Determining Economic Maintenance Frequency for a Family of Machines

This paper deals with the problem of determining economic maintenance frequency for a group of machines. The operating cost for each machine is assumed to increase with time since the last maintenance work carried out on the machine. The cost of carrying out maintenance work is known and assumed constant. A fixed cost is incurred whenever maintenance work is carried out, and this fixed cost is assumed to be independent of the number of machines on which maintenance work is carried out. The total cost of the system is given by the sum of maintenance and operating costs for all the machines. A heuristic method is proposed for determining the economic maintenance frequency of each machine. An example is given to illustrate the method.     

Characterization of rapidly solidified powder of high-speed steel

Ionization and excitation cross sections as well as electron-energy spectra and stopping powers of the alkali metal atoms Li, Na, K, and Rb colliding with antiprotons were calculated using a time-dependent channel-coupling approach. An impact-energy range from 0.25 to 4000 keV was considered. The target atoms are treated as effective one-electron systems using a model potential. The results are compared with calculated cross sections for antiproton-hydrogen atom collisions.     

Influence of γ-irradiation on the transition temperatures of crystalline polytetrafluorethylene

The influence of γ-irradiation on the melting and two solid-solid transitions, occurring near 19° and 30°C, of polytetrafluorethylene was studied by differential scanning calorimetry. A continuous depression of all three transition temperatures, with increasing dose was observed in a first scan of highly crystalline samples at a heating rate of 20°C/min. Additional information was obtained about the accompanying heats of transition. Values for the number of CF₂ units excluded from the crystal lattice per 100 eV energy deposition were calculated by using an equation for the depression of the melting point by chemical impurities. The value obtained of G(–units) = 3.3 ± 0.3 is in agreement with a value of G(chemically damaged units) = 3.0 ± 0.1 previously reported on the basis of scavenging techniques. It is concluded that chemical radiation-induced damage in this polymer may be estimated by reference to changes in the melting temperature. A value of G(–units) = 1.6 ± 0.2 was obtained by reference to the 19°C transition.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Microwave-assisted synthesis of 3-formyl substituted imidazo[1,2-a]pyridines

An efficient, metal-free method for the synthesis of 3-formyl imidazo[1,2-a]pyridines is reported. The method utilises commercially available substrates and features a broad substrate scope. The intermediate enamine was isolated and a plausible reaction mechanism proposed.     

A comparison of Bayesian,Hazard, and Mixed Logit model of bankruptcy prediction

Computational Management Science - The purpose of this study is to examine the impact of the choice of cut-off points, sampling procedures, and business cycles on the forecasting accuracy of...