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51.
Polymer‐based materials have drawn significant attention lately for their application in design and fabrication of thermomechanically stable highly sensitive three‐dimensional (3D) micromechanical sensor structures. Among these materials, 1,6 Hexane diol diacrylate (HDDA) has been extensively explored in laser‐based 3D microfabrication by microstereolithography. The thermomechanical properties of poly HDDA are important for their end use application in microcantilever‐based sensors. The present work explores the optimization of these properties by copolymerization of HDDA and methyl methacrylate (MMA) for these specific applications. The dynamic mechanical analysis, thermal expansion and mechanical studies were carried out for different compositions of poly (HDDA‐co‐MMA). An increase in MMA content in the copolymer matrix resulted in the enhancement of the thermomechanical stability. The variations of thermal expansion coefficient (CTE) for different compositions were also studied. Microhardness, uniaxial tensile, and flexural tests along with Poisson's ratio were determined to understand the mechanical properties of these compositions. The scanning electron micrographs of fractured surfaces of all the compositions were analyzed to understand the fracture mechanism of various compositions of this copolymer. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
52.
Swati Singh Ankur Kaushal Shashi Khare Ashok Kumar 《Applied biochemistry and biotechnology》2014,173(1):228-238
The 5′ amino-labeled DNA probe complementary to mga gene of Streptococcus pyogenes was immobilized on carboxylated multiwall carbon nanotubes electrode and hybridized with 0.1–100 ng/6 μl single-stranded genomic DNA (ssG-DNA) of S. pyogenes from throat swab of suspected rheumatic heart disease (RHD) patients. Electrochemical response was measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance (EI). The sensitivity of the sensor was 106.03?(μA/cm2)/ng and limit of detection (LOD) was found 0.014 ng/6 μl with regression coefficient (R 2) of 0.921 using DPV. The genosensor was characterized by FTIR and SEM, and electrode was found stable for 6 months on storage at 4 °C with 5–6 % loss in initial DPV current. mga genosensor is the first report on RHD sensor which can save life of several suspected patients by early diagnosis in 30 min. 相似文献
53.
Kamal Bauri Saswati Ghosh Roy Simran Arora Rajib Kumar Dey Ankur Goswami Giridhar Madras Priyadarsi De 《Journal of Thermal Analysis and Calorimetry》2013,111(1):753-761
Reversible addition-fragmentation chain transfer polymerization at 70 °C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by 1H NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r NIPAM = 0.838 and r DMA = 1.105, respectively, by the extended Kelen–Tüdös method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding. 相似文献
54.
Energetics and mechanistic details for the conversion of dinitrogen to ammonia mediated by vanadium triamidoamine has been studied theoretically involving various mechanistic possibilities. For most of the cases, protonation at the amido nitrogen atom is more favorable compared to the terminal one. Further, the most important steps of the mechanism were compared with the well established chemistry of nitrogen fixation mediated by molybdenum. Such a comparison helps in understanding why vanadium triamidoamine complex performs poorly compared to molybdenum. The main factors responsible for the poor performance of the vanadium complex toward NH(3) production are identified as low exergonic cleavage of the N-N bond and limitation of the ligand exchange step via a dissociative mechanism at the end of the cycle to only one possible pathway. A major aspect of the failure of the vanadium complex to mediate the reduction of N(2) to ammonia is the fact that the protonation steps involve major barriers, which cannot be surmounted thermally. Moreover, unlike molybdenum, the associative mechanism with vanadium triamidoamine complex is not likely to operate during the NH(3)/N(2) exchange step. 相似文献
55.
