685 research outputs found
30 Doradus - a Template for "Real Starbursts"?
30 Doradus is the closest massive star forming region and the best studied
template of a starburst. In this conference paper we first summarize the
properties of 30 Doradus and its stellar core, R136. We discuss the effects of
insufficient spatial resolution and cluster density profiles on dynamical mass
estimates of super star clusters, and show that their masses can be easily
overestimated by a factor of ten or more. From a very simple model, with
R136-like clusters as representative building blocks, we estimate typical
luminosities of the order 10^11 L_o for starburst galaxies.Comment: To be published in "Starbursts: From 30 Doradus to Lyman Break
Galaxies", eds. R. de Grijs & R.M. Gonzalez Delgad
Bullying behaviors and victimization experiences among adolescent students: the role of resilience
The role of resilience in the relationship between bullying behaviours, victimisation experiences, and self-efficacy was examined. Three hundred and 93 (191 male, 202 female) adolescents (mean age = 15.88, SD = .64) from schools in Coimbatore, India completed scales to assess bullying behaviours and victimisation experiences, resilience, and self-efficacy. Multigroup SEM, with separate groups created according to participant sex, revealed that resilience mediated the relationship between bullying behaviours and self-efficacy in males. Males engaged in bullying behaviours and experienced victimisation more frequently than females. The findings of the study have implication for designing intervention programs to enhance resilience among adolescents and young adults to enable them to manage bullying behaviours
Vacuum creation of quarks at the time scale of QGP thermalization and strangeness enhancement in heavy-ion collisions
The vacuum parton creation in quickly varying external fields is studied at
the time scale of order 1 fm/ typical for the quark-gluon plasma formation
and thermalization. To describe the pre-equilibrium evolution of the system the
transport kinetic equation is employed. It is shown that the dynamics of
production process at times comparable with particle inverse masses can deviate
considerably from that based on classical Schwinger-like estimates for
homogeneous and constant fields. One of the effects caused by non-stationary
chromoelectric fields is the enhancement of the yield of quark
pairs. Dependence of this effect on the shape and duration of the field pulse
is studied together with the influence of string fusion and reduction of quark
masses.Comment: REVTEX, 11pp. incl. 4 figures, to be published in Phys. Lett.
Elliptic flow at collider energies and cascade string models: The role of hard processes and multi-Pomeron exchanges
Centrality, rapidity, and transverse momentum dependence of hadron elliptic
flow is studied in Au+Au collisions at BNL RHIC energies within the microscopic
quark-gluon string model. The QGSM predictions coincide well with the
experimental data at AGeV. Further investigations reveal that
multi-Pomeron exchanges and hard gluon-gluon scattering in primary collisions,
accompanied by the rescattering of hadrons in spatially anisotropic system, are
the key processes needed for an adequate description of the data. These
processes become essentially important for heavy-ion collisions at full RHIC
energy AGeV.Comment: LATEX, 12 pages incl. 4 figures, to be published in Phys. Lett.
Transition to meson-dominated matter at RHIC. Consequences for kaon flow
Anisotropic flow of kaons and antikaons is studied in heavy-ion collisions at
CERN SPS and BNL RHIC energies within the microscopic quark-gluon string model.
