Stability and performance improvement of extremum seeking control with sliding mode

Extremum seeking control is an adaptive control strategy for a system to iteratively extremize a function in real-time. In this paper we investigate stability and performance improvement by using sliding mode concepts in extremum seeking controllers.     

Simultaneous scheduling of football games and referees using Turkish league data

Assignment decisions of referees to football (soccer) games are highly debated in sports media. Referee assignments are typically done on a weekly basis as the league progresses. However, this practice ignores important workload constraints on referees. Moreover, referees' skill levels should also be considered in determining their assignments. In this article, we first give a mixed integer linear program formulation for the problem of simultaneously generating a game schedule and assigning main referees to games by incorporating specific rules in the Turkish league. We also approach this problem using a genetic algorithm (GA) because of the computational difficulties in solving the problem. In the GA solution pool, we suggest using templates for referee assignments that follow several referee‐related workload constraints. We explain how these templates can be obtained by solving a mixed integer linear model prior to running the GA. The usage of these templates for referee assignments is conceptually similar to using a basic match schedule for game scheduling such as the one used in the Turkish Football League. We use the Turkish Football League fixtures for 2010–2013 as a case study. Experiments with the GA using real‐world data show a rather modest performance in terms of computation time and objective function value. Our numerical results indicate that the problem is extremely hard to solve.     

An educational software package for Thyristor Switched Reactive Power Compensators using Matlab/Simulink

In this paper, an educational software package called TSCOM (Thyristor Switched Reactive Power Compensators) has been developed. The TSCOM software package contains simulation models of Thyristor Switched Capacitor (TSC) and Thyristor Switched Reactor (TSR)-based Static VAr Compensator (SVC) which are two of the shunt Flexible AC Transmission Systems (FACTS) devices. The design and simulations of TSC and TSR-based SVC are proposed using the Matlab/Simulink 7.04® and SimPowerSystems. The TSC and TSR-based SVC devices are demonstrated at two bus, three bus, infinite-bus, single-phase, three-phase, static load, dynamic load and stair-case load conditions. The effects of TSC and TSR-based SVC devices on load voltage are also analyzed. Student feedback indicates that this package is user-friendly and considerably effective for students and researchers to study theory of switched compensators, the reactive power control and voltage regulation. The proposed package will help to design the practical prototypes for students and researchers.     

Use of tuffs from central Turkey as admixture in pozzolanic cements: Assessment of their petrographical properties

Tuffs from Galatean Volcanic Province were studied for their use as admixtures in pozzolanic cements. The effects of petrographical properties on the pozzolanic activity of mortar specimens were investigated by optical microscopy, X-ray powder diffraction (XRD), scanning electron microscope equipped with an energy dispersive X-ray system (SEM-EDX), and chemical analysis. The chemical compositions of tuffs conform well to the requirements of ASTM C 618 and the Turkish Standard TS 25, and SiO₂+Al₂O₃+total Fe₂O₃ exceeds 70%. Pozzolanic activities were determined according to their 7th day flexural and compressive strengths and vary between 1.7 and 3.0 MPa and 7.4 and 16.0 MPa, respectively. The mechanical strength of mortars is affected by alteration of tuffs used in the mixture. Clay minerals and zeolites form by the alteration of volcanic glass, which is the most reactive phase and has a reducing effect on mechanical strength. The alteration also causes the enrichment of tuffs with respect to K₂O+Na₂O. The methods used provided rapid evaluation of tuffs as potential admixtures in cements.     

Synthesis and characterization of lithium calcium phosphate ceramics

The crystal structure, thermal, dielectrical, alternating current conductivity and microstructure properties of lithium calcium phosphate ceramics synthesized by the sol–gel method were investigated. The average crystallite size, crystallinity, activation energy and enthalpy of crystallization of Ca₁₀Li(PO₄)₇ ceramics were determined. The X-ray diffraction (XRD) results indicated that the apatitic structure belonging to HAp was transformed fully to Ca₁₀Li(PO₄)₇ phase with the addition of Li. The Avrami exponents of the samples suggest that the crystallization mechanism is based on the surface nucleation and one-dimensional growth. It was found that the alternating current conductivity mechanism of the ceramics is controlled by the hopping motion involving a translational motion with a sudden hopping. The dielectric constant of the samples shows a small increase with increasing amount of Li.     

