New radiocarbon dates from Finnish mammoths indicating large ice-free areas in Fennoscandia during the Middle Weichselian     

Pirkko Ukkonen  Juha Pekka Lunkka  Hgne Jungner  Joakim Donner 《第四纪科学杂志》1999,14(7):711-714

New radiocarbon dates from Finnish subfossil mammoth material (Mammuthus sp.), transported by glacial ice, range in age from ca. 32000 to ca. 22500 yr BP. These results suggest that there was a larger ice-free area in Fennoscandia during the Middle Weichselian than previously assumed. In addition, two dates are also presented for bones found in clay with a different transport history. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Overview of groundwater sources and water-supply systems,and associated microbial pollution,in Finland,Norway and Iceland     

Bjørn Kløve  Hanne Margrethe Lund Kvitsand  Tarja Pitkänen  Maria J. Gunnarsdottir  Sylvi Gaut  Sigurdur M. Gardarsson  Pekka M. Rossi  Ilkka Miettinen 《Hydrogeology Journal》2017,25(4):1033-1044

The characteristics of groundwater systems and groundwater contamination in Finland, Norway and Iceland are presented, as they relate to outbreaks of disease. Disparities among the Nordic countries in the approach to providing safe drinking water from groundwater are discussed, and recommendations are given for the future. Groundwater recharge is typically high in autumn or winter months or after snowmelt in the coldest regions. Most inland aquifers are unconfined and therefore vulnerable to pollution, but they are often without much anthropogenic influence and the water quality is good. In coastal zones, previously emplaced marine sediments may confine and protect aquifers to some extent. However, the water quality in these aquifers is highly variable, as the coastal regions are also most influenced by agriculture, sea-water intrusion and urban settlements resulting in challenging conditions for water abstraction and supply. Groundwater is typically extracted from Quaternary deposits for small and medium municipalities, from bedrock for single households, and from surface water for the largest cities, except for Iceland, which relies almost entirely on groundwater for public supply. Managed aquifer recharge, with or without prior water treatment, is widely used in Finland to extend present groundwater resources. Especially at small utilities, groundwater is often supplied without treatment. Despite generally good water quality, microbial contamination has occurred, principally by norovirus and Campylobacter, with larger outbreaks resulting from sewage contamination, cross-connections into drinking water supplies, heavy rainfall events, and ingress of polluted surface water to groundwater.  相似文献   

Motion of animated streamlets appears to surpass their graphical alterations in human visual detection of vector field maxima     

Pyry Kettunen  Juha Oksanen 《制图学和地理信息科学》2013,40(6):489-501

ABSTRACT

Animations have become a frequently utilized illustration technique on maps but changes in their graphical loading remain understudied in empirical geovisualization and cartographic research. Animated streamlets have gained attention as an illustrative animation technique and have become popular on widely viewed maps. We conducted an experiment to investigate how altering four major animation parameters of animated streamlets affects people’s reading performance of field maxima on vector fields. The study involved 73 participants who performed reaction-time tasks on pointing maxima on vector field stimuli. Reaction times and correctness of answers changed surprisingly little between visually different animations, with only a few occasional statistical significances. The results suggest that motion of animated streamlets is such a strong visual cue that altering graphical parameters makes only little difference when searching for the maxima. This leads to the conclusion that, for this kind of a task, animated streamlets on maps can be designed relatively freely in graphical terms and their style fitted to other contents of the map. In the broader visual and geovisual analytics context, the results can lead to more generally hypothesizing that graphical loading of animations with continuous motion flux could be altered without severely affecting their communicative power.  相似文献   

Determination of discharge coefficients for a cross-flooding duct     

Mikael Stening  Juha Järvelä  Pekka Ruponen  Risto Jalonen 《Ocean Engineering》2011,38(4):570-578

Cross-flooding ducts are used to equalize asymmetric flooding and, thus, to decrease the heel angle of a ship in an emergency. The present design guidelines for cross-flooding arrangements involve uncertainties associated with the effect of variable structural factors. In this study, scale model experiments were carried out to determine discharge coefficients of a typical cross-duct, with a focus on the effect of structural components such as the girders, stiffeners, and web frame. Flow conditions and configuration of the components were varied in the experiments. The structural stiffeners in the cross-duct were found to notably increase the discharge coefficient whereas the effects of the web frame and the inclination of the duct at an angle of 7° were negligible. The experimentally obtained discharge coefficient values for the cross-duct were considerably lower than the corresponding values computed according to the generally used guidelines of the IMO Resolution MSC.245(83). This indicates that the geometrical properties of the girders in the cross-ducts need to be properly addressed to avoid overestimating the discharge coefficients. Overall, the experimental results formed an indispensable dataset for the validation and further development of CFD approaches.  相似文献   

Comparing a 1D hydraulic model with a 2D hydraulic model for the simulation of extreme glacial outburst floods   总被引：1，自引：0，他引：1  

Petteri Alho  Juha Aaltonen 《水文研究》2008,22(10):1537-1547

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Responses of aboveground biomass of alpine grasslands to climate changes on the Qinghai-Tibet Plateau     

