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1
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Analytical approximate solutions for two-dimensional viscous flow through expanding or contracting gaps with permeable walls

100%
Dinarvand S., Rashidi M., Doosthoseini A.
Open Physics
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2009
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vol. 7
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issue 4
791-799
EN
In this paper, the problem of laminar, isothermal, incompressible and viscous flow in a rectangular domain bounded by two moving porous walls, which enable the fluid to enter or exit during successive expansions or contractions is solved analytically by using the homotopy analysis method (HAM). Graphical results are presented to investigate the influence of the nondimensional wall dilation rate α and permeation Reynolds number Re on the velocity, normal pressure distribution and wall shear stress. The obtained solutions, in comparison with the numerical solutions, demonstrate remarkable accuracy. The present problem for slowly expanding or contracting walls with weak permeability is a simple model for the transport of biological fluids through contracting or expanding vessels.
2
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Pulsed laser treatment of gold and black gold thin films fabricated by thermal evaporation

100%
Novotný M., Fitl P. e., Sytchkova A., Bulíř J. Ã., Lanaok J., Pokorna P., Najdek D., Boan J.
Open Physics
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2009
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vol. 7
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issue 2
327-331
EN
The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm−2 to 250 mJ·cm−2 was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm−2 and 3.5 mJ·cm−2 for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser treatment.
3
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Comparative study of ZnO layers prepared by PLD from different targets at various oxygen pressure levels

100%
Haško D., Bruncko J., Vincze A., Uherek F. e.
Open Physics
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2009
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vol. 7
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issue 2
345-349
EN
Two series of polycrystalline zinc oxide (ZnO) layers, from Zn or ZnO targets, were grown on silicon (1 1 1) substrates by pulsed laser deposition (PLD) at ambient oxygen pressure levels, stepwise increased from 1 to 35 Pa. For ablation of targets, a pulsed Nd:YAG laser was used. The structural and morphological properties of the layers were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS). The SEM images of ZnO layers in SE mode show a uniform granular structure and modified surface morphology, depending on oxygen pressure. The mean grain size in height and lateral directions decreases with an increase of oxygen pressure from 1 to 5 Pa, while a subsequent rise of oxygen pressure from 5 to 35 Pa will cause an increase in the grain size. The AFM measurement revealed that the surface structures of zinc oxide layers grown from different targets were similar, and the layers formed at an ambient oxygen pressure of 5 Pa exhibited the smallest values of calculated roughness and granularity. SIMS depth profiling analyses confirmed that the ZnO composition was homogenous across the layer, up to the abrupt change of chemical composition at the interface between the ZnO layer and the Si substrate.
4
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Control of sputtering parameters for deposition of NbN thick films

100%
Jha R., Awana V. P. S.
Novel Superconducting Materials
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2015
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vol. 1
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issue 1
EN
We report a detailed study on control of sputtering parameters for synthesizing NbN superconducting thick films. The NbN films are deposited on single crystalline silicon (100) by DC reactive sputtering, i.e., deposition of Nb in the presence of reactive N2 gas. After several runs, samples were prepared with Ar:N2 partial gas ratios of 90:10, 80:20 and 70:30 for a deposition time of 10 minutes. The fabricated films (400 nm thick) crystallize with a cubic structure, with a small quantity of Nb/NbOx embedded in the main NbN phase. All three samples are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), to examine their microstructure and elemental compositional distributions, respectively. The roughness was mesured by atomic force microscopy (AFM). The optimized film prepared with Ar:N2 gas ratio of 80:20 has a Tc(R = 0) in zero and 140 kOe fields of 14.8 K and 8.8 K, respectively. The upper critical field Hc2(0) of the studied superconducting films is calculated from magneto-transport [R(T )H] measurements using GL and WHH equations.
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