Zur Dynamik einfacher Rotoren in aerodynamischen Radialgleitlagern mit Pufferfolie

In der Arbeit wird ein neues Modell eines aerodynamischen Radialgleitlagers mit Pufferfolie entwickelt, validiert und diskutiert. Durch die Anwendung eines Modellreduktionverfahrens ist das nichtlineare Modell rechenzeiteffizient und für den Einsatz in gekoppelten Rotor-Lager-Simulationen geeignet. Mittels numerischer Stabilitäts- und Bifurkationsanalysen wird das Verhalten einfacher Rotorsysteme in Radialgleitlagern mit gasförmigem Schmierstoff untersucht und verschiedene lineare und nichtlineare Schwingungsphänomene identifiziert

Digging for Dark Matter: Spectral Analysis and Discovery Potential of Paleo-Detectors

Paleo-detectors are a recently proposed method for the direct detection of Dark Matter (DM). In such detectors, one would search for the persistent damage features left by DM--nucleus interactions in ancient minerals. Initial sensitivity projections have shown that paleo-detectors could probe much of the remaining Weakly Interacting Massive Particle (WIMP) parameter space. In this paper, we improve upon the cut-and-count approach previously used to estimate the sensitivity by performing a full spectral analysis of the background- and DM-induced signal spectra. We consider two scenarios for the systematic errors on the background spectra: i) systematic errors on the normalization only, and ii) systematic errors on the shape of the backgrounds. We find that the projected sensitivity is rather robust to imperfect knowledge of the backgrounds. Finally, we study how well the parameters of the true WIMP model could be reconstructed in the hypothetical case of a WIMP discovery.Comment: 14 pages, 5 figures, code available at https://github.com/tedwards2412/paleo_detectors/ . v2: Added additional analysis theory details, matches version published in PR

Efficiency Improvement of a Constant Pressure System using an Intermediate Pressure Line

The paper introduces a new hydraulic system based on a constant pressure system with the aim to increase the efficiency of actuation of hydraulic cylinders in mobile machines. Using a third pressure level located between high pressure and tank pressure called intermediate pressure the system enables additional pressure potentials from high pressure to intermediate pressure and from intermediate pressure to tank pressure. This reduces throttle losses at hydraulic cylinders when driven at low or medium loads. An accumulator connected to the intermediate pressure line is being charged or discharged in function of which pressure potential is currently used. Using the example of a typical duty cycle of a wheel loader the paper describes how the accumulator can be applied in order to reach best efficiency results for the new system and it reveals a theoretical efficiency improvement of 20% compared to a conventional Load Sensing system. Furthermore it proposes an online control strategy using Model Predictive Control with an optimization algorithm created with the Dynamic Programming method

Foil air bearing rotor interaction -Bifurcation analysis of a Laval rotor

Air bearings offer a high potential for improving high speed rotating machinery. The major advantage is the low friction loss, due to the low viscosity of the lubricating fluid. However, these bearings require either an external pressure supply or high rotating speeds to build up a load carrying fluid film. Furthermore, aerodynamic bearings, which refer to the latter mentioned kind, are prone to instabilities, Gross et al. (1980). A compliant bearing structure is supposed to suppress these vibrations, or at least minimize the amplitudes, Howard et al. (2001). Within this contribution the effects of the bearing compliance, neglecting friction and damping, on the onset and resulting rotor vibration are investigated

Privacy-aware Publication of Wi-Fi Sensor Data for Crowd Monitoring and Tourism Analytics

Estimating visitor frequency in urban areas often relies on camera-based solutions or the active participation of individuals using smartphone applications or devices with RFID or Bluetooth technology. This paper presents the results of a preliminary study on anonymous data collection as a basis for data-driven visitor guidance in Bamberg’s Old Town, using passive, non-intrusive and low-cost Wi-Fi sensors. The study includes a field test installation to evaluate data quality under robust anonymization measures. The data collected as part of the project will be made available to the public in the Mobilithek of the Federal Ministry of Digital Affairs and Transport (BMDV). Still, the collection of Wi-Fi probe requests raises legitimate privacy concerns. We address potential attack models for identifying and tracking devices based on these requests and explain the data collection architecture and Technical Data Protection Concept implemented within CrowdAnym to mitigate these risks. We evaluate the impact of our approach on the quality of the CrowdAnym dataset by comparing the data from one sensor location with the number of people counted by a nearby laser scanner. We are able to show that our approach approximates visitor density well, however the deviation of our data from ground truth increases as visitor frequency increases

Computational Analysis of Foil Air Journal Bearings Using a Runtime-Efficient Segmented Foil Model

This contribution is concerned with the development and the implementation of a foil air journal bearing model. For this purpose, the numerical procedure solving the Reynolds equation for compressible fluids has to be coupled to a compliant foil model. The presented beam-based approach is supposed to reproduce most of the experimentally known particularities in the mechanical behavior of the foil structure, while being at least as runtime-efficient as the commonly used simple elastic foundation model. The developed modeling approach will be validated by comparing simulation results to data found with a more complex reference model. In the analysis part, most notably, the top foil compliance is shown to deteriorate the load-carrying capacity of air bearings. Moreover, the influence of the top foil compliance on the dynamics of a rigid rotor supported by two foil air journal bearings will be discussed.</jats:p

Selective or random panel dropout? An investigation of personality and relationship parameters

Klatzka C, Baum MA, Hahn E. Selective or random panel dropout? An investigation of personality and relationship parameters. TwinLife Working Paper Series. Vol 03. Bielefeld: Project TwinLife "Genetic and social causes of life chances" (Universität Bielefeld / Universität des Saarlandes); 2019.In social sciences, longitudinal studies represent a common form of study design. However, this form of data collection may face the special problem of panel attrition over subsequent waves – a circumstance that can lead to a biased sample. As a consequence, longitudinal analyses may become flawed if the bias is unknown or not corrected. Previous research on panel attrition revealed that dropout can be related to several specific characteristics, such as sex, personality, or relationship status of the participants. As twins are a core feature of twin-studies – twin similarity a key tool in behavioral genetics – relational characteristics of this special siblinghood may play a crucial role in re-participating, too. Therefore, the aim of the present study was to investigate panel attrition with respect to certain personality traits (Big Five) and relational characteristics (sibling relationship and satisfaction with sibling relationship) to estimate potential biases as a basis for corrections in future studies. Analyses were not only performed on an individual level but also regarding twin pair resemblance as this is the main source of information in behavior genetic twin studies. The sample consisted of 4,097 twin pairs and 8,281 of their family members from wave one of the German TwinLife study. 60.9 % of the initial sample re-participated in wave 2. Results indicate that there are no consistent patterns in personality or relational characteristics across family members, age cohorts of the twins, and sexes regarding panel attrition. There also seem to be no consistent patterns regarding differences in twin similarity across re- and non-re-participators. Subsequently, selective panel dropout with respect to personal characteristics seems to be of minor importance in the TwinLife study and corrections may only be necessary in selective cases