bluuebunny/crossref_metadata_2025 huggingface dataset:
A Degree Formula for Secant Varieties of Curves
Authors: Achilles Rüdiger , Manaresi Mirella , Schenzel Peter
Published: August 2013

Using the Stückrad–Vogel self-intersection cycle of an irreducible and reduced curve in pro-jective space, we obtain a formula that relates the degree of the secant variety, the degree and the genus of the curve and the self-intersection numbers, the multiplicities and the number of branches of the curve at its singular points. From this formula we deduce an expression for the difference between the genera of the curve. This result shows that the self-intersection multiplicity of a curve in projectiveN-space at a singular point is a natural generalization of the intersection multiplicity of a plane curve with its generic polar curve. In this approach, the degree of the secant variety (up to a factor 2), the self-intersection numbers and the multiplicities of the singular points are leading coefficients of a bivariate Hilbert polynomial, which can be computed by computer algebra systems.
Chevalley Supergroups of Type D(2, 1; a)
Authors: Gavarini F.
Published: August 2013

We present a construction ‘à la Chevalley’ of connected affine supergroups associated with Lie superalgebras of type D(2, 1; a), for any possible value of the parameter a. This extends the results by Fioresi and Gavarini, in which all other simple Lie superalgebras of classical type were considered. The case of simple Lie superalgebras of Cartan type is dealt with in a previous paper by the author, so this work completes the programme of constructing connected affine supergroups associated with any simple Lie superalgebra.
Intersection of Continua and Rectifiable Curves
Authors: Balka Richárd , Harangi Viktor
Published: August 2013

We prove that for any non-degenerate continuum K ⊆ ℝd there exists a rectifiable curve such that its intersection with K has Hausdorff dimension 1. This answers a question of Kirchheim.
Maximal regularity for degenerate differential equations with infinite delay in periodic vector-valued function spaces
Authors: Lizama Carlos , Ponce Rodrigo
Published: August 2013

Let A and M be closed linear operators defined on a complex Banach space X and let a ∈ L1(ℝ+) be a scalar kernel. We use operator-valued Fourier multipliers techniques to obtain necessary and sufficient conditions to guarantee the existence and uniqueness of periodic solutions to the equation

with initial condition Mu(0) = Mu(2π), solely in terms of spectral properties of the data. Our results are obtained in the scales of periodic Besov, Triebel–Lizorkin and Lebesgue vector-valued function spaces.
Anticommunist White Ethnics in Search of True Americanness: Ideas and Alliances in the 1950s–1970s
Authors: ZAKE IEVA
Published: August 2013

This study explores the ways in which certain groups of white ethnics understood the idea of the un-American between the 1950s and the 1970s. Their definition of the un-American was determined by their perception of true Americanness, which in turn was connected to their anticommunist beliefs. Such an understanding of true Americanness helped these white ethnics build political alliances, particularly with the Republican Party. However, by the mid-1970s, the white anticommunist ethnics found themselves outside of the political mainstream, with anticommunism a heavy ideological burden to carry. The article is based on archival materials from presidential libraries and sources from within the ethnic communities themselves.
Predicting the risk of an endemic focus ofLeishmania tropicabecoming established in south-western Europe through the presence of its main vector,Phlebotomus sergentiParrot, 1917
Authors: BARÓN S. D. , MORILLAS-MÁRQUEZ F. , MORALES-YUSTE M. , DÍAZ-SÁEZ V. , GÁLLEGO M. , MOLINA R. , MARTÍN-SÁNCHEZ J.
Published: August 2013

The aim of the study was the construction of risk maps for exposure toPhlebotomus sergenti, the main vector ofLeishmania tropica, with a view to identifying hot spots for the potential establishment of this parasite in the southwest of Europe. Data were collected on the presence/absence of this vector and the ecological and climatic characteristics of 662 sampling sites located in the southeast, centre and northeast of the Iberian Peninsula (south-western Europe). The environmental factors associated with the distribution ofP. sergentiwere determined. The best predictors for the presence of this dipteran were ‘altitude’, ‘land use’, ‘land surface temperature’, ‘aspect’, ‘adjacent land cover’, ‘absence of vegetation in wall’ and the ‘absence of PVC pipes in the drainage holes of retaining walls’. Risk maps for exposure to the vector were drawn up based on these variables. The validation of the predictive risk model confirmed its usefulness in the detection of areas with a high risk ofP. sergentibeing present. These locations represent potential hot spots for an autochthonous focus ofL. tropicabecoming established. The risk maps produced forP. sergentipresence revealed several areas in the centre and south of the Iberian Peninsula to be the most prone to this process, which would make it possible for the disease to enter south-western Europe.
Acriflavine treatment promotes dyskinetoplasty inTrypanosoma cruzias revealed by ultrastructural analysis
Authors: MANCHESTER THIAGO , CAVALCANTI DANIELLE PEREIRA , ZOGOVICH MARCELO , DE SOUZA WANDERLEY , MOTTA MARIA CRISTINA MACHADO
Published: August 2013

