Study of pyro-carbon coated alumina kernel using mixed contrast transfer based X-ray phase retrieval technique

We have used the contrast transfer function based X-ray phase retrieval technique for phase retrieval studies on a two-component system. Pyro-carbon coated alumina matrix was chosen as a two-component system for these studies. Simulations as well as experimental results are presented. This paper shows that X-ray phase contrast along with phase retrieval can become an alternative tool for non-destructive characterization of these materials. We have also attempted to retrieve the spatial distribution of the projected thickness map of the two different elements.     

Micromechanics of spatially uniform heterogeneous media: A critical review and emerging approaches

Outside of the classical microstructural detail-free estimates of effective moduli, micromechanical analyses of macroscopically uniform heterogeneous media may be grouped into two categories based on different geometric representations of material microstructure. Analysis of periodic materials is based on the repeating unit cell (RUC) concept and the associated periodic boundary conditions. This contrasts with analysis of statistically homogeneous materials based on the representative volume element (RVE) concept and the associated homogeneous boundary conditions. In this paper, using the above classification framework we provide a critical review of the various micromechanical approaches that had evolved along different paths, and outline recent emerging trends. We begin with the basic framework for the solution of micromechanics problems independent of microstructural representation, and then clarify the often confused RVE and RUC concepts. Next, we describe classical models, including the available RVE-based models, and critically examine their limitations. This is followed by discussion of models based on the concept of microstructural periodicity. In the final part, two recent unit cell-based models, which continue to evolve, are outlined. First, a homogenization technique called finite-volume direct averaging micromechanics theory is presented as a viable and easily implemented alternative to the mainstream finite-element based asymptotic homogenization of unit cells. The recent incorporation of parametric mapping into this approach has made it competitive with the finite-element method. Then, the latest work based on locally-exact solutions of unit cell problems is described. In this approach, the interior unit cell problem is solved exactly using the elasticity approach. The exterior problem is tackled with a new variational principle that successfully overcomes the non-separable nature of the overall unit cell problem.     

Effects of doping on the optical fiber drawing process

Optical fibers are typically drawn from silica preforms, which usually consist of two concentric cylinders called the core and the cladding, heated in a high-temperature furnace. For optical communication purposes, the core generally has a higher average refractive index than the cladding to obtain total internal reflection. This paper investigates the effects of adding dopants to the core or to the cladding, to change the refractive index values, on the optical fiber drawing process. Employing an analytical/numerical model developed earlier to simulate the core-cladding structure of a typical optical fiber, the paper considers different dopants and the effects resulting from the consequent changes in properties, particularly the radiation absorption properties, on the temperature distributions, flow, neck-down profile, thermally induced defects and draw tension. The zonal method is applied to model the radiation transfer in the glass perform and the purge gas is taken as non-participating. The numerical model has been validated by comparing with results available in the literature, wherever possible. It is found that the effects are significant because of changes in refractive index and absorption of radiation, which give rise to significant changes in temperature and tension. These can, in turn, substantially affect fiber quality and characteristics. Therefore, for an accurate and realistic modeling of the process, the effects of property changes due to dopants on the draw process must be included.     

Initial rapid wetting in metallic systems

The initial rapid wetting of a solid surface by a liquid phase is an important step in many industrial processes. Liquid-phase sintering of powder metallurgical steels is one such industrial process, where metallic powders of micrometer size are used. Investigating the dynamic wetting of a high-temperature metallic drop of micrometer size experimentally is very challenging. Here, a phase-field-based numerical model is first implemented and verified by accurately capturing the initial dynamic wetting of millimeter-sized metal drops and then the model is extended to predict the dynamic wetting of a micrometer-sized metal drop. We found, in accordance with recent observations, that contact line friction is required for accurate simulation of dynamic wetting. Our results predict the wetting time for a micrometer-sized metal drop and also indicate that the dynamic wetting patterns at the micro- and millimeter length scales are qualitatively similar. We also found that the wetting process is much faster for a micrometer-sized metal drop compared to a millimeter-sized metal drop.     

Receive antenna selection for MIMO systems over correlated fading channels

In this letter, we propose a novel receive antenna selection algorithm based on cross entropy optimization to maximize the capacity over spatially correlated channels in multiple-input multiple-output (MIMO) wireless systems. The performance of the proposed algorithm is investigated and compared with the existing schemes. Simulation results show that our low complexity algorithm can achieve near-optimal results that converge to within 99% of the optimal results obtained by exhaustive search. In addition, the proposed algorithm achieves near-optimal results irrespective of the mutual relationship between the number of transmit and receive antennas, the statistical properties of the channel and the operating signal-to-noise ratio.     

Stress Corrosion Cracking and Oil Leakage in a Control Oil Piping System

This article describes the results of an investigation concerning with the failure of a pipe which was carrying oil from the control oil unit to the steam turbine control valves servomotor. The failure was in the form of a crack, propagating horizontally along the pipe. The crack initiated on the outside of the pipe. The cause of the failure was investigated by conducting visual examination, detailed macro and microstructural examinations and determining the composition of material from the failed pipe. The composition of the pipe material was analyzed by atomic absorption spectrometer. The failure of the oil pipe was attributed to stress corrosion cracking. The pipe material is A312 TP 304L. Recommendation to minimize such failures includes coating the pipe to prevent contact with chloride from the surrounding marine environment.     

Fabrication of innovative charkha for pashmina spinning and its impact assessment

Pashmina, a finest natural animal fiber is utilized for preparation of world famous Kashmiri pashmina shawls by traditional practices. Hand spinning is one of the important processing step, wherein fibers are converted into a fine yarn on a traditional spinning wheel (yander). The task is usually carried out by women folk. It is a laborious process resulting in a lot of physical stress affecting the efficiency of artisans. An innovative charkha has been fabricated to reduce the physical stress and its effect on the spinning efficiency and remuneration of artisans over traditional one was evaluated. The study revealed that innovative charkha was efficient in terms of time consumed for spinning by 73.50% over traditional one besides decreasing physical drudgery. In terms of income, there was an increase of 146% over traditional one for same period of time without deteriorating the quality of yarn.     

Determining SPICE parameter values for BJTs

The roles of hybrid-π, two-port, and SPICE transistor parameter are compared. A step-by-step procedure is described for determining numerical parameter values for a dynamic SPICE model of a bipolar junction from transistor manufacturer's measured data. The procedure is illustrated with an example     

Application of selftuning regulator algorithm to generating unit controllers

The processing capability of computers makes it feasible to implement sophisticated techniques for process control. However, to minimize the software development costs, it is desirable to develop algorithms that can have a wider application. In keeping with this, an AVR and speed governor for a generating unit have been designed using the same algorithm, called the selftuning regulator. The selftuning AVR and speed governor have been implemented using a microprocessor and a minicomputer online. The feasibility of developing unified algorithms is demonstrated by means of realtime tests, in which the two controllers are used simultaneously for a generating unit physical model.     

Results of test on microprocessor-based voltage and speed regulators carried out on a large physical model complex

Results of experimental tests carried out with microprocessor-based voltage and speed regulators using a digital-analogue-physical model complex of a large power system at the Siberian Power Institute of the USSR Academy of Sciences are described. The physical test facility, and the test objectives and procedures are also outlined. Tests were carried out on a Soviet-built microprocessor AVR and a Canadian-built microprocessor AVR and speed governor. The work described shows that the development of speed and voltage regulators using microprocessors is a feasible and promising proposition.