Model-free adaptive control design using evolutionary-neural compensator

It is well-known that conventional control theories are widely suited for applications where the processes can be reasonably described in advance. However, when the plant’s dynamics are hard to characterize precisely or are subject to environmental uncertainties, one may encounter difficulties in applying the conventional controller design methodologies. In this case, an alternative design is a model-free learning adaptive control (MFLAC), based on pseudo-gradient concepts with compensation using a radial basis function neural network and optimization approach with differential evolution technique presented in this paper. Motivation for developing a new approach is to overcome the limitation of the conventional MFLAC design, which cannot guarantee satisfactory control performance when the nonlinear process has different gains for the operational range. Robustness of the MFLAC with evolutionary-neural compensation scheme is compared to the MFLAC without compensation. Simulation results for a nonlinear chemical reactor and nonlinear control valve are given to show the advantages of the proposed evolutionary-neural compensator for MFLAC design.     

Uncertainty propagation: Avoiding the expensive sampling process for real-time image-based measurements

A common way of evaluating the quality of a measuring device is to use it to measure the properties of some test objects, thus obtaining a large number of samples whose values are then compared to a known ground truth. Such a process tends to be labor intensive and time-consuming. A more convenient and elegant alternative is to statistically propagate the uncertainty of the measurement process throughout the computation chain. A clear advantage of such an approach over the conventional sampling-based method is its practical nature: it allows the continuous changes in input parameter values and sampling conditions, which are common in real-time applications, to be instantly taken into account.In order to demonstrate the benefits of using uncertainty propagation in real-time image metrology applications, we describe a method for automatic computation of box dimensions from single perspective projection images in real time. For this, we derive expressions for the uncertainty in the measurements based on the uncertainties present in all variables used in the computational flow. Our results show that these estimates are in accordance with the ones obtained using the conventional sampling process, thus safely replacing them. We also show that the uncertainty propagation approach is computationally efficient. This approach can be incorporated into applications that aim to make real-time measurements directly from images, and should also be useful in many other time-critical applications.     

An improved contrast enhancing approach for color-to-grayscale mappings

Despite the widespread availability of color sensors for image capture, the printing of documents and books are still primarily done in black-and-white for economic reasons. In this case, the included illustrations and photographs are printed in grayscale, with the potential loss of important information encoded in the chrominance channels of these images. We present an efficient contrast enhancement algorithm for color-to-grayscale image conversion that uses both luminance and chrominance information. Our algorithm is about three orders of magnitude faster than previous optimization-based methods, while providing some guarantees on important image properties. More specifically, our approach preserves gray values present in the color image, ensures global consistency, and locally enforces luminance consistency. Our algorithm is completely automatic, scales well with the number of pixels in the image, and can be efficiently implemented on modern GPUs. We also introduce an error metric for evaluating the quality of color-to-grayscale transformations.     

A Decentralized Grid Market Infrastructure for Service Oriented Grids

Service Oriented Computing has a deep impact on how IT infrastructures are conceived both in academia (e-science) and in industry (Service Oriented Architecture and commercial Web Services). Increasingly, economic models are being considered as suitable coordination mechanism for the management of service allocations to clients. However, few complete infrastructures have demonstrated the enabling of economics-based Service Oriented Grids (SOGs). The authors propose a complete infrastructure for economics-based SOGs and demonstrate its application in a prototype. They conduct experiments showing that practical agent-based automatic and fair trading of services at stable prices can be achieved using the proposed infrastructure.     

Using a Simple Prioritisation Mechanism to Effectively Interoperate Service and Opportunistic Grids in the EELA-2 e-Infrastructure

Grids currently in production can be broadly classified as either service Grids, composed of dedicated resources, or opportunistic Grids that harvest the computing power of non-dedicated resources when they are idle. While a service Grid provides high and well defined levels of quality of service, an opportunistic Grid provides only a best-effort service. Nevertheless, since opportunistic Grids do not require resources to be fully dedicated to the Grid, they have the potential to assemble a much larger number of resources. Moreover, these Grids cater very well to the execution of the so-called embarrassingly parallel applications, a type of application that is frequently found in practice, and that comprises the largest portion of the typical workload processed in production Grid systems. The EELA-2 e-infrastructure is comprised of a service Grid and an opportunistic Grid that federates computing resources from scientific institutions in both Europe and Latin America. Due to the complementary characteristics of these two types of Grids, a lot of attention has recently been placed in how to interoperate them. In this paper we focus on the less studied problem of assessing the feasibility of such interoperation. We analyse different prioritisation policies that define when the resources of one Grid can be used to run jobs originating from the other. Our results show that in the absence of a suitable prioritisation policy, the benefits that the users of one Grid may have, frequently come with an important negative impact on the users of the other Grid. We also show that a simple reciprocation mechanism is capable of arbitrating the interoperation in such a way that, whenever possible, users profit from the interoperation and, in no case, this benefit leads to a noticeable reduction on the quality of service that the users would experience were the Grids not to interoperate. We conclude discussing how we have implemented, in the context of the EELA-2 project, this prioritisation mechanism, allowing the effective interoperation of a service Grid based on the gLite middleware with an opportunistic Grid that uses the OurGrid middleware.     