Trypanosomatid mitochondrial DNA is structured as a giant network of thousands of interlocked DNA molecules enclosed within the kinetoplast. The structure and replication mechanism of kinetoplast DNA (kDNA) is unique, thereby making it an excellent chemotherapeutic target. Alteration in the structural organization of kDNA can give rise to dyskinetoplastic (Dk) strains. In Dk cells, the kDNA is dispersed in clumps throughout the mitochondrial matrix and not organized into a network. In this work,Trypanosoma cruziepimastigotes were treated with acriflavine, a DNA intercalating drug, which promoted a decrease in cell proliferation and induced the appearance of Dk protozoa. In treated cells, the kinetoplast lost its normal disc-shaped structure because the fibrillar arrangement was reduced to a compact, amorphous mass within the mitochondrion. Moreover, basic proteins associated with kDNA were redistributed throughout the Dk protozoal kinetoplast. We sought to understand how the disruption of the kDNA leads to the emergence of the Dk phenotype with atomic force microscopy (AFM) analysis of isolated networks. Our results demonstrate that the detachment of minicircles from the kDNA disk promotes the disassembly of the network, thereby generating Dk cells. Our data strongly suggest that acriflavine inhibitsT. cruzimultiplication by interfering with kDNA replication.
Trypanosoma evansiinfection impairs memory, increases anxiety behaviour and alters neurochemical parameters in rats
Authors: WOLKMER PATRÍCIA , PAIM FRANCINE C. , DA SILVA CÁSSIA B. , GAI BIBIANA M. , CARVALHO FABIANO B. , DA SOUZA ANA CRISTINA G. , DA ROSA MICHELLE M. , DA SILVA ALEKSANDRO S. , PEREIRA PAULA R. , LOPES SONIA T. A. , NOGUEIRA CRISTINA W. , RUBIN MARIBEL A. , MONTEIRO SILVIA G. , MAZZANTI CINTHIA M.
Published: August 2013

The aim of this study was to investigate neurochemical and enzymatic changes in rats infected withTrypanosoma evansi, and their interference in the cognitive parameters. Behavioural assessment (assessment of cognitive performance), evaluation of cerebral L-[3H]glutamate uptake, acetylcholinesterase (AChE) activity and Ca+2and Na+, K+-ATPase activity were evaluated at 5 and 30 days post infection (dpi). This study demonstrates a cognitive impairment in rats infected withT. evansi. At 5 dpi memory deficit was demonstrated by an inhibitory avoidance test. With the chronicity of the disease (30 dpi) animals showed anxiety symptoms. It is possible the inhibition of cerebral Na+, K+-ATPase activity, AChE and synaptosomal glutamate uptake are involved in cognitive impairment in infected rats byT. evansi. The understanding of cerebral host–parasite relationship may shed some light on the cryptic symptoms of animals and possibly human infection where patients often present with other central nervous system (CNS) disorders.
Cost-effectiveness of combining systematic identification and treatment of co-morbid major depression for people with chronic diseases: the example of cancer
Authors: Walker S. , Walker J. , Richardson G. , Palmer S. , Wu Q. , Gilbody S. , Martin P. , Hansen C. Holm , Sawhney A. , Murray G. , Sculpher M. , Sharpe M.
Published: August 2013

Background

Co-morbid major depression occurs in approximately 10% of people suffering from a chronic medical condition such as cancer. Systematic integrated management that includes both identification and treatment has been advocated. However, we lack information on the cost-effectiveness of this combined approach, as published evaluations have focused solely on the systematic (collaborative care) treatment stage. We therefore aimed to use the best available evidence to estimate the cost-effectiveness of systematic integrated management (both identification and treatment) compared with usual practice, for patients attending specialist cancer clinics.

Method

We conducted a cost-effectiveness analysis using a decision analytic model structured to reflect both the identification and treatment processes. Evidence was taken from reviews of relevant clinical trials and from observational studies, together with data from a large depression screening service. Sensitivity and scenario analyses were undertaken to determine the effects of variations in depression incidence rates, time horizons and patient characteristics.

Results

Systematic integrated depression management generated more costs than usual practice, but also more quality-adjusted life years (QALYs). The incremental cost-effectiveness ratio (ICER) was £11 765 per QALY. This finding was robust to tests of uncertainty and variation in key model parameters.

Conclusions

Systematic integrated management of co-morbid major depression in cancer patients is likely to be cost-effective at widely accepted threshold values and may be a better way of generating QALYs for cancer patients than some existing medical and surgical treatments. It could usefully be applied to other chronic medical conditions.
ISLANDS AND OBJECTS IN L2 SPANISH
Authors: Rothman Jason , Iverson Michael
Published: August 2013

