Aloe vera-based antibacterial porous sponges for wound dressing applications

Journal of Porous Materials - The antibacterial sponges with high macroporosity, high interconnectivity and high biocompatibility is a significant concern for wound healing applications. In this...     

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.     

Synthesis of Quaternary,Long-Chain N-Alkyl Amides and Their Corrosion Inhibition in Acidic Media

New cationic surfactants were synthesized by the quaternization of a number of straight-chain amide derivatives with triethylamine or pyridine. The corrosion inhibition tests of the surface-active compounds were performed at room temperature for 24 h on carbon steel coupons in acidic media using the gravimetric method. The acidic media used were 1.5 M HCl and 1.5 M H₂SO₄. Almost all of the synthesized cationic surfactants showed efficient inhibition of corrosion in the test. To establish the inhibition efficiencies of the inhibitors, surface characterization studies (contact angle measurements, SEM analysis and optical profilometer images) of the metal coupons used were performed.     

Conceptual Model for Prediction of FRP-Concrete Bond Strength under Moisture Cycles

Fiber-reinforced polymer (FRP) retrofit systems for concrete structural members such as beams, columns, slabs, and bridge decks have become increasingly popular as a result of extensive studies on short-term debonding behavior. Nevertheless, long-term performance and durability issues regarding debonding behavior in such strengthening systems still remain largely uncertain and unanswered. Because of its composite nature, the effectiveness of the strengthening system depends on the properties of the interfaces between the three constituent materials; namely, concrete, epoxy, and FRP. Certain factors, including those related to environmental exposures, can cause degradation of the interface properties during service life. This is particularly critical when predicting service life and planning maintenance of FRP-strengthened concrete structures. In this study, effect of moisture on an FRP-concrete bond system is characterized by means of the tri-layer fracture toughness, which can be obtained experimentally from peel and shear fracture tests. Fracture specimens were conditioned under various durations and numbers of wet-dry cycles at room temperature and 50°C. An irreversible weakening in bond strength was observed in fracture specimens under moisture cyclic condition. A conceptual model is developed based on the experimental results of the fracture specimens under variable cyclic moisture conditions for the bond strength prediction of the FRP-concrete bond system. A numerical study of a precracked FRP-strengthened reinforced concrete beam is then performed to show potential application of the proposed predictive model.     

Strain–Stress Analysis of AlGaN/GaN Heterostructures With and Without an AlN Buffer and Interlayer

Abstract: The strain–stress analysis of Al_xGa_1?xN/GaN (x = 0.3) heterostructures with and without a high‐temperature HT‐AlN interlayer (IL) grown on sapphire (Al₂O₃) substrates and AlN buffer/Al₂O₃ templates via metal organic chemical vapour deposition (MOCVD) was carried out based on the precise measurement of the lattice parameters by using high‐resolution X‐ray diffraction (HRXRD). The a‐ and c‐lattice parameters were measured from the peak positions that were obtained by rocking the theta axis at the vicinity of the symmetric and asymmetric plane reflection angles, followed by the in‐plane and out‐of‐plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values that were obtained and were then discussed in the present study as the effect of the HT‐AlN buffer and IL. The AlN buffer layer (BL) affects the strain values of the AlGaN ternary layer (TL). A further effect was realized by inserting an AlN IL between GaN BL and AlGaN TL. However, the experimental results also show that an AlN IL changes the strain behaviour in the a‐ and c‐directions of the AlGaN TL from the tensile to compressive and the compressive to tensile type, respectively. These similar behaviours were observed in hydrostatic strain, biaxial strain and stress. Their reasons are explained with an effective a‐lattice parameter, post‐growth cooling and lattice and thermal mismatches.