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Probing local structure of the morphotropic phase boundary composition of Na0.5Bi0.5TiO3-BaTiO3 using rare-earth photoluminescence as a technique
No full text(1-y)Na0.5Bi0.5TiO3-(y)BaTiO3 (NBT-BT) is one of the most investigated lead-free piezoelectric system in the recent past. Unlike the conventional piezoelectric alloys wherein the morphotropic phase boundary (MPB) compositions exhibiting maximum piezoelectric response, exhibit coexistence of ferroelectric phases with different symmetries on the global scale, the MPB composition (y = 0.06) of NBT-BT shows a cubic-like phase in the unpoled state. On poling it transforms to a non-cubic ferroelectric phase. Here we exploit the sensitivity of the photoluminescence (PL) property of doped rare-earth ions with regard to the local symmetry of the host crystal to investigate the local structure of the cubic-like phase of the MPB composition of NBT-BT. We performed a comparative study of the PL response by doping separately Er and Eu in very dilute concentration in the (i) MPB composition (y = 0.06) exhibiting a cubic-like phase, (ii) a sub-MPB composition (y = 0.03) exhibiting rhombohedral phase, and (iii) above the MPB composition (y = 0.10) exhibiting tetragonal phase. We found that both the Er and the Eu PL spectra of the MPB composition (y = 0.06) exhibits more number of Stark lines in its unpoled cubic-like phase as compared to that in the field-stabilized rhombohedral phase. The additional Stark lines in the cubic-like global phase are identified to be that of the tetragonal structure. Our study therefore confirms that what appears as a cubic-like phase on the global scale has intimately connected tetragonal and rhombohedral local structures. The success of our experiments suggests that rare-earth PL can be used as a simple yet powerful tool to investigate local structures in scenarios wherein the global structure need not comply with the local structure. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Assessment of the Weather Research and Forecasting (WRF) model for simulation of extreme rainfall events in the upper Ganga Basin
No full textReliable estimates of extreme rainfall events are necessary for an accurate prediction of floods. Most of the global rainfall products are available at a coarse resolution, rendering them less desirable for extreme rainfall analysis. Therefore, regional mesoscale models such as the advanced research version of the Weather Research and Forecasting (WRF) model are often used to provide rainfall estimates at fine grid spacing. Modelling heavy rainfall events is an enduring challenge, as such events depend on multi-scale interactions, and the model configurations such as grid spacing, physical parameterization and initialization. With this background, the WRF model is implemented in this study to investigate the impact of different processes on extreme rainfall simulation, by considering a representative event that occurred during 15-18 June 2013 over the Ganga Basin in India, which is located at the foothills of the Himalayas. This event is simulated with ensembles involving four different microphysics (MP), two cumulus (CU) parameterizations, two planetary boundary layers (PBLs) and two land surface physics options, as well as different resolutions (grid spacing) within the WRF model. The simulated rainfall is evaluated against the observations from 18 rain gauges and the Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis (TMPA) 3B42RT version 7 data. From the analysis, it should be noted that the choice of MP scheme influences the spatial pattern of rainfall, while the choice of PBL and CU parameterizations influences the magnitude of rainfall in the model simulations. Further, the WRF run with Goddard MP, Mellor-Yamada-Janjic PBL and Betts-Miller-Janjic CU scheme is found to perform ``best'' in simulating this heavy rain event. The selected configuration is evaluated for several heavy to extremely heavy rainfall events that occurred across different months of the monsoon season in the region. The model performance improved through incorporation of detailed land surface processes involving prognostic soil moisture evolution in Noah scheme compared to the simple Slab model. To analyse the effect of model grid spacing, two sets of downscaling ratios -(i) 1 : 3, global to regional (G2R) scale and (ii) 1 : 9, global to convection-permitting scale (G2C) -are employed. Results indicate that a higher downscaling ratio (G2C) causes higher variability and consequently large errors in the simulations. Therefore, G2R is adopted as a suitable choice for simulating heavy rainfall event in the present case study. Further, the WRF-simulated rainfall is found to exhibit less bias when compared with the NCEP FiNaL (FNL) reanalysis data
