1,721,092 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ammonium removal and recovery from wastewater with porous geopolymers
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Porous geopolymer granules are emerging as a promising material for high-value applications such as adsorption and ammonium (NH₄⁺) recovery from wastewater. This thesis presents a comprehensive investigation into the fabrication, characterization, and application of porous metakaolin-based geopolymer granules produced via direct foaming, one-part alkali activation, and high-shear granulation. Porosity was introduced using either hydrogen peroxide (H₂O₂) or municipal solid waste incineration fly ash containing metallic aluminum (Al0) as blowing agents. Increased porosity, particularly in the micro- and nanoscale range, significantly enhanced the specific surface area and NH₄⁺ adsorption capacity—up to 126% higher compared to nonporous granules, with optimal performance observed using 10% H₂O₂ solution. The granules demonstrated sufficient mechanical strength (≥2 MPa) and were evaluated for environmental safety and ion-exchange behavior. While fly ash improved porosity, it introduced leaching concerns for elements like antimony and vanadium, limiting its optimal content to 0.3 wt.% Al0. Adsorption-desorption studies showed that porous geopolymer granules achieved an average NH₄⁺ uptake capacity of up to 9.0 mg/g, and NH₄⁺ recovery of 51–98% over the 30 adsorption and desorption cycles using KNO₃ as a regenerant, though performance declined after 20 cycles. Application in municipal wastewater highlighted the need for pretreatment to mitigate pore blocking and surface fouling. Overall, these findings establish porous geopolymer granules as a feasible, regenerable, and effective material for NH₄⁺ recovery, contributing to circular nitrogen economy and sustainable wastewater treatment strategies. Original papers Yu, Y., Perumal, P., Corfe, I. J., Paul, T., Illikainen, M., & Luukkonen, T. (2023). Combined granulation–alkali activation–direct foaming process: A novel route to porous geopolymer granules with enhanced adsorption properties. Materials & Design, 227, 111781. https://doi.org/10.1016/j.matdes.2023.111781 https://doi.org/10.1016/j.matdes.2023.111781 Self-archived version Luukkonen, T., Yu, Y., Adhikary, S. K., Kauppinen, S., Finnilä, M., & Perumal, P. (2024). Metallic aluminium in municipal solid waste incineration fly ash as a blowing agent for porous alkali-activated granules. Royal Society Open Science, 11(8), 240598. https://doi.org/10.1098/rsos.240598 https://doi.org/10.1098/rsos.240598 Self-archived version Yu, Y., Perumal, P., Sithole, T., & Luukkonen, T. (2025). Recovery of ammonium and nitrate from wastewater using adsorption-based techniques: A review. Journal of Cleaner Production, 519, 145976. https://doi.org/10.1016/j.jclepro.2025.145976 https://doi.org/10.1016/j.jclepro.2025.145976 Self-archived version Yu, Y., Bhuyan, M., Perumal, P., Luukkonen, T. (2025). Ammonium removal and recovery from municipal wastewater by ion exchange using porous metakaolin geopolymer granules. Manuscript submitted for publication. Tiivistelmä
Huokoiset geopolymeerirakeet ovat nousemassa lupaavaksi materiaaliksi korkean lisäarvon sovelluksiin, kuten adsorptioon ja ammoniumin (NH₄⁺) talteenottoon jätevedestä. Tämä väitöskirja esittelee kattavan tutkimuksen metakaoliinipohjaisten huokoisten geopolymeerirakeiden valmistuksesta, karakterisoinnista ja käytöstä hyödyntäen vaahdotusta, alkaliaktivointia sekä granulointia. Huokoisuutta lisättiin käyttämällä vaahdotusaineina joko vetyperoksidia (H₂O₂) tai yhdyskuntajätteenpolton lentotuhkaa, joka sisälsi metallista alumiinia (Al0). Huokoisuuden lisääntyminen, erityisesti mikro- ja nanokokoluokissa, paransi merkittävästi rakeiden ominaispinta-alaa ja NH₄⁺-adsorptiokapasiteettia – jopa 126 % verrattuna ei-huokoisiin rakeisiin. Paras suorituskyky saavutettiin 10 % H₂O₂-liuoksella. Rakeet osoittivat riittävää mekaanista lujuutta (≥2 MPa), ja niitä arvioitiin myös ioninvaihtokyvyn osalta. Vaikka lentotuhka lisäsi huokoisuutta, se aiheutti haitallisten aineiden, kuten antimonin ja vanadiinin, liukenemista, minkä vuoksi optimaalinen tuhkapitoisuus rajoitettiin 0.3 paino-% Al0:aan. Adsorptio-desorptiotutkimukset