Control de agarre y posicionamiento en una plataforma robot con sensores táctiles

En este artículo se presenta una plataforma formada por un brazo robot de 5 grados de libertad y una pinza robot de 1 sólo grado de libertad, con superficies táctiles. Este sistema obtiene, en tiempo real, las distribuciones de presión cuando un objeto ha sido agarrado, produciendo una realimentación del control de la posición y fuerza

Collective ionic dynamics in the liquid Na-Cs alloy: An ab initio molecular dynamics study

Producción CientíficaWe present results for several structural and dynamical properties of the liquid Na-Cs alloy. The study has been carried out by means of the orbital-free ab initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. The results show good agreement with the available experimental data, reproducing the homocoordinating tendency exhibited by this alloy

Microscopic dynamics in the liquid Li-Na alloy: An ab initio molecular dynamics study

Producción CientíficaWe present results for several structural and dynamical properties of the liquid Li1-xNax alloy. The study has been carried out by means of the orbital-free ab initio molecular dynamics method, combined with local ionic pseudopotentials constructed within the same framework. We obtain good agreement with the available experimental data, reproducing accurately, the strong homocoordinating tendencies exhibited by this alloy. The calculated partial dynamic structure factors exhibit clear side peaks whose frequencies, for q<~0.25Å-1, correspond to the hydrodynamic sound dispersion of the binary alloy, whereas for larger q values fast and slow sound modes are identified. The mass ratio in this system, mNa/mLi≈3, is the smallest one so far for which the fast mode is observed

Testing for alpha-1 antitrypsin in COPD in outpatient respiratory clinics in Spain: A multilevel, cross-sectional analysis of the EPOCONSUL study

Background Alpha-1 antitrypsin deficiency (AATD) is the most common hereditary disorder in adults, but is under-recognized. In Spain, the number of patients diagnosed with AATD is much lower than expected according to epidemiologic studies. The objectives of this study were to assess the frequency and determinants of testing serum α1-antitrypsin (AAT) levels in COPD patients, and to describe factors associated with testing. Methods EPOCONSUL is a cross-sectional clinical audit, recruiting consecutive COPD cases over one year. The study evaluated serum AAT level determination in COPD patients and associations between individual, disease-related, and hospital characteristics. Results A total of 4,405 clinical records for COPD patients from 57 Spanish hospitals were evaluated. Only 995 (22.5%) patients had serum AAT tested on some occasion. A number of patient characteristics (being male [OR 0.5, p < 0.001], ≤55 years old [OR 2.38, p<0.001], BMI≤21 kg/m2 [OR 1.71, p<0.001], FEV1(%)<50% [OR 1.35, p<0.001], chronic bronchitis [OR 0.79, p < 0.001], Charlson index ≥ 3 [OR 0.66, p < 0.001], or history or symptoms of asthma [OR 1.32, p<0.001]), and management at a specialized COPD outpatient clinic [OR 2.73,p<0.001] were identified as factors independently associated with ever testing COPD patients for AATD. Overall, 114 COPD patients (11.5% of those tested) had AATD. Of them, 26 (22.8%) patients had severe deficiency. Patients with AATD were younger, with a low pack-year index, and were more likely to have emphysema (p<0.05). Conclusion Testing of AAT blood levels in COPD patients treated at outpatient respiratory clinics in Spain is infrequent. However, when tested, AATD (based on the serum AAT levels ≤100 mg/dL) is detected in one in five COPD patients. Efforts to optimize AATD case detection in COPD are needed.SEPA

Vortex motion channeling effects in Nb with mesoscopic arrays of Ni lines

Ordered arrays of submicrometric Ni lines have been fabricated in sputtered Nb films. Magnetotransport R(H) and (I, V) curves were measured close to the critical temperature using a cross-shape bridge that allows us to apply current in two directions: parallel or perpendicular to the lines. The experimental results show anisotropic vortex motion with clear channeling effects. In R(H) data, magnetic features appear but they are absent in the (I, V) curves

