The goals of this work were to synthesize high performance perovskite based thin film solid oxide fuel cell (TF-SOFC) cathodes by pulsed laser deposition (PLD), to study the structural, electrical and electrochemical properties of these cathodes and to establish structure-property relations for these cathodes in order to further improve their properties and design new structures. Nanostructured cathode thin films with vertically-aligned nanopores (VANP) were processed using PLD. These VANP structures enhance the oxygen-gas phase diffusivity, thus improve the overall TF-SOFC performance. La0.5Sr0.5CoO3 (LSCO) and La0.4Sr0.6Co0.8Fe0.2O3 (LSCFO) were deposited on various substrates (YSZ, Si and pressed Ce0.9Gd0.1O1.95 (CGO) disks). Microstructures and properties of the nanostructured cathodes were characterized by transmission electron microscope (TEM), high resolution TEM (HRTEM), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) measurements. A thin layer of vertically-aligned nanocomposite (VAN) structure was deposited in between the CGO electrolyte and the thin film LSCO cathode layer for TF-SOFCs. The VAN structure consists of the electrolyte and the cathode materials in the composition of (CGO) 0.5 (LSCO) 0.5. The self-assembled VAN nanostructures contain highly ordered alternating vertical columns formed through a one-step thin film deposition using a PLD technique. These VAN structures significantly increase the interface area between the electrolyte and the cathode as well as the area of active triple phase boundary (TPB), thus improving the overall TF-SOFC performance at low temperatures, as low as 400oC, demonstrated by EIS measurements. In addition, the binary VAN interlayer could act as the transition layer that improves the adhesion and relieves the thermal stress and lattice strain between the cathode and the electrolyte. The microstructural properties and growth mechanisms of CGO thin film prepared by PLD technique were investigated. Thin film CGO electrolytes with different grain sizes and crystal structures were prepared on single crystal YSZ substrates under different deposition conditions. The effect of the deposition conditions such as substrate temperature and laser ablation energy on the microstructural properties of these films are examined using XRD, TEM, SEM, and optical microscope. CGO thin film deposited above 500 ºC starts to show epitaxial growth on YSZ substrates. The present study suggests that substrate temperature significantly influences the microstructure of the films especially film grain size.

No description available.

This study investigates the cholesteric grating based on a hybrid alignment. The experiment results reveal that the ordered stripe of the hybridly aligned cholesteric grating (H-fingerprint) only exists for the d/p ratio between 1.5 and 3, and the stripe orientation of the H-fingerprint is difficult to control due to the variation of the d/p ratio. Optical properties of the H-fingerprint are also investigated. The results show that the 1st order diffraction efficiency of the H-fingerprint is higher than the diffraction efficiency 2nd order, and its two switching times are about 1500ms and 500ms for the off-time and the on-time, respectively. The H-fingerprint with an anti-parallel rubbing process and the thermal effect are also investigated. The results reveal that the anti-parallel rubbing and the thermal effect can effectively control the stripe orientation of the H-fingerprint. The results greatly increase the possibility of applications for the H-fingerprint.

Recently, Iwamoto[1] has proposed a passive-matrix LCD called VA-STN-LCD (Verically Aligned Super Twist Nemetic LCD), in which excellent electro-optic (EO) performance under high-multiplexing conditions has been demonstrated. It was pointed out that such a high EO performance was realized by achieving a pretilt angle of about 80 degree. In this study, we want to learn the different EO characteristic of separate pretilt angle and separate chiral-doped concentration of Negative Dielectric Anisotropy nemetic liquid crystal in vertically aligned cell.

This thesis presents the preparation of vertically aligned carbon nanotubes using porous anodic alumina templates via thermal chemical vapour deposition. The characteristics of prepared carbon nanotubes in terms of tube diameter, length, density, uniformity and alignment were investigated. The formation of porous anodic alumina membranes was studied. In order to prepare well-ordered porous anodic alumina templates, three approaches towards anodization of aluminium were examined. Effects of Al surface morphology and anodization conditions on the formation of the porous anodic alumina membrane were investigated. Co catalyst was electrochemically deposited at the bottom of the pores of porous anodic alumina templates by applying an alternating current. Prior to the AC electrodeposition, the barrier layer at the base of the pores was thinned in order to facilitate the deposition process. The thinning effect of three barrier layer thinning approaches was examined. The effect of electrodeposition duration on the pore filling was investigated. Carbon nanotubes were grown using Co-loaded porous anodic alumina templates via thermal chemical vapour deposition of C₂H₄. Effects of the presence of the Co catalyst, the amount of Co deposited at the bottom of the pores and the presence of water vapour on the carbon nanotube growth were examined. The characteristics of the grown carbon nanotubes in terms of tube diameter, length, density, uniformity and alignment were investigated. Moreover, a post-treatment after the carbon nanotube growth was proposed in order to obtain vertically aligned carbon nanotubes. In addition, vertically aligned carbon nanotubes were grown on Si chips. Two methods were used to prepare a catalytic layer on the Si chips for carbon nanotube growth.

