Effect of Nitrogen and Niobium on the Structure and Secondary Hardening of Super Hard High Speed Tool Steel

High‐speed steels have been used mostly for multi‐point cutting tools and for plastic working tools. High speed steels are ferrous based alloys of the Fe‐C‐X multi‐component system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. The properties of these steels can be improved by modifying their chemical composition or the technology of their production. One of the new trends in modifying the tool steels chemical composition consists in the addition of niobium and nitrogen. In this work, the effects of niobium and nitrogen on morphology of carbides and secondary hardening temperature of investigated high speed tool steels were studied. This experimental work shows that, the conventional ingots have many types of carbides of different shapes and sizes precipitate on the boundary together with thick needle like carbides. On the contrary, for nitrogen steel, the nitrogen alloying leads to form dense, fine and well distributed microstructure. While, on the case of niobium alloying, single carbide (MC), and different types of eutectic carbides were precipitated which have a major effect on the secondary hardening temperature.     

Optimized bandwidth allocation with fairness and service differentiation in multimedia wireless networks

In this article we present an optimal Markov Decision‐based Call Admission Control (MD‐CAC) policy for the multimedia services that characterize the next generation of wireless cellular networks. A Markov decision process (MDP) is used to represent the CAC policy. The MD‐CAC is formulated as a linear programming problem with the objectives of maximizing the system utilization while ensuring class differentiation and providing quantitative fairness guarantees among different classes of users. Through simulation, we show that the MD‐CAC policy potentially achieves the optimal decisions. Hence our proposed MD‐CAC policy satisfies its design goals in terms of call‐class‐differentiation, fairness and system utilization. Copyright © 2006 John Wiley & Sons, Ltd.     

Compatibilization of low‐density polyethylene/plasticized starch blends by reactive compounds and electron beam irradiation

Blends based on various compositions of low‐density polyethylene (LDPE) and plasticized starch (PLST) were prepared by melt extrusion and molding in the form of sheets under hot press. The rheology properties during mixing were studied in terms of torque and temperature against mixing time. The structural properties of LDPE/PLST blends before and after electron beam irradiation was characterized by IR spectroscopy, tensile mechanical testing, and scanning electron microscopy (SEM). The torque‐time curves during the mixing process showed that the values of torque in the first region of mixing for pure LDPE or LDPE/PLST blends are higher in the presence of the compatibilizer PEMA than that in the presence of EVA. In addition, the stability of mixing was attained after a short time in the presence of PEMA. The IR spectroscopy suggests that the compatibilization by EVA and PEMA compounds proceeds through the formation of hydrogen bonding during mixing and this compatibility was improved after electron beam irradiation. The stress–strain curves of pure LDPE and its blends with PLST showed the behavior of tough polymers with yielding properties. The SEM micrographs of the fracture surfaces give supports to the effect of EVA and PEMA as compatibilizers and the effect of electron beam irradiation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

A mathematical model for predicting spray atomization characteristics in an Eulerian–Eulerian framework

A new mathematical model is developed for calculating droplet break-up frequency based on both drag and turbulence induced fragmentation stresses. The droplet break-up model is introduced into a CFD methodology that is based on the Eulerian–Eulerian approach. The CFD solver couples the population balance equation along with the Navier–Stokes equations for predicting the droplets diameter. Finally, preliminary results using this CFD model are presented for the case of a coaxial airblast atomizer and a good agreement with the experimental data is achieved.     

Design of fault simulator

Fault simulator is proposed to understand and evaluate all possible fault propagation scenarios, which is an essential part of safety design and operation design and support of chemical/production processes. Process models are constructed and integrated with fault models, which are formulated in qualitative manner using fault semantic networks (FSN). Trend analysis techniques are used to map real time and simulation quantitative data into qualitative fault models for better decision support and tuning of FSN. The design of the proposed fault simulator is described and applied on experimental plant (G-Plant) to diagnose several fault scenarios. The proposed fault simulator will enable industrial plants to specify and validate safety requirements as part of safety system design as well as to support recovery and shutdown operation and disaster management.     

AutoRWN: automatic construction and training of random weight networks using competitive swarm of agents

Neural Computing and Applications - Random Weight Networks have been extensively used in many applications in the last decade because it has many strong features such as fast learning and good...     

Strength characteristics of dune sand stabilized with lime-silica fume mix

While more than half the land surface of Iraq consists of deserts covered mainly with sand dunes, little research has taken place to study the characteristics and the behaviour of sand dunes. The growth of economy, demography and building activities in Iraq necessitates carrying out geotechnical investigations for the dune sand. The purpose of the present work is to assess the suitability of sand dunes as subgrade layer for carrying roads and rail foundations. An extensive laboratory testing programme was carried out to study the geotechnical properties and the behaviour of sand dunes. Sand dune samples were collected from a region in Baiji area in Salah-Aldeen governorate, North of Iraq, in situ field density of the soil was measured by sand-cone test. The tests include moisture content, classification tests, compaction tests, relative density and direct shear test. Chemical tests and X-ray diffraction analyses were also carried out. Silica fume (SF) and lime-silica fume (L-SF) mix have been used for stabilising and their effects on the sand dunes were investigated. A grey-coloured densified SF is used. Four percentages are used for lime 0, 3, 6 and 9% and four percentages are used for SF 3, 6, 9 and 12% and the optimum percentage of SF is mixed with the percentages of lime. Several tests are made to investigate the soil behaviour after adding the lime, and SF. It was found that L-SF caused an increase in the angle of friction ? and cohesion c. Higher cohesion was reached; 10 kPa with higher percentage of 6% L + 12% SF. In addition, the angle of internal friction increases with increasing the maximum dry density, where the values of the angle of internal friction ranged between 35° and 41°.