The effect of chemistry and thermal fluctuations on charge injection barriers at aluminum/polyolefin interfaces

Charge injection at metal/polymer interfaces is a critical process in many technological devices, including high voltage capacitors and cables in which polyolefin materials, such as polyethylene (PE) and polypropylene (PP), are often used as insulation materials. We use simulations based on density-functional theory to study charge injection at aluminum/PE and aluminum/PP interfaces. Specifically, we investigate the influence of incorporating a variety of polar chemical impurities at the PE and PP chain ends on electron and hole injection barriers. Crucially, we account for the effect of thermal disorder by considering ensembles of thousands of interface structures obtained from ab initio molecular dynamics trajectories at 373 K. We show that the mean injection barrier can change by up to 1.1 eV for Al/PE and 0.6 eV for Al/PP, as compared to the pristine case, depending on which chemical impurity is introduced. We also show that the spread of injection barriers from thermal fluctuations also depends strongly on the chemistry of the impurity. The observed trends can be understood with a simple model based on thermal fluctuations of the dipole moment density associated with the chemical impurity at the interface. We further verify this model by considering larger interface models with lower impurity densities. Our results demonstrate that small chemical modifications, which may arise from oxidation, for example, have a significant influence on charge injection barriers in metal/polyolefin interfaces

Insect oviposition preference between Epichloe-symbiotic and Epichloe-free grasses does not necessarily reflect larval performance

Variation in plant communities is likely to modulate the feeding and oviposition behavior of herbivorous insects, and plant-associated microbes are largely ignored in this context. Here, we take into account that insects feeding on grasses commonly encounter systemic and vertically transmitted (via seeds) fungal Epichloe endophytes, which are regarded as defensive grass mutualists. Defensive mutualism is primarily attributable to alkaloids of fungal origin. To study the effects of Epichloe on insect behavior and performance, we selected wild tall fescue (Festuca arundinacea) and red fescue (Festuca rubra) as grass-endophyte models. The plants used either harbored the systemic endophyte (E+) or were endophyte-free (E-). As a model herbivore, we selected the Coenonympha hero butterfly feeding on grasses as larvae. We examined both oviposition and feeding preferences of the herbivore as well as larval performance in relation to the presence of Epichloe endophytes in the plants. Our findings did not clearly support the female's oviposition preference to reflect the performance of her offspring. First, the preference responses depended greatly on the grass-endophyte symbiotum. In F. arundinacea, C. hero females preferred E+ individuals in oviposition-choice tests, whereas in F. rubra, the endophytes may decrease exploitation, as both C. hero adults and larvae preferred E- grasses. Second, the endophytes had no effect on larval performance. Overall, F. arundinacea was an inferior host for C. hero larvae. However, the attraction of C. hero females to E+ may not be maladaptive if these plants constitute a favorable oviposition substrate for reasons other than the plants' nutritional quality. For example, rougher surface of E+ plant may physically facilitate the attachment of eggs, or the plants offer greater protection from natural enemies. Our results highlight the importance of considering the preference of herbivorous insects in studies involving the endophyte-symbiotic grasses as host plants

An improved lower bound for (1,<=2)-identifying codes in the king grid

We call a subset $C$ of vertices of a graph $G$ a $(1,\leq \ell)$-identifying code if for all subsets $X$ of vertices with size at most $\ell$, the sets $\{c\in C |\exists u \in X, d(u,c)\leq 1\}$ are distinct. The concept of identifying codes was introduced in 1998 by Karpovsky, Chakrabarty and Levitin. Identifying codes have been studied in various grids. In particular, it has been shown that there exists a $(1,\leq 2)$-identifying code in the king grid with density 3/7 and that there are no such identifying codes with density smaller than 5/12. Using a suitable frame and a discharging procedure, we improve the lower bound by showing that any $(1,\leq 2)$-identifying code of the king grid has density at least 47/111

New insight to the role of microbes in the methane exchange in trees : evidence from metagenomic sequencing

Methane (CH4) exchange in tree stems and canopies and the processes involved are among the least understood components of the global CH4 cycle. Recent studies have focused on quantifying tree stems as sources of CH4 and understanding abiotic CH4 emissions in plant canopies, with the role of microbial in situ CH4 formation receiving less attention. Moreover, despite initial reports revealing CH4 consumption, studies have not adequately evaluated the potential of microbial CH4 oxidation within trees. In this paper, we discuss the current level of understanding on these processes. Further, we demonstrate the potential of novel metagenomic tools in revealing the involvement of microbes in the CH4 exchange of plants, and particularly in boreal trees. We detected CH4-producing methanogens and novel monooxygenases, potentially involved in CH4 consumption, in coniferous plants. In addition, our field flux measurements from Norway spruce (Picea abies) canopies demonstrate both net CH4 emissions and uptake, giving further evidence that both production and consumption are relevant to the net CH4 exchange. Our findings, together with the emerging diversity of novel CH4-producing microbial groups, strongly suggest microbial analyses should be integrated in the studies aiming to reveal the processes and drivers behind plant CH4 exchange.Peer reviewe

The effect of substrate pre-treatment on durability of rubber-stainless steel adhesion

In many applications, rubber linings protect metal surfaces from the environment and prolong the service life of the metal components significantly. The loss of adhesion and resulting premature failure at the rubber-metal interface may generate an un-planned shutdown and production losses. This work focuses on the effect of various sand blasting methods on the long-term adhesion between bromobutyl rubber and stainless steel in a hot and humid environment. Softer austenitic stainless steel and harder, chemically more resistant super duplex stainless steel grades were used as substrates. It was found, that the developed interfacial area ratio Sdr, which is the additional surface area contributed by the texture as compared to the planar definition area, had the best correlation with the sand blasting media characteristics, namely to the hardness. The proportionality between other sand blasting medium characteristics and the Sdr value was poor. The initial adhesion between the rubber and the substrates was defined by the cohesive strength of the rubber and unaffected by the substrate characteristics and the sand blasting medium contaminants on the substrates. After a 4–12-week exposure in hot and humid environment, the use of corrosive sand blasting medium (steel grit) resulted in significant adhesion loss whereas the use of inert sand blasting media (feldspar or corundum) maintained the adhesion better. However, the adhesion system at the interface degraded causing performance loss. Neither the better corrosion resistance of super duplex stainless steel nor increased surface roughness improved the reliability of rubber lining in extreme conditions.acceptedVersionPeer reviewe

Spondylus crassisquama Lamarck, 1819 as a microecosystem and the effects of associated macrofauna on its shell integrity: isles of biodiversity or sleeping with the enemy?

In May 2009, we studied the bivalve Spondylus crassisquama and its relevance for macrobenthic biodiversity off the north Ecuadorian coast. We found that the large and heavy shells offer an exclusive substrate for numerous epibiont species and highly specialized carbonate-drilling endobiont species (71 species in total), which is a distinctly different and much more diverse habitat than the surrounding sandy bottoms (13 species, 4 of them found in both habitats). This is reflected by a Bray–Curtis dissimilarity index of 0.88. We discuss in detail the live habits of all 9 species of drilling endobionts that we found, and conclude that these can be seen as true mutualists, with the exception of boring sipunculids and bivalves. To further illustrate this complex co-existence, we visualize and quantify for the first time the tremendous effects of boring organisms on the shell structure of S. crassisquama by means of magnetic resonance imaging and a video appendix is provided