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Yes / Purpose - The COVID-19 pandemic has caused significant disruptions to global supply chains (SCs), affecting the production, distribution, and transportation of goods and ser- vices. To mitigate these disruptions, it is essential to identify the barriers that have im- peded the seamless operation of SCs. This study identifies these barriers and assesses their impact on supply chain network (SCN). Design/methodology/approach - To determine the relative importance of different bar- riers and rank the affected industries, a hybrid approach was employed, combining the best-worst method (BWM) and the technique for order preference by similarity to an ideal solution (TOPSIS). To accommodate the inherent uncertainties associated with the pan- demic, a triangular fuzzy TOPSIS was used to represent the linguistic variable ratings provided by decision-makers. Findings - The study found that the airlines and hospitality industry was the most affected by the barriers, accounting for 46% of the total, followed by the healthcare industry (23%), the manufacturing industry (19%), and finally the consumer and retail industry (17%). Research limitation/implications - This study is limited to the four critical industries and nine identified barriers. Other industries and barriers may have different weights and rankings. Nevertheless, the findings offer valuable insights for decision-makers in SC management, aiding them in mitigating the impact of COVID-19 on their operations and enhancing their resilience against future disruptions. Originality/value - This study enhances our understanding of COVID-19’s impact on SCN and provides a framework for assessing disruptions using multi-criteria decision-making processes. The hybrid approach of BWM and TOPSIS in a fuzzy environment is unique and offers potential applicability in various evaluation contexts.

An online algorithm must make decisions immediately and irrevocably based only on a part of the input without any knowledge of the future part of the input. We introduce the competitive analysis of online algorithms, a standard worst-case analysis, and present main results of this analysis on the problem of online Bin Packing and on some of its variants. In Bin Packing, a sequence of items of size up to 1 arrives to be packed into the minimal number of unit capacity bins. Mainly, we focus on Colored Bin Packing in which items have also a color and we cannot pack two items of the same color adjacently in a bin. For Colored Bin Packing, we improve some previous results on the problem with two colors and present the first results for arbitrarily many colors. Most notably, in the important case when all items have size zero, we give an optimal 1.5-competitive algorithm. For items of arbitrary size we present a lower bound of 2.5 and a 3.5-competitive algorithm. Powered by TCPDF (www.tcpdf.org)

Dans les systèmes informatiques temps réel, les tâches logicielles sont contraintes par le temps. Pour garantir la sûreté du système critique contrôlé par le système temps réel, il est primordial d'estimer de manière sûre le pire temps d'exécution de chaque tâche. Les performances des processeurs actuels du commerce permettent de réduire en moyenne le temps d'exécution des tâches, mais la complexité des composants d'optimisation de la plateforme rendent difficile l'estimation du pire temps d'exécution. Il existe différentes approches d'estimation du pire temps d'exécution, souvent ségréguées et difficilement généralisables ou au prix de modèles coûteux. Les approches probabilistes basées mesures existantes sont vues comme étant rapides et simples à mettre en œuvre, mais souffrent d'un manque de systématisme et de confiance dans les estimations qu'elles fournissent. Les travaux de cette thèse étudient les conditions d'application de la théorie des valeurs extrêmes à une suite de mesures de temps d'exécution pour l'estimation du pire temps d'exécution probabiliste, et ont été implémentées dans l'outil diagxtrm. Les capacités et les limites de l'outil ont été étudiées grâce à diverses suites de mesures issues de systèmes temps réel différents. Enfin, des méthodes sont proposées pour déterminer les conditions de mesure propices à l'application de la théorie des valeurs extrêmes et donner davantage de confiance dans les estimations. / Software tasks are time constrained in real time computing systems. To ensure the safety of the critical systems that embeds the real time system, it is of paramount importance to safely estimate the worst-case execution time of each task. Modern commercial processors optimisation components enable to reduce in average the task execution time at the cost of a hard to determine task worst-case execution time. Many approaches for executing a task worst-case execution time exist but are usually segregated and hardly scalable, or by building very complex models. Measurement-based probabilistic timing analysis approaches are said to be easy and fast, but they suffer from a lack of systematism and confidence in their estimates. This thesis studies the applicability of the extreme value theory to a sequence of execution time measurements for the estimation of the probabilistic worst-case execution time, leading to the development of the diagxtrm tool. Thanks to a large panel of sequences of measurements from different real time systems, capabilities and limits of the tool are enlightened. Finally, a couple of methods are provided for determining measurements conditions that foster the application of the theory and raise more confidence in the estimates.

