Mining the ESO WFI and INT WFC archives for known Near Earth Asteroids. Mega-Precovery software

The ESO/MPG WFI and the INT WFC wide field archives comprising 330,000 images were mined to search for serendipitous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 asteroids (44 PHAs and 108 other NEAs) were identified using the PRECOVERY software, their astrometry being measured on 761 images and sent to the Minor Planet Centre. Both recoveries and precoveries were reported, including prolonged orbital arcs for 18 precovered objects and 10 recoveries. We analyze all new opposition data by comparing the orbits fitted before and after including our contributions. We conclude the paper presenting Mega-Precovery, a new online service focused on data mining of many instrument archives simultaneously for one or a few given asteroids. A total of 28 instrument archives have been made available for mining using this tool, adding together about 2.5 million images forming the Mega-Archive.Comment: Accepted for publication in Astronomische Nachrichten (Sep 2012

Effect of postannealing process on Bi2Sr2.1Ca0.9Cu2O8+δ textured superconductors

Bi-2212 samples prepared by the classical solid-state method have been grown from the melt using the Laser Floating Zone (LFZ) method. They have shown good grain alignment and transport critical current densities (Jc). After postannealing processes designed to produce the Bi-2212 phase controlled decomposition, Jc values have been increased in an important manner. Maximum values have been achieved when samples were thermally treated at 680 ºC for 168 h with improvements around 80 %, compared with the original textured samples. The results clearly indicate that postannealing processes, when adequately controlled, produce the formation of effective pinning centers which are responsible for the raise in the measured Jc values.The authors acknowledge financial support from the Spanish MICINN-FEDER (Project MAT2008-00429), MINECO-FEDER (Project MAT2011-22719), the Universidad de Zaragoza (UZ2011-TEC-03) and the Gobierno de Aragón (Consolidated Research Groups T12 and T87).Peer Reviewe

Unstable states in QED of strong magnetic fields

We question the use of stable asymptotic scattering states in QED of strong magnetic fields. To correctly describe excited Landau states and photons above the pair creation threshold the asymptotic fields are chosen as generalized Licht fields. In this way the off-shell behavior of unstable particles is automatically taken into account, and the resonant divergences that occur in scattering cross sections in the presence of a strong external magnetic field are avoided. While in a limiting case the conventional electron propagator with Breit-Wigner form is obtained, in this formalism it is also possible to calculate $S$-matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2

Thermoelectric properties in Ca3Co4-xMnxOy ceramics

Ca3Co4-xMnxOy polycrystalline thermoelectric ceramics with small amounts of Mn have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca3Co4O9 is the major phase, with small amounts of the Ca3Co2O6 one. Moreover, they show that the Mn has been incorporated into these two phases. Electrical resistivity decreases, compared with the values for undoped samples, with Mn content until a minimum for the 0·03 doped ones, increasing for higher Mn substitution. Seebeck coefficient does not change in all the measured temperature range, independently of Mn content. The improvement in electrical resistivity leads ∼30% higher power factor values for the 0·03 Mn doped samples than that obtained in the undoped ones. The maximum power factor at 800°C, ∼0·28 mW K-2 m-1, is close to that obtained in much higher density samples, clearly indicating the good thermoelectric properties of these samples.The authors wish to thank the Gobierno de Aragón (Research Groups T12 and T87) and the MINECO-FEDER (MAT2013-46505-C3-1-R) for financial support. Authors would also like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. The technical contributions of C. Estepa and C. Gallego are also acknowledged. Sh. Rasekh acknowledges a JAE-PreDoc 2010 grant from CSIC.Peer Reviewe

Efecto del dopaje en la propiedades termoeléctricas de cerámicas Ca3Co4-xNixO9

[EN]: Ca3Co4-xNixO9 (x=0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. As a result of the Ni addition an increase in porosity has been detected. Moreover, the presence of Ni has been related with the increase of Ca2Co3O6 secondary phase and the appearance of a new NiO-CoO solid solution. However, for the 0.01-Ni doped samples an improvement in the thermoelectric performances has been measured. This effect has been related with a decrease in the resistivity values and an increase in the Seebeck coefficient. The raise in the power factor for the 0.01-Ni doped samples, compared with the undoped ones, is between 10 and 25% at 50 and 800 ºC respectively. Moreover, the maximum power at 800 ºC, around 0.25 mW/K2.m, is significantly higher than the best results obtained in Ni doped samples reported previously in the literature.[ES]: Se han preparado muestras policristalinas de Ca3Co4-xNixO9 (x = 0,01, 0,03 y 0,05) mediante reacción en estado sólido. Se ha detectado un incremento de la porosidad en las muestras dopadas con Ni. La adición de Ni también ha provocado el aumento de la fase secundaria Ca2Co3O6, así como la aparición de una nueva fase consistente en una solución sólida de NiO-CoO. A pesar de ello se ha detectado una mejora de las prestaciones termoeléctricas en las muestras con un 0,01 de Ni. Esta mejora ha sido provocada por una disminución de la resistividad eléctrica y un aumento del coeficiente Seebeck.The authors wish to thank the Gobierno de Aragón and the Fondo Social Europeo (Research Groups T12 and T87) and MINECO-FEDER (Project MAT2013-46505-C3-1-R) for financial support.Peer Reviewe

Effect of Na doping on the Ca3Co4O9 thermoelectric performance

Ca3-xNaxCo4O9 polycrystalline thermoelectric ceramics with small amounts of Na (x=0, 0.01, 0.03, 0.05, 0.07, and 0.10) have been prepared using the classical solid state method. Microstructural characterization has shown that Na has been incorporated into the Ca3Co4O9 phase and that no Na-based secondary phases have been produced. It has also been found that Na addition promotes grain growth and favours sintering due to the formation of a small amount of liquid phase. Electrical resistivity decreases when Na content increases until 0.07Na addition while Seebeck coefficient is maintained practically unchanged. The improvement in electrical resistivity leads to higher power factor values than the usually obtained in samples prepared by more complex and expensive techniques.This research has been supported by the Spanish MINECO-FEDER (MAT2013-46505-C3-1-R). The authors wish to thank the Gobierno de Aragón-Fondo Social Europeo (Consolidate research group T12 and consolidated research group T87) for financial support.Peer Reviewe

Effect of secondary annealing process on critical current density in highly textured Bi-2212 superconducting system

Bi-2212 samples prepared by a solid-state reaction technique have been grown from the melt using the laser floating zone method. After annealing the as-grown bars, the samples showed a good grain alignment and a high transport critical current density. Secondary annealing processes were performed on the annealed samples with the aim of producing Bi-2212 phase controlled decomposition. Hence, the Bi-2201 phase and the secondary phases, which act as effective pinning centers, were obtained with the secondary annealing process. After these thermal treatments, the transport critical current densities of samples significantly increased, when compared to the annealed ones. The maximum critical current density was achieved when the samples were subjected to secondary annealing at 680°C for 168 h with an improvement of ~80%, compared to the annealed ones. Moreover, it was found that magnetization of the secondarily annealed samples was also increased. The magnetic critical current densities in these secondary annealed samples were about 3 times higher than the values obtained for the annealed ones. These results clearly indicate that the secondary annealing processes lead to the formation of effective pinning centers in the bulk material.The authors acknowledge financial support from the Gobierno de Aragón (Grupos de Investigacion Consolidados T12 and T87) and the Spanish MINECO-FEDER (Project MAT2013-46505-C3-1-R).Peer Reviewe