Modelling Gas Holdup in Flotation Column Froths

A one‐dimensional steady‐state model is developed for the prediction of axial variation of the gas holdup in flotation column froths. Froth is considered as an inverse fluidized bed of bubbles and hence the frictional pressure gradient is obtained based on the energy balance. Pressure gradient can also be obtained from the Ergun equation with adjustable constants. The model correctly captures the effect of superficial gas velocity, superficial liquid velocity and bubble diameter on the variation of the gas holdup along the froth height. The predictions of the model are in agreement with the experimental data from the literature.     

The synthesis of pixelated metamaterial cross polarizer using binary wind driven optimization algorithm

Microsystem Technologies - In this paper synthesis of two wideband Metamaterial Cross Polarizer (MCPs) is proposed. The synthesis of proposed MCPs is done by using Binary Wind Driven Optimization...     

Non-equilibrium Thermodynamics of Rayleigh–Taylor Instability

Here, the fundamental problem of Rayleigh–Taylor instability (RTI) is studied by direct numerical simulation (DNS), where the two air masses at different temperatures, kept apart initially by a non-conducting horizontal interface in a 2D box, are allowed to mix. Upon removal of the partition, mixing is controlled by RTI, apart from mutual mass, momentum, and energy transfer. To accentuate the instability, the top chamber is filled with the heavier (lower temperature) air, which rests atop the chamber containing lighter air. The partition is positioned initially at mid-height of the box. As the fluid dynamical system considered is completely isolated from outside, the DNS results obtained without using Boussinesq approximation will enable one to study non-equilibrium thermodynamics of a finite reservoir undergoing strong irreversible processes. The barrier is removed impulsively, triggering baroclinic instability by non-alignment of density, and pressure gradient by ambient disturbances via the sharp discontinuity at the interface. Adopted DNS method has dispersion relation preservation properties with neutral stability and does not require any external initial perturbations. The complete inhomogeneous problem with non-periodic, no-slip boundary conditions is studied by solving compressible Navier–Stokes equation, without the Boussinesq approximation. This is important as the temperature difference between the two air masses considered is high enough (\(\Delta T = 70\) K) to invalidate Boussinesq approximation. We discuss non-equilibrium thermodynamical aspects of RTI with the help of numerical results for density, vorticity, entropy, energy, and enstrophy.     

An automated software reliability prediction system for safety critical software

Software reliability is one of the most important software quality indicators. It is concerned with the probability that the software can execute without any unintended behavior in a given environment. In previous research we developed the Reliability Prediction System (RePS) methodology to predict the reliability of safety critical software such as those used in the nuclear industry. A RePS methodology relates the software engineering measures to software reliability using various models, and it was found that RePS’s using Extended Finite State Machine (EFSM) models and fault data collected through various software engineering measures possess the most satisfying prediction capability. In this research the EFSM-based RePS methodology is improved and implemented into a tool called Automated Reliability Prediction System (ARPS). The features of the ARPS tool are introduced with a simple case study. An experiment using human subjects was also conducted to evaluate the usability of the tool, and the results demonstrate that the ARPS tool can indeed help the analyst apply the EFSM-based RePS methodology with less number of errors and lower error criticality.     

Structural and Luminescence Studies on Barium Sodium Borosilicate Glasses Containing Uranium Oxides

Barium sodium borosilicate glasses containing different amounts of uranium oxides were prepared by conventional melt quench method and investigated for their structural aspects by ²⁹Si and ¹¹B MAS NMR technique combined with steady‐state luminescence and lifetime measurements. Based on MAS NMR studies, it is confirmed that uranium ions act as network modifier up to 15 wt% and beyond which a separate uranium containing phase is formed. From the luminescence studies, it is inferred that uranyl species is in a highly distorted environment. For more than 15 wt% uranium oxide incorporation, weaker U–O–U linkages are formed at the expense stronger U–O–Si/B linkages, as suggested by the excited state lifetime value of the uranyl species as well as red shift in emission peak maximum. For glass samples containing more than 25 wt% uranium oxides, crystalline barium uranium silicate gets phase separated from glass matrix as confirmed by XRD studies.     

