924 research outputs found
Quantifying structure in networks
We investigate exponential families of random graph distributions as a
framework for systematic quantification of structure in networks. In this paper
we restrict ourselves to undirected unlabeled graphs. For these graphs, the
counts of subgraphs with no more than k links are a sufficient statistics for
the exponential families of graphs with interactions between at most k links.
In this framework we investigate the dependencies between several observables
commonly used to quantify structure in networks, such as the degree
distribution, cluster and assortativity coefficients.Comment: 17 pages, 3 figure
Social inertia in collaboration networks
This work is a study of the properties of collaboration networks employing
the formalism of weighted graphs to represent their one-mode projection. The
weight of the edges is directly the number of times that a partnership has been
repeated. This representation allows us to define the concept of "social
inertia" that measures the tendency of authors to keep on collaborating with
previous partners. We use a collection of empirical datasets to analyze several
aspects of the social inertia: 1) its probability distribution, 2) its
correlation with other properties, and 3) the correlations of the inertia
between neighbors in the network. We also contrast these empirical results with
the predictions of a recently proposed theoretical model for the growth of
collaboration networks.Comment: 7 pages, 5 figure
Estimating the number of planets that PLATO can detect
The PLATO mission is scheduled for launch in 2026. This study aims to
estimate the number of exoplanets that PLATO can detect as a function of
planetary size and period, stellar brightness, and observing strategy options.
Deviations from these estimates will be informative of the true occurrence
rates of planets, which helps constraining planet formation models. For this
purpose, we developed the Planet Yield for PLATO estimator (PYPE), which adopts
a statistical approach. We apply given occurrence rates from planet formation
models and from different search and vetting pipelines for the Kepler data. We
estimate the stellar sample to be observed by PLATO using a fraction of the
all-sky PLATO stellar input catalog (PIC). PLATO detection efficiencies are
calculated under different assumptions that are presented in detail in the
text. The results presented here primarily consider the current baseline
observing duration of four years. We find that the expected PLATO planet yield
increases rapidly over the first year and begins to saturate after two years. A
nominal (2+2) four-year mission could yield about several thousand to several
tens of thousands of planets, depending on the assumed planet occurrence rates.
We estimate a minimum of 500 Earth-size (0.8-1.25 RE) planets, about a dozen of
which would reside in a 250-500d period bin around G stars. We find that
one-third of the detected planets are around stars bright enough (V )
for RV-follow-up observations. We find that a three-year-long observation
followed by 6 two-month short observations (3+1 years) yield roughly twice as
many planets as two long observations of two years (2+2 years). The former
strategy is dominated by short-period planets, while the latter is more
beneficial for detecting earths in the habitable zone.Comment: 14 pages, 11 figures, accepted by A&A (July 5, 2023
Conformally invariant wave-equations and massless fields in de Sitter spacetime
Conformally invariant wave equations in de Sitter space, for scalar and
vector fields, are introduced in the present paper. Solutions of their wave
equations and the related two-point functions, in the ambient space notation,
have been calculated. The ``Hilbert'' space structure and the field operator,
in terms of coordinate independent de Sitter plane waves, have been defined.
The construction of the paper is based on the analyticity in the complexified
pseudo-Riemanian manifold, presented first by Bros et al.. Minkowskian limits
of these functions are analyzed. The relation between the ambient space
notation and the intrinsic coordinates is then studied in the final stage.Comment: 21 pages, LaTeX, some details adde
A method for the construction of strongly reduced representations of ATLAS experimental uncertainties and the application thereof to the jet energy scale
Deterministic and stochastic influence of nutrients on phytoplankton function and structure in coastal waters
Knowledge of how phytoplankton responds to nutrient inputs is essential for water management and for minimizing eutrophication. Only processes that are deterministic, i.e. that can respond as algorithms, are controllable. The study area is the chain of inshore waters (so-called Bodden) south of the Darss-Zingst peninsula - shallow eutrophic waters of estuarine character in the Southern Baltic. Monitoring programmes and laboratory experiments have revealed an annual periodicity of the phytoplankton and of the physico-chemical factors influencing it. On the basis of these results, experiments were carried out in enclosures to study the effects of nutrient loading on phytoplankton. The purpose was to test the feasibility of influencing phytoplankton development under field conditions during the transition period from late spring to mid-summer. This contribution presents results from the 1985 shallow water enclosure experiments (FLAK 85) which demonstrate that
- the scale of phytoplankton reactions and the species involved are stochastic in character and are governed by stochastic interactions between meteorological events and water exchange processes in the chain of Bodden;
- all processes affecting phytoplankton growth are deterministic in character, conforming to simple batch theories: simultaneous addition of nitrogen and phosphorus favours green algae, and in exceptional cases one algal species became dominant;
- nutrient loadings do not affect the time of transition to the mid-summer phytoplankton population, the most important regulating factor obviously being temperature
Anharmonic double-phonon excitations in the interacting boson model
Double- vibrations in deformed nuclei are analyzed in the context of
the interacting boson model. A simple extension of the original version of the
model towards higher-order interactions is required to explain the observed
anharmonicities of nuclear vibrations. The influence of three- and four-body
interactions on the moments of inertia of ground- and -bands, and on
the relative position of single- and double- bands is studied
in detail. As an example of a realistic calculation, spectra and transitions of
the highly -anharmonic nuclei Dy, Er, and Er
are interpreted in this approach.Comment: 38 pages, TeX (ReVTeX). 15 ps figures. Submitted to Phys. Rev.
QTLs for salt tolerance in three different barley mapping populations 2006
Soil salinity is one of the crucial factors limiting crop production. Progression of salinisation of agriculturally arable land is mainly connected with mismanagement of water in irrigation systems, in particular under arid and semiarid climate conditions and global changes of water flow in the landscape. Selection of salt tolerant genotypes is necessary to ensure yield and to reclaim salt affected soils. The development of molecular marker(s) could facilitate the selection process. Phenotyping of mapping populations under salt stress conditions and calculation of QTLs are suitable instruments to detect markers that are responsible for tolerance/sensitivity. However, a quantitative inherited trait like salt tolerance requires a range of adaptations, with a whole host of genes interacting with each other to produce the visible phenotype
Oportunidades e barreiras de ordem social e econĂ´mica para a preservação dos recursos hĂdricos por parte dos pequenos agricultores no Nordeste paraense.
Group theoretical approach to quantum fields in de Sitter space I. The principal series
Using unitary irreducible representations of the de Sitter group, we
construct the Fock space of a massive free scalar field.
In this approach, the vacuum is the unique dS invariant state. The quantum
field is a posteriori defined by an operator subject to covariant
transformations under the dS isometry group. This insures that it obeys
canonical commutation relations, up to an overall factor which should not
vanish as it fixes the value of hbar. However, contrary to what is obtained for
the Poincare group, the covariance condition leaves an arbitrariness in the
definition of the field. This arbitrariness allows to recover the amplitudes
governing spontaneous pair creation processes, as well as the class of alpha
vacua obtained in the usual field theoretical approach. The two approaches can
be formally related by introducing a squeezing operator which acts on the state
in the field theoretical description and on the operator in the present
treatment. The choice of the different dS invariant schemes (different alpha
vacua) is here posed in very simple terms: it is related to a first order
differential equation which is singular on the horizon and whose general
solution is therefore characterized by the amplitude on either side of the
horizon. Our algebraic approach offers a new method to define quantum field
theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc
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