Influence of Mg concentration on structural,morphological and optical properties of nanoceria

Nano crystalline pure and Mg doped ceriaparticles were synthesized by simple chemical co-precipitation method using cerium nitrate hexahydrate as a source material and magnesium nitrate as doping precursor at room temperature. The effect of doping were investigated by X-ray diffraction pattern(XRD), FT-Raman,fourier transform infrared spectroscopy(FTIR), Ultraviolet spectroscopy(UV), photoluminescence spectroscopy(PL), field emission scanning electron microscope(FESEM) and high resolution transmission electron microscopy with energy dispersive spectroscopy (HRTEM &EDS). The X-ray diffraction pattern and FT-Raman studies showed that the prepared samples were nano particulates with cubic fluorite structure. The XRD pattern analysis showed that the size of the particles ranged from 13 to 20?nm, however 4?wt% Mg doping results in reduction of particle size compared with other doping concentrations. The effects of Mg concentration on various structural parameters of the prepared samples were also determined. The slight blue shift observed upon doping in UV–Vis absorption region around 330–360nmrecorded for reduction in particle size. The FTIR unveils the presence of Metal oxygen bonds below 700?cm^?1in the prepared samples. All samples showed a broad emission band at 430?nm with linearly increasing intensity with respect to dopant concentrations. The Spherical morphology with weak agglomeration was identified through FESEM and HRTEM analysis. The elemental analysis of Ce, O and Mg were confirmed through EDS analysis.     

Thermal stability in bulk cryomilled ultrafine-grained 5083 Al alloy

Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation, and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673 K (0.55 to 0.79 T _m , where T _m is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures > 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ± 5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile tests, correlate well with substructural changes introduced in the alloy by the annealing treatment.     

An EKV-based high voltage MOSFET model with improved mobility and drift model

An EKV-based high voltage MOSFET model is presented. The intrinsic channel model is derived based on the charge based EKV-formalism. An improved mobility model is used for the modeling of the intrinsic channel to improve the DC characteristics. The model uses second order dependence on the gate bias and an extra parameter for the smoothening of the saturation voltage of the intrinsic drain. An improved drift model [Chauhan YS, Anghel C, Krummenacher F, Ionescu AM, Declercq M, Gillon R, et al. A highly scalable high voltage MOSFET model. In: IEEE European solid-state device research conference (ESSDERC), September 2006. p. 270–3; Chauhan YS, Anghel C, Krummenacher F, Maier C, Gillon R, Bakeroot B, et al. Scalable general high voltage MOSFET model including quasi-saturation and self-heating effect. Solid State Electron 2006;50(11–12):1801–13] is used for the modeling of the drift region, which gives smoother transition on output characteristics and also models well the quasi-saturation region of high voltage MOSFETs. First, the model is validated on the numerical device simulation of the VDMOS transistor and then, on the measured characteristics of the SOI-LDMOS transistor. The accuracy of the model is better than our previous model [Chauhan YS, Anghel C, Krummenacher F, Maier C, Gillon R, Bakeroot B, et al. Scalable general high voltage MOSFET model including quasi-saturation and self-heating effect. Solid State Electron 2006;50(11–12):1801–13] especially in the quasi-saturation region of output characteristics.     

Cover Feature: Superior Proton-Transfer Catalytic Promiscuity of Cytochrome c in Self-Organized Media (7/2021)

Evolutionarily elderly proteins commonly feature greater catalytic promiscuity. Cytochrome c is among the first set of proteins in evolution to have known prospects in electron transport and peroxidative properties. Here, we report that cyt c is also a proficient proton-transfer catalyst and enhances the Kemp elimination (KE; model reaction to show proton transfer catalytic property) by ∼750-fold on self-organized systems like micelles and vesicles. The self-organized systems mimic the mitochondrial environment in vitro for cyt c. Using an array of biophysical and biochemical mutational assays, both acid–base and redox mechanistic pathways have been explored. The histidine moiety close to hemin group (His18) is mainly responsible for proton abstraction to promote the concerted E2 pathway for KE catalysis when cyt c is in its oxidized form; this has also been confirmed by a H18A mutant of cyt c. However, the redox pathway is predominant under reducing conditions in the presence of dithiothreitol over the pH range 6–7.4. Interestingly, we found almost 750-fold enhanced KE catalysis by cyt c compared to aqueous buffer. Overall, in addition to providing mechanistic insights, the data reveal an unprecedented catalytic property of cyt c that could be of high importance in an evolutionary perspective considering its role in delineating the phylogenic tree and also towards generating programmable designer biocatalysts.     

