Wind turbine speed control of a contactless piezoelectric wind energy harvester

ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.     

Column solid‐phase extraction of sunset yellow and spectrophotometric determination of its use in powdered beverage and confectionery products

A new and simple solid‐phase extraction method for the determination of trace levels of sunset yellow has been developed on Diaion HP 2MG column system. The adsorbed sunset yellow on the resin was eluted with 3 mL of methanol and determined by UV–Vis spectrophotometry at 484 nm. Various experimental parameters such as pH, amount of sunset yellow, flow rates of sample and eluent solutions, resin amount, sample volumes, etc. were investigated. The influences of some alkali, alkali earth and transition metals on the recoveries of sunset yellow were investigated. The recovery values for sunset yellow were higher than 95%. Preconcentration factor was found as 150. The detection limit (three sigma) of the reagent blank for sunset yellow was 5.2 μg L^?1. The relative standard deviations (RSD) of the procedure were found as 3.9%. The validation of the presented procedure was performed by the method of standard addition. The procedure was successfully applied to the determination of trace levels of sunset yellow in powdered beverage and confectionery products.     

Zinc Oxide Nanowire Decorated Single‐Use Electrodes for Electrochemical DNA Detection

The surfaces of pencil graphite electrodes (PGEs) were decorated with zinc oxide nanowires (ZnO NWs) for the electrochemical detection of nucleic acids. ZnO NWs were synthesized through simple hydrothermal method. PGEs decorated with ZnO NWs (ZnO NW/PGEs) were electrochemically characterized through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) following morphological characterization through transmission (TEM) and scanning electron microscopy (SEM). Enhanced sensor response obtained using ZnO NW/PGEs contrary to the bare PGE (control) samples. Our preliminary results simply reveal the potential of combining ZnO NWs with disposable sensor technology for the electrochemical detection of DNA.     

Effects of mixing techniques and dentin moisture conditions on push-out bond strength of ProRoot MTA and Biodentine

Objective: To evaluate the influence of manual and mechanical mixing techniques as well as the effects of moisture on the push-out bond strength of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) and Biodentine (Septodont, Saint Maur des Fosses, France) to radicular dentin.

Material and methods: Two hundred and forty dentin discs were assigned into three groups with respect to the moisture condition tested: (1) dry, (2) paper points, (3) wet. The discs were further divided into four subgroups according to the calcium silicate cements (CSCs) and mixing techniques used: (1) ProRoot MTA mixed manually, (2) ProRoot MTA mixed mechanically, (3) Biodentine mixed manually, and (4) Biodentine mixed mechanically. Bond strengths of the cements to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using three-way ANOVA and Bonferroni post hoc test p = 0.05.

Results: The data indicated that the push-out bond strength values were significantly affected by CSCs, mixing techniques, and moisture conditions (p < 0.001). Dry conditions caused a significant decrease in bond strength values for both CSCs (p < 0.001). The mean bond strength of Biodentine was significantly higher than that of ProRoot MTA, regardless of the mixing techniques and moisture conditions (p < 0.001). Mechanical mixing favored bond strength values statistically compared to manual mixing (p < .001).

Conclusion: The mixing techniques and moisture conditions have an effect on the push-out bond strengths of ProRoot MTA and Biodentine. Dry samples and manual mixing of cements deteriorate the push-out bond strengths values.     

Functionalized Hybrid Coatings on ABS Surfaces by PLD and Dip Coatings

It is important to give water-repellent and antibacterial properties to the acrylonitrile butadiene styrene (ABS) surfaces of the hearing aids. In this study, the sol–gel Si and sol–gel Ti solutions were prepared from the reactions of silicon ethoxide, titanium butoxide and methacrylic acid. The catalyst and Dynasylan F8815 were added to the sol–gel solutions to give hydrophobic properties onto the ABS surfaces. Additionally, silver nanoparticles were synthesized by nanosecond laser and added to the coating solutions to give extra antibacterial properties. The surfaces of the ABS targets were coated using the sol–gel dip coating and pulsed laser deposition techniques. The coatings with good adhesion between film and substrate and good water-repellent properties were achieved. The average contact angles for the coated ABS surfaces were measured in the range between 120 and 125 degrees. The obtained sol–gel materials and produced thin films onto the ABS surfaces were also analyzed in terms of the antibacterial properties. The highly antibacterial properties were observed in the sol–gel solutions and the thin films.     

Preparation and evaluation of linseed oil based alkyd paints

Alkyd resins are produced with reaction of oil or fatty oil, polyol and polyacid. Alkyd resins are commonly used in coating and paint industry due to ease of application in changing environmental conditions. Linseed oil based paints executed all requirements of technical properties, drying time, storage properties, simplicity in maintenance, appearance, economy, etc. In this study, linseed oil based alkyd resins having different oil contents were synthesized     

Effect of calcium hydroxide removal techniques on the bond strength of root canal sealers

To evaluate the influence of calcium-hydroxide(CH) with different vehicles on the push-out bond strength of different canal sealers to radicular dentin. 152 decrowned single-rooted human teeth were used. After preparation of root canals with nickel-titanium rotary files, 8 roots served as control groups. Then, the roots were divided as follows: (1) Calasept and (2) Surepaste (n = 72). Roots were further subgrouped according to the CH removal techniques: (1) %17 ethylenediaminetetraacetic acid (EDTA) + rotary file, (2) %17EDTA + hand file, and (3) %17EDTA (n = 24). Eight roots from each group sectioned longitudinally, divided into two pairs and photographed by stereomicroscope (n = 16). The remaining 16 roots in CH intracanal dressing groups were further divided into 2 subgroups according to the sealer used: (1) AH-Plus-jet and (2) Apexit-Plus (n = 8). Bond strengths of the root canal sealers to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using multivariate analysis of variance p = 0.05. The push-out bond strength values were significantly affected by type of vehicle and the removal techniques (p < 0.05). The mean bond strength of AH-Plus-jet was significantly higher than Apexit-Plus, regardless of type of vehicle and the removal techniques (p < 0.05). There was no difference between vehicles on CH removal (p > 0.05). When examining the removal techniques, only irrigation with %17 EDTA left significantly larger amount of residue (p < 0.05). AH-Plus-jet showed better dislocation resistance than Apexit-Plus. Type of vehicle does not play a fundamental role in the degree of persistence of CH residues on the dentin walls. Instrumentation improves the removal efficiency of CH from root canal.     

Persistence Heterogeneity Testing in Panels with Interactive Fixed Effects

We consider large N,T panel data models with fixed effects, a common factor allowing for cross‐section dependence, and persistent data and shocks, which are assumed fractionally integrated. In a basic setup, the main interest is on the fractional parameter of the idiosyncratic component, which is estimated in first differences after factor removal by projection on the cross‐section average. The pooled conditional‐sum‐of‐squares estimate is consistent but the normal asymptotic distribution might not be centred, requiring the time series dimension to grow faster than the cross‐section size for correction. We develop tests of homogeneity of dynamics, including the degree of integration, that have no trivial power under local departures from the null hypothesis of a non‐negligible fraction of cross‐section units. A simulation study shows that our estimates and tests have good performance even in moderately small panels.