Relatively few studies have been carried out on the turbulent wake structure of a finite circular cylinder and a stack partially immersed in a flat-plate turbulent boundary layer. There is a need to develop a better understanding of the wakes of these structures, since they have many important engineering applications. This thesis investigates the influence of the aspect ratio on the wake of a finite circular cylinder and the effects of the ratio of jet flow velocity to crossflow velocity (velocity ratio, R) on the wake of a stack in a cross-flow. <p>The wake characteristics of flows over a finite circular cylinder at four different aspect ratios (AR = 3, 5, 7 and 9) were investigated experimentally at a Reynolds number of ReD = 6104 using two-component thermal anemometry. Each cylinder was mounted normal to a ground plane and was either completely or partially immersed in a flat-plate turbulent boundary layer. The ratio of boundary layer thickness to the cylinder diameter was 3. <p>A similar turbulent wake structure (time-averaged velocity, turbulence intensity, and Reynolds shear stress distributions) was found for the cylinders with AR = 5, 7, and 9, while a distinctly different turbulent wake structure was found for the cylinder with AR = 3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake. In addition, irrespective of the value of AR, high values were observed for the skewness and flatness factors around the free end of the cylinders, which may be attributed to the interaction of the tip vortex structures and downwash flow that dominates this region of the cylinder.<p>The wake characteristics of a stack of aspect ratio AR = 9 were investigated using both the seven-hole pressure probe and thermal anemometry. The seven-hole probe was used to measure the three components of the time-averaged velocity field, while the thermal anemometry was used to measure two components of the turbulent velocity field at various downstream locations from the stack. The stack was mounted normal to the ground plane and was partially immersed in a flat-plate turbulent boundary layer, for which the ratio of boundary layer thickness to the stack diameter was 4.5. In addition, measurements of the vortex shedding frequency were made with a single-component hot-wire probe. The cross-flow Reynolds number was ReD = 2.3 x 104, the jet Reynolds number ranged from Red = 7.6 x 103 to 4.7 x 104, and R was varied from 0 to 3. <p>In the stack study, three flow regimes were identified depending on the value of R: the downwash (R < 0.7), cross-wind-dominated (0.7 < R < 1.5), and jet-dominated (R ≥ 1.5) flow regimes. Each flow regime had a distinct structure for the time-averaged velocity and streamwise vorticity fields, and turbulence characteristics, as well as the variation of the Strouhal number and the power spectrum of the streamwise velocity fluctuations along the stack height. The turbulence structure is complex and changes in the streamwise and wall-normal directions within the near and intermediate stack and jet wakes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack (ground plane), respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.

Different approaches have been developed for TCP/IP fingerprinting, but none of these approaches is suited for Internet-wide fingerprinting. In this work, we develop approaches that rigorously tackle the issue of noise and packet loss while carrying out Internet-wide fingerprinting. We then carry out an Internet-wide scan to determine the distribution of different operating systems on the Internet. The results of our scan indicate that there are approximately 8.9 million publicly accessible web-servers on the Internet running Linux, while there are nearly 9.6 million web-servers with different embedded operating systems.

In this thesis, a new stack architecture for sensor networks is proposed. The stack consists of the following layers: application, query, aggregation, network, MAC and physical. Various algorithms are implemented using this stack and it is shown that this stack is modular. Following an overview of sensor networks, the previous protocol stack suggestions for sensor networks are examined. Sensor network algorithms that can be classified as sensor data management systems are surveyed and compared with each other. Four of the surveyed algorithms, namely, TAG, Synopsis Diffusion, Tributary-Delta and Directed Diffusion are implemented using the introduced stack. The implementation is performed using a sensor network model developed with OMNeT++ simulator. The simulation results are compared to the original results of these algorithms. Obtaining similar results, the stack and algorithm implementations are validated, moreover, it is shown that the stack does not induce any performance degradation. Using the implementation details of the algorithms, the modularity of the suggested stack is demonstrated. Finally, additional benefits of the stack are discussed.

