50175 research outputs found
Sort by
Effect of Bi addition on the optical properties of Ge30Se70-xBix thin films
No full textOptical and structural properties of vacuum evaporated Ge30Se70-xBix (x = 0, 5, 10, 15 and 20) thin films are discussed in the present report. The physical properties such as coordination number (<r>), average heat of atomisation (H-s), average bond energy (H-s/<r>), energy gap (E-g), and lone pair electrons (L) for different Bi concentration were calculated theoretically. The structural property in the film is not disturbed as probed by X-ray diffraction method. The SEM and EDAX were done for the composition and microstructural characterization. The optical transmission is measured by the Fourier Transform Infrared spectroscopy in the spectral range of 500-1200 nm. The mechanism of the optical absorption follows the rule of allowed non-direct transition. It was found that, the optical band gap E-g decreases while the width of localized states (Urbach energy) E-c increases by increasing Bi content. The relationship between Eg and chemical composition of the Ge30Se70-xBix system were discussed in terms of cohesive energy (CE), the average heat of atomisation Hs, and the average coordination number N-r. The variation in the optical behavior for different thin films is explained on the basis of defect states and the decrease in average bond energy of the system. The Raman spectroscopy was done to correlate the optical property change with Bi addition. (C) 2017 Elsevier B.V. All rights reserved
Distribution of soil organic carbon and glomalin related soil protein in reclaimed coal mine-land chronosequence under tropical condition
No full textThe revegetation onmine spoiled lands has potential to improve the status of reclaimed mine-soil quality. However, to date the temporal dynamics of labile and stable fractions of soil organic carbon (SOC) and glomalin related soil protein (GRSP) have not been satisfactorily demonstrated. We investigated SOC and GRSP fractions including labile particulate OC (POC) and easily extractable GRSP (EE-GRSP) and stable non-particulate OC (NPOC) and difficulty extractable GRSP (DE-GRSP) along with other important soil properties in six reclaimed mine lands chronosequence (1 to 26 years old) and a reference forest site in Raniganj Coalfield, India. Our results demonstrated that the accumulation of SOC and GRSP significantly increased with increasing age of the sites, with greater extent of increment after 26 years were seen in labile POC (6.6x) and EE-GRSP (11.5x) compared to stable NPOC (1.8x) and DE-GRSP (6.2x). The higher contribution of GRSP-C in NPOC compared to TOC across the sites, indicate the proximate role of GRSP in accumulation and stabilization of SOC during the pedogenesis. The multivariate analysis revealed strong association among arbuscular mycorrhizal fungi (AMF) spore density, microbial biomass carbon, SOCs and GRSPs, suggesting the factors involved in SOC accumulation likely contributed to AMF proliferation and GRSP enrichment during the reclamation process. Moreover, strong correlation of GRSP and SOC with soil's bulk density, pH, total N and C/N ratio, suggest increasing GRSP and SOC content resulted inmulti-level improvement in soil properties. Our results highlight the importance of using GRSP and SOC as indicator during mine land reclamation. (c) 2018 Elsevier B.V. All rights reserved
Microstructure and Mechanical Properties of Friction Stir Process Derived Al-TiO2 Nanocomposite
No full textAluminum-based composites have many advantages over their conventional counterparts. A major problem in such composites is the clustering of particles in the matrix. Friction stir processing (FSP) can homogenize particle distribution in aluminum-based composites. In this study, unannealed TiO2 particles were used to prepare Al-TiO2 nanocomposite using FSP. The TiO2 particles, about 1 A mu m, were dispersed into an aluminum matrix by 6 passes of FSP. The TiO2 particles were fractured by multiple FSP passes, leading to a nano-size particle distribution in the matrix. Nanoscale dispersion was confirmed by scanning electron microscopy and transmission electron microscopy. The fractured TiO2 particles reacted with the aluminum matrix to form Al3Ti intermetallic and Al2O3 ceramic. The progression of the Al-TiO2 reaction from the fourth to the sixth pass of FSP was revealed by x-ray diffraction. Due to the nanoscale dispersion, the yield and ultimate tensile strength of the composite increased to 97 and 145 MPa, respectively. Ductility of the composite decreased marginally compared to the as-received aluminum. As the dispersed particles pin dislocations, the strain-hardening rate of the composite was considerably increased and the same was seen in the Kocks-Mecking plot. The TiO2 particles are mechanically activated due to their fracture during FSP, hence leading to reaction with the matrix. The particle refinement and dispersion lead to a homogeneous matrix with higher strength
