<p>Many numerical approaches exist to solving models of electrical activity in the heart. These models consist of a system of stiff nonlinear ordinary differential equations for the voltage and other variables governing channels, with the voltage coupled to a diffusion term. In this work, we propose a new algorithm that uses two common discretization methods, operator splitting and finite elements. Additionally, we incorporate a temporal integration process known as spectral deferred correction. Using these approaches,</p><p>we construct a numerical method that can achieve arbitrarily high order in both space and time in order to resolve important features of the models, while gaining accuracy and efficiency over lower order schemes.</p><p>Our algorithm employs an operator splitting technique, dividing the reaction-diffusion systems from the models into their constituent parts. </p><p>We integrate both the reaction and diffusion pieces via an implicit Euler method. We reduce the temporal and splitting errors by using a spectral deferred correction method, raising the temporal order and accuracy of the scheme with each correction iteration.</p><p> </p><p>Our algorithm also uses continuous piecewise polynomials of high order on rectangular elements as our finite element approximation. This approximation improves the spatial discretization error over the piecewise linear polynomials typically used, especially when the spatial mesh is refined. </p><p>As part of these thesis work, we also present numerical simulations using our algorithm of one of the cardiac models mentioned, the Two-Current Model. We demonstrate the efficiency, accuracy and convergence rates of our numerical scheme by using mesh refinement studies and comparison of accuracy versus computational time. We conclude with a discussion of how our algorithm can be applied to more realistic models of cardiac electrical activity.</p> / Dissertation

The traditional AC/DC rectifier usually has the defects of low power factor and serious harmonic distortion and it results in serious pollution to the power system. This thesis proposes active power factor correction technique using a new AC/DC Dual Boost Converter. For power factor correction, inductor current is operated in the continuous conduction mode. First, the converter is analyzed by state space averaging method. Furthermore, we design applicable compensator by frequency analysis to implement a good power factor system. A classical PFC circuit with PI control law has low power factor under light load. In order to overcome problem, the thesis proposes a Dual Boost Converter circuit with robust performance. Comparing with circuits using PFC IC ¡§UC3854¡¨, the proposed system obtains higher power factor under the condition of the same light load.

In recent years, there are more and more researches on semi-fragile watermarking scheme which can resist JPEG compression. But, there are few researches focused on the recovery of semi-fragile watermarked image. Therefore, in this paper, we not only present a semi-fragile watermarking scheme which can resist JPEG compression but use the error correction code (Reed-Solomon Code) to recover the area being malicious manipulated. At first, we use the semi-fragile watermarking scheme proposed by Lin and Hsieh to detect the counterfeit under the JPEG compression [9]. Its main effect is to resist JPEG compression and to detect the attacked parts without the need of the original image. And then, we will introduce how we use RS code to recover the attacked parts being detected by the semi-fragile watermarking scheme. We use the scheme ¡§Interleaving¡¨ to spread the local pixels to the global area. Next, we encode to each little image block by RS code. The redundant symbols generated by RS code will be signed to be signature attached with the watermarked image. Finally, the receiver can use semi-fragile watermarking scheme to detect attacked part and use the information of the signature to decode these attacked parts. Additionally, we also discuss how to decrease the load of the signature, thus, it can not significant loading of the watermarked image.

This thesis mainly focuses on active power factor correction (PFC) circuit research. Based on DSP, a circuit with a digital controller is developed. Boost converter is used as the power stage. For power factor correction, the control law is realized with DSP and the control strategy of controller adopts the multi-loop method, i.e. voltage-loop and modified PI current-loop. Finally, compared with the circuit using the conventional PI control law, performances of the modified PI current-loop circuit are obviously optimized.

Quantum error correction codes were introduced as a means to protect quantum information from decoherance and operational errors. Based on their approach to error control, error correcting codes can be divided into two different classes: block codes and convolutional codes. There has been significant development towards finding quantum block codes, since they were first discovered in 1995. In contrast, quantum convolutional codes remained mainly uninvestigated. In this thesis, we develop the stabilizer formalism for quantum convolutional codes. We define distance properties of these codes and give a general method for constructing encoding circuits, given a set of generators of the stabilizer of a quantum convolutional stabilizer code, is shown. The resulting encoding circuit enables online encoding of the qubits, i.e., the encoder does not have to wait for the input transmission to end before starting the encoding process. We develop the quantum analogue of the Viterbi algorithm. The quantum Viterbi algorithm (QVA) is a maximum likehood error estimation algorithm, the complexity of which grows linearly with the number of encoded qubits. A variation of the quantum Viterbi algorithm, the Windowed QVA, is also discussed. Using Windowed QVA, we can estimate the most likely error without waiting for the entire received sequence.

This thesis mainly presents a LED driver circuit based on single-stage Flyback converter with power factor correction. Power factor correction technique is applied for constant current driver. Accroding to different magnetize inductance current operating mode, two methods are used to improve the drawbacks of Flyback converter which is operated in open loop. Discontinuous conduction mode is controlled by single loop which is called voltage follower control. Continuous conduction mode is controlled by dual loop, that applied to nonlinear carrier control(NLC). Multiplier is usually used to traditional power factor correction, but it is expensive. To reduce the system cost, a multiplier is removed from NLC. The designed circuit is verified by SPICE software and experiments. From simulation and experimental results, it shows the proposed system achieves the goal with high power factor and constant output current.

In the thesis, a LED driver circuit that is applied in low power LED lighting with constant output current and Power Factor Correction (PFC) is presented. For power stage of LED driver, a non-insulated switching Buck power converter without transformer is used, and develop equivalent mathematical model and block diagram of Buck converter while its inductor current operating in Continuous Conduction Mode(CCM). Furthermore, the closed loop PFC control circuit is designed by time-domain and frequency-domain analysis. In addition, because of the classical PFC control configuration needs the expensive multiplier, a LED driver circuit with PFC without multiplier is presented in this thesis in order to reduce the system cost and space of the circuit. Then, we confirm the designed circuit by simulation and experiment. By the results, the proposed system achieves constant output current control and power factor can reach to 0.92.

In the thesis, an LED driver circuit with Power Factor Correction (PFC) and constant output current is presented. For open-loop LED driver, an insulated switching Flyback power converter is designed, and the Flyback converter will be operated in Continuous Conduction Mode(CCM). One develops equivalent mathematical model for the drivers system. The main part of this thesis is about the design and the study of a closed loop PFC control circuit using inductor voltage sensing technology. In addition, one introduces another traditional inductor current sensing control technique is included to compare with the designed control circuit. Then, one confirms the designed circuits by simulation and the experiment. From the results, the power factor can reach to 0.97, and the expected constant output current control has also been achieved.

This thesis is to design an LED driver circuit with constant output current and Power Factor Correction(PFC) control. Switching power converter is applied for power stage of the LED driver circuit, a non-insulated Buck converter without transformer is used, and the inductor current of Buck converter is operating in Continuous Conduction Mode(CCM). According to the operating principle of Buck converter, the equivalent mathematical model and system block diagram is developed to establish the traditional closed loop PFC control circuit. The controller parameters are set up by time-domain and frequency-domain analysis to achieve the goal with constant output current and PFC control. Furthermore, the thesis presents a more effective PFC control method to reduce the cost of multiplier used in traditional PFC control method and overcome the congenital defect of Buck converter. Both two PFC control methods are confirmed and compared by simulation and experiment. The results show that the proposed control method has more effective performance and achieve constant output current for LED with high power factor by 0.966 under full-load condition.

Texte remanié de: Proefschrift--Erasmus Universiteit Rotterdam, 1995. / Résumé en anglais. Bibliogr. p. 307-316.