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Reactive Power Limits of Single-Phase and Three-Phase DC-Link VSC STATCOMs under Negative-Sequence Voltage and Current
Get PDFThis paper analyzes and compares the reactive power limits of single- and three-phase configured dc-link Voltage Source Converter (VSC) structures for Static Synchronous Compensator (STATCOM) to operate with negative-sequence voltage and current. The three-level Neutral Point Clamped (3L NPC) is used as an example of a three-phase dc-link topology. Likewise, the Cascaded H-Bridge (CHB) is used as a single-phase dc-link case, in both star and delta configurations. Modular Multilevel Converter is also considered as a combination of both dc-link configurations. The conclusions drawn are generic whichever the Power Electronics Building Block (PEBB) used in each VSC structure
Friction Stir Welding of AA2099-T83 and AA2060-T8E30 Aluminium Alloys with New Cr-Free Surface Treatments and Sealant Application
Get PDFThe feasibility for friction stir welding (FSW) surface-treated AA2099-T83 aluminium extrusions with AA2060-T8E30 aluminium sheets in the overlap configuration and using a sealant at the interface was investigated in this work. New Cr-free surface treatments such as thin film sulphuric acid anodising (TFSAA) and sol–gel were applied to the parent materials, and a sealant was applied before applying the FSW process. FSW welds were produced using several combinations of surface treatments and sealant application with no significant influence on FSW process stability and performance. The metallographic examination of the welds showed that a good protection of the crevice was achieved with some sealant ccumulation at the edges of the overlapping region. The microstructural analysis showed no sealant remnants but the presence of some oxide remnants in the stir zone (SZ) of the welds, especially in the TFSAA treated parent material cases. However, these remnants did not show any significant effect in the static pull-out strength of the joints and failures at the most stressed zone of the AA2099-T83 extrusions outside the FSW weld region were consistently obtained
High magnetization FeCo nanoparticles for magnetorheological fluids with enhanced response
Get PDFWe present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30–50 nm and high magnetization, 212 ± 2 A m2 kg−1. They agglomerate due to the strong magnetic dipolar interaction among them. These FeCo nanoparticles were used to synthesize a magnetorheological fluid by using oleic acid as surfactant, mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. The synthesized fluid showed a strong magnetorheological response with increasing shear stress values as the magnetic field intensity increases. Thus, we have measured a superior performance up to 616.7 kA m−1, with a yield stress value of 2729 Pa, and good reversibility after demagnetization process. This value competes with the best ones reported in the most recent literature. We have compared the obtained results with our previous reported ones by using high magnetization Fe NPs fabricated by the electrical explosion of wire method (Fe-EEW)
Irakasleen prestakuntza gogoetatsua, hezkuntza berritzeko giltza
Get PDFUrte asko dira irakasleen prestakuntzan ari garela, hasierako zein
etengabeko prestakuntzan, bai eta, gure ikerketetan oinarrituta,
ikastetxeei aholkularitza ematen ere. Horrek eraman gaitu, arian-arian,
elkarren arteko harremanak hurbiltzera, eskoletako behar eta ametsak
gure sentitzera, finean, eskolaren eta unibertsitatearen arteko elkarlana
sustatzera. Izan ere, tradizioan, zenbait begiradatik, elkarrengandik
urruti ikusi izan dira eskolaren eta unibertsitatearen interesak, estiloak,
beharrak eta izaerak. Alde batean egon da akademia eta ikerketa
akademikoa, eta beste aldean egon da errealitatea, praxia. Guk beste
modu bateko harremana eta elkarlana ikusten ditugu. “Teoria eta
praktikaren” arteko amildegia murriztu eta gure proposamena izan ohi
da elkarrekin lan egin eta elkarrengandik ikastea, eskolako irakasleekin
konplizitatea lantzea, elkarrekin aberastea ikaskuntza eta irakaskuntza
prozesuak, eta elkarrekin ezagutza pedagogiko eta didaktiko berria
sortzea. Horretarako, jakina, elkarri aitortu behar diogu bakoitzak duen
ezagutza eta erantzukizuna. Eta horrek eskatzen du, aldi berean, hori
gerta dadin giroa lantzea eta zaintzea. Azken batean, etorkizuneko
gizartea aldakorra eta ezegonkorra izango da, eta gizarte aldakor
horretara egokitzen lagunduko digun hezkuntza behar dugu, hortaz,
biziko garen gizartean begirada kontziente eta kritikoz moldatzeko
gai diren pertsonak trebatu nahi ditugu, espiritu kooperatibo batekin
eta modu kolektiboan lan egingo dutenak. Hezkuntza (komunitatea,
gizartea) eraldatu nahi badugu, bada, eskola eta unibertsitatearen arteko
elkarlana funtsezkoa izango da.