Thermodynamic properties of SrAl12O19 and SrAl4O7
No full textStrontium aluminates are important compounds with interesting properties such as long-duration phosphorescence and elastico-deformation luminescence. They have potential application in flexible light emitting panels. Since there are serious discrepancies in available thermodynamic data for these compounds, a redetermination of their Gibbs energies of formation was undertaken using solid-state electrochemical cells incorporating single-crystal SrF2 as the electrolyte in the temperature range from 1000 to 1300 K. However, the measurements were restricted to SrAl12O19 and SrAl4O7 because of the formation of strontium oxyfluoride phase between SrAl2O4 and SrF2. For the reactions, SrO + 6 Al2O3 -> SrAl12O19, Delta G (o)/J mol(-1) (+/- 280) = -83386 - 25.744 (T/K), and SrO + 2Al(2)O(3) -> SrAl4O7, Delta G (o)/J mol(-1) (+/- 240) = -80187 - 25.376 (T/K). The high entropy of SrAl4O7 and SrAl12O19 can be partly related to their complex structures. The results of this study are consistent with calorimetric data on enthalpy of formation of other Sr-rich aluminates and indicate only marginal stability for SrAl4O7 relative to its neighbours, SrAl12O19 and SrAl2O4. The thermodynamic data explain the difficulty in direct synthesis of phase pure SrAl4O7 and the formation of SrAl2O4 as the initial ternary phase when reacting SrO and Al2O3 or crystallizing from amorphous state, irrespective of composition
A FETI-DP based parallel hybrid stochastic finite element method for large stochastic systems
No full textThe computational cost of uncertainty propagation in a mechanics problem can become prohibitively large as the degrees of freedom (DOF) and the number of basic random variables - also referred to as stochastic dimensionality - increase. While a number of methods have been reported in the literature to address either large DOF or high stochastic dimensionality, there is no work addressing both. This work is aimed at filling this gap. Naturally, parallel computing becomes the only feasible option for these large problems. Accordingly, a parallel domain decomposition-based hybrid method combining stochastic Galerkin and Monte Carlo simulation is developed here. To achieve scalability, which is necessary for solving very large scale problems, first the dual-primal variant of the finite element tearing and interconnecting (FETI-DP) is chosen as the domain decomposition method. Then, three distinct approaches of parallel implementation are followed. Through a set of detailed numerical experiments, scalability and relative costs of computation and communication in these three approaches are studied. Finally, based on the observations in these experiments, the best approach is selected and used to solve a large three dimensional elasticity problem with high dimensional parametric uncertainty. (C) 2017 Elsevier Ltd. All rights reserved
Metal Templates and Boron Sources Controlling Borophene Structures: An Ab lnitio Study
No full textInterlayer binding of 2D borophene phases are determined as a function of hole density (HD) and metal surfaces Cu, Ag, and Au. The Cu surface prefers formation of monolayers whereas the Au surface shows multilayer stacking. Ag surface enables formation of monolayers with higher HD and bilayers for borophenes with lower HD. The growth pattern of bilayers on metal templates are investigated using ab-initio molecular dynamic simulations. Formation of icosahedral B-12 clusters and extension to sheets are also studied on Cu surface. Icosahedral sheet formation by boron atom deposition is found to be a thermodynamically unfavorable process on this surface. Thus, structure of borophene phases could also be tuned by modulating the parameters such as boron source or the metal templates, in addition to the substrate temperature and boron atom deposition rate
A novel concept of pseudo ternary diffusion couple for the estimation of diffusion coefficients in multicomponent systems
