Thermoluminescence characteristics of inorganically and organically capped ZnS:Cu nanophosphors

ZnS:Cu nanophosphors were prepared by wet chemical methods and characterized by X-ray diffraction (XRD). The typical morphologies of the nanophosphors were investigated by scanning electron microscopy (SEM). The thermoluminescence (TL) properties of inorganically and organically passivated ZnS:Cu nanophosphors were investigated after γ-irradiation using a ⁶⁰Co source at room temperature. The TL glow curve of capped ZnS:Cu showed variation in TL peak and intensity as the capping agent was changed. Amongst the synthesized samples the TL glow curve of SiO₂ capped ZnS:Cu showed the highest TL intensity. It has been found that TL response of SiO₂ capped ZnS:Cu is linear in the range 10-550 Gy. A discussion of the obtained results is also presented.     

Resonance effects in the nonadiabatic nonlinear quantum dimer

In the presence of 1/f ^β noise, we investigate the logical stochastic resonance (LSR) in an asymmetric bistable model driven by various cycling combinations of two logic inputs. The probability of correct logic outputs is calculated according to true table of logic relationships. Two major results are presented. Firstly, it is shown that the LSR effect can be obtained by changing noise strength. Over entire range of noise variance, white noise can be considered to be better than 1/f noise or 1/f ² noise to obtain clean logic operation. At a smaller noise level, 1/f noise can realize higher output probability than white noise or 1/f ² noise. In the sense, 1/f noise can be considered to be better than white noise or 1/f ². On the other hand, the correct probability can evolves nonmonotonically as noise exponent β increases, and a kind of SR-like effect can be obtained as a result of β. At certain intermediate noise variance, the output probability is able to attain its minimum at β = 1. It is also shown that actually some finite β sometime can be better than β = 0 at small range of noise variance. The study might provide some potential complement to LSR effect in the presence of 1/f ^β noise.     

Synthesis and characterization of β-Ga2O3 nanostructures grown on GaAs substrates

β-Ga₂O₃ nanostructures including nanowires, nanoribbons and nanosheets were synthesized via thermal annealing of gold coated GaAs substrates in N₂ ambient. GaAs substrates with different dopants were taken as the starting material to study the effect of doping on the growth and photoluminescence properties of β-Ga₂O₃ nanostructures. The nanostructures were investigated by Grazing Incident X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy, room temperature photoluminescence and optical absorbance. The selected area electron diffraction and High resolution-TEM observations suggest that both nanowires and nanobelts are single crystalline. Different growth directions were observed for nanowires and nanoribbons, indicating the different growth patterns of these nanostructures. The PL spectra of β-Ga₂O₃ nanostructures exhibit a strong UV-blue emission band centered at 410 nm, 415 nm and 450 nm for differently doped GaAs substrates respectively. A weak red luminescence peak at 710 nm was also observed in all the samples. The optical absorbance spectrum showed intense absorption features in the UV spectral region. The growth and luminescence mechanism in β-Ga₂O₃ nanostructures are also discussed.     

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature (T_g) of the blend was studied by differential scanning calorimetric technique (DSC), the T_g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.     

Nano-iron oxide-encapsulated chitosan microspheres as novel adsorbent for removal of Ni (II) ions from aqueous solution

The present study investigates the utility of composite beads of nano-particles of iron oxide and chitosan for removing Ni (II) ions from aqueous solution by batch and column adsorption techniques. In the batch mode experiment, the influence of pH, concentration, adsorbent dose, temperature, column mode, bed height, flow rate and initial concentration were studied on the adsorption profiles of nickel ions. The maximum uptake of Ni (II) ions was obtained at pH 4.0 in 30 min at room temperature.     

An eco-safe approach to benzopyranopyrimidines and 4H-chromenes in ionic liquid at room temperature

An environmentally benign, ionic liquid promoted multicomponent protocol to benzopyrano(2,3-d)pyrimidines and 4H-chromenes has been developed at room temperature. Results of the reaction depend on the nature of the nucleophile used in the reaction. Secondary amines result in the formation of benzopyrano(2,3-d)pyrimidines, whereas thiols give rise to 4H-chromenes under the same set of reaction conditions.     

Unprecedented Transformation of Thioglycosides to Their Corresponding 1‐O‐Acetates in the Presence of HClO4‐SiO2 §

An unprecedented conversion of thioalkyl/aryl glycoside to the corresponding 1‐O‐acetates has been described using acetic anhydride and HClO₄‐SiO₂ at rt. Although this transformation does not play an important role in the oligosaccharide synthesis in comparison to its reverse transformation, this gives useful information in selecting the reaction condition for the synthesis of oligosaccharides. The yields were excellent in all cases.     

Purification and Characterization of Enterocin LR/6, a Bacteriocin from <Emphasis Type="Italic">Enterococcus faecium</Emphasis> LR/6

Enterocin LR/6, a bacteriocin obtained from the culture filtrate of Enterococcus faecium strain LR/6, has been purified to homogeneity using ammonium sulfate precipitation, cation-exchange chromatography, gel-filtration, and checked on reverse-phase high-performance liquid chromatography. It is active at high temperatures (boiling as well as autoclaving) and over a wide range of pH (2.0–8.0). Also, it is sensitive to a number of proteolytic enzymes but is stable in the presence of surfactants and organic solvents. The protein could be stored at least up to 1 year at low temperatures (4 °C and −20 °C) without any loss of activity. The N-terminal sequence of enterocin LR/6 showed no homology with known enterocins or other bacteriocins present in the database, suggesting it to be a novel enterocin. Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed its mass to be ∼6.1 kDa. It showed a bactericidal mode of action against indicator strain, Micrococcus luteus.