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Method for the consideration of statistically distributed geometrical deviations in the design of cylindrical roller bearing arrangements
Get PDFRolling bearings are of great importance in all areas of mechanical engineering due to their precise and low-friction guidance of rotating components at low cost. The design of rolling bearing arrangements is usually based on approximately ideal geometries of bearings and adjacent parts on which the bearing seats are located. However, real components inevitably show statistically distributed deviations from their nominal shapes, which are limited by tolerances. Tight tolerances result in high manufacturing costs while on the other hand their expansion leads to an increase of occurring geometrical deviations which cause changes in the bearing-internal contact and load conditions and can thus impair the operating behavior of the bearing, e.g. with regard to fatigue life, frictional torque or vibration behavior. By taking these effects into account in the design stage, potential problems in operation can be identified early during development and countermeasures can be taken, e.g. by adjusting bearing and seat tolerances. This enables an improvement of overall product quality and a reduction of costs. This paper presents a method for the integration of component deviations in the computation of the fatigue life (Lnmr) and dynamic behavior of cylindrical roller bearing arrangements—both of which are crucial design criteria—based on a combination of statistical tolerance analysis and multi-body simulations. The method is applied to an exemplary use case for illustration
Antikörper-basierte Zytokinmimetika
Get PDFAntibody-based cytokine mimetics emerged as promising entities in order to modulate an immune response. These surrogate agonists are bi- and multifunctional antibody-derived molecules that mimic the function of a cytokine by agonizing a specific cytokine receptor. Due to the high modularity of antibody-based building blocks, cytokine functionalities can be highly engineered, for instance with regards to signalling strength and bias
Die intersektionale Perspektive auf letale autonome Waffensysteme: Eine Analyse der Diskurse innerhalb der UN-Waffenkonvention
Get PDFDie UNCCW diskutiert die Regulierung autonomer Waffensysteme mit Fokus auf technische und rechtliche Fragen. Zivilgesellschaftliche Akteure und NGOs bringen zudem intersektionale Perspektiven ein. Der Beitrag untersucht, inwiefern diese Perspektiven in der UN-Debatte sichtbar werden. Innerhalb der intersektionalen Kategorien werden die Ankerbegriffe Gender und Race am meisten berücksichtigt. Die Relevanz von NGOs in der Gesamtdebatte zeigt sich daran, dass sie neue Themen einbringen, die an etablierte Diskurse anknüpfen
A hydrogeological overview of the Upper Mega Aquifer System on the Arabian Platform
Get PDFWith an extent of ~1,860,000 km², the Upper Mega Aquifer System on the Arabian Platform forms one of the largest aquifer systems of the world. It is built up by several bedrock aquifers (sandstone and karstified limestone aquifers), which are imperfectly hydraulically connected to each other. The principal aquifers are the Wasia-Biyadh sandstone aquifer, and the karstified Umm Er Radhuma and Dammam limestone aquifers. The stored groundwater is mainly fossil. Groundwater recharge took place in the geologic past under more humid climatic conditions. Due to the good water quality and high yield, the aquifers are intensively exploited, which has caused depletion of the groundwater resources. The presented qualitative and semi-quantitative description of the hydrogeology and the groundwater budget is the basis for integrated groundwater management of the aquifer system
The temperature dependence of Mössbauer quadrupole splitting values: a quantum chemical analysis
Get PDFThe two key parameters extracted from Mössbauer spectroscopy, isomer shift and quadrupole splitting, have well-known temperature dependencies. While the behavior of the values following a temperature change has long been known, its microscopic origins are less clear. For quantum chemical calculations – formally representing the situation at 0 K – significant discrepancies with the experiment can arise, especially at elevated temperatures. Herein, we introduce an ensemble-based approach for capturing the temperature dependence of the quadrupole splitting. Our method is exemplified with [Fe(TPP)(2-MeHIm)], an iron(ii) high spin system. We rationalise the temperature dependence by changes in the shape of the charge distribution due to vibrational distortion. By using a normal mode fitting approach, we isolated collective nuclear movements associated with the change in the quadrupole splitting
Membrane Aerated Biofilm Reactors for Nitrogen Removal from Municipal Wastewater
Get PDFThis dissertation investigates Membrane Aerated Biofilm Reactors (MABRs) for nitrogen removal in the context of municipal wastewater treatment. As part of these studies, several MABR systems were constructed at the laboratory scale. Both hollow fiber and flat sheet membrane configurations were used in the reactors. These were operated and compared under a variety of operating conditions such as feed composition, surface loading, aeration, and scouring. Special attention was given to the comparison of intermittent and continuous aeration pattern, as well as the effect of different scouring frequencies on biofilm control. In addition to the analysis of dissolved nitrogen and organic carbon, the microbial community in the biofilm and the suspended biomass were studied (P1 and P2), the characteristics of the biofilm and sludge production were determined (P1, P2 and P3), and oxygen profiles in the biofilm and nitrous oxide emissions were measured with microelectrodes (P3).