In this dissertation, we propose using and analytically evaluate the predictive multicast polling scheme and the tree splitting algorithm for medium access control in interference dominating wireless access networks with random traffic and finite nodes. In an interference dominating wireless network, a receiver could simultaneously receive multiple packets from a variety of transmitters, as long as the signal-to-interference-plus-noise ratio exceeds a predetermined threshold. We concentrate on the case of in which the maximum queue size in a node is finite. We use discrete-time Markov chains, reward processes and regenerative processes to derive the throughput, the packet blocking probability, the average packet delay, and the average system size. We show that the system performance of the predictive multicast polling scheme can be significantly improved with a few additional buffers in the queues. Our study also shows that exact performance of the splitting algorithm depends on the total number of nodes in the networks. We verify our numerical results by rigorous mathematical proof and computer simulations.

Zugl.: Dresden, Techn. Univ., Diss., 2009

Agricultural operations across the United States are encountering difficulties complying with current air pollution regulations for particulate matter (PM). PM is currently regulated in terms of particle diameters less than or equal to a nominal 10 μm (PM10); however, current legislation is underway to regulate PM with diameters less than or equal to a nominal 2.5 μm (PM2.5). The goals of this research were to determine the biases and uncertainties associated with current PM10 and PM2.5 sampling methods and to determine the extent to which these errors may impact the determination of cotton gin emission factors. Ideally, PM samplers would produce an accurate measure of the pollutant indicator; for instance, a PM10 sampler would produce an accurate measure of PM less than or equal to 10 μm. However, samplers are not perfect and errors are introduced because of the established tolerances associated with sampler performance characteristics and the interaction of particle size and sampler performance characteristics. Results of this research indicated that a source emitting PM characterized by a mass median diameter (MMD) of 20 μm and a geometric standard deviation (GSD) of 1.5 could be forced to comply with a 3.2 and 14 times more stringent regulation of PM10 and PM2.5, respectively, than a source emitting PM characterized by a MMD of 10 μm and a GSD of 1.5. These estimates are based on both sources emitting the same concentrations of true PM or concentrations corresponding to the particle diameters less than the size of interest. Various methods were used to estimate the true PM10 and PM2.5 emission factors associated with cotton gin exhausts and the extent to which the sampler errors impacted the PM regulation. Results from this research indicated that current cotton gin emission factors could be over-estimated by about 40%. This over-estimation is a consequence of the relatively large PM associated with cotton gin exhausts. These PM sampling errors are contributing to the misappropriation of source emissions in State Implementation Plans, essentially forcing Air Pollution Regulatory Agencies to require additional controls on sources that may be incorrectly classified has high emitters.

The presence of gas hydrate and free gas within marine sediments, deposited along the South Shetland margin, offshore the Antarctic Peninsula, was confirmed by low and high resolution geophysical data, acquired during three research cruises. Seismic data analysis has revealed the presence of a bottom simulating reflector that is very strong and continuous in the eastern part of the margin. This area can be considered as a useful site to study the seismic characteristics of sediments containing gas hydrate, with a particular focus on the estimation of gas hydrate and free gas amounts in the pore space. Pre-stack depth migration and tomographic inversion were performed to produce a regional velocity field of gas-phase bearing sediments and to obtain information about the average thickness of gas hydrate and free gas layers. Using these data and theoretical models, the gas hydrate and free gas concentrations can be estimated. Moreover, the common image gather semblance analysis revealed the presence of detailed features, such as layers with small thickness characterised by low velocity alternating with high velocity layers, below and above the bottom simulating reflector. These layers are associated with free gas trapped within the hydrate stability zone and deeper sediments. Thus, the use of the detailed and the regional velocity field analysis is important to give a more reliable estimate of gas content in the marine sediments.

The CanX-4 and CanX-5 mission currently under development at The University of Toronto Institute for Aerospace Studies Space Flight Laboratory UTIAS/SFL is a challenging formation flying technology demonstration. Its requirements of sub-metre control accuracy have yet to be realized with nanosatellites. Many large technical challenges must be addressed in order to ensure the success of the CanX-4/5 mission. This includes the development of software for an intersatellite communication system, integration and optimization of key formation flying algorithms onto the Payload On-Board Computer as well as the development of a Hardware-In-The-Loop simulator for full on-orbit mission simulations. This thesis will provide background knowledge of the Space Flight Laboratory and its activities, the CanX-4/5 mission, and nally highlight the authors contributions to overcoming each of these technical challenges and ensuring the success of the CanX-4 and CanX-5 mission.

