Browsing by Author "Carvalho, Carlos"
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- Combined organic photovoltaic cells and ultra low power CMOS circuit for indoor light energy harvestingPublication . Batista, Duarte; Oliveira, Luis; Paulino, Nuno; Carvalho, Carlos; Oliveira, João P.; Farinhas, Joana; Charas, Ana; Mendonça Dos Santos, PedroThis paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) connected to a DC-DC converter, designed in a 130 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology, with a quasi- maximum power point tracking (MPPT) algorithm to maximize the system efficiency, for indoor applications. OPVs are an emerging technology with potential for low cost indoor light energy harvesting. The OPV current-voltage curves (I-V) under an irradiance of solar simulator Oriel Sol 3A, at room temperature, are obtained and an accurate electrical model is derived. The energy harvesting system is subjected to four different indoor light sources: 35 W halogen, 3.5 W LED, 5 W LED, and 7 W LED, positioned at three different heights (0.45 m, 0.26 m, and 0.11 m), to evaluate the potential of the system for indoor applications. The measurements showed maximum efficiencies of 60% for 35 W halogen and 45% for 7 W LED at the highest distance (0.45 m) and between 60% (5 W LED) and 70% (35 W halogen), at the shorter distance (0.11 m). Under irradiation, the integrated CMOS circuit presented a maximum efficiency of 75.76%, which is, to the best of the authors' knowledge, the best reported power management unit (PMU) energy system using organic photovoltaic cells.
- A DC-DC Step-Up mu-Power Converter for Energy Harvesting Applications, Using Maximum Power PointTracking, Based on Fractional Open Circuit VoltagePublication . Carvalho, Carlos; Lavareda, Guilherme; Paulino, NunoA DC-DC step-up micro power converter for solar energy harvesting applications is presented. The circuit is based on a switched-capacitorvoltage tripler architecture with MOSFET capacitors, which results in an, area approximately eight times smaller than using MiM capacitors for the 0.131mu m CMOS technology. In order to compensate for the loss of efficiency, due to the larger parasitic capacitances, a charge reutilization scheme is employed. The circuit is self-clocked, using a phase controller designed specifically to work with an amorphous silicon solar cell, in order to obtain themaximum available power from the cell. This will be done by tracking its maximum power point (MPPT) using the fractional open circuit voltage method. Electrical simulations of the circuit, together with an equivalent electrical model of an amorphous silicon solar cell, show that the circuit can deliver apower of 1132 mu W to the load, corresponding to a maximum efficiency of 66.81%.
- Educação (formação) de professores e alunosPublication . Carvalho, Carlos; Duarte, José; Rodrigues, MargaridaVários estudos centram-se no desenvolvimento profissional dos professores, nos seus percursos de formação e envolvimento em projectos de inovação, nomeadamente os que fazem recurso às TIC, aproveitando a sua versatilidade e potencial pedagógico. No âmbito do programa Nónio-Século XXI, vários professores têm desenvolvido um conjunto de experiências educativas em espaços diversificados como a sala de aula, os Clubes ou os Centros de Recursos. O registo destas experiências profissionais constitui um enorme potencial de material pedagógico e didáctico que, para além de valorizar o papel dos actores nesse processo, pode permitir uma reflexão sobre as práticas. No contexto do Projecto Àbolina (http://www.ese.ips.pt/abolina/index.html) temos vindo a disponibilizar um espaço com conteúdos em português, ‗memória viva‘ de algumas experiências significativas do quotidiano dos principais actores deste desafio colectivo que possam constituir fonte de ideias e recursos educativos para os professores, incentivando os processos de discussão e partilha de experiências. Assim, partindo de um relato de colegas da EB 2,3 de Aranguez — Setúbal que incide na formação de alunos monitores no Centro de Recursos, abrimos um Fórum subordinado a este tema, considerando que as dimensões da comunicação e da partilha/reflexão constituem etapas fundamentais no desenvolvimento profissional dos professores. Da polémica surgida daremos conta na comunicação, discutindo as concepções pedagógicas a este projecto de formação de alunos monitores, na sua relação com o desenvolvimento de competências gerais/transversais nos alunos, nomeadamente com a partilha de responsabilidades e o desenvolvimento da autonomia.
- eRF3a/GSPT1 12-GGC allele increases the susceptibility for breast cancer developmentPublication . Malta-Vacas, Joana; Chauvin, Celine; Gonçalves, Lucília; Nazaré, Antónia; Carvalho, Carlos; Monteiro, Carolino; Bagrel, Denyse; Jean-Jean, Olivier; Brito, MiguelIt is now widely recognized that translation factors are involved in cancer development and that components of the translation machinery that are deregulated in cancer cells may become targets for cancer therapy. The eukaryotic Release Factor 3 (eRF3) is a GTPase that associates with eRF1 in a complex that mediates translation termination. eRF3a/GSPT1 first exon contains a (GGC)n expansion coding for proteins with different N-terminal extremities. Herein we show that the longer allele (12-GGC) is present in 5.1% (7/137) of the breast cancer patients analysed and is absent in the control population (0/135), corresponding to an increased risk for cancer development, as revealed by Odds Ratio analysis. mRNA quantification suggests that patients with the 12-GGC allele overexpress eRF3a/GSPT1 in tumor tissues relative to the normal adjacent tissues. However, using an in vivo assay for translation termination in HEK293 cells, we do not detect any difference in the activity of the eRF3a proteins encoded by the various eRF3a/GSPT1 alleles. Although the connection between the presence of eRF3a/GSPT1 12-GGC allele and tumorigenesis is still unknown, our data suggest that the presence of the 12-GGC allele provides a potential novel risk marker for various types of cancer.