Effect of pH on the detailed chemical nature and metal-carbonate species in as synthesized zirconia alumina composites

Zirconia was deposition precipitated on γ-alumina in pH range 7-10 from zirconium oxy-nitrate and soda ash. Zirconium formed its hydroxycarbonate as deduced from ICP-EOS, CHN, and TGA-MS. Higher pH favored formation of carbonate species of zirconium over its hydroxide. TGA-MS indicated formation of three different types of carbonate species. FTIR results corroborated this. Monodentate metal carbonate was observed irrespective of pH of preparation. In addition, bridged bidentate species formed at pH ≤ 8 which changed to chelating bidentate at pH > 8. XRD indicated that all the samples formed tetragonal-zirconia upon calcination irrespective of pH of preparation. Higher pH resulted in smaller crystallites of t-ZrO₂. Changes in chemical moiety with pH reflected on acidity and the deactivation rate for 2-methyl-3-butyn-2-ol which decreased by two orders of magnitude in samples prepared at higher pH. Surface area and pore volume benefited from deposition precipitation. SEM-EDAX showed reasonable distribution of zirconia over γ-Al₂O₃.     

Determination of volume fraction of bainite in low carbon steels using artificial neural networks

Artificial neural networks have been used to estimate the volume fraction of bainite in low carbon steels containing various alloying elements. The network predicts the volume fraction for a given composition, isothermal transformation temperature and isothermal transformation time. Additionally, the maximum transformation temperature at which bainite formation takes place is also provided as an input to the neural network. The network was trained using the experimental data from three low carbon steels and it was found to perform quite well in predicting the volume fraction of bainite. The impact of the composition of alloying elements on the volume fraction of bainite was also studied and the results were in agreement with the known metallurgical theory.     

Dynamic Spectrum Access with QoS and Interference Temperature Constraints

Spectrum is one of the most precious radio resources. With the increasing demand for wireless communication, efficiently using the spectrum resource has become an essential issue. With the Federal Communications Commission's (FCC) spectrum policy reform, secondary spectrum sharing has gained increasing interest. One of the policy reforms introduces the concept of an interference temperature - the total allowable interference in a spectral band. This means that secondary users can use different transmit powers as long as the sum of these power is less than the interference threshold. In this paper, we study two problems in secondary spectrum access with minimum signal to interference noise ratio (quality of service (QoS)) guarantee under an interference temperature constraint. First, when all the secondary links can be supported, a nonlinear optimization problem with the objective to maximize the total transmitting rate of the secondary users is formulated. The nonlinear optimization is solved efficiently using geometric programming techniques. The second problem we address is, when not all the secondary links can be supported with their QoS requirement, it is desirable to have the spectrum access opportunity proportional to the user priority if they belong to different priority classes. In this context, we formulate an operator problem which takes the priority issues into consideration. To solve this problem, first, we propose a centralized reduced complexity search algorithm to find the optimal solution. Then, in order to solve this problem distributively, we define a secondary spectrum sharing potential game. The Nash equilibria of this potential game are investigated. The efficiency of the Nash equilibria solutions are characterized. It is shown that distributed sequential play and an algorithm based on stochastic learning attain the equilibrium solutions. Finally, the performances are examined through simulations     

Cell formation in flexible manufacturing systems under resource constraints

In this paper, the cell formation problem in Flexible Manufacturing Systems under resource constraints is discussed. A 0–1 integer programming model is developed to form the machine-part groups and to decide on the number of machines and the number of copies of tools required to achieve minimum overall system cost. The model takes into account the processing time available on any machine, tool lives and the processing requirements of the parts. The model is illustrated using a numerical example.     

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce_0.90Gd_0.06Y_0.02M_0.02O_2?δ (M?=?Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce_0.90Gd_0.06Y_0.02Sr_0.02O_2?δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.