osoittivat, että huokoiset geopolymeerirakeet saavuttivat keskimääräisen NH₄⁺-ottokapasiteetin jopa 9.0 mg/g ja NH₄⁺-saannon 51–98 % 30 adsorptio- ja desorptiosyklin aikana, kun KNO3 20:a regeneroivana aineena käytettiin, vaikka suorituskyky heikkeni syklin jälkeen. Pitkän aikavälin käytössä suorituskyky kuitenkin heikkeni. Kunnallisen jäteveden käsittelyssä havaittiin huokosten tukkeutumista ja pintaan kertyvää kiintoainesta, mikä korostaa esikäsittelyn merkitystä. Yhteenvetona voidaan todeta, että huokoiset geopolymeerirakeet ovat käyttökelpoinen, uudelleenkäytettävä ja tehokas materiaali NH₄⁺:n talteenottoon, edistäen typen kiertotaloutta ja kestävää jäteveden käsittelyä. Osajulkaisut Yu, Y., Perumal, P., Corfe, I. J., Paul, T., Illikainen, M., & Luukkonen, T. (2023). Combined granulation–alkali activation–direct foaming process: A novel route to porous geopolymer granules with enhanced adsorption properties. Materials & Design, 227, 111781. https://doi.org/10.1016/j.matdes.2023.111781 https://doi.org/10.1016/j.matdes.2023.111781 Rinnakkaistallennettu versio Luukkonen, T., Yu, Y., Adhikary, S. K., Kauppinen, S., Finnilä, M., & Perumal, P. (2024). Metallic aluminium in municipal solid waste incineration fly ash as a blowing agent for porous alkali-activated granules. Royal Society Open Science, 11(8), 240598. https://doi.org/10.1098/rsos.240598 https://doi.org/10.1098/rsos.240598 Rinnakkaistallennettu versio Yu, Y., Perumal, P., Sithole, T., & Luukkonen, T. (2025). Recovery of ammonium and nitrate from wastewater using adsorption-based techniques: A review. Journal of Cleaner Production, 519, 145976. https://doi.org/10.1016/j.jclepro.2025.145976 https://doi.org/10.1016/j.jclepro.2025.145976 Rinnakkaistallennettu versio Yu, Y., Bhuyan, M., Perumal, P., Luukkonen, T. (2025). Ammonium removal and recovery from municipal wastewater by ion exchange using porous metakaolin geopolymer granules. Manuscript submitted for publication. Academic dissertation to be presented with the assent of the Doctoral Programme Committee of Technology and Natural Sciences of the University of Oulu for public defence in the Oulun Puhelin auditorium (L5), Linnanmaa, on 10 October 2025, at 12 noonAbstract
Porous geopolymer granules are emerging as a promising material for high-value applications such as adsorption and ammonium (NH₄⁺) recovery from wastewater. This thesis presents a comprehensive investigation into the fabrication, characterization, and application of porous metakaolin-based geopolymer granules produced via direct foaming, one-part alkali activation, and high-shear granulation. Porosity was introduced using either hydrogen peroxide (H₂O₂) or municipal solid waste incineration fly ash containing metallic aluminum (Al0) as blowing agents. Increased porosity, particularly in the micro- and nanoscale range, significantly enhanced the specific surface area and NH₄⁺ adsorption capacity—up to 126% higher compared to nonporous granules, with optimal performance observed using 10% H₂O₂ solution. The granules demonstrated sufficient mechanical strength (≥2 MPa) and were evaluated for environmental safety and ion-exchange behavior. While fly ash improved porosity, it introduced leaching concerns for elements like antimony and vanadium, limiting its optimal content to 0.3 wt.% Al0. Adsorption-desorption studies showed that porous geopolymer granules achieved an average NH₄⁺ uptake capacity of up to 9.0 mg/g, and NH₄⁺ recovery of 51–98% over the 30 adsorption and desorption cycles using KNO₃ as a regenerant, though performance declined after 20 cycles. Application in municipal wastewater highlighted the need for pretreatment to mitigate pore blocking and surface fouling. Overall, these findings establish porous geopolymer granules as a feasible, regenerable, and effective material for NH₄⁺ recovery, contributing to circular nitrogen economy and sustainable wastewater treatment strategies.Tiivistelmä
