The optimal schedule to produce a given number of acceptable parts with a specified confidence level

This paper deals with the problem of finding the optimal schedule for producing, with a probability α, a finite number H, of parts which have a diameter within specified tolerance limits. It is assumed that the diameter is a normally distributed variable that exhibits a linear trend in the process mean. The solution involves determining the optimal run size(s), as well as the specific number of runs of each size, required to produce at least H parts, with probability α, at minimum cost. A solution algorithm is provided and computational experience reported.     

Thermo-economic analysis of a direct supercritical CO2 electric power generation system using geothermal heat

A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO₂ turbine expansion electric power generation system was proposed in this paper. Assisted by this integrated model, thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity (LCOE). Specifically, in geothermal heat extraction simulation, an integrated wellbore-reservoir system model (T2Well/ECO2N) was used to generate a database for creating a fast, predictive, and compatible geothermal heat mining model by employing a response surface methodology. A parametric study was conducted to demonstrate the impact of turbine discharge pressure, injection and production well distance, CO₂ injection flowrate, CO₂ injection temperature, and monitored production well bottom pressure on LCOE, system thermal efficiency, and capital cost. It was found that for a 100 MW_e power plant, a minimal LCOE of $0.177/kWh was achieved for a 20-year steady operation without considering CO₂ sequestration credit. In addition, when CO₂ sequestration credit is $1.00/t, an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.     

Magneto-dielectric effect in Pb(Zr0·52Ti0·48)O3 filled nanoporous Ni 0 ·5Zn 0 ·5Fe 2 O 4 composite

Nanoporous Ni_0·5Zn_0·5Fe₂O₄ particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m² g^???1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr_0·52Ti_0·48)O₃ was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni_0·5Zn_0·5Fe₂O₄ which exerted a compressive strain on Pb(Zr_0·52Ti_0·48)O₃ thereby lowering the tetragonality in its crystal structure.     

The ancient 11th century iron pillar at Dhar, India: a microstructural insight into material characteristics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

THE ECONOMIC DESIGN OF CONTROL CHARTS: A RENEWAL THEORY APPROACH

Economic models for the design of control charts based on Duncan's approach1 have been well studied in the recent past. We present an alternative approach to the development of a few of these models using renewal equations. The main emphasis here is to study the role of the probability model associated with the process failure mechanism. It is demonstrated that the expressions Tor the expected cycle length E( T) and the expected cost per cycle E( C) are easier to obtain by the proposed renewal equation approach than by adopting the traditional approach. Furthermore, it is observed that certain non-Markovian shock models may be analyzed by adopting a renewal equation approach, whereas Duncan's approach has not been used with any non-Markovian model.     

Improvement of Plasma Performance with Lithium Wall Conditioning in Aditya Tokamak

Lithiumization of the vacuum vessel wall of the Aditya tokamak using a lithium rod exposed to glow discharge cleaning plasma has been done to understand its effect on plasma performance. After the Li-coating, an increment of ～100 eV in plasma electron temperature has been observed in most of the discharges compared to discharges without Li coating, and the shot reproducibility is considerably improved. Detailed studies of impurity behaviour and hydrogen recycling are made in the Li coated discharges by observing spectral lines of hydrogen, carbon, and oxygen in the visible region using optical fiber, an interference filter, and PMT based systems. A large reduction in O I signal (up to ～ 40% to 50%) and a 20% to 30% decrease of H α signal indicate significant reduction of wall recycling. Furthermore, VUV emissions from O V and Fe XV monitored by a grazing incidence monochromator also show the reduction. Lower Fe XV emission indicates the declined impurity penetration to the core plasma in the Li coated discharges. Significant increase of the particle and energy confinement times and the reduction of Z eff of the plasma certainly indicate the improved plasma parameters in the Aditya tokamak after lithium wall conditioning.