Effect of post‐deposition annealing on surface morphology and gas sensing properties of palladium phthalocyanine thin films

The effect of post‐deposition annealing on surface morphology and gas sensing properties of palladium phthalocyanine (PdPc) nanostructured thin films has been studied. PdPc thin films were deposited on polyborosilicate substrate by thermal evaporation technique at room temperature. The surface morphology of thin films was investigated by SEM, X‐ray diffraction, and optical absorption. X‐ray diffraction patterns showed a phase transition from α to β based on post‐deposition annealing at temperatures above 200 °C. The SEM and optical absorption confirmed that annealing strongly influenced the surface morphology of nanostructured thin films. Sandwich devices (Au|PdPc|Al) were fabricated and exposed to different concentrations of NO₂ and NH₃ as oxidizing and reducing gases at different temperatures, and the sensitivity of devices were obtained versus gases. Obtained results showed α‐PdPc thin film devices had higher sensitivity in comparison with devices in β‐phase. In particular, it was found that the sensitivity of devices is temperature dependent and the best operating temperature range of devices was measured at about 90–100 °C. Devices showed good reversibility, response, and recovery time at room temperature. Finally, the stability of sensors was investigated for a period of about 1 year; results showed that the sensors were stable for 2 months and lost about 30% of their sensitivity after 1 year. Copyright © 2012 John Wiley & Sons, Ltd.     

Sounds of Instability from Generalized QCD Ghost Dark Energy

We investigate about the stability of generalized QCD ghost dark energy model against perturbations in the FRW background. For this purpose, we use the squared sound speed $v_{s}^{2}$ whose sign determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-flat geometry. In all cases we find almost a same result. Based on the square sound speed analysis, due to the existence of a free parameter in this model, the model is theoretically capable to lead a dark energy dominated stable universe. However, observational constraints rule out such a chance. In conclusion, we find evidences that the generalized ghost dark energy might can not lead to a stable universe favored by observations at the present time.     

On generalized m-th root finsler metrics

In this paper, we characterize locally dually flat generalized m-th root Finsler metrics. Then we find a condition under which a generalized m-th root metric is projectively related to a m-th root metric. Finally, we prove that if a generalized m-th root metric is conformal to a m-th root metric, then both of them reduce to Riemannian metrics.     

Study on the effect of laser parameters on wakefield excitation in femtosecond pulsed laser–plasma interaction using PIC method

Propagation of an intense short laser pulse through under-dense plasma can produce huge amplitude plasma wake field. A 3D particle in cell (PIC) method was used to simulate the wakefield generation for different laser parameters such as intensity, pulse duration, spot size and temporal pulse shape. Our study shows that the amplitude of wakefield is increased with laser intensity, but it is decreased with spot size. The results for pulse shape and pulse duration depend on their optimum values.     

The peculiar elongational viscosity of concentrated solutions of monodisperse PMMA in oligomeric MMA

Concentrated solutions of nearly monodisperse poly(methyl methacrylate), PMMA-270k and PMMA-86k, in oligo(methyl methacrylate), MMA o-4k and MMA o-2k, investigated by Wingstrand et al. (Phys Rev Lett 115:078302, 2015) and Wingstrand (2015) do not follow the linear-viscoelastic scaling relations of monodisperse polystyrenes (PS) dissolved in oligomeric styrene (Wagner in Rheol Acta 53:765–777, 2014a, in Non-Newtonian Fluid Mech 222:121–131, 2014b; Wagner et al. in J Rheol 59:1113–1130, 2015). Rather, PMMA-270k shows an attractive interaction with MMA, in contrast to the interaction of PMMA-86k and MMA. This different behavior can be traced back to different tacticities of the two polymers. The attractive interaction of PMMA-270k with o-4k creates pseudo entanglements, which increase the interchain tube pressure, and therefore, the solution PMMA-270k/o-4k shows, as reported by Wingstrand et al. (Phys Rev Lett 115:078302, 2015), qualitatively a similar scaling of the elongational viscosity with \( {\left(\dot{\varepsilon}{\tau}_R\right)}^{-1/2} \) as observed for polystyrene melts. For the solution PMMA-270/o-2k, this effect is only seen at the highest elongation rates investigated. The elongational viscosity of PMMA-86k dissolved in oligomeric MMA is determined by the Rouse time of the melt, as in the case of polystyrene solutions.

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Hydrocarbon oxidation catalyzed by vanadium polyoxometalate supported on mesoporous MCM-41 under ultrasonic irradiation

Vanadium polyoxometalate (PVMo) supported on mesoporous MCM-41, MCM-41-NH(2), as efficient and heterogeneous catalysts, with large surface area, for hydrocarbon oxidation with hydrogen peroxide is reported. Oxidation of the alkenes and alkanes gave product selectivities, which are similar to those observed for corresponding homogeneous catalyst. PVMo-MCM was prepared by introduction of PVMo into the mesoporous molecule sieves of MCM-41 by impregnation and adsorption techniques. The samples were characterized by X-ray diffraction (XRD), thermal gravimetric-differential thermal analysis (TG-DTA), FT-IR, scanning electron microscopy (SEM), UV-Vis and cyclic voltametry (CV). Ultrasonic irradiation has a particular effect on MCM-41 structural uniformity and reduced the reaction times and improved the product yields. In addition, the solid catalysts could be recovered and reused several times without loss of its activity.