La materia di Elena e del suo doppio: le derive artistiche di un mito

The paper reconsiders some aspects of the ancient legend of Helen, paying particular attention to her divine origin continued in the Spartan and Laconian traditions, which were collected and elaborated by the poet Stesichorus in two different versions of his Palinodia. Here he said that Proteus kept Helen in Aegypt giving to Paris / Alexander an eidôlon of Helen in her substitution. The author wonders about the matter of this eidôlon. The ‘drift’ of this myth is then considered in relationship with the history of visual arts, that seems to have been influenced by the fame of Helen’s beauty from Parrasios and Zeuxis’s time until modern age, in strict connections with its literary afterlife.&nbsp

Sistemas de cogeração baseados em células-combustível aplicados em hospitais

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica.Cogeração é a produção simultânea de energia eletromecânica e térmica, a partir de uma mesma fonte de energia primária. No presente trabalho são propostos e analisados sistemas de cogeração a gás natural aplicados no setor hospitalar em um contexto de Conservação de Energia. No Brasil, nesse momento em particular, a importância desse contexto é clara, devido à crise de suprimento de energia elétrica cujas principais causas são: (i) ausência de uma política energética capaz de atender ao alto crescimento da atividade industrial dos últimos anos; (ii) estiagem prolongada, uma vez que aproximadamente 90% da energia elétrica produzida no país vem de grandes hidrelétricas; (iii) baixa capacidade do sistema de distribuição integrado. Além disso, conservar energia traz reflexos diretos sobre a diminuição de impactos sociais e ambientais advindos da produção de energia elétrica, sejam devidos à emissão de gases poluentes em termelétricas ou devidos à formação de grandes reservatórios das hidrelétricas. Os sistemas de cogeração analisados são baseados em três tipos diferentes de células-combustível, visando avaliar e comparar os respectivos desempenhos energéticos, exergéticos e econômicos, além das emissões de CO2. Células-combustível são unidades que convertem diretamente a energia química de um combustível em eletricidade, num processo eletroquímico que não tem relação com a limitação imposta pela eficiência de Carnot. Assim, a eficiência das células-combustível é comparativamente mais alta do que um ciclo termodinâmico convencional de geração de energia eletromecânica - por exemplo, o ciclo de Rankine - e atinge valores em torno de 45%. Simulações numéricas são realizadas para a célula-combustível e para diferentes sistemas de cogeração, visando determinar da viabilidade técnica, econômica e do impacto ambiental decorrente da emissão de CO2. Os resultados das simulações mostram um desempenho energético, exergético e ambiental satisfatório. De um modo geral, todos os sistemas de cogeração propostos apresentam boa perspectiva de viabilização, dependendo do cenário econômico considerado, conforme resultados obtidos de análises de sensibilidade da tarifa de gás natural, tarifa de eletricidade, valor de excedente e taxas verdes sobre a taxa interna de retorno e o prazo de retorno de investimento

Sistemas baseados em conhecimento para projeto de plantas de cogeração a gás natural