Accelerating Time and Depth Seismic Migration by CPU and GPU Cooperation

In this paper, we discuss the porting strategy and the achieved performance of Petrobras production code that implements Kirchhoff prestack time and depth seismic migration algorithms on a cluster of 64 GPUs and 256 CPU cores. The time migration of a real-world survey was 20 times faster in the full cluster with GPUs than in the full cluster without GPUs. The introduction of GPUs accelerated the depth migration of another real-world survey by a factor of 5. In both cases, a large fraction of the achieved gains were due to the porting strategy that privileges CPU-GPU cooperation instead of pure GPU speed. Another strategy that contributed to the high gains was GPU overloading by multiple MPI processes. To cope with the heterogeneous load of real-world data, we developed a dynamic load balancing scheme that significantly speeds up computation.     

Improved creep performance of melt-extruded polycaprolactone/organo-bentonite nanocomposites

In this work, biodegradable nanocomposites based on polycaprolactone reinforced with pristine and organo-modified bentonites are prepared by melt extrusion. Bentonite is exchanged with benzalkonium chloride (CBK) in a pilot plant scale reactor. The influence of clay type and loading on morphology, rheology, mechanical properties, and creep performance of the resulting materials is analyzed. Besides, several theoretical models then applied to experimental creep data and master curves are used to relate time and temperature with the compliance of the materials. The morphology characterization of the nanocomposites show that the organo-modification of the clay greatly improves its dispersion in the polymer matrix. As a consequence, it is demonstrated that reinforcement of PCL with 3 wt% loading of organoclay produces the strongest improvement in creep resistance. The instantaneous creep strain and the experimental creep rate decrease more than 9% and 27%, respectively, in the range of temperatures analyzed. Moreover, the experimental values are used to adequately fit theoretical creep models for different clay loadings. On the other hand, the material with optimal creep behavior also shows the greatest improvements in tensile mechanical properties.     

Combined effects of SiO2 ratio and purity on physical properties and microstructure of in situ alumina-mullite ceramic

The in situ formation of mullite (Al₆Si₄O₁₃) is a complex process based on solid-state reactions strongly affected by the characteristics of Al₂O₃ and SiO₂ sources. This study investigated the combined effects of variable SiO₂/Al₂O₃ ratios and the presence of low-melting-point impurities on the physical properties and microstructure of in situ alumina-mullite ceramics. Two grades of synthetic amorphous silica, known as microsilica, of similar physical properties and significant differences in the content of alkali-based impurities (0.8 and 3.6 wt%), were combined with thin calcined alumina particles in different proportions (from silica-free up to stoichiometric mullite), pressed and sintered. The samples were tested for total porosity, flexural strength, and pore size distribution, and their crystalline phases and microstructures formed were investigated. Small amounts of both microsilica grades (up to 8.9 wt%) hindered the densification of the alumina-mullite matrix and favored grain growth events, increasing porosity and reducing strength. For samples containing higher microsilica loads (16.4–28.2 wt%), the impurities content significantly affected the amount of liquid phases formed. Such impurities altered the ratio and shape of the pores and the total amount of mullite after sintering. Therefore, different microstructures and levels of flexural strength and total porosity were observed.     

Eggshells as agro-industrial waste substitute for CaCO3 in glass foams: A study on obtaining lower thermal conductivity

In this work, discarded glass bottles (GB) and eggshells (ES) were used to produce foam glass designed for thermal insulation. The literature on the thermal conductivity of foam glasses produced with eggshells is sparse. This material was used as pore-forming agent at 3% and 5% weight fractions to obtain a foam glass with low thermal conductivity. Homogenized powders were uniaxially pressed, and the compacts were fired at three temperatures (800, 850, and 900°C). Raw materials were characterized by chemical analysis and particle size distribution. The foam glasses were characterized by their porosity, phases, compressive strength, and thermal conductivity. The best insulating properties were obtained for the composition containing 5 wt% ES fired at 800°C. This sample displayed a porosity of 91.4% while its thermal conductivity was of 0.037 W/m.K, with a compressive strength of 1.12 ± 0.38 MPa. Crystalline phases were observed in samples fired at 850 and 900°C as a result of the devitrification process. The final properties of the materials are comparable to those of commercial foam glasses obtained from non-renewable, more expensive raw materials, a great indicator that the studied compositions could be used as an environmentally friendly substitute.