531 research outputs found
Elevated CO\u3csub\u3e2\u3c/sub\u3e and Extreme Climatic Events Modify Nitrogen Content and Ruminal Protein Digestion of Temperate Grassland
This study was aimed at analyzing changes in nitrogen (N) content and in vitro protein rumen digestion of an upland grassland exposed to climate changes in controlled conditions. Monoliths of grassland were inserted in 12 macrocosms in which climatic conditions for the 2050s were simulated (i.e., +2.3°C and 33 mm less precipitation compared to the current climatic conditions). Six of them were subjected to ambient CO2 (390 ppm) while the other six were subjected to elevated CO2 (520 ppm). After four months, an extreme climatic event (ECE) consisting of four weeks of reducted precipitation (-50%) followed by two weeks without irrigation combined with a heat wave (+6°C) were applied in three macrocosms at ambient CO2 and three macrocosms at elevated CO2. Then, all the macrocosms were irrigated to allow the vegetation to recover. The N content and in vitro parameters of rumen protein digestion were measured on plant samples collected before the extreme event (two cuts) and after recovery. Our results indicate that, irrespective of the sampling date, elevated CO2 results in a decrease in plant N content (P \u3c 0.01). Inversely, the application of the extreme event resulted in a large increase in N content (P \u3c 0.001) without a significant interaction with the CO2 effect. These changes significantly impacted ruminal protein digestion as evidenced by changes in the production of the fermentation end-products indicators of the proteolysis, namely ammonia and iso-volatile fatty acids. We conclude that several components of climate change can impact the nitrogenous quality of the forage and its use by ruminants
The dam-break problem for viscous fluids in the high-capillary-number limit
Experiments were undertaken to investigate dam-break flows where a finite volume of highly viscous fluid (glucose with viscosity ÎŒ â 350 Pa s) maintained behind a lock gate was released into a horizontal or inclined flume. The resulting sequence of flow-depth profiles was tracked using a three-dimensional visualization system. In the low-Reynolds-number and high-capillary-number limits, analytical solutions can be obtained from the Navier-Stokes equations using lubrication theory and matched asymptotic expansions. At shallow slopes, similarity solutions can also be worked out. While the variation in the front position scaled with time as predicted by theory for both horizontal and sloping flumes, there was a systematic delay in the front position observed. Moreover, taking a closer look at the experimental flow-depth profiles shows that they were similar, but they noticeably deviated from the theoretical similarity form for horizontal planes. For sloping beds, the flow-depth profile is correctly predicted provided that different scalings are used at shallow and large slope
Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering
We report a Raman scattering investigation of columnar BiFeO3-CoFe2O4
(BFO-CFO) epitaxial thin film nanostructures, where BFO pillars are embedded in
a CFO matrix. The feasibility of a strain analysis is illustrated through an
investigation of two nanostructures with different BFO-CFO ratios. We show that
the CFO matrix presents the same strain state in both nanostructures, while the
strain state of the BFO pillars depends on the BFO/CFO ratio with an increasing
tensile strain along the out-of-plane direction with decreasing BFO content.
Our results demonstrate that Raman scattering allows monitoring strain states
in complex 3D multiferroic pillar/matrix composites.Comment: revised version submitted to Appl. Phys. Let
Experimental investigation of the spreading of viscoplastic fluids on inclined planes
We report experimental results related to the dam-break problem for viscoplastic fluids. Using image processing techniques, we were able to accurately reconstruct the free-surface evolution of fixed volumes of fluid suddenly released a plane. We used Carbopol Ultrez 10 as a viscoplastic material; its rheological behavior was closely approximated by a Herschel- Bulkley model for a fairly wide range of shear rates. Varying the Carbopol concentration allowed us to change the yield stress and bulk viscosity. The yield stress ranged from 78 to 109 Pa, producing Bingham numbers in the 0.07â0.35 range. We investigated the behavior of a 43-kg mass released on a plane, whose inclination ranged from 0 to 18° . For each run, we observed that the behavior was nearly the same: at short times, the mass accelerated vigorously on gate opening and very quickly reached a nearly constant velocity. At time , independently of plane inclination and yield stress, the mass reached a near-equilibrium regime, where the front position varied as a power function of time over several decades. We did not observe any run-out phase, during which the mass would have gradually come to a halt. The similarity in the flow behavior made it possible to derive an empirical scaling for the front position in the form {x}_{f\,=\, }{t}^{0.275\left{ (sin\, \alpha\right)}}^{\frac{1}{3}}\left (sin\, \alpha \right)}^{\frac{5}{4}}, where α and t denote plane inclination and time, respectively, and which holds for sloping beds
Tracking the free surface of time-dependent flows: Image processing for the dam-break problem
The dam-break problem (i.e., the sudden release of a given volume of fluid down a slope) has attracted a great deal of attention from mechanicians and physicists over the past few years, with particular interest devoted to the free-surface profile and the spreading rate. Experimentally, impediments to accurate measurements of the free-surface evolution are numerous because of the significant variations in its curvature and velocity. To accurately measure the surgeâs free-surface variations with time, we have developed a new imaging system, consisting of a digital camera coupled with a synchronized micromirror projector. The objectâs surface is imaged into a camera and patterns are projected onto the surface under an angle of incidence that differs from the imaging direction. From the deformed pattern recorded by the camera, the phase can be extracted and, by using unwrapping algorithms, the height can be computed and the free surface reconstructed. We were able to measure the free surface of the flow to within 1 mm over a surface of 1.8 · 1.1 m2. Although the techniques used in our system are not new when taken individually, the system in its entirety is innovative and more efficient than most methods used to-date in practical applications