Angular dependence of the artificially induced anistropy in α-axis-oriented EuBa_2Cu_3O_7/PrBa_2Cu_3O_7 superconducting superlattices

α-axis-oriented EuBa_2Cu_3O_7/PrBa_2Cu_3O_7 (EBCO/PBCO) superlattices allow us to separate contributions to the anisotropy coming from the natural layered structure of EBCO from that introduced by the artificial layering with PBCO. The angular dependence of the critical current and resistivity in a magnetic field has been studied with different superlattice modulation lengths (strong coupling regime). The increase in the insulating PBCO layer thickness produces a crossover from an a-axis-oriented three-dimensional (3D) superconductor with a distribution of planar pinning centers to a 3D superconductor with an angular anisotropy behavior similar to single-phase c-axis-oriented films

A methodology for the classification of gravel beaches

Beaches are highly flexible structures that can be deformed by several reasons, some natural as wind and swell and others not, as human actions. Gravel, considered as a component of the beach is not always separated from the rest of the materials. It is a part of the coastline sedimentary balance, usually with time and spatial scales much greater than those corresponding to the stretch of the coast under study. The conceptual and experimental difficulties of studying this kind of beach have meant that nowadays they are really unknown. In this paper, methodologies to classify and determinate the most important characteristics in gravel beaches are presented. The authors have studied 34 shingle beaches in the region of Alicante (Spain) from a database with their characteristics. Obtained data corresponds to the morphology of the beach, the materials that take part in its composition and the wave energy, considering its incidence, the wave height, the local period and its influence on the coastline. At the beginning, mathematical models are generated, allowing the expression of the relationships between the slope of berm and the rest of variables. To classify the beaches, a factor analysis has been used on the experimental data matrix, considering all the variables as predictive, obtaining in this way an index for beach classification with similar characteristics. Furthermore, to determine the predictive variables that allow characterizing the 34 beaches, a discriminant analysis has been applied over several sets of variables. In each case, a predictive model of cluster belonging is created, considering a discriminant function, and with the clustering function formed by different clusters. The methodologies developed in this paper will be applied later to other beaches as classification and variable selection methods

Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical

We present an experimental study of the {\em nonlinear} susceptibility of Mn$_{12}$ single-molecule magnets. We investigate both their thermal-equilibrium and dynamical nonlinear responses. The equilibrium results show the sensitivity of the nonlinear susceptibility to the magnetic anisotropy, which is nearly absent in the linear response for axes distributed at random. The nonlinear dynamic response of Mn$_{12}$ was recently found to be very large and displaying peaks reversed with respect to classical superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201 (2004)]. Here we corroborate the proposed explanation -- strong field dependence of the relaxation rate due to the detuning of tunnel energy levels. This is done by studying the orientational dependence of the nonlinear susceptibility, which permits to isolate the quantum detuning contribution. Besides, from the analysis of the longitudinal and transverse contributions we estimate a bound for the decoherence time due to the coupling to the phonon bath.Comment: 13 pages, 8 figures, resubmitted to Phys. Rev. B with minor change

Experimental vortex ratchet effect in nanostructured superconductors

Superconducting Nb thin films were grown on different arrays of triangle-shape metallic islands. The vortex lattice dynamics could be strongly modified by these asymmetric vortex traps. These asymmetric pinning potentials lead to a rectification effect on the vortex motion: Injecting an ac supercurrent on the sample yields a net dc vortex flow. This vortex ratchet ffect is adiabatic and reversible: The effect is frequency independent and the polarity of the dc voltage output could be tuned by the applied magnetic fields and the input ac currents

Experimental adiabatic vortex ratchet effect in Nb films with asymmetric pinning trap

Nb films grown on top of an array of asymmetric pinning centers show a vortex ratchet effect. A net flow of vortices is induced when the vortex lattice is driven by fluctuating forces on an array of pinning centers without reflection symmetry. This effect occurs in the adiabatic regime and it could be mimiced only by reversible DC driven forces