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The topic of this thesis is cognitive control: how the brain organises itself to perform the many tasks it is capable of and how it switches flexibly among them. Task-switching experiments reveal a substantial cost in reaction time and accuracy after a switch in tasks. This "switch cost" is reduced by preparation (suggesting anticipatory task-set reconfiguration), but not eliminated. The thesis focuses on the sources of the "residual" cost. Most accounts attribute it to response selection being prolonged on a task-switch trial by task conflict, e.g. by 'task-set inertia' — persisting activation/inhibition of the previous task's S-R rules — or their associative reactivation by the stimulus. Four experiments used event-related potentials (ERPs) to determine which stages of task processing are influenced by a change in tasks, looking for delays in process-specific markers in the ERP. Experiments 1 and 2 showed that a prepared switch to a reading task from a perceptual judgement delayed early ERP markers of lexical access by a large fraction of the RT switch cost, suggesting that a substantial part of the residual cost arises in processes earlier than response selection, possibly due to task-related attentional inertia. Markers of lexical access observed in the non-lexical task were larger on switch than repeat trials, providing the first electrophysiological evidence of task-set inertia. Experiment 3 examined the effects of an unprepared switch in the same way. ERP waveforms were modulated by a switch before markers of lexical access were evident, suggesting additional processing demands compete for resources with lexical access. A simple delay, however, was not found; post-stimulus task-set reconfiguration does not just insert an extra processing stage. Experiment 4 looked for a delay in the onset of an early ERP marker of emotional processing when the task switched between categorising facial expression and classifying a superimposed letter. No such delay was found in this case, and ERP markers of emotion processing were present to the same extent in the letter task. This suggests that, given appropriate spatial attention, processing facial emotion unfolds automatically, independent of attention allocation to the facial features. Experiments 5-7 further explored the link between conflict due to processing the irrelevant stimulus dimension and the ERP post-stimulus negativity that accompanies the residual cost. The negativity could be elicited even on trials of non-switching blocks by prior training on classifying the irrelevant attribute of the stimulus using the same responses. But this effect did not seem to result from the trained class of irrelevant attribute attracting more attention. Finally, Experiment 8 followed up an incidental observation in Experiment 1 to establish the novel observation that a task-switching context abolishes the usual ERP correlate of withholding a response in a go/no-go paradigm, suggesting an interesting interaction between task-set control and response inhibition.

This master thesis is driven by two main objectives. The first one is to provide a general overview of migration in economic theory with a specific focus on remittances and their aspects and impacts. We found that there is no clear consensus about effects of migration and remittances on source and target countries and thus further research is justified. The second aim of the thesis is to analyse migration and remittances between Ukraine and the Czech Republic using primary data from survey questionnaires collected by the Ukrainian Migration Project (UMP). According to our findings, remittances are determined mostly by demographic characteristics and levels of income on both the sending and receiving side, implying their altruistic origin. More importantly, it was not confirmed that remittances are channelled primarily into consumption. On the other hand, remittances do not influence productive spending of households either. These findings contribute to the overall discussion in the area of remittances and may suggest some policy implications.

