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Vibration energy harvesting techniques, which can convert the mechanical energy of ambient vibration into electricity, have drawn great attention in recent years owing to the development of the Internet of Things, industry 4.0 and smart cities and the advancement of sensor technologies that allow them to work with quite low power consumption. The number of the sensors connected to these networks can be enormous, and powering all of them with batteries or from the mains power source is infeasible considering the onerous as well as costly monitoring, replacement and recycling work incurred, especially for those embedded in structures or employed in remote or hazardous places. Therefore, vibration energy harvesters are introduced as an alternative means of power supplement. In addition to working as a powering unit, vibration energy harvesters can also be used for sensing, in which case they become self-powered sensors and are quite competitive over the conventional sensors. Apart from the utilization of the direct effect of an electrification mechanism in vibration energy harvesters, the study of the involved electromechanical coupling mechanisms can facilitate the development of relevant actuators which are based on the corresponding converse effect. Triboelectric energy harvesting is one of the common vibration energy harvesting techniques and is fairly new compared to electromagnetic and piezoelectric energy harvestings. Triboelectric energy harvesters (TEHs) are dependent on the repeated impact or relative sliding between materials of opposite tribopolarities. Relevant studies of TEHs from the perspectives of structural dynamics are very rare in the literature yet they play an important role in optimization. Therefore, this thesis focuses on studying TEHs of different working modes and improving the understanding of their working mechanisms through theoretical modelling, numerical simulation, and experimental investigation and validation. TEHs are usually non-smooth in terms of their mechanical behaviours, and vibro-impact and friction can be involved in TEHs of different working modes. Analysing the vibroimpact dynamics of TEHs, which are based on repeated contact and separation, is essential to optimization, and this constitutes the first part of this research. The complex vibroimpact dynamics of a three-degree-of-freedom vibro-impact oscillator, which corresponds to the mechanical system of a contact freestanding triboelectric-layer mode TEH, is unveiled, especially the effects of mass ratios and spacings investigated. The resulted electrical responses are obtained via a developed circuit simulator in Simulink and are compared in terms of efficient energy conversion for different types of vibrations. The second major part of this research deals with more advanced modelling and numerical methods and with experimental validations for a TEH of the same working mode with that presented in the first part but based on the vibro-impact of three cantilevered beams. A relationship between the just-before-impact velocity and the coefficient of restitution is experimentally identified and is used in the mechanical modelling. The theoretical model of the electrical system is established rather than using the previously developed circuit simulator. A numerical scheme, which is based on the TR-BDF2 (the trapezoidal rule and the second order backward differentiation formula) method, is proposed to integrate the non-smooth mechanical system and the stiff electrical system. Experimental validations of the proposed modelling and numerical methods and studies of the effects of key parameters are carried out in the end. A sliding mode TEH, which incorporates friction and magnetic multistability, is proposed and studied in the third main part of this research. The non-smoothness incurred by friction is considered in the modelling. The magnetic multistability is employed to broaden the energy harvesting frequency band. An algorithm that categorizes different types of stability of a multistable non-conservative system is developed and the influence of friction on the system multistability investigated. Comparisons among three types of stability indicate the superiority of bistability. The effects of excitation level and friction on the responses of the system are studied. Giving the fact that a multistable as well as non-smooth system is sensitive to initial conditions, an analysis of the basins of attraction is conducted. Having carried out analyses based on the "direct electromechanical coupling" in the previous three main parts, the effects of the electrical properties including the tribo-charge surface density and the load resistance on the behaviours of the mechanical systems in TEHs are studied in the final part, which is based on the "reverse electromechanical coupling". This part of study unveils the electromechanical coupling mechanisms and sheds some light on tuning the harvester from the electrical aspects.

