Repositório RCAAP

O objetivo primordial desta dissertação é o estudo do regime das secções nas cooperativas agrícolas polivalentes e multissectoriais portuguesas. Especificamente, pretende-se saber se as diferentes secções das cooperativas agrícolas polivalentes e multissectoriais têm contabilidade separada. Para o efeito, fizemos uma revisão ao estado da arte e reflexão sobre a matéria escrita. As cooperativas apresentam-se como uma das famílias da economia social, setor que tem um papel preponderante na economia. Especificamente, as cooperativas agrícolas são um ramo do setor cooperativo com características próprias e, por isso, torna-se pertinente fazer um estudo jurídico e contabilístico das especificidades impostas às cooperativas agrícolas polivalentes e multissetoriais, particularizando as secções. A metodologia utilizada é qualitativa, baseando-se num estudo de caso múltiplo, através do estudo de fenómenos. Através deste método pudemos validar se, as cooperativas agrícolas polivalentes estudadas cumprem os normativos jurídicos e contabilísticos. Verificámos que existem lacunas nos estatutos e relatórios de contas das cooperativas, nomeadamente no referente às secções. Conclui-se que as cooperativas agrícolas deveriam estar enquadradas num sistema contabilístico mais apropriado às suas especificidades.

Deterministic Synchronous Multichannel Extension (DSME) is a prominent MAC behavior of IEEE 802.15.4e can avail deterministic service using its multisuperframe structure. RPL is a routing protocol for wireless networks with low power consumption and generally susceptible to packet loss. A combination of these two protocols can integrate real-time QoS demanding and large-scale IoT networks. In this paper, we propose an architecture to integrate routing with DSME. We also show a simulation result by which we improve reliability by 40 % using routing.

In this work, a thorough analysis based on the two-ray model in the presence of tides is performed. The study aims to provide a tool to guide the deployment of near-surface overwater wireless sensor networks, and thus improve its overall link quality regardless of the variations of the tides. We consider realistic parameters, such as the distance between the nodes and the tide-levels range taken from the mouth of the Douro river, Porto and the Seixal Bay, Lisbon. In future works, we will complement the theoretical analysis with network level simulations and an extended experimental campaign.

An important element in urban traffic management is the Intersection Management (IM) that deals with traffic lights signaling (either real or virtual). Intersections are vulnerable to traffic congestion and accidents. Therefore, this paper investigates a synchronous intersection management protocol for mixed autonomous and humandriven vehicles in the context of decentralized traffic management.

This paper presents a demo of an extension developed to support an existing programming abstraction for IoT: mT-Res. mT-Res is an extension of the T-Res programming abstraction, which allows users to write applications using a web framework without low level knowledge of resources. The paper describes an automated mechanism for allocate resources to such applications and adapt to changes in those resources.

Deep learning based communication using autoencoder have revolutionized the design of physical layer in wireless communication. In this paper, we propose an adversarial autoencoder to mitigate vulnerability of autoencoder against adversarial attacks. Results confirm the effectiveness of adversarial training by reducing block error rate(BLER) from 90 percent to 56 percent.

Safety-critical systems commonly face unpredictable and hostile environments, with emergent behaviors and with a growing number of external, malicious attackers. These are risk factors that should be taken into account during these systems design phases, but that is not always possible due to the overall complexity of the interaction between the systems and its external operational environment. Cyber-Physical Systems (CPS) are notable examples of practical implementations of safety-critical systems. Being able to guarantee that safetycritical CPS do not fail upon operation can easily become a huge challenge, depending on how complex the system is. Among the most promising approaches to reduce the complexity of designing safety-critical CPS are Runtime Monitoring (RM) (Watterson and Heffernan 2017) and Runtime Verification (RV) (Bartocci Et al. 2018), where monitors are generated and orchestrated in a software architecture that can be coupled to the target system, observe it during its execution, and identify aspects that were not foreseen during design phase, or that could not be proved to be absent via static verification methods. Monitors can be used to verify the correct functioning of a system by analyzing direct (and/or indirect) aspects of it. This can be especially useful when considering a security-oriented point of view, where monitors can identify possible security attacks to a system when exposed to the events taking place or the patterns of data being processed.

