Local heat transfer and heat flux distributions in finned tube heat exchangers

A detailed analysis of the effect of local heat transfer distributions, which were determined experimentally, on temperature distributions in the fins and in the fluid between two adjacent fins of finned tube heat exchangers is presented. The heat transfer distributions, obtained by a mass transfer technique, prove to be very inhomogeneous over the fin surface, leading to variable results for fin efficiency calculated by the conventional method. In addition, the effect of temperature variation in the fluid, which is usually neglected in fin analysis, is shown in many cases to exert a very strong influence on fin efficiency and total heat flux. For the optimization of fin designs, a combined analysis of local heat transfer, conduction resistance in the fin and temperature variation in the passage is indispensable.     

New assessment methods for the residual safety of old steel bridges

A great part of existing steel bridges for roads and rails are riveted structures that were built in the last century. Many of these old bridges have undergone several phases of repair or strengthening after damages in the world wars or due to changes of service requirements. For these bridges the question of the actual safety for modern traffic loads and the remaining service life is put forward. This paper describes a procedure to determine the residual safety and service life of old steel bridges and how a basis can be established on which economic decisions for further strengthening or replacement by a new bridge may be made. This procedure has been developed in close cooperation between the Institute for Ferrous Metallurgy and the Institute for Steel Construction of RWTH since 1982. It has been applied to many steel bridges in particular in Eastern Germany and also to other structures susceptible to fatigue, e.g. guyed masts, antennae, machinery parts etc.     

Multi-level transaction management for complex objects: Implementation,performance, parallelism

Multi-level transactions are a varlant of open-nested transactions in which the subtransactions correspond to operations at different levels of a layered system architecture. They allow the exploitation of semantics of high-level operations to increase concurrency. As a consequence, undoing a transaction requires compensation of completed subtransactions. In addition, multi-level recovery methods must take into consideration that high-level operations are not necessarily atomic if multiple pages are updated in a single subtransaction. This article presents algorithms for multi-level transaction management that are implemented in the database kernel system (DASDBS). In particular, we show that multi-level recovery can be implemented in an efficient way. We discuss performance measurements using a synthetic benchmark for processing complex objects in a multi-user environment. We show that multi-level transaction management can be extended easily to cope with parallel subtransactions within a single transaction. Performance results are presented with varying degrees of inter- and intratransaction parallelism.     

Säuren der Zichorienwurzel

Malic and citric acids were determined by enzymatic analysis in a series of roasted chicory roots. The content of these acids decreased to about 30% with increasing degree of roast: 37% of the malic acid and 44% of the citric acid formed compounds with soluble and insoluble substances in the chicory root. These compounds can be hydrolysed by alkali. According to model experiments they appeared to be esters. These esters represent the main products during roasting besides the products of dehydration and decarboxylation and volatile compounds.     

Seasonal Variation of Pheromone Concentration in Mating Disruption Trials Against European Grape Vine Moth Lobesia botrana (Lepidoptera: Tortricidae) Measured by EAG

Spatial and temporal distributions and relative concentrations of the pheromone of the European grape vine moth Lobesia botrana (Lepidoptera: Tortricidae) were measured in mating disruption trials with electroantennograms. Measurements were carried out over several years during the flight season of the two generations of this pest insect. In three consecutive years significantly higher mean relative pheromone concentrations were measured in summer during the flight of the second generation of L. botrana than in spring during the flight of the first generation (P < 0.001). The relative pheromone concentrations in 1989 reached a maximum between late July and early August, when the highest mean daily temperatures were registered. In addition to the differences in mean relative pheromone concentrations, the spatial and temporal distributions of the pheromone differed significantly between spring and summer. EAG recordings taken in summer showed high, uniform pheromone concentrations in the treated plots, whereas in spring strong temporal and spatial fluctuations were recorded. In a vineyard defoliated by a hailstorm, the mean relative pheromone concentrations measured in summer were not significantly different from those measured in spring (P > 0.05), but were significantly lower than those of a nearby intact vineyard (P < 0.001). The results provided additional evidence that foliage is an important parameter determining mean pheromone concentrations and temporal and spatial distribution of pheromone in mating disruption trials.     

Introduction to a new class of high performance light stabilizers and the influence of light stabilizers structure on the polymer's life time

The mode of action of two classes of UV absorbers (2-(hydroxyphenyl)benzotriazoles and 2-(2′-hydroxyphenyl)-1,3,5-triazines) is discussed. Theoretical explanations for the superior light stability of the latter are given and confirmed by measured half life times in polycarbonate and solution. A mathematical model for the quantitative prediction of light protection factors is proposed.     

Influence of Inhomogeneities in a Stratified Ground on the Field of a Circular Loop Antenna

This paper extends earlier works on three-dimensional scattering from a finite obstacle in a stratified halfspace, treated by means of the T-matrix method. In this paper we consider a general source configuration above the ground, that excites the subsurface medium and its inhomogeneity. Explicit expressions are given for the magnetic dipole, the circular, and rectangular antenna loops. Numerical examples, which show the effect of an extended source on the ground, are given for the circular antenna loop.     

Nonlinear approximate observers for feedback control

A class of approximate nonlinear observers is presented and, when used to implement stabilizing state feedback control laws, shown to yield asymptotically stable output feedback regulation.