This thesis concerns face recognition in uncontrolled environments in which the images used for training and test are collected from the real world instead of laboratories. Compared with controlled environments, images from uncontrolled environments contain more variation in pose, lighting, expression, occlusion, background, image quality, scale, and makeup. Therefore, face recognition in uncontrolled environments is much more challenging than in controlled conditions. Moreover, many real world applications require good recognition performance in uncontrolled environments. Example applications include social networking, human-computer interaction and electronic entertainment. Therefore, researchers and companies have shifted their interest from controlled environments to uncontrolled environments over the past seven years. In this thesis, we divide the history of face recognition into four stages and list the main problems and algorithms at each stage. We find that face recognition in unconstrained environments is still an unsolved problem although many face recognition algorithms have been proposed in the last decade. Existing approaches have two major limitations. First, many methods do not perform well when tested in uncontrolled databases even when all the faces are close to frontal. Second, most current algorithms cannot handle large pose variation, which has become a bottleneck for improving performance. In this thesis, we investigate Bayesian models for face recognition. Our contributions extend Probabilistic Linear Discriminant Analysis (PLDA) [Prince and Elder 2007]. In PLDA, images are described as a sum of signal and noise components. Each component is a weighted combination of basis functions. We firstly investigate the effect of degree of the localization of these basis functions and find better performance is obtained when the signal is treated more locally and the noise more globally. We call this new algorithm multi-scale PLDA and our experiments show it can handle lighting variation better than PLDA but fails for pose variation. We then analyze three existing Bayesian face recognition algorithms and combine the advantages of PLDA and the Joint Bayesian Face algorithm [Chen et al. 2012] to propose Joint PLDA. We find that our new algorithm improves performance compared to existing Bayesian face recognition algorithms. Finally, we propose Tied Joint Bayesian Face algorithm and Tied Joint PLDA to address large pose variations in the data, which drastically decreases performance in most existing face recognition algorithms. To provide sufficient training images with large pose difference, we introduce a new database called the UCL Multi-pose database. We demonstrate that our Bayesian models improve face recognition performance when the pose of the face images varies.

Micro-Electro-Mechanical-System (MEMS) and Nanotechnology have both received significant attention in recent years due to their potential for manufacturing highly miniaturised devices which consume less raw materials and energy in their production, and function with greater efficiency, speed, and reliability. The first project described in this thesis concerns the development of a novel, low cost, contamination-free nanofabrication system. This system is enabled by a MEMS-based device which has the dual functions of a high-precision AFM (Atomic Force Microscope) cantilever probe and a shadow mask. This MEMS device, which is referred to as the Nanostencil device in this thesis, has been integrated with nanoscale apertures and an AFM scanning tip using the Focussed Ion Beam (FIB) technique. The finished Nanostencil device has been used successfully for both parallel nanoscale depositions and high precision nanoscale alignments. The second project presented in this thesis is concerned with the application of MEMS technology to benefit the aircraft industry by providing a compact and robust pressure sensor capable of measuring high frequency turbulent flow velocities with improved accuracy. The information provided by such probes could be of considering help in improving the design of the next generation of aeroplanes. With the help of finite-element analysis, a pressure sensor has been designed which has a footprint of 0.7 mm, a frequency response of a few megahertz and a high thermal stability. The fabrication of this prototype has been realised through a specially developed process sequence utilising a Deep Reactive-Ion-Etching (DRIE) system. Mechanical testing of the deflection versus pressure response of the sensor provides preliminary indications that the fabricated device meets the design requirements.

In this thesis, we start by considering a hyperelastic circular solid cylinder or tube that is rotating about its axis of symmetry with angular velocity ω. If the resultant axial force F is fixed, it is shown that the bifurcation condition for a solid cylinder or a tube that is shrink-fitted to a rigid circular cylindrical spindle is simply given by dω/dλz = 0, where λz is the axial stretch. When the spindle is absent (the case of unconstrained rotation), we also allow for the possibility that the tube is additionally subjected to an internal pressure P. It is shown that with P fixed, and ω and F both viewed as functions of the circumferential stretch λa and λz, the bifurcation condition for localized bulging is that the Jacobian of ω and F should vanish. The second part of the thesis studies localized bulging in an inflated bilayer tube under inflation and axial extension. Firstly, bulging prevention in a hyperelastic bilayer tube composed of the Gent material is investigated. We determine several critical parameter regimes where localized bulging disappears, when one layer (layer I) of the tube cannot bulge whereas the other part (layer II) can. Surprisingly, we find that localized bulging still occurs if the proportion of layer II exceeds a critical value, no matter whether it occupies the inner layer or outer layer. Secondly, we focus on the effect of modulus ratio between two layers on the bulge formation. If the thickness of the bilayer tube is specified, the composite tube is more stable when the stiffer part occupies the outer layer. Moreover, the critical volume ratio vcr as a function of the interfacial radius D has a maximum if s > 1 but a minimum if s < 1, where s is the ratio of the shear modulus of the outer layer to that of the inner layer. Finally, we turn our attention to study the effect of torsion on the onset of localized bulging. When the twisting moment M is fixed, the bifurcation condition for localized bulging is that the Jacobian of the internal pressure P and the resultant axial force F should vanish. It is found that the onset of localized bulging can be delayed or removed when a torsion is applied to the tube.