A new approach to the system reliability analysis using reverse Petri nets

Анализа стабла неисправности (АСН) је техника за анализу поузданости која се користи за одређивање узрока и вероватноће отказа система. АСН је базирана на стаблу неисправности (СН), графичком моделу који користи логичка кола и отказне догађаје за представљање узрочно-последичних веза између догађаја који претходе отказу система. Квалитативни део АСН састоји се у одређивању минималних скупова пресека. Скуп пресека је скуп примарних догађаја који, када се догоде истовремено, доводе до отказа ситема. Минимални скуп пресека (минипресек) је скуп пресека који је редукован на минимални број елемената који изазивају отказ система. У овој дисертацији је предложена нова метода за одређивање минипресека кохерентног СН, СН које садржи само И и ИЛИ логичка кола, са вишеструким догађајима. Метода је заснована на посебном типу Петријевих мрежа – инверзним Петријевим мрежама. Прво је представљен нови алгоритам за редукцију скупова пресека кохерентног СН. Одређивање свих минипресека кохерентног СН је НП тежак проблем. У дисертацији се разматрају приступи којима се прво одређују сви скупови пресека датог СН а затим се врши елиминисање надскупова, односно скупова пресека који нису минимални. У тим приступима, СН се трансформише у еквивалентну булову једначину у којој се, затим, елиминишу сви редундантни скупови пресека. Већ је доказано да су скупови пресека, који не садрже вишеструке догађаје, минимални. Тиме се редукција ограничава само на скупове пресека са вишеструким догађајима. У овој дисертацији се посматра још једна врста скупова пресека: они који, ако садрже неки вишеструки догађај, садрже сва његова понављања. Овакви скупови пресека су означени са C*. Показује се да је скуп пресека облика C*, ако постоји, такође минималан. Тиме се додатно скраћује поступак редукције булове једначине. Затим се, даље, доказују услови за постојање скупова пресека облика C* и одређује минимална број скупова пресека који се могу елиминисати као надскуп од C*. Предложен је нови алгоритам за редукцију булове једначине датог СН, који се базира на раздвајању скупова пресека у три групе: скупови пресека без вишеструких догађаја, скупови пресека облика C* и остали скупови пресека. Ефикасност алгоритма је илустрована на групи тест...The Fault Tree Analysis (FTA) is a reliability analysis technique used to determine the root causes and probability of occurrence of a specified top event. FTA is based on a Fault Tree (FT), a graphical model using logic gates and fault events to model the cause-effect relationships involved in causing the top event. Determining minimal cut sets is a qualitative part in the FTA. The cut set is a set of basic events which, when simultaneous, cause the top event to occur. The minimal cut set (minicut) is a cut set which has been reduced to the minimum number of events that cause the top event to occur. This Dissertation proposes a new method for minicuts generation of a coherent FT, constructed using AND and OR logic operator only, with repeated events. The approach is based on the special type of Petri Nets – Reverse Petri Net. First, a new algorithm for reducing cut sets in coherent fault trees is presented. Determining all minicuts of a fault tree is NP-hard problem. Coherent fault trees and the top-down approaches for minicuts generation are considered. The FT can be translated into an equivalent Boolean expression. Obtained Boolean expression then should be reduced by eliminating all redundant cut sets. It is already proved that the cut sets not containing any repeated event are minicuts. This limits the reduction only to the cut sets containing repeated events. Cut sets containing all repetitions of its events are denoted by {C*}. It is proved that C*, if exists, is also minicut. This further limits the reduction of the Boolean expression. In addition, we proved conditions for existence of C* and calculated the minimal number of cut sets that can be eliminated as subsets of C*. Finally, a new algorithm for reduction of the Boolean expression which is based on the partition of the cut sets into three families: those not containing any repeated event, those of type C*, and others, is proposed. The efficiency of the algorithm is shown by applying it to some benchmark fault trees..

Multi-period Customer Service Level Maximization under Limited Production Capacity

This paper will focus on a make-to-stock multi-period order fulfilment system with random orders from different classes of customers under limited production circumstances.For this purpose a heuristic algorithm has been developed aimed at maximizing the customer service level in any cycle and in the entire multi-period. In this paper, in order to validate the results obtained with this algorithm, a mixed integer programming model was developed that is based on the same assumptions as the algorithm. The model takes into account the priorities of customer groups and the balanced customer service level within the same group. The presented approaches are applied to a real example of Fast Moving Consumer Goods. Their comparison was carried out in several scenarios.

