Bayesian logistic regression for presence-only data     

Fabio Divino  Natalia Golini  Giovanna Jona Lasinio  Antti Penttinen 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(6):1721-1736

Presence-only data are referred to situations in which a censoring mechanism acts on a binary response which can be partially observed only with respect to one outcome, usually denoting the presence of an attribute of interest. A typical example is the recording of species presence in ecological surveys. In this work a Bayesian approach to the analysis of presence-only data based on a two levels scheme is presented. A probability law and a case-control design are combined to handle the double source of uncertainty: one due to censoring and the other one due to sampling. In the paper, through the use of a stratified sampling design with non-overlapping strata, a new formulation of the logistic model for presence-only data is proposed. In particular, the logistic regression with linear predictor is considered. Estimation is carried out with a new Markov Chain Monte Carlo algorithm with data augmentation, which does not require the a priori knowledge of the population prevalence. The performance of the new algorithm is validated by means of extensive simulation experiments using three scenarios and comparison with optimal benchmarks. An application to data existing in literature is reported in order to discuss the model behaviour in real world situations together with the results of an original study on termites occurrences data.  相似文献   

Palaeomagnetism of Middle Ordovician Carbonate Sequence,Vaivara Sinimäed Area,Northeast Estonia,Baltica     

Jüri Plado  Ulla Preeden  Argo JÕeleht  Lauri J. Pesonen  Satu Mertanen 《Acta Geophysica》2016,64(5):1391-1411

The hill range of Vaivara Sinimäed in northeast Estonia consists of several narrow east- to northeast-trending glaciotectonic fold structures. The folds include tilted (dips 4–75°) Middle Ordovician (early Darriwilian) layered carbonate strata that were studied by mineralogical, palaeomagnetic, and rock magnetic methods in order to specify the postsedimentational history of the area and to obtain a better control over the palaeogeographic position of Baltica during the Ordovician. Mineralogical studies revealed that (titano)magnetite, hematite, and goethite are carriers of magnetization. Based on data from 5 sites that positively passed a DC tilt test, a south-easterly downward directed component A (D^ref = 154.6°± 15.3°, I^ref = 60.9°± 9.7°) was identified. The component is carried by (titano)magnetite, dates to the Middle Ordovician (Plat = 17.9°, Plon = 47.3°, K = 46.7, A95 = 11.3°), and places Baltica at mid-southerly latitudes. Observations suggest that in sites that do not pass the tilt test, the glaciotectonic event has caused some rotation of blocks around their vertical axis.  相似文献   

Radiometric stability assessment of an airborne photogrammetric sensor in a test field     

Lauri Markelin  Eija Honkavaara  Teemu Hakala  Juha Suomalainen  Jouni Peltoniemi 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):409-421

Radiometric stability is a desired property of digital photogrammetric large-format sensors. This article presents a methodology for determining the radiometric stability of airborne imaging sensors in operational conditions in a test field and the results of stability evaluation of a large-format photogrammetric frame sensor DMC, from Intergraph. The imagery was collected in two days using nine different exposure settings, and images collected with variable exposure time and aperture were compared. The results showed promising stability in many cases, up to a level of 2% of the radiance, but less favorable results also appeared. Possible reasons for the unfavorable results could be the limitations of the experimental set-up or the instability of the sensor. DMC showed high radiometric performance potential, but high sensitivity to the exposure settings. Based on the results, recommendations for the future test field calibration and validation procedures were given. One limitation of the analysis was the insufficient information about the sensor stability potential; proposals were given to sensor manufacturers concerning the necessary information.  相似文献   

Comparative varve counting and magnetic properties of the 8400-yr sequence of an annually laminated sediment in Lake Valkiajärvi, Central Finland     

