Diffuse interface models of locally inextensible vesicles in a viscous fluid

We present a new diffuse interface model for the dynamics of inextensible vesicles in a viscous fluid. A new feature of this work is the implementation of the local inextensibility condition in the diffuse interface context. Local inextensibility is enforced by using a local Lagrange multiplier, which provides the necessary tension force at the interface. To solve for the local Lagrange multiplier, we introduce a new equation whose solution essentially provides a harmonic extension of the local Lagrange multiplier off the interface while maintaining the local inextensibility constraint near the interface. To make the method more robust, we develop a local relaxation scheme that dynamically corrects local stretching/compression errors thereby preventing their accumulation. Asymptotic analysis is presented that shows that our new system converges to a relaxed version of the inextensible sharp interface model. This is also verified numerically. Although the model does not depend on dimension, we present numerical simulations only in 2D. To solve the 2D equations numerically, we develop an efficient algorithm combining an operator splitting approach with adaptive finite elements where the Navier-Stokes equations are implicitly coupled to the diffuse interface inextensibility equation. Numerical simulations of a single vesicle in a shear flow at different Reynolds numbers demonstrate that errors in enforcing local inextensibility may accumulate and lead to large differences in the dynamics in the tumbling regime and differences in the inclination angle of vesicles in the tank-treading regime. The local relaxation algorithm is shown to effectively prevent this accumulation by driving the system back to its equilibrium state when errors in local inextensibility arise.Comment: 25 page

The link between marine sediment records and changes in Holocene Saharan landscape: simulating the dust cycle

Marine sediment records reveal an abrupt and strong increase in dust deposition in the North Atlantic at the end of the African Humid Period about 4.9 to 5.5 ka ago. The change in dust flux has been attributed to varying Saharan land surface cover. Alternatively, the enhanced dust accumulation is linked to enhanced surface winds and a consequent intensification of coastal upwelling. Here we demonstrate for the first time the direct link between dust accumulation in marine cores and changes in Saharan land surface. We simulate the mid-Holocene (6 ka BP) and pre-industrial (1850 AD) dust cycle as a function of Saharan land surface cover and atmosphere-ocean conditions using the coupled atmosphere–aerosol model ECHAM6.1-HAM2.1. Mid-Holocene surface characteristics, including vegetation cover and lake surface area, are derived from proxy data and simulations. In agreement with data from marine sediment cores, our simulations show that mid-Holocene dust deposition fluxes in the North Atlantic were two to three times lower compared with pre-industrial fluxes. We identify Saharan land surface characteristics to be the main control on dust transport from North Africa to the North Atlantic. We conclude that the increase in dust accumulation in marine cores is directly linked to a transition of the Saharan landscape during the Holocene and not due to changes in atmospheric or ocean conditions alone

Aufforstung, Wiederaufforstung und nachhaltige Waldbewirtschaftung für die Klimawandelmitigation

Afforestation, reforestation and sustainable forest management for climate change mitigation: Afforestation, reforesta­tion, and sustainable forest management are considered accepted negative emission technologies (NET) with great potential for climate change mitigation. However, future forest development is highly dependent on changing environmental conditions as well as adapted forest management. For example, the increase and intensification of disturbances and extreme weather conditions (e.g., windthrow, insect infestations, fires, and drought) can greatly reduce forest productivity, especially in monocultures; at the same time, rising atmospheric CO2 concentrations and forest productivity extended into boreal latitudes can favor the NET potential. In addition, the way wood products are used affects the future NET potential. For example, long-term usage as construction timber is particularly effective, especially if it replaces fossil building materials. Similarly, the usage of wood for energy can mitigate climate change, provided that wood extraction does not exceed regrowth. Biogeophysical effects can also influence local and non-local climate, for example through changes in albedo, roughness, and transpiration. This occurs depending on local conditions as well as forestry adaptation and underscores the need to weigh the various effects of an action that affect climate. In addition, a variety of potentially positive as well as negative side effects on other ecosystem services must be considered - most importantly, biodiversity, water availability, and the need for land for food production

Diffuse interface models of locally inextensible vesicles in a viscous fluid

We present a new diffuse interface model for the dynamics of inextensible vesicles in a viscous fluid with inertial forces. A new feature of this work is the implementation of the local inextensibility condition in the diffuse interface context. Local inextensibility is enforced by using a local Lagrange multiplier, which provides the necessary tension force at the interface. We introduce a new equation for the local Lagrange multiplier whose solution essentially provides a harmonic extension of the multiplier off the interface while maintaining the local inextensibility constraint near the interface. We also develop a local relaxation scheme that dynamically corrects local stretching/compression errors thereby preventing their accumulation. Asymptotic analysis is presented that shows that our new system converges to a relaxed version of the inextensible sharp interface model. This is also verified numerically. To solve the equations, we use an adaptive finite element method with implicit coupling between the Navier-Stokes and the diffuse interface inextensibility equations. Numerical simulations of a single vesicle in a shear flow at different Reynolds numbers demonstrate that errors in enforcing local inextensibility may accumulate and lead to large differences in the dynamics in the tumbling regime and smaller differences in the inclination angle of vesicles in the tank-treading regime. The local relaxation algorithm is shown to prevent the accumulation of stretching and compression errors very effectively. Simulations of two vesicles in an extensional flow show that local inextensibility plays an important role when vesicles are in close proximity by inhibiting fluid drainage in the near contact region

