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Si/ZnO heterostructures for efficient diode and water-splitting applications
No full textWe have developed thin zinc oxide (ZnO) layers protected highly conductive p-type silicon (Si) electrodes and investigated their diode and photoanode characteristics. ZnO layers have been deposited on the glass as well as p-Si substrates at a temperature of 400 degrees C by pulsed spray pyrolysis method. The crystal structure, surface morphology, and phase purity of the layers along with electrical characteristics of the heterostructures were investigated. Finally, the photocatalytic water oxidation performance of the ZnO/Si structures was studied in an alkaline electrolyte solution (pH = 10). The as-grown devices exhibited excellent diode characteristics with a turn-on voltage of 4.5 V, and applied bias-voltage dependent carrier transport mechanisms. As compared to bare Si, ZnO coated Si-based PEC devices showed good stability and durability along with very low onset potential of 0.07 V versus Ag/AgCl. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Impact of bacterial streamers on biofouling of microfluidic filtration systems
No full textWe investigate the effect of biofouling in a microfluidic filtration system. The microfluidic platform consists of cylindrical microposts with a pore-spacing of 2 mu m, which act as the filtration section of the device. One of our key findings is that there exists a critical pressure difference above which pronounced streamer formation is observed, which eventually leads to rapid clogging of the device with an accompanying exponential decrease in permeate flow. Moreover, when streamers do form, de-clogging of pores also occurs intermittently, which leads to small time scale fluctuations O(10(1) s)] superimposed upon the large time scale O(10(2) min)] clogging of the system. These de-clogging phenomena lead to a sharp increase in water permeation through the microfluidic filtration device but rates the water quality as biomass debris is transported in the permeate. Streamer-based clogging shares similarities with various fouling mechanisms typically associated with membranes. Finally, we also show that the pH of the feed strongly affects biofouling of the microfluidic filtration system. Published by AIP Publishing
Room temperature synthesis of amorphous Bi4V2O11 as cathode material for Li secondary batteries
No full textIn this paper, the amorphous Bi4V2O11 is synthesized by a simple precipitation method at room temperature. The as-prepared Bi4V2O11 was characterized by using powder XRD, FTIR, SEM/EDX techniques. The amorphous Bi4V2O11 has been tested as a cathode material for lithium secondary battery for the first time. The observed results were compared with the reported crystalline Bi4V2O11 wherein amorphous Bi4V2O11 exhibits better specific capacity and capacity retention at the charging rate of C/5. The specific capacity of 104 mA h g(-1) for the first cycle and 101 mA h g(-1) for the second cycle was observed and thereby the capacity retention of about 98% indicates the good reversibility
Modified Einstein's gravity to probe the sub- and super-Chandrasekhar limiting mass white dwarfs: a new perspective to unify under- and over-luminous type la supernovae
No full textType Ia supernovae (SNeIa), used as one of the standard candles in astrophysics, are believed to form when the mass of the white dwarf approaches Chandrasekhar mass limit. However, observations in last few decades detected some peculiar SNeIa, which are predicted to be originating from white dwarfs of mass much less than the Chandrasekhar mass limit or much higher than it. Although the unification of these two sub-classes of SNeIa was attempted earlier by our group, in this work, we, for the first time, explain this phenomenon in terms of just one property of the white dwarf which is its central density. Thereby we do not vary the fundamental parameters of the underlying gravity model in the contrary to the earlier attempt. We effectively consider higher order corrections to the Starobinsky- f (R) gravity model to reveal the unification. We show that the limiting mass of a white dwarf is similar to M-circle dot for central density rho(c)similar to 1.4 x 10(8) g/cc, while it is similar to 2.8M(circle dot) for rho(c) similar to 1.6 x 10(10) g/cc under the same model parameters. We further confirm that these models are viable with respect to the solar system test. This perhaps enlightens very strongly the long standing puzzle lying with the predicted variation of progenitor mass in SNeIa
Anomalous water dynamics at surfaces and interfaces: synergistic effects of confinement and surface interactions
