187 research outputs found
Effet d'une expérimentation de brassage artificiel epilimnique par aération sur les poussées cyanobactériennes dans la retenue hypereutrophe de Grangent (France)
Dans la retenue hypereutrophe de Grangent, le phytoplancton estival est dominé par la cyanobactérie Microcystis aeruginosa. Dans le but de lutter contre la formation de ces blooms cyanobactériens, une expérimentation de brassage artificiel épilimnique par aération a été réalisée en 1997-1998. Ce dispositif avait pour but de créer des turbulences supprimant l'avantage adaptatif que constitue, chez M. aeruginosa, la faculté de réguler sa flottabilité. Il devait également permettre l'homogénéisation des teneurs en oxygène dissous, la réduction des pics de pH, de la turbidité des eaux superficielles et des teneurs en ammonium.Les résultats escomptés ont été vérifiés pour les paramètres physicochimiques. Les valeurs se sont révélées plus homogènes, mais seulement à proximité des lignes de brassage et uniquement jusqu'à 10 m de profondeur. En revanche, les blooms cyanobactériens n'ont pas été réduits. Il apparaît même au contraire que, sous l'influence du mélange, les cyanobactéries ont eu à leur disposition une plus grande quantité de nutriments qu'elles ont utilisés pour constituer des réserves glucidiques. Ainsi, en aval de la zone brassée, ces réserves ont permis une synthèse protéique plus importante.Sur la retenue de Grangent, le dispositif de brassage peut offrir une solution palliative du point de vue touristique en limitant l'accumulation de cyanobactéries en surface, mais il ne permet pas d'éliminer, ni même de diminuer, les proliférations de M. aeruginosa en période estivale.In the reservoir of Grangent, a highly eutrophic lake located on the upper part of the Loire River, about 10 miles south of Saint-Étienne (France), Microcystis aeruginosa usually dominates the phytoplankton community in late summer and early autumn for many years. Mass developments of this cyanobacterium led to serious difficulties in multi-purpose usage. In order to fight against blooms, an epilimnic artificial mixing was experimented. M. aeruginosa is adapted to stable stratification of the water column. Therefore, partial destratification or bubbling with air are employed to replace M. aeruginosa by better grazable, non- " blooming " and non-toxic species. This cyanobacterium is supposed to lose its advantage of buoyancy and to reduce his growth. This system was also employed to reduce peaks of pH, turbidity of surface waters and concentration of NH4 and to homogenize the dissolved oxygen concentration inside the water column. Three lines of mixing were tested in 1998: one located at "Châtelet", upstream of reservoir, measuring 700 m at 11 m depth; one near the beach of Saint-Victor, with the same length and immersed to 15 m depth and, finally, a line of 400 m, near the port, at 16 m depth (figure 1).Data were collected from representative sites, upstream, near and downstream the artificial mixing. They were sampled weekly since April to November 1998. At each site the vertical profiles of temperature and dissolved oxygen were measured (figure 2). For each sample, the parameters following were analyzed: pH, NO3, NH4, PO4, carbohydrates, proteins, chlorophyll a and phytoplankton enumeration.Concerning the physicochemical parameters, the assumptions were checked: the values appeared more homogeneous near the lines of mixing than at the other stations. For example, the average temperatures varied between 20,6°C (at 10 m depth) and 21,3°C (at 0,5 m depth) at Saint-Victor. This variation reached 1,3°C at the station Camaldules. On the other hand, this effect was perceived only up to 10 m of depth and at a limited distance of mixing.In the same way, the colonies of M. aeruginosa were mixed in the water column but only up 10 m depth and near mixing. Moreover, their growth has not decreased on the whole of reservoir. In period of bloom (August 25), G/P ratio was higher in the mixing zone than in the neighbourhoods, primarily because of an increase in carbohydrates (figure 3). In the mixed zone, M. aeruginosa seemed to benefit greater quantity of mineral elements it could use to constitute carbohydrates reserves (figure 4). In this way, when the conditions that became less favourable, like downstream, cyanobacteria were able to follow their development by synthesizing proteins starting from their reserves in carbohydrates.In the reservoir of Grangent, artificial mixing did not allow to fight effectively against blooms of cyanobacteria. Colonies of M. aeruginosa were simply diluted in the water column near mixing but did not reduce their growth
Determination of diffusivities in fluid mixtures using light scattering techniques in and out of equilibrium
Particle diffusivities in free and porous media from dynamic light scattering applying a heterodyne detection scheme
Fick diffusion coefficients in binary liquid mixtures of n-alkanes or 1-alcohols with dissolved gases investigated by molecular dynamics simulations and dynamic light scattering
Translational and rotational diffusion coefficients in nanofluids from polarized dynamic light scattering
Nanofluids representing nanometer-sized solid particles dispersed in liquids are of interest in many
fields of process and energy engineering, e.g., heat transfer, catalysis, and the design of functionalized
materials [1]. The physical, chemical, optical, and electronic properties of nanofluids are strongly driven
by the size, shape, surface potential, and concentration of the nanoparticles. For the analysis of diffusive
processes in nanofluids allowing access to, e.g., particle size and its distribution, dynamic light scattering
(DLS) is the state-of-the-art technique. It is based on the analysis of microscopic fluctuations originating
from the random thermal movement of particles in the continuous liquid phase at macroscopic
thermodynamic equilibrium. For anisotropic particles or particle aggregates, besides translational
diffusion also rotational diffusion occurs. To obtain the sum of the orientation-averaged translational
