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Electrostatic interactions between charged species play a prominent role in determining structures and states of physical system, leading to important technological and biological applications. In coarse-grained simulations, accurate description of electrostatic interactions is crucial in addressing physical phenomena at larger spatial and longer temporal scales. In this thesis, we implement ENUF method, an abbreviation for Ewald summation based on non-uniform fast Fourier transform technique, into dissipative particle dynamics (DPD) scheme. With determined suitable parameters, the computational complexity of ENUF-DPD method is approximately described as O(N logN). The ENUF-DPD method is further validated by investigating dependence of polyelectrolyte conformations on charge fraction of polyelectrolyte and counterion valency of added salts, and studying of specific binding structures of dendrimers on amphiphilic membranes. In coarse-grained simulations, electrostatic interactions are either explicitly calculated with suitable methods, or implicitly included in effective potentials. The effect of treatment fashion of electrostatic interactions on phase behavior of [BMIM][PF6] ionic liquid (IL) is systematically investigated. Our systematic analyses show that electrostatic interactions should be incorporated explicitly in development of effective potentials, as well as in coarse-grained simulations to improve reliability of simulation results. Detailed image of microscopic structures and orientations of [BMIM][PF6] at graphene and vacuum interfaces are investigated by using atomistic simulations. Imidazolium rings and alkyl side chains of [BMIM] lie preferentially flat on graphene surface. At IL-vacuum interface, ionic groups pack closely together to form polar domains, leaving alkyl side chains populated at interface and imparting hydrophobic character. With the increase of IL filmthickness, orientations of [BMIM] change gradually from dominant flat distributions along graphene surface to orientations where imidazolium rings are either parallel or perpendicular to IL-vacuum interface with tilted angles. The interfacial spatial ionic structural heterogeneity formed by ionic groups also contributes to heterogeneous dynamics in interfacial regions.

Digital image processing and compression technologies have significant market potential, especially the JPEG2000 standard which offers outstanding codestream flexibility and high compression ratio. Strong demand for high performance digital image processing and compression system solutions is forcing designers to seek proper architectures that offer competitive advantages in terms of all performance metrics, such as speed and power. Traditional architectures such as ASIC, FPGA and DSPs have limitations in either low flexibility or high power consumption. On the other hand, through the provision of a degree of flexibility similar to that of a DSP and performance and power consumption advantages approaching that of an ASIC, coarse-grained dynamically reconfigurable architectures are proving to be strong candidates for future high performance digital image processing and compression systems. This thesis investigates dynamically reconfigurable architectures and especially the newly emerging RICA paradigm. Case studies such as Reed- Solomon decoder and WiMAX OFDM timing synchronisation engine are implemented in order to explore the potential of RICA-based architectures and the possible optimisation approaches such as eliminating conditional branches, reducing memory accesses and constructing kernels. Based on investigations in this thesis, a novel customised dynamically reconfigurable architecture targeting digital image processing and compression applications is devised, which can be tailored to adopt different applications. A demosaicing engine based on the Freeman algorithm is designed and implemented on the proposed architecture as the pre-processing module in a digital imaging system. An efficient data buffer rotating scheme is designed with the aim of reducing memory accesses. Meanwhile an investigation targeting mapping the demosaicing engine onto a dual-core RICA platform is performed. After optimisation, the performance of the proposed engine is carefully evaluated and compared in aspects of throughput and consumed computational resources. When targeting the JPEG2000 standard, the core tasks such as 2-D Discrete Wavelet Transform (DWT) and Embedded Block Coding with Optimal Truncation (EBCOT) are implemented and optimised on the proposed architecture. A novel 2-D DWT architecture based on vector operations associated with RICA paradigm is developed, and the complete DWT application is highly optimised for both throughput and area. For the EBCOT implementation, a novel Partial Parallel Architecture (PPA) for the most computationally intensive module in EBCOT, termed Context Modeling (CM), is devised. Based on the algorithm evaluation, an ARM core is integrated into the proposed architecture for performance enhancement. A Ping-Pong memory switching mode with carefully designed communication scheme between RICA based architecture and ARM is proposed. Simulation results demonstrate that the proposed architecture for JPEG2000 offers significant advantage in throughput.

