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| 2. |
- Albinsson, I., et al.
(författare)
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Ion association effects and ionic conduction in polyalkalene modified polydimethylsiloxanes
- 1992
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Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 53-56:Part 2, s. 1044-1053
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Tidskriftsartikel (refereegranskat)abstract
- Poly (ethylene oxide) and poly (propylene oxide) modified poly (dimethyl siloxane) (PDMS) have been complexed with LiCF3SO3, NaCF3SO3 and KCF3SO3. In order to study ion association in these systems, the nondegenerate symmetric stretch (A1, SO3) Raman modes have been studied as a function of temperature at several different salt concentrations. Ionic conductivity has also been measured. For the poly (ethylene oxide) modified PDMS (PEO-PDMS), ether oxygen to metal ratios ranged from 12500:1 to 9:1. Changing the cation from Li+ to Na+ to K+ increases the conductivity of the complex. Plots of the molar conductivity versus salt concentration show that the characteristic shape and the region of increase in the molar conductivity is influenced most by the fraction of “free” ions which increases with increasing salt concentration. Charged triplets and contact ion-pairs are also present at the higher salt concentrations; the number of triplets increases with concentration and temperature. Non-VTF behaviour is observed. For the poly (propylene oxide) modified PDMS (PPO-PDMS) (with excess PPO), phase separation is observed when these triflate salts are complexed in. These solutions above and below the boundary layer have been studied by Raman spectroscopy revealing that the upper region is siloxane rich. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in salt concentration. There is evidence of “free” ions, contact-ion pairs, triplets and aggregates. Values of conductivity of 2.2×10−6 and 1.6×10−5 S/cm are quoted for 293 K and 8 mol% LiCF3SO3 in respectively PPO-PDMS/PPO and PEO-PDMS/PEO. Both are better conductors than the corresponding 8 mol% PPG4000/LiCF3SO3 complex.
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| 4. |
- Cienciala, Emil, et al.
(författare)
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The effect of a north-facing forest edge on tree water use in a boreal Scots pine stand
- 2002
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Ingår i: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 32:4, s. 693-702
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Tidskriftsartikel (refereegranskat)abstract
- Tree water use and growth increment were studied in a north-facing forest edge of a 70 year old mono-specific stand of Scots pine (Pinus sylvestris) trees growing on poor sandy soils in the northern boreal zone of Sweden. The forest edge in this study bordered a clear-cut established two decades ago. There were differences in water use and growth increment during the growing season between trees growing at the forest edge and trees growing in the forest interior. These differences were likely related to soil conditions, such as access to soil moisture, soil temperature and soil frost conditions, whereas an effect of above ground microclimate was not found. The estimated tree water use and growth increment over one growing season tended to be larger for trees at the edge zone relative to those from the interior. The variability of the measured tree water fluxes was high, especially for the edge zone trees. There were also structural differences between the two groups of trees, most notably in the radial profile of conductive xylem, in tree height and in green crown length, but these differences were on the limits of statistical significance. The estimated seasonal transpiration was low, about 70 mm when estimated exclusively for trees from the forest interior and 107 mm when estimated exclusively for trees at the forest edge. This illustrates the likely magnitude of water use enhancement due to the conditions specific to forest edge.
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| 5. |
- Djodjic, Faruk, et al.
(författare)
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A Global Perspective on Phosphorus Management Decision Support in Agriculture: Lessons Learned and Future Directions
- 2019
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Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425 .- 1537-2537. ; 48, s. 1218-1233
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of phosphorus (P) management decision support tools (DSTs) and systems (DSS), in support of food and environmental security has been most strongly affected in developed regions by national strategies (i) to optimize levels of plant available P in agricultural soils, and (ii) to mitigate P runoff to water bodies. In the United States, Western Europe, and New Zealand, combinations of regulatory and voluntary strategies, sometimes backed by economic incentives, have often been driven by reactive legislation to protect water bodies. Farmer-specific DSSs, either based on modeling of P transfer source and transport mechanisms, or when coupled with farm-specific information or local knowledge, have typically guided best practices, education, and implementation, yet applying DSSs in data poor catchments and/or where user adoption is poor hampers the effectiveness of these systems. Recent developments focused on integrated digital mapping of hydrologically sensitive areas and critical source areas, sometimes using real-time data and weather forecasting, have rapidly advanced runoff modeling and education. Advances in technology related to monitoring, imaging, sensors, remote sensing, and analytical instrumentation will facilitate the development of DSSs that can predict heterogeneity over wider geographical areas. However, significant challenges remain in developing DSSs that incorporate "big data" in a format that is acceptable to users, and that adequately accounts for catchment variability, farming systems, and farmer behavior. Future efforts will undoubtedly focus on improving efficiency and conserving phosphate rock reserves in the face of future scarcity or prohibitive cost. Most importantly, the principles reviewed here are critical for sustainable agriculture.
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| 7. |
- Ferry, Anders, et al.
