The behaviour of copper-zinc alloys in alkaline solutions upon alternate anodic and cathodic polarization

Galvanostatic cyclic anodic and cathodic polarization curves for four CuZn alloys are traced in alkaline solutions of different concentrations. The anodic behaviour of the first three alloys, with 15.9, 46.8 and 50.5 wt% Zn, resembles that of pure Cu. Oxidation arrests, corresponding to the formation of Cu₂O, Cu(OH)₂, HCuO₂? and Cu₂O₃, are recorded before the evolution of O₂ on the passive electrode. The Zn of the electrodes does not develop its oxidation arrest. It affects, however, the behaviour of the alloys in a number of ways. The results are explained on the basis of kinetic interactions, and in relation to the phase diagram of the Cu-Zn system.The fourth alloy, with 85.9 wt% Zn (ε + η phases), yields upon oxidation in concentrated alkali solutions a series of five or six arrests. The first two of these represent the oxidation of the Zn of the η- and ε-phases, respectively. Calculations have shown that the activity of the Zn in the ε-phase is ～ 4.6 × 10^?10 times that of the free η-phase. The other oxidation steps correspond to the oxidation of the Cu of the alloy. In 0.1N NaOH the same alloy behaves as if it was pure Zn.Critical current densities for the passivation of Cu, Zn and the four alloys are determined in 0.1M Na₂SO₄. The ability of the tested materials to withstand electrochemical dissolution decreases in the succession: Alloy I > Alloy III > Cu > Alloy II > Alloy IV > Zn.     

An investigation into the eigen-nature of cracked composite beams

It is known that the presence of cracks in composite structures introduces local flexibility associated with the changes in the dynamic characteristics of composite structures. However the nature and variations of the natural frequencies due to the presence of cracks, are still under discussion and analysis.

The present work introduces an attempt to study the variations in the eigen-nature of cracked composite beams due to different crack depths and locations. A numerical and experimental investigation has been made. The numerical finite element technique is utilized to compute the eigen pairs of laminated composite beams through several state of cracks. The model is based on elastic-plastic fracture mechanics techniques in order to consider the crack tip plasticity in the analysis. A finite element model has been developed to formulate the stiffness matrices for single edge cracked structural elements using transfer matrix theory. These matrices take into account the effects of axial, flexural and shear deformations due to crack presence. The present model has been applied to investigate the effects of state of crack, lamina code number, boundary condition on the dynamic behavior of composite beams.

The experimental tests and frequency response spectrums (FRS) is displayed on [FFT] analyzer. In experimental work the eigen pairs versus several state of cracks with various code number are measured using inductive hammering technique. The results show that the changes of the eigen parameters provide a proper indicator for detection and predication the current state of crack.     

Fourier transform infrared spectroscopic and AC electrical conductivity studies of chitin and its derivatives

The vibrational modes and the purity index of chitin and its derivatives as biopolymers are studied by Fourier transform infrared spectroscopy in the wavenumber range from 4000 to 400 cm^?1. The absorption bands of chitin and its derivatives are assigned. New bands appeared at 1419, 1209, 915, and 800 cm^?1 for chitin derivatives due to the change of vibrational modes. The purity indexes are calculated from the ratio of the absorption band of C = O at 1662 cm^?1 and OH at 3443 cm^?1. Generally, the purity indexes of chitin derivatives are higher than that of chitin, which is due to the decrease of OH. The dielectric properties such as the real part of the dielectric constant (ε′) and loss tangent tan (δ) are measured as a function of temperature at different frequencies ranging from 200 to 2000 kHz. The increase of (ε′) and tan (δ) with increasing temperature is discussed on the basis of increasing polarizability and the decrease with increasing frequency can be attributed to the dielectric dispersion. AC electrical conductivities as a function of the reciprocal of the absolute temperature are also discussed. The mechanism of the charge carrier is discussed as a tunneling model in the temperature range from 300 to 360 K. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 936–943, 2005     

Effect of grain size on the primary and secondary creep behavior of Sn–3 wt.% Bi alloy

The effect of grain size as well as creep temperature on the primary and secondary creep parameters of Sn–3 wt.% Bi alloy has been studied. It was found that the creep parameters α, β, and έ _s were decreased with increasing grain size. This was explained in view of the dislocation interaction with the defects and different inclusions in the matrix. For both the primary and secondary creep, the activation energies estimated indicate that the rate-controlling mechanism is the grain boundary-sliding mechanism.     

