4 research outputs found
Effect of pressure on the superconducting Tc of MgB2
Measurements of the superconducting transition temperature Tc have been
performed by the inductive method on MgB2 at pressures up to 28 GPa. Tc
decreases with applied pressure, exhibiting a cusp at about 9 GPa. We interpret
the appearance of this anomaly in the Tc(P) dependence as a result of the
pressure-induced electronic transition. Recent band-structure calculations for
MgB2 give some support for such an explanation.Comment: 11 pages, including 4 figure
Explorar e Investigar em Matemática: Uma Actividade Fundamental no Ensino e na Aprendizagem
Investigar, ensinar e aprender são actividades que podem estar presentes, de forma
articulada, no ensino-aprendizagem da Matemática e na actividade profissional do
professor. Para isso, é necessário conceber tarefas que possam ser o ponto de partida para
investigações e explorações matemáticas dos alunos e discutir o modo como podem ser
trabalhadas na sala de aula. Recorrendo a exemplos de actividades realizadas por
professores de Matemática portugueses, analiso a actividade de aprendizagem suscitada
por tarefas deste tipo e discuto as respectivas potencialidades. Finalmente, refiro as
condições respeitantes à cultura profissional dos professores que podem favorecer uma
actividade de investigação sobre a sua própria profissional, com relevo para a colaboração
e a dimensão associativa.Researching, teaching and learning are activities that may be present, in coordination,
teaching and learning of mathematics in the work of the teacher. Therefore, it is necessary
to design tasks that may be the starting point for mathematical investigations and
explorations of the students and discuss how they can be worked in the classroom. Drawing
on examples of activities carried out by Portuguese teachers of mathematics by examining
the activity of learning raised by such tasks and discuss their potencial. Finally, I refer to
conditions relating to the professional culture of teachers who can promote the research
activity on their own training, with an emphasis on collaboration and associative dimension
Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta
In previous studies on a number of under- and overdoped high temperature
superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta},
the transition temperature T_c has been found to change with time in a manner
which depends on the sample's detailed temperature and pressure history. This
relaxation behavior in T_c is believed to originate from rearrangements within
the oxygen sublattice. In the present high-pressure studies on
HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation
effects in strongly under- and overdoped samples () with
an activation energy . For overdoped
HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than
previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of
+11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an
anomalous result for high-T_c superconductors in the present pressure range,
giving evidence for a change in the electronic and/or structural properties
near 0.4 GPa