During the studies, short-cut nitrogen removal was achieved in some of the MABRs under suitable conditions. Intermittent aeration and frequent scouring proved to be particularly beneficial to this process, resulting in high total nitrogen removal rates. In the experiments, continuous aeration, regardless of scouring, usually resulted in nitrification of the ammonium, which, together with organic carbon, tended to result in classical nitrogen removal by denitrification.
Analysis of the microbial community by qPCR and 16S amplicon sequencing revealed significant differences between the biofilm and the detached biomass or free-growing cells. Furthermore, the aeration and scouring strategies were shown to have a significant impact on the microbial community of the different MABR systems. The application of a high scouring frequency can help to limit NOB retention and promote AOB abundance in membrane-aerated biofilms due to the detachment of the biofilm. A low scouring frequency promotes NOB retention in the biofilm due to less biomass detachment and thus higher biofilm age. Continuously aerated MABRs were found to be more sensitive to high shear stress than intermittent-aerated reactors. Frequent scouring sheared off more biomass from the biofilm of the continuous-aerated reactor, whereas there were minor differences between the scouring strategies in terms of biofilm detachment in the intermittent-aerated reactors.
Analysis of the biofilm with oxygen microelectrodes revealed unique oxygen profiles depending on the operating conditions of the reactors. It is particularly noteworthy that the different oxygen exposure times and concentrations in the different layers of the biofilm could be precisely analyzed during intermittent aeration. Nitrous oxide emissions from the MABR systems were low compared to some conventional systems, but no hotspots of nitrous oxide production or reduction within the biofilm could be identified.
The studies showed that MABR have a high potential for efficient nitrogen removal in municipal wastewater treatment. Promising operating conditions were found to allow for short-cut nitrogen removal and targeted control of biofilm thickness. These studies provide a basis for future research in the field of MABR systems for municipal wastewater treatment
Aerodynamisches Verhalten eines transsonischen Gasturbinenverdichters unter realistischen Einlaufstörungen
Get PDFIn Gasturbinenkraftwerken erfolgt die Luftzuführung zum Verdichter über ein komplexes Einlaufsystem. Durch die Art der Luftführung entstehen neben Druckverlusten zusätzliche Sekundärströmungen, die in einem inhomogenen Strömungsfeld an der Verdichtereintrittsebene resultieren. Der Einfluss dieser Einlaufstörungen auf das Betriebsverhalten einer Verdichterfrontstufe wird in der vorliegenden Arbeit mittels experimenteller und begleitender numerischer Untersuchungen analysiert. Die Experimente wurden an einem transsonischen Verdichterprüfstand durchgeführt. Die Kopplung einer maschinenähnlichen Zuströmstrecke mit einer repräsentativen Verdichterstufe ermöglicht die Untersuchung unter anwendungsnahen Betriebsbedingungen.
