Bayesian Analysis of a Superimposed Renewal Process

Stochastic behavior of an aero-engine failure/repair process has been analyzed from a Bayesian perspective. Number of failures/repairs in the component-sockets of this multi-component system are assumed to follow independent renewal processes with Weibull inter-arrival times. Based on the field failure/repair data of a large number of such engines and independent Gamma priors on the scale parameters and log-concave priors on the shape parameters, an exact method of sampling from the resulting posterior distributions of the parameters has been proposed. These generated parameter values are next utilised in obtaining the posteriors of the expected number of system repairs, system failure rate, and the conditional intensity function, which are computed using a recursive formula.

Effect of process variables on die-billet temperature history in a slow speed hot coining type process

A computer code is developed as a part of an ongoing project on computer aided process modelling of forging operation, to simulate heat transfer in a die-billet system. The code developed on a stage-by-stage technique is based on an Alternating Direction Implicit scheme. The experimentally validated code is used to study the effect of process specifics such as preheat die temperature, machine ascent time, rate of deformation, and dwell time on the thermal characteristics in a batch coining operation where deformation is restricted to surface level only.

Semi-Supervised Classification Using Sparse Gaussian Process Regression

Gaussian Processes (GPs) are promising Bayesian methods for classification and regression problems. They have also been used for semi-supervised learning tasks. In this paper, we propose a new algorithm for solving semi-supervised binary classification problem using sparse GP regression (GPR) models. It is closely related to semi-supervised learning based on support vector regression (SVR) and maximum margin clustering. The proposed algorithm is simple and easy to implement. It gives a sparse solution directly unlike the SVR based algorithm. Also, the hyperparameters are estimated easily without resorting to expensive cross-validation technique. Use of sparse GPR model helps in making the proposed algorithm scalable. Preliminary results on synthetic and real-world data sets demonstrate the efficacy of the new algorithm.

Role of barriers to conformational changes in ketones undergoing the Norrish type II process

The Norrish type II process is examined in three ketones containing primary, secondary and tertiary C---H bonds in the γ position relative to the carbonyl groups; the MINDO/3 semiempirical self-consistent field (SCF) molecular orbital (MO) method was used with complete geometry optimization in the unrestricted Hartree—Fock frame for the open-shell species. Results show that barriers to conformational change in ketones play an important role in the triplet reaction.

The Mechanism Of The Hydrogen Abstraction Process By Photo-Excited Ketones

Qualitative potential energy surfaces for hydrogen abstraction from alkanes containing primary, secondary and tertiary C-H bonds by a photo-excited ketone have been reported, The results suggest that the activation barriers for these processes decrease in the order primary > secondary > tertiary in agreement with the observed trend in the rate constants. The analysis of the electronic structure of the transition-state reveal that electron-transfer from hydrocarbon to ketone and formation of a new bond are almost synchronous in the hydrogen transfer process. The tunneling of hydrogen is not important in the normal temperature region even though the barriers are small.

A New Liquid Level Sensor for Process-Control Applications

Many process-control systems are air-operated. In such an environment, it would be desirable and economical to use pneumatic sensors. Bubble-back pressure sensors perform quite satisfactorily, but in case of viscous inflammable and slurry-like liquids with a tendency to froth, this level sensor is inadequate. The method suggested in this paper utilizes a pneumatic capacitor, one boundary of which is formed by the liquid level, to modulate a fluid amplifier feedback oscillator. The absence of moving parts and economy obtained makes this method attractive for process-control applications. The system has been mathematically modeled and simulated on an IBM 360/44 digital computer. Experimental values compare fairly well with the theoretical results. For the range tested, the sensor is found to have a linear frequency variation with the liquid level Extended running in the laboratory shows that the system is very reliable. This system has been found insensitive to temperature variations of up to 15ðC.

Mechanism of gel-to-crystallite conversion process in the synthesis of nanocrystalline multinary oxides

Description of gel-to-crystallite conversion process is made towards the synthesis of nanocrystalline titanates and aluminates. Thermodynamic and kinetic factors governing the conversion of a gel to meta-stable and stable nanocrystalline products(s) are discussed. Correlations between these factors and the preparative conditions employed for the syntheses of titanates and aluminates are arrived at.

