The hydromorphology index IHM based on fish requirements

Stream ecosystems are diverse and dynamic habitats that are strongly influenced by the direct and indirect consequences of human interventions. Several initiatives have been started all over Europe to satisfy the European guidelines for the protection of local water bodies, but a standardised procedure across national borders fulfilling all relevant aspects and parameters of the Water Framework Directive (WFD) does not exist. In this context, we propose a new methodical approach based on salmonid fish populations to assess stream quality to increase the comparability of individual assessments due to standardized survey and evaluation methods for hydromorphology. Our approach is based on the Austrian and Italian methods, which account for the European standards, and it has been tested in 81 stream sections representative of different site and anthropogenic use conditions in the European Alps. The assessment procedure is composed of a set of 11 indicators, which were selected to evaluate longitudinal and lateral morphological and temporal dynamics of morphological and hydrological conditions. The indicators were combined into three indices, the morphology (I_M), hydrology (I_H), and hydromorphology indices (I_HM), to obtain a holistic picture with as few parameters as possible. The definition of indicators and indices, their methodical implementation and practical testing in the field, were carried out by an interdisciplinary team of international experts. The resulting and tested field manual is included with this publication as Supplementary material. The applicability, strengths, and weaknesses of the approach are discussed in the present paper.     

Improved Thermal and Mechanical Properties of [Ca24Al28O64]4+(4e−) Electride Ceramic by Adding Mo Metal

The low-work function material [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻)—named as C12A7:e- or electride—is a promising candidate to replace established materials such as BaO–W or LaB₆ electron emitters because of its good reported electron emission in plasma environments and decent chemical inertness. However, it has poor thermal conductivity and low mechanical behavior. Therefore, cracks due to thermal shock occur in applications under thermal load, when used as a thermionic emitter. The addition of a metal with high thermal conductivity to create a ceramic–metal composite (CerMet) is evident. Molybdenum has a very high thermal conductivity and a coefficient of thermal expansion comparable to C12A7:e-. This allows the crack-free sintering of a composite ceramic made of C12A7:e- and Mo with improved thermal and mechanical properties as well as still low work function of the C12A7:e-. Herein, the C12A7:e-/Mo CerMets are characterized in terms of their thermal conductivity, thermal expansion coefficient (CTE), hardness, toughness K_1C, and strength as a function of Mo content. The CerMets have been tested in a plasma-based cathode with disk-shaped emitters for electron emission characteristics. An optimal range of the Mo content for the stability of the plasma discharge and the required discharge potential has been evaluated.     

Sanierung der Drainage- und Kontrollbohrungen im Untergrund der Sorpetalsperre

Remediation of the underground drainage and control system of the Sorpe dam To ensure the structural stability of the Sorpe dam, the Ruhrverband is remediating the no longer fully functional underground drainage and control system. Built between 1926 and 1935, the 69 m high rockfill dam with a concrete core seal was damaged during the Second World War, which led to increased seepage water in the inspection gallery. In the 1950s the original drainage system was therefore grouted and a new system created. In the 2010s it was discovered that the boreholes in the bedrock were no longer at their original depth due to sediments containing iron and manganese. In the current remediation the existing drainage and monitoring boreholes are either being widened by drilling or filled with cement suspension and replaced with new borehole profiles. All boreholes will then be converted into measuring points for monitoring the water level, seepage water and pressure. The drilling work poses a particular challenge due to the limited space within the dam structure. In July 2022 the remediation work was temporarily halted due to the occurrence of chemical injection agents containing PAHs. The work is expected to continue in the first quarter of 2024 using strict separation of clean and contaminated areas with artificial ventilation as well as a flocculation and activated carbon filter system for the drilling fluid.     

Interrogation of an Enzyme Library Reveals the Catalytic Plasticity of Naturally Evolved [4+2] Cyclases

Stereoselective carbon-carbon bond forming reactions are quintessential transformations in organic synthesis. One example is the Diels-Alder reaction, a [4+2] cycloaddition between a conjugated diene and a dienophile to form cyclohexenes. The development of biocatalysts for this reaction is paramount for unlocking sustainable routes to a plethora of important molecules. To obtain a comprehensive understanding of naturally evolved [4+2] cyclases, and to identify hitherto uncharacterised biocatalysts for this reaction, we constructed a library comprising forty-five enzymes with reported or predicted [4+2] cycloaddition activity. Thirty-one library members were successfully produced in recombinant form. In vitro assays employing a synthetic substrate incorporating a diene and a dienophile revealed broad-ranging cycloaddition activity amongst these polypeptides. The hypothetical protein Cyc15 was found to catalyse an intramolecular cycloaddition to generate a novel spirotetronate. The crystal structure of this enzyme, along with docking studies, establishes the basis for stereoselectivity in Cyc15, as compared to other spirotetronate cyclases.