In this dissertation, two exactly solvable models from the Kitaev class [Ann. Phys. 321, 2 (2006)] of exactly solvable models are analysed. In the second chapter, Kitaev models and their generic properties are reviewed. Majorana fermions are introduced and discussed. Then their relationship with the solution of Kitaev models are discussed which involves the emergence of a Z₂ gauge symmetry and anyonic particles of both Abelian and non-Abelian varieties. The third chapter, which is based on the research article [Phys. Rev. B (Rapid Comm.) 83, (2011)], examines the Kitaev model on the kagome lattice. A rich phase diagram of this model is found to include a topological (gapped) chiral spin liquid with gapless chiral edge states, and a gapless chiral spin liquid phase with a spin Fermi surface. The ground state of the current model contains an odd number of electrons per unit cell which qualitatively distinguishes it from previously studied exactly solvable models with a spin Fermi surface. Moreover, it is shown that the spin Fermi surface is stable against weak perturbations. The fourth chapter is based on the article [Phys. Rev. B 84,(2011)] and analyses a disordered generalisation of the Yao-Kivelson [Phys. Rev. Lett. 99,247203 (2007)] chiral spin-liquid on the decorated honeycomb lattice. The model is generalised by the inclusion of random exchange couplings. The phase diagram was determined and it is found that disorder enlarges the region of the topological non-Abelian phase with finite Chern number. A study of the energy level statistics as a function of disorder and other parameters in the Hamiltonian show that the phase transition between the non-Abelian and Abelian phases of the model at large disorder can be associated with pair annihilation of extended states at zero energy. Analogies to integer quantum Hall systems, topological Anderson insulators, and disordered topological Chern insulators are discussed. / text

published_or_final_version / Dental Surgery / Master / Master of Dental Surgery

Obsessive-compulsive disorder (OCD) is associated with brain abnormalities in the areas that regulate emotions, and it is postulated that people with OCD have difficulty downregulating ( = reducing) their negative emotions. This study recruited 20 participants with OCD and 20 controls to rate 294 emotional photos (emotional stimuli not related to OCD) for emotional valence. Participants were then asked to downregulate while they saw the 20 photos with the highest negative ratings and 20 photos with the highest positive ratings. Participants with OCD had more difficulty downregulating their negative emotions than controls. Evidence for that is that (1) participants with OCD gave significantly higher ratings to the affectively negative photos in the postregulation phase, after adjusting for their preregulation ratings and (2) participants with OCD took significantly more time to regulate both their negative and positive emotions. The findings suggest that individuals with OCD not only present with the symptoms that are specified in the OCD diagnostic criteria of DSM-IV TR (American Psychiatric Association, 2000), but also with difficulty downregulating their negative emotions to non obsessive-compulsive (nonOC) affectively negative stimuli. Clinicians may consider adding emotion regulation skills to psychological treatments of OCD. / published_or_final_version / Clinical Psychology / Doctoral / Doctor of Psychology

Background. Earthquake is a natural event that can happen all around the world. And significant ones would cause great fatality, morbidity and huge economic damage to the local society. Posttraumatic Stress Disorder (PTSD) is a common psychiatric condition among the earthquake survivors. Some former studies indicated that being female experienced a higher risk of depression, a psychiatric symptoms after traumatic events, while others did not. It is not sure that whether females tend to be more easily suffer from PTSD after earthquakes. So the aim of the study is to conduct a systematic review to examine the sex difference of PTSD prevalence among surviving population after earthquake. Method. A keyword searching was performed using ‘earthquake’ and ‘PTSD’, ’posttraumatic stress disorder’ as keywords. Articles published in recent 5 years, in English and the ones full text could be accessed were included in the study. Among the articles being selected according to the inclusion criteria, those ones which fulfilled the exclusion criteria would be eliminated. Results. 11 articles included in this systematic review. In terms of the age of the subjects, there are seven articles studying the adult population and the remaining four studied children and adolescents. Six articles investigated the survivors from Chinese population after 2008 Wunchuan earthquake. Others studied survivors from local population after 2005 Pakistan earthquake(n=2), 2007 Peru earthquake(n=1), 2009 L’Aquila earthquake(n=1) and 1999 Jiji earthquake (n=1). On the other hand, the sex difference in earthquake-related PTSD in children and adolescents were inconsistent. Conclusion. Women tended to experience higher risk of PTSD after earthquake than men, while result on sex difference was not consistent in the children/adolescent population. Further studies are needed to examine PTSD prevalence between boys and girls. / published_or_final_version / Public Health / Master / Master of Public Health

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Boys with Attention-Deficit/Hyperactivity Disorder (ADHD) were recruited from a local neuropsychology office with controls recruited from the community to assess the relationship between prenatal androgen exposure and ADHD, as well as the possible cognitive correlates of this exposure. Putative physiological markers of prenatal androgen exposure that were measured for each child included several types of otoacoustic emissions (OAEs) as well as finger-length ratios (FLRs). Neurocognitive measures included tasks which assessed components of attention, general intelligence, reading ability, and visuospatial skills. Several other variables which may also be related to androgen exposure were included (e.g., sleep disturbance, handedness, number of older brothers) in the analyses. Children ranged in age from 7 to 12 years old with 13 controls, 19 children with ADHD/Combined Type (ADHD/C), 10 with ADHD/Inattentive Type (ADHD/IA), and an additional 11 children with ADHD/IA who were rated by their parents as having relatively high levels of an experimental construct (sluggish cognitive tempo; SCT). Because more boys than girls are diagnosed with ADHD, it was hypothesized that ADHD may be associated with prenatal masculinizing hormones (i.e., androgens), and that children with ADHD would appear more masculine on markers of androgen exposure (OAEs and FLRs) than controls. However, in our current study children with ADHD did not differ from controls on these measures. There was some evidence that children with SCT may represent a more homogenous group of children within the ADHD/IA diagnostic group, and that they may share a deficit in alerting attention. Consistent with theories suggesting subtype differences in attention, children with ADHD/C did not appear to have a deficit in alerting attention, but rather appeared more cognitively impulsive and to have a deficit in auditory attention. Children with SCT were more likely to be rated by their parents as having disrupted sleep.