Active absorption to reduce the noise transmitted out of an enclosure

This paper investigates the potential of active absorbers for reducing low-frequency noise transmission through an enclosure. Active absorbers are intended to obtain a purely real prescribed impedance at the front face of a porous layer. This is achieved by an active control system which cancels the acoustic pressure at the rear face. The test bench was a simplified enclosure: a rigid-wall cavity coupled to a baffled elastic plate. The modeling of the system was based on an analytical modal approach. The purpose of this simulation was first to calculate the optimal impedance, providing maximal reduction in radiated power, and then to define a sub-optimal strategy for actual absorber production. Two 3-cell configurations were implemented on the test bench. Active control used a multichannel feedforward algorithm. In line with prediction, the absorbers provided a 5.5 dB overall reduction while covering only 2% of the cavity surface.     

Nonlocal effects in flows of wormlike micellar solutions

The flow curve of wormlike micelles usually exhibits a stress plateau sigma* separating high and low viscosity branches, leading to shear-banded flows. We study the flow of semidilute wormlike micellar systems in a confined geometry: a straight microchannel. We characterize their local rheology thanks to particle image velocimetry. We show that flow curves cannot be described by a simple constitutive equation linking the local shear stress to the local shear rate. We demonstrate the existence of nonlocal effects in the flow of wormlike micellar systems and make use of a theoretical framework allowing the measurement of correlation lengths.     

Photocrosslinking of elastomer systems. I. UV light-induced reactions in a blend of EPDM-benzoin derivatives

Photocrosslinking experiments were performed on elastomeric polymer films (EPDM) that contained benzoin derivatives as photosensitive initiators. Infrared (IR) and ultraviolet (UV) spectroscopy investigations were used in conjunction with physical property measurements. The results all together make it possible to discuss the crosslinking mechanism and pose interesting questions about the reactivity of benzoin derivatives in their excited states in relation to their efficiency in the crosslinking process.     

Solvent resistance of a polymer chain chemically linked onto a solid surface

Polystyrene or polystyrene–polyisoprene copolymers have been grafted onto silica by an anionic procedure. The solvent resistance of the grafts has been examined. Linear relationships between the extractable amount of polymer and the solvent extraction temperatures are observed. The extrapolation of these lines leads to temperatures that are in close agreement with the ceiling temperatures of the grafted polymers.     

Velocity profiles in shear-banding wormlike micelles

Using dynamic light scattering in heterodyne mode, we measure velocity profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to exhibit both shear-banding and stress plateau behavior. Our data provide evidence for the simplest shear-banding scenario, according to which the effective viscosity drop in the system is due to the nucleation and growth of a highly sheared band in the gap, whose thickness linearly increases with the imposed shear rate. We discuss various details of the velocity profiles in all the regions of the flow curve and emphasize the complex, non-Newtonian nature of the flow in the highly sheared band.     

Observation of droplet size oscillations in a two-phase fluid under shear flow

Experimental observations of droplet size sustained oscillations are reported in a two-phase flow between a lamellar and a sponge phase. Under shear flow, this system presents two different steady states made of monodisperse multilamellar droplets, separated by a shear-thinning transition. At low and high shear rates, the droplet size results from a balance between surface tension and viscous stress, whereas for intermediate shear rates it becomes a periodic function of time. A possible mechanism for such kinds of oscillations is discussed.     

The N-donor stabilised cyclotriphosphazene hexacation [P3N3(DMAP)6]6+

The cyclotriphosphazene P(3)N(3)Cl(6) reacts with six equivalents of DMAP (4-(dimethylamino)pyridine) in superheated chloroform to form crystals of composition [P(3)N(3)(DMAP)(6)]Cl(6).19CHCl(3) comprising [P(3)N(3)(DMAP)(6)](6+) ions, which host five chloride ions in basket-type cavities on either side of the ring and at equatorial positions via tetradentate ortho-H-donor arrangements.     

Analytical methods for the determination of selected steroid sex hormones and corticosteriods in wastewater

An analytical method for the determination of 12 selected estrogens, progestagens and corticosteroids is presented. The optimization of the method, including liquid chromatography separation, extraction on a solid phase, purification on a silica gel cartridge and detection by mass spectrometry, is described. Both the repeatability, with relative standard deviation ranging from 1.4 to 2.7%, and the accuracy, with recoveries ranging from 92.7 to 102.4%, were very satisfactory for ten of the target analytes. The limits of detection were lower than 1 ng/L for progestagens, androgens and corticosteroids, and ranged between 0.9 and 4.3 ng/L for estrogens. The results of the analysis of two sewage treatment plants in the area of Lyon (France) by this method reveal that all the compounds investigated are present in the effluents. The estrogen most frequently detected was estrone, with a median of 26.1 ng/L. The target progestagens were detected with concentrations ranging between 5 and 41 ng/L. Androgens were also present in most of the samples in the range 1–30 ng/L, while the corticosteroids were present only in one plant, with a median of 31.9 ng/L.     

Bias of LS estimators in nonlinear regression models with constraints. Part II: Biadditive Models

General results giving approximate bias for nonlinear models with constrained parameters are applied to bilinear models in ANOVA framework, called biadditive models. Known results on the information matrix and the asymptotic variance matrix of the parameters are summarized, and the Jacobians and Hessians of the response and of the constraints are derived. These intermediate results are the basis for any subsequent second order study of the model. Despite the large number of parameters involved, bias formulae turn out to be quite simple due to the orthogonal structure of the model. In particular, the response estimators are shown to be approximately unbiased. Some simulations assess the validity of the approximations.