Este trabalho apresenta um estudo sobre sistemas operacionais de tempo real (RTOS) utilizados na implementação da infraestrutura de controle digital para sistemas mecatrônicos, mas serve também como referência para outros sistemas que possuam restrições de tempo. Além de ter um caráter experimental, onde foram medidos e analisados dados como o pior tempo de resposta dos sistemas e a latência para tratamento de interrupções, este trabalho de pesquisa ainda contempla a implementação e uso de RTOS em situações práticas, bem como contempla a construção de uma plataforma geral de pesquisa que servirá de base para futuros trabalhos no laboratório de mecatrônica. Os sistemas analisados neste trabalho foram o VxWorks, QNX, Linux, RTAI, Windows XP, Windows CE e \'mü\'C/OS-II. Outro produto gerado durante este trabalho foi um Live CD para auxiliar na implementação e ensino de conceitos e sistemas de tempo real. / This work presents a study about real time operating systems (RTOS) that are utilized as infrastructure to create digital control systems for mechatronics systems, and also for systems that have critical time constraints. Parameters like worst case response time and interrupt latency were measured for each operating system. This research project also covers the implementation and use of RTOS in practical situations. A general research platform for robotics and real time research was also developed and will be used for future works in the Mechatronics Laboratory. The tested systems were VxWorks, QNX, Linux, RTAI, Windows XP, Windows CE and \'mü\'C/OS-II. Another product released during this work was a Live CD to aid the implementation and teaching of real time systems and concepts.

L’essor des réseaux AFDX comme infrastructure de communication entre les équipements de bord des aéronefs civils motive de nombreux travaux de recherche pour réduire les délais de communication tout en garantissant un haut niveau de déterminisme et de qualité de service. Cette thèse traite de l’effet des accolements de trames sur l’End System de réception, notamment sur le buffer interne afin de garantir une non perte de trames et un dimensionnement mémoire optimal. Une modélisation pire cas du flux de trames est réalisée selon une première méthode pessimiste, basée sur un flux de trames périodiques ; puis une seconde, plus optimiste, basée sur des intervalles de réception et un placement de trames itératif. Une étude probabiliste met en œuvre des distributions gaussiennes pour évaluer les probabilités d’occurrences des pires cas d’accolements et apporte un éclairage qui ouvre une discussion sur la pertinence de ne considérer que la modélisation pire cas pour dimensionner le buffer de réception. Un gain mémoire supplémentaire peut être obtenu par la mise en œuvre de la compression sans perte LZW. / The rise of AFDX networks as a communication infrastructure between on-board equipment of civil aircraft motivates many research projects to reduce communication delays while guaranteeing a high level of determination and quality of service. This thesis deals with the effect of the back-ot-back frame reception on the reception End System, in particular, on the internal buffer, in order to guarantee a non-loss of frames and optimal memory dimensioning. A worst-case modeling of the frame flow is carried out according to a first pessimistic method, based on a periodic frame flow. Then a more optimistic method is presented based on the reception intervals and an iterative frame placement. A probabilistic study implements Gaussian distributions to evaluate the occurrence probabilities of the worst back-to-back frames and provides an illumination that opens a discussion on the relevance of not considering the worst-case modeling to size the reception buffer. Additional memory gain can be achieved by implementing LZW lossless compression.

<p>The increasing complexity in the development of a configurable real-time system has emerged new principles of software techniques, such as aspect-oriented software development and component-based software development. These techniques allow encapsulation of the system's crosscutting concerns and increase the modularity of the software. The properties of a component that influences the systems performance or semantics are specified separately in entities called aspects, while basic functionality of the property still remains in the component. </p><p>When building a real-time system, different sets of configurations of aspects and components can be combined, resulting in different configurations of the system. The temporal behavior of the system changes and a way to ensure the predictability of the system is needed. </p><p>This thesis presents a tool for aspect-level worst-case execution time analysis, which gives a priori information about the temporal behavior of the system, before the process of composing aspects with components.</p>

