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• 1
Article
Language: English
In: Transport in Porous Media, 2016, Vol.112(1), pp.207-227
Description: According to experimental observations, capillary trapping is strongly dependent on the roughness of the pore–solid interface. We performed imbibition experiments in the range of capillary numbers ( Ca ) from $$10^{-6}$$ 10 - 6 to $$5\times 10^{-5}$$ 5 × 10 - 5 using 2D-micromodels, which exhibit a rough surface. The microstructure comprises a double-porosity structure with pronounced macropores. The dynamics of precursor thin-film flow and its importance for capillary trapping are studied. The experimental data for thin-film flow advancement show a square-root time dependence. Based on the experimental data, we conducted inverse modeling to investigate the influence of surface roughness on the dynamic contact angle of precursor thin-film flow. Our experimental results show that trapped gas saturation decreases logarithmically with an increasing capillary number. Cluster analysis shows that the morphology and number of trapped clusters change with capillary number. We demonstrate that capillary trapping shows significant differences for vertical flow and horizontal flow. We found that our experimental results agree with theoretical results of percolation theory for $$Ca =10^{-6}$$ C a = 10 - 6 : (i) a universal power-like cluster size distribution, (ii) the linear surface–volume relationship of trapped clusters, and (iii) the existence of the cutoff correlation length for the maximal cluster height. The good agreement is a strong argument that the experimental cluster size distribution is caused by a percolation-like trapping process (ordinary percolation). For the first time, it is demonstrated experimentally that the transition zone model proposed by Wilkinson (Phys Rev A 30:520–531, 1984) can be applied to 2D-micromodels, if bicontinuity is generalized such that it holds for the thin-film water phase and the bulk gas phase.
Keywords: 2D-micromodel with rough surface ; Precursor thin-film flow ; Snap-off trapping ; Universal power law ; Ordinary bond percolation
ISSN: 0169-3913
E-ISSN: 1573-1634
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• 2
Article
Language: English
In: Plant and Soil, 2010, Vol.332(1), pp.163-176
Description: Water flow from soil to plants depends on the properties of the soil next to roots, the rhizosphere. Although several studies showed that the rhizosphere has different properties than the bulk soil, effects of the rhizosphere on root water uptake are commonly neglected. To investigate the rhizosphere’s properties we used neutron radiography to image water content distributions in soil samples planted with lupins during drying and subsequent rewetting. During drying, the water content in the rhizosphere was 0.05 larger than in the bulk soil. Immediately after rewetting, the picture reversed and the rhizosphere remained markedly dry. During the following days the water content of the rhizosphere increased and after 60 h it exceeded that of the bulk soil. The rhizosphere’s thickness was approximately 1.5 mm. Based on the observed dynamics, we derived the distinct, hysteretic and time-dependent water retention curve of the rhizosphere. Our hypothesis is that the rhizosphere’s water retention curve was determined by mucilage exuded by roots. The rhizosphere properties reduce water depletion around roots and weaken the drop of water potential towards roots, therefore favoring water uptake under dry conditions, as demonstrated by means of analytical calculation of water flow to a single root.
Keywords: Root water uptake ; Water retention curve ; Rhizosphere ; Neutron radiography ; Mucilage ; Hysteresis
ISSN: 0032-079X
E-ISSN: 1573-5036
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• 3
Article
Language: English
In: Environmental Earth Sciences, 2013, Vol.69(2), pp.317-333
Description: Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/ ) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples.
Keywords: Water and solute fluxes ; Water quality ; Catchments ; Land-surface atmosphere exchange ; Processes and feedbacks ; Modeling ; Monitoring
ISSN: 1866-6280
E-ISSN: 1866-6299
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• 4
Article
Language: English
In: Environmental Earth Sciences, 2017, Vol.76(1), pp.1-25
Description: This article provides an overview about the Bode River catchment that was selected as the hydrological observatory and main region for hydro-ecological research within the TERrestrial ENvironmental Observatories Harz/Central German Lowland Observatory. It first provides information about the general characteristics of the catchment including climate, geology, soils, land use, water quality and aquatic ecology, followed by the description of the interdisciplinary research framework and the monitoring concept with the main components of the multi-scale and multi-temporal monitoring infrastructure. It also shows examples of interdisciplinary research projects aiming to advance the understanding of complex hydrological processes under natural and anthropogenic forcings and their interactions in a catchment context. The overview is complemented with research work conducted at a number of intensive research sites, each focusing on a particular functional zone or specific components and processes of the hydro-ecological system.