Antti E.K. Ojala  Matti Saarnisto 《Journal of Paleolimnology》1999,22(4):335-348

Two varve counts made nearly 20 yrs apart and by different authors in the small and well sheltered meromictic lake of Valkiajärvi were compared with a view to establishing how similar, or otherwise, these two independent varve chronologies might be. The results were significant, the difference between the two varve counts being less than 2% for most of the sediment length, even though the average varve thickness was only 0.3 mm. The continuous and essentially uniform varve record - so far the longest in Finland - covers 8400 yrs and could be applied for accurate dating of palaeoenvironmental indicators in the sediment. As an example, we present a varve-dated pollen diagram for Lake Valkiajärvi.In addition, some magnetic parameters (susceptibility, ARM, SIRM) were measured on the sediment sequence to support the stratigraphic division and correlation of the cores, and to outline the development of the basin since the last deglaciation. Magnetic variables reflected mainly the variation in minerogenic material in the sediment, and were therefore related to changes in the catchment. The magnetic parameters also showed a drastic change some 6000 yrs ago, the reason for which, unfortunately, is still not fully understood.  相似文献   

Modelling effects of spatial variability of saturated hydraulic conductivity on autocorrelated overland flow data: linear mixed model approach     

Antti Taskinen  Hannu Sirviö  Michael Bruen 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(1):67-82

The mixed linear model approach was introduced and applied in studying the effects of spatial variation of the saturated hydraulic conductivity (K _s ) on the variation of the overland flow. Analysis was carried out with 2,000 rainfall-runoff events, all generated through transformation of real, observed rainfall events and different spatially variable K _s fields in a small (12 ha) agricultural catchment. The parameters accounting for the variation in the generation method were the coefficient of variation (cv) and correlation length (L _x L _y ) of K _s both having two levels of values obtained from field measurements of other studies. The analysis showed that the combinations with both parameters having the smaller or bigger value during flow peaks only caused different response in the overland flow. However, the parameters were statistically significant only at the 10% level. Most of the flow variation was explained by the event dynamics. The mixed models were able to model the structure of the data efficiently with less restrictive assumptions than for example the analysis of variance, hence producing more reliable results. The method was able to take into account autocorrelation of the test series, correlation between the factors and unequal variances. The usefulness of the method was supported by the fact that the conclusions drawn by it were confirmed by simple, conventional methods of a previous study, added with statistical criteria and confidence levels for each calculation moment. The findings of the study can be utilized in practise for example when designing the field sampling experiments.  相似文献   

Magnetic classification of stony meteorites: 3. Achondrites     

Pierre ROCHETTE  Jérôme GATTACCECA  Michèle BOUROT‐DENISE  Guy CONSOLMAGNO  Luigi FOLCO  Tomas KOHOUT  Lauri PESONEN  Leonardo SAGNOTTI 《Meteoritics & planetary science》2009,44(3):405-427

Abstract— A database of magnetic susceptibility measurements of stony achondrites (acapulcoite‐lodranite clan, winonaites, ureilites, angrites, aubrites, brachinites, howardite‐eucrite‐diogenite (HED) clan, and Martian meteorites, except lunar meteorites) is presented and compared to our previous work on chondrites. This database provides an exhaustive study of the amount of iron‐nickel magnetic phases (essentially metal and more rarely pyrrhotite and titanomagnetite) in these meteorites. Except for ureilites, achondrites appear much more heterogeneous than chondrites in metal content, both at the meteorite scale and at the parent body scale. We propose a model to explain the lack of or inefficient metal segregation in a low gravity context. The relationship between grain density and magnetic susceptibility is discussed. Saturation remanence appears quite weak in most metal‐bearing achondrites (HED and aubrites) compared to Martian meteorites. Ureilites are a notable exception and can carry a strong remanence, similar to most chondrites.  相似文献   

