Spatial relationships between polymers in Sitka spruce: proton spin-diffusion studies

The spatial arrangement of polymers in Sitka spruce (Picea sitchensis) was investigated by NMR proton spin-diffusion studies, supplemented by deuterium-exchange experiments monitored by FTIR spectroscopy. The FTIR spectra of earlywood sections after vapour-phase exchange with deuterium oxide showed that 43% of the hydroxyl groups were accessible to deuteration. This value is lower than predicted in the absence of aggregation of cellulose microfibrils into larger units, but greater than the predicted level of deuteration if 3.5-nm microfibrils surrounded by hemicellulose sheaths were aggregated into 4×4 arrays without space for deuterium oxide to penetrate between the microfibrils. The rate of proton spin diffusion between lignin and cellulose was consistent with the presence of microfibril arrays with approximately these dimensions and with lignin located outside them, in both earlywood and latewood. Proton spin-diffusion data for hemicelluloses were complicated by difficulties in assigning signals to glucomannans and xylans, but there was evidence for the spatial association of one group of hemicelluloses, including acetylated glucomannans, with cellulose surfaces, while another group of hemicelluloses was in spatial proximity to lignin. These data are consistent with a number of nanoscale models for the Sitka spruce cell wall, including a model in which glucomannans are associated with microfibril surfaces within the aggregate and water can penetrate partially between these surfaces, and one in which all non-cellulosic polymers and water are excluded from the interior of each microfibril aggregate

A comparison of coaxial and conventional rotor performance

The performance of a coaxial rotor in hover, in steady forward flight, and in level, coordinated turns is contrasted with that of an equivalent, conventional rotor with the same overall solidity, number of blades, and blade aerodynamic properties. Brown's vorticity transport model is used to calculate the profile, induced, and parasite contributions to the overall power consumed by the two systems, and the highly resolved representation of the rotor wake that is produced by the model is used to relate the observed differences in the performance of the two systems to the structures of their respective wakes. In all flight conditions, all else being equal, the coaxial system requires less induced power than the conventional system. In hover, the conventional rotor consumes increasingly more induced power than the coaxial rotor as thrust is increased. In forward flight, the relative advantage of the coaxial configuration is particularly evident at pretransitional advance ratios. In turning flight, the benefits of the coaxial rotor are seen at all load factors. The beneficial properties of the coaxial rotor in forward flight and maneuver, as far as induced power is concerned, are a subtle effect of rotor-wake interaction and result principally from differences between the two types of rotor in the character and strength of the localized interaction between the developing supervortices and the highly loaded blade-tips at the lateral extremities of the rotor. In hover, the increased axial convection rate of the tip vortices appears to result in a favorable redistribution of the loading slightly inboard of the tip of the upper rotor of the coaxial system

Subjective and Non-subjective Information in Children’s Allegations of Abuse

In this study, we were interested in how interviewers elicit subjective information in investigations of child abuse (e.g., descriptions of thoughts, emotions, opinions). Sixty-one interviews of children aged 4-12 years old were analyzed to determine the amount of subjective information versus non-subjective event details reported, and the type of question that elicited the information. Interviewers elicited more non-subjective than subjective information, although there was more focus on subjective information in the rapport-building phase than in the substantive phase when the allegations were elicited. Interviewer prompts and child responsiveness was congruent such that non-subjective questions elicited more non-subjective information, and subjective interviewer questions elicited more subjective information. The presence of subjective information in children’s testimony can influence children’s credibility, and the results of this study demonstrate that forensic interviewers play a significant part in the level of subjective information children provide

Network Marketing on a Small-World Network

We investigate a dynamic model of network marketing in a small-world network structure artificially constructed similarly to the Watts-Strogatz network model. Different from the traditional marketing, consumers can also play the role of the manufacturer's selling agents in network marketing, which is stimulated by the referral fee the manufacturer offers. As the wiring probability $\alpha$ is increased from zero to unity, the network changes from the one-dimensional regular directed network to the star network where all but one player are connected to one consumer. The price $p$ of the product and the referral fee $r$ are used as free parameters to maximize the profit of the manufacturer. It is observed that at $\alpha=0$ the maximized profit is constant independent of the network size $N$ while at $\alpha \neq 0$, it increases linearly with $N$. This is in parallel to the small-world transition. It is also revealed that while the optimal value of $p$ stays at an almost constant level in a broad range of $\alpha$, that of $r$ is sensitive to a change in the network structure. The consumer surplus is also studied and discussed.Comment: 12 pages, to appear in Physica

Spectral densities of scale-free networks

The spectral densities of the weighted Laplacian, random walk and weighted adjacency matrices associated with a random complex network are studied using the replica method. The link weights are parametrized by a weight exponent $\beta$. Explicit results are obtained for scale-free networks in the limit of large mean degree after the thermodynamic limit, for arbitrary degree exponent and $\beta$.Comment: 14 pages, two figure

MgB2 tunnel junctions with native or thermal oxide barriers

MgB2 tunnel junctions (MgB2/barrier/MgB2) were fabricated using a native oxide grown on the bottom MgB2 film as the tunnel barrier. Such barriers therefore survive the deposition of the second electrode at 300oC, even over junction areas of ~1 mm2. Studies of such junctions, and those of the type MgB2/native or thermal oxide/metal (Pb, Au, or Ag) show that tunnel barriers grown on MgB2 exhibit a wide range of barrier heights and widths.Comment: 9 pages, 3 figure

Scale-free networks with a large- to hypersmall-world transition

Recently there have been a tremendous interest in models of networks with a power-law distribution of degree -- so called "scale-free networks." It has been observed that such networks, normally, have extremely short path-lengths, scaling logarithmically or slower with system size. As en exotic and unintuitive example we propose a simple stochastic model capable of generating scale-free networks with linearly scaling distances. Furthermore, by tuning a parameter the model undergoes a phase transition to a regime with extremely short average distances, apparently slower than log log N (which we call a hypersmall-world regime). We characterize the degree-degree correlation and clustering properties of this class of networks.Comment: errors fixed, one new figure, to appear in Physica