Stripes in Cuprates as Dominoes Tilings of an (n×2)-Checkerboard

Using two types of bisoliton pairings leads to charged stripes in YBCO, Which are similar to tiling of (1×2)-dominoes in an (n×2)-checkerboard. We estimated the stripe length in YBCO and determined accurate values of T _c,max as a function of the golden ratio and the numbers of bisolitons in the stripes. This model predicted that the two possible orientations of stripes are vertical and horizontal. Our results agree well with experimental data.     

Interaction between multiply charged manganese nanoclusters and sulfur atoms in silicon

We have studied the interaction of manganese nanoclusters with sulfur atoms in silicon. The results indicate that both simultaneous and sequential codoping with manganese and sulfur has little effect on the electrical properties (resistivity, carrier mobility, and conductivity type) of silicon. There is no extrinsic photoconductivity in the IR spectral region, and the material has only a small positive magnetoresistance. According to electron paramagnetic resonance data, the material contains only atomic manganese. Sulfur atoms in the silicon lattice are assumed to facilitate the capture of doubly charged manganese interstitials (Mn²⁺) at negatively charged vacancies, resulting in the formation of a multicomponent impurity cluster of composition Si₂S²⁺Mn²⁻ in the silicon lattice throughout the crystal. The optimal thermal annealing conditions for the formation of such clusters are determined. The ability to produce Si₂S²⁺Mn²⁻ clusters with controlled concentration allows one to tailor the main fundamental parameters of silicon and opens up new possibilities for such materials in nano- and microelectronic device development.     

Neural-network simulation of diesel operation under a nonsteady load

The operation of diesel engines with nonsteady loads is considered. Numerical experiments are based on a model, a neural network, and test-bench data.     

Effect of doping with rare-earth elements (Eu,Tb, Dy) on the conductivity of Bi2Te3 layered single crystals

The temperature dependences of the resistivity in the directions parallel and perpendicular to the layer plane in the range of temperatures T = 5–300 K and the Hall and transverse magnetoresistance effects (magnetic fields <80 kOe, T = 5 K) are studied for doped and undoped Bi₂Te₃ layered single crystals. It is shown that, upon the doping of Bi₂Te₃ crystals with atoms of rare-earth elements (Eu, Tb, Dy), the resistivity in the directions parallel and perpendicular to the layer plane in Bi₂Te₃ increases. The increase in the resistivity is caused mainly by a decrease in the charge-carrier mobility because of an increased contribution of charge-carrier scattering at defects to scattering processes. The charge-carrier concentrations and mobilities as well as the Hall factor defined by the anisotropy of the effective masses and by the orientation of ellipsoids with respect to the crystallographic axes are estimated.

     

Pilot tests of a new domestic ZhKD catalyst for the dehydrogenation of isoamilenes into isoprene

