The Experts below are selected from a list of 12 Experts worldwide ranked by ideXlab platform

Steffen Birk - One of the best experts on this subject based on the ideXlab platform.

  • Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers
    Hydrology and Earth System Sciences, 2011
    Co-Authors: B. Hubinger, Steffen Birk
    Abstract:

    Abstract. Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete Pathways along fractures or bedding planes, thus creating highly conductive solution Conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving Conduit systems the aperture-size frequency distributions resulting from generic models of Conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoConduits are represented by tubes with log-normally distributed aperture sizes with a mean μ0 = 0.5 mm for the logarithm of the diameters. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of Conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving Conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a Conduit Pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a Conduit Pathway is inhibited and the Conduit Pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that Conduit development under suppressed flow conditions may significantly enhance the permeability of the formation, e.g. in deep-seated carbonate settings.

  • Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers
    2011
    Co-Authors: B. Hubinger, Steffen Birk
    Abstract:

    Abstract. Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete Pathways along fractures or bedding planes, thus creating highly conductive solution Conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving Conduit systems the aperture-size frequency distributions resulting from generic models of Conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoConduits are represented by tubes with log-normally distributed aperture sizes with a mean of 0.5 mm. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of Conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving Conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a Conduit Pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a Conduit Pathway is inhibited and the Conduit Pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that Conduit development under suppressed flow conditions may significantly enhance the permeability of the formation e.g. in deep-seated carbonate settings.

B. Hubinger - One of the best experts on this subject based on the ideXlab platform.

  • Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers
    Hydrology and Earth System Sciences, 2011
    Co-Authors: B. Hubinger, Steffen Birk
    Abstract:

    Abstract. Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete Pathways along fractures or bedding planes, thus creating highly conductive solution Conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving Conduit systems the aperture-size frequency distributions resulting from generic models of Conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoConduits are represented by tubes with log-normally distributed aperture sizes with a mean μ0 = 0.5 mm for the logarithm of the diameters. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of Conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving Conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a Conduit Pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a Conduit Pathway is inhibited and the Conduit Pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that Conduit development under suppressed flow conditions may significantly enhance the permeability of the formation, e.g. in deep-seated carbonate settings.

  • Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers
    2011
    Co-Authors: B. Hubinger, Steffen Birk
    Abstract:

    Abstract. Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete Pathways along fractures or bedding planes, thus creating highly conductive solution Conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving Conduit systems the aperture-size frequency distributions resulting from generic models of Conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoConduits are represented by tubes with log-normally distributed aperture sizes with a mean of 0.5 mm. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of Conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving Conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a Conduit Pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a Conduit Pathway is inhibited and the Conduit Pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that Conduit development under suppressed flow conditions may significantly enhance the permeability of the formation e.g. in deep-seated carbonate settings.

Yoshitaka Okamura - One of the best experts on this subject based on the ideXlab platform.

  • Total cavopulmonary connection with straight Conduit for apicocaval juxtaposition
    General Thoracic and Cardiovascular Surgery, 2009
    Co-Authors: Takahiro Hisaoka, Takeshi Hiramatsu, Yoshitaka Okamura
    Abstract:

    If the heart is malpositioned with apicocaval juxtaposition (ACJ), what constitutes the ideal course for the Conduit Pathway of a total cavopulmonary connection must be considered. When the Conduit is positioned between the inferior vena cava and the same side of the pulmonary artery behind the ventricle, potential stenosis of the Conduit due to compression by the ventricle or obstruction of the pulmonary vein due to compression by the Conduit must be recognized. We reported two cases of ACJ in which a straight Conduit Pathway behind the ventricle was accomplished. Comprehensive dissection of the heart, especially the posterior side of the ventricle, to make a wide opening into the thoracic cavity is needed to obtain enough space behind the ventricle. Postoperative catheter studies performed 6 months after the operations showed no obstruction or deformity of the Conduit or the pulmonary veins, and the mean pulmonary artery pressure measured 9 mmHg in both patients.

Takahiro Hisaoka - One of the best experts on this subject based on the ideXlab platform.

  • Total cavopulmonary connection with straight Conduit for apicocaval juxtaposition
    General Thoracic and Cardiovascular Surgery, 2009
    Co-Authors: Takahiro Hisaoka, Takeshi Hiramatsu, Yoshitaka Okamura
    Abstract:

    If the heart is malpositioned with apicocaval juxtaposition (ACJ), what constitutes the ideal course for the Conduit Pathway of a total cavopulmonary connection must be considered. When the Conduit is positioned between the inferior vena cava and the same side of the pulmonary artery behind the ventricle, potential stenosis of the Conduit due to compression by the ventricle or obstruction of the pulmonary vein due to compression by the Conduit must be recognized. We reported two cases of ACJ in which a straight Conduit Pathway behind the ventricle was accomplished. Comprehensive dissection of the heart, especially the posterior side of the ventricle, to make a wide opening into the thoracic cavity is needed to obtain enough space behind the ventricle. Postoperative catheter studies performed 6 months after the operations showed no obstruction or deformity of the Conduit or the pulmonary veins, and the mean pulmonary artery pressure measured 9 mmHg in both patients.

Takeshi Hiramatsu - One of the best experts on this subject based on the ideXlab platform.

  • Total cavopulmonary connection with straight Conduit for apicocaval juxtaposition
    General Thoracic and Cardiovascular Surgery, 2009
    Co-Authors: Takahiro Hisaoka, Takeshi Hiramatsu, Yoshitaka Okamura
    Abstract:

    If the heart is malpositioned with apicocaval juxtaposition (ACJ), what constitutes the ideal course for the Conduit Pathway of a total cavopulmonary connection must be considered. When the Conduit is positioned between the inferior vena cava and the same side of the pulmonary artery behind the ventricle, potential stenosis of the Conduit due to compression by the ventricle or obstruction of the pulmonary vein due to compression by the Conduit must be recognized. We reported two cases of ACJ in which a straight Conduit Pathway behind the ventricle was accomplished. Comprehensive dissection of the heart, especially the posterior side of the ventricle, to make a wide opening into the thoracic cavity is needed to obtain enough space behind the ventricle. Postoperative catheter studies performed 6 months after the operations showed no obstruction or deformity of the Conduit or the pulmonary veins, and the mean pulmonary artery pressure measured 9 mmHg in both patients.