Polarization behaviours of copper diffused p-type GaAs was studied in 1. 0M NaCl and 1. 0M NaNO₃ by means of pitting scan and linear sweep potentiodynamic polarization techniques. The thermodynamic potential-pH diagram of the GaAs-H₂O system was constructed. The observed electrode behaviours of GaAs were compared and correlated to the potential-pH diagram. Freely corroding potential, passivation behaviour and pitting potential were examined as a function of a number of factors. These included the effects of different annealing and polishing pretreatments, the bulk solution pH and polarization methods. The corrosion potential (Ecorr) , pitting potential (Epit) and passivation behaviour were affected by the different pretreatments which changed the surface condition of GaAs. For mechanically polished samples, pitting corrosion was found in pH 7.0 solution only. The Ecorr and Eplt were independent of NO₃⁻ and Cl⁻ at pH 7.0. Initial polarization behaviour of p-GaAs at pH 2.0 and 12.0 followed the Tafel Law for semiconductors quite well. There was a reasonable correlation between the experimental observations and the potential-pH diagram of GaAs-H₂O system. SEM images of polarized samples showed that pits formed in NaCl and NaNO₃ had a different shape, being more elongated in NaCl. However, the walls of all pits appeared to be composed of {111} planes. In general, the pit distribution appeared to be similar to the dislocation distribution. A model of pitting corrosion of GaAs was proposed based on strain induced breakdown of the oxide film, localized changes in solution chemistry and the structure of the compound semiconductor. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The Green's function method is applied to investigate the magnetic spin resonance spectra of three-dimensional and two-dimensional spin-polarized quantum gases. The Hartree-Fock approximation is employed to calculate the one-particle Green's function of the atoms, then this one-particle Green's function is used for the calculation of the vertex part of the Green's function. Such a combination yields a self-consistent result. The absorption spectra are obtained from the calculation of the susceptibility in terms of the two-particle Green's function (bubble diagram). Some general expressions for the dispersion relation, for the effective mass of a spin wave, and for the dipolar frequency shift are given in the calculation. In order to estimate the shift of the electron-spin-resonance (ESR) frequency, the effective dipole-dipole interactions among the hydrogen atoms are included in the calculation. These effective interactions are deduced from the ladder approximation, and hence are characterized by the scattering amplitude. The scattering amplitude is calculated numerically. The result shows that the theoretical value of the shift is smaller than the experimentally observed value by about 35%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21573号 / 理博第4480号 / 新制||理||1643(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 前田 啓一, 准教授 上田 佳宏, 教授 嶺重 慎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

[pt] Este trabalho apresenta o estudo e a realização de experimentos a fim de investigar os efeitos da PMD (Polarization Mode Dispersion) no controle de polarização implementado em um enlace de fibra óptica monomodo. Esse estudo permitirá a otimização de controladores de polarização em sistemas de transmissão que venham a utilizar multiplexação em polarização (PolMux) combinado a técnicas de UDWDM (Ultra Dense Wavelength Division Multiplexing), possibilitando o aumento da taxa de transmissão em um canal. Para tanto, foram realizadas medidas experimentais que demonstrem o desvio angular da polarização devido à descorrelação entre canais, através da análise da evolução da polarização do sinal óptico em função da PMD, do comprimento de onda e do espaçamento espectral; foram analisadas duas propostas para se utilizar no controle de polarização; estatísticas referentes à atenuação dos canais utilizados foram realizadas e também o cálculo da correlação com intuito de analisar como esses canais se relacionam. / [en] This work presents the study and conducting experiments to investigate the PMD (Polarization Mode Dispersion) effects in polarization control implemented in a single-mode fiber optic link. This study will allow the optimization of polarization controllers in transmission systems that will use polarization multiplexing (PolMux) combined with techniques like UDWDM (Ultra Dense Wavelength Division Multiplexing), and thereby to increase the transmission rate in a channel. Therefore, we performed experimental measurements showing the angular displacement of the polarization due to decorrelation between channels by analyzing the evolution of the polarization of the optical signal as a function of PMD, wavelength and the spectral spacing, analyzed using two proposals for the control of polarization, statistics of the fading channels used and also performed the calculate the correlation with the aim to analyze how these channels are related.

This paper presents and evaluates a new terahertz metamaterial absorber (MMA) for sensing applications. Because of its unique properties, metamaterial-based sensors are widely employed in a variety of applications. The reported structure comprises of two identical metallic patches, a dielectric spacer and a ground metal plane. The finite element approach has been utilized to simulate and analyse the design. It is found that the MMA offered a prominent resonant peak with near 100% absorbance at frequency 4.5 THz due to the resultant effect of coupling between the two identical patches. In addition, surface current distribution, absorption mechanism and structural parametric analysis has also been investigated. The peak is designated as 'A', with a line width of 0.02 THz and a quality factor (Q-factor) of 225, which is sensitive to the refractive index of the environment (RI). As a result of its highly sensitive sensing capabilities, the proposed design can be employed as a sensor for refractive index, having 1.6 THz per refractive index unit (RIU) sensitivity and figure of merit (FoM) of 80 in terms of change in RI of the environment. The majority of biomedical samples have RI of 1.3 to 1.36, which is worth highlighting. Thus, biomedical applications may be possible with the suggested sensor.

