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  • Yu, Huizhen; Rousu, Juho (2008)
    Dept. of Computer Science Series of Publications C
    We consider structured prediction problems with a parametrized linear prediction function, and the associated parameter optimization problems in large margin type of discriminative training. We propose a dual optimization approach which uses the restricted simplicial decomposition method to optimize a reparametrized dual problem. Our reparametrization reduces the dimension of the space of the dual function to one that is linear in the number of parameters and training examples, and hence independent of the dimensionality of the prediction outputs. This in conjunction with simplicial decomposition makes our approach efficient. We discuss the connections of our approach with related earlier works, and we show its advantages.
  • Kauppi, Olli; Liski, Matti (Helsinki Center of Economic Research, 2008)
    Discussion Paper No 232
  • Sollamo, Raija (Helsinki Collegium for Advanced Studies, 2012)
    COLLeGIUM: Studies across Disciplines in the Humanities and Social Sciences 7
  • Hyvärinen, Matti (Tutkijakollegium, 2006)
    COLLeGIUM: Studies Across Disciplines in the Humanities and Social Sciences, Volume 1: The Travelling Concept of Narrative
  • Järvinen, Onni (Helsingin yliopisto, 2013)
    Antarctica is a major component in the climate system of the earth, acting as a large heat sink in the energy balance. The climatic conditions of Antarctica maintain the snow and ice cover that blankets almost completely the surface area of the continent. Physical properties of snow readily respond to changing environmental conditions and remote sensing signals are sensitive to these properties. The annual changes in the physical properties of the snow cover, especially in the coastal area, must be taken into account when snow cover and climate models are produced. In situ observations are needed for calibration and validation of these models. The aim of the present study was to examine the annual cycle of the active 10-m surface layer in western Dronning Maud Land, Antarctica. The data were collected along a 300-km-long transect from the coast to the edge of the high plateau during the field campaigns in austral summers 2004-2005, 2009-2010 and 2010-2011 as a part of the Finnish Antarctic Research Programme (FINNARP). The studies were focused on the uppermost part of the ice sheet covering the most recent annual accumulation in the coastal area. The results showed that the present study lakes froze completely during winter and showed similar evolution but the exact timing depended on the location. In January, the general structure of lake Suvivesi was following: two layers, each about 1 m thick, an upper layer with a thin ice layer on top and main body of liquid water, and a lower layer containing slush and hard ice sub-layers. The formation and the depth scale of the present study lakes are determined by the light extinction distance and thermal diffusion coefficient, limiting the growth to less than ~1.5 m in one summer. In Antarctica, the mean spectral diffuse extinction coefficient varied between 0.04 and 0.31 cm-1 (10-20-cm snow layer) and varied only slightly between locations when the grain type was the same. The theoretically calculated average depth where broadband irradiance (400-700-nm band) was 1 % of the downwelling irradiance at the surface, was 50 cm. On the continental ice sheet, the compaction rate of the snowpack was 0.0201 ± 0.02 y-1 and the power spectra revealed a daily cycle, synoptic scale variability (~10 days), and variability in a low-frequency band of 60-120 days at a depth of 54 cm. The investigations of snow patches in Basen nunatak revealed that much more snow was lost in summer 2010-2011 (6.3 mm d-1 water equivalent (w.e.)) than in 2004-2005 (4 mm d-1 w.e.).