"Personal health record (PHR) service is an emerging model for health information exchange. It allows patients to create, manage, control and share their health information with other users as well as healthcare providers. In reality, a PHR service is likely to be hosted by third-party cloud service providers in order to enhance its interoperability. However, there have been serious privacy concerns about outsourcing PHR data to cloud servers, not only because cloud providers are generally not covered entities under HIPAA, but also due to an increasing number of cloud data breach incidents happened in recent years. In this thesis, we propose a privacy-preserving PHR system using attribute-based encryption (ABE). In this system, patients can encrypt their PHRs and store them on semi-trusted cloud servers such that servers do not have access to sensitive PHR contexts. Meanwhile patients maintain full control over access to their PHR files, by assigning fine-grained, attribute-based access privileges to selected data users, while different users can have access to different parts of their PHR. Our system also provides extra features such as populating PHR from professional electronic health record (EHR) using ABE. In order to evaluate our proposal, we create a Linux library that implement primitive of key-policy attribute-based encryption (KP-ABE) algorithms. We also build a PHR application based on Indivo PCHR system that allow doctors to encrypt and submit their prescription and diagnostic note to PHR servers using KP-ABE. We evaluate the performance efficiency of different ABE schemes as well as the data query time of Indivo PCHR system when PHR data are encrypted under ABE scheme."

Computational study of the structural, thermodynamic and transport properties of polymeric materials at equilibrium requires multi-scale modeling techniques due to processes occurring across a broad spectrum of time and length scales. Classical molecular-level simulation, such as Molecular Dynamics (MD), has proved very useful in the study of polymeric oligomers or short chains. However, there is a strong, nonlinear dependence of relaxation time with respect to chain length that requires the use of less computationally demanding techniques to describe the behavior of longer chains. As one of the mesoscale modeling techniques, Coarse-grained (CG) procedure has been developed recently to extend the molecular simulation to larger time and length scales. With a CG model, structural and dynamics of long chain polymeric systems can be directly studied though CG level simulation. In the CG simulations, the generation of the CG potential is an area of current research activity. The work in this dissertation focused on both the development of techniques for generating CG potentials as well as the application of CG potentials in Coarse-grained Molecular Dynamics (CGMD) simulations to describe structural, thermodynamic and transport properties of various polymer systems. First, an improved procedure for generated CG potentials from structural data obtained from atomistic simulation of short chains was developed. The Ornstein-Zernike integral equation with the Percus Yevick approximation was invoked to solve this inverse problem (OZPY-1). Then the OZPY-1 method was applied to CG modeling of polyethylene terephthalate (PET) and polyethylene glycol (PEG). Finally, CG procedure was applied to a model of sulfonated and cross-linked Poly (1, 3-cyclohexadiene) (sxPCHD) polymer that is designed for future application as a proton exchange membrane material used in fuel cell. Through above efforts, we developed an understanding of the strengths and limitations of various procedures for generating CG potentials. We were able to simulate entangled polymer chains for PET and study the structure and dynamics as a function of chain length. The work here also provides the first glimpses of the nanoscale morphology of the hydrated sxPCHD membrane. An understanding of this structure is important in the prediction of proton conductivity in the membrane.

Fine-grained access control for XML is about controlling access to XML documents at the granularity of individual elements or attributes. This thesis addresses two problems related to XML access controls. The first is efficient, secure evaluation of XPath expressions. We present a technique that secures path expressions by means of query modification, and we show that the query modification algorithm is correct under a language-independent semantics for secure query evaluation. The second problem is to provide a compact, yet useful, representation of the access matrix. Since determining a user's privilege directly from access control policies can be extremely inefficient, materializing the access matrix---the net effect of the access control policies---is a common approach to speed up the authorization decision making. The fine-grained nature of XML access controls, however, makes the space cost of matrix materialization a significant issue. We present a codebook-based technique that records access matrices compactly. Our experimental study shows that the codebook approach exhibits significant space savings over other storage schemes, such as the access control list and the compressed accessibility map. The solutions to the above two problems provide a foundation for the development of an efficient mechanism that enforces fine-grained access controls for XML databases in the cases of query access.

