Theory of Soft Centrifugation of Structured Fluids Based on Hydrotropes

Centrifugation is a versatile and powerful technique used in analytical or preparative procedures. In countless variants - low-speed/high-speed/ultracentrifugation, in batch process or continuously operated - it is indispensable in industrial applications and the laboratory. However, some phenomena that have been observed over the years in connection with centrifugation have not yet been conclusively clarified not to mention reliably predicted. The aim of this work is to gain deeper knowledge through the theoretical description of different systems in centrifugal fields. For this purpose, a general description of systems in external fields was developed as a classical density functional theory. The energy of a system is composed of internal (thermodynamic) and external (gravitational) contributions. This theoretical framework is universally applicable to all systems, but requires an adequate description of the internal force component. In the context of this work, several systems were considered with the method. On the one hand, specific composition profiles can be determined as a function of the radius, or more general Centrifugation Maps can be calculated for visualisation. The latter show the local composition changes in the entire phase diagram with the help of steam lines. The strength of this visualisation method is that it is completely independent of specific external fields, because only the magnitude of the gradients - but not the direction - is influenced by the external field. In this way, regions in the ternary phase diagram can be directly identified that react particularly strongly (or weakly) to centrifugation. The theory was applied to a simple, regular (water/ethanol/ethyl acetate) and a more complex, aggregating (water/ethanol/octanol) system. In both systems, it was shown consistently that compositions close to the phase boundary are significantly more influenced by the external field. Ethanol-rich compositions far in the single-phase range react almost not at all to centrifugation in the first system and only slightly in the second. Close to the phase boundary and especially around the critical point, centrifugation is clearly more efficient, which manifests itself in phase separations and extremely high composition gradients. As a third system, a binary mixture of a pair of enantiomers was investigated. It was shown that small compositional dependencies of the density can be used to separate racemates. Although these density changes have been described in detail in crystals, their occurrence in fluids is much less documented. The possibility of racemate resolution without any additives is nevertheless theoretically possible, albeit with increased equipment requirements. The last part of this work deals with the molecular dynamics study of a derivative of the surfactant AOT. In combination with small angle scattering, the aggregation behaviour was investigated. The increased critical micelle concentration and the absence of a liquid crystalline phase oppose the classification as a classical surfactant, the aggregation and scattering already in the binary aqueous mixture oppose classical hydrotropes, which is why the molecule is identified as a link between the two classes. The molecular dynamic investigation is only a first step towards a better understanding of progressively aggregating systems, which should ultimately enable the application of centrifugation theory to this and similar systems

Engineering Software Solution for Thermal Elastohydrodynamic Lubrication Using Multiphysics Software

The complexity of thermal elastohydrodynamic lubrication (TEHL) problems has led to a variety of specialised numerical approaches ranging from finite difference based direct and inverse iterative methods such as Multilevel Multi-Integration solvers, via differential deflection methods, to finite element based full-system approaches. Hence, not only knowledge of the physical and technical relationships but also knowledge of the numerical procedures and solvers is necessary to perform TEHL simulations. Considering the state of the art of multiphysics software, the authors note the absence of a commercial software package for solving TEHL problems embedded in larger multiphysics software. By providing guidelines on how to implement a TEHL simulation model in commercial multiphysics software, the authors want to stimulate the research in computational tribology, so that, hopefully, the research focus can be shifted even more on physical modelling instead of numerical modelling. Validations, as well as result examples of the suggested TEHL model by means of simulated coefficients of friction, coated surfaces, and nonsmooth surfaces, highlight the flexibility and simplicity of the presented approach

CFD Simulations of Splash Losses of a Gearbox

Efficiency is becoming a main concern in the design of power transmissions. It is therefore important, especially during the design phase, to have appropriate models to predict the power losses. For this reason, CFD (computational fluid dynamics) simulations were performed in order to understand the influence of geometrical and operating parameters on the losses in power transmissions. The results of the model were validated with experimental results

Two Types of Liquid Phase Separation Induced by Soft Centrifugation in Aqueous Ethyl Acetate Using Ethanol as Cosolvent

Water-ethyl acetate-ethanol is widely used as “green” extractant system. We show that two different types of phase separation can be induced upon centrifugation in this ternary system using ethanol as a co-solvent of water and ethyl acetate (EA): centrifuge-induced criticality and centrifuge-induced emulsification. The expected composition profiles of samples after centrifugation can be represented by bent lines in a ternary phase diagram when gravitational energy is added to the free energy of mixing. The experimental equilibrium composition profiles behave qualitatively as expected and can be predicted using a phenomenological theory of mixing. The concentration gradients are small except near the critical point, as expected for small molecules. Nevertheless, they are usable when accompanied by temperature cycles. These findings open new possibilities of centrifugal separation, even if control is delicate during temperature cycles. These schemes are accessible even at relatively low centrifugation speed for molecules that float and sediment with apparent molar masses several hundred times larger than the molecular mass

PowerShell Empire : Usage and activity identification of a command and control framework

Die einzelnen Phasen der Angriffe auf Computernetzwerke werden heute zunehmend mit speziell dafür konzipierter Software durchgeführt. Für die Aufrechterhaltung der Verbindung zum kompromittierten Netzwerk sind sogenannte Command & Control Frameworks ein gängiges Mittel. Ein Vertreter dieser Frameworks ist PowerShell Empire, welches hauptsächlich auf der Skriptsprache PowerShell von Microsoft basiert, die Angriffsziele jedoch nicht auf Windowssysteme beschränkt sind. In dieser Arbeit wird dieses Framework vorgestellt und Szenarien für den Einsatz aufgezeigt. Durch Untersuchung von Netzwerkmitschnitten, sollen zudem Erkennungsmerkmale zur Identifikation der Aktivität von Empire herausgearbeitet werden

Studien zu den Ethnika des Stephanos von Byzanz

von Eduard Stemplinge