Di- and Tetrameric Molybdenum Sulfide Clusters Activate and Stabilize Dihydrogen as Hydrides

NaY zeolite-encapsulated dimeric (Mo2S4) and tetrameric (Mo4S4) molybdenum sulfide clusters stabilize hydrogen as hydride binding to Mo atoms. Density functional theory (DFT) calculations and adsorption measurements suggest that stabilization of hydrogen as sulfhydryl (SH) groups, as typical for layered MoS2, is thermodynamically disfavored. Competitive adsorption of H2 and ethene on Mo was probed by quantifying adsorbed CO on partly hydrogen and/or ethene covered samples with IR spectroscopy. During hydrogenation, experiment and theory suggest that Mo is covered predominately with ethene and sparsely with hydride. DFT calculations further predict that, under reaction conditions, each MoxSy cluster can activate only one H2, suggesting that the entire cluster (irrespective of its nuclearity) acts as one active site for hydrogenation. The nearly identical turnover frequencies (24.7 ± 3.3 molethane·h–1·molcluster–1), apparent activation energies (31–32 kJ·mol–1), and reaction orders (∼0.5 in ethene and ∼1.0 in H2) show that the active sites in both clusters are catalytically indistinguishable

Zeolite-Stabilized Di- and Tetranuclear Molybdenum Sulfide Clusters Form Stable Catalytic Hydrogenation Sites

Supercages of faujasite (FAU)‐type zeolites serve as a robust scaffold for stabilizing dinuclear (Mo2S4) and tetranuclear (Mo4S4) molybdenum sulfide clusters. The FAU‐encaged Mo4S4 clusters have a distorted cubane structure similar to the FeMo‐cofactor in nitrogenase. Both clusters possess unpaired electrons on Mo atoms. Additionally, they show identical catalytic activity per sulfide cluster. Their catalytic activity is stable (> 150 h) for ethene hydrogenation, while layered MoS2 structures deactivate significantly under the same reaction conditions

Zeolite-Stabilized Di- and Tetranuclear Molybdenum Sulfide Clusters Form Stable Catalytic Hydrogenation Sites

Supercages of faujasite (FAU)‐type zeolites serve as a robust scaffold for stabilizing dinuclear (Mo2S4) and tetranuclear (Mo4S4) molybdenum sulfide clusters. The FAU‐encaged Mo4S4 clusters have a distorted cubane structure similar to the FeMo‐cofactor in nitrogenase. Both clusters possess unpaired electrons on Mo atoms. Additionally, they show identical catalytic activity per sulfide cluster. Their catalytic activity is stable (> 150 h) for ethene hydrogenation, while layered MoS2 structures deactivate significantly under the same reaction conditions

N2O emissions from the global agricultural nitrogen cycle – current state and future scenarios

Reactive nitrogen (Nr) is not only an important nutrient for plant growth, thereby safeguarding human alimentation, but it also heavily disturbs natural systems. To mitigate air, land, aquatic, and atmospheric pollution caused by the excessive availability of Nr, it is crucial to understand the long-term development of the global agricultural Nr cycle. For our analysis, we combine a material flow model with a land-use optimization model. In a first step we estimate the state of the Nr cycle in 1995. In a second step we create four scenarios for the 21st century in line with the SRES storylines. Our results indicate that in 1995 only half of the Nr applied to croplands was incorporated into plant biomass. Moreover, less than 10 per cent of all Nr in cropland plant biomass and grazed pasture was consumed by humans. In our scenarios a strong surge of the Nr cycle occurs in the first half of the 21st century, even in the environmentally oriented scenarios. Nitrous oxide (N2O) emissions rise from 3 Tg N2O-N in 1995 to 7–9 in 2045 and 5–12 Tg in 2095. Reinforced Nr pollution mitigation efforts are therefore required

Interdigital Resonators in Wideband Ridged-Waveguide Filters

An interdigital resonator approach for wideband filter applications in ridged-waveguide technology is presented. The interdigital arrangement of the ridged-waveguide resonators ensures stronger coupling between the resonators. As the coupling sections are consequently enlarged by the interdigital arrangement of the resonators, more feasible filter structures are possible at increasing frequencies. The approach itself can be easily implemented with conventional filter synthesis formulas, which is demonstrated by two 20 GHz examples with a bandwidth of 2 GHz and 100 MHz, respectively. The designed filters are subsequently compared to the standard implementation of ridged-waveguide filters.</p

