(S,S)-2,12-, (S,S)-2,13-, and (S,S)-2,14-diacetoxyheptadecanes: sex pheromone components of red cedar cone midge, Mayetiola thujae

We identified, synthesized, and field-tested the sex pheromone of female red cedar cone midge Mayetiola thujae (Hedlin) (Diptera: Cecidomyiidae), a pest insect in red cedar Thuja plicata seed orchards. Coupled gas chromatographic (GC)-electroantennographic detection analyses of pheromone extract revealed three components (A, B, C) that elicited responses from antennae of males, all of which occurred below the detection threshold of the mass spectrometer and thus had to be identified without spectroscopic data. Taking into account (1) their retention indices (RI) on three GC columns (DB-5, DB-23, and DB-210), (2) intercolumn RI differentials, and (3) the molecular structures of known cecidomyiid pheromones, we synthesized seven candidate pheromone components: 2,10-, 2,11-, 2,12-, 2,13-, 2,14-, 2,15- and 2,16-diacetoxyheptadecanes. Of these, 2,12-, 2,13-, and 2,14-diacetoxyheptadecane had RIs on all columns consistent with those of A, B, and C and elicited strong antennal responses when tested at picogram levels. In field experiments with the twelve stereoselectively synthesized stereoisomers, only the SS-stereoisomers of 2,12-, 2,13-, and 2,14-diacetoxyheptadecane attracted male M. thujae. The three-component SS-stereoisomer blend was more attractive than the 12-component blend of all stereoisomers, suggesting that one or several nonnatural stereoisomers are inhibitory. One-, two-, and three-component lures of the SS-stereoisomers were equally effective in attracting male M. thujae, indicating redundancy in the pheromone. Identification of the M. thujae sex pheromone will allow development of pheromone-based monitoring, and possibly control, of M. thujae populations in T. plicata seed orchards.     

Enhanced stabilization of inorganic cesium lead triiodide (CsPbI<Subscript>3</Subscript>) perovskite quantum dots with tri-octylphosphine

In recent years, significant attention has been paid to perovskite materials. In particular, lead triiodide-based perovskites have exhibited superb optoelectronic properties. Enhancing the stability of these materials is an essential step towards large-scale applications. In this study, by simply adding trioctylphosphine (TOP) as part of the post-synthesis treatment, we significantly enhance the stability of CsPbI₃ quantum dots (QDs) in the solution phase, which otherwise decay rapidly in hours. For CsPbI₃ QDs treated with TOP, the absorption and photoluminescence emission properties are unchanged over the course of weeks, and the quantum yield remains almost constant at 30% even after 1 month. The morphologies of both treated and untreated QDs are initially cubic; however, the treated QDs largely maintain their initial size and shape, while the untreated ones lose size uniformity, which is a sign of degradation. Infrared spectroscopy and X-ray photoelectron spectroscopy confirm the presence of P in the TOP-treated QDs. We insights that help to resolve the intrinsic instability issue of triiodide perovskite materials and devices.

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Stochastic optimization of a biologically plausible spino-neuromuscular system model

Simulations and modeling techniques are becoming increasingly important in understanding the behavior of biological systems. Detailed models help researchers answer questions in diverse areas such as the behavior of bacteria and viruses and aiding in the diagnosis and treatment of injuries and diseases. However, to yield meaningful biological behavior, biological simulations often include hundreds of parameters that correspond to biological components and characteristics. This paper demonstrates the effectiveness of genetic algorithms (GA) and particle swarm optimizer (PSO) based techniques in training biologically plausible behavior in a neuromuscular simulation of a biceps/triceps pair. The results are compared to human subjects during flexion/extension movements to show that these algorithms are effective in training biologically plausible behaviors on both neural and gross anatomical levels. Specific behaviors of interest that emerge include tonic tensions in both muscles during resting periods, biceps/triceps coactivation patterns, and recruitment-like behaviors. These are all fundamental characteristics of biological motor control and emerge without direct selection for these behaviors. This is the first time that all of these characteristic behaviors emerge in a model of this detail without direct selective pressure.

Extruded foams prepared from high amylose starch with sodium stearate to form amylose inclusion complexes*

Extruded starch foams were prepared from high amylose corn starch with and without sodium stearate and poly(vinyl alcohol) (PVOH) to determine how the formation of amylose–sodium stearate inclusion complexes and PVOH addition would affect foam properties. X‐ray diffraction and Differential Scanning Calorimetry (DSC) showed that amylose–sodium stearate inclusion complexes were formed by low temperature extrusion and did not dissociate during foam formation by a second extrusion at higher temperatures. In the absence of PVOH, water absorption, and foam shrinkage at 95% RH were decreased because of the hydrophobicity of the complex. PVOH addition increased both the expansion ratio and the shrinkage of the foam, although shrinkage at 95% RH was still less than that observed with uncomplexed amylose. The structural integrity and some tensile properties of stearate‐containing foams were improved by PVOH addition. These results provide the manufacturer of biodegradable starch foams with an inexpensive method for tailoring foam properties for specific end‐use applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43251.     

