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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of The Electrochemical Society, 2016, Vol.163(8), pp.A1595-A1606
    ISSN: 0013-4651
    E-ISSN: 1945-7111
    Source: Electrochemical Society (ECS) (via CrossRef)
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  • 2
    Language: English
    In: PLoS ONE, 01 January 2016, Vol.11(7), p.e0159948
    Description: Matter turnover in soil is tightly linked to soil structure which governs the heterogeneous distribution of habitats, reaction sites and pathways in soil. Thereby, the temporal dynamics of soil structure alteration is deemed to be important for essential ecosystem functions of soil but very little is known about it. A major reason for this knowledge gap is the lack of methods to study soil structure turnover directly at microscopic scales. Here we devise a conceptual approach and an image processing workflow to study soil structure turnover by labeling some initial state of soil structure with small garnet particles and tracking their fate with X-ray microtomography. The particles adhere to aggregate boundaries at the beginning of the experiment but gradually change their position relative to the nearest pore as structure formation progresses and pores are destructed or newly formed. A new metric based on the contact distances between particles and pores is proposed that allows for a direct quantification of soil structure turnover rates. The methodology is tested for a case study about soil compaction of a silty loam soil during stepwise increase of bulk density (ρ = {1.1, 1.3, 1.5} g/cm3). We demonstrate that the analysis of mean contact distances provides genuinely new insights about changing diffusion pathways that cannot be inferred neither from conventional pore space attributes (porosity, mean pore size, pore connectivity) nor from deformation analysis with digital image correlation. This structure labeling approach to quantify soil structure turnover provides a direct analogy to stable isotope labeling for the analysis of matter turnover and can be readily combined with each other.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 3
    Language: English
    In: Journal of Power Sources, 15 September 2013, Vol.238, pp.422-429
    Description: Electrochemical double layer capacitors (EDLCs) are conceived as high power devices. Generally, power improvement is mainly related to lowering the device impedance (  =  /4 ). However, the supercapacitor impedance is the sum of several contributions (electrolyte, active material, contact between the active material and the current collector, electrode porosity). In this work we demonstrate that the resistance at the interface between the electrode and the current collector and as well the diffusion resistance can be properly controlled during the electrode preparation. In our preparation method the electrodes are compacted by using a hot-press device. During the electrode fabrication parameters such as temperature and pressure are systematically modulated in order to find the best condition for increasing the contact between the electrode and the current collector while maintaining good electrode porosity.
    Keywords: Activated Carbon ; Supercapacitors ; Impedance Spectroscopy ; Electrode Porosity ; Image Analysis ; Engineering
    ISSN: 0378-7753
    E-ISSN: 1873-2755
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  • 4
    In: Physical Chemistry Chemical Physics, 2018, Vol.20(33), pp.21417-21429
    Description: Measurements of the open circuit voltage of Li-ion cells have been extensively used as a non-destructive characterisation tool. Another technique based on entropy change measurements has also been applied for this purpose. More recently, both techniques have been used to make qualitative statements about aging in Li-ion cells. One proposed cause of cell failure is point defect formation in the electrode materials. The steps in voltage profiles, and the peaks in entropy profiles are sensitive to order/disorder transitions arising from Li/vacancy configurations, which are affected by the host lattice structures. We compare the entropy change results, voltage profiles and incremental capacity (d Q /d V ) obtained from coin cells with spinel lithium manganese oxide (LMO) cathodes, Li 1+ y Mn 2 y O 4 , where excess Li y was added in the range 0 y 0.2. A clear trend of entropy and d Q /d V peak amplitude decrease with excess Li amount was determined. The effect arises, in part, from the presence of pinned Li sites, which disturb the formation of the ordered phase. We modelled the voltage, d Q /d V and entropy results as a function of the interaction parameters and the excess Li amount, using a mean field approach. For a given pinning population, we demonstrated that the asymmetries observed in the d Q /d V peaks can be modelled by a single linear correction term. To replicate the observed peak separations, widths and magnitudes, we had to account for variation in the energy interaction parameters as a function of the excess Li amount, y . All LiLi repulsion parameters in the model increased in value as the defect fraction, y , increased. Our paper shows how far a computational mean field approximation can replicate experimentally observed voltage, incremental capacity and entropy profiles in the presence of phase transitions.
