Thermo and mechanoluminescence studies of BZT phosphor

Mechanoluminescence (ML) and thermoluminescence (TL) in barium zirconium titanate (BZT) is reported for the first time. The BZT powder sample, belonging to perovskite category is synthesized using solid state reaction technique. The sample is prepared at a temperature of 1200 °C. The obtained specimen is thoroughly characterized paying particular attention to their structure, composition, morphology and optical properties. The surface morphology and structural properties are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns confirm the formation of crystalline perovskite type cubic structure. Also, highly agglomerated, porous and regular shaped particles are seen by SEM. The optical properties of as prepared sample is presented and discussed in terms of ML and TL. The ML intensity is found to be maximum for the sample irradiated for 10 min. More than one maxima in TL glow curve reveals that the traps are distributed in separate groups at different depths and corresponding values are calculated using initial rise method.     

Total synthesis and mechanism of action of the antibiotic armeniaspirol A

Emerging antimicrobial resistance urges the discovery of antibiotics with unexplored, resistance-breaking mechanisms. Armeniaspirols represent a novel class of antibiotics with a unique spiro[4.4]non-8-ene scaffold and potent activities against Gram-positive pathogens. We report a concise total synthesis of (±) armeniaspirol A in six steps with a yield of 20.3% that includes the formation of the spirocycle through a copper-catalyzed radical cross-coupling reaction. In mechanistic biological experiments, armeniaspirol A exerted potent membrane depolarization, accounting for the pH-dependent antibiotic activity. Armeniaspirol A also disrupted the membrane potential and decreased oxygen consumption in mitochondria. In planar lipid bilayers and in unilamellar vesicles, armeniaspirol A transported protons across membranes in a protein-independent manner, demonstrating that armeniaspirol A acted as a protonophore. We provide evidence that this mechanism might account for the antibiotic activity of multiple chloropyrrole-containing natural products isolated from various origins that share a 4-acylphenol moiety coupled to chloropyrrole as a joint pharmacophore. We additionally describe an efflux-mediated mechanism of resistance against armeniaspirols.

The antibiotic armeniaspirol A depolarized bacterial and mammalian cell membranes through a protonophore activity, that accounts for its potent antibiotic effects. A total synthesis of (±) armeniaspirol A was achieved in six steps.     

Effect of H-atom concentration on soot formation in premixed ethylene/air flames

Soot formation is a major challenge in the development of clean and efficient combustion systems based on hydrocarbon fuels. Fundamental understanding of the reaction mechanism leading to soot formation can be obtained by investigating the role of key reactive species such as atomic hydrogen taking part in soot formation pathways. In this study, two-dimensional laser induced incandescence (LII) measurements using λ?=?1064?nm laser have been used to measure soot volume fraction (f_V) in a series of rich ethylene (C₂H₄)/air flames, stabilized over a McKenna burner fitted with a flame stabilizing metal disc. Moreover, a comparison of UV (λ?=?283?nm), visible (λ?=?532?nm) and IR (λ?=?1064?nm) laser excited LII measurements of soot is discussed. Recently developed, femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique has been applied for obtaining spatially resolved H-atom concentration ([H]) profiles under the same flame conditions. The structure of the flames has also been determined using hydroxyl radical (OH) planar laser induced fluorescence (PLIF) imaging. The results indicate an inverse dependence of f_V on [H] for a range of C₂H₄/air rich flames up to an equivalence ratio, Φ?=?3.0. Although an absolute relationship between [H] and f_V cannot be easily derived owing to the multiple steps involving H and other intermediate species in soot formation pathways, the present study demonstrates the feasibility to couple [H] and f_V obtained using advanced optical techniques for soot formation studies.     

Characterization of Mn doped ZnS nanocrystalline powder dispersed in polyvinyl alcohol: 1st Nano Update

Manganese doped zinc sulfide nanocrystalline powder was synthesized with sodium citrate and its films were formed by mixing it with polyvinyl alcohol to study optical absorption of Mn doped ZnS dispersed in polyvinyl alcohol. The characteristics of the prepared powder and film samples were studied by X-ray diffraction, transmission electron microscopy and UV–visible absorption spectroscopy. Samples exhibited optical absorption at lower wavelength region and particle sizes were calculated from X-ray diffractogram.     