Lan honek Mondragon Unibertsitateko MIKER ikerketa-taldeak azken 15
urteetan izandako esperientziatik eraikitako markoa jasotzen du. Tarte
horretan ehundik gora ikastetxe eta erakunderekin jardun da lanean,
hizkuntzen ikaskuntza eta irakaskuntzaren gaia ardatz hartuta. Lan
horien bidez, taldeak prestakuntza-eredu bat sortu du, liburu honetan
aurkezten dena
SiC erdieroaleak energia eolikoan LCoEa hobetzeko
Get PDFThis research identifies the wind energy as the main renewable source. In order to improve its LCoE, SiC semiconductors are proposed, together with different voltage levels and topologies. After analyzing various configurations, two that improve current LCoE are found. The first considers current cost of SiC, and uses a two level topology, achieving little improvement. The second considers the expected cost reduction of SiC due to technological maturity, and it is shown that a three level NPC is the best topology, with higher LCoE improvement.Ikerketa honetan energia eolikoa energia berriztagarri nagusi bezala identifikatzen da. Beraren LCoEa (Levelized Cost of Energy ingelesez) hobetzeko, SiC erdieroaleak proposatzen dira, baita tentsio maila eta topologia berriak ere. Konfigurazio ezberdinak aztertzen dira, LCoEa hobetzen duten bi aurkituz. Lehenengoak, gaur egungo SiC-en kostua kontuan izanik bi mailako topologia erabiltzen du, hobekuntza txikia lortuz. Bigarrenean, teknologiaren heldutasunagatik iritsiko den kostu jaitsiera aurre ikusten da, eta hiru mailako NPC (Neutral Point Clamped ingelesez) topologia erabiltzea dela onena ikusten da, LCoE hobekuntza handia lortuz
Getting fair institutional conditions for district heating consumers: Insights from Denmark and Sweden
Get PDFDistrict heating is expected to play an important role in the EU for the implementation of a low carbon energy system with high shares of renewables. Empirical examples from several countries show that district heating companies can misuse their monopoly position, hampering district heating adoption. To address this issue, it is necessary to develop and implement institutional frameworks that promote fair conditions for consumers. However, it is still unclear how to do this. This article reviews the institutional conditions implemented in Denmark and Sweden from the start of district heating until the present and analyses why different institutional configurations have managed or failed to promote fair conditions for consumers. The analytical framework for consumer power in natural monopolies is applied. The data is collected via a structured literature review, interviews with experts and other data sources such as resolutions of consumer complaints, relevant stakeholders’ websites and legal documents. The results indicate that local ownership, transparency and communication have been of key importance to reduce prices in both countries. Further research is necessary to fully understand how the institutional conditions have influenced product and customer relation quality. Lessons from Denmark and Sweden are outlined
Validation of Random Forest Machine Learning Models to Predict Dementia-Related Neuropsychiatric Symptoms in Real-World Data
Get PDFBackground: Neuropsychiatric symptoms (NPS) are the leading cause of the social burden of dementia but their role is underestimated.
Objective: The objective of the study was to validate predictive models to separately identify psychotic and depressive symptoms in patients diagnosed with dementia using clinical databases representing the whole population to inform decisionmakers.
Methods: First, we searched the electronic health records of 4,003 patients with dementia to identify NPS. Second, machine learning (random forest) algorithms were applied to build separate predictive models for psychotic and depressive symptom clusters in the training set (N = 3,003). Third, calibration and discrimination were assessed in the test set (N = 1,000) to assess the performance of the models.
Results: Neuropsychiatric symptoms were noted in the electronic health record of 58% of patients. The area under the receiver operating curve reached 0.80 for the psychotic cluster model and 0.74 for the depressive cluster model. The Kappa index and accuracy also showed better discrimination in the psychotic model. Calibration plots indicated that both types of model had less predictive accuracy when the probability of neuropsychiatric symptoms was <25%. The most important variables in the psychotic cluster model were use of risperidone, level of sedation, use of quetiapine and haloperidol and the number of antipsychotics prescribed. In the depressive cluster model, the most important variables were number of antidepressants prescribed, escitalopram use, level of sedation, and age.
