EVALUATION OF A METHOD FOR MEASURING MIXING TIME USING NUMERICAL SIMULATION AND EXPERIMENTAL DATA

A method for measuring mixing performance in large-scale vessels is investigated. The method is evaluated experimentally in a pilotscale reactor and by using a model based on the three-dimensional calculation of the flow field. The method is based on injection of a tracer and measuring the concentration with several detectors at different locations. The mixing performance is measured as the decay rate of the difference between the concentration at the detectors and the final concentration.

The model predicts a strong dependence on injection point. The assumption of a first-order decay rate of the concentration deviation is more appropriate for some injection points.     

Urban qualities and residents’ strategies in compact global south cities: the case of Havana

Research and policy argue for more compact cities to respond to sustainable development challenges. However, what actually needs to be made more compact and how, is under examined, particularly in global South cities where north notions of urban qualities are adopted without being questioned. Informed by a qualitative study in informal and compact neighborhoods in Havana, this paper explores which qualities are important to deliver more just cities, and what strategies are developed by residents to strengthen beneficial qualities and address detrimental qualities in contexts of informal urbanization and compactness. It shows how the street, human capital, neighborhood, housing affordability, citizenship and vibrancy are significant compact city qualities neglected in the literature. Finally, the paper shows how diverse strategies are developed by residents to draw upon these qualities, such as self-help urbanism, learning and innovation, economic entrepreneurship, networks of solidarity, economies of reciprocity, local imaginaries and active citizenship.

     

Structural Changes during Milling of Silicon Carbide

The kinetics of milling and structural changes during milling of commercial silicon carbide powder in a ball mill lined with hard alloy are studied. Data are provided for the specific surface, x-ray patterns, and infrared spectra. It is shown that milling kinetics are described best of all by an exponential relationship and that milling of silicon carbide powder is accompanied by changes in polytype composition. The x-ray patterns and infrared spectra obtained make it possible to assume that during milling the 15R polytype content in the powder composition decreases while the content of structures with less layering (the 4H polytype and -SiC) increases; in this case the number of absorption bands in the infrared spectra decreases.     

Data Parallel Implementation of Belief Propagation in Factor Graphs on Multi-core Platforms

We investigate data parallel techniques for belief propagation in acyclic factor graphs on multi-core systems. Belief propagation is a key inference algorithm in factor graph, a probabilistic graphical model that has found applications in many domains. In this paper, we explore data parallelism for basic operations over the potential tables in belief propagation. Data parallel techniques for these table operations are developed for shared memory platforms. We then propose a complete belief propagation algorithm using these table operations to perform exact inference in factor graphs. The proposed algorithms are implemented on state-of-the-art multi-socket multi-core systems with additional NUMA-aware optimizations. Our proposed algorithms exhibit good scalability using a representative set of factor graphs. On a four-socket Intel Westmere-EX system with 40 cores, we achieve 39.5 $\times $ speedup for the table operations and 39 $\times $ speedup for the complete algorithm using factor graphs with large potential tables.     

Limit velocity of fracture front and dynamic strength of brittle solids

The theories of propagation of brittle fracture fronts in solid materials are compared with experimental data. Instead of the well-known theory of the limit fracture stress the theory of limit velocity of fracture front is developed. Accordingly between the moving boundary at which the static strength is attained and the front of fracture the material can stand essential dynamic over-loadings. The experimental data on contained explosions in optically transparent intact blocks show that the limit velocity of brittle cracks front takes place immediately after the separation of the shock front and the front of brittle fracture. The hypothesis of the existence of limit front velocity leads to the conclusion that in the two-front structure of plane shock waves the amplitude of elastic precursors, known as “the Hugoniot elastic limit”, exceeds the value of ultimate static strength of a solid material and has to increase with increasing of a finite shock pressure. This effect is justified by a number of experiments with brittle materials. The analogue with the plane problem of a self-supporting brittle burst is shown. The explanation of exceeding of the ultimate static strength and of “the delay time” of fracture under the spall condition is given. The increasing of internal fractures, which is described by the dilatancy loosening of materials is discussed. The well-known laws of “the geometrical similarity” of contained explosions are in accordance with expression of the strength in terms of the ultimate stress but not in terms of Griffith's energy for creating of new cracks. The possibility of the regime of a limit front velocity of fracture at explosion motions in real rocks, for which the dilatancy has place, is discussed.     

Inductive Learning with a Computational Network

This paper introduces a computational network which combines heterogeneous rule-extraction algorithms for intelligent data analysis. Combining induction programs may alleviate the possible negative effects of data set representation and individual program's influences, such as inductive bias. The application of the computational network to a diabetes data set shows that, when combining the various programs, an increase in rule set accuracy and comprehensibility are obtained.     

Physical Understanding of Active Control of Beam Scanning in Preventing Top Concavity in Electron Beam Welding

Metallurgical and Materials Transactions A - Low-frequency scanning electron beam welding (SEBW) is recently recognized as a possible control method for preventing the top concavity behavior in...     

Structure and Properties of B4C - SiC Composites

We have investigated how the composition, grain morphology, and method of preparing the starting mixture affect the processes that form the structure and phase composition of B₄C - SiC composites during hot pressing. We found that, depending on the composition of the initial powder mixtures, which is responsible for different mechanisms of consolidation of ceramic materials during hot pressing, the grain size of the main B₄C phase and its defect content as well as the nature of the SiC phase distribution within the material differ significantly. When B₄C - SiC composites with a low SiC content are made from initial B₄C - B₄Si - B - C powder mixtures those composites have a high cracking resistance because of their fine grain structure.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 112–119, March–April, 2005.