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Off-stoichiometry, structural-polar disorder and piezoelectricity enhancement in pre-MPB lead-free Na0.5Bi0.5TiO3-BaTiO3 piezoceramic
No full textWith increasing industrial acceptance of Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics, there is a need to develop insights into the way different factors influence the microstructural-structural-piezoelectric property correlations. In this work, we have examined the role of structural disorder on the piezoelectric response of the pre-MPB composition x=0.03 of the well-known solid solution series (1-x)Na0.5Bi0.5TiO3-(x)BaTiO3. Using off-stoichiometry on the A-site as a tuning parameter to vary the structural disorder, which we characterize in terms of the fraction of the cubiclike phase or variation in the thermal parameter of the A-site cation, it is shown that the piezo response maximizes for the composition, which retains an optimum degree of disorder after poling. Our study confirms the important role of structural disorder in enhancing piezoelectric response in ferroelectric ceramics
Tuning magnetoresistance and electrical resistivity by enhancing localization length in polyaniline and carbon nanotube composites
No full textWe report low temperature electrical resistivity and magnetoresistance (MR) measurements of conducting polyaniline (PANI) and multiwalled-carbon nanotube (MWCNT) composites. We have used an in-situ oxidative polymerization method to synthesize hydrochloric acid-doped PANI composites with MWCNT weight percentages of 0, 5, 10 and 15. The temperature dependence of resistivity is studied from room temperature to 4.2K and analysed by a Mott variable range hopping (VRH) model. The resistivity increases from 1.1 x 10 -3 m at 300K to 65.75 m at 4.2 K, almost four orders of the magnitude change with temperature for pure PANI. Whereas the PANI composite with 15% MWCNTs shows less variation from 4.6x10 -4 to 3.5x10 -2 m. The huge change in resistivity is due to the localization of charge carriers in the presence of disorder. At 4.2K MR shows transition from positive to negative with higher MWCNT loading. Samples with 5 and 10% MWCNTs show positive MR, whereas the 15% MWCNT loaded sample shows negative MR. The positive and negative MR are discussed in terms of the wave function shrinkage effect and quantum interference effect on VRH conduction
Novel carbonaceous ZnO composite prepared through inert-ambient pyrolysis of the zinc anthranilate complex
No full textIn this work we present the analysis of products of the pyrolysis, at 600 degrees C, of zinc anthranilate complex in open air and in the nitrogen ambient of a sealed tube. The resulting powder samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (FESEM), and transmittance electron microscopy (HR-TEM). Open-air pyrolysis (OAP) yields well-crystallized ZnO, whereas sealed-tube pyrolysis (STP) produces a black powder that is found to be a composite (ZnO/C) of graphitic carbon and nanocrystalline, nearly monodisperse ZnO. The composite is carbon-rich. The relatively large size of ZnO crystallites from OAP and their much smaller size in the STP product suggest that carbon formation in the sealed tube restricts the growth of ZnO nanocrystals. When ZnO/C was annealed in air at 650 degrees C for 1 h, the oxide crystallites retained their average size, with all carbon removed. To investigate the possibility of using ZnO/C as electrode material in capacitors, electrochemical investigations electrode were carried out using cyclic voltammetry and galvanostatic charge-discharge, with 0.5 M KOH as electrolyte. The specific capacitance of the ZnO/C composite was found to be 124.7 F g(-1) at 5 mV s(-1) scan rate, indicating the suitability of ZnO/C as electrode material because of the measured voltammograms and charge-discharge characteristics
Spatially resolved solid-phase temperature characterization in a sillimanite tube furnace using a broadband two-color ratio pyrometry
No full textTube furnaces are heating devices used for the synthesis of inorganic and organic compounds. It is essential to predict the spatially resolved temperature of solid substances placed inside tube furnaces in contact with its walls for a fixed steady temperature of the furnace walls. This enables efficient study of transport phenomena and control of the fabrication process in the furnace. In this work, the two-color ratio pyrometry (TCRP) using a digital single lens reflex camera has been used for the temperature characterization of a stainless steel metal sheet placed at the center of a 1000 mm long tube furnace. Temperature was measured for furnace walls set between 1000 K and 1426 K. The TCRP technique accounted for intensity from the heated target over the broadband visible region. The camera