Über „Gährung” und „gährende Pflänzchen”: Aus den Anfängen der Gärungsforschung im 19. Jahrhundert

The cultural history of alcoholic fermentation goes back to very early periods of human being. But only in the 19th century the nature of the biological production of alcohol was discovered. In that time chemistry and botany had a different, complementary view to alcoholic fermentation. While the positions of chemists are well-known and much discussed in the historiography of science the contribution of botanists to fermentation research is almost entirely forgotten nowadays. The work of the mycologist Oscar Brefeld, who studied yeast fermentation from 1873 to 1876, illustrates the special botanical view to the ontogenetical side of alcoholic fermentation, to morphological and physiological differences between growing and dying, fermenting and fermented yeast cells, and to the energetic and ecological role of fermentation as well as its universality in vegetable kingdom.     

Effect of the filler morphology on the crystallization behavior and dielectric properties of the polyvinylidene fluoride-based composite

Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO₃-Fe₂O₃ powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO₃-Fe₂O₃ core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured.     

Vulnerability and Robustness of a Security Skyscraper Subjected to Aircraft Impact

Abstract: Ultra‐high‐performance concrete (UHPC) is particularly suitable for application in aircraft‐impact‐resistant high‐rise buildings for combined load‐bearing and protective structures. The material provides very high—steel‐like—compressive strength, sufficient ductility, and fire resistance due to the addition of steel and polypropylene fibers. The following contribution is focused on two key aspects: hydro‐code simulations of structural UHPC walls which protect vertical escape and rescue routes and structural dynamic simulations of the global structure to investigate the impact resistance considering the sudden loss of external columns. A high‐speed dynamic material model for UHPC is obtained by implementing the results of a series of Hopkinson‐Bar experiments which were recently published. The strain‐rate‐dependent material properties are implemented in the established RHT‐Concrete‐Model for hydro‐code applications being furthermore extended by a tensile softening law for fiber‐reinforced UHPC. Based on this material model a series of aircraft‐engine impact experiments are configurated supported by three‐dimensional nonlinear hydro‐code prognosis simulations. With a total of six impact experiments on combined fiber‐ and rebar‐reinforced UHPC panels, all relevant damage states of the structural wall are obtained. The experimental results are compared to the hydro‐code prognosis simulations to validate the simulative approach and the material model for UHPC. In addition to the local impact behavior, structural dynamic numerical simulations of a global high‐rise structure are presented being focused on the effect of the sudden and notional loss of columns in coincidence with the aircraft impact load function.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete Part 1: Crack Mechanical Relationships When combining conventional non‐pre‐stressed or pre‐stressed reinforcement with fibres, differences in the load‐carrying and deformation behaviour arise in comparison to the well‐known reinforced and pre‐stressed concrete. This fact holds true comparably for all concrete classes. However, it is of special interest for ultra‐high‐performance concretes (UHPC), because fibres are added to these concretes generally to improve ductility. With regard to durability, the positive influence of the fibres on the crack formation process and the crack widths in the serviceability range is significant. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm) with combined reinforcement of rebars and fibres an essential improve compared to reinforced concrete can be achieved. The analysis of the crack formation process presumes the understanding of the different behaviours of the two reinforcing elements ”rebars” and ”fibres”. In part 1 of this contribution, the therefore required mechanical relationships are presented and linked with each other considering equilibrium and compatibility. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of UHPC. The application is furthermore illustrated by means of two examples. Because of its universal formulation, the presented proposal is generally applicable to all types of concrete reinforced with rebars and fibres, i.e. it is not limited to ultra‐high‐performance concrete.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Wegen des Problems möglicher Inhomogenitäten der Faserverteilung/‐ orientierung ist der Einsatz von Fasern als alleinige Bewehrung im konstruktiven Ingenieurbau auf wenige Anwendungsgebiete beschränkt (z. B. Aufnahme von Zwangbeanspruchungen). Unter Zugbeanspruchung lässt sich zudem mit den in der Praxis für normalfeste Betone gebräuchlichen Fasergehalten nach der Erstrissbildung kaum ein verfestigendes Verhalten erzielen. Kombiniert man jedoch Stabstahlbewehrung und Faserbewehrung zu einem stahlfaserverstärkten Stahlbeton, so addieren sich die Vorteile beider Verbundwerkstoffe gleichermaßen. Besonders bei erhöhten Anforderungen an die Rissbreite (Größenordnung: unter 0, 1 mm) kann durch gemischte Bewehrung aus Stabstahl und Fasern eine wesentliche Verbesserung gegenüber Stahlbeton erzielt werden. Im Teil 1 dieses Beitrags wurden die für das Verständnis der unterschiedlichen Wirkungsweisen der beiden Bewehrungselemente “Stabstahl” und “Fasern” erforderlichen mechanischen Zusammenhänge dargestellt. Im Teil 2 erfolgt eine Überprüfung der abgeleiteten Beziehungen anhand experimenteller Untersuchungen an gemischt bewehrten Zugelementen aus ultrahochfestem Beton (UHPC). Für UHPC erreicht die Thematik besondere Aktualität, da aus Gründen der Duktilität der Einsatz von Fasen bei diesen Betonen die Regel ist. Der Nachweis der Begrenzung der Rissbreite bei kombinierter Bewehrung wird zudem an zwei Rechenbeispielen veranschaulicht. Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete. Part 2: Experimental Investigations and Examples of Application Due to the problem of possible inhomogeneities of fibre distribution/orientation the use of fibres as sole reinforcement is limited in engineering practice to few applications (e. g. coverage of stresses due to constraints). In addition, it is hardly possible to obtain strain hardening after first crack formation with fibre contents commonly used for normal strength concretes. However, if steel fibre reinforcement is used in combination with bar reinforcement, the advantages of both components are additive in the composite material. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm), with combined reinforcement of rebars and fibres an essential improvement compared to reinforced concrete can be achieved. In part 1 of this contribution the mechanical relationships required for the understanding of the different behaviours of the two reinforcing elements “rebars” and “fibres” have been presented. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of ultra‐high‐performance concrete (UHPC). For UHPC the topic is of special interest, because fibres are added to these concretes generally to improve ductility. The crack width control with combined reinforcement is furthermore illustrated by means of two examples.     