Factors affecting the electro-optical and structural characteristics of nano crystalline Cu doped (Cd–Zn)S films

This work investigates the effects of the temperature, deposition time and annealing ambient on the electro-optical and structural properties of nano crystalline (Cd–Zn)S films prepared by chemical bath deposition (CBD). The deposited films being uniform and adherent to the glass substrates are amorphous in nature and the crystallinity as well as the grain size is found to increase on post-deposition annealing. The obtained specimens are thoroughly characterized before and after annealing paying particular attention to their structure, composition and morphology. Annealing in air reduces the extent of disorder in grain boundaries and energy band-gap. A correlation between the structural and optical properties is investigated in detail. The surface morphology and structural properties of the as-deposited and annealed (Cd–Zn)S thin films are studied using X-ray diffraction (XRD), scanning electron microscope (SEM) and optical transmission spectra. The optical transmission spectra are recorded within the range of 300–800 nm and 300–900 nm. The electroluminescent (EL) intensity is found to be maximum at a particular temperature, which decreases with further increase in temperature and peaks of photoluminescent (PL) and EL spectra are centered at 546 nm and 592 nm. The emission intensity also increases with increasing thickness of the film.     

Integrated mechanism for the morphological structure development in HDPE melt‐blown and machine‐direction‐oriented films

The morphologies of a series of blown films and machine‐direction‐oriented (MDO) films, all produced from high density polyethylene, were characterized. In the blown film process, the crystalline morphology develops while the melt is under extensional stress. In the MDO process, drawing takes place in the solid state and deforms the crystalline morphology of the starting film. The films were characterized by wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS) and atomic force microscopy to determine the lamellar morphology. The effect of the type of deformation on the lamellar morphology was studied and relationships were developed between the lamellar and polymer chain morphology using SAXS and WAXS. Blown and MDO films were found to have very different morphologies. However, an integrated mechanism was developed linking the sequential events in the deformation and morphology development in blown and MDO films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1834–1844, 2007     

Binding and templation of nanoparticle receptors to peptide alpha-helices through surface recognition

Nanoparticles featuring highly flexible sidechains template to peptides, demonstrating substantial pre-organization of the particle monolayer.     

CO Imaging in piloted liquid-spray flames using femtosecond two-photon LIF

Liquid-spray flames are encountered in many practical combustion devices such as gasoline direct injection and diesel engines, gas turbine combustors as well as industrial furnaces. As opposed to gaseous fuels, additional phase-change steps present in liquid sprays not only complicate the overall combustion process, but also make in-situ, laser-based combustion diagnostics challenging. In particular, the formation of carbon monoxide (CO) due to incomplete fuel-air mixing and partial oxidation becomes a major challenge. In this study, we apply femtosecond, two-photon laser-induced fluorescence (fs-TPLIF) to measure CO concentration in piloted liquid-spray flames, taking into account possible signal interferences in the 230.1-nm, B¹Σ⁺←X¹Σ⁺ excitation scheme. A modified, flat-flame McKenna burner fitted with a direct-injection high-efficiency nebulizer (DIHEN) was used to produce piloted liquid-methanol spray flames. Although single-laser-shot OH-PLIF images show the presence of strong turbulent interactions in the core region, shot-averaged OH-PLIF images indicate that near the nozzle-exit region, the primary reaction takes place in an annular region around the droplet cloud, in general. A detailed spectroscopic study reveals that the signal interference at 460?nm originating from the second-order scattering of the excitation laser, which becomes approximately an order of magnitude stronger than CO fluorescence spectral lines near the nozzle exit region. The specific spectral filtering scheme introduced in our recent work is proved to be capable of suppressing interferences primarily originating from C₂ Swan-band emissions. Two-dimensional CO maps along with OH-PLIF flame structure data provide key insights into the CO formation in piloted liquid-spray flames, while providing critical validation datasets for advanced computational models.