A Raman study of the interaction of electron-donor and -acceptor molecules with chemically doped graphene

Effect of interaction of tetracyanoethylene (TCNE) and tetrathia fulvalene (TTF) with boron- and nitrogen-doped graphene has been investigated by Raman spectroscopy. The G- and 2D bands of boron- and nitrogen-doped graphenes in the Raman spectra show significantly different changes on interaction with electron-donor and -acceptor molecules. Thus, tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) have different effects on the Raman spectra of boron- and nitrogen-doped graphenes. The changes in the Raman spectra brought about by electron-donor and -acceptor molecules can be understood in general terms on the basis of molecular charge transfer. (c) 2012 Elsevier B.V. All rights reserved.

Multilevel dodecagonal space-vector generation for induction motor drives by cascading three-level and two-level inverters

This study proposes an inverter circuit topology capable of generating multilevel dodecagonal (12-sided polygon) voltage space vectors by the cascaded connection of two-level and three-level inverters. By the proper selection of DC-link voltages and resultant switching states for the inverters, voltage space vectors whose tips lie on three concentric dodecagons, are obtained. A rectifier circuit for the inverter is also proposed, which significantly improves the power factor. The topology offers advantages such as the complete elimination of the fifth and seventh harmonics in phase voltages and an extension of the linear modulation range. In this study, a simple method for the calculation of pulse width modulation timing was presented along with extensive simulation and experimental results in order to validate the proposed concept.

Raman scattering, microstructural and dielectric studies on Ba1-xCaxBi4Ti4O15 ceramics

Polycrystalline powders of Ba1-xCaxBi4Ti4O15 (where x = 0, 0.25, 0.50, 0.75 and 1) were prepared via the conventional solid-state reaction route. X-ray diffraction (XRD) and Raman scattering techniques have been employed to probe into the structural changes on changing x. XRD analyses confirmed the formation of monophasic bismuth layered structure of all the above compositions with an increase in orthorhombic distortion with increase in x. Raman spectra revealed a redshift in A(1g) peak and an increase in the B-2g/B-3g splitting with increasing Ca content. The average grain size was found to increase with increasing x. The temperature of the maximum dielectric constant (T-m) increased linearly with increasing Ca-content whereas the diffuseness of the phase transition was found to decrease with the end member CaBi4Ti4O15 showing a frequency independent sharp phase transition around 1048 K. Ca doping resulted in a decrease in the remnant polarization and an increase in the coercive field. Ba0.75Ca0.25Bi4Ti4O15 ceramics showed an enhanced piezoelectric coefficient d(33) of 15 pC N-1 at room temperature. Low values of dielectric losses and tunability of temperature coefficient of dielectric constant (tau(epsilon)) in the present solid-solution suggest that these compounds can be of potential use in microwave dielectrics at high temperatures. (C) 2012 Elsevier B.V. All rights reserved.

Generation and analysis of drought stressed subtracted expressed sequence tags from safflower (Carthamus tinctorius L.)

Drought is the most crucial environmental factor that limits productivity of many crop plants. Exploring novel genes and gene combinations is of primary importance in plant drought tolerance research. Stress tolerant genotypes/species are known to express novel stress responsive genes with unique functional significance. Hence, identification and characterization of stress responsive genes from these tolerant species might be a reliable option to engineer the drought tolerance. Safflower has been found to be a relatively drought tolerant crop and thus, it has been the choice of study to characterize the genes expressed under drought stress. In the present study, we have evaluated differential drought tolerance of two cultivars of safflower namely, A1 and Nira using selective physiological marker traits and we have identified cultivar A1 as relatively drought tolerant. To identify the drought responsive genes, we have constructed a stress subtracted cDNA library from cultivar A1 following subtractive hybridization. Analysis of similar to 1,300 cDNA clones resulted in the identification of 667 unique drought responsive ESTs. Protein homology search revealed that 521 (78 %) out of 667 ESTs showed significant similarity to known sequences in the database and majority of them previously identified as drought stress-related genes and were found to be involved in a variety of cellular functions ranging from stress perception to cellular protection. Remaining 146 (22 %) ESTs were not homologous to known sequences in the database and therefore, they were considered to be unique and novel drought responsive genes of safflower. Since safflower is a stress-adapted oil-seed crop this observation has great relevance. In addition, to validate the differential expression of the identified genes, expression profiles of selected clones were analyzed using dot blot (reverse northern), and northern blot analysis. We showed that these clones were differentially expressed under different abiotic stress conditions. The implications of the analyzed genes in abiotic stress tolerance are discussed in our study.

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO2) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO2 films were investigated. The refractive index of TiO2 films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO2 film is of anatase phase after annealing at 300 degrees C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications. (C) 2012 Elsevier B.V. All rights reserved.

