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ON THE NUMERICAL SOLUTION OF ELLIPTIC AND PARABOLIC PDE IN THE REAL PROJECTIVE PLANE

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Journal of Computational Mathematics 2016年第1期34卷 12-29页

作者： Mahdieh Sattari jukka Tuomela Department of Physics and Mathematics University of Eastern Finland P.O. Box 111 FI-80101 Joensuu Finland

Some models dealing with fibers and liquid crystals can be formulated probabilistically in terms of orientation distributions. Since the orientation of a thin object can be specified by a point in a real projective plane this approach leads to elliptic and parabolic problems in the real projective plane. In most previous works these kind of problems have been considered on the unit sphere which is a double cover of the real projective plane. However, numerically this is inefficient because the resulting systems of equations are unnecessarily big. We formulate the problem directly in the real projective plane using a certain parametrization with three coordinate domains. After reducing the computations to the coordinate domains we can then use finite elements almost in a standard way. In particular the standard error estimates with usual Sobolev spaces remain valid in this setting. We consider both elliptic and parabolic cases, and demonstrate the validity of our approach.

关键词： Smoluchowski equation Real projective plane Finite elements Orientation distribution.

Extracting commuter-specific destination hotspots from trip destination data-comparing the boro taxi service with Citi Bike in NYC

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Geo-Spatial Information Science 2020年第2期23卷 141-152页

作者： Andreas Keler jukka M.Krisp Linfang Ding Department of Civil Geo and Environmental EngineeringTechnical University of MunichMunichGermany Applied Geoinformatics Institute of GeographyUniversity of Augsburg(UniA)AugsburgGermany The KRDB Research Centre for Knowledge and Data Free University of Bozen-BolzanoBozen-BolzanoItaly Department of Cartography Technical University of MunichMunichGermany

Taxi trajectories from urban environments allow inferring various information about the transport service qualities and commuter *** is possible to associate starting and end points of taxi trips with requirements of individual groups of people and even social *** research shows that due to service restrictions,boro taxis have typical customer destination locations on selected Saturdays:many drop-off clusters appear near the restricted zone,where it is not allowed to pick up customers and only few drop-off clusters appear at complicated *** crossings imply recent infrastructural *** want to follow up on these results and add one additional group of commuters:Citi Bike *** selected Saturdays in June 2015,we want to compare the destinations of boro taxi and Citi Bike *** is challenging due to manifold differences between active mobility and motorized road users,and,due to the fact that station-based bike sharing services are restricted to *** and end points of trips,as well as the volumes in between rely on specific numbers of bike sharing ***,we introduce a novel spatiotemporal assigning procedure for areas of influence around static bike sharing stations for extending available computational methods.

关键词： Urban transportation spatial analysis mobility patterns boro taxis vehicle fleets bicycle-sharing service

Influence of emergent macrophyte (Phragmites australis) density on water turbulence and erosion of organic-rich sediment

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Journal of Hydrodynamics 2013年第2期25卷 288-293页

作者： HORPPILA jukka KAITARANTA Joni JOENSUU Laura NURMINEN Leena Department of Environmental Sciences University of Helsinki

The effects of the emergent macrophyte Phragmites australis on water turbulence, bottom shear velocity and water turbidity were experimentally studied with the stem densities 0 stems/m2-100 stems/m2 and using organic-rich sediment. It is found that the maximum root-mean-square （rms） velocity and shear velocity decrease linearly with increasing stem density. By affecting the height of peak turbulence values, emergent plants can thus lower the frequency of sediment erosion events. Additionally, the slope of the rms turbulence increment decreases with increasing stem density. Thus, also the duration of strong turbulence is affected by the density of emergent macrophytes. The critical shear velocity for sediment resuspension is 0.0035 m/s-0.0055 rn/s and not affected by the stem density. In the absence of macrophytes, water flow causes a 6.3-fold increment in turbidity, but with macrophytes turbidity values remain lower. The experiments suggest that even relatively low densities of Phragmites can have substantial effects on water turbulence and consequently on water quality.

关键词： emergent macrophytes turbulence shear velocity resuspension turbidity

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Optimization of the Mean Radius Flow Path of a Multi-Stage Steam Turbine with Evolution Algorithms

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Journal of Thermal Science 2011年第4期20卷 318-323页

作者： jukka Huttunen Jaakko Larjola Teemu Turunen-Saaresti Jari Backman Savonia Power ljytie 678710 VarkausFinlandjukka Lappeenranta University of Technology P.O.Box 2053851 LappeenrantaFinland

