Effect of reactive flash sintering on the magnetic and hyperfine parameters of SrFe12O19 ceramic permanent magnets

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Duplex stainless steels for thermal energy storage: characterization of oxide scales formed in carbonate salts at 500 °C

Next generation concentrated solar power (CSP) plants promise a higher operating temperature and better efficiency. However, new issues related to the corrosion against protection of the construction alloys need to be solved. In this work, two different duplex stainless steels grades, namely 2205 (DS2205) and 2507 (DS2507), were evaluated for their compatibility with the eutectic molten salt mixture of Li2CO3-K2CO3-Na2CO3 at 500 °C in air for thermal energy storage applications. Corrosion tests combined with complementary microscopy, microanalysis and mechanical techniques were employed to study the oxide scales formed on the surface of the duplex steels. The corrosion tests evidenced that the attack morphology in both duplex steels was a uniform oxidative process without localized corrosion. DS2507 presented a better corrosion resistance than DS2205, due to the formation of thinner, compact and continuous oxide layers with higher compositional content in Cr, Ni and Mo than DS2205. The oxide scales of DS2507 showed more remarkable mechanical integrity and adhesion to the metallic substrate.Postprint (published version

Reactive Flash Sintering of High Entropy (Mn0.2Co0.2Ni0.2Cu 0.2X 0.2)Fe2O4 (X=Fe, Mg) Spinel Oxides

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Integral field spectroscopy of M1-67. A Wolf-Rayet nebula with LBVN appearance

This work aims to disentangle the morphological, kinematic, and chemical components of the nebula M1-67 to shed light on its process of formation around the central Wolf-Rayet (WR) star WR124. We have carried out integral field spectroscopy observations over two regions of M1-67, covering most of the nebula in the optical range. Maps of electron density, line ratios, and radial velocity were created to perform a detailed analysis of the two-dimensional structure. We studied the physical and chemical properties by means of integrated spectra selected over the whole nebula. Photoionization models were performed to confirm the empirical chemical results theoretically. In addition, we analysed infrared spectroscopic data and the MIPS 24micron image of M1-67 from Spitzer. We find that the ionized gas of M1-67 is condensed in knots aligned in a preferred axis along the NE-SW direction, like a bipolar structure. Both electron density and radial velocity decrease in this direction when moving away from the central star. From the derived electron temperature, Te~8200 K, we have estimated chemical abundances, obtaining that nitrogen appears strongly enriched and oxygen depleted. From the last two results, we infer that this bipolarity is the consequence of an ejection of an evolved stage of WR124 with material processed in the CNO cycle. The infrared study has revealed that the bipolar axis is composed of ionized gas with a low ionization degree that is well mixed with warm dust and of a spherical bubble surrounding the ejection at 24micron. Taking the evolution of a 60 Mo star and the temporal scale of the bipolar ejection into account, we propose that the observed gas was ejected during an eruption in the luminous blue variable. The star has entered the WR phase recently without apparent signs of interaction between WR-winds and interstellar material.Comment: Accepted for publication in section 6 of Astronomy and Astrophysics. The official date of acceptance is 15/03/2013. 17 pages, 14 figures and 8 table

The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts

We report optical and near-infrared broad band observations of the short-duration GRB 050724 host galaxy, used to construct its spectral energy distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs), which show younger stellar populations, the SED of the GRB 050724 host galaxy is optimally fitted with a synthetic elliptical galaxy template based on an evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to reproduce with non-evolving metallicity templates. In contrast, if the short GRB host galaxy metallicity enrichment is considered, the synthetic templates fit the observed SED satisfactorily. The internal host extinction is low (A_v \~< 0.4 mag) so it cannot explain the faintness of the afterglow. This short GRB host galaxy is more massive (~5x10^10 Mo) and luminous (~1.1 L*) than most of the long-duration GRB hosts. A statistical comparison based on the ages of short- and long-duration GRB host galaxies strongly suggests that short-duration GRB hosts contain, on average, older progenitors. These findings support a different origin for short- and long-duration GRBs.Comment: A&A in pres

PPAK Integral Field Spectroscopy survey of the Orion Nebula: Data Release

We present a low-resolution spectroscopic survey of the Orion nebula which data we release for public use. In this article, we intend to show the possible applications of this dataset analyzing some of the main properties of the nebula. We perform an integral field spectroscopy mosaic of an area of ~5' X 6' centered on the Trapezium region of the nebula, including the ionization front to the south-east. The analysis of the line fluxes and line ratios of both the individual and integrated spectra allowed us to determine the main characteristics of the ionization throughtout the nebula.The final dataset comprises 8182 individual spectra, which sample each one a circular area of \~2.7" diameter. The data can be downloaded as a single row-stacked spectra fits file plus a position table or as an interpolated datacube with a final sampling of 1.5"/pixel. The integrated spectrum across the field-of-view was used to obtain the main integrated properties of the nebula, including the electron density and temperature, the dust extinction, the Halpha integrated flux (after correcting for dust reddening), and the main diagnostic line ratios. The individual spectra were used to obtain line intensity maps of the different detected lines. These maps were used to study the distribution of the ionized hydrogen, the dust extinction, the electron density and temperature, and the helium and oxygen abundance...Comment: 13 pages, 8 figures, accepted for publishing in Astronomy & Astrophysic

