Steam-activated FeMFI zeolites as highly efficient catalysts for propane and N2O valorisation via oxidative conversions

The reaction between C3H8 and N2O over steam-activated FeMFI zeolites leads to high yields towards propene (24%) and propionaldehyde (6%) at 773-798 K.     

New and efficient high Stokes shift fluorescent compounds: unsymmetrically substituted 1,2-bis-(5-phenyloxazol-2-yl)benzenes via microwave-assisted nucleophilic substitution of fluorine

Two new unsymmetric derivatives of 1,2-bis-(5-phenyloxazol-2-yl)benzene (ortho-POPOP) were synthesized via microwave-assisted nucleophilic substitution of fluorine which appears to be significantly more efficient compared with conventional thermal activation. The compounds synthesized are characterized by high fluorescence Stokes shifts (6000-11,000 cm⁻¹) in solvents of various polarity, intermediate-to-high fluorescence quantum yields and lifetimes in the range of several nanoseconds.     

Energy level diagram and mechanism of photodissociation of triazenes and pentazenes

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 2, pp. 286–290, August, 1990.     

Nonclassical Impurity Transport in the Dykhne Model with Coordinate-Dependent Parameters. Fermat Principle

Journal of Experimental and Theoretical Physics - An asymptotic theory of impurity transport has been developed for the simplest regularly inhomogeneous medium (Dykhne model, demonstrating...     

Reactive diffusion in Sc/Si multilayer X-ray mirrors with CrB2 barrier layers

Processes undergoing in Sc/Si multilayer X-ray mirrors (MXMs) with periods of ∼27 nm and barrier layers of CrB₂0.3- and 0.7-nm thick within the temperature range of 420–780 K were studied by methods of small-angle X-ray reflectivity (λ=0.154 nm) and cross-sectional transmission electron microscopy. All layers with the exception of Sc ones are amorphous. Barrier layers are stable at least up to a temperature of 625 K and double the activation energy of diffusional intermixing at moderate temperatures. Introduction of barriers improves the thermal stability of Sc/Si MXMs at least by 80 degrees. Diffusion of Si atoms through barrier layers into Sc layers with formation of silicides was shown to be the main degradation mechanism of MXMs. A comparison of the stability for Sc/Si MXMs with different barriers published in the literature is conducted. The ways of further improvement of barrier properties are discussed.     

Micro diffuser flow modeling for cold gas propulsion systems

The use of highly diluted and hypersonic gas flow is in the scope of application of cold gas thrusters for space applications. Satellites and small spacecrafts are navigated to their orbital trajectory with these nozzles. Inside these propulsion systems high density gradients are dominating the efficiency and the thrust steering behavior of the propulsion systems. Micro flows in the transient regime between free molecular flow and continuous flow are not able to be computed with trustworthy results by using a continuous model with no-slip boundary conditions. Therefore boundary slip-velocity models are used for modeling the reduced wall shear stress. Molecular shear stresses decrease the molecular mean velocity near the wall. With a Knudsen number depending slip-velocity model the effective shear stress is computed by the mean gradient of the velocity profile near the wall. In the present study a trans-sonic nozzle flow is computed by using a calibrated velocity slip model what depends on the Knudsen number. The Knudsen numbers are lower the Kn=1 at the nozzle neck of the propulsion system. The results are compared with simulation results of a uniform channel flow and computations of the corresponding no-slip approach. The differences in the hypersonic region are following discussed. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Asymptotic regimes and structure of concentration tails in the Dykhne model

A transport problem is solved for a high-contrast regularly inhomogeneous medium. Transport regimes and structure of the concentration tails in high-permeability regions are analyzed for two geometries of such regions: a plane layer and a right cylinder. It is shown that changes with time of transport regimes lead to complex asymptotic particle distributions at long distances (concentration “tails”). The time dependence of the total number of active particles and depth of particle penetration into the low-permeability region are calculated.