1,285 research outputs found
Conflicting Selection in the Course of Adaptive Diversification: The Interplay between Mutualism and Intraspecific Competition
Adaptive speciation can occur when a population undergoes assortative mating and disruptive selection caused by frequency-dependent intraspecific competition. However, other interactions, such as mutualisms based on trait matching, may generate conflicting selective pressures that constrain species diversification. We used individual-based simulations to explore how different types of mutualism affect adaptive diversification. A magic trait was assumed to simultaneously mediate mate choice, intraspecific competition, and mutualisms. In scenarios of intimate, specialized mu- tualisms, individuals interact with one or few individual mutualistic partners, and diversification is constrained only if the mutualism is obligate. In other scenarios, increasing numbers of different partners per individual limit diversification by generating stabilizing selection. Stabilizing selection emerges from the greater likelihood of trait mismatches for rare, extreme phenotypes than for common intermediate phenotypes. Constraints on diversification imposed by increased numbers of partners decrease if the trait matching degree has smaller positive effects on fitness. These results hold after the relaxation of various assumptions. When trait matching matters, mutualism-generated stabilizing selection would thus often constrain diversification in obligate mutualisms, such as ant-myrmecophyte associations, and in low-intimacy mutualisms, including plant-seed disperser systems. Hence, different processes, such as trait convergence favoring the incorporation of nonrelated species, are needed to explain the higher richness of low-intimacy assemblages—shown here to be up to 1 order of magnitude richer than high-intimacy systems
The Scientific program with RIBRAS (Radioactive Ion Beams in Brasil)
The Radioactive Ion Beams Facility (RIBRAS) is in operation since 2004 at the Pelletron
Accelerator Laboratory of the University of São Paulo and consists of two superconducting
solenoids capable of producing low energy secondary beams of light exotic nuclei. Measurements of the elastic scattering, breakup and transfer reactions with radioactive projectiles such as 6He, 8Li, 7Be on several targets have been performed. A review of the research program carried on along the last four years using the RIBRAS facility is presented
Das CPCJ aos tribunais da relação : caracterização dos processos de promoção e proteção
O progressivo reconhecimento do lugar que as crianças e jovens ocupam na sociedade enquanto sujeitos de direitos e a importância de incentivar, desenvolver e assegurar o exercício efetivo dos mesmos, tem convocado os interventores políticos e sociais para a observância de boas práticas em matéria de infância e juventude. Mas nem sempre foi desta forma, e existirá ainda um longo caminho a percorrer no que respeita a esta temática.
Neste trabalho foi feito o enquadramento da evolução dos direitos da criança até se chegar à intervenção no âmbito da Lei 147/99. Esta intervenção foi depois seguida, desde o seu início até à chegada a sede judicial, através da análise de 92 acórdãos que implicam a matéria de facto.
Obtiveram-se resultados que apontam para a maior frequência da aplicabilidade das medidas de “confiança a instituição com vista a futura adoção” e “acolhimento residencial” pelos Tribunais de Família e Menores e da Relação.
Também foi possível apurar que a maioria dos recursos são indeferidos pelos Tribunais de Relação.
Este estudo aponta para a necessidade de intervenção precoce em matéria de promoção e protecção, para que se possam evitar muitas vezes situações remediativas que acontecem, assim como para a importância do trabalho de acompanhamento das famíliasThe progressive recognition of the place that children and young people have in society as subjects of rights and the importance of encourage, develop and secure its effective exercise, has summoned the political and social intervenors to observe good practices within childhood and youth. It hasn’t always been like this and there’s still a long way to run regarding this issue.
In this report we’ve approached the children’s rights evolution until reaching the intervention under the law 147/99.
This intervention has been followed since its beginning until reaching the judicial seat, through the analysis of judgements which imply this matter.Results were obtained which aim to a greater frequency of the applicability of measures related with “the trust on an institution regarding a future adoption” and “child residential reception”.
Among other results, it was also possible to gather that most of the appeals are denied by Supreme Court.
