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  • Tåg, Joacim (Helsinki Center of Economic Research, 2007)
  • Haaparanta, Pertti; Kuisma, Kirsti (Helsinki Center of Economic Research, 2006)
  • Lankoski, J.; Lichtenberg, E.; Ollikainen, M. (Helsingin yliopisto, taloustieteen laitos, 2004)
  • Honkapohja, Seppo; Mitra, Kaushik (University of Helsinki, 2003)
  • Honkapohja, Seppo; Mitra, Kaushik (University of Helsinki, 2003)
  • Kajanus, Anni; Meincke, Maylin (Renvall Institute, 2012)
  • Airo, Meri-Liisa; Kiuru, Risto (University of Helsinki, Division of Geophysics and Astronomy, 2012)
  • Raatikainen, Panu (Helsinki Collegium for Advanced Studies, 2012)
  • Galbrun, Esther (2010)
    Phrase-Based Statistical Machine Translation systems model the translation process using pairs of corresponding sequences of words extracted from parallel corpora. These biphrases are stored in phrase tables that typically contain several millions such entries, making it di cult to assess their quality without going to the end of the translation process. Our work is based on the examplifying study of phrase tables generated from the Europarl data, from French to English. We give some statistical information about the biphrases contained in the phrase table, evaluate the coverage of previously unseen sentences and analyse the e ects of pruning on the translation.
  • Elbra, Tiiu (Helsingin yliopisto, 2011)
    Physical properties provide valuable information about the nature and behavior of rocks and minerals. The changes in rock physical properties generate petrophysical contrasts between various lithologies, for example, between shocked and unshocked rocks in meteorite impact structures or between various lithologies in the crust. These contrasts may cause distinct geophysical anomalies, which are often diagnostic to their primary cause (impact, tectonism, etc). This information is vital to understand the fundamental Earth processes, such as impact cratering and associated crustal deformations. However, most of the present day knowledge of changes in rock physical properties is limited due to a lack of petrophysical data of subsurface samples, especially for meteorite impact structures, since they are often buried under post-impact lithologies or eroded. In order to explore the uppermost crust, deep drillings are required. This dissertation is based on the deep drill core data from three impact structures: (i) the Bosumtwi impact structure (diameter 10.5 km, 1.07 Ma age; Ghana), (ii) the Chesapeake Bay impact structure (85 km, 35 Ma; Virginia, U.S.A.), and (iii) the Chicxulub impact structure (180 km, 65 Ma; Mexico). These drill cores have yielded all basic lithologies associated with impact craters such as post-impact lithologies, impact rocks including suevites and breccias, as well as fractured and unfractured target rocks. The fourth study case of this dissertation deals with the data of the Paleoproterozoic Outokumpu area (Finland), as a non-impact crustal case, where a deep drilling through an economically important ophiolite complex was carried out. The focus in all four cases was to combine results of basic petrophysical studies of relevant rocks of these crustal structures in order to identify and characterize various lithologies by their physical properties and, in this way, to provide new input data for geophysical modellings. Furthermore, the rock magnetic and paleomagnetic properties of three impact structures, combined with basic petrophysics, were used to acquire insight into the impact generated changes in rocks and their magnetic minerals, in order to better understand the influence of impact. The obtained petrophysical data outline the various lithologies and divide rocks into four domains. Based on target lithology the physical properties of the unshocked target rocks are controlled by mineral composition or fabric, particularly porosity in sedimentary rocks, while sediments result from diverse sedimentation and diagenesis processes. The impact rocks, such as breccias and suevites, strongly reflect the impact formation mechanism and are distinguishable from the other lithologies by their density, porosity and magnetic properties. The numerous shock features resulting from melting, brecciation and fracturing of the target rocks, can be seen in the changes of physical properties. These features include an increase in porosity and subsequent decrease in density in impact derived units, either an increase or a decrease in magnetic properties (depending on a specific case), as well as large heterogeneity in physical properties. In few cases a slight gradual downward decrease in porosity, as a shock-induced fracturing, was observed. Coupled with rock magnetic studies, the impact generated changes in magnetic fraction the shock-induced magnetic grain size reduction, hydrothermal- or melting-related magnetic mineral alteration, shock demagnetization and shock- or temperature-related remagnetization can be seen. The Outokumpu drill core shows varying velocities throughout the drill core depending on the microcracking and sample conditions. This is similar to observations by Kern et al., (2009), who also reported the velocity dependence on anisotropy. The physical properties are also used to explain the distinct crustal reflectors as observed in seismic reflection studies in the Outokumpu area. According to the seismic velocity data, the interfaces between the diopside-tremolite skarn layer and either serpentinite, mica schist or black schist are causing the strong seismic reflectivities.
  • Kohout, Tomas (Helsingin yliopisto, 2009)
    Together with cosmic spherules, interplanetary dust particles and lunar samples returned by Apollo and Luna missions, meteorites are the only source of extraterrestrial material on Earth. The physical properties of meteorites, especially their magnetic susceptibility, bulk and grain density, porosity and paleomagnetic information, have wide applications in planetary research and can reveal information about origin and internal structure of asteroids. Thus, an expanded database of meteorite physical properties was compiled with new measurements done in meteorite collections across Europe using a mobile laboratory facility. However, the scale problem may bring discrepancies in the comparison of asteroid and meteorite properties. Due to inhomogenity, the physical properties of meteorites studied on a centimeter or millimeter scale may differ from those of asteroids determined on kilometer scales. Further difference may arise from shock effects, space and terrestrial weathering and from difference in material properties at various temperatures. Close attention was given to the reliability of the paleomagnetic and paleointensity information in meteorites and the methodology to test for magnetic overprints was prepared and verified.
  • Kultti, Klaus; Miettunen, Antti; Virrankoski, Juha (University of Helsinki, 2003)
  • Leppäranta, Matti (1998)
  • Leppäranta, Matti (1998)
  • Kymäläinen, Hanna-Riitta (2015)
  • Kanniainen, Vesa; Pääkkönen, Jenni (Helsinki Center of Economic Research, 2007)