26,402 research outputs found
The Apparent Fractal Conjecture
This short communication advances the hypothesis that the observed fractal
structure of large-scale distribution of galaxies is due to a geometrical
effect, which arises when observational quantities relevant for the
characterization of a cosmological fractal structure are calculated along the
past light cone. If this hypothesis proves, even partially, correct, most, if
not all, objections raised against fractals in cosmology may be solved. For
instance, under this view the standard cosmology has zero average density, as
predicted by an infinite fractal structure, with, at the same time, the
cosmological principle remaining valid. The theoretical results which suggest
this conjecture are reviewed, as well as possible ways of checking its
validity.Comment: 6 pages, LaTeX. Text unchanged. Two references corrected. Contributed
paper presented at the "South Africa Relativistic Cosmology Conference in
Honour of George F. R. Ellis 60th Birthday"; University of Cape Town,
February 1-5, 199
Spatial and observational homogeneities of the galaxy distribution in standard cosmologies
This work discusses the possible empirical verification of the geometrical
concept of homogeneity of the standard relativistic cosmology considering its
various definitions of distance. We study the physical consequences of the
distinction between the usual concept of spatial homogeneity (SH), as defined
by the Cosmological Principle, and the concept of observational homogeneity
(OH), arguing that OH is in principle falsifiable by means of astronomical
observations, whereas verifying SH is only possible indirectly. Simulated
counts of cosmological sources are produced by means of a generalized
number-distance expression that can be specialized to produce either the counts
of the Einstein-de Sitter (EdS) cosmology, which has SH by construction, or
other types of counts, which do, or do not, have OH by construction.
Expressions for observational volumes and differential densities are derived
with the various cosmological distance definitions in the EdS model. Simulated
counts that have OH by construction do not always exhibit SH features. The
reverse situation is also true. Besides, simulated counts with no OH features
at low redshift start showing OH characteristics at high redshift. The comoving
distance seems to be the only distance definition where both SH and OH appear
simultaneously. The results show that observations indicating possible lack of
OH do not necessarily falsify the standard Friedmannian cosmology, meaning that
this cosmology will not necessarily always produce observable homogeneous
densities. The general conclusion is that the use of different cosmological
distances in the characterization of the galaxy distribution lead to
significant ambiguities in reaching conclusions about the behavior of the
large-scale galaxy distribution in the Universe.Comment: 12 pages, 12 figures, LaTeX. Matches the final version sent to the
journal. Accepted for publication in "Astronomy and Astrophysics
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No sex-biased dispersal in a primate with an uncommon social system-cooperative polyandry.
An influential hypothesis proposed by Greenwood (1980) suggests that different mating systems result in female and male-biased dispersal, respectively, in birds and mammals. However, other aspects of social structure and behavior can also shape sex-biased dispersal. Although sex-specific patterns of kin cooperation are expected to affect the benefits of philopatry and dispersal patterns, empirical evidence is scarce. Unlike many mammals, Saguinus geoffroyi (Geoffroy's tamarin) has a breeding system in which typically multiple males mate with a single breeding female. Males typically form cooperative reproductive partnerships between relatives, whereas females generally compete for reproductive opportunities. This system of cooperative polyandry is predicted to result in female-biased dispersal, providing an opportunity to test the current hypotheses of sex-biased dispersal. Here we test for evidence of sex-biased dispersal in S. geoffroyi using demographic and genetic data from three populations. We find no sex bias in natal dispersal, contrary to the prediction based on the mating patterns. This pattern was consistent after controlling for the effects of historical population structure. Limited breeding opportunities within social groups likely drive both males and females to disperse, suggesting that dispersal is intimately related to the social context. The integration of genetic and field data revealed that tamarins are another exception to the presumed pattern of male-biased dispersal in mammals. A shift in focus from mating systems to social behavior, which plays a role in most all processes expected to influence sex-bias in dispersal, will be a fruitful target for research both within species and across taxa
Estado Confusional Agudo apĂłs Corticoterapia Inalada
Background: The connection between corticotherapy and neuropsychiatric symptoms is
widely known, being one of the first questions
we need to assess when presenting with first
episode psychiatric symptoms or confusional
state.
Aims: To date, data on cases related to inhaled
corticotherapy and neuropsychiatric effects is
scarce. In this paper we describe a rare case in
a young woman.
Methods: The clinical case presented led us
to try to understand the data published on the
subject in order to discuss it in greater length.
