198 research outputs found
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
Chemokine-guided angiogenesis directs coronary vasculature formation in zebrafish.
Supramolecular & Biomaterials Chemistr
Interaction of free-floating planets with a star-planet pair
The recent discovery of free-floating planets and their theoretical
interpretation as celestial bodies, either condensed independently or ejected
from parent stars in tight clusters, introduced an intriguing possibility.
Namely, that some exoplanets are not condensed from the protoplanetary disk of
their parent star. In this novel scenario a free-floating planet interacts with
an already existing planetary system, created in a tight cluster, and is
captured as a new planet. In the present work we study this interaction process
by integrating trajectories of planet-sized bodies, which encounter a binary
system consisting of a Jupiter-sized planet revolving around a Sun-like star.
To simplify the problem we assume coplanar orbits for the bound and the
free-floating planet and an initially parabolic orbit for the free-floating
planet. By calculating the uncertainty exponent, a quantity that measures the
dependence of the final state of the system on small changes of the initial
conditions, we show that the interaction process is a fractal classical
scattering. The uncertainty exponent is in the range (0.2-0.3) and is a
decreasing function of time. In this way we see that the statistical approach
we follow to tackle the problem is justified. The possible final outcomes of
this interaction are only four, namely flyby, planet exchange, capture or
disruption. We give the probability of each outcome as a function of the
incoming planet's mass. We find that the probability of exchange or capture (in
prograde as well as retrograde orbits and for very long times) is
non-negligible, a fact that might explain the possible future observations of
planetary systems with orbits that are either retrograde or tight and highly
eccentric.Comment: 19 pages, 12 figure
Formation, evolution and multiplicity of brown dwarfs and giant exoplanets
This proceeding summarises the talk of the awardee of the Spanish
Astronomical Society award to the the best Spanish thesis in Astronomy and
Astrophysics in the two-year period 2006-2007. The thesis required a tremendous
observational effort and covered many different topics related to brown dwarfs
and exoplanets, such as the study of the mass function in the substellar domain
of the young sigma Orionis cluster down to a few Jupiter masses, the relation
between the cluster stellar and substellar populations, the accretion discs in
cluster brown dwarfs, the frequency of very low-mass companions to nearby young
stars at intermediate and wide separations, or the detectability of Earth-like
planets in habitable zones around ultracool (L- and T-type) dwarfs in the solar
neighbourhood.Comment: "Highlights of Spanish Astrophysics V", Proceedings of the VIII
Scientific Meeting of the Spanish Astronomical Society (SEA) held in
Santander, 7-11 July, 2008. Edited by J. Gorgas, L. J. Goicoechea, J. I.
Gonzalez-Serrano, J. M. Diego. Invited oral contribution to plenary sessio
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
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