The thesis focuses on the broadband characteristic of asymmetric multiple quantum dots . The main sources of the samples are grown from our laboratory. We used molecular beam epitaxy to grow a series samples with different thickness and structures. We also add p type modulation doping in the active layer in asymmetric multiple quantum dots p-i-n laser structures. In our experiment, we use the electroluminescence measurement system to measure the optical signals by adding a forward bias. Then we discuss the spectrum shape, emission intensity, and peak distribution. We also analysis the jump migration between these similar samples. Besides, we use the photo current spectrum, differential absorption coefficient spectrum, and differential refractive coefficient spectrum to analysis the signals. We use sample C240 as our main structure. It organized by three different quantum dots ingredients: In0.64Ga0.36As, In0.75Ga0.25As, and InAs. We find that we get the intensity in C240 is very weak, and the FWMH is 108nm. When we add the quantum dots layer double, we find that the FWHM become 134nm. And then, when we grow 2nm InGaAs quantum well behind the quantum dots structures, the FWMH increases to 156nm. Finally, when we add p type modulation into quantum well, we find the intensity has increased a lot, and the emission wavelength is from 1.18£gm to 1.36£gm. It is about 196nm. By the conclusion, we can find that the emission intensity and FWMH is relative to the different quantum dots layers and doping, we also find that by increasing one quantum layer, we can get the higher FWMH. Finally, we expect that we can use our broadband characteristic of the AMQDs samples to produce broadly tunable laser and broad-band semiconductor optical amplifier in the future.

Metamorphic multiple quantum dots (QDs) on GaAs substrates were grown by molecular beam epitaxy (MBE). The metamorphic layers including In0.15Ga0.85As and AlAs were in-situ annealed at high temperature (T=800oC) to reduce the dislocations. InGaAs QDs were then grown on the metamorphic layers. We use the laser source and pulse voltage to modulate the dielectric constant of the samples in modulation reflectance measurement system. The inner electric field is obtained from the photo-reflectance Franz-Keldysh oscillation (FKO), and the energy transition is analyzed though the photoluminescence (PL), electroluminescence (EL), and photocurrent (PC) spectroscopy. The electroluminescence wavelength of InAs QDs on metamorphic In0.15Ga0.85As substrate can be push to ~1460 nm. The optimum emission quality is obtained by inserting 3-nm GaAs layer beneath the In0.15Ga0.85As buffer layer. The In0.15Ga0.85As buffer is flatter because of the GaAs layer, and the QDs become more uniform. We expect the InAs QDs on metamorphic GaAs substrate can be applied for optical communication in the £f=1550 nm region.

The reliability and stability of the Matrix Converter has improved during the last years due to the enhanced control algorithms. The traditional direct transfer function control mode has been replaced by more complex – digitally implemented control methodologies. These methodologies allow for real time calculation of the optimal switching interval of each individual switch of the matrix converter. These new switching algorithms allow optimal performances, ensuring sinusoidal outputs at any desired power factor. This paper will first revise the underlying theory of matrix converters, then review the various control limitations and finally review the current control algorithms.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Reflex control during walking has been shown to be specific to the behavioural context of a postural threat. Reflex modulation has been shown to be influenced by perturbations to the trunk, as well as by changes to arm activity that further affected the level of postural threat. The magnitudes of EMG responses in limbs and trunk to mechanical trip perturbations were differentially modulated depending on whether or not an earth- referenced railing was held. To further understand the neural control of limb and trunk muscles during walking contexts where changes to postural stability are solely linked to arm activity, we created 3 treadmill walking tasks each with the arms engaged differently to induce three levels of postural stability. Neurologically-intact participants walked on a treadmill using normal arm swing (NORMAL), holding a wheeled walker (WALKER), or holding the handrails (HANDRAIL). Subjects ranked the tasks according to degree of perceived challenge to stability; WALKER was ranked most challenging, followed by NORMAL and then HANDRAIL. Cutaneous reflexes were evoked via constant current stimulation (5 x 1.0 ms pulses at 300 Hz) of Superficial Peroneal (SP) nerve at the foot and Superficial Radial (SR) nerve at the wrist in separate trials during each walking task. EMG was recorded ipsilateral to nerve stimulation from arm and leg muscles and bilaterally from trunk muscles. Off-line analysis was conducted on eight phases of the step cycle after phase-averaging, contingent upon the timing of stimulation in the step cycle. The number of differences in bEMG and reflexes between tasks was graded with the proximity to the source of instability at the arms, progressively increasing from the legs to the arms. The gradient in bEMG differences suggests that the mechanical constraints of each task required different levels of muscle activation that was greatest for the arms, less for the trunk and least for the legs. The similar gradient seen for reflexes suggests functionally relevant changes in neural control of arm and trunk muscles in order to maintain postural stability during in each task. However, overall there were significantly fewer differences in reflexes between tasks compared to bEMG. We suggest that the mechanical constraints of the tasks yielded more significant changes in the muscle activation while requiring far fewer task-specific changes in reflex control suggesting a conservation of some elements of the neural control mechanisms across tasks. / Graduate