Controlled Formation of β-Si3N4 on Native Oxidized Silicon Wafers in Ammonia Flow

Crystallography Reports - The formation of β-Si3N4 for subsequent growth of AlGaN and GaN heterostructures of silicon wafers has been studied. It is established that the native oxide layer...     

3-Fluoroalkyl (CF3, CHF2, CH2F) Cyclobutane-Derived Building Blocks for Medicinal Chemistry: Synthesis and Physicochemical Properties

Synthesis and physicochemical characterization of all possible cis- and trans-1,3-disubstituted cyclobutane-derived amines and carboxylic acids bearing mono-, di- and trifluoromethyl groups at the C-3 position is disclosed. Tetramethylammonium fluoride (TMAF)- or morpholinosulfur trifluoride (Morph-DAST)-mediated nucleophilic fluorination of appropriate cis- and trans-diastereomeric substrates was used as the key step for the preparation of CH₂F- and CHF₂-substituted derivatives. To obtain the corresponding cis- and trans-isomeric CF₃-substituted derivatives, resolution of known 3-(trifluoromethyl)cyclobutanecarboxylic acid (obtained as a mixture of diastereomers) was applied. The proposed procedures were suitable for the preparation of corresponding fluoroalkyl-substituted cyclobutane-derived amines and carboxylic acids on up to 50 g scale. All 12 building blocks obtained were characterized by measuring dissociation constants (pK_a) and lipophilicities (LogP, for model derivatives) to evaluate the effect of the fluoroalkyl substituents on their physicochemical properties relevant to further drug discovery applications.     

Numerical modeling of a turbulent flow behind a heated grid

A numerical model of the dynamics of turbulence and temperature fluctuations behind a heated grid located in a wind tunnel is constructed on the basis of closed Kármán-Howarth and Corrsin equations. Results calculated by this model are in reasonable agreement with available experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 118–126, May–June, 2009.     

High-Quality AlN Layers Grown on Si(111) Substrates by Metalorganic Chemical Vapor Deposition

Crystallography Reports - The effect of trimethylaluminum preflow time on the crystalline quality of AlN films grown by metalorganic chemical vapor deposition on Si(111) substrates has been...     

Ion-plasma technologies for the preparation and modification of nanosized LiF layers

The characteristics of LiF films containing Ag nanoparticles prepared via vacuum thermal deposition and magnetron sputtering, and then painted in microwave discharge plasma, are investigated. It is shown that simple and freely available ion-plasma technologies allow us to obtain nanosized LiF layers promising for use in photonics.     

Silicate coatings on titanium, modified with transition metal oxides and their activity in CO oxidation

CuO+M _x O _y /TiO₂+SiO₂/Ti composites (M = Mn, Fe, Co, Ni) were produced by plasma-electrolytic oxidation and impregnation, followed by annealing. The elemental and phase composition of these composites were examined and their activity series in CO oxidation was determined.     

On numerical modeling of local density perturbation dynamics in a pycnocline using moving grids

The plane unsteady problem on evolution of the local mixed fluid region in a pycnocline is considered. Results of computations using stationary (fixed) inhomogeneous and orthogonal moving grids are presented.     

A comparative study of the performance of high-resolution non-oscillating advection schemes in the context of the motion induced by mixed region in a stratified fluid

The problem of a two-dimensional fully mixed region collapsing in continuously density-stratified medium is considered. This article deals with the numerical treatment of the advective terms in the Navier-Stokes equations in the Oberbeck-Boussinesq approximation. Comparisons are performed between the upwind scheme, flux-limiter schemes, namely, Minmod, Superbee, Van Leer, and Monotonized Centred (MC), the monotone adaptive stencil schemes, namely, ENO3 and SMIF, and weighted stencil scheme WENO5. We used laboratory experimental data of Wu as a benchmark test to compare performance of different numerical approaches. It is found that the flux-limiter schemes have the smallest numerical diffusion. The WENO5 scheme describes more accurately the width of collapse region variation with time. All considered schemes give a realistic pattern of internal gravity waves generated by collapse region.     

On the numerical modeling of the dynamics of homogeneous isotropic turbulence

Using a series of mathematical models based on the closed Karman-Howarth equation, the numerical modeling of the dynamics of homogeneous isotropic turbulence was carried out. Computational results agree with known experimental data. Mathematical models are compared.     

Medium energy ion scattering spectroscopy: Study of germanium amorphization under ion irradiation

An experimental setup for medium energy ion scattering spectroscopy allowing materials elemental composition diagnostics has been developed. A target composed of single-crystalline Ge with a smooth surface and structural inhomogeneity several nanometers thick has been prepared for conducting the experiments. Experiments have shown that the depth resolution of the method was 6 Å.