Debugging in real time is imperative for telecommunication networks with their ever increasing size and complexity. In event of an error or an unexpected occurrence of event, debugging the complex systems that controls these networks becomes an insurmountable task. With the help of tracing, it is possible to capture the snapshot of a system at any given point of time. Tracing, in essence, captures the state of the system along with the programs currently running on the system. LTTng is one such tool developed to perform tracing in both kernel space and user space of an application. In this thesis, we evaluate the effectiveness of LTTng and its impact on the performance on the applications traced by it. As part of this thesis we have formulated a comprehensive load matrix to simulate varying load demands in a telecommunication network. We have also devised a detailed experimental methodology which encompasses a collection of test suites used to determine the efficiency of various LTTng trace primitives. We were also able to prove that, in our experiments, LTTng’s kernel tracing is more efficient than User Space Tracing and LTTng’s User Space Tracing has a performance impact of around three to five percent.

Content distribution systems are essentially content protection systems that protect premium multimedia content from being illegally distributed. Physical content distribution systems form a subset of content distribution systems with which the content is distributed via physical media such as CDs, Blu-ray discs, etc. This thesis studies physical content distribution systems. Specifically, we concentrate our study on the design and analysis of three key components of the system: broadcast encryption for stateless receivers, mutual authentication with key agreement, and traitor tracing. The context in which we study these components is the Advanced Access Content System (AACS). We identify weaknesses present in AACS, and we also propose improvements to make the original system more secure, flexible and efficient.

Tables have been used for working and studying for years, and people continue using tables to work with digital artifacts. Collaborative tabletop activities such as planning, designing, and scheduling are common on traditional tables, but digital tables still face a variety of design issues to facilitate doing the same tasks. For example, due to the high cost of digital tables, it is unclear how large a digital table must be to support collaborative problem solving. This thesis examines the impact of physical features, in particular the table size, on collaborative tasks. This research leverages findings of previous studies of traditional and digital tables, and focuses on exploring the interaction of table size and users’ seating arrangement in collaborative problem solving. An experimental study is used to observe the behaviors of two-member groups while doing problem-solving tasks. Two tasks, storytelling and travel planning, were selected for this study, and the experiments were performed on two traditional tables, one small and one large. Although working on digital and traditional tables differs, investigating the impact of physical features in traditional tables can help us better understand how these features interact with workspace awareness and external cognition factors during taskwork. In the empirical study, external cognitive behaviors of participants were deeply analyzed to understand how physical settings of the table and seating arrangement affect the way people manipulate artifacts in the table workspace. Collaborators passed through different stages of problem solving using varied strategies, and the data analysis revealed that they manipulated material on the tabletop for understanding, organizing and solution making through visual separation, cognitive tracing and piling. Table size, task type and user seating arrangement showed strong effects on the external cognition of collaborators. In particular, the accessibility of sufficient space on the table influenced how much users could distribute their materials to improve workspace awareness and cognitive tracing. On the other hand, lack of space or inaccessible space forced people to use the space above the table—by holding materials in their hands—or to pile materials to compensate for space limitations. The insights gained from this research inform design decisions regarding size and seating arrangement for tabletop workspaces. For cases in which there is insufficient space, design alternatives are recommended to improve accessibility to artifacts to compensate for space limitations. These solutions aim to enhance the external cognition of users when space is insufficient to work with artifacts in problem-solving tasks.

The bidirectional reflectance distribution function (BRDF) that describes the scattered energy distribution is the most fundamental radiative property to calculate other properties. Although recent progress in surface metrology allows topography measurement in an atomic level, most studies still assume statistical distributions of roughness because of difficulty in roughness modeling. If the BRDF of rough silicon wafers is modeled with assumptions, predicted radiative properties may be inaccurate because non-Gaussian and anisotropic roughness of some wafers cannot be approximated with known statistics. Therefore, this thesis focuses on development of BRDF modeling that accounts for anisotropic roughness to accurately predict radiative properties of rough silicon surfaces with thin-film coatings. Monte Carlo ray-tracing methods are developed to consider multiple scattering and the change of polarization states and to satisfy physical laws such as the reciprocity principle. Silicon surface topographic data measured with an atomic force microscope are incorporated into the ray-tracing algorithms to model anisotropic roughness statistics. For validation, BRDF and emittance predictions are compared with measurements using an optical scatterometer and an integrating sphere. Good agreement between prediction and measurement demonstrates that the incorporation of topography measurement into BRDF modeling is essential for accurate property prediction. Roughness effects on the BRDF are so strong that BRDFs also reveal anisotropic features regardless of the presence of coating. Anisotropic roughness increases multiple scattering although first-order scattering is dominant, and thus enhances emittance noticeably. Silicon dioxide coating changes the magnitude of BRDF and emittance and reduces the anisotropic roughness effect on emittance enhancement. The research in this thesis advances the method to predict radiative properties by incorporating anisotropic rough statistics into BRDF modeling.