Massively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore, it is essential to selectively remove metallic nanotubes to obtain better transistor properties. It was recently found that although such a selective removal can be effective for a low density array, it does not work in a high density array and lead to a correlated breakdown of the entire array giving rise to a nanofissure pattern. In order to obtain a deeper understanding of such a correlated SWNT breakdown, we studied the breakdown power in the successive electrical breakdown of both low ( < 2 /um) and high density ( > 10 /um) SWNT arrays. We show that the breakdown voltage in successive electrical breakdown increases for low density array while it decreases for high density arrays. The estimated power required for the breakdown remains constant for low density arrays while it decreases for high density arrays in successive electrical breakdowns. We also show that, while a simple model of parallel resistor network can explain the breakdown of low density array, it cannot explain the behavior for the high density array implying that the correlation between the closely spaced parallel nanotubes plays a big role in the successive breakdowns of the high density SWNTs.

不結盟運動與一般的國際組織不同，事實上該運動沒有組織章程、成員國間沒有締結條約、未明白設定目的、角色及成員的權利和義務，嚴格來說，不結盟運動僅是鬆散的、以共識取得結論的非正式國際性組織。此外，該運動也沒有強制遵行共識的條件，個別國家立場有一定差距，不結盟運動可說是一種「聚會」(get togther)而己。但不可否認，透過不結盟運動的協調並取得相當的共識及立場後，身為新興國家不結盟運動的成員在國際上的力量大幅加強，以「集體外交」之力而得以在國際舞台上擁有發言權和影響力。同時該運動也成為第三世界國家最重要的國際論壇。自一九六一年的第一屆不結盟運動高峰會議在南斯拉夫的貝爾格勒舉行以來，至今已召開第十屆高峰會議，在成員國的數目及高峰會議所提出的建議，質量兩方面都有顯著的成長。本文從國際關係的角度來分析不結盟運動三十餘年來的演變，將不結盟運動十屆高峰會議分四個階段來看。第一屆至第三屆高峰會議，為不結盟運動的草創階段。在這一時期（一九六○年代）國際關係正處於東西兩大集團對立的情況。為因應國際情勢，以埃及、印度、南斯拉夫為首的不結盟國家召開第一屆高峰會議，希望對當時危及世界和平安全的情況能發生影響，改善國際緊張情勢。不結盟運動議題便著重支持各地區的獨立解放運動、呼籲國際進行裁軍行動。一九七○年代不結盟高峰會議，展露頭角時期。不結盟國家將改變現存經濟結構的議題提出，一九七三年第四屆的高峰會議首度提出了「新國際經濟秩序」，希望透過發展中國家與開發國家的合作、技術交流、資本流通等各種方式減緩南北國家間經濟的差距所產生的衝突。隨後的幾屆高峰會議經濟議題都是不結盟國家所討論的重點。該議題是不結盟運動所提出最受國際社會熟知的議題，雖然開發國家所給予的配合改變仍相當有限，但不結盟國家確已對國際事務產生一定程度的影響。一九八○年代不結盟高峰會議，內部衝突階段。由於美國意圖主導國際局勢，而對第三世界國家如古巴、利比亞、以阿問題介入干預，不結盟國家對此大加抨擊，因而不斷重申「不干涉、不干預」的原則。然而同為不結盟國家的伊朗、伊拉克間的戰爭，更是不結盟運動深感棘手的問題。一九九○年代不結盟高峰會議，全新定位時期。一九八九年，國際關係進入全新的局面。東歐、蘇聯共產政權相繼倒台，東西對峙已成歷史。美國成為唯一強權，後冷戰時期到來，「新國際秩序」已然成形。不結盟運動形成的背景，已不復存在，「不結盟」的外交政策也失去。

