Structure of premixed flames of propylene oxide: Molecular beam mass spectrometric study and numerical simulation

The knowledge of the combustion chemistry of oxygenated fuels is essential for the development of detailed kinetic mechanisms suitable for the combustion processes involving biofuels. Moreover, epoxidized olefins, are increasingly used as chemical intermediates or as bulk chemicals. Nevertheless, a dearth of data for their reactivity in the oxidative environment can be observed in the current literature. This study reports the experimental and the model characterization of the flame structure of propylene oxide at stoichiometric and fuel-rich conditions at atmospheric pressure. To this aim, the species mole fractions in three premixed flames stabilized on a flat-flame burner have been quantitatively measured by using the flame sampling molecular beam mass spectrometry. Three chemical kinetic mechanisms retrieved from the current literature involving propylene oxide chemistry have been validated against the novel experimental data. In general, the predictions appeared to be in satisfactory agreement with measurements except for acetaldehyde and ketene. The rate of production analysis in the flame has shown that the discrepancies observed for these species are related basically to the incorrect ratio between the rates of primary reaction pathways of propylene oxide destruction.     

The characterization and thermal stability of a cluster grafted on silica surface

Ru₃(CO)₁₂, supported on silica in the absence of oxygen, reacts with silanol groups of the surface to produce a grafted cluster

, which has been characterized by IR and Raman spectroscopy; the molecular formula of this cluster is in agreement with the stoichiometric balance of CO evolved during its formation from Ru₃(CO)₁₂. The grafted cluster is an intermediate step to produce by thermal decomposition small metallic ruthenium particles of 14 Å together with some Ru(II) carbonyl species encapsulated in the silica surface.     

Multipulse Phases in k-Mixtures of Bose–Einstein Condensates

For the system

$-\Delta U_i+ U_i=U_i^3-\beta U_i\sum_{j\neq i}U_j^2,\quad i=1,\dots,k,$

(with k ≧ 3), we prove the existence for β large of positive radial solutions on \({\mathbb R^N}\) . We show that as β →  + ∞, the profile of each component U _i separates, in many pulses, from the others. Moreover, we can prescribe the location of such pulses in terms of the oscillations of the changing-sign solutions of the scalar equation  ? ΔW  +  W  =  W³. Within an Hartree–Fock approximation, this provides a theoretical indication of phase separation into many nodal domains for the k-mixtures of Bose–Einstein condensates.

     

An optimal partition problem related to nonlinear eigenvalues

We extend to the case of many competing densities the results of the paper (Ann. Inst. H. Poincaré 6 (2002)). More precisely, we are concerned with an optimal partition problem in N-dimensional domains related to the method of nonlinear eigenvalues introduced by Nehari, (Acta Math. 105 (1961)). We prove existence of the minimal partition and some extremality conditions. Moreover, in the case of two-dimensional domains we give an asymptotic formula near the multiple intersection points. Finally, we show some connections between the variational problem and the behavior of competing species systems with large interaction.     

Kinetics and Thermodynamics of Binding of a Model Tripeptide to Teicoplanin and Analogous Semisynthetic Antibiotics

The thermodynamics and kinetics of binding of model tripeptides epsilon-N-acetyl-alpha-N-dansyl-L-Lys-D-Ala-D-Ala (ADLAA) or alpha-N,epsilon-N-diacetyl-L-Lys-D-Ala-D-Ala (AALAA) to teicoplanin (1a) and a series of semisynthetic derivatives with (1b-f) or devoid of (2a-g) the glycidic side arms and modified at the terminal amino acids of the peptide backbone have been studied by fluorescence or UV spectroscopy. The binding process is suggested to occur via a two-step mechanism. The first, fast process is likely governed by an electrostatic interaction between the C- and N-termini of the peptide chain of the substrate and of the antibiotic, respectively, while the second slower one, accounts for the formation of the hydrogen bonds responsible of the major contribution to the overall binding energy. The binding constants with all modified derivatives are smaller than that with native teicoplanin. Larger modification of the overall binding constant are observed when the sugar residues are removed and, to a lower extent, when the N-terminus of the peptide chain is acylated. The kinetic process is very little affected by the modifications introduced.     

Enantioselective addition of phenyl and alkyl acetylenes to imines catalyzed by chiral Cu(I) complexes

The stereoselective addition of phenyl acetylene and alkyl acetylenes to imines, catalyzed by chiral bis-imines-Cu(I) complexes was studied. A very simple experimental procedure allowed to obtain at room temperature optically active propargyl amines in very good yields and enantioselectivity up to 81%.     

Uniform Hölder Bounds for Nonlinear Schrödinger Systems with Strong Competition

For the positive solutions of the Gross–Pitaevskii system we prove that L^∞‐boundedness implies C^0,α‐boundedness for every α ? (0,1), uniformly as β → +∞. Moreover, we prove that the limiting profile as β → +∞ is Lipschitz‐continuous. The proof relies upon the blowup technique and the monotonicity formulae by Almgren and Alt, Caffarelli, and Friedman. This system arises in the Hartree‐Fock approximation theory for binary mixtures of Bose–Einstein condensates in different hyperfine states. Extensions to systems with k > 2 densities are given. © 2009 Wiley Periodicals, Inc.     

Four-wavelength time-resolved optical mammography in the 680-980-nm range

What is to our knowledge the first instrument for time-resolved optical mammography operating at wave-lengths longer than 900 nm has been developed. It is a scanning system that relies on the acquisition of time-resolved transmittance curves at 683, 785, 912, and 975 nm, with a total measurement time of approximately 5 min for an entire image. Breast structures and lesions can be discriminated based on the different absorption and scattering properties at the four wavelengths, which reflect different contributions of oxyhemoglobin, deoxyhemoglobin, water, and lipids, as well as distinct structures. The system is currently used in a European clinical trial.