bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Viscosity, Movable Oil, and Texture Evaluation in a Heavy-Oil Carbonate Reservoir With Advanced Dielectric and Nuclear-Magnetic-Resonance Log Integration
Authors: Ali M.. , Sangani P.. , Iqbal A.. , Yepes O.. , Murray M..
Published: May 2017

Textural and wettability variations are two main vexing problems in carbonate reservoirs. Adding heavy oil presents an incremental challenge to the reservoir description. Ineffectual analysis often leads to poor completion and high water production. Integrating multifrequency-dielectric and nuclear-magnetic-resonance (NMR) logs leads to improved carbonate-reservoir evaluation.

Dielectric and NMR logs have similar depths of investigation, both probing the flushed zone. It is difficult to distinguish bound water from heavy oil in rocks from NMR tools alone. The addition of accurate water-filled-porosity (ϕW) measurements from the dielectric log allows us to differentiate the fluids. Using ϕW as a reference and accounting for restricted molecular diffusion in small pores, NMR analysis on the basis of diffusion relaxation provides more-accurate oil viscosity and fluid volumes.

The computation of viscosity from NMR assumes that the oil relaxation is dominated by bulk relaxation; oil-wetting of pore surfaces causes viscosity to be overestimated. Conversely, the wetting state can be inferred if the viscosity is known. Dielectric dispersion with frequency provides a measure of the water-phase tortuosity MN_De, which in turn is affected by texture and wettability. We compared the in-situ NMR signal of oil to the surface NMR measurement of a bulk-oil sample. We also identified a correlation between MN_De and the Archie cementation exponent, mainly driven from NMR. This leads to interesting conclusions about texture and wettability, which are found to be coherent with the existing reservoir data.

Together with the viscosity profile, the comparison between the pore-fluid volumes in the flushed zone and the bulk volume of water from deep resistivity is used to identify the zones of movable oil and to estimate residual oil saturation. The method was applied to data sets from three wells in a shallow carbonate reservoir. The estimated viscosity was validated by pressure/volume/temperature (PVT) analysis. In two wells, the prediction of movable oil and water zones was confirmed by downhole test results. In the third well, the free-water zone was confirmed by production logging.
Personality and Psychopathology in Patients with Systemic Sclerosis
Authors: Csókási Krisztina , Hargitai Rita , Járai Róbert , Nagy László , Czirják László , Kiss Enikő C.
Published: May 2017

Background:

Systemic sclerosis is an autoimmune connective tissue disease with significant pain, fatigue, and disability. Patients with systemic sclerosis are at increased risk for psychiatric disorders.

Objective:

This study assessed the personality and psychopathological characteristics of scleroderma patients.

Method:

Consecutive, in-patient female cases with systemic sclerosis (N=72) from the tertiary care center of the University of Pécs and age- and sex-matched healthy volunteers (N=56) and fifty patients with rheumatoid arthritis were enrolled. Participants completed the Minnesota Multiphasic Personality Inventory-2. Demographical and clinical data were also collected.

Results:

Rheumatoid arthritis and scleroderma patients had similar profiles with high scores (≥65T) on Scales 1, 2 and 3. Additionally, they achieved moderate scores on Scales 5 and 0. The Scale 7 was elevated only in females with rheumatoid arthritis distinctively.

Conclusion:

High scores on Scales 1, 2 and 3 may reflect the severe somatic symptoms of systemic sclerosis (and rheumatoid arthritis), but may also refer to the disease-related emotional distress, anxiety and depression. Likewise, social withdrawal and less feminine interests may be the results of the chronic and disabling illness. The minor differences between the patient groups indicate that females with systemic sclerosis may be less vulnerable to specific anxiety disorders (obsessive-compulsive disorders, phobias). Study results highlight the importance of developing psychosocial interventions designed to meet the needs of scleroderma patients.
The Prevalence, Molecular Characterization and Antimicrobial Susceptibility of S. aureus Isolated from Impetigo Cases in Duhok, Iraq
Authors: Al Zebary Marwan K. , Yousif Samira Y. , Assafi Mahde S.
Published: May 2017

Background:

Staphylococcus aureusis one of the most important opportunistic pathogens. Impetigo is the common contagious bacterial infection of the skin caused byS. aureus.

Method:

Samples were taken from 204 patients with impetigo disease.S. aureusisolates were tested for their antimicrobial susceptibility. Genomic DNA ofS. aureuswas used to transformE. coliHB101 strain and expression capability ofS. aureusplasmids in transformedE. coliwas investigated. 68.62% (140/204) of the specimens were nonbullous impetigo and 31.38% (64/204) were bullous impetigo.S. aureusstrains were isolated from 41.66% (85/204) of impetigo cases (82.35% from nonbullous and 17.65% from the bullous impetigo). There was an inverse relationship between the incidence ofS. aureusisolated and age.

