Enhanced transformation of triclosan by laccase in the presence of redox mediators

Triclosan (TCS), an antimicrobial agent, is an emerging and persistent environmental pollutant that is often found as a contaminant in surface waters and sediments; hence, knowledge of its degradability is important. In this study we investigated laccase-mediated TCS transformation and detoxification, using laccase (from the fungus Ganoderma lucidum) in the presence and absence of redox mediators. Transformation products were identified using HPLC, ESI-MS and GC-MS, and transformation mechanisms were proposed. In the absence of redox mediator, 56.5% TCS removal was observed within 24 h, concomitant with formation of new products with molecular weights greater than that of TCS. These products were dimers and trimers of TCS, as confirmed by ESI-MS analysis. Among the various mediators tested, 1-hydroxybenzotriazole (HBT) and syringaldehyde (SYD) significantly enhanced TCS transformation (∼90%). The presence of these mediators resulted in products with lower molecular weights than TCS, including 2,4-dichlorophenol (2,4-DCP; confirmed by GC-MS) and dechlorinated forms of 2,4-DCP. When SYD was used as the mediator, dechlorination resulted in 2-chlorohydroquinone (2-CHQ). Bacterial growth inhibition studies revealed that laccase-mediated transformation of TCS effectively decreased its toxicity, with ultimate conversion to less toxic or nontoxic products. Our results confirmed the involvement of two mechanisms of laccase-catalyzed TCS removal: (i) oligomerization in the absence of redox mediators, and (ii) ether bond cleavage followed by dechlorination in the presence of redox mediators. These results suggest that laccase in combination with natural redox mediator systems may be a useful strategy for the detoxification and elimination of TCS from aqueous systems.     

Hybrid DSO-GA-based sensorless optimal control strategy for wind turbine generators

The operation of a wind turbine generator involves natural uncertainty due to aerodynamic characteristics, resulting in a system that performs inefficiently. In general, the conventional controller now in wide use is not suitable for every operating point, because its tuning parameters and set-points do not meet the varying system characteristics. A study into an optimal control technique is conducted to reduce the negative effects of inherent uncertainty in system operation. In order to resolve the uncertainty problem, an optimal control method for an effective wind turbine generator is designed on the basis of a sensorless frame by utilizing a hybrid of the direct search optimization method (DSO) and the genetic algorithm (GA). This method is easy to implement and computation of functional derivatives is not necessary. The conventional GA is well known for its high performance in global optimization and its effectiveness in making ideal choices for control variables. The proposed DSO-GA hybrid differs from the conventional GA in terms of the sampling survey and the crossover operation. Moreover, the proposed multivariable optimal control strategy is a sensorless optimization technique that determines the pitch angle of the blades and the yaw angle of the nacelles to produce stable maximum power from a wind turbine system under steady-state operation. The proposed DSO-GA controller is implemented for a lab-scale wind turbine generator exposed to artificial wind, and the experimental results constitute a 3-D performance surface model of output voltage, which is used as an objective function for simulation. The optimization procedure with the objective function is carried out by means of the conventional and proposed methods, whose results reveal that the proposed DSO-GA optimizer yields far better performance in terms of generation number, convergence rate, and robustness. Both techniques are applied to a wind power generator through simulation and experiments. The performances are compared, and conclusions are drawn for each case.     

Shape-controlled fabrication of polypyrrole microstructures by replicating organic crystals through electrostatic interactions

Polypyrrole (PPy) microstructures with diverse shapes were synthesized in an aqueous inorganic salt medium including organic crystals and pyrrole (Py). A series of sulfobenzoic acid salt forms with various cations (K⁺, Na⁺, Li⁺, NH₄⁺) in different positions (para, meta, ortho) of the sulfonate group on the benzene ring were used to form organic crystals as sacrificial templates. Using these crystals, we produced five different shapes of PPy microstructures (hexagonal microplates, curled nanofibers, lozenge-shaped microplates, rigid rods, parallelogram microplates), which replicated the shapes of the organic crystal templates through electrostatic interaction between the anionic crystal surfaces and the cationic PPy chains. In contrast, PPy that was polymerized without crystals showed bulky agglomerates of 200-500 nm size. The electrical properties were dictated by the molecular structures of the organic salt molecules used. While the highest conductivity (200.3 Scm⁻¹) was observed in PPy using crystals of para-linked 4-sulfobenzoic acid monopotassium salt, the lowest conductivity (0.8 Scm⁻¹) was observed in PPy prepared in the presence of crystals of ortho-linked 2-sulfobenzoic acid monoammonium salt.     

