Optical spectra of selected Chamaeleon I young stellar objects

We present optical spectra of eight candidate brown dwarfs and a previously known T Tauri star (Sz 33) of the Chamaeleon I dark cloud. We derived spectral types based on the strength of the TiO or VO absorption bands present in the spectra of these objects as well as on the PC3 index of Martin et al. (1999). Photometric data from the literature are used to estimate the bolometric luminosities for these sources. We apply D'Antona & Mazzitelli (1997) pre-main sequence evolutionary tracks and isochrones to derive masses and ages. Based on the presence of Halpha in emission, we confirm that most of the candidates are young objects. Our sample however includes two sources for which we can only provide upper limits for the emission in Halpha; whereas these two objects are most likely foreground/background stars, higher resolution spectra are required to confirm their true nature. Among the likely cloud members, we detect one new sub-stellar object and three transition stellar/sub-stellar sources.Comment: 22 pages - manuscript forma

Formation of asymmetric arms in barred galaxies

ABSTRACTWe establish a dynamical mechanism to explain the origin of the asymmetry between the arms observed in some barred disc galaxies, where one of the two arms emanating from the bar ends is very well defined, while the second one displays a ragged structure, extending between its ridge and the bar. To this purpose, we study the invariant manifolds associated with the Lyapunov periodic orbits around the unstable equilibrium points at the ends of the bar. Matter from the galaxy centre is transported along these manifolds to the periphery, forming this way the spiral arms that emanate from the bar ends. If the mass distribution in the galaxy centre is not homogeneous, because of an asymmetric bar with one side stronger than the other, or because of a non-centred bulge, the dynamics about the two unstable Lagrange points at the ends of the bar will not be symmetric as well. One of their invariant manifolds becomes more extended than the other, enclosing a smaller section and the escaping orbits on it are fewer and dispersed in a wider region. The result is a weaker arm and more ragged than the one at the other end of the bar

High-resolution study of a star-forming cluster in the Cep-A HW2 region

Due to its relatively small distance (725 pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. Goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1-arcsecond (about 725 AU) scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out, but such structure is likely to be detected on a smaller spatial scale, or using different molecular tracers.Comment: 6 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5_{0.5}Sr1.5_{1.5}Co2_2Fe12_{12}O22{22}

Single phase multiferroics in which ordered magnetic and ferroelectricity coexist, are of great interest for new multifunctional devices, and among them Y-type hexaferrites are good candidates. Transverse susceptibility measurements, which have been proved to be a versatile tool to study singular properties of bulk and nanoparticle magnetic systems, have been carried out with a broadband system on polycrystalline Y type hexaferrites with composition Ba$_{0.5}$Sr$_{1.5}$Co$_2$Fe$_{12}$O${22}$, optimal to exhibit multiferroic properties. In the temperature range 80-350 K transverse susceptibility measurements with DC fields up to $\pm$5000 Oe reveal different behaviour depending on the sintering temperature. The thermal evolution of the anisotropy field peak exhibit four regions with different slopes: positive in 80-130 K, negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which can be considered a signature of spin transitions in this compound.Comment: arXiv admin note: substantial text overlap with arXiv:2401.1614

Aprendizaje basado en juegos

Gracias al incremento de potencia de los ordenadores, gran cantidad de personas dedican horas y horas a aprovechar su aspecto más lúdico, los videojuegos. Por otro lado, existen programas educativos que aprovechan la infinita paciencia de los ordenadores que les hacen capaces de explicar conceptos una y otra vez hasta que los alumnos lo entiendan. En este artículo mostramos qué cosas pueden aportar las aplicaciones de enseñanza a los videojuegos y viceversa. Terminamos describiendo JV2M, como un ejemplo de sistema de aprendizaje basado en juegos

Preliminary Results from the Experimental Study of CO2-Brine-Rock Interactions at Elevated T & P: Implications for the Pilot Plant for CO2 Storage in Spain

AbstractA new experimental program has been carried out in order to study CO2-brine-rock interactions susceptible to take place in conditions close to those expected in the pilot plant that is being developed in Spain (a carbonate reservoir located at more than 800 m depth, with 15% porosity, and a salinity of the native brine between 20 – 90g/L). The combination of preliminary experimental and numerical modeling (PHREEQC) results suggests that the main geochemical processes are calcite dissolution and anhydrite precipitation

Tool wear evaluation in drilling by acoustic emission

AbstractA drilling process with different degrees of wear in the drill bit was studied to find relationships between acoustic emission (AE) and torque measured during the drilling process, and also with the degree of wear of the tool.SAE 1040 steel samples were drilled, making holes with 5 mm diameter twist drill bits in continuous feed. The drill bits were modified with “artificial” (produced by spark-erosion) and “real” (obtained by regular mechanical use) failures such as different degrees of wear in the cutting edge and the outer corner. For every drilled hole, torque and AE were simultaneously measured and acquired.In the first part of this work, the correlation between the AE parameters and torque measured during the drilling process is studied. Torque was measured as a control parameter to follow the dynamic behaviour of the drill bit. An alternative AE feature, called Mean Power (MP) showed a good correlation with torque when the moving average (MA) was computed.In the second part, the AE mean power (MP) was related to different degrees of wear in drill bits. Clusters for the different levels of wear in a 2-D plot were obtained. In that plot the moving variance of the MP vs. the moving average of the MP, for each case of wear, were represented.This application aims at repetitive manufacturing operations, where many signals per second may be obtained with fixed parameters as shape, drill bit diameter, spindle speed, feed, and a good statistical study can be done