Moral issues such as abortion, immigration, and gun rights are subject to constant debate. Yet such discussions are increasingly unproductive, perhaps because we enter such debates with closed, rather than open mindsets, which might rigidify our views, leading to perceptions of an objectively ‘correct’ answer to moral issues. This study tested whether different modes of interaction led to differences in levels of this ‘objectivist’ thought. The study also tested whether and whether threat, experienced in anticipation of a contentious interaction, mediated this effect. Participants were randomly assigned to conditions in which they received instructions on how they should approach an upcoming interaction on the topic of abortion. Instruction conditions included: competition, cooperation, persuasion, learning, neutral control, and no-opposition control (except for no-opposition control, all conditions specified that the other person disagreed with the participant on abortion). Although hypothesized group differences were not found, hypothesized mediation analyses were significant, such that competition, cooperation, and neutral control conditions produced increased threat for participants, while learning, persuasion, and no opposition control conditions produced reduced threat. Threat level positively predicted moral objectivity level for both abortion (the topic of discussion) and other moral issues. These results provide insight into why debating morally contentious issues can seem futile at best, and provides a glimpse of why this does not have to be the case.

This thesis is concerned with the development of a compact, sensitive and reliable instrument for determination of the polarization of fluorescence of fluorescein tagged molecules in solution. The instrument as designed and constructed differs from others (2,3,4,5,6,8,9). The difference is that all of its optical system is aligned on a single axis. This was accomplished by the use of an ellipsoidal mirror positioned between the excitation source and the phototube fluorescence signal receiver. In addition, the excitation source, a 45 watt tungsten-iodide light was electronically regulated to control the intensity. Two types of determinations were made to verify the performance of the instrument. The first was the absolute sensitivity to varying fluorescein concentrations. Concentrations of fluorescein in 0.1 molar sodium phosphate buffer were prepared ranging from 10-6 molar to 10-11 molar. After the minimum detectable concentration was determined, five runs on samples of each concentration from the minimum detectable to 10-6 were made. The second check was for the sensitivity and linearity of the system in the measurement of polarization. Solutions of glycerol ranging from 62% to 90% were prepared with 10-6 molar fluorescein concentration. The data from the fluorescein sensitivity and polarization runs were averaged and the averages plotted on linear paper. In each case the instrument exhibited excellent linear response and reasonable standard deviation.

The widespread use of electronics in more avenues of consumer use is increasing. Applications range from medical instrumentation that directly can affect someone's life, down hole sensors for oil and gas, aerospace, aeronautics, and automotive electronics. The increased power density and harsh environment makes the reliability of the packaging a vital part of the reliability of the device. The increased importance of analog devices in these applications, their high voltage and high temperature resilience is resulting in challenges that have not been dealt with before. In particular packaging where insulative properties are vital use polymer resins modified by ceramic fillers. The distinct dielectric properties of the resin and the filler result in charge storage and release of the polarization currents in the composite that have had unpredictable consequences on reliability. The objective of this effort is therefore to investigate a technique that can be used to measure the polarization in filled polymer resins and evaluate reliable molding compounds. A valuable approach to measure polarization in polymers where charge release is tied to the glass transition in the polymer is referred to as thermally stimulated depolarization current (TSDC) technique. In this dissertation a new TSDC measurement system was designed and fabricated. The instrument is an assembly of several components that are automated via a LabVIEW program that gives the user flexibility to test different dielectric compounds at high temperatures and high voltage. The temperature control is enabled through the use of dry air convection heating at a very slow rate enabling controlled heating and cooling. Charge trapping and de-trapping processes were investigated in order to obtain information on insulating polymeric composites and how to optimize it. A number of material properties were investigated. First, polarization due to charges on the filer were investigated using composites containing charged and uncharged particles using quartz and ion exchange montmorillonite silicates in an epoxy matrix. The thermally-activated charge release shows a difference in the composite characteristics and preparation. This difference indicates that the trap levels depend on the de-trapping process and on the chemical nature of the trap site. Using a numerical approach to the release spectra, a model was developed to examine through short time testing, important parameters such as glass transition temperature, residual polarization, depolarization peak, window polarization modeling and activation energy of relaxations. Second the design of mold compounds that could combine manufacturing (temperature of molding), geometric (thickness of packaging material), composition (amount and size of filler) effects was developed using a novel design of experiments approach. The statistical DOE enabled the determination of which causes should be considered when designing a mold compound that has minimal polarization both as singular variables as well as combined variables. Finally, the DOE approach was used to develop a high temperature reliable molding compound through use of combined fillers of thermally conductive and nonconductive fillers having different shapes. Through the systematic approach to developing a technique and designing a mold compound addressing the multiple impacts on reliability of packaging, the dissertation provides an approach to the design, selection, performance and durability of molding compounds.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21891号 / エネ博第392号 / 新制||エネ||76(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)准教授 中嶋 隆, 教授 大垣 英明, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Quantum mechanical calculations were used to examine the polarization of excited singlet states of twisted conjugated systems. This study began as an investigation of systems which are symmetric about a central double bond. Symmetry requires that when twisting about such a bold, there must be a crossing of two low-lying states. At the one election level of theory, this leads to a degeneracy between the ground state and first excited state at 90°of twist. Slight perturbations to the twisted system will mix the two degenerate states and lead to a highly polar condition. This was confirmed on the one-electron level with calculations on several symmetrically twisted conjugated systems. Further calculations indicated that there were crossings between two low-lying states for twisting about certain non-central double bonds as well. It was hypothesized from the results of simple calculations, that the pairing theorem of alternant hydrocarbons provides a framework that explains where and why these non-symmetry determined crossings occur. In general, the implications of the pairing theorem are that twisting a neutral even-alternant hydrocarbon about any double bond should lead to a crossing of two low-lying states. Upon further i:tivestigation of the connection between the pairing theorem and twisted excited states, the theorem's predictions were confirmed by MNDO calculations. Furthermore, it was shown that small perturbations applied to these systems when the two states become nearly degenerate led to a dramatic polarization across the twisted double bond. It was found that there are also highly polarizable twisted excited states whose existence is not predicted by the pairing theorem.