This study tests native Brazilian Portuguese (BP) speakers of second language (L2) Spanish in the domain of phonologically null object pronouns. This is a worthwhile first language (L1)-L2 pairing given that these languages are historically and typologically related and both seemingly allow for object drop. Nevertheless, the underlying syntax of phonologically null object pronouns is distinct in each language, resulting in differences in their respective syntactic reflexes. We pursue whether or not it is more difficult to acquire new syntactic structure for a L2 property that, on the surface, is shared by the L1. In other words, we explore whether advanced BP learners of L2 Spanish will be successful in the acquisition of Spanish object drop to the same degree as English learners and European Portuguese learners who were previously shown by Bruhn de Garavito and Guijarro-Fuentes (2001) to be quite successful. By means of a scalar grammaticality judgment task with context, we examine competence of the Spanish restrictions on the distribution of dropped objects that differ from BP in various syntactic positions (e.g., simple clauses vs. strong islands) while alternating the Spanish-specific semantic variable of definiteness as determined by the context. The data show that the semantic alternations are acquired as well as the new syntax; however, such acquisition does not guarantee preemption of the L1 syntactic option, which may result in target-deviant variability. We discuss the data in light of what they bring to bear on questions pertinent to formal SLA theory.
Linking minds and brains
Authors: BARLOW HORACE
Published: August 2013

When I first came across William James’ dictum that “ … this sense of sameness is the very keel and backbone of our thinking,” I thought he had foreseen the importance of cross-correlation in the brain, and told myself to find out how he had reached this conclusion. When I finally did this a year or two ago, I slowly came to realize that I had completely misunderstood him; from the full quote it is absolutely clear that his dictum cannot be referring to the process by which a cortical simple cell responds selectively to the orientation of features in a visual image, as I had originally supposed. If one translates the original dictum into two more prosaic modern versions, his version would say: “Our minds could not think at all without neural circuits in our brains that compute auto-correlations,” but in my mistaken interpretation the last word would be “cross-correlations.” Others may have made the same mistake, but the difference is profound, and finding what he really meant has been a revelation to me. This essay explains the revelation, describes how to determine experimentally whether the brain does auto- or cross-correlation, and gives the result of preliminary experiments showing clearly that it does both. A revised view of the visual cortex as autocorrelator as well as cross-correlator claims to tell us what complex cells in the visual cortex do, and it assigns a role to its columnar structure that is as important to fulfilling that role as the concept of the receptive field has been to understanding the simple cells’ fulfillment of theirs. The new view has compelling features, broad implications, and suggests a plausible model of how neural circuits in the cortex achieve thought, but it needs further testing.
A Plea for Risk
Authors: Ebert Philip A. , Robertson Simon
Published: August 2013

Mountaineering is a dangerous activity. For many mountaineers, part of its very attraction is the risk, the thrill of danger. Yet mountaineers are often regarded as reckless or even irresponsible for risking their lives. In this paper, we offer a defence of risk-taking in mountaineering. Our discussion is organised around the fact that mountaineers and non-mountaineers often disagree about how risky mountaineering really is. We hope to cast some light on the nature of this disagreement – and to argue that mountaineering may actually be worthwhilebecause ofthe risks it involves. Section 1 introduces the disagreement and, in doing so, separates out several different notions of risk. Sections 2–4 then consider some explanations of the disagreement, showing how a variety of phenomena can skew people's risk judgements. Section 5 then surveys some recent statistics, to see whether these illuminate how risky mountaineering is. In light of these considerations, however, we suggest that the disagreement is best framed not simply in terms ofhow riskymountaineering is but whether the risks it does involve arejustified. The remainder of the paper, sections 6–9, argues that risk-taking in mountaineering oftenisjustified – and, moreover, that mountaineering can itself be justified (in part)byandbecause ofthe risks it involves.
Not a Matter of Life and Death?
Authors: O'Hear Anthony
Published: August 2013

‘Come on, it's not a matter of life and death’, said some Job-like comforter, following a defeat in a football match. ‘No’, replied Bill Shankly, the granite-like Scot who was manager of Liverpool FC during their days of pre-eminence, whose team had just lost, ‘it is more important than that’.
In the Zone
Authors: Papineau David
Published: August 2013

On the Friday afternoon of the 3rd test at Trent Bridge in 2001, the series was in the balance. The Australians had won the first two tests easily, but England now found themselves in a position of some strength. They had restricted Australia to a first-innings lead of just 5 runs, and had built a lead of 120 with six wickets in hand. Mark Ramprakash was in and had been batting steadily for well over an hour. Even though this Australian side was as strong as any in cricket history, England had real hopes of getting back into the series.
Sex Differences in Jealousy: A Population-Based Twin Study in Sweden
Authors: Walum Hasse , Larsson Henrik , Westberg Lars , Lichtenstein Paul , Magnusson Patrik K. E.
Published: August 2013

