Dipole-dipole interactions in nanoparticle superlattices

Nanoparticles often self-assemble into hexagonal-close-packed (hcp) structures although it is predicted to be less stable than face-centered-cubic (fcc) packing in hard-sphere models. In addition to close-packed fcc and hcp superlattices, we observe formation of nonclose-packed simple-hexagonal (sh) superlattices of nearly spherical PbS, PbSe, and gamma-Fe2O3 nanocrystals. This surprisingly rich phase diagram of monodisperse semiconducting nanoparticles is explained by considering the interactions between nonlocal dipoles of individual nanoparticles. By calculating the total electrostatic and dispersive energies, we explain stability of the hcp and sh nanoparticle superlattices, introduce the superlattice phase diagram, and predict antiferroelectric ordering in dipolar nanoparticle superlattices.     

A control system of an electromagnetic bearing

A three-loop control system for the radial electromagnetic bearing of powerful rotating machines is proposed, the working clearances in which between the stator and rotor amount to tenths of a millimeter with a rotor weight of about 1 t. In the open state, the system is unstable and has features that need to be taken into account when creating the controllers. The control system is designed in accordance with general principles typical for the systems of subordinate regulation. The problems of design of the pulse-control system and various variants of constructing the internal current loop were considered. For calculating the parameters of controllers, the method of transfer functions and z-transformation method were used. At the initial stage, the internal current loop was investigated and it was revealed that the construction of the current loop of an electromagnetic bearing with a relay controller operating in a sliding mode is the most appropriate. In accordance with the mathematical model of an electromagnetic bearing and corresponding structural diagrams, simulation models were designed in the MATLAB/Simulink software package. As a result of simulating the pulsed control system of an electromagnetic bearing, oscillograms of transient processes under control and disturbance effects were obtained. Analysis of transient processes during simulation revealed that electromagnetic bearings equipped with a three-loop control system have a high static rigidity and high operating speed. The obtained results were used in constructing a control system using the electromagnetic bearing of the gas pressurizer at the Pomarskaya compressor station.     

High-Power Electric Ship Propulsion Systems with Advanced Frequency Converters

Russian Electrical Engineering - Three types of frequency converter (FC) structures are considered as parts of high-power electric ship propulsion systems—multilevel FCs, cascade FCs, and FCs...     

Physical–chemical model of processes at detonation synthesis of nanodiamonds

This article presents a principally new physical–chemical model of nanodiamond formation at explosion, which describes adequately all the existing experimental data on detonation synthesis of diamonds. According to this model, the detonation wave performs activation rapidly; then the reaction mixture composition keeps varying. In the diagram C – H – O this process results in continual motion of the point imaging the reaction mixture composition. The ratio of the diamond phase amount to the condensed carbon quantity in the explosion products is defined by the width of the section this point passes over in the diamond formation zone. Motion of the point in the area below the line H – CO results in decrease of the condensed carbon (CC) amount. Diamonds are formed by the free-radical mechanism in the unloading wave.     

Evaluation of the Potential and Technology for Development of Deposits of Copper-Pyrites Ores in the Circumpolar Ural Zone

Metallurgist - On the basis of geological assessment of reserves of copper ore in the territory of the Khanty-Mansiisk Autonomous Okrug–Ugra possibilities are considered for developing...     

Accident Tolerant Fuel with Chromium-Coated Fuel-Rod Cladding

Atomic Energy - The accident at the Fukushima NPP (Japan) showed the particular danger of a steam-zirconium reaction arising when the temperature of the fuel-rod cladding rises after loss of...     

Prospective Accident-Tolerant Uranium-Molybdenum Metal Fuel

Atomic Energy - Selection criteria based on density and uranium capacity are presented for fuel to be used in accident-tolerant fuel rods. The optimal composition of the uranium-molybdenum alloy is...     

Effect of the Cooling Rate on the Microstructure and Properties of C92900 Bronze

Russian Journal of Non-Ferrous Metals - In mechanical engineering, antifriction tin bronzes are used for manufacturing friction parts, for example, C92900 bronze, which is used on aircraft braking...