1,673 research outputs found
Subproton-scale cascades in solar wind turbulence: driven hybrid-kinetic simulations
A long-lasting debate in space plasma physics concerns the nature of
subproton-scale fluctuations in solar wind (SW) turbulence. Over the past
decade, a series of theoretical and observational studies were presented in
favor of either kinetic Alfv\'en wave (KAW) or whistler turbulence. Here, we
investigate numerically the nature of the subproton-scale turbulent cascade for
typical SW parameters by means of unprecedented high-resolution simulations of
forced hybrid-kinetic turbulence in two real-space and three velocity-space
dimensions. Our analysis suggests that small-scale turbulence in this model is
dominated by KAWs at and by magnetosonic/whistler fluctuations
at lower . The spectral properties of the turbulence appear to be in
good agreement with theoretical predictions. A tentative interpretation of this
result in terms of relative changes in the damping rates of the different waves
is also presented. Overall, the results raise interesting new questions about
the properties and variability of subproton-scale turbulence in the SW,
including its possible dependence on the plasma , and call for detailed
and extensive parametric explorations of driven kinetic turbulence in three
dimensions.Comment: 6 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
Factors influencing consideration of dental specialisation: a survey of current dental students at the University of Western Australia
Aim. At present, little research exists regarding factors that influence dental students and recent graduates to pursue specialist training. Through the provision of a questionnaire, the study investigated student's perceptions of dental specialities and factors impacting specialisation.Methods. Questionnaires (n=65) were undertaken by Doctor of Dental Medicine students in year three (n=34) and four (n=31) through paper means. An analysis was undertaken of the knowledge of speciality courses, speciality preferences and the main motivating and deterring factors influencing specialisation.Results. A response rate of 70% was observed, revealing that 13% of all participants correctly identified the speciality courses available in Western Australia, with 6% of students wanting to specialise in the long term. Altruistic factors were most motivating and financial most deterring when considering specialisation. Speciality preferences also varied between cohorts.Conclusions. Findings highlight that a small proportion of students want to pursue specialisation and the majority of students are unaware of the speciality courses available in Western Australia. This emphasises the need for greater exposure and education in dental specialties. Further research is advised in this field to better understand factors involved in the pathway to dental specialisation and how to encourage specialisation
Mesoscale dynamics on the Sun's surface from HINODE observations
Aims: The interactions of velocity scales on the Sun's surface, from
granulation to supergranulation are still not understood, nor are their
interaction with magnetic fields. We thus aim at giving a better description of
dynamics in the mesoscale range which lies between the two scales mentioned
above. Method: We analyse a 48h high-resolution time sequence of the quiet Sun
photosphere at the disk center obtained with the Solar Optical Telescope
onboard Hinode. The observations, which have a field of view of 100
\arcsec 100 \arcsec, typically contain four supergranules. We monitor
in detail the motion and evolution of granules as well as those of the radial
magnetic field. Results: This analysis allows us to better characterize Trees
of Fragmenting Granules issued from repeated fragmentation of granules,
especially their lifetime statistics. Using floating corks advected by measured
velocity fields, we show their crucial role in the advection of the magnetic
field and in the build up of the network. Finally, thanks to the long duration
of the time series, we estimate that the turbulent diffusion coefficient
induced by horizontal motion is approximately . Conclusions: These results demonstrate that the long living
families contribute to the formation of the magnetic network and suggest that
supergranulation could be an emergent length scale building up as small
magnetic elements are advected and concentrated by TFG flows. Our estimate for
the magnetic diffusion associated with this horizontal motion might provide a
useful input for mean-field dynamo models.Comment: to appear in A&A - 8 pages, 13 figures (degraded quality) - Full
resolution version available @
http://www.ast.obs-mip.fr/users/rincon/hinode_roudier_aa09.pd
Heavy flavor in relativistic heavy-ion collisions
We study charm production in ultra-relativistic heavy-ion collisions by using
the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm
quarks are produced by the PYTHIA event generator tuned to fit the transverse
momentum spectrum and rapidity distribution of charm quarks from Fixed-Order
Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks
scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses
and widths are given by the Dynamical Quasi-Particle Model (DQPM), which
reproduces the lattice QCD equation-of-state in thermal equilibrium. The
relevant cross sections are calculated in a consistent way by employing the
effective propagators and couplings from the DQPM. Close to the critical energy
density of the phase transition, the charm quarks are hadronized into
mesons through coalescence and/or fragmentation. The hadronized mesons then
interact with the various hadrons in the hadronic phase with cross sections
calculated in an effective lagrangian approach with heavy-quark spin symmetry.
The nuclear modification factor and the elliptic flow of
mesons from PHSD are compared with the experimental data from the STAR
Collaboration for Au+Au collisions at =200 GeV and to the ALICE
data for Pb+Pb collisions at =2.76 TeV. We find that in the
PHSD the energy loss of mesons at high can be dominantly attributed
to partonic scattering while the actual shape of versus reflects
the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation.
Also the hadronic rescattering is important for the at low and
enhances the -meson elliptic flow .Comment: 8 pages, 3 figures, to be published in the Proceedings of the 15th
International Conference on Strangeness in Quark Matter (SQM2015), 6-11 July
2015, JINR, Dubna, Russi
Physical Property and Chemical Characteristics of Surface Sediment Grab Samples from Narragansett Bay and the Providence and Seekonk Rivers
This document contains data tables, maps, plots, and documentation on Brown
University’s Narragansett Bay Sediment Project compiled by David W. Murray, Brown
University, for the New England Interstate Water Pollution Control Commission with
support from the U.S. Environmental Protection Agency. The data were compiled and
analyzed as part of a New England pilot project exploring the development of a
biological condition gradient applicable to estuarine systems
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