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[en] In this work, the performances of two optimized reflective secondary optics elements a CPC (Compound Parabolic Concentrator) and a Cone for use in a CPV concentrator system are studied using ray-tracing simulation for the same primary optical element: a Fresnel lens. These optical elements are compared in terms of concentration, acceptance angle, exit angle and output light distribution. Our results show that the power distribution at the end of the concentrator is more uniform in the case of the cone. The optical efficiency is higher when the secondary element is placed at a distance with f the focal length; R the input radius of the secondary optical element and θ the acceptance angle of the secondary optical element. Also, we found that the length and the input radius of each optical element decrease when the Fresnel lens diameter increases but the input radius of the CPC stills the larger. Finally, our calculation show that the CPC is longer than the cone while the Fresnel lens diameter is less than 200 mm and beyond this value both the cone and the CPC mostly present the same length. (paper)
[en] In order to investigate the corrosion behavior and impact toughness of 105SS drill pipe steel in the wet H2S environment, the impact and corrosion testing were carried out. The results show that the diffusible hydrogen concentration is mainly influenced by the morphology of the corrosion scales and the dynamic fracture toughness loss of 105SS drill pipe steels increases with the increase of diffusible hydrogen concentration. However, when hydrogen was released, the impact energy increases. The area of quasi-cleavage features on the fracture surfaces increases with the increase of hydrogen concentration. (paper)
[en] This work offers an effective size-controlled synthesis of platinum nanoparticle (Pt NP) arrays for electrocatalyst through self-assembled nanopatterns of block copolymers on titanium (Ti) wafers. Size, spacing and uniformity of Pt NP with loading of Pt to a minimum were investigated to be controlled and adjusted in order to improve the electrochemically active surface area (ECSA) and ECSA stability, and Pt concentration in copolymer/chloroplatinic acid (H2PtCl6) solution was verified to be one of the most important factors to control the arrays’ structure. In our case, the Pt NPs with predictable size of 5–16.5 nm could be obtained when the Pt concentration is larger than 0.05 mg ml−1, which the dominant diameter is proved to be proportional to one-third power of the Pt concentration according to the linear relation of templates’ Pt/N mass ratio versus Pt concentration, and the Pt NPs remain highly ordered arrays with predictable spacing when the Pt concentration is larger than 0.125 mg ml−1. Decrease in Pt concentration from 2 to 0.125 mg ml−1 is an effective method to improve the ECSA and durability simultaneously. The Pt NP arrays exhibit not only a remarkable initial ECSA value of 106.2 m2 g−1, but also a pseudo-zero particle aggregation possibility during 3000-cycle voltammetry, which is attributed to the high Pt NP dispersion and the ordered arrays that improve the Pt utilization and lower the possibility of aggregation.
[en] Effects of chloride, introduced with 0.03, 0.05, 0.10, 0.12, 0.22, 0.25 M, on the corrosion behavior of API-X100 pipeline steel in 0.15 M carbonate solutions were studied. The evaluations were carried out with monitoring the open-circuit potentials and electrochemical impedance spectroscopy (EIS). The open-circuit potentials gave an electrochemical evidence on the weakening opposite kinetics of the passive film formation to the kinetics of dissolution with higher chloride concentrations. The open-circuit potentials were less with higher chloride concentrations. The EIS tests indicated that the corrosion resistance decreased, and species diffusion increased with the chloride concentration, in multi-time constant interactions. In all tests, slippery transparent films formed with no presence of pitting on the sample surfaces.
[en] Highlights: • Electronic properties of bilayer graphene are investigated by exploring doping of a single or both layers. • Random tight-binding model and the coherent potential approximation are implemented. • Behavior of p or n doping is resulted in a conventional semiconductor, dependent on impurity type and concentration. - Abstract: In the framework of the Green's functions approach, random tight-binding model and using the coherent potential approximation, electronic characteristics of the bilayer graphene are investigated by exploring various forms of substitutional doping of a single or both layers of the system by either boron and (or) nitrogen atoms. The results for displacement of the Fermi level resemble the behavior of acceptor or donor doping in a conventional semiconductor, dependent on the impurity type and concentration. The particular pattern of doping of just one layer with one impurity type is most efficient for opening a gap within the energy bands which could be tuned directly by impurity concentration. Doping both layers at the same time, each with one impurity type, leads to an anomaly whereby the gap decreases with increasing impurity concentration.
[en] Highlights: • Microstructure and mechanical properties of 9Cr-ODS steel were investigated as a function of nitrogen concentration. • hardness and tensile strength were degraded as nitrogen concentration increased, due to the decreased amount of residual α-ferrite phase. • Formation of coarse YTi precipitates was observed, suggesting degradation of the nano-particle distribution. • Nitrogen concentration specification for 9Cr-ODS steel should be stricter than the current level. - Abstract: The objective of this study was to investigate the effect of nitrogen concentration on mechanical properties and nano-structure of 9Cr oxide dispersion strengthened (ODS) ferritic/martensitic steel. 9Cr-ODS specimens with the wide range of nitrogen concentration, from 0.004 to 0.110 wt%, were systematically investigated by hardness and tensile tests and several microstructural characterization methods. Hardness and tensile strength at 973 K were significantly decreased as nitrogen concentration increased, due to the decrease in the amount of the residual α-ferrite phase. Coarse inclusions containing Y and Ti, which could negatively affect creep strength and processability, were formed, and that suggested degradation of the nano-particle distribution. The technical knowledge obtained in this study will contribute towards the setting of a reasonable nitrogen concentration specification for 9Cr-ODS steel.
