Some air electricity phenomena caused by waterfalls: Correlative study of the spectra     

Aare Luts  Tiia-Ene Parts  Lauri Laakso  Anne Hirsikko  Tiia Grnholm  Markku Kulmala 《Atmospheric Research》2009,91(2-4):229-237

According to our previous measurements, waterfalls permanently modify air ion spectra. In this paper we performed a correlative study of these results and proposed some pathways which can produce the observed waterfall ions. The small ion composition near waterfalls should be different from that further away due to gaseous OH⁻ core (water shell) clusters. We assumed that the combination of factors (autoionization, fluctuating charge rearrangement, surface protrusions, collisions, Coulomb explosion) serves as the main source of observed intermediate ions, and an extra source for large ions. Evaporation of droplets produces nearly equal numbers of positive and negative intermediate and large ions. Waterfall-produced intermediate ions can attach to the waterfall-produced larger particles, which creates an additional link between the waterfall intermediate and large ions.  相似文献   

Relating spatial and temporal variability in sediment chlorophylla and carbohydrate distribution with erodibility of a tidal flat     

Cathy H. Lucas  John Widdows  Lauri Wall 《Estuaries and Coasts》2003,26(4):885-893

Trends in the spatial distribution of chlorophylla (chla) and colloidal and total carbohydrates on the Molenplaat tidal flat in the Westerschelde estuary, Netherlands, reflected spatial differences in physical properties of the sediment. Results from a Spearman Rank Order Correlation indicated that many of the physical and biological measures covaried. Multiple regression analyses describing the relationship between colloidal carbohydrates and sediment properties resulted in several highly significant equations, although in all cases chla was able to predict colloidal carbohydrate content. Relationships between sediment surface chla and colloidal carbohydrate, and sediment erodibility (i.e., critical erosion threshold, U_crit, and mass of sediment eroded at a velocity of 30 cm s^?1) determined in annular flume experiments were examined. Overall sediment erodibility was lowest (i.e., high thresholds, low mass eroded) for the siltiest sediments in June 1996 when chla and colloidal carbohydrates were high (56.9 μg gDW^?1 and 320.6 μg gluc.equ. gDW^?1, respectively), and greatest (i.e., low thresholds, high mass eroded) at the sandier sediments in September 1996, when chla and colloidal carbohydrates were low (1.0 μg gDW^?1 and 5.7 μg gluc.equ. gDW^?1, respectively). When sediments were grouped according to relative silt content, the most significant relationships were found in muddy sand with a finegrained fraction (<63 μm) of 25–50%. Thresholds of erosion increased, while mass of sediment eroded decreased, with increasing chla and colloidal carbohydrate. A similar trend was observed for the sand-muddy sand (63 μm 10–25%). In the sand (63 μm 0–10%), there were no relationships for U_crit, whereas mass eroded appeared to increase with increasing chla and colloidal carbohydrate. The increased carbohydrate may stick sand grains together, altering the nature of erosion from rolling grains to clumps of resuspension.  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   

Fish assemblages in coastal lagoons in land-uplift succession: The relative importance of local and regional environmental gradients     

Martin Snickars  Alfred Sandström  Antti Lappalainen  Johanna Mattila  Kajsa Rosqvist  Lauri Urho 《Estuarine, Coastal and Shelf Science》2009