Synthesis of ultra-thin polypyrrole nanosheets for chemical sensor applications

Ultra-thin polypyrrole nanosheets (UPNSs) are fabricated by organic crystal surface-induced polymerization (OCSP) of pyrrole in an aqueous suspension containing hydrated crystals of sodium decylsulfonate (C₁₀SO₃Na) below the Krafft temperature using FeCl₃ as an oxidant. The hydrated C₁₀SO₃Na crystals are used as templates through electrostatic binding of the cationic polypyrrole (PPy) chains oxidized by Fe(III) ions on the anionic C₁₀SO₃Na crystal surface. The resulting UPNSs have a single layer thickness of ∼21 nm, widths between 2 and 6 μm, and lengths greater than 10 μm. The UPNSs are composed of a single continuous PPy domain. Moreover, the UPNSs exhibit higher conductivity (30.6 Scm⁻¹) and longer conjugation lengths than the PPy nanoparticles (2.4 Scm⁻¹) prepared using emulsion polymerization. We systematically investigate the UPNSs as gas sensors for detecting and quantifying toxic gases such as HCl and NH₃. The UPNSs exhibit much higher gas sensitivity and faster response times compared with the PPy nanoparticles.     

Determination of glucose concentration in a scattering medium based on selected wavelengths by use of an overtone absorption band

A method and device for measuring glucose concentration in a scattering medium have been developed. A spectral range of 800-1800 nm is considered for wavelength selection because of its deeper penetration into biological tissue and the presence of a glucose absorption band. An algorithm based on selected wavelengths is proposed to minimize interference from other components. The optimal distance between the light source and the detector for diffuse reflectance measurement minimizes the influence of medium scattering. The proposed algorithm and measuring device are tested with a solution containing milk with added glucose. Glucose concentrations between 0 and 2000 mg/dl are determined with a correlation coefficient of 0.977. We also investigate the influence of concentration variations of other substances such as water, hemoglobin, albumin, and cholesterol when they are mixed in a scattering medium.     

Creep crack growth in brittle materials

During steady state crack growth by diffusive cavitation at grain boundaries, crack tip fields are relaxed due to the presence of a cavitation zone. In the present analysis, analytic solutions for the actual crack tip stress fields and the crack velocity in the presence of cavitation zone consisting of continuously distributed cavities ahead of the crack tip are derived using the smeared volume concept. Results indicate that the r ^–1/2 singularity is now attenuated to r ^{–1/2 +} (0<<1/2) singularity. The singularity attenuation parameter is a function of the crack velocity and material parameters. The crack growth rate is related to the mode I stress intensity factor K by K ² at relatively high load, K ⁿ at intermediate load, and approaches zero at small load near K _th. Meanwhile, the cavitation zone extends further into the material due to the stress relaxation at the crack tip and the subsequent stress redistribution. Such relaxation effects become very distinct at low crack velocity and low applied load. Key words: Creep crack growth, brittle material, diffusive cavity growth, sintering stress, crack tip stress field.     

An application of polarized domains in ferroelectric thin films using scanning probe microscope

The feasibility of utilizing PZT films as future data storage media was investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultra-high area density. The disappearance of the polarized images without any applied voltage was observed, which is a drawback in this application of PZT thin films.     

New linear phase QMF filter design for sub-band coding

A new technique for designing linear phase quadrature mirror filters (QMF) filters is proposed. These filters have the frequency responses of sharp and symmetrical transition characteristics, and the properties of perfect reconstruction and simple implementation.<>     

Application of Collaborative Optimization Using Genetic Algorithm and Response Surface Method to an Aircraft Wing Design

Collaborative optimization(CO) is a multi-level decomposed methodology for a large-scale multidisciplinary design optimization(MDO).CO is known to have computational and organizational advantages. Its decomposed architecture removes a necessity of direct communication among disciplines, guaranteeing their autonomy. However,CO has several problems at convergence characteristics and computation time. In this study, such features are discussed and some suggestions are made to improve the performance ofCO. Only for the system level optimization, genetic algorithm is used and gradient-based method is used for subspace optimizers. Moreover, response surface models are replaced as analyses in subspaces. In this manner,CO is applied to aero-structural design problems of the aircraft wing and its results are compared with the multidisciplinary feasible (MDF) method and the original CO. Through these results, it is verified that the suggested approach improves convergence characteristics and offers a proper solution.