In a multiuser DS-CDMA system with frequency selectivity, each user’s spreading sequence is transmitted through a different channel and the autocorrelation and the cross correlation properties of the received sequences will not be the same as that of the transmitted sequences. The best way of designing spreading sequences for frequency selective channels is to design them at the receiver exploiting the users’ channel characteristics. By doing so, we can show that the designed sequences outperform single user AWGN performance. In existing sequence design algorithms for frequency selective channels, the design is done in the time domain and the connection to frequency domain properties is not established. We approach the design of spreading sequences based on their frequency domain characteristics. Based on the frequency domain characteristics of the spreading sequences with unconstrained amplitudes and phases, we propose a reduced-rank sequence design algorithm that reduces the computational complexity, feedback bandwidth and improves the performance of some existing sequence design algorithms proposed for frequency selective channels. We propose several different approaches to design the spreading sequences with constrained amplitudes and phases for frequency selective channels. First, we use the frequency domain characteristics of the unconstrained spreading sequences to find a set of constrained amplitude sequences for a given set of channels. This is done either by carefully assigning an already existing set of sequences for a given set of users or by mapping unconstrained sequences onto a unit circle. Secondly, we use an information theoretic approach to design the spreading sequences by matching the spectrum of each user’s sequence to the water-filling spectrum of the user’s channel. Finally, the design of inner shaping codes for single-head and multi-head magnetic recoding channels is discussed. The shaping sequences are designed considering them as short spreading codes matched to the recoding channels. The outer channel code is matched to the inner shaping code using the extrinsic information transfer chart analysis. In this dissertation we introduce a new frequency domain approach to design spreading sequences for frequency selective channels. We also extend this proposed technique to design inner shaping codes for partial response channels.

A novel selective-filling technology of photonic crystal fibers (PCFs) employing a simple selective-blocking process using UV gel is demonstrated in this thesis. In this study the liquid-filled PCFs with the filling in inside three layers and whole four layers represent the insertion loss of gel 7.5dB and the photonic band gap (PBG) guiding effect at wavelength 1100nm~1300nm, having potential to be tunable optical filters by filling the liquid crystal. The liquid-filled PCFs without the filling of the most inside 1ayer represent low insertion loss of gel 2dB and the total index reflection (TIR) guiding effect, having potential to be low loss tunable fiber gratings by filling the liquid crystal. The liquid-filled PCFs with the filling in middle a layer represent the elliptical far field pattern and effect of birefringence at wavelength 1600nm.

Thesis (M. Phil.)--University of Hong Kong, 1980.

This study analyses the composition of outmigration flows regarding migrants’ characteristics such as family situation, educational attainment and labour market situation. To expand our research, out-migrants are separated into return and onward migrants. Results indicate that the labour market situation of immigrants (unemployment and uptake of social benefits) in the destination country is an important determinant in the decision to out-migrate. However, the effect varies among countries due to the political situation in the source country, the migration costs and the extensive welfare benefits in Sweden. Labour immigrants are more likely to return to their country of origin whereas refugee immigrants are more likely to move to another country. Other findings demonstrate that emigrants are negatively selected regarding educational attainment. High-educated individuals have a higher probability of returning home than moving to a third country. The likelihood of emigration also depends on other characteristics such as the family situation of immigrants and the duration of residence in the destination country. All in all, labour market outcomes are the most important factors in the decision of out-migration.

Development of wavelength selective detection, tunable multi-spectral capability with functionality in the infrared spectral region is highly desirable for a variety of applications such as thermography, chemical processing and environmental monitoring, spectroradiometry, medical diagnosis, Fourier transform infrared spectroscopy, night vision, mine detection, military defense and astronomy. Infrared detector with wavelength selective functionality have emerged as next generation infrared detectors. This study presents fabrication and characterization of wavelength selective Germanium dielectric coated Salisbury screen and novel 3D stacked microbolometer for multispectral infrared detection. This novel fabrication process helps produce much flatter, more robust device structure by using an un-patterned sacrificial layer to produce device legs that hold the central structural layer above the reflective mirror supported by a completely flat sacrificial layer with sufficient thermal isolation to allow microbolometer operation. For the fabricated wavelength selective Germanium dielectric coated Salisbury screen microbolometer using self aligned process, the FTIR measured spectral responses and numerical simulation results show excellent agreement with wavelength selectivity (9[mu]m, 10[mu]m, 11[mu]m) in long wave infrared (LWIR) region. To achieve multicolor infrared detection, recently a few device concepts using uncooled detectors have been reported. However, none of the proposed device designs have demonstrated fabrication. Moreover, Commercial Fabry-perot resonant cavity based uncooled microbolometers (Air gap: 2 to 2.5μm) have limited design parameters due to multicolor narrow band spectral response. In this study, a feasible device fabrication method for novel 3D stacked microbolometer is demonstrated for multispectral uncooled infrared detector that can achieve tunable narrowband absorption in mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectral regions. / text