According to the theory of evolved sex differences in jealousy, the challenge for women to ensure paternal investment increased their jealousy response to emotional infidelity, whereas paternal uncertainty exerted selective pressures that shaped men to become more distressed by sexual infidelity. Several studies have investigated whether the effect of these sexually dimorphic selection pressures can be detected in contemporary human populations, with conflicting results. To date, no genetically informed studies of sex differences in jealousy have been conducted. We used data from the Screening Across the Lifespan of Twins Younger (SALTY) sample, containing information concerning self-rated jealousy from 3,197 complete twin pairs collected by the Swedish Twin Registry. Intra-class correlations and structural equation models were used to assess the genetic influence on jealousy and to investigate sex differences at genetic level. We saw a highly significant sex effect on the relationship between infidelity types, indicating that men, relative to women, reported greater jealousy in response to sexual infidelity than in response to emotional infidelity. The twin models revealed significant heritabilities for both sexual (32%) and emotional (26%) jealousy. The heritabilities were of a similar magnitude in both sexes, and no qualitative sex differences could be detected. We show for the first time that variance in jealousy is to some extent explained by genetic factors. Even though our results from the mean value analyses are in line with the theory of evolved sex differences in jealousy, we could not identify any sex differences on a genetic level.
Pharmacometric Analyses to Support Early Development Decisions for LY2878735: A Novel Serotonin Norepinephrine Reuptake Inhibitor
Authors: Raddad E , Melhem MR , Sloan‐Lancaster JS , Miller JW , Van Wart SA , Rubino CM
Published: August 2013

LY2878735 is a novel dual serotonin (5‐hydroxytryptamine (5‐HT)) and norepinephrine (NE) reuptake inhibitor (SNRI) in development for chronic pain indications. In vitro profile suggests a more balanced profile as compared with other SNRI's, which is expected to confer superior clinical efficacy. LY2878735 is metabolized partly by the genetically polymorphic cytochrome P450 (CYP) 2D6 pathway, raising pharmacokinetic (PK) variability concerns. Phase 1 PK and biomarker data were analyzed by pharmacometric methods to characterize the balance between dual‐target engagement and adverse effects on heart rate (HR) and blood pressure (BP). A narrow range of plasma LY2878735 levels was associated with an acceptable balance. As compared with poor metabolizers (PM), CYP2D6 extensive metabolizers (EM) have 21‐ and threefold higher clearance and distribution volume, respectively. Even with a CYP2D6‐based dosing paradigm, a superior therapeutic index comparable to duloxetine, a widely used SNRI, was not achievable and LY2878735 development was thus terminated. Model‐based approach effectively synthesizes PK‐pharmacodynamic (PD) relationships, enabling efficient early development decisions.

CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e66; doi:10.1038/psp.2013.43; published online 21 August 2013
Use of a Biomarker in Exposure–Response Analysis to Support Dose Selection for Fingolimod
Authors: Lee J‐Y , Wang Y
Published: August 2013

Fingolimod 0.5 mg q.d. (once daily) has been approved for the treatment of patients with relapsing and remitting forms of multiple sclerosis (RRMS). Fingolimod at two doses (0.5 and 1.25 mg) showed superior effectiveness in the frequency of relapse with little difference between the two dose groups. At the same time, fingolimod manifests a number of dose‐dependent adverse events. Given the safety concerns and similar effect size at both dose groups, it was reasonable to raise the question whether doses even lower than 0.5 mg would produce sufficient effectiveness. Therefore, our analysis focused on estimating the effect size of the primary endpoint at doses lower than 0.5 mg via exposure–response analysis. Specifically, we aim to show how biomarker data can be used as a bridge in exposure–response analysis to estimate the clinical endpoint response at certain doses when the direct relationship between exposure and the clinical endpoint can not be quantified reliably.

CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e67; doi:10.1038/psp.2013.44; published online 21 August 2013
Determination of sulfonamides in blood using acetonitrile–salt aqueous two-phase extraction coupled with high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry
Authors: Yu Wei , Liu Zhongling , Gao Shiqian , Cui Shusen , Yang Xiao , Qiu Wei , Zhang Hanqi , Yu Aimin , Huan Yanfu
Published: August 2013

An ATPS was developed and applied in the extraction of sulfonamides in blood.
A novel biomass-based support (Starbon) for TiO2 hybrid photocatalysts: a versatile green tool for water purification
Authors: Colmenares Juan Carlos , Lisowski Paweł , Łomot Dariusz
Published: August 2013

Novel carbonaceous support (Starbon) for TiO2 photocatalysts synthesized by a simple ultrasound-assisted impregnation technique. High phenol photo-oxidation rate to complete mineralization. Renewable materials for a straightforward photocatalysts synthesis.
Dynamic modelling of the brushless doubly fed machine
Authors: Roberts Paul C. , Long Teng , McMahon Richard A. , Shao Shiyi , Abdi Ehsan , Maciejowski Jan M.
Published: August 2013

A coupled‐circuit model for the brushless doubly fed machine (BDFM) has been developed. The transformation of the model into the d–q axis form, ultimately in a synchronous reference frame in which machine currents and voltages have constant values in the steady state, has been carried out. A model‐reduction technique is presented, which gives a concise representation of the ‘nested‐loop’ rotor design using a single d–q pair. These models have been experimentally verified and give a convenient and accurate way of calculating the dynamic behaviour of a BDFM. The ability to represent the BDFM with a single d–q pair considerably simplifies the design of suitable controllers.
Sensorless position estimation of switched reluctance motor at startup using quadratic polynomial regression
Authors: Chang Yan‐Tai , Cheng Ka Wai Eric
Published: August 2013

Sensorless position sensing of switched reluctance motor (SRM) has been of great interests to researchers for reducing costs and increasing reliability of the system. The startup position estimation is a difficult task. This study presents a new method to estimate motor phase positions during startup. It is based on the general magnetic characteristics of the inductance profile in an SRM. All phase positions are estimated without using any specific magnetic information. The calculation is simple and can be implemented easily and executed efficiently in a microcontroller.
Three effective vectors‐based current control scheme for four‐switch three‐phase trapezoidal brushless DC motor
Authors: Xia Changliang , Xiao Youwen , Chen Wei , Shi Tingna
Published: August 2013

This study presents a novel three effective vectors (TEV) current control scheme for four‐switch three‐phase inverter in cost‐effective brushless DC motor drive with improved performance. This scheme overcomes the possible distortion of three‐phase currents caused by phase C back‐EMF, and quasi‐square current waveforms are attained by inserting two adjusting vectors in each control period based on the conventional switching modulation scheme. The duty cycles of the two adjusting vectors are further calculated using a simple P controller. Integral variable structure control principle with advantages of high bandwidth and strong robustness against external disturbance is used to control the tracing of reference current by actual currents. The stability of the proposed TEV current control scheme is demonstrated by selecting a candidate Lyapunov function, based on which the range of duty cycles of adjusting vectors are also determined. Experimental results verify that the proposed scheme is simple and can provide small current ripple, with good performance in speed.
Stator current model reference adaptive systems speed estimator for regenerating‐mode low‐speed operation of sensorless induction motor drives
Authors: Gadoue Shady M. , Giaouris Damian , Finch John W.
Published: August 2013

The performance of a stator current‐based model reference adaptive systems (MRAS) speed estimator for sensorless induction motor drives is investigated in this study. The measured stator currents are used as a reference model for the MRAS observer to avoid the use of a pure integrator. A two‐layer, online‐trained neural network stator current observer is used as the adaptive model for the MRAS estimator which requires the rotor flux information. This can be obtained from the voltage or current models, but instability and dc drift can downgrade the overall observer performance. To overcome these problems of rotor flux estimation, an off‐line trained multilayer feed‐forward neural network is proposed here as a rotor flux observer. Hence, two networks are employed: the first is online trained for stator current estimation and the second is off‐line trained for rotor flux estimation. Sensorless operation for the proposed MRAS scheme using current model and neural network rotor flux observers are investigated based on a set of experimental tests in the low‐speed region. Using a neural network rotor flux observer to replace the current model is shown to solve the stability problem in the low‐speed regenerating mode of operation.
Hybrid modelling of doubly fed induction generators with inter‐turn stator fault and its detection method using wavelet analysis
Authors: Yousefi kia Mohammad , Khedri Mostafa , Najafi Hamid Reza , Shamsi Nejad Mohammad Ali
Published: August 2013

Stator faults contribute to 38% of all electrical machine failures. The detection of inter‐turn stator fault has therefore been the focus of research for many years. The aim of this research is to provide new condition monitoring technique for doubly fed induction generator during inter‐turn fault. The contribution of this research is to formulate a method of doubly‐fed induction generator (DFIG) inter‐turn stator fault detection that is applicable when this machine operates during steady‐state condition. New proposed hybrid model (ABC/dq) has been presented for modelling of DFIG with inter‐turn stator fault. Finally a new index has been defined for the detection of inter‐turn stator fault in DFIG that employs wavelet analysis of the stator currents and energy of a signal which has been called fault detection index. Proposed index is robust to variation of operating point, percentage of turn fault, stator and rotor resistance and sampling frequency.
Unified framework for frequency and voltage control of autonomous microgrids
Authors: Sanjari Mohammad Javad , Gharehpetian Gevork B.
Published: August 2013

A general and effective framework for the secondary control of islanded microgrids (MGs) including inverter‐based distributed generators and conventional generator is proposed in this study. The proposed framework works based on fuzzy potential function method and provides a clear vision for system designer in order to set the cooperation of different distributed energy resources (DERs) in regulating MG variables. Different potential functions are deﬁned for each controllable microsource such that the minimum value of the potential function represents the microsource control target. The set points of DER units are dynamically updated by the optimisation unit located in MG central controller using available communication links. In addition, the small signal stability assessment is used to determine the parameter of the fuzzy potential function to guarantee the system stability. The simulation studies are carried out in the time‐domain, using the developed program in MATLAB environment. The results demonstrate the effectiveness and flexibility of the proposed framework in the frequency and voltage control of islanded MGs.
Fault ride through capability for grid interfacing large scale PV power plants
Authors: El Moursi Mohamed Shawky , Xiao Weidong , Kirtley Jim. L.
Published: August 2013

Integration of dynamic grid support is required for distributed power systems that are interconnected with medium voltage grids. This study proposes a comprehensive control solution to enhance fault ride through (FRT) capability for utility‐scale photovoltaic (PV) power plants. Based on positive and negative sequence control schemes and PV characteristics, the approach alleviates dc‐bus double‐line‐frequency ripples, reduces voltage stress on inverter power switches and DC‐link capacitors, and minimises undesirable low‐order voltage and current harmonics that are presented on the ac side. The study proposes a new feature to achieve superior FRT performance by using the overload capability of grid‐tied inverters. A weak electric grid is used for the test case including a wind turbine induction generator, diesel engine driven synchronous generators and various loads. A comprehensive simulation verified the capability of the proposed control schemes for mitigating the voltage dip, enhancing the voltage response and further improving the stability of interconnected distributed generation in reaction to severe unbalanced voltage conditions because of asymmetrical grid faults.
Switching regulator using a high step‐up voltage converter for fuel‐cell modules
Authors: Leyva‐Ramos Jesus , Lopez‐Cruz Juan Manuel , Ortiz‐Lopez Maria Guadalupe , Diaz‐Saldierna Luis Humberto
Published: August 2013

