Mathematical representation of radiality constraint in distribution system reconfiguration problem

Distribution systems are most commonly operated in a radial configuration for a number of reasons. In order to impose radiality constraint in the optimal network reconfiguration problem, an efficient algorithm is introduced in this paper based on graph theory. The paper shows that the normally followed methods of imposing radiality constraint within a mixed-integer programming formulation of the reconfiguration problem may not be sufficient. The minimum-loss network reconfiguration problem is formulated using different ways to impose radiality constraint. It is shown, through simulations, that the formulated problem using the proposed method for representing radiality constraint can be solved more efficiently, as opposed to the previously proposed formulations. This results in up to 30% reduction in CPU time for the test systems used in this study.     

An effective approach for parameter determination of the digital phase-locked loop in the z-domain

In digital communication systems, typical methodologies in determining loop parameters of the digital phase-locked loop (DPLL) are based on the mapping transformation from the analog domain to the digital domain. However, such transform based algorithms are relatively complicated and not straightforward, and they also cause the problem that loop parameters are affected by the pre-detection integration time greatly. To solve these issues, an effective direct method of determining loop parameters of the second-order DPLL in the z-domain is proposed in this paper. Through ascertaining specific positions of the closed-loop system function's poles inside the right-hand side of the z-plane's unit circle, unknown parameters are calculated directly and flexibly in this method, which enables the DPLL to acquire good low-pass filtering characteristic and system stability. This novel method not only reduces the complexity of solving the parameters, but also eliminates the effect of the pre-detection integration time on loop parameters. Simulation results are provided to confirm the feasibility of the proposed method and to show that the DPLL obtained by this method achieves the similar tracking performance to the discretized PLL.     

Retardation of High-Temperature Fuel Ash Corrosion of Fireside Boiler Tubes via Nanoparticles

The high-temperature corrosion rate of boiler tubes was studied as a function of inhibitor concentration, time, and temperature in the absence and presence of fuel ash. Samples of steel tubes were taken from boilers that operate in Northern Baghdad Station for Electric Power Generation. Fuel ash was collected from the boiler combustion chamber, as well. Normal and nano-MgO were used as a corrosion inhibitor in different mixing ratios. A weight loss technique was used to evaluate the corrosion rates, while scanning electron microscopy was used to study the surface morphology. It was seen that corrosion rates increased with both time and temperature, and decreased with the addition of inhibitors. The maximum inhibitor efficiency was 81 %, obtained via using nano-MgO at mixing weight ratio 2:1, 600 °C, and 10 h. The Presence of fuel ash had harmful effects on the steel surface.     

Effect of annealing temperature on the multiferroic properties of 0.7BiFeO3–0.3Bi0.5Na0.5TiO3 solid solution prepared by sol–gel method

Room-temperature multiferroic 0.7BiFeO₃–0.3Bi_0.5Na_0.5TiO₃ solid solution ceramics have been prepared by the sol–gel method. We have discussed the annealing temperature dependence of the multiferroic properties. The samples are annealed at 1023, 1123, 1223 and 1323 K for 3 h, respectively. X-ray diffraction patterns identify that all samples are pure. Scanning electron micrographs present the increasing grain size with higher annealing temperature. Magnetic, ferroelectric and dielectric properties are enhanced obviously with the increase in annealing temperature. The coexistence of ferroelectric and ferromagnetic properties is also proved at room temperature. In addition, it reveals that the optimal annealing temperature accompanied with favorable multiferroic properties of 0.7BiFeO₃–0.3Bi_0.5Na_0.5TiO₃ solid solution ceramics is near 1223 K.     

Flash pyrolysis of an Italian low rank coal

Flash pyrolysis of low rank Italian coal (Sulcis coal) has been studied in a fluidized bed pyrolyser using temperatures between 460 and 900°C. The maximum yield of oils (tars) was obtained at about 600°C. Yields of C₁C₃ hydrocarbons increased with increasing temperature, reaching 6% at 900°C. Fractionation of tars showed that the composition was strongly dependent on pyrolysis temperature. By the behaviour of the composition of tars on temperature, a possible reaction mechanism is suggested.     

