THE INVERSE FLUIDIZATION AIRLIFT BIOREACTOR, PART I: HYDRODYNAMIC STUDIES

The inverse fiuidization airlift bioreactor offers a simple solution to the problem of handling shear sensitive cultures and/or systems requiring biofilm growth control. This unit combines in a single vessel the hydrodynamic behavior of concentric tube airlift aerators or contactors and liquid-solid fluidized beds. The effects of the diameter of the concentric tubes, liquid level, bed properties and gas flow rate on gas holdup, bed expansion and liquid circulation velocity were investigated in this study. The Zuber and Findlay relation (1965) gives satisfactory results for gas holdup. The inverse bed expansion can be predicted by the Richardson and Zaki correlation (1953). The liquid circulation velocity can be calculated using a mechanical energy balance     

The Addressing Fragment of Mitogaligin: First Insights into Functional and Structural Properties

Mitogaligin is a mitochondrion‐targeting protein involved in cell death. The sequence of the protein is unrelated to that of any known pro‐ or antiapoptotic protein. Mitochondrial targeting is controlled by an internal sequence from residues 31 to 53, and although this sequence is essential and sufficient to provoke cell death, the precise mechanism of action at the mitochondrial membrane remains to be elucidated. Here, by focusing on the [31–53] fragment, we first assessed and confirmed its cell cytotoxicity by microinjection. Subsequently, with the aid of membrane models, we evaluated the impact of the membrane environment on the 3D structure of the peptide and on how the peptide is embedded and oriented within membranes. The fragment is well organized, even though it does not contain a canonical secondary structure, and adopts an interfacial location. Structural comparison with other membrane‐interacting Trp‐rich peptides demonstrated similarities with the antimicrobial peptide tritrpcidin.     

Rheological and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins

Ambarella and mango peels are good sources of pectins (15–20%), with high degree of methylation (60–78%) and high molar masses. Ambarella and mango ( Améliorée and Mango varieties) peel pectins were extracted using HCl or oxalic acid/ammonium oxalate (OAAO). Purified pectins were analysed for their flow behaviour and phase diagrams were established at pH 3 as sucrose vs. pectin concentration. The gelation kinetics and mechanical spectra of these pectin gels were studied and compared to those of commercial citrus (lime) pectins. At a concentration of 1% (w/v), all pectic solutions had a shear thinning behaviour but at 0.6% (w/v), only OAAO-extracted pectins exhibited such behaviour. Phase diagrams showed that at pH 3, gelation of OAAO mango extracted pectins was possible at low polymer concentration (0.2%; w/w) for a sucrose concentration of 60% (w/w). OAAO-extracted pectins exhibited a higher gelling ability than HCl-extracted ones. Sucrose (45–50%) and pectin (0.2–0.6%) concentration had a deep impact on the gel strength. Our results enable to conclude that the OAAO extraction from mango and ambarella peels allowed the recovery of pectins that exhibit high gelling properties.     

Rheology-structure properties of waxy maize starch–gellan mixtures

Dynamic oscillatory shear and confocal laser scanning microscopy were used, respectively, to study the viscoelastic properties and ultrastructure of mixtures of unmodified waxy maize starch (3%) and gellan (0.005–0.05%), pasted at 75 and 90 °C. The two temperatures resulted in different rheological properties and ultrastructure. At 75 °C swollen and partially disrupted granules were observed, while at 90 °C the dominant feature was the presence of granule remnants. Addition of gellan produced mixtures with different elastic properties depending on the extent of granular disruption and gellan concentration in the mixture. Below 0.02% gellan, swollen and disrupted starch granules were surrounded by compact, yet slightly interconnected, gellan networks resulting in enhanced blends at both temperatures. Above such gellan concentration no enhancement was observed and gellan dominated the viscoelastic behavior of the mixtures because of the existence of more evenly distributed networks with swollen or disrupted starch granules exerting a weakening effect on the resulting structure.     

Statistical distribution of the convergence time of evolutionaryalgorithms for long-path problems

The behavior of a (1+1)-ES process on Rudolph's binary long k paths is investigated extensively in the asymptotic framework with respect to string length l. First, the case of k=l^α is addressed. For α⩾1/2, we prove that the long k path is a long path for the (1+1)-ES in the sense that the process follows the entire path with no shortcuts, resulting in an exponential expected convergence time. For α<1/2, the expected convergence time is also exponential, but some shortcuts occur in the meantime that speed up the process. Next, in the case of constant k, the statistical distribution of convergence time is calculated, and the influence of population size is investigated for different (μ+λ)-ES. The histogram of the first hitting time of the solution shows an anomalous peak close to zero, which corresponds to an exceptional set of events that speed up the expected convergence time with a factor of l². A direct consequence of this exceptional set is that performing independent (1+1)-ES processes proves to be more advantageous than any population-based (μ+λ)-ES     

Real time TEM observation of alumina ceramic nano-particles during compression

The behavior of alumina nano-particles taken from a commercial powder is investigated during in situ compression experiments in a transmission electron microscope (TEM). Small particles of 40 nm in diameter can undergo severe plastic deformation without failure, whereas brittle fracture is observed for 120 nm sized nano-particles. This is evidence of a critical size under which alumina, at least in the form of nano-particles, cannot be considered as brittle materials even at room temperature and a direct observation of the grinding limit generally observed during ball milling.     

Acoustoelastic effect in concrete material under uni-axial compressive loading

This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δc=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions.     

Study of xenon thermal migration in sintered titanium nitride using nuclear micro-probe

Micro-Rutherford backscattering spectrometry experiments were performed on a set of sintered titanium nitride samples implanted with xenon to a depth of about 150 nm. Implanted samples were annealed at 1500 °C during 5 h. Xe depth profile and its lateral distribution on the surface were measured. Surface morphology was observed using scanning electron microscopy. The results reveal that the microstructure plays an important role on xenon release. Moreover, the crystalline orientation of each grain could be a key parameter to explain the heterogeneous evolution of the surface during thermal treatments as well as Xe release from surface.     

Les pratiques éducatives en sciences et en technologie: Points de vue d'enseignants et d'enseignantes

Résumé:

L'enseignement des sciences et des techniques fait l'objet de préoccupations en raison de leur importance dans la formation des élèves du secondaire et de l'impact qu'elles ont sur leur orientation scolaire et socioprofessionnelle future. Les conceptions que les éducateurs entretiennent au regard des disciplines scientifiques et les pratiques qu'ils exercent influencent pour une bonne part celles des élèves ainsi que les apprentissages qu'ils font. Le présent article, qui s'inscrit dans le cadre d'une étude d'ensemble sur les représentations sociales des sciences et des technologies chez les différents acteurs éducatifs et chez les élèves du secondaire, fait état des postures spécifiques endossées par des enseignants de sciences en lien avec un tel enseignement et tente, sur la base des discours qu'ils produisent, d'en dégager les significations, les préoccupations sociales invoquées et le caractère médiateur de l'activité didactico‐pédagogique engagée nous intéressant particulièrement.