105,018 research outputs found
Lens structures from novel materials for fixed and steerable beams antenna systems at sub-THz range
No full textAbstract
In this thesis, the feasibility of four different composite materials as a lens to be integrated into an antenna at frequencies 110–170 GHz or 220–330 GHz was investigated. The investigated lens structures were based on two different ways of refracting the wave with the lens, refraction due to the surface shape and permittivity of the lens, and diffraction. The performance of the lenses was examined using simulation methods and measurements. The refraction-based lens sizes used were at most 30 mm in diameter and 49.5 mm high, and the diffraction-based lens size was 25×27×3 mm3.
Nanocellulose-glass composite, lithium molybdate oxide-glass composite, nanocellulose-coated silica foam, and silica-polymethyl methacrylate composite were investigated. The first two of the composites used are water soluble and could be prepared at room temperature. The water solubility can facilitate the recycling of lenses in the future, and manufacturing at room temperature significantly reduces the need for energy during manufacture. Silica foam coated with nanocellulose is almost 100% air and is suitable as a substrate for diffraction based lenses when the diffraction pattern is sputtered onto the surface of the foam. The above-mentioned composites are environmentally friendly because they do not contain plastic. The silicon oxide-polymethyl methacrylate composite is a plastic composite, but the amount of plastic in it was reduced with silica so that the final composite contained ~20% silica and 80% plastics.
The dielectric properties of the composites used in the work were as follows: relative permittivity 1.018–1.5 and loss tangent 3–40×10−4. In addition, the very low relative permittivity also resulted in very low reflection from the lens surface (reflectivity Original papers Kokkonen, M., Nelo, M., Liimatainen, H., Ukkola, J., Tervo, N., Myllymäki, S., Juuti, J., & Jantunen, H. (2022). Wood-based composite materials for ultralight lens antennas in 6G systems. Materials Advances, 3(3), 1687–1694. https://doi.org/10.1039/D1MA00644D https://doi.org/10.1039/D1MA00644D Self-archived version Kokkonen, M., Ghavidel, A., Tervo, N., Nelo, M., Myllymäki, S., & Jantunen, H. (2021). An ultralight high-directivity ceramic composite lens antenna for 220–330 GHz. IEEE Access, 9, 156592–156598. https://doi.org/10.1109/ACCESS.2021.3130319 https://doi.org/10.1109/ACCESS.2021.3130319 Self-archived version Kokkonen, M., Pálvölgyi, P. S., Sliz, R., Jantunen, H., Kordas, K., & Myllymäki, S. (2023). An ultralow-loss and lightweight cellulose-coated silica foam for planar fresnel zone plate lens applications in future 6G devices. IEEE Antennas and Wireless Propagation Letters, 22(1), 99–103. https://doi.org/10.1109/LAWP.2022.3203434 https://doi.org/10.1109/LAWP.2022.3203434 Self-archived version Palvölgyi, P. S., Kokkonen, M., Sliz, R., Jantunen, H., Kordas, K., & Myllymäki, S. (2023). Porous low‐loss silica–PMMA dielectric nanocomposite for high‐frequency bullet lens applications. Advanced Photonics Research, 4(3), 2200208. https://doi.org/10.1002/adpr.202200208 https://doi.org/10.1002/adpr.202200208 Self-archived version Tiivistelmä
Tässä tutkimuksessa tutkittiin neljän eri komposiittimateriaalin soveltuvuutta antenniin integroitavaksi linssiksi taajuuksilla 110–170 GHz tai 220–330 GHz. Tutkittavat linssirakenteet perustuivat kahteen eri tapaan taittaa aaltoa linssillä, linssin pinnamuodosta ja permittiivisyydestä johtuvaan taittumiseen sekä diffraktioon. Linssien toiminnan tarkastelu tapahtui simulaatio menetelmin sekä mittauksin. Työssä käytetyt taittumiseen perustuvat linssit olivat enintään 30 mm halkaisijaltaan ja 49,5 mm korkeita ja diffraktioon perustuvan linssin koko oli 25×27×3 mm3.
