Absorption/desorption of calcium ions on polypyrrole-loaded reticulated vitreous carbon

Polypyrrole/polystyrene sulfonate-loaded reticulated vitreous carbon electrodes RVC/PPy/PSS were studied as electrochemical cation exchangers for the absorption of Ca²⁺ ions from aqueous solutions. Two grades of RVC were used mainly with 20 and 45 PPI. The preparation and characterization of the PPy/PSS layers on RVC are described. The structure and morphology of the porous electrodes were characterized using cyclic voltammetry (CV) and scanning electron microscopy (SEM). The potential dependent absorption and desorption of Ca²⁺ on RVC/PPy/PSS electrodes was studied in 0.1 M CaCl₂ solution using chronoamperometry and atomic adsorption spectroscopy (AAS). The extent of Ca²⁺ ions absorbed into RVC/PPy/PSS was found to increase with decreasing absorption potential, the specific surface area and the extent of polymer loading. Recovery of the RVC/PPy/PSS electrode was performed by anodic polarization at potentials at which Ca²⁺ ions are desorbed. The coulomb efficiency for the Ca²⁺ desorption process was found to be higher than that for the Ca²⁺ absorption process. From these results the feasibility of using RVC/PPy/PSS for water softening was determined under the prevailing experimental conditions.     

On the Performance of FFT/DWT/DCT-based OFDM Systems with Chaotic Interleaving and Channel Estimation Algorithms

The efficiency of data transmission over fading channels in orthogonal frequency division multiplexing (OFDM) systems depends on the employed interleaving method. In this study, we propose an improved chaotic interleaving scheme which aims to improve the performance of OFDM system under fading channel. In the proposed scheme, the binary data is interleaved with chaotic Baker map prior to the modulation process. In the sequel, significant degree of encryption is being added during data transmission. The performance of the proposed approach is tested on the conventional fast Fourier transform OFDM, discrete wavelet transform OFDM, and discrete cosine transform OFDM with and without chaotic interleaving. Furthermore, an expectation–maximization (EM) algorithm is proposed for improving channel impulse response (CIR) estimation based on a maximum likelihood principle. The proposed scheme makes use of EM algorithm to update the channel estimates until convergence is reached. The simulation results show the efficiency of the proposed algorithms under Rayleigh fading environments where the symbol error rate essentially coincides with that of the perfect channel case after the fifth EM iteration.     

Phase I Analysis of Individual Observations with Missing Data

The effect of the methods for handling missing values on the performance of Phase I multivariate control charts has not been investigated. In this paper, we discuss the effect of four imputation methods: mean substitution, regression, stochastic regression and the expectation maximization algorithm. Estimates of mean vector and variance covariance matrix from the treated data set are used to estimate the unknown parameters in the Hotelling's T² chart statistic. Based on a Monte Carlo simulation study, the performance of each of the four methods is investigated in terms of its ability to obtain the nominal in‐control and out‐of‐control overall probability of a signal. We consider three sample sizes, five levels of the percentage of missing values and three types of variable numbers. Our simulation results show that the stochastic regression method has the best overall performance among all the competing methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics

Stretchable conductive fibers have received significant attention due to their possibility of being utilized in wearable and foldable electronics. Here, highly stretchable conductive fiber composed of silver nanowires (AgNWs) and silver nanoparticles (AgNPs) embedded in a styrene–butadiene–styrene (SBS) elastomeric matrix is fabricated. An AgNW‐embedded SBS fiber is fabricated by a simple wet spinning method. Then, the AgNPs are formed on both the surface and inner region of the AgNW‐embedded fiber via repeated cycles of silver precursor absorption and reduction processes. The AgNW‐embedded conductive fiber exhibits superior initial electrical conductivity (σ₀ = 2450 S cm^?1) and elongation at break (900% strain) due to the high weight percentage of the conductive fillers and the use of a highly stretchable SBS elastomer matrix. During the stretching, the embedded AgNWs act as conducting bridges between AgNPs, resulting in the preservation of electrical conductivity under high strain (the rate of conductivity degradation, σ/σ₀ = 4.4% at 100% strain). The AgNW‐embedded conductive fibers show the strain‐sensing behavior with a broad range of applied tensile strain. The AgNW reinforced highly stretchable conductive fibers can be embedded into a smart glove for detecting sign language by integrating five composite fibers in the glove, which can successfully perceive human motions.     

Consolidation of nano-crystalline copper powder by cold and hot pressing

This paper investigates preparation of bulk nano-structured Cu through cold and hot pressing. In particular, the effects of different consolidation parameters, such as temperature and pressure, on the properties of bulk nano-structured samples were studied. Microstructure, density, hardness, and electrical conductivity showed strong dependence on the consolidation parameters. All results were compared with those for micron-size Cu powder. Relatively fully dense compacts with minimal grain growth up to 57 nm, maximum hardness of 83 Vickers, and electrical resistivity of 1.93 × 10⁻⁸ Ωm could be achieved.     

Experimental and theoretical investigation of running-in

In this paper, the running-in and steady-state wear in the mixed-EHL line contact problem are analytically and experimentally studied. An experimental apparatus is designed and built to investigate the transient wear process during the initial stage of contact of two rollers with fresh surfaces as well as the contact of broken-in surfaces, when wear rate becomes steady. Seven experiments are conducted with five running-in experiments on fresh rollers and two steady-state experiments on the run-in rollers. The results of experimental tests and a series of simulations of an analytical model that uses the load-sharing concept and accounts for plastic deformation of asperities during the running-in stage are presented. The comparison of experimentally measured wear weight, wear depth, surface roughness, friction coefficient, and surface temperature of these seven experiments are shown to be in good agreement with the simulation results.     

Intergranular corrosion behavior of the 7075-T6 aluminum alloy under different annealing conditions

The effect of annealing conditions producing various grain sizes on the intergranular corrosion behavior of high-strength aluminum alloy type 7075-T6 was investigated using electrochemical polarization techniques. Aluminum alloy specimens with large grain size exhibited lower breakdown potentials in deaerated 0.5 M NaCl solution. The breakdown potentials decreased with increasing grain size. Microscopic observations of the exposed surfaces during potentiostatic polarization testing showed that the coarse grain structure promotes intergranular crack growth.     

Barrier properties of poly(vinyl alcohol) membranes containing carbon nanotubes or activated carbon

Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations.     

Synthesis and characterization of alumina-coated carbon nanotubes and their application for lead removal

Alumina-coated multi-wall carbon nanotubes were synthesized and characterized by scanning electron microscopy, X-ray diffraction, and FTIR. They were used as an adsorbent for the removal of lead ions from aqueous solutions in two modes, batch and fixed bed. In the batch mode, experiments were carried out to investigate the effect of contact time, agitation speed, adsorbent dosage and solution pH on the removal of lead. The coated nanotubes exhibit better removal ability over uncoated. For fixed-bed columns, thickness of the layer and flow rate were investigated. Increasing the thickness and decreasing the flow rate enhanced the removal of lead. The prepared adsorbent displayed the main advantage of separation convenience when a fixed-bed column was used compared to the batch adsorption treatment.