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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of Hydrology, 06 June 2012, Vol.442-443, pp.63-74
    Description: ► We investigated the effects of liquid penetration kinetics on aggregate stability. ► Stability was assessed by immersion in liquids with different surface tension. ► Penetration was related to aggregate contact angle and liquid surface tension. ► Aggregate stability was inversely related to wettability in terms of contact angle. ► Aggregate stability was controlled by solid and liquid interfacial properties. Aggregate stability is frequently shown to be enhanced by strong soil water repellency, however, there is limited systematic evidence on this effect for moderately (subcritically) water repellent soils. This study aimed to investigate the specific effects of interfacial properties on the liquid penetration kinetics in relation to the stability of subcritically water repellent aggregates (4–6.3 mm) from various arable and forest soils against breakdown by slaking. In contrast to many other studies, where aggregate stability was determined by wet sieving, we here assessed the stability by immersion of air-dry aggregates in water–ethanol solutions with surface tensions ranging from 30 to 70 mN m . This approach allowed a highly sensitive discrimination of different stability levels and the determination of breakdown kinetics also for less stable aggregates. Interfacial properties were characterized in terms of contact angle measured on crushed aggregates, , and calculated for intact aggregates, , based on infiltration measurements with water and ethanol. Aggregate stability turned out to be higher in forest soils compared to arable soils with topsoil aggregates generally found to be more stable than subsoil aggregates. For water repellent aggregates, characterized by contact angles 〉40° and low water infiltration rates (〈0.2 mm s ), the fraction of disrupted aggregates after 30 s of immersion was generally below 10%, whereas in case of the more wettable aggregates, characterized by contact angles 〈10° and higher infiltration rates (〉0.25 mm s ) more than 80% of the aggregates were disrupted. In accordance, we found a close relationship between aggregate stability and wettability with differences between and being generally small. In addition, aggregate stability turned out to be related to organic carbon content. However, correlation analysis revealed that both persistence of aggregate stability and kinetics of aggregate breakdown were more strongly affected by the contact angle, ( = 0.90 and = −0.83, respectively) and ( = 0.89 and = −0.76, respectively) than the organic carbon content ( = 0.62 and −0.52, respectively), suggesting that stability was primarily controlled by aggregate interfacial properties. Calculation of liquid penetrativity as a function of surface tension and contact angle clearly demonstrated the importance of both solid and liquid interfacial properties in determining the stability of subcritically water repellent aggregates against slaking.
    Keywords: Aggregate Stability ; Contact Angle ; Infiltration Rate ; Repellency Index ; Soil Water Repellency ; Surface Tension ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 2
    Language: English
    In: Journal of hydrology, 2012, Vol.442, pp.63-74
    Description: Aggregate stability is frequently shown to be enhanced by strong soil water repellency, however, there is limited systematic evidence on this effect for moderately (subcritically) water repellent soils. This study aimed to investigate the specific effects of interfacial properties on the liquid penetration kinetics in relation to the stability of subcritically water repellent aggregates (4–6.3mm) from various arable and forest soils against breakdown by slaking. In contrast to many other studies, where aggregate stability was determined by wet sieving, we here assessed the stability by immersion of air-dry aggregates in water–ethanol solutions with surface tensions ranging from 30 to 70mNm⁻¹. This approach allowed a highly sensitive discrimination of different stability levels and the determination of breakdown kinetics also for less stable aggregates. Interfacial properties were characterized in terms of contact angle measured on crushed aggregates, θc, and calculated for intact aggregates, θᵢ, based on infiltration measurements with water and ethanol. Aggregate stability turned out to be higher in forest soils compared to arable soils with topsoil aggregates generally found to be more stable than subsoil aggregates. For water repellent aggregates, characterized by contact angles 〉40° and low water infiltration rates (0.25mm³s⁻⁰.⁵) more than 80% of the aggregates were disrupted. In accordance, we found a close relationship between aggregate stability and wettability with differences between θc and θᵢ being generally small. In addition, aggregate stability turned out to be related to organic carbon content. However, correlation analysis revealed that both persistence of aggregate stability and kinetics of aggregate breakdown were more strongly affected by the contact angle, θc (r=0.90 and r=−0.83, respectively) and θᵢ (r=0.89 and r=−0.76, respectively) than the organic carbon content (r=0.62 and −0.52, respectively), suggesting that stability was primarily controlled by aggregate interfacial properties. Calculation of liquid penetrativity as a function of surface tension and contact angle clearly demonstrated the importance of both solid and liquid interfacial properties in determining the stability of subcritically water repellent aggregates against slaking. ; p. 63-74.
