Cellular Membranes as a Playground for Semliki Forest Virus Replication Complex

All positive-strand RNA viruses utilize cellular membranes for the assembly of their replication complexes, which results in extensive membrane modification in infected host cells. These alterations act as structural and functional scaffolds for RNA replication, providing protection for the viral double-stranded RNA against host defences. It is known that different positive-strand RNA viruses alter different cellular membranes. However, the origin of the targeted membranes, the mechanisms that direct replication proteins to specific membranes and the steps in the formation of the membrane bound replication complex are not completely understood. Alphaviruses (including Semliki Forest virus, SFV), members of family Togaviridae, replicate their RNA in association with membranes derived from the endosomal and lysosomal compartment, inducing membrane invaginations called spherules. Spherule structures have been shown to be the specific sites for RNA synthesis. Four replication proteins, nsP1-nsP4, are translated as a polyprotein (P1234) which is processed autocatalytically and gives rise to a membrane-bound replication complex. Membrane binding is mediated via nsP1 which possesses an amphipathic α-helix (binding peptide) in the central region of the protein. The aim of this thesis was to characterize the association of the SFV replication complex with cellular membranes and the modification of the membranes during virus infection. Therefore, it was necessary to set up the system for determining which viral components are needed for inducing the spherules. In addition, the targeting of the replication complex, the formation site of the spherules and their intracellular trafficking were studied in detail. The results of current work demonstrate that mutations in the binding peptide region of nsP1 are lethal for virus replication and change the localization of the polyprotein precursor P123. The replication complex is first targeted to the plasma membrane where membrane invaginations, spherules, are induced. Using a specific regulated endocytosis event the spherules are internalized from the plasma membrane in neutral carrier vesicles and transported via an actin-and microtubule-dependent manner to the pericentriolar area. Homotypic fusions and fusions with pre-existing acidic organelles lead to the maturation of previously described cytopathic vacuoles with hundreds of spherules on their limiting membranes. This work provides new insights into the membrane binding mechanism of SFV replication complex and its role in the virus life cycle. Development of plasmid-driven system for studying the formation of the replication complex described in this thesis allows various applications to address different steps in SFV life cycle and virus-host interactions in the future. This trans-replication system could be applied for many different viruses. In addition, the current work brings up new aspects of membranes and cellular components involved in SFV replication leading to further understanding in the formation and dynamics of the membrane-associated replication complex.

Decomposition technique for composite signals

A new method for decomposition of compo,.~itsei gnals is presented. It is shown that high freyuency portion of composite signal spectrum possesses information on echo structure. The proposed technique does not assume the shape of basic wavelet and does not place any restrictions on the amplitudes and arrival times of echoes inm the composite signal. In the absence of noise any desirrd resolution can he obtained The effect of sampling rate and jFequency window function on echo resolutio.~ are di.wussed. Voiced speech segment is considered as an example of conzpxite sigrnl to demonstrate the application of the decomposition technique.

Towards stress freezing in birefringent orthotropic composite models

Birefringent composite models are fabricated using epoxy resin reinforced with unidirectionally oriented glass fibers. The mechanical and photoelastic properties of the material at room temperature are determined. To explore the possibility of application of stress-freezing technique to birefringent composite models, the behavior and properties of this material are studied at elevated temperature (at stress-freezing temperature of the resin). The properties of the material at room and at elevated temperatures are reported. The feasibility of stress freezing glass-fiber-reinforced epoxy composites with low-fiber-volume fraction is discussed.

Mechanistic Studies on Composite-Solid Propellants

Abstract is not available.

Cooling of a composite slab

A mixed boundary value problem associated with the diffusion equation, that involves the physical problem of cooling of an infinite parallel-sided composite slab, is solved completely by using the Wiener-Hopf technique. An analytical expression is derived for the sputtering temperature at the quench front being created by a cold fluid moving on the upper surface of the slab at a constant speed v. The dependence of the various configurational parameters of the problem under consideration, on the sputtering temperature, is rather complicated and representative tables of numerical values of this important physical quantity are prepared for certain typical values of these parameters. Asymptotic results in their most simplified forms are also obtained when (i) the ratio of the thicknesses of the two materials comprising the slab is very much smaller than unity, and (ii) the quench-front speed v is very large, keeping the other parameters fixed, in both the cases.

