25,117 research outputs found
On the relation between the mass of Compact Massive Objects and their host galaxies
Supermassive black holes and/or very dense stellar clusters are found in the
central regions of galaxies. Nuclear star clusters are present mainly in faint
galaxies while upermassive black holes are common in galaxies with masses M. In the intermediate galactic mass range both types of
central massive objects (CMOs) are found. Here we present our collection of a
huge set of nuclear star cluster and massive black hole data that enlarges
significantly already existing data bases useful to investigate for
correlations of their absolute magnitudes, velocity dispersions and masses with
structural parameters of their host galaxies. In particular, we directed our
attention to some differences between the correlations of nuclear star clusters
and massive black holes as subsets of CMOs with hosting galaxies. In this
context, the mass-velocity dispersion relation plays a relevant role because it
seems the one that shows a clearer difference between the supermassive black
holes and nuclear star clusters. The has a slope of while has the much smaller slope of .
The slopes of the CMO mass- host galaxy B magnitude of the two types of CMOs
are indistinguishable within the errors while that of the NSC mass-host galaxy
mass relation is significantly smaller than for supermassive black holes.
Another important result is the clear depauperation of the NSC population in
bright galaxy hosts, which reflects also in a clear flattening of the NSC mass
vs host galaxy mass at high host masses.Comment: 12 pages, 22 figures, 2 tables, accepted for publication in MNRA
C*-Structure and K-Theory of Boutet de Monvel's Algebra
We consider the norm closure of the algebra of all operators of order and
class zero in Boutet de Monvel's calculus on a manifold with boundary .
We first describe the image and the kernel of the continuous extension of the
boundary principal symbol to . If the is connected and is not empty,
we then show that the K-groups of are topologically determined. In case the
manifold, its boundary and the tangent space of the interior have torsion-free
K-theory, we prove that is isomorphic to the direct sum of
and , for i=0,1, with denoting the compact
ideal and the tangent bundle of the interior of . Using Boutet de
Monvel's index theorem, we also prove this result for i=1 without assuming the
torsion-free hypothesis. We also give a composition sequence for .Comment: Final version, to appear in J. Reine Angew. Math. Improved
K-theoretic result
Development and standardization of a protocol for sperm cryopreservation of two important commercial oyster species
Dissertação de mestrado, Aquacultura e Pescas, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015Aquaculture activities have a huge contribution for the world food production and their development is extremely necessary to answer to the lack of resources, especially to the demand for seafood. Bivalve production, especially Crassostrea angulata (Portuguese oyster) has been practiced from long ago, and although its production suffered several constraints, in recent years it has been increasing the interests in recovering production and in preserving nature populations. In this sense, new research needs to guarantee an efficient and economically viable production, contributing to a relatively new environmental concern: wild population restoration.
Nowadays, pure wild populations of Crassostrea angulata are rare to find due to multiple factors that affected this oyster industry. Cryopreservation technology could promote alternative techniques to contribute for the resource management efficiency of the Portuguese oyster and associated economic activity. In this sense, standardization of procedures is important for Crassostrea genus. At the present there are no cryopreservation reports on Crassostrea angulata sperm, and therefore, one of the objectives of this work is to design a cryopreservation protocol for this species, testing the more adequate cryoprotectant solution, its ideal concentration, different freezing rates and types of containers. In parallel, this stablished protocol was applied in Crassostrea gigas and compared to other previously published for this species.
Analysis of motility, viability, agglutination and fertilizations were used as guides for the establishment of the protocol in C. angulata. Moreover, ATP content, DNA fragmentation and lipid peroxidation were done in order to standardize the same protocol for both species. Movement analysis were assessed by CASA system, viability through common staining techniques and flow cytometer, agglutination was quantified according to the scale developed by Dong et al., (2007), ATP content determined by bioluminescence, Comet assay was performed to quantify the DNA fragmentation and lipid peroxidation determined spectrophotometrically by measuring the absorbance of the malondialdehyde (MDA).
