A comparison of CPU and GPU implementations for solving the Convection Diffusion equation using the local Modified SOR method

In this paper we study a parallel form of the SOR method for the numerical solution of the Convection Diffusion equation suitable for GPUs using CUDA. To exploit the parallelism offered by GPUs we consider the fine grain parallelism model. This is achieved by considering the local relaxation version of SOR. More specifically, we use SOR with red-black ordering using two sets of parameters _ω1ij${\omega }_{1\mathit{ij}}$ and _ω2ij${\omega }_{2\mathit{ij}}$ for the 5 point stencil. The parameter _ω1ij${\omega }_{1\mathit{ij}}$ is associated with each red (i + j   even) grid point (i,j)$(i\text{,}j)$, whereas the parameter _ω2ij${\omega }_{2\mathit{ij}}$ is associated with each black (i+j$(i+j$ odd) grid point (i,j)$(i\text{,}j)$. The use of a parameter for each grid point avoids the global communication required in the adaptive determination of the best value of ω$\omega$ and also increases the convergence rate of the SOR method (Varga, 1962) [38] and (Young, 1971) [41]. We present our strategy and the results of our effort to exploit the computational capabilities of GPUs under the CUDA environment. Additionally, two parallel CPU programs utilizing manual SSE2 (Streaming SIMD Extensions 2) and AVX (Advanced Vector Extensions) vectorization were developed as performance references. The optimizations applied on the GPU version were also considered for the CPU version. Significant performance improvement was achieved with all three developed GPU kernels differentiated by the degree of recomputations thus affecting the flops per element access ratio.     

Heat transport limitations and reaction scheme of partial oxidation of methane to synthesis gas over supported rhodium catalysts

The partial oxidation of methane to synthesis gas over supported Rh catalysts is investigated, paying particular attention to removing heat transport limitations and identifying the reaction conditions within the kinetic-controlling regime. The results obtained suggest that the reaction follows the sequence of total oxidation to CO₂ and H₂O, followed by reforming reactions to synthesis gas.     

Electricity supply on the island of Dia based on renewable energy sources (R.E.S.)

This paper presents a methodology for determining the specifications of an isolated R.E.S. power production system on an environmentally sensitive ecosystem. The wind and solar power constitute the primary power generation system and diesel generators act as backup. Real wind and solar potential measurements are used. The wind atlas of the island has been constructed. The specifications of the proposed system are optimized by the life cycle cost method. The renewable energy sources (R.E.S.) total annual energy production exceeds 90%. As a result, the dependence on the diesel generator set annual energy production is limited and the system’s operational cost is not practically influenced by the increasing fossil fuel prices. The introduction of a small size desalination plant for the production of drinkable water is also investigated. Both the available R.E.S. potential and the minimization of environmental impacts are considered for the siting of the equipment. The methodology of the present paper may be applied to other regions rich in R.E.S. potential, where the introduction of small size environmentally friendly isolated R.E.S. power systems is investigated.     

Investigation of critical equivalence ratio and chemical speciation in flames of ethylbenzene–ethanol blends

This work investigates five different one-dimensional, laminar, atmospheric pressure, premixed ethanol/ethylbenzene flames (0%, 25%, 50%, 75% and 90% ethanol by weight) at their soot onset threshold (?_critical). Liquid ethanol/ethylbenzene mixtures were pre-vaporized in nitrogen, blended with an oxygen–nitrogen mixture and, upon ignition, burned in premixed one-dimensional flames at atmospheric pressure. The flames were controlled so that each was at its visual soot onset threshold, and all had similar temperature profiles (determined by thermocouples). Fixed gases, light volatile hydrocarbons, polycyclic aromatic hydrocarbons (PAH), and oxygenated aromatic hydrocarbons were directly sampled at three locations in each flame. The experimental results were compared with a detailed kinetic model, and the modeling results were used to perform a reaction flux analysis of key species. The critical equivalence ratio was observed to increase in a parabolic fashion as ethanol concentration increased in the fuel mixture. The experimental results showed increasing trends of methane, ethane, and ethylene with increasing concentrations of ethanol in the flames. Carbon monoxide was also seen to increase significantly with the increase of ethanol in the flame, which removes carbon from the PAH and soot formation pathways. The PAH and oxygenated aromatic hydrocarbon values were very similar in the 0%, 25% and 50% ethanol flames, but significantly lower in the 75% and 90% ethanol flames. These results were in general agreement with the model and were reflected by the model soot predictions. The model predicted similar soot profiles for the 0%, 25% and 50% ethanol flames, however it predicted significantly lower values in the 75% and 90% ethanol flames. The reaction flux analysis revealed benzyl to be a major contributor to single and double ring aromatics (i.e., benzene and naphthalene), which was identified in a similar role in nearly sooting or highly sooting ethylbenzene flames. The presence of this radical was significantly reduced as ethanol concentration was increased in the flames, and this effect in combination with the lower carbon to oxygen ratios and the enhanced formation of carbon monoxide, are likely what allowed higher equivalence ratios to be reached without forming soot.     