Result:

Three biotypes ofS. aureuswere identified based on their fermentation of different sugars. All isolates were resistant to penicillin and most isolates were resistant to ampicillin (95.3%), amoxicillin, (94.11%) and cephalexin (90.95%). Most isolates were sensitive against vancomycin and rifampicin (98.83%). 5.88% (5/85) ofS. aureusisolates were identified as MRSA. A maximum of 5 markers fromS. aureusisolates were capable to be expressed in transformedE. coliHB101 strains. The incidence of impetigo caused byS. aureusis comparable with reports from elsewhere.S. aureusisolates showed multidrug resistance against antibiotics.

Conclusion:

Plasmids ofS. aureusare capable to show its expression inE. coliHB101. Molecular study is needed to investigate the role of plasmids in different patterns of multi drug resistance.
A clinical study on management of Gridhrasi
Authors: Singhal Ankur , Gupta Komal
Published: May 2017

Gridhrasi is a painful condition in which the person can’t sit and walk properly that hampers his normal activity. Almost all signs and symptoms of Gridhrasi resemble with the condition of sciatica described by the modern texts. Its detail symptomatology has been described in Ayurvedic classics since 5000 years, while this condition was known to modern medical science just two centuries ago. According to Ayurveda principles treatment for Vatavyadhi should be Shodhana followed by Shamana therapy. According to present era it should be less time consuming and more effective. Keeping this in mind, A clinical study in the management of Gridhrasi with Shodhana and Shamana therapy was undertaken in VYDSAMC and Hospital, Khurja,Bulandshahr, with the aim to give promising results to the patient of Gridhrasi. Shodhana therapy as Mridu Virechana followed by Shamana with Yograja Guggulu and Maharasnadi Kwatha was given to 29 patients with classical symptoms of Gridhrasi, it showed significant results. The following study can be taken for further research in this field.
Concept of Sushrutokta Guda Shareera
Authors: Kumar Nithin , Govindaraju U.
Published: May 2017

Swastha Rakshana and Vikara Prashamana are the prime goals of Ayurveda. Knowledge about structural and functional aspect of Shareera is considered as a key to reach these goals. Guda is one such structural entity explained in Ayurveda, which play a role in elimination of Pureesha and Apana Vata. In Basti Chikitsa, one of the prime treatment modality of Vata medicine usually administered through Guda Marga only. Hence knowledge of Guda is helpful in understanding the physiology of Pureesha Bahirgamana and concept of Basti Chikitsa. In this article an attempt is made to understand the concept of Sushrutokta Guda Shareera.
Uttar Basti - A Therapeutic Measure In Yonivyapada
Authors: Trivedi Bharvi B.
Published: May 2017

Without Tridosha not a single disease can form or manifest. Among the Tridosha, Kapha and Pitta are non motile where as motility is attributed only to Vata. So to get vitiate Kapha and Pitta mostly requires an initiation from Vata Dosha. As per the therapeutic approach is concerned Basti have good efficacy to neutralise or normalise the vitiated as Vata is the primary humour which is responsible for all Yonivyapada. Yonivyapada described under Striroga covers almost all the diseases of women. Uttarbasti having both the effects of Shamana as well as the Shodhana effect. Hence, hypothesis – whether Uttarbasti can be taken as a major therapeutical approach for majority of Yonivyapadas? The drugs used in Uttarbasti mostly prepared with an oil base. Along with the oil Ushna, Tikshna, Vyavayi, sometimes Sheeta, Balya, Brimhana medicines act with respective to their above properties. The mode of action may be due to Srotoshuddhikara, stimulation on follicular cells also by giving nutrition to endometrium. Present study covers the methodology of Uttara Basti.
Auditory comprehension performance of college students with and without sport concussion on Computerized-Revised Token Test Subtest VIII
Authors: Salvatore Anthony P , Cannito Michael , Brassil Heather E , Bene Edina R , Sirmon-Taylor Bess
Published: May 2017

Aim: Auditory comprehension (AC) and visually assessed cognitive functions were compared in early stage postconcussed (PC) athletes and healthy controls using the Subtest VIII of the Computerized-Revised Token Test (C-RTT) and Immediate Postconcussion Assessment and Cognitive Test (ImPACT). Results: As compared with healthy controls (n = 30), PC subjects (n = 30) had significantly lower C-RTT efficiency scores (p = 0.018), and lower ImPACT scores; total symptom score (p = 0.000.), verbal memory (p = 0.000), visual memory (p = 0.000), visual motor speed (p = 0.000) and reaction time (p = 0.004) in this post-test only matched subject design. Impulse Control was not significant (p = 0.613). Multiple regression and ANOVA indicated an association with reaction time only (p = 0.012) for the PC subjects. After controlling for reaction time, a significant difference in AC remained. Conclusion: The relationship between AC and other visually assessed cognitive functions was inconsistent suggesting that the C-RTT and ImPACT assessed different functional systems.
Claves de la política exterior de Colombia
Authors: Dallanegra Pedraza Luis
Published: May 2017