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-graduaçao em Engenharia MecânicaCogeração é definida como a produção simultânea de energia eletromecânica e energia térmica útil a partir de uma mesma fonte energética, permitindo assim que a energia contida no combustível seja utilizada de modo mais eficiente e racional do que a geração independente de energia elétrica e calor. Conseqüentemente, tem um forte apelo tanto do ponto de vista de eficiência, devido principalmente aos custos de ombustíveis e impactos ambientais, como do ponto de vista de geração distribuída de energia, já que, dada a proximidade entre a planta e o local de consumo, dispensam-se subestações e linhas de transmissão de alta tensão. O projeto de uma planta de cogeração é um problema de síntese sujeito fundamentalmente a restrições termodinâmicas. Inclui a alocação e dimensionamento de componentes diversos, de modo a satisfazer as demandas de energia elétrica e de calor útil. Apesar de sua complexidade, é um problema que é resolvido de modo robusto por especialistas, o que sugere o uso de ferramentas de inteligência artificial (IA) para resolvê-lo computacionalmente, tais como Sistemas Especialistas (SE) e Raciocínio Baseado em Casos (RBC). No presente trabalho são desenvolvidos dois protótipos de sistemas computacionais inteligentes, baseados nas técnicas SE e RBC, respectivamente. Os protótipos são utilizados para apoio às fases de projeto conceitual e preliminar de plantas de cogeração, considerando cargas de energia elétrica, vapor saturado e água gelada como requisitos de projeto. Os protótipos apresentam características que não são encontradas em nenhum sistema computacional para esse domínio disponível até o momento, tais como explicação da solução (no protótipo SE) e aprendizado a partir da própria experiência (no protótipo RBC). A combinação das duas técnicas em um único protótipo é também discutida. Finalmente, o uso dos protótipos é demonstrado através da resolução de alguns casos selecionados, sendo que cada um representa um diferente conjunto de requisitos de projeto. Cogeneration is defined as the simultaneous production of power and useful thermal energy from the same energy source, so that the fuel energy is used in a more rational and efficient way when compared to the separated production of power and heat. Thus, it has a strong appeal from both an efficiency point of view (due mainly to the fuel costs and environmental impact) and a distributed generation point of view, for the proximity between the plant and the user makes substations and transmission lines superfluous. The design of a cogeneration plant is a synthesis problem subject to thermodynamic constraints. It includes allocation and sizing of several components, such that power and useful heat demands must be satisfied. Despite its complexity, it is a problem that is robustly solved by human experts, which suggests the use of artificial intelligence (AI) tools to solve it computationally. Well known AI tools are Expert Systems (ES) and Case-Based Reasoning (CBR). In this work, two intelligent computational prototypes are developed, based on ES and CBR techniques, respectively. The prototypes are used to support the conceptual and preliminary phases of the cogeneration plant design, considering power, saturated steam and chilled water as design requirements. The prototypes present characteristics # such as solution explanation (ES prototype) and learning from previous experiences (CBR prototype) # that are not known in any of the available computational systems in this engineering domain. The combination of both ES and CBR techniques in a single prototype is discussed as well. Finally, the prototype use is shown by solving some selected cases, each case representing a different set of design requirements

Three-dimensional reconstruction and visualization of the cerebral cortex in primates

We present a prototype interactive application for the direct analysis in three dimensions of the cerebral cortex in primates. The paper provides an overview of the current prototype system and presents the techniques used for reconstructing the cortex shape from data derived from histological sections as well as for rendering it at interactive rates. Results are evaluated by discussing the analysis of the right hemisphere of the brain of a macaque monkey used for neuroanatomical tract-tracing experiments.147-15

An Additional Motor-Related Field in the Lateral Frontal Cortex of Squirrel Monkeys

Our earlier efforts to document the cortical connections of the ventral premotor cortex (PMv) revealed dense connections with a field rostral and lateral to PMv, an area we called the frontal rostral field (FR). Here, we present data collected in FR using electrophysiological and anatomical methods. Results show that FR contains an isolated motor representation of the forelimb that can be differentiated from PMv based on current thresholds and latencies to evoke electromyographic activity using intracortical microstimulation techniques. In addition, FR has a different pattern of cortical connections compared with PMv. Together, these data support that FR is an additional, previously undescribed motor-related area in squirrel monkeys

Interregional compensatory mechanisms of motor functioning in progressing preclinical neurodegeneration.

Understanding brain reserve in preclinical stages of neurodegenerative disorders allows determination of which brain regions contribute to normal functioning despite accelerated neuronal loss. Besides the recruitment of additional regions, a reorganisation and shift of relevance between normally engaged regions are a suggested key mechanism. Thus, network analysis methods seem critical for investigation of changes in directed causal interactions between such candidate brain regions. To identify core compensatory regions, fifteen preclinical patients carrying the genetic mutation leading to Huntington's disease and twelve controls underwent fMRI scanning. They accomplished an auditory paced finger sequence tapping task, which challenged cognitive as well as executive aspects of motor functioning by varying speed and complexity of movements. To investigate causal interactions among brain regions a single Dynamic Causal Model (DCM) was constructed and fitted to the data from each subject. The DCM parameters were analysed using statistical methods to assess group differences in connectivity, and the relationship between connectivity patterns and predicted years to clinical onset was assessed in gene carriers. In preclinical patients, we found indications for neural reserve mechanisms predominantly driven by bilateral dorsal premotor cortex, which increasingly activated superior parietal cortices the closer individuals were to estimated clinical onset. This compensatory mechanism was restricted to complex movements characterised by high cognitive demand. Additionally, we identified task-induced connectivity changes in both groups of subjects towards pre- and caudal supplementary motor areas, which were linked to either faster or more complex task conditions. Interestingly, coupling of dorsal premotor cortex and supplementary motor area was more negative in controls compared to gene mutation carriers. Furthermore, changes in the connectivity pattern of gene carriers allowed prediction of the years to estimated disease onset in individuals. Our study characterises the connectivity pattern of core cortical regions maintaining motor function in relation to varying task demand. We identified connections of bilateral dorsal premotor cortex as critical for compensation as well as task-dependent recruitment of pre- and caudal supplementary motor area. The latter finding nicely mirrors a previously published general linear model-based analysis of the same data. Such knowledge about disease specific inter-regional effective connectivity may help identify foci for interventions based on transcranial magnetic stimulation designed to stimulate functioning and also to predict their impact on other regions in motor-associated networks