Effect of natural and forced charge air humidity on the performance and emissions of a compression-ignition engine operating at high warm altitude

[EN] The effect of ambient humidity on the performance and pollutant emissions of internal combustion engines is not considered in the literature despite type-approval criteria are moving closer to real driving conditions. This work analyses experimentally the effects of charge air humidity at high warm altitudes, where the use of exhaust gas recirculation (EGR) is typically lowered and even avoided to recover engine performance at the expense of NOx emissions increase, on the response of a compression-ignition engine under a wide range of steady-state con-ditions in terms of engine-out emissions and specific fuel consumption. The impact of specific humidity varia-tions within the atmospheric range was analysed by coupling the engine to an altitude simulator with pressure, temperature, and humidity control capabilities. High altitudes and warm & high ambient temperatures were explored (2000 m at 30 degrees C and 2500 m at 45 degrees C) to cover ambient specific humidity up to 30 gwater/kgdry_air. In addition, the effects of increasing the specific humidity above the atmospheric levels were considered at 2500 m and 45 degrees C to emulate forced injection of water in the engine intake line corresponding to 60 gwater/kgdry_air. With this approach, understanding of the role of humidity is provided to highlight its importance as additional ambient property in emission control. In parallel, the assessment of the forced water content increase to control NOx emissions when EGR must be lowered was performed due to the altitude impact on the engine performance and turbocharger limits. The results showed a consistent and significant reduction in engine-out NOx emissions as the ambient humidity increased, reaching up to 300% with respect to the dry case, caused by the decrease in O2 availability due to the water content increase. The benefits of high humidity in NOx emission control at high altitudes when EGR is not feasible were complemented by an improved trade-off with particulate matter emission compared to the standard from EGR use. The results evidenced a reduction in opacity close to 250% for a given engine-out NOx emission when EGR was replaced by water content. By contrast, the slowdown of the combustion process as the fresh air humidity increased deteriorated the specific fuel consumption significantly as the engine load and speed increased. Nevertheless, these penalties ranged from 2 to 2.7% in the worst conditions and showed the same sensitivity for EGR and humidity increases.This research has been supported by Grant PID2020-114289RB-I00 funded by the Spanish Ministerio de Ciencia e Innovacion - Agencia Estatal de Investigacion (MCIN/AEI/10.13039/501100011033). The PhD candidate Roberto Tabet has been funded by Universitat Politecnica de Valencia through grant PAID -01-18.Serrano, J.; Martín, J.; Piqueras, P.; Tabet-Aleixandre, R.; Gómez-Gil, J. (2023). Effect of natural and forced charge air humidity on the performance and emissions of a compression-ignition engine operating at high warm altitude. Energy. 266:1-11. https://doi.org/10.1016/j.energy.2022.12640911126

Distribution of individual wave overtopping volumes on mound breakwaters

[EN] Conventional mound breakwaters are usually designed to withstand low mean wave overtopping discharges and a low proportion of overtopping waves (P-ow). Existing formulas to estimate P-ow, and maximum individual wave overtopping volume are usually based on tests with high P-ow; this study is focused on mound breakwaters subjected to P-ow, < 0.2. The performance of the 2-parameter Weibull and Exponential distributions is examined in order to describe individual wave overtopping volumes of mound breakwaters in non-breaking wave conditions. A new methodology is applied to 164 small-scale 2D physical tests to identify the number of overtopping waves, and the corresponding individual wave overtopping volumes. Utility functions are used to consider the relative relevance of the observed data: in this study, a quadratic utility function depending on all the individual wave overtopping volumes and step utility functions with 10%, 30% and 50% of the highest volumes are used to fit the Weibull and Exponential distributions. In this study, a new estimator of P-ow is proposed to improve the predictions required to estimate the maximum individual wave overtopping volume. Existing estimators of P-ow, underpredict the largest values of P-ow, measured in the physical tests. The parameters fitted to the Weibull and Exponential distributions using the quadratic utility function provide estimations of the dimensionless maximum individual wave overtopping volume with relative mean squared errors rMSE = 10.4% and 10.6%, respectively. When CLASH Neural Network-estimated mean overtopping rates are used to predict the maximum individual wave overtopping with the quadratic utility function, the 2-parameter Weibull and Exponential distributions provide rMSE = 31.6% and rMSE = 33.3%, respectively. The new estimators proposed in this study improve the predictions of P-ow and maximum individual wave overtopping volumes on conventional mound breakwaters designed for low wave overtopping rates.The authors are grateful for financial support from European FEDER and Spanish Ministerio de Economia y Competitividad (Grants BIA2012-33967 and BIA2015-70435-R), SATO (OHL Group), Universitat Politecnica de Valencia (Grant SP20180111, Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Transferencia de la Universitat Politecnica de Valencia) and CDTI (Centro para el Desarrollo Tecnologico e Industrial). The authors also thank Debra Westall for revising the manuscript.Molines, J.; Herrera, MP.; Gómez-Martín, ME.; Medina, JR. (2019). Distribution of individual wave overtopping volumes on mound breakwaters. Coastal Engineering. 149:15-27. https://doi.org/10.1016/j.coastaleng.2019.03.006S152714