226 research outputs found
Modelling the microfiltration of lactic acid fermentation broths and comparison of operating modes
clarification of fermentation broths by cross-flow microfiltration. Microfiltration experiments conducted under
constant transmembrane pressure and under constant permeate fluxes (higher and lower than the critical flux)
were represented by the resistance in series model in which the membrane resistance, the adsorption resistance,
the bacteria cake resistance and the soluble compounds concentration polarisation resistance were taken into
account. The different operating modes were compared in terms of two industrial interest criteria: the
productivity and fouling rates. Higher productivities were obtained during constant transmembrane pressure
runs whereas the lowest fouling rate was observed during the run conducted with a constant permeate flux lower
than the critical flux. However, this fouling was mainly due to adsorption and solute components concentration
polarisation.
Key words
How Herbivores Optimise Diet Quality and Intake in Heterogeneous Pastures, and the Consequences for Vegetation Dynamics
Understanding the interplay between foraging behaviour and vegetation dynamics in heterogeneous pasture is an essential requirement for evaluating the value of the resource for large herbivores and for managing that resource. The orientation of selective grazing behaviour between intake and diet quality depends on the spatial and temporal scales considered. In the short-term scale of a grazing sequence, there is evidence that large herbivores tend to optimise the intake rate of digestible materials by adaptation of their biting behaviour and by patch choice. On a day-to-day scale, there is evidence that large herbivores tend to prioritise the quality of the diet to minimise digestive constraints within the time that they can spend grazing. On a pasture scale, the search for areas giving the best trade-off between quantity and quality of intake leads to the optimisation of their foraging paths, in particular by modulating their sinuosity in response to heterogeneity. Repeated grazing of preferred patches creates a positive feedback on forage quality and enhances heterogeneity. Long-term consequences on vegetation dynamics, botanic composition and grassland quality are less understood
Room temperature Giant Spin-dependent Photoconductivity in dilute nitride semiconductors
By combining optical spin injection techniques with transport spectroscopy
tools, we demonstrate a spin-photodetector allowing for the electrical
measurement and active filtering of conduction band electron spin at room
temperature in a non-magnetic GaAsN semiconductor structure. By switching the
polarization of the incident light from linear to circular, we observe a Giant
Spin-dependent Photoconductivity (GSP) reaching up to 40 % without the need of
an external magnetic field. We show that the GSP is due to a very efficient
spin filtering effect of conduction band electrons on Nitrogen-induced Ga
self-interstitial deep paramagnetic centers.Comment: 4 pages, 3 figure
Spin and recombination dynamics of excitons and free electrons in p-type GaAs : effect of carrier density
Carrier and spin recombination are investigated in p-type GaAs of acceptor
concentration NA = 1.5 x 10^(17) cm^(-3) using time-resolved photoluminescence
spectroscopy at 15 K. At low pho- tocarrier concentration, acceptors are mostly
neutral and photoelectrons can either recombine with holes bound to acceptors
(e-A0 line) or form excitons which are mostly trapped on neutral acceptors
forming the (A0X) complex. It is found that the spin lifetime is shorter for
electrons that recombine through the e-A0 transition due to spin relaxation
generated by the exchange scattering of free electrons with either trapped or
free holes, whereas spin flip processes are less likely to occur once the
electron forms with a free hole an exciton bound to a neutral acceptor. An
increase of exci- tation power induces a cross-over to a regime where the
bimolecular band-to-band (b-b) emission becomes more favorable due to screening
of the electron-hole Coulomb interaction and ionization of excitonic complexes
and free excitons. Then, the formation of excitons is no longer possible, the
carrier recombination lifetime increases and the spin lifetime is found to
decrease dramatically with concentration due to fast spin relaxation with free
photoholes. In this high density regime, both the electrons that recombine
through the e-A0 transition and through the b-b transition have the same spin
relaxation time.Comment: 4 pages, 5 figure
Transient colonization of the airways by unusual Aspergillus species in two cystic fibrosis patients
Date du colloque : 06/2009</p
Improving the reliability of material databases using multiscale approaches
This article addresses the propagation of constitutive uncertainties between
scales occurring in the multiscale modelling of fibre-reinforced composites.
