Meissner effect and critical fields in an inhomogeneous Ba2HoCu3O7-x high-Tc superconductor

The Meissner and diamagnetic shielding effects and the upper, lower, and thermodynamical critical fields have been studied in a Ba2HoCu3O7-x sample using magnetization measurements in fields up to 55 kOe. The diamagnetic shielding curve shows the existence of a transition at Tc=91.5 K followed by a broad transition extending from 85 to 25 K which may be related to inhomogeneities in the oxygen content of the sample. A rather low flux expulsion (13.5%) is observed which we attribute to flux pinning or trapping. We show that the coexistence of superconducting and nonsuperconducting regions within the sample at temperatures just below Tc leads to strong reductions in the critical magnetic fields.

Particle orientation distribution in Y-Fe2O3magnetic tapes by Mössbauer and hysteresis loop measurements

The particle orientation in several Y-Fe2O3magnetic tapes has been quantitatively evaluated by using the data of both Mössbauer and hysteresis loop measurements performed in the three orthogonal directions. A texture function has been obtained as a development of real harmonics. The profile of the texture function gives the quality of the different magnetic tapes. A different degree of particle orientation at the surface of the tape is evidenced by means of conversion electron Mössbauer spectra.

Mossbauer and magnetization studies of amorphous NdFeB compositionally modulated thin films

Several NdFeB compositionally modulated thin films are studied by using both conversion electron Mossbauer spectra and SQUID (superconducting quantum-interference-device) magnetometry. Both the hyperfine fields and the easy magnetization magnitude are not correlated with the modulation characteristic length (lambda) while the magnetization perpendicular to the thin-film plane decreases as lambda increases. The spectra were recorded at room temperature being the gamma rays perpendicular to the substrate plane. The magnetization measurements were recorded by using a SHE SQUID magnetometer in applied magnetic fields up to 5.5 T and in the temperature range between 1.8 and 30 K.

Effective t-J model Hamiltonian parameters of monolayered cuprate superconductors from ab initio electronic structure calculations

The magnetic coupling constant of selected cuprate superconductor parent compounds has been determined by means of embedded cluster model and periodic calculations carried out at the same level of theory. The agreement between both approaches validates the cluster model. This model is subsequently employed in state-of-the-art configuration interaction calculations aimed to obtain accurate values of the magnetic coupling constant and hopping integral for a series of superconducting cuprates. Likewise, a systematic study of the performance of different ab initio explicitly correlated wave function methods and of several density functional approaches is presented. The accurate determination of the parameters of the t-J Hamiltonian has several consequences. First, it suggests that the appearance of high-Tc superconductivity in existing monolayered cuprates occurs with J/t in the 0.20¿0.35 regime. Second, J/t=0.20 is predicted to be the threshold for the existence of superconductivity and, third, a simple and accurate relationship between the critical temperatures at optimum doping and these parameters is found. However, this quantitative electronic structure versus Tc relationship is only found when both J and t are obtained at the most accurate level of theory.

Qualitat i consum ceràmic de la sigillata augustal. Noves vies d'estudi i interpretació a partir de l'Arqueometria

[spa] En este estudio se presentan los resultados del trabajo realizado sobre la calidad de las diferentes producciones de terra sigillata comercializadas en época de Augusto, como paso previo al estudio del consumo. A partir de la apiicación de técnicas arqueométricas, se han establecido criterios objetivos en algunos casos, cuantitativos como son la resistencia a la ruptura de las diferentes vajillas analizadas y la adherencia y el estado de sinterización de su barniz. De este modo, ha sido posible determinar la existencia de las diversas calidades, que deben influenciar el consumo cerámico.

Magnetism of isolated Mn12 single-molecule magnets detected by magnetic circular dichroism: Observation of spin tunneling with a magneto-optical technique

We report magnetic and magneto-optical measurements of two Mn12 single-molecule magnet derivatives isolated in organic glasses. Field-dependent magnetic circular dichroism (MCD) intensity curves (hysteresis cycles) are found to be essentially identical to superconducting quantum interference device magnetization results and provide experimental evidence for the potential of the optical technique for magnetic characterization. Optical observation of magnetic tunneling has been achieved by studying the decay of the MCD signal at weak applied magnetic field

Morphological and Magnetic Properties of Superparamagnetic Carbon-Coated Fe Nanoparticles Produced by Arc Discharge.

