Search results for "Temperature gradient"
showing 10 items of 73 documents
Shifts in size, genetic structure and activity of the soil denitrifier community by nematode grazing
2010
International audience; Bacterial-feeding nematodes represent an important driver of the soil microbial activity and diversity. This study aimed at characterizing the impact of nematode grazing on a model functional bacterial guild involved in N-cycling, the denitrifiers. Bacterial-feeding nematodes (Cephalobus pseudoparvus) were inoculated into soil microcosms whose indigenous nematofauna had previously been removed. The size, genetic structure and activity of the soil denitrifier community were characterized 15 and 45 days after nematodes inoculation using quantitative PCR of the nirK, nirS and nosZ denitrification genes, fingerprinting of the nirK and nirS genes and denitrification enzym…
Use of Biocides for the Control of Fungal Outbreaks in Subterranean Environments: The Case of the Lascaux Cave in France
2012
The Lascaux Cave in France suffered an outbreak of the fungus Fusarium solani in 2001. Biocides were applied for three years to control this outbreak. Four months after the initial biocide application, a new outbreak appeared in the form of black stains that progressively invaded the cave. The black stains on the ceiling and passage banks were so evident by 2007 that they became one of the caves major problems. Therefore, biocides were used again in 2008. The present study investigated the fungal communities associated with the black stains and the effectiveness of the biocides applied, by using cloning, denaturing gradient gel electrophoresis, and culture-dependent methods. A novel species…
Influence of the Richardson number on EM force driven flow structures in square-shaped crucible
2014
Abstract This study is devoted to the experimental investigation of the turbulent melt motion in a square crucible where the flow is created by Lorentz forces generated by an external AC magnetic field. As a strong vertical thermal gradient is present in melt during a directional solidification process, a stratification effect takes place and motion in the vertical direction is damped by buoyancy forces. Such a situation arises if density of fluid layers decreases with height. Experimental velocity and temperature measurements are conducted. Transient effects, like collapse of stratification, are observed experimentally. The significance of stratification in the directional solidification m…
Electrophoresis of Unlabeled Proteins in a Sequencing Gel Apparatus
2000
Generalized transport coefficients in a gas with large shear rate
1987
We get a solution of the Bhatnagar-Gross-Krook (BGK) model kinetic equation by means of a perturbative expansion of a temperature gradient to study the transport properties in a gas with large shear rate. The irreversible fluxes are evaluated exactly to first order in the expansion for Maxwell molecules. The transport coefficients obtained are highly nonlinear functions of the shear rate. This dependence on shear rate is analysed and compared with previous results for several transport coefficients. Finally, we have found a solution for a simple model of constant collision frequency for which a large shear rate coexists with an arbitrary temperature gradient.
Evaluation of dynamic microbial communities in a styrene-degrading biotrickling filter using 16S rDNA tag pyrosequencing and denaturing gradient gel …
2014
Accurately characterizing microbial communities within bioreactors undergoing dynamic operating conditions is an essential first step towards understanding the relationship between microbial community structure and bioreactor performance. A detailed assessment of the changes in microbial populations within a styrene-degrading biotrickling filter was carried out using samples collected at multiple time points ranging from 21 to 155 days of biotrickling filter operation. Examination of microbial populations was conducted by 16S rDNA tag pyrosequencing and denaturing gradient gel electrophoresis (DGGE). Validation of pyrosequencing results was performed by quantitative polymerase chain reactio…
Direct chill casting of aluminium alloys under electromagnetic interaction by permanent magnet assembly
2018
Direct chill casting is one of the methods used in industry to obtain good microstructure and properties of aluminium alloys. Nevertheless, for some alloys grain structure is not optimal. In this study, we offer the use of electromagnetic interaction to modify melt convection near the solidification interface. Solidification under various electromagnetic interactions has been widely studied, but usually at low solidification velocity and high thermal gradient. This type of interaction may succeed fragmentation of dendrite arms and transport of solidification nuclei thus leading to improved material structure and properties. Realization of experimental small-scale crystallizer and electromag…
CdTe crystal growth process by the Bridgman method: numerical simulation
2001
Abstract Numerical simulation of the CdTe crystal growth process by the Bridgman method is made by using the commercial computational code FLUENT for the mathematical solution of the governing equations. To reduce computational effort, we have made use of a two level strategy. In the first level we have considered the whole system formed by the ampoule with the liquid–solid charge, the furnace, and the air between them. The heat transfer is assumed to occur by conduction, convection and radiation between the furnace and the ampoule, and only by conduction through the ampoule wall and the solid and liquid CdTe. In the second level we focus on the ampoule and its content, using the values of …
Instability of the melt flow in VGF growth with a traveling magnetic field
2009
The linear instability of a thermally stratified melt flow in the VGF configuration driven by a traveling magnetic field (TMF) is considered numerically and experimentally. The dependency of the instability threshold on the governing parameters is found for several cuts through the parameter space covering a wide range of possible applications. In a first approximation the linear instability occurs when the dimensionless TMF forcing parameter reaches the magnitude of the Grashof number. This is particularly true in a medium-sized crucible where the first instability is axisymmetric and sub-critical. As the Grashof number increases the flow develops self-similar boundary layers and the insta…
Heat and mass transfer phenomena in magnetic fluids
2007
In this article the influence of a magnetic field on heat and mass transport phenomena in magnetic fluids (ferrofluids) will be discussed. The first section is dealing with a magnetically driven convection, the so called thermomagnetic convection while in the second section the influence of a temperature gradient on the mass transport, the Soret effect in ferrofluids, is reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)