On-chip optical transduction scheme for graphene nano-electro-mechanical systems in silicon-photonic platform
No full textWe present a scheme for on-chip optical transduction of strain and displacement of graphene-based nano-electromechanical systems (NEMS). A detailed numerical study on the feasibility of three silicon-photonic integrated circuit configurations is presented: the Mach-Zehnder interferometer (MZI), the micro-ring resonator, and the ring-loaded MZI. An index sensing based technique using an MZI loaded with a ring resonator with a moderate Q-factor of 2400 can yield a sensitivity of 28 fm/root Hz and 6.5 x 10(-6)%/root Hz for displacement and strain, respectively. Though any phase-sensitive integrated-photonic device could be used for optical transduction, here we show that optimal sensitivity is achievable by combining resonance with phase sensitivity. (C) 2018 Optical Society of Americ
ppb level detection of NO2 using a WO3 thin film-based sensor: material optimization, device fabrication and packaging
No full textIn this study, we have investigated the thickness-dependent nitrogen dioxide (NO2) sensing characteristics of a reactive-ion magnetron sputtered tungsten trioxide (WO3) film, followed by morphological and electrical characterizations. Subsequently, the sensing material was integrated with an MEMS platform to develop a sensor chip to integrate with electronics for portable applications. Sputtered films are studied for their sensing performance under different operating conditions to discover the optimum thickness of the film for integrating it with a CMOS platform. The optimized film thickness of similar to 85 nm shows the 16 ppb lower limit of detection and 39 ppb detection precision at the optimum 150 degrees C operating temperature. The film exhibits an extremely high sensor response (R-g - R-a)/R-a x 100 = 26%] to a low (16 ppb) NO2 concentration, which is a comparatively high response reported to date among reactively sputtered films. Moreover, this optimum film has a longer recovery time than others. Thus, an intentional temperature overshoot is made part of the sensing protocol to desorb the NO2 species from the film surface, resulting in full recovery to the baseline without affecting the sensing material properties. Finally, the optimized film was successfully integrated on the sensor platform, which had a chip size of 1 mm(2), with an inbuilt micro-heater. The minimum power consumption of the microheater is similar to 6.6 mW (similar to 150 degrees C), which is practically acceptable. Later, the sensor device was packaged on a Kovar heater for the detailed electrical and sensing characterizations. This study suggests that optimization of the sensing material and optimum operating temperature help to develop a highly sensitive, selective, stable, and portable gas sensor for indoor or outdoor applications
Influence of electrodeposition modes on the electrochemical performance of MnO2 films prepared using anionic MnO4- (Mn7+) precursor
No full textIn this work, we report the comparative electrochemical performance of the nanostructured MnO2 films prepared via three different electrodeposition modes, namely, potentiostatic (PS), potentiodynamic (PD), and galvanostatic (GS), using anionic MnO4- (Mn7+) precursor. All the MnO2 films have been found to exhibit the hexagonal crystallographic phase of epsilon manganese dioxide (e-MnO2, akhtenkite), consistent with the JCPDS card no. 12-0141. The potentiostatically electrodeposited MnO, film has surface morphology exhibiting a porous microstructure comprising of sparsely distributed grains, which is conducive for easy diffusion of electrolyte ions during electrochemical process. The analyses of atomic force microscopy images reveal that the surface area is maximum for the film deposited via PS mode. Cyclic voltammetry studies reveal that the film deposited via PS mode has the maximum specific capacitance 259.4 F/g, followed by 187.1 F/g and 180.3 F/g for the films deposited via PD and GS modes, respectively at the scan rate of 5 mV/s. The galvanostatic charge/discharge measurements at the current density of 1 mA/cm(2) show the specific capacitance to be maximum 325.6 F/g for the MnO2 film prepared via PS mode, followed by 194.6 F/g and 182.5 F/g for the films prepared by PD and GS modes, respectively. The variation in specific capacitances of the films is attributed to varying morphological features of the films. In conclusion, the PS mode has been found to be the optimum electrodeposition mode to prepare MnO2 films using anionic MnO4- (Mn7+) precursor for improved electrochemical performance of the films
Root multiplicities for Borcherds algebras and graph coloring
No full textWe establish a connection between root multiplicities for Borcherds Kac Moody algebras and graph coloring. We show that the generalized chromatic polynomial of the graph associated to a given Borcherds algebra can be used to give a closed formula for certain root multiplicities. Using this connection we give a second interpretation, namely that the root multiplicity of a given root coincides with the number of acyclic orientations with a unique sink of a certain graph (depending on the root). Finally, using the combinatorics of Lyndon words we construct a basis for the root spaces corresponding to these roots and determine the Hilbert series in the case when all simple roots are imaginary. As an application we give a Lie theoretic proof of Stanley's reciprocity theorem of chromatic polynomials. (C) 2017 Elsevier Inc. All rights reserved
N6-methyladenosine landscape of mRNAs in glioma: Essential role of METTL3 and m(6)A modification in glioma stem cell growth
No full textMultidimensional Index Modulation in Wireless Communications
No full textIn index modulation schemes, information bits are conveyed through indexing of transmission entities, such as antennas, subcarriers, times slots, precoders, subarrays, and radio frequency (RF) mirrors. Index modulation schemes are attractive for their advantages, such as good performance, high rates, and hardware simplicity. This paper focuses on index modulation schemes in which multiple transmission entities, namely, antennas, time slots, and RF mirrors, are indexed simultaneously. Recognizing that such multidimensional index modulation schemes encourage sparsity in their transmit signal vectors, we propose efficient signal detection schemes that use compressive sensing based reconstruction algorithms. Results show that, for a given rate, improved performance is achieved when the number of indexed transmission entities is increased. We also explore indexing opportunities in load modulation (LM), which is a modulation scheme that offers power efficiency and reduced RF hardware complexity advantages in multiantenna systems. Results show that indexing time and RF mirrors in load modulated multiantenna systems can achieve improved performance. A stagewise algorithm based on message passing suited for the detection of indexed LM signals is also proposed
Enhanced Raman and photoluminescence response in monolayer MoS2 due to laser healing of defects
No full textBound quasiparticles, negatively charged trions and neutral excitons are associated with the direct optical transitions at the K-points of the Brillouin zone for monolayer MoS2. The change in the carrier concentration, surrounding dielectric constant, and defect concentration can modulate the photoluminescence and Raman spectra. Here, we show that exposing the monolayer MoS2 in air to a modest laser intensity for a brief period of time enhances simultaneously the photoluminescence intensity associated with both trions and excitons, together with similar to 3 to 5 times increase of the Raman intensity of first-order and second-order modes. The simultaneous increase of photoluminescence from trions and excitons cannot be understood based only on known scenario of depletion of electron concentration in MoS2 by adsorption of O-2 and H2O molecules. This is explained by laser-induced healing of defect states resulting in reduction of nonradiative Auger processes. This laser healing is corroborated by an observed increase of intensity of both the first-order and second-order longitudinal acoustic Raman modes at the M-point of Brillouin zone by a factor of similar to 3 to 5. The A(1g) mode hardens by similar to 1.4 cm(-1), whereas the E-2g(1) mode softens by similar to 1 cm(-1). The second-order longitudinal acoustic Raman mode at the M-point of Brillouin zone at similar to 440 cm(-1) shows an increase in wavenumber by similar to 8 cm(-1) with laser exposure. These changes are a combined effect of change in electron concentrations and oxygen-induced lattice displacements. Copyright (c) 2017 John Wiley & Sons, Ltd
Synthesis and characterization of biocompatible carbon-gold (C-Au) nanocomposites and their biomedical applications as an optical sensor for creatinine detection and cellular imaging
No full textHighlights
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This study demonstrates the synthesis of photoluminescent C-Au nanocomposites (C-Au NC) for multi-color cellular imaging in replacement of high priced fluorescence molecules and synthetic dyes.
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The synthesized C-Au NC can be used to detect both normal and abnormal levels of creatinine.
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The reducing and capping capabilities of Citrullus lanatus derived carbon nano dots (CNDs) for C-Au NC synthesis were investigated.
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C-Au NC showed excellent biocompatibility against cancer and normal cell lines which can be used for biomedical applications