Includes bibliographical references (p. 74-79).

Thesis--University of FLorida. / Description based on print version record. Typescript. Bibliography: leaves 140-142.

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<p> The semiconductor distributed feedback (DFB) laser is mainly characterised by the single-longitudinal-mode operation with a narrow spectral linewidth, which leads to its wide application in fiber-optic communication systems. Several numerical models ranging from physics-based to phenomenological ones have been developed with different level of complexities and for different applications. However, with the continuous improvement in designs of DFB lasers, more efficient simulation methods with sufficient accuracy are highly desirable. In this thesis, I mainly focus on developing new one-dimensional (ID) simulation methods of DFB lasers with improved computational efficiency and physical insight without compromise on accuracy. Further, a new design idea for DFB lasers are explored and investigated by using the simulation techniques developed.</p> <p> Starting with the well-known ID time-dependent coupled-wave equations, we have examined two different solution schemes, i.e. the traveling wave model (TWM) and the standing wave model (SWM). The TWM has the merits of straightforward implementation, and being able to simulate a large variety of the structure even if the laser cavity has a small quality factor (Q-factor). Firstly, the existing time-domain solution schemes are reviewed and compared under a unified framework. A high-order split-step traveling wave method is then developed. Its validity and efficiency are examined through the comparison made with the conventional split-step scheme.</p> <p> For laser structures with large variations of the carrier/photon density, however, the TWM is not computationally economical. The SWM on the other hand has its advantages in dealing with the laser cavity with a relatively large Q-factor. Two different standing wave models are proposed to simulate the index-coupled and gain-coupled DFB lasers, respectively. The complexities of these two numerical models are further reduced through an approximation made on the time-dependent carrier distribution. Finally, the proposed SWMs are reduced to a similar form to the rate equation formulations for establishing the linkage between the 1D model and the rate equation model. More physical insights into the conventional and powerful rate equations will be gained through this linkage.</p> <p> The final part of the thesis focus on the analysis of a novel design of single-mode operation DFB laser employing the dispersive grating. The design idea is verified by the proposed SWM.</p> / Thesis / Doctor of Philosophy (PhD)

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Ultrasonic anemometer (UA) is a core application in natural environment measurement. As well known, mechanical anemometer works well in good weather but it is not suitable to be applied in bad environment such as polar region and upper air. On the other hand, ultrasonic anemometer works well in most situations. Moreover, ultrasonic anemometer has wider detectable wind speed range. It can be said that ultrasonic anemometer is a more advanced instrument to measure wind velocity. In this paper, the theory of ultrasonic anemometer is first discussed. Using the theory, a test bed is then designed and constructed to measure one-dimensional wind speed. Active Butterworth filter is introduced into the circuit in order to increase the stability and accuracy. Furthermore, we test the one-dimensional ultrasonic anemometer and compare the measured wind speed with theoretical wind speed measured by a thermal anemometer device. Error is also discussed and improvement has also made during the experiment.

A systematic investigation into the growth of one-dimensional nanostructures of select II-VI compounds with the wurtzite crystal structure. Two process parameters are systematically altered to observe how each affects deposition. The results of which give a further understanding into the formation of one nanostructure over another, as well as experimental parameters for optimizing the growth of particular CdSe nanomaterials. A statistical analysis is conducted on the experimental data to quantitatively determine the variability and robustness of the experimental setup and process. The information complied from this extensive study will yield a more complete understanding of the experimental setup and how improvements can be made to reduce variability, increase yield, and gain insight into the mechanisms controlling this class of materials.

Section Steel usually is a order-oriented production and not easy to resell. The material cost is large percentages of overall production cost. Hence, the key to boost efficient management is to increase the material output rate. In other words, we need to publish a efficient and reasonable cutting plan before production. And the cutting plan can cope with change to meet the market demand. The cutting plan designing is a one-dimensional cutting stock problem, and also is a typical bin packing problem. In this study we examine a combined heuristic approach for this problem. The proposed approach combines two themes of solving method¡Ga neighborhood search algorithm with threshold accepting techniques, and a Branch and Bound method. The performance of the combined heuristic approach was verified by running several benchmarking problems and the results were reported. Experimental results indicate that the proposed solving process can effectively search the feasible region and avoid being trapped in local optimal.

Numerical modeling techniques commonly used to compute the response of soil and rock media under earthquake shaking are evaluated by analyzing the observations provided by instrumented borehole arrays. The NIED Kik-Net database in Japan is selected as the main source of borehole array data for this study. The stiffness of the site and the availability of high intensity motions are the primary factors considered towards the selection of appropriate Kik-Net borehole arrays for investigation. Overall, 13 instrumented vertical arrays are investigated using over 750 recorded ground motions characterized by low (less than 0.05 g) to high (greater than 0.3 g) recorded peak ground accelerations at the downhole sensor. Based on data from the selected borehole arrays, site response predictions using 1-D linear elastic (LE) analysis, equivalent linear (EQL) analysis, equivalent linear analysis with frequency-dependent soil properties (EQL-FD), and fully nonlinear analysis (NL) are compared with the borehole observations. Initially, the low intensity motions are used to evaluate common assumptions regarding 1-D site response analysis. First, we identify the borehole wavefield best simulating the actual boundary condition at depth by comparing the theoretical linear-elastic (LE) and observed responses. Then, we identify the best-fit small-strain damping profiles that can incorporate the additional in-situ attenuation mechanisms. Finally, we assess the validity of the one-dimensional modeling assumption. Our analyses indicate that the appropriate boundary condition for analysis of a borehole array depends on the depth of the borehole sensor and that, for most of the considered vertical arrays, the one-dimensional assumption reasonably simulates the actual wave propagation pattern. In the second part of this study, we evaluate the accuracy of the EQL, EQL-FD and NL site response methods by quantifying the misfit (i.e., residual) between the simulations and observations at different levels of shaking. The evaluation of the performance of the theoretical models is made both on a site-by-site basis and in an aggregated manner. Thereafter, the variability in the predicted response from the three site response methods is assessed. Comparisons with the observed responses indicate that the misfit of simulations can be significant at short periods and large strains. Moreover, all models seem to be characterized by the same level of variability irrespectively of the level of shaking. Finally, several procedures that can be used to improve the accuracy of the one-dimensional EQL, EQL-FD and NL site response analyses, are investigated. First, an attempt to take into account the shear strength of the soil materials at large shear strains is made. Additionally, several modifications to the EQL-FD approach are proposed. The proposed modifications are evaluated against recordings from the borehole arrays. Our analyses indicate that the accuracy of the theoretical models can be, partly, increased by incorporating the proposed modifications. / text