Probing polymer chain constraint and synergistic effects in nylon 6-clay nanocomposites and nylon 6-silica flake sub-micro composites with nanomechanics

In this study, we report that a synergistic effect exists in the surface mechanical properties of nylon 6–clay nanocomposites (NC) that can be shown by nanomechanical testing. The hardness, elastic modulus, and nanoindentation creep behavior of nylon 6 and its nanocomposites with different filler loading produced by melt compounding were contrasted to those of model nylon 6 sub-microcomposites (SMC) reinforced by sub-micro-thick silica flakes in which constraint cannot occur due to the difference in filler geometry. Polymer chain constraint was assessed by the analysis of nanoindentation creep data. Time-dependent creep decreased with increasing the filler loading in the NC consistent with the clay platelets exerting a constraint effect on the polymer chains which increases with filler loading. In contrast, there was no evidence of any reduced time-dependent creep for the SMC samples, consistent with a lack of constraint expected due to much lower aspect ratio of the silica flake

Large Networks of Diameter Two Based on Cayley Graphs

In this contribution we present a construction of large networks of diameter two and of order $\frac{1}{2}d^2$ for every degree $d\geq 8$, based on Cayley graphs with surprisingly simple underlying groups. For several small degrees we construct Cayley graphs of diameter two and of order greater than $\frac23$ of Moore bound and we show that Cayley graphs of degrees $d\in\{16,17,18,23,24,31,\dots,35\}$ constructed in this paper are the largest currently known vertex-transitive graphs of diameter two.Comment: 9 pages, Published in Cybernetics and Mathematics Applications in Intelligent System

Directing Selectivity of Electrochemical Carbon Dioxide Reduction Using Plasmonics

Catalysts for electrochemical carbon dioxide reduction in aqueous electrolytes suffer from high energy input requirements, competition with hydrogen evolution from water reduction, and low product selectivity. Theory suggests that plasmonic catalysts can be tuned to selectively lower the energy barrier for a specific reaction in a set of competitive reactions, but there has been little experimental evidence demonstrating plasmon-driven selectivity in complicated multielectron electrochemical processes. Here, the photoactivity at a plasmonically active silver thin film electrode at small cathodic potentials selectively generates carbon monoxide while simultaneously suppressing hydrogen production. At larger cathodic potentials, the photoactivity promotes production of methanol and formate. Methanol production is observed only under illumination, not in dark conditions. The preference of the plasmonic activity for carbon dioxide reduction over hydrogen evolution and the ability to tune plasmonic activity with voltage demonstrates that plasmonics provide a promising approach to promote complex electrochemical reactions over other competing reactions

On the logarithmic probability that a random integral ideal is A\mathscr A-free

This extends a theorem of Davenport and Erd\"os on sequences of rational integers to sequences of integral ideals in arbitrary number fields $K$. More precisely, we introduce a logarithmic density for sets of integral ideals in $K$ and provide a formula for the logarithmic density of the set of so-called $\mathscr A$-free ideals, i.e. integral ideals that are not multiples of any ideal from a fixed set $\mathscr A$.Comment: 9 pages, to appear in S. Ferenczi, J. Ku{\l}aga-Przymus and M. Lema\'nczyk (eds.), Chowla's conjecture: from the Liouville function to the M\"obius function, Lecture Notes in Math., Springe

Unraveling the Cationic and Anionic Redox Reactions in a Conventional Layered Oxide Cathode

Increasing interest in high-energy lithium-ion batteries has triggered the demand to clarify the reaction mechanism in battery cathodes during high-potential operation. However, the reaction mechanism often involves both transition-metal and oxygen activities that remain elusive. Here we report a comprehensive study of both cationic and anionic redox mechanisms of LiNiO2 nearly full delithiation. Selection of pure LiNiO2 removes the complication of multiple transition metals. Using combined X-ray absorption spectroscopy, resonant inelastic X-ray scattering, and operando differential electrochemical mass spectrometry, we are able to clarify the redox reactions of transition metals in the bulk and at the surface, reversible lattice oxygen redox, and irreversible oxygen release associated with surface reactions. Many findings presented here bring attention to different types of oxygen activities and metal-oxygen interactions in layered oxides, which are of crucial importance to the advancement of a Ni-rich layered oxide cathode for high capacity and long cycling performance