Die Ergebnisse zeigen, dass sich infolge der Strömungsumlenkung im Zuluftsystem zwei gegenläufig rotierende Wirbel ausbilden, die eine kombinierte Winkel- und Totaldruckstörung am Eintritt des Verdichters hervorrufen. Die Einlaufstörung wirkt sich auf das globale, stationäre Betriebsverhalten der Verdichterstufe in Form eines erhöhten Eintrittsdruckverlusts aus. Darüber hinaus breiten sich die Strömungsinhomogenitäten durch den Verdichter hindurch aus und beeinflussen das Betriebsverhalten der nachfolgenden Stufen in der Gesamtmaschine. Die axiale Störungsfortpflanzung durch den Rotor und den Stator verändert sich dabei grundlegend mit dem Betriebspunkt des Verdichters. Zusätzlich beeinflusst das Zuluftsystem das transiente Verhalten der Verdichterstufe an der aerodynamischen Stabilitätsgrenze. Zum einen wird für das Vorhandensein von Einlaufstörungen eine Erweiterung der Kennfeldbreite beobachtet. Zum anderen verändert sich mit der Zuströmgeometrie die Varianz und die Ausprägung der Phänomene, die sich nach Überschreitung der Stabilitätsgrenze einstellen
A Summary of McEliece-Type Cryptosystems and their Security
No full textIn this paper we give an overview of some of the cryptographic applications which were derived from the proposal of R. J. McEliece to use error correcting codes for cryptographic purposes. Code based cryptography is an interesting alternative to number theoretic cryptography. Many basic cryptographic functions like encryption, signing, hashing, etc. can be realized using code theoretic concepts.
In this paper we briefly show how to correct errors in transmitted data by employing Goppa codes and describe possible applications to public key cryptography.
The main focus of this paper is to provide detailed insight into the state of art of cryptanalysis of the McEliece cryptosystem and the effect on different cryptographic applications. We conclude, that for code based cryptography a public key of 88KB offers sufficient security for encryption, while we need a public key of at least 597KB for secure signing
Ekkehard Felder (Hg.). 2013. Faktizitätsherstellung in Diskursen. Die Macht des Deklarativen
Get PDFSeit dem Jahr 2005 besteht das Forschungsnetzwerk Sprache und Wissen, dessen Mitglieder Wissenschaftlerinnen und Wissenschaftler verschiedener Disziplinen sind, die sich für das Verhältnis von Sprache und Wissen interessieren und dieses aktiv beforschen. Dem Netzwerk „liegt die Sprachauffassung zugrunde, dass jede Erkenntnis auch sprachabhängig ist“ (Felder 2008: 270). Dass Sprache die Wirklichkeit nicht bloß abbildet, sondern häufig erst konstituiert, dass „die gesamtgesellschaftlich relevanten Wissensbestände durch die eingesetzten sprachlichen Mittel (mit)geformt“ (Felder 2008: 270) werden, ist eine Prämisse, die inzwischen vielen diskurslinguistischen Arbeiten zugrunde liegt (z. B. Radeiski 2011, Spieß 2011, Vogel 2012, Kalwa 2013). Der von Ekkehard Felder herausgegebene Sammelband fragt, „wie kommunikativ in Sprache erst hergestellt wird, was schon da zu sein scheint“ (S. V)
Crystal structure of di[potassium(18-crown-6)]dipotassium nonastannide(4–)—diethylenediamine solvate (1:1.5), [K(C₁₂H₂₄O₆)]₂K₂[Sn₉] · 1.5C₂N₂H₈
No full textC₂₇H₆₀K₄N₃O₁₂Sn₉, monoclinic, P12₁/n1(No. 14), a = 10.410(2) Å, b = 25.659(5) Å, c = 20.636(4) Å, β = 102.56(3)°, V = 5380.2 ų, Z = 4, Rgt(F) = 0.030, wRref(F²) = 0.072, T = 150 K