Superconducting Bands Stabilizing Superconductivity in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> and MgB<Subscript>2</Subscript>

It is shown that the ceramic superconductor YBa₂Cu₃O₇ as well as the superconducting intermetallic compound MgB₂ possesses a narrow, partly filled “superconducting band” with Wannier functions of special symmetry in their band structures. This result corroborates previous observations about the band structures of numerous superconductors and non-superconductors showing that evidently superconductivity is always connected with such superconducting bands. These findings are interpreted in the framework of a nonadiabatic extension of the Heisenberg model. Within this new group-theoretical model of correlated systems, Cooper pairs are stabilized by a nonadiabatic mechanism of constraining forces effective in narrow superconducting bands. The formation of Cooper pairs in a superconducting band is mediated by the energetically lowest boson excitations in the considered material that carry the crystal-spin angular momentum 1⋅ℏ. These crystal-spin-1 bosons are proposed to determine whether the material is a conventional low-T _c or a high-T _c superconductor. This interpretation provides the electron–phonon mechanism that enters the BCS theory in conventional superconductors.     

Einfluß der Erstarrungsgeschwindigkeit auf die Gehalte der Legierungselemente an und vor der Phasengrenze flüssig-fest bei der Kristallisation verschiedener Legierungen der Systeme Kupfer—Mangan und Kupfer—Nickel

Modellvorstellungen zum Kristallisationsverlauf einphasig erstarrender Legierungen. Erörterung der Profile der chemischen Zusammensetzung im Kristall und, in der Schmelze bei zwei Geschwindigkeiten am Beispiel einer Kupfer-Mangan-Legierung. Einfluß der Erstarrungsgeschwindigkeit und des Ausgangsgehaltes auf die Gehalte des Legierungselementes an der Kristallisationsfront im Feststoff und in der Schmelze. Vergleich der eigenen Ergebnisse mit den Erstarrungsmodellen des Schrifttums.