Tutkittavana olivat nanoselluloosa-lasi komposiitti, litium molybdaatti oksidi-lasi komposiitti, nanoselluloosa pinnoitettu piioksidi vaahto, ja piioksidi-polymetyylimetakrylaatti komposiitti. Käytetyistä komposiiteista kaksi ensimmäistä on vesiliukoisia ja ne voitiin valmistaa huoneen lämpötilassa. Vesiliukoisuus voi tulevaisuudessa helpottaa linssien kierrätystä ja huoneenlämpötilassa tapahtuva valmistus vähentää huomattavasti energian tarvetta valmistuksen aikana. Nanoselluloosa pinnoitettu piioksidi vaahto osoittautui olevan lähes 100 % ilmaa ja se soveltuu erinomaisesti diffraktioon perustuvien linssien alustaksi, kun diffraktiokuvio sputteroidaan vaahdon pinnalle. Edellä mainitut komposiitit ovat myös ympäristöystävällisiä, koska ne eivät sisällä ollenkaan muovia. Piioksidi-polymetyylimetakrylaatti on muovikomposiitti, mutta muovin määrää siinä vähennettiin piioksidilla siten, että lopullinen komposiitti sisälsi ~20 % piioksidia ja ~80 % muovia.
Työssä käytettyjen komposiittien dielektriset ominaisuudet olivat seuraavat. Suhteellinen permittiivisyys 1.018–1.5 ja häviötangentti 3–40×10−4. Lisäksi erittäin alhainen suhteellinen permittiivisyys johtaa myös erittäin alhaiseen heijastukseen linssin pinnalta (heijastuskyky Osajulkaisut Kokkonen, M., Nelo, M., Liimatainen, H., Ukkola, J., Tervo, N., Myllymäki, S., Juuti, J., & Jantunen, H. (2022). Wood-based composite materials for ultralight lens antennas in 6G systems. Materials Advances, 3(3), 1687–1694. https://doi.org/10.1039/D1MA00644D https://doi.org/10.1039/D1MA00644D Rinnakkaistallennettu versio Kokkonen, M., Ghavidel, A., Tervo, N., Nelo, M., Myllymäki, S., & Jantunen, H. (2021). An ultralight high-directivity ceramic composite lens antenna for 220–330 GHz. IEEE Access, 9, 156592–156598. https://doi.org/10.1109/ACCESS.2021.3130319 https://doi.org/10.1109/ACCESS.2021.3130319 Rinnakkaistallennettu versio Kokkonen, M., Pálvölgyi, P. S., Sliz, R., Jantunen, H., Kordas, K., & Myllymäki, S. (2023). An ultralow-loss and lightweight cellulose-coated silica foam for planar fresnel zone plate lens applications in future 6G devices. IEEE Antennas and Wireless Propagation Letters, 22(1), 99–103. https://doi.org/10.1109/LAWP.2022.3203434 https://doi.org/10.1109/LAWP.2022.3203434 Rinnakkaistallennettu versio Palvölgyi, P. S., Kokkonen, M., Sliz, R., Jantunen, H., Kordas, K., & Myllymäki, S. (2023). Porous low‐loss silica–PMMA dielectric nanocomposite for high‐frequency bullet lens applications. Advanced Photonics Research, 4(3), 2200208. https://doi.org/10.1002/adpr.202200208 https://doi.org/10.1002/adpr.202200208 Rinnakkaistallennettu versio Academic dissertation to be presented with the assent of the Doctoral Programme Committee of Information Technology and Electrical Engineering of the University of Oulu for public defence in the Wetteri auditorium (IT115), Linnanmaa, on 1 March 2024, at 12 noonAbstract
In this thesis, the feasibility of four different composite materials as a lens to be integrated into an antenna at frequencies 110–170 GHz or 220–330 GHz was investigated. The investigated lens structures were based on two different ways of refracting the wave with the lens, refraction due to the surface shape and permittivity of the lens, and diffraction. The performance of the lenses was examined using simulation methods and measurements. The refraction-based lens sizes used were at most 30 mm in diameter and 49.5 mm high, and the diffraction-based lens size was 25×27×3 mm3.
