Theory of stimulated Raman scattering in optical fibers in thepulse walkoff regime

It is shown that the process of forward stimulated Raman scattering in a single-mode fiber, which involves the pump pulse and the first Stokes wave, is an exactly soluble problem, provided that the temporal duration of these waves is sufficiently long. The analysis takes into account the effects of pulse walkoff arising from the dispersion of the fiber as well as self- and cross-phase modulation. The procedure is applied to two examples: the first is that of stimulated Raman scattering as it builds up from spontaneous Raman emission; the second is that of launching pump and Stokes pulses     

Mass transfer modelling of the osmotic dehydration of some fruits

An empirical model was developed to predict the water loss and solid gain during osmotic dehydration of apple, banana and kiwi fruit. The model is based on a first-order kinetic equation, in which the rate constant is a function of the main process variables (speed of agitation, solute concentration, size of fruit and process temperature). This model was applied to a wide range of experimental data on the osmotic dehydration of apple, banana and kiwi fruit, and its parameters were estimated using non-linear regression analysis. The results showed that all of the above process variables have a significant effect on the mass transfer phenomena during osmotic dehydration.     

Coupling efficiency and sensitivity of an LED to a single-mode fibre

Simple expressions are derived to estimate the coupling efficiency and sensitivity of an LED butt-coupled to a single-mode fibre. The concept of the single-mode numerical aperture is revised so as to incorporate the wave nature of the coupling process. Our analysis agrees well with experimental results.     

Static plastic behavior of a strand

The static plastic collapse of a single strand which is idealised as m bars with circular cross-sections and helical axes has been examined using the limit theorems of plasticity. An exact theoretical solution which retains the influence of contact forces was obtained for a strand subjected to an axial load accompanied by a torsional moment.     

Reliability-based topology optimization for offshore wind farm collection system

An optimization framework for global optimization of the cable layout topology for offshore wind farm (OWF) is presented. The framework designs and compares closed-loop and radial layouts for the collection system of OWFs. For the former, a two-stage stochastic optimization program based on a mixed integer linear programming (MILP) model is developed, while for the latter, a hop-indexed full binary model is used. The purpose of the framework is to provide a common base for assessing both designs economically, using the same underlying contingency treatment. A discrete Markov model is implemented for calculating the cable failure probability, useful for estimating the time under contingency for multiple power generation scenarios. The objective function supports simultaneous optimization of (i) initial investment (network topology and cable sizing), (ii) total electrical power loss costs and (iii) operation costs due to energy curtailment from cable failures. Constraints are added accounting for common engineering aspects. The applicability of the full method is demonstrated by tackling three differently sized real-world OWFs. Results show that (i) the profitability of either topology type depends strongly on the project size and wind turbine rating. Closed loop may be a competitive solution for large-scale projects where large amounts of energy are potentially curtailed. (ii) The stochastic model presents low tractability to tackle large-scale instances, increasing the required computing time and memory resources. (iii) Strategies must be adopted in order to apply stochastic optimization for modern OWFs, intending analytically or numerically simplification of mathematical models.     

Morphology and electrochemical activity of SOFC composite cathodes: I. experimental analysis

This paper describes the first part of an experimental and theoretical study performed on composite Lanthanum Strontium Manganite (LSM) and Yttria-stabilized Zirconia (YSZ) electrodes. Cathode electrocatalytic activity was investigated using different cell configurations and carrying out potentiodynamic polarisation and electrochemical impedance spectroscopy measurements (EIS). Measurements were carried out at different oxygen partial pressures, overpotentials, temperatures and electrode geometries. In order to identify the main steps involved in cathodic oxygen reduction, the NLLS-Fit procedure was used. The results for different cell geometries agree with each other, suggesting a transition in the overall reaction mechanism, from charge transfer to mass transfer control, at a critical temperature of about 750 °C. The experimental results also show a remarkable effect of electrode thickness on the overall reaction rate, throughout the temperature range tested. A grey level gradient along the thickness of the thicker electrodes were detected by analyzing microscopic images of the cells. These results, together with electrochemical measurements on cathodes with different thickness, confirm that morphology plays a key role in determining the performance of Solid Oxide Fuel Cells (SOFC) composite cathodes.     

Adsorption layer and its characteristic to modulate the electro-oxidation runway of organic species

Studies of organic compounds oxidation at constant current conditions with different anodes, indicate that the oxidative action of these anodes is related to their absorption characteristic i.e. the low or high difficulty of the generated hydroxyl radicals in reaching the solution. This paper shows that the adsorption does not concern the anodic surface, but an adjacent thin layer (adsorption layer) of the aqueous solution. An estimation of the fraction of hydroxyl radicals that move from the adsorption layer to the adjacent reactive/diffusive layer is obtained as well as a suitable tool for comparison the result of this approach with the experimental results. This comparison shows how the adsorption layer modulates the runway of the organic species oxidation.     

Reformulated radial basis function neural networks with adjustable weighted norms

This article presents a new family of reformulated radial basis function (RBF) neural networks that employ adjustable weighted norms to measure the distance between the training vectors and the centers of the radial basis functions. The reformulated RBF model introduced in this article incorporates norm weights that can be updated during learning to facilitate the implementation of the desired input‐output mapping. Experiments involving classification and function approximation tasks verify that the proposed RBF neural networks outperform conventional RBF neural networks and reformulated RBF neural networks employing fixed Euclidean norms. Reformulated RBF neural networks with adjustable weighted norms are also strong competitors to conventional feedforward neural networks in terms of performance, implementation simplicity, and training speed. © 2003 Wiley Periodicals, Inc.     

A microchip-based multianalyte assay system for the assessment of cardiac risk

The development of a novel chip-based multianalyte detection system with a cardiac theme is reported. This work follows the initial reports of "electronic taste chips" whereby multiple solution-phase analytes such as acids, bases, metal cations, and biological cofactors were detected and quantitated. The newly fashioned "cardiac chip" exploits a geometry that allows for isolation and entrapment of single polymeric spheres in micromachined pits while providing to each bead the rapid introduction of a series of reagents/washes through microfluidic structures. The combination of these miniaturized components fosters the completion of complex assays with short analysis times using small sample volumes. Optical signals derived from single beads are used to complete immunological tests that yield outstanding assay characteristics. The power and utility of this new methodology is demonstrated here for the simultaneous detection of the cardiac risk factors, C-reactive protein and interleukin-6, in human serum samples. This demonstration represents the first important step toward the development of a useful cardiac chip that targets numerous risk factors concurrently and one that can be customized readily for specific clinical settings.     

Optical characteristics of multitransverse-mode two-dimensionalvertical-cavity top surface-emitting laser arrays

We observe for the first time up to nine transverse modes lasing in the individual elements of a two-dimensional vertical-cavity top surface-emitting laser array under pulsed operation. These modes consist of the TEM_0,0, TEM_0,1, TEM_1,0, TEM_1,1, TEM_0,2, TEM_2,0, TEM_1,2 , TEM_2,1, and TEM_2,2 modes, Each of these modes couples coherently across the array to form very distinct supermodes. The transverse modes as well as the resulting supermodes are identified by examining the near-field and far-field profiles as well as the corresponding spectra. We also obtain a record 1.4 W (pulsed) of coherent output power from the array during multitransverse-mode operation. In addition, the polarization properties of the array are investigated, It is found that the TEM_0,1 mode is horizontally polarized along the [011] crystalline axis while all the other modes are dominantly vertically polarized along the [011¯] axis