A typical fuel‐cell stack produces a low DC voltage with wide variations; therefore a DC–DC switching converter is required to step up and regulate the output voltage. In this work, a model based on electrical variables is developed for a fuel‐cell stack. This model is later combined with the model of a high step‐up voltage converter to obtain a combined model that incorporates the behaviour of fuel‐cell stack. The resulting model is then used to design an average‐current mode controller for a switching regulator. To test the proposed regulator, a power module with polymer electrolyte membrane fuel cells is used as an input source. This module delivers an output voltage between 26 and 42 V depending on the current being drawn. Experimental results exhibit the robustness of the switching regulator to step changes in the output load and the output voltage of the fuel‐cell stack.
Active closed‐loop gate voltage control method to mitigate metal‐oxide semiconductor field‐effect transistor turn‐off voltage overshoot and ring
Authors: Wang Xiaowei , Sun Yue , Li Tiecai , Shi Jian
Published: August 2013

Voltage overshoot and ring will occur during metal‐oxide semiconductor field‐effect transistor (MOSFET) turn‐off, when it is embedded in circuits with inductive load and operates in pulse width modulation mode. The voltage overshoot and ring not only increase the system voltage stress, but also produce radiated and conducted electromagnetic interference. Based on the analysis of the influence of the gate voltage on the MOSFET turn‐off behaviour, this study presents an active closed‐loop gate voltage control method to mitigate the voltage overshoot and ring. The proposed method senses the instant when the MOSFET drain current starts to fall by comparing the drain voltage with the bus voltage. Once the instant has been detected, a turn‐off assistance voltage with proper amplitude and adjustable duration is generated and applied to the gate to mitigate the overshoot and ring. The delay of the gate control loop, including the delay of the comparator, can be compensated by proper choice of the components. Both simulations and experiments results indicate that the MOSFET turn‐off voltage overshoot is largely reduced and the ring is almost completely eliminated. At the same time, the turn‐off loss and EMI are also minimised.
Design of a zero‐voltage‐switching large‐air‐gap wireless charger with low electric stress for electric vehicles
Authors: Duan Chen , Jiang Chenguang , Taylor Allan , Bai Kevin (Hua)
Published: August 2013

This study proposes a design and development of a wireless power transfer system to charge the battery in electric vehicles. A parallel–parallel topology is adopted to realise 10–15 cm‐distance power transfer using the resonance theory. Finite‐element method is used to extract the coil parameters. The advantages of the proposed design compared with the previous similar research are (i) low operational frequency (42 kHz) which avoids the electromagnetic interference to the on‐board automotive electronics equipment and (ii) low electric stress to the semi‐conductor switches through using zero‐voltage‐switching technique. A 2 kW prototype to charge 200 V battery was built to experimentally verify the theoretical analysis. The overall system efficiency is ∼ 86%.
Hybrid split capacitors and split inductors applied in positive output super‐lift Luo‐converters
Authors: Luo Fang Lin , Ye Hong
Published: August 2013

Voltage lift technique has been successfully employed in design of DC/DC converters, for example, three series Luo‐converters. However, the output voltage increases in arithmetic progression. Super lift (SL) technique is the most significant contribution in power electronics, for example, four series SL converters. Their output voltage increases in geometric progression. This study introduces a novel approach – SL technique armed by split capacitors and split inductors that implements the output voltage increasing in higher geometric progression. It effectively enhances the voltage transfer gain in power series as well. From the authors experimental results, the power rates of these converters can be few kW.
Analysis and design of split‐capacitor resistive‐inductive passive damping for LCL filters in grid‐connected inverters
Authors: Balasubramanian Arun Karuppaswamy , John Vinod
Published: August 2013

Grid‐connected inverters require a third‐order LCL filter to meet standards such as the IEEE Std. 519‐1992 while being compact and cost‐effective. LCL filter introduces resonance, which needs to be damped through active or passive methods. Passive damping schemes have less control complexity and are more reliable. This study explores the split‐capacitor resistive‐inductive (SC‐RL) passive damping scheme. The SC‐RL damped LCL filter is modelled using state space approach. Using this model, the power loss and damping are analysed. Based on the analysis, the SC‐RL scheme is shown to have lower losses than other simpler passive damping methods. This makes the SC‐RL scheme suitable for high power applications. A method for component selection that minimises the power loss in the damping resistors while keeping the system well damped is proposed. The design selection takes into account the influence of switching frequency, resonance frequency and the choice of inductance and capacitance values of the filter on the damping component selection. The use of normalised parameters makes it suitable for a wide range of design applications. Analytical results show the losses and quality factor to be in the range of 0.05–0.1% and 2.0–2.5, respectively, which are validated experimentally.
Lithium‐ion battery state of charge estimation based on square‐root unscented Kalman filter
Authors: Gholizade‐Narm Hossein , Charkhgard Mohammad
Published: August 2013