Colombia, como América Latina, ha sido y es más “objeto” que “sujeto” en la escena internacional. Sus relaciones con Estados Unidos obedecen a lógicas que nada tienen que ver con el orden vigente, sino con opciones políticas y decisiones de la élite dominante. De acuerdo con las características de esa tendencia, ha estado prácticamente anclado a lo que se denominó simbólicamente Respice Polum –mirar hacía la “Estrella Polar”- que para este país ha sido Estados Unidos. Ha habido épocas en las que desarrolló una política, simbólicamente llamada Respice Similia –“mirar a los semejantes”- vinculada a una diversificación de las relaciones en forma más “horizontal” respondiendo al criterio “Sur-Sur”; sin embargo esos momentos han sido fugaces y débiles, que sólo demuestran que tan cerca o que tan lejos se ha estado de Estados Unidos, aunque siempre gravitando en su esfera de influencia.
Aunque las aguas nos dividan: las relaciones chileno-bolivianas y la construcción de una agenda común
Authors: Loreto Correa Vera , García Pinzón Viviana
Published: May 2017

En el primer semestre de 2011, el gobierno de Bolivia anunció la creación de la División de Reivindicación Marítima en la perspectiva de llevar ante tribunales internacionales su reclamo a Chile por una salida soberana al Océano Pacífico. Esta decisión representó un cambio en la dinámica de la relación bilateral, que en los últimos años había priorizado el diálogo a través de un instrumento bilateral conocido como la Agenda de los 13 puntos. El artículo analiza las fuentes de cooperación y conflicto entre los dos países durante las dos últimas décadas a partir de los planteamientos teóricos del neoliberalismo institucional.
La experiencia de los centroamericanos becados en México (1922-1928). Entre carencias, vida académica y propaganda revolucionaria
Authors: Rivera Mir Sebastián
Published: May 2017

Esta investigación analiza el arribo a México de un grupo de becarios centroamericanos durante los gobiernos de Álvaro Obregón y Plutarco Elías Calles. Estos apoyos buscaron consolidar los lazos culturales de la región y exponer una imagen positiva de México. Este trabajo intenta conjugar estas políticas estatales con las vivencias de los becarios, sus carencias, sus esfuerzos académicos y sus decepciones. Se trata de observar cómo los planes gubernamentales latinoamericanistas entraron en diálogo con las metas de los estudiantes y cómo dicho proceso significó un avance en la consolidación del sistema mexicano de intercambio académico.
Effects of structural and textural grain characteristics on leaching of sulphide minerals from a polymetallic concentrate by sodium nitrate and sulphuric acid solution
Authors: Sokic Miroslav , Stojanovic Jovica , Markovic Branislav , Bugarcic Mladen , Strbac Nada , Kamberovic Zeljko , Manojlovic Vaso
Published: May 2017

In this paper, the influence of structural and textural characteristics of sulfide minerals on their leaching from a polymetallic concentrate by sulfuric acid and sodium nitrate solution is presented. The starting material was Pb?Zn?Cu sulphide polymetallic concentrate enriched during the flotation of a polymetallic ore in the "Rudnik" flotation plant (Rudnik ? Serbia). Leaching experiments were carried out in a closed glass reactor, which provides stable hermetic conditions and allows heating at constant temperature. Chemical, XRD, qualitative and quantitative microscopic and SEM/EDX analyses were used to characterizes samples of the polymetallic concentrate and leach residue. It was determined that chalcopyrite, sphalerite, galena, pyrrhotite and quartz were present in the polymetallic concentrate. The content of sulphide minerals was 69.5%, of which 60.9% occurred as liberated grains: 88.3% of chalcopyrite, 59.3% of sphalerite, 25.1% of galena and 51.6% of pirrhotite. The rest of chalcopyrite, sphalerite, galena and pirrhotite grains were in the forms of inclusions, impregnations, and simple and complex intergrowths. During the leaching process by sodium nitrate and sulphuric acid solution, it was shown previously that the leaching rate of sulphide minerals decreased with time while a part of the sulphide minerals remained in the leach residue. After leaching at 80?C for 120 min, the yields were 69.8, 82.7 and 67.1% for Cu, Zn and Fe, respectively. Lead, in the form of insoluble anglesite, remained in the leach residue. In addition to the anglesite, unleached sulfide minerals and quartz, elemental sulfur was found in the solid residue. The content of sulphide minerals was 35% of which 33.7% minerals occur independently. In specific, 54.7% of chalcopyrite, 31.9% of sphalerite, 8.2% of galena and 37.6% of pyrrhotite appear as separate grains with highly corroded surfaces. Therefore, the structural assembly of sulphide grains in the polymetallic concentrate is favourable and it is not the reason for the observed decrease in the leaching rate in the final process stages. The obtained findings may be explained by the presence of elemental sulphur that is formed during the reaction and precipitated at the grain surfaces, thus creating a diffusion barrier for the leach solution.
Eccentricity samples: Implications on the potential and the velocity distribution
Authors: Cubarsi R. , Stojanovic M. , Ninkovic S.
Published: May 2017