This study aims to the need of early intervention, which can avoid many of the fixing situations happening, as well as the importance of working with the families and families monitoring
Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy ion collisions
Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created during relativistic heavy-ion collisions. These
domains are predicted to lead to charge separation of quarks along the orbital
momentum of the system created in non-central collisions. To study this effect,
we investigate a three particle mixed harmonics azimuthal correlator which is a
\P-even observable, but directly sensitive to the charge separation effect. We
report measurements of this observable using the STAR detector in Au+Au and
Cu+Cu collisions at =200 and 62~GeV. The results are presented
as a function of collision centrality, particle separation in rapidity, and
particle transverse momentum. A signal consistent with several of the
theoretical expectations is detected in all four data sets. We compare our
results to the predictions of existing event generators, and discuss in detail
possible contributions from other effects that are not related to parity
violation.Comment: 17 pages, 14 figures, as accepted for publication in Physical Review
C
Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations
Charged-particle spectra associated with direct photon () and
are measured in + and Au+Au collisions at center-of-mass energy
GeV with the STAR detector at RHIC. A hower-shape
analysis is used to partially discriminate between and .
Assuming no associated charged particles in the direction (near
side) and small contribution from fragmentation photons (), the
associated charged-particle yields opposite to (away side) are
extracted. At mid-rapidity () in central Au+Au collisions,
charged-particle yields associated with and at high
transverse momentum ( GeV/) are suppressed by a factor
of 3-5 compared with + collisions. The observed suppression of the
associated charged particles, in the kinematic range and GeV/, is similar for and , and
independent of the energy within uncertainties. These
measurements indicate that the parton energy loss, in the covered kinematic
range, is insensitive to the parton path length.Comment: submitted to Phys. Rev. Lett, 6 pages, 4 figure
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Hadronic resonance production in +Au collisions at = 200 GeV at RHIC
We present the first measurements of the , (892),
(1232), (1385), and (1520) resonances in +Au
collisions at = 200 GeV, reconstructed via their hadronic
decay channels using the STAR detector at RHIC. The masses and widths of these
resonances are studied as a function of transverse momentum (). We observe
that the resonance spectra follow a generalized scaling law with the transverse
mass (). The of , , and . The , ,
, , and ratios in
+Au collisions are compared to the measurements in minimum bias
interactions, where we observe that both measurements are comparable. The
nuclear modification factors () of the , , and
scale with the number of binary collisions () for 1.2 GeV/.Comment: STAR Collaboration. Submitted to PR
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Are Nested Networks More Robust to Disturbance? A Test Using Epiphyte-Tree, Comensalistic Networks
Recent research on ecological networks suggests that mutualistic networks are
more nested than antagonistic ones and, as a result, they are more robust
against chains of extinctions caused by disturbances. We evaluate whether
mutualistic networks are more nested than comensalistic and antagonistic
networks, and whether highly nested, host-epiphyte comensalistic networks fit
the prediction of high robustness against disturbance. A review of 59 networks
including mutualistic, antagonistic and comensalistic relationships showed that
comensalistic networks are significantly more nested than antagonistic and
mutualistic networks, which did not differ between themselves. Epiphyte-host
networks from old-growth forests differed from those from disturbed forest in
several topological parameters based on both qualitative and quantitative
matrices. Network robustness increased with network size, but the slope of this
relationship varied with nestedness and connectance. Our results indicate that
interaction networks show complex responses to disturbances, which influence
their topology and indirectly affect their robustness against species
extinctions
Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV
We report on the observed differences in production rates of strange and
multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp
interactions at the same energy. The strange baryon yields in Au+Au collisions,
then scaled down by the number of participating nucleons, are enhanced relative
to those measured in pp reactions. The enhancement observed increases with the
strangeness content of the baryon, and increases for all strange baryons with
collision centrality. The enhancement is qualitatively similar to that observed
at lower collision energy sqrts =17.3 GeV. The previous observations are for
the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange
baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR
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