A hybrid particle swarm optimization based algorithm for high school timetabling problems

In this contribution a hybrid particle swarm optimization (PSO) based algorithm is applied to high school timetabling problems. The proposed PSO based algorithm is used for creating feasible and efficient high school timetables. In order to demonstrate the efficiency of the proposed PSO based algorithm, experiments with real-world input data coming from many different Greek high schools have been conducted. Computational results show that the proposed hybrid PSO based algorithm performs better than existing approaches applied to the same school timetabling input instances using the same evaluation criteria.     

A perturbation-based numerical method for solving a three-dimensional axisymmetric indentation problem

The three-dimensional axisymmetric problem of the indentation of a thin compressible linear elastic layer bonded to a rigid foundation is considered. Approximate analytical solutions of the problem that incorporate a large portion of the singular deformation gradients near the edge of the indenter are presented. An accurate closed-form expression for the deformation as well as the deformation gradient throughout the layer is provided and its effectiveness in solving the problem numerically is demonstrated. By incorporating the approximate solution into the numerical scheme the accuracy and convergence rate increase dramatically.     

Improved multimode pushover procedure for asymmetric in plan buildings under biaxial seismic excitation—application to tall buildings

An improved version of a recently developed multimode pushover procedure for asymmetric in plan buildings under biaxial seismic excitation is presented and evaluated. The proposed methodology is quite similar to the well‐known modal pushover analysis. However, the establishment of the equivalent single‐degree‐of‐freedom systems is based on a new concept, which takes into account multidirectional seismic effects. The proposed methodology does not require independent analysis in the two orthogonal directions, and therefore, the application of simplified directional combination rules is avoided. The improvement presented here consists in definition of correction factors to be applied to the response values at the stiff side of buildings. An extensive evaluation study comprising applications to tall buildings is presented. The response parameters obtained from the proposed methodology in most cases envelope the values resulting from nonlinear dynamic analysis (NDA). Furthermore, the mean errors with regard to the NDA results are smaller than those obtained from a multimode pushover procedure comprising independent analysis along two horizontal axes and directional combination of the results. In general, the proposed methodology provides a reasonable estimation of the seismic performance of asymmetric buildings.     

A linear,ultra wideband,low‐power, 2.1–5 GHz,VCO

A linear, Ultra Wideband, low‐power VCO, suitable for UWB‐FM applications is proposed, forming the main part of a UWB‐FM transmitter. The VCO is designed in TSMC 90thinspacenm digital CMOS process and includes a Source‐Coupled Multivibrator, used as current‐controlled oscillator (CCO) which generates output frequencies between 2.1 and 5 GHz and a voltage‐to‐current (V‐to‐I) converter which translates the VCO input voltage modulation signal to current. Two single‐ended inverter buffers are employed to drive either a differential or a single‐ended UWB antenna. The presented VCO is designed for 1 V power supply and exhibits a linear tuning range of 2.1–5 GHz, a differential output power of ?7.83 dBm±0.78 dB and low power consumption of 8.26 mW, including the output buffers, at the maximum oscillation frequency. It is optimized for a very high ratio of tuning range (81.69%) over power consumption equal to 9.95 dB. The desired frequency band of 3.1–5 GHz for UWB‐FM applications is covered for the entire industrial temperature range (?40 to 125^°C). Copyright © 2010 John Wiley & Sons, Ltd.     

Diverse metabolism of cell wall components of melting and non‐melting peach genotypes during ripening after harvest or cold storage

