Control of vortex shedding by thermal effect at low Reynolds numbers

An experimental study has been made of the control of vortex shedding in the wake of two two-dimensional bluff bodies, a circular cylinder and a flat ribbon. The study has shown that this control, easily realized by heating the bluff body, depends on the nature of the fluid. In the absence of buoyancy effects, related to the temperature dependence of the dynamic viscosity, the heating is found to stabilize the wake in air while the opposite result is obtained in water. Detailed measurements of the velocity fields in air, in isothermal and in heated body, show that this control is linked to slight modifications of the flow in the near wake and can be taken into account by the effective Reynolds number approach. The measurements also show that the degree of instability can be related to the level of interaction between the two initial shear layers at the end of the recirculation zone.     

A rhenium tris-carbonyl derivative as a single core multimodal probe for imaging (SCoMPI) combining infrared and luminescent properties

A rhenium tris-carbonyl derivative has been designed to couple infrared and luminescent detection in cells. Both spectroscopies are consistent with one another; they point out the reliability of the present SCoMPI (for Single Core Multimodal Probe for Imaging) for bimodal imaging and unambiguously indicate a localization at the Golgi apparatus in MDA-MB-231 breast cancer cells.     

Gas-phase reactivity of silver and copper coordinated monosaccharide cations studied by electrospray ionization and tandem mass spectrometry

The analytical distinction of the most common isomeric underivatized hexoses was investigated by means of mass spectrometry experiments. Electrospray ionization and tandem mass spectrometry were used in the analysis of silver and copper-coordinated monosaccharides (D-glucose, D-galactose, D-fructose, O-methyl-alpha-D-glucose and O-methyl-beta-D-glucose). The results show that cationization by Ag(+) allows the differentiation of the three first monosaccharides while the complexes formed by association of Cu(+) with these three monosacharides display a similar reactivity that prevents stereoisomer distinction. Unlike copper, silver adduct-ions of both alpha and beta anomeric O-methyl-D-glucoses exhibit specific decomposition patterns (i.e. a loss of methanol for the alpha-anomer and a loss of silver hydride for the beta-anomer), which allow an easy characterization. A theoretical survey of selected complexes, based on the use of DFT calculations were carried out on both anomers in order to rationalize the experimental findings.     

Unusual odd-electron fragments from even-electron protonated prodiginine precursors using positive-ion electrospray tandem mass spectrometry

Reports of anticancer and immunosuppressive properties have spurred recent interest in the bacterially produced prodiginines. We use electrospray tandem mass spectrometry (ES-MS/MS) to investigate prodigiosin, undecylprodiginine, and streptorubin B (butyl-meta-cycloheptylprodiginine) and to explore their fragmentation pathways to explain the unusual methyl radical loss and consecutive fragment ions that dominate low-energy collision-induced dissociation (CID) mass spectra. The competition between the formation of even-electron ions and radical ions is examined in detail. Theoretical calculations are used to optimize the structures and calculate the energies of both reactants and products using the Gaussian 03 program. Results indicate that protonation occurs on the nitrogen atom that initially held no hydrogen, thus allowing formation of a pseudo-seven-membered ring that constitutes the most stable ground state [M + H](+) structure. From this precursor, experimental data show that methyl radical loss has the lowest apparent threshold but, alternatively, even-electron fragment ions can be formed by loss of a methanol molecule. Computational modeling indicates that methyl radical loss is the more endothermic process in this competition, but the lower apparent threshold associated with methyl radical loss points to a lower kinetic barrier. Additionally, this characteristic and unusual loss of methyl radical (in combination with weaker methanol loss) from each prodiginine is useful for performing constant neutral loss scans to quickly and efficiently identify all prodiginines in a complex biological mixture without any clean-up or purification. The feasibility of this approach has been proven through the identification of a new, low-abundance prodigiosin analog arising from Hahella chejuensis.     

Easy and effective method to produce functionalized particles for cellular uptake

In this contribution, a versatile approach for the synthesis of functionalized particles for drug delivery is presented, using two nonaggressive standardized procedures. The first procedure considered is the functionalization of an azido‐terminated α‐norbornenyl poly(ethylene oxide) (PEO) macromonomer with an alkyne‐containing active molecule via the copper catalyzed azide alkyne cycloaddition, click type reaction. The functionalized macromonomer is then polymerized by Ring‐Opening Metathesis Polymerization (ROMP) in dispersion to form functionalized particles. The second procedure consists in synthesizing particles by ROMP in dispersed media of norbornene with azido‐terminated α‐norbornenyl PEO macromonomer. The ROMP was initiated by the first generation Grubbs catalyst. Such functionalized core‐shell particles have stealthy properties due to their PEO shell and can be viewed as universal nanocarriers on which any alkyne‐modified active molecule can be grafted by click chemistry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Slipping zone location in squeeze flow

In squeeze flow rheometry, the main problem is the boundary condition between the squeezed material and the plates. Therefore, the crucial assumption is to know the location and the shape of the sample part where wall slip may or may not occur. This question is investigated from experimental results. For this, squeeze flow experiments are carried out to visualize the flow pattern at the walls. Influence of boundary conditions is particularly studied using different plate surface condition. As a result, with wall slipping conditions, we propose a flow modelling divided into two zones: a circular central zone of the sample sticks on the plates and, beyond that zone, the sample slips at the plates with friction.     

A Non-Linear SGS Model Based On The Spatial Velocity Increment

A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flow is proposed based on the three-dimensional spatial velocity increment δ u _i . The new model is inspired by the structure function formulation developed by Métais and Lesieur [39] and applied in the context of the scale similarity type formulation. First, the similarity between the SGS stress tensor τ _ij and the velocity increment tensor Q _ij = δ u _i δ u _j is analyzed analytically and numerically using a priori tests of fully developed pipe flow at Re _τ = 180. Both forward and backward energy transfers between resolved and unresolved scales of the flow are well predicted with a SGS model based on Q _ij . Secondly, a posteriori tests are performed for two families of turbulent shear flows. LES of fully developed pipe flow up to Re _τ = 520 and LES of round turbulent jet at Re _D = 25000 carried out with a dynamic version of the model provide promising results that confirm the power of this approach for wall-bounded and free shear flows.     

Asymptotic Analysis of the Stresses in Thin Elastic Shells

. In this paper, we identify the limiting stress tensor of a thin elastic shell whose thickness approaches zero. In the linear case, we use a convergence result established for the displacement field in order to get the convergence of the contravariant components of the linearised stress tensor. In the nonlinear case, the identification of the first Piola‐Kirchhoff stress tensor is made through a formal asymptotic analysis. In both cases, we show that these limiting stress fields depend on the geometry of the shell and on the boundary conditions. (Accepted June 1, 1998)