Full-wave spectral-domain analysis for open microstrip discontinuities of arbitrary shape including radiation and surface-wave losses (invited paper)

This article is a survey of the theoretical background for full-wave spectral-domain analysis of open microstrip discontinuities of arbitrary shape. The spectral-domain dyadic Green's function, which takes into account all the physical effects, such as radiation and surface waves, is used to formulate an electric field integral equation. The method of moments is then employed to find the current distribution on the microstrips, and subsequently, the scattering parameters of the junctions. Since all field components can be expressed in terms of the dyadic Green's function and the current distribution, the losses due to both radiation and surface waves are further determined through a rigorous Poynting vector analysis. To model the discontinuities of arbitrary shape, both rectangular and triangular subdomain functions are used as the current expansion functions in the moment method procedure. In addition, the semi-infinite traveling wave functions are applied to simulate the feeding structure and isolate individual junction effects. Several examples are demonstrated to illustrate the utility of different techniques in this analysis. Comparison of some numerical results with available experimental data shows excellent agreement. Finally, this approach is most natural for the characterization of 3-D integrated circuits and the design of printed antennas including excitation circuit effects. © 1992 John Wiley & Sons, Inc.     

Modeling of the dynamics of wind to power conversion including high wind speed behavior

This paper proposes and validates an efficient, generic and computationally simple dynamic model for the conversion of the wind speed at hub height into the electrical power by a wind turbine. This proposed wind turbine model was developed as a first step to simulate wind power time series for power system studies. This paper focuses on describing and validating the single wind turbine model, and is therefore neither describing wind speed modeling nor aggregation of contributions from a whole wind farm or a power system area. The state‐of‐the‐art is to use static power curves for the purpose of power system studies, but the idea of the proposed wind turbine model is to include the main dynamic effects in order to have a better representation of the fluctuations in the output power and of the fast power ramping especially because of high wind speed shutdowns of the wind turbine. The high wind speed shutdowns and restarts are represented as on–off switching rules that govern the output of the wind turbine at extreme wind speed conditions. The model uses the concept of equivalent wind speed, estimated from the single point (hub height) wind speed using a second‐order dynamic filter that is derived from an admittance function. The equivalent wind speed is a representation of the averaging of the wind speeds over the wind turbine rotor plane and is used as input to the static power curve to get the output power. The proposed wind turbine model is validated for the whole operating range using measurements available from the DONG Energy offshore wind farm Horns Rev 2. Copyright © 2015 John Wiley & Sons, Ltd.     

Morphological changes in segmented polyurethane elastomers by varying the NCO/OH ratio

The morphological changes induced to segmented polyurethane elastomers by varying the NCO/OH ratio during the second step of polymerization, while keeping constant the total hard-segment content (～ 30%), were studied by means of fourier transform infared spectroscopy (FTIR), differential scanning calorimetry (DSC), and the thermally stimulated depolarization current method (TSDC). The DSC results gave evidence for the existence of phase separation in thermoplastic polyurethanes, whereas the elastomerc ones appeared to form a more homogeneous network. The FTIR results gave additional evidence regarding phase separation be detecting the sterength of the hydrogen bonds. Moreover, an attempt was made to assess the relative contribution made to the hydrogen bonding in such systems by the two potential acceptors: ester and urethane carbonyls. The TSDC results gave a relaxation mechnism that is due to interfacial (Maxwell–Wagner–Sillars) polarization, providing evidence of the existence of an interfacial phase. The introduced secondary chemical cross-links was found to affect mainly the irregularly packed hard domains and to form a more homegeneous network at higher values of the NCO/OH ratio. © 1994 John Wiley & Sons, Inc.     