Fine-grained access control for XML is about controlling access to XML documents at the granularity of individual elements or attributes. This thesis addresses two problems related to XML access controls. The first is efficient, secure evaluation of XPath expressions. We present a technique that secures path expressions by means of query modification, and we show that the query modification algorithm is correct under a language-independent semantics for secure query evaluation. The second problem is to provide a compact, yet useful, representation of the access matrix. Since determining a user's privilege directly from access control policies can be extremely inefficient, materializing the access matrix---the net effect of the access control policies---is a common approach to speed up the authorization decision making. The fine-grained nature of XML access controls, however, makes the space cost of matrix materialization a significant issue. We present a codebook-based technique that records access matrices compactly. Our experimental study shows that the codebook approach exhibits significant space savings over other storage schemes, such as the access control list and the compressed accessibility map. The solutions to the above two problems provide a foundation for the development of an efficient mechanism that enforces fine-grained access controls for XML databases in the cases of query access.

Al-Mg solid solution alloys of various grain sizes were prepared by friction stir processing (FSP). The mechanical properties and micro-structure evolution were studied. The results show that the mechanical properties including tensile strength and ductility are improved by increasing Mg weight fraction. The homogeneous deformation is enhanced by fined slip bands within the grains. On the other hand, Dynamic strain aging or serrated flow stress has been wildly investigated in Al-Mg alloys. Effects of strain rate and magnesium content on dynamic strain aging are also discussed.

The thermal conductivity of PMMA films with thicknesses from 5 to 50 nanometers and layered over a treated silicon substrate is explored numerically by the application of the reverse non-equilibrium molecular dynamics (NEMD) technique and the development of a coarse-grained model for PMMA, which allows for the simulation time of hundreds of nanoseconds required for the study of large polymer systems. The results showed a constant average thermal conductivity of 0.135 W/m_K for films thickness ranging from 15 to 50 nm, while films under 15 nm in thickness showed a reduction of 30% in their conductivity. It was also observed that polymer samples with a degree of polymerization equal to 25% of the entanglement length had 50% less thermal conductivity than films made of longer chains. The temperature profiles through the films thickness were as predicted by the Fourier equation of heat transfer. The relative agreement between the thermal conductivity from experiments (0.212 W/m_K for bulk PMMA) and the results from this investigation shows that with the proper interpretation of results, the coarse-grained NEMD is a useful technique to study transport coefficients in systems at larger nano scales.

Title: Microstructure and mechanical properties of ultra-fine grained titanium alloys Author: Bc. Kristína Václavová Department / Institute: Department of Physics of Materials Supervisor of the master thesis: PhDr. RNDr. Josef Stráský, Ph.D. Abstract: Metastable β-Ti alloys Ti-15Mo and Ti-6.8Mo-4.5Fe-1.5Al (TIMETAL LCB) were subjected to severe plastic deformation by high pressure torsion. Microhardness of Ti-15Mo and TIMETAL LCB alloys increases with increasing inserted deformation, i.e. with increasing number of HPT rotations and also with increasing distance from the centre of the sample. The highest microhardness after HPT exceeds significantly the microhardness of two- phase α + β heat-treated material. Increasingly deformed microstructure was also demonstrated by scanning electron microscopy and by electron back-scatter diffraction. Significant twinning was observed in both studied alloys. Mechanism of multiple twinning contributes notably to the fragmentation of grains and thus to the refinement of the microstructure. Defect structure in Ti-15Mo alloy was studied by positron annihilation spectroscopy. It was proved that dislocations are the only detectable defects in the material by positron annihilation spectroscopy and that dislocation density increases with the number of HPT revolution and with...