355 research outputs found
Phase diagram of turbulent Taylor-Couette flow
No full textWe will present the results of our recent numerical work on the nature of the phase diagram of turbulent Taylor-Couette (TC) flow, both with co- and counterrotating cylinder. The work can be seen as the extension of the famous experimental Andereck et al. phase diagram for Taylor-Couette flow just above the onset of instabilities, towards the ultimate turbulence regime, and now obtained numerically. In particular, we will understand when and why optimal transport of angular velocity from the inner to the outer cylinder is achieved and how this is connected to the angular velocity profile and the structures in the flow
Double diffusive convection between two parallel plates with different boundary conditions
No full textWe investigate the double diffusive convection between two parallel plates with either no-slip or free-slip boundary conditions. Direct numerical simulations have been conducted systematically for a series of control parameters. Salt fingers can be observed for both boundary conditions and all parameters explored. Compared to the no-slip case, salt fingers are stronger in the free-slip case, which is accompanied by larger salinity flux and flow velocity. For both boundary conditions, thin boundary regions develop adjacent to two plates. The salinity flux and the Reynolds number show similar dependences on the control parameter, namely, the Rayleigh number of the salinity field
The scientific author
No full textThis presentation connects developments in the science studies with those in scientific discourse analysis. Science studies has undergone a veritable anthropological revolution and come to pay more attention to the concrete situations in which science is elaborated in the laboratory. The focus is now on the rhetoric mobilised to convince peers or potential funding bodies, and on genres that had been heretofore neglected such as letter writing, oral exchanges, notes, memos, reports and paper submissions. A parallel renewal of linguistic and rhetorical approaches is all the more necessary because of this empirical focus: how is the writing process – with its linguistic and iconic characteristics – informed by production conditions? How is it informed by cognitive, epistemological and social issues? However, the role of the scientific author must not be forgotten as it is central to understanding scientific positioning. To succeed in initiating much-needed interdisciplinary dialogue, we need to clarify the subjects at stake – authorship and scientific discourse –, as well as their connection to linguistic and semiotic forms.On se propose ici de mettre en relation les évolutions des études de la science avec celles de l’analyse des discours scientifiques. Une véritable révolution anthropologique a conduit les Science Studies à porter plus d’attention aux conditions concrètes dans lesquelles se fabrique la science au sein du laboratoire. Les chercheurs se sont davantage intéressés aux rhétoriques mobilisées pour convaincre les pairs ou les éventuels financeurs, et ont pris en compte des genres de discours parfois peu étudiés : échanges épistolaires ou oraux, notes, mémos, rapports, propositions de communication. Cette attention au concret montre tout l’intérêt d’un renouvellement parallèle des approches linguistiques et rhétoriques, qui ont à mieux comprendre comment l’écriture scientifique – texte et image – est informée par la situation de production, mais aussi par les enjeux cognitifs, épistémologiques et sociaux d’une recherche. La question de l’auteur scientifique n’est pas pour autant évacuée : elle reste centrale pour mieux comprendre les jeux du positionnement scientifique. Si l’on veut initier efficacement le nécessaire dialogue pluridisciplinaire, des clarifications s’imposent, concernant les objets concernés – l’auctorialité et les discours scientifiques – dans leurs rapports avec les formes linguistiques ou sémiotiques.La problemática de esta presentación busca entrecruzar las evoluciones de los estudios de la ciencia con las evoluciones del análisis de discursos