    Keywords: Forest Soils ; Soil Water ; Water Repellent Soils ; Quantitative Analysis ; Aggregate Stability ; Surface Tension ; Soil Aggregates ; Arable Soils ; Pharmacokinetics ; Contact Angle
    ISSN: 0022-1694
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 3
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 05 May 2017, Vol.520, pp.532-543
    Description: Due to the complexity of flow conditions as well as solid matrix and colloid surface properties, solid knowledge about the transport of iron oxide colloids in soils remains scarce. In order to analyze the influence of flow conditions on iron oxide colloid transport and retention, breakthrough behavior of negatively charged, organic matter-coated goethite (OMCG) colloids in saturated quartz sand columns was investigated under continuous and stagnant flow conditions. Classic DLVO and extended DLVO (XDLVO) interaction energies including Lewis acid/base parameters were evaluated using measurements of sessile drop contact angles and zeta potentials of OMCG colloids and quartz. Results elucidated that under continuous flow conditions, OMCG colloids were highly mobile, which was in agreement with calculated unfavorable attachment conditions revealed by predictions of both DLVO approaches. In contrast, during intervals of flow interruption, significant amounts of OMCG colloids were retained in the solid matrix and could not be remobilized via re-establishment of flow. The magnitude of colloid retention increased with the duration of flow interruption; OMCG colloids were almost completely immobilized after 112 h. Further experiments were conducted in order to determine possible colloid retention mechanisms. Results indicated that the major cause for retention during flow stagnation was OMCG colloid capture at locations with attractive DLVO/XDLVO interactions, promoted by fast gravitational settling of colloids onto the solid matrix. We compared breakthrough curves to model predictions, where we demonstrated that an attachment term with a stagnant fluid switch was required in the mass balance in order to reproduce the measurements. We conclude that high mobility of OMCG colloids and prediction of that transport behavior with the applied DLVO approaches were only valid under continuous flow conditions. Under more discontinuous hydraulic conditions relevant in natural soils, such as flow interruption, OMCG colloid transport behavior was modified significantly.
    Keywords: Iron Oxide Colloids ; Flow Interruption ; Dlvo ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 4
    Language: English
    In: Journal of Hydrology, 2010, Vol.382(1), pp.10-19
    Description: An accurate method to determine contact angles (CA) of soils as a measure of water repellency is still missing. In the present research, we evaluated and compared different methods to determine the CA of dry soil samples. Experiments were made by using a set of porous materials (silt, sand and glass beads) with different levels of water repellency. The CAs were measured with the Capillary Rise Method ( ; liquid penetration into a 3-d system), the Wilhelmy plate method ( ; measurement of capillary forces acting on a plane sample) and the Sessile Drop Method ( ; optical CA analysis of drop contour on a plane sample). Results were compared with the CAs calculated from capillary rise in long vertical columns ( ), where liquid profiles of the final capillary rise of water and ethanol, respectively, were used to derive the contact angle under the assumed equilibrium conditions. The results showed the overestimation of the CA by using the well established bi-liquid CRM technique for porous materials, in particular for material with a low degree of water repellency (CA 〈 40°) and for the finer textured materials. In contrast, a variant of the Wilhelmy plate method, i.e. the cosine-averaged advancing CA and receding CA ( ), as well as the Sessile Drop CA, , were close to the ones of . We concluded that and are apparent CA, but nevertheless able to predict the impact of wettability on the final capillary rise which is affected by pore topology as well as by wettability.
    Keywords: Capillary Rise ; Contact Angle ; Mixed Water Repellency ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Source: ScienceDirect Journals (Elsevier)
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  • 5
    Language: English
    In: Journal of Hydrology, 25 March 2013, Vol.484, pp.45-54
    Description: ► In a sandy soil the persistence of water repellency increases with depth. ► Stable contact angles in the subsoil were determined in the laboratory. ► Ponded infiltration showed slight saturation overshoot indicating unstable flow. ► The excavated tracer pattern was conical shaped. ► The persistent water repellency triggered the non-ideal dye pattern. Despite growing knowledge about water repellent soils it is not well investigated how soil water repellency (SWR) of a lower level influences the in situ water infiltration into soils. Hence, we investigated a sandy soil where we found subcritical water repellency and unexpected stable (persistent) contact angles (CAs) in the subsoil characterized by CA measurements in the laboratory. To characterize the influence of this persistence on in situ water infiltration, a ponded tracer infiltration experiment was carried out. During the infiltration, hydraulic sensors revealed a slight saturation at the wetting front which is a sign for unstable flow. The excavated dye-stained infiltration zone was conical and its lateral extent decreased with increasing depth, showing characteristics of a macro-finger. We suggest the subsoil to exhibit a strong hysteretic water retention characteristic governing the infiltration process, but we could not verify this by standard laboratory measurements, as strongly persistent SWR prevented the fast wetting of the soil samples. Close to saturation the persistence of SWR led to a wetting period of soil samples of at least 56 days to overcome SWR and reaching an equilibrium state. There are three major conclusions of this study: 1. In contrast to many other studies we found persistent SWR also in the subsoil and not only in the humic topsoil, 2. The shape of the wetting front is contrary to common expectations for homogeneous sandy soils and 3. The wettability characteristics found might also be relevant for assessing infiltration dynamics at other sites regarding the fact that those observations are not obvious.