A prototype model of the mean radius flow path of a four-stage, high speed 1 MWe axial steam turbine was optimized by using evolution algorithms, DE （differential evolution） algorithm in this case. Also the cost-benefits of the optimization were inspected. The optimization was successfully performed but the accuracy of the optimization was slightly less than hoped when compared to the control modeling executed with the CFD （computational fluid dynamics）. The mentioned inaccuracy could have been hardly avoided because of problems with an initial presumption involving semi-empiric calculations and of the uncertainty concerning the absolute areas of qualification of the functions. This kind of algebraic modeling was essential for the success of the optimization because e.g. CFD-calculation could not have been done on each step of the optimization. During the optimization some problems occurred with the adequacy of the computer capacity and with finding a suitable solution that would keep the algorithms within mathematically allowable boundaries but would not restrict the progress of the opti- mization too much. The rest of the problems were due to the novelty of the application and problems with pre- ciseness when handling the areas of qualification of the functions. Although the accuracy of the optimization re- suits was not exactly in accordance with the objective, they did have a favorable effect on the designing of the turbine. The optimization executed with the help of the DE-algorithm got at least about 3.5 % more power out of the turbine which means about 150 000 ε cost-benefit per turbine in the form of additional electricity capacity.

关键词： steam turbine evolution algorithm optimization mean radius flow path semi-empirical loss correlations

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Detecting vehicle traffic patterns in urban environments using taxi trajectory intersection points

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Geo-Spatial Information Science 2017年第4期20卷 333-344页

作者： Andreas Keler jukka M.Krisp Linfang Ding Institute of Geography University of Augsburg Augsburg Germany

Detecting and describing movement of vehicles in established transportation infrastructures is an important *** helps to predict periodical traffic patterns for optimizing traffic regulations and extending the functions of established transportation *** detection of traffic patterns consists not only of analyses of arrangement patterns of multiple vehicle trajectories,but also of the inspection of the embedded geographical *** this paper,we introduce a method for intersecting vehicle trajectories and extracting their intersection points for selected rush hours in urban *** vehicle trajectory intersection points (TIP) are frequently visited locations within urban road networks and are subsequently formed into density-connected clusters,which are then represented as *** representing temporal variations of the created polygons,we enrich these with vehicle trajectories of other times of the day and additional road network *** a case study,we test our approach on massive taxi Floating Car Data (FCD) from Shanghai and road network data from the OpenStreetMap (OSM) *** first test results show strong correlations with periodical traffic events in *** on these results,we reason out the usefulness of polygons representing frequently visited locations for analyses in urban planning and traffic engineering.

关键词： Floating Car Data (FCD) moving objects transportation infrastructure spatio-temporal patterns

Application of a littoral Baltic Sea resuspension model in a eutrophic lake-factors behind differences in the model performance

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International Journal of Sediment Research 2015年第2期30卷 100-106页

作者： jukka Horppila Joni Kaitaranta Leena Nurminen Department of Environmental Sciences University of Helsinki

The performance of a linear resuspension model developed in the Baltic Sea was studied in the conditions of a eutrophic Lake Kirkkoj(a|¨)rvi(southern Finland).The model predicts sediment resuspension rate using data on vegetation cover,wind and sediment quality as an *** the original model coefficients were used,the model resulted on average 1.8 fold overestimation of the resuspension rate in Kirkkoj(a|¨)*** was due to lower fetch and water depth,and less consolidated sediment of Kirkkoj(a|¨)rvi compared with the Baltic Sea study *** coefficients were adjusted for Kirkkoj(a|¨)rvi,the model predictions were 1.1 times the measured *** to the continuous resuspension,the effect of the wind term in the model was so low that it could be excluded without affecting the accuracy of model *** study demonstrated that in a shallow eutrophic lake accurate predictions on resuspension rate can be made using only data on sediment quality and on factors inhibiting resuspension(macrophytes).The model residuals increased with increasing resuspension rate and high rates of resuspension were underestimated by the *** to the fluffy sediment in Kirkkoj(a|¨)rvi,erosion of sediment increases more than linear with increasing shear *** in such conditions,even better predictions could be achieved by a non-linear resuspension model.

关键词： Linear model Sediment resuspension Macrophytes Wind Sediment quality

Uptake of radioiodide by Paenibacillus sp., Pseudomonas sp.,Burkholderia sp. and Rhodococcus sp. isolated from a boreal nutrient-poor bog

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Journal of Environmental Sciences 2016年第6期28卷 26-37页

作者： Merja Lusa jukka Lehto Hanna Aromaa Jenna Knuutinen Malin Bomberg Laboratory of Radiochemistry Department of Chemistry University of Helsinki 00014 Heisinki Finland VTT Technical Research Centre of Finland 02044 Espoo Finland