(DT) and rotational (DR) diffusivities by depolarized DLS [2], a homodyne detection scheme is usually
applied which can hardly be fulfilled in the experimental realization. Furthermore, the experiments are
restricted to limited ranges for temperature, particle concentration, and viscosity
Melting of Partially Fluorinated Graphene: From Detachment of Fluorine Atoms to Large Defects and Random Coils
The melting of fluorographene is very unusual and depends strongly on the
degree of fluorination. For temperatures below 1000 K, fully fluorinated
graphene (FFG) is thermo-mechanically more stable than graphene but at
T2800 K FFG transits to random coils which is almost twice lower
than the melting temperature of graphene, i.e. 5300 K. For fluorinated graphene
(PFG) up to 30 % ripples causes detachment of individual F-atoms around 2000 K
while for 40-60 % fluorination, large defects are formed beyond 1500 K and
beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The
results agree with recent experiments on the dependence of the reversibility of
the fluorination process on the percentage of fluorination.Comment: 16 pages, 6 figure
Failure to Detect Critical Auditory Alerts in the Cockpit: Evidence for Inattentional Deafness
Objective: The aim of this study was to test whether inattentional deafness to critical alarms would be observed in a simulated cockpit. Background: The inability of pilots to detect unexpected changes in their auditory environment (e.g., alarms) is a major safety problem in aeronautics. In aviation, the lack of response to alarms is usually not attributed to attentional limitations, but rather to pilots choosing to ignore such warnings due to decision biases, hearing issues, or conscious risk taking. Method: Twenty-eight general aviation pilots performed two landings in a flight simulator. In one scenario an auditory alert was triggered alone, whereas in the other the auditory alert occurred while the pilots dealt with a critical windshear. Results: In the windshear scenario, 11 pilots (39.3%) did not report nor react appropriately to the alarm whereas all the pilots perceived the auditory warning in the no-windshear scenario. Also, of those pilots who were first exposed to the no-windshear scenario and detected the alarm, only three suffered from inattentional deafness in the subsequent windshear scenario. Conclusion: These findings establish inattentional deafness as a cognitive phenomenon that is critical for air safety. Pre-exposure to a critical event triggering an auditory alarm can enhance alarm detection when a similar event is encountered subsequently. Application: Case-based learning is a solution to mitigate auditory alarm misperception
Diffusion in liquid mixtures
The understanding of transport and mixing in fluids in the presence and in the absence of external fields and reactions represents a challenging topic of strategic relevance for space exploration. Indeed, mixing and transport of components in a fluid are especially important during long-term space missions where fuels, food and other materials, needed for the sustainability of long space travels, must be processed under microgravity conditions. So far, the processes of transport and mixing have been investigated mainly at the macroscopic and microscopic scale. Their investigation at the mesoscopic scale is becoming increasingly important for the understanding of mass transfer in confined systems, such as porous media, biological systems and microfluidic systems. Microgravity conditions will provide the opportunity to analyze the effect of external fields and reactions on optimizing mixing and transport in the absence of the convective flows induced by buoyancy on Earth. This would be of great practical applicative relevance to handle complex fluids under microgravity conditions for the processing of materials in space
WNT signalling in prostate cancer
Genome sequencing and gene expression analyses of prostate tumours have highlighted the potential importance of genetic and epigenetic changes observed in WNT signalling pathway components in prostate tumours-particularly in the development of castration-resistant prostate cancer. WNT signalling is also important in the prostate tumour microenvironment, in which WNT proteins secreted by the tumour stroma promote resistance to therapy, and in prostate cancer stem or progenitor cells, in which WNT-β-catenin signals promote self-renewal or expansion. Preclinical studies have demonstrated the potential of inhibitors that target WNT receptor complexes at the cell membrane or that block the interaction of β-catenin with lymphoid enhancer-binding factor 1 and the androgen receptor, in preventing prostate cancer progression. Some WNT signalling inhibitors are in phase I trials, but they have yet to be tested in patients with prostate cancer
Melting of Partially Fluorinated Graphene: From Detachment of Fluorine Atoms to Large Defects and Random Coils
The melting of fluorographene is very unusual and depends strongly on the degree of fluorination. For temperatures below 1000 K, fully fluorinated graphene (FFG) is thermo-mechanically more stable than graphene but at T m ≈ 2800 K FFG transits to random coils which is almost twice lower than the melting temperature of graphene, i.e. 5300 K. For fluorinated graphene (PFG) up to 30% ripples causes detachment of individual F-atoms around 2000 K while for 40-60% fluorination, large defects are formed beyond 1500 K and beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The results agree with recent experiments on the dependence of the reversibility of the fluorination process on the percentage of fluorination.Fil: Singh, Sandeep Kumar. Universiteit Antwerpen. Department of Physics; BélgicaFil: Costamagna, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Neek Amal, M.. Universiteit Antwerpen. Department of Physics; BélgicaFil: Peeters, F. M.. Universiteit Antwerpen. Department of Physics; Bélgic
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