High-pressure phases of lead chalcogenides

Ab initio electronic structures have been carried out to find the pressure-induced structural phase transitions of lead chalcogenides (PbS, PbSe and PbTe) compounds. The zinc-blende, wurtzite, rocksalt, CsCl, GeS, TlI and orthorhombic Pnma phases are considered. Results show that the intermediate phase transition for these compounds is not the GeS nor the TlI type structures, as previously reported, but the orthorhombic Pnma phase. All these compounds are predicted to undergo a structural phase transition from the rocksalt to Pnma phase at about 8.13, 7.45 and 5.40 GPa for PbS, PbSe and PbTe respectively. Moreover, further structural phase transitions from this intermediate phase to the CsCl phase have been predicted at about 25.3, 18.76 and 15.43 GPa for PbS, PbSe and PbTe respectively.     

Investigation of the glass transition temperature and damping of an acrylic/epoxy bonding tape using the peak damping method

The dynamic properties of a structural tape used for adhesive bonding applications have been measured at different temperatures to determine its glass transition temperature and damping properties. For this purpose, free layer beams consisting of a base layer steel and the tape layer were vibrated using a resonant beam technique with free-free end conditions. To measure the dynamic values (elastic modulus and loss factor) of the tape, the necessary equations were derived and the frequency dependence of the beams was investigated from –55°C to +60°C. Three beams with different layers were tested. Results have shown that as the temperature increases, the elastic modulus of the tape decreases, while the loss factor of the tape increases up to 20°C and then decreases to a constant level. The results from the three beams are in agreement, showing that the glass transition temperature of the tape is about 20°C, which implies viscoelastic properties at room temperature.     

A study of photomodulated reflectance on staircase-like,n-doped GaAs/AlxGa1?xAs quantum well structures

In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped Al_xGa_1−xAs barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes’ third derivative functional form.Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature.     

Partial order semantics for use case and task models

Use case models are the specification medium of choice for functional requirements, while task models are employed to capture User Interface (UI) requirements and design information. In current practice, both entities are treated independently and are often developed by different teams, which have their own philosophies and lifecycles. This lack of integration is problematic and often results in inconsistent functional and UI design specifications causing duplication of effort while increasing the maintenance overhead. To address these shortcomings, we propose a formal semantic framework for the integrated development of use case and task models. The semantic mapping is defined in a two step manner from a particular use case or task model notation to the common semantic domain of sets of partially ordered sets. This two-step mapping results in a semantic framework that can be more easily reused and extended. The intermediate semantic domains have been carefully chosen by taking into consideration the intrinsic characteristics of use case and task models. As a concrete example, we provide a semantics for our own DSRG use case formalism and an extended version of ConcurTaskTrees, one of the most popular task model notations. Furthermore, we use the common semantic model to formally define a set of refinement relations for use case and task models.     

Alkaline sulfide pretreatment of an antimonial refractory Au-Ag ore for improved cyanidation

This paper presents the alkaline sulfide pretreatment of an antimonial refractory gold and silver ore. In the ore, gold occurs mainly as gold-silver alloys and as associated with quartz and framboidal pyrite grains, and, to a small extent, as the inclusions within antimonial sulfides. Silver is present extensively as antimonial sulfides such as andorite. Alkaline sulfide pretreatment was shown to allow the decomposition of the antimonial sulfide minerals (up to 98% Sb removal) and to remarkably improve the amenability of gold (e.g., from <49% up to 83%) and silver (e.g., from <18% up to 90%) to subsequent cyanide leaching. An increase in reagent concentration (1–4 mol/L Na₂S or NaOH) and temperature (20–80°C), and a decrease in particle size seem to produce an enhancing effect on metal extraction. These findings suggest that alkaline sulfide leaching can be suitably used as a chemical pretreatment method prior to the conventional cyanidation for antimonial refractory gold and silver ores.     

Benefits of considering inventory in service parts logistics network design problems with time-based service constraints

We study the integrated logistics network design and inventory stocking problem as characterized by the interdependency of the design and stocking decisions in service parts logistics. These two sets of decisions are usually considered sequentially in practice, and the associated problems are tackled separately in the research literature. The overall problem is typically further complicated due to time-based service constraints that provide lower limits on the percentage of demand satisfied within specified time windows. We introduce an optimization model that explicitly captures the interdependency between network design (location of facilities, and allocation of demands to facilities) and inventory stocking decisions (stock levels and their corresponding stochastic fill rates), and present computational results from our extensive experiments that investigate the effects of several factors including demand levels, time-based service levels and costs. We show that the integrated approach can provide significant cost savings over the decoupled approach (solving the network design first and inventory stocking next), shifting the whole efficient frontier curve between cost and service level to superior regions. We also show that the decoupled and integrated approaches may generate totally different solutions, even in the number of located facilities and in their locations, magnifying the importance of considering inventory as part of the network design models.     

