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High temperature deformation in fine grained high entropy alloys
No full textThere is considerable interest currently in developing and understanding microstructural evolution, stability and deformation in the new class of highly concentrated, multi-principal element solid solution high entropy alloys. This overview provides a brief description of potential high temperature deformation mechanisms in such fine grained alloys, discusses the significance of diffusion, and compares the available experimental results with appropriate theoretical models. It is shown that diffusion is not substantially slower in such alloys, and that superplastic deformation follows the standard model established for conventional polycrystals. The data also suggest that deformation at higher stresses occurs by dislocation glide creep, followed by a power-law breakdown regime. It is necessary to exercise caution in interpreting spherical nanoindentation creep data, although some data on a nanocrystalline HEA suggest that deformation at room temperature occurs by Coble diffusion creep. Based on the available data and understanding, a deformation mechanism map is developed highlighting the dominance over different regimes of grain size and stress of Coble diffusion creep, superplastic flow, dislocation creep and power-law breakdown. (C) 2017 Elsevier B.V. All rights reserved
Self-heating oxidized suspended Pt nanowire for high performance hydrogen sensor
No full textIn this work, joule-self-heating of a suspended Pt nanowire, under oxygen ambient, is utilized to form PtOx/Pt nanostructure to develop a new type of 1-dimensional sensor device architecture for detection of hydrogen at room temperature. An optimum design space for the sensor is elucidated with the initial Pt nanowire thickness ranging between 10 nm and 80 nm. Single PtOx/Pt nanowire sensor, based on optimum metal (Pt) to metal-oxide (PtOx) junction can detect down to 100 ppm H-2 with ultra-low power consumption of similar to 45 nW. This study also investigates hydrogen sensing characteristics of an array of oxidized Pt nanowires, which enhances the response with the maximum sensitivity of similar to 936%, compared to single PtOx/Pt nanowire sensor sensitivity of similar to 13% for 100 ppm hydrogen. Nanowire array sensor provides the minimum detection limit of 500 ppb (similar to 18.1%) with very fast response (similar to 25 s) and recovery (similar to 108 s) time. A phenomenological model is proposed to elaborate the nature of oxidation of joule-self heated Pt nanowire in oxygen ambient. (C) 2017 Elsevier B.V. All rights reserved
Ultra-Sensitive Detection of Proteins Using Chemically Modified Nanoporous PVDF Membrane with Attenuated Near IR Autofluorescence
No full textWe report the lowest autofluorescent nanoporous polyvinylidene fluoride (PVDF) membranes exhibit near infra-red (NIR) emission properties for western blot detection of high and low molecular weight proteins. The design involves post modification of PVDF membranes by an alkali treatment that reduces the native of PVDF at 450-520nm. The background fluorescence of these modified membranes is eight times lower than the commercial available PVDF membranes and displayed NIR emission at 750nm. Imparted alkene conjugated double bonds in the polymeric backbone by alkali treatment causes the NIR emission in the modified PVDF membranes and this translates improvement in detection of, in particular, high molecular weight proteins (130 kDa) compared to traditional western blot. To validate the pore size effect, two different pores sized (similar to 100nm and similar to 0.8m) PVDF membranes were prepared, surface modified and subjected for protein profiling. High linearity was achieved in detection of high molecular weight proteins and significant protein binding was noticed for the alkali treated membranes of similar to similar to 100nm size. The methodology permits the design of modified PVDF membranes with lesser pore size could be an alternative for existing membranes with minimal autofluorescence for efficient and quick detection of high molecular weight proteins
Cobalt(III)-Catalyzed C-H Activation: A Secondary Amide Directed Decarboxylative Functionalization of Alkynyl Carboxylic Acids Wherein Amide NH-group Remains Unreactive
No full textA Co(III)-catalyzed C-H activation reaction for ortho-alkenylation of benzamides (aryl/heteroaryl) and C2-alkenylation of indole derivatives have been developed using alkynyl carboxylic acid as an alkene source. A high regioselectivity has been achieved in the formation of disubstituted alkenes, and the possible cyclic products were not observed. This efficient alkenylation shows a broad range of substrate scope with a good functional group tolerance. The application of the methodology has been showcased by transforming an alkenylated amide to a 3-hydroxy isoindolinone derivative
Optimal Index Codes For A New Class of Interlinked Cycle Structure
No full textThe interlinked cycle (IC) structure that generalizes cycles and cliques was defined by Thapa, Ong, and Johnson. Interlinked-cycle-cover (ICC) scheme that leverages IC structures in digraphs to construct scalar linear index codes was proposed. A class of infinitely many digraphs, where the proposed scalar linear codes based on ICC scheme are optimal were characterized by Thapa et. al. In this paper, we provide an addition to this class by providing optimal length index codes for IC structures with one cycle among non-inner vertex set
Fluorescence Recovery after Photobleaching in Ultrathin Polymer Films
