Computational analysis of projectile impact resistance on aluminium (a356) curvilinear surface reinforced with carbon nanotubes (cnts) for applications in systems of protection

Computational tests for ballistic impact energy absorption were developed on A356/CNTs composite material with the goal of estimating the improvement of the material’s mechanical properties by the contribution of the CNTs [1]. For the implementation of computational tests on the material exposed to projectile impact, A356/CNTs was configured by means of generalized Hooke’s model for anisotropic materials [1] and Johnson-Cook’s model was used to determine material failure and propagation of energy [2]. A curvilinear surface (semi-spheres on a plaque) with an area of 23x23 cm and thickness of 12 mm was elaborated to represent the composite material. The impact on surface was done with a 9 mm projectile and the surface was developed with 4.5 mm radium semi-spheres. It was used a 0.3% of nanotube insertions on the composite total volume. The results indicated the plaque stopped the impact without drilling. Incidence of damage to wearer, as well as possibility of composite material improvement and the diffusion/dispersion analysis on the curvilinear surface was also done

An X-ray characterization of the central region of the SNR G332.5-5.6

We present an X-ray analysis of the central region of supernova remnant (SNR) G332.5-5.6 through an exhaustive analysis of XMM-Netwon observations with complementary infrared observations. We characterize and discuss the origin of the observed X-ray morphology, which presents a peculiar plane edge over the west side of the central region. The morphology and spectral properties of the X-ray supernova remnant were studied using a single full frame XMM-Newton observation in the 0.3 to 10.0 keV energy band. Archival infrared WISE observations at 8, 12 and 24 \mu m were also used to investigate the properties of the source and its surroundings at different wavelengths. The results show that the extended X-ray emission is predominantly soft (0.3-1.2 keV) and peaks around 0.5 keV, which shows that it is an extremely soft SNR. X-ray emission correlates very well with central regions of bright radio emission. On the west side the radio/X-ray emission displays a plane-like feature with a terminal wall where strong infrared emission is detected. Our spatially resolved X-ray spectral analysis confirms that the emission is dominated by weak atomic emission lines of N, O, Ne, and Fe, all of them undetected in previous X-ray studies. These characteristics suggest that the X-ray emission is originated in an optically thin thermal plasma, whose radiation is well fitted by a non-equilibrium ionization collisional plasma (VNEI) X-ray emission model. Our study favors a scenario where G332.5-5.6 is expanding in a medium with an abrupt density change (the wall), likely a dense infrared emitting region of dust on the western side of the source.Comment: 7 pages, 5 figures and 2 tables. Accepted for publication in A&

Detailed study of SNR G306.3-0.9 using XMM-Newton and Chandra observations

We used combined data from XMM-Newton and Chandra observatories to study the X-ray morphology of SNR G306.3-0.9. A spatially-resolved spectral analysis was used to obtain physical and geometrical parameters of different regions of the remnant. Spitzer infrared observations were also used to constrain the progenitor supernova and study the environment in which the SNR evolved. The X-ray morphology of the remnant displays a non-uniform structure of semi-circular appearance, with a bright southwest region and very weak or almost negligible X-ray emission in its northern part. These results indicate that the remnant is propagating in a non-uniform environment as the shock fronts are encountering a high-density medium, where enhanced infrared emission is detected. The X-ray spectral analysis of the selected regions shows distinct emission-line features of several metal elements, confirming the thermal origin of the emission. The X-ray spectra are well represented by a combination of two absorbed thermal plasma models: one in equilibrium ionization with a mean temperature of ~0.19 keV, and another out of equilibrium ionization at a higher temperature of ~1.1 or 1.6-1.9 keV. For regions located in the northeast, central, and southwest part of the SNR, we found elevated abundances of Si, S, Ar, Ca, and Fe, typical of ejecta material. The outer regions located northwest and south show values of the abundances above solar but lower than to those found in the central regions. This suggests that the composition of the emitting outer parts of the SNR is a combination of ejecta and shocked material of the interstellar medium. The comparison between the S/Si, Ar/Si, and Ca/Si abundances ratios (1.75, 1.27, and 2.72 in the central region, respectively), favor a Type Ia progenitor for this SNR, a result that is also supported by an independent morphological analysis using X-ray and IR data.Comment: 8 pages, 7 figures. Accepted by Astronomy and Astrophysic

Water maser detections in southern candidates to post-AGB stars and Planetary Nebulae