The effects of coupling parameters of active-passive and passive-passive coupling components on the coupling efficiency and signal mixed proportion for polymer optical fiber (POF) communication are investigated. A high sensitivity and easy fabricated POF displacement sensor is proposed by using cycling bending POF. Also, light sources for both Laser diode (LD) and light emitting diode (LED) are employed in this study. Experimental approaches and numerical analysis of rays tracing method and finite element method are performed to investigate the effects of coupling scheme and bent deformation on the optical power attenuation. Experimental results also illustrate the feasibility of using numerical analysis in coupling components and POF displacement sensor design. The effect of V-grooved array¡¦s POF on the coupling efficiency and signal mixed proportion are presented in active-passive components. The results indicate that the effect of the V-groove¡¦s shape and size on the coupling efficiency is very significant for all designed parameters of V-grooved array¡¦s POF. Compared with the parallel V-grooved array, the skew V-grooved array reduces the length of the coupling component and increases the output power between light source and POF. In the Y-branch POF coupler for passive-passive components, both the excess loss and the output power ratio of the Y-branch couplers are very sensitive to the couple angle, the coupling distance and the refractive index of the filling medium between the emitting-end and receiving-end of fibers. The results also show that the proposed model can be used to analyze the coupling efficiencies in the asymmetrical Y-branch or axial symmetrical couplers with acceptable accuracy. In the POF displacement sensor using by cycling bending loss, the results show that the effect of roller¡¦s number, interval and wavelength on light power attenuation is very significant. Based on the experimental data, a linear equation is derived to estimate the relationship between the power loss and the relative displacement. The difference between the estimated results and the experimental results is less than 8%.

To combat channel fading, cooperative communication achieves spatial diversity for the transmission between source and destination through the help of relay. However, if the relay behaves abnormally or maliciously and the destination is not aware, the diversity gain of the cooperative system will be significantly reduced, which degrades system performance. In our thesis, we consider an one-relay decode and forward cooperative network, and we assume that the relay may misbehave with a certain probability. If the relay is malicious, it will garble transmission signal, resulting in severe damage to cooperative system. In this work, we discuss three kinds of malicious behavior detection. More specifically, we adopt sequential detection to detect the behavior of relay. If tracing symbols are inserted among the source message, the destination detects malicious after extracting the received tracing symbols. We adopt log-likelihood ratio test to examine these tracing symbols, and then determine the behavior of relay. If the source does not transmit tracing symbols, the destination detects misbehavior according to the received data signal. Furthermore, we employ sequential detection to reduce detection time for a given probabilities of false alarm and miss detection. Through simulation results, for a certain target on probability of errors, our proposed methods can effectively reduce numbers of observations. On the other works, the destination can effectively detect misbehavior of relay, and eliminating the damage causes by malicious relay without requiring large numbers of observations.

The graphics hardware have evolved from simple feed forward triangle rasterization devices to flexible, programmable, and powerful parallel processors. This evolution allows the researchers to use graphics processing units (GPU) for both general purpose computations and advanced graphics rendering. Sophisticated GPUs hold great opportunities for the acceleration of computationally expensive photorealistic rendering methods. Rendering of photorealistic images in real-time is a challenge. In this work, we investigate efficient ways to utilize GPUs for real-time photorealistic rendering. Specifically, we studied uniform grid based ray tracing acceleration methods and GPU friendly traversal algorithms. We show that our method is faster than or competitive to other GPU based ray tracing acceleration techniques. The proposed approach is also applicable to the fast rendering of volumetric data. Additionally, we devised GPU based solutions for real-time stereoscopic image generation which can be used in companion with GPU based ray tracers.

Ray tracing is a computationally complex global illumination algorithm that is used for producing realistic images. In addition to parallel implementations on commodity PC clusters, recently, Graphics Processing Units (GPU) have also been used to accelerate ray tracing. In this thesis, ray tracing is accelerated on a GPU cluster where the viewing plane is divided into unit tiles. Slave processes work on these tiles in a task parallel manner which are dynamically assigned to them. To decrease the number of ray-triangle intersection tests, Bounding Volume Hierarchies (BVH) are used. It is shown that almost linear speedup can be achieved. On the other hand, it is observed that API and network overheads are obstacles for scalability.

Understanding and modeling seismic wave propagation is important in regional and exploration seismology. Ray tracing is a powerful and popular method for this purpose. Wavefront construction (WFC) method handles wavefronts instead of individual rays, thereby controlling proper ray density on the wavefront. By adaptively controlling rays over a wavefront, it efficiently models wave propagation. Algorithms for a quasi-P wave wavefront construction method and a new coordinate system used to generate wavefront construction mesh are proposed and tested for numerical properties and modeling capabilities. Traveltimes, amplitudes, and other parameters, which can be used for seismic imaging such as migrations and synthetic seismograms, are computed from the wavefront construction method. Modeling with wavefront construction code is applied to anisotropic media as well as isotropic media. Synthetic seismograms are computed using the wavefront construction method as a new way of generating synthetics. To incorporate layered velocity models, the model based interpolation (MBI) ray tracing method, which is designed to take advantage of the wavefront construction method as well as conventional ray tracing methods, is proposed and experimental codes are developed for it. Many wavefront construction codes are limited to smoothed velocity models for handling complicated problems in layered velocity models and the conventional ray tracing methods suffer from the inability to control ray density during wave propagation. By interpolating the wavefront near model boundaries, it is possible to handle the layered velocity model as well as overcome ray density control problems in conventional methods. The test results revealed this new method can be an effective modeling tool for accurate and effective computing.

<p>When the Tsunami occurred on Boxing Day 2004 it caused a major stress upon the governmental agencies in not only the affected areas but also in states that had a large number of citizens in the affected area. The governmental agencies were not prepared for the demands from the citizenry in these countries to deal with rescue and crisis management in areas situated halfway around the globe. This thesis main purpose is to research what the causal mechanisms of Sweden’s and Finland’s crisis management were through the method of process tracing. Taking its theoretical stance in Allison’s & Zelikow’s three models of decision making, the thesis compares the course of events of the first two critical days in Sweden and Finland to establish what mistakes were made during this critical period. The main findings of the essay show that none of the theories is on its own capable of explaining the chain of events, but a combination of the organisational model and the governmental politics model do prove the necessity of trained crisis personnel as decision-makers early on in crisis management as well as the need for an organisational structure with a linear and clear chain of command.</p>