Polymeric film formation in spin coating

The results of numerical modeling of polymeric film formation under mass force action are presented. The instability of non‐Newtonian liquid front edge at the initial stage of flow over a disk is studied. The quasi‐stationary shape of the liquid film (in front edge vicinity) speading over the surface is determined for certain rheology laws. At the modeling of the second stage of coating flow, the special attention was paid to the effects connected with the two‐dimensional character of the flow. The impact of rheological properties of a liquid on the free surface shape was studied using codes that calculate the two‐dimensional non‐stationary flow of non‐Newtonian liquid. The factors that determine the final shape of polymeric coating free surface are discussed.     

Calcium phosphate powders synthesized from calcium chloride and potassium hydrophosphate

Porous ceramics based on Ca₃(PO₄)₂ (TCP) was obtained by sintering of a mixture of hydroxyapatite (HAp) and brushite (CaHPO₄·2H₂O) powders. The main interaction of HAp + CPP (Ca₂P₂O₇) → TCP type in the composite sample HAp/brushite takes place at temperatures higher than 700 °C and leads to rather uniform porous microstructure. We have suggested that CPP-like phases (and especially K₂CaP₂O₇) undergo partial decomposition accompanied by evaporation of P₂O₅. The role of KCl—the by-product of solution synthesis of HAp and brushite powder precursors, consists in (i) it replace in part Ca in CPP phase making last one more reactive, (ii) it switches sintering of the ceramics in liquid-phase regime, (iii) at higher temperature it evaporates and, thus, contributes to formation of pores in the ceramics.     

Homogeneous algorithms for multiextremal optimization

The class of homogeneous algorithms for multiextremal optimization is defined, and a number of theorems are proved, including a sufficient condition for the convergence of homogeneous algorithms to a global minimizer. An approach to the synthesis of homogeneous algorithms based on model multi-peak functions is proposed. The existing algorithms are reviewed, and a new efficient multidimensional algorithm based on the Delaunay triangulation is constructed. Some numerical results are presented.     

On the effect of “Dead Water” in a stratified liquid on a solid bottom

The influence of a solid bottom on the ??dead water?? effect for gravitational and fluctuation waves (having the same dispersion law), as well as capillary waves, is calculated in a linear statement. It is found that the presence of a solid bottom aggravates the dead water effect.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Structural instability and superconductivity in B{a_{1 - x}}{K_x}Bi{o_3}

We report results of the ultrasonic investigation of Ba_1-xK_xBiO₃ superconducting (SC) single crystals for two potassium concentrations and in a wide temperature range including the normal and the SC states. An instability of the crystal lattice that develops above the superconducting phase transition leads to a softening of both the transverse c₄₄ and the longitudinal c₁₁ modes at temperatures between 200 K and 50 K. In the case of Ba_0.65K_0.35BiO₃ a pronounced hysteresis was discovered. Low temperature X-ray powder diffraction analysis does not reveal any change of the cubic structure in the samples within a resolution of our X-ray technique. The softening of the elastic moduli, the hysteresis, the maximum in the attenuation of sound along with the possible short- (or long-) range structural distortion can be explained qualitatively in a simple model by assuming a coupling of the acoustic modes with the anharmonic oscillations of BiO₆ octahedra. Some weak anomalies are discovered in the velocity of the longitudinal sound in the vicinity of the superconducting phase transition. Received 25 June 1999 and Received in final form 14 February 2000     

Synthesis of 4-Substituted N-Alkyl-1,3-dithiolan-2-imines

Russian Journal of Organic Chemistry - S-(2-Thiocyanatopropyl) N-alkyl-N-methylcarbamothioates were synthesized from N-alkyl-1,3-oxathiolan-2-imines by reaction with potassium thiocyanate, and...     

Synthesis of diacetylamino and diamino derivatives of adamantane series

1,3-Diacetylamino derivatives were synthesized directly from adamantane series hydrocarbons or from adamantan-1-ylacetic acids by a one-pot method with a succession of an oxidation stage and Ritter’s reaction in nitric acid and in a mixture of sulfuric and nitric acids. The hydrolysis of 1,3-diacetylamino derivatives in an acidic medium leads to scaffold diamines and diaminoacids.     

Frequency characteristics of air-structural and structural sound transmission in human lungs

From an independent sampling of data on luminal probing of the lungs of 20 people, based on an analysis of the phase characteristics of the coherency function of the signal with linear frequency modulation in a frequency band of 80–1000 Hz recorded above the trachea and different areas of the chest, the frequency selectivity of the structural and air-structural transmission variants has been revealed. It has been established that structural sound transmission on average is observed in a band from 100 to 280 Hz and air-structural propagation lies in the frequency range from 100 to 500–700 Hz. Over areas of the lungs characterized by the presence of aerated tissues (the apex and lower lobe), more frequently there is air-structural transmission, whereas in the vicinity of dense organs of the mediastinum (intercapsular region), on the contrary, structural propagation dominates.