Controlling the quantum states of charge (excitons) or spin-polarized carriers in semiconductor quantum dots (QDs) has been the focus of a considerable research effort in recent years due to the strong promise of using this approach to develop solid state quantum computing hardware. The long-term scalability of this type of quantum computing architecture is enhanced by the use of QDs emitting in the telecom band, which would exploit the established photonic infrastructure. This thesis reports the use of all optical infrared experimental techniques to control exciton dynamics in two different QD samples consisting of InAs/GaAs QDs and InAs/InP QDs within a planar microcavity. An infrared quantum control apparatus was developed and used to apply optimized shaping masks to ultrafast pulses from an optical parametric oscillator. Pulse shaping protocols designed to execute a two-qubit controlled-rotation operation on an individual semiconductor QD were demonstrated and characterized. The quantum control apparatus was then implemented in simultaneous single qubit rotations using two uncoupled, distant InAs/GaAs QDs. These optimal control experiments demonstrated high fidelity optical manipulation of exciton states in the two QDs using a single broadband laser pulse, representing a step forward on the path to a scalable QD architecture and showcasing the power of pulse shaping techniques for quantum control on solid state qubits. As an alternative to single QDs, which have very low optical signals, subsets of QDs within an ensemble can be used in quantum computing applications. To investigate the mediation of inhomogeneities in a QD ensemble, pump-probe experiments were performed on InAs/InP QDs within a dielectric Bragg stack microcavity. Two different excitation geometries showed that the angle dependence of the microcavity transmission allowed for the spectral selection of QD subsets with transition energies resonant with the cavity mode. The microcavity mitigated inhomogeneities in the ensemble while providing a basis for addressing QD subsets which could be used as distinguishable quantum bits. This thesis work shows significant advances towards an optical computing architecture using quantum states in semiconductor QDs.

Baigiamajame magistro darbe aprašyta apvaliosios medienos rietuvių fotonuotraukų analizė, siekiant įvertinti medienos rietuvių glaudumo koeficientą. Darbo tikslas – Įvertinti fotometrinio metodo taikymo apvaliosios medienos rietuvių glaudumo koeficiento nustatymui galimybes. Uždaviniai: • Įvertinti atsitiktinių ir sisteminių paklaidų dydžius, gaunamus apvaliosios medienos rietuvių glaudumo koeficientą, nustatant fotometriniu metodu. • Įvertinti fotometrinio metodo paklaidų priklausomybę nuo sortimentų rūšies. • Įvertinti paklaidų priklausomybę nuo medienos rietuvių glaudumo. Tyrimo objektas – į transporto priemonę sukrauti apvaliosios madienos popiermedžiai. Tyrimo metodika Darbe naudoti mokslinio tyrimo metodai: • Dokumentų analizė; • Vaizdų analizė; • Statistinė analizė; • Loginė analizė. Darbo rezultatai – mano pasirinktas fotometrinis metodas, apvaliosios madienos rietuvių glaudumo koeficientui įvertinti, gali būti taikomas. Paklaidos yra daromos tačiau jos nėra esminės. Iš pasirnktų trijų analizuojamojo vaizdo išskyrimo būdų tiksliausi rezultatai buvo stačiakampio forma išskirtas vaizdas. / Digital photographs of spruce and birch bundles were analised by photometric method using ArcView GIS 3.2. program to determine stacking coefficient of wood in the work. The main aim – to determine ability of photometric method to avaluate stacking coefficient of bundles. The main tasks: • To determine randon and systematic bias of photometric method to estimating stacking of wood bundles. • To determine volume of bias, using photometric method, dependents of roundwood species. • To aveluate dependense of errors in stacking coefficients of bundles volume. Research object. –solid wood which is loaded in a bundles of a truck. Methods: • Dokument analysis; • Image analysis; • Statistic analysis; • Logical analysis. Calculations were made using software ArcView GIS 3.2., STATISTICA v6.0 and EXCEL. The main results. photometric method can be applied to timber stacking precision ratios. Articularly accurate are obtained with the bundle of analyzing image maked rectangle.