168 research outputs found
Slip flow over structured surfaces with entrapped microbubbles
On hydrophobic surfaces, roughness may lead to a transition to a
superhydrophobic state, where gas bubbles at the surface can have a strong
impact on a detected slip. We present two-phase lattice Boltzmann simulations
of a Couette flow over structured surfaces with attached gas bubbles. Even
though the bubbles add slippery surfaces to the channel, they can cause
negative slip to appear due to the increased roughness. The simulation method
used allows the bubbles to deform due to viscous stresses. We find a decrease
of the detected slip with increasing shear rate which is in contrast to some
recent experimental results implicating that bubble deformation cannot account
for these experiments. Possible applications of bubble surfaces in microfluidic
devices are discussed.Comment: 4 pages, 4 figures. v2: revised version, to appear in Phys. Rev. Let
Quantitative characterization of pore structure of several biochars with 3D imaging
Pore space characteristics of biochars may vary depending on the used raw
material and processing technology. Pore structure has significant effects on
the water retention properties of biochar amended soils. In this work, several
biochars were characterized with three-dimensional imaging and image analysis.
X-ray computed microtomography was used to image biochars at resolution of 1.14
m and the obtained images were analysed for porosity, pore-size
distribution, specific surface area and structural anisotropy. In addition,
random walk simulations were used to relate structural anisotropy to diffusive
transport. Image analysis showed that considerable part of the biochar volume
consist of pores in size range relevant to hydrological processes and storage
of plant available water. Porosity and pore-size distribution were found to
depend on the biochar type and the structural anisotopy analysis showed that
used raw material considerably affects the pore characteristics at micrometre
scale. Therefore attention should be paid to raw material selection and quality
in applications requiring optimized pore structure.Comment: 16 pages, 4 figures. The final publication is available at Springer
via http://dx.doi.org/10.1007/s11356-017-8823-
Lattice Boltzmann simulations in microfluidics: probing the boundary condition
In this contribution we summarize our investigations of the effect of boundary slip by utilizing lattice Boltzmann simulations. We investigate fluid flow in hydrophobic and rough microchannels and show that a slip due to hydrophobic interactions increases with increasing hydrophobicity and is independent on the shear rate. If surface roughness is not treated properly while analysing experimental results, a large apparent slip might be measured. We show that the no-slip boundary condition holds in this case if an effective surface position at an intermediate position between peaks and valleys of the surface is considered. Further, we study the effect of microbubbles present on a surface and show that gas bubbles can have a strong impact on the flow properties. They can cause negative slip and due to their deformability, a shear rate dependent slip might be detected in experiments
Suomen peltojen karttapohjainen eroosio-luokitus: Valtakunnallisen kattavuuden saavuttaminen ja WMS-palvelu
