Parameters affecting TGO growth rate and the lifetime of TBC systems with MCrAlY‐bondcoats

In the present work different parameters which affect the oxide growth on MCrAlY‐bondcoats have been studied, in an attempt to find a reliable way to define the critical oxide thickness to failure of an EB‐PVD thermal barrier coatings (TBC). It was found that the variation of selected parameters such as oxidation temperature, surface roughness, and bondcoat thickness certainly alters the thermally grown oxide (TGO) growth rate. However, simultaneously the morphology, composition, and/or microstructure of the oxide are changed, which can affect the critical TGO thickness to failure in a TBC system. In contrast, the variation of the oxygen partial pressure of the oxidizing atmosphere led to different TGO growth rates without significantly changing the oxide morphology and composition. Comparing the TGOs grown at different rates in the specimens exposed to high pO₂ and low pO₂ atmospheres, it was estimated that at failure the oxide scales in both specimens have reached a similar critical thickness.     

Effect of calcination temperature of mesoporous alumina xerogel (AX) supports on hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/AX catalysts

Mesoporous alumina xerogel (AX) supports prepared by a sol–gel method were calcined at various temperatures. Ni/mesoporous alumina xerogel (Ni/AX) catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AX supports on the catalytic performance of Ni/AX catalysts in the steam reforming of LNG was investigated. Physical and chemical properties of AX supports and Ni/AX catalysts were strongly influenced by the calcination temperature of AX supports. Crystalline structure of AX supports was transformed in the sequence of γ-alumina → (γ + θ)-alumina → θ-alumina → (θ + α)-alumina with increasing calcination temperature from 700 to 1000 °C. Nickel species were strongly bonded to the divalent vacancy of γ-alumina, (γ + θ)-alumina, and θ-alumina through the formation of nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AX supports. Among the catalysts tested, Ni/AX-900 (nickel catalyst supported on AX that had been calcined at 900 °C) showed the best catalytic performance. The smallest nickel crystalline size and the strongest nickel–alumina interaction were responsible for high catalytic performance of Ni/AX-900 catalyst in the steam reforming of LNG.     

Effect of temperature on GaN nanowires fabricated via thermal heating of GaN powders

GaN nanowires have been successfully synthesized by heating GaN powders under flowing ammonia gas in a temperature range of 950–1050 °C. The nanowire morphology was changed with varying temperature, and higher temperature favored thinner nanowires. The growth mechanisms of GaN nanowires at 950 °C included a vapor-liquid-solid process. The photoluminescence (PL) spectra of the samples commonly exhibited violet to yellow emission, whereas red emission occurred preferentially in samples synthesized at lower temperature. We have discussed the possible mechanisms by which growth temperature affected the nanowire morphology and PL spectrum.     

A Simulated Annealing-based parallel multi-objective approach to vehicle routing problems with time windows

The Capacitated Vehicle Routing Problem with Time Windows (VRPTW) consists in determining the routes of a given number of vehicles with identical capacity stationed at a central depot which are used to supply the demands of a set of customers within certain time windows. This is a complex multi-constrained problem with industrial, economic, and environmental implications that has been widely analyzed in the past. This paper deals with a multi-objective variant of the VRPTW that simultaneously minimizes the travelled distance and the imbalance of the routes. This imbalance is analyzed from two perspectives: the imbalance in the distances travelled by the vehicles, and the imbalance in the loads delivered by them. A multi-objective procedure based on Simulated Annealing, the Multiple Temperature Pareto Simulated Annealing (MT-PSA), is proposed in this paper to cope with these multi-objective formulations of the VRPTW. The procedure MT-PSA and an island-based parallel version of MT-PSA have been evaluated and compared with, respectively, sequential and island-based parallel implementations of SPEA2. Computational results obtained on Solomon’s benchmark problems show that the island-based parallelization produces Pareto-fronts of higher quality that those obtained by the sequential versions without increasing the computational cost, while also producing significant reduction in the runtimes while maintaining solution quality. More specifically, for the most part, our procedure MT-PSA outperforms SPEA2 in the benchmarks here considered, with respect to the solution quality and execution time.     