    Keywords: Lithiumionenbatterie ; Spannungsform ; Kathode ; Gitterstruktur ; Amplitude ; Wechselwirkungsparameter ; Elektrodenwerkstoff ; Lithiumoxid ; Strukturverhalten ; Punktfehler ; Gelände ; Leerlaufspannung ; Spannung (Elektrisch) ; Separation ; Replikat ; Erdbebenmagnitude ; Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 5
    Language: English
    In: PLoS ONE, 01 January 2018, Vol.13(3), p.e0193669
    Description: X-ray CT is a powerful technology to study root growth in soil in-situ. Root systems can be studied in its true 3D geometry over time. Hence, the same plant can be scanned multiple times during development. A downside is the potential of X-rays to interfere with biological processes and therefore plant growth. The aim of this study is to evaluate the influence of cumulative X-ray dose on Vicia faba and Hordeum vulgare during a growth period of 17 days. One control treatment without X-ray scanning was compared to two treatments being scanned every two and four days, respectively. Scanned treatments received a maximum cumulative dose of less than 8 Gy. Plant species differed in their susceptibility to X-ray dose. For Vicia faba, mean total root length was reduced significantly. Leave growth was reduced as well. Number and length of second order laterals was reduced significantly, as well as length of first order laterals. Hordeum vulgare showed no negative impact of X-ray dose on any of the root parameters. Large differences between the two species investigated were detected in respect to susceptibility to X-ray dose. Results indicate that for X-ray CT studies involving temporal resolution a control treatment without scanning is required.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 6
    In: Global Change Biology, April 2018, Vol.24(4), pp.1637-1650
    Description: Global change contributes to the retreat of glaciers at unprecedented rates. The deglaciation facilitates biogeochemical processes on glacial deposits with initiating soil formation as an important driver of evolving ecosystems. The underlying mechanisms of soil formation and the association of soil organic matter () with mineral particles remain unclear, although further insights are critical to understand carbon sequestration in soils. We investigated the microspatial arrangement of coatings at intact soil microaggregate structures during various stages of ecosystem development from 15 to 〉700 years after deglaciation in the proglacial environment of the Damma glacier (Switzerland). The functionally important clay‐sized fraction (2.2 g/cm). To quantify how extends across the surface of mineral particles (coverage) and whether coatings are distributed in fragmented or connected patterns (connectivity), we developed an image analysis protocol based on nanoscale secondary ion mass spectrometry (Nano). We classified and mineral areas depending on the O, C, and CN distributions. With increasing time after glacial retreat, the microspatial coverage and connectivity of increased rapidly. The rapid soil formation led to a succession of patchy distributed to more connected coatings on soil microaggregates. The maximum coverage of 55% at 〉700 years suggests direct evidence for sequestration being decoupled from the mineral surface, as it was not completely masked by and retained its functionality as an ion exchange site. The chemical composition of coatings showed a rapid change toward a higher :C ratio already at 75 years after glacial retreat, which was associated with microbial succession patterns reflecting high N assimilation. Our results demonstrate that rapid sequestration drives the microspatial succession of coatings in soils, a process that can stabilize for the long term. The pronounced retreat of glaciers due to climate change leads to the exposure of glacial deposits where initial soil formation starts along with the accrual of soil carbon. Soil organic matter (SOM) coatings at soil microaggregates were investigated in a chronosequence of soils 15 to 〉700 years after glacial retreat at the Damma glacier (Switzerland). Our results show a rapidly increasing coverage of mineral surfaces by SOM up to a maximum of 55% and a development from patchy distributed to more connected SOM coatings. The microspatial patterns of SOM coatings shaped the sequestration of SOM and partially decoupled it from the mineral particle surfaces, which retain their functionality as an ion exchange sites.
    Keywords: Biogeochemical Soil Interfaces ; Glacier Forefield ; Mineral‐Associated Organic Matter ; Nanoscale Secondary Ion Mass Spectrometry ; Organic Coating ; Organo‐Mineral Associations ; Soil Carbon Sequestration ; Spatial Complexity
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 7
    Language: English
    In: PLoS ONE, 2011, Vol.6(5), p.e19931
    Description: The actin cytoskeleton is continuously remodeled through cycles of actin filament assembly and disassembly. Filaments are born through nucleation and shaped into supramolecular structures with various essential functions. These range from contractile and protrusive assemblies in muscle and non-muscle cells to actin filament comets propelling vesicles or pathogens through the cytosol. Although nucleation has been extensively studied using purified proteins in vitro, dissection of the process in cells is complicated by the abundance and molecular complexity of actin filament arrays. We here describe the ectopic nucleation of actin filaments on the surface of microtubules, free of endogenous actin and interfering membrane or lipid. All major mechanisms of actin filament nucleation were recapitulated, including filament assembly induced by Arp2/3 complex, formin and Spir. This novel approach allows systematic dissection of actin nucleation in the cytosol of live cells, its genetic re-engineering as well as screening for new modifiers of the process.
