A comparative study of finite element methodologies for the prediction of torsional response of bladed rotors

The prevention of torsional vibration-induced fatigue damage to turbo-generators requires determining natural frequencies by either field testing or mathematical modelling. Torsional excitation methods, measurement techniques and mathematical modelling are active fields of research. However, these aspects are mostly considered in isolation and often without experimental verification. The objective of this work is to compare one dimensional (1D), full three dimensional (3D) and 3D cyclic symmetric (3DCS) Finite element (FE) methodologies for torsional vibration response. Results are compared to experimental results for a small-scale test rotor.It is concluded that 3D approaches are feasible given the current computing technology and require less simplification with potentially increased accuracy. Accuracy of 1D models may be reduced due to simplifications but faster solution times are obtained. For high levels of accuracy model updating using field test results is recommended.     

The nature of the passive film on cathodically modified stainless steels

This paper discusses the effect of additions of platinum group metals (PGMs) on the composition of the passive surface layer formed on stainless steels in reducing acid media. It has been shown that there is an accumulation of these noble metals on the surface of the alloy during the period of active dissolution. The morphology and factors influencing this accumulation of PGMs on the surface are discussed. It was also found that there are differences between passive films formed spontaneously and those formed under potentiostatic control. An interesting fact emerging from the investigations is that different PGMs form different types of oxides on the passivated surfaces. Areas for possible future research are mentioned.     

The development of a tunable vibration absorbing isolator

This paper describes a tunable vibration absorbing isolator. The device is based on the liquid inertia vibration eliminator, which is modified so that the frequency at which maximum isolation occurs can be changed in real time. This is achieved by using adjustable pneumatic springs. A theoretical model describing the device is derived using Lagrange's equations. The model is used to design a practical device and experimental results confirm the validity of the model. With the experimental device a roll-off of about 90 dB/decade over a 12 Hz frequency band was achieved.     

Zur Frage der Entstehung von Nitrosaminen bei der Reaktion von Monosacchariden mit Aminos?uren (Maillard-Reaktion)

Zusammeufassung Zur Überprüfung des Auftretens von Nitrosaminen [2] im Rahmen der Maillard-Reaktion wurden die flüchtigen Produkte verschiedener Glucose-Aminosäure-Modell-gemische durch Kombination von Gaschromatographie and Massenspektrometrie, Polarographie und Dünnschicht-Chromatographie untersucht. Das Auftreten von Nitrosaminen kann durch die Ergebnisse eindeutig ausgeschlossen werden.

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The problem of formation of nitrosamines by reacting monosaccharides with aminoacids (maillard-reaction)

Summary For proving the formation of nitrosamines applying maillardconditions [2] we tested the volatile reaction products of various glucose-aminoacid mixtures by coupling gas chromatography and mass spectrometry, polarography and thin-layer chromatography. The appearence of nitrosamines could undoubtedly be excluded according to the results.

     

Pancytopenia and aplastic anemia: a retrospective study

During January 1971--June 1975 we examined 195 patients with pancytopenia. The cause was bone marrow failure in 67.7% of cases (classic aplastic anaemia in 11.3%) hypersplenism in 7.7%, massive blood transfusions in 1.5%, severe infections in 9.7% (Gram-negative in 3%), and various other conditions in 7.8%. Records were insufficient for diagnosis in 5.6% of cases. Analysis of the 22 patients with aplastic anaemia showed no apparent aetiology in 16 (72.7%), previous phenylbutazone ingestion in 2, and Fanconi-type anaemia in 4 of 7 children. One-year survival was 73.7%, 2-year survival 71.4%, 3-year survival 63.6% and 4-year survival 57.1%. Marrow-investigation of the 21 available samples showed that 6 were acellular, 11 hypocellular and 4 normocellular. All patients received at least temporary therapy with anabolic steroids but its effectivity could not be satisfactorily assessed. Five patients died within 7 months and 5 patients went into remission, needing no further therapy. The initial haematological features of the 5 patients who died were not significantly different from those of the rest of the patients.     

Study of the Reliability Impact of Chlorine Precursor Residues in Thin Atomic-Layer-Deposited HfO2 Layers

Atomic layer deposition (ALD) with HfCl₄ as a precursor is widely used for HfO₂ fabrication. Due to the nature of the precursor under study, i.e., HfCl₄ and H₂O, the presence of chlorine residues in the film due to insufficient hydrolysis is eminent. Obviously, the chlorine residue in the HfO₂ film is suspected to affect the quality of the HfO₂ film. In this paper, The authors reduced the concentration of chlorine residues by increasing the H₂O oxidant pulse time in between the deposition cycles from 0.3 to 10 and 90 s. Time-of-flight secondary ion mass spectrometry analysis shows that this decreases the chlorine concentration in the HfO₂ film by more than one order of magnitude. However, time-dependent dielectric breakdown analysis shows that the lifetime remains quasi unaffected (within identical error bars) for the different injection cycles. Charge pumping analysis was done by varying both pulse frequency and amplitude to investigate the creation of defects, but negligible differences were observed. Therefore, the presence of chlorine residues has no significant impact on the trap generation and reliability of ALD HfO₂ layers, and this result corresponded with the mobility result. The experimental picture is confirmed with first-principle calculations that show that the presence of chlorine residues does not induce defect levels in the bandgap of HfO₂     

Reactions in the formation of Na3Zr2Si2PO12

Nasicon ceramics of formula Na₃Zr₂Si₂PO₁₂ were prepared from two systems, namely NH₄H₂PO₄-Na₂CO₃-SiO₂-ZrO₂ and Na₃PO₄-SiO₂-ZrO₂. The partial reactions and sequence of reactions was studied using differential thermal analysis and X-ray diffraction analysis. Kinetic restraints to completeness of reaction are indicated and sodium oxide volatilization is shown to occur. The rate-determining partial reaction involves zirconia and a sodium phosphosilicate intermediate.     

Potential remedies for the VT/Vfb-shift problem of Hf/polysilicon-based gate stacks: a solution-based survey

In this paper, we report on several different approaches that were implemented on both capacitor and scaled planar MOS transistor devices in order to prevent or undo the commonly observed V_T/V_fb-shift and –instability for Hf-based high-κ gate stacks in conjunction with a poly-Si electrode. While the latter issue can eventually be mitigated, the V_T-shift problem jeopardizes initial high-κ integration with poly-Si for the 65 nm and also for the 45 nm node. The different attempts to circumvent this problem include (1) bulk modifications of the high-κ stack/process, (2) the use of various thin capping layers at the poly/high-κ interface and (3) chemical and process modifications of the gate electrode deposition. We have observed that, although considerable improvements have been made in terms of e.g. yield, performance and instability, none of these techniques succeeded in obtaining V_T-values in line with the ITRS device specifications, i.e. avoiding Fermi Level Pinning to occur for poly-Si/Hf(Si)O(N) stacks.     

Application of computed order tracking, Vold-Kalman filtering and EMD in rotating machine vibration

This paper presents a study on rotating machine vibration signals by using computed order tracking, Vold-Kalman filtering and intrinsic mode functions from the empirical mode decomposition method. Through the sequential use of intrinsic mode function and order tracking methods, both speed synchronous and non-synchronous vibrations that modulate orders in rotating machine vibrations are distinguished, which is difficult when using each of the techniques in isolation alone. Simulation and experimental studies demonstrate the ability of extracting vibrations that modulate order signals through combining the techniques.