Performance Modelling and Optimisation of Multi-hop Networks

A major challenge in the design of large-scale networks is to predict and optimise the total time and energy consumption required to deliver a packet from a source node to a destination node. Examples of such complex networks include wireless ad hoc and sensor networks which need to deal with the effects of node mobility, routing inaccuracies, higher packet loss rates, limited or time-varying effective bandwidth, energy constraints, and the computational limitations of the nodes. They also include more reliable communication environments, such as wired networks, that are susceptible to random failures, security threats and malicious behaviours which compromise their quality of service (QoS) guarantees. In such networks, packets traverse a number of hops that cannot be determined in advance and encounter non-homogeneous network conditions that have been largely ignored in the literature. This thesis examines analytical properties of packet travel in large networks and investigates the implications of some packet coding techniques on both QoS and resource utilisation. Specifically, we use a mixed jump and diffusion model to represent packet traversal through large networks. The model accounts for network non-homogeneity regarding routing and the loss rate that a packet experiences as it passes successive segments of a source to destination route. A mixed analytical-numerical method is developed to compute the average packet travel time and the energy it consumes. The model is able to capture the effects of increased loss rate in areas remote from the source and destination, variable rate of advancement towards destination over the route, as well as of defending against malicious packets within a certain distance from the destination. We then consider sending multiple coded packets that follow independent paths to the destination node so as to mitigate the effects of losses and routing inaccuracies. We study a homogeneous medium and obtain the time-dependent properties of the packet’s travel process, allowing us to compare the merits and limitations of coding, both in terms of delivery times and energy efficiency. Finally, we propose models that can assist in the analysis and optimisation of the performance of inter-flow network coding (NC). We analyse two queueing models for a router that carries out NC, in addition to its standard packet routing function. The approach is extended to the study of multiple hops, which leads to an optimisation problem that characterises the optimal time that packets should be held back in a router, waiting for coding opportunities to arise, so that the total packet end-to-end delay is minimised

Compositional structures in mural design : towards a site-specific deconstructive mural methodology

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements of the degree of Doctor of Philosophy (PhD)Murals have been the formal visual interpretation of the cultural, social and political life of all ages. Throughout they have been consistently combined with their architectural setting, for example, in ancient Egyptian tombs, in Renaissance churches and on the external walls of buildings in Mexico in the twentieth century. This is a central feature of mural painting. However many contemporary murals do not integrate with their architectural settings, in other words, do not fulfil the site-specificity of the architectural spaces for which they were made. This means that the most important aspect that distinguishes murals from other types of painting is absent. I studied and analysed a number of murals produced in the Italian Renaissance, Baroque and Rococo as this particular period is considered to be not only one of the most significant in the history of art but also a period in which painting and architecture were very closely allied as practices. In particular the radical developments in painting of pictorial space took place along side the developments in architecture. I argue that Renaissance murals could be described, using the terminology of contemporary art, as site-specific art. By identifying the relationship between pictorial space, architectural space and compositional structure I was able to test, through my own practice, the importance of these relationships in understanding the site-specificity of the compositional structure of murals. To address the issue of sitespecificity in murals, I investigated and developed a set of compositional structures through my mural practice that could be applied in the design, execution, and teaching of contemporary mural design. I have developed the notion of a deconstructive method of mural design in which the illusory space of the mural derives its compositional structure from the architectural space in which it sited. I have applied it, tested it and refined it through the execution of a number of hypothetical and live mural commissions. I believe that the approach to the study and practice of mural design I have developed from the perspective of a practice lead researcher contributes to the furtherance of mural design as both a profession and field of study. In particular the identification of compositional structures in mural design and the proposal of a deconstructive method contributes to our understanding of what a mural is as well as current notions of site-specificity in contemporary art

Improving the indoor air quality (IAQ) through application of the air cleaning technologies for offices building simulated in environmental chamber

Indoor air quality (IAQ) is very important issue in residential and commercial buildings, because human spend almost 90% of their life indoor. IAQ problems effect on the health of the occupants, and lead to reduction of the efficiency and output in workplaces. The main objective of this study is to improving the (IAQ) and to reduce energy consumption in offices building, through experimental and simulation investigation. The method used in this study was by using environmental chamber to represent the real office. The results of the experimental were validated the simulation. The chamber was modified by installing two mechanical filters with low pressure drop; minimum efficiency reporting value rate 13 (MERV 13) and activated carbon filter (ACF) on the air handling unit. The IAQ parameters which include temperature, relative humidity, air velocity, air flow rate, pressure drop, CO2 concentration and particle matters PM 10 and PM 2.5 concentration for upstream and downstream were considered in this study. These variables were measured inside the chamber using IAQ devices and these data were used as an input data for simulation by using ANSYS 16.1 software. The simulation generated the air distribution via air velocity, temperature, CO2 concentration and the particle distribution in the room. The results from experiment showed good agreement for combining filters efficiency value from 86.20% to 84.60% and from 86% to 82.35% for PM 10 and PM 2.5 particle removal respectively during occupied period. The CO2 concentration decreased during the measurement period from 816 ppm to 700 ppm and the distribution was in the acceptable range compare with ASHRAE standard 55-2004 and Malaysian industry code of practice on IAQ. Also, the validation with simulation showed below 10% error ratio compare with experiment results. The significance of study is to balance between enhancing thermal comfort inside workplace and (IAQ) for occupants, leading to reduction of energy consumption