  • Kultti, Klaus; Vartiainen, Hannu (University of Helsinki, )
  • Kanniainen, Vesa; Pääkkönen, Jenni (University of Helsinki, 2004)
    Discussion Paper No 607
  • Kanniainen, Vesa; Pääkkönen, Jenni (Helsinki Center of Economic Research, 2004)
    Discussion Paper No 17
  • Wang, Caixin (Helsingin yliopisto, 2011)
    Earth s ice shelves are mainly located in Antarctica. They cover about 44% of the Antarctic coastline and are a salient feature of the continent. Antarctic ice shelf melting (AISM) removes heat from and inputs freshwater into the adjacent Southern Ocean. Although playing an important role in the global climate, AISM is one of the most important components currently absent in the IPCC climate model. In this study, AISM is introduced into a global sea ice-ocean climate model ORCA2-LIM, following the approach of Beckmann and Goosse (2003; BG03) for the thermodynamic interaction between the ice shelf and ocean. This forms the model ORCA2-LIM-ISP (ISP: ice shelf parameterization), in which not only all the major Antarctic ice shelves but also a number of minor ice shelves are included. Using these two models, ORCA2-LIM and ORCA2-LIM-ISP, the impact of addition of AISM and increasing AISM have been investigated. Using the ORCA2-LIM model, numerical experiments are performed to investigate the sensitivity of the polar sea ice cover and the Antarctic Circumpolar Current (ACC) transport through Drake Passage (DP) to the variations of three sea ice parameters, namely the thickness of newly formed ice in leads (h0), the compressive strength of ice (P*), and the turning angle in the oceanic boundary layer beneath sea ice (θ). It is found that the magnitudes of h0 and P* have little impact on the seasonal sea ice extent, but lead to large changes in the seasonal sea ice volume. The variation in turning angle has little impact on the sea ice extent and volume in the Arctic but tends to reduce them in the Antarctica when ignored. The magnitude of P* has the least impact on the DP transport, while the other two parameters have much larger influences. Numerical results from ORCA2-LIM and ORCA2-LIM-ISP are analyzed to investigate how the inclusion of AISM affects the representation of the Southern Ocean hydrography. Comparisons with data from the World Ocean Circulation Experiment (WOCE) show that the addition of AISM significantly improves the simulated hydrography. It not only warms and freshens the originally too cold and too saline bottom water (AABW), but also warms and enriches the salinity of the originally too cold and too fresh warm deep water (WDW). Addition of AISM also improves the simulated stratification. The close agreement between the simulation with AISM and the observations suggests that the applied parameterization is an adequate way to include the effect of AISM in a global sea ice-ocean climate model. We also investigate the models capability to represent the sea ice-ocean system in the North Atlantic Ocean and the Arctic regions. Our study shows both models (with and without AISM) can successfully reproduce the main features of the sea ice-ocean system. However, both tend to overestimate the ice flux through the Nares Strait, produce a lower temperature and salinity in the Hudson Bay, Baffin Bay and Davis Strait, and miss the deep convection in the Labrador Sea. These deficiencies are mainly attributed to the artificial enlargement of the Nares Strait in the model. In this study, the impact of increasing AISM on the global sea ice-ocean system is thoroughly investigated. This provides a first idea regarding changes induced by increasing AISM. It is shown that the impact of increasing AISM is global and most significant in the Southern Ocean. There, increasing AISM tends to freshen the surface water, to warm the intermediate and deep waters, and to freshen and warm the bottom water. In addition, increasing AISM also leads to changes in the mixed layer depths (MLD) in the deep convection sites in the Southern Ocean, deepening in the Antarctic continental shelf while shoaling in the ACC region. Furthermore, increasing AISM influences the current system in the Southern Ocean. It tends to weaken the ACC, and strengthen the Antarctic coastal current (ACoC) as well as the Weddell Gyre and the Ross Gyre. In addition to the ocean system, increasing AISM also has a notable impact on the Antarctic sea ice cover. Due to the cooling of seawater, sea ice concentration and thickness generally become higher. In austral winter, noticeable increases in sea ice concentration mainly take place near the ice edge. In regards with sea ice thickness, large increases are mainly found along the coast of the Weddell Sea, the Bellingshausen and Amundsen Seas, and the Ross Sea. The overall thickening of sea ice leads to a larger volume of sea ice in Antarctica. In the North Atlantic, increasing AISM leads to remarkable changes in temperature, salinity and density. The water generally becomes warmer, more saline and denser. The most significant warming occurs in the subsurface layer. In contrast, the maximum salinity increase is found at the surface. In addition, the MLD becomes larger along the Greenland-Scotland-Iceland ridge. Global teleconnections due to AISM are studied. The AISM signal is transported with the surface current: the additional freshwater from AISM tends to enhance the northward spreading of the surface water. As a result, more warm and saline water is transported from the tropical region to the North Atlantic Ocean, resulting in warming and salt enrichment there. It would take about 30 40 years to establish a systematic noticeable change in temperature, salinity and MLD in the North Atlantic Ocean according to this study. The changes in hydrography due to increasing AISM are compared with observations. Consistency suggests that increasing AISM is highly likely a major contributor to the recent observed changes in the Southern Ocean. In addition, the AISM might contribute to the salinity contrast between the North Atlantic and North Pacific, which is important for the global thermohaline circulation.
