Background： Two approaches mark the difference between the ＂ecological＂ and ＂agricultural＂ view of the biodiversity/ growth relation. In ecology the trend is averaged by taking monocultures of all species as base...Background： Two approaches mark the difference between the ＂ecological＂ and ＂agricultural＂ view of the biodiversity/ growth relation. In ecology the trend is averaged by taking monocultures of all species as baseline to evaluate mixtures. This contrasts the ＂agricultural＂ view focusing on the most productive species or species combination as baseline to evaluate mixtures. The present study investigates the change of highest rates （maximum） productivities in grasslands and forests with increasing plant （or tree） diversity, and compares these with the average response. Methods： We base our analysis on existing published datasets relating the growth of plant stands （growth rate per land area） to the diversity on the same plot. We use a global dataset （Ellis et al. 2012 and MODIS-data, see Fig. 1）, the grassland experiment in lena （Buchmann et al. 2017）, the regional study on forests in Romania and Germany by Bouriaud et al. （2016）, and data from the German National Forest inventory （BWl 3, see Fig. 3）. In all cases the average response of growth to changes in biodiversity as well as the boundary line of the maximum values was calculated. Results： in both vegetation types a decreasing trend of maximum productivity with any added species emerges, contrasting the average trend that was positive in grassland, but absent in forests. The trend of maximum values was non-significant in grasslands probably due to the fact that not all combinations of species mixtures were available. In temperate forests, maximum productivity decreases significantly by about 10% in regional studies and by 8% at national scale with each added species. Maximum biomass per area was the same for managed and unmanaged conditions. A global assessment of NPP and biodiversity could also not confirm a general positive biodiversity- productivity relationship. Conclusions： Managed grasslands and forests reach highest productivity and volumes at low diversity. Also globally we could not confirm a biodiversity effect on productivity. Despite this, for long-living organisms, such as trees, the incentive for land managers exists to reduce the risk of failure due to climate extremes and diseases by taking a loss in productivity into account and to actively maintain a mixture of species.展开更多
In this paper the physical influences on the mechanical behavior of a Polyamide 6 (PA 6)/Mont- morillonit (MMT)-nanocomposite are examined by a selected structure modification in a numerical parameter study. Experimen...In this paper the physical influences on the mechanical behavior of a Polyamide 6 (PA 6)/Mont- morillonit (MMT)-nanocomposite are examined by a selected structure modification in a numerical parameter study. Experimental data of tensile tests of three different volume fractions at ambient temperature are used as reference. These were compared to homogenized stress-strain curves calculated with 3D representative volume elements (RVE) under periodic boundary conditions, in which the curve areas are considered until the tensile yield strength is reached. Besides the influence of filler orientation, exfoliation and its volume fraction, both adhesive interface behavior between the filler and matrix, and local partially crystalline interphases around the MMT-plates were also taken into account. A good approximation of the numerical representation of the experimental curves was achieved only after the introduction of the 30 - 40 nm thick partially crystalline interphases with higher stiffness and strength around the MMT-plates. The use of an exclusively isotropic matrix led to an underestimation of the mechanical values. The local modifications of the morphology were assumed to be transversely isotropic both in the elastic and in the plastic region. The transverse plane is defined by the lateral particle surface. Compared with the experimentally determined values of the corresponding Young’s Modulus, an excellent correlation was achieved. The yield strength for the largest volume fraction shows the best agreement with experimental values.展开更多
文摘Background： Two approaches mark the difference between the ＂ecological＂ and ＂agricultural＂ view of the biodiversity/ growth relation. In ecology the trend is averaged by taking monocultures of all species as baseline to evaluate mixtures. This contrasts the ＂agricultural＂ view focusing on the most productive species or species combination as baseline to evaluate mixtures. The present study investigates the change of highest rates （maximum） productivities in grasslands and forests with increasing plant （or tree） diversity, and compares these with the average response. Methods： We base our analysis on existing published datasets relating the growth of plant stands （growth rate per land area） to the diversity on the same plot. We use a global dataset （Ellis et al. 2012 and MODIS-data, see Fig. 1）, the grassland experiment in lena （Buchmann et al. 2017）, the regional study on forests in Romania and Germany by Bouriaud et al. （2016）, and data from the German National Forest inventory （BWl 3, see Fig. 3）. In all cases the average response of growth to changes in biodiversity as well as the boundary line of the maximum values was calculated. Results： in both vegetation types a decreasing trend of maximum productivity with any added species emerges, contrasting the average trend that was positive in grassland, but absent in forests. The trend of maximum values was non-significant in grasslands probably due to the fact that not all combinations of species mixtures were available. In temperate forests, maximum productivity decreases significantly by about 10% in regional studies and by 8% at national scale with each added species. Maximum biomass per area was the same for managed and unmanaged conditions. A global assessment of NPP and biodiversity could also not confirm a general positive biodiversity- productivity relationship. Conclusions： Managed grasslands and forests reach highest productivity and volumes at low diversity. Also globally we could not confirm a biodiversity effect on productivity. Despite this, for long-living organisms, such as trees, the incentive for land managers exists to reduce the risk of failure due to climate extremes and diseases by taking a loss in productivity into account and to actively maintain a mixture of species.
文摘In this paper the physical influences on the mechanical behavior of a Polyamide 6 (PA 6)/Mont- morillonit (MMT)-nanocomposite are examined by a selected structure modification in a numerical parameter study. Experimental data of tensile tests of three different volume fractions at ambient temperature are used as reference. These were compared to homogenized stress-strain curves calculated with 3D representative volume elements (RVE) under periodic boundary conditions, in which the curve areas are considered until the tensile yield strength is reached. Besides the influence of filler orientation, exfoliation and its volume fraction, both adhesive interface behavior between the filler and matrix, and local partially crystalline interphases around the MMT-plates were also taken into account. A good approximation of the numerical representation of the experimental curves was achieved only after the introduction of the 30 - 40 nm thick partially crystalline interphases with higher stiffness and strength around the MMT-plates. The use of an exclusively isotropic matrix led to an underestimation of the mechanical values. The local modifications of the morphology were assumed to be transversely isotropic both in the elastic and in the plastic region. The transverse plane is defined by the lateral particle surface. Compared with the experimentally determined values of the corresponding Young’s Modulus, an excellent correlation was achieved. The yield strength for the largest volume fraction shows the best agreement with experimental values.