An Algorithm for Production Planning Based on Supply Chain KPIs

This paper observe multi-period multi-product production planning problem in make-to-stock production environment with limited production capacity. Such problem is identified in Fast Moving Consumer Goods industry. The goal was to develop an algorithm for supporting dynamic production triggering decisions in relation with two supply chain key performance indicators: stock cover and customer service level. The presented approach is applied to a real example in several scenarios based on different decision criteria

Book review of: Metaheuristics for Business Analytics. A Decision Modeling Approach by Abraham Duarte, Manuel Laguna,and Rafael Martí

Book review of: Metaheuristics for Business Analytics. A Decision Modeling Approach by Abraham Duarte, Manuel Laguna,and Rafael Martí. Springer International Publishing, Series: EURO Advanced Tutorials on Operational Research, 2018, 136 pp. Hardcover ISBN: 978-3-319-68117-7, eBook ISBN: 978-3-319-68119-

Development of a Quality-Based Model for Software Architecture Optimization: A Case Study of Monolith and Microservice Architectures

Various architectures can be applied in software design. The aim of this research is to examine a typical implementation of Jakarta EE monolithic and microservice software architectures in the context of software quality attributes. Software quality standards are used to define quality models, as well as quality characteristics and sub-characteristics, i.e., software quality attributes. This paper evaluates monolithic and microservice architectures in the context of Coupling, Testability, Security, Complexity, Deployability, and Availability quality attributes. The performed examinations yielded a quality-based mixed integer goal programming mathematical model for software architecture optimization. The model incorporates various software metrics and considers their maximal, minimal or targeted values, as well as upper and lower deviations. The objective is the sum of all deviations, which should be minimal. Considering the presented model, a solution which incorporated multiple monoliths and microservices was defined. This way, the internal structure of the software is defined in a consistent and symmetrical context, while the external software behavior remains unchanged. In addition, an intersection point of monolithic and microservice software architectures, where software metrics obtain the same values, was introduced. Within the intersection point, either one of the architectures can be applied. With the exception of some metrics, an increase in the number of features leads to a value increase of software metrics in microservice software architecture, whilst these values are constant in monolithic software architecture. An increase in the number of features indicated a quality attribute’s importance for the software system should be examined and an appropriate architecture should be selected accordingly. Finally, practical recommendations regarding software architectures in terms of software quality were given. Since each software system needs to meet non-functional in addition to functional requirements, a quality-driven software engineering can be established

Economic Activities Structure and Development: Evidence From Serbia

Differences in the level of economic achievement in different countries are determined by the availability of resources and economic policies. Economic development could be influenced by the structure of economic activities. The paper brings the analysis of Serbian economic activities structure and its influence on the level of development during the period 2008-2011. The optimization model has been used to show economic activities to be invested in in order to achieve development. The results show that the most important economic activities in enhancing development are information and communication; finance and insurance; water supply, sewerage, waste management and remediation activities

Optimization of the layout of departments in hospitals

Planning the layout of departments in hospitals or reconstructing existing ones is a complex task at the strategic decision-making level. Confusing layouts can contribute to patients' anxiety, increase the time spent in clinical procedures and total distance travelled by patients. The development of quantitative approaches in solving this problem dates back to the late seventies of the twentieth century. In this paper, we present an approach to the hospital layout based on a Variable Neighborhood Search (VNS). The proposed approach was tested on artificial and two real-world instances: University Clinic Regensburg, Germany and Ahmed Maher Hospital in Cairo, Egypt. Presented computational results show that the proposed VNS quickly reaches all optimal solutions for small-scale instances obtained by exact solver and provides quality solutions on large-scale instances that are relatively close to the best known solutions in literature

The effects of economic activities diversification on development: The perspective of Serbia

Each economy specializes in certain economic activities depending on the development level and availability of resources. During their development, countries undergo sectoral transformation. In order to achieve a higher level of economic development, it is necessary for a country to diversify its economic activities and determine which economic activities should be invested in. The aim of this paper is to analyse the effects of economic structure and diversification activities on the development of Serbia for the period 2007-2012. Optimization model has been used to present diversification of activities. Furthermore, the efficiency frontier is used to show returns, risks and correlation among activities. The results show that the economic activities - Mining and quarrying, Public administration and defence, Compulsory social security, Other service activities, Financial and insurance activities, Arts, entertainment and recreation should be drivers of economic growth, because they provide a balance between growth and security regarding GVA in economic activities