Huokoiset geopolymeerirakeet ovat nousemassa lupaavaksi materiaaliksi korkean lisäarvon sovelluksiin, kuten adsorptioon ja ammoniumin (NH₄⁺) talteenottoon jätevedestä. Tämä väitöskirja esittelee kattavan tutkimuksen metakaoliinipohjaisten huokoisten geopolymeerirakeiden valmistuksesta, karakterisoinnista ja käytöstä hyödyntäen vaahdotusta, alkaliaktivointia sekä granulointia. Huokoisuutta lisättiin käyttämällä vaahdotusaineina joko vetyperoksidia (H₂O₂) tai yhdyskuntajätteenpolton lentotuhkaa, joka sisälsi metallista alumiinia (Al0). Huokoisuuden lisääntyminen, erityisesti mikro- ja nanokokoluokissa, paransi merkittävästi rakeiden ominaispinta-alaa ja NH₄⁺-adsorptiokapasiteettia – jopa 126 % verrattuna ei-huokoisiin rakeisiin. Paras suorituskyky saavutettiin 10 % H₂O₂-liuoksella. Rakeet osoittivat riittävää mekaanista lujuutta (≥2 MPa), ja niitä arvioitiin myös ioninvaihtokyvyn osalta. Vaikka lentotuhka lisäsi huokoisuutta, se aiheutti haitallisten aineiden, kuten antimonin ja vanadiinin, liukenemista, minkä vuoksi optimaalinen tuhkapitoisuus rajoitettiin 0.3 paino-% Al0:aan. Adsorptio-desorptiotutkimukset osoittivat, että huokoiset geopolymeerirakeet saavuttivat keskimääräisen NH₄⁺-ottokapasiteetin jopa 9.0 mg/g ja NH₄⁺-saannon 51–98 % 30 adsorptio- ja desorptiosyklin aikana, kun KNO3 20:a regeneroivana aineena käytettiin, vaikka suorituskyky heikkeni syklin jälkeen. Pitkän aikavälin käytössä suorituskyky kuitenkin heikkeni. Kunnallisen jäteveden käsittelyssä havaittiin huokosten tukkeutumista ja pintaan kertyvää kiintoainesta, mikä korostaa esikäsittelyn merkitystä. Yhteenvetona voidaan todeta, että huokoiset geopolymeerirakeet ovat käyttökelpoinen, uudelleenkäytettävä ja tehokas materiaali NH₄⁺:n talteenottoon, edistäen typen kiertotaloutta ja kestävää jäteveden käsittelyä
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Alkali-activated materials containing mine tailings and zeolite for seepage water treatment in a closed nickel mine
Get PDFIn the present study, alkali-activated materials were assessed as adsorbents for mine water treatment. The composition of alkali-activated materials, involving mixtures of metakaolin, blast-furnace slag, mine tailings, and zeolite, was optimized based on their leaching behavior and adsorption performance. The most effective adsorbent contained solely blast furnace slag as an aluminosilicate precursor and was selected for a pilot-scale study at a closed nickel mine in Finland. In the pilot, seepage water from a gangue area with an influent flow rate of 0.5 m3/d was treated using a permeable reactive barrier set-up containing 10 kg of slag-based adsorbent prepared by a granulation-alkali activation process. During a one-week experiment, the adsorbent granules were capable of effectively uptaking Ni, Fe, and Mn from the seepage water; the removal percentages of Ni, Fe, and Mn were 82.4%, 81.6%, and 82.5%, respectively. The results indicated the feasibility of blast furnace slag-based adsorbents for toxic element removal in a potentially sustainable approach
Reverse osmosis reject water management by immobilization into alkali-activated materials
Get PDFWater-intensive industries face challenges due to water scarcity and pollution. In the management of these challenges, membrane processes play an important role. However, they produce significant amounts of reject waters, in which the separated salts and pollutants are concentrated. This study aims to develop a novel management concept for reject waters using alkali activation to immobilize salts in a solid phase using metakaolin, blast furnace slag (BFS), or their mixture as precursors and to create alkali-activated materials with sufficient properties to be potentially used in construction applications. Seven different waters were used to prepare the NaOH-based alkali activator solution: deionized water, three simulated seawaters with increasing salinity, and three reverse osmosis (RO) reject waters from mining or pulp and paper industries. Overall, BFS-based samples had the highest immobilization efficiency, likely due to the formation of layered double hydroxide phases (hydrotalcite, with anion exchange capacity) and hydrocalumite (chloride-containing mineral). Moreover, high-salinity water enhanced the dissolution of precursors, prolonged the setting time, and increased the compressive strength compared with nonsaline water. Thus, the obtained materials could be used in construction applications, such as backfilling material at mines where RO concentrates are commonly produced
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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