No processo de indicação e adaptação do Aparelho de Amplificação Sonora Individual, as informações obtidas por meio dos Potenciais Evocados Auditivos de Longa Latência, geralmente pesquisado em campo livre, têm sido utilizadas para a avaliação dos benefícios e limitações dos dispositivos eletrônicos aplicados à surdez. O objetivo foi o de analisar de forma comparativa, a influência do transdutor no registro dos componentes P1, N1 e P2 eliciados por estímulo de fala, quanto à latência e amplitude, em crianças ouvintes. A casuística foi formada por 30 crianças ouvintes de quatro a 12 anos de idade de ambos os sexos. Os potenciais evocados auditivos de longa latência foram pesquisados por meio dos transdutores, fone de inserção e caixa acústica, eliciados por estímulo de fala /da/ apresentado com 526ms de intervalo interestímulos, na intensidade de 70dBNA e taxa de apresentação de 1,9 estímulos por segundo. A estimulação foi definida aleatoriamente, ora na orelha direita ora na esquerda, assim como a ordem do tipo do transdutor, iniciando ora pelo fone de inserção ora pela caixa acústica. Foram analisados os componentes P1, N1 e P2 quando presentes, quanto à latência e amplitude. Para verificar a reprodutibilidade dos registros, realizou-se uma análise de concordância entre a pesquisadora e um juiz, que mostrou um nível de concordância forte. Não houve diferença estatisticamente significante ao comparar os valores de latência e amplitude dos componentes P1, N1 e P2, para cada tipo de transdutor, considerando o sexo e orelha, assim como entre os tipos de transdutores utilizados ao comparar os valores de latências dos componentes do potencial evocado auditivo de longa latência. Entretanto, houve diferença estatisticamente significante na amplitude dos componentes P1 e N1 obtidos com os transdutores caixa acústica e fone de inserção, com maior amplitude para o transdutor caixa acústica. Os valores de latência dos componentes P1, N1 e P2 e amplitude de P2 obtidos com fone de inserção podem ser utilizados como referência para análise do registro obtido com o transdutor caixa acústica. / In the process of indication and fitting of Hearing Aids, the data obtained through Long Latency Auditory Evoked Potentials, generally researched in free field, have been utilized to assess the benefits and limitations of electronic devices applied to deafness. The goal was to analyze, in a comparative manner, the influence of the transducer on the recordings of components P1, N1 and P2, elicited through speech stimulus, as to the latency and amplitude, in hearing children. The sample was comprised of 30 hearing children aged 4-12 yrs, of both genders. The long latency auditory evoked potentials were researched by means of transducers, insertion phone and speakers, elicited through speech stimulus /da/ presented with 526ms of interstimuli interval, in the intensity of 70dBNA and presentation rate of 1.9 stimuli per second. The stimulation was randomly defined, sometimes on the right ear, sometimes on the left one, as well as the order of the type of transducer, beginning, sometimes, with the insertion phone, and sometimes, with the speaker. Whenever present, components P1, N1 and P2 were analyzed as to latency and amplitude. In order to verify the reproducibility of the recordings, an agreement analysis was carried out between the researcher and a referee, showing a strong agreement level. No statistically significant difference was seen when comparing the latency and amplitude values of components P1, N1 and P2, for each type of transducer, taking into account the gender and ear, as well as among the types of transducers utilized when comparing the latency values of the components of long latency auditory evoked potential. Nevertheless, there was a statistically significant difference in the amplitude of components P1 and N1, obtained with the speaker and insertion phone transducers, with greater amplitude for the speaker transducer. The latency values of components P1, N1 and P2 and amplitude of P2 obtained with the insertion phone may be utilized as a reference for the analysis of the recording obtained with the speaker transducer.

Thesis advisor: David A. Broido / A theory is presented for describing the lattice thermal conductivities of graphene and single-walled carbon nanotubes. A phonon Boltzmann transport equation approach is employed to describe anharmonic phonon-phonon, crystal boundary, and isotopic impurity scattering. Full quantum mechanical phonon scattering is employed and an exact solution for the linearized Boltzmann transport equation is determined for each system without use of common relaxation time and long-wavelength approximations. The failures of these approximations in describing the thermal transport properties of nanotubes is discussed. An efficient symmetry based dynamical scheme is developed for carbon nanotubes and selection rules for phonon-phonon scattering in both graphene and nanotubes are introduced. The selection rule for scattering in single-walled carbon nanotubes allows for calculations of the thermal conductivities of large-diameter and chiral nanotubes that could not be previously studied due to computational limitations. Also due to this selection rule, no acoustic-only umklapp scattering can occur, thus, acoustic-optic scattering must be included in order to have thermal resistance from three-phonon processes. The graphene selection rule severely restricts phonon-phonon scattering of out-of-plane modes. This restriction leads to large contributions to the total thermal conductivity of