by Kwong-hon Lee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [112-115]). / Chapter CHAPTER 1. --- INTRODUCTION / Chapter CHAPTER 2. --- PRINCIPLE OF ELLIPSOMETER / Chapter CHAPTER 3. --- MATHEMATICAL REPRESENTATION OF ELLIPSOMETRY / Chapter Section 3.1 --- Ambient Substrate / Chapter Section 3.2 --- Single Layer (Ambient-film substrate) / Chapter Section 3.3 --- Multilayer system (Isotropic Stratified planar structure) / Chapter CHAPTER 4. --- CLASSIFICATION OF ELLIPSOMETER / Chapter Section 4.1 --- Null-type Ellipsometer / Chapter Section 4.2 --- Photometric Ellipsometer / Chapter Section 4.3 --- Spectroscopic Ellipsometer / Chapter CHAPTER 5. --- CONSTRUCTION AND CALIBRATION OF THE SPECTROSCOPIC ELLIPSOMETER / Chapter Section 5.1 --- Design and construction / Chapter 5.1.1 --- Optical Assembly / Chapter 5.1.2 --- Electronic Circuit / Chapter 5.1.3 --- Micro-computer (Software) / Chapter 5.1.4 --- Modification of configuration / Chapter Section 5.2 --- Alignment and Calibration / Chapter 5.2.1 --- Alignment of Optical units / Chapter 5.2.2 --- Calibration of the system / Chapter 5.2.3 --- Measurements on standard samples / Chapter CHAPTER 6. --- ANALYSIS OF ELLIPSOMETRIC PARAMETERS / Chapter Section 6.1 --- Ambient-substrate model / Chapter Section 6.2 --- Ambient-layers model / Chapter 6.2.1 --- Parameter generator / Chapter 6.2.2 --- Least square fitting / Chapter 6.2.3 --- Choice of error function / Chapter CHAPTER 7. --- EXPERIMENTAL RESULT / Chapter Section 7.1 --- Spectra of Refractive index / Chapter 7.1.1 --- Low temperature MBE growth GaAs / Chapter 7.1.2 --- Amorphous Carbon / Chapter 7.1.3 --- High order x AlxGa1-xAs with different cooling rate / Chapter Section 7.2 --- Comparison of ellipsometric spectrum of SOI samples / Chapter 7.2.1 --- Difficulty in the analysis of multi-layer structure / Chapter 7.2.2 --- Silicon on insulator (SOI) / Chapter 7.2.2.1 --- The beam current effects / Chapter 7.2.2.2 --- Annealing after implantation / Chapter CHAPTER 8. --- CONCLUSION / Chapter Section8.1 --- Summary of the results / Chapter Section8.2 --- Suggestions for future work / REFERENCE / APPENDIX(A)MARQUART ALGORITHM / Chapter (B) --- CIRCUIT DIAGRAM

We investigate the behaviour of the intensity noise in a multi-longitudinal mode Nd:YAG laser. This type of laser is a nonlinear system which exhibits complicated dynamics within the intensity noise. For example, antiphase dynamics is where there is cancellation of one or more collective modes of oscillation, which are distinct from the longitudinal modes, in the total output. Commonly lasers are studied experimentally to discriminate between models used to describe them. They are convenient since many external influences can be controlled and the oscillations of interest are low frequency (in the kHz regime) making their direct measurement relatively simple. In our laser, the collective modes of oscillation are excited by broadband ambient noise. Because the phase of the excitation is unknown, we develop the cross spectral technique to measure the antiphase dynamics directly and form a picture of the intensity noise interference for two to five mode operation. For three mode operation, we measure the contributions of the longitudinal modes to the collective modes. We also calculate power spectral densities of the individual longitudinal modes and the total intensity. We test relationships between these quantities, at the collective mode frequencies, which are derived from modal rate equation theory. For two mode operation, the theoretical relations are satisfied. For three mode operation, the relations are satisfied when the picture of interferences is taken into account. The cross spectral technique is therefore shown to be a sensitive test of the model developed by Pieroux and Mandel [T. Hill et al., Phys. Rev. A 66, 063803 (2002)]. The behaviour of the multimode laser operating near the threshold of a longitudinal mode is measured. Transitions in the cross spectrum are noted in some pairs of longitudinal modes, for an arbitrary but small pump rate above threshold of a longitudinal mode. It has been shown that longitudinal modes with a high threshold pump power may become more intense than those with a lower threshold [K. Otsuka et al., Opt. Lett. 23, 201 (1998), L. Stamatescu and M.W. Hamilton, (unpublished) (1999), N.B. Abraham et al., Phys. Rev. A 62, 013810 (2000), P.A. Khandokhin, E.A. Ovchinnikov and E.Yu. Shirokov, Phys. Rev. A 61, 053807 (2000)]. The AC noise component of the first two longitudinal modes to reach threshold, is found to exhibit similar properties to their intensity. The implications of the results of this thesis, on models used to describe the behaviour of solid state lasers, are also discussed. / Thesis (Ph.D.)--Physics, 2003.

With the increasing system clock, a clock circuit will cause an amount of electromagnetic interference. To reduce EMI of the products, various EMI strategies have been developed. In the thesis, we study the suppression of electromagnetic interference of a clock circuit by using the spread spectrum technique. The basic idea of the spread spectrum is to slightly modulate the frequency of the clock signal and the energy of the signal will be dispersed to a controllable range to reduce the peak energy of each harmonic wave in the spectrum, and the products can pass the electromagnetic compatibility test more easily. We obtain the attenuation factor of spread spectrum from the theoretical derivation, including modulation index and modulation profiles. From the numerical simulation, we verify that spread spectrum technique can suppress the peak energy. We propose the attenuation formulas which can control the attenuation of every frequency point. To verify our findings, we use a spread spectrum clock generator from market to perform measurement. The trapezoidal waveform can be used to represent a clock circuit. Its waveform includes rise time and duty cycle. We will discuss the influence of rise time and duty cycle on the spread spectrum technique. Shorter rise time will cause high order harmonics in the high speed clock circuit. We verify that spread spectrum technique can suppress high order harmonics from both the simulation and experiment. Because every harmonic can be suppressed, the spread spectrum technique has the good suppression effect for the whole system.