- On the feasibility of GPON fiber light energy harvesting for the internet of thingsPublication . Casaleiro, João; Carvalho, Carlos; Fazenda, Pedro; Duarte, R. P.The emerging concept of smart cities demands for a large number of electronic devices, like sensors and actuators, distributed over several public spaces and buildings. The Internet of Things (IoT) has a key role in connecting devices to the Internet. However, the significant number of devices makes the maintenance task of the entire network difficult and expensive. To mitigate this problem, considerable research efforts have been made to develop energy-aware devices capable of self-sustainable operation, by harvesting their energy from various sources. In this paper, we study the possibility of harvesting energy from the light flowing in the Gigabit Passive Optics Network (GPON) to supply low-power devices. Since most cities already have a working GPON installation, using this installation to interconnect and power IoT devices can be a viable and less expensive solution, instead of installing new dedicated networks. This is also an interesting solution to convey communications and energy to low-power applications where access to the power grid is unfeasible. This study is focused in the 1550 nm wavelength, whose available optical power, in residential premises, is between -7 dBm and +2 dBm. With this range of optical power, and with a 30% efficiency photodiode, we show, for the worst-case scenario of the GPON, how it is possible to harvest 62 μW of energy at the Maximum Power Point (MPP).
- A Step-up mu-Power Converter for Solar Energy Harvesting Applications, using Hill Climbing Maximum Power Point TrackingPublication . Carvalho, Carlos; Lameiro, José; Paulino, Nuno; Lavareda, GuilhermeThis paper presents a step-up micro-power converter for solar energy harvesting applications. The circuit uses a SC voltage tripler architecture, controlled by an MPPT circuit based on the Hill Climbing algorithm. This circuit was designed in a 0.13 mu m CMOS technology in order to work with an a-Si PV cell. The circuit has a local power supply voltage, created using a scaled down SC voltage tripler, controlled by the same MPPT circuit, to make the circuit robust to load and illumination variations. The SC circuits use a combination of PMOS and NMOS transistors to reduce the occupied area. A charge re-use scheme is used to compensate the large parasitic capacitors associated to the MOS transistors. The simulation results show that the circuit can deliver a power of 1266 mu W to the load using 1712 mu W of power from the PV cell, corresponding to an efficiency as high as 73.91%. The simulations also show that the circuit is capable of starting up with only 19% of the maximum illumination level.
- Stochastic theater: stochastic datapath generation framework for fault-tolerant IoT sensorsPublication . Duarte, Rui Policarpo; Véstias, Mário; Carvalho, Carlos; Casaleiro, JoãoStochastic Computing has emerged as a competitive computing paradigm that produces fast and simple implementations of arithmetic operations, while offering high levels of parallelism, and graceful degradation of the results when in the presence of errors. IoT devices are often operate under limited power and area constraints and subjected to harsh environments, for which, traditional computing paradigms struggle to provide high availability and fault-tolerance. Stochastic Computing is based on the computation of pseudo-random sequences of bits, hence requiring only a single bit per signal, rather than a data-bus. Notwithstanding, we haven’t witnessed its inclusion in custom computing systems. In this direction, this work presents Stochastic Theater, a framework to specify, simulate, and test Stochastic Datapaths to perform computations using stochastic bitstreams targeting IoT systems. In virtue of the granularity of the bitstreams, the bit-level specification of circuits, high-performance characteristics and reconfigurable capabilities, FPGAs were adopted to implement and test such systems. The proposed framework creates Stochastic Machines from a set of user defined arithmetic expressions, and then tests them with the corresponding input values and specific fault injection patterns. Besides the support to create autonomous Stochastic Computing systems, the presented framework also provides generation of stochastic units, being able to produce estimates on performance, resources and power. A demonstration is presented targeting KLT, typical method for data compression in IoT applications.
- A voltage limiter circuit for indoor light energy harvesting applicationsPublication . Carvalho, Carlos; Paulino, NunoA voltage limiter circuit for indoor light energy harvesting applications is presented. This circuit is a part of a bigger system, whose function is to harvest indoor light energy, process it and store it, so that it can be used at a later time. This processing consists on maximum power point tracking (MPPT) and stepping-up, of the voltage from the photovoltaic (PV) harvester cell. The circuit here described, ensures that even under strong illumination, the generated voltage will not exceed the limit allowed by the technology, avoiding the degradation, or destruction, of the integrated die. A prototype of the limiter circuit was designed in a 130 nm CMOS technology. The layout of the circuit has a total area of 23414 mu m(2). Simulation results, using Spectre, are presented.