Application of Filippov method for the analysis of subharmonic instability in dc–dc converters

We propose a method of estimating the fast‐scale stability margin of dc–dc converters based on Filippov's theory—originally developed for mechanical systems with impacts and stick‐slip motion. In this method one calculates the state transition matrix over a complete clock cycle, and the eigenvalues of this matrix indicate the stability margin. Important components of this matrix are the state transition matrices across the switching events, called saltation matrices. We applied this method to estimate the stability margins of a few commonly used converter and control schemes. Finally, we show that the form of the saltation matrix suggests new control strategies to increase the stability margin, which we experimentally demonstrate using a voltage‐mode‐controlled buck converter. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of light irradiation on esterification of oleic acid with ethanol catalyzed by immobilized Pseudomonas cepacia lipase

The present study demonstrates the effect of light irradiation on the esterification of oleic acid catalyzed by immobilized Pseudomonas cepacia lipase. The reaction rates of all the experiments under light irradiation were found to be higher than dark conditions. The kinetics of reactions supported the Ping‐Pong Bi‐Bi mechanism with dead end inhibition by both the alcohol and acid substrates. Moreover, circular dichroism (CD) spectroscopy was used to analyze the effect of light on lipase enzyme. The CD spectroscopic studies confirmed that the conformational changes in the secondary structure of the lipase enzyme increased the reaction rate of light‐illuminated experiments, which might have opened up the active sites of enzymes and thus, resulted in higher reaction rates compared to dark reactions. These results have successfully demonstrated that the light illumination positively influenced the rate of P. cepacia enzyme‐catalyzed esterification reactions.     

Hybrid electrically conductive polyaniline/polyurethane foams

Electrically conductive polyaniline/polyurethane foams were prepared. The DC conductivity of the composite prepared at pH = 0.505 is about 0.9 S/cm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 893–897, 2001     

Synthesis and electrochemical characterization of La0.75Sr0.25Mn0.5Cr0.5−xAlxO3, for IT- and HT-SOFCs

The main emphasis of this work is to create a new perovskite material with three different compositions (La_0.75Sr_0.25Mn_0.5Cr_0.5−xAlxO₃, x = 0.1, 0.2, 0.3) applied in both Intermediate- and High-temperature Solid Oxide Fuel Cells (IT- and HT-SOFCs). Perovskite-type polycrystalline La_0.75Sr_0.25Mn_0.5Cr_0.5−xAl_xO_3−δ (x = 0.1, 0.2, 0.3) powders were synthesized and formed in a single phase structure by a dry chemistry route (standard solid-state reaction method). The effect of Al doping on physicochemical and surface properties has been discovered. The compounds were crystallized in single phase rhombohedral symmetry (R-3C Space. Group). Total conductivity of Al doping in wet 5% H₂ was higher than both dry 5% H₂ and air. The obtained results enhance the electro-catalytic performance and the material conductivity as well, which will be good for anode materials in IT- and HT-SOFCs and the optimum doping is 10%.     

Nonionic surfactant based thymoquinone loaded nanoproniosomal formulation: in vitro physicochemical evaluation and in vivo hepatoprotective efficacy

Context: The present study was carried out to formulate thymoquinone proniosomal formulation (TQP) and evaluate their efficacy in methotrexate (Mtx) induced hepatotoxicity in rats.

Objective: The objective of the study was to explore a new therapeutic approach focusing on hepatoprotective activity using thymoquinone proniosomal formulation.

Material and methods: TQP was formulated using span60, cholesterol and phospholipid by film hydration technique. The animals were divided into six groups with five animals each receiving different treatments for 7?days. On the 8th day, rats were anesthetized with ether, blood samples were withdrawn, livers were dissected out for biochemical tests and histopathological examinations.

Results and discussion: The size of vesicle was found to be in the nanometric range with higher entrapment efficiency. The high entrapment efficiency is probably due to the lipophilic character of TQ. The morphological structure showed the outline and core of the well-identified spherical vesicle, and also displaying the retention of sealed vesicular structure. The release of TQ from developed formulation was found to be significantly higher compared to control. Mtx treated rats showed significant elevation in ALT, AST, ALP and TBARs, whereas, TQP treated group showed significant reduction.

Conclusion: The developed formulation (TQP) significantly inhibited the elevated levels of serum marker enzymes and showed improved histopathological deformities.     