Nanocellulose-glass composite, lithium molybdate oxide-glass composite, nanocellulose-coated silica foam, and silica-polymethyl methacrylate composite were investigated. The first two of the composites used are water soluble and could be prepared at room temperature. The water solubility can facilitate the recycling of lenses in the future, and manufacturing at room temperature significantly reduces the need for energy during manufacture. Silica foam coated with nanocellulose is almost 100% air and is suitable as a substrate for diffraction based lenses when the diffraction pattern is sputtered onto the surface of the foam. The above-mentioned composites are environmentally friendly because they do not contain plastic. The silicon oxide-polymethyl methacrylate composite is a plastic composite, but the amount of plastic in it was reduced with silica so that the final composite contained ~20% silica and 80% plastics.
The dielectric properties of the composites used in the work were as follows: relative permittivity 1.018–1.5 and loss tangent 3–40×10−4. In addition, the very low relative permittivity also resulted in very low reflection from the lens surface (reflectivity < 1%). Low reflectivity and a low loss tangent can be considered useful properties in lenses, because the electromagnetic wave propagating through the lens is only slightly weakened, i.e. the efficiency of the lenses is high.Tiivistelmä
Tässä tutkimuksessa tutkittiin neljän eri komposiittimateriaalin soveltuvuutta antenniin integroitavaksi linssiksi taajuuksilla 110–170 GHz tai 220–330 GHz. Tutkittavat linssirakenteet perustuivat kahteen eri tapaan taittaa aaltoa linssillä, linssin pinnamuodosta ja permittiivisyydestä johtuvaan taittumiseen sekä diffraktioon. Linssien toiminnan tarkastelu tapahtui simulaatio menetelmin sekä mittauksin. Työssä käytetyt taittumiseen perustuvat linssit olivat enintään 30 mm halkaisijaltaan ja 49,5 mm korkeita ja diffraktioon perustuvan linssin koko oli 25×27×3 mm3.
Tutkittavana olivat nanoselluloosa-lasi komposiitti, litium molybdaatti oksidi-lasi komposiitti, nanoselluloosa pinnoitettu piioksidi vaahto, ja piioksidi-polymetyylimetakrylaatti komposiitti. Käytetyistä komposiiteista kaksi ensimmäistä on vesiliukoisia ja ne voitiin valmistaa huoneen lämpötilassa. Vesiliukoisuus voi tulevaisuudessa helpottaa linssien kierrätystä ja huoneenlämpötilassa tapahtuva valmistus vähentää huomattavasti energian tarvetta valmistuksen aikana. Nanoselluloosa pinnoitettu piioksidi vaahto osoittautui olevan lähes 100 % ilmaa ja se soveltuu erinomaisesti diffraktioon perustuvien linssien alustaksi, kun diffraktiokuvio sputteroidaan vaahdon pinnalle. Edellä mainitut komposiitit ovat myös ympäristöystävällisiä, koska ne eivät sisällä ollenkaan muovia. Piioksidi-polymetyylimetakrylaatti on muovikomposiitti, mutta muovin määrää siinä vähennettiin piioksidilla siten, että lopullinen komposiitti sisälsi ~20 % piioksidia ja ~80 % muovia.