Conclusion: Given their relatively good performance, the predictive models can be used to estimate prevalence of NPS in population databases
Innovar la gobernanza de la investigación y la innovación: la experimentación de prácticas deliberativas en Europa
Get PDFEn el marco de las políticas de investigación europeas hay una inclinación creciente por abrir a debate la propia definición de los problemas y los beneficios esperados asociados a su resolución. Ello ha adoptado la forma de lo que se ha denominado “RRI” (Responsible Research and Innovation), que viene a ser un principio-guía para la innovación tendente a encarar los grandes retos sociales sobre la base de un proceso de responsabilidad mutua facilitado por la institucionalización de mecanismos efectivos de gobernanza. En este artículo sostenemos que el desarrollo práctico de mecanismos inclusivos y deliberativos de gobernanza contribuye a facilitar la integración de actores con potencial interés en los procesos de investigación socio-técnica. Para ello, elucidamos un conjunto de procesos deliberativos implementados en Europa en aras a mejorar la corresponsabilidad a través de la implicación pública. Nuestra revisión revela una serie de tensiones que afectan a las concepciones sobre participación y deliberación, al diseño institucional de las iniciativas y a la fase de la investigación en la que se implementan. El artículo sugiere la necesidad de innovar las experiencias democráticas incidiendo en la fase temprana de las actividades científico-tecnológicas e impulsando la contribución epistémica y social de los actores para robustecer la reflexividad y la responsabilidad mutua en el sistema de gobernanza de la investigación
Surface Integrity When Machining Inconel 718 Using Conventional Lubrication and Carbon Dioxide Coolant
Get PDFSurface integrity induced by machining process affects strongly the performance of functional products, for instance, the fatigue life as well as the resistance to stress corrosion cracking. Consequently, it is relevant to evaluate the induced properties on and beneath the machined surface to ensure the good performance of the mechanical components while operating under either static or cyclic loads. Furthermore, this is even more important when designing critical components that withstand high loads at high temperatures. In this context, many studies have been carried out in order to characterize the surface integrity (residual stresses, surface roughness, micro-hardness of the affected layer) when machining Inconel 718. However, so far, the cryogenic effect on surface integrity of Inconel 718 is not well established although some preliminary works have already been developed. Therefore, this work aimed to point out the performance of cryogenic machining using the carbon dioxide CO2 as a cryogenic cutting fluid, considering as a reference the conventional lubrication. A comparative study has been carried out during turning operations of Inconel 718 using the same cutting parameters and the same tool geometry. Microhardness measurements showed that the CO2 condition induced higher strain hardening near the surface while conventional condition did not generate notable difference compared to the bulk material microhardness. With respect to residual stresses, results showed that conventional lubrication generated higher tensile residual stress near the surface along the cutting direction when using new tools. As for CO2 cryogenic condition, lower tensile residual stresses have been obtained near the surface. In addition, CO2 condition induced the largest compressive peak when using new and semi−worn tools in comparison with conventional lubrication
Persona Cooperativa en un contexto de transformación educativa y social
Get PDFEl objetivo del presente artículo es definir y caracterizar el perfil de la denominada “Persona Cooperativa” (PC) dentro de las instituciones educativas, facultades universitarias y empresas vinculadas al ámbito educativo cooperativo y dentro del ecosistema cooperativista del País Vasco. Para alcanzar dicho objetivo se realizó una investigación cualitativa mediante el método de la Teoría Fundamentada. Después de constatar que el concepto PC a analizar no es nuevo, la revisión bibliográfica realizada en las principales bases de datos (WOS, Scopus…) no ha aportado una clara definición ni caracterización del perfil. De este modo, se llevaron a cabo 4 entrevistas semiestructuradas, observaciones panorámicas no participantes (14 sesiones, 30 profesionales) y análisis de documentos internos en 3 de las organizaciones participantes en el estudio. El análisis y la triangulación de datos se ha efectuado mediante el método comparativo constante hasta lograr la saturación teórica. El trabajo de investigación ha permitido, por un lado, situar los valores y actitudes individuales, cooperativos y comunitarios como Categoría Central y, por otro, clasificarlo en tres categorías conceptuales principales: ser autosuficiente, ejercer la cooperación y ser emprendedora socio-comunitaria. Entendemos que este trabajo puede contribuir a establecer las bases para el desarrollo del perfil de PC y su evaluación con la implementación de programas educativos asociados a las dimensiones personales, relacionales y socio-comunitarios que lo definen