Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 111-114).

Thesis (M.S.)--Ohio State University, 1956. / Includes bibliographical references. Available online via OhioLINK's ETD Center

This project is to analyse the energy spectrum of a spin-molecular tunnelling junction which is composed of molecules confined between two conducting metallic leads. By letting a continuous stream of electrons flow across the junction the molecules can interact with each other with an indirect force called exchange interaction, and those exchange interactions which are of interest in this project are described by models called the Heisenberg, the Ising and the Dzyaloshinski-Moriya models. The molecules may also interact with themselves anisotropically and if there is an external magnetic field there will be yet another kind of interaction. The goal of this project is to see the contribution of all these spin interactions and how they affect the resulting energy spectrum under the variation of the junction's chemical potential and the voltage bias between the leads. This project is of a theoretical nature where the models are analytically adapted for a restricted scenario and is later on numerically calculated to be graphed and analysed. The models are restricted to only consider molecules of same spin and approximated to only consider interactions between closest neighbouring molecules. The results are composed of both analytically derived energy values and numerical computed values which show that there exists certain critical values of the variation parameters which naturally splits the ground state of the system and that the self-interaction may further split the degenerate ground state. A possible outcome of these result could be the possibility to control the magnetic order of the molecules to either be locked in an anti-ferromagnetic configuration or be easily mixed by manipulating the chemical potential or the voltage bias. / Detta projekt handlar om att analysera energispektrumet från en spinn-molekyl-tunnelkor-sning som består av molekyler instängda mellan två ledande metaller. När en kontinuerlig elektronström korsar tunnelkorsningen så kan molekylerna växelverka med varandra via en indirekt kraft kallad utbytesinteraktion, och de utbytesinteraktioner som är relevanta i denna uppställning beskrivs av de så kallade Heisenberg-, Ising- och Dzyaloshinski-Moriya-modellerna. Molekylerna kan också växelverka med sig själva anisotropt och om det finns ett externt magnetfält så tillkommer ytterligare en interaktionsterm. Målet för detta projekt är att se hur alla dessa spinnbidrag påverkar det slutliga energispektrumet under variation av korsningens kemiska potential och spänningen mellan metalledarna.       Projektet är teoretiskt lagt på så sätt att modellerna är analytiskt anpassade för ett begränsat scenario samt att de är numeriskt beräknade så att energispektrumet kan plottas i grafer och analyseras. Modellerna är begränsade för molekyler av samma spinn och är approximerade så att endast närmsta-granne-interaktioner är beaktade.       Resultaten är uppdelade i både analytiskt framtagna energivärden samt numeriskt beräknande energinivåer och båda visar att det finns kritiska värden på variationsparametrarna som automatiskt delar grundtillståndet för systemet samt att självinteraktionerna ytterligare kan dela det degenererade grundtillståndet. Ett möjligt utfall av dessa resultat är att de kan användas till att kontrollera systemets magnetiska ordning på så sätt att det antingen är låst i en antiferromagnetisk konfiguration eller med enkelhet kan mixas genom att ändra den kemiska potentialen eller spänningen mellan metalledarna.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder affecting individuals along a continuum of severity in communication, social interaction and behaviour. The impact of ASD significantly varies amongst individuals, and the cause of ASD can originate broadly between genetic and environmental factors. Previous ASD researches indicate that early identification combined with a targeted treatment plan involving behavioural interventions and multidisciplinary therapies can provide substantial improvement for ASD patients. Currently there is no cure for ASD, and the clinical variability and uncertainty of the disorder still remains. Hence, the search to unravel heterogeneity within ASD by subgroup classification may provide clinicians with a better understanding of ASD and to work towards a more definitive course of action. In this study, a norm of physical measurements including height, weight, head circumference, ear length, outer and inner canthi, interpupillary distance, philtrum, hand and foot length was collected from 658 Typical Developing (TD) Chinese children aged 1 to 7 years (mean age of 4.19 years). The norm collected was compared against 80 ASD Chinese children aged 1 to 12 years (mean age of 4.36 years). We then further attempted to find subgroups within ASD based on identifying physical abnormalities; individuals were classified as (non)dysmorphic with the Autism Dysmorphology Measure (ADM) from physical examinations of 12 body regions. Our results show that there were significant differences between ASD and TD children for measurements in: head circumference (p=0.009), outer (p=0.021) and inner (p=0.021) canthus, philtrum length (p=0.003), right (p=0.023) and left (p=0.20) foot length. Within the 80 ASD patients, 37(46%) were classified as dysmorphic (p=0.00). This study attempts to identify subgroups within ASD based on physical measurements and dysmorphology examinations. The information from this study seeks to benefit ASD community by identifying possible subtypes of ASD in Chinese population; in seek for a more definitive diagnosis, referral and treatment plan. / published_or_final_version / Paediatrics and Adolescent Medicine / Master / Master of Philosophy

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by communication difficulties, social interaction impairments, and stereotyped patterns of behavior. Prior studies have shown that ASD is associated with differences in neuroanatomy in the cerebral cortex and the subcortical regions as well as the connectivity among these regions. However, findings have been mixed due to the varying age group sampled and the methods used to measure these brain structures. In view of the heterogeneous findings in ASD, three cross-sectional design studies were conducted in this thesis to examine brain structural pathologies that may be related to the clinical and behavioural phenotype of the disorder across development. In the childhood and adolescent sample, two studies were carried out. The first one examined cortical thickness using a vertex-wise approach. Results revealed thinner cortex in the occipital, parietal and frontal regions, and thicker cortex in the inferior parietal and caudal anterior cingulate regions. These regions also showed age-related differences that deviated markedly from the typical developmental trajectories observed in the control group. Some of these regions with significant differences in cortical thickness were found to be associated with clinical symptoms in ASD. The second study in the childhood and adolescent sample examined the volume of subcortical structures and CSF using a spatially non-biased parcellation approach. It was found that intracranial volume was enlarged in children with ASD, accompanied by smaller bilateral cerebellum and left thalamus. These regions showed an age-related increase in volume in children with ASD, whereas the typically developing children showed a general age-related decrease in volume of the same regions. The volumes of the cerebellum, thalamus and basal ganglia structures were associated with relatively weaker motor control in ASD, and in particular greater volume of the left thalamus rather than age predicted worse motor performance in the clinical group. The third study was carried out in a large adult sample. The cerebellar white matter system, that interconnects cortical and subcortical targets, was examined. Using a diffusion-tensor imaging tractography approach, the cerebellar input and output white matter pathways were dissected. Both the input and output pathways were observed to be disrupted in ASD, supporting the hypothesis that ASD may be a “disconnectivity disorder”. Lower fractional anisotropy of the left middle cerebellar peduncles was associated with increased difficulties in communication and social interaction, and lower fractional anisotropy in the right superior cerebellar peduncle was linked to worse motor performance in adults with ASD. Therefore, my studies confirmed differences in neuroanatomy of cortical and subcortical regions with altered brain developmental trajectories in children and adolescence with ASD, and revealed disrupted cerebellar network system in adults with ASD. Dysmaturation of cortical and subcortical regions as well as cerebellar white matter pathways may contribute to clinical and motor phenotype of the disorder. Lastly, postmortem and early life imaging studies, together with evidence that prenatal stressors during 21 to 32 weeks of gestation may increase incidence of ASD, lead me to speculate whether the abnormalities reported here may have origins prior to 31 weeks of gestation. / published_or_final_version / Psychiatry / Doctoral / Doctor of Philosophy

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published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy