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Start Over Coverage 3-8 Format svazek

12. Small-scale contact angle mapping on undisturbed soil surfaces

Creator:
Bachmann, Joerg, Goebel, Marc-O., and Woche, Susanne K.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
hydrophobicity, sessile drop method, soil water repellency, water drop penetration time, and wettability
Language:
Slovak
Description:
Research of the last years pointed out that most soils are neither completely hydrophilic nor hydrophobic, but exhibit a subcritical level of water repellency (i.e. contact angle, CA > 0° and < 90°). Soil water repellency (SWR) is mainly caused by organic compounds of different origin and structure, showing the relevance of biofilms and organic coatings present at many particle surfaces. Despite the importance of SWR for hydraulic processes like preferential flow phenomena, generation of heterogeneous moisture patterns, or surface run-off generation, detailed investigations on the spatial variability of SWR at various scales have rarely been carried out. We introduce a new and easy-to-apply operation for measuring the spatial distribution of SWR using a modified sessile drop method for direct optical assessment of CA at a small scale. The specific objectives of this paper are to apply a sampling and preparation technique that preserves the original spatial arrangement of soil particles and to characterize soil wettability in terms of CA at a high spatial resolution. Results revealed that the sampling and preparation technique allows determination of CA at the millimeter scale using droplets of 1 µL volume. Direct measurement on grain surfaces of the sand fraction is possible for grain sizes > 300 µm using drop volumes down to 0.1 µL. Geostatistical evaluation showed that the measurement grid scale is below the range of spatial dependency for droplets of 1 µL volume, but not for measurements on single grains (pure nugget effect). Results show further that the small-scale differences in wettability, especially for CA < 90°, cannot be detected by the conventional WDPT test. From these findings it can be concluded that the proposed technique allows the identification of small-scale variations in wettability that may promote the formation of heterogeneous flow fields and moisture patterns in soil under unsaturated conditions.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

13. The peroxidase activity of cytochrome b6f complex from spinach chloroplasts

Creator:
Chen, X. B., Hou, C., Li, L. B., and Kuang, T. Y.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
botanika, botany, cytochrome b6f complex, guaiacol, heme-containing protein, hydrogen peroxide, and peroxidase activity
Language:
Multiple languages
Description:
The cytochrome b6f (Cyt b6f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence of hydrogen peroxide (H2O2) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and temperature 35°C. The apparent Michaelis constant (Km) values for H2O2 and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k obs) was about 26 M-1 s-1 and the turnover number (K cat) was about 60 min-1 (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H2O2]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c. and X. B. Chen ... [et al.].
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public