científicos. En efecto, una verdadera revolución antropológica ha llevado los estudios de ciencia a prestar más atención a las condiciones concretas en las cuales se fabrica la ciencia al interior del laboratorio. Nos interesamos igualmente de manera especial a las retoricas movilizadas para convencer a los colegas investigadores o a las personas que eventualmente financian la investigación y tomamos en cuenta géneros de discurso muchas veces poco estudiados: intercambios epistolares u orales, notas, memorandos, reportes, proposiciones de comunicación. La atención que se presta a estos objetos concretos muestra el gran interés que representa una renovación paralela de los análisis lingüísticos y retóricos, que permiten comprender como la realización del texto y, algunas veces, la realización de la imagen, se dan a conocer gracias a la situación de producción, y a los aportes cognitivos, epistemológicos y sociales de una investigación. La cuestión del autor científico no está sin embargo resuelta: esta cuestión sigue siendo central para comprender el rol de la position científica. Si se quiere maniobrar eficazmente el ineludible dialogo pluridisciplinario, algunas clarificaciones son necesarias, estas tienen que ver con los objetos implicados –la «autorialidad» y los discursos científicos – en sus relaciones con las formas lingüísticas o semiótica
Oberflächenspannungen und Struktur von Festkörperoberflächen
No full textThe change of the surface stress induced by adsorbates and monoatomically thin epitaxialmetal layers on nickel and platinum single crystal surfaces has been studied using acantilever bending technique. The surface stress was obtained from a capacitivemeasurement of the radius of curvature of the 0.3 mm thin Ni and Pt samples.The adsorbate induced surface stress of carbon monoxide, carbon, oxygen andsulfur on Ni( 111) has been determined. All adsorbates cause a compressive surface stresswhich can be explained by a dominant transfer of negative charge from the metal surfacestates into the adsorbate. The dilution of negative charge in the metal surface reduces thescreening between the metal ion cores and causes a repulsion of adjacent metal surfaceatoms. At higher adsorbate coverages this effect is enhanced by direct repulsiveadsorbate-adsorbate interactions. The stress-coverage dependence for C/Ni(111) can bedescribed by an ansatz which includes the contribution of the adsorbate induced chargetransfer as weil as the lateral repulsive interaction among the adsorbate atoms giving riseto a non-linear increase of the surface stress. Deviations from the calculated stresscoveragedependence have been observed at increasing coverages for carbon and sulfuron Ni( 111) and can be interpreted in terms of a reconstruction of the surface. The resultsemphazise the intimate relationship between surface stress and surface reconstruction.The oxidation reaction of carbon monoxide on a Pt( 111) surface has been studiedin the temperature range between 300 and 360 K. The time-dependent variation of thesurface stress was monitared in situ during the evolution of the surface reaction and hasbeen compared with the results of kinetic Monte Carlo (MC) simulations. The MCcalculations take into account the activation energy of both, the CO diffusion on thesurface and the oxidation reaction of CO and oxygen
Modelling and analysis of offshore energy hubs
No full textClean, multi-carrier Offshore Energy Hubs (OEHs) may become pivotal for
efficient offshore wind power generation and distribution. In addition, OEHs
may provide decarbonised energy supply for maritime transport, oil and gas
recovery, and offshore farming while also enabling conversion and temporary
storage of liquefied decarbonised energy carriers for export. Here, we
investigate the role of OEHs in the transition of the Norwegian continental
shelf energy system towards zero-emission energy supply. We develop a
mixed-integer linear programming model for investment planning and operational
optimisation to achieve decarbonisation at minimum costs. We consider clean
technologies, including offshore wind, offshore solar, OEHs and subsea cables.
