Sliding Mode Control in Power Converters and Drives: A Review

Sliding mode control (SMC) has been studied since the 1950s and widely used in practical applications due to its insensitivity to matched disturbances. The aim of this paper is to present a review of SMC describing the key developments and examining the new trends and challenges for its application to power electronic systems. The fundamental theory of SMC is briefly reviewed and the key technical problems associated with the implementation of SMC to power converters and drives, such chattering phenomenon and variable switching frequency, are discussed and analyzed. The recent developments in SMC systems, future challenges and perspectives of SMC for power converters are discussed.      

Markov chain model for performance analysis of transmitter power control in contention based wireless MAC protocol

We have developed a three-state discrete-time Markov-chain model for the performance evaluation of contention-based medium access control (MAC) protocol. The proposed Markov-chain model is then used to analyze the carrier sense multiple access (CSMA) type MAC protocol for its delay and throughput characteristics with and without transmitter power control. Using simulations, the conditional capture probability (p _cap ), which gives a measure of the effectiveness of transmitter power control due to the capture effect, is quantified and experiments are performed to validate these simulated data for the p _cap . To analyze the effect of transmitter power variation, the Markov-chain model is modified by incorporating the p _cap . Numerical results show significant throughput as well as delay performance improvement using transmitter power control.     

Characterization of BCN film after wet process for interconnection integration

In this study, we investigate the influence of the wet chemical processes involved in the chemical treatment of boron carbon nitride (BCN) films deposited by plasma-assisted chemical vapor deposition (PACVD). BCN film is expected to be a low dielectric constant (low-K) material useful in fabricating future generation LSI devices. BCN film with less than 10% oxygen was hardly etched. The etching rate of the BCN film with an oxygen composition ratio more than 10% depends on the pH of the solution. The relationship between the film etching rate and the atomic bonds in BCN film is also investigated using XPS and FTIR. It was found that the BCN films without C–O and B–O bonds are not etched by acid and alkaline solutions. Therefore, suppression of oxygen concentration in the BCN film is important for LSI integration.     

Formulation development and accelerated stability testing of a novel sunscreen cream for ultraviolet radiation protection in high altitude areas

The present study is aimed at the development of a sunscreen cream for use in high altitude areas which have been found to possess superior sun protection factor (SPF) along with remarkable antioxidant activity. The topical formulation is a standard oil-in-water emulsion of a combination of United States Food and Drug Administration (US FDA) approved ultraviolet filters; along with melatonin and pumpkin seed oil. The in-silico optimized formulation was characterized using established methods and the stability study was carried out as per International Conference on Harmonization guidelines. The formulation was prepared after requisite pre-formulation analysis by Fourier-transform infrared spectroscopy, differential scanning calorimetric and thermogravimetric analyses; followed by characterization based on color, odor, phase separation, spreadability, specific gravity, homogeneicity, centrifugation and sensitivity. For the stability study, a total of three samples from three batches of the finished product were subjected to the stability study. The samples were analyzed for content uniformity, pH, in vitro SPF, rheology, zeta potential, droplet diameter and microbial analysis of the 0th day and also the the end of the storage period. Results obtained from the stability study indicated that the formulation possesses 50+ in vitro SPF value and remained stable for 6?months and 12?months under storage at 40?±?2?°C and 75?±?5% relative humidity; and ?20?°C?±?5?°C respectively.     

Effects of nonlinear chemical reactions on the transport coefficients associated with steady and oscillatory flows through a tube

The paper concerns with the determination of effective transport coefficients associated with the oscillatory flow through a tube where a solute undergoes nonlinear chemical reactions both within the fluid and at the boundary. Method of homogenization, a multiple-scale method of averaging, is adopted to derive the transport equation that contains advection, diffusion and reaction. The resultant equation shows how the transport coefficients are influenced by the rate and degree of the nonlinear chemical reaction. Two different nonlinear reactions are considered at the bulk flow and the boundary. The reactions at the boundary may be reversible and irreversible in nature. Several facts are established from the model by fixing the rate or degree of the nonlinear reactions. Results demonstrate that the reaction at the boundary is more influential than the bulk-flow reaction in determining the transport coefficients. Also fluid-phase reaction coefficient diminishes as the nonlinearity increases, whereas the trend is opposite for the nonlinear wall-phase reaction coefficient. Different controlling parameters are found to play significant role on the transport coefficients when the ratio of wall-phase concentration to the fluid-phase concentration is low.     

Microstructure and Wear Behavior of Laser-Aided Direct Metal Deposited Co-285 and Co-285?+?WC Coatings

The laser-aided direct metal deposition technique was used to form Co-285 superalloy (A) and Co-285 + 30 wt pct WC (B) wear-resistant coatings on 1018 mild steel. Microstructure, element distribution, phases, microhardness distribution, and wear properties of the two coatings were investigated using scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectrometry, scanning transmission electron microscopy (TEM), X-ray diffractometry (XRD), microhardness testing, and wear testing. Results indicate that both of the coatings had dense structures, as well as a metallurgical bonding with the substrate. In addition, coating B had microcracks and randomly distributed undissolved WC particles in it. Coating A was composed of α-Co dendrites, Co₃W precipitates, and eutectics, while coating B was composed of undissolved WC, Co-rich dendrites, eutectics, and the W-rich third phases with various shapes. Crack behavior in coating B was also discussed. The average microhardness of the matrix in coating B was 751 HV_0.5, which was almost 1.8 times that of coating A (420 HV_0.5). Wear results indicate that the wear resistance of coating B was improved by 6.8 times compared with that of coating A. The improvement in wear resistance is believed to be partially due to the undissolved WC and the formation of large numbers of carbides in the matrix working as wear-resistant phases and partially due to the good bonding between the hard phases and the tough matrix.     

Recent Development of Active Nanoparticle Catalysts for Fuel Cell Reactions

This review focuses on the recent advances in the synthesis of nanoparticle (NP) catalysts of Pt‐, Pd‐ and Au‐based NPs as well as composite NPs. First, new developments in the synthesis of single‐component Pt, Pd and Au NPs are summarized. Then the chemistry used to make alloy and composite NP catalysts aiming to enhance their activity and durability for fuel cell reactions is outlined. The review next introduces the exciting new research push in developing CoN/C and FeN/C as non‐Pt catalysts. Examples of size‐, shape‐ and composition‐dependent catalyses for oxygen reduction at cathode and formic acid oxidation at anode are highlighted to illustrate the potentials of the newly developed NP catalysts for fuel cell applications.     

Microstructure development in the directionally solidified Al–4.0 wt% Cu alloy system

The effect of convection on microstructure formation is examined experimentally and theoretically for the vertically upwards-directional solidification of Al–4.0 wt% Cu alloys. In this alloy system, the rejected solute is heavier than the solvent so that fluid flow occurs due to the presence of radial gradients in temperature and composition. A numerical model is presented which shows that convection effects cause the composition to vary along the interface such that the composition increases from the center to the periphery of the sample. This composition variation causes the macroscopic interface to become convex, and give rise to a systematic variation in microstructure along the interface. Critical experiments have been carried out to examine planar to cellular (and cellular to dendritic) transition in a given sample due to the increase in concentration along the interface, and the experimental results are analyzed through the measurements of interface composition and thermal gradient. In addition, the variation in local primary spacing with interface composition is also characterized and compared with the results of the numerical model. It is shown that microstructure transitions and microstructural scales can be correlated quantitatively with the theoretical results based on interface composition and on temperature and solute gradients at the interface.