was calibrated and tested for signal linearity in its color channels for a fixed source illumination. The technique yields a mean sheet temperature of 979.5 K +/- similar to 24% (attributed to camera noise and uncertainties in gray level intensity, calibration lamp output, and monochromator and photodetector efficiency) and 1391 K +/- 6.7% for a furnace wall temperature of 1000 K and 1426 K, respectively. Experiments showed that the effect of distance between the target and the camera on temperature measurement was negligible. Emission spectroscopy in the vis-near-infrared region (650-1100 nm) was also performed to predict sheet temperature. It yields results within 4.5% of TCRP at low furnace temperature but deviates by about 8.6% for temperatures above 1150 K, most likely due to experimental errors in spectroscopy. Analytical heat balance on the sheet, IR imaging, and numerical simulations yield temperatures within 5% of TCRP. This work shows that the TCRP technique can be used for spatially resolved temperature measurements of metals in tube furnaces and can readily be extended to ceramics or other class of solid materials whose emissivity can be shown to be invariant with wavelength in the visible region
MoSe2 nanoflakes based chemiresistive sensors for ppb-level hydrogen sulfide gas detection
No full textDetection and quantification of hydrogen sulfide (H2S) gas is important as it influences directly human health, our environment, and operations of several industries including food and beverages, oil, construction, and medicine. It also acts as biomarker in diagnosis of halitosis at early stage. We report herein liquid exfoliated MoSe2 nanoflakes based stable chemiresistive H2S gas sensor which operate at moderate temperature of 200 degrees C. The response of p-type MoSe2 gas sensor device (when operated in ambient environment) was found to be varying between 15.87%-53.04% when the concentration of H2S was varied between 50 ppb - 5.45 ppm. The response of the device decreases when the measurements were done in synthetic air environment and it varies between 7.13%-19.87% for the concentration range of 500 ppb - 5.45 ppm. The response (%), recovery rate (%), hysteresis, experimental lowest detection limit etc. of the device suggest that the device performs better when operated in ambient than in synthetic air which suggest its real time device application. The response time and recovery time of the sensor are 15 s and 43 s respectively for 100 ppb of H2S. The sensor performance was found to be highly repeatable with sensitivity of 5.57%/ppm of H2S. The theoretical limit of detection and limit of quantization of the device were found to be 6.73 ppb and 22.44 ppb respectively. Based on chemical analysis, a plausible mechanism based on charge transfer phenomenon has been proposed for this sensor
Epigenetic silencing of genes enhanced by collective role of reactive oxygen species and MAPK signaling downstream ERK/Snail axis: Ectopic application of hydrogen peroxide repress CDH1 gene by enhanced DNA methyltransferase activity in human breast cancer
No full textLoss of E-cadherin and epithelial to mesenchymal transition (EMT) are key steps in cancer progression. Reactive oxygen species (ROS) play significant roles in cellular physiology and homeostasis. Roles of E-cadherin (CDH1), EMT and ROS are intriguingly illustrated in many cancers without focusing their collective concert during cancer progression. We report that hydrogen peroxide (H2O2) treatment modulate CDH1 gene expression by epigenetic modification(s). Sublethal dosage of H2O2 treatment decrease E-cadherin, increase DNMT1, HDAC1, Snail, Slug and enrich H3K9me3 and H3K27me3 in the CDH1 promoter. The effect of H2O2 was attenuated by ROS scavengers; NAC, lupeol and beta-sitosterol. DNMT inhibitor, AZA prevented the H2O2 induced promoter-CpG-island methylation of CDH1. Treatment of cells with U0126 (inhibitor of ERK) reduced the expression of DNMT1, Snail and Slug, increased CDHL This implicates that CDH1 is synergistically repressed by histone methylation, DNA methylation and histone deacetylation mediated chromatin remodelling and activation of Snail and Slug through ERK pathway. Increased ROS leads to activation of epigenetic machineries and EMT activators Snail/Slug which in their course of action inactivates CDH1 gene and lack of E-cadherin protein promotes EMT in breast cancer cells. ROS and ERK signaling facilitate epigenetic silencing and support the fact that subtle increase of ROS above basal level act as key cell signaling molecules. Free radical scavengers, lupeol and beta-sitosterol may be tested for therapeutic intervention of breast cancer. This work broadens the amplitude of epigenome and open avenues for investigations on conjoint effects of canonical and intrinsic metabolite signaling and epigenetic modulations in cancer
