ESTG - Comunicações em conferências e congressos internacionais
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- Clock Repeater Characterization for Jitter-Aware Clock Tree SynthesisPublication . Figueiredo, Monica; Aguiar, Rui L.This paper presents a simple jitter model for clock repeaters. The model is scalable and technology independent, which makes it suitable for integration in current clock tree synthesis algorithms. It is based on the timing characterization of a reference inverter, which can be performed for different process corners to account for process variability. Simulation results show that the model is accurate to within 10% for the most common inverter and NAND based repeaters.
- Performance study about biodiesel impact on buses engines using dynamometer tests and fleet consumption dataPublication . Serrano, Luis M.V.; Câmara, Rui M.O.; Carreira, Vasco J.R.; Gameiro da Silva, M.C.The problem of reducing harmful emissions, mainly particulate matter (PM) and nitrogen oxides (NOxs) originated in compression ignition combustion engines, and also the mandatory intention of lowering the CO2 impacts of road transportation define the need to improve our knowledge on biodiesel use in engines. A 6 in line cylinders Volvo engine was submitted to a 100 min cycle with 27 stabilized steps for seven different fuel blends from pure fossil diesel (B0) to pure biodiesel (B100), considering also B10, B15, B20, B30, B50 fuel blends. The cycle imposed tries to simulate a normal use of a bus in an urban and extraurban circuit, considering different engine rotation and loads applied. An analysis on consumption data obtained of a fleet was made. The fleet had near 200 buses, used different fuel blends, and operated in the north of Portugal. Results reveal that the cycle imposed reflects very well the tendency of consumption, allowing to confirm the methodology and also to check influences on consumption, mainly associated with possibilities to decrease CO2 emissions by using some biodiesel blends on buses. This allows increasing the quality of data in vehicle real use and tightening the uncertainties on the actual effects of using biodiesel.
- Evolutionary Multi-objective Scheduling for Anti-Spam Filtering Throughput OptimizationPublication . Ruano-Ordás, David; Basto-Fernandes, Vitor; Yevseyeva, Iryna; Méndez, José RamónThis paper presents an evolutionary multi-objective optimization problem formulation for the anti-spam filtering problem, addressing both the classification quality criteria (False Positive and False Negative error rates) and email messages classification time (minimization). This approach is compared to single objective problem formulations found in the literature, and its advantages for decision support and flexible/adaptive anti-spam filtering configuration is demonstrated. A study is performed using the Wirebrush4SPAM framework anti-spam filtering and the SpamAssassin email dataset. The NSGA-II evolutionary multi-objective optimization algorithm was applied for the purpose of validating and demonstrating the adoption of this novel approach to the anti-spam filtering optimization problem, formulated from the multi-objective optimization perspective. The results obtained from the experiments demonstrated that this optimization strategy allows the decision maker (anti-spam filtering system administrator) to select among a set of optimal and flexible filter configuration alternatives with respect to classification quality and classification efficiency.
- Enabling Object Reuse on Genetic Programming-Based Approaches to Object-Oriented Evolutionary TestingPublication . Ribeiro, José Carlos Bregieiro; Zenha-Rela, Mário Alberto; Vega, Francisco Fernández deRecent research on search-based test data generation for Object-Oriented software has relied heavily on typed Genetic Programming for representing and evolving test data. However, standard typed Genetic Programming approaches do not allow Object Reuse; this paper proposes a novel methodology to overcome this limitation. Object Reuse means that one instance can be passed to multiple methods as an argument, or multiple times to the same method as arguments. In the context of Object-Oriented Evolutionary Testing, it enables the generation of test programs that exercise structures of the software under test that would not be reachable otherwise. Additionally, the experimental studies performed show that the proposed methodology is able to effectively increase the performance of the test data generation process.
- Dynamic jitter accumulation in clock repeaters considering power and ground noise correlationsPublication . Figueiredo, Mónica; Aguiar, Rui L.This paper discusses the mechanism behind dynamic jitter accumulation in clock repeaters, considering the impact of power supply noise correlations. We show that differential and common mode noise have a different impact on jitter accumulation, depending on correlations between cascaded repeater stages. We also propose a simple accumulation model that can be used to replace time-consuming transient noise simulations. Besides providing an useful insight regarding the impact of noise correlations on jitter accumulation, the model's accuracy is shown to be within 10% of SPICE results.
