A framework for generating tunable test functions for multimodal optimization

Multimodal function optimization, where the aim is to locate more than one solution, has attracted growing interest especially in the evolutionary computing research community. To evaluate experimentally the strengths and weaknesses of multimodal optimization algorithms, it is important to use test functions representing different characteristics and various levels of difficulty. The available selection of multimodal test problems is, however, rather limited and no general framework exists. This paper describes an attempt to construct a software framework which includes a variety of easily tunable test functions. The aim is to provide a general and easily expandable environment for testing different methods of multimodal optimization. Several function families with different characteristics are included. The framework implements new parameterizable function families for generating desired landscapes. Additionally the framework implements a selection of well known test functions from the literature, which can be rotated and stretched. The software module can easily be imported to any optimization algorithm implementation compatible with the C programming language. As an application example, 8 optimization approaches are compared by their ability to locate several global optima over a set of 16 functions with different properties generated by the proposed module. The effects of function regularity, dimensionality and number of local optima on the performance of different algorithms are studied.     

Shuffle or update parallel differential evolution for large-scale optimization

This paper proposes a novel algorithm for large-scale optimization problems. The proposed algorithm, namely shuffle or update parallel differential evolution (SOUPDE) is a structured population algorithm characterized by sub-populations employing a Differential evolution logic. The sub-populations quickly exploit some areas of the decision space, thus drastically and quickly reducing the fitness value in the highly multi-variate fitness landscape. New search logics are introduced into the sub-population functioning in order to avoid a diversity loss and thus premature convergence. Two simple mechanisms have been integrated in order to pursue this aim. The first, namely shuffling, consists of randomly rearranging the individuals over the sub-populations. The second consists of updating all the scale factors of the sub-populations. The proposed algorithm has been run on a set of various test problems for five levels of dimensionality and then compared with three popular meta-heuristics. Rigorous statistical and scalability analyses are reported in this article. Numerical results show that the proposed approach significantly outperforms the meta-heuristics considered in the benchmark and has a good performance despite the high dimensionality of the problems. The proposed algorithm balances well between exploitation and exploration and succeeds to have a good performance over the various dimensionality values and test problems present in the benchmark. It succeeds at outperforming the reference algorithms considered in this study. In addition, the scalability analysis proves that with respect to a standard Differential Evolution, the proposed SOUPDE algorithm enhances its performance while the dimensionality grows.     

‘Podracing’: experimenting with mobile TV content consumption and delivery methods

Recently, mobile TV has been launched in several countries. While mobile TV integrates television contents into mobile phones, the most personal of communication devices, it becomes interesting to know how this feature will be used throughout the day and in varying contexts of everyday life. This paper presents empirical results on the use of mobile TV with different delivery mechanisms and both quantitative and qualitative results on how end-users prefer to use mobile TV contents in different situations. The data is based on ongoing empirical research in Finland in 2006 and 2007. The mobile TV services under study included both news and entertainment contents, and were tested in 3G, DVB-H and Wi-Fi networks using different delivery paradigms: broadcast, on-demand and download. To explore the use of different delivery methods and content consumption, we have developed a mobile TV service protoype, called Podracing. The analysis shows that users appreciated up-to-date information and information-rich media forms and contents especially for mobile news delivery. There was high demand for only the latest news on mobiles. The real-time property was considered important. Most of the users looked at the headlines or followed the news several times a day – much more often than the traditional TV and news prime times would allow.     

Line‐Sweep Ambient Obscurance

Screen‐space ambient occlusion and obscurance have become established methods for rendering global illumination effects in real‐time applications. While they have seen a steady line of refinements, their computational complexity has remained largely unchanged and either undersampling artefacts or too high render times limit their scalability. In this paper we show how the fundamentally quadratic per‐pixel complexity of previous work can be reduced to a linear complexity. We solve obscurance in discrete azimuthal directions by performing line sweeps across the depth buffer in each direction. Our method builds upon the insight that scene points along each line can be incrementally inserted into a data structure such that querying for the largest occluder among the visited samples along the line can be achieved at an amortized constant cost. The obscurance radius therefore has no impact on the execution time and our method produces accurate results with smooth occlusion gradients in a few milliseconds per frame on commodity hardware.     

Processing characteristics of tin and tungsten oxides relevant to production of gas sensors

Tungsten trioxide and two types of tin dioxide were compacted at different pressures and then sintered at different temperatures in order to study how the microstructure formed is dependent on these parameters. The structures were studied using dilatometric and porosimetric techniques and also using electron microscopy. X-ray diffraction was used to ascertain the completeness of the decomposition reaction of SnSO₄ being converted to SnO₂. Tin dioxide, which was prepared from tin sulphate by calcining, was characterised by a large specific surface area. For all three materials studied the mean pore size was found to increase and the specific surface area was found to decrease with increasing sintering temperature. In the case of WO₃ the total pore volume decreased markedly as the sintering temperature was increased from 900 to 1000° C. However, in the case of SnO₂, the total pore volume remained almost constant in the sintering temperature range of 600 to 1500° C. In the case of SnO₂ derived from SnSO₄ the sintered density was about 45% of the theoretical value while for the conventionally made SnO₂ the sintered density was about 55% of the theoretical value. The sintered density of WO₃ was found to show a marked increase, from 55% to 70% of the theoretical value, as the sintering temperature was raised from 1000 to 1100° C.     

Stacked GaAs quantum dots fabricated by refilling of self-organized nanoholes: optical properties and post-growth annealing

We study the photoluminescence and impact of post-growth annealing of stacked, strain-free GaAs quantum dots fabricated by refilling of self-organized nanoholes using molecular beam epitaxy. Temperature- and power-dependent photoluminescence studies reveal an excellent optical quality of the quantum-dot stack. After high-temperature post-growth annealing only slight blueshifts and an increase in full width at half-maximum of the photoluminescence peak are observed, indicating very high-temperature stability and crystalline quality of the stacked GaAs quantum-dot structure.     

Development of an Efficient Acid Digestion Procedure Utilizing High-Pressure Asher Technique for the Determination of Iodine and Metallic Elements in Milk Powder

An effective wet digestion procedure for the determination of total iodine contents in milk powder samples was developed utilizing a high-pressure asher technique. The optimized method based on a two-stage digestion procedure. In the first stage, 500 mg samples were digested at 300 °C for 2 h using 15.2 mol L^?1 HNO₃ (5 mL) and 30 % H₂O₂ (3 mL). After the first digestion stage, digestion vessels were allowed to cool down and 1.2 mL of 20 % (w/v) Na₂S₂O₈ solution was added as an additional oxidizing agent to the samples. After that, the vessels were closed, and they were heated at 100 °C for 30 min, resulting in clear and colorless sample solutions. Iodine concentrations in the digested samples were measured with inductively coupled plasma mass spectrometry. The accuracy of the optimized method was confirmed by analyzing milk powder reference material (BCR-151, milk powder). The obtained value for iodine (5.29?±?0.37 mg kg^?1, n?=?6) was in good agreement with the certified value (5.35?±?0.14 mg kg^?1). Furthermore, the results obtained for reference material showed that the developed method can be applied also for the determination of other elements, e.g., copper, iron, and lead in the digested milk powder samples.