Characterization of polyacrylonitrile,poly(acrylonitrile‐co‐vinyl acetate), and poly(acrylonitrile‐co‐itaconic acid) based activated carbon nanofibers

In this study, three different acrylonitrile (AN)‐based polymers, including polyacrylonitrile (PAN), poly(acrylonitrile‐co‐vinyl acetate) [P(AN‐co‐VAc)], and poly(acrylonitrile‐co‐itaconic acid) [P(AN‐co‐IA)], were used as precursors to synthesize activated carbon nanofibers (ACNFs). An electrospinning method was used to produce nanofibers. Oxidative stabilization, carbonization, and finally, activation through a specific heating regimen were applied to the electrospun fibers to produce ACNFs. Stabilization, carbonization, and activation were carried out at 230, 600, and 750 °C, respectively. Scanning electron microscopy, thermogravimetric analysis (TGA), and porosimetry were used to characterize the fibers in each step. According to the fiber diameter variation measurements, the pore extension procedure overcame the shrinkage of the fibers with copolymer precursors. However, the shrinkage process dominated the scene for the PAN homopolymer, and this led to an increase in the fiber diameter. The 328 m²/g Brunauer–Emmett–Teller surface area for ACNFs with PAN precursor were augmented to 614 and 564 m²/g for P(AN‐co‐VAc) and P(AN‐co‐IA), respectively. The TGA results show that the P(AN‐co‐IA)‐based ACNFs exhibited a higher thermal durability in comparison to the fibers of PAN and P(AN‐co‐VAc). The application of these copolymers instead of AN homopolymer enhanced the thermal stability and increased the surface area of the ACNFs even in low‐temperature carbonization and activation processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44381.     

Simplex lattice mixture design approach on physicochemical and sensory properties of wheat chips enriched with different legume flours: An optimization study based on sensory properties

In this study, physicochemical and sensory characteristics of wheat chips enriched with different legume flours were investigated. Wheat chips formulations were composed with the mixture of wheat flour and the mixture of three different legume flours (wheat–legume ratio 80:20). Mixture design approach was used to determine the effect of interactions between pea, chickpea and soy flour on the physicochemical and sensory properties of chips produced with wheat–legume flour mixture. In addition, product optimization was carried out by using ridge analysis to determine the optimum legume flour mixture proportions based on sensory properties of chips samples. Chickpea flour was found to be highest desired component depending on the general acceptability scores of chips. Protein content of chips increased significantly with the addition of soy flour. Optimum limit values of chickpea, pea and soy flour in the legume flour mixture used for the enrichment of the wheat chips were found to be 50–100 g/100 g, 0–60 g/100 g and 0–45 g/100 g legume flour, respectively, with respect to sensory properties. Additionally, ridge analysis results showed that the wheat chips should include only chickpea flour in the legume flour fraction to obtain maximum overall preference score (6.08).     

Improvement of Silver Extraction by Ultrafine Grinding Prior to Cyanide Leaching of the Plant Tailings of a Refractory Silver Ore

Ultrafine grinding (UFG) was proposed as a pretreatment method prior to cyanide leaching of old plant tailings of a refractory silver ore. Direct cyanidation of the as-received tailings (d₈₀: 100 µm) led to a low silver extraction of only ≤43% over 24 h. A size-based diagnostic study has demonstrated that the refractoriness of the tailings is essentially physical in character. Therefore, effects of particle size/UFG (d₉₉: 5–75 µm), concentrations of NaCN (0.75–2.25 g/L) and Pb(NO₃)₂ (0–500 g/t) on the extraction of silver were investigated using a Box–Behnken design. The statistical analysis of the experimental data (%Ag extraction at 1 h) revealed that particle size/UFG was the most significant parameter for the extraction of silver, which was substantially improved after UFG. A positive effect of increasing the concentration of NaCN was also observed particularly at finer particle sizes while the effect of concentration of Pb(NO₃)₂ was insignificant. Almost complete extraction for silver (i.e., ≥99%) was demonstrated to be possible at even higher concentrations of cyanide (>2.25 g/L NaCN) when using the finest material (d₉₉: 5 µm) over only 1 h of leaching. Albeit, the consumption of cyanide tended to increase with UFG or increasing the initial concentration of cyanide. The findings showed that UFG can be used as a suitable and environmentally sound pretreatment method to improve the extraction of silver from the refractory silver ore tailings. The diagnostic approach adopted in the current study has proved to be a useful analytical tool to determine the amenability of the ore to ultrafine-grinding as a pretreatment process.