Eroosio on merkittĂ€vĂ€ maatalouden fosforikuormituksen aiheuttaja, ja peltojen eroosioriskin kehittyminen on yksi maatalouden kansainvĂ€lisistĂ€ ympĂ€ristöindikaattoreista. Maatalouden ympĂ€ristötoimenpiteiden suuntaamiseksi peltojen eroosioriskin arviointi on tĂ€rkeÀÀ ja peltolohkot, ja jopa niiden osat, on kyettĂ€vĂ€ luokittelemaan eroosioriskin suhteen. TĂ€mĂ€n tutkimushankkeen tavoitteena oli tuottaa valtakunnallisesti kattava jĂ€rjestelmĂ€ Mapero hankkeessa (2010-2013) kehitetylle kartta-pohjaiselle RUSLE -mallille. Jotta mallia ja siihen perustuvia palveluja voitaisiin jatkossa hyödyntÀÀ neuvonnassa ja mahdollisesti tukipolitiikassa, on tasapuolisuuden vuoksi vĂ€lttĂ€mĂ€töntĂ€ saavuttaa koko maan kattavuus. Maanmittauslaitoksen suunnitelmien mukaan laserkeilausaineistopohjainen 2m:n erotuskyvyn korkeusmalli kattaisi koko Suomen vuonna 2019. Mapero 2 -hankkeessa kehitettiin tuotantojĂ€rjestelmĂ€, jonka avulla tarkkaan korkeusmalliin pohjautuvat eroosioherkkyyskartat voidaan luoda koko Suomen alueelle tehokkaasti. Uusi suurteholaskentatekniikka myös mahdollistaa mallin nopean pĂ€ivittĂ€misen tarvittaessa ja mahdollisimman suuren automaation. JĂ€rjestelmĂ€n laskentaperiaatteet on kuvattu tieteellisessĂ€ julkaisussa. Karttojen kvalitatiivinen tarkkuus (ts. suhteellisen eroosioriskin esiintyminen) on arvioitu hyvĂ€ksi niin koekentiltĂ€ saatujen tulosten kuin viljelijöidenkin antaman palautteen perusteella. Kvantitatiivinen tarkkuus (t/ha/v) sen sijaan ei ole ollut yhtĂ€ hyvĂ€. Euroopan komission yhteinen tutkimuskeskus (JRC) julkaisi vuonna 2015 Euroopan oloihin sÀÀdetyn RUSLE2015 â mallin, jonka kĂ€yttöönotto paransi kvantitatiivista tarkkuutta verrattuna RUSLE-malliin. Hankkeen aikana laaditussa julkaisussa âEva-luation of RUSLE2015 erosion model for boreal conditionsâ arvioitiin RUSLE2015 mallia kuudella suomalaisella koekentĂ€llĂ€ (Geoderma Regional lehti). Tuotetut kartat ovat nyt RUSLE2015-mallin mukaisia ja nĂ€in yhteensopivia EU:n laajuisten karttojen kanssa. Hankkeessa valmistuva kartta-aineisto annetaan vapaasti hyödynnettĂ€viksi Luonnonvarakeskuksen tulevan WMS - katselupalvelun kautta, mutta peltolohkoon liittyvĂ€ ominaisuustieto, t/ha/v ja sen avulla laaditut luokitukset voidaan tarvittaessa antaa vain viljelijöiden ja neuvojien kĂ€yttöön esim. Vipu-palvelun kautta. Uusi malli soveltuu kĂ€ytettĂ€viksi yksittĂ€isillĂ€ maatiloilla ja vesiensuojelun kannalta kriittisillĂ€ valuma-alueilla kohdentamaan toimenpiteitĂ€ kustannustehokkaasti.201
Suomen peltojen maalajit, multavuus ja fosforipitoisuus : Vuodet 1996â2000 ja 2005â2009
Julkaisuun on koottu tietoja Suomen peltomaiden muokkauskerroksen lajitekoostumuksesta (maalajista), orgaanisen aineksen mÀÀrĂ€stĂ€ (multavuudesta), happamuudesta ja maan viljavuusfosforipitoisuudesta vuosilta 1996â2000 (noin 880 000 maanĂ€ytettĂ€) ja 2005â2009 (noin miljoona nĂ€ytettĂ€). MaanĂ€ytteet ovat viljelijöiden tai maatalousneuvojien ottamia osana vapaaehtoista maatalouden ympĂ€ristökorvausta.
Aiemmissa yhteenvedoissa tiedot on esitetty jakaumien keskilukuina ja varsinaiset jakaumat vain kuvina ilman jaottelua maalajien mukaan. TÀssÀ julkaisussa tiedot on raportoitu maalajiryhmittÀin koko valtakunnan, ELY-keskusten ja yksittÀisten kuntien tasolla. Kuntatason tietoja on mahdollista koota esimerkiksi vesistöjen valuma-alueita kattaviksi tietueiksi.
