Magnetic separation studies on ferruginous chromite fine to enhance Cr:Fe ratio

The Cr:Fe ratio (chromium-to-iron mass ratio) of chromite affects the production of chrome-based ferroalloys. Although the lit-erature contains numerous reports related to the magnetic separation of di...     

Linearizer for pulse-shaping of received pulse in ultra-wideband radio systems

This paper presents a novel concept of pulse-shaping in an ultra-wide band radio system. Instead of attempting to design an antenna with flat group delay, the emphasis has been shifted to the signal processing aspect of pulse shaping. The received pulse which has broadened due to non-linear phase response of the propagating channel is shaped back closer to the ideal pulse using a linearizer. The block schematic of the linearizer is presented along with simulated results. Though only a Rayleigh first order pulse has been used for simulation purpose, the method can easily be generalized to incorporate other pulse shapes.     

Failure analysis of titanium alloy (Ti6Al4V) fastener used in aerospace application

Titanium alloy fasteners are being used in space programme. These fasteners are coated with MoS₂, which serves the purpose of solid lubricant. During the trial assembly of flight spin motor to the bracket mounted on subsystem, one of the two fasteners failed such that the head of the bolt had sheared off the shank. Metallographic analysis carried out on the failed fasteners revealed variations in the microstructures all along the shank axis. Microstructure consisted of equiaxed primary alpha in transformed beta matrix within lower portion of the shank, while it was elongated primary alpha with little bulging all along prior beta grain boundaries as well as acicular alpha at some other location towards the head side, features, typical of, as if worked above beta transus temperatures.This paper highlights the details of investigations carried out on the failed fasteners.     

Modeling without categorical variables: a mixed-integer nonlinear program for the optimization of thermal insulation systems

Optimal design applications are often modeled by using categorical variables to express discrete design decisions, such as material types. A disadvantage of using categorical variables is the lack of continuous relaxations, which precludes the use of modern integer programming techniques. We show how to express categorical variables with standard integer modeling techniques, and we illustrate this approach on a load-bearing thermal insulation system. The system consists of a number of insulators of different materials and intercepts that minimize the heat flow from a hot surface to a cold surface. Our new model allows us to employ black-box modeling languages and solvers and illustrates the interplay between integer and nonlinear modeling techniques. We present numerical experience that illustrates the advantage of the standard integer model.     

Effect of Nb doping on structural and electric properties of PZT (65/35) ceramic

The aim of this study is to determine the effect of Nb⁵⁺ doping on PZT (65/35) based bulk materials in their structure, micro structure and electrical properties. The Nb content was chosen 0-9 mole%. These materials were prepared by conventional mixed oxide method. X ray diffraction studies suggest the compound to be of rhombohedral perovskite phase. Excess addition of Nb result in pyrochlore and fluorite phase develops in PZT (65/35) sample. Detailed studies of dielectric constant as a function of temperature (40degC to 500degC) and frequency (100 Hz to 1 MHz) suggest that the compounds undergo diffuse type of phase transition. Maximum dielectric constant and resistivity were found to be strongly dependent on doping and measuring frequencies. Using complex impedance analysis micro structural parameters such as bulk and grain boundary resistance, bulk charge carrier concentration and relaxation time were determined     

Electric field effect on metallic particle contamination in a common enclosure gas insulated busduct

Sulphur hexaflouride (SF₆) is generally found to be very sensitive to field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. A study of CIGRE group suggests that 20% of failures in gas insulated substations (GIS) is due to the existence of various metallic contaminations in the form of loose particles. The presence of contamination can therefore be a problem with gas-insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substation. It would also offer the possibility of operating at higher fields to affect a potential reduction in the GIS size with subsequent savings in the cost of manufacture and installation. The purpose of this paper is to develop techniques, which will formulate the basic equations that will govern the movement of metallic particles like aluminum and copper in a bus duct. The simulation considers the electric field effect on particle movement and the results have been presented and analyzed     

自复原电网的前景

最近全世界不断发生的停电事故,将电力系统的可靠性变成了引人瞩目的焦点.这些停电事故造成的社会和经济损失累计起来每年达到数十亿美元.随着数字时代的到来,以计算机和电力电子为基础的效率更高的制造工艺在行业里占据了优势地位,随着电力在总能源消耗中所占比重继续增加,电力系统可靠性的价值也在增加.在如何提高监测和控制水平,改善电力系统方面,存在各种解决方案,本文试图探讨一些最新解决方案的前景.     

Theoretical computation of input impedance of gap-coupled circular microstrip patch antennas loaded with shorting post

In this paper, theoretical analysis of the input impedance of the two gap-coupled circular microstrip path antennas loaded with shorting post has been performed. The concept of coupled microstrip lines is applied to the gap-coupled microstrip antennas loaded with shorting post and using circuit theory approach the input impedance of the structure is calculated. The effect of mutual coupling between the radiating apertures has been taken into account. Simulated results are presented for input impedance of the gap-coupled circular microstrip patch antenna loaded with shorting post which supports the theoretical predictions. The simulation work has been performed using the method-of-moment based commercially available simulator IE3D. The comparison shows good agreement between simulated and numerically computed results.     

Development of ANN model and study the effect of temperature on strain ratio and sensitivity index of EDD steel

Anisotropy and strain rate sensitivity index (m) plays a very important role in the formability of materials. In the present investigation strain ratios in 0°, 45° and 90° to the rolling direction and the strain rate sensitivity index were calculated at different temperatures. After developing the data from experiments, Artificial Neural Network (ANN) models are trained for different properties. Trained ANN models are used to calculate different strain ratios and sensitivity index at unknown temperatures. The results are promising and the percentage error in ANN prediction is found to be around 10%.     

Fatigue crack growth behaviour of nickel based superalloys at ambient temperature

The present investigation deals with the study of fatigue crack growth rate (FCGR) behaviour of conventional IN 718 (Ni-0.02%C-19.0%Cr-19.35%Fe-3.0%Mo-5.10%Nb-0.50%Al-1.00%Ti-0.0033%B, all in wt%) and modified IN 718 (Ni-0.02%C-19.04%Cr-19.31%Fe-3.04%Mo-4.73%Nb-1.01%Al-1.16%Ti-0.0033%B, all in wt%) alloys at ambient temperature. Modified IN 718 alloy exhibits enhanced crack growth resistance due to roughness induced crack closure as compared to conventional IN 718 alloy.