The eis gene of M. tuberculosis is believed to play a role in the intracellular survival of this pathogen. Significantly higher levels of antibodies to Eis were detected by ELISA in the sera of patients with tuberculosis as compared to healthy controls. PBMCs from recovered TB donors were also found to demonstrate significantly higher levels of proliferation in response to stimulation with the Eis protein than PBMCs from either active TB cases or healthy controls. Neither the active TB population nor the healthy controls showed significant levels of IFN- or IL-4 secretion in response to stimulation of PBMC with Eis or ESAT-6. Far Western analysis determined that Eis interacts with a ~65 kDa protein that localizes to the cytoplasmic fraction of M. tuberculosis lysate. Real-time PCR analysis of M. tuberculosis infected U-937 macrophages showed that the eis gene is constitutively expressed during infection. Using immunofluorescence microscopy (IF), the Eis protein was detected within the cytoplasm of M. tuberculosis infected macrophages indicating that the protein was being released/secreted from the mycobacterium containing phagosomes. Western blot analysis of the cytoplasm of macrophages infected with M. tuberculosis expressing green fluorescent protein confirmed these results. Western blot analysis also detected the presence of native Eis both in the culture supernatant of infected macrophages and vesicles released from the macrophages. IF also detected the presence of Eis in uninfected macrophages. The Eis protein in the cytoplasm of M. tuberculosis infected macrophages was also found to colocalize with EEA1, an endosomal marker, indicating a possible association of the protein with early endosomes. Eis was also shown to elicit higher levels of IL-10 secretion than PPD in human monocytes. Infection of monocytes from healthy tuberculin reactors with M. tuberculosis wild type and eis mutant demonstrated that eis plays a role in modulation of IL-10/TNF- secretion in response to infection. Bioinformatic analysis of the amino acid sequence of Eis indicates that Eis is an acetyltransferase of the GCN5 related family of N-acetyltransferases. Further work is required to determine the role Eis plays in the survival of M. tuberculosis within the macrophage.

The effects of gravity modulation on the instability of double-diffusive convections in a horizontal tank with aspect ratio (width/height) of 11 have been investigated by experiments and numerical simulations. The stably stratified fluid layer is set up with ethanol-water solution of 0.0 and 2.0% (by weight). The tank is fixed on a platform that can oscillate in the vertical direction. A constant temperature difference is maintained across the tank at thermal Rayleigh number . The fluid layer becomes unstable as the initially stable solute gradient slowly decreases due to the non-diffusive boundary conditions. The experiments determine that the instability onset under steady gravity is at with onset vortices of wavelength and oscillatory frequency . When the tank is oscillated at modulation frequency and amplitude , the fluid layer is destabilized slightly with a critical and onset vortices of and . A two-dimensional numerical simulation has accurately reproduced the experimental results of steady gravity, and demonstrated that the slight destability effect of gravity modulation is contributed by the asymmetry of the actual gravity modulation.Further simulations have yielded following results: (1) Under steady gravity, the kinetic energy and mechanical work components oscillate synchronously with . Under modulated gravity, they only oscillate synchronously with when is low, whereas not only synchronously with locally but also synchronously with globally when is high; (2) The resonance phenomenon predicted by Chen (2001) also exists under the present lab conditions. Such instability is in the sub-harmonic mode and the destability effect increases as increases. (3) The double-diffusive fluid layer may experience density-mode instability before the double-diffusive instability onset at certain and . Such density-mode instability is generally in the sub-harmonic mode, although it may be in the synchronous mode when is low and is large. This instability accelerates the mixing of the density gradient across the fluid layer and thus affects the succeeding double-diffusive instability; (4) When the background gravity is absent, the purely modulated gravity destabilizes the fluid layer when is low. On the contrary, it stabilizes the fluid layer when is high and the instability onset is in the synchronous mode.