This work presents different approaches to calculate CPRO for set-associative caches. The PCB-ECB approach uses PCBs of the task under analysis and ECBs of all other tasks in the system to provide sound estimates of CPRO for set-associative caches. The resilienceP analysis then removes some of the pessimism in the PCB-ECB approach by considering the resilience of PCBs during CPRO calculations. We show that using the state-of-the-art (SoA) resilience analysis to calculate resilience of PCBs may result in underestimating the CPRO tasks may suffer. Finally, we have also presented a multi-set alike resilienceP analysis that highlights the pessimism in the resilienceP analysis and provides some insights on how it can be removed.

The quest for comfort and practicality is commonplace in contemporary society, but such benefits are still not offered satisfactorily to all. Among these, special attention is given to people with Disabilities, who often do not enjoy the latest technologies in applications and automated systems because they do not have their needs covered by these technologies (Domingo 2012). The aim of this work was to develop an automation system that would increase the level of inclusion. Tis work also propose a low cost residential automated system, developed using electronic waste, open hardware and open software, to increase the application of the system. There were used platforms of easy access, and easy replication, aiming at the dissemination of technology (Trihinas, Pallis, and Dikaiakos 2018). Among these platforms, it is possible to highlight the Google Assistant (Chatterjee, n.d.). All the platforms used helps the development of an Internet of Things (IOT) system, with multiple capabilities. Finally, functional tests were performed of three physical modules to control a door, a set of sockets and some lamps, using RFID, cellular and voice cards for its activation.

This paper describes an architecture conceived to integrate Power Sys-tems tools in a Power System Control Centre, based on an Ambient Intelligent (AmI) paradigm. This architecture is an instantiation of the generic architecture proposed in [1] for developing systems that interact with AmI environments. This architecture has been proposed as a consequence of a methodology for the inclu-sion of Artificial Intelligence in AmI environments (ISyRAmI - Intelligent Sys-tems Research for Ambient Intelligence). The architecture presented in the paper will be able to integrate two applications in the control room of a power system transmission network. The first is SPARSE expert system, used to get diagnosis of incidents and to support power restoration. The second application is an Intelligent Tutoring System (ITS) incorporating two training tools. The first tutoring tool is used to train operators to get the diagnosis of incidents. The second one is another tutoring tool used to train operators to perform restoration procedures.

This work describes the development and implementation of a linear trajectory controller in a five degree of freedom (DOF) robot manipulator (Filho and Quintero 2013). An open loop control architecture was designed and embedded in a Field Programable Gate Array (FPGA), for the first threeDOF. In this paper, we present the direct and inverse kinematics and the Jacobian of the manipulator, used to extract the control equations of the system (Motta, Llanos-Quintero, and Coral Sampaio 2016). This model aims the trajectory planning in a rectilinear path, described in Cartesian Coordinates. For the control implementation embedded in the FPGA, was used the NIOS II microprocessor. This one is responsible for the path planning and for the speed control of the manipulator joints, with some accelerated functions in hardware. The validation of the equations and path planning were done using software simulation. The final structure and experiments of the manipulator are also presented.

