Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant. We also use SiO2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.     

Mimicking the biomineralization of aragonite (calcium carbonate) using reverse-micelles under ambient conditions

Reverse micelles have been used, for the first time, to mimic the conditions suitable for the low-temperature (40 degrees C) synthesis of the high temperature and high pressure orthorhombic phase of calcium carbonate (aragonite) normally crystallizing in the sea as abalone shells and as natural pearls. The aragonite phase undergoes morphological changes under higher temperatures with long Y-junctions (at 40 degrees C) to shorter rod-like structures (at 85 degrees C). Pure calcite is obtained at higher reaction temperature. At a lower temperature (5 degrees C) homogeneous and monodisperse spheres of vaterite is obtained. The spherical particles after longer aging (168 h) aggregate to form nanorods and the self assembly is clearly seen at various stages by electron microscopic images.     

In vitro Digestibility of Raw Starches Extracted from five Yam (Dioscorea spp.) Species Grown in Jamaica

Starch granules from Round leaf yellow yam, Negro yam, Sweet yam, Bitter yam and Chinese yam grown in Jamaica were isolated and characterized. The amylose content, granular size, crystallinity, and digestibility by α‐amylase were determined. The granules obtained were of three crystalline types. Round leaf yellow yam, Negro yam and Sweet yam were found to be type‐B, while Chinese yam and Bitter yam were type‐C and type‐A, respectively. Round leaf yellow yam had the highest amylose content (26.5%) while Chinese yam had the lowest (11.1%). The granule size varied between 1–3 μm for Chinese yam and 16–42 μm for Round leaf yellow yam. Significant variations in digestibility of the granules were observed. Raw starches from Chinese yam and Bitter yam were the most susceptible to α‐amylase digestion (porcine pancreatic α‐amylase, pH 5.5, 0.02% CaCl₂, 40°C, 24 h) with 21.27 ± 0.01% and 18.11 ± 0.02% degradation, respectively, while Round leaf yellow yam, Negro yam and Sweet yam starches were the least susceptible, with 13.74 ± 0.03%, 14.98 ± 0.08%, and 15.32 ± 0.04% enzymatic degradation, respectively.     

A design and implementation of fully programmable switched-currentIIR filters

An approach to switched-current filter design based on digital multiply-accumulator and delay blocks is presented. The characteristics of the filter are made fully programmable by simply changing the ratios of the coefficient transistors. To reduce the effect of switch charge injection and channel-length modulation, a high-performance, single-ended differential, switched-current memory cell is developed and used as a basic building block. To reduce the chip area and to maintain the required accuracy of the coefficients, an array consisting of three different sizes of transistors is designed instead of using a unit transistor array as coefficient transistors. An experimental prototype infinite impulse response filter array consisting of six second-order switched-current sections is designed and fabricated with a standard 1.2-μ CMOS process technology. A hard-wiring technique is used to program the filters. The test results show that the characteristics of the filters satisfy the design requirements     

Microstructure-Property Relations of Hot-Pressed Silicon Carbide-Aluminum Nitride Compositions at Room and Elevated Temperatures

A series of SiC-AlN compositions of 0, 10, 25, 50, 75, 90, and 100 mol% AlN were hot pressed at 2100°C for a 1 h soak at a pressure of 35 MPa under vacuum. 2H-wurtzite SiC-AlN solid-solution structures were formed for compositions with 25-100 mol% AlN. The associated lattice parameters for these solid solutions followed Vegard's law. The microstructures varied with composition; the number of needlelike grains decreased for compositions up to 25 mol% AlN and the amount of equiaxed grains increased for compositions with 25–100 mol% AlN. Densities for all the specimens were >99% of the theoretical density. Coefficients of thermal expansion varied from 4.80 × 10^-6/°C to 6.25 × 10^-6/°C in the 20°-1400°C range. Young's moduli varied from 451 GPa to 320 GPa at room temperature (RT) and retained 98%, 96%, and 94% of their RT values at 500°, 1000°, and 1250°C, respectively. These three properties correlated linearly with composition. RT microhardness varied from 21.6 GPa to 11.2 GPa and correlated linearly with composition within the solid-solution range. Flexural strengths increased from 487 MPa to 604 MPa from 0 mol% AlN to 25 mol% AlN and then decreased to 284 MPa for 100 mol% AlN. At 1250°C, flexural strengths decreased from 90% to 65% of the RT values. Fracture toughness increased from 3.6 MPa·m^1/2 to 4.2 MPa·m^1/2 from 0 mol% AlN to 10 mol% AlN and then decreased to 2.5 MPa·m^1/2 for 100 mol% AlN.     

Formation and decay of neutron—deficient nuclei Po and Pb

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A hybrid discontinuous spectral element method and filtered mass density function solver for turbulent reacting flows

Abstract

We present a novel hybrid scheme for the large eddy simulation (LES) of turbulent reacting flows. The scheme couples the discontinuous spectral element method (DSEM) solver for the unsteady compressible Navier-Stokes equations with a Monte Carlo particle filtered mass density function (FMDF) solver for the transport of reacting species. The method is capable of high-order simulations on unstructured grids. Mean particle estimate construction mimics the DSEM numerical procedure and utilizes variable basis functions. The scheme is tested on non-reacting and reacting Taylor-Green vortex flows. Studies of varying polynomial order, different basis functions for constructing particle estimates, and varying particle quantities are conducted. We demonstrate that a tent kernel, in conjunction with high polynomial order, produces the most accurate results. The chemically reacting simulations validate the hybrid scheme and demonstrate its applicability across a range of reaction regimes. The hybrid scheme's computational cost is 2.1 times the DSEM-LES solver.