Nitrogen dissociation and its excitation/vibrational temperature with hydrogen admixture in 50 Hz DC discharge

Trace rare gas optical emission spectroscopy (TRG-OES) is carried out to determine the excitation temperature, vibrational temperature, dissociation fraction and nitrogen (N) atom density in 50?Hz active screen cage nitrogen plasma, as a function of discharge parameters (current density and fill pressure) and hydrogen concentrations. The excitation temperature is determined from Ar–I emission lines and is found to increase with hydrogen mixing. In a similar fashion, the vibrational temperature of second positive system is determined and found to have increasing trend with hydrogen addition. The dissociation fraction increases with hydrogen concentration up to 40% H₂ in the nitrogen plasma, so as the nitrogen atom density.     

Structural,morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10?cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10?cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4?±?0.4?GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10?cm axial distance with 15 PFS.     

Ultra-lightweight cellulose foam material: preparation and properties

Ultra-lightweight cellulose foams were prepared by regeneration of sodium dodecyl sulfate (SDS)/cellulose/NaOH/urea blend solution via mechanical agitation and then freeze-drying. The morphology and properties of the blend solutions and foams were investigated via optical microscope, rheometer, BET and SEM. As a result, it was found that the inclusion complex structure between cellulose macromolecules and the solvent molecules was not destroyed. Moreover, the bubbles were about 20–50 μm in the solutions and larger (>100 μm) in the foams. Not only the micropores (bubbles) but also the nanopores could be observed in the wet and dried foams. The cellulose foams possessed ultra-low density of about 30 mg/cm³ and high specific surface area. The result of X-ray diffraction and Fourier transform infrared spectroscopy indicated that the cellulose foams were transited from cellulose I to cellulose II after dissolution and gelation. Bubbles inside the wet foams weakened the mechanical properties, but inversely increased the mechanical properties in the dried foams. Typical “J”-shaped curves were observed during the mechanical test, which revealed good compressive strength of dried foams. In this work, cellulose foams with ultra-lightweight and good mechanical properties were obtained, which exhibited great potentials for further development and comprehensive utilization of cellulose.     

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Molecularly Imprinted Polypyrrole for DNA Determination

In this study graphite electrodes modified by a thin DNA‐imprinted polypyrrole layer, which was able to bind specific target‐DNA, are reported. For this aim, electrochemical synthesis of polypyrrole was performed on a pencil graphite electrode by cyclic voltammetry (CV) or by potential pulse sequences (PPS). The modified electrode surface was used for electrochemical determination of target‐DNA by differential pulse voltammetry. According to our best knowledge this is a first report on the application of DNA‐imprinted polymer for the determination of target‐DNA. The results showed that the molecularly imprinted polypyrrole (MIPPy) layer that formed on the carbon electrode surface was sensitive for target‐DNA, while the nonimprinted polypyrrole layer was not sensitive to the same target‐DNA. Comparison of electrodes modified using PPS and CV techniques is presented.     

Enantio- and Diastereoselective Oxidation of N-Alkylimines Using Chiral α-Bromonitriles and Hydrogen Peroxide System

Chiral α-bromonitriles were prepared with good chemical and optical yields starting from natural α-amino acids by dehydrating the corresponding α-bromoamides with thionyl chloride. The combined system α-bromonitriles/hydrogen peroxide was examined for the enantio- and diastereoselective oxidation of N-alkylimines in basic media at room temperature. The oxidation of N-tertiobutylarylimines leads to optically active oxaziridines with moderate enantiomeric excess. However, the oxidation of (S)-1-phenylethylarylimines affords the corresponding oxaziridines with good diasteromeric excess up to 97/3 as proved by gaseous-phase chromatography.     

Surface and Catalytic Properties of K/V Catalysts Coating on Porous Al2O3 Substrate

The morphology of different ratio K/V catalysts supported on porous α‐alumina substrate was investigated by atomic force microscopy (AFM). Changes in the particle size distribution, pore size distribution were analyzed respectively using AFM software. In addition, their catalytic activities and compositions for carbon oxidation were studied by x‐ray diffraction (XRD), differential scanning calorimetry (DSC), and temperature‐programmed reactions (TPR). As a result, with the increase of K concentration, the mean particle size gradually increased and the mean pore size decreased. According to the catalytic activity studies, the catalytic activity of the KVO₃ and K₃V₅O₁₄ phases are more effective than KCl.     

Kinetics of the Oxidation of Phenylhydrazine by [Fe(CN)6]3− in Water‐in‐Oil Microemulsions

The oxidation reaction of phenyl hydrazine (Phh) by hexacyanoferrate ([Fe(CN)₆]^3?) has been studied in water‐in‐oil (w/o) microemulsion media. The kinetic profile of the reaction was investigated as a function of [Phh], droplet size, and droplet concentration. Comparison of the kinetic profiles of the reaction in microemulsion, water‐urea, and water‐AOT‐urea media indicates that the kinetic profile of the reaction in microemulsion shows a behavior similar to that of the reaction in water‐AOT‐urea medium at 4 M urea. An initial increase and then a decrease in k_obs is observed with increasing molar ratio, W_o(=[H₂O]/[AOT]) at constant [AOT] (=0.4 M), whereas k_obs decreases upon increasing the AOT concentration at constant molar ratio.     

Effect of temperature on the fluorescence emission of carbazole-substituted methylcellulose in dilute aqueous solutions

Fluorescent-labeled polymers, carbazole-substituted methylcelluloses (Cz-MCs) were synthesized through a two-step reaction by firstly introducing epoxy group to carbazole, and then reacting with MC. Structure of Cz-MC was characterized by using FTIR, NMR, elemental analysis and UV–vis spectroscopy. Aggregation behavior of Cz-MCs in dilute aqueous solution was investigated by a thermotropic study performed with dynamic laser light scattering. Cz-MCs displayed concentration self-quenching properties of fluorescence spectra both in H₂O and DMSO. The temperature effect on the fluorescent emission in dilute aqueous solution was explored. The results showed that the degree of substitution of carbazole and thermal aggregation of Cz-MC contributed to the formation of network structure between the molecules, consequently leading to the enhancement or quenching in fluorescence intensity.     

Consequences of weak Allee effect on prey in the May–Holling–Tanner predator–prey model

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different ω ? limit sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd.