra of the stars are modeled to obtain Teff, log g and the metallicity. Radial velocities are obtained with an accuracy of 5--10 km s$^{-1}$. Implications for the nature of the companion star in SNeIa follow.Comment: 8 pages, 2 Postscript figures. Appeared in "From Twilight to Highlight: the Physics of Supernovae", ed. W. Hillebrandt & B. Leibundgut (Springer), pp. 140-14

Modulo-Counting First-Order Logic on Bounded Expansion Classes

We prove that, on bounded expansion classes, every first-order formula with modulo counting is equivalent, in a linear-time computable monadic lift, to an existential first-order formula. As a consequence, we derive, on bounded expansion classes, that first-order transductions with modulo counting have the same encoding power as existential first-order transductions. Also, modulo-counting first-order model checking and computation of the size of sets definable in modulo-counting first-order logic can be achieved in linear time on bounded expansion classes. As an application, we prove that a class has structurally bounded expansion if and only if is a class of bounded depth vertex-minors of graphs in a bounded expansion class. We also show how our results can be used to implement fast matrix calculus on bounded expansion matrices over a finite field.Comment: submitted to CSGT2022 special issu

Peanut-shaped bulges in face-on disk galaxies

We present high resolution absorption-line spectroscopy of 3 face-on galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for box/peanut (B/P)-shaped bulges. These observations test and confirm the prediction of Debattista et al. (2005) that face-on B/P-shaped bulges can be recognized by a double minimum in the profile of the fourth-order Gauss-Hermite moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find a significant B/P shape.Comment: 4 pages, 1 figure. To appear in "Tumbling, twisting, and winding galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P. Debattista (eds.), Memorie della Societa` Astronomica Italian

Multi-screen and multi-device game development

Users are interacting with an increasing number of devices and screens. However, these screens are usually used independently without collaboration between them. Although there have been several advances in multi-screen applications the game community does not seem to have fully explored this opportunity as yet. This paper presents an approach for the development of mobile multi-screen and multi-device games. The approach aims to enable and foster the creation of multi-device games sharing information via a centralized screen and is demonstrated by means of an example, the well-known Casino Roulette game. The results of a preliminary evaluation of the game are also presented.info:eu-repo/semantics/acceptedVersio

Coupled radio and X-ray emission and evidence for discrete ejecta in the jets of SS 433

We present five epochs of simultaneous radio (VLA) and X-ray (Chandra) observations of SS 433, to study the relation between the radio and X-ray emission in the arcsecond-scale jets of the source. We detected X-ray emission from the extended jets in only one of the five epochs of observation, indicating that the X-ray reheating mechanism is transient. The reheating does not correlate with the total flux in the core or in the extended radio jets. However, the radio emission in the X-ray reheating regions is enhanced when X-ray emission is present. Deep images of the jets in linear polarization show that outside of the core, the magnetic field in the jets is aligned parallel to the local velocity vector, strengthening the case for the jets to be composed of discrete bullets rather than being continuous flux tubes. We also observed anomalous regions of polarized emission well away from the kinematic trace, confirming the large-scale anisotropy of the magnetic field in the ambient medium surrounding the jets.Comment: Accepted for publication in ApJ. 11 pages (emulateapj), 9 figures, 3 table

Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression

Resistance, magnetoresistance and their temperature dependencies have been investigated in the 2D hole gas at a [001] p-GaAs/Al$_{0.5}$Ga$_{0.5}$As heterointerface under [110] uniaxial compression. Analysis performed in the frame of hole-hole scattering between carriers in the two spin splitted subbands of the ground heavy hole state indicates, that h-h scattering is strongly suppressed by uniaxial compression. The decay time $\tau_{01}$ of the relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3 kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.

Correlated Timing and Spectral Variations of the Soft X-ray Transient Aquila X-1: Evidence for an Atoll classification

Based on Rossi X-ray Timing Explorer data, we discuss the classification of the soft X-ray transient Aquila X-1 in the Z/atoll scheme, and the relation of its kilohertz quasi-periodic oscillations (kHz QPO) properties to the X-ray colors. The color-color diagram shows one elongated ("banana") structure and several "islands" of data points. The power spectra of the island are best represented by a broken power-law, whereas those of the banana by a power-law below ~ 1 Hz plus an exponentially cut-off component at intermediate frequencies (30-60 Hz). The parameters of these two components change in correlation with the position of the source in the color-color diagram. Based on the pattern that the source shows in the color-color diagram and its aperiodic variability we conclude that Aquila X-1 is an atoll source. We have also investigated the possible correlation between the frequency of the kHz QPO and the position of the source in the color-color diagram. The complexity seen in the frequency versus count rate diagram is reduced to a single track when the frequency is plotted against hard or soft color.Comment: 9 pages, 5 figures. Accepted for publication in Ap

Formative research: challenges and tendencies

21st century teachers are not only required to develop top teaching skills, but also strong research ones that allow them to expand their understanding of teaching-learning phenomena and improve their school practices. This relatively recent trend has also impacted the Language Teaching field, making language programs in universities to develop different approaches to Formative Research for their student-teachers. This paper aims to contrast how two different universities (a private and a state one) understand and carry out formative research processes. The analysis attempts to specifically describe how two Bachelors of Arts in Education of teachers in Foreign Languages programs have dealt with formative research revealing goals and difficulties when initiating student-teachers in research

Mentoring in pre-service teaching: from reflection on practice to a didactic proposal

This article offers a review of different methodologies to mentor pre-service teachers’ pedagogical experience in EFL contexts in Colombia and their pedagogical implications when training future teachers. It also gives an overview of models presented for the purpose of mentoring. Finally, it proposes a model to guide the mentoring of pre-service teachers’ pedagogical experiences at schools in Bogotá considering the implications of talking about the mentoring in the teaching practicum and the roles of the participants. This model is a selection of mentoring strategies that can be extended to other contexts with similar characteristics