3,872 research outputs found
Wavelet transforms and their applications to MHD and plasma turbulence: a review
Wavelet analysis and compression tools are reviewed and different
applications to study MHD and plasma turbulence are presented. We introduce the
continuous and the orthogonal wavelet transform and detail several statistical
diagnostics based on the wavelet coefficients. We then show how to extract
coherent structures out of fully developed turbulent flows using wavelet-based
denoising. Finally some multiscale numerical simulation schemes using wavelets
are described. Several examples for analyzing, compressing and computing one,
two and three dimensional turbulent MHD or plasma flows are presented.Comment: Journal of Plasma Physics, 201
Substructure recovery by 3D Discrete Wavelet Transforms
We present and discuss a method to identify substructures in combined
angular-redshift samples of galaxies within Clusters. The method relies on the
use of Discrete Wavelet Transform (hereafter DWT) and has already been applied
to the analysis of the Coma cluster (Gambera et al. 1997). The main new
ingredient of our method with respect to previous studies lies in the fact that
we make use of a 3D data set rather than a 2D. We test the method on mock
cluster catalogs with spatially localized substructures and on a N-body
simulation. Our main conclusion is that our method is able to identify the
existing substructures provided that: a) the subclumps are detached in part or
all of the phase space, b) one has a statistically significant number of
redshifts, increasing as the distance decreases due to redshift distortions; c)
one knows {\it a priori} the scale on which substructures are to be expected.
We have found that to allow an accurate recovery we must have both a
significant number of galaxies ( for clusters at z or
about 800 at z 0.4) and a limiting magnitude for completeness .
The only true limitation to our method seems to be the necessity of knowing
{\it a priori} the scale on which the substructure is to be found. This is an
intrinsic drawback of the method and no improvement in numerical codes based on
this technique could make up for it.Comment: Accepted for publication in MNRAS. 7 pages, 2 figure
Conditional vorticity budget of coherent and incoherent flow contributions in fully developed homogeneous isotropic turbulence
We investigate the conditional vorticity budget of fully developed
three-dimensional homogeneous isotropic turbulence with respect to coherent and
incoherent flow contributions. The Coherent Vorticity Extraction based on
orthogonal wavelets allows to decompose the vorticity field into coherent and
incoherent contributions, of which the latter are noise-like. The impact of the
vortex structures observed in fully developed turbulence on statistical balance
equations is quantified considering the conditional vorticity budget. The
connection between the basic structures present in the flow and their
statistical implications is thereby assessed. The results are compared to those
obtained for large- and small-scale contributions using a Fourier
decomposition, which reveals pronounced differences
A Multiresolution Census Algorithm for Calculating Vortex Statistics in Turbulent Flows
The fundamental equations that model turbulent flow do not provide much
insight into the size and shape of observed turbulent structures. We
investigate the efficient and accurate representation of structures in
two-dimensional turbulence by applying statistical models directly to the
simulated vorticity field. Rather than extract the coherent portion of the
image from the background variation, as in the classical signal-plus-noise
model, we present a model for individual vortices using the non-decimated
discrete wavelet transform. A template image, supplied by the user, provides
the features to be extracted from the vorticity field. By transforming the
vortex template into the wavelet domain, specific characteristics present in
the template, such as size and symmetry, are broken down into components
associated with spatial frequencies. Multivariate multiple linear regression is
used to fit the vortex template to the vorticity field in the wavelet domain.
