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  • 1
    Language: English
    In: PLoS Computational Biology, 2011, Vol.7(4), p.e1002025
    Description: Non-intermingling, adjacent populations of cells define compartment boundaries; such boundaries are often essential for the positioning and the maintenance of tissue-organizers during growth. In the developing wing primordium of Drosophila melanogaster , signaling by the secreted protein Hedgehog (Hh) is required for compartment boundary maintenance. However, the precise mechanism of Hh input remains poorly understood. Here, we combine experimental observations of perturbed Hh signaling with computer simulations of cellular behavior, and connect physical properties of cells to their Hh signaling status. We find that experimental disruption of Hh signaling has observable effects on cell sorting surprisingly far from the compartment boundary, which is in contrast to a previous model that confines Hh influence to the compartment boundary itself. We have recapitulated our experimental observations by simulations of Hh diffusion and transduction coupled to mechanical tension along cell-to-cell contact surfaces. Intriguingly, the best results were obtained under the assumption that Hh signaling cannot alter the overall tension force of the cell, but will merely re-distribute it locally inside the cell, relative to the signaling status of neighboring cells. Our results suggest a scenario in which homotypic interactions of a putative Hh target molecule at the cell surface are converted into a mechanical force. Such a scenario could explain why the mechanical output of Hh signaling appears to be confined to the compartment boundary, despite the longer range of the Hh molecule itself. Our study is the first to couple a cellular vertex model describing mechanical properties of cells in a growing tissue, to an explicit model of an entire signaling pathway, including a freely diffusible component. We discuss potential applications and challenges of such an approach. ; In developing animal tissues, cells can often re-arrange locally and mix relatively freely. However, in some stereotypic and crucially important instances during body development, cells will strictly not intermingle, and instead form sharp boundaries along which they will sort out from each other. This mechanism helps organisms to establish signaling centers and to maintain distinct cellular identities. Often, cells at such boundaries will remain in close physical contact and are morphologically alike. Thus, the boundary itself can be difficult to observe unless the expression status of specific marker genes is monitored experimentally. How are these ‘compartment boundaries’ established? Here we devise a computational model that aims to describe one such boundary in a well-studied animal tissue: the developing wing primordium of . We model the production, diffusion and local sensing of an essential signaling molecule, the protein. We reveal one possible mechanism by which Hedgehog sensing can influence the mechanical properties of cells, and compare the simulated outcome to observations in experimentally perturbed, actual wing discs. Our relatively simple model suffices to establish a straight and stable compartment boundary.
    Keywords: Research Article ; Biology ; Computational Biology ; Developmental Biology
    ISSN: 1553-734X
    E-ISSN: 1553-7358
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  • 2
    Language: English
    In: Hydrology and Earth System Sciences, July 19, 2018, Vol.22(7), p.3903
    Description: pSuspended sediments impact stream water quality by increasing the turbidity and acting as a vector for strongly sorbing pollutants. Understanding their sources is of great importance to developing appropriate river management strategies. In this study, we present an integrated sediment transport model composed of a catchment-scale hydrological model to predict river discharge, a river-hydraulics model to obtain shear stresses in the channel, a sediment-generating model, and a river sediment-transport model. We use this framework to investigate the sediment contributions from catchment and in-stream processes in the Ammer catchment close to T#xFC;bingen in southwestern Germany. The model is calibrated to stream flow and suspended-sediment concentrations. We use the monthly mean suspended-sediment load to analyze seasonal variations of different processes. The contributions of catchment and in-stream processes to the total loads are demonstrated by model simulations under different flow conditions. The evaluation of shear stresses by the river-hydraulics model allows the identification of hotspots and hot moments of bed erosion for the main stem of the Ammer River. The results suggest that the contributions of suspended-sediment loads from urban areas and in-stream processes are higher in the summer months, while deposition has small variations with a slight increase in summer months. The sediment input from agricultural land and urban areas as well as bed and bank erosion increase with an increase in flow rates. Bed and bank erosion are negligible when flow is smaller than the corresponding thresholds of 1.5 and 2.5 times the mean discharge, respectively. The bed-erosion rate is higher during the summer months and varies along the main stem. Over the simulated time period, net sediment trapping is observed in the Ammer River. The present work is the basis to study particle-facilitated transport of pollutants in the system, helping to understand the fate and transport of sediments and sediment-bound pollutants.
