50175 research outputs found
Sort by
Impedance spectroscopic study on microwave sintered (1-x) Na0.5Bi0.5TiO3-x BaTiO3 ceramics
No full textComplex impedance spectroscopic technique has been implemented to study the detailed electrical transport properties of Lead free ferroelectric ceramic solid solutions of (1 - x) Na0.5Bi0.5TiO3-x BaTiO3 (NBT-BT) (0.00 <= x <= 0.10). The NBT-BT ceramics have been synthesized by sol-gel auto combustion method and sintered via microwave sintering technique. Room temperature X-ray diffraction patterns confirmed the formation of the single phase materials with perovskite structure. The surface morphology of the samples has been studied using field emission scanning electron microscopic (FESEM) technique. The FESEM micrographs confirm that the grain size decreases with increasing BaTiO3 (BT) concentration. Complex impedance, complex electric modulus formalism, and frequency dependent ac conductivity analysis have been used to study the relaxation and conduction mechanism in these materials. The presence of grain- and grain boundary contribution to impedance spectra in NBT-BT ceramics were analyzed using complex impedance plot in association with complex modulus plot. The grain- and grain boundary contributions were discerned in NBT-BT ceramic through least-squares fitting of the experimental data with a suitable equivalent circuit model. Complex impedance and complex electric modulus spectroscopic analysis indicate that the dielectric relaxation in these materials are of non-Debye type. A negative temperature coefficient of resistance (NTCR) behavior of our NBT-BT ceramics was seen from the temperature dependent conductivity studies. We have obtained similar activation energies from the conduction and relaxation process
Stable Oxygen and Carbon Isotopic Composition of Rice (Oryza sativa L.) Grains as Recorder of Relative Humidity
No full textSouthwest monsoon season over India exhibits spatial variation in the relative humidity (RH) levels. We took advantage of rice (Oryza sativa L.), cultivated in varied RH condition during the southwest monsoon season, to study the relationship of oxygen and carbon isotopic composition in the bulk grain organic matter (O-18(OM), C-13(OM)) with the hydroclimatic parameter of RH. Seasonal harvests of the years 2010 through 2014, sampled from 23 sites located in different climatic zones over India, were used for this experiment. Several fields and different genotypes (n=105) were sampled at each site to arrive at representative values of O-18(OM) and C-13(OM). Based on regression analyses, the O-18(OM) variation across sites showed significant dependence on the O-18 of source water (O-18(SW)) used by the crops, with the humid region registering the strongest correlation (r(2)=0.95, p<0.0001). After normalizing O-18(OM) values with respect to O-18(SW) and expressing the deviation as O-18(OM), we obtained a significant relationship between the growing-season average RH and O-18(OM) (r(2)=0.90, p<0.0001)(.) This is represented by a linear response function: Delta O-18(OM)=(-0.450.03)xRH+(66.42.7). The relationship established in this study enables the reconstruction of RH level from the isotopic measurement of rice grain OM in modern-day and palaeo samples. Further, the relationship of the carbon isotope discrimination in rice grain OM (C-13(OM)) with RH gradient demonstrates the role of the evaporative demand in governing the dual-isotope variability
Transfection efficiencies of alpha-tocopherylated cationic gemini lipids with hydroxyethyl bearing headgroups under high serum conditions
No full textHerein, five new -tocopheryl cationic gemini lipids with hydroxyethyl bearing headgroups (THnS, n = 4, 5, 6, 8, 12) have been synthesized for efficient plasmid DNA (pDNA) delivery into cancer cells. Among these gemini lipid formulations, the lipid with an octamethylene -(CH2)(8)] spacer (TH8S) showed the highest transfection efficiency (TE) that was comparable to that of the commercial standard lipofectamine 2000 (L2K) in terms of luciferase expression in HepG2 (liver hepatocellular carcinoma) cells. The addition of the helper lipid DOPE (1,2-dioleoyl phosphatidyl ethanolamine) with cationic lipids in mixed liposomes further enhanced the TE and the optimized molar ratio was 2:1 (DOPE:cationic lipid). The optimized co-liposomal formulation of TH8S (DOPE:TH8S = 2:1) showed a higher TE in HepG2, A549 (human lung carcinoma) and MCF7 (human breast adenocarcinoma) cells than other optimized co-liposomal formulations and was also significantly more potent than L2K. The comparison of the TE of DOPE-TH8S (2:1) with the gemini lipid T8T (the headgroup devoid of the hydroxyl group) further demonstrated the importance of the hydroxyethyl functionality at the level of the headgroup. Relatively good binding efficiency and easy release of pDNA (pGL3) were also observed with DOPE-TH8S (2:1) in the ethidium bromide (EB)-exclusion and re-intercalation assay, which may be the plausible reason for high TE. The