1,037 research outputs found

    Analysis of the Performance of MMC Under Fault Conditions in HVDC-Based Offshore Wind Farms

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    This paper analyzes the behavior of a modular multilevel converter-high-voltage direct-current (MMC-HVDC)-connected offshore wind power plant (WPP) during dc faults. For that purpose, detailed models of the dc cable, MMC stations, and transformers have been used in order to obtain reliable results. The influence of the WPP control method in the short-circuit behavior of the HVDC link has also been studied. Results show that the dynamics of the WPP contribution to pole-to-ground faults are slightly slower than those of the wind turbines current control loops. Therefore, the wind turbine front-end converters can be used to reduce the peak and average value of the fault current in such a system. Moreover, it has been found that ferroresonant oscillations can appear in the offshore ac grid when the WPP delivers constant power during faults.This work was supported in part by the Spanish Ministry of Economy funds under Grant DPI2014-53245-R, in part by Universitat Jaume I under Grants P1·1B2013-51 and E-2014-24, and in part by CONICYT/FONDAP/15110019 and Fondecyt/1151325. Paper no. TPWRD-01518-2014

    Field scale biodegradation of total petroleum hydrocarbons and soil restoration by Ecopiles: microbiological analysis of the process

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    Ecopiling is a method for biodegradation of hydrocarbons in soils. It derives from Biopiles, but phytoremediation is added to biostimulation with nitrogen fertilization and bioaugmentation with local bacteria. We have constructed seven Ecopiles with soil heavily polluted with hydrocarbons in Carlow (Ireland). The aim of the study was to analyze changes in the microbial community during ecopiling. In the course of 18 months of remediation, total petroleum hydrocarbons values decreased in 99 and 88% on average for aliphatics and aromatics, respectively, indicating a successful biodegradation. Community analysis showed that bacterial alfa diversity (Shannon Index), increased with the degradation of hydrocarbons, starting at an average value of 7.59 and ending at an average value of 9.38. Beta-diversity analysis, was performed using Bray-Curtis distances and PCoA ordination, where the two first principal components (PCs) explain the 17 and 14% of the observed variance, respectively. The results show that samples tend to cluster by sampling time instead of by Ecopile. This pattern is supported by the hierarchical clustering analysis, where most samples from the same timepoint clustered together. We used DSeq2 to determine the differential abundance of bacterial populations in Ecopiles at the beginning and the end of the treatment. While TPHs degraders are more abundant at the start of the experiment, these populations are substituted by bacterial populations typical of clean soils by the end of the biodegradation process. Similar results are found for the fungal community, indicating that the microbial community follows a succession along the process. This succession starts with a TPH degraders or tolerant enriched community, and finish with a microbial community typical of clean soil

    Systemic lupus erythematosus in northwestern Spain: a 20-year epidemiologic study

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    To further investigate the epidemiology of systemic lupus erythematosus (SLE) in southern Europe, we assessed the incidence, prevalence, clinical spectrum of the disease, flares, and survival of patients diagnosed with SLE in the Lugo region of northwestern Spain. Between January 1987 and December 2006, 150 Lugo residents were diagnosed as having SLE according to the 1982 American College of Rheumatology criteria for the classification of SLE. Women outnumbered men (127 [84.7%] vs. 23 [15.3%]). The mean age at the time of disease diagnosis was 46.1 ± 19.6 years. The mean follow-up from the time of disease diagnosis was 7.8 ± 4.5 years. The age- and sex-adjusted annual incidence rate over the 20-year study period was 3.6 (95% confidence interval [CI], 3.0-4.2) per 100,000 population aged 15 years and older. The overall annual incidence rate over the 20-year study period in women (5.9/100,000 population aged ≥15 yr; 95% CI, 4.9-7.0) was higher than in men (1.1/100,000 population aged ≥15 yr; 95% CI, 0.7-1.7) (p < 0.001). By December 31, 2006, the overall age-adjusted SLE prevalence in the Lugo region for patients who fulfilled at least 4 of 1982 American College of Rheumatology criteria was 17.5 per 100,000 population aged 15 years and older (95% CI, 12.6-24.1). Prevalence in women (29.2/100,000 population aged ≥15 yr; 95% CI, 20.0-40.7) was higher than in men (5.8/100,000 population aged ≥15 yr; 95% CI, 2.0-12.0). The most frequent clinical manifestation was arthritis. As reported in population-based studies on SLE patients of European descent, renal disease was observed in only 27.3% of the patients. The rate of flares was 0.084/year. A younger age and the presence of nephritis at the time of disease diagnosis were associated with the development of flares during the follow-up of Lugo patients. Compared with the general population the probability of survival in patients with SLE was significantly reduced (p = 0.04). In conclusion, the present study establishes a baseline estimate of the incidence and clinical spectrum of SLE in northwestern Spain. According to our results, the incidence of SLE in northwestern Spain is slightly higher than that reported in most European regions. Patients with SLE from northwestern Spain have a later average age onset and a lower frequency of nephritis than in the African-American population. However, our data show a reduced probability of survival in Spanish patients with SLE

