The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual ...characterization in solution and later in solid state did only fuel the discussion about their existence and initially created a lot of controversy. This perception has completely changed today, and silyl cations and their donor-stabilized congeners are now widely accepted compounds with promising use in synthetic chemistry. This review provides a comprehensive summary of the fundamental facts and principles of the chemistry of silyl cations, including reliable ways of their preparation as well as their physical and chemical properties. The striking features of silyl cations are their enormous electrophilicity and as such reactivity as super Lewis acids as well as fluorophilicity. Known applications rely on silyl cations as reactants, stoichiometric reagents, and promoters where the reaction success is based on their steady regeneration over the course of the reaction. Silyl cations can even be discrete catalysts, thereby opening the next chapter of their way into the toolbox of synthetic methodology.
For discrete time nonlinear systems we study the relation between strict dissipativity and so called turnpike-like behavior in optimal control. Under appropriate controllability assumptions we ...provide several equivalence statements involving these two properties. The relation of strict dissipativity to an exponential variant of the turnpike property is also studied.
Annual removal of crop residues may lead to depletion of soil organic carbon and soil degradation. Gasification biochar (GB), the carbon-rich byproduct of gasification of biomass such as straw and ...wood chips, may be used for maintaining the soil organic carbon content and counteract soil degradation if applied to soil. This study investigated the effect of straw removal and GB addition on soil biological, chemical and physical properties in a 22-months soil incubation study with a temperate sandy loam soil.
Soil application of wood and straw GB (WGB and SGB) resulted in very low CO2 emissions, confirming the stability of the material against microbial degradation. Both GBs increased total organic carbon, cation exchange capacity and pH of the soil. The application of SGB and WGB did not affect aggregate stability, whereas SGB did not affect and WGB decreased clay dispersibility. In contrast, the addition of straw resulted in a high soil respiration rate, and about 80% of the added carbon was respired at the end of the incubation. However, the addition of straw increased aggregate stability and decreased clay dispersibility. Results from Fourier transformed infrared photoacoustic spectroscopy revealed a lower content of O–H and aliphatic C–H together with a higher content of aromatic groups in soils amended with GB compared to soils amended with straw. This suggested that the improvement in aggregate stability in straw treatments could be related to microbial derived aliphatics and simple sugars, and that increased stability against microbial degradation in biochar amended soil was related to highly condensed aromatic groups. Addition of nutrients (N, P and S) together with straw resulted in higher soil respiration compared to the straw treatment, but did not cause differences in other soil processes.
Results from this study suggest that GB has a potential for increasing soil carbon sequestration, CEC and pH. However, the straw turnover process plays a vital role for aggregate stability and clay dispersibility. Thus, annual straw removal on loamy soil needs to be considered with care in order to avoid soil degradation and risk of soil compaction or erosion.
•Wood and straw gasification biochar are highly stable towards microbial degradation.•Gasification biochar has a potential for increasing soil C sequestration, CEC and pH.•Application of straw increased aggregate stability and decreased clay dispersibility.•Straw and wood biochar had no effect on aggregate stability whereas wood biochar increased clay dispersibility.
In this paper, we analyze economic model predictive control schemes without terminal constraints, where the optimal operating behavior is not steady-state operation, but periodic behavior. We first ...show by means of a counterexample, that a classical receding horizon control scheme does not necessarily result in an optimal closed-loop behavior. Instead, a multi-step MPC scheme may be needed in order to establish near optimal performance of the closed-loop system. This behavior is analyzed in detail, and we show that under suitable dissipativity and controllability conditions, desired closed-loop performance guarantees as well as convergence to the optimal periodic orbit can be established.
Animal models point towards a key role of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in mediating exercise-induced ...structural and functional changes in the hippocampus. Recently, also platelet derived growth factor-C (PDGF-C) has been shown to promote blood vessel growth and neuronal survival. Moreover, reductions of these neurotrophic and angiogenic factors in old age have been related to hippocampal atrophy, decreased vascularization and cognitive decline. In a 3-month aerobic exercise study, forty healthy older humans (60 to 77years) were pseudo-randomly assigned to either an aerobic exercise group (indoor treadmill, n=21) or to a control group (indoor progressive-muscle relaxation/stretching, n=19). As reported recently, we found evidence for fitness-related perfusion changes of the aged human hippocampus that were closely linked to changes in episodic memory function. Here, we test whether peripheral levels of BDNF, IGF-I, VEGF or PDGF-C are related to changes in hippocampal blood flow, volume and memory performance. Growth factor levels were not significantly affected by exercise, and their changes were not related to changes in fitness or perfusion. However, changes in IGF-I levels were positively correlated with hippocampal volume changes (derived by manual volumetry and voxel-based morphometry) and late verbal recall performance, a relationship that seemed to be independent of fitness, perfusion or their changes over time. These preliminary findings link IGF-I levels to hippocampal volume changes and putatively hippocampus-dependent memory changes that seem to occur over time independently of exercise. We discuss methodological shortcomings of our study and potential differences in the temporal dynamics of how IGF-1, VEGF and BDNF may be affected by exercise and to what extent these differences may have led to the negative findings reported here.
•Exercise-related changes in BDNF, IGF, VEGF and PDGF were measured in older adults•Changes in hippocampal perfusion, volume (via 7T MRI) and memory were assessed•Fitness-related vascular hippocampal plasticity was not linked to growth factors•Changes in IGF-I, hippocampal volume and memory were linked independent of exercise•Potential reasons for negative findings and methodological shortcomings are discussed
Der Begriff »Roma« ist in der deutschen Gesellschaft ein Reizwort. Er steht für die Gefährdung des Wohlfahrtsstaates durch Armutsmigration und repräsentiert die Unsicherheit, die in den situierten ...Europäischen Norden einzudringen sucht. Die Chiffre »Roma« hat dementsprechend auch in lokalen Konflikten um Armutsmigration eine spezifische Funktion.Die AutorInnen des Bandes haben im Rahmen einer lokalpolitischen Feldstudie soziale Konflikte um Migration aus Südosteuropa und ihre Dynamiken untersucht und eröffnen eine neue Perspektive auf die Situation von Roma in der bundesdeutschen Gesellschaft.
Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts en route, with substantial water column losses by ...mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. We know DOM losses are significant at the global scale, yet little is known about how the reactivity of DOM varies across landscapes and climates. DOM reactivity is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment, and climate characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water retention time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red‐shifted components, were most reactive. In contrast, protein‐like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between −6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases in runoff in the boreal region may force lake DOM toward a higher overall amount and proportion of humic‐like substances.
A series of isomeric dithieno1,4thiazines is accessible through an intermolecular–intramolecular Buchwald–Hartwig amination starting from dihalodithienyl sulfides. The electronic properties of ...dithieno1,4thiazine isomers differ conspicuously over a broad range depending on the thiophene–thiazine anellation: a large cathodic (340 mV) or an anodic shift (130 mV) of the redox potentials relative to corresponding phenothiazines is possible. Structure–property relationships of the dithieno1,4thiazine constitution derived from DFT calculations and cyclic voltammetry not only reveal increased electron density but also different delocalization of the radical cations that determines the electrochemical properties significantly. In addition, photophysical properties (absorption and emission) qualify dithieno1,4thiazines as promising substitutes of phenothiazine and beyond due to increased tunable electron richness.
Structure–property relationships: Four isomeric dithieno1,4thiazines, thieno congeners of phenothiazines, are synthesized by inter‐intra‐molecular Buchwald–Hartwig coupling. Their electronic properties open new avenues as donor systems for molecular electronics.
The European Centre for Medium-Range Weather Forecasts' (ECMWF's)
next-generation reanalysis ERA5 provides many improvements, but it
also confronts the community with a “big data” challenge. Data
...storage requirements for ERA5 increase by a factor of ∼80
compared with the ERA-Interim reanalysis, introduced a decade ago.
Considering the significant increase in resources required for
working with the new ERA5 data set, it is important to assess its
impact on Lagrangian transport simulations. To quantify the
differences between transport simulations using ERA5 and ERA-Interim
data, we analyzed comprehensive global sets of 10-day forward
trajectories for the free troposphere and the stratosphere for the
year 2017. The new ERA5 data have a considerable impact on the
simulations. Spatial transport deviations between ERA5 and
ERA-Interim trajectories are up to an order of magnitude larger than
those caused by parameterized diffusion and subgrid-scale wind
fluctuations after 1 day and still up to a factor of 2–3 larger
after 10 days. Depending on the height range, the spatial
differences between the trajectories map into deviations as large as
3 K in temperature, 30 % in specific humidity, 1.8 % in potential
temperature, and 50 % in potential vorticity after 1 day. Part of
the differences between ERA5 and ERA-Interim is attributed to the better
spatial and temporal resolution of the ERA5 reanalysis, which allows for
a better representation of convective updrafts, gravity waves,
tropical cyclones, and other meso- to synoptic-scale features of the
atmosphere. Another important finding is that ERA5 trajectories
exhibit significantly improved conservation of potential temperature
in the stratosphere, pointing to an improved consistency of ECMWF's
forecast model and observations that leads to smaller data
assimilation increments. We conducted a number of downsampling
experiments with the ERA5 data, in which we reduced the numbers of
meteorological time steps, vertical levels, and horizontal grid
points. Significant differences remain present in the transport
simulations, if we downsample the ERA5 data to a resolution similar
to ERA-Interim. This points to substantial changes of the forecast
model, observations, and assimilation system of ERA5 in addition to
improved resolution. A comparison of two Lagrangian trajectory
models allowed us to assess the readiness of the codes and workflows
to handle the comprehensive ERA5 data and to demonstrate the
consistency of the simulation results. Our results will help to
guide future Lagrangian transport studies attempting to navigate the
increased computational complexity and leverage the considerable
benefits and improvements of ECMWF's new ERA5 data set.
Many boreal waters are currently becoming browner with effects on biodiversity, fish production, biogeochemical processes and drinking water quality. The question arises whether and at which speed ...this browning will continue under future climate change. To answer the question we predicted the absorbance (a₄₂₀) in 6347 lakes and streams of the boreal region under future climate change. For the prediction we modified a numerical model for a₄₂₀ spatial variation which we tested on a temporal scale by simulating a₄₂₀ inter-annual variation in 48 out of the 6347 Swedish waters. We observed that inter-annual a₄₂₀ variation is strongly driven by precipitation that controls the water flushing through the landscape. Using the predicted worst case climate scenario for Sweden until 2030, i.e., a 32 % precipitation increase, and assuming a 10 % increase in imports of colored substances into headwaters but no change in land-cover, we predict that a₄₂₀ in the 6347 lakes and streams will, in the worst case, increase by factors between 1.1 and 7.6 with a median of 1.3. This increase implies that a₄₂₀ will rise from the present 0.1–86 m⁻¹ (median: 7.3 m⁻¹) in the 6347 waters to 0.1–154 m⁻¹ (median: 10.1 m⁻¹), which can cause problems for the preparation of drinking water in a variety of waters. Our model approach clearly demonstrates that a homogenous precipitation increase results in very heterogeneous a₄₂₀ changes, where lakes with a long-term mean landscape water retention time between 1 and 3 years are particularly vulnerable to climate change induced browning. Since these lake types are quite often used as drinking water resources, preparedness is needed for such waters.
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