    Keywords: Sediment Transport – Models ; Sediment Transport – Analysis ; Water Resource Management – Methods
    ISSN: 1027-5606
    ISSN: 16077938
    E-ISSN: 16077938
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  • 3
    Language: English
    In: Hydrology and Earth System Sciences, Oct 13, 2016, Vol.20(10), p.4159
    Description: Droughts are serious natural hazards, especially in semi-arid regions. They are also difficult to characterize. Various summary metrics representing the dryness level, denoted drought indices, have been developed to quantify droughts. They typically lump meteorological variables and can thus directly be computed from the outputs of regional climate models in climate-change assessments. While it is generally accepted that drought risks in semi-arid climates will increase in the future, quantifying this increase using climate model outputs is a complex process that depends on the choice and the accuracy of the drought indices, among other factors. In this study, we compare seven meteorological drought indices that are commonly used to predict future droughts. Our goal is to assess the reliability of these indices to predict hydrological impacts of droughts under changing climatic conditions at the annual timescale. We simulate the hydrological responses of a small catchment in northern Spain to droughts in present and future climate, using an integrated hydrological model calibrated for different irrigation scenarios. We compute the correlation of meteorological drought indices with the simulated hydrological time series (discharge, groundwater levels, and water deficit) and compare changes in the relationships between hydrological variables and drought indices. While correlation coefficients linked with a specific drought index are similar for all tested land uses and climates, the relationship between drought indices and hydrological variables often differs between present and future climate. Drought indices based solely on precipitation often underestimate the hydrological impacts of future droughts, while drought indices that additionally include potential evapotranspiration sometimes overestimate the drought effects. In this study, the drought indices with the smallest bias were the rainfall anomaly index, the reconnaissance drought index, and the standardized precipitation evapotranspiration index. However, the efficiency of these drought indices depends on the hydrological variable of interest and the irrigation scenario. We conclude that meteorological drought indices are able to identify years with restricted water availability in present and future climate. However, these indices are not capable of estimating the severity of hydrological impacts of droughts in future climate. A well-calibrated hydrological model is necessary in this respect.
    Keywords: Weather – Analysis ; Weather – Models ; Climate Change – Analysis ; Climate Change – Models ; Droughts – Analysis ; Droughts – Models ; Arid Regions – Analysis ; Arid Regions – Models
    ISSN: 1027-5606
    E-ISSN: 16077938
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  • 4
    Language: English
    In: Revista Águas Subterrâneas, 01 February 2015
    Description: Um modelo de transporte reativo foi desenvolvido com intuito de entender a evolução hidrogeoquímica de geração de drenagem ácida de minas (DAM) para o Bota Fora 4 (BF-4) na Mina Osamu Utsumi. O código numérico TOUGHREACT foi utilizado para a geração do modelo bidimensional representado uma seção típica do BF-4. O fluxo dentro da pilha foi considerado como em regime estacionário e os processos geoquímicos foram simulados por um período de 30 anos. Os valores obtidos pelo modelo para carga hidráulica, pH e concentração das principais espécies químicas não reativas relacionadas à DAM equipararam-se àquelas medidas em pontos de observação. O modelo de fluxo indicou que a maior parte do BF-4 encontra-se na zona vadosa, onde baixas velocidades resultam em longo tempo de residência indicando a importância desta zona para os processos geoquímicos. Simulações indicaram que apenas 0,5% da massa inicial de pirita foi consumida o que implica no fato do processo de DAM ter potencial para perdurar por longo tempo. O pH diminui com a profundidade e observa-se um aumento da concentração ao longo do tempo para a maior parte das espécies químicas indicando que o equilíbrio químico na pilha ainda não foi atingido.
    Keywords: Geography
    ISSN: 0101-7004
    E-ISSN: 2179-9784
    Source: Directory of Open Access Journals (DOAJ)
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