50175 research outputs found
Sort by
Catalytic synthesis of fatty acid methyl esters from Madhuca indica oil in supercritical methanol
No full textFatty acid methyl esters (FAMEs) that are used as biodiesel can be synthesized in supercritical methylating agents such as supercritical methanol. While the synthesis can be conducted both non-catalytically and catalytically, the synthesis in the presence of oxides is significantly faster. In this study, FAMEs were synthesized by transesterification of a non-edible oil (Mahua, Madhuca indica) in supercritical methanol with a wide variety of oxides. The reaction was extensively studied with eleven different oxides, synthesized using the solution combustion method, as catalysts. In addition, the best two catalysts, namely MgO and Mn3O4, were synthesized using four different fuels in the combustion synthesis. The catalytic effect of all these oxides was investigated and conversions ranging from 5% to 100% were obtained over the investigated range of temperature from 503 K to 583 K, and with reaction time varying between 2 min and 80 min. Among all the catalysts, MgO synthesized with ascorbic acid as the fuel for the solution combustion gave the best results. Therefore, this catalyst was chosen and the influence of operating temperature for the transesterification reaction (503-583 K) on the rate of the reaction was studied. A pseudo first order kinetic model was obtained based on the proposed Eley-Rideal reaction mechanism and, the rate constants were obtained. The rate constants varied between 1.61 x 10(-3) s(-1) to 4.93 x 10(-3) s(-1) with an activation energy of 36 kJ/mol and a pre-exponential factor of 9.33 s(-1). The rate constant obtained for the non-catalytic supercritical transesterification with oxide as catalyst was significantly higher than the rate constant of 9.9 x 10(-5) s(-1) obtained for the non-catalytic reaction at 523 K. The activation energy for the catalyzed reaction (36 kJ/mol) was notably lower than the activation energy (75 kJ/mol) for the uncatalyzed reaction indicating the efficacy of the catalyst
Marginally Self-Averaging One-Dimensional Localization in Bilayer Graphene
No full textThe combination of a field-tunable band gap, topological edge states, and valleys in the band structure makes insulating bilayer graphene a unique localized system, where the scaling laws of dimensionless conductance g remain largely unexplored. Here we show that the relative fluctuations in ln g with the varying chemical potential, in strongly insulating bilayer graphene (BLG), decay nearly logarithmically for a channel length up to L/xi approximate to 20, where xi is the localization length. This ``marginal'' self-averaging, and the corresponding dependence of < ln g > on L, suggests that transport in strongly gapped BLG occurs along strictly one-dimensional channels, where xi approximate to 0.5 +/- 0.1 mu m was found to be much longer than that expected from the bulk band gap. Our experiment reveals a nontrivial localization mechanism in gapped BLG, governed by transport along robust edge modes
Deterministic, Reversible, and Nonvolatile Low-Voltage Writing of Magnetic Domains in Epitaxial BaTiO3/Fe3O4 Heterostructure
No full textThe ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO3/Fe3O4 fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO3 have been confirmed by macro- and microscale measurements, for which Fe(3)O(4 )serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe2+ and Fe3+ at O-h sites and Fe3+ at T-d sites in Fe3O4, while the room-temperature magnetic domains of Fe3O4 are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of Fe(3)O(4 )can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in Fe3O4, and thus its magnetic state, making it attractive for electrically written magnetic memories
The vertebrate limb: An evolving complex of self-organizing systems
No full textThe paired appendages (fins or limbs) of jawed vertebrates contain an endoskeleton consisting of nodules, bars and, in some groups, plates of cartilage, or bone arising from replacement of cartilaginous templates. The generation of the endoskeletal elements occurs by processes involving production and diffusion of morphogens, with, variously, positive and negative feedback circuits, adhesion, and receptor dynamics with similarities to the mechanism for chemical pattern formation proposed by Alan Turing. This review presents a unified interpretation of the evolution and functioning of these mechanisms. Studies are described indicating that protocondensations, compacted mesenchymal cell aggregates that prefigure the appendicular skeleton, arise through the adhesive activity of galectin-1, a matricellular protein with skeletogenic homologs in all jawed vertebrates. In the cartilaginous and lobe-finned fishes (and to a variable extent in ray-finned fishes) it additionally cooperates with an isoform of galectin-8 to constitute a self-organizing network capable of generating arrays of preskeletal nodules, bars and plates. Further, in the tetrapods, a putative galectin-8 control module was acquired that may have enabled proximodistal increase in the number of protocondensations. In parallel to this, other self-organizing networks emerged that acted, via Bmp, Wnt, Sox9 and Runx2, as well as transforming factor-beta and fibronectin, to convert protocondensations into skeletal tissues. The progressive appearance and integration of these skeletogenic networks over evolution occurred in the context of an independently evolved system of Hox protein and Shh gradients that interfaced with them to tune the spatial wavelengths and refine the identities of the resulting arrays of elements. (C) 2018 Elsevier Ltd. All rights reserved
Improved electrochemical performances of LiMnPO4 synthesized by a hydrothermal method for Li-ion supercapatteries
No full textDeveloping high-performance positrode materials are essential to attain high energy supercapatteries. In this regard, the electrochemical performances of the hydrothermally synthesized LiMnPO4 are studied. The crystal structures of the materials are elucidated using Full-profile XRD Rietveld refinement. The LiMnPO4 particles showed uniform elongated spherical shape with rice-like morphology. The rice-like LiMnPO4 showed a higher specific capacity of 492Cg(-1) at 2mVs(-1) than highly agglomerated particles synthesized through sol-gel thermolysis method (191Cg(-1)) in 1M LiOH aqueous electrolyte. The supercapattery is fabricated with rice-like LiMnPO4 and activated carbon (AC) as positrode and negatrode, respectively. The supercapattery (AC||LMP-H) delivered a higher capacitance around 99Fg(-1) along with an improved energy density of 31Whkg(-1). On the other hand, the LiMnPO4 prepared by sol-gel thermolysis method exhibited a very low capacitance of 35Fg(-1) at 0.6mA for the fabricated device (AC||LMP-S) with the lesser energy density about 11WhKg(-1) at a power density of 198Wkg(-1). The reason behind the improved performance is explained based on the crystal structure as well as lower charge transfer resistance