Water vapor thermal treatment effects on spark plasma sintered nanostructured ferritic alloy‐silicon carbide systems

Spark plasma sintered pure silicon carbide (SiC) and nanostructured ferritic alloy‐silicon carbide (NFA‐SiC) systems are investigated in a water vapor containing air atmosphere at elevated temperatures up to 1000°C. Both of them exhibit excellent corrosion resistance with a dense amorphous SiO₂ layer as the main oxidation barrier. Crystalline α‐quartz and α‐cristobalite from the oxidation of silicides and SiC, respectively, further benefit the corrosion resistance. For the new NFA‐SiC system, the original graphite and silicide phases can be desirably sustained. The NFA‐SiC materials have promising applications in high temperature moist environments and are especially important for nuclear reactor cladding.     

Flash pyrolysis of polymer-derived SiOC ceramics

For the first time, flash pyrolysis was carried out to fabricate polymer derived silicon oxycarbide (SiOC) ceramics. With the application of a DC electric field at a furnace temperature of only 780?°C, the SiOC ceramics exhibit characteristics that usually have to be pyrolyzed at ～1300?°C. Both electric field and current density accelerate the SiOC microstructure development, causing carbon and SiC phases to form at >520?°C lower pyrolysis temperatures than conventional within the SiOC matrix. With higher electric fields, the samples experience greater mass loss and linear shrinkage, while also forming more SiC and a more ordered carbon phase. The SiC formation inversely impacts the carbon content, causing a decrease in electrical conductivity. Further, reducing current density results in significant carbon precipitation without SiC formation. The fundamentals can be explained based on increased nucleation rate by the electrical field, accompanied by Joule heating and electromigration. This work is the first to demonstrate the great potential of flash pyrolysis on accelerated phase separation of polymer derived SiOC.     

Students’ appraisal of emotional and relational experience whilst collaborating online using text based communication

The impacts that the lack of physical cues and non-verbal cues of emotional expression has on the student learning experience in text based online environments were targeted separately in this study. A questionnaire was constructed with separate items for non-verbal cues of emotional expression and cues to physical identity. The survey also included questions about students’ previous experience with technology and collaboration, and their motivations for undertaking the course. Views about their interactions with other students were also sought. The responses of 256 students who had undertaken a text based online course where collaboration was a mandatory requirement were collected and subsequently analysed using cluster analysis. Four distinct cohorts of students were identified. Using a conceptual approach borrowed from neuroscience, modularity, it has been possible to encapsulate the effects of three distinct aspects of collaborating in text based online contexts, lack of cues to physical identity, lack of cues to emotional expression and interaction experience. These aspects were analysed alongside the student profiles for each of the four cohorts. The findings indicate that the external factors that an individual student brings to a learning context can impact on the learning experience. Neuroscientifically based knowledge that is relevant for the findings of the survey are identified and considered in terms of the questions raised from an interdisciplinary perspective.     

Sub-micron features from polymer-derived SiOC via imprint lithography

Silicon oxycarbide (SiOC) is a unique class of materials with great potential for facile manufacturing of complex shaped high temperature parts and devices. In this study, we examine the characteristics of micron-sized ridge and rod patterns of SiOC created by imprint lithography. Feature fidelity, shape change, and shrinkage are studied as a function of pyrolysis condition and feature size. All the features have acceptable surface fidelity under the pyrolysis conditions studied. However, pronounced rounding and flattening of patterned features are observed as the pyrolysis temperature increases or the feature size decreases. Based on the Kelvin and Gibbs-Thomson equations, we can predict the feature evolution and show that the feature rounding and flattening are due to surface diffusion and evaporation-condensation. As a result, the features also have more linear shrinkage than the bulk.     

Aflatoxin in household maize for human consumption in Kenya,East Africa

ABSTRACT

The objective of this study is to determine the occurrence and level of aflatoxins (AFs) contamination in freshly harvested maize for human consumption in rural Kenya. Maize kernels and freshly milled maize flour (n = 338) were collected from households in Siaya and Makueni counties. While both counties are representatives of different environmental and climate conditions, Makueni County is the area with reported outbreaks of aflatoxicosis. Samples were analysed for AFB₁, AFB₂, AFG₁, and AFG₂ using Ultra High-Pressure Liquid Chromatography with Fluorescence detection. AFs were detected in 100% of the samples with the range of 2.14–411 µg/kg. The geometric mean of total AFs in all samples from Makueni County is 62.5 μg/kg with 95% CI: 53.7, 71.4 while in Siaya County is 52.8 μg/kg with 95% CI: 44.0, 61.7. This study showed that AFs contamination is prevalent in maize-based foods in the region.