High performance millimeter-wave microstrip circulators and isolators

Millimeter wave systems, phased array antennas, and high performance components all require wideband circulators (and isolators) to perform diplexing and switching, to improve isolation and Voltage Standing Wave Ratio (VSWR), and to construct IMPATT diode reflection amplifiers. Presently, most of the millimeter-wave circulators and isolators are available in the configurations of waveguide or stripline, both of which suffer from the shortcomings of bulky size/weight, narrow bandwidth, and poor compatibility with monolithic millimeter-wave integrated circuits (MMIC). MMW microstrip circulators/isolators can eliminate or improve these shortcomings. Stub-tuned microstrip circulator configuration were developed utilizing the electromagnetic fields perturbation technique, the adhesion problems of microstrip metallization on new ferrite substrate were overcome, the fabrication, assembly, packaging techniques were improved, and then successfully designed, fabricated a Ka band circulator which has isolation and return loss of greater than 16dB, insertion loss less than 0.7dB. To assess the steady and reliable performance of the circulator, a temperature cycling test was done over the range of -20 to +50 C for 3 continuous cycles and found no significant impact or variation of circulator performance

Geometry modeling and multi-block grid generation for turbomachinery configurations

An interactive 3D grid generation code, Turbomachinery Interactive Grid genERation (TIGER), was developed for general turbomachinery configurations. TIGER features the automatic generation of multi-block structured grids around multiple blade rows for either internal, external, or internal-external turbomachinery flow fields. Utilization of the Bezier's curves achieves a smooth grid and better orthogonality. TIGER generates the algebraic grid automatically based on geometric information provided by its built-in pseudo-AI algorithm. However, due to the large variation of turbomachinery configurations, this initial grid may not always be as good as desired. TIGER therefore provides graphical user interactions during the process which allow the user to design, modify, as well as manipulate the grid, including the capability of elliptic surface grid generation

Constructing interactive multi-view videos based on image-based rendering

[[abstract]]In this paper, we use image-based rendering (IBR) to develop a scene rotation mechanism. We shot several images in the same scene and computed the angles between images. A video is then composed, allowing users to select viewing angles when the video is playing. We made three kinds of assumptions that may affect the resulting video, and proved our assumptions by a series of experiments. Finally, we use video of realistic scenario and produce interactive video by the proposed method. The contribution also includes techniques to compute geometric parameters of the scene from one or more images.[[notice]]補正完

Economic analysis in the context of incomplete knowledge

The overall objective of this research is to provide a methodology for determining a complete and final decision line when evaluating a set of mutually exclusive alternatives under the context of incomplete knowledge for both weak and strict ranking;A procedure was developed to search for the extreme variances of payoffs for alternatives under strict ranking. It was proved that the extreme variances under conditions of strict ranking must occur at corner boundary points of the feasible region if more than two distinct payoffs exist for n possible states of nature. If only two distinct payoffs exist for n states of nature, the global maximum of the variance can occur inside the feasible region;The variances and the expected values of payoffs were combined into the index of utility with a coefficient of risk aversion. In order to reduce the chances of unwanted results, a negative coefficient of risk aversion was used to apply heavier penalties for greater variances. An algorithm was developed to search for the extreme indexes of utility under conditions of strict ranking in the context of incomplete knowledge. It was proved that the extreme indexes of utility under conditions of strict ranking must occur at corner boundary points of the feasible region if more than two distinct payoffs exist for n possible states of nature. If only two distinct payoffs exist for n states of nature, the global minimum index of utility can occur inside the feasible region;As the coefficient of risk aversion can be expressed in terms of the minimum attractive rates of return and an angular coefficient, a method of determining the appropriate value of the angular coefficient for a set of mutually exclusive alternative was introduced under the context of uncertainty. This method was then modified and was successfully applied to both the context of uncertainty and the context of risk;The technique of finding the appropriate angular coefficients was then extended to conditions of weak ranking and strict ranking, respectively. After the angular coefficient was determined, it was possible to find the extreme rates of return on index of utility by applying the algorithm of searching for the extreme indexes of utility. A complete and final decision line was then constructed based on the minimum rates of return on index of utility