The amplification of such uncertainties through upward or downward transitions
by a homogenisation model is emphasized and exemplified with the Mori-Tanaka
model. In particular, the sensitivity to data uncertainty in the inverse
determination of constituent parameters based on downward transitions is
stressed on an example. Then a database improvement method, which exploits
simultaneously the available information on constitutive uncertainties at all
scales instead of just propagating those associated with one scale, is
presented and shown to yield substantial reductions in uncertainty for both the
constitutive parameters and the response of structures. The latter finding is
demonstrated on two examples of structures, with significant gains in
confidence obtained on both
Durée de la survie des Brucella dans le fromage de Roquefort
CarrĂšre Louis, LafenĂȘtre Henri, Quatrefages H., De Noronha Fernando. DurĂ©e de la survie des Brucella dans le fromage de Roquefort. In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 113 n°8, 1960. pp. 469-473
Production of negative ions on graphite surface in Hâ/Dâ plasmas: experiments and SRIM calculations
In previous works, surface-produced negative-ion distribution-functions have been measured in H2 and D2 plasmas using graphite surfaces (highly oriented pyrolitic graphite). In the present paper, we use the srim software to interpret the measured negative-ion distribution-functions. For this purpose, the distribution-functions of backscattered and sputtered atoms arising due to the impact of hydrogen ions on a-CH and a-CD surfaces are calculated. The srim calculations confirm the experimental deduction that backscattering and sputtering are the mechanisms of the origin of the creation of negative ions at the surface. It is shown that the srim calculations compare well with the experiments regarding the maximum energy of the negative ions and reproduce the experimentally observed isotopic effect. A discrepancy between calculations and measurements is found concerning the yields for backscattering and sputtering. An explanation is proposed based on a study of the emitted-particle angular-distributions as calculated by srim
In situ relationships between microbiota and potential pathobiota in Arabidopsis thaliana.
A current challenge in microbial pathogenesis is to identify biological control agents that may prevent and/or limit host invasion by microbial pathogens. In natura, hosts are often infected by multiple pathogens. However, most of the current studies have been performed under laboratory controlled conditions and by taking into account the interaction between a single commensal species and a single pathogenic species. The next step is therefore to explore the relationships between host-microbial communities (microbiota) and microbial members with potential pathogenic behavior (pathobiota) in a realistic ecological context. In the present study, we investigated such relationships within root-associated and leaf-associated bacterial communities of 163 ecologically contrasted Arabidopsis thaliana populations sampled across two seasons in southwest of France. In agreement with the theory of the invasion paradox, we observed a significant humped-back relationship between microbiota and pathobiota α-diversity that was robust between both seasons and plant organs. In most populations, we also observed a strong dynamics of microbiota composition between seasons. Accordingly, the potential pathobiota composition was explained by combinations of season-specific microbiota operational taxonomic units. This result suggests that the potential biomarkers controlling pathogen\u27s invasion are highly dynamic
A new phase in the production of quality-controlled sea level data
Sea level is an essential climate variable (ECV) that has a direct effect on many people through inundations of coastal areas, and it is also a clear indicator of climate changes due to external forcing factors and internal climate variability. Regional patterns of sea level change inform us on ocean circulation variations in response to natural climate modes such as El Niño and the Pacific Decadal Oscillation, and anthropogenic forcing. Comparing numerical climate models to a consistent set of observations enables us to assess the performance of these models and help us to understand and predict these phenomena, and thereby alleviate some of the environmental conditions associated with them. All such studies rely on the existence of long-term consistent high-accuracy datasets of sea level. The Climate Change Initiative (CCI) of the European Space Agency was established in 2010 to provide improved time series of some ECVs, including sea level, with the purpose of providing such data openly to all to enable the widest possible utilisation of such data. Now in its second phase, the Sea Level CCI project (SL_cci) merges data from nine different altimeter missions in a clear, consistent and well-documented manner, selecting the most appropriate satellite orbits and geophysical corrections in order to further reduce the error budget. This paper summarises the corrections required, the provenance of corrections and the evaluation of options that have been adopted for the recently released v2.0 dataset (https://doi.org/10.5270/esa-sea_level_cci-1993_2015-v_2.0-201612). This information enables scientists and other users to clearly understand which corrections have been applied and their effects on the sea level dataset. The overall result of these changes is that the rate of rise of global mean sea level (GMSL) still equates to âŒâ3.2âŻmmâŻyrâ1 during 1992â2015, but there is now greater confidence in this result as the errors associated with several of the corrections have been reduced. Compared with v1.1 of the SL_cci dataset, the new rate of change is 0.2âŻmmâŻyrâ1 less during 1993 to 2001 and 0.2âŻmmâŻyrâ1 higher during 2002 to 2014. Application of new correction models brought a reduction of altimeter crossover variances for most corrections
- âŠ