A first principle study of SO3 decomposition on silver nano-clusters: Implications toward hydrogen production

In this work, based on first principles density functional theory, we have investigated the interaction of SO₃ molecule on three different substrates; (i) clean Al₂O₃ surface (0001) (ii) an isolated Ag₆ cluster and (iii) Ag₆ clusters deposited on the Al₂O₃ surface. All calculations were carried out using the plane wave based pseudopotential method under the framework of density functional theory. For the clean Al₂O₃ surface, the SO₃ molecule was adsorbed in parallel orientation on the surface resulting in an elongation of the S–O bond from 1.44 to 1.52 Å with interaction energy of 1.67 eV. In contrast, the interaction of SO₃ with Ag₆ was found to be weak with 0.4 eV interaction energy and 1.47 Å as the largest S–O bond length. Remarkably, when SO₃ molecule interacted with Ag₆ cluster deposited on the Al₂O₃ support, the binding was found to be higher than both Al₂O₃ and Ag₆ clusters in their isolated state. In particular, upon adsorption of SO₃ on Ag₆/@Al₂O₃, the S–O bond length was found to increases from 1.44 to 1.64 Å and the interaction energy was estimated to be 2.00 eV. As the bond elongation bears the signature of bond weakening, a comparison of the above three results clearly suggests that the dissociation barrier of S–O bond on the Ag₆@Al₂O₃ support will be significantly lower than that on the isolated Ag₆ or Al₂O₃ surface. The nature of chemical interaction of SO₃ on these three systems has been discussed based on the electronic density of states analysis.     

Indication of formation of charge density waves in silver nanoparticles dispersed poly(methyl methacrylate) thin films

Silver nanoparticles of various sizes have been prepared through the chemical synthesis and dispersed into poly(methyl methacrylate) (PMMA) matrix resulting in solution cast nanocomposite thin films. For characterization of the films, UV–vis absorption spectroscopy and FESEM were used. Observed blue shift of the surface plasmon absorption band position of the nanocomposite films is an indication of gradually smaller size of the silver nanoparticles that have been dispersed into the PMMA matrix. Dark current (I_d) vs. time profiles and the fluctuations in current–voltage characteristics for the PMMA films with dispersed silver nanoparticles were found to depend on the position of surface plasmon absorption band. Results of electrical studies have been found to be temperature- and voltage-dependent manifesting nonlinear nature of the I_d which may be an indication of formation of charge density waves in the silver nanoparticles–PMMA nanocomposite films. The increase in the standard deviation in I_d (calculated from the I_d vs. time profiles) for the silver nanoparticles–PMMA nanocomposite films may be due to the increase in the plasmon oscillations. Thermal hysteresis has been observed in the PMMA films and in the silver nanoparticles–PMMA nanocomposite films. Results on the observed electrical properties have been discussed in the light of interaction of silver nanoparticles with PMMA matrix, structural reorientation of PMMA, role of electric field in the manipulation of silver nanoparticles in the polymer matrix etc.     

Analytical Performance Evaluation of a STBC Coded OFDM FSO Communication System over Turbulent Atmospheric Channel

Journal of Communications Technology and Electronics - An analytical approach is presented for an optical IM/DD system with STBC coded OFDM RF subcarrier modulation over a free space optical...     

Structural,electronic and thermodynamic properties of ZrCo and ZrCoH3: A first-principles study

The ZrCo intermetallic is considered to be strategically important for hydrogen isotope storage and its use in the International Thermonuclear Experimental Reactor (ITER) system. Here we report the structural, electronic and thermodynamic properties of ZrCo and ZrCoH₃ using the first-principles approach. The calculations are performed using a plane-wave based pseudo-potential approach under the framework of spin-polarized density-functional theory. The ground state properties like lattice constants, bulk moduli, and enthalpy of formation have been determined by optimizing the atomic and electronic structure of ZrCo and ZrCoH₃ compounds. From the total energy calculations, the enthalpy of formation of ZrCoH₃ from ZrCo is estimated to be −91 kJ/mol H₂ at 0 K. Both lattice parameters and formation energy are found to be in good agreement with their corresponding experimental values. The nature of chemical bonding in ZrCo and ZrCoH₃ has been analyzed from the electronic density of states spectrum of the constituent materials.     

Electrical and optical properties of chemical solution deposited barium hafnate titanate thin films

We have investigated the electrical and optical properties of Ba(Hf_xTi_1 − x)O₃ (x = 0, 0.1, 0.2, 0.3, 0.4) (BHT) thin films deposited on platinized silicon and fused quartz substrates. Analyses of the X-ray diffraction patterns reveal that with the increase in Hf contents there is a systematic increase of the lattice constants of BHT films. Irrespective of the measurement frequencies the dielectric constants was found to be systematically decreased, whereas their frequency dispersion was found to be reduced with increasing Hf contents. The leakage current data measured using a metal-insulator–metal configuration reveal that the Schottky emission is the dominant leakage current mechanism in these films. BHT films, deposited on transparent fused quartz substrates, were also characterized in terms of their optical properties. For this purpose the transmittance of the undoped as well as Hf doped barium titanate thin films was measured as a function of wavelength in the range of 290 nm to 800 nm. The transmission spectra were analysed to estimate the wavelength dependence of the refractive indices/extinction coefficients as well as the variation of optical band gap of these films. With the increase of Hf contents, a systematic increase of the band gap [from 3.65 eV (undoped film) to 4.15 eV (40 at.% Hf doped barium titanate film)] was observed. The reduction of the leakage current with increasing hafnium substitution is discussed on the basis of an increasing Schottky barrier height and due to a simultaneous increase in the band gap of the material.     

