Nanoflower arrays of rutile TiO2

Stacks of multilayered rutile TiO(2) nanoflowers can grow on a titanium film through a simple acid vapour oxidation (AVO) method. The growth of this interesting hierarchical architecture is due to the formation of rutile {101} twinned structures and a subtle mismatching between the lattice spacings of the substrate and product.     

Trace level vanadium determination using thermal lens spectrophotometry

Trace level vanadium determination is reported using a dual beam thermal lens spectrometer. The thermal lens was generated using an argon ion beam laser (pump beam) which was focused into a sample cuvette. The thermal lens signal (TLs) was monitored with a He-Ne laser beam and a photodiode detector. Multichannel averager software was developed for processing the transient TLs. The optimal set up, ensuring maximum sensitivity and linear calibration graphs was obtained using experimental design techniques. Under optimized conditions, the detection limits for aqueous and ethanol-water (2+3 v/v) and (4+1 v/v) vanadium complex solutions were, respectively, 0.0071 mg/l, 0.0065 and 0.0039 mg/l.     

Determination of total gaseous lead in the atmosphere by honeycomb denuder/electrothermal atomic absorption spectrometry.

A technique is described for the determination of total gaseous lead in the atmosphere by honeycomb denuder collection, followed by an electrothermal atomic absorption spectrometry (ETAAS) measurement. The collection efficiency of the honeycomb denuder in which a solution containing 2% HNO3/2% glycerine/1% ammonium dihydrogenphosphate was coated for trapping the gaseous lead in the atmosphere was 98.8%. The linear absorbance response was obtained for a concentration range of 0-1.39 microg m(-3) of lead in the atmosphere. A precision of 4.8% RSD (peak-height absorbance, n = 11) for an aqueous solution of 1 ng of lead standard, characteristic masses (CM) of 23 pg and detection limit (3sigma) of 54 pg for an aqueous solution of 0.01 ng lead standard was achieved with 100 microg ammonium dihydrogenphosphate as a chemical modifier. The average recovery of lead in three standard samples prepared by the independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 97.8%. The total content of the gaseous lead in the atmosphere of our laboratories was 0.35-0.38 microg m(-3).     

Hydrodynamic properties of model 3-miktoarm star copolymers

The synthesis of well-defined, nearly monodispersed, 3-miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A₂B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η], R_H and R_v of the A₂B and one A₂B₂ miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wiley & Sons, Inc.     

Precise measurement of theX K emission rate following the electron capture-decay of54Mn-fluorescence yield ω K of Cr

This determination was made using the electron capture decay of⁵⁴Mn. Two methods were employed to measure theK X-ray emission rate: by means of a pressurized 4π proportional counter with the gas at 1.5 MPa, and by means of a medium geometry-defined solid angle counter. The final result wasω _k=0.2901±0.003. Special care was taken in determining the corrections, some of which do not appear to have been allowed for so far. It is noteworthy that additional corrections, each about +3 %, had to be applied to the results obtained with each of the two methods. Thus there remains complete agreement between them, but at a higher value ofω _k than those appearing in recent publications.     

Asymmetric, anti-selective scandium-catalyzed Sakurai additions to glyoxyamide. Applications to the syntheses of N-boc D-alloisoleucine and D-isoleucine

[reaction: see text] An enantio- and diastereoselective Sakurai-Hosomi reaction, catalyzed by chiral scandium pyridyl-bis(oxazoline) (pybox) complexes, has been developed. Both alkyl- and aryl-substituted allylsilanes are effective coupling partners with N-phenylglyoxamide. Applications of this reaction to the asymmetric syntheses of N-Boc D-alloisoleucine and D-isoleucine are described.     

Associative,Idempotent, Symmetric,and Order-preserving Operations on Chains

We characterize the associative, idempotent, symmetric, and order-preserving binary operations on (finite) chains in terms of properties of (the Hasse diagram of) their associated semilattice order. In particular, we prove that the number of associative, idempotent, symmetric, and order-preserving operations on an n-element chain is the n^th Catalan number.

     

The Obstacle Version of the Geometric Dynamic Programming Principle: Application to the Pricing of American Options Under Constraints

We provide an obstacle version of the Geometric Dynamic Programming Principle of Soner and Touzi (J. Eur. Math. Soc. 4:201–236, 2002) for stochastic target problems. This opens the doors to a wide range of applications, particularly in risk control in finance and insurance, in which a controlled stochastic process has to be maintained in a given set on a time interval [0,T]. As an example of application, we show how it can be used to provide a viscosity characterization of the super-hedging cost of American options under portfolio constraints, without appealing to the standard dual formulation from mathematical finance. In particular, we allow for a degenerate volatility, a case which does not seem to have been studied so far in this context.