Damage evaluation and deformation behavior of mine tailing-based Geopolymer under uniaxial cyclic compression

Geopolymerized mine tailings (MTs), as an alternative to reuse the mine wastes, can be used for construction materials (e.g., geopolymer concrete and bricks) depending on their mechanical properties. Their strength values, which can range from a couple of MPa to tens of MPa, are significant evidence for their application in the construction industry. In practice, geopolymers activated with different NaOH molarities can significantly affect the mechanical properties of MTs. The mechanical behavior of geopolymers under monotonic loading also has been widely investigated. However, the potential hazard of the exposure of geopolymer concrete/bricks to cyclic loading has received limited attention. This paper presents a study we conducted on geopolymers made by activation of MTs under cyclic loading to understand their crack and damage behaviors, including the influence of factors such as NaOH molarity and loading patterns. The influence of NaOH molarity on the elastic and plastic strains of the geopolymer specimen at different cycles was explored. A series of unconfined compression tests of cubic specimens with different NaOH molarities as well as microscopic investigations and observations via XRD, FTIR, and SEM were carried out in this study. The Young's modulus of the geopolymer was found to increase followed by a decrease with the cycles for all the selected NaOH molarities. The geopolymers activated with lowest NaOH molarity were first to start damage and activated with the highest NaOH molarity were the last to damage. The damage variable was shown to increase rapidly at the initial cycles and then gradually approached the maximum value.     

A gender matching effect in learning with pedagogical agents in an immersive virtual reality science simulation

The main objective of this study is to determine whether boys and girls learn better when the characteristics of the pedagogical agent are matched to the gender of the learner while learning in immersive virtual reality (VR). Sixty‐six middle school students (33 females) were randomly assigned to learn about laboratory safety with one of two pedagogical agents: Marie or a drone, who we predicted serve as a role models for females and males, respectively. The results indicated that there were significant interactions for the dependent variables of performance during learning, retention, and transfer, with girls performing better with Marie (d = 0.98, d = 0.67, and d = 1.03; for performance, retention, and transfer, respectively) and boys performing better with the drone (d = ?0.41, d = ?0.45, d = ?0.23, respectively). The results suggest that gender‐specific design of pedagogical agents may play an important role in VR learning environments.     

Multiobjective evolutionary feature selection and fuzzy classification of contact centre data

In this work, a data set describing phone interactions arising in a multichannel and multiskill contact centre is considered with the aim of classifying inbound sessions into those that will be eventually managed by an agent and those that, instead, will be abandoned before. More precisely, the goal of the work is to extract interpretable pieces of information that allow us to predict whether a user will or will not abandon a call, which may turn out to be very useful for the purpose of contact centre managing. To this end, the performance of two well‐known, state‐of‐the‐art evolutionary algorithms for feature selection (evolutionary nondominated radial slots based algorithm and nondominated sorted genetic algorithm) is compared for the task of feature selection, under the criteria of accuracy and cardinality of the selection, as well as for the task of fuzzy rule extraction, under the criteria of interpretability, accuracy, and hypervolume test. The best obtained fuzzy classifier, chosen after a decision making process, is validated and interpreted by domain experts.     

Social returns to education in Italian local labor markets

The paper estimates social returns to education in the Italian local labor markets. It shows that there is an important correlation between local human capital and average wages after controlling for individual characteristics. Estimated social returns to education range from 2 to 3%, whereas the private returns amount roughly to 6–7%. To find some support about causality running from local human capital to wages, the paper performs a number of robustness checks. It shows that: the estimated social returns are unlikely to be driven by spatially correlated omitted variables; they survive to the introduction of individual- and territorial-level variables; they are not due to imperfect substitutability across workers or spatial sorting; they are robust to IV techniques that deal with both local human capital and individual human capital endogeneity.

Synthesis of core-shell nanoparticles using organic surface-functionalized gold and Au@SiO2 nanoparticles as multifunctional initiators in atom transfer radical polymerization

Gold and Au@SiO2 nanoparticles were synthesized and surface-functionalized by initiators for atom transfer radical polymerization (ATRP), either using a thiol or a trialkoxysilane anchor group for the immobilization of the initiating functionality. The thus obtained initiator-capped gold systems were applied in polymerizations of various monomers, such as styrene, methacrylic acid trimethyloxysilyl propylester and isoprene and copolymers thereof. The final inorganic-organic core-shell nanoparticles were characterized applying different techniques such as electron microscopy and light scattering. Kinetic studies of the polymerizations revealed that they were highly controlled and therefore the thickness of the polymer shell could be easily adjusted. The obtained nanoparticles formed stable suspensions in various organic solvents and can therefore be used as building blocks for polymer nanocomposites.     

