The aim of this work was to investigate the precipitation and stability of nm-sized Ti oxides in vanadium-based alloys, a prime candidate material for future nuclear fusion reactors based on the magnetic confinement of the plasma. Fusion energy reproduces the nuclear reactions occurring in stars. It can potentially produce more energy than current nuclear fission power plants, and it is meant to be a solution to the clash of today's increasing energy demand with the continuous decrease of fossil-based energy sources, whose use is harmful for the environment. The operating conditions in a fusion reactor will be unprecedented in terms of ultra-high temperatures, stresses, radiation fields and very corrosive media. Only a limited number of materials may be able to withstand such combination of harsh environmental conditions, and vanadium-based alloys are among them. Recent research efforts have identified V-4Cr-4Ti as the most promising vanadium-based alloy for application in the first wall of future fusion nuclear reactors such as DEMO and beyond. The presence of TiO-type precipitates, containing relatively small amounts of C and N, strongly influences the final mechanical properties and radiation resistance of the alloy. Therefore, a thorough understanding of the precipitate structure and evolution at both relatively high temperatures and radiation dose levels is primordial to predict and optimise the final performance of the structural component in the fusion reactor. This thesis is written in alternative format and collects one article already published in Scripta Materialia, and two additional articles to be submitted to peer-review scientific journals. Atomic resolution imaging of the precipitates, coupled with chemical analysis, constitutes the main body of the first article: a novel intergrowth of the fcc Ti oxide in the bcc V matrix is revealed at the precipitate/matrix interface. The evolution of the vacancies present in the TiO precipitates above 400°C, together with the recovery of dislocations in the matrix and the formation of extra precipitates, is studied in the second article by positron annihilation spectroscopy and micro-hardness measurements. The formation of additional precipitates below 400°C induced by radiation is assessed in the third article using proton irradiation as a surrogate of neutron damage. The structure of those additional precipitates and of the dislocation loops induced by the proton bombardment is characterized by advanced analytical electron microscopy.

Gong, Xiangjun = 新型全內反射顯微鏡的搭建及其在膠體研究中的應用 / 龔湘君. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Gong, Xiangjun = Xin xing quan nei fan she xian wei jing de da jian ji qi zai jiao ti yan jiu zhong de ying yong / Gong Xiangjun. / Abstract (Chinese) --- p.i / Abstract --- p.iii / Contents --- p.v / Acknowledgement --- p.vii / Chapter Chapter 1 --- Introduction to Total Internal Reflection Microscopy (TIRM) / Chapter 1.1 --- History of TIRM --- p.1 / Chapter 1.2 --- Instrumentation --- p.1 / Chapter 1.2.1 --- Apparatus --- p.1 / Chapter 1.2.2 --- Optical Tweezer --- p.3 / Chapter 1.3 --- The principle of the technique --- p.5 / Chapter 1.3.1 --- Total Internal Reflection --- p.5 / Chapter 1.3.2 --- Details on Scattering of the Evanescent Wave --- p.7 / Chapter 1.3.3 --- Data analysis --- p.14 / Chapter 1.3.4 --- A typical potential energy profile --- p.17 / Chapter 1.4 --- Noise Analysis and Removal Method --- p.19 / Chapter 1.4.1 --- Noise analysis --- p.19 / Chapter 1.4.2 --- Noise removal: low-pass filtering --- p.22 / Chapter 1.5 --- Other techniques on force measurement --- p.25 / Chapter 1.6 --- References --- p.27 / Chapter Chapter 2 --- Experiments on TIRM Calibration / Chapter 2.1 --- Introduction --- p.30 / Chapter 2.2 --- Pre-Experimental Section --- p.30 / Chapter 2.2.1 --- Glass Surface Preparation Methods --- p.30 / Chapter 2.2.2 --- Experimental Setup --- p.33 / Chapter 2.3 --- Calibration Results and Discussion --- p.36 / Chapter 2.4 --- Conclusions --- p.42 / Chapter 2.5 --- References --- p.43 / Chapter Chapter 3 --- TIRM investigation on polymer-induced collodial interactions / Chapter 3.1 --- Introduction to polymer-induced forces --- p.45 / Chapter 3.1.1 --- Non-absorbing case - depletion force --- p.46 / Chapter 3.1.2 --- Attached polymer layers --- p.49 / Chapter 3.2 --- Applications of TIRM in polymer-mediated colloidal interactions --- p.54 / Chapter 3.2.1 --- Measurements on depletion force --- p.54 / Chapter 3.2.2 --- Measurements on Steric Forces --- p.56 / Chapter 3.3 --- Direct measurement of thermosensitive Poly(N-isopropylacrylamide)-mediated colloidal interactions with TIRM --- p.56 / Chapter 3.3.1 --- Introduction --- p.56 / Chapter 3.3.2 --- Experimental Section --- p.57 / Chapter 3.3.3 --- Results and Discussion --- p.60 / Chapter 3.3.4 --- Conclusions --- p.73 / Chapter 3.4 --- References --- p.74 / Publication List --- p.77