Since all levels of the template decomposition may be used to model each level
in the field decomposition, the resulting model need not be identical to the
template. Application to a vortex census algorithm that records quantities of
interest (such as size, peak amplitude, circulation, etc.) as the vorticity
field evolves is given. The multiresolution census algorithm extracts coherent
structures of all shapes and sizes in simulated vorticity fields and is able to
reproduce known physical scaling laws when processing a set of voriticity
fields that evolve over time
Rose - Buds : Intermezzo - Redowa
https://digitalcommons.library.umaine.edu/mmb-ps/2124/thumbnail.jp
Dance Of The Daisies : Intermezzo
https://digitalcommons.library.umaine.edu/mmb-ps/1472/thumbnail.jp
Effects of condensed tannins on established populations and on incoming larvae of Trichostrongylus colubriformis and Teladorsagia circumcincta in goats
The use of tanniferous plants or tannins represents one alternative approach to the
control of gastrointestinal parasites in ruminants but most data have been obtained in sheep. The
current study was therefore performed in goats with two objectives: firstly, to investigate the effects
of condensed tannins (CT) on adult populations of Trichostrongylus colubriformis and Teladorsagia
circumcincta; secondly, to examine their effects on the establishment of infective larvae of these
two species. In experiment 1, two groups of kids were infected with 6 000 L3 of T. colubriformis
and 6 000 L3 of T. circumcincta. After 7 weeks, quebracho extracts were administered per os for
8 days to one group. A comparable group which did not receive tannins was included as the control.
The kids were slaughtered on week 11. Parasitological and pathophysiological parameters were
measured weekly. Worm counts were assessed and mast cells, globule leukocytes and eosinophils
were counted in the abomasal and intestinal mucosae. Tannin administration was associated with a
decrease in egg excretion, and a decrease in female fecundity, but with no changes in worm numbers.
These changes were associated with an increased number of intestinal mast cells. In experiment
2, 24 goats were used according to a 2 2 factorial design, depending on infection and tannin
administration. Two groups were either infected with 6 000 L3 of T. colubriformis or T. circumcincta.
Within each group, the goats were either drenched or undrenched with tannin extracts.
Pathophysiological parameters were measured weekly. Twelve days after the cessation of tannin
administration, the goats were slaughtered. Worm counts and female worm fecundity were determined.
Tannin consumption was associated with a significant reduction (P < 0.001) of Trichostrongylus
populations and a close to significant reduction for Teladorsagia. No effect on fecundity
was observed. Our results (1) confirm the consequences of condensed tannins on nematodes in goats
as in sheep and (2) indicate divergent effects depending on the parasitic stage exposed to the condensed
tannins
Effects of the repeated distribution of sainfoin hay on the resistance and the resilience of goats naturally infected with gastrointestinal nematodes
Due to the high prevalence of anthelmintic resistance in goats, the need to explore novel approaches to control nematodes and
to reduce the exclusive reliance on chemotherapy is strongly demanded in this host species. In sheep, several studies have shown
that the consumption of tannin-rich legume forages was associated with positive effects on host resilience and resistance to
parasite infection. In goats, studies on such interactions between tanniferous plants and nematode infections remain few. The
objectives of the current study were to examine under natural conditions the effects of consumption of sainfoin hay by goats on
the parasite populations and on host resilience.
Eighteen adult cull goats naturally infected with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus
colubriformis were used in the study. At the start of the assay, the goats were allocated into two groups, balanced according to
weight and the levels of egg excretion. The two groups grazed separate pastures for 3 months with similar stocking rates. Goats
from group S received each month indoors, for 7 days, sainfoin hay and control goats (group C) received hay of ryegrass. The
diets in both groups were made isoenergetic and isoproteic and the refusals measured. Individual parasitological and
pathophysiological measurements were performed fortnightly in order to compare host resistance and resilience. At the
end of the study, five goats per group were necropsied. The distribution of sainfoin was associated with: (1) a higher consumption
of hay; (2) significant, lower levels of nematode egg excretion which was associated with a decrease in worm fertility but no
change in worm population; however, the number of intestinal worms was reduced by 50% in group S; (3) a better host
resilience. In particular, after 2 months of grazing, two control goats died and half of the remaining animals needed to be treated
whereas this was not the case in group S. These differences were related to significant changes in pepsinogen and phosphate
values (PCV) but not in pepsinogen and phosphate concentrations. These results demonstrate that a repeated distribution of
sainfoin hay to grazing goats might be beneficial in regard of pasture contamination and host resilience. They suggest that
administration of sainfoin hay might represent a valuable alternative and adjunct to reduce nematode infections in dairy goat flock.
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