Polyvanadate-stimulated NADH oxidation by plasma membranes-The need for a mixture of deca and meta forms of vanadate

Polyvanadate solutions obtained by extracting vanadium pentoxide with dilute alkali over a period of several hours contained increasing amounts of decavanadate as characterized by NMR and ir spectra. Those solutions having a metavanadate:decavanadate ratio in the range of 1-5 showed maximum stimulation of NADH oxidation by rat liver plasma membranes. Reduction of decavanadate, but not metavanadate, was obtained only in the presence of the plasma membrane enzyme system. High simulation of activity of NADH oxidation was obtained with a mixture of the two forms of vanadate and this further increased on lowering the pH. Addition of increasing concentrations of decavanadate to metavanadate and vice versa increased the stimulatory activity, reaching a maximum when the metavanadate:decavanadate ratio was in the range of 1-5. Increased stimulatory activity can also be obtained by reaching these ratios by conversion of decavanadate to metavanadate by alkaline phosphate degradation, and of metavanadate to decavanadate by acidification. These studies show for the first time that both deca and meta forms of vanadate present in polyvanadate solutions are needed for maximum activity of NADH oxidation.

Vibrations of Multifiber Composite Shells-Some Numerical Results

A study of vibrations of multifiber composite shells is presented. Special attention is paid to the effect of composition of different fibers on the frequency spectrum of a freely vibrating cylindrical shell. The numerical results indicate clustering of frequency spectrum of a freely vibrating cylindrical composite shell as compared with the isotropic shell, and the spectrum varies considerably with the composition of the constituent materials.

Thin nanoporous metal-insulator-metal membranes

Insulating nanoporous materials are promising platforms for soft-ionizing membranes; however, improvement in fabrication processes and the quality and high breakdown resistance of the thin insulator layers are needed for high integration and performance. Here, scalable fabrication of highly porous, thin, silicon dioxide membranes with controlled thickness is demonstrated using plasma-enhanced chemical-vapor-deposition. The fabricated membranes exhibit good insulating properties with a breakdown voltage of 1 × 107 V/cm. Our calculations suggest that the average electric field inside a nanopore of the membranes can be as high as 1 × 106 V/cm; sufficient for ionization of wide range of molecules. These metal–insulator–metal nanoporous arrays are promising for applications such soft ionizing membranes for mass spectroscopy.

Comprehensive view of the combustion models of composite solid propellants

Abstrat is not available.

Acoustic emission source location in composite structure by Voronoi construction using geodesic curve evolution

Conventional analytical/numerical methods employing triangulation technique are suitable for locating acoustic emission (AE) source in a planar structure without structural discontinuities. But these methods cannot be extended to structures with complicated geometry, and, also, the problem gets compounded if the material of the structure is anisotropic warranting complex analytical velocity models. A geodesic approach using Voronoi construction is proposed in this work to locate the AE source in a composite structure. The approach is based on the fact that the wave takes minimum energy path to travel from the source to any other point in the connected domain. The geodesics are computed on the meshed surface of the structure using graph theory based on Dijkstra's algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first intersection point of these waves, one can get the AE source location. In this work, the geodesic approach is shown more suitable for a practicable source location solution in a composite structure with arbitrary surface containing finite discontinuities. Experiments have been conducted on composite plate specimens of simple and complex geometry to validate this method.

Atomic layer-by-layer Co3O4/graphene composite for high performance lithium-ion batteries

An "atomic layer-by-layer" structure of Co3O4/graphene is developed as an anode material for lithium-ion batteries. Due to the atomic thickness of both the Co3O4 nanosheets and the graphene, the composite exhibits an ultrahigh specific capacity of 1134.4 mAh g-1 and an ultralong life up to 2000 cycles at 2.25 C, far beyond the performances of previously reported Co3O4/C composites.