Modeling and performance evaluation of supply chains using batch deterministic and stochastic Petri nets

Batch deterministic and stochastic Petri nets are introduced as a tool for modeling and performance evaluation of supply chains. The new model is developed by enhancing deterministic and stochastic Petri nets (DSPNs) with batch places and batch tokens. By incorporating stochastic Petri nets (SPNs) with the batch features, inhibitor arcs, and marking-dependent weights, operational policies of supply chains such as inventory policies can be easily described in the model. Methods for structural and performance analysis of the model are developed by extending existing ones for DSPNs. As applications, an inventory system and an industrial supply chain are modeled and their performances are evaluated analytically and by simulation, respectively, using this BSPN model. The applications demonstrate that our model and associated methods can solve some important supply chain modeling and analysis issues. Note to Practitioners-This paper was motivated by the problem of performance analysis and optimization of supply chains but it also applies to other discrete event systems where materials are processed in finite discrete quantities (batches) and operations are performed in a batch way because of batch inputs and/or in order to take advantages of the economies of scale. Existing Petri net modeling and analysis tools for such systems ignore their batch features, making their modeling complicated. This paper suggests a new model called batch deterministic and stochastic Petri nets (BDSPNs) by enhancing deterministic and stochastic Petri nets with batch places and batch tokens. Methods for structural and performance analysis of the model are developed. We then show how an inventory system and a real-life supply chain can be modeled and their performances can be evaluated analytically and by simulation respectively based on the model. The model and associated analysis methods therefore provide a promising tool for modeling and performance evaluation of supply chains.     

Numerical Simulation of Brittle Damage in Concrete Specimens

A framework for damage mechanics of concrete is applied to simulate the nonlinear elastic deformation behavior of concrete using finite element method (FEM). A rather simple isotropic damage model containing essentially no adjustable parameters is shown to produce results in remarkably good agreement with sample experimental data: the damage law requires only the fracture energy to be defined completely. The model is achieved by introducing a damage surface that is similar to the yield function in the conventional theory of plasticity. A special form of damage surfaces is constructed to illustrate the application of the model. A new damage criterion, defined as an equivalent strain norm, is proposed, in order to take into consideration the asymmetric behavior of concrete. For verifying the FEM program including the model, deformations predicted by this model are compared with both the experimental ones for the concrete structural model and the ones calculated without application of the continuum damage mechanics.__________Translated from Problemy Prochnosti, No. 3, pp. 57 – 74, May – June, 2005.     

Modeling and Performance Evaluation of Inventory Systems Using Batch Deterministic and Stochastic Petri Nets

This paper presents our work on modeling and performance analysis of inventory systems using batch deterministic and stochastic Petri nets (BDSPNs). It addresses issues frequently raised by industrial companies, but did not receive enough attention by the Petri nets (PNs) community in spite of its important role in the study of discrete event systems. The BDSPN is a new class of PNs capable of describing the synchronization of discrete and batch token flows in discrete batch processes. Such processes appear in inventory systems or more general supply chains where materials are purchased in finite discrete quantities (batches of different sizes), and many operations such as inventory replenishment and customer order fulfillment are usually performed in a batch way because of the batch nature of customer orders and/or in order to take advantages of the economies of scale. In this paper, the BDSPN model is formally introduced, and its conflict resolutions of transitions and batch firing indexes are addressed. The model is then applied to the modeling and performance evaluation of various inventory systems. Analytic performance evaluation techniques are developed for the model with illustrative applications to the inventory systems. Our study shows that the model is powerful for both modeling and performance evaluation of the systems.     

Application of AHP and a mathematical index to estimate livability in tourist districts:The case of Al Qasba in Sharjah

Urban planners must ensure that urban public spaces are enjoyable to use to create a lively city that expresses their culture and traditions and welcomes social diversity. This study aims to develop a theoretical index for assessing the livability levels in tourist districts. Therefore, a survey-based study accompanied by a literature review is used to derive criteria for livability. In addition to using the analytic hierarchy process to develop an importancebased hierarchy of criteria, mathematical analysis is applied to derive the livability index. Furthermore, one of Sharjah’s well-known public spaces, Al Qasba Tourist District, is assessed as a case study. This study discussed the main concepts and factors of livability in urban public spaces to examine the livable extent of Qasba and the significance of criteria. Results show that the current livability level in Al Qasba is less than 50%, confirming its urgent need for further urban improvement. This study explores the livability assessment criteria and their influencing parameters. Using the suggested conceptual livability index enables decision makers to assess the livability level, analyze the influencing factors, and suggest solutions to improve the overall livability levels of open public spaces.     

Performance evaluation of nonlinear weighted T-system

This article deals with the analysis of discrete event systems which can be modelled by timed event graphs with multipliers (TEGMs). These graphs are an extension of weighted T-systems studied in the Petri net literature. These models do not admit a linear representation in (min,?+) algebra. This nonlinearity is due to the presence of weights on arcs. To mitigate this problem of nonlinearity and to apply some basic results used to analyse the performances of linear systems in dioid algebra, we propose a linearisation method of mathematical model reflecting the behaviour of a TEGM in order to obtain a (min,?+) linear model.     

Intended boundaries detection in topic change tracking for text segmentation

This paper presents a topical text segmentation method based on intended boundaries detection and compares it to a well known default boundaries detection method, c99. We compared the two methods by running them on two different corpora of French texts and results are evaluated by two different methods: one using a modified classic measure, the FScore, the other based on a manual evaluation one the Internet. Our results showed that algorithms that are close when automatically evaluated can be quite far when manually evaluated.     

Purification and characterisation of milk‐clotting and caseinolytic activities of pepsin isolated from adult sheep abomasa

Ovine pepsin was isolated and assessed for its milk‐clotting properties and caseinolytic activity in comparison with commercial chymosin. Ovine pepsin showed similar responses to variations in pH, temperature and CaCl₂ concentration of milk compared with chymosin, although its pH sensitivity was higher. SDS‐PAGE electrophoretic analysis of the casein fractions treated with ovine pepsin showed that alpha‐casein was more susceptible to proteolysis than beta‐casein, in contrast to chymosin. Curd‐firming properties of skim milk gels obtained with ovine pepsin and chymosin were evaluated by Gelograph under the same conditions. Curd produced using ovine pepsin was less firm than that made with chymosin.