A gap theorem for positive Einstein metrics on the four-sphere
No full textWe show that there exists a universal positive constant e0 > 0 with the following property: let g be a positive Einstein metric on the four-sphere S4. If the Yamabe constant of the conformal class g] satisfies Y (S4, g]) > 1 v 3 Y (S4, gS]) - e0, where gS denotes the standard round metric on S4, then, up to rescaling, g is isometric to gS. This is an extension ofGursky's gap theorem for positive Einstein metrics on S-4
Quantifying Cancer Epithelial-Mesenchymal Plasticity and its Association with Stemness and Immune Response
No full textCancer cells can acquire a spectrum of stable hybrid epithelial/mesenchymal (E/M) states during epithelial-mesenchymal transition (EMT). Cells in these hybrid E/M phenotypes often combine epithelial and mesenchymal features and tend to migrate collectively commonly as small clusters. Such collectively migrating cancer cells play a pivotal role in seeding metastases and their presence in cancer patients indicates an adverse prognostic factor. Moreover, cancer cells in hybrid E/M phenotypes tend to be more associated with stemness which endows them with tumor-initiation ability and therapy resistance. Most recently, cells undergoing EMT have been shown to promote immune suppression for better survival. A systematic understanding of the emergence of hybrid E/M phenotypes and the connection of EMT with stemness and immune suppression would contribute to more effective therapeutic strategies. In this review, we first discuss recent efforts combining theoretical and experimental approaches to elucidate mechanisms underlying EMT multi-stability (i.e., the existence of multiple stable phenotypes during EMT) and the properties of hybrid E/M phenotypes. Following we discuss non-cell-autonomous regulation of EMT by cell cooperation and extracellular matrix. Afterwards, we discuss various metrics that can be used to quantify EMT spectrum. We further describe possible mechanisms underlying the formation of clusters of circulating tumor cells. Last but not least, we summarize recent systems biology analysis of the role of EMT in the acquisition of stemness and immune suppression
The role of the soft phase in rigidity enhancements in a particulate composite
No full textFilling a non-conducting soft matrix with a hard conducting phase leads to two critical transitions: a percolation threshold with a drastic increase in conductivity and a rigidity threshold marking a substantial increase in the elastic modulus. A metal-particulate polymer composite has interpenetrating phases with substantial rigidity beyond the rigidity threshold. Experimental results show that the Young's modulus of the composite is enhanced significantly when an entrapped incompressible polymer phase exerts high hydrostatic stresses in uniaxial compression at the rigidity threshold. Additional experiments beyond the glass transition temperature of the polymer reveal a substantial reduction in the modulus of the composite at the rigidity threshold, as the polymer compressibility is increased significantly, confirming the role of the soft phase in rigidity enhancements. The present investigation provides a potential new designing criterion for enhancing the Young's modulus of an interpenetrating composite structure, by utilizing an incompressible second phase and negative volumetric strain
Sensitivity of aerosol radiative forcing to various aerosol parameters over the Bay of Bengal
No full textIn the shortwave solar spectrum (0.25-5 mml:mspace width=3.33333ptmml:mspacem), radiation is affected by the change in various aerosol properties and also by water vapour and other gas molecules. The presence of a variety of aerosols over the Bay of Bengal (BoB) during different seasons results in a change in aerosol properties, including the aerosol layer height. The BoB is an integral part of the Indian monsoon, and hence it is essential to understand the radiation budget over the BoB. The sensitivity of the aerosol forcing due to the changes in aerosol properties and other parameters has been studied using the Santa Barbara discrete ordinates radiative transfer model. The aerosol forcing at the top of the atmosphere was found to depend on the aerosol loading (aerosol optical depth), aerosol type (single scattering albedo) and the angular distribution of the scattered radiation (asymmetry parameter). The analysis also shows the presence of a relationship between aerosol layer height and the total amount of water vapour present in the atmosphere. The present study highlights the need for better retrievals of vertical aerosol distribution and water vapour profiles for a better understanding of the role of aerosols in the climate