Transmission electron tomography: quality assessment and enhancement for three-dimensional imaging of nanostructures

Nanotechnology has revolutionised humanity's capability in building microscopic systems by manipulating materials on a molecular and atomic scale. Nan-osystems are becoming increasingly smaller and more complex from the chemical perspective which increases the demand for microscopic characterisation techniques. Among others, transmission electron microscopy (TEM) is an indispensable tool that is increasingly used to study the structures of nanosystems down to the molecular and atomic scale. However, despite the effectivity of this tool, it can only provide 2-dimensional projection (shadow) images of the 3D structure, leaving the 3-dimensional information hidden which can lead to incomplete or erroneous characterization. One very promising inspection method is Electron Tomography (ET), which is rapidly becoming an important tool to explore the 3D nano-world. ET provides (sub-)nanometer resolution in all three dimensions of the sample under investigation. However, the fidelity of the ET tomogram that is achieved by current ET reconstruction procedures remains a major challenge. This thesis addresses the assessment and advancement of electron tomographic methods to enable high-fidelity three-dimensional investigations. A quality assessment investigation was conducted to provide a quality quantitative analysis of the main established ET reconstruction algorithms and to study the influence of the experimental conditions on the quality of the reconstructed ET tomogram. Regular shaped nanoparticles were used as a ground-truth for this study. It is concluded that the fidelity of the post-reconstruction quantitative analysis and segmentation is limited, mainly by the fidelity of the reconstructed ET tomogram. This motivates the development of an improved tomographic reconstruction process. In this thesis, a novel ET method was proposed, named dictionary learning electron tomography (DLET). DLET is based on the recent mathematical theorem of compressed sensing (CS) which employs the sparsity of ET tomograms to enable accurate reconstruction from undersampled (S)TEM tilt series. DLET learns the sparsifying transform (dictionary) in an adaptive way and reconstructs the tomogram simultaneously from highly undersampled tilt series. In this method, the sparsity is applied on overlapping image patches favouring local structures. Furthermore, the dictionary is adapted to the specific tomogram instance, thereby favouring better sparsity and consequently higher quality reconstructions. The reconstruction algorithm is based on an alternating procedure that learns the sparsifying dictionary and employs it to remove artifacts and noise in one step, and then restores the tomogram data in the other step. Simulation and real ET experiments of several morphologies are performed with a variety of setups. Reconstruction results validate its efficiency in both noiseless and noisy cases and show that it yields an improved reconstruction quality with fast convergence. The proposed method enables the recovery of high-fidelity information without the need to worry about what sparsifying transform to select or whether the images used strictly follow the pre-conditions of a certain transform (e.g. strictly piecewise constant for Total Variation minimisation). This can also avoid artifacts that can be introduced by specific sparsifying transforms (e.g. the staircase artifacts the may result when using Total Variation minimisation). Moreover, this thesis shows how reliable elementally sensitive tomography using EELS is possible with the aid of both appropriate use of Dual electron energy loss spectroscopy (DualEELS) and the DLET compressed sensing algorithm to make the best use of the limited data volume and signal to noise inherent in core-loss electron energy loss spectroscopy (EELS) from nanoparticles of an industrially important material. Taken together, the results presented in this thesis demonstrates how high-fidelity ET reconstructions can be achieved using a compressed sensing approach.

Transmission, Legitimation, and Adaptation: A Study of Western Lamas in the Construction of ‘American Tibetan Buddhism’

This thesis presents a study of the role of western lamas within Tibetan Buddhism in America, arguing that the role of the lama is as an influential and central aspect in the development and transformation of the Tibetan Buddhist tradition in the west. This thesis argues how western lamas holding a position of authority act as a catalyst of change within their group and in the overall process of change and adaptation of the Tibetan Buddhist tradition in America, creating what may become ‘American Tibetan Buddhism.’ Three relevant areas regarding the role of the lama within the transforming tradition are identified: 1) the basis of authority of the lama, or how authority is obtained; 2) the use of such authority as a tool for change; and 3) transmission of the teachings and lineage.

Knowledge of HIV transmission risk behavior, and perceptions of risk among Haitian women living in Miami, Florida

This study was conducted to gain a more comprehensive understanding of HIV risk among Haitian women. The variables measured were: knowledge of HIV transmission, sexual risk behaviors, and perceptions of risk among Haitian women. The sociocultural aspect of the Haitian women's lives with regard to their risky behaviors was also examined. A total of 101 Haitian women (aged 25-53) who attended two comprehensive health clinics were interviewed. A combined questionnaire derived from both the ARM-Q and the RBA was used. In general, the women had good knowledge of the sexual transmission of HIV I AIDS and indicated that they were susceptible to HIV infection. However, knowledge and perceptions of risk were not translated into sexual risk-reduction behaviors with their partners. Multiplicity of partners and low incidence of condom use were the two major sexual risk factors isolated in this study. Results indicate Haitian women were more likely to use condoms if they possessed greater HIV knowledge and their sexual partners held more positive attitudes toward using condoms. Also, Haitian women may have failed to protect themselves because behavior changes could have involved threats to their social and economic survival, relationships and culturally sanctioned roles. This suggests the need to include male partners in HIV prevention interventions with Haitian women. Future research should focus on preventing high-risk behavior by improving knowledge, altering the male partners' attitudes toward condoms, and enhancing communication and negotiation skills. Nursing implications and recommendations for culturally sensitive and relevant AIDS prevention efforts are discussed.