Gong, Xiangjun = 基於磁鑷和全反射顯微鏡的單粒子追踪微流變方法 / 龔湘君. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Gong, Xiangjun = Ji yu ci nie he quan fan she xian wei jing de dan li zi zhui zong wei liu bian fang fa / Gong Xiangjun.

M.S. / Applied Physics / A noble gas ion laser with strong transitions in the 196-225 nm wavelength region has been developed for use as an illuminator in a photoelectron microscope. The laser is pulsed, and it can be operated at repetition rates up to 200 Hz to produce average output powers up to 5.0 mW at 219 nm. This is comparable to the output of the brightest available incoherent source, a Hg-Xe-Cd arc lamp that produces 2.6 mW of usable light in the 221-226 nm range. The laser has the advantage that it can be focused to produce much higher intensities than the arc lamp, and less total power is necessary. But the pulsed laser has a low duty cycle (~ 10[superscript minus 5]), and the corresponding peak powers (~ 300 watts) result in a space-charge-limited resolution of approximately 500 Å when the laser illuminates a phthalocyanine target. The magnitude of this aberration is proportional to beam current. Consequently, the resolution o can be improved to about 50 Å by decreasing the input power, or increasing the duty cycle, by a factor of 100-1000. Techniques for achieving such an improvement are suggested.

Three-dimensional (3D) structural determination of biological macromolecules is not only critical to understanding their mechanisms, but also has practical applications. Combining the high resolution imaging of transmission electron microscopy (TEM) and efficient computer processing, protein structures in solution or in two-dimensional (2D) crystals can be determined. The lipid monolayer technique uses the high affinity binding of 6His-tagged proteins to a Ni-nitrilotriacetic (NTA) lipid to create high local protein concentrations, which facilitates 2D crystal formation. In this study, several proteins have been crystallized using this technique, including the SARS virus Nsp15 endonuclease and the human Toll-like receptor (TLR) 3 extracellular domain (ECD). Single particle analysis can determine protein structures in solution without the need for crystals. 3D structures of several protein complexes had been solved by the single particle method, including IniA from Mycobacterium tuberculosis, Nsp15 and TLR3 ECD. Determining the structures of these proteins is an important step toward understanding pathogenic microbes and our immune system.

