Densification of SiCp/Al-Fe-V-Si Composites by the Wedge Rolling Method.

The densification of a SiCp/Al-Fe-V-Si billet was achieved by reducing the pores and oxide film between the particles by rolling. The wedge pressing method was used to improve the formability of the composite after jet deposition. The key parameters, mechanisms, and laws of wedge compaction were studied. The results showed that the pass rate was reduced by 10 to 15 percent when using steel molds during the wedge pressing process if the distance between the two ends of the billet was about 10 mm, which was beneficial to improve the compactness and formability of the billet. The density and stress of the surface of the material were higher than those of the interior, where the distribution of density and stress tended to be uniform as the overall volume of the material shrank. During the wedge extrusion process, the material in the preforming area was thinned along the thickness direction, while the material in the main deformation area was lengthened along the length direction. Under plane strain conditions, the wedge formation of spray-deposited composites follows the plastic deformation mechanism of porous metals. The true relative density of the sheet was higher than the calculated value during the initial stamping phase, but was lower than the calculated value when the true strain exceeded 0.55. This was due to the accumulation and fragmentation of SiC particles, which made the pores difficult to remove.

Omnivorous Notoxus trinotatus Pic (Coleoptera: Anthicidae) is a newly recognized vector of northern leaf blight in maize.

The adaptations of omnivorous insects to food are manifested in a multifaceted manner, and the availability of food resources directly determines insect feeding tendencies, which contribute to a complex insect-food relationship and impact insect functionality in the environment. Stable isotope analysis was applied to test the feeding preference and further define the functional role of omnivorous beetles in cropland. Our results confirmed that as an omnivorous beetle, the fungivorous nature of Notoxus trinotatus accounted for a prominent proportion food selection at the adult stage, and more importantly, this dietary feature contributed to the dispersal of the northern corn leaf blight in maize (NLB) during the feeding trials. In addition to the preference for fungi, water supplementation was an essential element extending adult longevity, which directly prolonged the contact time of adults with pathogenic fungi in agricultural fields. Consistent with the herbivorous characteristics of beetles, before the emergence of NLB fungal pathogens, corn tissues served as the main food, which provided the beetles with more opportunities to transmit fungal pathogen propagules. We conclude that the role of N. trinotatus in carrying NLB pathogen is due to its feeding on this plant mycopathogen, and an increased abundance of beetles carrying the pathogen may increase the rate of NLB disease infestation. More focus should be concentrated on the functions of fungivorous beetles, not only as pathogen-transmitting pests, but also as an element among the balanced biotic factors in farmland.

Food origin influences microbiota and stable isotope enrichment profiles of cold-adapted Collembola (Desoria ruseki).

Collembola are a group of globally distributed microarthropods that can tolerate low temperature and are active in extremely cold environments. While it is well known that animal diets can shape their microbiota, the microbiota of soil animals is not well described, particularly for animals with limited food resources, such as Collembola active in winter at low temperatures. In this study, we explored the effects of three different food sources; corn litter (agriculture grain residuals), Mongolian oak litter (natural plant residuals), and yeast (common food for Collembola culture), on the microbiota of a winter-active Collembola species, Desoria ruseki. We found that microbial diversity and community composition of the Collembola were strongly altered after feeding with different food sources for 30 days. Collembola individuals fed on corn litter harbored the highest bacterial richness and were dominated by a representative of Microbacteriaceae. In contrast, those fed on yeast exhibited the lowest bacterial richness and were primarily colonized by Pseudomonas. The microbial communities associated with the winter-active Collembola differed significantly from those observed in the food. Collembola nutrient turnover also differed when cultured with different food sources, as indicated by the C and N stable isotopic signatures. Our study highlights microbial associations with stable isotopic enrichments of the host. Specifically, the Arthrobacter was positively correlated with δ13C enrichment in the host. Representatives of Microbacteriaceae, Micrococcaceae, TM7a, Devosia, and Rathayibacter were positively correlated with δ15N enrichment of the host. Our study indicates that food sources are major determinants for Collembola microbiota that simultaneously alter consumers' isotopic niches, thereby improving our understanding of the roles played by host-microbiota interactions in sustaining soil biodiversity during the winter.

General Decay Stability for Nonautonomous Neutral Stochastic Systems With Time-Varying Delays and Markovian Switching.

A new type of asymptotic stability for nonlinear hybrid neutral stochastic systems with constant delays was investigated recently, where the criteria depended on the delays' sizes. Unfortunately, developed theory so far is not sufficient to deal with challenging problems of the decay rate, time-varying delays, and nonautonomous issues. These problems have not been tackled in the existing literature. Consequently, under the weak constraints, this article focuses on the general decay, including the exponential stability and the polynomial stability, for nonlinear nonautonomous hybrid neutral stochastic systems with time-varying delays by the approach of the multiple degenerate functionals. Moreover, this article derives the interesting assertions related to the general H∞ stability and the polynomial growth at most.

