Closed-loop control strategy with improved current for a flashing ratchet

We show how to switch on and off the ratchet potential of a collective Brownian motor, depending only on the position of the particles, in order to attain a current higher than or at least equal to that induced by any periodic flashing. Maximization of instant velocity turns out to be the optimal protocol for one particle but is nevertheless defeated by a periodic switching when a sufficiently large ensemble of particles is considered. The protocol presented in this article, although not the optimal one, yields approximately the same current as the optimal protocol for one particle and as the optimal periodic switching for an infinite number of them.Comment: 4 pages, 4 figure

Performance assessment of wireless power transfer links for implantable microsystems

Wireless power transfer is a hot topic due to the growth of implanted device solutions which, as they get smaller and smarter, demand new solutions to power them up. These solutions need to keep the power level, namely SAR (specific absorption ratio) below a determined safety standard and to allow the device to be as small as possible. Current fabrication techniques allow the creation of ultra-small 3D antennas integrated on silicon wafers, which can lead to the miniaturization of implantable devices due to the possible reduction or even elimination of battery size. To evaluate this possibility, the antenna must be tested in conditions close to real working conditions, requiring the use of human body phantoms. This paper proposes a solution to measure the power received by an ultra-small antenna placed inside a phantom, without the use of coaxial cables attached to the device. Instead, an optoelectronic mechanism is used to route the received power to an optical fiber, and an optical spectrum analyzer is used to measure the received power.This work was supported by Portuguese Foundation for Science and Technology: FCT-PTDC/EEI-TEL/2881/2012, Programa Operacional Temático Fatores de Competitividade (COMPETE) and Fundo Comunitário Europeu FEDER.info:eu-repo/semantics/publishedVersio

Recent Advances on Implantable Wireless Sensor Networks

Implantable electronic devices are undergoing a miniaturization age, becoming more efficient and yet more powerful as well. Biomedical sensors are used to monitor a multitude of physiological parameters, such as glucose levels, blood pressure and neural activity. A group of sensors working together in the human body is the main component of a body area network, which is a wireless sensor network applied to the human body. In this chapter, applications of wireless biomedical sensors are presented, along with state-of-the-art communication and powering mechanisms of these devices. Furthermore, recent integration methods that allow the sensors to become smaller and more suitable for implantation are summarized. For individual sensors to become a body area network (BAN), they must form a network and work together. Issues that must be addressed when developing these networks are detailed and, finally, mobility methods for implanted sensors are presented

Sondagens arqueológicas no Monte da Ola, Vila Fria, Viana do Castelo (Norte de Portugal)

Este trabalho dá a conhecer os resultados das prospecções e das sondagens arqueológicas realizadas no Monte da Ola, Vila Fria, Viana do Castelo. Foi possível identificar a existência de uma necrópole de cistas no local atribuível, provavelmente, aos inícios do Bronze Final.This article draws upon the recent archaeological excavations at the site of Monte da Ola (Viana do Castelo). This site was disturbed by urban development from 1920’s. Then earthworks uncovered important archaeological finds, which are kept in the Museu Municipal de Viana do Castelo. The excavations, integrated in the project The Entre-Douro-e-Minho landscape since middle of III to the end of II millenium BC, corroborated the existence of a cemetery dating to the Bronze Age

Performance evaluation of IB-DFE-based strategies for SC-FDMA systems

The aim of this paper is to propose and evaluate multi-user iterative block decision feedback equalization (IB-DFE) schemes for the uplink of single-carrier frequency-division multiple access (SC-FDMA)-based systems. It is assumed that a set of single antenna users share the same physical channel to transmit its own information to the base station, which is equipped with an antenna array. Two space-frequency multi-user IB-DFE-based processing are considered: iterative successive interference cancellation and parallel interference cancellation. In the first approach, the equalizer vectors are computed by minimizing the mean square error (MSE) of each individual user, at each subcarrier. In the second one, the equalizer matrices are obtained by minimizing the overall MSE of all users at each subcarrier. For both cases, we propose a simple yet accurate analytical approach for obtaining the performance of the discussed receivers. The proposed schemes allow an efficient user separation, with a performance close to the one given by the matched filter bound for severely time-dispersive channels, with only a few iterations

Variability of Indoor Radon Level Accumulation: a Study in Portuguese Thermal Spas

The aim of this work was to measure the concentration of the indoor radon in 16 Portuguese thermal spas (38% of the thermal spas in Portugal) and assess its variability within each establishment as well as its contribution to the effective dose. The measurements were performed with CR-39 passive detectors placed at different workplaces within each thermal spa, for an average period of 42 days, in different seasons of the year. The indoor radon concentrations ranged from 68 to 4335 Bq/m3 with a geometric mean of 437 Bq/m3 and an arithmetic mean of 702 Bq/m3. Geological factors that can lead to such behaviour are discussed. The results showed that the EU reference level of 300 Bq/m3 (Directive 2013/59/EURATOM) was exceeded in several cases. No significant differences were observed among measurements taken during different seasons of the year, however, large differences of radon concentrations in different rooms of the same thermal establishment were noted as well as significant difference when comparing to other thermal establishments. The effective dose resulting from the inhalation of radon ranged between 2 and 32 mSv/y. In 43% of the thermal spas, the effective dose is likely to be higher than 6 mSv/y, which means that the exposure should be managed as a "planned exposure situation" according to the European Directive 2013/59/EURATOM. Also, in 19% of the cases, the annual effective dose exceeds 20 mSv/y, and in these cases, monitoring and radiological protection is required as laid down in the European Directive 2013/59/EURATOM. (c) RAD Conference Proceedings. All rights reserved