- Experimental study of the energy portions control in Series Resonant ConvertersPublication . Valtchev, Stanimir; Valtchev, SvilenAlthough the Series Resonant Converter (SRC) is not yet fully explored and widely applied it is becoming more and more important for the contactless charging of the Electric Vehicles (EV) batteries. From the point of view of the modern propulsion batteries the careful and reliable charging is very important and good solutions will be the SRC contactless battery charging and the online resonant energy transfer. To their high efficiency must be added the high stability of an instantaneous method of control. The proposed solution is based on correcting the portion of energy that is sent to the load in each half period through the resonant circuit. Experimental results are shown from the implementation of this idea in the SRC working on a loosely coupled (contactless) magnetic connection.
- Concept Maps for the Modelling of Controlled Flexibility in Software ProcessesPublication . Martinho, Ricardo; Domingos, Dulce; Varajão, JoãoSoftware processes and corresponding models are dynamic entities that are often changed and evolved by skillful knowledge workers such as the members of a software development team. Consequently, process flexibility has been identified as one of the most important features that should be supported by both Process Modelling Languages (PMLs) and software tools that manage the processes. However, in the everyday practice, most software team members do not want total flexibility. They rather prefer to have controlled flexibility, i.e., to learn and follow advices previously modelled by a process engineer on which and how they can change the elements that compose a software process. Since process models constitute a preferred vehicle for sharing and communicating knowledge on software processes, the process engineer needs a PML that can express this controlled flexibility, along with other process perspectives. To achieve this enhanced PML, we first need a sound core set of concepts and relationships that defines the knowledge domain associated with the modelling of controlled flexibility. In this paper we capture and represent this domain by using Concept Maps (Cmaps). These include diagrams and descriptions that elicit the relationships between the concepts involved. The proposed Cmaps can then be used as input to extend a PML with modelling constructs to express controlled flexibility within software processes. Process engineers can use these constructs to define, in a process model, advices on changes that can be made to the model itself or to related instances. Software team members can then consult this controlled flexibility information within the process models and perform changes accordingly.
- Characterization and testing of a shock absorber embedded sensorPublication . Ferreira, C.; Ventura, P.; Grinde, C.; Morais, R.; Valente, A.; Neves, C.; Reis, M.This article presents the characterization of a shock absorber embedded sensor (SAES) for real-time monitoring of the condition of vehicle shock absorbers in everyday use. A prototype system was built using a custom designed monolithic silicon combined accelerometer, pressure and temperature sensors. The characterization of the SAES was performed and the obtained results meet and even outperform the specification requirements. The SAES was installed in a shock absorber, with adjustable damping properties, and submitted to road tests. Results show that the condition of a shock absorber can be effectively assessed with the presented SAES. Ensuring that shock absorbers are replaced before reach unacceptable condition, this system will increase onboard comfort and vehicle safety.
- Making Software Accessible, but not Assistive: A Proposal for a First Insight for StudentsPublication . Silva, João de Sousa e; Gonçalves, Ramiro; Martins, José; Pereira, AntónioThe academy can and should have a major role in the promotion of software accessibility. To try to clarify a number of empirical arguments and certainties regarding the usage of accessible, but not assistive, software, the answers to a survey given to 15 blind or low vision people are depicted. To demonstrate how under addressed this topic is by the academy an experiment was made, and its results are portrayed. The novel contribution that this paper offers is the relation between relevant accessibility documentation to its appropriate type of user interface, which is intended to encourage the introduction of the topic of software accessibility implementation. Also, a proposal for a first slide, regarding accessibility implementation in software meant to be shown to software engineering students, who should produce accessible software in their future, is presented. As a conclusion, some insights are given and new possible research avenues are depicted.
- A Comparison of Roundabout Capacity ModelsPublication . Vasconcelos, Luís; Seco, Álvaro; Silva, Ana Bastos; Abreu, Tiago; Silva, João P.In the present study four roundabout capacity models - Siegloch, Cowan M3-1L, Cowan M3-2L and TRL - are presented and compared against microscopic simulation results. The evaluation framework is centered mostly on the characteristics of the entering and circulating traffic and it is shown that the more popular models - TRL and Siegloch, are unable to generate consistent capacity estimates for the whole range of conflicting flows. The models based on Cowan M3 headway distribution are more robust but still they aren't sensible to differences in the vehicles destinations, both in the entry and in the circulating traffic. This aspect is also poorly handled by the microscopic simulation model.