Optimal design of railway vehicles

Summary A well-designed railway vehicle has to meet two conflicting requirements. Firstly, it must be able to move freely through a curve. Secondly, the fundamental movement must be stable even at high running speeds.A. H. Wickens has indicated how these requirements can be formulated in a quantitative way. In the present paper we shall describe, explain and slightly extend his method and, moreover, we shall show that the calculations can be simplified by using linear algebra. The method is illustrated by applying the results on the case that the vehicle has a running gear with two wheelsets.

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Optimaler Entwurf von Eisenbahnfahrzeugen

Übersicht Bin richtig entworfenes Eisenbahnfahrzeug soll zwei einander widersprechende Forderungen erfüllen. Erstens soll es imstande sein, frei durch einen Gleisbogen zu laufen. Zweitens soll die Grundbewegung auch bei großen Fahrgeschwindigkeiten stabil sein.A. H. Wickens hat angegeben, wie diese Forderungen quantitativ formuliert werden können. Im vorliegenden Aufsatz werden wir seine Methode beschreiben, erklären und ein wenig erweitern. Zudem werden wir zeigen, daß die Berechnungen sich vereinfachen lassen, indem man lineare Algebra benützt. Die Methode wird dadurch erläutert, daß die Ergebnisse auf den Fall eines Fahrzeug-Laufwerks mit zwei Radsätzen angewandt werden.

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Dedicated to Academician Yu. A. Mitropolski, member of the Ukrainian Academy of Sciences, on the occasion of bis 70^th anniversary. January 3, 1987     

Pre- and postfunctionalized self-assembled π-conjugated fluorescent organic nanoparticles for dual targeting

There is currently a high demand for novel approaches to engineer fluorescent nanoparticles with precise surface properties suitable for various applications, including imaging and sensing. To this end, we report a facile and highly reproducible one-step method for generating functionalized fluorescent organic nanoparticles via self-assembly of prefunctionalized π-conjugated oligomers. The engineered design of the nonionic amphiphilic oligomers enables the introduction of different ligands at the extremities of inert ethylene glycol side chains without interfering with the self-assembly process. The intrinsic fluorescence of the nanoparticles permits the measurement of their surface properties and binding to dye-labeled target molecules via F?rster resonance energy transfer (FRET). Co-assembly of differently functionalized oligomers is also demonstrated, which enables the tuning of ligand composition and density. Furthermore, nanoparticle prefunctionalization has been combined with subsequent postmodification of azide-bearing oligomers via click chemistry. This allows for expanding ligand diversity at two independent stages in the nanoparticle fabrication process. The practicability of the different methods entails greater control over surface functionality. Through labeling with different ligands, selective binding of proteins, bacteria, and functionalized beads to the nanoparticles has been achieved. This, in combination with the absence of unspecific adsorption, clearly demonstrates the broad potential of these nanoparticles for selective targeting and sequestration. Therefore, controlled bifunctionalization of fluorescent π-conjugated oligomer nanoparticles represents a novel approach with high applicability to multitargeted imaging and sensing in biology and medicine.     

Simultaneous cavity-enhanced and cavity ringdown absorption spectroscopy using optical feedback

We present a scheme of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) including a fast optical switch to produce cavity ringdown spectra (OF-CRDS) simultaneously. This also works as a dynamically adjustable variable attenuator allowing to compensate for reduced signal levels in correspondence with absorption lines. For this, an acousto-optic deflector is used in a double-pass configuration to eliminate the single-pass frequency shift, which is incompatible with optical feedback. This is probably the most effective device providing the required fast response and the high extinction ratio necessary to perform clean ringdown measurements. The resulting direct comparison of OF-CEAS and OF-CRDS shows that these produce almost equivalent spectral data, with 0.3 % maximal difference at the top of an absorption line having a signal-to-noise ratio (S/N) of 3,300. OF-CEAS is largely winning on the short-term noise level while OF-CRDS appears to be more immune from interference fringes, delivering cleaner spectra after longer averaging.     

Soil collapse computations with finite elements

Summary The elastic-plastic finite element method is reviewed with a view to predict collapse loads of geotechnical constructions. The basic technique of using an incremental-iterative approach with a constant stiffness matrix is well-known, but we fill a gap by proving that the procedure converges not only for small steps but also for large load increments. Here restriction is made to associated plasticity, as uniqueness of solution is not ensured for non-associated plasticity problems. Differences between associated and nonassociated problems are illustrated by showing results of numerical analyses. Finally, a number of practical aspects associated with the method are discussed.

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Finite-Element-Berechnungen des Versagens von Böden

Übersicht Im Hinblick auf die Vorhersage der Versagenlasten von Erdbauten wird ein Überblick über die elastisch-plastische Finite-Element-Methode gegeben. Das grundlegende Verfahren mit inkrementelliterativem Vorgehen mit einer konstanten Steifigkeitsmatrix ist wohlbekannt. Durch den Beweis, daß das Verfahren nicht nur bei kleinen Schrittweiten, sondern auch bei großen Laststufen konvergiert, werden jedoch neuartige Erkenntnisse vorgestellt. Hierbei muß einschränkend assoziierte Plastizität gelten, da bei nicht-assoziierter Plastizität die Eindeutigkeit von Lösungen nicht gewährleistet ist. Anhand von numerischen Ergebnissen werden Unterschiede zwischen Aufgabenstellungen mit assoziierter und nichtassoziierter Plastizität aufgezeigt. Schließlich werden auch noch praktische Gesichtspunkte des Verfahrens erörtert.

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Presented at the workshop on Limit Analysis and Bifurcation Theory, held at the University of Karlsruhe (FRG), February 22–25, 1988     

Influence of Pore Structure and Metal-Node Geometry on the Polymerization of Ethylene over Cr-Based Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have received increasing interest as solid single-site catalysts, owing to their tunable pore architecture and metal node geometry. The ability to exploit these modulators makes them prominent candidates for producing polyethylene (PE) materials with narrow dispersity index (Ð) values. Here a study is presented in which the ethylene polymerization properties, with Et₂AlCl as activator, of three renowned Cr-based MOFs, MIL-101(Cr)-NDC (NDC=2,6-dicarboxynapthalene), MIL-53(Cr) and HKUST-1(Cr), are systematically investigated. Ethylene polymerization reactions revealed varying catalytic activities, with MIL-101(Cr)-NDC and MIL-53(Cr) being significantly more active than HKUST-1(Cr). Analysis of the PE products revealed large Ð values, demonstrating that polymerization occurs over a multitude of active Cr centers rather than a singular type of Cr site. Spectroscopic experiments, in the form of powder X-ray diffraction (pXRD), UV/Vis-NIR diffuse reflectance spectroscopy (DRS) and CO probe molecule Fourier transform infrared (FTIR) spectroscopy corroborated these findings, indicating that indeed for each MOF unique active sites are generated, however without alteration of the original oxidation state. Furthermore, the pXRD experiments indicated that one major prerequisite for catalytic activity was the degree of MOF activation by the Et₂AlCl co-catalyst, with the more active materials portraying a larger degree of activation.