  • Koistinen, Esa (2007)
    Report series in Geophysics 54
  • Bućko, Michał (Helsingin yliopisto, 2012)
    Road traffic is at present one of the major sources of environmental pollution in urban areas. Magnetic particles, heavy metals and others compounds generated by traffic can greatly affect ambient air quality and have direct implications for human health. The general aim of this research was to identify and characterize magnetic vehicle-derived particulates using magnetic, geochemical and micro-morphological methods. A combination of three different methods was used to discriminate sources of particular anthropogenic particles. Special emphasis was placed on the application of various collectors (roadside soil, snow, lichens and moss bags) to monitor spatial and temporal distribution of traffic pollution on roadsides. The spatial distribution of magnetic parameters of road dust accumulated in roadside soil, snow, lichens and moss bags indicates that the highest concentration of magnetic particles is in the sampling points situated closest to the road edge. The concentration of magnetic particles decreases with increasing distance from the road indicating vehicle traffic as a major source of emission. Significant differences in horizontal distribution of magnetic susceptibility were observed between soil and snow. Magnetic particles derived from road traffic deposit on soil within a few meters from the road, but on snow up to 60 m from the road. The values of magnetic susceptibility of road dust deposited near busy urban motorway are significantly higher than in the case of low traffic road. These differences are attributed to traffic volume, which is 30 times higher on motorway than on local road. Moss bags placed at the edge of urban parks situated near major roads show higher values of magnetic susceptibility than moss bags from parks located near minor routes. Enhanced concentrations of heavy metals (e.g. Fe, Mn, Zn, Cu, Cr, Ni and Co) were observed in the studied samples. This may be associated with specific sources of vehicle emissions (e.g. exhaust and non-exhaust emissions) and/or grain size of the accumulated particles (large active surface of ultrafine particles). Significant correlations were found between magnetic susceptibility and the concentration of selected heavy metals in the case of moss bags exposed to road traffic. Low-coercivity magnetite was identified as a major magnetic phase in all studied roadside collectors (soil, snow, moss bags and lichens). However, magnetic minerals such as titanomagnetite, ilmenite, pyrite and pyrrhotite were also observed in the studied samples. The identified magnetite particles are mostly pseudo-single-domain (PSD) with a predominant MD fraction (>10 μm). The ultrafine iron oxides (>10 nm) were found in road dust extracted from roadside snow. Large magnetic particles mostly originate from non-exhaust emissions, while ultrafine particles originate from exhaust emissions. The examined road dust contains two types of anthropogenic particles: (1) angular/aggregate particles composed of various elements (diameter ~1-300 µm); (2) spherules (~1-100 µm) mostly composed of iron. The first type of particles originates from non-exhaust emissions such as the abrasion of vehicle components, road surface and winter road maintenance. The spherule-shaped particles are products of combustion processes e.g. combustion of coal in nearby power plants and/or fuel in vehicle engines. This thesis demonstrates that snow is an efficient collector of anthropogenic particles, since it can accumulate and preserve the pollutants for several months (until the late stages of melting). Furthermore, it provides more information about spatial and temporal distribution of traffic-generated magnetic particles than soil. Since the interpretation of data obtained from magnetic measurements of soil is problematic (due to its complexity), this suggests the application of alternative collectors of anthropogenic magnetic particulates (e.g. snow and moss bags). Moss bags and lichens are well suited for magnetic biomonitoring studies, since they effectively accumulate atmospheric pollution and can thus be applied to monitor the spatio-temporal distribution of pollution effects.
  • Llorente, Juan Carlos; Sacona, Unai (Käyttäytymistieteiden laitos / Insitute of Behavioural Sciences, 2013)
  • Llorente, Juan Carlos; Kantasalmi, Kari; Simón, Juan de Dios (Helsinki University Press, 2010)
  • Somos, Mark (Tutkijakollegium, 2011)
    COLLeGIUM: Studies Across Disciplines in the Humanities and Social Sciences, volume 10: Trade and War :The Neutrality of Commerce in the Inter-State System
  • Seppälä, Timo (Helsinki Center of Economic Research, 2007)
    Discussion Paper No 163
  • Nyberg, Henri (HECER – Helsinki Center of Economic Research,, 2013)
    HECER Discussion Paper No. 369
  • Vuorenmaa, Tommi (Helsinki Center of Economic Research, 2006)
    Discussion Paper No 117
  • Tuja Pehkonen (Helsingin yliopisto, 2009)
    Helsingin yliopiston hallinnon julkaisuja 61; Hakemistot, oppaat ja ohjeet