246 research outputs found
Prestressed vibrations of partially filled tanks containing a free-surface fluid: finite element and reduced order models
In linear vibration analysis of partially filled elastic tanks [1], even if the the structure is submitted by a gaz or a liquid pressure, the reference configuration is generally used without the effect of static loads. In the case of very thin structures or soft material, the static state is considered as prestressed, due to geometrical nonlinearities of the deformed tank. The global stiffness of the structure may change in function of the fluid volume amount [2, 3, 4]. The aim of the paper is to quantify the prestressed effets on the linearized dynamic behavior of the fluid-structure system. The chosen methodology is the following: (i) A quasi-static solution is computed from an empty to a fully filled state of the tank, by considering geometrical nonlinearities and hydrostatic follower forces [5] (no volumetric mesh of the fluid is needed for this step); (ii) after a volumetric remeshing of the fluid at each states, a linearized hydroelastic displacement-pressure formulation around the prestressed state, without gravity effects, is established; (iii) a reduced basis of the hydroelastic problem is generated by using prestressed dry modes to minimize the computation of the added mass matrix. Numerical examples are given to illustrate the proposed approaches
Effects of solar activity on noise in CALIOP profiles above the South Atlantic Anomaly
We show that nighttime dark noise measurements from the spaceborne lidar
CALIOP contain valuable information about the evolution of upwelling
high-energy radiation levels. Above the South Atlantic Anomaly (SAA), CALIOP
dark noise levels fluctuate by ±6% between 2006 and 2013, and follow
the known anticorrelation of local particle flux with the 11-year cycle of
solar activity (with a 1-year lag). By analyzing the geographic distribution
of noisy profiles, we are able to reproduce known findings about the SAA
region. Over the considered period, it shifts westward by
0.3° year<sup>−1</sup>, and changes in size by 6° meridionally and
2° zonally, becoming larger with weaker solar activity. All results are
in strong agreement with previous works. We predict SAA noise levels will
increase anew after 2014, and will affect future spaceborne lidar missions
most near 2020
Projection-based reduced order model for prestressed hydroelastic vibrations
In aerospace industry, the computations of liquid-propelled launchers vibrations are based on linear elastic tanks coupled with an inviscid, incompressible fluid with free surface. In this specific case, the fluctuation of pressure on the free surface is supposed to be zero (i.e. the sloshing effects are neglected). Those vibrations are usually called hydroelastic vibrations. The discretized finite element dynamic problem is commonly expressed only in terms of displacements considering an added mass matrix, which represents the kinetic energy of the moving liquid expressed in terms of normal displacement interface. Those computations can be performed for various fluid level configurations, but no prestressing from geometrical nonlinearity is usually considered [1]. In the present study, the evaluation of the prestressed state influence on the coupled fluid structure vibrations is estimated numerically. This prestressing is supposed to be due to a gas or liquid pressurization, acting on the internal surface of the tank, inducing relatively large static displacement compared to the tank thickness. In reference [2], we have evaluated efficiently and accurately the nonlinear displacements for various filling rate with the use of an original level-set approach. We present here the hydroelastic vibrations around each known prestressed state corresponding to different level of liquid with the use of the added mass matrix. Using the open-source computing finite element platform FEniCS [3], numerical results are in very good agreements with experimental studies from the literature [4]. Comparisons with and without prestressing illustrates the contribution of the efect. To overcome an expensive added mass matrix computation, an appropriate reduced order model obtained by projection on prestressed dry modes is also proposed and show very encouraging results
A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapour and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system
A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour profiles and cirrus cloud using a preliminary Raman channels setup on an existing Rayleigh lidar above La Reunion over the period 2002–2005. With this instrument, we performed a first measurement campaign of 350 independent water vapour profiles. A statistical study of the distribution of water vapour profiles is presented and some investigations concerning the calibration are discussed. Analysis regarding the cirrus clouds is presented and a classification has been performed showing 3 distinct classes. Based on these results, the characteristics and the design of a future lidar system, to be implemented at the new Reunion Island altitude observatory (2200 m) for long-term monitoring, is presented and numerical simulations of system performance have been realised to compare both instruments
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Attempted re-establishment of a sooty tern Onychoprion fuscatus breeding colony on Denis Island, Seychelles
Seychelles supports around three million nesting pairs of sooty terns. However, there have been recent declines and the colonies continue to face ongoing threats from habitat change and excessive commercial harvesting of their eggs, as well as potential threats by commercial fishing and climate change. A possible method to counter these threats is to re-establish breeding colonies on islands from which they have disappeared. An attempt was made to attract birds to a previously occupied island through habitat management, decoy birds and playback of recorded sooty tern calls. Habitat preparation involved predator eradication and tree removal to provide open ground with bare sandy areas and low herb vegetation. Overflying birds were attracted by broadcast calls, with some circling over and landing among the decoys. Large three-dimensional plastic models were superior to other models presented. This study demonstrated that large numbers of birds can be attracted by these means and that the birds then undertook behaviour associated with breeding, including egg laying by a few birds. However, after five seasons a breeding colony has not yet been established; one possible cause is the emergence of unexpected egg predators, common moorhen Gallinula chloropus and common myna Acridotheres tristis
2022 Update of the consensus on the rational use of antithrombotics and thrombolytics in Veterinary Critical Care (CURATIVE) Domain 1‐ Defining populations at risk
Objectives
To expand the number of conditions and interventions explored for their associations with thrombosis in the veterinary literature and to provide the basis for prescribing recommendations.
