Robust Variable-Step Perturb-and-Observe Sliding Mode Controller for Grid-Connected Wind-Energy-Conversion Systems

In order to extract efficient power generation, a wind turbine (WT) system requires an accurate maximum power point tracking (MPPT) technique. Therefore, a novel robust variable-step perturb-and-observe (RVS-P&O) algorithm was developed for the machine-side converter (MSC). The control strategy was applied on a WT based permanent-magnet synchronous generator (PMSG) to overcome the downsides of the currently published P&O MPPT methods. Particularly, two main points were involved. Firstly, a systematic step-size selection on the basis of power and speed measurement normalization was proposed; secondly, to obtain acceptable robustness for high and long wind-speed variations, a new correction to calculate the power variation was carried out. The grid-side converter (GSC) was controlled using a second-order sliding mode controller (SOSMC) with an adaptive-gain super-twisting algorithm (STA) to realize the high-quality seamless setting of power injected into the grid, a satisfactory power factor correction, a high harmonic performance of the AC source, and removal of the chatter effect compared to the traditional first-order sliding mode controller (FOSMC). Simulation results showed the superiority of the suggested RVS-P&O over the competing based P&O techniques. The RVS-P&O offered the WT an efficiency of 99.35%, which was an increase of 3.82% over the variable-step P&O algorithm. Indeed, the settling time was remarkably enhanced; it was 0.00794 s, which was better than for LS-P&O (0.0841 s), SS-P&O (0.1617 s), and VS-P&O (0.2224 s). Therefore, in terms of energy efficiency, as well as transient and steady-state response performances under various operating conditions, the RVS-P&O algorithm could be an accurate candidate for MPP online operation tracking.     

Green Synthesis and Characterization of Silver Nanoparticles Using Myrsine africana Leaf Extract for Their Antibacterial,Antioxidant and Phytotoxic Activities

Nanotechnology is the study and control of materials at length scales between 1 and 100 nanometers (nm), where incredible phenomena enable new applications. It affects all aspects of human life and is the most active research topic in modern materials science. Among the various metallic nanoparticles used in biomedical applications, silver nanoparticles (AgNPs) are among the most important and interesting nanomaterials. The aim of this study was to synthesize AgNPs from the leaf extract of Myrsine africana to investigate their antibacterial, antioxidant, and phytotoxic activities. When the leaf extract was treated with AgNO₃, the color of the reaction solution changed from light brown to dark brown, indicating the formation of AgNPs. The UV-visible spectrum showed an absorption peak at 438 nm, confirming the synthesis of AgNPs. Scanning electron microscopy (SEM) showed that the AgNPs were spherical and oval with an average size of 28.32 nm. Fourier transform infrared spectroscopy confirms the presence of bio-compound functional groups on the surface of the AgNPs. The crystalline nature of the AgNPs was confirmed by XRD pattern. These biosynthesized AgNPs showed pronounced antibacterial activity against Gram-positive and Gram-negative bacteria, with higher inhibitory activity against Escherichia coli. At 40 µg/mL AgNPs, the highest antioxidant activity was obtained, which was 57.7% and an IC50 value of 77.56 µg/mL. A significant positive effect was observed on all morphological parameters when AgNPs were applied to wheat seedlings under constant external conditions at the different concentrations. The present study provides a cost-effective and environmentally friendly method for the synthesis of AgNPs, which can be effectively used in the field of therapeutics, as antimicrobial and diagnostic agents, and as plant growth promoters.     

