Development of Interatomic ReaxFF Potentials for Au-S-C-H Systems

We present fully reactive interatomic potentials for systems containing gold, sulfur, carbon, and hydrogen, employing the ReaxFF formalism. The potential is designed especially for simulating goldthiol systems and has been used for studying cluster deposition on self-assembled monolayers. Additionally, a large number of density functional theory calculations are reported, including molecules containing the aforementioned elements and adsorption energetics of molecules and atoms on gold

Phosphorus status of diverse soils in Finland as influenced by long-term P fertilisation 2.Changes of soil test values in relation to P balance with references to incorporation depth of residual and freshly applied P

Fertilising with phosphorus (P) ensures continuous supply of an essential growth factor as necessary for productive and sustainable agriculture. The amounts of P required to attain and maintain an adequate P status in the soil were investigated in field experiments at 22 sites in Finland on soils containing large amounts of residual fertiliser P. The effects of five rates (0, 15, 30, 45 and 60 kg ha-1) of annual P application were measured in the soil by chemical methods after 9 to 15 experimental years, and the changes in soil test P values (STP) were compared with P balances. Stratification of P in ley soil by broadcast application of fertilisers was assessed at four sites. The mean changes of STP in the whole topsoil caused by P fertilisation expressed as per cent of the balance difference were 3.5% (0.0159 mg dm-3)/(kg ha-1) in the acid ammonium acetate test (PAc), 4.7% (0.0214 mg dm-3)/(kg ha-1) in water extraction (Pw) and 9.7% (0.058 mg kg-1)/(kg ha-1) in sodium bicarbonate extraction (modified Olsen P). Initially high PAc values tended to slowly decrease at zero P balance, while low values did not change without some particular reason, such as soil acidification or mixing of the topsoil with some of the less fertile subsurface soil. A thin layer of the uppermost soil was quickly enriched by broadcast application of P fertiliser.;Fosforilannoituksella tehostetaan kasvintuotantoa jaturvataan välttämättömän kasvutekijän jatkuva saanti kestävän maatalouden vaatimusten mukaisesti. Hyvien satojen edellyttämän maan fosforitilan saavuttamiseen ja ylläpitoon tarvittavaa lannoitusta tutkittiin pitkäaikaisilla kenttäkokeilla 22 koepaikalla ominaisuuksiltaan vaihtelevilla mailla, joihin oli edellisinä vuosikymmeninä kertynyt runsaasti fosforia. Viiden vuosittain annetun fosforimäärän (0, 15, 30, 45 ja 60 kg ha-1) vaikutuksia maan fosforitilaan tutkittiin useilla kemiallisilla menetelmillä 915 koevuoden jälkeen, ja analyysituloksia verrattiin pellon fosforitaseeseen. Nurmelle levitetyn fosforin kerrostumista tutkittiin neljällä koepaikalla. Fosforilannoituksen koko kyntökerroksessa aiheuttamat maan fosforipitoisuuden keskimääräiset erot prosentteina fosforitaseesta olivat asetaattitestillä 3,5 % (0,0159 mg P dm-3 maata)/(P-taseen ero 1 kg ha-1), vesiuutolla 4,7 % (0,0214 mg P dm-3)/(kg P ha-1) ja Olsenin menetelmällä 9,7 % (0,058 mg P kg-1)/(kg P ha-1). Mailla, jotka pidättivät liukoista fosforia tehokkaimmin, enimmillään yli 500 kg ha-1 sadoissa poistuneita suuremmat fosforimäärät eivät riittäneet nostamaan asetaatti- ja vesiuutolla määritettyjä fosforipitoisuuksia enempää kuin hyvään kasvuun tarvittiin. Alussa korkeat asetaattiuuttoisen fosforin pitoisuudet pienenivät hitaasti fosforilannoituksen ollessa yhtä suuri kuin fosforin poistuma sadoissa, mutta pienet alkupitoisuudet eivät muuttuneet ilman erityistä syytä kuten maan happamoitumista ja niukkafosforisen jankon sekoittumista kyntökerrokseen. Asetaattimenetelmän mukaan lannoitefosforia tarvittiin maan fosforitilan ylläpitoon keskimäärin noin 10 kg ha-1 enemmän kuin sadoissa poistui. Tulosten mukaan syvällä perusmuokkauksella homogenisoitujen kivennäismaiden fosforitilan hitaat ja säännölliset muutokset voidaan määrittää riittävän tarkasti ja luotettavasti suhteellisen harvoin tehtävillä viljavuustutkimuksilla. Maatalouden ympäristönsuojelua varten turvemaiden liukoisen fosforin pitoisuus tulisi määrittää myös muokkauskerrosta syvempää. Pintalannoitettujen nurmien ohut pintakerros rikastui paljon nopeammin kuin koko kyntökerros. Jos fosforia levitetään maan pinnalle toistuvasti ilman välillä tehtävää kunnollista multausta, huuhtoutumisriskin luotettava arviointi edellyttää pintaa pitkin valuvan veden huuhtoman maan tutkimista erikseen ohuesta pintakerroksesta otetuttujen maanäytteiden avulla