Keywords: Monitoring ; Catchment ; Water quality ; Observatory ; Water fluxes
ISSN: 1866-6280
E-ISSN: 1866-6299
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• 5
Article
Language: English
In: Wireless Personal Communications, 1999, Vol.11(1), pp.45-62
Description: One of the most widely used buzzwords in mobile communications of the recent years is Space Division Multiple Access (SDMA). The introduction of an additional space domain multiple access component is likely to boost system capacity, due to the spatial reuse of physical channels within one cell. While early approaches of SDMA system modelling show capacity to be gained in the order of 300 to 400%, there remains some more in depth system analysis to be done, as inhomogeneities in the user distribution are expected to likely cause dramatic drops in the additional capacity gained by SDMA. The spatial distribution of terminals directly influences the number of channels to be gained by spatial multiplexing. Therefore, it is not until detailed models for user distribution, user mobility and the traffic load generated by users are combined with a model of the SDMA radio subsystem, that realistic approximations for these capacity gains are possible. In this paper, we discuss the issues in modelling and simulation of SDMA systems. We present an approach for integrated SDMA system modelling, discuss analytic teletraffic dimensioning methods for macro- and microcellular environments and their relevance to SDMA systems, and present some early simulation results.
Keywords: SDMA ; smart antenna systems ; capacity ; traffic models ; mobility models ; simulation
ISSN: 0929-6212
E-ISSN: 1572-834X
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• 6
Article
Language: German
In: Medizinische Klinik, 1997, Vol.92(7), pp.410-414
Description: Die Anwendung hämatopoetischer Wachstumsfaktoren und die Retransfusion patienteneigener, aus dem Blut gewonnener peripherer Blutstammzellen (PBSZ) hat in den letzten Jahren die Option zur Durchführung einer Hochdosischemotherapie (HDT) auch bei fortgeschrittenen soliden Tumoren ermöglicht. Da mit der Transfusion von peripheren Blutstammzellen die Myelosuppression beherrschbar wurde, bestimmt die nichthämatologische Toxizität den Grad der Dosiseskalation.In der Regel wurden Hochdosischemotherapien nach vorausgegangener dosisintensivierter Chemotherapie durchgeführt. Durch die vorgeschaltete Chemotherapie soll einerseits die Chemosensibilität der Tumorerkrankung nachgewiesen und andererseits eine Stammzellmobilisierung bewirkt werden. Früher wurde die Hochdosischemotherapie durch eine autologe Knochenmarktransplantation (AKMT), heute fast ausnahmslos durch die Retransfusion von peripheren Blutstammzellen als spezifische Supportivmaßnahme begleitet. Die peripheren Blutstammzellen werden durch die Apherese der mononukleären Zellfraktion am Zellseparator gesammelt.Nennenswerte Erfahrungen mit der Hochdosischemotherapie beim Erwachsenen liegen für das Mamma-, Hoden-, Ovarial-, kleinzellige Bronchialkarzinom (SCLC), Melanom, Glioblastom und Weichgewebssarkom vor. Die Studien belegen die Durchführbarkeit und Effektivität der Hochdosischemotherapie bei tolerabler Toxizität.Die Hochdosischemotherapie wird zukünftig eine zunehmende Bedeutung in dem primären Chemotherapiekonzept von soliden Tumoren bekommen.The availability of hemopoetic growth factors and the retransfusion of autologous peripheral blood stem cells (PBSC) have enabled high-dose chemotherapy (HDT) options for the treatment of advanced solid tumours, during recent years. Though the transfusion of PBSC can manage the myelosuppression, dose-escalation ist still limited by non-haematological toxicity.Usually, HDT has been given after a preceeding dose-intense chemotherapy that allowed the evaluation of chemosensitivity of the disease and resulted in a stem cell mobilization into the peripheral blood. The autologous bone marrow transplantation has almost completely been replaced by retransfusion of PBSC together with hemopoetic growth factors as specific supportive treatment. The PBSC are harvested by apheresis using a blood cell separator.Results on the efficacy of HDT are available for breast, testicular, ovarian, small cell lung cancer as well as melanoma, glioblastoma and soft-tissue sarcoma. The studies showed the feasibility and efficacy of HDT with tolerable toxicity.High-dose chemotherapy will be of increasing importance in the treatment strategies of primary solid tumors, in the near future.
Keywords: High-dose chemotherapy ; Peripheral blood stem cells ; Solid tumors
ISSN: 0723-5003
E-ISSN: 1615-6722
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• 7
Article
Language: English
In: Annals of Hematology, 1992, Vol.65, pp.A1-A146
ISSN: 0939-5555
E-ISSN: 1432-0584
Source: Springer Science & Business Media B.V.
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