Effectiveness of landmark analysis for establishing locality in p2p networks

Locality to other nodes on a peer-to-peer overlay network can be established by means of a set of landmarks shared among the participating nodes. Each node independently collects a set of latency measures to landmark nodes, which are used as a multi-dimensional feature vector. Each peer node uses the feature vector to generate a unique scalar index which is correlated to its topological locality. A popular dimensionality reduction technique is the space filling Hilbert’s curve, as it possesses good locality preserving properties. However, there exists little comparison between Hilbert’s curve and other techniques for dimensionality reduction. This work carries out a quantitative analysis of their properties. Linear and non-linear techniques for scaling the landmark vectors to a single dimension are investigated. Hilbert’s curve, Sammon’s mapping and Principal Component Analysis have been used to generate a 1d space with locality preserving properties. This work provides empirical evidence to support the use of Hilbert’s curve in the context of locality preservation when generating peer identifiers by means of landmark vector analysis. A comparative analysis is carried out with an artificial 2d network model and with a realistic network topology model with a typical power-law distribution of node connectivity in the Internet. Nearest neighbour analysis confirms Hilbert’s curve to be very effective in both artificial and realistic network topologies. Nevertheless, the results in the realistic network model show that there is scope for improvements and better techniques to preserve locality information are required

Investigations of boundary layer phenomena using a new method or observation

This thesis is a study of the boundary layer on a flat plate, using a new method of observation. The boundary layer, and in particular, the laminar region, has been examined using a new device, which takes the form of a small vane. This vane is freely hinged and suspended at its leading edge, lies vertically in the xz plane, and its dimensions are of the same order as the wavelengths of the disturbances, to which it is expected to respond. Such an instrument responds only to v fluctuations of velocity and is uninfluenced by those of u and w.The ultimate aim of the research programme is to use the vane in the transition and turbulent regions, and attempt to obtain information on the formation of turbulence. Before the vane can be put in the turbulent region, however, its own performance has to be ascertained, by investigating relatively well known phenomena in the laminar region, and this forms the subject of the thesis

Validating Color Doppler Ultrasound Performance Via A Quantitative Comparison with Particle Image Velocimetry

Color Doppler Ultrasound (CDUS) is a method of non-invasive fluid velocity measurement that is used for regular cardiac screenings as well as during complex surgeries such as valve replacements. A Color Doppler image is a contour map of the velocity field and can thereby indicate the presence of abnormal flows or be used to quantitatively measure velocities. CDUS is inexpensive and completely non-invasive. It is for these same reasons that CDUS has the potential to be a powerful tool not only in the medical field, but in the industrial and engineering research fields as well. While there are many devices that use ultrasonic transducers to determine either pipe-wall corrosion or mean flow rate, to date making accurate velocity measurements has required either a clear visualization section or an invasive form of measurement. An experimental method to quantify the accuracy of Color Doppler Ultrasound velocity measurements in both the laminar and turbulent flow regime through a non-biological media is presented. A clear acrylic tube with a conical nozzle, throat, and a sudden expansion is used to generate a well characterized flow field that includes features typical of physiologic flows and flows within medical devices such as high speed jets and recirculation. The velocity field is measured at three locations using both Color Doppler Ultrasound and Particle Image Velocimetry (PIV) and the measurements are used to generate velocity profiles, which are compared quantitatively. It was found that although it is possible to resolve phenomena such as recirculation and high speed jets, the media through which the imaging occurs has a significant impact on the accuracy of the Ultrasound generated velocity measurements. Due to the large amount of attenuation of sound through acrylic media, the Color Doppler readings show significant error in velocity measurements. For laminar parabolic flows this shifts both the mean and peak velocities down, with a percent difference in both as high as 42% and 55% respectively. However, at the sudden expansion where high speed jets and recirculation zones occur, the velocity profile becomes wider and flatter, and though the peak velocity measurements have a percent difference of approximately 50%, the percent difference in the mean velocity varied from less than 1% to a maximum of 10%

Online Learning and Experimentation via Interactive Learning Resources

Recent trends in online learning like Massive Open Online Courses (MOOCs) and Open Educational Resources (OERs) are changing the landscape in the education sector by allowing learners to self-regulate their learning and providing them with an abundant amount of free learning materials. This paper presents FORGE, a new European initiative for online learning and experimentation via interactive learning resources. FORGE provides learners and educators with access to world- class facilities and high quality learning materials, thus enabling them to carry out experiments on e.g. new Internet protocols. In turn, this supports constructivist and self-regulated learning approaches, through the use of interactive learning resources, such as eBooks

Average decay estimates for Fourier transforms of measures supported on curves

We consider Fourier transforms of densities supported on curves in R^d. We obtain sharp lower and close to sharp upper bounds for the L^q decay rates.Comment: We have learned about an important reference on the subject matter, and revised the paper accordingl

Volatility Prediction using Financial Disclosures Sentiments with Word Embedding-based IR Models

Volatility prediction--an essential concept in financial markets--has recently been addressed using sentiment analysis methods. We investigate the sentiment of annual disclosures of companies in stock markets to forecast volatility. We specifically explore the use of recent Information Retrieval (IR) term weighting models that are effectively extended by related terms using word embeddings. In parallel to textual information, factual market data have been widely used as the mainstream approach to forecast market risk. We therefore study different fusion methods to combine text and market data resources. Our word embedding-based approach significantly outperforms state-of-the-art methods. In addition, we investigate the characteristics of the reports of the companies in different financial sectors