No full textIn nature, water is often found in contact with surfaces that are extended on the scale of molecule size but small on a macroscopic scale. Examples include lipid bilayers and reverse micelles as well as biomolecules like proteins, DNA and zeolites, to name a few. While the presence of surfaces and interfaces interrupts the continuous hydrogen bond network of liquid water, confinement on a mesoscopic scale introduces new features. Even when extended on a molecular scale, natural and biological surfaces often have features (like charge, hydrophobicity) that vary on the scale of the molecular diameter of water. As a result, many new and exotic features, which are not seen in the bulk, appear in the dynamics of water close to the surface. These different behaviors bear the signature of both water-surface interactions and of confinement. In other words, the altered properties are the result of the synergistic effects of surface-water interactions and confinement. Ultrafast spectroscopy, theoretical modeling and computer simulations together form powerful synergistic approaches towards an understanding of the properties of confined water in such systems as nanocavities, reverse micelles (RMs), water inside and outside biomolecules like proteins and DNA, and also between two hydrophobic walls. We shall review the experimental results and place them in the context of theory and simulations. For water confined within RMs, we discuss the possible interference effects propagating from opposite surfaces. Similar interference is found to give rise to an effective attractive force between two hydrophobic surfaces immersed and kept fixed at a separation of d, with the force showing an exponential dependence on this distance. For protein and DNA hydration, we shall examine a multitude of timescales that arise from frustration effects due to the inherent heterogeneity of these surfaces. We pay particular attention to the role of orientational correlations and modification of the same due to interaction with the surfaces
Highly efficient removal of toxic organic dyes, chemical solvents and oils by mesoporous exfoliated graphite: Synthesis and mechanism
No full textExfoliated graphite (EG) has been receiving much global attention in the last decade because of the growing number of potential applications. However, the production of EG has several disadvantages such as, requiring more than one chemical compound, consuming more chemical quantity, time and energy, etc. Here, we report a simple low cost one compound based rapid and efficient production of EG using microwave irradiation technique. As prepared EG material shows multifunctional outstanding performance including adsorption of various toxic organic dyes and absorption of various organic solvents, as well as, oils. The maximum adsorption capacity reaches 384.6 (+/- 10.2), 222.32 (+/- 8.6), 151.51 (+/- 9.2) and 196.08 (+/- 5.4) mg/g for malachite green (MG), methylene blue (MB), rhodamine 6 g (Rh6 g) and congo red (CR) dyes at equilibrium. It shows an efficient flow through filtration of dye contaminated water, showing potential as the best technique for industrial waste water treatment. It absorbs 40-120 g of various chemical solvents and oils per one gram of EG. To the best of our knowledge, this is the first report on single compound based rapid and efficient synthesis of EG in about one minute with multifunctional outstanding application performance
Unique Features of Metformin: A Combined Experimental, Theoretical, and Simulation Study of Its Structure, Dynamics, and Interaction Energetics with DNA Grooves
No full textThere are certain small molecules that exhibit extraordinarily diverse biological activities. Metformin is one of them. It is widely used as an antidiabetic drug for type-two diabetes. Recent lines of evidence of its role in antitumor activities and increasing the survival rates of cancer patients (namely, colorectal, breast, pancreas, and prostate cancer) are emerging. However, theoretical studies of the structure and dynamics of metformin have not yet been fully explored. In this work, we investigate the characteristic structural and dynamical features of three monoprotonated forms of metformin hydrochloride with the help of experiments, quantum chemical calculations, and atomistic molecular dynamics simulations. We validate our force field by comparing simulation results to those of the experimental findings. Energetics of proton transfer between two planar monoprotonated forms reveals a low energy barrier, which leads us to speculate a possible coexistence of them. Nevertheless, among the protonation states, we find that the nonplanar tautomeric form is the most stable. Our calculated values of the self diffusion coefficient agree quantitatively with NMR results. Metformin forms strong hydrogen bonds with surrounding water molecules, and its solvation dynamics shows unique features. Because of an extended positive charge distribution, metformin possesses features of being a permanent cationic partner toward several targets. We study its interaction and binding ability with DNA using UV spectroscopy, circular dichroism, fluorimetry, and metadynamics simulation. We find a nonintercalative mode of interaction. Metformin feasibly forms a minor/major groove-bound state within a few tens of nanoseconds, preferably with AT rich domains. A significant decrease in the free energy of binding is observed when it binds to a minor groove of DNA