Design
A population exposure comparison outcome format was used to represent patient, exposure, comparison, and outcome. Population Exposure Comparison Outcome questions were distributed to worksheet authors who performed comprehensive searches, summarized the evidence, and created guideline recommendations that were reviewed by domain chairs. The revised guidelines then underwent the Delphi survey process to reach consensus on the final guidelines. Diseases evaluated in this iteration included heartworm disease (dogs and cats), immune-mediated hemolytic anemia (cats), protein-losing nephropathy (cats), protein-losing enteropathy (dogs and cats), sepsis (cats), hyperadrenocorticism (cats), liver disease (dogs), congenital portosystemic shunts (dogs and cats) and the following interventions: IV catheters (dogs and cats), arterial catheters (dogs and cats), vascular access ports (dogs and cats), extracorporeal circuits (dogs and cats) and transvenous pacemakers (dogs and cats).
Results
Of the diseases evaluated in this iteration, a high risk for thrombosis was defined as heartworm disease or protein-losing enteropathy. Low risk for thrombosis was defined as dogs with liver disease, cats with immune-mediated hemolytic anemia, protein-losing nephropathy, sepsis, or hyperadrenocorticism.
Conclusions
Associations with thrombosis are outlined for various conditions and interventions and provide the basis for management recommendations. Numerous knowledge gaps were identified that represent opportunities for future studies
Direct U–Pb dating of carbonates from micron-scale femtosecond laser ablation inductively coupled plasma mass spectrometry images using robust regression
Uranium–lead (U–Pb) dating of carbonates by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analysis is
an increasingly used method in the field of geosciences, as it brings very
strong constraints over the geological history of basins, faults or
reservoirs. Most ages currently published are based on the measurement of U
and Pb ratios on spot ablations, using nanosecond lasers coupled to
sector field or multi-collector ICP-MS. Here, we test a new strategy for the
U–Pb dating of carbonates from 2D isotopic ratio maps, based on the use of a
robust regression approach in the data reduction workflow. The isotopic
maps, with a minimum area of 0.65 mm2 (∼ 1000 pixels of 13×25 µm resolution), are obtained using a 257 nm femtosecond laser
ablation system at a high repetition rate (500 Hz) coupled to a high-resolution ICP-MS. The maps commonly show significant variations in isotope
ratios at the pixel scale, allowing the plotting of pixel U–Pb ratios in
concordia or isochron diagrams and the calculation of U–Pb ages. Due to the
absence of individual ratio uncertainties, the ages are calculated using
MM-robust linear regression rather than the more commonly used York-type
regression. The goodness of fit to the data is assessed by the calculation
of the residual standard error (RSE) of the regression and by the
calculation of a mean square of weight deviates (MSWD) on discretised data. Several examples are provided
that compare the ages calculated by robust regression with those obtained by
other techniques (e.g. isotope dilution, LA-ICP-MS spot analyses and the pixel-pooling
approach). For most samples, characterised by high U concentrations
(> 1 ppm), robust regression allows for the calculation of ages and
uncertainties similar to those obtained with the other approaches. However,
for samples with lower U concentrations (< 0.5 ppm), the ages
obtained are up to 10 % too young due to pixels with high U ∕ Pb acting as
leverage points for the regression. We conclude that the U–Pb ages
calculated by the regression method tested here, although
statistically robust, should be critically analysed before validation,
especially for samples with low U concentrations.</p
An efficient method to find potentially universal population genetic markers, applied to metazoans
<p>Abstract</p> <p>Background</p> <p>Despite the impressive growth of sequence databases, the limited availability of nuclear markers that are sufficiently polymorphic for population genetics and phylogeography and applicable across various phyla restricts many potential studies, particularly in non-model organisms. Numerous introns have invariant positions among kingdoms, providing a potential source for such markers. Unfortunately, most of the few known EPIC (Exon Primed Intron Crossing) loci are restricted to vertebrates or belong to multigenic families.</p> <p>Results</p> <p>In order to develop markers with broad applicability, we designed a bioinformatic approach aimed at avoiding multigenic families while identifying intron positions conserved across metazoan phyla. We developed a program facilitating the identification of EPIC loci which allowed slight variation in intron position. From the <it>Homolens </it>databases we selected 29 gene families which contained 52 promising introns for which we designed 93 primer pairs. PCR tests were performed on several ascidians, echinoderms, bivalves and cnidarians. On average, 24 different introns per genus were amplified in bilaterians. Remarkably, five of the introns successfully amplified in all of the metazoan genera tested (a dozen genera, including cnidarians). The influence of several factors on amplification success was investigated. Success rate was not related to the phylogenetic relatedness of a taxon to the groups that most influenced primer design, showing that these EPIC markers are extremely conserved in animals.</p> <p>Conclusions</p> <p>Our new method now makes it possible to (i) rapidly isolate a set of EPIC markers for any phylum, even outside the animal kingdom, and thus, (ii) compare genetic diversity at potentially homologous polymorphic loci between divergent taxa.</p
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