Observability and Controllability Analysis of Linear Systems Subject to Data Losses
No full textWe provide algorithmically verifiable necessary and sufficient conditions for fundamental system theoretic properties of discrete-time linear, systems subject to data losses. More precisely, the systems in our modeling framework are subject to disruptions (data losses) in the feedback loop, where the set of possible data loss sequences is captured by an automaton. As such, the results are applicable in the context of shared (wireless) communication networks and/or embedded architectures where some information on the data loss behavior is available a priori. We propose an algorithm for deciding observability (or the absence of it) for such systems, and show how this algorithm can be used also to decide other properties including constructibility, controllability, reachability, null-controllability, detectability, and stabilizability by means of relations that we establish among these properties. The main apparatus for our analysis is the celebrated Skolem's Theorem from Linear Algebra. Moreover, we study the relation between the model adopted in this paper and a previously introduced model where, instead of allowing dropouts in the feedback loop, one allows for time-varying delays
CONCATENATIVE ARTICULATORY VIDEO SYNTHESIS USING REAL-TIME MRI DATA FOR SPOKEN LANGUAGE TRAINING
No full textSpoken language training benefits from showing a video of native speakers' articulatory movements to train the second language learners. Typically, the articulatory video is prepared in conjunction with the audio which is collected simultaneously with the articulatory recording. Articulatory video recording requires specialized equipment and, hence, is expensive and time consuming. In this work, we propose a concatenative synthesis approach to obtain articulatory videos for an audio, which may not have a simultaneous articulatory recording. In the training stage of the proposed approach, we make a repository for phoneme specific articulatory image sequence from the available articulatory video. During testing, image sequences are selected from this repository to ensure a smooth transition across phonetic events. The selected image sequences are finally stitched to synthesize the articulatory video for the test audio. Articulatory videos are synthesized for 50 words randomly selected from the MRI-TIMIT database, not seen in the training data. Subjective evaluation on the quality of the synthesized videos using twelve subjects suggests that the videos are close to the original ones with a rating of 3.78 out of 5, where a score of 5 (1) indicates that there is no (great) difference in quality between the original and the synthesized videos
Effective chemical potential in spontaneous baryogenesis
No full textModels of spontaneous baryogenesis have an interaction term partial derivative(mu)theta j(B)(mu) in the Lagrangian, where j(B)(mu) is the baryonic current and theta can be a pseudo-Nambu-Goldstone boson. Since the time component of this term (theta) over dot j(B)(0), equals (theta) over dot n(B) for a spatially homogeneous current, it is usually argued that this term implies a splitting in the energy of baryons and antibaryons, thereby providing an effective chemical potential for baryon number. In thermal equilibrium, one then obtains nB similar to (theta) over dot T-2. We however argue that a term of this form in the Lagrangian does not contribute to the single particle energies of baryons and antibaryons. We show this for both fermionic and scalar baryons. However, similar to some recent work, we find that despite the above result the baryon number density obtained from a Boltzmann equation analysis can be proportional to (theta) over dot T-2. Our arguments are very different from that in the standard literature on spontaneous baryogenesis
Evidence for trivial Berry phase and absence of chiral anomaly in semimetal NbP (vol 7, 46062, 2017)
No full textUnderstanding Surface Degradation on Polymeric Insulators Using Rotating Wheel and Dip Test under DC Stress
No full textIn the present work, surface degradation studies are performed on silicone rubber based polymeric insulators using rotating wheel and dip test under DC voltage application. This work gains importance as number of HVDC lines are being constructed for transferring bulk power over long distances particularly in the country. A newly developed rotating wheel and dip test arrangement is used for the study; provision is made in the experimental set up to apply two different contaminants simulating different environmental conditions simultaneously. In one tank standard contaminant NH4Cl as per IEC 62217/ IEC TR 62730 is used and in other tank acidic contaminant is used to simulate normal and acidic rain conditions. A comparative study is conducted on the insulator specimen under different environmental stresses to evaluate long term performance. The conductivity of both normal and acidic contaminants is kept 2.5 mS/cm approximately to observe the effect of acidic environment on long term performance. During the experimental duration of 1000 hours leakage current was regularly measured and recorded. Samples were visually investigated and degradation was found to be more under acidic environment and tracking was observed. After the experiment, physico-chemical analysis is conducted on the degraded samples. Fourier transform infrared (FTIR) spectroscopy is utilized to analyze the surface chemical changes on degraded insulators samples. Salt deposition was detected on aged samples in the FTIR spectrum. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX) were conducted to detect elemental presence over the surface of degraded/ aged samples. Thermo-Gravimetric Analysis (TGA) is utilized to analyze thermal stability and loss of ATH fillers before and after aging experiment