Some reflections on a model to predict the erosion rate of the passive film on pure metals

A model to predict the erosion rate of the passive films on metals is proposed. The model investigates the effect of eroded particles on a metal on which a passive (oxide) film has formed. To date, many of the existing erosion models have concentrated on normal angle erosion of the oxide layer. This new approach considers the effect of oblique impacts on the oxide layer and the effect of its thickness on the amount of metal and oxide layer removal. The model is then tested by comparision to previous experimental work

CFD modelling of erosion-corrosion of steel in aqueous environments : particle concentration effects on the regime boundaries

In this study, a new methodology is used to model the effects of particle concentration on the inner surfaces of a circular pipe 90º bend, assuming applied potential controlled aqueous slurry flow at room temperature. This enables the regimes of the component to be mapped according to the intensity of erosion and corrosion contributions. The results show that for a constant inlet particle concentration, it is shown how transitions between erosion-corrosion regimes are observed around the pipe. For increases in particle concentration, significant variation of the erosion-corrosion regimes are observed, with a reduction of the corrosion dominated regime. The results are interpreted in the terms of the changes in local erosion conditions along the component in the flowing environments. Typical results from the model are shown illustrating how this new mapping method can be used effectively to optimize process conditions and materials in such environments

Playing Pairs with Pepper

As robots become increasingly prevalent in almost all areas of society, the factors affecting humans trust in those robots becomes increasingly important. This paper is intended to investigate the factor of robot attributes, looking specifically at the relationship between anthropomorphism and human development of trust. To achieve this, an interaction game, Matching the Pairs, was designed and implemented on two robots of varying levels of anthropomorphism, Pepper and Husky. Participants completed both pre- and post-test questionnaires that were compared and analyzed predominantly with the use of quantitative methods, such as paired sample t-tests. Post-test analyses suggested a positive relationship between trust and anthropomorphism with $80\%$ of participants confirming that the robots' adoption of facial features assisted in establishing trust. The results also indicated a positive relationship between interaction and trust with $90\%$ of participants confirming this for both robots post-testComment: Presented at AI-HRI AAAI-FSS, 2018 (arXiv:1809.06606

Search in the Universe of Big Networks and Data

Searching in the Internet for some object characterised by its attributes in the form of data, such as a hotel in a certain city whose price is less than something, is one of our most common activities when we access the Web. We discuss this problem in a general setting, and compute the average amount of time and the energy it takes to find an object in an infinitely large search space. We consider the use of N search agents which act concurrently. Both the case where the search agent knows which way it needs to go to find the object, and the case where the search agent is perfectly ignorant and may even head away from the object being sought. We show that under mild conditions regarding the randomness of the search and the use of a time-out, the search agent will always find the object despite the fact that the search space is infinite. We obtain a formula for the average search time and the average energy expended by N search agents acting concurrently and independently of each other. We see that the time-out itself can be used to minimise the search time and the amount of energy that is consumed to find an object. An approximate formula is derived for the number of search agents that can help us guarantee that an object is found in a given time, and we discuss how the competition between search agents and other agents that try to hide the data object, can be used by opposing parties to guarantee their own success.Comment: IEEE Network Magazine - Special Issue on Networking for Big Data, July-August 201

Signalling Storms in 3G Mobile Networks

We review the characteristics of signalling storms that have been caused by certain common apps and recently observed in cellular networks, leading to system outages. We then develop a mathematical model of a mobile user's signalling behaviour which focuses on the potential of causing such storms, and represent it by a large Markov chain. The analysis of this model allows us to determine the key parameters of mobile user device behaviour that can lead to signalling storms. We then identify the parameter values that will lead to worst case load for the network itself in the presence of such storms. This leads to explicit results regarding the manner in which individual mobile behaviour can cause overload conditions on the network and its signalling servers, and provides insight into how this may be avoided.Comment: IEEE ICC 2014 - Communications and Information Systems Security Symposiu

Modal analysis of wave propagation in dispersive media

Surveys on wave propagation in dispersive media have been limited since the pioneering work of Sommerfeld [Ann. Phys. 349, 177 (1914)] by the presence of branches in the integral expression of the wave function. In this article, a method is proposed to eliminate these critical branches and hence to establish a modal expansion of the time-dependent wave function. The different components of the transient waves are physically interpreted as the contributions of distinct sets of modes and characterized accordingly. Then, the modal expansion is used to derive a modified analytical expression of the Sommerfeld precursor improving significantly the description of the amplitude and the oscillating period up to the arrival of the Brillouin precursor. The proposed method and results apply to all waves governed by the Helmholtz equations.Comment: 10 pages, 9 figure