graphene from the acoustic, out-of-plane modes which have been previously neglected. Empirical potentials used to model interactions in carbon-based materials are optimized to better describe the lattice dynamics of graphene-derived systems. These potentials are then used to generate the interatomic force constants needed to make calculations of the thermal conductivities of graphene and carbon nanotubes. Calculations of the thermal conductivities of single-walled carbon nanotubes and graphene for different temperatures and lengths are presented. The thermal conductivities of SWCNTs saturate in the diffusive regime when the effects of higher-order scattering processes are estimated and correctly reproduce the ballistic limit for short-length nanotubes at low temperatures. The effects of isotopic impurity scattering on the thermal conductivities of graphene and SWCNTs are explored. Isotopic impurities have little effect in the low (high) temperature regime where boundary (umklapp) scattering dominates the behavior of the thermal conductivities. In the intermediate temperature regime, modest reductions in the thermal conductivities, 15-20%, occur due to impurities. The thermal conductivities of a wide-range of SWCNTs are explored. The thermal conductivities of successively larger-diameter, one-dimensional nanotubes approach the thermal conductivity of two-dimensional graphene. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Os potenciais evocados auditivos de longa latência fornecem dados objetivos sobre a funcionalidade das estruturas corticais auditivas. O objetivo do presente estudo foi caracterizar a maturação do sistema auditivo central em crianças com audição normal por meio destes potenciais. Foram avaliados 56 indivíduos de ambos os sexos, com audição dentro dos padrões de normalidade, comprovada por audiometria e imitanciometria, sendo 46 crianças, de três a 12 anos, e 10 adultos jovens, os quais foram incluídos a título de comparação com a casuística infantil. O equipamento utilizado disponibilizava dois canais de registro, sendo um destinado à captação dos potenciais evocados auditivos de longa latência e outro, ao registro do artefato gerado pelo movimento ocular, visando ao seu controle. Os potenciais foram registrados com os indivíduos em estado de alerta, assistindo a um vídeo mudo, por meio de eletrodos posicionados em Cz (ativo) e A2 (referência) e os movimentos oculares, por eletrodos em posição supra e infra-orbital esquerda; o eletrodo terra foi colocado em A1. Foram analisados os valores de latência e de amplitude dos componentes P1, N1 e P2, bem como a morfologia destes componentes de acordo com a idade. Para verificar a reprodutibilidade dos potenciais registrados, foi realizado um estudo duplo-cego com a introdução da análise de uma avaliadora experiente em Eletrofisiologia, a qual não mostrou diferenças estatisticamente significantes da análise feita pela autora da pesquisa. Como resultado, constatou-se, quanto à morfologia, melhora na definição dos componentes com o avanço da idade. Foi observada diminuição nos valores de latência dos componentes P1, N1 e P2 com o avanço da idade. Não foi observada variação nos valores de amplitude com o avanço da idade para os componentes N1 e P2, exceto para o componente P1, que teve sua amplitude diminuída. Não foi observada diferença estatisticamente significante entre os sexos. Pôde-se observar que o processo maturacional do sistema auditivo central acontece de maneira gradativa, sendo as maiores modificações observadas ao se comparar crianças e adultos. / The long latency auditory evoked potentials provide objective data on the function of hearing cortical structures. This study aims at characterizing the maturation of the central hearing system, in normally hearing children, through these potentials. Fifty-six subjects from both genders, with hearing within normality patterns, verified by means of audiometry and imitanciometry, were evaluated, being 46 children in the age range 3-12, and 10 young adults, who were included for comparison with the infantile sample. The equipment utilized had two recording channels: one to catch the long latency auditory evoked potentials, and the other, to record the artifact generated by ocular movement, aiming at its control. The potentials were recorded with subjects alert, while watching a mute video, through electrodes positioned in Cz (active) and A2 (reference), and the ocular movements, through electrodes in left supra and infra-orbital position and the ground electrode was placed in A1. Values of latency and of amplitude for components P1, N1 and P2, as well as the morphology of these components, according to age, were analyzed. In order to verify the reproducibility of the recorded potentials, a double blind study was carried out, by introducing the analysis of an experienced Electrophysiology evaluator, whose analysis did not show statistically significant differences, as compared to that performed by the author of the research. Thus, as to morphology, improvement in the definition of components was seen, as age increased. A decrease in latency values of components P1, N1 and P2 was observed, as age advanced. No variation was verified in amplitude values, as age increased, for components N1 and P2, except for component P1, whose amplitude was diminished. No statistically significant difference was seen between genders. It was verified that the maturational process of the central hearing system takes place in a gradual fashion, being the greatest modifications seen, when comparing children and adults.