    Keywords: Stable Contact Angles ; Ponded Infiltration ; Unstable Flow ; Macro-Finger ; Water Repellency ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 20 August 2013, Vol.431, pp.150-160
    Description: The effect of grain water repellency on transport and deposition of hydrophilic colloids was studied by analyzing the breakthrough behavior of carboxylate-modified microspheres in water-saturated wettable and hydrophobic sand columns at different ionic strengths. Interaction free energies calculated from zeta ( )-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Experimental breakthrough data could be well described with the finite-element code HYDRUS-1D using a one kinetic site model with attachment and detachment kinetics. Higher colloid deposition rates found for the hydrophobic sand could primarily be explained by its small electron-donor component of surface free energy ( = 1.6 × 10 mJ m , compared to = 64.1 mJ m for the wettable sand), leading to strongly attractive acid–base interactions at separation distances 〈 5 nm. Increasing ionic strength reduced the repulsive electrostatic interactions and generally increased colloid deposition with the effect being more pronounced in the hydrophobic sand. It can be concluded that grain water repellency tends to increase the deposition of negatively charged hydrophilic colloids, which can be ascribed to specific acid–base interactions. However, our results further revealed that the calculated interaction free energy profiles should be considered only as an approximation showing general trends because surface chemical heterogeneity as detected by atomic forces microscopy impeded the determination of the actual interaction energy conditions, resulting in an overestimation of electrostatic repulsion.
    Keywords: Acid–Base Interaction ; Carboxylate-Modified Microspheres ; Colloid Breakthrough ; Interaction Free Energy ; Surface Free Energy Components ; Wettability ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 7
    Language: English
    In: Colloids and surfaces, 2013, Vol.431, pp.150-160
    Description: The effect of grain water repellency on transport and deposition of hydrophilic colloids was studied by analyzing the breakthrough behavior of carboxylate-modified microspheres in water-saturated wettable and hydrophobic sand columns at different ionic strengths. Interaction free energies calculated from zeta (ζ)-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Experimental breakthrough data could be well described with the finite-element code HYDRUS-1D using a one kinetic site model with attachment and detachment kinetics. Higher colloid deposition rates found for the hydrophobic sand could primarily be explained by its small electron-donor component of surface free energy (γₛ ⁻=1.6×10⁻²mJm⁻², compared to γₛ ⁻=64.1mJm⁻² for the wettable sand), leading to strongly attractive acid–base interactions at separation distances〈5nm. Increasing ionic strength reduced the repulsive electrostatic interactions and generally increased colloid deposition with the effect being more pronounced in the hydrophobic sand. It can be concluded that grain water repellency tends to increase the deposition of negatively charged hydrophilic colloids, which can be ascribed to specific acid–base interactions. However, our results further revealed that the calculated interaction free energy profiles should be considered only as an approximation showing general trends because surface chemical heterogeneity as detected by atomic forces microscopy impeded the determination of the actual interaction energy conditions, resulting in an overestimation of electrostatic repulsion. ; p. 150-160.
    Keywords: Models ; Sand ; Colloids ; Hydrophilicity ; Electrostatic Interactions ; Microscopy ; Hydrophobicity ; Energy ; Contact Angle ; Ionic Strength
    ISSN: 0927-7757
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 8
    Language: German
    Description: Einleitung: Eine Gefahr bei HNO-Eingriffen ist ein bis dahin unentdeckter, atypischer Gefäßverlauf der A. carotis (z.B. ein Kinking der ACI), da dies u.U. zu gravierenden hämorrhagischen Komplikationen führen kann; die Spanne derartiger atypischer Gefäßverläufe wird in der Literatur mit 10-56% angegeben. Zur Risikominimierung ist daher bei einem klinischen Verdacht eine adäquate präoperative Diagnostik zwingend angezeigt. Material: Es werden 4 Fälle mit entsprechenden Gefäßanomalien vorgestellt: bei 3 Kindern zeigten sich vor AT bzw. TE auffällige Befunde im Epi- bzw. im Oropharynx. Bei einem Erwachsenen zeigte sich im Rahmen einer Neck Dissection ein abnormer Verlauf der ACC im Halsbereich. Ergebnisse: In 2 Fällen wurde vor der geplanten Operation zunächst ein Angio-MRT durchgeführt, um eine dezidierte Aussage zur vorliegenden Gefäßsituation zu erhalten. Die Eingriffe konnten daraufhin unter endoskopischer Kontrolle durchgeführt werden. In einem Fall wurde wegen der besonderen Gefäßsituation von der Operation Abstand genommen. Im Fall der Neck Dissection handelte es sich um einen intraoperativen Zufallsbefund, erst die postoperativ veranlasste 3D-Rekonstruktion der Bilddaten konnte den atypischen Gefäßverlauf darstellen. Schlussfolgerung: Ungewöhnliche Gefäßverläufe, wie z.B. das Kinking der A. carotis, stellen meist Zufallsbefunde dar. Insofern ist hier auch vor hno-ärztlichen Routineoperationen wie...
