Time filter

Source Type

Al Qurayn, Egypt

Semmar N.,French Institute of Health and Medical Research | Semmar N.,University and oacute
Advances in Botanical Research | Year: 2013

The metabolism is a complex system interacting with several intrinsic and extrinsic factors of biological organisms, viz. genome expressions, physiological states, environmental conditions, etc. This multifactorial interaction means that the metabolism works as a reactive and flexible system providing reliable biochemical pictures on the effects of different governing factors. Metabolic flexibility and reliability are linked to conservation laws, constraining the metabolism to a close system linking input (resources) to output (products) signals: any entering signal will be decomposed into weighted parts through different metabolic pathways. This gives to metabolic trends different functional degrees highlighted by different relative levels of metabolites. Sharing the same unit resource, the different metabolic pathways are statistically constrained to be regulated within a simplex space characterized by a unit sum of its components. Output metabolic responses and their inside regulatory processes can be analyzed by using two simplex-based approaches: correspondence analysis (CA) and weighted metabolic profiles analysis (WMPA), respectively. These two approaches are based on two opposite (complementary) principles consisting of decomposition and combination of metabolic variability. In CA, metabolic datasets are decomposed into extreme trends representing elementary components of metabolic polymorphism called metabotypes. In WMPA, iterated combinations between different metabolic components help to extract functional information on their generator backbone system. © 2013 Elsevier Ltd.

Mazat J.-P.,University and oacute | Beauvoit B.,French National Institute for Agricultural Research
Advances in Botanical Research | Year: 2013

There are several theoretical approaches to metabolism. Some of them give a greater place to the structure of the metabolic network symbolized by its stoichiometry matrix. The constraints in a metabolic network are very strong so that a lot of information can be derived from the stoichiometry matrix without any knowledge of the kinetic parameters of its steps, such that the elementary flux modes and even in some cases, the values of fluxes by the flux balance analysis method. However, a deeper understanding of metabolic network necessitates the values of the kinetic parameters. It is particularly the case for a fine determination of the fluxes taking into account the metabolic regulations and of the determination of the flux and metabolites control coefficients. A short presentation of softwares and tools that can be used in the study of metabolic networks is presented at the end of this chapter. © 2013 Elsevier Ltd.

Fourati M.,University and oacute | Roig V.,University and oacute | Raynal L.,French Institute of Petroleum
Chemical Engineering Science | Year: 2013

In order to optimize the design of gas-liquid packed columns used in distillation or in absorption processes, it is of high importance to be able to predict liquid dispersion. Indeed, dispersion phenomena will impact the choice and design of liquid distributing devices and the height of the packed beds. For this, one mainly relies on industrial feedback and on some experimental results obtained at laboratory scale which cannot be directly extrapolated since their geometric characteristics are at least one order of magnitude less than industrial columns in terms of columns diameter and height. To fill this gap CFD simulation tools should be more used since they can apply to any scale. However the latter option requires adequate modeling in particular for dispersion forces which are little studied due to the lack of data for validation. The present paper aims at developing, from original dispersion experimental measurements, closure laws that can be implemented in CFD codes. Liquid spreading from a source point has been investigated for Mellapak 250.X packing via gamma-ray tomography measurements. Closure laws are discussed from a simple 1D model which enables to go further within the Eulerian two-fluid framework with original user-defined functions and associated models that take into account liquid dispersion in the packed bed. The latter is modeled as a porous medium with appropriate closure laws. The comparison between experiments and CFD results shows that the present approach is adequate and should be further developed in order to be more precise and adapted to more packings. © 2013 Elsevier Ltd.

Korrida A.,University and oacute | Gutierrez J.P.,Complutense University of Madrid | Aggrey S.E.,University of Georgia | Amin-Alami A.,University and oacute
Zoo Biology | Year: 2013

A Moroccan Houbara Bustard pedigree was analyzed to evaluate the genetic variability in captive breeding population using genealogical approaches. The whole Houbara breeding flock (WP) for the period 1993-2004 was made up of 531 birds comprising 346 females and 185 males. The reference population (RP) comprised 198 individuals ready for reproduction from 2000 to 2004 cohorts. The corresponding percentage of known ancestors was estimated as 98.23% for the parent generation, 41.19% for the grandparent generation and 7.00% for the great grandparents generation. The average generation interval for Houbara was computed as 4.64 years. Genetic variability loss per generation was ascertained using the effective population size (Ne), the founder genome equivalent (fge), the effective number of ancestors and founders (fa) and (fe), respectively, for the RP and across each cohort. The results showed no bottleneck events in the breed but some loss of genetic variability just after the initiation of the conservation program. However, the annual effective population size based on the realized increase in inbreeding (ΔF-) was estimated to be 207 for the RP and 1,000 for the WP. With regard to conservation breeding schemes, the genealogical evidence presented here is very useful as it revealed the positive effect of migration on Houbara breeding. The mating strategies will assist in the future control and management of the genetic variability of this population. © 2012 Wiley Periodicals, Inc.

Hernandez-Raquet G.,French National Institute for Agricultural Research | Hernandez-Raquet G.,University and oacute | Durand E.,French National Institute for Agricultural Research | Braun F.,French National Institute for Agricultural Research | And 2 more authors.
Environmental Microbiology Reports | Year: 2013

Microbial diversity is generally considered as having no effect on the major processes of the ecosystem such as respiration or nutrient assimilation. However, information about the impact of diversity on minor functions such as xenobiotic degradation is scant. We studied the role of diversity on the capacity of an activated-sludge microbial community to eliminate phenanthrene, a polycyclic aromatic hydrocarbon. We also assessed the impact of diversity erosion on the ability of activated sludge to oxidize a wide range of organic compounds. The diversity of activated sludge was artificially modified by dilution to extinction followed by regrowth stage which led to communities with similar biomass but displaying a diversity gradient. The capacity of activated-sludge community to degrade phenanthrene was greatly modified: at high levels of diversity, the community was able to mineralize phenanthrene whereas at medium levels it first of all partially lost its ability to mineralize this pollutant and at the lowest diversity, the activated sludge completely lost its capacity to transform phenanthrene. Diversity depletion also reduced the metabolic diversity and biomass productivity of sewage-activated sludge. This study demonstrates that diversity erosion can greatly affect major ecosystem services such as pollutant removal. © 2013 John Wiley & Sons Ltd and Society for Applied Microbiology.

Discover hidden collaborations