<p>Rising complexity in the development of real-time systems has made it crucial to have reusable components and a more flexible way of configuring these components into a coherent system. Aspect-oriented system development (AOSD) is a technique that allows one to put a system’s crosscutting concerns into"modules"that are called aspects. Applying AOSD in real-time and embedded system development one can expect reductions in the complexity of the system design and development. </p><p>A problem with AOSD in its current form is that it does not support predictability in the time domain. Hence, in order to use AOSD in real-time system development, we need to provide ways of analyzing temporal behavior of aspects, components and resulting system (made from weaving aspects and components). Aspect analyzer is a tool that computes the worst-case execution time (WCET) for a set of components and aspects, thus, enabling support for predictability in the time domain of aspect-oriented real-time software. </p><p>A limitation of the aspect analyzer, until now, were that no verification had been made whether the aspect analyzer would produce WCET values that were close to the measured or computed (with another WCET analysis technique) WCET of an aspect-oriented real-time system. Therefore, in this thesis we perform a verification of the correctness of the aspect analyzer using a number of different methods for WCET analysis. These investigations of the correctness of the output from the aspect analyzer gave confidence to the automated WCET analysis. In addition, performing this verification led to the identification of the steps necessary to compute the WCETs of a piece of program, when using a third party tool, which gives the ability to write accurate input files for the aspect analyzer.</p>

<p>Increasing complexity of real-time systems and demands for enabling their configurability and tailorability are strong motivations for applying new software engineering principles such as aspect-oriented and component-based software development. The integration of these two techniques into real-time systems development would enable: (i) efficient system configuration from the components in the component library based on the system requirements, (ii) easy tailoring of components and/or a system for a specific application by changing the behavior (code) of the component by aspect weaving, and (iii) enhanced flexibility of the real-time and embedded software through the notion of system configurability and component tailorability.</p><p>In this thesis we focus on applying aspect-oriented and component-based software development to real-time system development. We propose a novel concept of aspectual component-based real-time system development (ACCORD). ACCORD introduces the following into real-time system development: (i) a design method that assumes the decomposition of the real-time system into a set of components and a set of aspects, (ii) a real-time component model denoted RTCOM that supports aspect weaving while enforcing information hiding, (iii) a method and a tool for performing worst-case execution time analysis of different configurations of aspects and components, and (iv) a new approach to modelling of real-time policies as aspects.</p><p>We present a case study of the development of a configurable real-time database system, called COMET, using ACCORD principles. In the COMET example we show that applying ACCORD does have an impact on the real-time system development in providing efficient configuration of the real-time system. Thus, it could be a way for improved reusability and flexibility of real-time software, and modularization of crosscutting concerns.</p><p>In connection with development of ACCORD, we identify criteria that a design method for component-based real-time systems needs to address. The criteria include a well-defined component model for real-time systems, aspect separation, support for system configuration, and analysis of the composed real-time system. Using the identified set of criteria we provide an evaluation of ACCORD. In comparison with other approaches, ACCORD provides a distinct classification of crosscutting concerns in the real-time domain into different types of aspects, and provides a real-time component model that supports weaving of aspects into the code of a component, as well as a tool for temporal analysis of the weaved system.</p> / Report code: LiU-TEK-LIC-2003:23.

Our main focus in this thesis is on providing guidelines, methods, and tools for design, configuration, and analysis of configurable and reusable real-time software, developed using a combination of aspect-oriented and component-based software development. Specifically, we define a reconfigurable real-time component model (RTCOM) that describes how a real-time component, supporting aspects and enforcing information hiding, could efficiently be designed and implemented. In this context, we outline design guidelines for development of real-time systems using components and aspects, thereby facilitating static configuration of the system, which is preferred for hard real-time systems. For soft real-time systems with high availability requirements we provide a method for dynamic system reconfiguration that is especially suited for resourceconstrained real-time systems and it ensures that components and aspects can be added, removed, or exchanged in a system at run-time. Satisfaction of real-time constraints is essential in the real-time domain and, for real-time systems built of aspects and components, analysis is ensured by: (i) a method for aspectlevel worst-case execution time analysis; (ii) a method for formal verification of temporal properties of reconfigurable real-time components; and (iii) a method for maintaining quality of service, i.e., the specified level of performance, during normal system operation and after dynamic reconfiguration. We have implemented a tool set with which the designer can efficiently configure a real-time system to meet functional requirements and analyze it to ensure that non-functional requirements in terms of temporal constraints and available memory are satisfied. In this thesis we present a proof-of-concept implementation of a configurable embedded real-time database, called COMET. The implementation illustrates how our methods and tools can be applied, and demonstrates that the proposed solutions have a positive impact in facilitating efficient development of families of realtime systems.