INFLUENCE OF A LEVELNESS DEFECT IN A THRUST BEARING ON THE DYNAMIC BEHAVIOUR OF AN ELASTIC SHAFT

This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis.     

Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Lanthanide induced shifts of aromatic 1,2,3-trimethoxy compounds: Conformational analysis of tetrahydrofurofuran-lignans in solution

Summary The solution conformations of 1,4-diaryl-tetrahydro-1H,3H-furo[3,4-c]furans were determined by means of the LIS technique using a modified LIS-simulation program specially designed for the requirements of the aromatic 1,2,3-trimethoxy arrangement as a bidentate coordination site for the NMR shift reagent. The resulting geometries were confirmed by force field calculations (MM2-87) and compared with X-ray derived structures. Reliable data for the conformations in solution allowed a quantitative estimation of the circular dichroism based on the coupled oscillator model.

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Lanthanideninduzierte Verschiebungen von aromatischen 1,2,3-Trimethoxy-Verbindungen: Konformationsanalyse von Tetrahydrofurofuran-Lignanen in Lösung

Zusammenfassung Es wurden mittels der LIS-Technik die Konformationen von 1,4-Diaryl-tetrahydro-1H,3H-furo[3,4-c]furanen in Lösung bestimmt. Dazu mußte ein modifiziertes LIS-Simulationsprogramm entworfen werden, das auf die besonderen Verhältnisse der aromatischen 1,2,3-Trimethoxy-Gruppierung eingeht, welche in den untersuchten Verbindungen als zweizähnige Koordinationsstelle für das NMR-Verschiebungsreagens fungiert. Die resultierenden Geometrien wurden mittels Kraftfeldrechnungen (MM2-87) überprüft und soweit vorhanden auch mit Röntgenstrukturdaten verglichen. Für die Lösungskonformationen wurde eine quantitative Abschätzung des Circulardichroismus auf der Basis des Modells für gekoppelte Oszillatoren durchgeführt.

     

Manufacturing technology for the fabrication a discrete actuator using a magnetic shape memory alloy

To demonstrate the feasibility of combining thin-film fabrication techniques and discrete MSM stripes, a hybrid actuator system was designed. The actuator system consists of four thin-film stators and two discrete MSM stripes mounted in a row. For creating an actuator motion, one of the MSM stripes has to be excited by a pair of stators to cause variant switching. This results in an elongation plus a compression of the second stripe and vice versa. The technologies required for fabricating the thin-film stator are sputter deposition, PECVD, electroplating, etching, and photolithography. This paper describes the fabrication process for a thin-film stator used for the MSM micro actuator system. It also presents technology study results indicating the feasibility of the planned fabrication sequence.     

A miniature mass analyser for in-situ elemental analysis of planetary material-performance studies

The performance of a laser ablation mass analyser designed for in-situ exploration of the chemical composition of planetary surfaces has been investigated. The instrument measures the elemental and isotopic composition of raw solid materials with high spatial resolution. The initial studies were performed on NIST standard materials using IR laser irradiance (< 1 GW cm⁻²) at which a high temporal stability of ion formation and sufficiently low sample consumption was achieved. Measurements of highly averaged spectra could be performed with typical mass resolution of m/Δm ≈ 600 in an effective dynamic range spanning seven decades. Sensitive detection of several trace elements can be achieved at the ~ ppm level and lower. The isotopic composition is usually reproduced with 1% accuracy, implying good performance of the instrument for quantitative analysis of the isotopic fractionation effects caused by natural processes. Using the IR laser, significant elemental fractionation effects were observed for light elements and elements with a high ionization potential. Several diatomic clusters of major and minor elements could also be measured, and sometimes these interfere with the detection of trace elements at the same nominal mass. The potential of the mass analyser for application to sensitive detection of elements and their isotopes in realistic samples is exemplified by measurements of minerals. The high resolution and large dynamic range of the spectra makes detection limits of ~100 ppb possible.     

The emission of secondary clusters and its relevance for analytical Laser-SNMS

Summary The emission of secondary dimers and trimers under 8 keV Ar⁺ ion bombardment has been investigated under the aspects of its relevance for quantitative SNMS analysis and its implication for the basic understanding of the sputtering process. The measurements have been performed with a newly developed Laser-Multiphoton-Ionization-TOF-SNMS apparatus. The problematic of saturation and fragmentation of multimers in Laser-SNMS is addressed and compared for different ionization techniques. Cu and Cr metal as well as a CuAgAu alloy with known element concentrations have been investigated using 308 and 193 nm laser radiation for post-ionization. The data imply, that for these materials and primary ion energies dimer/atoms ratios of 10–30% are characteristic. These numbers also imply, that neglecting cluster-contributions can lead to substantial errors in quantitative analysis.     

Synthesis and conformational behaviour of ditosyldiaza[2.2]orthometacyclophanes

Summary The N,N-ditosyl-diaza[2.2]orthometacyclophanes5a, b were synthesized from N,N-ditosyl-metaphenylenediamine by reaction with (Z)-1,4-dichlorobutene and 1,2-bis-bromomethylbenzene, respectively. Low temperature NMR studies showed that the compound5b exists as a 1:1 mixture of chair and boat form of the strained (E,Z)-diazanonadiene ring. At room temperature all corresponding resonances are averaged on the NMR time scale (including all four ethylene bridge protons). Going to lower temperatures, in a first step the methylene bridge inversion is frozen (giving twoexo H and twoendo H, G ca. 52kJmol^–1). In a second step the chair and boat form can be observed separately (G ca. 43.5 kJ mol^–1 for the chair/boat flip). The assignments were confirmed by 2D NMR experiments.Dedicated to Prof. Dr. E. L. Eliel on the occasion of his 70th anniversary     

Synthesis of α‐Nitro‐α‐diazocarbonyl Derivatives and Their Applications in the Cyclopropanation of Alkenes and in O?H Insertion Reactions

A facile and highly efficient method for the preparation of α‐nitro‐α‐diazocarbonyl derivatives by a diazo‐transfer reaction involving (trifluoromethyl)sulfonyl azide has been developed. These substrates undergo a rhodium‐catalyzed cyclopropanation reaction with a variety of alkenes. A systematic study of the reaction indicated that the diastereoselectivity of the cyclopropanation could be effectively controlled through the modification of the steric bulk of the diazo reagent. A novel O? H insertion reaction of the metal? carbene complex derived from the α‐nitro‐α‐diazocarbonyl reagent afforded the corresponding novel α‐nitro‐α‐alkoxy carbonyl derivatives.