L’interface politico-administrative au Québec : champ de bataille? Transmission stratégique de l’information dans les affaires d’État

En vertu de l’expertise qu’il détient, l’agent public contribue à la réflexion du politique. L’acteur public est en quelque sorte un outil d’aide à la décision. Le paradigme classique en théorie des organisations assume que le bureaucrate est un acteur programmé dont les actions sont guidées par la règlementation et la codification juridico-légale entourant sa pratique. Quant à elle, l’École de la nouvelle gestion publique suppose que l’agent public doit opérer librement selon les indicateurs de la sphère privée ; il doit viser l’efficacité au moindre coût et prioriser la culture du résultat. De plus, dans des conditions respectant l’environnement où se dessine le partage de renseignements, les chercheurs ne s’entendent pas sur le principe de l’allié qui postule conventionnellement que des préférences similaires favorisent la transmission optimale de l’information entre le politique et la fonction publique. Quel modèle prévaut au Québec ? Sous quelles formes s’opérationnalise-t-il en contexte de transfert ? La thèse d’une compatibilité préférentielle est-elle garante d’une translation informationnelle améliorée ? En usant du modèle canonique principal-agent, ce mémoire confronte la croyance répandue voulant que l’État québécois soit foncièrement webérien en adressant certaines des plus importantes conclusions théoriques dans la discipline. Les résultats démontrent que l’appareil d’État est issu d’un croisement entre les deux principaux paradigmes reconnus dans la littérature. Aussi, le mémoire fait état d’une similarité entre l’interprétation traditionnelle de l’ally principle et la réalité empirique retrouvée dans la relation entre le haut fonctionnaire et le législateur québécois. Ultimement, l’étude démontre que l’administrateur d’État est stratégique dans certaines situations qu’il sait instrumentaliser et où il peut occuper un espace discrétionnaire suffisant pour valoriser ses intérêts professionnels et ceux de son organisation.

An investigation of contact transmission of methicillin-resistant staphylococcus aureus

Hand hygiene is critical in the healthcare setting and it is believed that methicillin-resistant Staphylococcus aureus (MRSA), for example, is transmitted from patient to patient largely via the hands of health professionals. A study has been carried out at a large teaching hospital to estimate how often the gloves of a healthcare worker are contaminated with MRSA after contact with a colonized patient. The effectiveness of handwashing procedures to decontaminate the health professionals' hands was also investigated, together with how well different healthcare professional groups complied with handwashing procedures. The study showed that about 17% (9–25%) of contacts between a healthcare worker and a MRSA-colonized patient results in transmission of MRSA from a patient to the gloves of a healthcare worker. Different health professional groups have different rates of compliance with infection control procedures. Non-contact staff (cleaners, food services) had the shortest handwashing times. In this study, glove use compliance rates were 75% or above in all healthcare worker groups except doctors whose compliance was only 27%.

Electronic and vibrational spectra of gaspeite

Visible, near-infrared, IR and Raman spectra of magnesian gaspeite are presented. Nickel ion is the main source of the electronic bands as it is the principal component in the mineral where as the bands in IR and Raman spectra are due to the vibrational processes in the carbonate ion as an entity. The combination of electronic absorption and vibrational spectra (including near-infrared, FTIR and Raman) of magnesian gaspeite are explained in terms of the cation co-ordination and the behaviour of CO32– anion in the Ni–Mg carbonate. The electronic absorption spectrum consists of three broad and intense bands at 8130, 13160 and 22730 cm–1 due to spin-allowed transitions and two weak bands at 20410 and 30300 cm–1 are assigned to spin-forbidden transitions of Ni2+ in an octahedral symmetry. The crystal field parameters evaluated from the observed bands are Dq = 810; B = 800 and C = 3200 cm–1. The two bands in the near-infrared spectrum at 4330 and 5130 cm–1 are overtone and combination of CO32– vibrational modes. For the carbonate group, infrared bands are observed at 1020 cm–1(1 ), 870 cm–1 (2), 1418 cm–1 (3) and 750 cm–1 (4), of which3, the asymmetric stretching mode is most intense. Three well resolved Raman bands at 1571, 1088 and 331 cm–1 are assigned to 3, 1 and MO stretching vibrations.