Thermally reversing window in Ge15Te85-xInx glasses: Nanoindentation and micro-Raman studies

Nanoindentation studies on Ge15Te85-xInx glasses indicate that the hardness and elastic modulus of these glasses increase with indium concentration. While a pronounced plateau is seen in the elastic modulus in the composition range 3 <= x <= 7, the hardness exhibits a change in slope at compositions x = 3 and x = 7. Also, the density exhibits a broad maximum in this composition range. The observed changes in the mechanical properties and density are clearly associated with the thermally reversing window in Ge15Te85-xInx glasses in the composition range 3 <= x <= 7. In addition, a local minimum is seen in density and hardness around x = 9, the chemical threshold of the system. Further, micro-Raman studies reveal that as-quenched Ge15Te85-xInx samples exhibit two prominent peaks, at 123 cm(-1) and 155 cm(-1). In thermally annealed samples, the peaks at 120 cm(-1) and 140 cm(-1), which are due to crystalline Te, emerge as the strongest peaks. The Raman spectra of polished samples are similar to those of annealed samples, with strong peaks at 123 cm(-1) and 141 cm(-1). The spectra of lightly polished samples outside the thermally reversing window resemble those of thermally annealed samples; however, the spectra of glasses with compositions in the thermally reversing window resemble those of as-quenched samples. This observation confirms the earlier idea that compositions in the thermally reversing window are non-aging and are more stable. (C) 2012 Elsevier B.V. All rights reserved.

Cobalt(II), Nickel(II) and Copper(II) complexes of a tetradentate Schiff base as photosensitizers: Quantum yield of O-1(2) generation and its promising role in anti-tumor activity

In the present investigation, a Schiff base N'(1),N'(3)-bis(E)-(5-bromo-2-hydroxyphenyl)methylidene]benzene-1,3-d icarbohydrazide and its metal complexes have been synthesized and characterized. The DNA-binding studies were performed using absorption spectroscopy, emission spectra, viscosity measurements and thermal denatuaration studies. The experimental evidence indicated that, the Co(II), Ni(II) and Cu(II) complexes interact with calf thymus DNA through intercalation with an intrinsic binding constant K-b of 2.6 x 10(4) M-1, 5.7 x 10(4) M-1 and 4.5 x 10(4) M-1, respectively and they exhibited potent photo-damage abilities on pUC19 DNA, through singlet oxygen generation with quantum yields of 0.32, 0.27 and 0.30 respectively. The cytotoxic activity of the complexes resulted that they act as a potent photosensitizers for photochemical reactions. (C) 2012 Elsevier B.V. All rights reserved.

Eulerian two-phase flow simulation and experimental validation of semisolid slurry generation process using cooling slope

Experimental and numerical studies of slurry generation using a cooling slope are presented in the paper. The slope having stainless steel body has been designed and constructed to produce semisolid A356 Al alloy slurry. The pouring temperature of molten metal, slope angle of the cooling slope and slope wall temperature were varied during the experiment. A multiphase numerical model, considering liquid metal and air, has been developed to simulate the liquid metal flow along the cooling channel using an Eulerian two-phase flow approach. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling channel following Schiel's equation. The continuity, momentum and energy equations are solved considering thin wall boundary condition approach. During solidification of the melt, based on the liquid fraction and latent heat of the alloy, temperature of the alloy is modified continuously by introducing a modified temperature recovery method. Numerical simulations has been carried out for semisolid slurry formation by varying the process parameters such as angle of the cooling slope, cooling slope wall temperature and melt superheat temperature, to understand the effect of process variables on cooling slope semisolid slurry generation process such as temperature distribution, velocity distribution and solid fraction of the solidifying melt. Experimental validation performed for some chosen cases reveals good agreement with the numerical simulations.

Multilevel Dodecagonal Voltage Space Vector Generation using Flying Capacitor topology for Induction motor drives

In this paper, a multilevel flying capacitor inverter topology suitable for generating multilevel dodecagonal space vectors for an induction motor drive, is proposed. Because of the dodecagonal space vectors, it has increased modulation range with the absence of all 6n +/- 1, (n=odd) harmonics in the phase voltage and currents. The topology, realized by flying capacitor three level inverters feeding an open-end winding induction motor, does not suffer the neutral point voltage imbalance issues seen in NPC inverters and the capacitors have inherent charge-balancing capability with PWM control using switching state redundancies. Furthermore, the proposed technique uses lesser number of power supplies compared to cascaded H-bridge or NPC based dodecagonal schemes and has better ride-through capability. Finally, the voltage control is obtained through a simple carrier-based space vector PWM scheme implemented on a DSP.