Curva de Laffer - Enquadramento, Estudos e Considerações

Os recursos humanos são apontados como um importante ativo para as organizações em geral, sendo particularmente relevantes para as organizações sociais. Este estudo procede à recolha de dados primários, por questionário, junto dos responsáveis das organizações sociais em Portugal, com o objetivo de conhecer as suas práticas de gestão de recursos humanos. Um objetivo complementar do estudo consistiu em compreender se essas práticas variavam (ou não) em função do perfil da organização social e do seu responsável. A investigação quantitativa realizada indicou uma forte valorização das práticas de gestão de recursos humanos, com perfis distintos em função das organizações sociais. Assim, enquanto algumas organizações procuram valorizar a gestão de colaboradores remunerados, outras tendem a concentrar a sua atenção essencialmente na gestão de voluntários. A investigação revela ainda que a valorização de diferentes práticas de gestão de recursos humanos é condicionada pelas características do empreendedor social e do nível de concorrência do ambiente em que as organizações atuam.

A Curva de Laffer postula que a partir de determinados níveis de taxas de impostos, uma redução destas pode aumentar as receitas fiscais. O argumento estático subjacente é de que, na zona proibitiva (fase descendente da Curva), uma redução na taxa de imposto, num dado período, deverá proporcionar um aumento suficientemente forte na base fiscal do mesmo período. Tendo presente os recentes desenvolvimentos da teoria do crescimento económico, que predizem que a política fiscal tem efeitos permanentes de longo prazo na taxa de crescimento económico (contrariamente ao paradigma neoclássico, em que o crescimento é exógeno) e, admitindo a validade do paradigma do crescimento endógeno, aquele argumento pode ser encarado num contexto dinâmico: a fiscalidade afecta permanentemente a taxa de crescimento económico de longo prazo, alterando as bases fiscais futuras. A redução de impostos, embora possa, no curto prazo, gerar perdas de receitas fiscais, a economia pode deparar-se com um efeito Laffer de longo prazo: a redução de impostos acelera o crescimento económico, permitindo aumentar as receitas fiscais no longo prazo, de forma que o valor actualizado de todas as receitas fiscais futuras aumenta, melhorando, em consequência, a posição orçamental de longo prazo. Neste trabalho procurou-se averiguar a validação de um efeito Laffer dinâmico para os Estados- Membros (doravante EM) da União Europeia dos 15 (UE15). Para o efeito, por um lado, procurouse aferir se a política fiscal tem um impacto permanente na taxa de crescimento económico, validando o paradigma do crescimento endógeno, ou se apenas afecta o nível de output e, por outro, se esse impacto é suficientemente forte para, no longo prazo, o aumento da base fiscal compensar a redução de impostos, de forma a aumentar as receitas fiscais.

The well-known model of Vestal aims to avoid excessive pessimism in the quantification of the processing requirements of mixedcriticality systems, while still guaranteeing the timeliness of highercriticality functions. This can bring important savings in system costs, and indirectly help meet size, weight and power constraints. This efficiency is promoted via the use of multiple worst-case execution time (WCET) estimates for the same task, with each such estimate characterised by a confidence associated with a different criticality level. However, even this approach can be very pessimistic when the WCET of successive instances of the same task can vary greatly according to a known pattern, as in MP3 and MPEG codecs or the processing of ADVB video streams. In this paper, we present a schedulability analysis for the multiframe mixed-criticality model, which allows tasks to have multiple, periodically repeating, WCETs in the same mode of operation. Our work extends both the analysis techniques for Static Mixed-Cricality scheduling (SMC) and Adaptive Mixed-Criticality scheduling (AMC), on one hand, and the schedulability analysis for multiframe task systems on the other. Our proposed worst-case response time (WCRT) analysis for multiframe mixed-criticality systems is considerably less pessimistic than applying the SMC, AMC-rtb and AMC-max tests obliviously to the WCET variation patterns. Experimental evaluation with synthetic task sets demonstrates up to 63.8% higher scheduling success ratio (in absolute terms) compared to the best of the frame-oblivious tests