Biophysical and biochemical characterization of Rv3405c, a tetracycline repressor protein from Mycobacterium tuberculosis
No full textMycobacterium tuberculosis, the causative agent of tuberculosis disease, is one among the deadliest pathogens in the world. Due to long treatment regimen, HIV co-infection, persistence of bacilli in latent form and development of XDR and TDR strains of Mtb, tuberculosis has posed serious concerns for managing the disease, and calls for discovery of new drugs and drug targets. Using a computational pipeline involving analysis of the structural models of the Mtb proteome and an analysis of the ATPome, followed by a series of filters to identify druggable proteins, solubility and length of the protein, several candidate proteins were shortlisted. From this, Rv3405c, a tetR family of DNA binding protein involved in antibiotic resistance, was identified as one of the good drug targets. Rv3405c binds to the upstream non coding region of Rv3406 and causes repression of Rv3406 activity there by affecting the downstream processes involved in antibiotic resistance was further characterized. The Rv3405c gene was cloned; the gene product was over-expressed in E. coli and purified by Ni NTA chromatography. DNA binding studies by EMSA showed that the recombinant Rv3405c protein binds to the DNA sequence corresponding to the promoter region of Rv3406 and upon addition of tetracycline, the DNA binding activity was lost. P-galactosidase reporter assay in E. coli using both wild type and a DNA binding defective mutant protein indeed proved that Rv3405c acts as a repressor. (C) 2018 Elsevier Inc. All rights reserved
Alternate approach for calculating hardness based on residual indentation depth: Comparison with experiments
No full textIt is well known that plastic deformation is a highly nonlinear dissipative irreversible phenomenon of considerable complexity. As a consequence, little progress has been made in modeling some well-known size-dependent properties of plastic deformation, for instance, calculating hardness as a function of indentation depth independently. Here, we devise a method of calculating hardness by calculating the residual indentation depth and then calculate the hardness as the ratio of the load to the residual imprint area. Recognizing the fact that dislocations are the basic defects controlling the plastic component of the indentation depth, we set up a system of coupled nonlinear time evolution equations for the mobile, forest, and geometrically necessary dislocation densities. Within our approach, we consider the geometrically necessary dislocations to be immobile since they contribute to additional hardness. The model includes dislocation multiplication, storage, and recovery mechanisms. The growth of the geometrically necessary dislocation density is controlled by the number of loops that can be activated under the contact area and the mean strain gradient. The equations are then coupled to the load rate equation. Our approach has the ability to adopt experimental parameters such as the indentation rates, the geometrical parameters defining the Berkovich indenter, including the nominal tip radius. The residual indentation depth is obtained by integrating the Orowan expression for the plastic strain rate, which is then used to calculate the hardness. Consistent with the experimental observations, the increasing hardness with decreasing indentation depth in our model arises from limited dislocation sources at small indentation depths and therefore avoids divergence in the limit of small depths reported in the Nix-Gao model. We demonstrate that for a range of parameter values that physically represent different materials, the model predicts the three characteristic features of hardness, namely, increase in the hardness with decreasing indentation depth, and the linear relation between the square of the hardness and the inverse of the indentation depth, for all but 150 nm, deviating for smaller depths. In addition, we also show that it is straightforward to obtain optimized parameter values that give good fit to the hardness data for polycrystalline cold worked copper and single crystals of silver
Reductive Ring Opening of a Cyclo-Tri(phosphonio)methanide Dication to a Phosphanylcarbodiphosphorane: In Situ UV-Vis Spectroelectrochemistry and Gold Coordination
No full textThe formal two-electron reduction of the cyclotri(phosphonio)methanide dication I2+ results in a ring-opening reaction via C-P bond cleavage to yield the unique phosphanyl-functionalized carbodiphosphorane 2. In situ spectroelectrochemical investigations of the reduction of dication I2+ and the oxidation of 2 give insights into the mechanism of this unusual and reversible bond cleavage reaction. Compound 2 features in total three lone pairs of electrons, facilitating the preparation of mono-, di-, and trigold complexes