The effect of mixed diluent on the porous structure of crosslinked PMMA beads

Summary In this work copolymer beads, based on MMA (methyl methacrylate) and EGDM (ethylene glycol dimethacrylate), were prepared by suspension polymerization. A mixed solvent, composed of two different solvents, namely toluene and cyclohexane, was used as the diluent in the polymerization medium. The porous structure of the beads was found to be affected by the solvent composition used to dissolve the monomers initially. It was observed that the porosity and pore size increased gradually with the increase of cyclohexane content of the solvent composition. It was also detected that the pore radii changed from 2–10 nm to 700–1000 nm as the cyclohexane content of the diluent changed from nil to 100 % (v/v) respectively. These results indicate that pore size of the copolymer beads is a function of solvent composition. Received: 10 January 1999/Revised version: 15 February 2000/Accepted: 1 March 2000     

Relaxation phenomenon of poly(vinyl alcohol)/sodium carboxy methyl cellulose blend by thermally stimulated depolarization currents and thermal sample technique

The dipolar relaxation in poly(vinyl alcohol) (PVA), sodium carboxy methyl cellulose (NaCMC_s), and their blends were studied using a thermally stimulated depolarization current (TSDC) technique. The mutual effects of polarization conditions such as heating rate, poling temperature, time, and field on the properties of TSDC were investigated. Quantitative analysis of the experimental data is given in terms of dipolar and space charge polarization. A thermal sampling (TS) technique was applied to decompose the complex relaxations in individual polymers and their blend of 0.5/0.5 wt/wt into its normal distribution components. The activation energy of TS‐formed electrets was determined by fitting the experimental curve to Bucci and Fieschi equations. Peak parameters such as activation energy and preexponential factor τ₀ were obtained. A linear relationship between the activation energy and logarithm of the preexponential factor was found, thus confirming operation of the compensation law. In addition, by using the Eyring equation of the rate theory, the activation enthalpy ΔH^≠ and the activation entropy ΔS^≠ were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1342–1353, 2005     

A Cross Layer Scheduling Framework for Supporting Bursty Data Applications in WCDMA Networks

In future wireless networks multimedia applications are expected to finally dominate the overall traffic volume. Shared channels are more suitable for the transmission of this type of traffic, as they are able to periodically adjust their transmission rate. In this paper, we introduce a cross-layer framework for WCDMA based networks which aims to make the packet scheduling procedure more efficient. In addition to that, we further propose a traffic scheduling scheme which serves the connections not only according to their delay sensitivity, but also according to the predicted state of their wireless channel. The efficiency of the proposed scheme, in terms of average packet delay and channel utilization is verified via simulations.     

The Effect of Some Surfactants on the in- Vitro Properties of Double Compressed Tablets

The effect of different types and concentrations of some surface active agents as well as the method of surfactant incorporation on the in - vitro properties of aspirin tablets as a model for double compressed tablets was studied. The formulated tablets were evaluated using the U. S. P. official tests and some other selected non-official tests. These tests include: uniformity of weight, uniformity of content, disintegration, dissolution, hardness, friability and thickness. Incorporation of a low concentration (0.2 % w/w) of surface active agents i n the formulation of tablets decreased the disintegration time but did not affect their dissolution rate. Higher concentrations of surface active agents retarded the dissolutiono of tablets. Non ionic surfactants showed higher regarding effect than ionic surfactants . Changing the method of surfactant incorporation did not greatly affect the dissolution rate of tablets.     

Pitting Corrosion of Some α-Brasses in Neutral and Alkaline Solutions Containing Halide Ions

The pitting corrosion behaviour of some α-brasses (Cu%: 85, 70, 67, 63 and 60) in neutral and alkaline solution containing various halide ions was studied. The pitting corrosion resulted in dezincification in all cases and the pitting potential was found with few exceptions to increase in the order; Cu 60 < Cu 67, Cu 70 < Cu 63 < Cu 85 < Cu 100. Increase of pH was found to shift the pitting potential to more positive values and at highly enough pH values the pitting corrosion was inhabited in some cases. The instantaneous current, at constant potential and in absence of pitting was found to varies linearly with (1/time)^1/2 at time ?20 seconds. During the initial stage of pitting, the current was found to fit Engell-Stolica equation. The steady corrosion potentials in presence of Br^? and I^? ions were found to be nearly coincident with those of Cu/Cu halide couples while they were far from the theoretical values in presence of CI^? ions and they changed negligibly presence of F^? ions.     

Characterizing multi‐hop localization for Internet of things

Deployments over large geographical areas in the Internet of Things (IoT) pose a major challenge for single‐hop localization techniques, giving rise to applications of multi‐hop localizations. And while many proposals have been made on implementations for multi‐hop localization, a close understanding of its characteristics is yet to be established. Such an understanding is necessary, and is inevitable in extending the reliability of location based services in IoT. In this paper, we study the characteristics of multi‐hop localization and propose a new solution to enhance the performance of multi‐hop localization techniques. We first examine popular assumptions made in simulating multi‐hop localization techniques, and offer rectifications facilitating more realistic simulation models. We identify the introduced errors to follow the Gaussian distribution, and the estimated distance follows the Rayleigh distribution. We next use our simulation model to characterize the effect of the number of hops on localization in both dense and sparse deployments. We find that, contrary to common belief, it is better to use long hops in sparse deployments, while short hops are better in dense deployments – despite the traffic overhead. Finally, we propose a new solution that decreases and manages the overhead generated during the localization process. Copyright © 2016 John Wiley & Sons, Ltd.