Planar and vertical epicycle frequencies and local angular velocity are
related to the derivatives up to the second order of the local potential and
can be used to test the shape of the potential from stellar disc samples.
These samples show a more complex velocity distribution than halo stars and
should provide a more realistic test. We assume an axisymmetric potential
allowing a mixture of independent ellipsoidal velocity distributions, of
separable or Staeckel form in cylindrical or spherical coordinates. We prove
that values of local constants are not consistent with a potential separable
in addition in cylindrical coordinates and with a spherically symmetric
potential. The simplest potential that fits the local constants is used to
show that the harmonical and non-harmonical terms of the potential are
equally important. The same analysis is used to estimate the local
constants. Two families of nested subsamples selected for decreasing planar
and vertical eccentricities are used to borne out the relation between the
mean squared planar and vertical eccentricities and the velocity dispersions
of the subsamples. According to the first-order epicycle model, the radial
and vertical velocity components provide accurate information on the planar
and vertical epicycle frequencies. However, it is impossible to account for
the asymmetric drift which introduces a systematic bias in estimation of the
third constant. Under a more general model, when the asymmetric drift is
taken into account, the rotation velocity dispersions together with their
asymmetric drift provide the correct fit for the local angular velocity. The
consistency of the results shows that this new method based on the
distribution of eccentricities is worth using for kinematic stellar samples.
A future of island studies
Authors: Grydehøj Adam
Published: May 2017

Island studies has developed into an established, interdisciplinary research field. It is important that island studies not only continue deepening its internal theoretical understandings but also reach out to other fields and regions that have received limited attention within island studies. It is also necessary for island studies to grapple with a number of problematic tendencies within the field and the wider scholarship, including by challenging the misuse of island spatiality to produce idealised visions of islands (for example in island sustainability research). Similarly, it is important to pursue a decolonial island studies that rethinks the ways in which island development research can end up marginalising Indigenous voices at the same time as it seeks to understand islands ‘on their own terms’.
Permanent magnet wind generators: control strategies to manage voltage unbalances
Authors: F. Belloni  , R. Chiumeo  , C. Gandolfi
Published: May 2017

The paper presents four different control strategies for grid connected voltage source inverters, devoted to the interface of permanent magnet synchronous wind generators with the distribution network. A common dq-axes control is compared with two modified controls in the dq frame which take into account also negative sequence components of voltages, and currents and a control approach in the stationary αβ frame which reduces the computational complexity of the control itself. An ATPDraw model of a 2 MW wind generator has been developed and employed for simulating the responses of the four control schemes to voltage unbalances and voltage dips. The improved control strategies have shown better performances in terms of reduction of 100 Hz oscillating power components during network voltage unbalances
Extending the Lifetime of Power Transformers by using Fault Current Limiting Devices in the Network Distribution
Authors: T. Madiba  , A. A. Jimoh  , W.M. Siti  , B. Numbi
Published: May 2017

This paper investigates the advantages of Fault Current Limiting (FCL) technologies in extending the life span of power transformers within a power system distribution network. Power transformers being expensive equipments, this must be protected against unforeseen short circuit currents and power quality disturbances. The economic and capability of the fault current limiter is very important for reducing the lifecycle cost of a power transformer. In this paper, the results of a fault current limiter under normal, fault and post-fault conditions of the circuit are presented and compared to the results obtained with circuit breaker. It is found that the fault current limiter provides better results in limiting the fault current.
Survey of Inductance Curves in Switched Reluctance Machines Using Finite Elements
Authors: M. B. Rego  , L. C. Gomes  , A. B. F. Neves  , A. W. F. V. Silveira  , E. A. A. Coelho
Published: May 2017

The aim of this document is combine theoretical knowledge, computational tools and mathematical analysis so that the curves of inductance of two topologies for switched reluctance machines can be studied and analyzed. This article shows how to obtain the inductance curves for many values of current, using a magnetic simulation software named FEMM (Finite Elements Method Magnetics) and the programming language Lua script. The data analyses are to the 6x4 machine, three phase, and the 6x6 machine, single phase. Lastly, the computational simulations are compared with the real simulations made with the machines available in the university’s research laboratory.
Signal injection techniques for fault location in distribution networks
Authors: G. Buigues  , V. Valverde  , V. Valverde  , I. Zamora  , J. Mazón  , E. Torres
Published: May 2017

Over the last 50 years, fault location in transmission systems has been a subject of interest to utility engineers and researchers. Nevertheless, it has not been until the last decades that fault location in distribution networks has started to gain prominence. Traditionally, fault location techniques for distribution networks have been classified in three different groups: fundamental frequency measurements, high frequency measurements and the use of artificial intelligence (AI). Yet despite this rigid classification, a new approach has started to be developed over the last years based on the injection of a discernible signal into the distribution systems, mainly in non-effectively grounded networks. However, even when recent developments of new grounding systems reinforce the possibility of using this kind of techniques, these are not usually cited by general reviews and overviews of fault location systems in distribution networks. Accordingly, this paper aims to provide a general but clear overview on the existing techniques for fault location in distribution networks based on signal injection. Apart from describing the different options presented to date, the most important aspects that characterize them and the injected signal are briefly outlined, as well as a comparative performance analysis.
Effect of Biomass Composition on Combustion Characteristics and Energy Quality
Authors: I. Barmina  , A. Lickrastina  , M. Zake  , A. Arshanitsa  , V.Solodovnik  , G. Telysheva
Published: May 2017