    Keywords: Medical Sciences; Medicine
    ISSN: 1865-1038
    Source: DataCite
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  • 9
    Language: English
    In: Journal of Soils and Sediments, 2012, Vol.12(1), pp.75-85
    Description: Byline: Gawan Jacob Hilma Muehl (1), Joerg Ruehlmann (1), Marc-Oliver Goebel (2), Joerg Bachmann (2) Keywords: Film; Fluorescence; Porous media; Segmentation; Visualization; Wettability Abstract: Purpose Wettability affects water configuration and thereby transport processes and microbial activity in soil. Approaches to visualize the effect of porous media wettability on water films surrounding particles are rarely available in the literature. The aim of this study is therefore (1) to visualize the effect of wettability on area and connectivity of the water phase and (2) to develop a segmentation strategy to enable water films and bulk water to be differentiated. Materials and methods Wettability of silica sand was rendered by silanization using dichlorodimethylsilane. The resulting contact angle was measured using the sessile drop method. Furthermore, wettability was characterized by the water penetration time test in air-dry samples and at a volumetric water content of 8 vol.%. Sulforhodamine B was used to stain distilled water at a concentration of 40 mg/l. By means of the Wilhelmy plate method, the influence of the dye on the liquid surface tension was tested. Confocal laser scanning microscopy (CLSM) was used to visualize the area and connectivity of the fluorescent-dyed water phase and the thickness of water films in untreated and silanized samples at water contents of 8, 16, and 32 vol.%. Results and discussion The silanization significantly increased the contact angle of silica sand, whereas the surface tension of the dye solution did not differ significantly from that of undyed water. CLSM visualized the distribution of water, focused across the surface grain layer. Thresholding of fluorescence signal in two-dimensional intensity projections enables the discrimination between film and bulk water. It was shown that even subcritical water repellency (contact angle 〈90) leads to a decrease in area and connectivity of the water phase by affecting film instead of bulk water. CLSM detects decreasing effects of wettability with increasing water content, which were no longer significant at a water content of 32 vol.%. CLSM was found to be more sensitive for detecting the effects of wettability than the water drop penetration time test. Conclusions CLSM provides new insight into wettability-dependent water configuration. One advantage over conventional microscopy arises from the capability to visualize water focused over the pore space. Compared to other three-dimensional imaging techniques, the advantage of CLSM is its simplicity. If only the optically accessible upper layer of the porous media is of interest, sample preparation, measurements, and image analysis can easily be carried out with a cost- and time-saving setup. Author Affiliation: (1) Institute of Vegetable and Ornamental Crops Grossbeeren/Erfurt, Theodor-Echtermeyer-Weg 1, 14979, Grossbeeren, Germany (2) Institute of Soil Science, Leibniz University of Hannover, Herrenhauser Str. 2, 30419, Hannover, Germany Article History: Registration Date: 29/06/2011 Received Date: 02/03/2011 Accepted Date: 27/06/2011 Online Date: 04/08/2011 Article note: An erratum to this article can be found at http://dx.doi.org/10.1007/s11368-011-0422-8
    Keywords: Film ; Fluorescence ; Porous media ; Segmentation ; Visualization ; Wettability
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 10
    Language: English
    In: Journal of Soils and Sediments, 2012, Vol.12(1), pp.116-116
    Description: Byline: Gawan Jacob Hilma Muehl (1), Joerg Ruehlmann (1), Marc-Oliver Goebel (2), Joerg Bachmann (2) Author Affiliation: (1) Institute of Vegetable and Ornamental Crops Grossbeeren/Erfurt, Theodor-Echtermeyer-Weg 1, 14979, Grossbeeren, Germany (2) Institute of Soil Science, Leibniz University of Hannover, Herrenhauser Str. 2, 30419, Hannover, Germany Article History: Registration Date: 22/08/2011 Online Date: 06/09/2011 Article note: The online version of the original article can be found at http://dx.doi.org/10.1007/s11368-011-0395-7.
    Keywords: Environment ; Environmental Physics ; Soil Science & Conservation ; Environment, General ; Agriculture;
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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