Artificial neural network‐based photovoltaic module temperature estimation for tropical climate of Malaysia and its impact on photovoltaic system energy yield

This article presents an artificial neural network (ANN)‐based approach for predicting photovoltaic (PV) module temperature using meteorological variables. The proposed approach utilizes actual hourly records of various meteorological parameters, such as ambient temperature T_a, solar irradiation G, relative humidity RH, and wind speed Ws as input variables. The hourly meteorological data were collected over 9 months in the year 2009 from a 92‐kWp installed PV system in Selangor, Malaysia. The data were divided into two sets: training data, which are a set of 1849 (April–October) hourly data, and 578 (November–December) hourly records of working as test data. Four ANN models have been developed by using different combination of meteorological parameters as inputs, and, for each model, the output is the PV module temperature T_m. It was found that the model using all parameters, including RH and Ws as inputs, gave the most accurate results with correlation coefficient (r) 95.9%, and 0.41, 0.1, and 4.5% for MBE, RMSE, and MPE, respectively. To show the superiority and applicability of the developed ANN model, results from the proposed ANN model have been compared with the conventional model adopted by Malaysia Energy Center and another mathematical model based on regression. With the model's simplicity, the proposed approach can be used as an effective tool for predicting the PV module temperature, for any type of PV systems, in remote or rural locations with no direct measurement equipments. The developed model also will be very useful in studying PV system performance and estimating its energy output. Copyright © 2013 John Wiley & Sons, Ltd.     

Field-induced strain and polarization response in lead-free Bi1/2(Na0.80K0.20)1/2TiO3–SrZrO3 ceramics

The structure, field-induced strain, polarization and dielectric response of lead-free SrZrO₃-modified Bi_1/2(Na_0.80K_0.20)_1/2TiO₃ (abbreviated as BNKT–SZ100x, with x = 0–0.05) ceramics were investigated. The X-ray diffraction analysis of BNKT–SZ100x ceramics reveals no remarkable change in the crystal structure within the studied composition range. Around critical composition (x = 0.03) at a driving field of 6 kV mm⁻¹, large unipolar strain of 0.37% (S_max/E_max = 617) was obtained at room temperature. The ferroelectric and piezoelectric properties of BNKT ceramics were significantly increased at 2 mol%. At x = 0.02, remnant polarization reached a maximum value of 34 μC cm⁻², while the piezoelectric constant (d₃₃) attained maximum value of 190 pC/N. These results indicate that BNKT–SZ100x ceramics can be considered as promising candidate materials for lead-free piezoelectric actuator applications.     

Development of meloxicam in situ implant formulation by quality by design principle

Objective: The focus of this study was to develop and optimize in situ implant formulation of meloxicam by quality by design (QbD) principle for long-term management of musculoskeletal inflammatory disorders.

Methods: The formulation was optimized by Box–Behnken design with polylactide-co-glycolide (PLGA) level (X₁), N-methyl pyrrolidone level (X₂) and PLGA intrinsic viscosity (X₃) as the independent variables and initial burst release of drug (Y₁), cumulative release (Y₂), and dissolution efficiency (Y₃) as the dependent variables. The formulation was physicochemically characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (PXRD). Pharmacokinetic studies of the optimized formulation were performed on Sprague--Dawley rats.

Results: Y₁ was significantly affected by X₂ and X₃. Y₂ was affected by X₁ and X₃ while Y₃ was affected by all three independent variables employed in the formulations. Responses for the optimized formulation were in close agreement with the values predicted by the model. SEM photomicrographs indicated uniform gel formulation. No chemical interaction between the components of formulation was observed by FT-IR and meloxicam was found to be present in the amorphous form in the gel matrix as revealed by PXRD. The maximum plasma concentration (C_max), time to achieve C_max and area under plasma concentration curve were significantly different from those of the solution formulation used as the control. Plasma concentration of meloxicam was maintained above its IC₅₀ concentration required for COX-2 inhibition for 23 days.

Conclusion: Meloxicam in situ implant may provide long-term management of inflammatory conditions with improved patient compliance and better therapeutic index.     

Influence of filament-to-substrate distance on the spectroscopic,structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp ² bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.     

Effects of Lupin Oil on Carp Lipids during Chilling 2. Changes in Fatty Acid Composition

Rearing carp for 6 weeks on diets containing 5% lupin oil slightly affected the composition of the component fatty acids in various lipid classes of the fillets. On the other hand, the incorporation of lupin oil in the diet did not affect the trend in the changes occurring in the component fatty acids of the different lipid classes during chilling storage of the carp fillets. Thus, the percentage of saturated and monounsaturated fatty acids increased whereas the percentages of polyunsaturated fatty acids decreased during storage.     