Effect of chlorine substitution on triplet state structure of thioxanthone: A time-resolved resonance Raman study

Substitution plays an important role in determining the triplet state reactivity. In this paper, we have studied the effect of chlorine substitution on the triplet state structure and the reactivity of thioxanthone (TX). We have employed time-resolved resonance Raman technique to understand the structure of the lowest triplet excited state of 2-chlorothioxanthone (CTX). The experimental findings have been corroborated with the computational results using density functional theory. Akin to the parent compound (TX), coexistence of two lowest triplet states has been observed in case of CTX, which has been substantiated using resonant probe wavelength dependence study. The relative contribution of 3n-pi* to 3 pi-pi* to the equilibrated triplet state has been found to be more for CTX compared to TX suggesting increase in the triplet state reactivity after the substitution. The above observation has been further supported by the flash photolysis experiments. Copyright (C) 2013 John Wiley & Sons, Ltd.

Force Biased Molecular Dynamics Simulation Study of Effect of Dendrimer Generation on Interaction with DNA

We have studied the effect of dendrimer generation on the interaction between dsDNA and the PAMAM dendrimer using force biased simulation of dsDNA with three generations of dendrimer: G3, G4, and G5. Our results for the potential of mean force (PMF) and the dendrimer asphericity along the binding pathway, combined with visualization of the simulations, demonstrate that dendrimer generation has a pronounced impact on the interaction. The PMF increases linearly with increasing generation of the dendrimer. While, in agreement with previous results, we see an increase in the extent to which the dendrimer bends the dsDNA with increasing dendrimer generation, we also see that the deformation of the dendrimer is greater with smaller generation of the dendrimer. The larger dendrimer forces the dsDNA to conform to its structure, while the smaller dendrimer is forced to conform to the structure of the dsDNA. Monitoring the number of bound cations at different values of force bias distance shows the expected effect of ions being expelled when the dendrimer binds dsDNA.

Layer-dependent resonant Raman scattering of a few layer MoS2

We report resonant Raman scattering of MoS2 layers comprising of single, bi, four and seven layers, showing a strong dependence on the layer thickness. Indirect band gap MoS2 in bulk becomes a direct band gap semiconductor in the monolayer form. New Raman modes are seen in the spectra of single- and few-layer MoS2 samples which are absent in the bulk. The Raman mode at similar to 230 cm(-1) appears for two, four and seven layers. This mode has been attributed to the longitudinal acoustic phonon branch at the M point (LA(M)) of the Brillouin zone. The mode at similar to 179 cm(-1) shows asymmetric character for a few-layer sample. The asymmetry is explained by the dispersion of the LA(M) branch along the G-M direction. The most intense spectral region near 455 cm(-1) shows a layer-dependent variation of peak positions and relative intensities. The high energy region between 510 and 645 cm(-1) is marked by the appearance of prominent new Raman bands, varying in intensity with layer numbers. Resonant Raman spectroscopy thus serves as a promising non invasive technique to accurately estimate the thickness of MoS2 layers down to a few atoms thick. Copyright (C) 2012 John Wiley & Sons, Ltd.

Development of a New Generation of Vectors for Gene Expression, Gene Replacement, and Protein-Protein Interaction Studies in Mycobacteria

Escherichia coli-mycobacterium shuttle vectors are important tools for gene expression and gene replacement in mycobacteria. However, most of the currently available vectors are limited in their use because of the lack of extended multiple cloning sites (MCSs) and convenience of appending an epitope tag(s) to the cloned open reading frames (ORFs). Here we report a new series of vectors that allow for the constitutive and regulatable expression of proteins, appended with peptide tag sequences at their N and C termini, respectively. The applicability of these vectors is demonstrated by the constitutive and induced expression of the Mycobacterium tuberculosis pknK gene, coding for protein kinase K, a serine-threonine protein kinase. Furthermore, a suicide plasmid with expanded MCS for creating gene replacements, a plasmid for chromosomal integrations at the commonly used L5 attB site, and a hypoxia-responsive vector, for expression of a gene(s) under hypoxic conditions that mimic latency, have also been created. Additionally, we have created a vector for the coexpression of two proteins controlled by two independent promoters, with each protein being in fusion with a different tag. The shuttle vectors developed in the present study are excellent tools for the analysis of gene function in mycobacteria and are a valuable addition to the existing repertoire of vectors for mycobacterial research.

Generation of a short-duration ultrawideband chirped-pulse using CRLH transmission lines

In this paper we present the various design issues related to CRLH-Transmission lines for the generation of short duration Ultra-Wideband chirped-pulse. The major parameters of the CRLH Transmission lines affecting the BandWidth are discussed and methods to increase BandWidth are also suggested. Also presented is the role of components of CRLH Transmission lines in determining the chirp duration. The techniques of controlling the chirp duration by regulating these components are also discussed. Simulations results are also included.

Sharp raman anomalies and broken adiabaticity at a pressure induced transition from band to topological insulator in Sb2Se3

The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E-g(2) phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb2Se3 crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator. DOI: 10.1103/PhysRevLett.110.107401