Compensator for constant relative stability in process control systems

Process control systems are designed for a closed-loop peak magnitude of 2dB, which corresponds to a damping coefficient () of 0.5 approximately. With this specified constraint, the designer should choose and/or design the loop components to maintain a constant relative stability. However, the manipulative variable in almost all chemical processes will be the flow rate of a process stream. Since the gains and the time constants of the process will be functions of the manipulative variable, a constant relative stability cannot be maintained. Up to now, this problem has been overcome either by selecting proper control valve flow characteristics or by gain scheduling of controller parameters. Nevertheless, if a wrong control valve selection is made then one has to account for huge loss in controllability or eventually it may lead to an unstable control system. To overcome these problems, a compensator device that can bring back the relative stability of the control system was proposed. This compensator is similar to a dynamic nonlinear controller that has both online and offline information on several factors related to the control system. The design and analysis of the proposed compensator is discussed in this article. Finally, the performance of the compensator is validated by applying it to a two-tank blending process. It has been observed that by using a compensator in the process control system, the relative stability could be brought back to a great extent despite the effects of changes in manipulative flow rate.

Solid State Electrochemical Sensors in Process Control

The basic principles of operation of gas sensors based on solid-state galvanic cells are described. The polarisation of the electrodes can be minimised by the use of point electrodes made of the solid electrolyte, the use of a reference system with chemical potential close to that of the sample system and the use of graded condensed phase reference electrodes. Factors affecting the speed of response of galvanic sensors in equilibrium and non-equilibrium gas mixtures are considered with reference to products of combustion of fossil fuels. An expression for the emf of non-isothermal galvanic sensors and the criterion for the design of temperature compensated reference electrodes for non-isothermal galvanic sensors are briefly outlined. Non-isothermal sensors are useful for the continuous monitoring of concentrations or chemical potentials in reactive systems at high temperatures. Sensors for oxygen, carbon, and alloying elements (Zn and Si) in liquid metals and alloys are discussed. The use of auxiliary electrodes permits the detection of chemical species in the gas phase which are not mobile in the solid electrolyte. Finally, the cause of common errors in galvanic measurements, and tests for correct functioning of galvanic sensors are given. 60 ref.--AA

Lipid-amphotericin B complex structure in solution: A possible first step in the aggregation process in cell membranes

The interactions between the polyene antibiotic amphotericin B with dipalmitoylphosphatidylcholine were investigated in vesicles (using circular dichroism) and in chloroform solution (using circular dichroism and IH, I3C, and 31P nuclear magnetic resonance). The results show that amphotericin B readily aggregates in vesicles and that the extent of aggregation depends on the 1ipid:drug concentration ratio. Introduction of sterol molecules into the membrane hastens the process of aggregation of amphotericin B. In chloroform solutions amphotericin B strongly interacts with phospholipid molecules to form a stoichiometric complex. The results suggest that there are interactions between the conjugated heptene stretch of amphotericin B and the methylene groups of lipid acyl chains, while the sugar moiety interacts with the phosphate head group by the formation of a hydrogen bond. A model is proposed for the lipid-amphotericin B complex, in which amphotericin B interacts equally well with the two lipid acyl chains, forming a 1:l complex.

Low-temperature preparation and characterization of phase-pure lanthanide chromates (V) by the citrate gel process

Phase-pure, crystalline lanthanide chromates LnCrO4 (V), where Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Yb, Lu and Y, have been prepared by the controlled combustion of the corresponding lanthanide biscitrato chromium (III) complexes at comparatively low temperatures. Formation of chromates (V) was confirmed by X-ray diffraction, infrared and electronic spectroscopy. Phase purity of the materials has also been confirmed by X-ray photoelectron spectroscopy.

Plasma diagnostics of the high pressure oxygen-sputtering process

The characteristics of the high pressure oxygen-sputtering plasma in the pressure range 0.8–2.4 mbar have been studied using the Langmuir probe technique. The variation in plasma parameters such as positive ion density, electron density, mean electron energy and floating potential with pressure and temperature has been investigated. It has been observed that the positive ion density increases at high substrate temperatures whereas the negative ion density decreases. The study of the variation in mean electron energy and floating potential also indicated the possibility that the number of negative ions is less when the substrates are at elevated temperatures. Since the negative ions are supposed to cause re-sputtering and make the films off-stoichiometric, the reduction in the negative ion density as observed at elevated substrate temperatures is better suited for depositing stoichiometric YBa2Cu3O7−δ superconducting thin films.