Modal prediction for closed-loop adaptive optics

The correction efficiency of adaptive optics is limited mainly by measurement noise and time delay. To overcome this problem, we describe a new modal linear predictive controller whose parameters are optimized by means of a recursive least-squares algorithm to minimize the residual optical phase variance. The method copes with the recursivity of the closed-loop operation. We demonstrate that the optimal rejection transfer function for adaptive optics is proportional to the frequency signal-to-noise ratio. Finally, we present what we believe to be the first experimental results obtained with a predictor used to control the tip-tilt mirror of an adaptive-optics system.     

Determination of major antimony species in seawater by continuous flow injection hydride generation atomic absorption spectrometry

The capabilities and limitations of the continuous flow injection hydride generation technique, coupled to atomic absorption spectrometry, for the speciation of major antimony species in seawater, were investigated. Two pre-concentration techniques were examined. After continuous flow injection hydride generation and collection onto a graphite tube coated with iridium, antimony was determined by graphite furnace atomic absorption spectrometry. The low detection limits obtained (∼5 ng l⁻¹ for Sb(III) and ∼10 ng l⁻¹ for Sb(V) for 2.5 ml seawater samples) permitted the determination of Sb(III) and total antimony in seawater with the use of selective hydride generation and on-line UV photooxidation. The number of samples that can be analyzed is about 15 per hour for Sb(III) determinations and 10 per hour for total antimony determinations. The analysis of seawater samples showed that Sb(V) was the predominant species, even in the presence of important biological activity.     

Square‐Wave Voltammetry of the Molybdenum‐1,10 Phenanthroline‐Fulvic Acids Complex: Redox Kinetics Measurements

The reduction process of molybdenum in the presence of fulvic acids and phenanthroline was investigated by square-wave voltammetry (SWV). The mixed-ligand complex of molybdenum exhibits a pronounced tendency to adsorb onto the mercury electrode surface. The electrode reaction proceeds as a surface process in which both components of the redox couple are firmly confined to the electrode surface. The kinetics of the electrode reaction is studied utilizing the properties of “split SW peaks” and “quasireversible maximum”. The kinetic parameters obtained with two different square-wave voltammetric methods are in good agreement. In 0.5 mol/L NaCl solution with pH 2.5 the kinetic parameters are: standard rate constant k_s=8±2 s⁻¹, cathodic electron transfer coefficient α=0.41±0.05, and number of exchanged electrons n=2. The SW kinetic measurements are confirmed by cyclic voltammetric method.     

Enantioselective synthesis of bicyclo[3.n.1]alkanes by chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations

2,2-Disubstituted cyclic 1,3-diketones containing a tethered electron-deficient alkene undergo chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations to give bridged bicyclic products in high enantioselectivities. Both bicyclo[3.2.1]octanes and bicyclo[3.3.1]nonanes are accessible using this methodology.     

Kinetic Studies of Block Polycondensation. I. Aggregation of Various Carboxylic Acids in Solvents of Low Dielectric Constant

Self-association of benzoic, octanoic, and octadecanoic acids was studied in solvents with a range of dielectric constants between 2.3 and 10. The number-average molecular weights were determined by means of vapor pressure measurements and were carried out at temperatures ranging from 25 to 90° C. It appears that, in these solvents of low dielectric constant, carboxylic acids are present mainly as molecular or ionic aggregates.     

Preparation and Flame Retardancy Properties of Novel PA12 and PE/Layered Titanoniobates Nanocomposites

Summary: We report herein a study performed on a layered titanoniobate KTiNbO₅ modified by octadecylamine to evaluate the fire retardancy properties of this novel hybrid nanofiller dispersed in PA12 and LLDPE, by polymer melt intercalation. The nanocomposites have been characterized using Electron Microscopy techniques to evaluate the degree of exfoliation and the morphologies. Thermogravimetric analyses and cone calorimeter tests have been carried out to assess the fire retardant performances.     

Multiple periodic solutions for a nonlinear suspension bridge equation

We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created.     

Synthesis and characterization of poly(butadiene-b-sulphone) by block-copolycondensation—II. Synthesis from α,ω-dicarboxylic oligobutadienes and α,ω-diepoxy oligosulphones

The synthesis of poly(butadiene-b-sulphone) by two methods was described in part I (Eur. Polym. J. 20, 305 [1]). The results obtained by reaction of α,ω-dicarboxylic oligobutadiene with α,ω-diepoxy oligosulphones are reported here. The kinetics of the reaction are studied on models: reaction orders, rate constants, activation parameters are determined. Their values fit Madec's kinetic pattern [2] and are close to those obtained by Crépeau [6] for the grafting of hydroxybenzoic acid onto a copolymer bearing epoxy side-groups. Contribution of the side-reaction [2] is quantified. Block-copolycondensation of the reactive oligomers are carried out both in solution and in the melt. Contribution of the side-reaction is higher in the melt than in solution, but in both cases block-copolymers are obtained and characterized by GPC.