Results and Conclusions: We present and
discuss a 27-year-old patient’s case, with no
previous psychiatric disease, who was admitted to our Psychiatric ward after the onset of
severe acute behavioural disturbance characterized by aggressiveness, visual and auditory
hallucinatory activity, misidentification and
altered conscience status. It was later found
that seven days earlier she had been prescribed
inhaled corticotherapy for a minor respiratory
infection. A few days after corticotherapy withdrawal, the clinical symptoms improved significantly.info:eu-repo/semantics/publishedVersio
Western iberian granites: a contribution to their geodynamic interpretation
[Resumo] Este trabalho apresenta fundamentalmente urna sĂntese do conhecimento dos granitos peninsulares, obtido atravĂ©s das várias abordagĂ©ns c1ássicas (geocronolĂłgica, peuográfica, estrutural e geoquĂmica). Existem já muitos dados disponĂveis que «catalogados» e reinterpretados no quadro do conhecimento fornecido por outras disciplinas da Geologia, possibilitam a sua interpreta~ao geodinamica. Dá-se enfase ás c1assifica~6es baseadas em datos mineralĂłgicos e estruturais, possiveis de obter no campo que, conjuntamente com dados geocronolĂłgicos, permitem reconhecer, como primeiros grandes grupos: granitos prĂ© orogĂ©nicos, orogĂ©nicos e tardi/pĂłs orogĂ©nicos. Os granitos prĂ© orogĂ©nicos sao contemporaneos do vulcanismo estratificado, com que se procuram relacionar. Ocorrem em alinhamentos, referenciados no texto, e que se procuram interpretar como resultantes de falhas profundas, recorrentes, que terao permitido a ascensao, de magmas gerados em nĂveis profundos da crusta (e manto?). Contudo, a maioria dos granitos peninsulares antĂ©-mesozoicos, sao contemporaneos da deforma~aohercĂnica (orogĂ©nicos). Estes granitos, onde tem sido reconhecida a existencia de vários subgrupos, ocorrendo geralmente associados a entidades estruturais importantes, apresentam caracterĂsticas diferentes conforme as zonas paleogeográficas e estruturais peninsulares em que ocorrem e o periodo da sua instala~ao. As suas associaçoes com rochas de naturaleza mais máfica sao menos frequentes nas ZCI e ZAWL, indicando maior envolvimento da crusta continental nestas zonas (maior espessamento da crusta, durante a colisao hercĂnica?). Os granitos tardi/pĂłs orogĂ©nicos ocorrem em todas as regi6es muitas vezes associados a grandes desligamentos de rejogo tardio. Tecem-se ainda algumas considera~6es relativas ao significado da escassez de rochas granĂticas no domĂnio meridional da ZCI que se considera como urna regiao de divergencia da estrutura~aoprĂ©-hercĂnica, e apresenta-se um modelo geodinamico do enquadramento dos tipos principais de granitos orogĂ©nicos. Faz-se ainda urna sĂntese dos resultados obtidos em domĂniosmenos clássicos, tais como a geoquĂmica estatĂstica e a geofĂsica, no sentido de suscitar novas abordagens do tema.[Abstract] These paper presents an integrated review ()f the current geochronological, petrological, structural and geochemical knowledge on the western iberian granites.
The available database is now large enough to allow a geodynamic interpretation of their genesis and installation. The field classifications based on petrographic and structural criteria together with geochronological data lead to the recognization of three first order groups: pre-orogenic, orogenic an tardi- post-orogenic granites. The pre-orogenic granites are contemporaneous with the stratified paleozoic volcanic rocks with which they are geneticaly correlated. They occur along lineaments which are interpreted as resulting from deep recurrent faults along which the magmas carne up. Many rocks from these lineaments present low Sri ratios suggesting generation at deep (rustal (or mantelic?) regions. However, the great majority of Iberia ante-mesozoic granites, are contemporaneous with the hercynian deformation (orogenic granites). Several subgroups of these granites have been recognised, all of them usually associated with important tectonic structures. They present characteristcs which are specific of the paleogeographic and structural zones where they accur and of its time of intrusion. Tardi- post-orogenic granites, usually assoeiated with younger deep fracturation, occur aH over Iberia. The granite /maphic rock associations are more frequent in the Ossa Morena and the Cantabric zones than in the Centro-Iberian and the Asturic-West-Leonesa zones, suggesting more crustal intervention on the generation of the granites in these two last zones (more crustal thickness at the time of the hercynian F32 collisiona!. phase). The scarcity of granitic rocks in the southern part of the Centro-Iberian zone is discussed. The general absence of granites and other data suggest that this region could have been a «continental plateau» from which the pre-hercynan structuration was divergent. A geodinamic model is proposed based in these ideas. A review of data obtained by less conventional means -such as geophysics and statistical geochemistry- is presented in the hope of suggestin new approaches to the study of the iberian granite
Desempenho produtivo de oito clones de cajueiro-anĂŁo precoce cultivados sob regime de sequeiro no cerrado sul maranhense.
bitstream/CPAMN-2009-09/17841/1/CT153.pd
Group theory for structural analysis and lattice vibrations in phosphorene systems
Group theory analysis for two-dimensional elemental systems related to
phosphorene is presented, including (i) graphene, silicene, germanene and
stanene, (ii) dependence on the number of layers and (iii) two stacking
arrangements. Departing from the most symmetric graphene space
group, the structures are found to have a group-subgroup relation, and analysis
of the irreducible representations of their lattice vibrations makes it
possible to distinguish between the different allotropes. The analysis can be
used to study the effect of strain, to understand structural phase transitions,
to characterize the number of layers, crystallographic orientation and
nonlinear phenomena.Comment: 24 pages, 3 figure
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