We intended to study the incidence and characteristics of water masers in the envelopes of stars in the post-AGB and PN evolutionary stages. We have used the 64-m antenna in Parkes (Australia) to search for water maser emission at 22 GHz, towards a sample of 74 sources with IRAS colours characteristic of post-AGB stars and PNe, at declination $< -32 \deg$. In our sample, 39% of the sources are PNe or PNe candidates, and 50% are post-AGB stars or post-AGB candidates. We have detected four new water masers, all of them in optically obscured sources: three in PNe candidates (IRAS 12405-6219, IRAS 15103-5754, and IRAS 16333-4807); and one in a post-AGB candidate (IRAS 13500-6106). The PN candidate IRAS 15103-5754 has water fountain characteristics, and it could be the first PN of this class found. We confirm the tendency suggested in Paper I that the presence of water masers in the post-AGB phase is favoured in obscured sources with massive envelopes. We propose an evolutionary scenario for water masers in the post-AGB and PNe stages, in which ``water fountain'' masers could develop during post-AGB and early PN stages. Later PNe would show lower velocity maser emission, both along jets and close to the central objects, with only the central masers remaining in more evolved PNe.Comment: 11 pages, 5 figures. Accepted by Astronomy and Astrophysic

E-pSylon: una herramienta para la teleenseñanza síncrona

Muchas de las herramientas de teleenseñanza actuales corresponden al modelo asíncrono, donde instructor y alumnos interactúan desde espacios y tiempos diferentes. El modelo de teleenseñanza síncrona permite incorporar estrategias probadas con éxito en la enseñanza presencial, donde el apoyo visual del instructor a las explicaciones facilita la comprensión por parte de los alumnos. Se consigue así una enseñanza guiada y una realimentación inmediata de los alumnos. En este trabajo se propone una herramienta de teleenseñanza síncrona de sencillo manejo que permite el desarrollo de clases virtuales donde instructor y alumnos interactúan en tiempo real. También se presenta la experiencia con el uso de la herramienta en asignaturas relacionadas con la Ingeniería Informática y algunas conclusiones al respecto.Peer Reviewe

Observational Δν\Delta\nu-ρˉ\bar\rho relation for δ\delta Sct stars using eclipsing binaries and space photometry

Delta Scuti ($\delta$ Sct) stars are intermediate-mass pulsators, whose intrinsic oscillations have been studied for decades. However, modelling their pulsations remains a real theoretical challenge, thereby even hampering the precise determination of global stellar parameters. In this work, we used space photometry observations of eclipsing binaries with a $\delta$ Sct component to obtain reliable physical parameters and oscillation frequencies. Using that information, we derived an observational scaling relation between the stellar mean density and a frequency pattern in the oscillation spectrum. This pattern is analogous to the solar-like large separation but in the low order regime. We also show that this relation is independent of the rotation rate. These findings open the possibility of accurately characterizing this type of pulsator and validate the frequency pattern as a new observable for $\delta$ Sct stars.Comment: 11 pages, including 2 pages of appendix, 2 figures, 2 tables, accepted for publication in ApJ

Current sensorless power factor correction based on digital current rebuilding

A new digital control technique for power factor correction is presented. The main novelty of the method is that there is no current sensor. Instead, the input current is digitally rebuilt, using the estimated input current for the current loop. Apart from that, the ADCs used for the acquisition of the input and output voltages have been designed ad-hoc. Taking advantage of the slow dynamic behavior of these voltages, almost completely digital ADCs have been designed, leaving only a comparator and an RC filter in the analog part. The final objective is obtaining a low cost digital controller which can be easily integrated in an ASIC along with the controller of paralleled and subsequent power section

Experimental study of solid mixing mechanism in a 2D fluidized bed

The main mechanism of solids mixing in bubbling fluidized beds is well understood. When a bubble rises through the bed, it carries a wake of particles to the bed surface. A downflow of solids exists in the region surrounding the rising bubbles, resulting on an overall convective circulation of particles in the axial direction (1). In this work, a new method to characterize solids mixing in a 2D fluidized bed is developed. This mixing index is able to macroscopically characterize the rate of mixing in a fluidized bed by means of DIA. The mixing index is analogous to the Lacey’s mixing index of particle mixing (2). The experiments are carried out in a pseudo-2D fluidized bed using glass beads as bed material. These glass beads have the same density and diameter but half of them are painted in black (Figure-1). At the beginning of each experiment, the particles are placed in a perfectly lateral segregated state and then the fluidizing air is suddenly injected while images are recorded. Two different regions are detected in the time evolution of the mixing index. The first one is a region with a fast convective mixing, where the initial boundary between the black and white particles is broken. The second one is a region where diffusive mixing is dominant and the particles clusters are mixed with the bulk following an exponential trend (Figure-1). These two mechanisms, as well as the overall mixing time are characterized for different superficial gas velocities and particle sizes. REFERENCES M.J. Rhodes, X.S. Wang, M. Nguyen, P. Stewart, K. Liffman. Study of mixing in gas-fluidized beds using DEM model. Chem. Eng. Sci., 56(8):2859-2866, 2001. P.M.C. Lacey. Developments in the theory of particle mixing. J. Appl. Chem., 4:257-268, 1954. Please click Additional Files below to see the full abstract