Growth of thiourea-doped TGS crystals and their characterisation

Thiourea-doped Triglycine sulphate (ThTGS) crystal with three different concentrations of thiourea was grown from aqueous solution by slow cooling technique. The cell parameters were determined from powder X-ray diffraction analysis. A qualitative analysis of the presence of thiourea in doped crystals was estimated by FTIR analysis. Microhardness studies were carried out using Leitz Weitzler hardness tester at room temperature. Dielectric properties of the crystals were studied which showed a shift in the T_c when compared to pure TGS crystal. Pyroelectric studies were carried out and the pyroelectric coefficient was found. Piezoelectric studies (d₃₃ coefficient) has also been carried out.     

Stochastic makespan minimization in structured set systems

Mathematical Programming - We study stochastic combinatorial optimization problems where the objective is to minimize the expected maximum load (a.k.a. the makespan). In this framework, we have a...     

Luminescence studies of thallium co-doped KBr:Eu2+ powder phosphors

In this study, photoluminescence (PL) and photostimulated luminescence (PSL) properties in KBr:Eu²⁺, Tl⁺ powder phosphors are reported. PL emission spectra of these Tl⁺ co-doped KBr:Eu²⁺ phosphors show four overlapping bands around 310, 325, 360 and 375 nm in addition to the characteristic of Eu²⁺ ions at 420 nm. These additional short wavelength bands were attributed to centres involving Tl⁺ ions. The decrease in PSL intensity of γ-irradiated KBr:Eu²⁺, Tl⁺ powder phosphors with Tl⁺ concentration and the absence of thallium emission bands in PSL were attributed to the efficient electron trapping by Tl⁺ ions during irradiation.     

Structure-property relationships and moisture sensitivity of PDMS/PTMO mixed soft segment urethane elastomers

The structure-property relationships of polyurethane elastomers based on 4,4′-diphenylmethane diisocyanate (MDI) and 4,4′-dicyclohexylmethane diisocyanate (HMDI) with PTMO, PDMS, and mixed PTMO/PDMS soft segments were investigated using DSC, dynamic mechanical spectroscopy, tensile testing, and SAXS. Changes in water absorption and moisture sensitivity with compositional changes were investigated through water absorption and physical property measurements. Differences in tensile properties and moisture sensitivity with varying hard and soft segment composition are interpreted in terms of the phase mixing characteristics of the various polymers studied.     

An atomistic assessment of the impact of flaw orientation on the elastic and failure behavior of single-crystal Si nanometre-thick slabs

Abstract

Failure of nanoscale Si thin films was examined using molecular dynamics (MD) simulations that employed the modified embedded atom method (MEAM) interatomic potential. Specifically, nanometre-thick slabs of different crystallographic orientations containing asymmetric, high aspect ratio surface flaws were subjected to uniaxial tensile strains with the strain applied perpendicular to the flaw major axis. The ensuing elastic response and failure behaviour were examined as a function of variation in crystallographic orientation relative to the surface flaw. For certain flaw orientations, crack propagation was accompanied by slip along preferred directions, while in other cases, failure was purely brittle. In addition, a significant dependence of the computed elastic constants and yield stress, on the relative orientation of the surface flaw was observed. This work offers new insights into the role of surface flaws on the mechanical failure of silicon-based, nanoscale, engineered structures.     

Influence of laser power on POCl3 diffused back surface field on n-type PERT silicon solar cells with local back contact

We report n-type passivated emitter rear totally diffused (PERT) silicon solar cells with local back contacts (LBC) formed by laser process. With passivated back surface field (BSF), the PERT cell design shows an improved open circuit voltage (V_oc) with reduced recombination at the rear due to improved optical confinement. The rear side was diffused by POCl₃ diffusion with low sheet resistance (R_s) BSF and passivated using SiN_x. Laser ablation was used to open the SiN_x on the rear for LBC. The Nd:YAG laser power (mW) parameters and POCl₃ doping temperature were varied to obtain the BSF with lower sheet resistance. Laser power of 44 mW with 10 kHz resulted in 30 Ω/sq BSF layer with effective lifetime (τ_eff) of 90 μs and a higher V_oc of 646 mV. With the optimized laser parameters the best electrical results yielded a short circuit current density (J_sc) of 36 mA/cm² and efficiency of 18.54%.     

An unusual hydrogen addition of indolo-2,3-quinodimethanes to dimethylindoles in the presence of 1,3-azoles

Indolo-2,3-quinodimethane generatedin situ frombis-(bromomethyl)indole with NaI/DMF at 70°C was expected to undergo cycloaddition with 1,3-azoles to give carboline derivatives, which form the backbone of many indole alkaloids. However, the reaction did not give the anticipated product but proceeded via hydrogen addition to exocyclic methylene groups, furnishing dimethylindoles in good yields     

Mechano-thermal nanoparticulate coatings for enhancing the cycle stability of LiCoO2

A mechano-thermal coating method was adopted for obtaining LiCoO₂ coated particles with pre-formed pseudo-boehmite nanoparticulate, followed by calcination at 723 K for 10 h. From X-ray diffraction (XRD) analysis it was seen that the coated cathode materials did not show any extraneous phase peaks corresponding to the pseudo-boehmite and the crystal structure, α-NaFeO₂, remained the same as pristine LiCoO₂. Scanning electron micrograph (SEM) of the coated samples showed that above the 1.0 wt.% coating level, the excess pseudo-boehmite got glued to the coated cathode particles as spherules. TEM images showed that the Al₂O₃ particles derived from pseudo-boehmite formed ∼20 nm thickness coating layer on the LiCoO₂ particles. The XPS/ESCA results revealed that the presence of two different O 1s corresponds to the surface coated Al₂O₃ and the core material. The electrochemical performance of the coated materials by a cycling study suggest that 1.0 wt.% coated Al₂O₃ derived from pseudo-boehmite on the two commercial LiCoO₂ samples improved cycle stability by a factor of five and 11 times over the pristine LiCoO₂ cathode material. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations were retained for the coated cathode materials upon continuous cycling.     

Antimicrobial flavonoids isolated from Indian medicinal plant Scutellaria oblonga inhibit biofilms formed by common food pathogens

Scutellaria oblonga Benth., a hitherto phytochemically unexplored Indian medicinal folklore plant was extracted with acetone and subjected to chromatography to yield nine flavonoids, for the first time from this plant. Antimicrobial assays were performed against 11 foodborne pathogens, and three molecules (Techtochrysin, Negletein and Quercitin-3-glucoside) depicted significant activity. These molecules were assessed for their rate of antibacterial action using time–kill curves which depicted complete inhibition of most of the bacteria within 12–16 h. The significant biofilm-reducing capability exhibited by these three molecules formed a significant finding of the current study. In most of the experiments, a 90–95% reduction in biofilms was observed. Thus, flavonoids as natural molecules from S. oblonga could be further researched to be used as potent antimicrobial and antibiofilm agents.