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No description available.

Several short oligoribonucleotide sequences containing modified purine residues of biological significance were synthesized using the phosphotriester method developed in Neilson's laboratory. Variable temperature proton nuclear magnetic resonance (NMR) spectroscopy was used to examine the solution conformations of these oligomers. Studies of the effect of position, type and extent of alkyl modifications on helix structure and stability were undertaken. The triribonucleotide GpCpA was the first trimer shown to form a stable RNA duplex (Tm 33°C) (Alkema, et al, 1981(a)). This duplex contained two G:C base pairs and two 3'-dangling adenosine residues, and had a stability equal to that of the tetramer duplex UpGpCpA, having four Watson Crick base pairs. A series of GpCpN trimers was prepared (N= m⁶A, m⁶₂A, m¹G, m⁶G, e⁶G, m²m⁶G), using GpCpA as a reference, to determine how N-or O-alkylation of the dangling residue affected duplex stability. Both the studies of the N-alkylated (N=m⁶A, m⁶₂A, m¹G) (D'Andrea, et al, 1983) and 0-alkylated (N=m⁶G, e⁶G, m²m⁶G) sequences (present work) led to the conclusion that site and degree of modification were important factors for stability. Comparison of N-versus O-alkylated sequences revealed how the hydrophobic regions surrounding the alkylated nitrogen or alkylated oxygen atoms, and the spatial location of these regions, contributed to duplex stability. Examination of the effect of modified guanosine residues within a short squence, was performed through studies on ApGpNpCpU pentamers (N=m⁶G, e⁶G, m²m⁶G), having N in internal non-base-pairing and. in internal base-pairing positions. No duplex formation was seen, in contrast to studies involving reference compounds : ApGpGpCpU (a qualitative reference), ApGpGpCpU : ApGpUpCpU (Tm 31.4 C), and ApGpGpCpU : ApGpCpCpU (Tm 47.0 C). As no melting temperatures could be calculated for the modified strands, and because their NMR analyses were so similar, no comparisions regarding degree of destabilization, could be made amongst the various modified residues. Never the less, it is clear that O-alkylation of the central G residue significantly disrupts duplex formation, through generation of a centre of great instability. This result sharply contrasts that when the same modified residues are located in terminal, non-bonding positions. / Thesis / Master of Science (MSc)

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No / Analysis of strategic stability in South Asia has been predominantly viewed through the bipolar Cold War prism of US-Soviet relations and has thus been insufficiently cognisant of the specificities of nuclear dynamics in South Asia. This paper argues that security analysis in South Asia needs to give attention to the economic, political and social factors which condition the core politico-military relationship as well as to that relationship itself. It argues further that nuclear dynamics in South Asia, characterised by asymmetries, may not play out as Cold War models would predict and consequently that there is a need for an agenda for the promotion of strategic stability which reflects the distinct dynamics of nuclear rivalry in South Asia (deterrence, command and control and arms control and confidence-building measures).

Low back disorders and their prevention is of great importance for companies and their employees. Whole-body vibration is a risk factor for low back disorders, but the neuromuscular, biomechanical, and/or physiological mechanisms responsible for this increased risk are unclear. These studies investigated changes in the biomechanics and control of the trunk in order to further the understanding of the mechanisms responsible for this increased risk. The purpose of the first study was to measure the acute effect of seated whole-body vibration on the postural control of the trunk during unstable seated balance. The findings show that whole-body vibration impaired the postural control of the trunk as evidenced by increased kinematic variance and non-linear stability control measures during unstable sitting. These findings imply an impairment in spinal stability control. The purpose of the second study was to measure the effect of seated whole-body vibration on the parameters of spinal stability control: passive stiffness, active stiffness, and neuromuscular reflexes. The findings show that whole-body vibration altered trunk stiffness (passive stiffness and equivalent reflex stiffness) as well as reflex dynamics. There was no evidence of compensation by active muscle co-contraction recruitment for the decreased trunk stiffness and reflex gain. The purpose of the third study was to measure the changes in the natural frequency characteristics of the trunk (which can be related to trunk stiffness and damping) during exposure to seated whole-body vibration. The findings show that whole-body vibration caused a decrease in natural frequency suggesting a decrease in the trunk stiffness, and also an increase in the peak amplitude of the frequency response functions suggesting a decrease in overall trunk damping. The rate of change of the natural frequency characteristics suggest that the majority of effects happen within the first 10 minutes of vibration exposure. These findings reveal changes in the biomechanical properties of the trunk with exposure to seated whole body vibration, and a mechanism by which vibration may increase the risk of low back injury. / Ph. D.

In this thesis, the design of a voltage-source inverter (VSI)-based three-phase impedance analyzer's perturbation injection unit (PIU) is described including all relevant power stage and control design. Both series and shunt injection are examined from .1 Hz to 1000Hz. Both types of injection are performed using only energy from the system under test stored in a DC link capacitor. Sinusoidal, square (pulse), and chirp perturbation waveforms are explored. Results from a constructed realization of the design are presented, and the limits of the device characterized. The maximum achievable perturbation power is 10 kW in shunt and 8 kW in series on a 460 V, 100 kW bus. Using the same conditions, maximum power is achievable from 10Hz to 100Hz, at .1Hz, .72 kW is achievable, and at 1000Hz, 6.0 kW is achievable. / Master of Science