Lifespan theories of emotion suggest that the ability to regulate emotion improves with age. The supporting evidence, however, is indirect: older adults pay less attention to negative events, remember less negative information, and report fewer experiences of negative emotion. Few studies directly measure emotion regulation by explicitly instructing older adults to modulate their feelings while exposed to emotion-evoking stimuli. The purpose of this thesis was to directly compare younger and older adults in their ability to modulate feelings to investigate whether aging results in decline, stability, or improvement in emotion regulation and also to examine potential mechanisms underlying regulation skills. The study employed a startle modulation paradigm to measure both emotional reactivity and regulation. Two experimental tasks (Stroop colour-word interference, reversal learning) were also administered to explore the relationship between emotion regulation and two theoretically-relevant processes: (a) cognitive control and (b) modification of learned emotional associations. There were three main findings: (1) emotional reactivity was preserved in older adults. Both age groups showed emotion-modulated startle (negative > neutral) during the pre-regulation viewing period; (2) age-related decline in emotion regulation was evident on an objective measure of emotion regulation (startle eyeblink reflex) but not on a subjective measure (self-ratings). Specifically, for older adults, startle eyeblink was not enhanced or attenuated following increase and decrease instructions, respectively. In contrast, both groups showed similar modulation of valence and arousal ratings by regulation instruction (increase > look > decrease); (3) for older adults, reversal learning performance correlated positively with the degree of reappraisal-related startle attenuation in the decrease condition, suggesting a possible mechanism for impaired down-regulation. These findings suggest that even when emotional reactivity is similar, older adults are less effective at modulating their physiological responses.

Adaptive modulation has been actively researched as a means to increase spectral efficiency of wireless communications systems. In general, analytic closed form models have been derived for the performance of the communications system as a function of the control parameters. However, in systems where general error correction coding is employed, it may be difficult to derive closed form performance functions of the communications systems. In addition, in closed form optimization, real time adaptation is not possible. Systems designed with deterministic state optimization are developed offline for a certain set of parameters and hardwired into mobile devices. In this thesis we present stochastic learning algorithms for adaptive modulation design. The algorithms presented allow for adaptive modulation system design in-dependent of error correction coding and modulation constellation requirements. In real time, the performance of the system is measured and stochastic approximation techniques are used to learn the optimal transmission parameters of the system. The technique is applied to Software Defined Radio (SDR) platforms, an emerging wireless technology which is currently being researched as a means of designing intelligent communications devices. The fundamental property that sets SDR apart from traditional radios is that the communications parameters are controlled in software, allowing for real-time control of physical layer communications. Our treatment begins by modeling the time evolution of the adaptive modulation process as a general state space Markov chain. We show the existence and uniqueness of the invariant measure and model performance functions as expectations with respect to the invariant measure. We consider constrained and unconstrained throughput optimization. We show that the cost functions considered are convex. Next we present stochastic approximation algorithms that are used to estimate the gradient of the cost function given only noisy estimates. We conclude by presenting simulation results obtained by the presented method. The learning based method is able to achieve the maximum throughput as dictated by exhaustive Monte Carlo simulation of the communications system, which provide an upper bound on performance. In addition, the learning algorithm is able to optimize communications under various error correction schemes. The tracking abilities of the algorithm are also demonstrated. We see that the proposed method is able to track optimal throughput settings as constraints are changed in time.

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Space-time coded systems developed in the last ten years have been designed primarily using linear modulation. Non-linear continuous phase modulation has desirable constant envelope properties and considerable potential in space-time coded systems. The work in this thesis is focussed on developing and analysing an integrated space-time coded continuous phase modulated (STC-CPM) system. The coding of the space-time encoder and the modulation is incorporated into a single trellis encoder. This allows state combining, which leads to complexity reduction due to the reduced number of states. Design criteria for STC-CPM are summarized and the Euclidean distance is shown to be important for code design. The integrated STC-CPM system design enables systematic spacetime code searches that find optimal space-time codes, to be easily implemented. Optimal rate-1/2 and rate-2/3 space-time codes are found by maximizing the system's minimum squared Euclidean distance. These codes can provide high throughput and good coding gains over un-optimized full rank codes, such as delay diversity, in a quasi-static flat fading environment. Performance bounds are developed using a union bound argument and the pairwise error probability. Approximations of the bounds are evaluated. These truncated upper bounds predict the slopes of the simulated performance curves at low error rates.