In this paper, an adaptive terminal-integral sliding mode force control of elastic joint robot manipulators in the presence of hysteresis is proposed. One of the most important issues that is solved in this study is that the hysteresis phenomenon is considered something that provokes losses in the manipulator motion and controller errors. Force control is necessary because it can be implemented and very useful in the area of industrial robotics such as collaborative and cooperative robotics. Therefore, it can be implemented for precise control in which robot-operator or robot-robot interaction is needed. An adaptive terminal-integral sliding mode force control is proposed by considering the hysteresis and the effects between the end effector and a flexible environment. Force control has not been studied extensively nowadays and even less for elastic joint robot manipulators. Thus, to improve the system precision control, the adaptive sliding mode controller (ASMC) is designed by a Lyapunov approach obtaining the adaptive and controller laws, respectively. As an experimental case study, two links elastic joint robot manipulator is considered by obtaining the elastic joint model with hysteresis using a Bouc-Wen model.

Developing complex safe and secure Cyber-Physical Systems (CPS) applications for the automotive domain is typically a complex task, due to the criticality inherent to this domain. Considering such known complexity of the development process, we propose a novel solution that aims to provide a quasiautomatic1 integration process between the different components of such CPS systems via the support of a Domain Specific Language (DSL) that provides several views of the system, abstracting away the more technical implementation details, while imposing system properties and restrictions that have the potential to be formally verified (either statically or at run-time) during design, and facilitates the process of customization and quasi-automatic build and deployment processes. In this paper, we briefly analyze the tools that are available and that cover partially the characteristics of our envisioned DSL, describe its building blocks, and show how it can be applied in a small, yet sufficiently complex CPS application whose architecture is very close to what we may expect for the modern and future generation of CPS application in the automotive domain.

The Event Handler – a publish-subscribe broker implemented over REST/HTTP(S) – is an auxiliary system of the Arrowhead framework for IoT applications. During this work we found that the existing implementation of the Event Handler suffers from serious performance issues. This paper describes the reengineering effort that ultimately enabled it to reach much more acceptable levels of performance, by using appropriate software configurations and design patterns. Additionally, we also illustrate how this enhanced version of the Event Handler can be modeled using Petri nets, to depict the performance impact of different thread pool configurations and CPU core availability. The main objective of this modeling process is to enable the estimation of the system’s performance to guarantee the required quality of service.

Electricity markets are complex environments with very particular characteristics. MASCEM is a market simulator developed to allow deep studies of the interactions between the players that take part in the electricity market negotiations. This paper presents a new proposal for the definition of MASCEM players’ strategies to negotiate in the market. The proposed methodology is multiagent based, using reinforcement learning algorithms to provide players with the capabilities to perceive the changes in the environment, while adapting their bids formulation according to their needs, using a set of different techniques that are at their disposal. Each agent has the knowledge about a different method for defining a strategy for playing in the market, the main agent chooses the best among all those, and provides it to the market player that requests, to be used in the market. This paper also presents a methodology to manage the efficiency/effectiveness balance of this method, to guarantee that the degradation of the simulator processing times takes the correct measure.

In mixed-criticality systems, tasks of different criticality share system resources, mainly to reduce cost. Cost is further reduced by using adaptive mode-based scheduling arrangements, such as Vestal’s model, to improve resource efficiency, while guaranteeing schedulability of critical functionality. To simplify safety certification, servers are often used to provide temporal isolation between tasks. In its simplest form, a server is a periodically recurring time window, in which some tasks are scheduled. A server’s computational requirements may greatly vary in different modes, although state-of-the-art techniques and schedulability tests do not allow different budgets to be used by a server in different modes. This results in a single conservative execution budget for all modes, increasing system cost. The goal of this paper is to reduce the cost of mixed-criticality systems through three main contributions: (i) a scheduling arrangement for uniprocessor systems employing fixed-priority scheduling within periodic servers, whose budgets are dynamically adjusted at run-time in the event of a mode change, (ii) a new schedulability analysis for such systems, and (iii) heuristic algorithms for assigning budgets to servers in different modes and ordering the execution of the servers. Experiments with synthetic task sets demonstrate considerable improvements (up to 52.8%) in