• R Ramanujam

      Articles written in Sadhana

    • Models and logics for true concurrency

      Kamal Lodaya Madhavan Mukund R Ramanujam P S Thiagarajan

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      A distributed computer system consists of different processes oragents that function largely autonomously and coordinate their actions by communicating with each other. In such a situation, actions may be performed by different agents of the system locally, in a concurrent manner.

      In this paper, we first discuss formal models of distributed systems in which concurrency is specifiedexplicitly, in contrast to more traditional approaches where concurrency is representedimplicitly as a nondeterministic choice between all possible sequentializations of concurrent actions. This naturally leads to models based on partially-ordered sets of actions rather than sequences of actions and is often called thetrue concurrency approach. The models we focus on are distributed transition systems, elementary net systems and event structures.

      In the second half of the paper, we develop a family of logics to specify and reason about the behavioural properties of the models we have described. The logics we define are extensions of temporal logic with new modalities to directly describe concurrency.

      This paper is essentially a survey of work done by the authors during the last few years on modelling distributed systems with true concurrency and using logic to reason about these models. The emphasis is on motivating definitions through examples and on presenting major results, without going into too many formal details. We provide pointers to the literature where these details can be found.

    • Statistical modelling and analysis of material removal rate and surface roughness during wire electrical discharge hybrid turning (WEDHT) process


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      The non-traditional machining process is highly recommended for machining difficult-to-cut materials with increased hardness, toughness, work hardening effect, and poor thermal diffusivity, etc. Wire electrical discharge machining (Wire-EDM) is one of the above said processes used to machine material whichare electrically conductive. One of the variants of Wire-EDM process is wire electrical discharge hybrid turning (WEDHT) process, in which, the work material is made to rotate during material removal resulting in cylindrical components manufacturing. This process follows the principle of sparking and erosion for material removal with moving wire as a tool electrode. In the present study, WEDHT process is performed on Ti-6Al-4V alloy, which has applications in the areas of biomedical, marine, chemical, aerospace, etc. 27 experiments are performed using diffusion annealed zinc coated brass wire as the tool electrode by varying servo feed, pulse ON time and wire feed rate at three different levels to study the surface quality and material removal as the output performances. Atomic force microscopy (AFM) technique gives a 3D profile of the machined surface and measures the surface roughness. These measured 3D results are validated once again in 2D surface profile meter. The factor effects of all three input parameters are analyzed individually and analysis of variance (ANOVA) for all the performance responses are studied to know the most contributing factor in deciding the surface roughness (SR) and material removal, respectively. The regression analysis is performed for the response measures and the model parameters are analysed for goodness of fit using residual plot. Pulse ON time contributes more in deciding the SR and material removal rate (MRR) of the component followed by servo feed and wire feed rate.The interaction effects of the parameters are found to be insignificant.

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