High static gain single-phase PFC based on a hybrid boost converter

In this paper, a single-phase unity power factor rectifier, based on a hybrid boost converter, resulting from the integration of a conventional dc–dc boost converter and a switched-capacitor voltage doubler is proposed, analysed, designed and tested. The high-power rectifier is controlled by two feedback loops with the same control strategy employed in the conventional boost-based rectifier. The main feature of the proposed rectifier is its ability to output a dc voltage larger than the double of the peak value of the input line voltage, while subjecting the power switches to half of the dc-link voltage, which contributes to reducing the cost and increasing the efficiency. Experimental data were obtained from a laboratory prototype with an input voltage of 220 Vrms, line frequency of 60 Hz, output voltage of 800 Vdc, load power of 1000 W and switching frequency of 50 kHz. The efficiency of the prototype, measured in the laboratory, was 96.5% for full load and 97% for half load.     

Short communication: Activity of nisin,lipid bilayer fragments and cationic nisin-lipid nanoparticles against multidrug-resistant Staphylococcus spp. isolated from bovine mastitis

Staphylococci are the main etiological agents of bovine mastitis. Bacteriocins and nanoparticles have emerged as promising alternatives for the future development of antimicrobial agents. This study evaluated the activity of the bacteriocin nisin and bicelles of the synthetic cationic lipid dioctadecyldimethylammonium bromide, alone and in combination, against multidrug-resistant Staphylococcus spp. strains isolated from bovine mastitis. In summary, cationic nisin/dioctadecyldimethylammonium bromide nanoparticles are shown to be a promising alternative for the control of mastitis caused by multidrug-resistant Staphylococcus spp.     

Growth of II-IV-V<Subscript>2</Subscript> chalcopyrite nitrides by molecular beam epitaxy

Synthesis of crystalline MgGeN₂ thin solid films is achieved using the technique of molecular beam epitaxy (MBE). The details of the epitaxial process are described. The microstructures of these films are investigated by both x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Comparison of the lattice structure with powder diffraction standards suggests the lattice structure may be orthorhombic with a high degree of texture. Morphology is evaluated by atomic force microscopy, and a periodic pattern of growth mounds is observed. A formalism for dynamical roughening is applied to quantify the mounded surface features. Mounds are found to have an average spacing of 235 nm, and the surface exhibits a saturation value of 22 nm for the root mean correlated height difference. Diffusion bias is discussed as a mechanism for the formation of surface mounds.     

Alternative techniques for forecasting mineral commodity prices

Forecasting mineral commodity(MC) prices has been an important and difficult task traditionally addressed by econometric, stochastic-Gaussian and time series techniques. None of these techniques has proved suitable to represent the dynamic behavior and time related nature of MC markets. Chaos theory(CT) and machine learning(ML) techniques are able to represent the temporal relationships of variables and their evolution has been used separately to better understand and represent MC markets. CT can determine a system's dynamics in the form of time delay and embedding dimension. However, this information has often been solely used to describe the system's behavior and not for forecasting.Compared to traditional techniques, ML has better performance for forecasting MC prices, due to its capacity for finding patterns governing the system's dynamics. However, the rational nature of economic problems increases concerns regarding the use of hidden patterns for forecasting. Therefore, it is uncertain if variables selected and hidden patterns found by ML can represent the economic rationality.Despite their refined features for representing system dynamics, the separate use of either CT or ML does not provide the expected realistic accuracy. By itself, neither CT nor ML are able to identify the main variables affecting systems, recognize the relation and influence of variables though time, and discover hidden patterns governing systems evolution simultaneously. This paper discusses the necessity to adapt and combine CT and ML to obtain a more realistic representation of MC market behavior to forecast long-term price trends.     

Improved xylitol production in media containing phenolic aldehydes: application of response surface methodology for optimization and modeling of bioprocess

BACKGROUND: The combined effects of vanillin and syringaldehyde on xylitol production by Candida guilliermondii using response surface methodology (RSM) have been studied. A 2² full‐factorial central composite design was employed for experimental design and analysis of the results. RESULTS: Maximum xylitol productivities (Q_P = 0.74 g L^?1h^?1) and yields (Y_P/S = 0.81 g g^?1) can be attained by adding only vanillin at 2.0 g L^?1 to the fermentation medium. These data were closely correlated with the experimental results obtained (0.69 ± 0.04 g L^?1 h^?1 and 0.77 ± 0.01 g g^?1) indicating a good agreement with the predicted value. C. guilliermondii was able to convert vanillin completely after 24 h of fermentation with 94% yield of vanillyl alcohol. CONCLUSIONS: The bioconversion of xylose into xylitol by C. guilliermondii is strongly dependent on the combination of aldehydes and phenolics in the fermentation medium. Vanillin is a source of phenolic compound able to improve xylitol production by yeast. The conversion of vanillin to alcohol vanilyl reveals the potential of this yeast for medium detoxification. Copyright © 2009 Society of Chemical Industry     

Insights from a text mining survey on Expert Systems research from 2000 to 2016

This study presents a literature analysis using a semiautomated text mining and topic modelling approach of the body of knowledge encompassed in 17 years (2000–2016) of literature published in the Wiley's Expert Systems journal, a key reference in Expert Systems (ESs) research, in a total of 488 research articles. The methodological approach included analysing countries from authors' affiliations, with results emphasizing the relevance of both U.S. and U.K. researchers, with Chinese, Turkish, and Spanish holding also a significant relevance. As a result of the sparsity found on the keywords, one of our goals became to devise a taxonomy for future submissions under 2 core dimensions: ESs' methods and ESs' applications. Finally, through topic modelling, data‐driven methods were unveiled as the most relevant, pairing with evaluation methods in its application to managerial sciences, arts, and humanities. Findings also show that most of the application domains are well represented, including health, engineering, energy, and social sciences.     

Energy sector in Ecuador: Current status

This paper describes the current energy sector in Ecuador, its present structure, the oil industry, subsidies, and renewable energy, focusing on the evolution and reform of the electricity sector. Currently, 86% of the primary energy originates from nonrenewable sources. In 2005, the gross electricity generation was 15 127 GWh (45.5% hydropower, 43.11% thermal, and 11.39% imported). Ecuador is the fifth largest oil producer in South America but lacks sufficient oil refining capacity. Reserves of natural gas (NG) are small, and most of NG is produced from oil fields without energy recovery. Several projects are underway to increase the utilization of NG and renewable energies to meet Ecuador commitments to the Kyoto Protocol.     

The Supporting Role of the Mangasarian-Fromovitz Constraint Qualification in Calculus of Variations

Journal of Dynamical and Control Systems - The Mangasarian-Fromovitz constraint qualification has played a fundamental role in mathematical programming problems involving inequality constraints. It...