4,185 research outputs found
Impact of microphysics on the growth of one-dimensional breath figures
Droplet patterns condensing on solid substrates (breath figures) tend to
evolve into a self-similar regime, characterized by a bimodal droplet size
distribution. The distributions comprise a bell-shaped peak of monodisperse
large droplets, and a broad range of smaller droplets. The size distribution of
the latter follows a scaling law characterized by a non-trivial polydispersity
exponent. We present here a numerical model for three-dimensional droplets on a
one-dimensional substrate (fiber) that accounts for droplet nucleation, growth
and merging. The polydispersity exponent retrieved using this model is not
universal. Rather it depends on the thickness of the fiber and on details of
the droplet interaction leading to merging. In addition, its values
consistently differ from the theoretical prediction by Blackman (Phys. Rev.
Lett., 2000). Possible causes of this discrepancy are pointed out
Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438
Ram pressure stripping of the multiphase ISM is studied in the perturbed
Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction
~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA
radio continuum observations at 6 and 20 cm are presented. We detect prominent
extraplanar emission to the west of the galactic center, which extends twice as
far as the other tracers of extraplanar material. The spectral index of the
extraplanar emission does not steepen with increasing distance from the galaxy.
This implies in situ re-acceleration of relativistic electrons. The comparison
with multiwavelength observations shows that the magnetic field and the warm
ionized interstellar medium traced by Halpha emission are closely linked. The
kinematics of the northern extraplanar Halpha emission, which is ascribed to
star formation, follow those of the extraplanar CO emission. In the western and
southern extraplanar regions, the Halpha measured velocities are greater than
those of the CO lines. We suggest that the ionized gas of this region is
excited by ram pressure. The spatial and velocity offsets are consistent with a
scenario where the diffuse ionized gas is more efficiently pushed by ram
pressure stripping than the neutral gas. We suggest that the recently found
radio-deficient regions compared to 24 mum emission are due to this difference
in stripping efficiency.Comment: 8 pages, 6 figures, A&A, accepted for publicatio
Simultaneous epidemic development of scald and net blotch on single leaf layers of a spring barley crop
Background and objectives
Two pathogens growing on the same leaf compete for the same resources, i.e. space and plant nutrients. This may lead to density dependent disease development. The pathogens may also influence each other directly such that the influence of one on the other is more complex than a simple function of the area of the other pathogen. Different interaction types are, for example, competition, mutualism and exploitation. The importance of such interactions for epidemics of simultaneously occurring pathogens has received little attention. The objective of this study is to investigate the simultaneous epidemic development of Rhynchosporium secalis (causing scald) and Drechslera teres (causing net blotch) on spring barley under field conditions.
Materials and methods
The field trial was performed with artificial inoculation of R. secalis and D. teres on three spring barley varieties differing in their susceptibility towards the pathogens. The pathogens were inoculated in three combinations: only one was inoculated, they were inoculated together, the second pathogen was inoculated 26 days after the first. A non-inoculated treatment was included. The trial had three replications. Nine plants were harvested from each plot five times during the season. Leaves were dried and disease severity and senescence observed. Only leaves with < 50 % senescence were included in the analysis.
Whole-plant disease severity over time was calculated as average of disease severity on leaves weighted by leaf area. Disease development per leaf layer was evaluated by fitting an exponential model to severity data over time for each leaf layer per variety, treatment and replicate. Association between scald and net blotch severity on individual leaves was analysed using Kendall’s tau.
Results and discussion
Net blotch developed on all leaf layers and reached whole-plant disease severities up to 15%. Scald did not develop on upper leaf layers and whole-plant severity was less than 2%. Disease severity curves at whole-plant level showed no effect of inoculating the other pathogen. The analysis of the growth rate of each disease per leaf layer showed a significant effect of variety and leaf layer within variety but no effect of treatment. However, we observed significant negative associations between the diseases on individual leaves for several combinations of leaf layer and variety. These results show that the individual leaf approach can provide new information and underline the importance of considering interactions between pathogens in the field.
Acknowledgement
This work was funded by the DARCOF II project BAR-O
Peli1 facilitates virus replication and promotes neuroinflammation during West Nile virus infection
The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies
We investigate the influence of ram-pressure stripping on the internal gas
kinematics of simulated spiral galaxies. Additional emphasis is put on the
question of how the resulting distortions of the gaseous disc are visible in
the rotation curve and/or the full 2D velocity field of galaxies at different
redshifts. A Milky-Way type disc galaxy is modelled in combined
N-body/hydrodynamic simulations with prescriptions for cooling, star formation,
stellar feedback, and galactic winds. This model galaxy moves through a
constant density and temperature gas, which has parameters similar to the
intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields of the
gas are extracted from these simulations in a way that follows the procedure
applied to observations of distant, small, and faint galaxies as closely as
possible. We find that the appearance of distortions of the gaseous disc due to
ram-pressure stripping depends on the direction of the acting ram pressure. In
the case of face-on ram pressure, the distortions mainly appear in the outer
parts of the galaxy in a very symmetric way. In contrast, in the case of
edge-on ram pressure we find stronger distortions. The 2D velocity field also
shows signatures of the interaction in the inner part of the disc. At angles
smaller than 45 degrees between the ICM wind direction and the disc, the
velocity field asymmetry increases significantly compared to larger angles.