Green and Durable Lightweight Aggregate Concrete: The Role of Waste and Recycled Materials.

Lightweight aggregate concrete manufactured by solid waste or recycled by-products is a burgeoning topic in construction and building materials. It has significant merits in mitigating the negative impact on the environment during the manufacturing of Portland cement and reduces the consumption of natural resources. In this review article, the agricultural and industrial wastes and by-products, which were used as cementitious materials and artificial lightweight aggregate concrete, are summarized. Besides, the mechanical properties, durability, and a few advanced microstructure characterization methods were reviewed as well. This review also provides a look to the future research trends that may help address the challenges or further enhance the environmental benefits of lightweight aggregate concrete manufactured with solid waste and recycled by-products.

What Is the Carcass-Usage Mode of the Collembola? A Case Study of Entomobrya proxima in the Laboratory.

Collembola display a variety of feeding habits, and prey on many types of food at different trophic levels in the soil. In most cases, their feeding selections are widely varied. In the interest of the food preferences of E. proxima, we attempted to confirm how the Collembola utilize food when feeding on carrion (unusual sources). Four different soil animals (with different stable isotope values and increasing trophic levels) were used to examine whether collembolans can use dead insects as a food resource in specific manners, depending on food preference. Our results demonstrated that the food preference of a collembolan changed significantly after feeding on insects with different feeding habits for 60 days. We found that stable isotope values (δ13C) of Entomobrya proxima approached those of the food sources. A large proportion of the diet (more than 50%) should directly consist of insect body parts, with the remainder consisting of indirectly used, mixed microorganisms naturally growing on animal food, such as fungi (Rhizopus sp., Alternaria sp., Penicillium sp., and Aspergillus sp.) and bacteria (Bacillus sp1. and Bacillus sp2.). Based on this research, the food preference of collembolans is more focused on carcasses (dead insect bodies) than microorganisms during the animal-food decomposition process.

Dry Spin Graphene Oxide Fibers: Mechanical/Electrical Properties and Microstructure Evolution.

Dry-spinning method is extensively employed in fiber industry, comparing to the counter-part of wet-spinning process, it has advantages of environmentally friendly, high yield rate and no need for purification. Here, we report the synthesis of graphene oxide (GO) fibers via dry spinning GO inks with extremely high concentrations. The proper rheology properties of such GO inks allow us to dry spin GO fiber directly. Various dry spinning conditions are investigated, and the relationship between mechanical performance and micro-structure of the obtained GO fiber are established. We found that the existence of larger GO liquid crystal domains does not necessarily result to higher mechanical properties, and it is because those large GO liquid crystal domains evolve into thick GO films during drying process and thus prevent the intimate compaction of the whole GOF and leave behind gaps. This is detrimental for the mechanical properties, and thus the dry spin GOF are much weaker than that of wet spin ones. Importantly, Barus effects, that generally arise during the melt spinning of polymers, were not observed, indicating that caution must be taken when classical polymer rheology theories are applied to investigate the dynamic behaviors of GO solution.

Microstructure and Properties of Thermal Electrode Material Si3N4⁻MoSi2 Composite Ceramics.

With good high temperature and corrosive resistance performance, ceramic based composites can be used as promising materials to replace metal thermocouple materials. In this study, Si3N4⁻MoSi2 composites were prepared via hot pressing technology. X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM) were used to analyze the microstructure of the composites. The mechanical properties and electrical conductivity were tested. The results showed that the composites were composed of β-Si3N4, MoSi2, a small amount of Mo5Si3, and an amorphous glassy phase. The MoSi2 phase was evenly distributed in the matrix. The percolation network was formed with increasing MoSi2 content. The strength of the composites reached its maximum value when the MoSi2 content reached a critical point. The electrical conductivity behaved like a typical percolation phenomenon. The percolation threshold was about 30% to 45%.

Carbon Nanofibers and Their Composites: A Review of Synthesizing, Properties and Applications.

Carbon nanofiber (CNF), as one of the most important members of carbon fibers, has been investigated in both fundamental scientific research and practical applications. CNF composites are able to be applied as promising materials in many fields, such as electrical devices, electrode materials for batteries and supercapacitors and as sensors. In these applications, the electrical conductivity is always the first priority need to be considered. In fact, the electrical property of CNF composites largely counts on the dispersion and percolation status of CNFs in matrix materials. In this review, the electrical transport phenomenon of CNF composites is systematically summarized based on percolation theory. The effects of the aspect ratio, percolation backbone structure and fractal characteristics of CNFs and the non-universality of the percolation critical exponents on the electrical properties are systematically reviewed. Apart from the electrical property, the thermal conductivity and mechanical properties of CNF composites are briefly reviewed, as well. In addition, the preparation methods of CNFs, including catalytic chemical vapor deposition growth and electrospinning, and the preparation methods of CNF composites, including the melt mixing and solution process, are briefly introduced. Finally, their applications as sensors and electrode materials are described in this review article.