Bildung eines Hydroxypyrrols aus Methylglyoxal und Methylammoniumacetat

Zusammenfassung Methylglyoxal reagiert mit Methylammoniumacetat in wäßriger Lösung bei erhöhter Temperatur rasch unter Brdunung. Aus dem Gemisch von Umsetzungsprodukten ist 3-Hydroxy-1,2-dimethyl-5-formyl-pyrrol [1] isolierbar.

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Formation of a hydroxypyrrole from methylglyoxal and methylammoniumacetate.VIII. studies on the maillard reaction

Summary Methylglyoxal rapidly reacts in water solution at increased temperatures with methylammoniumacetate by browning. Out of this mixture 3-hydroxy-1.2-dimethyl-5-formvipyrrole can be isolated.

     

Spannungs‐ und Porenwasserdruckentwicklung infolge Schlitzwand‐Herstellung in weichen bindigen Böden

Stress and pore water pressure development during the construction process of dipahragm walls in soft clay. The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure.     

Gilt die Minersche Regel für Sand?

Is Miner's rule applicable to sand? In calculations with an explicit (high‐cycle) accumulation model a loading with varying amplitudes is replaced by packages of cycles each with a constant amplitude. This assembling of packages according to the criteria of amplitude is based on the assumption, that the sequence of the packages is of minor importance with respect to the final value of the residual deformation, i.e. that the Miner's rule is applicable. Unfortunately, for sand only few experimental studies with a low number of cycles exist. This paper presents the results of triaxial tests with packages of cycles in which the validity of the Miner's rule was checked for sand and larger numbers of cycles (N ≥ 10⁵). It is shown that the influence of the sequence of the packages can be neglected (at least for cycles with a constant polarisation), i.e. that the procedure of explicit models is legitimate.     

Berücksichtigung des Frischbetondrucks bei der FE‐Simulation der Schlitzwandherstellung

Fresh concrete pressures as a boundary condition for FE‐simulations of a diaphragm wall construction. Underground deformations adjacent to a diaphragm wall pit excavation are generated by the pit excavation as well as by the wall construction itself. For the numerical simulation of the construction process, a 3D Finite Element model is required accounting for the construction sequence and the intermediate stress states generated by the slurry and fresh concrete pressures. Regarding the development of fresh concrete pressures, centrifuge model tests and element tests were conducted and an analytical algorithm for the calculation of the fresh concrete pressures is derived. A backcalculation of available literature data shows good agreement and enables a more detailed consideration of the fresh concrete pressures for the numerical simulation of a diaphragm wall construction.