Temporal variations in black carbon concentrations with different time scales in Helsinki during 1996?2005

International audienceVariations in black carbon (BC) concentrations over different timescales, including annual, weekly and diurnal changes, were studied during ten years in Helsinki, Finland. Measurements were made in three campaigns between 1996 and 2005 at an urban area locating two kilometres of the centre of Helsinki. The first campaign took place from November 1996 to June 1997, the second from September 2000 to May 2001 and the third from March 2004 to October 2005. A detailed comparison between the campaigns was only made for winter and spring months when data from all campaigns existed. The effect of traffic and meteorological variables on the measured BC concentrations was studied by means of a multiple regression analysis, where the meteorological data was obtained from a meteorological pre-processing model (MPP-FMI). The BC concentrations showed annual pattern with maxima in fall and late winter due to the weakened mixing and enhanced emissions. Between 1996 and 2005, the campaign median BC concentrations decreased slightly from 1.11 to 1.00 ?g m?3. The lowest campaign median concentration (0.93 ?g m?3) was measured during the second campaign in 2000?2001, when also the lowest traffic rates were measured. The strongest decrease between Campaigns 1 and 3 was observed on weekday daytimes, when also the traffic rates are highest. The variables affecting the measured BC concentrations most were traffic, wind speed and mixing height. On weekdays, traffic had clearly the most important influence before the wind speed and on weekends the effect of wind speed diluted the effect of traffic. The affecting variables and their influence on the BC concentrations were similar in winter and spring. The separate examination of the three campaigns showed that the effect of traffic on the BC concentrations had decreased during the studied years. This reduction was caused by lower emitting vehicles, since between years 1996 and 2005 the traffic rates had increased

Black carbon concentration trends in Helsinki during 1996?2005

International audienceThe black carbon (BC) concentration trends were studied during ten years in Helsinki, Finland. Measurements were made in three campaigns between 1996 and 2005 at an urban area locating two kilometres from the centre of Helsinki. The first campaign was from November 1996 to June 1997, the second from September 2000 to May 2001 and the third from March 2004 to October 2005. In this study, only data from winter and spring months was analysed. The effect of traffic and meteorological variables on the measured BC concentrations was studied by means of a multiple regression analysis, where the meteorological data was obtained from a meteorological pre-processing model (MPP-FMI). During the ten years, the campaign median BC concentrations were found to decrease slightly from 1.11 to 1.00 ?g m?3. The lowest campaign median concentration (0.93 ?g m?3) was measured during the second campaign in 2000?2001, when also the lowest traffic rates were measured. The strongest decrease between campaigns 1 and 3 was observed during weekday daytimes, when the traffic rates are highest. The variables affecting the measured BC concentrations most were traffic, wind speed and mixing height. On weekdays, traffic had clearly the most important influence and on weekends the effect of wind speed diluted the effect of traffic. The affecting variables and their influence on the BC concentration were similar in winter and spring. The separate examination of the three campaigns showed that the effect of traffic on the BC concentrations had decreased during the studied years. This reduction was caused by cleaner emissions from vehicles, since between years 1996 and 2005 the traffic rates had increased. A rough estimate gave that vehicle number-scaled BC mass concentrations have decreased from 0.0028 to 0.0020 ?g m?3 between campaigns 1 and 3

Development of the Surface Urban Energy and Water balance Scheme (SUEWS) for cold climate cities

