Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 275-286).

Principal neurons of the medial superior olive (MSO) encode low-frequency sound localization cues by comparing the relative arrival time of sound to the two ears. In mammals, MSO neurons display biophysical specializations, such as voltage-gated sodium (Na[subscript v]) and potassium (K[subscript v]) channels that enable them to detect these cues with microsecond precision. In this dissertation electrophysiological techniques were used to examine the specific channel properties and functional role these channels play in MSO neurons following hearing onset. In addition, computational models that incorporated these physiological data were used to further study how the specific properties of these channels facilitate MSO function. Experiments in this dissertation showed that Na[subscript v] channels are heavily expressed in the persisomatic region of MSO neurons, but unlike those expressed in other neurons they minimally contribute to action potential generation. This is likely due to the low percentage of channels available for activation at the resting membrane potential. Current clamp recordings determined that Na[subscript v] channels counterbalance K[subscript v] channels voltage rectification by boosting near action potential threshold excitatory post-synaptic potentials (EPSPs). Further, computational modeling revealed that synaptic inputs are larger at the soma with Na[subscript v] channels restricted to the soma than when they are evenly distributed throughout the soma and dendrites. During the first few weeks after hearing onset current clamp experiments showed EPSP duration decreased while the temporal resolution for detecting the arrival time of synaptic inputs increased. These changes in EPSP duration are due in part to both the development of faster membrane response properties and increases in the expression of low voltage-activated K[subscript v] channels (K[subscript LVA]). Further investigation determined these channels display a somatically enriched distribution and act to counterbalance the distortions that result from dendritic cable filtering. This is accomplished by K[subscript LVA] actively decreasing the duration of EPSPs in a voltage dependent manner. Computational modeling confirmed these results as well as illustrating their effects on the integration of mono- versus bilateral excitation. Together these findings indicate that the expression of specialized Na[subscript v] and K[subscript v] channels facilitate the neuron’s computational task, detecting and comparing the relative timing of synaptic inputs used in low frequency sound localization. / text

The glycine receptor (GlyR) is the major inhibitory ligand-gated ion channel in the brainstem and spinal cord. It is a member of the Cys-loop superfamily of ligand-gated ion channels that includes serotonin-3, GABA[subscript A] and nicotinic acetylcholine (nAChR) receptors. Individual subunits are comprised of a large extracellular N-terminal agonist binding domain, four transmembrane (TM) segments and a large cytoplasmic loop between TM3 and TM4, containing phosphorylation sites (Brejc et al. 2001, Unwin, 2005). These receptors are pentameric in structure, with the TM2 region of each subunit contributing to the formation of a central ion pore (Lynch 2004). While the TM2-3 linker region has been hypothesized to be important for signal transduction thoughout the Cys-loop family, the precise structure and function of this region is unclear. We hypothesized that the TM2-3 linker region is a point of connection between subunits. We used disulfide bond trapping to show that the TM2-3 is able to interact with adjacent subunits and plays a critical role in signal transduction. In addition, we provide experimental evidence that the structure of the TM2-3 linker region in the [alpha]1 GlyR is a [beta]-sheet. We next sought to determine the role of the TM2-3 linker region in allosteric modulation. Using two-electrode voltage clamp electrophysiology we found that the TM2-3 linker can determine the direction of modulation without affecting modulator binding. Finally, we wanted to determine if a single alcohol and anesthetic binding site could be occupied to prevent EtOH molecules from binding. Using a combination of thiol reagents and disulfide bond trapping we show that a residue previously identified as important for the binding of alcohols and anesthetics interacts within the pore. We were unable to increase the volume at residue-267 such that EtOH was unable to bind, suggesting that EtOH may have more than one binding pocket. Together, these findings suggest that the TM2-3 linker plays a critical role in signal transduction and receptor modulation providing a foundation for future work on this region in the GlyR. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

abstract / Medicine / Doctoral / Doctor of Philosophy

Not available / text

Not available / text

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / This paper shows the design and testing of a test bed at Morgan State University as part of the development of a Link Dependent Adaptive Radio (LDAR). It shows the integration of variable rate QAM/OFDM modulation and a variable rate Punctured Convolutional Coder. It also shows a dynamic aeronautical channel simulator developed to capture the dynamics of these channels. Performance results are show for combinations of modulation, coding and channel variations that provide motivation for the potential of the LDAR system.

Internal communication is pivotal for the effectiveness of company procedures and ultimately the success of the company. Understanding more about the communicative needs of different employee groups is therefore important in order to convey a message in a satisfying manner to those employees. This explorative study is investigating communication preferences from a stakeholder perspective to find out what influences the appropriateness of using different communication channels when transmitting information to different stakeholder groups. Interviews with employees at different levels and functions at PostNord were conducted and analysed. We conclude that the top level stakeholder prefers face-to-face communication due to complex topics being discussed with a high need for feedback. The stakeholder at the middle organisational level preferred e-mail due to being constantly interrupted and therefore need to access information at later times. The bottom level consisted of two stakeholder groups that had high degree, respectively low degree of customer interaction. They both preferred face-to-face, for reasons that had grounds in strict working schedules and work tasks - they were not given time to take in information properly in any other way than scheduled meetings, and the stakeholder with low customer interaction mostly worked alone which made this stakeholder value meetings with other colleagues.