Distributed control parallelism in multidisciplinary aircraft design

Multidisciplinary design optimization (MDO) for large-scale engineering problems poses many challenges (e.g. the design of an efficient concurrent paradigm for global optimization based on disciplinary analyses, expensive computations over vast data sets, etc.). This work focuses on the application of distributed schemes for massively parallel architectures to MDO problems, as a tool for reducing computation time and solving larger problems. The specific problem considered here is configuration optimization of a high speed civil transport (HSCT), and the efficient parallelization of the embedded paradigm for reasonable design space identification. Two distributed dynamic load balancing techniques (random polling and global round robin with message combining) and two necessary termination detection schemes (global task count and token passing) were implemented and evaluated in terms of effectiveness and scalability to large problem sizes and a thousand processors. The effect of certain parameters on execution time was also inspected. Empirical results demonstrated stable performance and effectiveness for all schemes, and the parametric study showed that the selected algorithmic parameters have a negligible effect on performance. Copyright © 1999 John Wiley & Sons, Ltd.     

An approach to enhance the efficiency of opportunistic grids

Opportunistic grid computing middleware has as a main concern the need to preserve the performance of the local applications running on machines that donate resources to the grid. This concern, together with the fact that it happens in an extremely dynamic environment, causes the adoption of a treatment based on thetextitbest‐effort principle for grid applications. This means that efficient application management schemes are usually not employed, which results in less than optimal performance as grid applications often need to be restarted due to (often temporary) resource claims by local user applications. This paper presents a method to improve the performance of grid applications, taking into account resource usage profiles for local applications, trying to identify when such resource claims are temporary and avoiding costly actions such as the migration of grid tasks. The approach is proposed as an extension to the InteGrade middleware and its evaluation shows promising results for the efficient management of grid applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterisation of land types and agro-ecological conditions for production of Jatropha as a feedstock for biofuels in Zimbabwe

There is increasing interest in Zimbabwe in developing a biofuels industry based on the production of biodiesel using Jatropha as the main feedstock. This has led to the introduction of Jatropha as a commercial energy crop in the country. There are plans to grow 1220 km² of Jatropha which will supply about 365,000 t of seed. This will provide about 110 dam³ of biodiesel required to achieve a blending level of 10% with petro-diesel. The availability and suitability of land for the production of Jatropha cannot be taken for granted, particularly given the fact that the concept and practice of production of feedstocks for biofuels remain contested on the threat they pose to food security. Determining the land that is potentially available for biofuels is a non-trivial task. A multiplicity of factors needs to be considered. It is important to determine the spatial extent of areas with suitable growth conditions for Jatropha. The interaction of soil type and land use is an important interface in agriculture. Added to this is the need to balance food, fodder and fuel supply in land use planning. This paper attempts to assess the availability and suitability of various land types as well as agro-ecological conditions for the production of Jatropha in Zimbabwe.     

Fatigue and Fracture Behavior of a Ca-Based Bulk-Metallic Glass

The compression and fatigue behavior of a Ca₆₅Mg₁₅Zn₂₀ bulk-metallic glass (BMG) was studied in air at room temperature. During the preparation of cubical samples of the Ca₆₅Mg₁₅Zn₂₀ for compression and fatigue investigations, small spherical cavities were found. Under both monotonic and cyclic compression loadings of the samples, fractures initiated at these cavities and propagated in a direction generally parallel to the loading axis. Finite-element analysis (FEA) was used to model the fracture behavior. The FEA of a centrally located spherical void showed that under compression loading, large tensile stresses evolved in the cavities. The orientation of the maximum principal stress (P1) was found to be normal to the direction of crack propagation, which is consistent with the experimental finding. Stresses in deeply embedded adjacent voids and those in superficial voids were also studied. The influence of the void location in the cubical sample on the fracture behavior was quantitatively discussed.     

Determination of nitrate concentration in soil via photoacoustic spectroscopy analysis of ion exchange membranes

Numerous works have demonstrated that ion exchange membranes can be used for accurate determination of the availability of nitrate and other key nutrients in soils. After letting the ion exchange membrane interact with the soil for a known period of time, the membrane is typically immersed in a strong reagent to desorb the ions and the resulting solution is analyzed by standard chemical methods. The present study shows that mid-infrared photoacoustic spectroscopy can be used to estimate directly the amount of nitrate sorbed onto such membranes and could replace advantageously the standard chemical analysis. The study was conducted with two commercially available membranes, and in both cases the average determination error achieved with a simple partial least squares model was approximately 1.6-1.8 microeq, which under the specific experimental conditions corresponds to approximately 4.5-5.0 mg[N]/kg[dry soil]. Such errors are about 30% larger than those reported in a previous study in which the membrane was analyzed by transmittance spectroscopy. However, the present method is suitable for a much wider range of membranes, such as those commonly used for water treatment and that are too thick for transmittance measurements. For such membranes, photoacoustic spectroscopy is a very cheap and rapid alternative to standard chemical analysis.     

Nanoplasmonic sensing of metal-halide complex formation and the electric double layer capacitor

Many nanotechnological devices are based on implementing electrochemistry with plasmonic nanostructures, but these systems are challenging to understand. We present a detailed study of the influence of electrochemical potentials on plasmon resonances, in the absence of surface coatings and redox active molecules, by synchronized voltammetry and spectroscopy. The experiments are performed on gold nanodisks and nanohole arrays in thin gold films, which are fabricated by improved methods. New insights are provided by high resolution spectroscopy and variable scan rates. Furthermore, we introduce new analytical models in order to understand the spectral changes quantitatively. In contrast to most previous literature, we find that the plasmonic signal is caused almost entirely by the formation of ionic complexes on the metal surface, most likely gold chloride in this study. The refractometric sensing effect from the ions in the electric double layer can be fully neglected, and the charging of the metal gives a surprisingly small effect for these systems. Our conclusions are consistent for both localized nanoparticle plasmons and propagating surface plasmons. We consider the results in this work especially important in the context of combined electrochemical and optical sensors.