Compared to distortions caused by tidal interactions, the effects of
ram-pressure stripping on the velocity field are relatively low in all cases
and difficult to observe at intermediate redshift in seeing-limited
observations. (abridged)Comment: 9 pages, 11 figures, accepted for publication in A&
Undergraduate and Graduate Students’ Retrospective Perception of Flipped Learning in Dietetics Curricula
Most studies investigating flipped learning fail to assess how student perceptions of flipped learning may change once the class is complete, and students have a chance to reflect on the experience. Follow-up studies are needed to evaluate the sustainability of the benefits from flipped learning among students and how they feel it prepares them, if at all, for future classes and/or their professional lives. Therefore, the objective of this study was to explore how graduate and undergraduate dietetics students retrospectively perceive a course that used flipped learning 2 years after they completed the course. Two focus groups with undergraduate (n=5) and graduate (n=6) students were conducted regarding their perception and experience in a flipped advanced metabolism class with the same instructor. Content analysis was applied to the focus group transcripts by two investigators. Six themes were discovered from the focus group transcripts: 1) metacognition and the learning process, 2) roles and responsibility for learning, 3) collaborative learning, 4) class experience, 5) adjustment to flipped learning, and 6) flipped learning is conditional. Overall, students felt that the flipped class helped them learn how they learn and they have to put in work to achieve deeper learning. Students thought that the class activities used in a flipped class were engaging, added variety, and allowed them to apply their knowledge. Students reflected that using flipped learning helped them build relationships in their class, created a safe space for questions, and there was more time and opportunities to ask questions vs. traditional lecture
Testing coupled dark energy with next-generation large-scale observations
Coupling dark energy to dark matter provides one of the simplest way to
effectively modify gravity at large scales without strong constraints from
local (i.e. solar system) observations. Models of coupled dark energy have been
studied several times in the past and are already significantly constrained by
cosmic microwave background experiments. In this paper we estimate the
constraints that future large-scale observations will be able to put on the
coupling and in general on all the parameters of the model. We combine cosmic
microwave background, tomographic weak lensing, redshift distortions and power
spectrum probes. We show that next-generation observations can improve the
current constraint on the coupling to dark matter by two orders of magnitude;
this constraint is complementary to the current solar-system bounds on a
coupling to baryons.Comment: 18 pages, 12 figs, 8 table
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). II. Constraints on star formation in ram-pressure stripped gas
Context: Several galaxies in the Virgo cluster are known to have large HI gas
tails related to a recent ram-pressure stripping event. The Virgo cluster has
been extensively observed at 1539 A in the far-ultraviolet for the GALEX
Ultraviolet Virgo Cluster Survey (GUViCS), and in the optical for the Next
Generation Virgo Survey (NGVS), allowing a study of the stellar emission
potentially associated with the gas tails of 8 cluster members. On the
theoretical side, models of ram-pressure stripping events have started to
include the physics of star formation. Aim: We aim to provide quantitative
constraints on the amount of star formation taking place in the ram-pressure
stripped gas, mainly on the basis of the far-UV emission found in the GUViCS
images in relation with the gas content of the tails. Methods: We have
performed three comparisons of the young stars emission with the gas column
density: visual, pixel-by-pixel and global. We have compared our results to
other observational and theoretical studies. Results: We find that the level of
star formation taking place in the gas stripped from galaxies by ram-pressure
is low with respect to the available amount of gas. Star formation is lower by
at least a factor 10 compared to the predictions of the Schmidt Law as
determined in regular spiral galaxy disks. It is also lower than measured in
dwarfs galaxies and the outer regions of spirals, and than predicted by some
numerical simulations. We provide constraints on the star formation efficiency
in the ram-pressure stripped gas tails, and compare these with current models.Comment: Accepted in A&A, 17 pages (including the appendix and "on-line"
figures of the paper
Challenges and Opportunities of Superhydrophobic/Superamphiphobic Coatings in Real Applications
A multibaker map for shear flow and viscous heating
A consistent description of shear flow and the accompanied viscous heating as
well the associated entropy balance is given in the framework of a
deterministic dynamical system. A laminar shear flow is modeled by a
Hamiltonian multibaker map which drives velocity and temperature fields. In an
appropriate macroscopic limit one recovers the Navier-Stokes and heat
conduction equations along with the associated entropy balance. This indicates
that results of nonequilibrium thermodynamics can be described by means of an
abstract, sufficiently chaotic and mixing dynamics. A thermostating algorithm
can also be incorporated into this framework.Comment: 11 pages; RevTex with multicol+graphicx packages; eps-figure
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