No full textFluorescence recovery after photobleaching (FRAP) is a widely used technique to study the transport of molecules in biological systems. Recently, FRAP has been used to study molecular transport in polyelectrolyte multilayers (PEMs). Through numerical simulations verified by experiments, it is shown that the FRAP behavior of PEM films in an aqueous medium differs significantly from that in previously explored systems such as single cells. This is because fluorescence recovery can take place through the aqueous medium surrounding the PEM film. The simulations show the critical role of the time scale of the different processes, namely, diffusion through PEM, diffusion through surrounding medium, and the unbinding rate of fluorophore-labeled species in the interpretation of FRAP data. An important conclusion from the numerical and experimental study is that, for ultrathin PEM films with approximate to 100 nm thicknesses, recovery is dominated through the solution medium and hence, classical FRAP analysis is not sufficient to probe diffusion in PEM. The numerical study reveals several aspects of the FRAP phenomena in thin polymer films that are critical for the proper interpretation of experimental data
Development of super convergent Euler finite elements for the analysis of sandwich beams with soft core
No full textSandwich structures are well known for their use in aircraft, naval and automobile industries due to their high strength resistance with light weight and high energy absorption capability. Sandwich beams with soft core are very common and simple structures that are employed in day to day general use appliances. Modeling and analysis of sandwich structures is not straight forward due to the interactions between core and face sheets. In this paper, formulation of Super Convergent finite elements for analysis of the sandwich beams with soft core based on Euler Bernoulli beam theory are presented. Two elements, Eul4d with 4 degrees of freedom assuming rigid core in transverse direction and EullOd with 10 degrees of freedom assuming the flexible core were developed are presented. The formulation considers the top, bottom face sheets and core as separate entities and are coupled by beam kinematics. The performance of these elements are validated by results available in the published literature. Number of studies are performed using the formulated elements in static, free vibration and wave propagation analysis involving various boundary and loading conditions. The paper highlights the advantages of the elements developed over the traditional elements for modeling of sandwich beams and, in particular wave propagation analysis
Factors influencing the coupling between non-180 degrees domain switching and lattice strain in perovskite piezoceramics
No full textDomain switching and lattice strain are known to be important processes contributing to the large electromechanical response observed in perovskite-based piezoelectrics. However, there is a lack of clarity regarding the coupling between the two phenomena, and the factors which influence this coupling. Here, we report a systematic investigation to understand the factors influencing the coupling between domain switching and lattice strain in perovskite piezoelectrics by x-ray diffraction in situ with electric field. In a slight departure from the conventional approach, we employ a strategy which enables x-ray diffraction study in situ with electric field on randomly oriented piezoelectric grains in their unclamped (free) state. Experiments were carried out on two different systems (1-x)PbTiO3-(x)BiScO3 and (1-x)PbTiO3-(x)PbZrO3 in their rhombohedral phase. We found that lattice strain along the nonpolar < 100 >(R) rhombohedral direction varies linearly with the non-180 degrees domain switching fraction (eta(111)). We introduce a parameter beta to characterize the strength of coupling between the two phenomena and show that the coupling is enhanced when the system approaches the morphotropic phase boundary. We also demonstrate that the grain-to-grain interaction nearly doubles this coupling in a dense piezoelectric ceramic
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
Mitochondria-localizing BODIPY-copper(II) conjugates for cellular imaging and photo-activated cytotoxicity forming singlet oxygen
No full textCopper(ii) acetylacetonates of N,N,N-donor dipicolylamine (dpa) ligands, viz. Cu(L-1)(acac)]ClO4 (1), Cu(L-2)(acac)]ClO4 (2) and Cu(L-3)(acac)]ClO4 (3), where L-1 is benzyldipicolylamine (bzdpa), L-2 and L-3 are non-iodinated and diiodinated BODIPY (borondipyrromethene) ligands and Hacac is acetylacetone, were synthesized and characterized and their photocytotoxicity was studied. The BODIPY complex 2, structurally characterized by X-ray crystallography, has copper(ii) in a distorted square-pyramidal geometry (degree of trigonality, (5) = 0.28). The one-electron paramagnetic and redox active copper(ii) complexes displayed 1:1 electrolytic behaviour in polar organic solvents. The BODIPY complexes 2 and 3 showed respective visible bands at 498 and 539 nm in 5% DMSO-phosphate buffered saline (PBS). Complex 2 displayed an emission band at 511 nm in 5% DMSO-PBS ((ex) = 465 nm) with a fluorescence quantum yield (phi(F)) value of 0.15. Cellular imaging using this complex showed significant mitochondrial localization in HeLa and MCF-7 cancer cells. Complex 3 with a diiodo-BODIPY moiety was non-emissive (phi(F) = 0.01) but acted as an efficient photosensitizer with a singlet oxygen quantum yield value of 0.59 (phi). Complex 3 showed a remarkable PDT effect with apoptotic cell death due to singlet oxygen giving IC50 values within 0.04-0.06 M in HeLa and MCF-7 cells using visible light (400-700 nm), while being less toxic in the dark