Die Bestimmung von Schwefelanteilen im Stahl unter 10 μg/g

Analytische Möglichkeiten einer neuen Gerätegeneration. Weiterentwicklung des Verfahrens mit synthetischer Eichung bis zur Bestimmungsgrenze 2 μg/g.     

On convection in aluminum reduction cells

The convection pattern in the bath electrolyte and the cathode metal of 150 kamp prebaked anode aluminum reduction cells has been studied by means of radioactive tracers. The initial distribution of the tracers—²⁴Na for the bath and¹⁹⁸Au for the metal phase-indicates a fast circulating movement with vortices at the ends in both phases. Circulation rates up to 100 cm per sec were observed, and an average value seemed to be 10 cm per sec. The implications of the convection on the mechanism of the secondary reactions, the dissolution of alumina in the bath electrolyte and the distribution of carbon particles in the cell are discussed.     

Optimierung spektrometrischer Verfahren durch ein Datenverarbeitungssystem

Einsatz von Prozeßrechnern in Laboratorien. Aufbau eines Systems zur Produktionsüberwachung eines Sauerstoffaufblasstahlwerkes. Beschreibung des Rechners und der Programmgestaltung. Ablauf der emissionsspektrometrischen und röntgenfluoreszenzspektrometrischen Roheisen-, Stahl- und Schlackenanalysen. Erste Ergebnisse und Erfahrungen.     

Synthesis of branched 'nanotrees' by controlled seeding of multiple branching events

The formation of nanostructures with controlled size and morphology has been the focus of intensive research in recent years. Such nanostructures are important in the development of nanoscale devices and in the exploitation of the properties of nanomaterials. Here we show how tree-like nanostructures ('nanotrees') can be formed in a highly controlled way. The process involves the self-assembled growth of semiconductor nanowires via the vapour-liquid-solid growth mode. This bottom-up method uses initial seeding by catalytic nanoparticles to form the trunk, followed by the sequential seeding of branching structures. Each level of branching is controlled in terms of branch length, diameter and number, as well as chemical composition. We show, by high-resolution transmission electron microscopy, that the branching mechanism gives continuous crystalline (monolithic) structures throughout the extended and complex tree-like structures. The controlled seeding method that we report here has potential as a generic means of forming complex branching structures, and may also offer opportunities for applications, such as the mimicking of photosynthesis in nanotrees.     

Zur Interaktion von Mathematik und Melancholie

The copperplate Melencolia I engraved by Dürer in 1514 illustrates various interdependencies between mathematics and melancholy. Dürer's engraving is one of the best known works of art in our western history. Up to our own times it has been interpreted repeatedly.The significance of Dürer's Melencolia I for our cultural history is subject of this essay. On the one hand the various changes of the conception of melancholy from antiquity up to Dürer' s times will be called in mind. In addition to it some examples will assert that during the last five centuries the correlation between mathematics and melancholy has been contemplated and shaped as well.     

Monte Carlo and discrete-ordinate simulations of irradiances in the coupled atmosphere-ocean system

We compare Monte Carlo (MC) and discrete-ordinate radiative-transfer (DISORT) simulations of irradiances in a one-dimensional coupled atmosphere-ocean (CAO) system consisting of horizontal plane-parallel layers. The two models have precisely the same physical basis, including coupling between the atmosphere and the ocean, and we use precisely the same atmospheric and oceanic input parameters for both codes. For a plane atmosphere-ocean interface we find agreement between irradiances obtained with the two codes to within 1%, both in the atmosphere and the ocean. Our tests cover case 1 water, scattering by density fluctuations both in the atmosphere and in the ocean, and scattering by particulate matter represented by a one-parameter Henyey-Greenstein (HG) scattering phase function. The CAO-MC code has an advantage over the CAO-DISORT code in that it can handle surface waves on the atmosphere-ocean interface, but the CAO-DISORT code is computationally much faster. Therefore we use CAO-MC simulations to study the influence of ocean surface waves and propose a way to correct the results of the CAO-DISORT code so as to obtain fast and accurate underwater irradiances in the presence of surface waves.     

Evaluation of IP over WDM Network Architectures

The commonly used IP-backbone network architecture of today is IP/ATM/SDH/WDM. This architecture has many redundant functionalities and is not optimized to transport IP traffic. New approaches for simplified network architectures try to eliminate redundant functionalities and to decrease the protocol overhead and thereby transport IP as efficiently as possible over WDM-based optical networks. EURESCOM project P918 Integration of IP-over-optical networks: networking and management investigated scenarios for optimized IP transport in WDM-based backbone networks. In this paper, three architectures, namely Gigabit Ethernet, Packet over Sonet/SDH and Dynamic Packet Transport are investigated and evaluated as an alternative to the IP/ATM/SDH/WDM architecture.     

Faster to Sound Parts by Advanced Forming Process Simulation ‐ Advanced Forming Process Model Including the Elastic Effects of the Forming Press and Tool

This article addresses process, stamping, and manufacturing engineers, as well as tool designers (prototype and series production tools), and press shop planners in the range of metal forming. The paper deals with methods of modelling and simulating the metal forming process and their application in product design, production, and forming process planning. In models usually applied major effects on the forming process are neglected. For instance, the elastic behaviour of presses and die tools is not considered in process and tool planning. Thus, reworking of tools is a consequence of this model oversimplification. The paper illustrates how interactions between forming press, die tool and metal forming processes can be modelled by enhancing conventional FE models. Several examples demonstrate the information value of the Advanced Forming Process Model (AFPM).     

On time-triggered and event-based control of integrator systems over a shared communication system

When analyzing networked control systems, where the control loop is closed over a communication system, it is crucial to take the communication system into account. Hence, time-triggered and event-based control of an integrator system with noise over a shared communication system is analyzed. Thereby, analytical models of different communication systems are used and the analysis is focused on the effect of the communication system on the performance, as well as the interaction between control and communication. For time-triggered control, where the event times are known in advance, a deterministic communication protocol can be used. Hence, time-triggered control with the two most well-known deterministic communication protocols, time division multiple access (TDMA) and frequency division multiple access (FDMA), is analyzed. For event-based control, where the events appear at random times, a contention-based communication protocol should be used. Hence, event-based control is analyzed with different contention-based communication protocols: pure ALOHA, slotted ALOHA, a queueing system, and Erlang’s loss model. It turns out that time-triggered control with either TDMA or FDMA outperforms event-based control with pure or slotted ALOHA. However, event-based control with a properly designed queueing system gives an even better performance. Thus, we conclude that it is crucial to take the details of the communication system into account.