Operation of TCSU with Internal Flux-Conserving Rings

The Translation, Confinement, and Sustainment Upgrade (TCSU) device is a facility to form and sustain a field-reversed configuration (FRC) in quasi-steady state using rotating magnetic fields (RMF). Recent campaigns include Ti gettering, the installation of a set of internal flux rings, and RMF frequency scans. The Ti gettering campaign was successful, reduced impurities, and reduced deuterium recycling from the walls allowing density control and hotter FRCs [J.A. Grossnickle et al., Phys. Plasmas 17, 032506 (2010)]. Internal flux rings have been installed to provide a uniform flux surface and minimize plasma-wall contact. Results from the internal flux ring operation and an additional Ti gettering campaign are reported. RMF frequencies of 123 kHz and 170 kHz have been investigated and initial results are reported.     

Section modulus of corner joints in furniture frames as engineering design criteria for their efficient construction

Since joints are often the weakest points in furniture construction a detailed analysis of the factors influencing their load bearing capacity and its effectiveness in utilizing the full strength of the wood is reported here.     

Structural and Dielectrical Properties of Ag- and Ba-Substituted Hydroxyapatites

Ag- and Ba-doped hydroxyapatite (HAp) samples were synthesized by sol–gel method. The crystallite sizes for all the samples were found to vary from 26 to 39 nm. Neither Ag nor Ba did result in dramatic changes in the morphology of all the samples, and the Ca/P molar ratio was varied. The dielectric parameters of the samples were changed with the dopant content. The maximum and minimum values of the dielectric constant were observed for 2.0 %Ba-HAp and 0.5 %Ba-HAp samples. The alternating current conductivity indicates that all the samples exhibit the insulator behavior. The results of the biological tests revealed that Ag-containing samples have an antimicrobial activity, while no antimicrobial activity was detected for both HAp and Ba-doped HAp samples.     

The effects of Ni-addition on the crystal structure,thermal properties and morphology of Mg-based hydroxyapatites synthesized by a wet chemical method

Four Mg-based hydroxyapatites (HAps) doped with Ni at various amounts of 0, 0.6, 1.2 and 1.8?at% were prepared at the temperature of 870?°C by a wet chemical synthesis. The crystallite size, lattice parameters and crystallinity percent dramatically decreased with adding of Ni. The amount of HAp phase for all the Ni-containing samples is smaller than that of the Ni-free MgHAp. Furthermore, the lattice strain, stress and anisotropic energy density values were affected by the amount of Ni. The differential thermal analysis (DTA) measurements taken in the temperature range from 25 to 1000?°C showed that all the samples are thermally stable. No significant change in the morphology was observed. It was observed that the gradual introduction of Ni caused the Ca-deficiency.     

Investigations the effects of fastener, glue, and composite material types on the strength of corner joints in case-type furniture construction

This study was carried out to determine the performance of different construction techniques on the diagonal compression and tension strength of case-type furniture corner joints, and to determine the effects on these joints of some factors including the type of joint, the type of composite board and the glue type. For this purpose, melamine-coated particleboard (MCP) and melamine-coated fiberboard (MCF) panels were bonded with polyvinyl acetate D3 (PVA D3), polyvinyl acetate D4 (PVA D4) and Desmodur VTKA (DVTKA) adhesives on spline joint (Sj), butt joints (Buj), biscuit joints (Bij), plain dowel joints (PDj), grooved dowel joints (GDj). It became evident that the diagonal tension and compression strength of the joints is influenced by panel material, type of adhesive and joints. The diagonal tension strength was greater than the diagonal compression strength of all L-type corner joints. The highest diagonal tension strength was obtained in MCF with DVTKA adhesive and GDj while highest diagonal compression strength was obtained in MCP with PVA D4 and Sj. In both tests, MCF corner joints were stronger than MCP corner joints. Furthermore, diagonal tension and compression strength of the joints glued with PVA D4 adhesive was higher than the similar joints glued with PVA D3 and DVTKA adhesives.