Steel corrosion in concrete marine structures

Considering this problem in relation to work in developing countries, the authors review an extensive literature and report on their own tests. The results highlight the aggressive effects of magnesium sulphate, but the experiments also show that a small quantity of bentonite added to the mixing water can effectively improve resistance.     

Self-gated two-photon photorefractive effect induced by light upconversion in Er-Doped LiTaO3

It is demonstrated that Er doping increases the photorefractive effect in LiTaO(3). Raman and fluorescence spectra are used to establish that the upconverted green emission of Er(3+) clusters acts as a gating source, significantly increasing the two-photon photorefractive effect of a monochromatic red or near-infrared pump source.     

Minimum-mode-size low-loss Ti: LiNbO3channel waveguides for efficient modulator operation at 1.3 µm

Efficient operation of Ti-diffused LiNbO3modulators and switches requires small, tightly guiding channel waveguide modes which effectively overlap the applied modulating field. This in turn requires Ti:LiNbO3channel waveguides with minimum mode size. The small-mode-size waveguides are obtained inz-cut crystals by optimizing the fabrication parameters to achieve maximum index change in the wave-guiding region and the optimum diffusion depth and width. For 6 h diffusion at 1025°C, and Ti strip thickness of 800 Å and strip width of 4 μm, the TM mode has a1/eintensity full width of 3.9 μm and full depth of 2.8 μm. This is by far the smallest mode size atlambda = 1.32 mum presented to date for Ti:LiNbO3waveguides. Since these waveguides have small mode size, largeDelta n, and low propagation loss (0.2 dB/cm) atlambda = 1.32 mum, it should be possible to fabricate modulators and switches with small voltage-length products and optical circuits that incorporate small bending radii curves, thus decreasing the total device length.     

Semi-implicit and explicit finite element schemes for coupled fluid/thermal problems

A comparative investigation, based on a series of numerical tests, of two purely explicit and one semi-implicit finite element methods used for incompressible flow computation is presented. The ‘segregated’ approach is followed and the equations of motion are considered sequentially. The fundamental concepts and characteristics of the formulations and the solution methodology used are described in technical detail. Various modifications to Chorin's projection algorithm are investigated, particularly with respect to their effects on stability and accuracy. The stability of the semi-implicit method is shown to be less restrictive when compared to the explicit methods as the Reynolds number increases. At large time steps the artificial viscosity is also reduced and higher accuracy is obtained. The performance of the methods discussed in this paper is illustrated by the numerical solutions obtained for the cavity flow and flow past a rearward-facing step problems at high Reynolds numbers, and free convection flow problem at high Rayleigh numbers. It is shown that the semi-implicit method needs fewer iterations than the explicit methods, and the accuracy of the present methods is guaranteed by comparison with the existing methods.     

Influence of ferrite-martensite microstructural morphology on the low cycle fatigue of a dual-phase steel

A CMnSi dual-phase steel has been heat-treated to yield three different microstructures — a dispersion of martensite in fine-grained ferrite (Type I), a continuous network of martensite around ferrite grains (Type II) and martensite islands encapsulated in a ferrite matrix (Type III) — and low cycle fatigue tests have been conducted. All three conditions have been found to exhibit cyclic hardening. The lower hardening in the Type I microstructure and its cyclic softening at lower strains are attributed to a more uniform initial distribution of dislocations because of the dispersion of the martensite. The Type I microstructure displays the best fatigue performance and is shown to obey the Coffin-Manson law. The deviation of the other two microstructures from this law is shown to be due to a transition from a ductile mode of fracture at lower strains to a brittle type of fracture at higher strains.     

Significance of structure-property relationship in alumina based porcelain insulators to achieve quality

The catastrophic failures of porcelain insulators in power lines can be minimized by understanding the structure-property relationship that governs the performance. A study addressing the materials aspects has been conducted on alumina based porcelain insulators used in 25 kV railway traction lines. This article asserts the controls exercised by chemical composition, crystalline structural phases and microstructure on the functional reliability and durability of the insulators. Influences of the total alumina, α-Al₂O₃ (corundum) and α-quartz contents, microstructural features including morphologies of mullite needles, quartz and corundum grains in the alumino silicate glassy matrix, large inhomogeneities in matrix constituents and composition have been highlighted.     

PSO based economic emission dispatch for fixed head hydrothermal systems

The insufficient hydropower resources along with the deleterious effects of thermal generations necessitate an ingenious scheduling scheme to comply with the growing power demand. The rapidly depleting coal reserve further strengthens the need to develop a new strategy to accomplish generation-load balance at minimum fuel cost over the scheduling horizon, in addition to ensuring reduced emissions. The existing approaches appear to offer suboptimal solutions or suffer from the computational burden due to the large number of problem variables involved. This paper presents an efficient economic emission dispatch strategy involving reduced number of decision variables for hydrothermal scheduling through the use of particle swarm optimisation. The results on three test systems highlight its superior performance and suitability for systems of any size.     

Highly Linear Coherent Receiver With Feedback

We propose and demonstrate a novel coherent receiver with feedback for high-linearity analog photonic links. In the proposed feedback receiver, a local phase modulator tracks the phase change of the signal and reduces the effective swing across the phase demodulator without reducing the transmitted signal. The signal-to-noise-ratio is thus maintained while linearity is improved. Up to 20-dB improvement in spur-free dynamic range (SFDR) is achieved experimentally. At 3.13 mA of average photocurrent per photodiode, the measured SFDR is 124.3 dBmiddotHz^2/3, which corresponds to an SFDR of 131.5 dBmiddotHz^2/3 when the link is shot-noise-limited     

Bandpass traveling-wave Mach-Zehnder modulator in LiNbO/sub 3/ with domain reversal

A bandpass traveling-wave Mach-Zehnder modulator is demonstrated in a Z-cut LiNbO/sub 3/ substrate where quasi-phase-matching is achieved by using a crystal domain reversal and a simple uniform coplanar waveguide electrode structure. The domain reversal was created, by using electric-field poling, to implement the three-section alternating electrooptic interaction. At the operating wavelength /spl lambda/=1.32 /spl mu/m, the modulator has a 15 GHz-broad bandpass response centered at 25-GHz 3.6-dB fiber-to-fiber insertion loss, 12 V on-off voltage at the center frequency, and -33-dB extinction ratio.