Significant differences were observed (p<0.05) for lipid peroxidation and fertilization trials whereas ATP content and fragmentation of DNA of the cryopreserved samples did
not differ significantly from the control. In C. gigas, the same analysis were performed and did not reveal post-thaw quality differences in the samples cryopreserved with 10% DMSO.
The established protocol revealed to be effective and with a low degree of cellular damage on C. angulata sperm and, at the same time, viable to apply in other species, such as Crassostrea gigas
Scaling Correlations Among Central Massive Objects and Their Host Galaxies
The central regions of galaxies show the presence of super massive black
holes and/or very dense stellar clusters. Both such objects seem to follow
similar host-galaxy correlations, suggesting that they are members of the same
family of Compact Massive Objects. Here we investigate a huge data collection
of Compact Massive Objects properties to correlate them with absolute
magnitude, velocity dispersion and mass of their host galaxies. We draw also
some preliminary astrophysical conclusions
A K-Theoretic Proof of Boutet de Monvel's Index Theorem for Boundary Value Problems
We study the C*-closure A of the algebra of all operators of order and class
zero in Boutet de Monvel's calculus on a compact connected manifold X with
non-empty boundary. We find short exact sequences in K-theory
0->K_i(C(X))->K_i(A/K)->K_{1-i}(C_0(T*X'))->0, i= 0,1, which split, where K
denotes the compact ideal and T*X' the cotangent bundle of the interior of X.
Using only simple K-theoretic arguments and the Atiyah-Singer Index Theorem, we
show that the Fredholm index of an elliptic element in A is given as the
composition of the topological index with mapping K_1(A/K)->K_0(C_0(T*X'))
defined above. This relation was first established by Boutet de Monvel by
different methods.Comment: Title slightly changed. Accepted for publication in Journal fuer die
reine und angewandte Mathemati
Light-front quark distributions in the nucleon and nucleon electromagnetic form factors
Longitudinal and transverse quark momentum distributions in the nucleon are
calculated from a phenomenological quark-nucleon vertex function obtained
through an investigation of the nucleon electromagnetic form factors within a
light-front framework.Comment: 6 pages, 11 figs. proceedings of LC2009, to appear in Nucl. Phys.
Magnetoresistive Effects in Ferromagnet-Superconductor Multilayers
We consider a nanoscale system consisting of Manganite-ferromagnet and
Cuprate-superconductor multilayers in a spin valve configuration. The
magnetization of the bottom Manganite-ferromagnet is pinned by a
Manganite-antiferromagnet. The magnetization of the top Manganite-ferromagnet
is coupled to the bottom one via indirect exchange through the superconducting
layers. We study the behavior of the critical temperature and the
magnetoresistance as a function of an externally applied parallel magnetic
field, when the number of Cuprate-superconductor layers are changed. There are
two typical behaviors in the case of a few monolayers of the Cuprates: a) For
small magnetic fields, the critical temperature and the magnetoresistance
change abruptly when the flipping field of the top Manganite-ferromagnet is
reached. b) For large magnetic fields, the multilayered system re-enters the
zero-resistance (superconducting) state after having become resistive (normal).Comment: 3 pages, 3 figures. 2004 Magnetism and Magnetic Materials Conferenc
Right-to-Choose Auctions: A Field Study of Water Markets in the Limari Valley of Chile
Field experiments were conducted with farmers in the Limarà Valley of Chile to test extant theory on right-to-choose auctions. Water volumes that differed by reservoir source and time of availability were offered for sale by the research team. The auctions were supplemented by protocols to elicit risk and time preferences of bidders. We find that the right-to-choose auctions raise significantly more revenue than the benchmark sequential auction. Risk attitudes explain a substantial amount of the difference in bidding between auction institutions, consonant with received theory. The auction bidding revealed distinct preferences for water types, which has implications for market re-design.auction design, field experiments,water market
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