No full textA pseudo ternary diffusion couple technique in a multicomponent system by simplifying the mathematical complications of Onsager formalism is proposed for the estimation of composition dependent values of the interdiffusion coefficients. This is otherwise impossible following the conventional method in a system with more than three components. Other alternative methods estimate the average diffusion coefficients over a composition range of random choice and lack physical significance. This method can be followed in a multicomponent system with any number of components on the condition that only three components develop diffusion profiles keeping others as constant. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Origin of silica in rice plants and contribution of diatom Earth fertilization: insights from isotopic Si mass balance in a paddy field
No full textThe benefits of Si for crops is well evidenced but the biogeochemical cycle of Si in agriculture remains poorly documented. This study aims at identifying and quantifying the Si sources (primary and secondary soil minerals, amorphous silica, irrigation, Si-fertilizer) to rice plants. Field experiments were carried out with and without application of diatomaceous earth (DE) under rice and bare conditions to determine the water and dissolved mass balance in paddy fields (Karnataka, Southern India). The fate of the Si brought by irrigation (DSi) (uptake by rice, uptake by diatoms, adsorption) was assessed through a solute mass balance combined with silicon isotopic signatures. Above the ground-surface, about one third of the DSi flux brought by borewell irrigation (545 mmol Si.m(-2)) to bare plots and half of DSi in rice plots were removed from solution within minutes or hours following irrigation. Such rate is consistent with the rate of DSi adsorption onto Fe-oxyhydroxides but not with diatom blooms. In rice and rice + DE experiments, the isotopic fractionation factor ((30)epsilon) between bore well and stagnant water compositions is close to -1 aEuro degrees, i.e. the isotopic fractionation factor known for rice, indicating that above-ground DSi removal would be dominated by plant uptake upon adsorption. Within the soil layer, pore water DSi decreases much faster in rice experiments than in bare ones, demonstrating the efficiency of DSi rice uptake upon adsorption. Total irrigation-DSi to plant-Si would then represent 24 to 36% in rice experiments (over 1460 +/- 270 mmol Si m(-2) in biomass) and 15 to 23% in rice + DE ones (over 2250 +/- 180 mmol Si m(-2)). The delta Si-30 signature of whole plants was significantly different in the rice + DE plot analyzed, 0.99 +/- 0.07 aEuro degrees, than in the rice one, 1.29 +/- 0.07 aEuro degrees. According to these delta Si-30 signatures, the main Si source from the soil would be the amorphous silica pool (ASi). A slight contribution of DE to the rice plant could be detected from the Si isotopic signature of rice. The delta Si-30 signatures of the various soil-plant compartments, when associated to Si mass balance at soil-plant scale, constitute a reliable proxy of the Si sources in paddy fields. The solute Si balance is controlled by rice uptake in rice plots and by adsorption in bare ones. The main Si sources for the rice plants were soil ASi, irrigation Si and to a lesser extent Si fertilizer when it was applied
Photo- and thermally induced property change in Ag diffusion into Ag/As2Se3 thin films
No full textIn the present report, we have prepared As2Se3 and bilayer Ag/As2Se3 chalcogenide thin films prepared by thermal evaporation process. The top Ag layer is being diffused into the bottom As2Se3 layer by 532 nm laser irradiation and thermal annealing process. The photo and thermal energy drives the Ag+ ions into the As2Se3 matrix that enhances the formation of As-Se-Ag solid solution which shows the changes of optical properties such as transmission, absorption power, refractive index, and optical band gap. The transmission power drastically decreased for the thermal-induced film than the laser induced one; and the reverse effect is seen for the absorption coefficient. The non-linear refractive index is found to be increased due to the Ag diffusion into -As2Se3 film. The indirect allowed optical band gap is being reduced by a significant amount of 0.17 eV (thermal diffusion) and 0.03 eV (photo diffusion) from the Ag/As2Se3 film. The Ag diffusion creates chemical disorderness in the film observed from the two parameters which measures the degree of disorder such as Urbach energy and Tauc parameter. The structural change is not noticed in the studied film as seen from the X-ray diffraction pattern. Scanning electron microscopy and atomic force microscopy investigations showed that the surface morphology was influenced by the diffusion phenomena. The change in optical constants in such type of film can be used in optical waveguides and optical devices