Ming Lui. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 44-53). / Abstracts in English and Chinese. / Introduction --- p.6-22 / Method --- p.23-30 / Results --- p.31-34 / Discussion --- p.35-42 / References --- p.43-51 / Tables --- p.52-55 / Figure Caption --- p.56 / Figures --- p.57-62

Wing-Keung Sim. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 109-114). / Abstracts in English and Chinese. / Abstract --- p.2 / 摘要 --- p.3 / Acknowledgements --- p.4 / Contents --- p.5 / List of Figures --- p.8 / List of Tables --- p.9 / Introductions --- p.10 / Chapter 1.1 --- Motivation & Aims --- p.10 / Chapter 1.2 --- Contributions --- p.11 / Chapter 1.3 --- Structure of Thesis --- p.11 / Electrophysiological Spike Discrimination --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Cellular Physiology --- p.13 / Chapter 2.2.1 --- Action Potential --- p.13 / Chapter 2.2.2 --- Recording of Spikes Activities --- p.15 / Chapter 2.2.3 --- Demultiplexing of Multi-Neuron Recordings --- p.17 / Chapter 2.3 --- Application of Clustering for Mixed Spikes Train Separation --- p.17 / Chapter 2.3.1 --- Design Principles for Spike Discrimination Procedures --- p.17 / Chapter 2.3.2 --- Clustering Analysis --- p.18 / Chapter 2.3.3 --- Comparison of Clustering Techniques --- p.19 / Chapter 2.4 --- Literature Review --- p.19 / Chapter 2.4.1 --- Template Spike Matching --- p.19 / Chapter 2.4.2 --- Reduced Feature Matching --- p.20 / Chapter 2.4.3 --- Artificial Neural Networks --- p.21 / Chapter 2.4.4 --- Hardware Implementation --- p.21 / Chapter 2.5 --- Summary --- p.22 / Correlation of Perceived Headphone Sound Quality with Physical Parameters --- p.23 / Chapter 3.1 --- Introduction --- p.23 / Chapter 3.2 --- Sound Quality Evaluation --- p.23 / Chapter 3.3 --- Headphone Characterization --- p.26 / Chapter 3.3.1 --- Frequency Response --- p.26 / Chapter 3.3.2 --- Harmonic Distortion --- p.26 / Chapter 3.3.3 --- Voice-Coil Driver Parameters --- p.27 / Chapter 3.4 --- Statistical Correlation Measurement --- p.29 / Chapter 3.4.1 --- Correlation Coefficient --- p.29 / Chapter 3.4.2 --- t Test for Correlation Coefficients --- p.30 / Chapter 3.5 --- Summary --- p.31 / Algorithms --- p.32 / Chapter 4.1 --- Introduction --- p.32 / Chapter 4.2 --- Principal Component Analysis --- p.32 / Chapter 4.2.1 --- Dimensionality Reduction --- p.32 / Chapter 4.2.2 --- PCA Transformation --- p.33 / Chapter 4.2.3 --- PCA Implementation --- p.36 / Chapter 4.3 --- Traditional Clustering Methods --- p.37 / Chapter 4.3.1 --- Online Template Matching (TM) --- p.37 / Chapter 4.3.2 --- Online Template Matching Implementation --- p.40 / Chapter 4.3.3 --- K-Means Clustering --- p.41 / Chapter 4.3.4 --- K-Means Clustering Implementation --- p.44 / Chapter 4.4 --- Unsupervised Neural Learning --- p.45 / Chapter 4.4.1 --- Neural Network Basics --- p.45 / Chapter 4.4.2 --- Artificial Neural Network Model --- p.46 / Chapter 4.4.3 --- Simple Competitive Learning (SCL) --- p.47 / Chapter 4.4.4 --- SCL Implementation --- p.49 / Chapter 4.4.5 --- Adaptive Resonance Theory Network (ART). --- p.50 / Chapter 4.4.6 --- ART2 Implementation --- p.53 / Chapter 4.6 --- Summary --- p.55 / Experimental Design --- p.57 / Chapter 5.1 --- Introduction --- p.57 / Chapter 5.2 --- Electrophysiological Spike Discrimination --- p.57 / Chapter 5.2.1 --- Experimental Design --- p.57 / Chapter 5.2.2 --- Extracellular Recordings --- p.58 / Chapter 5.2.3 --- PCA Feature Extraction --- p.59 / Chapter 5.2.4 --- Clustering Analysis --- p.59 / Chapter 5.3 --- Correlation of Headphone Sound