Elucidating the Role of Santalol as a Potent Inhibitor of Tyrosinase: In Vitro and In Silico Approaches

This research work focuses on the potential application of an organic compound, santalol, obtained from santalum album, in the inhibition of the enzyme tyrosinase, which is actively involved in the biosynthesis of melanin pigment. Over-production of melanin causes undesirable pigmentation in humans as well as other organisms and significantly downgrades their aesthetic value. The study is designed to explain the purification of tyrosinase from the mushroom Agaricus bisporus, followed by activity assays and enzyme kinetics to give insight into the santalol-modulated tyrosinase inhibition in a dose-dependent manner. The multi-spectroscopic techniques such as UV-vis, fluorescence, and isothermal calorimetry are employed to deduce the efficiency of santalol as a potential candidate against tyrosinase enzyme activity. Experimental results are further verified by molecular docking. Santalol, derived from the essential oils of santalum album, has been widely used as a remedy for skin disorders and a potion for a fair complexion since ancient times. Based on enzyme kinetics and biophysical characterization, this is the first scientific evidence where santalol inhibits tyrosinase, and santalol may be employed in the agriculture, food, and cosmetic industries to prevent excess melanin formation or browning.     

(Lp,Lq)-Boundedness of Hausdorff Operators with Power Weight on Euclidean Spaces

In this paper, we prove the (Lp,Lq)-boundedness of (fractional) Hausdorff operators with power weight on Euclidean spaces.As special cases, we can obtain some well known results about Hardy operators.     

One Pot Esterification as Well as Transesterification of Waste Cooking Oil using Potassium and Phosphotungstic Acid Supported Silica: Optimization and Kinetic Modeling

Kinetics and Catalysis - In order to prepare the heterogeneous catalyst, phosphotungstic acid (PTA, H3PW12O40) and K+ were supported over silica matrix for simultaneous transesterification as well...     

Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass: Role of silver nanoparticles

Phosphate glasses with compositions (59.5–x)P₂O₅–MgO–xAgCl–0.5Er₂O₃ (0.0≤x≤1.5 mol%) containing fixed concentration of Er³⁺ ion with and without silver nanoparticles (NPs) are prepared using melt quenching technique. The amorphous nature of the glass is confirmed using the X-ray diffraction method. The homogeneous distribution of spherical Ag NPs (average size ～37 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM) analyses. The UV–vis–NIR absorption spectra shows 10 bands corresponding to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2, ⁴F_7/2, ⁴F_5/2, ²G_9/2, ⁴G_11/2 transitions in which the most intense bands are ²H_11/2 and ⁴G_11/2. The absorption spectrum of Er³⁺ ions free glass sample containing Ag NPs displays a prominent surface Plasmon resonance (SPR) band located at 528 nm. The infrared to visible frequency upconversion (UC) emission under 797 nm excitation shows two emission bands green (⁴S_3/2–⁴I_15/2) and red (⁴F_9/2–⁴I_15/2) centered at 540 nm and 634 nm, respectively, corresponding to Er³⁺ transitions. An enhancement in UC emission intensity of green band (⁴S_3/2–⁴I_15/2) is observed in the presence of silver NPs and the maximum enhancement occurred for 1.5 mol% AgCl. However, the enhancement of emission intensity of the red band (⁴F_9/2–⁴I_15/2) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.     

Energy‐efficient multi‐level and distance‐aware clustering mechanism for WSNs

Most sensor networks are deployed at hostile environments to sense and gather specific information. As sensor nodes have battery constraints, therefore, the research community is trying to propose energy‐efficient solutions for wireless sensor networks (WSNs) to prolong the lifetime of the network. In this paper, we propose an energy‐efficient multi‐level and distance‐aware clustering (EEMDC) mechanism for WSNs. In this mechanism, the area of the network is divided into three logical layers, which depends upon the hop‐count‐based distance from the base station. The simulation outcomes show that EEMDC is more energy efficient than other existing conventional approaches. Copyright © 2013 John Wiley & Sons, Ltd.     

Slow Relaxation of Magnetization in an Isostructural Series of Zinc–Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH₄)₂](NO₃)₃ ? 6 H₂O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff‐base ligand, LH₅. The Ln^III ions in these systems show a distorted square‐antiprism geometry with an LnO₈ coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy^III derivative showed single‐ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single‐crystal level in the isostructural Y^III derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm^?1, which is among the highest reported for a dinuclear Zn–Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non‐negligible intermolecular interactions, even at the lowest concentration of 1 %.