Optically active poly(dimethylsiloxane) elastomer films through doping with gold nanoparticles

Poly(dimethylsiloxane) (PDMS) elastomer films synthesized through a cross-linking reaction between hydroxyl-terminated or vinyl-terminated PDMS have been homogeneously doped with silica-coated Au nanoparticles. The nanocomposite synthesis involves mixing a preformed colloid of surface-modified metal nanoparticles with the elastomer film precursors. The homogeneous distribution of nanoparticles is demonstrated through the presence of well defined plasmon absorbance bands in the visible, which clearly show that the composites retain the characteristic optical properties of single Au nanoparticles. The metal particle concentration could be easily tailored either through the amount or the concentration of the nanoparticle colloid added. Since the Au nanoparticles are not cross-linked to the polymer and the concentration of particles is relatively low, we postulate that the presence of the nanoparticles does not affect the mechanical properties of the films, though this remains to be confirmed.     

Thermo and electrochemical characterization of sulfonated PEEK–WC membranes and Krytox-Si-Nafion® composite membranes

Two types of membranes, the sulfonated PEEK-WC (poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxyphenylene)(SPWC) and Krytox-Si-Nafion® (KSiN) composite membranes are proposed for DMFC applications.The properties based on water uptake, ion exchange capacity, proton conductivity, gas permeability, thermal stabilityand methanol crossover are summarized. The comparative studies on SPWC and Nafion® 117 membranes clarify us that the amorphous sulfonated PEEK-WC polymer shows thermal and mechanical stability with less methanol flux and gas permeability. The membrane also exhibits the increase in water uptake, ion exchange capacity and proton conductivity as sulfuric acid doping agent concentration was increased. The KSiN is unique in term of its miscible hybrid structure of silica particles modified with Nafion® structured Krytox 157 FSL chain (KSi) andNafion®. Based on the KSiN membranes with different KSi content, it was found that when KSi content increased, the reduction of gas permeability, methanol crossover and thermal stability are improved. The composite membrane performs the proton conductivity in the wide range of high temperature (60–130°C).     

Volatiles Emission Patterns in Poplar Clones Varying in Response to Ozone

The volatiles emitted from young and old leaves of two poplar clones (Populus deltoides x maximowiczii, Eridano, and P. x euramericana, I-214) were sampled after exposure to ozone (80 ppb, 5 h?d(-1), for 10 consecutive days) by solid phase microextraction and characterized by GC-MS. Only mature leaves of the ozone-sensitive Eridano clone developed necrosis in response to ozone exposure, and their membrane integrity was significantly affected by ozone (+86 and +18 % of levels of thiobarbituric acid reactive substances in mature and young leaves). The headspace of the poplar clones studied here contained mono- and sesquiterpenes, both hydrocarbons and oxygenated ones in Eridano, and only hydrocarbons in the clone I-214. Furthermore, some non-terpenes, such as C(9)-C(15) straight-chain aldehydes and C(12)-C(16) saturated and unsaturated aliphatic hydrocarbons, were detected. Other common non-terpene volatiles were oxygenated aliphatic compounds, mainly C(6)-alcohols and their acetates. Ozone exposure induced a strong change in volatile profiles, depending on clones and leaf age. Regardless of leaf age, in clone I-214, quantities of oxygenated monoterpenes tended to increase after ozone exposure, however, "O(3) x leaf age" was not significant. In clone Eridano, increases were observed in emissions of hydrocarbons and oxygenated sesquiterpenes in response to ozone treatment. (Z)-3-Hexen-1-ol and (Z)-3-hexenol acetate were present in traces in the headspace of untreated Eridano mature leaves, but quantities slightly increased after ozone treatment. Quantities of non-terpene oxygenated compounds dropped in the headspace of young leaves of both clones (-24 and -44 % in Eridano and I-214) and also in mature ones of I-214 (-50 %) after ozone exposure. Similarly, quantities of non-terpene hydrocarbons in the emissions from mature leaves of both clones (-58 and -49 %, respectively) decreased, while these compounds increased in young leaves of Eridano (+83 %). We suggest that the resistance of the poplar clone I-214 to O(3) is achieved by: i) monoterpenes constitutively present in young leaves and ii) increase of monoterpene content induced by O(3) in mature leaves.