Recent work has shown that preschoolers track informants’ past reliability concerning familiar information and labels, and they use this information to judge the correctness of novel information and labels they provide. But linguistic factors also sway children’s choices for social interaction, for which native-accented speakers are preferred. The present study uses the selective trust paradigm to consider how accentedness interacts with speaker reliability with native- and foreign-accented informants. The results show that speaker reliability and accentedness affect four-year-olds’ choices, but the impact of these factors differed by response type. Preschoolers preferred to ask the native-accented speaker for information, regardless of his reliability. However, in choosing which label to learn, preschoolers selected the reliable speaker’s label, regardless of accent, and correctly identified the unreliable speaker. This study provides evidence suggesting that young children separate their social biases from their objective assessment of novel information. / text

published_or_final_version / Chemistry / Master / Master of Philosophy

Biomimetics is defined as an approach in which naturally occurring materials processes are mimicked in laboratory situations. The ultimate goal is to develop synthetic analogues of naturally occurring materials such as bone and teeth, classified as biocomposites, which possess similar chemical and mechanical properties. The work presented here provides the initial work in furthering the progress of biomimetic materials processing.The first element of the work utilizes molecular imprinting as a selective recognition, or sensing tool, for detection of low molecular weight organic molecules. Molecular imprinting is a phenomenon in which crosslinked synthetic polymers exhibit selective binding towards small organic molecules. Initial work in the field was done in which numerous processing steps were involved with bulk polymer samples while the achievement here lies in the development of molecular imprinted polymer films which greatly facilitate the processing and characterization. Molecularly imprinted polymers are sometimes referred to as artificial antibodies due to the selective binding aspects that are highly analogous to natural antibodies.Additional work involves transforming the recognition aspects of molecular imprinting into a biomineralization analogue. Biomineralization is the process in which organisms convert freely soluble minerals (namely calcium carbonates and calcium phosphates) into solid parts, such as bones and teeth, at ambient conditions via the influence of organic molecules such as proteins and carbohydrates. The molecular imprinting approach with biomineralization led to limited success but formed the foundation for a more detailed study into the effects of small organic functional groups (COOH-, OH-) on the growth of calcium carbonates and calcium phosphates, the core components of important biocomposites such as bone.In order to study the effects of organic molecules on the calcium based crystals, a mineralization assay was developed in an agarose gel matrix for studying inhibition and growth as influenced by various organic molecule functionalities. The gel mineralization assay is a novel approach in which quantitative and qualitative data could be generated in a high throughput fashion to determine organic molecule mediation of calcium based crystal growth. Such methods provide an approach for eventually providing control in development of synthetic biocomposites with customized materials properties.

Cognition is dynamic and complex, requiring specific sets of brain areas to cooperate for specific tasks. Neural synchronization is a proposed mechanism for transient functional integration of specific neural populations, enabling feature flexible binding and dynamic assignment of functional connectivity in the brain according to task demands. This thesis addresses the role of neural synchronization in selective attention and perceptual consciousness. The goals of this thesis are to test the hypothesis that synchronization between brain regions is relevant to network dynamics in selective attention and for perceptual organization, and to elucidate the function of synchronization in different frequency ranges. Using a selective visuospatial cuing paradigm it is shown that deploying attention to one visual hemifield yields transient long-distance gamma-band synchronization between contralateral visual cortex and other, widespread, brain regions. This is interpreted as a mechanism for establishing anticipatory biasing of communication in the cortex. Long-distance gamma synchrony, moreover, is periodically 'refreshed' at a theta rate, possibly serving to maintain this gamma network. While local alpha-band activity was found to be greater ipsilateral to the attended visual hemifield, alpha-band synchronization between primary visual cortex and higher visual areas was greater contralateral to attended locations. This suggests that local alpha synchrony is relevant for inhibition, while long-range alpha synchronization enacts functional coupling. The onset of a new conscious percept during binocular rivalry coincides with large-scale gamma-band synchronization which recurs at a theta rate. This suggests that gamma synchronization integrates features into a unified conscious percept while the theta cycle maintains that network. Using an audiovisual speech integration paradigm it is shown that large-scale gamma synchronization is greater when incongruence is detected between auditory and visual streams. This highlights an important distinction: neural synchronization reflects neural integration, not perceptual integration. Perceptual integration typically requires neural integration (feature binding), however, in this case detection of audiovisual mismatches requires cooperation within a distributed network, whereas audiovisual speech integration is largely accomplished in superior temporal cortex. These studies indicate that long-distance gamma synchronization establishes neural integration, the theta cycle maintains gamma synchronous networks, and local and long-range alpha synchrony reflect sustained inhibition and functional coupling mechanisms, respectively.

Nickeliferous laterite ores are currently processed using complex energy intensive flowsheets. Limited mineral upgrading can be achieved by low-cost mineral processing as the nickel is not found as a separable mineral phase but finely disseminated throughout the host goethite mineral. Whole ore extraction processes are required which result in intrinsically higher capital and operating costs. Market pressure has provided incentives to develop alternative upgrading techniques that can produce a nickel concentrate and reduce the material input to downstream processing facilities. Thermal upgrading through a selective reduction mechanism to produce a ferronickel concentrate has been studied extensively and has shown promising potential. In this research, a two stage selective reduction of nickeliferous laterite ore was investigated at 600oC and 1000 – 1100oC with varying coal and sulphur additions. Experiments showed that the limonite ore could be selectively reduced using a coal additive to a ferronickel and wustite phase. A combination of XRD and bromine/methanol diagnostic leach tests confirmed the presence of metallic nickel and iron in the calcine. Higher degrees of metallization corresponded with higher sulphur additions and growth zone temperatures. Sulphur was added to improve particle growth through the establishment of a Fe-O-S liquid phase, which was found to improve Ni recovery from 13.8% to 75.8% over the range of 0 – 4 wt% S. Ferronickel particles ranging in size from 20 – 60 microns were shown to be present but highly dispersed throughout the upgraded ore. Particle growth improved with higher growth zone temperatures and longer retention times. Magnetic separation of the calcine showed maximum upgrading of grades to 3 – 4 wt% nickel with recoveries ranging from 83.7 – 93.2%. Partial oxidation of wustite particles to magnetite caused the particles to be magnetic and resulted in recovery of unwanted iron oxides. The presence of iron oxide fines was believed to allow for rapid oxidation of wustite phase and also produce slimes that hindered physical separation of the upgraded ore. / Thesis (Master, Mining Engineering) -- Queen's University, 2013-12-29 22:34:20.417