In investigating ocean surface waves at a location, it is often to describe the waves with spectrum. A wave spectrum measures the distribution of wave energy from the wave trains in all different directions and all different periods at a location. Since the waves at a location contain seas and swells (which are the waves generated by local and remote wind systems respectively), a wave spectrum is viewed composing of different portions of the seas and swell spectrum. How to precisely partition a wave spectrum for each wave system (seas and swells) is of practical need in engineering practice, wave forecast, and coastal water management. At present, there are many different partitioning schemes, but not all are reliable and feasible enough for operational use. This report presents a wave system partition scheme followed by an identification scheme, which uses TMA spectrum, to identify different wave systems. This partition and identification scheme is intended for operationally use in partitioning the swell and wind sea in spectrum at finite water depth. Automated spectral partition and identification have been developed to evaluate swell systems in data during typhoon Meari.

Structural evolution and its effect on optical absorption/emission behavior of fluorene-thiophene conjugated alternate copolymers and naphthalene-thiophene conjugated alternate copolymers and polystyrene-poly-3octylthiophene-polystyrene triblock copolymer of upon isothermal heat treatment at elevated temperatures, and the well £k-£k stack at interchain species (ordered aggregates) be formed in dilute solutions and its effect the UV-vis and PL spectra. These conjugated polymer with mono- or disubstituted with alkyl side chain and with alkyl or alkoxyl flexible side-chains. This studied by means of a combination of polarized light microscopy, x-ray diffraction, ultraviolet-visible spectroscopy, light scattering spectroscopy and photoluminescence spectroscopy. According to the results of the experiment, the fluorene-based polymer can be observed emission from order aggregate in the solution state, but not found in naphthalene-based and triblock copolymer.

Cognitive radio refers to the technology that the devices can intelligently access unused frequency resources which are originally reserved for legacy services in order to increase the spectrum utilization. At the mean time, the legacy services should not be affected by the access of cognitive radio devices. The common problems in cognitive radio are how to find unused frequency resources (spectrum sensing) and how to access them (spectrum accessing). This dissertation focuses on the robust methods of spectrum sensing as well as spectrum accessing strategies with the statistics of channel availabilities. The first part of the thesis studies non-parametric robust hypothesis testing problem to eliminate the effect of the uncertainty and instability introduced by non-stationary noise, which is constantly observed in communication systems. An empirical likelihood ratio test with density function constraints is proposed. This test outperforms many popular goodness-of-fit tests, including the robust Kolmogorov-Smirnov test and the Cramér-von Mises test, etc. Examples using spectrum sensing data with real-world noise samples are provided to show their performance. The second part focuses on channel idle time distribution based spectrum accessing strategies. Through the study of the real-world wireless local area network traffic, it is identified that the channel idle time distribution can be modeled using hyper-exponential distribution. With this model, the performance of a single cognitive radio, or the secondary user, is studied when the licensed user, or the primary user, does not react to interference. It is also shown that with the complete information of the hyper-exponential distribution, the secondary user can achieve a desirable performance. But when the model exhibits uncertainty and time non-stationarity, which would happen for any kind of wireless traffic, the secondary user suffers from huge performance loss. A strategy that is robust to the uncertainty is proposed. The performance of this strategy is demonstrated using experimental data. Another aspect of the problem is when the PU is reactive. In this case, a spectrum accessing strategy is devised to avoid large-duration interference to the PU. Additionally, the spectrum accessing strategies are also extended to the cognitive radio networks with multiple secondary users. A decentralized MAC protocol is devised which reaches a total secondary capacity performance close to the optimal. A discussion of the engineering aspects with practical consideration of spectrum sensing and accessing is given at the end. / text

Dynamic spectrum access based on cognitive radio has been regarded as a prospective solution to improve spectrum utilization for wireless communications. By considering the allocation efficiency, fairness, and economic incentives, spectrum marketing has been attracting more and more attentions in recent years. In this thesis, we focus on one of the most effective spectrum marketing methods, i.e., auction approach, in multi-channel cognitive radio networks. After presenting some fundamentals and related works, we begin our discussion in a recall-based auction system where buyers have various service requirements and the seller could recall some sold items after the auction to deal with a sudden increase of its own demand. Both single-winner and multi-winner auctions are designed and analyzed. In addition, we also consider the heterogeneity of radio resource sellers and formulate a framework of combinatorial spectrum auction. With theoretical analyses and simulation results, we show that our proposed algorithms can improve spectrum utilization while satisfy the heterogeneous requirements of different wireless users.

Diss. med. - Karolinska institutet, Stockholm. / At head of title: From Department for Cell Research, Karolinska Institutet, Stockholm. Summary in English. "References": p. 103-106.

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In September 2016, work was initiated on the subprojects which comprise the Conformal C-Band/Multiband Antenna project: SARD #1: Broadband Conformal C-Band Missile Wraparound Antennas; SARD #2: Beam Switching Array Antennas; SARD #3: Multiband Conformal Antennas for Aircraft Applications; SARD #4: High Altitude Coronal Efforts on Antenna Performance; and SARD #5: Small, Medium Gain Multiband Receive Antennas. A brief status of each of them will be discussed and detail the technology areas being developed by each.