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.     

Dynamische Steifigkeit und Dämpfung von Sand bei kleinen Dehnungen

Dynamic stiffness and damping of non‐cohesive soils at small strains. The dynamic stiffness and material damping of sand at small strains (10^–7 ≤ γ^ampl ≤ 10^–3) were studied in resonant column tests and triaxial tests with measurements of P‐ and S‐wave velocities. The influence of the parameters stress, void ratio, strain amplitude (threshold shear strain), time (aging), fabric of grain skeleton (cyclic preloading), temperature and grain size distribution was studied. The results are compared with published test data or with the recommendations of the working committee “Soil Dynamics” of the DGGT, respectively, whereby mostly a good coincidence was observed. It is shown, that the resonant column test and the measurement of the travel time of waves deliver similar results.     

Setzungsakkumulation in nichtbindigen Böden unter hochzyklischer Belastung

Accumulation of settlement in granular materials under highcyclic loading. The numerical prognosis of the accumulation of settlements and/or stress in soils under a high‐cyclic loading (e.g. high speed railway tracks, offshore wind power plants) has gained in importance during the last years. This article presents a special constitutive model for the calculation of the accumulation in non‐cohesive soil under a high number of load cycles. The model is based on numerous cyclic laboratory tests whose results are shown in this paper.     

Personal Rapid Transit in an open-control framework

Over the last decade, authorities have begun inquiring about the use of safe, comfortable, ecological vehicles for operation in an urban context as an alternative to private cars. Several on-demand transport projects have emerged with new automated vehicles known as cybercars or Personal Rapid Transit (PRT). Our state-of-the-art survey of the literature about automated On-Demand Transport (ODT) control solutions highlighted the desirability of a decentralized approach, although centralized approaches do have some advantages. In order to benefit from the advantages of both centralized/hierarchical and decentralized/heterarchical control approaches, we propose a new concept of control: open-control. In this paper, the context is intelligent transportation, where vehicles (e.g., PRTs) can be seen as autonomous decisional entities that are part of a transport system. In this context, the open-control concept is used to support two solutions to PRT routing with uncertainty and perturbations. This open-control concept, developed in our lab, exhibits the traditional explicit control, as well as an innovative type of control called implicit control, which allows system entities to be influenced via an Optimization Mechanism (OM). After introducing the open-control paradigm, we illustrate two applications of the implicit control of a PRT fleet, one based on a stigmergic method and the second based on an embedded version of the Dijkstra’s algorithm. We present a real implementation of the second approach applied to an experimental PRT network. We describe our experimental platform for PRT control and report our first experimental results. These experiments clearly show the reactivity of the control faced with unpredictable events, such as path perturbation or dynamic insertion of PRT in the network.     

Side-reactions in diisocyanate-derived bulk polyurea synthesis

Polyureas comprise a versatile family of polymers, widely applied mainly due to their outstanding mechanical properties. Nevertheless, due to the inherently very high reactivity of the isocyanate groups, polyurea synthesis is accompanied by crosslinking side-reactions, strongly affecting the polymers properties, and possible applications. The present research focused on the direct investigation and diagnostic determination in solid state, of the possible chemical structures formation in bulk polyurea synthesis, using a combination of Fourier transform infrared (FTIR) and solid-state ¹³C Nuclear magnetic resonance (NMR) analysis. Syntheses of polyureas were hereby designed to yield a very high density of the newly formed chemical structures and, consequently obtaining strong and accurate diagnostic analytical signals. The results of the present research, conclusively revealed that even in so-designed linear polyureas, there is a predominant occurrence of biuret formation and a significantly lower urea group occurrence. Polyureas of a 2:1 excess of diisocyanate:diamine, exhibited an almost exclusive biuret content. Synthesis of a new branched and crosslinked polymer using a monoamine and diisocyanate, provided strong evidence of a preferential further side-reaction of isocyanate groups with formed biurets, rather than with the very abundantly remaining urea groups to form new biurets. An energetically-favorable mechanism for the further side-reaction of formed biurets is hereby suggested. Solid-state ¹³C NMR analysis results were highly consistent with the FTIR results.