Spherical carbon coated iron particles of nanometric diameter in the 510 nm range have been produced by arc discharge at near-atmospheric pressure conditions (using 58·10 4 Pa of He). The particles exhibit a crystalline dense iron core with an average diameter 7.4 ± 2.0 nm surrounded by a sealed carbon shell, shown by transmission electron microscopy (TEM), selected-area diffrac- tion (SAED), energy-dispersive X-ray analysis (STEM-EDX) and electron energy loss spectroscopy (EELS). The SAED, EDX and EELS results indicate a lack of traces of core oxidized phases showing an efficient protection role of the carbon shell. The magnetic properties of the nanoparticles have been investigated in the 5300 K temperature range using a superconducting quantum interference device (SQUID). The results reveal a superparamagnetic behaviour with an average monodomain diameter of 7.6 nm of the nanoparticles. The zero field cooled and field cooled (ZFC-FC)magnetization curves show a blocking temperature (TB)at room temperature very suitable for biomedical applications (drug delivery, magnetic resonance imaging MRI, hyperthermia).

Magnetism of isolated Mn12 single-molecule magnets detected by magnetic circular dichroism: Observation of spin tunneling with a magneto-optical technique

We report magnetic and magneto-optical measurements of two Mn12 single-molecule magnet derivatives isolated in organic glasses. Field-dependent magnetic circular dichroism (MCD) intensity curves (hysteresis cycles) are found to be essentially identical to superconducting quantum interference device magnetization results and provide experimental evidence for the potential of the optical technique for magnetic characterization. Optical observation of magnetic tunneling has been achieved by studying the decay of the MCD signal at weak applied magnetic field

Reduced microwave losses of YBa2Cu3O7_thin films on electro-optic LiNbO3 crystals

We report on the growth of epitaxial YBa2Cu3O7 thin films on X-cut LiNbO3 single crystals. The use of double CeO2/YSZ buffer layers allows a single in-plane orientation of YBa2Cu3O7, and results in superior superconducting properties. In particular, surface resistance Rs values of 1.4 m¿ have been measured at 8 GHz and 65 K. The attainment of such low values of Rs constitutes a key step toward the incorporation of high Tc materials as electrodes in photonic and acoustic devices.

Systematic study of the temperature dependence of the saturation magnetization in Fe, Fe-Ni and Co-based amorphous alloys

Magnetization versus temperature in the temperature interval 2-200 K was measured for amorphous alloys of three different compositions: Fe 81.5B14.5Si4, Fe40Ni38 Mo4B18, and Co70Fe5Ni 2Mo3B5Si15. The measurements were performed by means of a SQUID (superconducting quantum interference device) magnetometer. The aim was to extract information about the different mechanisms contributing to thermal demagnetization. A powerful data analysis technique based on successive minimization procedures has demonstrated that Stoner excitations of the strong ferromagnetic type play a significant role in the Fe-Ni alloy studied. The Fe-rich and Co-rich alloys do not show a measurable contribution from single-particle excitations.

General electromagnetic simulation tool to predict the microwave nonlinear response of planar, arbitrarily-shaped HTS structures

This work describes a simulation tool being developed at UPC to predict the microwave nonlinear behavior of planar superconducting structures with very few restrictions on the geometry of the planar layout. The software is intended to be applicable to most structures used in planar HTS circuits, including line, patch, and quasi-lumped microstrip resonators. The tool combines Method of Moments (MoM) algorithms for general electromagnetic simulation with Harmonic Balance algorithms to take into account the nonlinearities in the HTS material. The Method of Moments code is based on discretization of the Electric Field Integral Equation in Rao, Wilton and Glisson Basis Functions. The multilayer dyadic Green's function is used with Sommerfeld integral formulation. The Harmonic Balance algorithm has been adapted to this application where the nonlinearity is distributed and where compatibility with the MoM algorithm is required. Tests of the algorithm in TM010 disk resonators agree with closed-form equations for both the fundamental and third-order intermodulation currents. Simulations of hairpin resonators show good qualitative agreement with previously published results, but it is found that a finer meshing would be necessary to get correct quantitative results. Possible improvements are suggested.

Growth and magnetic characterization of Co nanoparticles obtained by femtosecond pulsed laser deposition.

