Signalverarbeitungsverfahren und virtuelle Instrumente zur Messung von elektrischen Signalen und zur Fehlerdiagnose an Maschinen

Es wird in dieser Arbeit gezeigt, dass sich die Chirp-z-Transformation (CZT) und das Zeropadding-Verfahren (ZP), kombiniert mit der Anwendung geeigneter Fensterfunktionen, zur Bestimmung der Größen von Spannungs- und Stromsignalen bezüglich der Zuverlässigkeit bei kurzen Messzeiten eignen. Die allgemeinen Bedingungen für die Anwendung der CZT bzw. des ZP bei reellen Multifrequenz-Signalen unter dem Einsatz der Fensterfunktionen dargestellt. Der Einfluß eines reellen weißen Rauschsignals auf die geschätzten Größen eines reellen Multifrequenz-Signals wurde untersucht. Das TDA-Verfahren wird zur Verarbeitung der harmonischen Komponenten der Ausgangssignale eines Frequenzumformers untersucht. Zur Detektion und Messung der interharmonischen Komponenten wird ein digitales Differenz-Filter vorgestellt. Die Anwendbarkeit des TDA-Verfahrens und des digitalen Differenz-Filters wird durch die Ergebnisse aus Simulationen und praktischen Anwendungen gezeigt. Virtuelle Instrumente wurden zur Fehldiagnose und Schwingungsanalyse an Planetengetrieben entwickelt. Die praktischen Anwendungen zeigen, dass das Spektrum der demodulierten hochfrequenten mechanischen Schwingungen – Hüllkurvenspektrum – eine spektrale Struktur bei den Frequenzen enthält, die mit den Fehlern auf Innenring- oder Außenringlaufbahn in Verbindung stehen.It will be shown that the chirp-z-transform and zero-padding, combined with a appropriate window, are suitable for the estimation of the parameters of the voltage and current signals with moderate computational complexity. Through the analysis of the spectral interference in the discrete time Fourier transform the conditions for the simultaneous use of the windows and the chirp-z-transform or zero-padding will be presented. The statistical errors of the estimations will be discussed. The time domain averaging will be here investigated to process harmonic components in the output signals of frequency converters. For the detection and measurement of interharmonics a digital difference-filter will be proposed. Simulations and field test results are provided to illustrate the utility of the time domain averaging and the difference-filter. Based on the analysis of the faults of gears and rolling bearings the virtual instruments for the fault diagnosis and vibration analysis in epicyclic gearboxes are developed. The practical applications show that the spectrum of the demodulated high-frequency vibration – envelope spectrum – contains a pattern of spectral lines at frequencies which can be related to the faults on the inner or outer race of rolling bearings

Tailoring acidity of HZSM-5 nanoparticles for methyl bromide dehydrobromination by Al and Mg incorporation

Three kinds of HZSM-5 nanoparticles with different acidity were tailored by impregnating MgO or varying Si/Al ratios. Both the textural and acidic properties of the as-prepared nanoparticles were characterized by nitrogen adsorption-desorption measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH(3)-TPD) and Fourier transform infrared spectroscopy (FTIR or Py-FTIR). It was found that the intensity of Lewis acid sites with weak strength was enhanced by impregnating MgO or reducing Al concentration, and such an enhancement could be explained by the formation of Mg(OH)(+) or charge unbalance of the MgO framework on the surface of HZSM-5 support. The effect of HZSM-5 nanoparticles' acidity on methyl bromide dehydrobromination as catalyst was evaluated. As the results, MgHZ-360 catalyst with the highest concentration of Lewis acid sites showed excellent stability, which maintained methyl bromide conversion of up 97% in a period of 400 h on stream. Coke characterization by BET measurements and TGA/DTA and GC/MS analysis revealed that polymethylated naphthalenes species were formed outside the channels of the catalyst with higher acid intensity and higher Brønsted acid concentration during the initial period of reaction, while graphitic carbon formed in the channels of catalyst with lower acid intensity and higher Lewis acid concentration during the stable stage

Towards the Tradeoff Between Service Performance and Information Freshness

The last decade has witnessed an unprecedented growth in the demand for data-driven real-time services. These services are fueled by emerging applications that require rapidly injecting data streams and computing updated analytics results in real-time. In many of such applications, the computing resources are often shared for processing both updates from information sources and queries from end users. This requires joint scheduling of updates and queries because the service provider needs to make a critical decision upon receiving a user query: either it responds immediately with currently available but possibly stale information, or it first processes new updates and then responds with fresher information. Hence, the tradeoff between service performance and information freshness naturally arises in this context. To that end, we propose a simple single-server two-queue model that captures the coupled scheduling of updates and queries and aim to design scheduling policies that can properly address the important tradeoff between performance and freshness. Specifically, we consider the response time as a performance metric and the Age of Information (AoI) as a freshness metric. After demonstrating the limitations of the simplest FCFS policy, we propose two threshold-based policies: the Query-k policy that prioritizes queries and the Update-k policy that prioritizes updates. Then, we rigorously analyze both the response time and the Peak AoI (PAoI) of the threshold-based policies. Further, we propose the Joint-(M,N) policy, which allows flexibly prioritizing updates or queries through choosing different values of two thresholds M and N. Finally, we conduct simulations to evaluate the response time and the PAoI of the proposed policies. The results show that our proposed threshold-based policies can effectively control the balance between performance and freshness.Comment: Submitted to 2019 IEEE International Conference on Communications (ICC

