Nacre in Mollusk Shells as a Multilayered Structure with Strain Gradient

How do living organisms attain the complicated shapes of grown bio‐composites? This question is answered when studying the mechanics of the nacre layer in the bivalve mollusk shells. In this study, the internal strains/stresses across the shell thickness are profiled as a function of depth by strain gauge measurements during controlled etching in the selected areas. Measurements of stress release under etching provide clear evidence that the investigated shells, in fact, are strained multilayered structures, which are elastically bent due to the forces evolving at the organic/inorganic interfaces. The stresses are mostly concentrated in the “fresh” nacre sub‐layers near the inner surface of the shell adjacent to the mollusk mantle. This analysis unexpectedly shows that the elastic bending of the nacre layer is due to strain gradients which are originated in the gradual in‐depth changes of the thickness of ceramic lamellae. The changes mentioned were directly observed by scanning electron microscopy. By this sophisticated design of the ultra‐structure of the nacre layer, the bowed shape of the bivalve shells is apparently achieved.     

Highly Efficient Ge-Rich Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te Thermoelectric Alloys

The search for alternative energy sources is presently at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This paper is concerned with the development of highly efficient p-type Ge _x Pb_1−x Te alloys for thermoelectric applications, using spark plasma sintering. The carrier concentration of GeTe was varied by alloying of PbTe and/or by Bi₂Te₃ doping. Very high ZT values up to ~1.8 at 500°C were obtained by doping Pb_0.13Ge_0.87Te with 3 mol% Bi₂Te₃.     

Self‐Assembling,Bioinspired Wax Crystalline Surfaces with Time‐Dependent Wettability

One of the most fascinating properties of materials in nature is the superhydrophobic and self‐cleaning capabilities of different plant surfaces. This is usually achieved by the hydrophobic cuticles that are made of cutin and contain wax crystals both within them and on their surfaces. Here, bioinspired n‐hexatriacontane wax films are deposited via thermal evaporation and it is shown that the surface evolves in time via self‐assembly. This leads to a dramatic change in the wetting properties with a transition from hydrophobic to superhydrophobic characteristics, which takes place within several days at room temperature. This phenomenon is investigated and strain‐induced recrystallization is proposed to be the mechanism for it. This work could become the basis for the inspiration and production of tuned, time‐dependant, temperature‐sensitive, variable‐wettability surfaces.     

Structural Evolution Following Spinodal Decomposition of the Pseudoternary Compound (Pb0.3Sn0.1Ge0.6)Te

Pseudoternary (Ge,Sn,Pb)Te compounds display favorable thermoelectric properties. Spinodal decomposition in the quasiternary (Ge,Sn,Pb)Te system is at the origin of a wide solubility gap at low Sn concentrations. The structural evolution of the spinodal decomposition was investigated as a function of aging time at 500°C, using x-ray diffraction, electron microscopy, and scanning electron microscopy. The evolution of the structure at 500°C consists initially of a short diffusion-controlled demixing stage into Pb- and Ge-rich coherent areas, with compositions corresponding to the inflection points of the free-energy curve. The Pb-rich areas adopt configurations associated with the directions of the soft elastic moduli of the cubic compound. Both the Pb- and Ge-rich areas are supersaturated and undergo in a second stage a nucleation and growth process and give rise to a biphased structure with equilibrium compositions corresponding to the boundaries of the miscibility gap. The resulting Pb-rich areas display a relatively stable microstructure suggesting the presence of long-range interactions between the Pb-rich precipitates in the Ge-rich matrix.     

Multichannel, Single Tral Event Related Potential Classification

We report on the effect of electrode placement and number of electrodes on the classification of single trial event related potentials (ERP's). The subjects read propositions relating fictitious people and their occupations while ERP's were recorded. The subjects decided if the proposition was correct or incorrect and responded as per instructions. The single trial, multichannel ERP data were classified using various methods, e. g., hold-out, leave-one-out, resubstitution. Several other factors were examined to determine their effect on ERP classification, including taking a majority vote among channels, using the single best channel, and averaging the data across channels for a single ERP. The results from other experiments are compared to those presented here.     

From data to knowledge: The interaction between data management systems in educational institutions and the delivery of quality education

No school is an island; it is a part of a continuum or a pipeline of institutions which together form an educational pipeline through which groups of students pass. To turn a body of data into useful information for knowledge-based decision-making at any level, data must be collected, organised, analysed and reflected upon. The purpose of this paper is to discuss how schools and other educational institutions can not only collect better data but learn how to transform that data so that the information held within can be effectively shared among all stakeholders. This process will help to ensure that the school and the entire education system provide a more seamless and effective educational pipeline for students, and ultimately improve the quality of education delivered in the country as a whole.     

Nondestructive quality evaluation of fresh prunes by NMR spectroscopy

The potential for utilizing nuclear magnetic resonance measurements for evaluating the quality of fresh prunes was investigated. In a 2 T magnetic flux density, the chemical shift between proton hydrogens of soluble solids and those of water is less than 100 Hz. The band width of the water resonance spectrum of fruits is relatively large and therefore it is difficult to resolve between the spectral peaks of water and soluble solids. Measurements with a 100 mm Birdcage coil failed to resolve between the resonance peaks of soluble solids and water. Good resolution was achieved with a 20 mm diameter Surface coil. Signals (free induction decay) of 30 sugar prunes were acquired, and the spectra were calculated. Tuning and matching the coil before each measurement were not necessary, and the results were better when the magnetic field was not shimmed. The ratio of the soluble solids peak height to the water peak height correlated well (r = 0.907) with the soluble solids content of the prunes, as estimated by a refractometer.     

Combinatorial Optimization and Performance Analysis of a Multi-arm Cartesian Robotic Fruit Harvester—Extensions of Graph Coloring

A mobile melon robotic harvester consisting of multiple Cartesian manipulators, each with three degrees of freedom, is being developed. In order to design an optimal robot in terms of number of arms, manipulator capabilities, and robot speed, a method of allocating the fruits to be picked by each manipulator in a way that yields the maximum harvest has been developed. Such a method has already been devised for a multi-arm robot with 2DOF each. The maximum robotic harvesting problem was shown there to be an example of the maximum k-colorable subgraph problem (MKCSP) on an interval graph. However, for manipulators with 3DOF, the additional longitudinal motion results in variable intervals. To overcome this issue, we devise a new model based on the color-dependent interval graph (CDIG). This enables the harvest by multiple robotic arms to be modeled as a modified version of the MKCSP. Based on previous research, we develop a greedy algorithm that solves the problem in polynomial time, and prove its optimality using induction. As with the multi-arm 2DOF robot, when simulated numerous times on a field of randomly distributed fruits, the algorithm yields a nearly identical percentage of fruit harvested for given robot parameters. The results of the probabilistic analysis developed for the 2DOF robot was modified to yield a formula for the expected harvest ratio of the 3DOF robot. The significance of this method is that it enables selecting the most efficient actuators, number of manipulators, and robot forward velocity for maximal robotic fruit harvest.