This study represents a method for estimating the state of charge (SOC) of lithium‐ion batteries using radial basis function (RBF) networks and square‐root unscented Kalman filter (KF). The RBF network is trained offline by sampled data from the battery in the charging process. This type of neural network finds the non‐linear relation which is required in the state‐space equations. The state variables include the battery terminal voltage and the SOC, at the previous sample and the present sample, respectively. The proposed method is tested experimentally on a lithium‐ion battery with 1.2 Ah capacity to estimate the actual SOC of the battery. The experimental results of the proposed method show some advantages, which include: (i) it is not very sensitive to determine, precisely, the measurement and process noise covariance matrices such as Kalman filter and (ii). It contains lower noise on the output, in comparison with Adaptive extended Kalman filter (EKF).
Complex state variable‐ and disturbance observer‐based current controllers for AC drives: an experimental comparison
Authors: Dal Mehmet , Teodorescu Remus , Blaabjerg Frede
Published: August 2013

In vector‐controlled AC drives, the design of current controller is usually based on a machine model defined in synchronous frame coordinate, where the drive performance may be degraded by both the variation of the machine parameters and the cross‐coupling between the d‐ and q‐axes components of the stator current. In order to improve the current control performance an alternative current control strategy was proposed previously aiming to avoid the undesired cross‐coupling and non‐linearities between the state variables. These effects are assumed as disturbances arisen in the closed‐loop path, extracted by a disturbance observer and then injected into the current controller. In this study, a revised version of a disturbance observer‐based controller and a well known complex variable model‐based design with a single set of complex pole are compared in terms of design aspects and performance evaluation by simulation and by experiment for two different sampling rates. Several comparative results that verify the promising performance of the proposed control scheme are presented. The advantages of the proposed controller are an easy implementation and offering a unique solution for the variation of the parameter and the cross‐coupling effect. Moreover, it provides a better performance, smooth and low noisy operation with respect to the complex variable controller.
Improved performance of multilevel inverter‐based distribution static synchronous compensator with induction furnace load
Authors: Nijhawan Parag , Bhatia Ravinder Singh , Jain Dinesh Kumar
Published: August 2013

Owing to the presence of large number of non‐linear loads in the power distribution network, power quality levels are deteriorating. One such load is an induction furnace. The problem with the induction furnace load is that it introduces appreciable amount of harmonic distortion in the power system network. The performances of other loads connected in the power system network are also affected because of the presence of induction furnace load. In this study, the performance of a carrier phase shifted pulse‐width modulation (PWM) multilevel inverter (five‐level)‐based distribution static synchronous compensator (DSTATCOM) is compared with that of a PWM inverter based‐DSTATCOM with induction furnace load. The simulation results based on MATLAB/SIMULINK are presented to illustrate the effectiveness of multilevel inverter based‐DSTATCOM for reducing harmonic distortion in the load current with induction furnace load in the distribution network.
Zero‐voltage switching current‐fed flyback converter for power factor correction application
Authors: Quang Nha Trong , Chiu Huang‐Jen , Lo Yu‐Kang , Alam Mohammed Mahmood
Published: August 2013

Previous research on flyback power factor correction (PFC) converters exposes some inherent shortcomings, such as high‐voltage spike on the metal oxide semiconductor field effect transistor (MOSFET), frequency variation, pulsating input current and hard switching operation. This study presents a new topology for PFC applications named zero‐voltage switching (ZVS) current‐fed flyback converter to not only achieve spike‐free voltage, ZVS on the MOSFETs, but also improve the input current quality. By utilising quasi‐z‐source configuration, the voltage spikes on the MOSFET are effectively eliminated using only a capacitive clamper, resulting in no‐loss consumption. Low‐voltage MOSFETs with low on‐resistance Rds(on) are used to improve the efficiency. In addition, by taking advantage of the average current mode control with the continuous conduction mode operation, the input current perfectly tracks the input voltage. To demonstrate the circuit's feasibility, a 100–140 V input, 28 V/5 A output laboratory prototype was built. The experimental results showed that the proposed topology completely eliminated the voltage spikes on the MOSFETs. The efficiency was improved using low Rds(on) MOSFETs, and ZVS was achieved. In summary, the proposed topology meets the high efficiency and high‐input current quality requirements.
Optimal selective harmonic elimination for cascaded H‐bridge‐based multilevel rectifiers
Authors: Marzoughi Alinaghi , Imaneini Hossein
Published: August 2013