Direct Derivatization vs Aqueous Extraction Methods of Fecal Free Fatty Acids for GC–MS Analysis

A comprehensive and accurate determination of free fatty acids (FFA) is required for fecal metabolomic investigations. The present study compares three aqueous extraction methods (1) ULTRA‐TURRAX^®, (2) whirl mixing and (3) basic ULTRA‐TURRAX extraction of fecal FFA with a direct derivatization approach using ethyl chloroformate as the derivatization reagent before determination by gas chromatography–mass spectrometry. The direct derivatization method resulted in significantly higher estimations (P < 0.01) of short‐ and long‐chain fatty acids than was the case when applying the aqueous extraction methods using ULTRA‐TURRAX, whirl mixing, or basic ULTRA‐TURRAX extraction before the derivatization step. Thus, avoiding an aqueous extraction before derivatization reduces the loss of volatile short‐chain FFA and the less water‐soluble long‐chain FFA.     

Desorption isotherms,net isosteric heat and the effect of temperature and water activity on the antioxidant activity of two varieties of onion (Allium cepa L)

The standard static gravimetric method was used to determine moisture desorption isotherms (MDIs) of two onion varieties (Goudami and Galmi Violet) at 30 °C, 45 °C and 60 °C in the water activity ranging from 0.055 to 0.83. The combined effects of temperature and water activity on the antioxidant activities of the onion varieties were also studied. GAB, Oswin, Smith and BET equations were tested to fit the experimental data. The net isosteric heat of sorption was calculated. Equilibrium moisture content (EMC), total phenolic content (TPC) and antiradical activity were also measured. The isotherm and the EMC vary significantly with the onion variety and drying temperature, irrespective of water activity (a_w). Desorption isotherms were best described by the GAB model. The maximum net isosteric heats for Galmi Violet (32.58 kJ mol^?1) were greater than those of Goudami (23.50 kJ mol^?1) at each EMC. The TPC and antiradical activity of the Galmi Violet were significantly (P ≤ 0.05) higher than that of the Goudami at all investigated temperatures and water activities.     

Defect structures in silicon merged epitaxial lateral overgrowth

Merging of two epitaxial lateral overgrowth fronts has been achieved to produce thin silicon-on-insulator (SOI) structures. The electronic quality of the material is generally of high quality; however, at the merger interface are defects associated with improper merging. Defects at the oxide/silicon interface and the merging interface were characterized using transmission electron microscopy. Device performance indicated the need for a process modification to improve the material quality for potential electronic applications.     

Regeneration of spent earth in aqueous medium

A simple method of regeneration of spent earth at a relatively low temperature has been developed. Deoiled spent earth was regenerated in the form of a slurry using water as an aqueous phase, in the temperature range of 170–270°C. The effects of temperature, slurry concentration and cycle of regeneration have been studied. An attempt has been made to discern the controlling mechanism. Regenerated earth from the present method does not impart any malodor to the oil as against theramlly regenerated earth.     

Pharmacokinetic advantages of a newly developed tacrolimus oil-in-water-type emulsion via the enteral route

We developed an oleic acid oil-in-water (o/w)-type emulsion of a new tacrolimus formulation that presented an improvement in the delivery of the drug for oral absorption. This investigation was undertaken to assess a sustained release drug delivery system and selective drug transfer into the lymphatic system. The whole blood concentration profiles after oral administration at a dose of 2mg/kg and bone marrow, spleen, liver, lung, small intestine, kidney, brain, and whole blood distribution after oral administration at a dose of 1 mg/kg of o/w emulsion formulation of tacrolimus (O/W group) were compared with those of commercially available formulation (T group) in the rat. The mean diameter of the o/w emulsion droplets was 0.47 μm immediately after preparation. The tacrolimus entrapping efficiency of o/w emulsion was 71.3+5.0% in 12 h and did not change for 2 d. The area under the whole blood concentration-time curve (AUC) in the O/W group was significantly higher (P<0.01) than that in the I group. In contrast, the values of constant elimination rate and total clearance in the O/W group were significantly lower (P<0.01) than those in the T group, with a comparative bioavailability of 115.9%. The tissue concentration of tacrolimus in the O/W group was significantly higher levels in the bone marrow, spleen, liver, lung, and small intestine, and significantly lower in the brain and kidney, relative to the T group. The o/w emulsion of tacrolimus may be an improved dosage form via the enteral route.