Polytechnic Institute of Porto
Repositório Científico do Instituto Politécnico do PortoNot a member yet
26471 research outputs found
Sort by
Voids in Kesterites and the Influence of Lamellae Preparation by Focused Ion Beam for Transmission Electron Microscopy Analyses
No full textKesterite solar cells based on Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 (CZTSe) are potential future candidates to be used in thin-film solar cells. The technology still has to be developed to a great extent and for this to happen, high levels of confidence in the characterization methods are required, so that improvements can be made on solid interpretations. In this study, we show that the interpretations of one of the most used characterization techniques in kesterites, scanning transmission electron microscopy (STEM), might be affected by its specimen preparation when using focused ion beam (FIB). Using complementary measurements based on scanning electron microscopy and Raman scattering spectroscopy, compelling evidence shows that secondary phases of ZnSe mixed in the bulk of CZTSe are the likely cause of the appearance of voids in STEM lamellae. Sputtering simulations support this interpretation by showing that Zn in a ZnSe matrix is preferentially sputtered compared with any metal atom in a CZTSe matrix.info:eu-repo/semantics/publishedVersio
The AMPERE Project: A Model-driven development framework for highly Parallel and EneRgy-Efficient computation supporting multi-criteria optimization
No full textThe high-performance requirements needed to implement the most advanced functionalities of current and future Cyber-Physical Systems (CPSs) are challenging the development processes of CPSs. On one side, CPSs rely on model-driven engineering (MDE) to satisfy the non-functional constraints and to ensure a smooth and safe integration of new features. On the other side, the use of complex parallel and heterogeneous embedded processor architectures becomes mandatory to cope with the performance requirements. In this regard, parallel programming models, such as OpenMP or CUDA, are a fundamental brick to fully exploit the performance capabilities of these architectures. However, parallel programming models are not compatible with current MDE approaches, creating a gap between the MDE used to develop CPSs and the parallel programming models supported by novel and future embedded platforms.The AMPERE project will bridge this gap by implementing a novel software architecture for the development of advanced CPSs. To do so, the proposed software architecture will be capable of capturing the definition of the components and communications described in the MDE framework, together with the non-functional properties, and transform it into key parallel constructs present in current parallel models, which may require extensions. These features will allow for making an efficient use of underlying parallel and heterogeneous architectures, while ensuring compliance with non-functional requirements, including those on real-time performance of the system.info:eu-repo/semantics/publishedVersio
An EPS@ISEP 2019 Project
No full textThis paper provides an overview of the development of a solar
dehydrator, a project undertaken by a team of six Erasmus students
from different countries during the European Project Semester at
the Instituto Superior de Engenharia do Porto in the spring of 2019.
The main objective of the European Project Semester is to develop
teamwork, communication and problem-solving skills through
team work and project-based learning. The purpose of the project
was to design a sustainable solution to dehydrate and preserve food,
build and test the corresponding proof-of-concept prototype, while
respecting requirements such as the budget, the use of reusable
materials and components or European Union directives. To
achieve this goal, the team considered the technological, ethical and
deontological, economic and environmental perspectives in the
design of the Dryfoo prototype. This paper describes, after a short
introduction, the performed research, the development and the
testing of the proof-of-concept prototype, as well as the personal
outcomes of this learning experience.info:eu-repo/semantics/publishedVersio
DynaMO: dynamically tuning DSME networks
No full textDeterministic Synchronous Multichannel Extension (DSME) is a
prominent MAC behavior first introduced in IEEE 802.15.4e supporting deterministic guarantees using its multisuperframe structure.
DSME also facilitates techniques like multi-channel and Contention
Access Period (CAP) reduction to increase the number of available
guaranteed timeslots in a network. However, any tuning of these
functionalities in dynamic scenarios is not explored in the standard.
