16,523 research outputs found
Stellar populations in superclusters of galaxies
A catalogue of superclusters of galaxies is used to investigate the influence
of the supercluster environment on galaxy populations, considering galaxies
brighter than M-21+5 h. Empirical spectral synthesis techniques are
applied to obtain the stellar population properties of galaxies which belong to
superclusters and representative values of stellar population parameters are
attributed to each supercluster. We show that richer superclusters present
denser environments and older stellar populations. The galaxy populations of
superclusters classified as filaments and pancakes are statistically similar,
indicating that the morphology of superclusters does not have a significative
influence on the stellar populations. Clusters of galaxies within superclusters
are also examined in order to evaluate the influence of the supercluster
environment on their galaxy properties. Our results suggest that the
environment affects galaxy properties but its influence should operate on
scales of groups and clusters, more than on the scale of superclusters.Comment: 7 pages, 4 figures; accepted to MNRA
Constraining Elko Dark Matter at the LHC with Monophoton Events
A mass dimension one fermion, also known as Elko, constitutes a dark matter
candidate which might interact with photons at the tree level in a specific
fashion. In this work, we investigate the constraints imposed by unitarity and
LHC data on this type of interactions using the search for new physics in
monophoton events. We found that Elkos which can explain the dark matter relic
abundance mainly through electromagnetic interactions are excluded at the
95\%CL by the 8 TeV LHC data for masses up to 1 TeV.Comment: 6 pages, 4 figure
A unification in the theory of linearization of second order nonlinear ordinary differential equations
In this letter, we introduce a new generalized linearizing transformation
(GLT) for second order nonlinear ordinary differential equations (SNODEs). The
well known invertible point (IPT) and non-point transformations (NPT) can be
derived as sub-cases of the GLT. A wider class of nonlinear ODEs that cannot be
linearized through NPT and IPT can be linearized by this GLT. We also
illustrate how to construct GLTs and to identify the form of the linearizable
equations and propose a procedure to derive the general solution from this GLT
for the SNODEs. We demonstrate the theory with two examples which are of
contemporary interest.Comment: 8 page
Clone size distributions in networks of genetic similarity
We build networks of genetic similarity in which the nodes are organisms
sampled from biological populations. The procedure is illustrated by
constructing networks from genetic data of a marine clonal plant. An important
feature in the networks is the presence of clone subgraphs, i.e. sets of
organisms with identical genotype forming clones. As a first step to understand
the dynamics that has shaped these networks, we point up a relationship between
a particular degree distribution and the clone size distribution in the
populations. We construct a dynamical model for the population dynamics,
focussing on the dynamics of the clones, and solve it for the required
distributions. Scale free and exponentially decaying forms are obtained
depending on parameter values, the first type being obtained when clonal growth
is the dominant process. Average distributions are dominated by the power law
behavior presented by the fastest replicating populations.Comment: 17 pages, 4 figures. One figure improved and other minor changes. To
appear in Physica
Crossbreeding and new beef cattle breeds in Brazil.
Crossbreeding and new beef cattle breeds in Brazil.198
On a generalised model for time-dependent variance with long-term memory
The ARCH process (R. F. Engle, 1982) constitutes a paradigmatic generator of
stochastic time series with time-dependent variance like it appears on a wide
broad of systems besides economics in which ARCH was born. Although the ARCH
process captures the so-called "volatility clustering" and the asymptotic
power-law probability density distribution of the random variable, it is not
capable to reproduce further statistical properties of many of these time
series such as: the strong persistence of the instantaneous variance
characterised by large values of the Hurst exponent (H > 0.8), and asymptotic
power-law decay of the absolute values self-correlation function. By means of
considering an effective return obtained from a correlation of past returns
that has a q-exponential form we are able to fix the limitations of the
original model. Moreover, this improvement can be obtained through the correct
choice of a sole additional parameter, . The assessment of its validity
and usefulness is made by mimicking daily fluctuations of SP500 financial
index.Comment: 6 pages, 4 figure
A calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian/Pliensbachian (early Jurassic, ~191Ma) in Portugal
The Sinemurian/Pliensbachian boundary (~ 191 Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the São Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths
Phytoplankton production modelling in three marine ecosystems—static versus dynamic approach
Phytoplankton productivity is usually determined from water samples incubated at a number of irradiance levels during
several hours. The resultant productivity-irradiance (P–E) curves are then used to estimate local and/or global phytoplankton
production. However, there is growing evidence that these curves, referred as static, underestimate phytoplankton photosynthesis
to a great deal, by assuming a stable response to light over the incubation period. One of the drawbacks of static P–E curves is
the overestimation of photoinhibition.
In this work, three one-dimensional vertically resolved models were developed as simply as possible, to investigate differences
between static and dynamic phytoplankton productivity in three marine ecosystems: a turbid estuary, a coastal area and an
open ocean ecosystem. The results show that, when photoinhibition development time is considered (dynamic model), the
primary production estimates are always higher than when calculated with the static model. The quantitative importance of these
differences varies with the type of ecosystem and it appears to be more important in coastal areas and estuaries (from 21 to 72%)
than in oceanic waters (10%). Thus, these results suggest that primary production estimates, obtained under the assumption of a
static behaviour response to light, may underestimate the real values of global phytoplankton primary production. Calculations
suggest that the quantitative importance of this underestimation may be larger than the global missing carbon sink
Phytoplankton production modelling in three marine ecosystems—static versus dynamic approach
Phytoplankton productivity is usually determined from water samples incubated at a number of irradiance levels during
several hours. The resultant productivity-irradiance (P–E) curves are then used to estimate local and/or global phytoplankton
production. However, there is growing evidence that these curves, referred as static, underestimate phytoplankton photosynthesis
to a great deal, by assuming a stable response to light over the incubation period. One of the drawbacks of static P–E curves is
the overestimation of photoinhibition.
In this work, three one-dimensional vertically resolved models were developed as simply as possible, to investigate differences
between static and dynamic phytoplankton productivity in three marine ecosystems: a turbid estuary, a coastal area and an
open ocean ecosystem. The results show that, when photoinhibition development time is considered (dynamic model), the
primary production estimates are always higher than when calculated with the static model. The quantitative importance of these
differences varies with the type of ecosystem and it appears to be more important in coastal areas and estuaries (from 21 to 72%)
than in oceanic waters (10%). Thus, these results suggest that primary production estimates, obtained under the assumption of a
static behaviour response to light, may underestimate the real values of global phytoplankton primary production. Calculations
suggest that the quantitative importance of this underestimation may be larger than the global missing carbon sink
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