We present a detailed study on the morphology and magnetic properties of Co nanostructures deposited onto oxidized Si substrates by femtosecond pulsed laser deposition. Generally, Co disks of nanometric dimensions are obtained just above the ablation threshold, with a size distribution characterized by an increasingly larger number of disks as their size diminishes, and with a maximum disk size that depends on the laser power density. In Au/Co/Au structures, in-plane magnetic anisotropy is observed in all cases, with no indication of superparamagnetism regardless of the amount of material or the laser power density. Magnetic force microscopy observations show coexistence of single-domain and vortex states for the magnetic domain structure of the disks. Superconducting quantum interference device magnetometry and x-ray magnetic circular dichroism measurements point to saturation magnetization values lower than the bulk, probably due to partial oxidation of the Co resulting from incomplete coverage by the Au capping layer.

Modelo de indicadores para evaluar los formatos digitales para la preservación de video

La preservación de los fondos audiovisuales en soporte analógico está amenazada por la degradación de las cintas magnéticas. La revisión de la literatura científica indica que este proceso de degradación no se puede evitar y que su solución pasa por la migración de los contenidos audiovisuales a soportes digitales. La complejidad técnica de los formatos de vídeo digital y la no existencia de formatos claros con finalidades de preservación hacen que sea difícil la elección del formato al cual migrar. Ante este panorama se propone la utilización de un modelo de indicadores que sirva para valorar las características de los formatos de vídeo digital de cara a su uso en la preservación de los fondos audiovisuales Abstract: The preservation of audiovisual content recorded on analogical media is threatened by the physical degradation of magnetic tape over time. A review of the literature shows that this degradation cannot be avoided and that the only solution consists of migrating audiovisual content to digital media. Choosing a digital format for this migration is difficult due to the technical complexity of video formats and to the lack of a specific format aimed at preservation. In this context, the article suggests the use of a model of indicators to evaluate the features of existing digital video formats for their potential use in audiovisual content preservation

Posibles beneficios fisiológicos y psicológicos del método madre canguro (MMC) en bebés prematuros y sus madres

Objetivos: La preocupación por la crisis económica que azota España y por lo tanto, a la comunidad autónoma de Navarra, sumado a la evidencia científica de las consecuencias que sufre el bebé al ser separado de su madre tras el nacimiento, siendo más notable por debajo de las 37 semanas de gestación, y al elevado estrés y sufrimiento de los padres cuando su hijo está encerrado en una incubadora, llevó al planteamiento de querer demostrar los posibles beneficios fisiológicos y psicológicos del método madre canguro (MMC) en bebés prematuros y sus madres. Metodología: Será un estudio experimental, longitudinal y prospectivo dirigido a 40 mujeres y a sus bebés prematuros, que den a luz en el hospital Virgen del Camino. El grado de satisfacción se determinará con preguntas extraídas de la escala validada Caring Assement Instrument (CARE- Q) y con otro cuestionario no validado. Los parámetros fisiológicos se medirán con un termómetro de mercurio y una cinta métrica. El programa informático SPSS® vs 21.0. será el elegido para el análisis estadístico. Limitaciones del estudio: La larga duración de la participación de la unidad madre-hijo, la tercera etapa domiciliaria del MMC, las restricciones de la UCIN del hospital Virgen del Camino junto al uso de una escala no validada, podría conllevar a la aparición de obstáculos a la hora, tanto de poder llevar a cabo el proyecto, como de la obtención de sus resultados.

Morphological and Magnetic Properties of Superparamagnetic Carbon-Coated Fe Nanoparticles Produced by Arc Discharge.

Spherical carbon coated iron particles of nanometric diameter in the 5-10 nm range have been produced by arc discharge at near-atmospheric pressure conditions (using 5-8·10 4 Pa of He). The particles exhibit a crystalline dense iron core with an average diameter 7.4 ± 2.0 nm surrounded by a sealed carbon shell, shown by transmission electron microscopy (TEM), selected-area diffrac- tion (SAED), energy-dispersive X-ray analysis (STEM-EDX) and electron energy loss spectroscopy (EELS). The SAED, EDX and EELS results indicate a lack of traces of core oxidized phases showing an efficient protection role of the carbon shell. The magnetic properties of the nanoparticles have been investigated in the 5-300 K temperature range using a superconducting quantum interference device (SQUID). The results reveal a superparamagnetic behaviour with an average monodomain diameter of 7.6 nm of the nanoparticles. The zero field cooled and field cooled (ZFC-FC)magnetization curves show a blocking temperature (TB)at room temperature very suitable for biomedical applications (drug delivery, magnetic resonance imaging-MRI-, hyperthermia).