In the midrapidity range the directed flow of kaons v_1 differs considerably
from that of antikaons at SPS energy (E_{lab} = 160 AGeV), while at RHIC energy
(\sqrt{s} = 130 AGeV) the excitation functions of both, kaon and antikaon,
flows coincide within the statistical error bars. The change is attributed to
formation of dense meson-dominated matter at RHIC, where the differences in
interaction cross-sections of kaons and antikaons become unimportant. The time
evolution of the kaon anisotropic flow is also investigated. The elliptic flow
of these hadrons is found to develop at midrapidity at times 3 < t < 10 fm/c,
which is much larger than the nuclear passing time t^{pass} = 0.12 fm/c. As a
function of transverse momentum the elliptic flow increases almost linearly
with rising p_t. It stops to rise at p_t > 1.5 GeV/c reaching the saturation
value .Comment: REVTEX, 14 pages, 4 figure
Preschool Children and Behaviour Problems: A Prospective Study
Toddler/child behaviour problems have received relatively little previous attention. Prior studies have implicated a wide variety of factors in the aetiology of child behaviour problems but many of these factors are correlated and little is known about their independent contributions. Four broad categories of factors have been associated with child behaviour problems: (1) maternal social and economic characteristics; (2) maternal lifestyle; (3) maternal mental state/child-rearing practices; and (4) maternal and child physical health. The study took a sample of 5296 families from the Mater-University of Queensland Study of Pregnancy (MUSP) for whom 5-year prospective data are available. The major predictors of toddler behaviour problems were the mother's and child's health, and the mother's mental state. The mother's sociostructural characteristics and lifestyle made little or no additional contribution to the prediction models. It is, however, salutary to note that the majority of children who are classified as having high levels of troublesome behaviour do not fall into any of the risk categories. A variety of explanations and interpretations of the data is considered
Homogeneous nucleation of quark-gluon plasma, finite size effects and long-lived metastable objects
The general formalism of homogeneous nucleation theory is applied to study
the hadronization pattern of the ultra-relativistic quark-gluon plasma (QGP)
undergoing a first order phase transition. A coalescence model is proposed to
describe the evolution dynamics of hadronic clusters produced in the nucleation
process. The size distribution of the nucleated clusters is important for the
description of the plasma conversion. The model is most sensitive to the
initial conditions of the QGP thermalization, time evolution of the energy
density, and the interfacial energy of the plasma-hadronic matter interface.
The rapidly expanding QGP is first supercooled by about . Then it reheats again up to the critical temperature T_c. Finally it
breaks up into hadronic clusters and small droplets of plasma. This fast
dynamics occurs within the first . The finite size effects and
fluctuations near the critical temperature are studied. It is shown that a drop
of longitudinally expanding QGP of the transverse radius below 4.5 fm can
display a long-lived metastability. However, both in the rapid and in the
delayed hadronization scenario, the bulk pion yield is emitted by sources as
large as 3-4.5 fm. This may be detected experimentally both by a HBT
interferometry signal and by the analysis of the rapidity distributions of
particles in narrow p_T-intervals at small p_T on an event-by-event basis.Comment: 29 pages, incl. 12 figures and 1 table; to be published in Phys. Rev.
The functional role of biodiversity in ecosystems: incorporating trophic complexity
Understanding how biodiversity affects functioning of ecosystems requires integrating diversity within trophic levels (horizontal diversity) and across trophic levels (vertical diversity, including food chain length and omnivory). We review theoretical and experimental progress toward this goal. Generally, experiments show that biomass and resource use increase similarly with horizontal diversity of either producers or consumers. Among prey, higher diversity often increases resistance to predation, due to increased probability of including inedible species and reduced efficiency of specialist predators confronted with diverse prey. Among predators, changing diversity can cascade to affect plant biomass, but the strength and sign of this effect depend on the degree of omnivory and prey behaviour. Horizontal and vertical diversity also interact: adding a trophic level can qualitatively change diversity effects at adjacent levels. Multitrophic interactions produce a richer variety of diversity‐functioning relationships than the monotonic changes predicted for single trophic levels. This complexity depends on the degree of consumer dietary generalism, trade‐offs between competitive ability and resistance to predation, intraguild predation and openness to migration. Although complementarity and selection effects occur in both animals and plants, few studies have conclusively documented the mechanisms mediating diversity effects. Understanding how biodiversity affects functioning of complex ecosystems will benefit from integrating theory and experiments with simulations and network‐based approaches
Pond canopy cover: a resource gradient for anuran larvae
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72395/1/j.1365-2427.2005.01497.x.pd
Dynamic screening in solar and stellar nuclear reactions
In the hot, dense plasma of solar and stellar interiors, the Coulomb
interaction is screened by the surrounding plasma. Although the standard
Salpeter approximation for static screening is widely accepted and used in
stellar modeling, the question of dynamic screening has been revisited. In
particular, Shaviv and Shaviv apply the techniques of molecular dynamics to the
conditions in the solar core in order to numerically determine the dynamic
screening effect. By directly calculating the motion of ions and electrons due
to Coulomb interactions, they compute the effect of screening without the
mean-field assumption inherent in the Salpeter approximation. Here we reproduce
their numerical analysis of the screening energy in the plasma of the solar
core and conclude that the effects of dynamic screening are relevant and should
be included in the treatment of the plasma, especially in the computation of
stellar nuclear reaction rates.Comment: Astrophysics and Space Science, Special Issue Solar & Stellar
Modelling Corrected sign error. Now consistent with final published versio
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