The assemblages of young-of-the-year fish were studied in coastal lagoons in an archipelago with post-glacial land-uplift, which affects environmental gradients at local and regional scale, i.e. lagoon habitat isolation and archipelago position, respectively. The categorisation of 40 undisturbed lagoons into nine habitat types based on habitat isolation and archipelago position was supported by clear relationships with spring temperature and total fish abundance. Rutilus rutilus, breams (Abramis/Blicca sp.) and Perca fluviatilis were the most abundant and frequently occurring species. The fish assemblage differed among the nine habitat types. Rutilus rutilus, P. fluviatilis and breams were discriminating species in the majority of habitat types with low physical harshness, whereas Alburnus alburnus and Gasterosteus aculeatus increased their contributions in habitat types with high physical harshness. Rutilus rutilus and breams were thus common in lagoons with high habitat isolation situated in the inner archipelago. These lagoons were characterised by warm water and high vegetation coverage. Gasterosteus aculeatus was restricted to lagoons with low habitat isolation and exposure and low vegetation coverage, situated in the outer archipelago. Perca fluviatilis had the widest distribution of all species. The coverage of two macrophytes, Potamogeton perfoliatus and Zannichellia palustris, and salinity matched best the distance among habitat types. These habitat characteristics, as well as the fish abundances and assemblages differed most across the habitat types in the outer and mid archipelago zones and in the lowest habitat isolation. These patterns suggest that the structuring effect of habitat isolation increases along the archipelago gradient as differences between local and regional conditions increase. In the inner archipelago, overall low physical harshness induces homogeneous conditions and the habitat isolation is less important here than in the other zones. We suggest that this difference in the relative importance of the two gradients depending on the level of respective gradient ultimately forms these heterogeneous coastal habitats in a successional landscape. Rutilus rutilus and P. fluviatilis were responsible for large parts of the assemblage patterns. Although sympatric due to similar habitat requirements, differences in dispersal capability, competitive ability and predation vulnerability may add explanation to detected differences in distribution and abundance in these two species in an open system. Our results also stress the structuring role of vegetation in terms of total coverage and species composition, as these two aspects of macrophyte diversity may act as complementary habitat modifiers across gradients of physical harshness.  相似文献   

The lherzolitic shergottite Grove Mountains 99027: Rare earth element geochemistry     

Weibiao Hsu  Yunbin Guan  Henian Wang  Laurie A. Leshin  Rucheng Wang  Wenlan Zhang  Xiaoming Chen  Fusheng Zhang  Chengyi Lin 《Meteoritics & planetary science》2004,39(5):701-709

Abstract— We report here on an ion probe study of rare earth element (REE) geochemistry in the lherzolitic shergottite Grove Mountains (GRV) 99027. This meteorite shows almost identical mineralogy, petrology, and REE geochemistry to those of the lherzolitic shergottites Allan Hills (ALH) A77005, Lewis Cliff (LEW) 88516, and Yamato (Y‐) 793605. REE concentrations in olivine, pyroxenes, maskelynite, merrillite, and melt glass are basically comparable to previous data obtained from ALH A77005, LEW 88516, and Y‐793605. Olivine is the dominant phase in this meteorite. It is commonly enclosed by large (up to several mm) pigeonite oikocrysts. Non‐poikilitic areas consist of larger olivine grains (?mm), pigeonite, augite, and maskelynite. Minor merrillite (up to 150 μm in size) is widespread in non‐poikilitic regions, occurring interstitially between olivine and pyroxene grains. It is the main REE carrier in GRV 99027 and has relatively higher REEs (200–1000 × CI) than that of other lherzolitic shergottites. A REE budget calculation for GRV 99027 yields a whole rock REE pattern very similar to that of other lherzolites. It is characterized by the distinctive light REE depletion and a smooth increase from light REEs to heavy REEs. REE microdistributions in GRV 99027 strongly support the idea that all lherzolitic shergottites formed by identical igneous processes, probably from the same magma chamber on Mars. Despite many similarities in mineralogy, petrography, and trace element geochemistry, subtle differences exist between GRV 99027 and other lherzolitic shergottites. GRV 99027 has relatively uniform mineral compositions (both major elements and REEs), implying that it suffered a higher degree of sub‐solidus equilibration than the other three lherzolites. It is notable that GRV 99027 has experienced terrestrial weathering in the Antarctic environment, as its olivine and pyroxenes commonly display a light REE enrichment and a negative Ce anomaly. Caution needs to be taken in future chronological studies.  相似文献   

Oxygen isotopic composition of chondritic interplanetary dust particles: A genetic link between carbonaceous chondrites and comets     