Methacrylic acid and dodecyl methacrylate (MAc‐DMA) hydrogel for enhanced catalytic activity of lipase of Bacillus coagulans MTCC‐6375

An alkaline thermotolerant bacterial lipase of Bacillus coagulans MTCC‐6375 was purified and immobilized on a methacrylic acid and dodecyl methacrylate (MAc‐DMA) hydrogel. The lipase was optimally bound to the matrix after 20 min of incubation at 55°C and pH 9 under shaking conditions. The matrix‐bound lipase retained approximately 50% of its initial activity at 70–80°C after 3 h of incubation. The immobilized lipase was highly active on medium chain length p‐nitrophenyl acyl ester (C: 8, p‐nitrophenyl caprylate) than other p‐nitrophenyl acyl esters. The presence of Fe³⁺, NH₄⁺, K⁺, and Zn²⁺ ions at 1 mM concentration in the reaction mixture resulted in a profound increase in the activity of immobilized lipase. Most of the detergents partially reduced the activity of the immobilized lipase. The immobilized lipase performed ～62% conversion in 12 h at temperature 55°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1420–1426, 2006     

BUBBLE TEMPERATURES OF THE BINARY MIXTURES OF 1,2-DIMETHYLBENZENE WITH 2-PROPANOL, 1-BUTANOL, 2-BUTANOL, 2-METHYLPROPAN-1-OL AND 2-METHYLPROPAN-2-OL AT 95 kPa

Bubble temperatures at 95 kPa over the entire composition range are measured for the five binary systems formed by 1,2-dimethylbenzene with 2-propanol, 1-butanol, 2-butanol, 2- methylpropan-1-ol, and 2-methylpropan- 2-ol. A Swietoslawski - type ebulliometer was used for the measurements. The composition versus temperature measurements are well represented by the Wilson model.     

Effect of organic modifiers on dynamic and static nanomechanical properties and crystallinity of intercalated clay–polycaprolactam nanocomposites

Polymer clay nanocomposites (PCN) of Polyamide6 and sodium montmorillonite are prepared using different organic modifiers (12‐aminolauric acid, n‐dodecylamine, and 1,12‐diaminododecane) to study effect of organic modifiers on structure and nanomechanical properties of PCN. Using X‐ray diffraction and differential scanning calorimetry, crystalline nature of PCNs are evaluated. Nanoscale viscoelastic properties of PCNs are evaluated using nanodynamic mechanical analyzer (NanoDMA). Nanoscale elastic modulus and hardness of PCNs are evaluated using nanoindenter. PCNs show enhancement in elastic modulus, storage modulus, loss modulus, and loss factor by maximum amount of 62.88%, 56.38%, 145.74%, and 71.43%, respectively, and decrease in percentage crystallinity by 16.52% compared to pure polymer. This result indicates that organic modifiers have effect on crystallinity and nanomechanical properties of PCN. To evaluate effect of clay loading on nanomechanical properties of PCN, PCN containing 12‐aminolauric acid is synthesized with different weight percent (3, 6, and 9% of weight of polymer) of organically modified montmorillonite (OMMT), which shows that nanomechanical properties of PCN improves with increase in clay loading. Our study reveals that change in crystallinity of polymer in PCN may have role in the enhancement of nanomechanical properties of PCNs in comparison to pristine polymer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of ethyl propionate catalyzed by poly(N‐AEAAm‐co‐AAc)‐cl‐MBAm hydrogel‐immobilized lipase of Bacillus coagulans MTCC‐6375

A purified alkaline thermotolerant bacterial lipase of Bacillus coagulans MTCC‐6375 was efficiently immobilized onto poly(N‐AEAAm‐co‐AAc‐cl‐MBAm)‐hydrogel at pH 8.5 and at temperature 55°C in 16 h. The hydrogel‐bound matrix possessed 1.04 U/g (matrix) lipase activity with a specific activity of 1.8 U/mg of protein. The immobilized lipase resulted in formation of 52.5 mM of ethyl propionate (52% conversion) at 55°C in 9 h in n‐nonane. Ethanol and propionic acid when used in a ratio of 300 : 100 mM, respectively, in n‐nonane along with 10 mg of hydrogel‐bound lipase resulted in optimal synthesis of ethyl propionate (82.5 mM). Addition of molecular sieves (3 Å, 0.7 g/reaction volume) further enhanced the conversion rate to 82.4% resulting in 83.5 mM of ethyl propionate. Incubation temperature below or above 55°C had a marked effect on the synthesis of ethyl propionate. However, esterification performed in n‐heptane at 65°C resulted in 87.5 mM of ethyl propionate with a conversation rate of 89.3%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007