The interplay between ionized gas and massive stars in the HII galaxy IIZw70: integral field spectroscopy with PMAS

We performed an integral field spectroscopic study for the HII galaxy IIZw70 in order to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation (SF). Observations were taken in the optical spectral range (3700-6800 A) with the Potsdam Multi-Aperture Spectrophotometer (PMAS) attached to the 3.5 m telescope at CAHA. We created and analysed maps of spatially distributed emission-lines, continuum emission and properties of the ionized ISM (e.g. physical-chemical conditions, dust extinction, kinematics). We investigated the relation of these properties to the spatial distribution and evolutionary stage of the massive stars. For the first time we have detected the presence of Wolf-Rayet (WR) stars in this galaxy. The peak of the ionized gas emission coincides with the location of the WR bump. The region of the galaxy with lower dust extinction corresponds to the region that shows the lowest values of velocity dispersion and radial velocity. The overall picture suggests that the ISM of this region is being disrupted via photoionization and stellar winds, leading to a spatial decoupling between gas+stars and dust clouds. The bulk of dust appears to be located at the boundaries of the region occupied by the probable ionizing cluster. We also found that this region is associated to the nebular emission in HeII4686 and to the intensity maximum of most emission lines. This indicates that the hard ionizing radiation responsible for the HeII4686 nebular emission can be related to the youngest stars. Within $\sim$ 0.4 x 0.3 kpc^2 in the central burst, we derived O/H using direct determinations of Te[OIII]. We found abundances in the range 12+log(O/H)=7.65-8.05, yielding an error-weighted mean of 12+log(O/H)=7.86 $\pm$0.05.Comment: 10 pages, 10 figures, accepted for publication in A&A, minor changes adde

Two-port multimode interference reflectors based on aluminium mirrors in a thick SOI platform

