25,737 research outputs found
NoSOCS in SDSS. VI. The Environmental Dependence of AGN in Clusters and Field in the Local Universe
We investigated the variation in the fraction of optical active galactic
nuclei (AGN) hosts with stellar mass, as well as their local and global
environments. Our sample is composed of cluster members and field galaxies at
and we consider only strong AGN. We find a strong variation in the
AGN fraction () with stellar mass. The field population comprises a
higher AGN fraction compared to the global cluster population, especially for
objects with log . Hence, we restricted our analysis to more
massive objects. We detected a smooth variation in the with local
stellar mass density for cluster objects, reaching a plateau in the field
environment. As a function of clustercentric distance we verify that
is roughly constant for R R, but show a steep decline inwards. We
have also verified the dependence of the AGN population on cluster velocity
dispersion, finding a constant behavior for low mass systems ( km s). However, there is a strong decline in
for higher mass clusters ( 700 km s). When comparing the in
clusters with or without substructure we only find different results for
objects at large radii (R R), in the sense that clusters with
substructure present some excess in the AGN fraction. Finally, we have found
that the phase-space distribution of AGN cluster members is significantly
different than other populations. Due to the environmental dependence of
and their phase-space distribution we interpret AGN to be the result
of galaxy interactions, favored in environments where the relative velocities
are low, typical of the field, low mass groups or cluster outskirts.Comment: 11 pages, 10 figures, Accepted to MNRA
Black hole entropy functions and attractor equations
The entropy and the attractor equations for static extremal black hole
solutions follow from a variational principle based on an entropy function. In
the general case such an entropy function can be derived from the reduced
action evaluated in a near-horizon geometry. BPS black holes constitute special
solutions of this variational principle, but they can also be derived directly
from a different entropy function based on supersymmetry enhancement at the
horizon. Both functions are consistent with electric/magnetic duality and for
BPS black holes their corresponding OSV-type integrals give identical results
at the semi-classical level. We clarify the relation between the two entropy
functions and the corresponding attractor equations for N=2 supergravity
theories with higher-derivative couplings in four space-time dimensions. We
discuss how non-holomorphic corrections will modify these entropy functions.Comment: 21 pages,LaTeX,minor change
Contexts for questioning: Two zones of teaching and learning in undergraduate science
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ Springer Science+Business Media B.V. 2012.Higher education institutions are currently undertaking a challenging process in moving from teacher-orientated to student-focused approaches. Students’ ability to asking questions is fundamental to developing critical reasoning, and to the process of scientific enquiry itself. Our premise is that questioning competences should become a central focus of current reforms in higher education. This study, part of a broader naturalistic research project, aims at developing a theoretical framework for conceptualizing different contexts for questioning, illustrating the application of the proposed framework (contextual questioning zones) and reflecting about some of the dimensions of teaching and learning, for overcoming some of the challenges that higher education institutions are facing presently. The discussion of two ‘opposite’ contexts of enquiry is based on qualitative data, gathered through close collaboration with four teachers of undergraduate biology at a Portuguese university. These teachers were observed during their ‘daily activity’ during an academic year. Data was also gathered by interviewing these teachers and 8 selected students, at the end of the year, and used to sustain the argumentation. The paper concludes with some reflections and suggestions to promote authentic enquiry-based learning experiences.Portuguese Fundação para a Ciência e a Tecnologi
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