lipoplexes were also characterized by atomic force microscopy (AFM), dynamic light scattering (DLS), zeta potential and small angle X-ray diffraction experiments. Greater cellular internalization of fluorescein tagged pDNA was also observed with DOPE-TH8S (2:1) lipoplexes compared to that with L2K. Retention of the TE of DOPE-TH8S (2:1) lipoplexes under high serum conditions was conferred by the presence of the tocopherol backbone and also the hydroxyethyl functionalities. The cellular internalization pathway of the lipoplexes was characterized by performing transfection experiment in the presence of inhibitors of different endocytic pathways and it was found to be caveolae mediated. An MTT based cell viability assay indicated that the lipoplex mediated gene delivery vectors exhibited low toxicity in all the three cancer cell lines studied
Mass spectrometric identification of bromotryptophan containing conotoxin sequences from the venom of C. amadis
No full textFour 30 residue conotoxin have been identified from the venom of C. amadis. MS/MS analysis of crude venom subjected to global reduction/alkylation yielded fragmentation patterns, which permitted searching and matching with a database of putative mature toxin sequences obtained from transcriptomic analysis. Of the four sequences identified, Am3408(Am6.1b), Am3452(Am6.1c), Am3136(Am6.2a) and Am3214(Am6.2b), three contain bromotryptophan residues, while an additional post translational modification, gamma carboxylation of glutamic acid, is present in Am3408(Am6.lb)/3452(Am6.1c). The conotoxins belong to the O1/O2 gene superfamily and possess cysteine framework VI/VII. While, the cysteine patterns show a similarity to omega conotoxins, the three C. amadis peptides are highly negatively charged and possess a significant content of hydrophobic residues. (C) 2018 Published by Elsevier Ltd
Risk-sensitive stochastic differential games with reflecting diffusions
No full textWe study risk-sensitive differential games for controlled reflecting diffusion processes in a bounded domain. We consider both nonzero-sum and zero-sum cases. We treat two cost evaluation criteria; namely, discounted cost and ergodic cost. Under certain assumptions we establish the existence of Nash/saddle-point equilibria for relevant cases
Effect of interface defect density on performance of perovskite solar cell: Correlation of simulation and experiment
No full textExperimental data from a 17.5% efficient perovskite solar cell has been used to develop a self-consistent device model using Solar Cell Capacitance Simulator (SCAPS). Electronic properties of the individual layers, such as doping density of compact TiO2 (c-TiO2), doping and defect density of perovskite, etc. are extracted from experimental data. The only fitting parameters in the model are the defect densities at spiro-MeOTAD/perovskite interface (IL-1) and perovskite/TiO2 interface (IL-2). The simulated current-voltage (J-V) characteristics and Mott-Schottky plot results match extremely well with the experimentally measured plots, validating the device model. The model was further used to extract insights into the loss mechanism of the high-efficiency perovskite solar cells. Simulations revealed that defect density at IL-1 interface has strong impact on the open-circuit voltage (V-OC), while defect density in the perovskite and IL2 interface has a major impact on short-circuit current density (J(SC)). (C) 2018 Elsevier B.V. All rights reserved
Family of columns isospectral to gravity-loaded columns with tip force: A discrete approach
No full textA discrete model is introduced to analyze transverse vibration of straight, clamped-free (CF) columns of variable cross-sectional geometry under the influence of gravity and a constant axial force at the tip. The discrete model is used to determine critical combinations of loading parameters - a gravity parameter and a tip force parameter - that cause onset of dynamic instability in the CF column. A methodology, based on matrix-factorization, is described to transform the discrete model into a family of models corresponding to weightless and unloaded clamped-free (WUCF) columns, each with a transverse vibration spectrum isospectral to the original model. Characteristics of models in this isospectral family are dependent on three transformation parameters. A procedure is discussed to convert the isospectral discrete model description into geometric description of realistic columns i.e. from the discrete model, we construct isospectral WUCF columns with rectangular cross-sections varying in width and depth. As part of numerical studies to demonstrate efficacy of techniques presented, frequency parameters of a uniform column and three types of tapered CF columns under different combinations of loading parameters are obtained from the discrete model. Critical combinations of these parameters for a typical tapered column are derived. These results match with published results. Example CF columns, under arbitrarily-chosen combinations of loading parameters are considered and for each combination, isospectral WUCF columns are constructed. Role of transformation parameters in determining characteristics of isospectral columns is discussed and optimum values are deduced. Natural frequencies of these WUCF columns computed using Finite Element Method (FEM) match well with those of the given gravity-loaded CF column with tip force, hence confirming isospectrality. (C) 2018 Elsevier Ltd. All rights reserved