The impact of high-end climate change on agricultural welfare

Climate change threatens agricultural productivity worldwide, resulting in higher food prices. Associated economic gains and losses differ not only by region but also between producers and consumers and are affected by market dynamics. On the basis of an impact modeling chain, starting with 19 different climate projections that drive plant biophysical process simulations and ending with agro-economic decisions, this analysis focuses on distributional effects of high-end climate change impacts across geographic regions and across economic agents. By estimating the changes in surpluses of consumers and producers, we find that climate change can have detrimental impacts on global agricultural welfare, especially after 2050, because losses in consumer surplus generally outweigh gains in producer surplus. Damage in agriculture may reach the annual loss of 0.3% of future total gross domestic product at the end of the century globally, assuming further opening of trade in agricultural products, which typically leads to interregional production shifts to higher latitudes. Those estimated global losses could increase substantially if international trade is more restricted. If beneficial effects of atmospheric carbon dioxide fertilization can be realized in agricultural production, much of the damage could be avoided. Although trade policy reforms toward further liberalization help alleviate climate change impacts, additional compensation mechanisms for associated environmental and development concerns have to be considered

Striatal glucose metabolism and dopamine D2 receptor binding in asymptomatic gene carriers and patients with Huntington's disease

We used PET scans with the tracers [18F]fluorodeoxyglucose (FDG) and [11C]raclopride (RACLO) to study glucose metabolism and dopamine D2 receptor binding in the caudate nucleus and putamen of 18 carriers of the Huntington's disease gene mutation (10 asymptomatic subjects and eight untreated symptomatic Huntington's disease patients in an early disease stage). We also performed MR1 scans and measured the bicaudate ratio (BCR) in the same subjects. Data were compared with those from nine mutation-negative members of Huntington's disease families and separate groups of age matched controls. The PET scans were repeated 1.5-3 years later in six of the asymptomatic gene carriers. Symptomatic Huntington's disease patients showed a marked reduction of FDG and RACLO uptake in the caudate nucleus and putamen and a significant increase of BCR. Asymptomatic mutation carriers revealed significant hypometabolism in the caudate nucleus and putamen. The RACLO binding was significantly decreased in the putamen. Decrements of caudate nucleus tracer uptake, particularly RACLO, correlated significantly with BCR increases in both symptomatic and asymptomatic gene carriers. In asymptomatic carriers, metabolic and receptor binding decreases were also significantly associated with the CAG repeat number but not with the individual's age. Discriminant function analysis correctly classified clinical and genetic status in 24 of 27 subjects on the basis of their striatal PET values (83% sensitivity and 100% specificity). Three asymptomatic mutation carriers were classified/grouped together with mutation-negative subjects, indicating that these individuals had normal striatal RACLO and FDG uptake. Follow-up PET data from gene-positive subjects showed a significant reduction in the mean striatal RACLO binding of 6.3% per year. Striatal glucose metabolism revealed an overall non significant 2.3% decrease per year These data indicate that asymptomatic Huntington's disease mutation carriers may show normal neuronal function for a long period of life. These findings also suggest that it may be possible to predict when an asymptomatic gene carrier will develop clinical symptoms from serial PET measurements of striatal functio

Does collaborative farm-scale modelling address current challenges and future opportunities?

Resources required increasing, resources available decreasingFarm-scale modellers will need to make strategic decisionsSingle-owner modelsMay continue with additional resourcesRisk of ‘succession’ problemCommunity modelling is an alternativeNeed to continue building a community of farm modellersThe results will be published as a peer-reviewed article

Large scale cosmic-ray anisotropy with KASCADE

The results of an analysis of the large scale anisotropy of cosmic rays in the PeV range are presented. The Rayleigh formalism is applied to the right ascension distribution of extensive air showers measured by the KASCADE experiment.The data set contains about 10^8 extensive air showers in the energy range from 0.7 to 6 PeV. No hints for anisotropy are visible in the right ascension distributions in this energy range. This accounts for all showers as well as for subsets containing showers induced by predominantly light respectively heavy primary particles. Upper flux limits for Rayleigh amplitudes are determined to be between 10^-3 at 0.7 PeV and 10^-2 at 6 PeV primary energy.Comment: accepted by The Astrophysical Journa