Työssä käytettyjen komposiittien dielektriset ominaisuudet olivat seuraavat. Suhteellinen permittiivisyys 1.018–1.5 ja häviötangentti 3–40×10−4. Lisäksi erittäin alhainen suhteellinen permittiivisyys johtaa myös erittäin alhaiseen heijastukseen linssin pinnalta (heijastuskyky < 1 %). Matalaa heijastusta ja pientä häviötangenttia voidaan pitää hyödyllisinä ominaisuuksina linsseissä, koska linssin läpi etenevä sähkömagneettinen aalto heikkenee vain hieman, eli linssien hyötysuhde on korkea
V. I. Lytkin käänsi J. H. Erkkoa komiksi
No full textKirjoitus on laajennettu versio V. I. Lytkinin syntymän 100-vuotismuistoseminaarissa Syktyvkarissa 1996 pidetystä esitelmästä. Se on julkaistu otsikolla Илля Васьлӧн финн кывйысь кывбуръяс комиӧдӧм teoksessa В.И.Лыткин и финно-угорский мир (Kokkonen 1999)
Maj Lind 1973 : Alkuerä [Vähälä]
No full textAlkuerä 27.10.1973 (6) klo 13-20, Konservatorio. "Jatkuu nauhalta 41952. Alkuerä loppuu nauhaan 41952". Teos- ja esittäjätiedot Rondo-lehden numerosta 6/1973. Sis. [Bach, Johann Sebastian, säv. Ouverture nach Französischer Art, BWV831, h-molli. Ouverture], [Chopin, Frédéric, säv. Etydit, piano, op10. Nro 10, As-duuri], [Chopin, Frédéric, säv. Etydit, piano, op25. Nro 5, e-molli], [Kokkonen, Joonas, säv. Bagatellit, piano (1968-1969)].Soitinnus: piano.Arto Vähälä (piano).Äänitetty: 27.10.1973, Helsinki, Sibelius-Akatemian konserttisali (konserttitaltiointi).Digitoitu 23. 9. 2008
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Horizontal Holonomy for Affine Manifolds
No full textIn this paper, we consider a smooth connected finite-dimensional manifold M, an affine connection a double dagger with holonomy group H (a double dagger) and Delta a smooth completely non integrable distribution. We define the Delta-horizontal holonomy group as the subgroup of H (a double dagger) obtained by a double dagger-parallel transporting frames only along loops tangent to Delta. We first set elementary properties of and show how to study it using the rolling formalism Chitour and Kokkonen (2011). In particular, it is shown that is a Lie group. Moreover, we study an explicit example where M is a free step-two homogeneous Carnot group with m >= 2 generators, and a double dagger is the Levi-Civita connection associated to a Riemannian metric on M, and show in this particular case that is compact and strictly included in H (a double dagger) as soon as m >= 3
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Contribution of Information and Communication Technology (ICT) in Country’S H-Index
No full textThe aim of this study is to examine the effect of Information and Communication Technology (ICT) development on country’s scientific ranking as measured by H-index. Moreover, this study applies ICT development sub-indices including ICT Use, ICT Access and ICT skill to find the distinct effect of these sub-indices on country’s H-index. To this purpose, required data for the panel of 14 Middle East countries over the period 1995 to 2009 is collected. Findings of the current study show that ICT development increases the H-index of the sample countries. The results also indicate that ICT Use and ICT Skill sub-indices positively contribute to higher H-index but the effect of ICT access on country’s H-index is not clear
Fully Turbulent Mean Velocity Profile for Purely Viscous non-Newtonian Fluids
No full textThe characteristic near wall behavior of turbulent flow of purely-viscous non-Newtonian fluids is discussed for both power-law (P.-L.) and Herschel-Bulkley (H.-B.) rheological models. A proper scaling is presented for H.-B. fluids to establish an analogy with power-law fluids with same flow index. To provide reference data for turbulent flow of non-Newtonian fluids, DNS simulations of power-law fluids are conducted in a rectangular channel for a large range of power-law indices ( = 0.5, 0.69, 0.75, 0.9, 1, 1.2). The DNS data show that the mean velocity profile in the viscous and logarithmic layers follow expressions of the form and respectively, where shows a logarithmic dependency on the flow index.Comparison with some experimental data shows the above formulation to be valid for Reynolds numbers (based on shear velocity) as high as 1000
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