High performance printed oxide field-effect transistors processed using photonic curing
No full textOxide semiconductors are highly promising candidates for the most awaited, next-generation electronics, namely, printed electronics. As a fabrication route for the solution-processed/printed oxide semiconductors, photonic curing is becoming increasingly popular, as compared to the conventional thermal curing method; the former offers numerous advantages over the latter, such as low process temperatures and short exposure time and thereby, high throughput compatibility. Here, using dissimilar photonic curing concepts (UV-visible light and UV-laser), we demonstrate facile fabrication of high performance In2O3 field-effect transistors (FETs). Beside the processing related issues (temperature, time etc.), the other known limitation of oxide electronics is the lack of high performance p-type semiconductors, which can be bypassed using unipolar logics from high mobility n-type semiconductors alone. Interestingly, here we have found that our chosen distinct photonic curing methods can offer a large variation in threshold voltage, when they are fabricated from the same precursor ink. Consequently, both depletion and enhancement-mode devices have been achieved which can be used as the pull-up and pull-down transistors in unipolar inverters. The present device fabrication recipe demonstrates fast processing of low operation voltage, high performance FETs with large threshold voltage tunability
Electrochemical behavior of SnNi-graphene oxide composite coatings
No full textIt has been illustrated by researchers that graphene and graphene oxide can be embedded into metal matrix to produce highly corrosion resistant composite coatings. This paper investigates the effect of graphene oxide (GO) on microstructure and corrosion behavior of Sn-rich, SnNi-GO composite coatings. SnNi-GO composite coatings were electrodeposited on mild steel substrate by dispersing chemically synthesized GO into the electrolyte bath. Amount of GO in the composite coatings was varied by changing the concentration of GO in the electrolyte bath used for the electrodeposition. Morphological characterization of the coatings revealed the presence of rod shaped features in a flat matrix. Volume fraction of the rod-shaped features progressively increased with the addition of GO into the coatings. Structural characterization revealed the presence of Sn rich phase along with Ni3Sn4, Ni3Sn2 and Ni3Sn intermetallic phases in all the coatings. Crystallite size of the Sn-rich phase decreased significantly due to the addition of GO into the coatings. Corrosion behavior of the coatings was examined through potentiodynamic polarization and electrochemical impedance spectroscopy methods. A significant improvement in the corrosion resistance in terms of reduction in corrosion current and corrosion rate and increase in polarization resistance was noted in the case of SnNi coating containing GO. Corrosion resistance of the coatings increased with increase in the GO content. Microstructural characterization of the cross-section coating sample performed using transmission electron microscopy (TEM) technique revealed differences between the microstructures of coating containing different amounts of GO. All the coatings with GO contained almost pure Sn grains with Ni present at the grain boundaries. Size of the Sn sub-grains within the larger Sn grains, however, decreased with increase in the GO content in the coatings. Smaller Sn sub-grains and presence of Ni at the grains boundaries led to quicker formation of the corrosion products that are SnO and NiO with increasing GO content in the coatings eventually yielding the highest corrosion resistance value for the coating containing maximum amount of GO
Generation of tunable, high repetition rate optical frequency combs using on-chip silicon modulators
No full textWe experimentally demonstrate tunable, highly-stable frequency combs with high repetition-rates using a single. charge injection based silicon PN modulator. In this work, we demonstrate combs in the C-band with over eight lines in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also demonstrate through simulations the potential for bandwidth scaling using an optimized silicon PIN modulator. We find that the time varying free carrier absorption due to carrier injection, an undesirable effect in data modulators, assists here in enhancing flatness in the generated combs. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen