Ph.D. / Applied Physics / This work was undertaken to determine the feasibility of using a field ionization (FI) source to produce fine focus ion beams. Operating parameters for a FI source have been measured and a source sensitivity of ~ 5 x 10[superscript-5] A sr[superscript -1] torr[superscript -1] was found for both H[subscript 2] and Ar at 77 K. The source is gas phase, differentially pumped with typical operating pressures of 1 - 30 x 10[superscript -3] torr at 77 K, resulting in a maximum source brightness ≈ 10[superscript 8] A cm[superscript -2] sr[superscript -1] and angular intensity of ≈ 10[superscript -6] A sr[superscript -1] with beam energies of 10 - 20 keV. Angular distributions were measured and found to be uniform near θ = 0°, with the beam confined to ±20°. A scanning ion microscope (SIM) was built to further evaluate the source. The SIM has been operated with currents on the specimen of 10[superscript -11] – 10[superscript -10 amperes in the secondary electron mode with contrast provided primarily by the sec (θ) dependence of the secondary electron yield, where θ is the angle between the beam and the specimen normal. Secondary electrons are detected and amplified with a channeltron multiplier and images generated as with a conventional SEM. All electrostatic optics are used in a doublet arrangement, and with this configuration current is independent of working distance which is 3 - 4 cm. A current of 5 x 10[superscript -11] A was focused into a spot of ≈ 6500 Å with H[subscript 2] gas, the resolution being limited by chromatic aberration caused by the ≈ 4 eV energy spread of the two component (H[superscript +] H[superscript +, subscript 2]) beam. Signal to noise ratio measurements on the source made at the specimen position show that the bulk of the noise power spectrum falls below f = 30 Hz.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 158-169). Available also in a digital version from Dissertation Abstracts.

Thesis--M.D., University of Hong Kong, 1983. / Vol. 2: Appendix.

Dengue is the most common mosquito-borne human disease, leading to 2.5 billion people at risk, 50-100 millions infections each year worldwide and among them, 500 000 severe dengue cases (dengue hemorrhagic fever, DHF/ dengue shock syndrome, DSS) plus more than 20 000 deaths. It can be caused by any of four dengue virus serotypes, which are antigenicly distinct and belong to the Flaviviridae family, genus Flavivirus. However, up till now there is no specific drug and vaccine against dengue. Understanding mechanisms developed by dengue virus to exploit host cells during all stages of the replication cycle is a first step towards the rationale design of anti-viral strategies. Very little is known about the late stages, which consist of assembly, budding and secretion of the virus. It is therefore very important to develop tools in order to study the egress of the virus. In this study, I investigated a stable cell line named Hela-prME that expresses serotype 1 dengue virus (DENV-1) prM and E native structural envelope proteins and constitutively produces dengue recombinant subviral particles (RSPs). Biochemical characterization of DENV-1 RSPs has validated that this cell line is a potential tool to study the dengue viral late-stage. Indeed, the maturation process observed with RSPs is similar to the pathway described for real virus (cleavage of prM fragment, homodimerization of E, acquisition of complex sugars). To better understand and depict the dengue virus late-stage secretion, I combined various electron microscopy (EM) techniques e.g. classical transmission electron microscopy (TEM), negative staining, immunogold labeling on cryo-ultrathin sections (Tokuyashu method) and tomography (ET) with such RSPs tool. The EM results obtained illustrate that electron dense particles and tubules labeled by antibodies directed against E and prM proteins were abundantly found in the lumen of endoplasmic reticulum (ER)-related cisternae of HeLa prME cells. Epositive particles were also found in other structures such as Golgi stacks and vesicles nearby as well as in aggregates with electron dense materials inside and surrounded by membrane. These particles are most likely corresponding to DENV-1 RSPs whereas the tubules may be other structures induced by assembly of prM and E proteins. This study has clearly shown that DENV-1 RSPs assemble in the ER and transport through the secretory pathway before being released. This work further validates the use of dengue RSPs and RSPs-producing cells as a model to study viral egress. / published_or_final_version / Pathology / Master / Master of Philosophy

No description available.

No description available.

No description available.

No description available.

No description available.

Thesis (M.S.)--Rochester Institute of Technology, 1992. / Typescript. Includes bibliographical references (leaves 114-116).