Fibrous Cellular Structures are Found in a Commercial Fruit Smoothie and Remain Intact during Simulated Digestion

The intactness of cell wall structures in foods has important repercussions for nutrient digestion and availability. In this study, we show the presence of intact cell wall structures in a commercial fruit smoothie (blend of banana, mango, orange and apple) and fruit purée (banana, mango), but not in fruit juices (apple or orange). Small clusters of cells were observed in fresh crushed fruit (banana, mango, and apple), the size of the cluster dependent on the type of fruit. When the smoothie was subjected to simulated gastro-intestinal digestion, cell wall structures were found abundantly even after 16 hrs of agitated incubation with digestive enzymes (protease, amylase and amyloglucosidase). Total dietary fibre (TDF) content of the smoothie was measured using the AOAC (991.43) and integrated fibre (IF) analysis methods. TDF-AOAC value was significantly lower (1.61%) than the TDF-IF (2.22%), but the ratio of insoluble to soluble dietary fibre (IDF: SDF) was consistently 1:3. Disruption of the cell wall structures in the smoothie by high shear homogenisation led to a 68% reduction in viscosity, 30% reduction in TDF content and a 10% increase in SDF. These experiments suggest that cell wall structures similar to those observed in crushed fruit are preserved during commercial smoothie manufacture and are retained during digestion. Their presence may have implications for fibre quantification and fibre functionality in the gut. We discuss the need to consider fibre structure, as well as content, when evaluating the nutritional properties of fruit and their products

Do red deer stags (Cervus elaphus) use roar fundamental frequency (F0) to assess rivals?

It is well established that in humans, male voices are disproportionately lower pitched than female voices, and recent studies suggest that this dimorphism in fundamental frequency (F0) results from both intrasexual (male competition) and intersexual (female mate choice) selection for lower pitched voices in men. However, comparative investigations indicate that sexual dimorphism in F0 is not universal in terrestrial mammals. In the highly polygynous and sexually dimorphic Scottish red deer Cervus elaphus scoticus, more successful males give sexually-selected calls (roars) with higher minimum F0s, suggesting that high, rather than low F0s advertise quality in this subspecies. While playback experiments demonstrated that oestrous females prefer higher pitched roars, the potential role of roar F0 in male competition remains untested. Here we examined the response of rutting red deer stags to playbacks of re-synthesized male roars with different median F0s. Our results show that stags’ responses (latencies and durations of attention, vocal and approach responses) were not affected by the F0 of the roar. This suggests that intrasexual selection is unlikely to strongly influence the evolution of roar F0 in Scottish red deer stags, and illustrates how the F0 of terrestrial mammal vocal sexual signals may be subject to different selection pressures across species. Further investigations on species characterized by different F0 profiles are needed to provide a comparative background for evolutionary interpretations of sex differences in mammalian vocalizations

An adaptive prefix-assignment technique for symmetry reduction

This paper presents a technique for symmetry reduction that adaptively assigns a prefix of variables in a system of constraints so that the generated prefix-assignments are pairwise nonisomorphic under the action of the symmetry group of the system. The technique is based on McKay's canonical extension framework [J.~Algorithms 26 (1998), no.~2, 306--324]. Among key features of the technique are (i) adaptability---the prefix sequence can be user-prescribed and truncated for compatibility with the group of symmetries; (ii) parallelizability---prefix-assignments can be processed in parallel independently of each other; (iii) versatility---the method is applicable whenever the group of symmetries can be concisely represented as the automorphism group of a vertex-colored graph; and (iv) implementability---the method can be implemented relying on a canonical labeling map for vertex-colored graphs as the only nontrivial subroutine. To demonstrate the practical applicability of our technique, we have prepared an experimental open-source implementation of the technique and carry out a set of experiments that demonstrate ability to reduce symmetry on hard instances. Furthermore, we demonstrate that the implementation effectively parallelizes to compute clusters with multiple nodes via a message-passing interface.Comment: Updated manuscript submitted for revie