The main aim of this study is to provide the experimental research of the combustion characteristics for the different types of the biomass pellets during their thermo chemical conversion with estimation the correlations between the main characteristics of pelletized plant biomass and combustion characteristics. The experiments include first, the preparation of the pelletized biomass samples of different origin with certain elemental composition, heating values, moisture content, bulk and energetic density, and second, kinetic study of the combustion characteristics with local measurements of the temperature and composition of the flame reaction zone and heat production rates at different stages of the thermo chemical conversion of pelletized biomass and different air supply rates into the combustor to obtain optimal combustion conditions of plant biomass. Correlations between the main characteristics of pelletized samples and combustion/emission characteristics of pelletized biomass fuel have been derived and analyzed.
Output DC Voltage Control Strategy for Switched Reluctance Generator
Authors: Julio R. Martinez  , Eliane A. Fadigas
Published: May 2017

The concept of MicroGrid (MG) has been proposed as a way to solve several problems associated with the integration of small generators in distribution feeders. The ability of MG operates either connected to the main grid or as an island, without the need of a fast and sophisticated central control, allows exploring in large scale, the use of the renewable and nonrenewable electricity generating technologies in the local consumption. However, new solutions are required to become MicroGrids technically secure and reliable as well as economically attractive. This work presents the results of economic dispatch applied to MGs operating as an island and connected to the grid. The optimization algorithm was developed and implemented in Matlab®. The profits obtained when MicroGrid operates in Optimal Power Flow (OPF) allow assessing the degree of complexity that the Local Supervisory Controller can achieve without compromising the economic viability of MicroGrid. The controller performance is evaluated by using power flow for various combinations of generation and load.
Impact of High Penetration Level of Grid-Connected Photovoltaic Systems on the UK Low Voltage Distribution Network
Authors: S. Ali  , N. Pearsall  , G. Putrus
Published: May 2017

The connection and use of Renewable Energy Sources (RES) such as Grid-Connected Photovoltaic (GCPV) systems in distribution networks have been increasing over the last few decades. The grid-connected PV system is one of the most promising renewable energy solutions which could offer many benefits to both the end user and the utility network. Such systems may cover the consumer’s own power demand and reduce electricity bills, while feeding any surplus power into the grid or use the grid as a backup system in times of insufficient PV generation. However, integrating a high penetration level of small-scale grid-connected PV systems into the low voltage distribution network (LVDN) could cause operational problems. One of the technical issues is a possible voltage rise along distribution feeders as a result of reverse power flow, especially at low demand and high generation conditions. This paper assesses the effect of high penetration levels of small-scale gridconnected PV systems on the voltage quality of a residential electricity distribution network in the UK. Different scenarios for both penetration and solar irradiation level are considered under various loading conditions. The MATLAB/Simulink software package was used to carry out this assessment.
Modelling, Iterative Procedure and Simulation Results for a Monocrystalline Solar Cell
Authors: S. Saraiva  , R. Melício  , J.C.O. Matias  , C.M.P. Cabrita  , J.P.S. Catalão
Published: May 2017

This paper focuses on the modelling and simulation for a photovoltaic system formed by monocrystalline solar modules. The objective is to find the parameters of the nonlinear I-V equation by adjusting the curve at three points: open circuit, maximum power, and short circuit. This paper brings a novel iterative procedure to find the value of diode ideality factor, series and equivalent shunt resistances. Simulation studies are carried out in order to uncover temperature dependence, solar radiation change, and output power variation. Finally, conclusions are duly drawn.
Development of Diagnosis System for Rolling Bearings Faults on Real Time Based on FPGA
Authors: M. Kashiwagi  , C. da Costa  , M. H. Mathias
Published: May 2017

The real-time monitoring of events in an industrial plant is an advanced technique that presents the real conditions of operation of the machinery responsible for the manufacturing process. A predictive maintenance program includes various rotating machinery condition monitoring techniques of the machine to determine the conditions of failure. To increase the operational reliability and to reduce preventive maintenance, it is necessary an efficient tool for analysis and process monitoring, in real time, enabling the detection of incipient faults for rolling bearings. Over the past few years there has been a major technological developments related to digital system, including innovations in both hardware and software. These innovations enable the development of new design methodologies that take into account the ease of future modifications, upgrades and expansions of the designed system. This paper presents a study of new design tools for embedded digital systems based on open hardware architecture with reconfigurable logic. Will be discussed a case study in the area of fault detection of rolling bearings, as well as its implementation and testing.
High efficiency energy supply in residential sector using Fuel Cells
Authors: J.I. San Martín  , I. Zamora  , J.J. San Martín  , V. Aperribay  , P. Eguía  , F.J. Asensio  , J. García
Published: May 2017

Increasing the overall efficiency of power generation systems has become a priority of research in the field of energy. In this sense, a conventional thermal power plant is able to convert around 33% of the energy contained in the primary fuel into electricity. The rest of the unused energy corresponds to energy dissipated as heat. By contrast, the overall efficiency of polygeneration systems is within 80-90% of fuel utilization. This combined production of heat-cold and electricity can be applied in the residential, industrial and service sectors.
Considering the increase in energy efficiency that cogeneration involves, this paper presents an analysis of the possibilities of PEM fuel cells for cogeneration applications. To do this, a set of experimental measurements on a real fuel cell (PEM HP600) has been developed, in order to identify its electrical and thermal aspects, for different loading rates.
Research On 400Hz Input Multi-Level PFC Techniques
Authors: A. Xiaolan Ji  , B. Yundong Ma  , C. Di Xu
Published: May 2017