We conduct sensitivity analysis on CO tax, CO budget and the capacity
of power from shore. The results show that (a) a hard carbon cap is necessary
for stimulating a zero-emission offshore energy system; (b) offshore wind
integration and power from shore can more than halve current emissions, but
OEHs with storage are necessary for zero-emission production and (c) at certain
CO tax levels, the system with OEHs can potentially reduce CO emissions
by 50% and energy losses by 10%, compared to a system with only offshore
renewables, gas turbines and power from shore
Integration der Markte und wettbewerbspolitischer Handlungsbedarf
No full textInternational Relations/Trade,
Jäännösmusteen mittaus kierrätysmassoista
No full textAbstractThe amount of printing ink in a pulp suspension produced from recovered paper and its impact on overall brightness is commonly estimated from the reflectance-based ink content measured at a wavelength of 700 nm or 950 nm. The method uses a light scattering coefficient that can be measured from a slightly translucent test medium, i.e. of an opacity less than 97%. This is the case with machine-made papers in most instances. Alternatively, suitable opacity can be achieved by preparing a standard low-grammage sheet on a wire screen, but this results in poor retention of fibre fines, mineral fillers and printing inks, which is especially detrimental to ink measurement when the pulp suspension contains substantial amounts of printing inks. Hence opaque pads are often prepared on filter paper to achieve high retention. Unfortunately their high opacity prevents measurement of the light scattering coefficient, and thus a constant coefficient must be used for the determination of ink content. The aim of this thesis was to clarify the effects of retention and fine material changes on the light scattering coefficient in ink content measurement. The results showed that the light scattering properties of pulp in the wavelength region used for ink content analysis do not remain constant when the fine material content varies. The grade of the recovered paper, hyperwashing and flotation alter the fine material content and thus affect the light scattering. Printing ink also affects light scattering, but its practical impact is smaller than that of fibre fines and mineral fillers. The light scattering coefficient used for each ink content measurement needs to be representative, otherwise a systematic bias in ink content measurements may result from changes in the nature of the fine material and in its content. It is recommended that the light scattering coefficient should be measured in order to avoid this. The measurement should preferably be performed from a low-grammage sheet prepared on filter paper, as this ensures high retention and a measured value that represents better the initial state of the pulp suspension. TiivistelmäMustepitoisuusmittaus perustuu hajaheijastukseen joko 700 nm tai 950 nm aallonpituudella ja sitä käytetään usein arvioitaessa keräyspaperista valmistetun massasuspension soveltuvuutta painopaperien valmistukseen ja painomusteen vaikutusta massan vaaleuteen. Mustepitoisuuden mittauksessa käytetään valonsirontakerrointa, joka voidaan mitata hieman läpikuultavasta näytteestä eli näytteen opasiteetin on oltava pienempi kuin 97 %. Tämä opasiteettiraja toteutuu useimmiten paperikoneella tehdyille painotuotteille. Riittävän alhainen opasiteetti saavutetaan myös valmistamalla standardin mukainen matalaneliömassainen arkki viiralle, mutta tämä johtaa kuitumaisten hienoaineiden, mineraalisten täyteaineiden ja painomusteiden alhaiseen retentioon. Matala retentio on erityisen haitallinen piirre mustemittauksen kannalta massoilla, jotka sisältävät huomattavia määriä painomusteita. Siten usein valmistetaan läpikuultamattomia arkkeja suodatinpaperin päälle, joiden retentio on korkea. Korkeasta opasiteetista johtuen näistä arkeista ei voida määrittää valonsirontakerrointa, jolloin mustepitoisuuden määritys perustuu vakiokertoimeen. Tämän väitöskirjan tavoitteena oli selvittää retention ja hienoaineiden muutoksien vaikutuksia valonsirontakertoimeen ja mustemittaustulokseen. Tutkimuksen tulokset osoittivat että valonsirontakerroin, joka mitataan mustepitoisuuden yhteydessä, ei pysy vakiona hienoainepitoisuuden muuttuessa. Hienoainepitoisuuteen ja siten valonsirontakertoimeen vaikuttavat keräyspaperin laji, hyperpesu ja vaahdotus. Myös painomuste vaikuttaa valonsirontakertoimeen, mutta käytännössä vaikutuksen suurusluokka on pienempi kuin hieno- ja täyteaineilla. Mustepitoisuuden määrityksessä käytetyn valonsirontakertoimen on oltava edustava, muutoin arvot voivat olla systemaattisesti virheellisiä hienoainemäärän tai laadun muuttuessa. Virheen välttämiseksi olisi suositeltavaa määrittää valonsirontakerroin mustepitoisuusanalyysin yhteydessä. Tämä olisi mahdollista tehdä suodatinpaperin päälle valmistetusta matalaneliömassaisesta arkista, jolloin saavutetaan korkea retentio ja näin mitattu arvo edustaa paremmin massasuspension alkuperäistä tilaa. Academic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public defence in Arina-sali (Auditorium TA105), Linnanmaa, on 27 July 2012, at 12 noonAbstract
The amount of printing ink in a pulp suspension produced from recovered paper and its impact on overall brightness is commonly estimated from the reflectance-based ink content measured at a wavelength of 700 nm or 950 nm. The method uses a light scattering coefficient that can be measured from a slightly translucent test medium, i.e. of an opacity less than 97%. This is the case with machine-made papers in most instances. Alternatively, suitable opacity can be achieved by preparing a standard low-grammage sheet on a wire screen, but this results in poor retention of fibre fines, mineral fillers and printing inks, which is especially detrimental to ink measurement when the pulp suspension contains substantial amounts of printing inks. Hence opaque pads are often prepared on filter paper to achieve high retention. Unfortunately their high opacity prevents measurement of the light scattering coefficient, and thus a constant coefficient must be used for the determination of ink content. The aim of this thesis was to clarify the effects of retention and fine material changes on the light scattering coefficient in ink content measurement.
