Measurement of Workability of Fresh Concrete Using a Mixing Truck

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer resultsSuggestions are given on how to improve the mixing truck for better use as a rheometer.     

Methanol synthesis from CO2 and H2 in multi-tubular fixed-bed reactor and multi-tubular reactor filled with monoliths

This work investigates the impact of catalyst structuring into particles or monoliths on methanol production from only CO₂ and H₂ at a large scale. Methanol synthesis in multi-tubular reactors is evaluated using packed-bed and monolithic reactors by modeling heat and mass transfer in each reactor. The obtained simulation results show that, at low gas hourly space velocity (GHSV = 10,000 h⁻¹), the performances of both reactor technologies are similar. In this case, the packed-bed reactor technology is the most appropriate technology due to its simplicity of installation and operation. At high GHSV (25,000 h⁻¹), the packed-bed reactor technology is limited by a considerable pressure drop that causes an important loss in productivity due to thermodynamic equilibrium, whereas the monolithic reactors exhibit negligible pressure drop and achieve far better performances.     

A distance measure for large graphs based on prime graphs

Graphs are universal modeling tools. They are used to represent objects and their relationships in almost all domains: they are used to represent DNA, images, videos, social networks, XML documents, etc. When objects are represented by graphs, the problem of their comparison is a problem of comparing graphs. Comparing objects is a key task in our daily life. It is the core of a search engine, the backbone of a mining tool, etc. Nowadays, comparing objects faces the challenge of the large amount of data that this task must deal with. Moreover, when graphs are used to model these objects, it is known that graph comparison is very complex and computationally hard especially for large graphs. So, research on simplifying graph comparison gainedan interest and several solutions are proposed. In this paper, we explore and evaluate a new solution for the comparison of large graphs. Our approach relies on a compact encoding of graphs called prime graphs. Prime graphs are smaller and simpler than the original ones but they retain the structure and properties of the encoded graphs. We propose to approximate the similarity between two graphs by comparing the corresponding prime graphs. Simulations results show that this approach is effective for large graphs.     

A proposal for a classification of product-related dependencies in development of mechatronic products

When designing mechatronic products, ‘complex dependencies’ are often reported to be a major challenge. This paper focuses on managing dependencies between attributes of the product during the design process. The literature study shows that there is a gap in the literature with regard to the classification of product-related dependencies. Traditionally, these dependencies have been described as appearing between the following product attributes: function, properties and structure. By analysing three mechatronic projects from industry, we identified and classified 13 types of product-related dependencies. Each product-related dependency is described and illustrated using the practical examples from the industrial projects. The value of the classification is evaluated by applying it to an industrial development setting not used for the analysis. The evaluation shows that delays in the project schedule, loss of functionality and quality issues can be avoided if attention is directed toward the product-related dependencies in the development process.     

Experimental investigation and numerical modeling of the thermal behavior of a micro-heater

In micro-heater, heat flux is generated by Joule effect thanks to short electric pulses. This leads to a rapid increase of the micro-heater temperature that reaches a few hundreds degree Celsius in a few microseconds. In addition to this, the cyclic nature of the energizing signal may cause an excessive heat accumulation and hence a reduction of the device life expectancy. It is thus of utmost importance to accurately model heat transfer in the whole device. This work focuses on a 200 dots per inch printing head system which consists of a row of micro-heaters. Structure and chemical composition of a single micro-heater are determined by scanning electron microscopy coupled to an EDX analyzer (energy dispersive X-ray spectrometry). These data are used to build a two dimensional numerical model which represents a micro-heater cross-section. This model gives the spatiotemporal evolution of the temperature field which highlights clearly the thermal loading phenomenon in the micro-heaters. In parallel, electric measurements are performed during the printing process to access to the actual power supplied to the micro-heaters. Infrared thermography was used to measure the thermal response of the micro-heaters to the electrical solicitation. The comparison of experimental and numerical results shows that the numerical model correctly predicts the thermal behavior of micro-heaters.     

Analysis of model parameters affecting the pressure profile in a circulating fluidized bed

This study focuses on continuum model validation of the flow of air and small catalyst particles in a circulating fluidized bed. Comparison with available experimental data of pressure drop and solids circulation rate in the riser clearly demonstrates the need to modify the homogeneous drag model to accurately predict the formation of clusters of particles, which are typically observed in the fluidization of small particles. The need to correct the drag law is also demonstrated in simulations of polydisperse powder flows wherein three solids species are used to represent a typical catalyst size distribution. Finally, particle‐wall friction is found to have the most significant effect on the vertical gas pressure gradient while particle–particle friction has only a minor effect. Published 2011 American Institute of Chemical Engineers AIChE J, 58: 427–439, 2012     

Synthesis,characterization and electrochemical performance of Sn3F3PO4 anode material for lithium-ion batteries

Tin fluorophosphate (Sn₃F₃PO₄) powder was synthesized via a microemulsion route. Physical properties of the synthesized material were investigated by means of X-ray powder diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The investigation showed that the synthesized powder was crystalline Sn₃F₃PO₄ with needle-like morphology with a thickness of 300–500 nm and length of 5–10 μm. The electrochemical performance of the synthesized powder as a negative electrode for Li-ion batteries was studied. The results showed that the synthesized Sm₃F₃PO₄ possessed an initial discharge capacity of 1370 mAh g^?1 and charge capacity of 968 mAh g^?1 in a potential range of 0.005–3 V. In addition, the material showed capacity retention of 70.8% after 30 cycles at a constant current density of 100 mA g^?1.     

Accurate,dense and shading-aware multi-view stereo reconstruction using metaheuritic optimization

Among the modern means of 3D geometry creation that exist in the literature, there are the Multi-View Stereo (MVS) reconstruction methods that received much attention from the research community and the multimedia industry. In fact, several methods showed that it is possible to recover geometry only from images with reconstruction accuracies paralleling that of excessively expensive laser scanners. The majority of these methods perform on images such as online community photo collection and estimate the surface position with its orientation by minimizing a matching cost function defined over a small local region. However, these datasets not only they are large but also contain more challenging scenes setups with different photometric effects; therefore fine-grained details of an object’s surface cannot be captured. This paper presents a robust multi-view stereo method based on metaheuristic optimization namely the Particle Swarm Optimization (PSO) in order to find the optimal depth, orientation, and surface roughness. To deal with the various shading and stereo mismatch problems caused by rough surfaces, shadows, and interreflections, we propose to use a robust matching/energy function which is a combination of two similarity measurements. Finally, our method computes individual depth maps that can be merged into compelling scene reconstructions. The proposed method is evaluated quantitatively using well-known Middlebury datasets and the obtained results show a high completeness score and comparable accuracy to those of the current top performing algorithms.

     

Influence of process parameters on thermal and mechanical properties of polylactic acid fabricated by fused filament fabrication

Fused filament fabrication is considered one of the most used processes in additive manufacturing rapid prototypes out of polymeric material. Poor strength of the deposited layers is still one of the main critical problems in this process, which affects the mechanical properties of the final parts. To improve the mechanical strength, investigation into various process parameters must be considered. In this article, the influence of different process parameters has been experimentally investigated by means of physicochemical and mechanical characterizations. Special attention was given to the thermal aspect. In that respect, the in situ measurement of temperature profile during deposition indicated that several parameters affect the cooling rate of material and consequently have an influence on the final parts. It was found that the influence of increasing the extruder temperature is more significant in comparison with other process parameters.