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Significant grain refinement has been achieved in a cast Mg-based AZ91 alloy via large strain hot rolling. This is a simple processing method consisting of one rolling pass at intermediate temperatures with a large thickness reduction. The as-cast material was first homogeneized in order to obtain a homogeneous and equiaxed grain structure with a random texture. During processing, a double-peak basal texture develops, typical of rolled Mg alloys, that results from the operation of basal, prismatic and pyramidal 〈c+a〉 slip. The stabilization of this deformation texture during rolling suggests that the mechanism for grain refinement is continuous dynamic recrystallization

We measured the electrical resistivity of RMn122xFex (R5Y, Er! polycrystalline systems with 0, This work was partially supported by Grant No. MAT 02/166 of Ministerio de Ciencia y Tecnologia of Spain and by LEA MANES, a Spanish-French collaboration program.

Nd2Fe14-xSixB (x = 0.25, 0.5, 0.75, 1.0, 1.5, 2.0) intermetallic compounds were investigated by magnetometry, 57Fe Mössbauer effect, electric resistivity, and differential scanning calorimetry mainly in the vicinity of the spin reorientation temperature, TSR. The Curie temperature, TC, and TSR were determined for different compositions and the spin phase diagram was constructed. 57Fe Mössbauer spectra showed noticeable changes in the reorientation region. For temperatures above the transition, the spectra were analysed using 6 Zeeman patterns associated with 6 inequivalent crystal sites in Nd2Fe14B according to site occupations (16k1:16k2:8j1:8j2:4c:4e). In the transition region, 12 subspectra had to be incorporated in the analysis. Electric resistivity measurements showed a typical metallic behaviour with no anomalies in the magnetic transition region. Differential scanning calorimetry measurements revealed broad endothermic two stage peaks around TSR.

Numerosos estudios revelan un considerable descenso del interés y de la participación en actividades físicas y deportivas en la población joven, fundamentalmente en el periodo de la adolescencia. El entrenamiento y la competición pueden ser contextos ideales para fomentar el compromiso deportivo del adolescente, siempre y cuando el joven deportista alcance una adecuada motivación, ya que esta es clave para lograr la adherencia a la práctica fisicodeportiva. Así, basándonos en la teoría de la autodeterminación y la teoría de metas de logro, el objetivo principal de la tesis fue analizar los factores motivacionales que influyen de manera positiva en el compromiso deportivo de los adolescentes. Para ello, se estudiaron los climas motivacionales, el apoyo a la autonomía por parte del entrenador, las metas de logro, las metas sociales, la satisfacción de las necesidades psicológicas básicas, la motivación autodeterminada, y la intención de seguir siendo físicamente activo. La presente tesis está compuesta por seis publicaciones, donde, en primer lugar, se analizaron las relaciones entre dichas variables de forma correlacional, y en segundo lugar, se profundizó en su estudio utilizando una metodología cualitativa. Se administró un cuestionario a una muestra total de 608 deportistas de diferentes modalidades (de edades comprendidas entre los 12 y los 17 años). Además, 15 de estos deportistas fueron entrevistados.

The electrical resistivity and Hall effect of a single crystal of Nd2Fe14B have been measured over the temperature range of 10 to 300 K in magnetic fields of up to 12 T. At low temperature, a positive ~both transverse and longitudinal! magnetoresistance is observed. It can be attributed to scattering of carriers by magnetization-dependent mechanisms. The magnetoresistance decreases strongly with increasing temperature as the suppression of spin fluctuations by an external field becomes more important. Hall resistivity data are holelike and follow the magnetization of the material. The low-field Hall resistivity peaks at about 130 K, in the vicinity of the spin-reorientation temperature in Nd2Fe14B. Away from the peak, the Hall resistivity is proportional to the square of the total resistivity. We find that both skew scattering and side-jump scattering contribute to the Hall effect. However, spin fluctuations are important only in a small region close to the spin-reorientation temperature whereas side-jump scattering governs the Hall effect in the whole temperature range studied., This work was supported by Project MAT 96-448 of Comision Interministerial de Ciencia y Tecnologia (CICYT).

Se reflexiona sobre el concepto salud, entendido como valor, y se proponen un conjunto de ejercicios prácticos para que los maestros hallen sugerencias de cómo introducir el concepto seguridad y salud en el trabajo en el marco escolar. Tanto en los contenidos como en el método, es una propuesta a modo de enseñanza transversal. El colectivo de los maestros son los profesionales que, conjuntamente con el resto de estamentos que conforman la sociedad, tienen como labor la enseñanza de comportamientos seguros, tanto en la lógica interpretación de su material de trabajo como seres humanos, como en la necesaria incorporación de sus alumnos al mundo laboral. Los tres grandes campos de acción son la seguridad, la higiene y la ergonomía, cada uno, se materializa en la escuela aportando datos que sugieran posibles actuaciones docentes. Se citan además, las posibilidades de control y eliminación de los factores que provocan los accidentes, las enfermedades profesionales y las alteraciones de la salud por motivos ergonómicos. Madrid Biblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5; 28014 Madrid; Tel. +34917748000; biblioteca@mecd.es ESP

The magnetic ac susceptibility x of oriented Mn12Ac crystallites has been measured as a function of temperature, field, and frequency. The field has been applied at different values of the angle u with respect to the sample easy axis. For T55 K, the isothermal and adiabatic x limits have been determined as a function of field. For u50° and intermediate frequencies, Lorentzian-shaped peaks have been observed at magnetic field values Hn5nH1 with n50, 1, and 2 where H154.1 kOe. As u increases these maxima shift to higher fields, that satisfy Hncosu5const, and decrease in amplitude. The relaxation time t 1 follows Arrhenius’ law with respect to temperature and decreases sharply at H5Hn . The observed phenomenology unambiguously proves the existence of field-tuned tunneling between excited magnetic states which are thermally populated. At 5 K, the effective activation energy and the spin states involved in the tunneling process have been obtained.

The electrical resistivity of R2Fe14B (R=lanthanide series) polycrystalline samples was measured over the temperature range of 4–700 K. Even though the overall behavior of the resistivity in R2Fe14B is determined mainly by Fe atoms, interesting features follow from the presence of rare-earth atoms. At low temperatures, the resistivity ρ increases with temperature as T2. We find that scattering of electrons by modes involving all spins, with a dispersion given by the R-Fe exchange interaction, contributes to this behavior. On the other hand, the high-temperature anomaly in ρ observed just below the Curie temperature is quite likely produced by electron-phonon scattering arising from a pronounced lattice softening in this temperature region. Saturation values of the high-temperature magnetic resistivity are in agreement with de Gennes and Friedel's prediction for spin-disorder scattering., This work was supported by Project Nos. MAT 93-0240-C04-04 and MAT 94-0043 of Comision Interministerial de Ciencia y Tecnologia (CICYT).

El objetivo fue estudiar la satisfacción del alumnado con los boletines editados, y además, conocer los aspectos concretos en los que había que mejorar. Se utilizó una muestra estudiantes de segundo de Maestro de Educación Física. Se emplearon dos instrumentos: un cuestionario diseñado para el estudio y un grupo nominal. Los datos resultados muestran que puede ser una herramienta útil para el desarrollo de diferentes competencias.