Effects of Liquid Whey Protein Concentrate on Functional and Sensorial Properties of Set Yogurts and Fresh Cheese

The production and incorporation of liquid whey protein concentrates (LWPCs) in fresh cheese and set yogurt is proposed as a solution for immediate reutilization of whey produced by small- and medium-scale dairy plants avoiding expensive processing steps (e.g., evaporation and drying) for the recovery of this by-product. Accordingly, the incorporation of LWPCs in such products was performed in order to compare the functional and sensorial properties of modified products with the conventional ones. The use of LWPC in fresh cheese increased water-holding capacity as well as product stability during storage. Fresh cheese hardness, chewiness, and gumminess decreased during storage in a more pronounced way in products with LWPC. The fat content influences significantly all the physicochemical properties tested in set yogurts. Incorporating LWPC in set yogurts does not produce appreciable differences in the visual properties when considering products with medium-fat content, but these differences become significant for full-fat yogurts. Adhesiveness and springiness were not significantly affected with storage time or by the amount of LWPC incorporated for medium-fat yogurts. Higher values of hardness and gumminess were obtained for full-fat yogurts, but these parameters decreased with LWPC incorporation. Syneresis was reduced using LWPC but increased with storage time. During storage, viscosity differences between LWPC incorporated yogurts and the conventional ones were only maintained in the case of creamy yogurts. The sensory panel detected differences between conventional and modified products in the case of fresh cheeses but no significative differences were detected between yogurts. LWPCs can be a good alternative to conventional dry products used in fresh cheese and set yogurt manufacture since their utilization reduces milk consumption and allows for the increase in total solids content. Additionally, their incorporation in milk originates end products with attractive physicochemical and sensorial characteristics at lower production costs.     

Theoretical comparison of alternative delivery systems for projects in unpredictable environments

A project delivery process simulation is presented based upon empirical studies in the design‐build environment of semiconductor fabrication facilities (‘fabs’). The model captures key tasks and decisions in design, procurement and construction, as well as design criteria changes along the delivery of a R&D fab utility system. Simulation shows that to involve the specialty contractor from the project start on average expedites project delivery since it prevents delays caused by bidding and by contractors' unfamiliarity with the design product definition. Yet, in unpredictable project environments – environments in which design criteria are likely to change irrespectively of the project progress status – simulation reveals that the averages of construction rework and waste increase if design is prematurely frozen. Assuming that work methods do not change and design criteria remain uncertain, results indicate that a system that combines early contractor involvement with judicious postponement of the design start reduces the average duration of the fab utility delivery in relation to the expected duration if competitive bidding was used, with limited increase in the averages of construction rework and waste. Additional efficiency is gained when specialty contractors relax conservative assumptions on anticipated site conditions. An economic model uses simulation results to assess the tradeoffs between alternative project delivery systems for the case of R&D fabs.     

Fractional integration and structural breaks at unknown periods of time

Abstract. This article deals with the analysis of structural breaks in the context of fractionally integrated models. We assume that the break dates are unknown and that the different sub‐samples possess different intercepts, slope coefficients and fractional orders of integration. The procedure is based on linear regression models using a grid of values for the fractional differencing parameters and least squares estimation. Several Monte Carlo experiments conducted across the study show that the procedure performs well if the sample size is large enough. Two empirical applications are described at the end of the article.     

In vitro evaluation of surface topographic changes and nickel release of lingual orthodontic archwires

The objective of the article is to study surface topographic changes and nickel release in lingual orthodontic archwires in vitro. Stainless steel (SS), nickel–titanium (NiTi) and copper–nickel–titanium (CuNiTi) lingual orthodontic archwires were studied using atomic absorption spectrometry for nickel release after immersion in a saline solution. Surface roughness changes were measured using atomic force microscopy. Differences between groups were analyzed using independent sample t-tests. Statistically significant changes in roughness were seen in all archwires except NiTi. Surface changes were most severe in the CuNiTi alloy. SS archwires released the highest amount of nickel. In conclusion, only roughness changes in CuNiTi archwires seemed to be clinically significant. The amount of nickel released for all archwires tested is below the levels known to cause cell damage.     

Original article: Effect of modified atmosphere packaging using different CO2 and N2 combinations on physical,chemical, microbiological and sensory changes of fresh sea bass (Dicentrarchus labrax) fillets

The effect of different modified atmosphere packaging (MAPs) on physical, chemical, microbiological and sensory changes of sea bass fillets when stored at 4 °C and standard light conditions was investigated for up to 21 days and compared to a control batch stored in overwrap. Sea bass fillets were packed using different CO₂ and N₂ combinations (40% CO₂–60% N₂; 50% CO₂–50% N₂; 60% CO₂–40% N₂), and quality assessment was based on instrumental, chemical, microbiological and sensory analysis. The results showed that MAP extended shelf‐life of sea bass fillets from 7 days (overwrap packaging) to 14 days. Drip loss, pH values and thiobarbituric acid reactive substances (TBARS) measurements were higher in overwrap samples but no differences (P ≤ 0.05) were found between MAP samples. Bacteria grew most quickly and showed higher counts in overwrap samples followed by 40% CO₂–60% N₂; 50% CO₂–50% N₂ and finally 60% CO₂–40% N₂. Sensory analyses were in good relation with chemical and microbiological results establishing best scores and an extended shelf‐life for MAP samples especially in MAPs with high CO₂ levels.