This study was concerned with the most common reverse flow type of cyclones where the flow enters the cyclone through a tangential inlet and leaves via an axial outlet pipe at the top of the cyclone. Numerical computations of two different cyclones were based on the so-called Stairmand cyclone. The difference in geometry between these two cyclones was basically characterized by the geometrical swirl number Sg of 3.5 and 4. Turbulent secondary flows inside a straight square channel have been studied numerically by using Large Eddy Simulation (LES) in order to verify the implementation process. Prandtl’s secondary motion calculated by LES shows satisfying agreement with both, Direct Numerical Simulation (DNS) and experimental results. Numerical calculations were carried out at various axial positions and at the apex cone of a gas cyclone separator. Two different NS-solvers (a commercial one, and a research code), based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behavior. The flow was assumed as unsteady, incompressible and isothermal. A k − epsilon turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as RSM (Reynolds Stress Model) and LES (Large Eddy Simulation) have been used as well. The RSM simulation was performed using the commercial package CFX4.4, while for the LES calculations the research code MISTRAL/PartFlow-3D code developed in our multiphase research group has been applied utilizing the Smagorinsky model. It was found that the k − epsilon model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. These calculations of the continuous phase flow were the basis for modeling the behavior of the solid particles in the cyclone separator. Particle trajectories, pressure drop and the cyclone separation efficiency have been studied in some detail. This thesis is organized into five chapters. After an introduction and overview, chapter 2 deals with continuous phase flow turbulence modeling including the governing equations. The emphasis will be based on LES modelling. Furthermore, the disperse phase motion is treated in chapter 3. In chapter 4, the validation process of LES implementation with channel flow is presented. Moreover, prediction profiles of the gas flow are presented and discussed. In addition, disperse phase flow results are presented and discussed such as particle trajectories; pressure drop and cyclone separation efficiency are also discussed. Chapter 5 summarizes and concludes the thesis.

No description available.

No description available.

Single-particle tracking is a technique that allows for quantitative analysis of the localization and movement of particles. In this technique, trajectories are constructed by determining and connecting the positions of individual particles from consecutive images. Recent advances have made it possible to track hundreds of particles in an individual cell by labeling the particles of interest with photoactivatable or photoconvertible fluorescent proteins and tracking one or a few at a time. Single-particle tracking can be used to study the diffusion of particles. Here, we use intracellular single-particle tracking and trajectory simulations to study the diffusion of the fluorescent protein mEos2 in living Escherichia coli cells. Our data are consistent with a simple model in which mEos2 diffuses normally at 13 µm2 s−1 in the E. coli cytoplasm. Our approach can be used to study the diffusion of intracellular particles that can be labeled with mEos2 and are present at high copy numbers. Single-particle tracking can also be used to determine whether an individual particle is bound or free if the free particle diffuses significantly faster than its binding targets and remains bound or free for a long time. Here, we use single-particle tracking in living E. coli cells to determine the fractions of free ribosomal subunits, classify individual subunits as free or mRNA-bound, and quantify the degree of exclusion of bound and free subunits separately. We show that, unlike bound subunits, free subunits are not excluded from the nucleoid. This finding strongly suggests that translation of nascent mRNAs can start throughout the nucleoid, which reconciles the spatial separation of DNA and ribosomes with co-transcriptional translation. We also show that, after translation inhibition, free subunit precursors are partially excluded from the compacted nucleoid. This finding indicates that it is active translation that normally allows ribosomal subunits to assemble on nascent mRNAs throughout the nucleoid and that the effects of translation inhibitors are enhanced by the limited access of ribosomal subunits to nascent mRNAs in the compacted nucleoid.

The circulation and gradual transformation in properties of oceanic water masses is a matter of great interest for short-term weather and biological forecasting, as well as long-term climate change. It is usually agreed that the Nordic Seas between Greenland and Norway are key to these transformations since they are an important producer of dense water, a process central to the theory of the global thermohaline circulation. In this study, one component of this deep water is examined – that formed in the Nordic Seas themselves from the inflowing North Atlantic Current. Using Lagrangian particle tracking applied to a 50-year global ocean hindcast simulation, it is concluded that only about 6% of the inflowing North Atlantic Current is thus transformed, and that most of these transformations occur in boundary currents. Furthermore, it is found that the densified North Atlantic water attains only medium depths instead of joining the deep overflows. The model’s poor representation of vertical mixing, however, limits the applicability of this study to deep water formation.

Essen, Universiẗat, Diss., 2005--Duisburg.

No description available.

Fluid jet polishing (FJP) is a new advanced polishing technology that finds applications in many industries, especially in the optics industry. With the broad application of various surfaces in optics, the sub-micrometric scale and the nanometric surface roughness accuracy are major challenges. Fluid jet polishing is a technology developed from abrasive water jet machining. This technology is a water jet cutting technology, which uses high-pressure flow to cut/remove materials. In this thesis, the working principle, and simulations, as well as verification of fluid jet polishing are thoroughly investigated. The verification of fluid jet polishing in this thesis includes velocity distribution and material removal derivations. The amount of material removed is directly related to the impact velocity of a particle with a surface, which helps define its abrasive particle velocity. During polishing, the particles travel in a solution called slurry. Due to the relatively similar velocity of the particles and the slurry, the particles and the slurry are assumed to be traveling at the same rate. In this thesis, three specific examples are investigated through the creation of an advanced model using FLUENT, a computational fluid dynamics software. The model simulates the particle path during the fluid jet polishing process, and this thesis compares the simulation results to prior analytical and experimental results. The results indicate that the fluid jet polishing erosion area at a particular location is axisymmetric when the 2D cross-section shape is investigated. As the impingement angle of the fluid jet is reduced, the center dead area, where no polishing is observed, approaches zero. vii Additionally, the horizontal component of the velocity vector initially increases then decreases as one moves away from the center stagnation point. Finally, this thesis demonstrates that the erosion depth into the surface that is polished increases when the working pressure of the fluid is increased. This thesis finds that when the distance between the fluid jet and the workpiece is 7 mm, material removal is maximum.

No description available.

This thesis describes searches for a heavy charged Higgs boson decaying into a top and bottom quark pair, and the development of a hardware track trigger with theATLAS experiment. The data for the two searches was collected with the ATLAS detector at the Large Hadron Collider(LHC) with pp collision energies of √s = 8 and 13 TeV, and corresponds to an integrated luminosity of 20.3 and 13.2 fb-1 respectively. The main background for this signal is the production of tt̄ pairs with additional heavy flavor radiation. The searches with a single lepton in the final state found no evidence of a charged Higgs boson, and set 95% CLS upper limits on the production times branching ratio for masses ranging between 200-1000 GeV. The preparation of using the final state with two leptons in future searches is discussed. The design of a hardware track trigger based on pattern matching and linear track fitting was studied for the purpose of reducing the high event rates of the High-Luminosity LHC, which is expected to provide pp collisions with a luminosity about five times the nominal value, in the second half of the 2020’s. A simulation framework was developed to emulate the pattern matching and was used to test its ability to filter hits in high pile-up environments. The results of this simulation, together with simulations of the track fitting and latency, show that such a track trigger is a viable option for the ATLAS experiment in the High Luminosity-LHC era.