“© 2015 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited"Multimode interference reflectors (MIRs) were recently introduced as a new type of photonic integrated devices for on-chip, broadband light reflection. In the original proposal, different MIRs were demonstrated based on total internal reflection mirrors made of two deep-etched facets. Although simpler to fabricate, this approach imposes certain limits on the shape of the field pattern at the reflecting facets, which in turn restricts the types of MIRs that can be implemented. In this work, we propose and experimentally demonstrate the use of aluminium-based mirrors for the design of 2-port MIRs with variable reflectivity. These mirrors do not impose any restrictions on the incident field, and thus give more flexibility at the design stage. Devices with different reflectivities in the range between 0 and 0.5 were fabricated in a 3 um thick SOI platform, and characterization of multiple dies was performed to extract statistical data about their performance. Our measurements show that, on average, losses both in the aluminium mirror and in the access waveguides reduce the reflectivities to about 79% of their target value. Moreover, standard deviations lower than +/- 5% are obtained over a 20 nm wavelength range (1540-1560 nm). We also provide a theoretical model of the aluminium mirror based on the effective index method and Fresnel equations in multilayer thin films, which shows good agreement with FDTD simulations.This work was supported by projects TEC2010-21337 (ATOMIC), FEDER UPVOV10-3E-492, FEDER UPVOV08-3E-008, TEC2013-42332-P (PIC4ESP), and PROMETEO 2013/012. The work of J. S. Fandino was supported by Grant FPU-2010 (ref: AP2010-1595).Sánchez Fandiño, JA.; Doménech Gómez, JD.; Muñoz Muñoz, P. (2015). Two-port multimode interference reflectors based on aluminium mirrors in a thick SOI platform. Optics Express. 23(16):20219-20233. https://doi.org/10.1364/OE.23.020219S20219202332316Besse, P. A., Bachmann, M., Melchior, H., Soldano, L. B., & Smit, M. K. (1994). Optical bandwidth and fabrication tolerances of multimode interference couplers. Journal of Lightwave Technology, 12(6), 1004-1009. doi:10.1109/50.296191Soldano, L. B., & Pennings, E. C. M. (1995). Optical multi-mode interference devices based on self-imaging: principles and applications. Journal of Lightwave Technology, 13(4), 615-627. doi:10.1109/50.372474Besse, P. A., Gini, E., Bachmann, M., & Melchior, H. (1996). New 2×2 and 1×3 multimode interference couplers with free selection of power splitting ratios. Journal of Lightwave Technology, 14(10), 2286-2293. doi:10.1109/50.541220Domenech, J. D., Fandino, J. S., Gargallo, B., & Munoz, P. (2014). Arbitrary Coupling Ratio Multimode Interference Couplers in Silicon-on-Insulator. Journal of Lightwave Technology, 32(14), 2536-2543. doi:10.1109/jlt.2014.2329994Kwong, D., Covey, J., Hosseini, A., Zhang, Y., Xu, X., & Chen, R. T. (2012). Ultralow-loss polycrystalline silicon waveguides and high uniformity 1x12 MMI fanout for 3D photonic integration. Optics Express, 20(19), 21722. doi:10.1364/oe.20.021722Ortega-Moñux, A., Alonso-Ramos, C., Maese-Novo, A., Halir, R., Zavargo-Peche, L., Pérez-Galacho, D., … Janz, S. (2013). An ultra-compact multimode interference coupler with a subwavelength grating slot. Laser & Photonics Reviews, 7(2), L12-L15. doi:10.1002/lpor.201200106Maese-Novo, A., Halir, R., Romero-García, S., Pérez-Galacho, D., Zavargo-Peche, L., Ortega-Moñux, A., … Cheben, P. (2013). Wavelength independent multimode interference coupler. Optics Express, 21(6), 7033. doi:10.1364/oe.21.007033Chen, H., & Poon, A. W. (2006). Low-Loss Multimode-Interference-Based Crossings for Silicon Wire Waveguides. IEEE Photonics Technology Letters, 18(21), 2260-2262. doi:10.1109/lpt.2006.884726Fan Wang, Jianyi Yang, Limei Chen, Xiaoqing Jiang, & Minghua Wang. (2006). Optical switch based on multimode interference coupler. IEEE Photonics Technology Letters, 18(2), 421-423. doi:10.1109/lpt.2005.863201Hosseini, A., Rahimi, S., Xu, X., Kwong, D., Covey, J., & Chen, R. T. (2011). Ultracompact and fabrication-tolerant integrated polarization splitter. Optics Letters, 36(20), 4047. doi:10.1364/ol.36.004047Hu, Y., Jenkins, R. M., Gardes, F. Y., Finlayson, E. D., Mashanovich, G. Z., & Reed, G. T. (2011). Wavelength division (de)multiplexing based on dispersive self-imaging. Optics Letters, 36(23), 4488. doi:10.1364/ol.36.004488Fukuda, T., Okamoto, K., Hinokuma, Y., & Hamamoto, K. (2009). Phase-Locked Array Laser Diodes (LDs) by Using $1\times N$ Active Multimode-Interferometer (MMI). IEEE Photonics Technology Letters, 21(3), 176-178. doi:10.1109/lpt.2008.2009470Berry, M. V., & Klein, S. (1996). Integer, fractional and fractal Talbot effects. Journal of Modern Optics, 43(10), 2139-2164. doi:10.1080/09500349608232876Kaplan, A. E., Marzoli, I., Lamb, W. E., & Schleich, W. P. (2000). Multimode interference: Highly regular pattern formation in quantum wave-packet evolution. Physical Review A, 61(3). doi:10.1103/physreva.61.032101Azana, J., & Muriel, M. A. (2001). Temporal self-imaging effects: theory and application for multiplying pulse repetition rates. IEEE Journal of Selected Topics in Quantum Electronics, 7(4), 728-744. doi:10.1109/2944.974245Kleijn, E., Smit, M. K., & Leijtens, X. J. M. (2013). Multimode Interference Reflectors: A New Class of Components for Photonic Integrated Circuits. Journal of Lightwave Technology, 31(18), 3055-3063. doi:10.1109/jlt.2013.2278187Cherchi, M., Ylinen, S., Harjanne, M., Kapulainen, M., & Aalto, T. (2015). MMI resonators based on metal mirrors and MMI mirrors: an experimental comparison. Optics Express, 23(5), 5982. doi:10.1364/oe.23.005982Seimetz, M., & Weinert, C.-M. (2006). Options, feasibility, and availability of 2 /spl times/ 4 90/spl deg/ hybrids for coherent optical systems. Journal of Lightwave Technology, 24(3), 1317-1322. doi:10.1109/jlt.2005.863251Pennings, E. C. M., van Roijen, R., van Stralen, M. J. N., de Waard, P. J., Koumans, R. G. M. P., & Verbeck, B. H. (1994). Reflection properties of multimode interference devices. IEEE Photonics Technology Letters, 6(6), 715-718. doi:10.1109/68.300172Kleijn, E., Melati, D., Melloni, A., de Vries, T., Smit, M. K., & Leijtens, X. J. M. (2014). Multimode Interference Couplers With Reduced Parasitic Reflections. IEEE Photonics Technology Letters, 26(4), 408-410. doi:10.1109/lpt.2013.2295624Gordón, C., Guzmán, R., Leijtens, X., & Carpintero, G. (2014). On-chip mode-locked laser diode structure using multimode interference reflectors. 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Transcellular communication at the immunological synapse: A vesicular traffic-mediated mutual exchange

The cell's ability to communicate with the extracellular environment, with other cells, and with itself is a crucial feature of eukaryotic organisms. In the immune system, T lymphocytes assemble a specialized structure upon contact with antigen-presenting cells bearing a peptide-major histocompatibility complex ligand, known as the immunological synapse (IS). The IS has been extensively characterized as a signaling platform essential for T-cell activation. Moreover, emerging evidence identifies the IS as a device for vesicular traffic-mediated cell-to-cell communication as well as an active release site of soluble molecules. Here, we will review recent advances in the role of vesicular trafficking in IS assembly and focused secretion of microvesicles at the synaptic area in naïve T cells and discuss the role of the IS in transcellular communication