Sharif Digital Repository

Actor-based modeling, with encapsulated active objects which communicate asynchronously, is generally recognized to be well-suited for representing concurrent and distributed systems. In this paper we discuss the actor-based language Rebeca which is based on a formal operational interpretation of the actor model. Its Java-like syntax and object-based style of modeling makes it easy to use for software engineers, and its independent objects as units of concurrency leads to natural abstraction techniques necessary for model checking. We present a front-end tool for translating Rebeca to the languages of existing model checkers in order to model check Rebeca models. Automated modular... 

Almost all multi-echelon inventory models assume that demands which are not satisfied immediately can be backordered. In some situations, this assumption may not be realistic. For example, we can model stockouts as lost sales when the retailers are in a competitive market and customers can easily turn to another retailer for purchasing goods. So, in this study, assuming lost sales at the retailers, we consider a one-warehouse, several retailers, two-item inventory system where the items can be interchangeably used. Using the well-known METRIC-approximation as a framework, we present a heuristic for finding cost effective base-stock policies. In a numerical study with simulation, we find that... 

This paper presents a dynamic programming methodology for finding the optimum preventive maintenance schedule of generating units of a GENCO in open power systems. The objective function for the GENCO is to sell electricity as much as possible, according to the market price forecast. Various constraints such as generation capacity, duration of maintenance and maintenance crew are taken into account. In a case study, introducing a GENCO with six generating units, and implementing dynamic programming, we obtain the optimal maintenance schedule over the planning period. © 2002 IEEE  

Pricing for an insurance policy can be described as the process of calculation of expected compensation to be paid to property losers as well as associated costs of potential risks. Loss forecast is accurate if the risks will be identified appropriately in order to calculate the frequency and expected severity of losses.This is particularly important about environmental risks since most of them appear in the long run. Environmental risk assessment model is both able to estimate the environmental liability premium for environmental pollution and degradation, and it can play a valuable role in promoting this industry. ELIS (Environmental Liability Insurance) software calculates the... 

This paper presents recent developments on effects of rest and fatigue loading on properties of healthy vertebra discs. A comparison of different approaches used in literature to study the properties of intervertebral disc is presented. The major achievements in this area so far are discussed in the context of their advantages and disadvantages. The past approaches are based on bio-mechanical models which mostly used statistical techniques for the analysis and estimation of fatigue loaded Intervertebral Disc (IVD). However, those modeling techniques were not flexible enough for analysis of customized tests. In this paper, we applied System Identification (SI) based NLARX modeling technique... 

Test Driven Development (TDD), as a quality promotion approach, suffers from some shortages that discourage its usage. One of the most challenging shortcomings of TDD is the low level of granularity and abstraction. This may lead to production of software that is not acceptable by the end users. Additionally, exploiting of TDD is not applicable in the enterprise systems development. To overcome this defect, we have merged TDD with Model Based Testing (MBT) and suggested a framework named Model Based Test Driven Development (MBTDD). According to TDD, writing test cases comes before programming, and based on our improved method of TDD, modeling precedes writing test cases. To validate the... 

In this paper, model reference control of a fractional order system has been discussed. In order to control the fractional order plant, discrete-time approximation methods have been applied. Plant and reference model are discretized by Grünwald-Letnikov definition of the fractional order derivative using "Short Memory Principle". Unknown parameters of the fractional order system are appeared in the discrete time approximate model as combinations of parameters of the main system. The discrete time MRAC via RLS identification is modified to estimate the parameters and control the fractional order plant. Numerical results show the effectiveness of the proposed method of model reference adaptive... 

Application of Volterra series to the modeling of static and dynamic nonlinear systems is investigated in this paper and compared to other methods. For nonlinear systems with memory, Volterra series serves as a generalization of convolution integral. To parameterize the Volterra kernels for limited dimension series, different methods are discussed. We use Laguerre functions and wavelet packets as orthonormal basis and we find the poles for the basis through a genetic algorithm search. Our test system is a hydraulic actuator with a highly nonlinear dynamics which is modeled with Volterra series. The results show that dynamic model with wavelet packets give a more accurate model with respect... 

Large technology-intensive enterprises and companies face a constant challenge: How can a set of selected high-tech projects get done in a manner that would minimize the total cost across all projects? In majority of cases, projects are assumed independent, leading to a separate cost evaluation. This assumption often does not hold for real-world project portfolios, frequently sharing overlapping technologies. In this paper, we show how the order of the execution of the projects can directly affect the total cost of the portfolio, due to shared dependencies. Modeling the problems in this area can be achieved by combining two main fields: graph theory and technology mining. A novel method is... 

Artificial Neural networks offer viable solution to identification and modeling of aerospace dynamic systems. This paper proposes a new approach to the nonlinear modeling of agile aircraft which is applicable to develop flight simulators. In contrary to classical methods, neural-network-based modeling of aircraft dynamics does not require any aerodynamic or propulsion model and a few flight test measured data suffice. The obtained model is shown valid for arbitrary pilot inputs within a region of mach-altitude around the pre-specified flight condition  

Valveless micropumps are widely used due to simple structure, durability and low maintenance. Understanding the fluid-membrane interaction and performance criteria is still a challenging problem for the scientists. In this work, a new model for side mounted valve micropumps is developed to obtain dynamic response of micropump with respect to piezoelectric actuation. The parameters of this model are obtained in terms of actuation frequency and geometrical dimensions of the micropump. Balancing elastic, inertial and damping forces result in the governing equation of the micropump system model. Analytical studies for the bottom mounted valve micropump indicate pump flux is independent of the... 

An integrated view of energy markets has led to the introduction of new market participants named energy retailers (ERs). Competition among ERs in an integrated market greatly improves market performance in areas such as sustainability, supply security, and environmental awareness. ER performance is evaluated in an integrated market with emission penalty reduction in the objective function. Bi-level programming is used to model an ER game, and the equilibria of different configurations are compared. In the game's first level, ERs offer various energy carrier selling prices to optimise profits. In the second level, consumers respond by switching from the retail market to minimise their energy... 

Optimal allocation of resources for R&D on new energy technologies is an important issue in the process of development of energy system models. In this study, a model of R&D planning in energy sector has been developed and it is then linked to the energy system model. Energy system model is used as a tool for the technology assessment and prioritization of new energy technologies is evaluated with the help of this model. Based on the economic and environmental impact of new technologies, the optimal allocation of resources for R&D of new technology is estimated with the help of the R&D planning model. The conceptual formulation of the model and its integration with the energy technology... 

Stochastic activity networks (SANs) are a stochastic generalization of Petri nets. SAN models have been used for performance, dependability and performability evaluation and are supported by several powerful modeling tools. We have recently introduced object stochastic activity networks (OSANs) to overcome some restrictions of these models. OSANs integrate the concepts of object-orientation into SAN models. Elements of OSANs and their submodels are defined as classes. In this paper, we briefly introduce OSANs and SANBuilder tool for modeling and evaluation with these models. © 2004 IEEE  

In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. Distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance - one for faults behind the series capacitors and another one for faults in front of the series capacitors. Then a special procedure to select the correct solution is utilized. Samples of voltages and currents at both ends of the line are taken synchronously and used to calculate the location of the fault. The proposed algorithm is independent of fault resistance and does not require any knowledge of source impedance. The...