1,354 research outputs found
Chromosome analysis in Saccodon wagneri (Characiformes) and insights into the karyotype evolution of Parodontidae
Parodontidae is a relatively small group of Neotropical characiform fishes
consisting of three genera (Apareiodon, Parodon, and Saccodon) with 32 valid
species. A vast cytogenetic literature is available on Apareiodon and Parodon, but
to date, there is no cytogenetic data about Saccodon, a genus that contains only
three species with a trans-Andean distribution. In the present study the karyotype
of S. wagneri was described, based on both conventional (Giemsa staining, Ag-
NOR, C-bands) and molecular (repetitive DNA mapping by fluorescent in situ
hybridization) methods. A diploid chromosome number of 2n = 54 was observed
in both sexes, and the presence of heteromorphic sex chromosomes of the ZZ/
ZW type was detected. The W chromosome has a terminal heterochromatin band
that occupies approximately half of the long arm, being this band approximately
half the size of the Z chromosome. The FISH assay showed a synteny of the
18S-rDNA and 5S-rDNA genes in the chromosome pair 14, and the absence
of interstitial telomeric sites. Our data reinforce the hypothesis of a conservative
karyotype structure in Parodontidae and suggest an ancient origin of the sex
chromosomes in the fishes of this family
Modeling the quantum evolution of the universe through classical matter
It is well known that the canonical quantization of the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads
to nonsingular universes which, for later times, behave as their classical
counterpart. This means that the expectation value of the scale factor
never vanishes and, as , we recover the classical expression for
the scale factor. In this paper, we show that such universes can be reproduced
by classical cosmology given that the universe is filled with an exotic matter.
In the case of a perfect fluid, we find an implicit equation of state (EoS). We
then show that this single fluid with an implict EoS is equivalent to two
non-interacting fluids, one of them representing stiff matter with negative
energy density. In the case of two non-interacting scalar fields, one of them
of the phantom type, we find their potential energy. In both cases we find that
quantum mechanics changes completely the configuration of matter for small
values of time, by adding a fluid or a scalar field with negative energy
density. As time passes, the density of negative energy decreases and we
recover the ordinary content of the classical universe. The more the initial
wave function of the universe is concentrated around the classical big bang
singularity, the more it is necessary to add negative energy, since this type
of energy will be responsible for the removal of the classical singularity.Comment: updated version as accepted by Gen. Relativ. Gravi
Mortar-based systems for externally bonded strengthening of masonry
Mortar-based composite materials appear particularly promising for use as externally bonded reinforcement (EBR) systems for masonry structures. Nevertheless, their mechanical performance, which may significantly differ from that of Fibre Reinforced Polymers, is still far from being fully investigated. Furthermore, standardized and reliable testing procedures have not been defined yet. The present paper provides an insight on experimental-related issues arising from campaigns on mortar-based EBRs carried out by laboratories in Italy, Portugal and Spain. The performance of three reinforcement systems made out of steel, carbon and basalt textiles embedded in inorganic matrices has been investigated by means of uniaxial tensile coupon testing and bond tests on brick and stone substrates. The experimental results contribute to the existing knowledge regarding the structural behaviour of mortar-based EBRs against tension and shear bond stress, and to the development of reliable test procedures aiming at their homogenization/standardization
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