Quality with physical Parameters --- p.61 / Chapter 5.3.1 --- Experimental Design --- p.61 / Chapter 5.3.2 --- Frequency Response Clustering --- p.62 / Chapter 5.3.3 --- Additional Parameters Measurement --- p.68 / Chapter 5.3.4 --- Listening Tests --- p.68 / Chapter 5.3.5 --- Confirmation Test --- p.69 / Chapter 5.4 --- Summary --- p.70 / Results --- p.71 / Chapter 6.1 --- Introduction --- p.71 / Chapter 6.2 --- Electrophysiological Spike Discrimination: A Comparison of Methods --- p.71 / Chapter 6.2.1 --- Clustering Labeled Spike Data --- p.72 / Chapter 6.2.2 --- Clustering of Unlabeled Data --- p.78 / Chapter 6.2.3 --- Remarks --- p.84 / Chapter 6.3 --- Headphone Sound Quality Control --- p.89 / Chapter 6.3.1 --- Headphones Frequency Response Clustering --- p.89 / Chapter 6.3.2 --- Listening Tests --- p.90 / Chapter 6.3.3 --- Correlation with Measured Parameters --- p.90 / Chapter 6.3.4 --- Confirmation Listening Test --- p.92 / Chapter 6.4 --- Summary --- p.93 / Conclusions --- p.97 / Chapter 7.1 --- Future Work --- p.98 / Chapter 7.1.1 --- Clustering Analysis --- p.98 / Chapter 7.1.2 --- Potential Applications of Clustering Analysis --- p.99 / Chapter 7.2 --- Closing Remarks --- p.100 / Appendix --- p.101 / Chapter A.1 --- Tables of Experimental Results: (Spike Discrimination) --- p.101 / Chapter A.2 --- Tables of Experimental Results: (Headphones Measurement) --- p.104 / Bibliography --- p.109 / Publications --- p.114

This study served to further investigate learning and memory, and to offer a potential tool to support educational interventions. More specifically, this was accomplished by an investigation of the physiologic changes in the brain that occurred while students learned medical anatomy. A group of 29 students taking the Gross Anatomy course at Boston University School of Medicine participated in the study. Testing occurred in two sessions: prior to the course and at the completion of the course. For each session, scalp EEG was recorded while participants were shown 176 anatomical terms (132 relevant to the course and 44 obscure) and asked to respond with "Can Define", "Familiar", or "Don't Know". Behavioral results indicated a positive correlation between participants' course grades and performance on the experimental tasks. EEG results were analyzed for event-related potential (ERP) components related to two memory components: familiarity and recollection. Results had a number of indications. For Don't Know responses, a stronger early frontal, late parietal, and late frontal effect occurred more so for terms of Session 1 compared to Session 2. For an analysis of just Session 2 data, results indicated increased activity of the early frontal, late parietal, and late frontal effects for Can Define responses only. Session 2 Can Define responses elicited a stronger early frontal ERP, occurring between 300 and 500 milliseconds yet, the most post-retrieval processing and monitoring appeared for Can Define terms of Session 2. Ultimately, we focused on investigating two points: 1) the effect of classroom learning on memory, and 2) the examination of ERPs as a tool to guide education interventions. Specifically, ERPs would potentially indicate markers to predict whether students would retain materials long before behavioral measures indicate these results. This has potential to determine whether long-lasting or transient learning will occur; as well as the potential to support early intervention strategies for not just students, but also individuals with learning disabilities or memory impairments.