J. Aléon  C. Engrand  L.A. Leshin  K.D. McKeegan 《Geochimica et cosmochimica acta》2009,73(15):4558-5365

Oxygen isotopes were measured in four chondritic hydrated interplanetary dust particles (IDPs) and five chondritic anhydrous IDPs including two GEMS-rich particles (Glass embedded with metal and sulfides) by a combination of high precision and high lateral resolution ion microprobe techniques.All IDPs have isotopic compositions tightly clustered around that of solar system planetary materials. Hydrated IDPs have mass-fractionated oxygen isotopic compositions similar to those of CI and CM carbonaceous chondrites, consistent with hydration of initially anhydrous protosolar dust. Anhydrous IDPs have small ¹⁶O excesses and depletions similar to those of carbonaceous chondrites, the largest ¹⁶O variations being hosted by the two GEMS-rich IDPs. Coarse-grained forsteritic olivine and enstatite in anhydrous IDPs are isotopically similar to their counterparts in comet Wild 2 and in chondrules suggesting a high temperature inner solar system origin. The small variations in the ¹⁶O content of GEMS-rich IDPs suggest that most GEMS either do not preserve a record of interstellar processes or the initial interstellar dust is not ¹⁶O-rich as expected by self-shielding models, although a larger dataset is required to verify these conclusions.Together with other chemical and mineralogical indicators, O isotopes show that the parent-bodies of carbonaceous chondrites, of chondritic IDPs, of most Antarctic micrometeorites, and comet Wild 2 belong to a single family of objects of carbonaceous chondrite chemical affinity as distinct from ordinary, enstatite, K- and R-chondrites. Comparison with astronomical observations thus suggests a chemical continuum of objects including main belt and outer solar system asteroids such as C-type, P-type and D-type asteroids, Trojans and Centaurs as well as short-period comets and other Kuiper Belt Objects.  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   

Comparison of Monte Carlo simulation methods for the calculation of the nucleation barrier of argon     

Antti Lauri  Joonas Merikanto  Evgeni Zapadinsky  Hanna Vehkamki 《Atmospheric Research》2006,82(3-4):489

We compare two molecular Monte Carlo simulation methods, the discrete summation method and the growth/decay method, which calculate the vapor-liquid nucleation free energy barrier by simulating isolated clusters of fixed size without the surrounding vapor. The methods are applied to calculations of nucleation barriers of Lennard–Jones argon at 60 K and 80 K. Both of these methods are computationally efficient, as only isolated clusters without the surrounding vapor are simulated, and the methods can be applied with any given cluster definition. They give equivalent results to other methods where the vapor phase is also included. The discrete summation method is based on the calculation of the difference in free energies between two systems containing an n-cluster and an (n − 1)-cluster plus one non-interacting (free) molecule. We show that the configurational space is not equivalent in the two systems. Hence, there has to be an additional term in the free energy calculation that accounts for several kT in magnitude. In contrast to previous studies we also show that it is not correct to prevent the overlap of the non-interacting molecule and another molecule by a zero or an arbitrarily small repulsive potential, but with a small excluded space around the free molecule.  相似文献   

Modelling surface drifting of buoys during a rapidly-moving weather front in the Gulf of Finland, Baltic Sea     

Maria Gstgifvars  Hannu Lauri  Annakaisa Sarkanen  Kai Myrberg  Oleg Andrejev  Cecilia Ambjrn 《Estuarine, Coastal and Shelf Science》2006,70(4):567

The Gulf of Finland is an elongated estuary located in the north-eastern extremity of the Baltic Sea. This semi-enclosed sea-area is subject to heavy sea traffic, and is one of the main risk areas for oil accidents in the Baltic. The continuous development and validation of operational particle drift and oil-spill forecasting systems is thus seen to be essential for this sea-area.Here, the results of a three-day drift experiment in May 2003 are discussed. The field studies were performed using GPS-positioned surface floating buoys. The aim of this paper is to evaluate how well models can reproduce the drift of these buoys. Model simulations, both in forecast and hindcast modes, were carried out by three different 3D hydrodynamic models, the results of which are evaluated by comparing the calculated drifts with observations. These models were forced by HIRLAM (High Resolution Limited Area Model) and ECMWF (European Centre for Medium-Range Weather Forecasts) meteorological forecast fields.The simulated drift of the buoys showed a good agreement with observations even when, during the study period, a rapidly-changing wind situation was observed to affect the investigation area; in this situation the winds turned about 100 degrees in half an hour. In such a case it is a very complicated task to forecast the drifters' routes: there is a need to regularly update the meteorological forcing fields and to use these regularly-updated fields throughout the simulations. It is furthermore recommended that forecasts should be made using several circulation models and several meteorological forecasts, in order to get an overview of the accuracy of the forecasted drifts and related differences in between the forecasts.  相似文献