Simulation of the process of scaling of tube heat exchangers

A semiempirical model of the process of deposit formation on the inner surface of heat exchanger tubes is obtained. By experimental investigation, constants of the scaling process that close this model are obtained for carbonate-type deposits.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 3, pp. 353–357, March, 1994.     

Efficiency of two pancreatic extracts in patients with cystic fibrosis

Mechanical cell damage was studied in vitro with three types of prostheses: Starr-Edwards, Kay-Shiley and Bj?rk-Shiley valves. Mechanical cell damage was found to be closely related to the flow characteristics in the prosthesis. Considering valves of similar orifice diameter, Bj?rk-Shiley valves produced the lowest rate of haemolysis. This is due to the improved haemodynamic characteristics of the valve which resulted from the laminar type of flow. With Starr-Edwards valves, smaller sizes produced unacceptably high rates of haemolysis. Increasing the mean forward flow across the valve resulted in a disproportionate rise in the energy loss and the rate of haemolysis when compared with Bj?rk-Shiley valves of similar annulus diameters.     

Preparation of MgO nano-rods with strong catalytic activity via hydrated basic magnesium carbonates

MgO nano-rods of several microns in length and 50–100 nm in width were prepared by calcining nesquehonite phase, obtained by simple precipitation using (NH₄)₂CO₃ under ambient condition. The MgO nano-rod with reasonably high surface area (75–120 m² g⁻¹) exhibits strong activity in solvent-free base catalyzed Claisen-Schmidt condensation giving 99% conversion in 2 h and is easily recyclable with no significant change in catalytic activity. Presence of numerous basic sites of different strengths (surface hydroxyl groups, low coordinate O²⁻ sites) is attributed to the observed effect.     

Characterization of various Eu2+ sites in Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ by high-pressure spectroscopy

Photoluminescence of Ba₂SiO₄ and Ca₂SiO₄ activated with Eu²⁺ was investigated at various temperatures (from 10 K to 300 K) and pressures (from ambient to 200 kbar). At ambient pressure and room temperature, under UV excitation both phosphors yielded a green emission band with maxima at 505 nm and 510 nm for Ba₂SiO₄ and Ca₂SiO₄, respectively. The energies of these bands depended on pressure; the pressure shifts were ?12:55 cm^?1/kbar for Ba₂SiO₄:Eu²⁺; and ?5:59 cm^?1/kbar for Ca₂SiO₄:Eu²⁺. In the case of Ca₂SiO₄:Eu²⁺, we observed additional broadband emission at lower energies with a maximum at 610 nm (orange band). The orange and green emission in Ca₂SiO₄:Eu²⁺ had different excitation spectra: the green band could be excited at wavelengths shorter than 470 nm, whereas the orange band — at wavelengths shorter than 520 nm. The pressure caused a red shift of orange emission of 7.83 cm^?1/kbar. The emission peaked at 510 nm was attributed to the 4f⁶5d→4f⁷(⁸S₇₌₂) transition of Eu²⁺ in the β — Ca₂SiO₄:Eu²⁺ phase, whereas the emission peaked at 610 nm — to the γ — Ca₂SiO₄:Eu²⁺ phase. The emission of Ba₂SiO₄:Eu²⁺ peaked at 505 nm was attributed to the 4f⁶5d→ 4f⁷(⁸S_7/2) transition of Eu²⁺ in the β — Ba₂SiO₄ phase.     

Combined chemical peeling and dermabrasion for deep acne and posttraumatic scars as well as aging face

We provide an introduction to genetic linkage analysis. We discuss methods for the genetic analysis of common, complex disease such as diabetes, heart disease or hypertension. We describe the analysis of affected sibling pairs and discuss some of the challenges in applying these methods.     

Broadband down-conversion in Bi–Yb-codoped yttrium and yttrium–aluminum oxides

Comparative study of the broadband down-conversion processes in Bi³⁺–Yb³⁺-codoped yttrium oxide (Y₂O₃) and various yttrium–aluminum oxides (Y₃Al₅O₁₂, YAlO₃ and Y₄Al₂O₉) has been performed from the point of view of search for materials suitable for enhancement of efficiency of silicon solar cells. The studied materials in the form of nanopowders have been synthesized by sol–gel method and characterized by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. Relative down-conversion efficiency for studied materials has been estimated. It was shown that optimal concentration of Yb³⁺ ions should be 2–4 at.% simultaneously with Bi³⁺ ions in the amount of about 1 at.%. Such dopants content provides the highest emission intensity of Yb³⁺ ions in near-infrared when excited into Bi³⁺ ions absorption in ultraviolet. Perspectives of the studied materials for enhancement of silicon solar cells are discussed.     

Effect of metal content on the structure and phase composition of Fullerite-Sn films

This paper reports a study of fullerite-Sn films containing 4, 6, 8, 10, 12, or 20 at % Sn grown by thermal evaporation in vacuum using a combined atomic-molecular flow. The influence of metal content and thermal annealing on the surface topography, structure, and elemental and phase compositions of the fullerite-Sn films has been studied by atomic force microscopy, X-ray and electron diffraction, scanning electron microscopy, and X-ray microanalysis. The results demonstrate that films grown by codeposition of Sn atoms and fullerene molecules on oxidized single-crystal silicon substrates have a granular structure. The phase composition of the fullerite-Sn films varies widely, depending on the percentage of Sn: from an intercalated structure to a mixed-phase composite containing a hexagonal fullerite phase, tetragonal Sn, and fullerite-like structures containing Sn nanoparticles. Thermal annealing of the fullerite-Sn films leads to the formation of a new phase.