An Integrated CMOS Front-End for Optical Absolute Rotary Encoders

This paper presents a front-end circuit for optical rotary encoders. The light pulses modulated by the encoder disc are transduced into current signals, which are pre-processed and converted into digital waveforms related to the disc angular position information. The proposed front-end circuit is compensated against temperature drifts. Digitally programmable calibration is provided to account for spreads in impinging light pulse power. Measurement results on integrated prototypes are shown, demonstrating correct operation of the front-end with an optical input power from 0.5 W to 3 W up to a signal frequency of 500 kHz in a temperature range from 0 °C to 80 °C.     

Design of an enhanced access point to optimize TCP performance in Wi-Fi hotspot networks

In the last years, the number of Wi-Fi hotspots at public venues has undergone a substantial growth, promoting the WLAN technologies as the ubiquitous solution to provide high-speed wireless connectivity in public areas. However, the adoption of a random access CSMA-based paradigm for the 802.11 MAC protocol makes difficult to ensure high throughput and a fair allocation of radio resources in 802.11-based WLANs. In this paper we evaluate extensively via simulations the interaction between the flow control mechanisms implemented at the TCP layer and the contention avoidance techniques used at the 802.11 MAC layer. We conducted our study considering initially M wireless stations performing downloads from the Internet. From our results, we observed that the TCP downlink throughput is not limited by the collision events, but by the inability of the MAC protocol to assign a higher chance of accessing the channel to the base station. We propose a simple and easy to implement modification of the base station’s behavior with the purpose of increasing the TCP throughput reducing useless MAC protocol overheads. With our scheme, the base station is allowed to transmit periodically bursts of data frames towards the mobile hosts. We design a resource allocation protocol aimed at maximizing the success probability of the uplink transmissions by dynamically adapting the burst length to the collision probability estimated by the base station. By its design, our scheme is also beneficial to achieve a fairer allocation of the channel bandwidth among the downlink and uplink flows, and among TCP and UDP flows. Simulation results confirm both the improvement in the TCP downlink throughput and the reduction of system unfairness.     

An approximate theoretical impedance analysis of the anodic dissolution of nickel across nickel(II) stabilised by means of competitive anions

A theoretical impedance function for the anodic dissolution of nickel is developed by considering the hypothesis that there are two competitive anions which participate in the stabilization of the electrogenerated Ni(II) species. The experimental effect of chloride ion concentration on nickel electrodissolution process is analyzed by means of a mechanism that considers this competency. It is observed that an increased Cl⁻ concentration causes an increase in Ni(I) surface concentration and a decrease in the kinetic constant rates of the considered mechanism. Moreover, an increased chloride concentration causes a flattening in the low frequencies inductive loop in the Nyquist plot recorded at relatively low stabilization potentials. In the active anodic dissolution/passive transition potential range chloride ions favours a salt layer precipitation which interferes with the passive layer formation.     

A kinetic interpretation of a negative time constant in impedance equivalent circuits for the dissolution/passive transition

A theoretical impedance function is proposed for the active/passive transition of nickel in an acid sulphate medium. It is considered that passivating species progressively covers the electrode surface. This approximated model predicts the appearance of negative time constants in the impedance spectra when coverage coefficient θ values for passive species are greater than 0.5.     

Validation of a Gas Chromatography-Mass Spectrometry Method for the Measurement of the Redox State Metabolic Ratios Lactate/Pyruvate and β-Hydroxybutyrate/Acetoacetate in Biological Samples

The metabolic ratios lactate/pyruvate and β-hydroxybutyrate/acetoacetate are considered valuable tools to evaluate the in vivo redox cellular state by estimating the free NAD+/NADH in cytoplasm and mitochondria, respectively. The aim of the current study was to validate a gas-chromatography mass spectrometry method for simultaneous determination of the four metabolites in plasma and liver tissue. The procedure included an o-phenylenediamine microwave-assisted derivatization, followed by liquid-liquid extraction with ethyl acetate and silylation with bis(trimethylsilyl)trifluoroacetamide:trimethylchlorosilane 99:1. The calibration curves presented acceptable linearity, with a limit of quantification of 0.001 mM for pyruvate, β-hydroxybutyrate and acetoacetate and of 0.01 mM for lactate. The intra-day and inter-day accuracy and precision were within the European Medicines Agency’s Guideline specifications. No significant differences were observed in the slope coefficient of three-point standard metabolite-spiked curves in plasma or liver and water, and acceptable recoveries were obtained in the metabolite-spiked samples. Applicability of the method was tested in precision-cut liver rat slices and also in HepG2 cells incubated under different experimental conditions challenging the redox state. In conclusion, the validated method presented good sensitivity, specificity and reproducibility in the quantification of lactate/pyruvate and β-hydroxybutyrate/acetate metabolites and may be useful in the evaluation of in vivo redox states.     

Electrospinning highly oriented and crystalline poly(lactic acid) fiber mats

In recent years, there has been an increased focus on sustainable, green alternatives with similar properties to conventional petroleum-based polymers. Poly(lactic acid) (PLA) is a biodegradable biopolymer which exhibits mild piezoelectric properties and has good processability which gives it potential for use in numerous existing and novel applications. The purpose of this study was to produce highly oriented and crystalline PLA electrospun fiber mats for piezoelectric applications. In order to yield a high piezoelectric constant, high crystallinity and fiber orientation are necessary. A two parallel collector set up was used to mechanically orient the fibers in the space between two copper electrodes. Voltage and feed rate were adjusted to produce smooth, oriented fibers with average diameters ranging 0.73–1.19 μm. Crystallinity and orientation were increased via hot drawing of the fiber mats and were maximized between 40 and 50 % and greater than 50 %, respectively.     

The impact of IXPs on the AS-level topology structure of the Internet

The AS-level topology of the Internet has been quite a hot research topic in the last few years. However, only a small number of studies have been developed that give a structural interpretation of this graph. Such an interpretation is crucially important in order to test protocols and optimal routing algorithms, to design efficient networks, and for failure detection purposes. Moreover, most research does not highlight the role that IXPs have on the AS-level structure of the Internet, although their role is recognized as fundamental.The initial contribution of this study is an analysis of the most important AS-level topologies that are publicly found on the web and an analysis of the topology obtained when they are merged. We compiled structural information from this topology making considerable use of the k-core decomposition technique to delineate various particular classes of nodes. Next, we associated node properties with a reasonable modus operandi of the ASs on the Internet. The second contribution is a study of the impact that ASs connected to IXPs and BGP connections crossing IXPs have on the AS-level topology. To achieve this, we developed a procedure to gather reliable information related to IXPs and their participants.     

Cloning and nucleotide sequence analysis of a gene encoding an OXA-derived beta-lactamase in Acinetobacter baumannii

A clinical strain of Acinetobacter baumannii (strain Ab41) that was resistant to all beta-lactam antibiotics tested except ceftazidime, ceftriaxone, ceftizoxime, and imipenem produced three beta-lactamases: a presumptive chromosomal cephalosporinase, a TEM-1-like beta-lactamase (pI 5.4), and a novel OXA-derived beta-lactamase named OXA-21 (pI 7.0). The gene encoding OXA-21 was located in an integron. The nucleotide sequence showed three mutations compared with the sequence of OXA-3, with two being silent; the nonsilent mutation generated a substitution of Ile-217 to Met.