The results showed that the light scattering properties of pulp in the wavelength region used for ink content analysis do not remain constant when the fine material content varies. The grade of the recovered paper, hyperwashing and flotation alter the fine material content and thus affect the light scattering. Printing ink also affects light scattering, but its practical impact is smaller than that of fibre fines and mineral fillers. The light scattering coefficient used for each ink content measurement needs to be representative, otherwise a systematic bias in ink content measurements may result from changes in the nature of the fine material and in its content. It is recommended that the light scattering coefficient should be measured in order to avoid this. The measurement should preferably be performed from a low-grammage sheet prepared on filter paper, as this ensures high retention and a measured value that represents better the initial state of the pulp suspension.Tiivistelmä
Mustepitoisuusmittaus perustuu hajaheijastukseen joko 700 nm tai 950 nm aallonpituudella ja sitä käytetään usein arvioitaessa keräyspaperista valmistetun massasuspension soveltuvuutta painopaperien valmistukseen ja painomusteen vaikutusta massan vaaleuteen. Mustepitoisuuden mittauksessa käytetään valonsirontakerrointa, joka voidaan mitata hieman läpikuultavasta näytteestä eli näytteen opasiteetin on oltava pienempi kuin 97 %. Tämä opasiteettiraja toteutuu useimmiten paperikoneella tehdyille painotuotteille. Riittävän alhainen opasiteetti saavutetaan myös valmistamalla standardin mukainen matalaneliömassainen arkki viiralle, mutta tämä johtaa kuitumaisten hienoaineiden, mineraalisten täyteaineiden ja painomusteiden alhaiseen retentioon. Matala retentio on erityisen haitallinen piirre mustemittauksen kannalta massoilla, jotka sisältävät huomattavia määriä painomusteita. Siten usein valmistetaan läpikuultamattomia arkkeja suodatinpaperin päälle, joiden retentio on korkea. Korkeasta opasiteetista johtuen näistä arkeista ei voida määrittää valonsirontakerrointa, jolloin mustepitoisuuden määritys perustuu vakiokertoimeen. Tämän väitöskirjan tavoitteena oli selvittää retention ja hienoaineiden muutoksien vaikutuksia valonsirontakertoimeen ja mustemittaustulokseen.
Tutkimuksen tulokset osoittivat että valonsirontakerroin, joka mitataan mustepitoisuuden yhteydessä, ei pysy vakiona hienoainepitoisuuden muuttuessa. Hienoainepitoisuuteen ja siten valonsirontakertoimeen vaikuttavat keräyspaperin laji, hyperpesu ja vaahdotus. Myös painomuste vaikuttaa valonsirontakertoimeen, mutta käytännössä vaikutuksen suurusluokka on pienempi kuin hieno- ja täyteaineilla. Mustepitoisuuden määrityksessä käytetyn valonsirontakertoimen on oltava edustava, muutoin arvot voivat olla systemaattisesti virheellisiä hienoainemäärän tai laadun muuttuessa. Virheen välttämiseksi olisi suositeltavaa määrittää valonsirontakerroin mustepitoisuusanalyysin yhteydessä. Tämä olisi mahdollista tehdä suodatinpaperin päälle valmistetusta matalaneliömassaisesta arkista, jolloin saavutetaan korkea retentio ja näin mitattu arvo edustaa paremmin massasuspension alkuperäistä tilaa
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