Recent research results have shown that the MIMO wireless communication architecture is a promising approach to achieve high bandwidth efficiencies. MIMO wireless channels can be simply defined as a link for which both the transmitting and receiving ends are equipped with multiple antenna elements. Adaptive modulation and power allocation could be used to further improve the performance of MIMO systems. This thesis focuses on developing a fast and high performance power allocation algorithm. Three power allocation algorithms are proposed in this thesis and their performances are compared in various system sizes and transceiver architectures. Among the three algorithms proposed in this thesis, the fast algorithm may be considered as the best power allocation algorithm since the performance of the fast algorithm is almost as good as the fullsearch (optimal)algorithm and the mean processing time is considerably less than the fullsearch algorithm. The fast algorithm achieves about 97.6% agreement with the optimal throughput on average. In addition, the time taken to find the power scaling factors using the fullsearch algorithm is about 2300 times longer than the processing time of the fast algorithm in a 6 x 6 system when the SNR is 20dB. As an extension to the power allocation process, excess power allocation methods are introduced. Excess power is the unused power during the power allocation process. The power allocation algorithm allocates power to each received SNR to maximize the throughput of the system whereas the excesspower allocation distributes the excess power to each SNR to improve both the instantaneous and temporal behavior of the system. Five different excess power allocation methods are proposed in this thesis. These methods were simulated in the Rayleigh fading channel with different Doppler frequencies, fD = 10Hz,50Hz and 100Hz, where the ACF of the channel coefficients are given by the Jakes' model. The equal BER improvement method showed a slightly better performance than the other methods. The equal BER improvement method enables the system to maintain the power scaling factors without sacrificing QoS for 19.6 ms on average when the maximum Doppler shift is 10Hz.

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A two-dimensional (2-D) time-dependent cosmic ray modulation model is used to calculate the modulation of cosmic-ray protons and electrons for 11-and 22-year modulation cycles using a compound approach to describe solar cycle related changes in the transport parameters. The compound approach was developed by Ferreira and Potgieter (2004) and incorporates the concept of propagation diffusion barriers, global changes in the magnetic field, time-dependent gradient, curvature and current-sheet drifts, and other basic modulation mechanisms. By comparing model results with 2.5 GV Ulysses observations, for both protons and electrons, it is shown that the compound approach results in computed intensities on a global scale compatible to observations. The model also computes the expected latitudinal dependence, as measured by the Ulysses spacecraft, for both protons and electrons. This is especially highlighted when computed intensities are compared to observations for the different fast latitude scan (FLS) periods. For cosmic ray protons a significant latitude dependence was observed for the first FLS period which corresponded to solar minimum conditions. For the second, which corresponded to solar maximum, no latitude dependence was observed as was the case for the third FLS period, which again corresponded to moderate to minimum solar activity. For the electrons the opposite occurred with only an observable latitude dependence in intensities for the third FLS period. It is shown that the model results in compatible intensities when compared to observations for these periods. Due to the success of the compound approach, it is also possible to compute charge-sign dependent modulation for 2.5 GV protons and electrons. The electron to proton ratio is presented at Earth and along the Ulysses trajectory. Lastly, it is also shown how the modulation amplitude between solar minimum and maximum depends on rigidity. This is investigated by computing cosmic ray intensities for both protons and electrons, not only at 2:5 GV, but also up to 7:5 GV. A refinement for the compound approach at higher rigidities is proposed. / Thesis (M.Sc. (Space Physics))--North-West University, Potchefstroom Campus, 2011.