Measurements of DC Resistivity of Insulating Oils

Insulating oils are widely used in power transformers. The oil insulation degrades under multiple stresses during the transformer operation, which affects the insulation integrity and consequently could cause transformer failures. DC resistivity is one of the dielectric parameters of insulating oil for assessing transformer insulation conditions. This paper presents results of DC resistivity measurements of oil samples including a mineral oil and a synthetic ester in fresh and thermally-aged conditions as well as two in-service aged oil samples in a cylindrical test cell under temperature range of 20oC to 100oC.Two standards of DC resistivity measurement namely IEC 60247 and ASTM D 1169 were applied. For mineral oil, the results of ASTM D 1169 are higher than those of IEC 60247 which is caused by polarity dependence of DC resistivity. For the other samples, the results are the same for both standards. Further investigation on polarity dependence shows that it might be caused by different ion injection strength of the inner and outer electrodes

Inception and Breakdown Voltages of Insulating Liquids under DC Stress

This paper investigated the streamer inception and breakdown properties of a mineral oil and a synthetic ester liquid under DC stress up to 100 kV. To observe the effect of tip radius on streamer inception, the point-plane electrodes configuration with a fixed gap distance of 10 mm and point electrode with theradii of 5 μm, 10 μm, 20 μm and 50 μm were used. To observe the effect of gap distance on breakdown voltage, a point-to-plane electrode configuration with a fixed tip radius of 10 μm and variable gap distances of 2 mm, 5 mm, 10 mm, 20 mm and 30 mm were used. Streamer current and emitted light signals were measured by using a 10 Ω current shunt and photomultiplier tube (PMT) respectively. The results indicated that initiation voltages of the synthetic ester liquid are slightly lower than those of the mineral oil for all the tip radii under both positive and negative polarities. Moreover, the synthetic ester liquid has lower breakdown voltages than the mineral oil for all the gap distance under both positive and negative polaritie

Chinese women in white : a study of nurses in Taiwan.

The work started when I first registered as a part time Postgraduate student at Warwick, after finishing my MSc degree in medical sociology at Bedford College, London University in October 1982. Some preliminary investment had been done and a few essays written while I was in Taiwan teaching in a medical school. But it was only after April 1985, when I secured a grant from the Chinese Central Government in Taiwan to come over to England again and switched to full time study that the real work could really start. Since then, many parts of the work have been changed, such as the target problems and the methodology to tackle them. The whole working process was dynamic. Ideas exchanged, floating to and fro between my supervisor, Professor Margaret Stacey and me over years to find out results, as well as problems and methods. Only the original purpose of the study (Chinese women) and the sample group (nurses) have remained the same and still fascinate me. The problems were focussed gradually. The process of emergence of the problems and the conceptual framework used in the study will be described in part 1: introduction. The methodology changed in response to the focusing of the problems. Both the original plan and the evolving current design will be presented in Part 2: the research process. The field work and data analysis will be also dealt with in the same part. Some further but small alterations away from the research pIan were made to adjust to the situation of the field work as it happened in practice. Part 3 will be the results of the historical and literature review. The literature review gave me a more clear and closer look at my sample against their background of Chinese women's life in the past (chapter 8) and at the present day in Taiwan (chapter 10). Also traditional Chinese women healers and carers and the modern nursing history (chapter 9) were brought to light to elucidate the problems in nursing today. Part 4 will be the emergent themes which were attained through analysis of the field work. From these themes, a general profile of the life of these women in our sample in present day Taiwan gradually emerged. In part 5 conclusions are drawn concerning 'the new patriarchy', in which our respondents' lives are formed, as always around their menfolk – father, husband and son - although with certain differences from the situation in the past

A Worst-Case Approximate Analysis of Peak Age-of-Information Via Robust Queueing Approach

A new timeliness metric, called Age-of-Information (AoI), has recently attracted a lot of research interests for real-time applications with information updates. It has been extensively studied for various queueing models based on the probabilistic approaches, where the analyses heavily depend on the properties of specific distributions (e.g., the memoryless property of the exponential distribution or the i.i.d. assumption). In this work, we take an alternative new approach, the robust queueing approach, to analyze the Peak Age-of-Information (PAoI). Specifically, we first model the uncertainty in the stochastic arrival and service processes using uncertainty sets. This enables us to approximate the expected PAoI performance for very general arrival and service processes, including those exhibiting heavy-tailed behaviors or correlations, where traditional probabilistic approaches cannot be applied. We then derive a new bound on the PAoI in the single-source single-server setting. Furthermore, we generalize our analysis to two-source single-server systems with symmetric arrivals, which involves new challenges (e.g., the service times of the updates from two sources are coupled in one single uncertainty set). Finally, through numerical experiments, we show that our new bounds provide a good approximation for the expected PAoI. Compared to some well-known bounds in the literature (e.g., one based on Kingman's bound under the i.i.d. assumption) that tends to be inaccurate under light load, our new approximation is accurate under both light and high loads, both of which are critical scenarios for the AoI performance.Comment: Published in IEEE INFOCOM 202

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic

In this study, we have prepared starch and Brown algae sugar ester dodecenylsuccinic, and by using infrared rays, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), we studied the structures and properties of the starch and Brown algae sugar ester dodecenylsuccinic. In addition, we studied the possibility of using this modified starch and Brown algae as emulsifier that can be used in ice cream

Infrared Optical Path Adjustment Method for Common-path Optical Coherence Tomography

A new, common-path, in-axis concentric beam-splitting Michelson interferometer is demonstrated for optical coherence tomography (OCT), which can be used to perform high resolution cross-sectional in vivo and in situ imaging of biological tissues. a piece of glass tube with its inner diameter smaller than the beamwidth of the collimated light is used to split the light into a reference and sample beam. in order to obtain the optimal spectral interferogram of this OCT system, an infrared optical path adjustment method was introduced in this paper. © (2012) Trans Tech Publications, Switzerland