Characterisation of anatomical and functional deficits in a mouse model of Rett Syndrome

Rett syndrome (RTT), a disorder caused almost exclusively by mutations in the X-linked gene, MECP2, has a clinical phenotype thought to be primarily of neurological origin. Disruption of Mecp2 in mice results in a prominent RTT-like phenotype and Mecp2 knock-out animal models provide an excellent platform for investigating the role of MeCP2 in the brain development. In this thesis, I used the Mecp2-stop mouse model to address the effects of MeCP2 deficiency in the central nervous system. First, I assessed the genotype-phenotype relationship at the level of the whole organism by detailed temporal mapping of the RTT-like neurological signs. I also addressed the genotype-phenotype relationship at the level of neuronal networks by assessing alterations in neuronal (cortical) density including potential alterations across morphologically discrete cell subtypes. Finally, I also investigated the genotype-phenotype relationship at the level of the synapse by assessing RTT-related changed in synaptic plasticity. Whole organism phenotyping using observational scoring revealed the male hemizygous Mecp2-mutant mice (Mecp2stop/y) to show an early (from ~5 weeks) and aggressive onset of signs including locomotor and other general features. Correlated studies at the level of the synapse revealed the severity of gross organismal pathology to mirror a progressive decline in both short- and long-term forms of synaptic plasticity as measured in the CA1 region of the hippocampus. Specifically, extracellular field recordings in acute hippocampal slices from strongly symptomatic Mecp2-stop mice showed long-term plasticity (LTP) at the Schaffer-collateral-to-CA1 pyramidal synapse to be 40.2 ± 1.6 % of age-matched wild-type littermate controls. In addition, putative presynaptic short-term forms of plasticity (post-tetanic potentiation (PTP) and paired-pulse facilitation (PPF)) were also decreased in the Mecp2-stop hippocampus (45 ± 18.8 % and 78 ± 0.1 % of wild type for PTP and PPF respectively; all p<0.05). Moreover, the impairment in LTP was associated with symptom severity score whereby mice with a more ‘severe’ symptom score showed a more profound deficit in LTP. Refined axon stimulation protocols revealed evidence of pronounced LTP saturation in symptomatic Mecp2stop/y mice, suggesting an LTP ‘ceiling’ effect. I therefore assessed the action of the weak NMDA receptor blocker memantine, shown previously to reverse LTP saturation-related LTP deficits, in the hippocampus of control and Mecp2-stop mice. Application of memantine (1μM), resulted in substantial reversal of short-term plasticity deficits in the Mecp2-stop samples, without affecting plasticity in wild-type mice. However, systemic administration of memantine (30mg/Kg) in vivo did not have any observable effect on RTT-like phenotype at the organismal level including symptom onset, progression and survival. Utilising immunohistochemistry (NeuN) and histological staining (DAPI) to quantify cell density in layer five of the somatosensory cortex, I demonstrated that the symptomatic Mecp2-stop mouse had a higher cortical cell density compared to wild-type controls (1.28 times of whole cortical cell density and 1.41 times of neuronal cell density). Detailed analyses of distinct neuronal subpopulations (parvalbumin-, somatostatin-, calretinin- and calbindin-immunopositive cells) showed that calretinin (CR)- and somatostatin (SOM)- immunopositive cells had a lower cell density in Mecp2-stop mouse somatosensory cortex. However, the distribution patterns of different neuronal subtypes (using the same markers) in Mecp2-stop hippocampus were preserved and were grossly similar to those of WT brains. In summary, in this thesis, I demonstrated that the cell densities of CR- and SOM- positive neurons were altered in the somatosensory cortex in symptomatic Mecp2-stop mice. At the synaptic functional level, I showed both short-term and long-term plasticity deficits in the hippocampus of Mecp2-stop brains. Memantine, a clinically widely-used Alzheimer drug, partially restored the synaptic plasticity deficits in vitro. These data together supported that deficits in specific neuronal populations and progressive functional synaptic impairment may be key features in the RTT brain and also demonstrated the potential for the pharmacological restoration of synaptic plasticity function