Input current distortion in the vicinity of input voltage zero crossings is a major concern for conventional singlephase Boost PFC applications, especially under high ac line frequencies. This paper discusses the previously known causes for the input current distortion and points out that the multi-level power conversion technique can effectively reduce the zerocrossing distortion under high frequencies. A three-level (TL) Boost converter containing flying capacitors is then presented as the PFC topology. The system control method of the converter is also discussed. Experimental results are presented to validate the effectiveness of the proposed method
Power Quality Analyzer implemented with Matlab and Data Acquisition Toolbox
Authors: O. Pinzón-Ardila
Published: May 2017

In this work was designed an equipment capable of monitoring electric grids and measure mayor perturbations that affect the grid. The prototype has it foundations on a Via EpiaMS embedded system, a data acquisition card, measurement probes (Voltage and Current), and software developed using MatLab’s Data Acquisition Toolbox. The GUI provides a user friendly environment for visualization and management of the equipment. By other side the system allows to provide a briefing to the user where the times of the perturbations affecting the electrical grid are shown.
Satellite actuator balancing based on the disturbance measurement table data
Authors: Dong-Ik Cheon  , Eun-Jeong Jang  , Hwa-Suk Oh
Published: May 2017

Reaction wheel is one of primary actuators for satellite attitude control. Since it uses electrical power supplied by the solar panels and thus consumes no invaluable fuel of satellite, it has been used as primary actuator. However, rotation of reaction wheel induces torque and force disturbances which degrade the satellite attitude stability quality. The disturbances are mainly due to static and dynamic imbalances of the wheel. These imbalances shall be reduced on the stage of manufacturing. In this his paper a method for the imbalance reduction of the wheel is suggested. Torque/force measurement table is used to measure the disturbances of the reaction wheel and the measured data are used for the identification of location and magnitude of the imbalances. The corrections of the imbalances are performed by adding proper counter masses on the wheel. Through iterative balancing steps, the static and dynamic imbalances are remarkably reduced.
An optimization approach to calculation of passive filter parameters based on particle swarm optimization
Authors: L. I. Kovernikova  , Nguyen Chi Thanh
Published: May 2017

The paper presents an optimization approach to calculation of parameters of passive filters of different types for centralized reduction of harmonic voltages in the high-voltage network with distributed nonlinear loads. An optimization problem in which the minimum active power losses in the filter are used as an objective function has been formulated. Two forms of constraints for the objective function are suggested: constraints common to all types of filters and individual constraints to consider specific features of each type of filter. A two-stage algorithm based on the particle swarm optimization has been developed to solve the optimization problem. The application of the suggested algorithm to calculation of the thirdorder passive filter parameters is exemplified by a real 220 kV network.
Loss-Optimising-Management-Algorithm and the usage in an energy management for low-voltage grids
Authors: J. Teuscher  , V. Zeising  , W. Schufft
Published: May 2017

Since the amount of decentralised power generation is increasing it is important to develop an energy management system for low-voltage grids. This paper presents a method to operate such a management. The system is designed for managing a network of smart homes which can consume or supply electrical energy. The aims are to reduce the transmission losses and to stay within the limits of both, the voltage drop and the utilisation of lines and transformers. The reduction of the losses is implemented in the Loss-Optimising-ManagementAlgorithm (LOMA). This algorithm tries to find the power flow situation where minimal losses occur. The results of LOMA, the actual power situation (in low- and medium-voltage system) and the maximum power situation (based on the grid parameters) are summarised in an individual incentive signal for every smart home. The simulations show the feasibility of such an energy management and that significant loss reduction is achieved.
A Parallel Approach for Real-Time Power Flow in Distribution Networks
Authors: Rafael G. Milbradt  , Luciane N. Canha  , Paulo R. Pereira  , Alzenira R. Abaide  , Lukas Neusser  , Lidia M. Garcia  , Sandro R. Schmaedecke
Published: May 2017

The new reality of smart distribution systems with use of generation sources of small and medium sizes brings new challenges for the operation of these systems. The complexity and the large number of nodes requires use of methods which can reduce the processing time of algorithms such as power flow, allowing its use in real time. This paper presents a known methodology for calculating the power flow in three phases using backward/forward sweep method, and also considering others network elements such as voltage regulators, shunt capacitors and sources of dispersed generation PV and PQ. After that, new elements are introduced that allow the parallelization of this algorithm and an adequate distribution of work between the available processors. The algorithm was implemented using a multi-tiered architecture which allows its use even in environments with low processing power, such as smartphones and tablets, and the processing times were measured in many network configurations and compared with the same algorithm in the serial version.
Energy Storage for Active Network Management on Electricity Distribution Networks with Wind Power
Authors: Stephen Carr  , Giuliano C. Premier  , Richard M. Dinsdale  , Alan J. Guwy  , Jon Maddy
Published: May 2017