In this paper, we present a multisuperframe tuning technique called
DynaMO which tunes the CAP reduction and Multisuperframe
Order in an effective manner to improve flexibility and scalability,
while guaranteeing bounded delay. We also provide simulations to
prove that DynaMO with its dynamic tuning feature can offer up
to 15-30% reduction in terms of latency in a large DSME network.info:eu-repo/semantics/publishedVersio
CAP: Context-Aware Programming for Cyber Physical Systems
No full textContext-awareness is a prominently desired feature in computing systems. Smartphones, smart cards or tags, wearables, sensor nodes, and many other devices enable a system to compute context for different users and environment. With ever increasing advances in hardware for such devices, the interactions with users are increasing every day. This enables the collection of a large amount of data about users, systems, and physical environment. With such data available to be leveraged, context-awareness will soon become a necessity. Such type of data collection happens most frequently in sensing applications enabled by wireless sensor network (WSN) devices. This paper discusses the concept of context for sensing applications, specifically related to Cyber Physical Systems (CPS). The paper highlights key aspects of context and its definition. This paper proposes, to the best of the author's knowledge, the first programming approach to build context-aware applications for WSN-based CPS. This paper provides a proof of concept for a framework to detect, manage and deploy context-aware applications.info:eu-repo/semantics/publishedVersio
Work-In-Progress: Assessing Supply/Demand-Bound Based Schedulability Tests For Wireless Sensor-Actuator Networks
No full textThe rising adoption of wireless technologies in the Industrial Internet of Things has stressed the need for traffic schedulability validation at system design-time to support safety and time critical streams (e.g., process control and emergency response). In this context, the demand-based schedulability tests have recently been proposed in the literature. This work revisits two well-established techniques borrowed from the multi-processor scheduling theory, namely the demand-bound-function (DBF) and the forced-forward-demand-bound-function (FFDBF), and evaluates their performances when adapted to the field of wireless sensor-actuator networks. Simulation experiments when varying network configurations confirm the equal or better accuracy of FFDBF over DBF to estimate both network demand and schedulability. In future work, we aim at building upon these promising results in order to design novel admission control and adaptation strategies that improve network schedulability under varying workload conditions.info:eu-repo/semantics/publishedVersio
Tightening Up Security In Low Power Deterministic Networks
No full textThe unprecedented pervasiveness of IoT systems is pushing this technology into increasingly stringent domains. Such application scenarios become even more challenging due to the demand for encompassing the interplay between safety and security. The IEEE 802.15.4 DSME MAC behavior aims at addressing such systems by providing additional deterministic, synchronous multi-channel access support. However, despite the several improvements over the previous versions of the protocol, the standard lacks a complete solution to secure communications. In this front, we propose the integration of TAKS, an hybrid cryptography scheme, over a standard DSME network. In this paper, we describe the system architecture for integrating TAKS into DSME with minimum impact to the standard, and we venture into analysing the overhead of having such security solution over application delay and throughput. After a performance analysis, we learn that it is possible to achieve a minor impact of 1% to 14% on top of the expected network delay, depending on the platform used, while still guaranteeing strong security support over the DSME network.info:eu-repo/semantics/publishedVersio
ARx: Reactive Programming for Synchronous Connectors
No full textPart of the Lecture Notes in Computer Science book series (LNCS, volume 12134)Reactive programming (RP) languages and Synchronous Coordination (SC) languages share the goal of orchestrating the execution of computational tasks, by imposing dependencies on their execution order and controlling how they share data. RP is often implemented as libraries for existing programming languages, lifting operations over values to operations over streams of values, and providing efficient solutions to manage how updates to such streams trigger reactions, i.e., the execution of dependent tasks. SC is often implemented as a standalone formalism to specify existing component-based architectures, used to analyse, verify, transform, or generate code. These two approaches target different audiences, and it is non-trivial to combine the programming style of RP with the expressive power of synchronous languages.
This paper proposes a lightweight programming language to describe component-based Architectures for Reactive systems, dubbed ARx, which blends concepts from RP and SC, mainly inspired to the Reo coordination language and its composition operation, and with tailored constructs for reactive programs such as the ones found in ReScala. ARx is enriched with a type system and with algebraic data types, and has a reactive semantics inspired in RP. We provide typical examples from both the RP and SC literature, illustrate how these can be captured by the proposed language, and describe a web-based prototype tool to edit, parse, and type check programs, and to animate their semantics.info:eu-repo/semantics/publishedVersio
Server Based Task Allocation to Reduce Inter-Task Memory Interference in Multicore Systems
No full textIn multicore systems tasks running on one core may experience inter-task interference from tasks running on other cores. This inter-task interference is due to contention in using shared resources such as caches, system bus and the main memory. In this work, we focus on one of the major sources of cross-core interference in multicore systems, i.e., main memory. The idea is to allocate tasks to cores in a way that the total memory demand of all tasks executing at a time instant t is less than the minimum available memory bandwidth, i.e., DRAM min. The problem is formulated as a server-to-core mapping problem where each server constitute a set of tasks corresponding to an application. As mapping problems in multicore systems are NP-hard, we use different heuristic and meta-heuristic based approaches to find a feasible solution. Results show that our approach can perform well in multicore systems with ≤ 8 processing cores with the memory demand of each server upper bounded by DRAM min/2.info:eu-repo/semantics/publishedVersio
Reconfiguring TDMA Communications for Dynamic Formation of Vehicle Platoons
No full textPlatooning is a promising concept used within the Intelligent Transportation System to increase efficiency and safety of road transportation. It is based on periodically sharing the kinematic status of the platoon members to allow reducing inter-vehicle distances in a safe way. This coordination is automatic and depends heavily on the wireless channel. A common technique to improve the channel properties is to use Time-Division Multiple Access (TDMA) that organizes the access to the wireless medium in slots assigned exclusively to each vehicle. However, while platoons are physical and dynamic, the corresponding dynamic reconfiguration of a logical TDMA frame is non-trivial. In this paper we address this Cyber-Physical problem resorting to the RA-TDMAp protocol to track the dynamics of a platoon, specifically joining, merging and leaving. In our solution, we include an adequate admission control block, to verify whether joining or merging can be accepted, and we present the state-machine that handles the reconfiguration process. We validate our TDMA reconfiguration mechanism with simulations using the Plexe/Vein/OMNeT++ framework. We show the effectiveness of the proposed mechanisms which ensures a synchronized start of the platoon control with the TDMA frame reconfiguration.info:eu-repo/semantics/publishedVersio