4U 1626-67 as seen by Suzaku before and after the 2008 torque reversal

Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. The main goal of the present work is to study this recent torque reversal that occurred in 2008 February. Methods. We present a spectral analysis of this source using two pointed observations performed by Suzaku in 2006 March and in 2010 September. Results. We confirm with Suzaku the presence of a strong emission-line complex centered on 1 keV, with the strongest line being the hydrogen-like Ne Ly-alpha at 1.025(3) keV. We were able to resolve this complex with up to seven emission lines. A dramatic increase of the intensity of the Ne Ly-alpha line after the 2008 torque reversal occurred, with the equivalent width of this line reaching almost the same value measured by ASCA in 1993. We also report on the detection of a cyclotron line feature centered at ~37 keV. In spite of the fact that an increase of the X-ray luminosity (0.5-100 keV) of a factor of ~2.8 occurred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the ~1 keV line complex increased by an overall factor of ~8. Conclusions. Our results favor a scenario in which the neutron star in 4U 1626-67 accretes material from a geometrically thin disk during both the spin-up and spin-down phases.Comment: 7 pages, 5 figures and 2 tables. Accepted in A&

The Poincare-Birkhoff theorem in Quantum Mechanics

Quantum manifestations of the dynamics around resonant tori in perturbed Hamiltonian systems, dictated by the Poincar\'e--Birkhoff theorem, are shown to exist. They are embedded in the interactions involving states which differ in a number of quanta equal to the order of the classical resonance. Moreover, the associated classical phase space structures are mimicked in the quasiprobability density functions and their zeros.Comment: 5 pages, 3 figures, Full resolution figures available at http://www.df.uba.ar/users/wisniaki/publications.htm

Maximum population transfer in a periodically driven two-level system

We study the dynamics of a two-level quantum system under the influence of sinusoidal driving in the intermediate frequency regime. Analyzing the Floquet quasienergy spectrum, we find combinations of the field parameters for which population transfer is optimal and takes place through a series of well defined steps of fixed duration. We also show how the corresponding evolution operator can be approximated at all times by a very simple analytical expression. We propose this model as being specially suitable for treating periodic driving at avoided crossings found in complex multi-level systems, and thus show a relevant application of our results to designing a control protocol in a realistic molecular modelComment: 7 pages, 6 figure

Setting conclitions, Petrology ancl Geochemistry of calc-alkaline rhyolites, stephanian-permian, in the iberian chains

[Resumen] Se exponen los caracteres del emplazamiento, la composición petrológica y geoquímica de unos sills riolíticos que, con afinidad calco-alcalina, se emplazaron, bajo un ambiente sin-colisional, en diversos sectores de la Cadena Ibérica. Estas riolitas representan un origen crustal, con baja tasa de fusión, previo a un magmatismo calco-alcalino de origen subcrustal.[Abstract] The setting characters, the petrological and geochemical composition are exposed for sorne rhyolitic sills, with calc-alkaline affinity, which were set, in a syncollisional environment, in several areas of the Iberian Chains. These rhyolites represent a crustal origin, with a low degree of fussion, previous to a calc-alkaline magmatism of subcrustal origino

The pre-outburst flare of the A 0535+26 August/September 2005 outburst

We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=103.3960(5)s is measured until periastron passage, followed by a spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s at MJD 53618, and P remains constant again at the end of the main outburst. The spin-up provides evidence for the existence of an accretion disk during the normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies significantly during both pre-outburst flare and main outburst, evolves strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be published in parallel to Postnov et al. 200

Nd3+-doped TeO2–PbF2–AlF3 glasses for laser applications

A study of the optical properties of Nd3+ ion in TeO2–PbF2–AlF3 glasses has been carried out for different Nd3+ concentrations. Based on the Judd–Ofelt theory, intensity parameters and radiative properties were determined from the absorption spectra. Focusing on the suitability of this host for laser applications, the spectroscopic quality factor v was obtained with a value of 1.07, a value of the order of other compositions proposed as laser hosts. For the most intense emission corresponding with the 4F3/2?4I11/2 transition (1.06 lm), the absorption and emission and have been calculated with values of 1.20 10 20 cm2, 2.08 10 20 cm2. A positive value for the gain cross-sections has been found for a population inversion factor c of 0.4 in the spectral range from 1060 to 1110 nm. All these results suggest the potentially use of this system as a laser host

Age of the Cretaceous alkaline magmatism in northeast Iberia: implications for the Alpine cycle in the Pyrenees

Cretaceous magmatism in northeast Iberia is related to the opening of the Bay of Biscay and counterclockwise rotation of Iberia with respect to Europe and predates the collision between Iberia and Europe that resulted in the formation of the Pyrenees. To better constrain the age of this magmatism, we have undertaken a Ar/Ar study on samples from the Pyrenees and the Catalonian Coastal Ranges. In the Basque-Cantabrian Basin and the North Pyrenean Basins, we have obtained Albian ages (ca. 102 Ma). In the northern Catalonian Coastal Ranges, we have obtained Campanian ages (ca. 79 Ma). We integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance. The Cretaceous magmatism in the Pyrenees is Albian-Santonian (mostly occurring between 105 to 85 Ma) and was emplaced in a tectonically unclear context after the opening of the Bay of Biscay and rotation of Iberia. The magmatism in the Catalonian Coastal Ranges is well constrained to ca. 79 Ma and could mark the onset of Alpine shortening in the Pyrenean realm in northeasternmost Iberia. Finally, we describe a Late Triassic (ca. 232 Ma)-Early Jurassic (ca. 180 Ma) phase of magmatism in the Central Pyrenees, previously considered to be Cretaceous, that widens temporally and geographically the extent of the rift-related alkaline magmatism in southwestern Europe at that time. Key Points New Ar/Ar data update the age of the Cretaceous magmatism in NE Iberia Magmatism in the Pyrenees postdates the rotation of Iberia Magmatism in the Catalonian Coastal Ranges could mark the onset of Alpine shortenin

Tetraspanin 6: A novel regulator of hippocampal synaptic transmission and long term plasticity

Tetraspanins (Tspan) are transmembrane proteins with important scaffold and signalling functions. Deletions of Tetraspanin 6 (Tspan6) gene, a member of the tetraspanin family, have been reported in patients with Epilepsy Female-restricted with Mental Retardation (EFMR). Interestingly, mutations in Tspan7, highly homologous to Tspan6, are associated with X-linked intellectual disability, suggesting that these two proteins are important for cognition. Considering recent evidences showing that Tspan7 plays a key role in synapse development and AMPAR trafficking, we initiated the study of Tspan6 in synaptic function using a Tspan6 knock out mouse model. Here we report that hippocampal field recordings from Tspan6 knock out mice show an enhanced basal synaptic transmission and impaired long term potentiation (LTP). A normal paired-pulse facilitation response suggests that Tspan6 affects the properties of the postsynaptic rather than the presynaptic terminal. However, no changes in spine morphology or postsynaptic markers could be detected in Tspan6 KO mice compared with wild types. In addition, Tspan6 KO mice show normal locomotor behaviour and no defects in hippocampus-dependent memory tests