Application of the Harmony Search optimization algorithm for the solution of the multiple dam system scheduling

During the last few years Harmony Search Algorithm (HSA), a new optimization technique, has been used effectively in solving large scale problems. In this paper along with a brief presentation of HSA, an application on classic Dam Scheduling problem is presented. This application concerns the optimum operation of a four-reservoir system over 24 hours. The water released from each dam is used for hydropower generation and irrigation. The objective is to maximize the daily benefits gained from the reservoir system over 12 (two-hour) time steps. Two programs were created in order to optimize this particular problem using Visual-Basic and MATLAB respectively. Both programs converged successfully to optimum management, and their main characteristics and results, are presented. The comparison between them reveals some interesting differences regarding their efficiency. The purpose of this paper is to show the potential of HSA and prove its efficiency to optimize complex optimization problems successfully. Major findings of the present paper are the 15 different solutions leading to the same global optimum. These 15 variations of the optimum management practices comprise all possible solutions, as it is proven, and they are detected for the first time ever.     

Impact of fault ride‐through requirements on fixed‐speed wind turbine structural loads

The emphasis in this article is on the impact of fault ride‐through requirements on wind turbines structural loads. Nowadays, this aspect is a matter of high priority as wind turbines are required more and more to act as active components in the grid, i.e. to support the grid even during grid faults. This article proposes a computer approach for the quantification of the wind turbines structural loads caused by the fault ride‐through grid requirements. This approach, exemplified for the case of a 2MW active stall wind turbine, relies on the combination of knowledge from complimentary simulation tools, which have expertise in different specialized wind turbines design areas. Two complimentary simulation tools are considered i.e. the detailed power system simulation tool PowerFactory from DIgSILENT and the advanced aeroelastic computer code HAWC2, in order to assess of the dynamic response of wind turbines to grid faults. These two tools are coupled sequently in an offline approach, in order to achieve a thorough insight both into the structural as well as the electrical wind turbine response during grid faults. The impact of grid requirements on wind turbines structural loads is quantified by performing a rainflow and a statistical analysis for fatigue and ultimate structural loads, respectively. Two cases are compared i.e. one where the turbine is immediately disconnected from the grid when a grid fault occurs and one where the turbine is equipped with a fault ride‐through controller and therefore it is able to remain connected to the grid during the grid fault. Copyright copy; 2010 John Wiley & Sons, Ltd.     

Detection of pseudosinusoidal epileptic seizure segments in the neonatal EEG by cascading a rule-based algorithm with a neural network

This paper presents an approach to detect epileptic seizure segments in the neonatal electroencephalogram (EEG) by characterizing the spectral features of the EEG waveform using a rule-based algorithm cascaded with a neural network. A rule-based algorithm screens out short segments of pseudosinusoidal EEG patterns as epileptic based on features in the power spectrum. The output of the rule-based algorithm is used to train and compare the performance of conventional feedforward neural networks and quantum neural networks. The results indicate that the trained neural networks, cascaded with the rule-based algorithm, improved the performance of the rule-based algorithm acting by itself. The evaluation of the proposed cascaded scheme for the detection of pseudosinusoidal seizure segments reveals its potential as a building block of the automated seizure detection system under development.     

Quantifying motion in video recordings of neonatal seizures by regularized optical flow methods.

This paper presents the development of regularized optical flow computation methods and an evaluation of their performance in the extraction of quantitative motion information from video recordings of neonatal seizures. A general formulation of optical flow computation is presented and a mathematical framework for the development of practical tools for computing optical flow is outlined. In addition, this paper proposes an alternative formulation of the optical flow problem that relies on a discrete approximation of a family of quadratic functionals. These regularized optical flow computation methods are used to extract motion strength signals from video recordings of neonatal seizures.     

Nanoscale organic light-emitting diodes

This study reports the fabrication and characterization of nanoscale organic light-emitting diodes (nano-OLEDs) based on poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The nano-OLEDs were fabricated by spin casting MEH-PPV into cylindrical nanoholes lithographically patterned into silicon nitride. The electroluminescence (EL) spectrum of MEH-PPV was similar to its photoluminescence spectrum, confirming radiative decay from the same excited state. Device characteristics in the form of current density and EL versus applied electric field are presented and compared with those of a large-scale OLED.     

Frame synchronisation using two frame alignment words

The use of two frame alignment words (FAWs) in a frame synchronisation system is investigated. This has the advantage of reducing the overhead when compared to conventional single FAW schemes. The scheme is of benefit when fast synchronisation and low overhead are important.<>