Photoexcitation of 2-bromo-2-nitropropane (BNP) at 248 and 193 nm generates OH, Br, and NO(2) among other products. The OH fragment is detected by laser-induced fluorescence spectroscopy, and its translational and internal state distributions (vibration, rotation, spin-orbit, and Λ-doubling components) are probed. At both 248 and 193 nm, the OH fragment is produced translationally hot with the energy of 10.8 and 17.2 kcal∕mol, respectively. It is produced vibrationally cold (v" = 0) at 248 nm, and excited (v" = 1) at 193 nm with a vibrational temperature of 1870 ± 150 K. It is also generated with rotational excitation, rotational populations of OH(v" = 0) being characterized by a temperature of 550 ± 50 and 925 ± 100 K at 248 and 193 nm excitation of BNP, respectively. The spin-orbit components of OH(X(2)Π) are not in equilibrium on excitation at 193 nm, but the Λ-doublets are almost in equilibrium, implying no preference for its π lobe with respect to the plane of rotation. The NO(2) product is produced electronically excited, as detected by measuring UV-visible fluorescence, at 193 nm and mostly in the ground electronic state at 248 nm. The Br product is detected employing resonance-enhanced multiphoton ionization with time-of-flight mass spectrometer for better understanding of the dynamics of dissociation. The forward convolution analysis of the experimental data has provided translational energy distributions and anisotropy parameters for both Br((2)P(3∕2)) and Br?((2)P(1∕2)). The average translational energies for the Br and Br? channels are 5.0 ± 1.0 and 6.0 ± 1.5 kcal∕mol. No recoil anisotropies were observed for these products. Most plausible mechanisms of OH and Br formation are discussed based on both the experimental and the theoretical results. Results suggest that the electronically excited BNP molecules at 248 and 234 nm relax to the ground state, and subsequently dissociate to produce OH and Br through different channels. The mechanism of OH formation from BNP on excitation at 193 nm is also discussed. 相似文献
56.
Ankur Basu 《The Ramanujan Journal》2011,26(2):193-207
The object of study in this paper is some Tornheim type sums \(\sum_{n=1}^{\infty}\sum_{m=1}^{\infty} \frac{1}{n^{r}m^{s}(n+m)^{t}}\) which are close relatives of the so-called Euler sums \(\sum_{n=1}^{\infty}\frac{1}{n^{s}}\sum_{m=1}^{\infty}\frac{1}{m^{t}}\). Closed form evaluations of several such double sums are obtained using elementary summation techniques earlier developed by the same author. 相似文献
57.
Shivani Agarwal Annalisa Aurora Ankur Jain Amelia Montone 《Journal of nanoparticle research》2011,13(11):5719-5726
Magnesium and its hydride MgH2 are widely regarded as promising candidates for hydrogen storage materials due to its benefits of high gravimetric and volumetric capacity, excellent reversibility, abundance in the earth and a low cost. Much attention has been paid to improve its absorption/desorption kinetics, trying to make it useful for practical applications. To make composite of MgH2 with other hydrogen storage compounds is an effective method to improve the hydrogen storage properties. In this study nano-composite of MgH2 with ZrCrCu alloy was prepared using high energy ball-milling for 5 h under Ar atmosphere. Microstructure and morphology of the composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM). XRD patterns show that no alloy formation between MgH2 and elements of the alloys takes place during milling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure?Ccomposition isotherms of these composites have been obtained in the pressure range 0.1?C10 bar at 275 and 300 °C. The absorption/desorption kinetics data have been analyzed using pressure 0.1?C5.0 bar at 275 and 300 °C to understand the mechanism of the hydriding/dehydriding reaction processes. A comparison of these results has been attempted with our previous published results of MgH2?C10 wt%ZrCrNi in order to find the better composite for storage applications. It is observed by DSC curves that the onset temperature of hydrogen desorption is decreased for MgH2?C10%ZrCrNi in comparison to MgH2 which further decreased for MgH2?C10%ZrCrCu. However, little loss in hydrogen absorption/desorption capacity is also observed for ZrCrCu composite in comparison to that of ZrCrNi composite. 相似文献
58.
We have reported here the catalytic activity of a unique Cu–salen type complex in N-arylation of anilines with arylboronic acids in water. The protocol is found to be applicable for a wide range of electronically diversified arylboronic acids and anilines with excellent yields of the isolated product. Further the scope of this protocol has been extended to the synthesis of various N-aryl imidazoles in iso-propanol. 相似文献
59.
Structural Chemistry - A quantum-chemical study on some super tocopherol derivatives and their heavier chalcogen derivatives has been undertaken to evaluate the antioxidant abilities through... 相似文献
60.
Kalita Amlan Jyoti Sahu Prem Prakash Borah Ritam Raj Rohman Shahnaz Sultana Kashyap Chayanika Ullah Sabnam Swabaka Baruah Indrani Mazumder Lakhya Jyoti Konwar Dimpul Guha Ankur Kanti 《Structural chemistry》2021,32(6):2313-2318
Structural Chemistry - Sandwich complexes find their interests among the chemists after the breakthrough discovery of ferrocene. Since then, a number of sandwich and half-sandwich complexes were... 相似文献