In medium‐voltage medium‐ and high‐power converters, it is of great importance to reach high‐quality waveforms with low switching frequency. In active rectifiers, both converter's ac‐side harmonics and grid preexisting distortions affect the quality of the input current, which according to the existing standards is restricted from both the individual harmonics amplitude and total harmonic distortion point of view. The well known selective harmonic elimination pulse‐width modulation technique is able to completely eliminate certain harmonics from the ac‐side voltage of the converter, and as a result increases the quality of the input current. In this study, an optimal selective harmonic elimination control strategy is introduced for cascaded H‐bridge (CHB) rectifiers. By fully manipulating the ac‐side waveform of the rectifier, maximum number of harmonics is eliminated for a specific number of switching transitions. Moreover, this method can be easily extended for any number of H‐bridge cells and it uses only one lookup table for the whole interval of modulation index. Also using an effective voltage balancing technique, dc‐link voltages are balanced to the reference value and the rectifier does not encounter any difficulty under equal or non‐equal loads conditions. Using this method, the size of the bulky line‐side filters can be reduced which leads to lower overall cost of implementation. To prove the feasibility of the proposed scheme, simulation and experimental results for a seven‐level CHB‐based rectifier are reported.
Support vector regression‐based distortion compensator for three‐phase DC–AC boost‐inverters: analysis and experiments
Authors: Eskandari Bahman , Tavakoli Bina Mohammad
Published: August 2013

Distortion existence in output of power electronics DC–AC converters is inevitable. The amount of distortion in boost‐type converters is higher than other types, which is difficult to mitigate. This study introduces a new modification of three‐phase boost‐inverters in order to mitigate excessive distortions. The compensation process is modified to take advantage of non‐linear operation of boost converters and a differential connection of DC–DC converters is employed. Considering DC–AC boost‐inverter, it is shown that the outcomes are usually different from the expected desired waveforms. This is because of the non‐linear structure of the switching converter. Thus, a compensation method based on support vector regression (SVR) is proposed in a way that the desired waveforms appear at the output of the converter. Analysis and simulations are first introduced for defining the limitations of a boost‐inverter because of the non‐linear structure. Then, the simulated SVR applied to the external‐layer control, comparing the effects of the suggested algorithm with those of the uncompensated cases. Furthermore, practical verification is taken place on an implemented 500 VA boost‐inverter in order to confirm the proposed technique as well as theoretical analysis and simulations. The proposal is particularly useful when considering high penetration of inverter‐based interfaces for renewable energy sources such as solar panels.
Field programmable gate array implementation of space‐vector pulse‐width modulation technique for five‐phase voltage source inverter
Authors: Renukadevi Govindasamy , Rajambal Kalyanasundaram
Published: August 2013

This study analyses a field programmable gate array (FPGA) implementation of space‐vector pulse‐width modulation (SVPWM) technique for five‐phase voltage source inverter (VSI). The five‐phase VSIs are dominantly used to supply the five‐phase drives that are used for high‐power applications. It is necessary to develop an appropriate SVPWM technique for the inverters to provide the required output voltages to five‐phase induction motor load. In the proposed work, SVPWM algorithm is described in high‐speed integrated circuit hardware description language coding and implemented in an XILINX XC3SD1800A FPGA processor. The relationship between the SVPWM technique for medium, large and combinations of large and medium space vectors for five‐phase VSI is analysed. The selection of active space vector and zero vectors is discussed and the possibilities of FPGA implementations are explored. The experimental results with 1 hp five‐phase induction motor drive are presented for the different SVPWM techniques. The best SVPWM scheme is identified based on the output voltage and total harmonic distortion.
Integral‐resonant control for stand‐alone voltage source inverters
Authors: Lidozzi Alessandro , Lo Calzo Giovanni , Solero Luca , Crescimbini Fabio
Published: August 2013

This study deals with a newly‐conceived voltage control method for three‐phase four‐leg voltage source inverters (VSIs) which are being required in autonomous power generating units devoted to supply both three‐phase and single‐phase electrical loads in four‐wire electric power distribution systems. To deal with VSI operating conditions providing three‐phase voltage supply of both unbalanced loads and non‐linear loads, an integral + resonant (I + R) voltage control structure is discussed and experimentally verified by means of a 25 kVA rated power converter prototype. It is shown that the proposed voltage control allows simplifying the overall control configuration, achieving zero‐overhead power factor regulation and fast compensation of load unbalances. Further to that, a complete current limiting strategy is described and tested under different load conditions.
Improved modal method of moments technique to compensate the effect of wall dimension in shielding effectiveness evaluation
Authors: Nobakhti Marzieh , Dehkhoda Parisa , Tavakoli Ahad
Published: August 2013

In the conventional modal method of moments (MoM) method, when shielding effectiveness (SE) of a rectangular enclosure is the goal, it is assumed that the incident wave is reflected from an infinite wall. This assumption makes the results inaccurate specifically at low frequencies where the wall size is not large compared to the illumination wavelength. In this study, the mentioned reflected wave is corrected by considering the reflection from a box without any aperture. To obtain the reflected wave from the box, an induced electric current on the metallic surface is assumed. Using Rao Wilton Glisson basis functions along with free space Green's function, the unknown electric currents and consequently the reflected wave are calculated. The results are compared with full wave numerical methods. A very good agreement is observed between the results and it is shown that for lower frequencies the proposed method has more accuracy rather than the modal MoM itself specifically for an enclosure with a very large aperture.