Compact binary coalescing systems: binary neutron stars, neutron star black hole pairs and binary black hole systems, represent promising candidates for gravitational wave first detection and have the potential to provide precise tests of the strong-field predictions of general relativity. Observations of binary black hole (BBH) systems will provide a wealth of information relevant to fundamental physics, astrophysics and cosmology. The search for such systems is a major priority of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo collaborations. A major area of research within LIGO-Virgo analysis groups is incorporation of spin into the search template banks used for binary black hole systems. In this dissertation, I compare the injection efficiency and parameter recovery from three binary black hole searches. One of the searches presented here uses non-spinning templates and represents the standard LIGO search for binary black holes with total masses between 35 and 100M[circle with dot]. The other two use spin aligned and anti-aligned templates representing a future search for black hole binary systems with total masses between 35-100M[circle with dot]. One of the two spinning searches has the spin parameter set to zero, nonspinning, as a check of the spinning method. (Additionally the (anti-)aligned spin searches use a retooling of the standard pipeline taking advantage of a code base designed specifically to handle Advanced LIGO data.) All three searches were run on artificial data created by the Numerical Injection Analysis 2 collaboration (NINJA2) containing Gaussian noise and numerically generated signals modeling aligned and anti-aligned spinning binary black holes. I found that for the analyzed two weeks of data the three searches recover injections with nearly equal efficiency; however, the spinning search recovers the parameters of the injections more accurately than the non-spinning search. Specifically, the parameter recovery of the spins shows a correlation between the injected and recovered spins, and the addition of spin to the template bank improves the recovery of the signal-to-noise ratio and the chirp mass for an injected signal. While spin aligned situations are geometrically low probability configurations, there are plausible astrophysical effects that lead to alignment of spins prior to merger. Therefore my results show that the spin-aligned template bank search represents an improvement on the standard non-spinning search in the highmass region and should be pursued on real data. / text

Thesis (M. A.)--University of South Africa, Pretoria, 2002.

Electrospinning process is a simple and widely used method for producing polymeric nanofibres. However, despite its popularity, significant challenges remain in controlling the fibre deposition due to the complex nature of electrospinning process. The process is renowned for its chaotic motion of fibre deposition, also known as the whipping instability. This instability is caused by electrostatic and fluid dynamics interactions of the charged jet and it is partly responsible for the thinning of the fibres into nanoscale diameters. Due to the instability, an electrospinning process typically deposits random orientated fibres in a circular deposition area. Furthermore, there is no control over the location where the fibres land on the collector electrode except that the fibres always travel through the shortest trajectory between the source and the collector electrodes. In this study, an alternative controlled deposition technique was proposed based on electric field manipulation (EFM). The main hypothesis of this study is that a consistent and repeatable method of controlled deposition can be achieved by using EFM. EFM was achieved by introducing a pair of charged auxiliary electrodes positioned adjacent and perpendicular to the fibre deposition direction. The applied voltage of either direct current (dc) or time-varying (ac) voltage at the auxiliary electrodes act as control to influence the spatial location and size of the deposition area. Samples were produced on black paper substrates and scanned into greyscale images. An image analysis technique was developed to measure the shift and size of the deposition area. A computer simulation was used to calculate the electric field strength and to simulate the behaviour of fibre response based on the trajectory of a charged particle. An image analysis based on greyscale intensity measurement was also developed to examine the uniformity of the deposition area. Finally, fibre characterisation was carried out to examine the fibre morphology, diameter, and orientation based on scanning electron micrographs. The results from this study showed that EFM can provide a consistent and repeatable control of the deposition area. When the auxiliary electrodes were independently charged with two dc voltages, it was observed that the deposition area moved away from the most positive electrode. The magnitude of shift of the deposition area was found to increase linearly with voltage difference between the auxiliary electrodes. Furthermore, the aspect ratio of the deposition area (ratio of width over height) decreased linearly with base voltage i.e. lower of the two auxiliary electrode voltages. These two controls were found to act independently from each other and can be described as two separate controls i.e. voltage difference for spatial location and base voltage for aspect ratio of the deposition area. A similar response was observed in simulation i.e. the particle moved away from the most positive electrode. Simulation results also showed that the x-axis component of the electric field (Ex) was responsible for the shift in location and the reduction of aspect ratio of the deposition area. When the auxiliary electrodes were charged with two antiphase time-varying voltages, continuous scanning of the electrospinning jet was observed producing a wide electrospun fibre mat. It was first thought the smooth oscillation of a sine wave would produce a more uniform deposition pattern compared to a triangle wave, but the results showed otherwise. The inferior uniformity of the sine wave sample was found due to the variability of the jet scanning speed when compared to the constant speed achieved when using a triangle wave. It was also observed that the deposition pattern can be further improved by using two clipped triangle wave voltages. The results open up the possibility for further exploiting the control voltage to achieve the desired deposition pattern. Two case studies were presented to demonstrate the applicability of the technique in real electrospinning applications. In the first case study, it was demonstrated that the continuous scanning of electrospinning jet was capable of eliminating the stripe deposition pattern which is commonly associated to a multi-spinneret electrospinning system. In the second case study, it was found that the alignment and distribution of aligned fibres in a gap electrospinning system can be improved by using the EFM technique. A new technique was also introduced to produce a multi-layer orientated fibre construct. These application examples showed that the EFM technique is ready for the production of engineered electrospun fibre constructs. This would extend the use of electrospun fibres to applications which is currently limited by geometrical constraints of the fibre constructs.