    Keywords: Research Article ; Biology ; Cell Biology ; Biophysics
    E-ISSN: 1932-6203
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  • 8
    Language: English
    In: Environmental Modelling and Software, May 2014, Vol.55, pp.32-48
    Description: In this study we describe and compare four numerical methods for the generation of random fields with a truncated power-law variogram; the Fourier method, the Randomization method, the Hybrid method as well as the Fourier–Wavelet method. We evaluate these methods with respect to their ability to represent the variogram function over a number of spatial scales as well as the Gaussianity of the generated fields. We furthermore compare these methods with respect to computational costs and investigate structural features. Results show that the Randomization method performs well if only a few number of spatial scales (4–6 orders of magnitude) need to be represented. Due to its simpler implementation it can be preferred over the Fourier–Wavelet method. For a larger interval of spatial scales (9–12 orders of magnitude) however, the Randomization method fails to represent the variogram. Under such circumstances the Hybrid method or the Fourier–Wavelet method should be used. The Matlab code, used for the simulations can be accessed on our institution website at .
    Keywords: Random Fields ; Numerical Methods ; Variogram Function ; Truncated Power Law ; Fractal Fields ; Hierarchical Fields ; Connectivity ; Engineering ; Environmental Sciences ; Computer Science ; Ecology
    ISSN: 1364-8152
    E-ISSN: 1873-6726
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  • 9
    Language: English
    In: Advances in Water Resources, 2011, Vol.34(2), pp.314-325
    Description: ► Stochastic reconstruction with a combination of multi-point statistics. ► Good rendition of connectivity with Minkowski functions and Chord length distributions. ► Transport behavior compares well between reference media and reconstructed media. ► Pressure field tends to bridge local discontinuities within highly conductive regions. Flow and transport in porous media is determined by its structure. Beside spatial correlation, especially the connectivity of heterogeneous conductivities is acknowledged to be a key factor. This has been demonstrated for well defined random fields having different topological properties. Yet, it remains an open question which morphological measures carry sufficient information to actually predict flow and transport in porous media. We analyze flow and transport in classical, two-dimensional random fields showing different topology and we determine a selection of structural characteristics including classical two-point statistics, chord-length distribution and Minkowski functions (four-point statistics) including the Euler number as a topological measure. Using the approach of simulated annealing for global optimization we generate analog random fields that are forced to reproduce one or several of theses structural characteristics. Finally we evaluate in how far the generated analogons reproduce the original flow and transport behavior as well as some more elaborate structural characteristics including percolation probabilities and the pair connectivity function. The results confirm that two-point statistics is insufficient to capture functional properties since it is not sensitive to connectivity. In contrast, the combination of Minkowski functions and chord length distributions carries sufficient information to reproduce the breakthrough curve of a conservative solute. Hence, global topology provided by the Euler number together with local clustering provided by the chord length distribution seems to be a powerful condensation of structural complexity with respect to functional properties.
    Keywords: Simulated Annealing ; Solute Transport ; Minkowski Functionals ; Chord Length Distribution ; Local Percolation Probability ; Pair Connectivity Function ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 10
    Language: English
    In: Advances in Water Resources, August 2012, Vol.44, pp.101-112
    Description: ► New averaging approach that conserves hydraulic non-equilibrium during rapid infiltration of water. ► New indicators to describe hydraulic non-equilibrium quantitatively. ► Direct link between front morphology and hydraulic non-equilibrium. ► Insights into how structural connectivity affects hydraulic non-equilibrium. ► Shortcomings of an upscaled Richards model extended by hydraulic non-equilibrium. Water infiltration into heterogeneous, structured soil leads to hydraulic non-equilibrium across the infiltration front. That is, the water content and pressure head are not in equilibrium according to some static water retention curve. The water content increases more rapidly in more conductive regions followed by a slow relaxation towards an equilibrium state behind the front. An extreme case is preferential infiltration into macropores. Since flow paths adapt to the structural heterogeneity of the porous medium, there is a direct link between structure and non-equilibrium. The aim of our study is to develop an upscaled description of water dynamics which conserves the macroscopic effects of non-equilibrium and which can be directly linked to structural properties of the material. A critical question is how to define averaged state variables at the larger scale. We propose a novel approach based on flux-weighted averaging of pressure head, and compare its performance to alternative methods for averaging. Further, we suggest some meaningful indicators of hydraulic non-equilibrium that can be related to morphological characteristics of infiltration fronts in quantitative terms. These methods provide a sound basis to assess the impact of structural connectivity on hydraulic non-equilibrium. We demonstrate our approach using numerical case studies for infiltration into two-dimensional heterogeneous media using three different structure models with distinct differences in connectivity. Our results indicate that an increased isotropic, short-range connectivity reduces non-equilibrium, whereas anisotropic structures that are elongated in the direction of flow enforce it. We observe a good agreement between front morphology and effective hydraulic non-equilibrium. A detailed comparison of averaged state variables with results from an upscaled model that includes hydraulic non-equilibrium outlines potential improvements in the description of non-equilibrium dynamics including preferential flow in simplified, upscaled models based on Richards equation.
    Keywords: Transient Flow ; Upscaling ; Pressure Head Averaging ; Hydraulic Non-Equilibrium ; Preferential Flow ; Connectivity ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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