Increasing amounts of variable renewable generation are likely to enter our energy systems in the near future. In order to accommodate this generation onto our electricity networks, the concept of active network management (ANM) has become a significant area of research interest. Network connected energy storage is considered here as a means to actively control the network in order to increase the amount of generation it is possible to connect to a network. Energy storage is one of several potential methods of ANM, but has not been widely researched in this context. In this paper the ability of energy storage to increase the amount of wind energy accepted onto a network is assessed over a range of round trip storage efficiencies. The results show that energy storage is able to increase the energy accepted onto a distribution network, with the efficiency of the energy storage, energy storage capacity, wind farm size, network losses and network characteristics being important in determining the relative effectiveness of energy storage.
Analysis of a Single-Phase Line-Interactive UPS System
Authors: R. Barriviera  , S. A. O. Silva  , M. Kaster  , R. Barriviera
Published: May 2017

This paper presents an analysis of a single-phase line interactive uninterruptible power supply (UPS) system, allowing output voltage conditioning, such as voltage harmonic suppression and sag/swell compensation. Additionally, the UPS input current is also compensated, allowing current harmonic suppression and reactive power compensation. In other words, the UPS system acts as a true unified power quality conditioner (UPQC), when working in standby operation mode. The power rate handled by both series and parallel PWM converters depend on the operation conditions of the UPS system, such as the amplitude of the fundamental input voltage, the total harmonic distortion of the load current, fundamental power factor of the load, battery charging, among others. In standby mode, the amplitude of the UPS output voltage will be allowed to vary in order to follow the amplitude of the input voltage within a limited range defined by design requirements. This strategy will allow an effective optimization of the efficiency of the UPS system. Mathematical analyses of the single-phase line interactive UPS system are presented in order to obtain the state space models of the two PWM converters. Validation results are presented in order to evaluate the performance of the line interactive UPS system
Comparison of PV Cell Temperature Estimation by Different Thermal Power Exchange Calculation Methods
Authors: M. Bardhi  , G. Grandi  , G.M. Tina
Published: May 2017

A steady-state thermal model for calculate the tem-perature  of  a  photovoltaic  (PV)  module  has  been  developed  for outdoor  installation  such  as  ground-mounted  systems.  The  PV temperature  is  influenced by  environmental  variables  such  as: irradiance  ambient  temperature,  intensity  and  direction  of  the wind,  module  design,  orientation  and  mounting  structure.  As well  as  it  is  influenced  by  electrical  parameters.  In  literature some single layer thermal balance consider only an overall heat transfer  coefficient  as  a  function  of  wind  speed,  neglecting  the radiative  thermal  flux. In  this  paper,  five  thermal  balance  are compared  and  it  is  shown  that  the  radiative  term  cannot  be neglected, otherwise the PV temperature could be overestimated for  low  solar  radiation  intensity  and  it  could  be  underestimated for high solar radiation intensity. For this reason, the percentage contribution  of  the  heat  exchanges,  normalized  as  function  of normal  incoming  solar  radiation,  are  evaluated  for  wind  speed within 1 m/s (natural convection).
Research on Control Strategies of a Stand-alone Photovoltaic System
Authors: Qiu Bin  , Ma Yundong
Published: May 2017

In  order  to  assure  that  the  system  can  run  stably  under  different  modes,  energy  storage  equipment—Lead-Acid  battery  is  added  to  the  conventional  two-stage  PV  system.  PV  panels and batteries are parallel connected to the DC-bus through a  unidirectional  Boost  converter  and  a  bidirectional  Buck/Boost  converter respectively. A full bridge inverter is linked to the DC-bus as the second stage of the system which is in charge of DC-AC  power  transforming  for  the  AC  loads.  Control  methods  and  power   management   strategies   of   a   two-stage   stand-alone   photovoltaic   system   are   proposed   in   this   paper.   A   500W   experiment  prototype  is  constructed  to  verify  the  theoretical  analysis   of   the   control   methods   and   power   management   strategies.
Stability Support of Autonomous Networks with Dispersed Generation Using Rotary Ride Through Systems
Authors: J.C. Soriano  , P. Karaliolios  , E. Beermann  , J.F.G. Cobben  , W.L. Kling
Published: May 2017

Dispersed generation (DG) could allow networks to operate autonomously. However, technical challenges need to be addressed to diminish transients in voltage and frequency. In this paper a commercial flywheel ride through system (FRT) is modeled using DigSILENT Power Factory and validated using experimental data. The model is tested with dispersed generation in a test network to simulate transients when disconnection of the grid occurs. The model is also simulated in two study cases: a remote autonomous network supplied by a wind farm and a section of the Dutch electricity grid called “Tiel Zuid” with high penetration of dispersed generation. The results indicate that a FRT can successfully be used to stabilize frequency within regulation limits and maintain stable conditions during disconnections. Additionally, the number of dispersed generation units and the voltage control deeply affect the performance of the RTs and the behavior of the grid.
Comparison of methods for implementing virtual synchronous machine on inverters
Authors: Yong Chen  , Ralf Hesse  , Dirk Turschner  , Hans-Peter Beck
Published: May 2017