At the Synthetic Rubber Plant of OAO Nizhnekamskneftekhim, the dehydrogenation of isoamilenes into isoprene is currently performed on KDOM-08 catalysts with an insufficiently high yield of isoprene throughout the period of its industrial operation. More stable and highly active catalysts must be used to make the process more efficient. Under Russian Federation Government Decree No. 218, ZhKD-1 and ZhKD-2 iron-potassium catalysts have been developed by improving their formulas and optimizing their phase composition through selecting the proper ratio of initial compounds. To evaluate the possibility of transitioning to the new domestically-produced iron-potassium catalysts, we have performed pilot tests of the ZhKD-1 and ZhKD-2 catalysts in the dehydrogenation of methylbutenes into isoprene in adiabatic flow fixed-bed reactors at the Synthetic Rubber Plant of OAO Nizhnekamskneftekhim. The KDOM-08 catalyst used in the amount of 25 t in reactor 1 of the first system is taken as a base for comparison. The ZhKD-1 and ZhKD-2 catalysts are loaded into parallel reactors 7 and 8 of the fourth system. The KDOM-08 catalyst is shown to operate more efficiently under industrial conditions at loads of 1.0–2.0 t/h for 1000–3000 h, after which its performance characteristics deteriorate due to its gradual deactivation. The ZhKD-1 and ZhKD-2 catalysts are substantially superior to their industrial analogues in isoprene yield. It has been found that the ZhKD-2 catalysts operate more efficiently at even longer runs (4000–5000 h) and feedstock flow rates of 1.0–2.0 t/h, and the ZhKD-1 catalysts exhibits better activity (30–33 %) and selectivity (87–92 %) at higher loads of 2.3–3.0 t/h for up to 5000 h. From our analysis of the catalysts’ operation over the last 1000 h, it follows that at the same process temperatures (619°C) and feedstock loads (2.5 t/h), the ZhKD-1 and ZhKD-2 catalysts operate at a lower steam dilution coefficient (6.1 t/t) than the KDOM-08 catalyst (6.8 t/t). The rebuilding of reactors 7 and 8 allows the loaded catalyst mass to be reduced from 25 to 17 t, thereby almost doubling the daily output of isoprene per ton of catalyst. It is obvious that higher activity and selectivity along with smaller loads makes the use of the ZhKD-1 and ZhKD-2 catalysts economically profitable.     

Photoelectric determination of the series resistance of multijunction solar cells

A method for determining the series resistance R _s of multijunction solar cells is suggested and sub-stantiated. The method uses the presence of a maximum in the dependence of the efficiency on the sunlight concentration ratio ??(X) or in that of the operating voltage on the photogenerated current, V _m (J _g ). The study employs the concept that, in a limited but practically important range of photogenerated currents (up to the maximum ??), the series resistance can be represented by a fixed quantity that is linear and independent of J _g . It is analytically substantiated that this resistance can be found from the formula R _S = (E/J _g )_{?? = max}, where E = AkT/q and A and J _g are local values of the ideality factor and photogenerated current at the maximum ?? (or V _m ). It is shown that the value of R _s , determined by this method, is independent of the spectral composition of the incident light, which was experimentally confirmed in a study of the photovoltaic characteristics of triple-junction InGaP/GaAs/Ge solar cells. The method is suitable for both multi- and single-junction photoelectric converters.     

Salient features of deactivation of an iron oxide catalyst for dehydrogenation of methylbutenes to isoprene in industrial adiabatic reactors

The problems of deactivation of iron oxide catalysts in the process of industrial dehydrogenation of methylbutenes to isoprene have been considered. The dependence of deactivation of the catalyst fixed bed on the time on-stream of different sections of the catalyst along the reactor height has been examined. The cause of poor performance of a part of the catalyst bed has been revealed and substantiated. Based of the results of the study, the authors propose an approach to predicting the catalyst performance during a long time on-stream.     

Tin- and copper-based electrochemical coatings for sliding bearings

Copper- and tin-based electrochemical coatings are obtained. The results of disk-shoe couple tests show the wear and wear rate of the coatings; their structure is studied demonstrating that bi- and tricomponental electrochemical coatings boost considerably the copper and bronze wear resistance, making them useful for the manufacture of sliding bearings.     

Magneto-rotation-fibre-reinforced thermoelastic with gravity and energy dissipation

In this article, two theories of the generalized thermoelasticity Green-Naghdi theory (of type II and III) are applied, as well as the coupled theory to study the effect of magnetic field and rotation under influence of gravity on 2D problem of a fibre-reinforced thermoelastic. The normal mode analysis is used to obtain the expressions for the temperature, displacement components and the thermal stresses distributions. The resulting formulation is applied for two different concrete problems. The first concerns the case of a punch moving across the surface of semi-infinite thermoelastic half-space subjected to appropriate boundary conditions. The second deals with a thick plate subjected to a time-dependent heat source on each face. Numerical results are illustrated graphically for each problem considered. A comparison is made with the results predicted obtained by the two theories in the presence and absence of magnetic field, rotation and gravity field.