Hydraulic Behavior of Mechanically and Chemically Activated Synthetic Merwinite

The hydraulic behavior of synthetic merwinite was investigated after activation by two different methods, aiming to enhance its hydraulic activity which is weak in water. Mechanical activation, by means of extensive milling in a bead mill, led to amorphization of merwinite and a decrease in its crystallite size. The combined effect of higher specific surface area and of structural disorder resulted in a notable increase of hydraulic reactivity. The hydraulic reactivity was substantially more pronounced with chemical activation compared to mechanical activation. Crystalline and amorphous C‐S‐H and brucite were the main hydration products formed in the hydrated, mechanically activated merwinite, whereas portlandite precipitated additionally in the case of chemical activation. Spectroscopic analyses of FTIR and ²⁹Si MAS NMR verified the C‐S‐H formation. TEM investigations revealed formation of Mg‐low C‐S‐H gel around the merwinite particles. Both mechanically and chemically activated merwinite systems were capable of developing mechanical strength.     

Graph-based multimodal clustering for social multimedia

Real world datasets often consist of data expressed through multiple modalities. Clustering such datasets is in most cases a challenging task as the involved modalities are often heterogeneous. In this paper we propose a graph-based multimodal clustering approach. The proposed approach utilizes an example relevant clustering in order to learn a model of the “same cluster” relationship between a pair of items. This model is subsequently used in order to organize the items of the collection to be clustered in a graph, where the nodes represent the items and a link between a pair of nodes exists if the model predicted that the corresponding pair of items belong to the same cluster. Eventually, a graph clustering algorithm is applied on the graph in order to produce the final clustering. The proposed approach is applied on two problems that are typically treated using clustering techniques; in particular, it is applied on the problem of detecting social events and to the problem of discovering different landmark views in collections of social multimedia.     

Blast response simulation of an elastic structure: Evaluation of the fluid–structure interaction effect

Blast pressure wave interaction with an elastic structure is investigated using a numerical analysis approach, which considers fluid–structure interaction (FSI) within an Arbitrary Lagrange Euler (ALE) framework. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The structural displacement predicted by ignoring FSI is larger than the corresponding displacement considering FSI. The influence of the structural and blast pressure wave parameters on the importance of FSI is studied using an analysis of variables. Two non-dimensional parameters corresponding to the ratios of blast duration to the time period of the structure and the velocity of the structure to the particle velocity of the incident blast pressure wave are identified. It is shown that for a given blast pressure wave, the error in the maximum displacement predicted by ignoring FSI effect during structural motion is directly proportional to the ratio of the structure velocity to the particle velocity of the incident blast pressure wave. There is a continuous exchange of energy between the structure and air during the structural motion, which is significant when the structural velocity is significant compared to the particle velocity of incident blast pressure wave. FSI effect become insignificant when the ratio of velocities starts approaching zero.     

Effects of Errors in the Viewing Geometry on Shape Estimation

A sequence of images acquired by a moving sensor contains information about the three-dimensional motion of the sensor and the shape of the imaged scene. Interesting research during the past few years has attempted to characterize the errors that arise in computing 3D motion (egomotion estimation) as well as the errors that result in the estimation of the scene's structure (structure from motion). Previous research is characterized by the use of optic flow or correspondence of features in the analysis as well as by the employment of particular algorithms and models of the scene in recovering expressions for the resulting errors. This paper presents a geometric framework that characterizes the relationship between 3D motion and shape in the presence of errors. We examine how the three-dimensional space recovered by a moving monocular observer, whose 3D motion is estimated with some error, is distorted. We characterize the space of distortions by its level sets, that is, we characterize the systematic distortion via a family of iso-distortion surfaces, which describes the locus over which the depths of points in the scene in view are distorted by the same multiplicative factor. The framework introduced in this way has a number of applications: Since the visible surfaces have positive depth (visibility constraint), by analyzing the geometry of the regions where the distortion factor is negative, that is, where the visibility constraint is violated, we make explicit situations which are likely to give rise to ambiguities in motion estimation, independent of the algorithm used. We provide a uniqueness analysis for 3D motion analysis from normal flow. We study the constraints on egomotion, object motion, and depth for an independently moving object to be detectable by a moving observer, and we offer a quantitative account of the precision needed in an inertial sensor for accurate estimation of 3D motion.     

Parameterized real-time moment computation on gray images using block techniques

Moments constitute a well-known tool in the field of image analysis and pattern recognition, but they suffer from the drawback of high computational cost. Efforts for the reduction of the required computational complexity have been reported, mainly focused on binary images, but recently some approaches for gray images have been also presented. In this study, we propose a simple but effective approach for the computation of gray image moments. The gray image is decomposed in a set of binary images. Some of these binary images are substituted by an ideal image, which is called “half-intensity” image. The remaining binary images are represented using the image block representation concept and their moments are computed fast using block techniques. The proposed method computes approximated moment values with an error of 2–3% from the exact values and operates in real time (i.e., video rate). The procedure is parameterized by the number m of “half-intensity” images used, which controls the approximation error and the speed gain of the method. The computational complexity is O(kL ²), where k is the number of blocks and L is the moment order.