Virtual Synchronous Machine also called VISMA [1] is a control algorithm   to   make   an   inverter   operated   as   a   conventional electromechanical   synchronous   machine.   It   is   a   promising solution  to  overcome  the  problems  of  the  grid  stability  and quality, which have been exacerbated by increasing integration of distributed   generation   units   into   the   grid.   Compared   to   the conventional  power  plants,  in  which  the  synchronous  machine dominate,    the    distributed    generation    units    have    either significantly  smaller  or  no  rotating  mass  and  damping  effect. These  weaknesses  can  be  compensated  by  using  the  VISMA concept  and  thus  the  power  system  quality  will  be  improved. Furthermore,  the  penetration  level  of  the  DG  sources  won’t  berestricted any more.  Up  to  now  the  VISMA  was  implemented  by  using  a  voltage-to-current  model  on  a  hysteresis  controlled  inverter  [1][2][3].  This method  will  be  called  VISMA-Method  1  here.    Since  the  most products  of  inverters  in  the  market  are  PWM  controlled,  the VISMA-Method  1  cannot  be  easily  applied  on  these  inverters. Therefore, a new method is developed to implement the VISMA by  using  a  current-to-voltage  model  on  the  currently  widely applied  PWM  controlled  inverter.  This  new  method  is  called VISMA-Method  2  in  this  paper  and  will  be  compared  with  the VISMA-Method 1 by simulation results.
Remodelling of the heating systems of a sports centre based on life cycle assessment. Part I: Boiler replacement.
Authors: I. Oribe-García  , A. Alonso-Vicario  , A.M. Macarulla-Arenaza
Published: May 2017

Based  on  existing  installations  of  heating  and  cooling  of  the  municipal  sports  centre  of  Ordizia  (Spain)  and  its  operating data, the remodelling of these facilities has been discussed according to new regulations. In   order   to   facilitate   decision-making   reform   of   the   facilities,   this   will   be   approached   from   eco-efficiency   criteria,   i.e.   taking   into   account   not   only   the   usual   economic  and  technological  criteria  (business  as  usual-BAU),   but   also   integrating   the   concept   of   life   cycle   analysis  (LCA)  of  the  installation,  allowing  therefore  to  analyze     the     environmental     impact     prior     to     its     implementation.The  comparison  between  two  types  of  boilers,  the  current  diesel  one  and  a  high  performance  natural  gas  equipment,  is  presented  in  this  first  part.  In  both  cases,  the  major  impact has been found during the use stage compared with the  stages  of  construction  and  dismantling,  due  mainly  to  the  use  of  fuel.  Thus,  the  used  fuel  has  great  influence  on  environmental impact, resulting to be the natural gas boiler the best option.
Influence of small solar power plants on power quality
Authors: S. Seme  , J. Voh  , J. Voršič
Published: May 2017

The solar power plants are usually connected to the distribution network in node with transformer. Small, mini and micro solar power plants are connected as real dispersed production in the middle or at the end of line as consumers. This paper describes measurements, according to standard SIST EN 50160, at 274 m long line, fed at one side from 20/0,4 kV transformer and at the other side from small solar power plant and in between are 15 users (houses).
A Current Sharing Using Switched-Capacitor ZVS Driver for Power LEDs
Authors: P. H. A. Miranda  , E. M. Sá Jr  , F. L. M. Antunes
Published: May 2017

This paper proposes a switched-capacitor converter to source power light emitting diodes (LEDs). In contrast to conventional constant DC current drivers, the current pulse is provided by switched-capacitor LED driver. In the present driver it is possible to obtain several output circuits, where the capacitor is charged and discharged through the output circuit and the transfer of power from the grid for the LED is controlled by the switch. The effects of switching devices on the proposed converter are presented and evaluated. The experimental results demonstrated the technical feasibility of using the proposed circuit for the parallel association of LEDs, as well as to improve current sharing among LED strings. The proposed circuit driver with two output circuits presented an efficiency of 91%
Os professores no ensino superior brasileiro: transformações do trabalho docente na última década
Authors: Locatelli Cleomar
Published: May 2017

O artigo objetiva analisar a composição e as modificações do trabalho docente na última década, considerando as mudanças que ocorrem no mundo do trabalho em função dos interesses econômicos e políticos dominantes. Do ponto de vista teórico, apresentam-se algumas definições conceituais sobre a reestruturação produtiva e os processos de regulação (ou reformas educacionais), no propósito de discutir a realidade do trabalho de forma geral e do trabalho docente em especial. Do ponto de vista empírico, levantam-se alguns dados referentes ao quadro de professores do ensino superior no Brasil, observando o ocorrido na última década, mais precisamente entre 2003 e 2013.  Constata-se que as condições atuais do trabalho docente no ensino superior continuam fortemente impactadas pelas transformações do mundo do trabalho e que em suas particularidades e singularidades residem contradições próprias de um setor com objetivos e finalidades não necessariamente alinhadas às regras do mercado.