Room-temperature single phase multiferroic magnetoelectrics: Pb(Fe,M)x(Zr,Ti)(1−x)O3 [M=Ta, Nb]

We describe extensive studies on a family of perovskite oxides that are ferroelectric and ferromagnetic at ambient temperatures. The data include x-ray diffraction, Raman spectroscopy, measurements of ferroelectric and magnetic hysteresis, dielectric constants, Curie temperatures, electron microscopy
(both scanning electron microscope and transmission electron microscopy (TEM)) studies, and both longitudinal and transverse magnetoelectric constants a33 and a31. The study extends earlier work to lower Fe, Ta, and Nb concentrations at the B-site (from 15%–20% down to 5%). The magnetoelectric
constants increase supralinearly with Fe concentrations, supporting the earlier conclusions of a key role for Fe spin clustering. The room-temperature orthorhombic C2v point group symmetry inferred from earlier x-ray diffraction studies is confirmed via TEM, and the primitive unit cell size is found to be the basic perovskite Z¼1 structure of BaTiO3, also the sequence of phase transitions with increasing temperature from rhombohedral to orthorhombic to tetragonal to cubic mimics barium titanate.

Switching ferroelectric domain configurations using both electric and magnetic fields in Pb(Zr,Ti)O3–Pb(Fe,Ta)O3 single-crystal lamellae

Thin single-crystal lamellae cut from Pb(Zr,Ti)O3–Pb(Fe,Ta)O3 ceramic samples have been integrated into simple coplanar capacitor devices. The influence of applied electric and magnetic fields on ferroelectric domain configurations has been mapped, using piezoresponse force microscopy. The extent to which magnetic fields alter the ferroelectric domains was found to be strongly history dependent: after switching had been induced by applying electric fields, the susceptibility of the domains to change under a magnetic field (the effective magnetoelectric coupling parameter) was large. Such large, magnetic field-induced changes resulted in a remanent domain state very similar to the remanent state induced by an electric field. Subsequent magnetic field reversal induced more modest ferroelectric switching.

Studies of the Room-Temperature Multiferroic Pb(Fe0.5Ta0.5)0.4(Zr0.53Ti0.47)0.6O3: Resonant Ultrasound Spectroscopy, Dielectric, and Magnetic Phenomena

Recently, lead iron tantalate/lead zirconium titanate (PZTFT) was demonstrated to possess large, but unreliable, magnetoelectric coupling at room temperature. Such large coupling would be desirable for device applications but reproducibility would also be critical. To better understand the coupling, the properties of all 3 ferroic order parameters, elastic, electric, and magnetic, believed to be present in the material across a range of temperatures, are investigated. In high temperature elastic data, an anomaly is observed at the orthorhombic mm2 to tetragonal 4mm transition, Tot = 475 K, and a softening trend is observed as the temperature is increased toward 1300 K, where the material is known to become cubic. Thermal degradation makes it impos- sible to measure elastic behavior up to this temperature, however. In the low temperature region, there are elastic anomalies near ≈40 K and in the range 160–245 K. The former is interpreted as being due to a magnetic ordering transition and the latter is interpreted as a hysteretic regime of mixed rhom- bohedral and orthorhombic structures. Electrical and magnetic data collected below room temperature show anomalies at remarkably similar temperature ranges to the elastic data. These observations are used to suggest that the three order parameters in PZTFT are strongly coupled.

The Nature of Magnetoelectric Coupling in Pb(Zr,Ti)O3-Pb(Fe,Ta)O3

The coupling between magnetization and polarization in a room temperature multiferroic (Pb(Zr,Ti)O3–Pb(Fe,Ta)O3) is explored by monitoring changes in capacitance that occur when a magnetic field is applied in each of three orthogonal directions. Magnetocapacitance effects, consistent with P2M2 coupling, are strongest when fields are applied in the plane of the single crystal sheet investigated.

Reliability and factorial validity of Adolescent Time Inventory-Time Attitude (ATI-TA) Scores in Scottish and Northern Irish adolescents

The contemporary literature investigating the construct broadly known as time perspective is replete with methodological and conceptual concerns. These concerns focus on the reliability and factorial validity of measurement tools, and the sample-specific modification of scales. These issues continue to hamper the development of this potentially useful psychological construct. An emerging body of evidence has supported the six-factor structure of scores on the Adolescent Time Inventory-Time Attitudes Scale, as well as their reliability. The present study utilized data from the first wave of a longitudinal study in the United Kingdom to examine the reliability, validity, and cross-cultural invariance of the scale. Results showed that the hypothesized six-factor model provided the best fit for the data; all alpha and omega estimates were >. .70; scores on ATI-TA factors related meaningfully to self-efficacy scores; and the factor structure was invariant across both research sites. Results are discussed in the context of the extant temporal literature.

Lo que cuento no es mi cuento: Cultura andina y tradición oral

Alfredo Mires asumió en 1982 la conducción de la Red de Bibliotecas Rurales de Cajamarca. Apuntaló desde entonces la organícidad y principios que ahora caracterizan este movimiento. Desde antes ya habia acompañado procesos de rescate cultural y sustentó el inicio de esta tarea al interior de la Red. En 1986, via asambleas y reuniones con campesinos y en las propias comunidades, fundó el Proyecto Enciclopedia Campesina. Fruto de esos andares es este trabajo, reflexión de la experiencia que afirma la convicción de mirar hacia las raices para seguir creciendo. Aquí se suman muchas lunas y soles, armadas con Ia hoja sagrada y caminatas interminables acompañando este proceso éducativo-cultural desde y con las propias comunidades campesinas. Lo que cuento no es mi cuento fue concebido inicialmente como una tesis, pero revisado y ampliado, precisa la concepción y la experiencia sostenida. Porque hablar del saber andino y de las experiencias mencionadas, es habitual de una población que vive, recrea, fortalece y recupera de manera permanente y desde siempre el equilibrio sagrado entre sociedad y naturaleza.

¿Qué hacer si a mi hijo le derivan a Educación Especial?

Durante el proceso de escolarización de su hijo con síndrome de Down, la mayoría de las familias escucha que “tiene necesidades educativas especiales”. Son muchas las dudas que asaltan a los padres con relación a este término: ¿A qué se refiere exactamente? ¿Cuándo se puede decir que un alumno tiene necesidades educativas especiales? ¿Qué debemos hacer y cómo actuar si le derivan a un Centro de Educación Especial? La asesora en educación de Down España, Ana Belén Rodríguez Plaza, ofrece en este texto las claves y la orientación para que los padres sepan qué deben hacer frente a esta situación.

Mi-Carême 1920, char de l'Alimentation [passant sur le pont de la Concorde] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58407

Mi-Carême 1920, char de la Reine des reines [passant sur le pont de la Concorde] : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58408

Mi-Carême 1920, [char de la] reine de Metz : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58413

Mi-Carême 1920, étudiants : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58418

Mi-Carême 1920, char des étudiants : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58421