    Geographic mobility and social inequality among Peruvian university students

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    The purpose of this study was to explore geographic mobility among university students in Peru and to understand how mobility patterns differ by region and by demographic indicators of inequality. The ways that students may be able to move geographically in order to access quality higher education within the educational system can be a driver of equality or inequality, depending on who is able to take advantage. Using data from a university census, we examine how demographic indicators of inequality are related to geographic mobility for university attendance, how prior geographic mobility predicts later mobility for university attendance, and how these relationships differ based on the number and quality of universities in a region. Results show that sociodemographic variables related to social inequality explain a substantial amount of students\u27 postsecondary mobility. However, some of these relationships do not operate in the same way in all of the regions. Depending on the availability of universities and their quality, patterns of association between inequality and geographic mobility change. Implications for higher education policy as well as further research examining geographic mobility and inequality in education are discussed

    Emergence of complexity in hierarchically organized chiral particles

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    The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties

    OCCASO - II. Physical parameters and Fe abundances of red clump stars in 18 open clusters

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    Open clusters have long been used to study the chemodynamical evolution of the Galactic disc. This requires a homogeneously analysed sample covering a wide range of ages and distances. In this paper, we present the Open Clusters Chemical Abundances from Spanish Observatories (OCCASO) second data release. This comprises a sample of high-resolution (R > 65 000) and high signal-to-noise spectra of 115 red clump stars in 18 open clusters. We derive atmospheric parameters (Teff, log g, ξ), and [Fe/H] abundances using two analysis techniques: equivalent widths and spectral synthesis. A detailed comparison and a critical review of the results of the two methods are made. Both methods are carefully tested between them, with the Gaia FGK benchmark stars, and with an extensive sample of literature values. We perform a membership study using radial velocities and the resulting abundances. Finally, we compare our results with a chemodynamical model of the Milky Way thin disc concluding that the oldest open clusters are consistent with the models only when dynamical effects are taken into account

    Current and emerging diagnosis tools and therapeutics for giant cell arteritis

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    Introduction: Giant cell arteritis (GCA) is the most common large-vessel vasculitis in individuals older than 50 years from Western countries. The goal of the treatment is to achieve improvement of symptoms and clinical remission as well as decrease the risk of severe vascular complications. Areas covered: The review summarizes the main epidemiological and clinical features of GCA and discusses in depth both the classic and the new therapies used in the management of GCA. Expert commentary: Prednisone/prednisolone of 40-60 mg/day is the mainstay in GCA therapy. It yields improvement of clinical features and reduces the risk of permanent visual loss in patients with GCA. Other drugs are used in patients who experience relapses (flares of the disease) or side effects related to glucocorticoids. Methotrexate is the most common conventional immunosuppressive drug used as a glucocorticoid sparing agent. Among the new biologic agents, the most frequently used is the recombinant humanized anti-IL-6 receptor antibody, which is effective to improve clinical symptoms, decrease the cumulative prednisone dose and reduce the frequency of relapses in these patients. Anti-tumor necrosis factor-α therapy is not useful in GCA. Experience with other biologic agents, such as abatacept or ustekinumab, looks promising but it is still scarce

    The Future of the Louisiana Waterways Transport System: A System Analysis and Plan to Move Commerce by Water

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    LTRC Project Number: 20-1SSSIO Number: DOTLT1000330Moving commerce by water represents 25 percent of all goods movements within the state of Louisiana and is a critical component of the multimodal transportation system in the state [1]. To be best positioned for future development and investment, the Louisiana Department of Transportation and Development's (DOTD) Office of Multimodal Commerce (OMC) requested a comprehensive, statewide waterways transportation system plan. The plan would be capable of dovetailing into, and be a complement for, the Louisiana Statewide Transportation Plan. In doing so, it will provide the OMC the ability to identify potential chokepoints in the multimodal commerce network and ultimately assist in the development of strategies and capital investment programs to relieve these chokepoints through running \u201cwhat-if\u201d scenarios of the impacts of potential modal shifts on localized congestion
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