Facile synthesis of different morphologies of Te-doped ZnO nanostructures

Te-doped ZnO nanostructures were synthesized by an annealing (vapor–solid) process under ambient conditions, and characterized in terms of their morphological, structural, compositional and optical properties. The structural and morphological characterizations revealed that the synthesized nanostructures were well-defined multipods, needles and spherical particles, and possessed well-crystalline ZnO wurtzite hexagonal phase. Also, in the X-ray diffraction studies, the presence of a shift in the peak positions towards a lower angle, and a decrease in the intensity, with an increase in the Te concentration, as compared to the undoped ZnO, were observed. The chemical composition confirmed the presence of Te, in the case of multipod and needle morphologies. The effect of doping on the crystalline quality and optical properties was also investigated, by using photoluminescence (PL) and Raman spectrometers. The Raman results demonstrated that the doped ZnO nanostructures had a lower crystalline quality than the undoped ZnO. Moreover, the PL results showed a decrease in the band gap for the doped ZnO nanostructures, in comparison to the undoped ZnO. A possible growth mechanism was also proposed.     

Study for prevention of steel corrosion by sacrificial anode cathodic protection

Corrosion of steel tube in sea water was controlled by cathodic protection. Sacrificial anode technique was used. In this technique, weight loss method was used to determine the rate of zinc consumption as a function of temperature, time, pH and solution velocity. Reaction kinetics studies showed that the rate of zinc consumption was first order. Activation parameters were obtained from Arrhenius equation and transition state equation. Two mathematical models were suggested to represent the consumption data. Statistical analysis proved that the second-order multi-terms model was better than the one-term model.     

Carbon nanotubes-templated assembly of LaCoO3 nanowires at low temperatures and its excellent catalytic properties for CO oxidation

This work reports the mild synthesis of LaCoO₃ catalyst with the interesting nanowire morphology in the presence of both carbon nanotubes (CNTs) and citrate. In comparison, LaCoO₃ nanoparticles were prepared by conventional citrate method. The samples were characterized by TEM (Transmission electron microscopy), XRD (X-ray diffraction), N₂ adsorption isotherm and CO-TPD (Temperature-programming desorption), etc. The results showed that the morphology of LaCoO₃ catalyst was controlled effectively by the CNTs template; and that the adding of citrate not only controlled effectively the stoichiometric ratio of La to Co, but also reduced the crystallizing temperature of LaCoO₃ crystal greatly. Moreover, after calcined at 750 °C for 48 h, LaCoO₃ nanowires exhibited higher thermal stability and catalytic activity for CO oxidation, compared with the nanoparticles.     

A thermal model of friction stir welding applied to Sc-modified Al–Zn–Mg–Cu alloy extrusions

A thermal model of friction stir welding is presented that proposes an energy-based formulation of the Johnson–Cook plasticity model in order to account for heat generation due to plastic deformation. The proposed formulation is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature of the alloy and the welding energy. The thermal model is applied to Sc-modified Al–Zn–Mg–Cu alloy extrusions joined by friction stir welding at 225, 250, 300 and 400 RPM (all other weld parameters held constant). With the incorporation of heat generation due to plastic deformation, the thermal model accurately predicts the maximum weld temperatures and temperature profiles at the higher energy weld conditions, i.e. 300 and 400 RPM. At the lower energy welds (i.e. 225 and 250 RPM) where plastic deformation contributes a larger portion to the total heat generation, the model under-predicts the maximum weld temperatures under the tool shoulder but shows good agreement with the remaining experimental temperature data.     

Characterization and design of out-of-ecliptic trajectories using deterministic crowding genetic algorithms

This paper investigates the application of Deterministic Crowding Genetic Algorithms to the characterization and design of special trajectories in the spatial circular restricted three-body problem with the Sun and the Earth as the primary gravitational bodies. These trajectories are characterized by large displacements normal to the Sun–Earth ecliptic plane. This attribute renders them particularly suitable for space-borne infrared observatories, because the normal component of motion results in a significantly reduced noise from the interplanetary (zodiacal) dust and a concomitant reduction in the necessary size of the optical collecting area. The characterization process yields three new types of trajectories with large normal displacement. By using the results of the characterization process, we continue with genetic algorithms-based trajectory design, which yields promising results in terms of reduction of the zodiacal dust noise.