The mode of change in a range of physiological, physicochemical and biochemical parameters during fruit ripening between distinct peach genotypes (Prunus persica L. Batsch) after cold storage for up to 4 weeks was determined. The nectarine cultivar ‘Caldesi 2000’ was selected as a genotype with melting flesh (MF) characteristic (fruits characterized by extensive flesh softening during ripening) and the cultivar ‘Andross’ as a genotype with non‐melting flesh (NMF) characteristic (fruits characterized by limited flesh softening during ripening). Flesh firmness, ethylene production, physicochemical and biochemical properties of the cell wall were determined and significant differences between the fruits of the two genotypes were recorded. Fruits of the NMF genotype were characterized by higher tissue retention and ethylene production during their ripening, higher content of uronic acids, as well as higher capacity for calcium binding in the water‐insoluble pectin fraction compared with fruits of the MF genotype. Additionally, the ripening of MF‐type fruits was characterized by higher losses of neutral sugars, especially those of arabinose and galactose than the NMF‐type fruits and these losses were more intense after extended cold storage periods. In fruits of the NMF genotype the decreased activity of pectin methyl esterase (PME) combined with higher levels of calcium in the water‐insoluble pectin fraction possibly provided less substrate for polygalacturonase (exo‐, endo‐PG) activity and less solubility of cell wall pectin compared with fruits of the MF genotype. Overall, the data indicate the existence of a wide range of diverse metabolic pathways during fruit ripening of fresh fruits with MF and NMF characteristics. Copyright © 2005 Society of Chemical Industry     

Heavy metal characterization of CFB-derived coal fly ash

The present study investigates the heavy metal content of coal fly ash (FA) samples coming from three different sampling points (secondary cyclone, cooler and filter) of a pilot plant combustion facility. The combustion experiments were carried out in a 0.1 MW Circulated Fluidized Bed (CFB) boiler using South African coal, with the addition of limestone for sulfur capture. FA was tested for the presence of selected heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES); batch leaching tests were conducted as well. The samples were also characterized in terms of their microstructure, chemical and mineralogical composition, total surface area and particle size distribution. Most of the studied metals (Cd, Cr, Cu, Ni, Mn, Zn) showed enrichment in the fine, filter FA particles, while Pb was mostly concentrated in the cooler sample. Regarding leaching characteristics of the examined samples, Cr was found to occur in considerable amounts. Although the use of CFB technology for the combustion of solid fuels steadily gets bigger worldwide, only a very limited number of studies have environmentally assessed CFB-coal FAs to date. Thus, the current study aims to contribute toward building a more integrated knowledge on the environmental impact of this abundant power production by-product.     

Spectral multivariate calibration with wavelength selection using variants of Tikhonov regularization

Tikhonov regularization (TR) is a general method that can be used to form a multivariate calibration model and numerous variants of it exist, including ridge regression (RR). This paper reports on the unique flexibility of TR to form a model using full wavelengths (RR), individually selected wavelengths, or multiple bands of selected wavelengths. Of these three TR variants, the one based on selection of wavelength bands is found to produce lower prediction errors. As with most wavelength selection algorithms, the model vector magnitude indicates that this error reduction comes with a potential increase in prediction uncertainty. Results are presented for near-infrared, ultraviolet-visible, and synthetic spectral data sets. While the focus of this paper is wavelength selection, the TR methods are generic and applicable to other variable-selection situations.     

Comparison of Interpolation Methods for the Prediction of Reference Evapotranspiration—An Application in Greece

The objective of this paper is to evaluate four interpolation methods, concerning their suitability for spatial prediction of long-term mean daily reference evapotranspiration (calculated by Penman–Monteith equation) for each month in Greece. The methods studied were ordinary kriging (OK) and inverse distance squared (IDS) and their modifications in which elevation data was incorporated into the interpolation process. The modified methods were named residual kriging (RK), and gradient-plus-inverse distance squared (GIDS). Apart from interpolation methods, two different approaches were studied in order to define what the proper sequence of steps is in the case of the interpolation of reference evapotranspiration. More particularly the ‘calculate first, interpolate later’ (CI) procedure was compared to the reverse procedure, namely ‘interpolate first, calculate later’ (IC). The assessment criteria of the methods accuracy were: mean error (ME), mean absolute error (MAE) and root mean squared error (RMSE). The results revealed that the incorporation of elevation significantly improved the performance of interpolation methods. On the contrary, procedures CI and IC were very similar since they had no effect on the performance of the four interpolation methods studied.