Avance de los resultados obtenidos mediante datación isotópica de algunos espeleotemas subacuáticos mallorquines

[eng] Speleothems from two coastal caves in Mallorca (Spain) have been dated by means of the 230Th / 234 U method. The results obtained confirm a speleomorphological interpretation previously established by some of the authors. Two of the samples are very close to the limits of these dating techniques (more than 300 Ka) and at the same time the position of both speleothems (at an elevation of aproximately 30 metres above sea level) correlates well with a Paleotirrenian age, according to the speleomorphological interpretation.[cat] Alguns espeleotemes procedents de dues coves costeres de Mallorca han estat datats mitjançant el mètode Th 230 /U 234. Els resultats obtenguts tenden a confirmar el model espeleomorfològic establert prèviament per alguns dels autors. Dues de les mostres es troben molt a prop dels límits de resolució vàlids per aquesta tècnica de datació (més de 300.000 anys), al temps que la posició de ambdos espeleotemes (a més de 30 metres d'altura per damunt el nivell de la mar) se correlaciona bé amb una edat paleotirreniana, coincidint així amb el model espeleomorfològic

Effective nonlinear Ehrenfest hybrid quantum-classical dynamics

The definition of a consistent evolution equation for statistical hybrid quantum-classical systems is still an open problem. In this paper we analyze the case of Ehrenfest dynamics on systems defined by a probability density and identify the relations of the non-linearity of the dynamics with the obstructions to define a consistent dynamics for the first quantum moment of the distribution. This first quantum moment represents the physical states as a family of classically-parametrized density matrices $\hat \rho(\xi)$, for $\xi$ a classical point; and it is the most common representation of hybrid systems in the literature. Due to this obstruction, we consider higher order quantum moments, and argue that only a finite number of them are physically measurable. Because of this, we propose an effective solution for the hybrid dynamics problem based on approximating the distribution by those moments and representing the states by them.Comment: 21 pages. Minor correction in the list of affiliation

Engineering the microstructure and magnetism of La2_2CoMnO6_6 thin films by tailoring oxygen stoichiometry

We report on the magnetic and structural properties of ferromagnetic-insulating La$_2$CoMnO$_6$ thin films grown on top of (001) STO substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen stoichiometry and to the features (coercive fields and remanence) of the hysteresis loops. Both Curie temperature and magnetic hysteresis turn out to be dependent on the oxygen stoichiometry. In situ annealing conditions allow tailoring the oxygen content of the films, therefore controlling their microstructure and magnetic properties

Critical Dynamics of a Vortex Loop Model for the Superconducting Transition

We calculate analytically the dynamic critical exponent $z_{MC}$ measured in Monte Carlo simulations for a vortex loop model of the superconducting transition, and account for the simulation results. In the weak screening limit, where magnetic fluctuations are neglected, the dynamic exponent is found to be $z_{MC} = 3/2$. In the perfect screening limit, $z_{MC} = 5/2$. We relate $z_{MC}$ to the actual value of $z$ observable in experiments and find that $z \sim 2$, consistent with some experimental results

La fusión glaciar en el Pirineo: condicionantes ambientales y primeros resultados bianuales en el glaciar de Infiernos (Pirineo aragonés)

Data are presented about the environmental characters of the Infiernos glacier and of the regression suffered in the last century, as well as the meltwater flow values corresponding to two daily cycle of the Infierno glacier. These values were measured at the end of the summer of 1998 and 1999. There is a close relationship between these data and both thermic rythms. This fact suggests that meltwater flow should become a useful additional parameter to explain the environmental control of the drainage systems derived from the glacier fusion, as well as the serious glacier regression happened in the last decades, indicative of balances between the accumulation nival and the ablation clearly negative. The data are accompanied of measures of regression glacier among the summers of 1998 and 1999.Se presentan datos acerca de las características ambientales del Glaciar del Infierno y de la regresión sufrida en el Último siglo, así como los valores de los caudales de fusión de dos ciclos diarios en este glaciar, medidos a finales de dos veranos consecutivos (años 1998 y 1999). La relación entre este dato y los ritmos térmicos es muy estrecha, lo cual permite disponer de un dato más, de gran importancia, para explicar el control ambiental en los sistemas de drenaje de la fusión glaciar, así como la acusada regresión glaciar de las últimas décadas, indicativa de balances entre la acumulación nival y la ablación claramente negativos. Los datos se acompañan de medidas de retroceso glaciar entre los veranos de 1998 y 1999

Temperature and magnetic-field dependence of the conductivity of YBaCuO films in the vicinity of superconducting transition: Effect of Tc-inhomogeneity

Temperature and magnetic field dependences of the conductivity of YBaCuO films in the transition region are analyzed taking into account spatial inhomogeneity in transition temperature, Tc. (i) An expression for the superconducting contribution to conductivity, \sigma_s(T,H,Tc), of a homogeneous superconductor for H<<Hc2(T=0) is obtained using the solution of the Ginzburg-Landau equation in form of perturbation expansions [S.Ullah, A.T.Dorsey, PRB 44, 262 (1991)]. (ii) The error in \sigma_s(T,H,Tc) occurring due to the presence of Tc-inhomogeneity is calculated and plotted on an H-T plane diagram. These calculations use an effective medium approximation and a Gaussian distribution of Tc. (iii) Measuring the temperature dependences of a voltage, induced by a focused electron beam, we determine spatial distributions of the critical temperature for YBaCuO microbridges with a 2 micron resolution. A typical Tc-distribution dispersion is found to be approximately 1K. For such dispersion, error in \sigma_s(T,H,Tc) due to Tc-inhomogeneity exceeds 30% for magnetic fields H < 1 T and temperatures |T-Tc| < 0.5 K. (iv) Experimental R(T,H) dependences of resistance are well described by a numerical solution of a set of Kirchoff equations for the resistor network based on the measured spatial distributions of Tc and the expression for \sigma_s(T,H,Tc).Comment: REVTeX, 12 pages including 7 figures, resubmitted to Phys. Rev.

Less invasive aortic valve surgery: rationale and technique

The unquestionable aims for a less invasive operations are less morbidity, less discomfort, and a reduced hospital stay through an operation which proves equally durable to the conventional approach. Such an operation must be carried out without further risk to the patient or increased difficulty for the surgeon. Whilst most definitions of less invasive coronary surgery include the phrase without cardiopulmonary bypass, this is clearly not yet possible in valve surgery. In valve surgery, the definition of less invasive relates only to the size of incision and rate of recovery. As a result of the discussions during the Heart Lab International Workshop on video-assisted heart surgery in Zurich, October 22-25, 1998, the following conclusions emerged. The partial upper sternotomy with J- or L- shaped extension to the right is the preferred approach for minimally invasive aortic valve surgery. Other methods which sacrify the internal thoracic arteries, open pleural cavities or predispose to long hernia are less satisfactory. A detailed description of the technique proposed is given and its indications and contraindications are discussed

Evolución reciente del glaciar del Infierno (Panticosa, Huesca)

Este artículo analiza la evolución del glaciar del pico Infierno desde un glaciar blanco hacia un glaciar cubierto y, tal vez, hacia un glaciar rocoso