Effect of the addition of the surfactant Tetronic 1307 on poly(ether sulfone) porous hollow-fiber membrane formation

Poly(ether sulfone) (PES) hollow-fiber membrane was prepared via a nonsolvent-induced phase-separation method, and the effect of the addition of the surfactant Tetronic 1307 on the membrane performance and characteristics was investigated. The phase diagram of the PES/N-methyl-2-pyrrolidone (NMP)/water system was clarified. When the polymer solution involved Tetronic 1307, the amount of water required to induce the phase separation decreased, which indicated that Tetronic 1307 was one kind of nonsolvent. The kinetics of phase separation for the PES/NMP/Tetronic 1307 system were studied by light-scattering measurements. With the addition of Tetronic 1307, delayed phase separation was observed, and the structure growth rate decreased. Scanning electron microscopy images for all of the membranes showed the formation of fingerlike macrovoids through the cross section. Membrane surface morphologies were measured by atomic force microscopy. The obtained results indicated that membrane with 7 wt % Tetronic 1307 had higher roughness parameters than original membrane without the addition of surfactant. Ultrafiltration experiment results showed that the addition of Tetronic 1307 brought about an increase in water permeability and decreased the rejection of dextran with a molecular weight of about 10,000. The contact angles of water on the membrane outer surface decreased with the addition of Tetronic 1307. This mean the membrane surface became more hydrophilic. Thus, the addition of Tetronic 1307 was useful for improving the water permeability and for obtaining a hydrophilic membrane surface. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A solid state direct on line starter for medium voltage inductionmotors with minimized current and torque pulsations

This paper describes a thyristorized static switch which is designed and implemented specifically for frequent direct-on-line starting of medium voltage large induction motors. The circuit configuration chosen utilizes back-to-back connected series thyristor strings on two of the supply lines. Both the starting current and the torque pulsations of the induction motor are minimized by a controlled, nonsimultaneous switching of motor phases to the supply. This reduces the electrical stresses on the power system and the mechanical stresses on the shaft as compared to conventional switching elements. The optimum switching strategy is found by the use of a hybrid mathematical model in ABC/dqO form. The validity of the results obtained for medium voltage, squirrel-cage induction machine are verified by the use of a physical simulator consisting of a low voltage, small induction machine and a shaft torque measuring system. The system has been in operation successfully in an iron and steel plant since 1991     

Fabrication of complex shape electrodes by localized electrochemical deposition

Localized electrochemical deposition (LECD) is a promising technology for fabrication of high-aspect ratio electrode of various materials. This technology is found to be one of the simple and inexpensive ways to fabricate electrodes for micro-EDM. This study presents a novel method to manufacture electrodes with complex cross-section using mask of non-conductive material. In this study, the mask is placed between the anode and cathode, which is immersed in mixed electrolyte of copper sulfate, 1.0 M sulfuric acid and as an additive agent 0.04 g/l of thiourea. The deposition of copper is localized on the cathode surface using a mask and applying ultra short voltage pulses between the anode and cathode. In this setup the cathode is placed above the anode and mask, so that the deposited electrode can be used directly for EDM or any application without changing tool orientation. The deposition characteristics such as size, shape, surface, and structural density according to gap between the anode and mask, applied voltage, pulse frequency and duty ratio have been investigated in this study. Finally, appropriate conditions have been found out for effective fabrication of smooth and fine-grained deposited electrodes based on the findings of the various experiments.     

Anion incorporation and its effect on the dielectric constant and growth rate of zirconium oxides

Mechanically polished zirconium electrodes were potentiodynamically polarized in phosphate buffer solutions of various pH values and in 0.5 lvl NaOH. The results show that the shape of the I-E curves is independent of the solution pH. At relatively low scan rates, oxygen gas evolution was observed. The oxide film thickness was calculated from the values of the charge consumed in the anodic process assuming 100% current efficiency for oxide formation below oxygen evolution (lower values for the current efficiency are assumed for potentials above oxygen evolution). Capacitance measurements, together with the calculated oxide thickness, were used to estimate values for the dielectric constant of the oxide. Two different values of the dielectric constant were obtained for the oxides formed in the range of potential below and above oxygen evolution. Also, higher dielectric constant values were obtained with increasing solution pH. Anion incorporation was assumed to increase the conductivity of the oxide films and, hence, decrease the dielectric constant. A two-layer structure is proposed for the anodically formed oxide on zirconium in aqueous solutions; an anion-free layer near the metal and an outer layer containing the incorporated anions.     

Analysis of field oriented control for permanent magnet hysteresissynchronous motors

A microprocessor implementation of the field-oriented control scheme for the permanent magnet (PM) hysteresis synchronous motor is reported. The basic principle is to decouple the torque-current component from the flux-current component so that these two components can be independently controlled. A d-q axis model of the PM hysteresis synchronous motor is presented, and the field-oriented control obtained from the basic machine model. A control scheme that decouples the stator current components and orients it to the rotor frame is described. A scheme for detecting the rotor position is proposed. A software package based on the Intel 8086 microprocessor has been developed. A sine PWM voltage source inverter is used in the experimental work. The test results validate the theoretical steady state and dynamic performances of the laboratory prototype motor