Li WANG  Haiying YU  Qiang ZHANG  Yunjia XU  Zexing TAO  Juha ALATALO  Junhu DAI 《地理学报(英文版)》2018,28(12):1953-1964

Aboveground biomass in grasslands of the Qinghai-Tibet Plateau has displayed an overall increasing trend during 2003-2016, which is profoundly influenced by climate change. However, the responses of different biomes show large discrepancies, in both size and magnitude. By applying partial least squares regression, we calculated the correlation between peak aboveground biomass and mean monthly temperature and monthly total precipitation in the preceding 12 months for three different grassland types (alpine steppe, alpine meadow, and temperate steppe) on the central and eastern Qinghai-Tibet Plateau. The results showed that mean temperature in most preceding months was positively correlated with peak aboveground biomass of alpine meadow and alpine steppe, while mean temperature in the preceding October and February to June was significantly negatively correlated with peak aboveground biomass of temperate steppe. Precipitation in all months had a promoting effect on biomass of alpine meadow, but its correlations with biomass of alpine steppe and temperate steppe were inconsistent. It is worth noting that, in a warmer, wetter climate, peak aboveground biomass of alpine meadow would increase more than that of alpine steppe, while that of temperate steppe would decrease significantly, providing support for the hypothesis of conservative growth strategies by vegetation in stressed ecosystems.  相似文献   

Dental mesowear reflects local vegetation and niche separation in Pleistocene proboscideans from Britain          下载免费PDF全文

Juha Saarinen  Adrian M. Lister 《第四纪科学杂志》2016,31(7):799-808

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Book reviews     

Juha J. Uitto  A. K. P. Mochtan  Ashok K. Dutt  Anindita Pari 《GeoJournal》1993,31(2):213-214

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Geometric test field calibration of digital photogrammetric sensors   总被引：1，自引：0，他引：1  

Eija Honkavaara  Eero Ahokas  Juha Hyypp  Juha Jaakkola  Harri Kaartinen  Risto Kuittinen  Lauri Markelin  Kimmo Nurminen 《ISPRS Journal of Photogrammetry and Remote Sensing》2006,60(6):387

Test field system calibration will be a fundamental part of the future photogrammetric production line. Accurate calibration and performance evaluations are necessary for fully assessing the stability and accuracy of digital sensing techniques. In this paper, a method of comprehensive geometric calibration in a test field has been developed and empirically tested using eight image blocks collected with three UltraCamD digital large format photogrammetric cameras. Permanent photogrammetric test fields form the basis of the method. Important components of the method are determination of system parameters, evaluation of systematic errors, and assessment of geometric accuracy. The results showed that UltraCamD images contained systematic deformations that could not be modeled with single lens additional parameter models. Good point determination accuracy was obtained despite the systematic errors; the typical accuracy was 2–3 μm in image space in the horizontal coordinates and 0.05–0.09‰ of the object distance in height. One of the cameras had significantly poorer performance. In the worst cases, the horizontal accuracy was 5 μm in image space and the height accuracy was 0.18‰ of the object distance. The analog cameras gave better results than the UltraCamD, but the development of appropriate mathematical models for UltraCamD as well as improvements in digital sensors may change the situation in the near future.  相似文献   

Protostellar classification using supervised machine learning algorithms     

O. Miettinen 《Astrophysics and Space Science》2018,363(9):197

Classification of young stellar objects (YSOs) into different evolutionary stages helps us to understand the formation process of new stars and planetary systems. Such classification has traditionally been based on spectral energy distribution (SED) analysis. An alternative approach is provided by supervised machine learning algorithms, which can be trained to classify large samples of YSOs much faster than via SED analysis. We attempt to classify a sample of Orion YSOs (the parent sample size is 330) into different classes, where each source has already been classified using multiwavelength SED analysis. We used eight different learning algorithms to classify the target YSOs, namely a decision tree, random forest, gradient boosting machine (GBM), logistic regression, naïve Bayes classifier, \(k\)-nearest neighbour classifier, support vector machine, and neural network. The classifiers were trained and tested by using a 10-fold cross-validation procedure. As the learning features, we employed ten different continuum flux densities spanning from the near-infrared to submillimetre wavebands (\(\lambda= 3.6\mbox{--}870~\upmu\mbox{m}\)). With a classification accuracy of 82% (with respect to the SED-based classes), a GBM algorithm was found to exhibit the best performance. The lowest accuracy of 47% was obtained with a naïve Bayes classifier. Our analysis suggests that the inclusion of the \(3.6~\upmu\mbox{m}\) and \(24~\upmu\mbox{m}\) flux densities is useful to maximise the YSO classification accuracy. Although machine learning has the potential to provide a rapid and fairly reliable way to classify YSOs, an SED analysis is still needed to derive the physical properties of the sources (e.g. dust temperature and mass), and to create the labelled training data. The machine learning classification accuracies can be improved with respect to the present results by using larger data sets, more detailed missing value imputation, and advanced ensemble methods (e.g. extreme gradient boosting). Overall, the application of machine learning is expected to be very useful in the era of big astronomical data, for example to quickly assemble interesting target source samples for follow-up studies.  相似文献