907 research outputs found
Scaling state of dry two-dimensional froths: universal angle deviations and structure
We characterize the late-time scaling state of dry, coarsening,
two-dimensional froths using a detailed, force-based vertex model. We find that
the slow evolution of bubbles leads to systematic deviations from 120degree
angles at three-fold vertices in the froth, with an amplitude proportional to
the vertex speed, v ~ sqrt(t), but with a side-number dependence that is
independent of time. We also find that a significant number of T1
side-switching processes occur for macroscopic bubbles in the scaling state,
though most bubble annihilations involve four-sided bubbles at microscopic
scales.Comment: 7 pages, 7 figure
Star-forming galaxies in low-redshift clusters: Effects of environment on the concentration of star formation
We attempt to determine the dominant processes acting on star-forming disk
galaxies as a result of the cluster environment by studying the normalised
rates and radial distributions of star formation in galaxies within
low-redshift clusters. We develop indicators of different processes based on
the radial concentrations of R-band and H alpha light within each of the
galaxies studied. The tests are applied to galaxies in each of 3 environments -
cluster, supercluster (outside the cluster virial radius) and field. We develop
new diagnostic diagrams combining star-formation rate and spatial distribution
information to differentiate between stripping of outer disk gas, general gas
depletion, nuclear starbursts and galaxy-wide enhancement of star formation.
Hubble type classifications of cluster galaxies are found to correlate only
weakly with their concentration indices, whereas this correlation is strong for
non-cluster populations of disk galaxies. We identify a population of
early-type disk galaxies in the cluster population with both enhanced and
centrally-concentrated star formation compared to their field counterparts. The
enhanced cluster galaxies frequently show evidence of disturbance. A small but
non-negligible population of cluster galaxies with truncation of star formation
in their outer disks is also found.Comment: 14 pages, 16 figures; accepted for publication in Astronomy and
Astrophysic
The EU and Asia within an evolving global order: what is Europe? Where is Asia?
The papers in this special edition are a very small selection from those presented at the EU-NESCA (Network of European Studies Centres in Asia) conference on "the EU and East Asia within an Evolving Global Order: Ideas, Actors and Processes" in November 2008 in Brussels. The conference was the culmination of three years of research activity involving workshops and conferences bringing together scholars from both regions primarily to discuss relations between Europe and Asia, perceptions of Europe in Asia, and the relationship between the European regional project and emerging regional forms in Asia. But although this was the last of the three major conferences organised by the consortium, it in many ways represented a starting point rather than the end; an opportunity to reflect on the conclusions of the first phase of collaboration and point towards new and continuing research agendas for the future
Angular momentum transport by internal gravity waves III - Wave excitation by core convection and the Coriolis effect
This is the third in a series of papers that deal with angular momentum
transport by internal gravity waves. We concentrate on the waves excited by
core convection in a 3Msun, Pop I main sequence star. Here, we want to examine
the role of the Coriolis acceleration in the equations of motion that describe
the behavior of waves and to evaluate its impact on angular momentum transport.
We use the so-called traditional approximation of geophysics, which allows
variable separation in radial and horizontal components. In the presence of
rotation, the horizontal structure is described by Hough functions instead of
spherical harmonics. The Coriolis acceleration has two main effects on waves.
It transforms pure gravity waves into gravito-inertial waves that have a larger
amplitude closer to the equator, and it introduces new waves whose restoring
force is mainly the conservation of vorticity. Taking the Coriolis acceleration
into account changes the subtle balance between prograde and retrograde waves
in non-rotating stars. It also introduces new types of waves that are either
purely prograde or retrograde. We show in this paper where the local deposition
of angular momentum by such waves is important.Comment: 9 pages, 10 figures, accepted for publication by A&
Ozone depletion, greenhouse gases, and climate change
This symposium was organized to study the unusual convergence of a number of observations, both short and long term that defy an integrated explanation. Of particular importance are surface temperature observations and observations of upper atmospheric temperatures, which have declined significantly in parts of the stratosphere. There has also been a dramatic decline in ozone concentration over Antarctica that was not predicted. Significant changes in precipitation that seem to be latitude dependent have occurred. There has been a threefold increase in methane in the last 100 years; this is a problem because a source does not appear to exist for methane of the right isotopic composition to explain the increase. These and other meteorological global climate changes are examined in detail
The role of tank-treading motions in the transverse migration of a spheroidal vesicle in a shear flow
The behavior of a spheroidal vesicle, in a plane shear flow bounded from one
side by a wall, is analysed when the distance from the wall is much larger than
the spheroid radius. It is found that tank treading motions produce a
transverse drift away from the wall, proportional to the spheroid eccentricity
and the inverse square of the distance from the wall. This drift is independent
of inertia, and is completely determined by the characteristics of the vesicle
membrane. The relative strength of the contribution to drift from tank-treading
motions and from the presence of inertial corrections, is discussed.Comment: 16 pages, 1 figure, Latex. To appear on J. Phys. A (Math. Gen.
Periodic and Quasiperiodic Motion of an Elongated Microswimmer in Poiseuille Flow
We study the dynamics of a prolate spheroidal microswimmer in Poiseuille flow
for different flow geometries. When moving between two parallel plates or in a
cylindrical microchannel, the swimmer performs either periodic swinging or
periodic tumbling motion. Although the trajectories of spherical and elongated
swimmers are qualitatively similar, the swinging and tumbling frequency
strongly depends on the aspect ratio of the swimmer. In channels with reduced
symmetry the swimmers perform quasiperiodic motion which we demonstrate
explicitely for swimming in a channel with elliptical cross section
- …