The dam-break problem for Herschel-Bulkley viscoplastic fluids down steep flumes
In this paper we investigate the dam-break problem for viscoplastic (Herschel- Bulkley) fluids down a sloping flume: a fixed volume of fluid initially contained in a reservoir is released onto a slope and flows driven by gravitational forces until these forces are unable to overcome the fluidâs yield stress. Like in many earlier investigations, we use lubrication theory and matched asymptotic expansions to de- rive the evolution equation of the flow depth, but with a different scaling for the flow variables, which makes it possible to study the flow behavior on steep slopes. The evolution equations takes on the form a nonlinear diffusion-convection equation. To leading order, this equation simplifies into a convection equation and reflects the balance between gravitational forces and viscous forces. After presenting analytical and numerical results, we compare theory with experimental data obtained with a long flume. We explore a fairly wide range of flume inclinations from 6° to 24° , while the initial Bingham number lies in the 0.07â0.26 range. Good agreement is found at the highest slopes, where both the front position and flow-depth profiles are properly described by theory. In contrast, at the lowest slopes, theoretical pre- dictions substantially deviate from experimental data. Discrepancies may arise from the formation of unsheared zones or lateral levees that cause slight flow acceleration
Gastro-intestinal bleeding in 1211 ventilated trauma patients: a multivariate analysis of the risk factors
Multi-taxa neo-taphonomic analysis of bone remains from barn owl pellets and cross-validation of observations: a case study from Dominica (Lesser Antilles)
Paleo- and neo-taphonomic analyses of bone assemblages rarely consider all the occurring taxa in a single study and works concerning birds of prey as accumulators of microvertebrate bone remains mostly focus on small mammals such as rodents and soricomorphs. However, raptors often hunt and consume a large range of taxa, including vertebrates such as small mammals, fishes, amphibians, squamates and birds. Bone remains of all these taxonomic groups are numerous in many paleontological and archaeological records, especially in cave deposits. To better characterize the predators at the origin of fossil and sub-fossil microvertebrate accumulations and the taphonomic history of the deposit, it is thus mandatory to conduct global and multi-taxa taphonomic approaches. The aim of this study is to provide an example of such a global approach through the investigation of a modern bone assemblage from a sample of pellets produced by the Lesser Antillean Barn Owl (Tyto insularis) in the island of Dominica. We propose a new methodology that allows us to compare different taxa (rodents, bats, squamates and birds) and to experiment with a cross-validation process using two observers for each taxonomic group to test the reliability of the taphonomic observations.1. Introduction 2. Materials and Methods 2.1. Owl Pellets Sampling 2.2. Prey Identification 2.3. Taphonomic Analysis 2.3.1. Anatomical Representation 2.3.2. Fragmentation 2.3.3. Surface Modifications 2.3.4. Size/Weight Classes of Preys 2.4. Cross-Validation of Observations 3. Results 3.1. Faunal Spectrum 3.2. Anatomical Representation 3.3. Fragmentation 3.4. Modifications of Bone Surface 4. Discussion 4.1. Diet of Tyto Insularis in Dominica 4.2. Taphonomic Impact of Tyto Insularis on Small Vertebrate Bone Assemblage 4.2.1. Remarks on the Size/Weight Classes of Preys 4.2.2. Anatomical Representation 4.2.3. Fragmentation 4.2.4. Digestion 4.3. Degree of Inter-Observer Differences and Potential Outcomes 4.4. Towards an âInter-Taxa Calibrationâ 5. Conclusion
The water relations of two tropical rainforest species (Virola surinamensis and Eperua falcata): Is Virola unusual as previously reported?
HYDROInternational audienceThe objective of this study was to examine the water relations and hydraulic architecture and vulnerability to cavitation in Virola surinamensis and V. michelii and to compare to similar measurements in Eperua falcata. In several previous reports Virola was seen to have a rather narrow range of xylem pressure potentials (Κx) near zero in the course of a wet-season day while having water fluxes quite close to Eperua. We tested the hypothesis that the narrow range of Κx might be consistent with very high hydraulic conductivities of stems, roots and shoots and high vulnerability to cavitation in Virola compared to Eperua. When this hypothesis proved false we concluded that the previous determinations of Κx might be wrong in Virola due to latex. We re-examined the determination of Κx in Virola by the pressure chamber technique and compared results to determination of Κleaf by the thermocouple psychrometer technique and found that the likely range of Κx are more negative than previously reported. Problems concerning the determination of Κx in species with latex are discussed
Herbaceous angiosperms are not more vulnerable to drought-induced embolism than angiosperm trees
The water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent
embolisms (gas bubbles), which could be removed by the occurrence of root pressure, especially in grasses. Here, we studied
hydraulic failure in herbaceous angiosperms by measuring the pressure inducing 50% loss of hydraulic conductance (P50) in stems
of 26 species, mainly European grasses (Poaceae). Our measurements show a large range in P50 from 20.5 to 27.5 MPa, which
overlaps with 94% of the woody angiosperm species in a worldwide, published data set and which strongly correlates with an
aridity index. Moreover, the P50 values obtained were substantially more negative than the midday water potentials for five grass
species monitored throughout the entire growing season, suggesting that embolism formation and repair are not routine and
mainly occur under water deficits. These results show that both herbs and trees share the ability to withstand very negative water
potentials without considerable embolism formation in their xylem conduits during drought stress. In addition, structure-function
trade-offs in grass stems reveal that more resistant species are more lignified, which was confirmed for herbaceous and closely
related woody species of the daisy group (Asteraceae). Our findings could imply that herbs with more lignified stems will
become more abundant in future grasslands under more frequent and severe droughts, potentially resulting in lower forage
digestibility.
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