Understanding on the effect of morphology towards the hydrogen and carbon monoxide sensing characteristics of tin oxide sensing elements

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.     

Isothermal reactivating Whiplash PCR for locally programmable molecular computation

Whiplash PCR (WPCR; Hagiya et al., in Rubin H, Woods DH (eds) DNA based computers, vol III, pp 55–72. American Mathematical Society, Providence, RI, 1999) is a novel technique for autonomous molecular computation where a state machine is implemented with a single stranded DNA molecule and state transition is driven by polymerase and thermal cycles. The primary difference between WPCR computation and other forms of molecular computing is that the former is based on local, rather than global rules. This allows many (potentially distinct) WPCR machines to run in parallel. However, since each state transition requires a thermal cycle, multi-step WPCR machines are laborious and time-consuming, effectively limiting program execution to only a few steps. To date, no WPCR protocol has been developed which is both autocatalytic (self-executing) and isothermal (with no change in temperature). In this paper, we describe some isothermal and autocatalytic protocols that use a combination of strand displacement and DNA polymerization events. Our designs include (1) a protocol where transition rules cannot be reused in subsequent computing (2) a protocol where rules can be reused using an auxiliary strand displacement event but does not prevent back-hybridization (an event responsible for limiting the program execution to only a few state transitions before the machine stalls), (3) a reusable rule protocol that prevents back-hybridization. Furthermore, we show that the third machine which gets rid of thermal cycles and still prevents back-hybridization, is computationally equivalent to the original WPCR machine. We also compute the state transition likelihood and the corresponding rate in this protocol. Finally we present a DNA sequence design of a 3-state isothermal and reactivating WPCR machine along with an experimental verification plan.     

Assessment of molecular events during in vitro re-epithelialization under honey-alginate matrix ambience

Re-epithelialization is one of the most important stages of cutaneous regeneration and its success requires supportive micro-ambience which may be provided with suitable bio-matrix. Biocompatibility and efficacy of such bio-matrix in re-epithelialization could be explored by multimodal analysis of structural and functional attributes of in vitro wound healing model including evaluation of prime molecular expressions of the epithelial cells during repair. Present study examines the influence of honey-alginate and alginate matrices on re-epithelialization in keratinocyte (HaCaT) population in a 2-D wound model. Cellular viability, proliferation and cell–cell adhesion status were assessed during wound closure using live/dead cell assay and by evaluating expressions of Ki67, p63 and E-cadherin along-with % change in cellular electrical impedance. Efficacy of honey-alginate matrix in comparison to only alginate one was demonstrated by a quicker reduction in wound gap, improved cellular viability, enhanced expressions of Ki67, p63 and its isoforms (TAp63, ΔNp63) as well as E-cadherin. Faster restoration of electrical attribute (% of impedance change) after wounding also indicated better impact of honey-alginate matrix in re-epithelialization.     

A segmentation approach to classification of remote sensing imagery

In this paper we propose a new approach for land cover classification of remote sensing imagery. It is a two-stage technique, where in the first stage the global feature-based technique of histogram thresholding generalized to multidimensional cases developed by Khotanzad and Bouarfa (1990) is used, and in the second stage a local feature-based region growing technique is generalized to grow multiple non-contiguous regions in parallel. The Khotanzad and Bouarfa technique has the advantage of being a non-iterative unsupervised classification technique, but suffers from a failure to detect regions of small spatial extent which may have high local contrast but low weightage in the global feature space. Our proposed technique divides the image into blocks of suitable size so that regions of small spatial extent are detected in the block's histogram, and they are grown across neighboring blocks. The proposed technique is illustrated with actual remote sensing imagery. A number of choices of feature space for the first stage, and different measures of similarity for the second stage were investigated on remote sensing data, both visually as well as quantitatively in terms of classification accuracy. It was found that the xyz colour space (Ohta et al. 1980) for the first stage, and the J-M distance for the second stage similarity measure, gave the best results in terms of classification accuracy. Though the approach is unsupervised and non-iterative in nature, it has given a classification accuracy of better than 91 per cent for a five-class landcover classification.     

Hydrogen storage on Ti decorated SiC nanostructures: A first principles study

In the present study we report the hydrogen adsorption behavior of two SiC nanostructures; a planar sheet and a nanotube (10, 0) of 1 nm diameter decorated by Ti atoms on it. All calculations have been performed using a plane-wave based pseudopotential method. The lowest energy structure of the Ti adsorbed SiC sheet shows that Ti atom distorts the sheet in such a way that one of the Si atoms goes down the plane and the Ti atom bind with nearest three C atoms. The interaction of this Ti decorated sheet with hydrogen suggests that each Ti atom can bind up to four hydrogen molecules (all hydrogens are adsorbed in the molecular form) with an average binding energy of 0.37 eV. For SiC nanotube, the adsorption of Ti favors the hexagonal hollow site. Moreover, on interaction of this Ti decorated tube with hydrogen leads to dissociation of the first hydrogen molecule in the atomic form and thereafter adsorbs hydrogen in the molecular form. The average binding energy of hydrogen molecules on this Ti decorated tube is estimated to be 0.65 eV. Based on these results we infer that the Ti decorated SiC nanostructures moderately bind with hydrogen molecules (within the energy window for hydrogen storage materials) and therefore, can be considered as one of the potential hydrogen storage material.