Double stranded DNA bacteriophages achieve release of phage progeny by disrupting the cell envelope of the host cell. This is accomplished by two phage-encoded proteins, the holin and the endolysin. In bacteriophage lambda, the S holin is a small three TMD membrane protein that creates a lesion in the inner membrane of the host at a specific time, programmed in its primary structure. Lesion formation permits the cytoplasmic endolysin R access to the murein cell wall for degradation and cell lysis. Although it has been shown that S oligomerizes in the membrane, the structural nature of this complex has not been elucidated. In this study the S holin was purified using a mild non-ionic detergent and the structure of a ring complex formed by the holin was determined by electron microscopy and single particle analysis at a resolution of 2.6 nm. Biochemical characterization of the rings suggests that such a complex might represent the assembly formed by S in the membrane. Protein translocation in all organisms allows the export of proteins destined for localization outside the cytoplasm. In eubacteria, newly synthesized proteins are directed to the heterotrimeric membrane complex SecYEG by signals embedded in their sequence. The driving force through this complex is provided by the cytoplasmic ATPase SecA which combines ATP hydrolysis to mechanically insert proteins through the protein conducting channel. Using electron microscopy and single particle analysis we have obtained the structure of SecA from M. tuberculosis. The structure indicates that four SecA monomers assemble to form an elongated molecule with D2 symmetry. Docking of the EM map to the crystal structure of tb SecA confirms this arrangement of the subunits. This finding, that M. tuberculosis SecA forms a tetramer raises intriguing possibilities about SecA function.

Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology. In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques. In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.</p>

The goal of fully decoding how the brain works requires a detailed wiring diagram of the brain network that reveals the complete connectivity matrix. Recent advances in high-throughput 3D electron microscopy (EM) image acquisition techniques have made it possible to obtain high-resolution 3D imaging data that allows researchers to follow axons and dendrites and to identify pre-synaptic and post-synaptic sites, enabling the reconstruction of detailed neural circuits of the nervous system at the level of synapses. However, these massive data sets pose unique challenges to structural reconstruction because the inevitable staining noise, incomplete boundaries, and inhomogeneous staining intensities increase difficulty of 3D reconstruction and visualization. In this dissertation, a new set of algorithms are provided for reconstruction of neuronal morphology from stacks of serial EM images. These algorithms include (1) segmentation algorithms for obtaining the full geometry of neural circuits, (2) interactive segmentation tools for manual correction of erroneous segmentations, and (3) a validation method for obtaining a topologically correct segmentation when a set of segmentation alternatives are available. Experimental results obtained by using EM images containing densely packed cells demonstrate that (1) the proposed segmentation methods can successfully reconstruct full anatomical structures from EM images, (2) the editing tools provide a way for the user to easily and quickly refine incorrect segmentations, (3) and the validation method is effective in combining multiple segmentation results. The algorithms presented in this dissertation are expected to contribute to the reconstruction of the connectome and to open new directions in the development of reconstruction methods.

No description available.

Double stranded DNA bacteriophages achieve release of phage progeny by disrupting the cell envelope of the host cell. This is accomplished by two phage-encoded proteins, the holin and the endolysin. In bacteriophage lambda, the S holin is a small three TMD membrane protein that creates a lesion in the inner membrane of the host at a specific time, programmed in its primary structure. Lesion formation permits the cytoplasmic endolysin R access to the murein cell wall for degradation and cell lysis. Although it has been shown that S oligomerizes in the membrane, the structural nature of this complex has not been elucidated. In this study the S holin was purified using a mild non-ionic detergent and the structure of a ring complex formed by the holin was determined by electron microscopy and single particle analysis at a resolution of 2.6 nm. Biochemical characterization of the rings suggests that such a complex might represent the assembly formed by S in the membrane. Protein translocation in all organisms allows the export of proteins destined for localization outside the cytoplasm. In eubacteria, newly synthesized proteins are directed to the heterotrimeric membrane complex SecYEG by signals embedded in their sequence. The driving force through this complex is provided by the cytoplasmic ATPase SecA which combines ATP hydrolysis to mechanically insert proteins through the protein conducting channel. Using electron microscopy and single particle analysis we have obtained the structure of SecA from M. tuberculosis. The structure indicates that four SecA monomers assemble to form an elongated molecule with D2 symmetry. Docking of the EM map to the crystal structure of tb SecA confirms this arrangement of the subunits. This finding, that M. tuberculosis SecA forms a tetramer raises intriguing possibilities about SecA function.