Identifying Strengths and Obstacles to Climate Change Adaptation in the German Agricultural Sector: A Group Model Building Approach

In the past 30 years, there has been a significant increase in drought events in Europe. It is expected that climate change will make droughts more frequent and intense. This situation is particularly concerning for areas with no drought management culture. This study focuses on North East Lower Saxony (NELS), an important agricultural region in northern Germany. We implement a novel approach to Group Model Building to assess the preparedness of NELS to deal with climate change and droughts. Our novel approach includes the creation of a preliminary model based on individual interviews and a triangulation of information after the workshop. We conclude that stakeholders are aware of climate change, but insufficient attention is given to adaptive solutions mainly because they require high initial investments. Given its existing political infrastructure, the region has the potential to adjust. With efficient government bodies are already in place, beneficial updates could be made to established water withdrawal regulations

Identifying Strengths and Obstacles to Climate Change Adaptation in the German Agricultural Sector: A Group Model Building Approach

In the past 30 years, there has been a significant increase in drought events in Europe. It is expected that climate change will make droughts more frequent and intense. This situation is particularly concerning for areas with no drought management culture. This study focuses on North East Lower Saxony (NELS), an important agricultural region in northern Germany. We implement a novel approach to Group Model Building to assess the preparedness of NELS to deal with climate change and droughts. Our novel approach includes the creation of a preliminary model based on individual interviews and a triangulation of information after the workshop. We conclude that stakeholders are aware of climate change, but insufficient attention is given to adaptive solutions mainly because they require high initial investments. Given its existing political infrastructure, the region has the potential to adjust. With efficient government bodies are already in place, beneficial updates could be made to established water withdrawal regulations

Better define beta–optimizing MDD (minimum detectable difference) when interpreting treatment-related effects of pesticides in semi-field and field studies

The minimum detectable difference (MDD) is a measure of the difference between the means of a treatment and the control that must exist to detect a statistically significant effect. It is a measure at a defined level of probability and a given variability of the data. It provides an indication for the robustness of statistically derived effect thresholds such as the lowest observed effect concentration (LOEC) and the no observed effect concentration (NOEC) when interpreting treatment-related effects on a population exposed to chemicals in semi-field studies (e.g., micro-/mesocosm studies) or field studies. MDD has been proposed in the guidance on tiered risk assessment for plant protection products in edge of field surface waters (EFSA Journal 11(7):3290, 2013), in order to better estimate the robustness of endpoints from such studies for taking regulatory decisions. However, the MDD calculation method as suggested in this framework does not clearly specify the power which is represented by the beta-value (i.e., the level of probability of type II error). This has implications for the interpretation of experimental results, i.e., the derivation of robust effect values and their use in risk assessment of PPPs. In this paper, different methods of MDD calculations are investigated, with an emphasis on their pre-defined levels of type II error-probability. Furthermore, a modification is suggested for an optimal use of the MDD, which ensures a high degree of certainty for decision-makers

Treatment of invasive fungal infections in cancer patients—updated recommendations of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Oncology (DGHO)

Invasive fungal infections are a main cause of morbidity and mortality in cancer patients undergoing intensive chemotherapy regimens. Early antifungal treatment is mandatory to improve survival. Today, a number of effective and better-tolerated but more expensive antifungal agents compared to the former gold standard amphotericin B deoxycholate are available. Clinical decision-making must consider results from numerous studies and published guidelines, as well as licensing status and cost pressure. New developments in antifungal prophylaxis improving survival rates result in a continuous need for actualization. The treatment options for invasive Candida infections include fluconazole, voriconazole, and amphotericin B and its lipid formulations, as well as echinocandins. Voriconazole, amphotericin B, amphotericin B lipid formulations, caspofungin, itraconazole, and posaconazole are available for the treatment of invasive aspergillosis. Additional procedures, such as surgical interventions, immunoregulatory therapy, and granulocyte transfusions, have to be considered. The Infectious Diseases Working Party of the German Society of Hematology and Oncology here presents its 2008 recommendations discussing the dos and do-nots, as well as the problems and possible solutions, of evidence criteria selection

Global cycling and climate effects of aeolian dust controlled by biological soil crusts

Biological soil crusts (biocrusts) cover similar to 12% of the global land surface. They are formed by an intimate association between soil particles, photoautotrophic and heterotrophic organisms, and they effectively stabilize the soil surface of drylands. Quantitative information on the impact of biocrusts on the global cycling and climate effects of aeolian dust, however, is not available. Here, we combine the currently limited experimental data with a global climate model to investigate the effects of biocrusts on regional and global dust cycling under current and future conditions. We estimate that biocrusts reduce the global atmospheric dust emissions by similar to 60%, preventing the release of similar to 0.7 Pg dust per year. Until 2070, biocrust coverage is expected to be severely reduced by climate change and land-use intensification. The biocrust loss will cause an increased dust burden, leading to a reduction of the global radiation budget of around 0.12 to 0.22W m(-2), corresponding to about 50% of the total direct forcing of anthropogenic aerosols. This biocrust control on dust cycling and its climate impacts have important implications for human health, biogeochemical cycling and the functioning of the ecosystems, and thus should be considered in the modelling, mitigation and management of global change.ISSN:1752-0908ISSN:1752-089