(författare)
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Spectroscopic studies of luminescent and ionically conducting Eu[N(CF3SO2)2]3-PPG4000 complexes
- 1998
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 109:7, s. 2921-2928
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Tidskriftsartikel (refereegranskat)abstract
- Alternating current impedance, Fourier transform Raman/infrared (IR), and luminescence excitation (continuous and time-resolved) measurements have been conducted on solutions of poly(propylene glycol) (MW 4000) complexed with Eu[N(CF3SO2)2]3 salt, EuTFSI3, along with differential scanning calorimetry (DSC) studies. From observed frequency shifts of characteristic internal anionic vibrational modes (Raman and IR), we conclude that the salt is solvated by the polymer host. The TFSI anions, however, interact extensively with Eu3+ cations at all concentrations investigated. Ion-polymer interactions are manifested as changes in characteristic vibrational modes of the polymer. Continuous and time-resolved site-selective luminescence data give, respectively, evidence for two different types of chemical environments for solvated Eu3+ cations. In particular, the strongly forbidden non-degenerate 5D0 - 7F0 transition exhibits a structured two-component profile in the spectra. DSC data show that the glass transition temperature, Tg, is only marginally affected by the introduction of a relatively high concentration of salt into the host matrix, whereas the resulting polymer-salt complex is of rubbery character, distinctly different from the pure host polymer, which is a viscous liquid at room temperature. The present findings are interpreted in terms of a phase-segregated microstructure. This conjecture is supported by previous studies on PPG4000-based electrolytes indicating microscopic phase anomalies.
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| 8. |
- Furlani, Maurizio, et al.
(författare)
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Time resolved luminescence and vibrational spectroscopic studies on complexes of poly(ethylene oxide) oligomers and EuTFSI3 salt
- 1998
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Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 113-115:1-2, s. 129-138
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Tidskriftsartikel (refereegranskat)abstract
- AC impedance, FT-Raman/IR, DSC, continuous and time resolved luminescence measurements have been conducted on solutions of poly(ethylene glycol) (PEG), MW 400, and poly(ethylene glycol)-dimethyl ether (DME), MW 425, complexed with Eu[N(CF3SO2)2]3 salt, EuTFSI3. Ion-polymer interactions are manifested as changes in characteristic vibrational modes of the polymer, including CH, and -OH stretching motions at ∼2700-3700 cm-1, and also in cation-induced polymer modes at ∼ 865-910 cm-1. Comparing the vibrational features of the TFSI anion (i.e., both Raman and IR), we find no modes that are substantially changing with increasing salt concentration, or upon change of cation (i.e., M = Li+, Na+ or Eu3+). This observation suggests that TFSI-salts are highly dissociated in PEO oligomer solvents even up to relatively high salt concentrations (i.e., O:M = 26: 1). Clear evidence of -OH end-group coordination in the PEG systems emerges from IR spectra and the strong dependence of T-g upon salt concentration, and also from the pronounced temperature dependence of the ionic conductivity. Despite of this, however, few distinct differences could be observed in the luminescence spectra between the PEG and the DME host materials. Luminescence spectra of Eu3+ show a relatively small distribution of energies (30 cm-1 FWHM in 5D0 - 7F0) in a low-symmetry site throughout the entire concentration range investigated for both PEG and DME solvents. The population decays of the 5D0 excited state, measured by exciting to the degenerate state 5D1 with a pulsed dye laser, are also very similar for the PEG and DME hosts (lifetimes = 0.35 ms).
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| 9. |
- Gebrehiwot, Solomon, et al.
(författare)
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Hydrological change detection using modeling : Half a century of runoff from four rivers in the Blue Nile Basin
- 2013
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:6, s. 3842-3851
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Tidskriftsartikel (refereegranskat)abstract
- Land cover changes can have significant impacts on hydrological regime. The objective of this study was to detect possible hydrological changes of four watersheds in the Blue Nile Basin using a model-based method for hydrological change detection. The four watersheds, Birr, Upper-Didesa, Gilgel Abbay, and Koga range in size from 260 to 1800 km(2). The changes were assessed based on model parameters, model residuals, and in the overall function of the watersheds in transferring rainfall into runoff. The entire time series (1960-2004) was divided into three periods based on political and land management policy changes. A conceptual rainfall-runoff model, the HBV (Hydrologiska Byrans Vattenbalansavdelning) model, was used for the analysis, and suitable parameter sets for each period were found based on a Monte Carlo approach. The values of six out of nine parameters changed significantly between the periods. Model residuals also showed significant changes between the three periods in three of the four watersheds. On the other hand, the overall functioning of the watersheds in processing rainfall to runoff changed little. So even though the individual parameters and model residuals were changing, the integrated functioning of the watersheds showed minimal changes. This study demonstrated the value of using different approaches for detecting hydrological change and highlighted the sensitivity of the outcome to the applied modeling and statistical methods.
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