Radionuclides, like radioiodine（^129I）, may escape deep geological nuclear waste repositories and migrate to the surface ecosystems. In surface ecosystems, microorganisms can affect their movement. Iodide uptake of six bacterial strains belonging to the genera Paenibacillus,Pseudomonas, Burkholderia and Rhodococcus isolated from an acidic boreal nutrient-poor bog was tested. The tests were run in four different growth media at three temperatures. All bacterial strains removed iodide from the solution with the highest efficiency shown by one of the Paenibacillus strains with 〉 99% of iodide removed from the solution in one of the used growth media. Pseudomonas, Rhodococcus and one of the two Paenibacillus strains showed highest iodide uptake in 1% yeast extract with maximum values for the distribution coefficient（Kd） ranging from 90 to 270 L/kg DW. The Burkholderia strain showed highest uptake in 1% Tryptone（maximum Kd170 L/kg DW）. The Paenibacillus strain V0-1-LW showed exceptionally high uptake in 0.5% peptone ＋ 0.25% yeast extract broth（maximum Kd〉 1,000,000 L/kg DW）. Addition of 0.1% glucose to the 0.5% peptone ＋ 0.25% yeast extract broth reduced iodide uptake at 4℃ and 20℃ and enhanced iodide uptake at 37℃ compared to the uptake without glucose. This indicates that the uptake of glucose and iodide may be competing processes in these bacteria. We estimated that in in situ conditions of the bog,the bacterial uptake of iodide accounts for approximately 0.1%–0.3% of the total sorption of iodide in the surface, subsurface peat, gyttja and clay layers.

关键词： Radioiodide Uptake Paenibacillus Pseudomonas Burkholderia Rhodococcus

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Determination of fracture toughness using the area of micro-crack tracks left in brittle materials by Vickers indentation test

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Journal of Advanced Ceramics 2013年第1期2卷 87-102页

作者： Alireza MORADKHANI Hamidreza BAHARVANDI Mehdi TAJDARI Hamidreza LATIFI jukka MARTIKAINEN Department of Mechanical Engineering Science and Research BranchIslamic Azad UniversityHesarakPoonakP.O.Box 14515/775TehranIran Department of Materials Engineering Malek Ashtar University of TechnologyLavizanP.O.Box 15875/1774TehranIran Department of Mechanical Engineering Science and Research BranchIslamic Azad UniversityVahdat St.Hafezieh Sq.P.O.Box 381814/6775ArakIran Department of Mechanical Engineering Laboratory of Welding TechnologyLappeenranta University of TechnologySkinnarilankatu 34P.O.Box 20FI-53851 LappeenrantaFinland

In this article,a new method has been presented for the estimation of fracture toughness in brittle materials,which enjoys improved accuracy and reduced costs associated with fracture toughness testing procedure compared to similar previous methods,because a vast range of specimens with irregular cracks can be accommodated for ***-sized alumina powders containing 0.05 wt%magnesium oxide(MgO)nanoparticles were mixed and also together with 2.5 vol%,5 vol%,7.5 vol%,10 vol%,and 15 vol%of silicon carbide(SiC)nanopowders *** making and testing various types of ceramics with different mechanical properties,and considering the irregular cracks around the indented area caused by Vickers diamond indenter,a semi-empirical fracture toughness equation has been obtained.

关键词： fracture toughness mechanical properties nanocomposites indentation

Bayesian inference of atomistic structure in functional materials

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npj Computational Materials 2019年第1期5卷 836-842页

作者： Milica Todorović Michael U.Gutmann jukka Corander Patrick Rinke Department of Applied Physics Aalto UniversityP.O.Box 11100Aalto FI-00076Finland School of Informatics University of Edinburgh10 Crichton StreetEdinburgh EH89ABUK Institute of Basic Medical Sciences University of OsloSognsvannsveien 90372 OsloNorway Department of Mathematics and Statistics University of HelsinkiP.O.Box 68Helsinki FI-00014Finland

Tailoring the functional properties of advanced organic/inorganic heterogeneous devices to their intended technological applications requires knowledge and control of the microscopic structure inside the *** quantum mechanical simulation methods deliver accurate energies and properties for individual configurations,however,finding the most favourable configurations remains computationally *** propose a‘building block’-based Bayesian Optimisation Structure Search(BOSS)approach for addressing extended organic/inorganic interface problems and demonstrate its feasibility in a molecular surface adsorption *** BOSS,a Bayesian model identifies material energy landscapes in an accelerated fashion from atomistic configurations sampled during active *** allowed us to identify several most favourable molecular adsorption configurations for C_(60) on the(101)surface of TiO_(2) anatase and clarify the key molecule-surface interactions governing structural *** structures were in good agreement with detailed experimental images of this surface adsorbate,demonstrating good predictive power of BOSS and opening the route towards large-scale surface adsorption studies of molecular aggregates and films.

关键词： adsorption functional inorganic