[en] The assessment of the toxicity of airborne nanofibers is an important task. It relies on toxicological inhalation studies and validated exposure measurement techniques. Both require nanofiber-containing aerosols of known morphological composition and controlled fraction of individual fibers. Here, a dry powder dispersion method is presented that operates with mixtures of nanofibers and microscale beads. Aerosolization experiments of mixtures of multi-walled carbon nanotubes (MWCNTs) and glass beads that were continuously fed into a Venturi nozzle enabled high generation rates of aerosols composed of individual and agglomerate nanofiber structures. The aerosol process achieved good stability over more than 2 h with respect to concentration and aerodynamic size distribution. Its operation duration is limited only by the reservoir volume of the cyclone used to separate the beads from the aerosol. The aerosol concentration can be controlled by changing the mass ratio of MWCNTs and glass beads or by adapting the mass feed rate to the nozzle. For two agglomerated MWCNT materials, aerosol concentrations ranged from 1700 to 64,000 nano-objects per cm3. Comprehensive scanning electron microscope analysis of filter samples was performed to categorize and determine the morphological composition of the aerosol, its fiber content as well as fiber length and diameter distributions. High fractions of individual fibers of up to 34% were obtained, which shows the setup to be capable of dispersing also highly tangled MWCNT agglomerates effectively.
[en] Encapsulation and controlled release of substances using polymeric nanoparticles require that these have a high reproducibility, homogeneity, and control over their properties (diameter and polydispersity), especially when they are to be used in medical, pharmaceutical, or nutritional applications among others. In conventional production systems, it is tough to ensure these characteristics; hence, the cost increases when we try to control these properties. This paper shows a comparison between a recirculating system and the standard nanoprecipitation technique for producing polymeric nanoparticles. In previous investigations, we evaluate the effect of recirculating flow and the ratio between the organic and aqueous phase. For this paper, we evaluated the effect of polymer and surfactant concentrations using a multifactorial design of experiments on the recirculating system and on the standard nanoprecipitation system. The response of the design was the average diameter of the nanoparticles and polydispersity index. Finally, we found that the polymer and surfactant concentrations could change the average diameter and polydispersity index of the nanoparticles obtained. On the other hand, it was found that the effect of the polymer concentration was stronger than the surfactant concentration to reduce the average diameter of the nanoparticles. The results of the present study show that the proposed recirculation system presents a high potential to produce polymer nanoparticles with good morphological characteristics, particle size distributions in the nano range, and with a low polydispersity. The average mean size of nanoparticles of polycaprolactone for the design using the recirculating system was of 61 to 140 nm and the values of polydispersity index PDI for this design were between 0.097 and 0.22, while for the design using the standard nanoprecipitation technique, the obtained diameters were 74 to 176 nm and the polydispersity was between 0.26 and 0.41.
[en] The effect of Cr, Mn, and the isothermal holding temperature on inverse bainitic transformation in hypereutectoid steels is investigated. Thermodynamic driving force is calculated for the onset of nucleation of cementite and ferrite from parent austenite, Hultgren extrapolation of Ae3 and Acm phase boundaries, and the molar Gibbs energy change for austenite to ferrite transformation. For a given carbon concentration above the eutectoid carbon concentration, inverse bainite is favored at a lower Cr and higher Mn concentrations in the steel. With the increase in Cr concentration, the inverse bainitic start temperature has been found to increase. Cr partitioning from parent austenite to form Cr7C3 or Cr23C6 occurs only at prolonged transformation time (10000 s and above), by when the inverse bainitic transformation is complete. Cementite is the favored carbide nucleating from parent austenite during the inverse bainitic transformation. With the increase in Mn concentration, both the inverse bainitic start and finish temperatures have been found to decrease. For a given chemical composition, inverse bainite is generally favored below the pearlitic transformation temperature. Inverse bainitic transformation gets suppressed when the isothermal transformation temperature is lowered, in which case conventional upper/lower bainite is the favored transformation product.
[en] Concentration dependences of sodium dodecyl sulfate (SDS) in the concentration range of 0.005 - 0.03 mole (with the step of 0.001 mole) in water-ethanol solutions with a percentage ratio of 100:0, 92:8, 85:15, 70:30 were investigated by the methods of pH and conductometry. It was shown that micelle formation occurs at concentrations of SDS ∼11 mol/L, ∼9 mol/L, ∼11 mol/L, and ∼17 mol/L in aqueous ethanolic solutions. From the concentration dependence of SDS, it was found that a noticeable decrease in the critical concentration of micellization occurs in aqueous ethanol solutions at 8% ethanol content. (authors)