3,446 research outputs found

    Evaluation of a Local Fault Detection Algorithm for HVDC Systems

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    A great increase in the amount of energy generated from clean and renewable sources integrated in the electric power system is expected worldwide in the coming years. High Voltage Direct Current (HVDC) systems are seen as a promising alternative to the traditional Alternating Current (AC) systems for the expansion of the electric power system. However, to achieve this vision, there are some remaining challenges regarding HVDC systems which need to be solved. One of the main challenges is related to fault detection and location in HVDC grids. This paper reviews the main protection algorithms available and presents the evaluation of a local fault detection algorithm for DC faults in a multi-terminal Voltage Source Conversion (VSC) based HVDC grid. The paper analyses the influence of the DC voltage sampling frequency and the cable length in the performance of the algorithm. © 2019, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ).The authors thank the support from the Spanish Ministry of Economy, Industry and Competitiveness (project ENE2016-79145-R AEI/FEDER, UE) and GISEL research group IT1083-16), as well as from the University of the Basque Country UPV/EHU (research group funding PPG17/23)

    Kinetics of crystallization of FeB-based amorphous alloys studied by neutron thermo-diffractometry

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    Kinetics of crystallization of two amorphous alloys, Fe70Cr10B20 and Fe80Zr10B10, have been followed up by neutron thermodiffractometry experiments performed in the two axis diffractometer D20 (ILL, Grenoble). The structural changes are directly correlated with the temperature dependence of the magnetization. Fe70Cr10B20 crystallizes following a two-step process: an eutectic crystallization of alfa-Fe (bcc) and the metastable tetragonal phase (Fe0.8Cr0.2)3B followed by another eutectic transformation to the stable phase (Fe0.75Cr0.25)2B and more segregation of alfa-Fe. These tetragonal phases are magnetically anisotropic, giving rise to a large increase of the coercivity. This behaviour is similar to that of Fe80B20 alloys, with Cr atoms replacing the Fe positions in both crystalline phases. Fe80Zr10B10 shows also a two-step process in which two polymorphic transformations take place.Comment: 3 pages. Proceedings International Workshop Non-Crystalline Solids 2006, Gijon (Spain

    Solitons in systems of coupled scalar fields

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    We present a method to obtain soliton solutions to relativistic system of coupled scalar fields. This is done by examining the energy associated to static field configurations. In this case we derive a set of first-order differential equations that solve the equations of motion when the energy saturates its lower bound. To illustrate the general results, we investigate some systems described by polynomial interactions in the coupled fields.Comment: RevTex4, 5 page

    Zeros of polynomials orthogonal with respect to a signed weight

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    AbstractIn this paper we consider the monic polynomial sequence (Pnα,q(x)) that is orthogonal on [−1,1] with respect to the weight function x2q+1(1−x2)α(1−x),α>−1,q∈N; we obtain the coefficients of the tree-term recurrence relation(TTRR) by using a different method from the one derived in Atia et al. (2002) [2]; we prove that the interlacing property does not hold properly for (Pnα,q(x)); and we also prove that, if xn,nα+i,q+j is the largest zero of Pnα+i,q+j(x), x2n−2j,2n−2jα+j,q+j<x2n−2i,2n−2iα+i,q+i,0≀i<j≀n−1


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    Background: Spontaneous Intracranial Hypotension (SIH) is a rare condition caused by a spinal cerebrospinal fluid (CSF) leak. It is usually described as an orthostatic headache, frequently associated with neck pain, nausea, vomiting, diplopia, blurred vision and distorted hearing. Initial treatment consists of bed rest, fluid supplementation, caffeine and analgesics. If conservative treatment fails, an epidural blood patch (EBP) therapy should be considered. Methods: A healthy 31-year-old female patient presented with a spontaneous occipital headache during the expulsive period of a miscarriage. Six days later, she was referred to Neurology due to worsening symptoms (orthostatic headache, vertigo and diplopia). CAT scan, lumbar puncture and carotid ecodoppler were normal. Magnetic Resonance Imaging (MRI) revealed an epidural CSF collection suggesting a CSF fistula. After 21 days of conservative treatment and no clinical improvement, she was referred to Anaesthesiology to perform a lumbar EBP. Hospital discharged occurred five days later with no symptoms. The follow-up MRI was normal. Discussion: Treatment of SIH aims to maintain CSF volume. The effect of EBP is twofold: an early effect related to volume replacement and a latent effect that results from sealing the leak. Symptomatic relief is usually obtained in few days but EBP may be repeated if symptoms recur. Complications such as transient paraesthesia, radicular pain, repeated inadvertent dural puncture and epidural infection are possible but rare. Conclusions: The high success rate and the low incidence of complications have established the EBP as the best available treatment of SIH refractory to conservative measures

    Solutions of the reflection equations for the Uq[G2]U_q[G_2] vertex model

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    We investigate the possible regular solutions of the boundary Yang-Baxter equation for the fundamental Uq[G2]U_q[G_2] vertex model. We find four distinct classes of reflection matrices such that half of them are diagonal while the other half are non-diagonal. The latter are parameterized by two continuous parameters but only one solution has all entries non-null. The non-diagonal solutions do not reduce to diagonal ones at any special limit of the free-parameters.Comment: 18 page

    Biomechanical responses to water fitness programmes: a narrative review

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    In the past years, there was an increasing interest in the biomechanical responses in water fitness sessions. The present review consolidates the current “state-of-art” on the biomechanical responses in water fitness programmes. The literature was searched and screened studies on: (i) healthy subjects; and (ii) water fitness sessions and programmes reporting physical condition outcomes. A total of 36 studies met the inclusion criteria and categorized into four categories: (i) kinematics (n = 5); (ii) ground reaction force (n = 10); (iii) neuromuscular (n = 8); and (iv) strength (n = 14). There was a larger amount of evidence on strength, whereas some gaps in the body of knowledge still persist in the remaining categories. The existent studies cover a large range of age brackets (from young adults to the elderly). Women were recruited more often than men to be part of the studies. The effect of music cadence, body segments, exercise type (e.g., alternated or simultaneous), water depth, resistance equipment, and training protocols were the main topics under research.info:eu-repo/semantics/publishedVersio

    Effects of genotype, salt content and calibre on quality of traditional dry-fermented sausages

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    The increasing demand for traditional food products is concomitant with higher nutritional and health concerns. The effect of genotype, salt content and calibre on physicochemical, microbiological and texture parameters, along with sensory acceptability, was studied on low-salt Portuguese traditional dry-fermented sausages. A few significant differences were found in different microbial counts between pork genotypes' sausages. Lauric and stearic fatty acids showed significantly higher values for hybrid genotype products, while contents in gadoleic, heneicosanoic, linoleic and linolenic acids were higher in Alentejano pork sausages. Unexpectedly, there are no significant differences between genotypes for oleic acid, although lower contents were found in the Alentejano genotype.Texture Profile Analysis revealed significant differences in hardness, adhesiveness, resilience and chewiness between genotypes, with Alentejano pork sausages being softer and thus easier to chew. Salt reduction does not negatively affect the quality and acceptability of sausages. Furthermore, the use of hybrid genotype meat does not mischaracterise a product traditionally made exclusively of Alentejano pig meat