The Surface Urban Energy and Water Balance Scheme (SUEWS) is developed to include snow. The processes addressed include accumulation of snow on the different urban surface types: snow albedo and density aging, snow melting and re-freezing of meltwater. Individual model parameters are assessed and independently evaluated using long-term observations in the two cold climate cities of Helsinki and Montreal. Eddy covariance sensible and latent heat fluxes and snow depth observations are available for two sites in Montreal and one in Helsinki. Surface runoff from two catchments (24 and 45 ha) in Helsinki and snow properties (albedo and density) from two sites in Montreal are also analysed. As multiple observation sites with different land-cover characteristics are available in both cities, model development is conducted independent of evaluation. The developed model simulates snowmelt related runoff well (within 19% and 3% for the two catchments in Helsinki when there is snow on the ground), with the springtime peak estimated correctly. However, the observed runoff peaks tend to be smoother than the simulated ones, likely due to the water holding capacity of the catchments and the missing time lag between the catchment and the observation point in the model. For all three sites the model simulates the timing of the snow accumulation and melt events well, but underestimates the total snow depth by 18–20% in Helsinki and 29–33% in Montreal. The model is able to reproduce the diurnal pattern of net radiation and turbulent fluxes of sensible and latent heat during cold snow, melting snow and snow-free periods. The largest model uncertainties are related to the timing of the melting period and the parameterization of the snowmelt. The results show that the enhanced model can simulate correctly the exchange of energy and water in cold climate cities at sites with varying surface cover

Sensitivity of Surface Urban Energy and Water Balance Scheme (SUEWS) to downscaling of reanalysis forcing data

Often the meteorological forcing data required for urban hydrological models are unavailable at the required temporal resolution or for the desired period. Although reanalysis data can provide this information, the spatial resolution is often coarse relative to cities, so downscaling is required prior to use as realistic forcing. In this study, WATCH WFDEI reanalysis data are used to force the Surface Urban Energy and Water Balance Scheme (SUEWS). From sensitivity tests in two cities, Vancouver and London with different orography, we conclude precipitation is the most important meteorological variable to be properly downscaled to obtain reliable surface hydrology results, with relative humidity being the second most important. Overestimation of precipitation in reanalysis data at the three sites gives 6-21% higher annual modelled evaporation, 26-39% higher runoff at one site and 4% lower value at one site when compared to modelled values using observed forcing data. Application of a bias correction method to the reanalysis precipitation reduces the model bias compared to using observed forcing data, when evaluated using eddy covariance evaporation measurements. (c) 2017 Elsevier B.V. All rights reserved.Often the meteorological forcing data required for urban hydrological models are unavailable at the required temporal resolution or for the desired period. Although reanalysis data can provide this information, the spatial resolution is often coarse relative to cities, so downscaling is required prior to use as realistic forcing. In this study, WATCH WFDEI reanalysis data are used to force the Surface Urban Energy and Water Balance Scheme (SUEWS). From sensitivity tests in two cities, Vancouver and London with different orography, we conclude precipitation is the most important meteorological variable to be properly downscaled to obtain reliable surface hydrology results, with relative humidity being the second most important. Overestimation of precipitation in reanalysis data at the three sites gives 6-21% higher annual modelled evaporation, 26-39% higher runoff at one site and 4% lower value at one site when compared to modelled values using observed forcing data. Application of a bias correction method to the reanalysis precipitation reduces the model bias compared to using observed forcing data, when evaluated using eddy covariance evaporation measurements. (c) 2017 Elsevier B.V. All rights reserved.Often the meteorological forcing data required for urban hydrological models are unavailable at the required temporal resolution or for the desired period. Although reanalysis data can provide this information, the spatial resolution is often coarse relative to cities, so downscaling is required prior to use as realistic forcing. In this study, WATCH WFDEI reanalysis data are used to force the Surface Urban Energy and Water Balance Scheme (SUEWS). From sensitivity tests in two cities, Vancouver and London with different orography, we conclude precipitation is the most important meteorological variable to be properly downscaled to obtain reliable surface hydrology results, with relative humidity being the second most important. Overestimation of precipitation in reanalysis data at the three sites gives 6-21% higher annual modelled evaporation, 26-39% higher runoff at one site and 4% lower value at one site when compared to modelled values using observed forcing data. Application of a bias correction method to the reanalysis precipitation reduces the model bias compared to using observed forcing data, when evaluated using eddy covariance evaporation measurements. (c) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Sputtering yields exceeding 1000 by 80keV Xe irradiation of Au nanorods

Using experiments and computer simulations, we find that 80 keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100