Fosfori on tÀrkeÀ kasvinravinne ja samalla kriittinen maatalouden vesistövaikutusten kannalta. Raportin liitetaulukoissa esitetÀÀn maan viljavuusfosforin keskiarvot, mediaanit ja jakaumat. Fosforilukujen jakaumat esitetetÀÀn tiiviisti summajakaumina, joista voidaan palauttaa alkuperÀisten jakaumien muodot. Palautetut jakaumat vastaavat alkuperÀisiÀ jakaumia sitÀ paremmin, mitÀ suurempaan tulosjoukkoon tiedot perustuvat.
Summaries based on large data sets on soil test phosphorus (STP) concentrations, soil types, organic matter contents and pH of Finnish agricultural soils have been earlier published at intervals, and they cover data analysed from 1955 to 1985. This report is another publication in this tradition and it covers two more recent 5-yr periods, 1996â2000 and 2005â2009.
Data for our report were obtained from commercial soil testing laboratories, and includes results of about 880,000 soil samples for the period 1996â2000, and about one million samples for the period 2005â2009. The Finnish Agri-Environmental Programme (FAEP), in effect since 1995, stipulates farmers to sample their fields every 5 years in a commercial soil testing laboratory. Hence, data of the two reported 5-yr periods should, by and large, include data from the same field population. Commitment to the FAEP has been high ever since the Programmes were launched; FEAP regulations cover over 90% of the farms and about 95% of the agricultural land in the country. Agricultural land in Finland comprises of about 2.3 million hectares, so one sample in our dataset would on average correspond to about 2.5 hectare field area.
In the earlier statistics, STP were reported as means and median values, distributions were only shown in figures, and the STP distributions of different soil types were not separable. In this report, we tabulate STP distributions according to soil types as cumulative frequencies. These can be backtransformed to original distributions with one STP unit resolution; the larger are the number of data and the narrower itâs distribution over the STP scale, the better back-transformed distributions correspond to the original ones. Data are made available for different scales: the whole country, administrative regions, and individual municipalities. The municipality level data allows building subsets according to river or lake catchment borders, as example.201
Are there environmental or agricultural benefits in using forest residue biochar in boreal agricultural clay soil?
Short-term agronomic and environmental benefits are fundamental factors in encouraging farmers to use biochar on a broad scale. The short-term impacts of forest residue biochar (BC) on the productivity and carbon (C) storage of arable boreal clay soil were studied in a field experiment. In addition, rain simulations and aggregate stability tests were carried out to investigate the potential of BC to reduce nutrient export to surface waters. A BC addition of 30 t haâ1 increased soil test phosphorus and decreased bulk density in the surface soil but did not significantly change pH or water retention properties, and most importantly, did not increase the yield. There were no changes in the bacterial or fungal communities, or biomasses. Soil basal respiration was higher in BC-amended plots in the spring, but no differences in respiration rates were detected in the fall two years after the application. Rain simulation experiments did not support the use of BC in reducing erosion or the export of nutrients from the field. Of the C added, on average 80% was discovered in the 0â45 cm soil layer one year after the application. Amendment of boreal clay soil with a high rate of BC characterized by a moderately alkaline pH, low surface functionalities, and a recalcitrant nature, did not induce such positive impacts that would unambiguously motivate farmers to invest in BC. BC use seems unviable from the farmer's perspective but could play a role in climate change mitigation, as it will likely serve as long-term C storage.202
A novel solution for utilizing liquid fractions from slow pyrolysis and hydrothermal carbonization - Acidification of animal slurry
Pyrolysis and hydrothermal carbonization (HTC) have recently gained much interest in the field of biomass processing. This is due to the process flexibility with respect to raw materials and the range of potential applications proposed for the end products. In addition to the main product, biochar, the processes yield a liquid fraction that has turned out to be challenging to productize. Considering the feasibility of the thermochemical conversion technologies, it is crucial that all the produced fractions can be utilized reasonably and no waste fractions expensive to dispose remain. In spite of active research and development work, unambiguous uses for the liquid fractions have not been recognized yet.
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