Retention properties of flow paths in fractured rock     

Antti Poteri 《Hydrogeology Journal》2009,17(5):1081-1092

There is no straightforward way to extrapolate solute retention properties from typical site characterisation scales to typical scales in the performance assessment of the geological disposal of nuclear wastes. Solutes diffuse much deeper into the rock matrix under performance assessment flow conditions than under site characterisation flow conditions. The modelling approach applied in this study, associated with the Äspö Task Force, enables evaluation of the contribution of the individual immobile layers to the overall retention. This makes it possible to determine the influence of the immobile zone heterogeneity on solute retention under different flow conditions. It appears that there is a significant difference between the dominating immobile retention zones on site characterisation and performance assessment scales. Fractured rock is characterised by heterogeneity and in particular a large spread of hydraulic properties. This favours formation of the preferential flow paths by leading to a few dominating transport paths. Large hydraulic features are, on average, better hydraulic conductors than smaller ones. This causes spatial scale effects for the solute retention properties. In particular, the hydraulic properties at the early parts of flow paths are more favourable to retention than those at the later parts of the flow paths.  相似文献   

Computations with finite element methods for the Brinkman problem     

Antti Hannukainen  Mika Juntunen  Rolf Stenberg 《Computational Geosciences》2011,15(1):155-166

Various finite element families for the Brinkman flow (or Stokes–Darcy flow) are tested numerically. Particularly, the effect of small permeability is studied. The tested finite elements are the MINI element, the Taylor–Hood element, and the stabilized equal order methods. The numerical tests include both a priori analysis and adaptive methods.  相似文献   

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld     

Andrew D. Venter  Pieter G. van Zyl  Johan P. Beukes  Jan-Stefan Swartz  Miroslav Josipovic  Ville Vakkari  Lauri Laakso  Markku Kulmala 《Journal of Atmospheric Chemistry》2018,75(3):285-304

Aerosols consist of organic and inorganic species, and the composition and concentration of these species depends on their sources, chemical transformation and sinks. In this study an assessment of major inorganic ions determined in three aerosol particle size ranges collected for 1 year at Welgegund in South Africa was conducted. SO₄^2? and ammonium (NH₄⁺) dominated the PM₁ size fraction, while SO₄^2? and nitrate (NO₃) dominated the PM_1–2.5 and PM_2.5–10 size fractions. SO₄^2? had the highest contribution in the two smaller size fractions, while NO₃^? had the highest contribution in the PM_2.5–10 size fraction. SO₄^2? and NO₃^? levels were attributed to the impacts of aged air masses passing over major anthropogenic source regions. Comparison of inorganic ion concentrations to levels thereof within a source region influencing Welgegund, indicated higher levels of most species within the source region. However, the comparative ratio of SO₄^2? was significantly lower due to SO₄^2? being formed distant from SO₂ emissions and submicron SO₄^2? having longer atmospheric residencies. The PM at Welgegund was determined to be acidic, mainly due to high concentrations of SO₄^2?. PM₁ and PM_1–2.5 fractions revealed a seasonal pattern, with higher inorganic ion concentrations measured from May to September. Higher concentrations were attributed to decreased wet removal, more pronounced inversion layers trapping pollutants, and increases in household combustion and wild fires during winter. Back trajectory analysis also revealed higher concentrations of inorganic ionic species corresponding to air mass movements over anthropogenic source regions.  相似文献   

Early Farming in the Northern Boreal Zone: Reassessing the History of Land Use in Southeastern Finland through High‐Resolution Pollen Analysis     

Teija Alenius  Teemu Mkknen  Antti Lahelma 《Geoarchaeology》2013,28(1):1-24

The early stages of agriculture in the Boreal forests of Northern Europe remain poorly understood. Although pottery appeared during the 6th millennium B.C., this has not been seen as an indication of a true Neolithic in the north. In later prehistory, vast parts of the region are thought to have remained a wilderness. In order to test these assumptions, a high‐resolution pollen analysis and an archaeological survey were carried out at Lake Huhdasjärvi, SE Finland. The results indicate signs of cultivation already by the early Neolithic, 5260–4260 B.C., and slash‐and‐burn cultivation concentrated on deciduous forests is recorded from ca. A.D. 600 onwards. By A.D. 930, an intensive form of swidden cultivation began in the coniferous forests, indicating a well‐established agricultural settlement. The discovery of Neolithic (late 6th millennium B.C.) buckwheat pollen suggests that the roots of agriculture in northernmost Europe may have to be searched for in China rather than the Near East.  相似文献