Motor Properties of Peripersonal Space in Humans

Background: A stimulus approaching the body requires fast processing and appropriate motor reactions. In monkeys, fronto-parietal networks are involved both in integrating multisensory information within a limited space surrounding the body (i.e. peripersonal space, PPS) and in action planning and execution, suggesting an overlap between sensory representations of space and motor representations of action. In the present study we investigate whether these overlapping representations also exist in the human brain. Methodology/Principal Findings: We recorded from hand muscles motor-evoked potentials (MEPs) induced by single-pulse of transcranial magnetic stimulation (TMS) after presenting an auditory stimulus either near the hand or in far space. MEPs recorded 50 ms after the near-sound onset were enhanced compared to MEPs evoked after far sounds. This near-far modulation faded at longer inter-stimulus intervals, and reversed completely for MEPs recorded 300 ms after the sound onset. At that time point, higher motor excitability was associated with far sounds. Such auditory modulation of hand motor representation was specific to a hand-centred, and not a body-centred reference frame. Conclusions/Significance: This pattern of corticospinal modulation highlights the relation between space and time in the PPS representation: an early facilitation for near stimuli may reflect immediate motor preparation, whereas, at later time intervals, motor preparation relates to distant stimuli potentially approaching the body

Activity in ventral premotor cortex is modulated by vision of own hand in action

Parietal and premotor cortices of the macaque monkey contain distinct populations of neurons which, in addition to their motor discharge, are also activated by visual stimulation. Among these visuomotor neurons, a population of grasping neurons located in the anterior intraparietal area (AIP) shows discharge modulation when the own hand is visible during object grasping. Given the dense connections between AIP and inferior frontal regions, we aimed at investigating whether two hand-related frontal areas, ventral premotor area F5 and primary motor cortex (area F1), contain neurons with similar properties. Two macaques were involved in a grasping task executed in various light/dark conditions in which the to-be-grasped object was kept visible by a dim retro-illumination. Approximately 62% of F5 and 55% of F1 motor neurons showed light/dark modulations. To better isolate the effect of hand-related visual input, we introduced two further conditions characterized by kinematic features similar to the dark condition. The scene was briefly illuminated (i) during hand preshaping (pre-touch flash, PT-flash) and (ii) at hand-object contact (touch flash, T-flash). Approximately 48% of F5 and 44% of F1 motor neurons showed a flash-related modulation. Considering flash-modulated neurons in the two flash conditions, ∼40% from F5 and ∼52% from F1 showed stronger activity in PT- than T-flash (PT-flash-dominant), whereas ∼60% from F5 and ∼48% from F1 showed stronger activity in T- than PT-flash (T-flash-dominant). Furthermore, F5, but not F1, flash-dominant neurons were characterized by a higher peak and mean discharge in the preferred flash condition as compared to light and dark conditions. Still considering F5, the distribution of the time of peak discharge was similar in light and preferred flash conditions. This study shows that the frontal cortex contains neurons, previously classified as motor neurons, which are sensitive to the observation of meaningful phases of the own grasping action. We conclude by discussing the possible functional role of these populations

The Observation and Execution of Actions Share Motor and Somatosensory Voxels in all Tested Subjects: Single-Subject Analyses of Unsmoothed fMRI Data

Many neuroimaging studies of the mirror neuron system (MNS) examine if certain voxels in the brain are shared between action observation and execution (shared voxels, sVx). Unfortunately, finding sVx in standard group analyses is not a guarantee that sVx exist in individual subjects. Using unsmoothed, single-subject analyses we show sVx can be reliably found in all 16 investigated participants. Beside the ventral premotor (BA6/44) and inferior parietal cortex (area PF) where mirror neurons (MNs) have been found in monkeys, sVx were reliably observed in dorsal premotor, supplementary motor, middle cingulate, somatosensory (BA3, BA2, and OP1), superior parietal, middle temporal cortex and cerebellum. For the premotor, somatosensory and parietal areas, sVx were more numerous in the left hemisphere. The hand representation of the primary motor cortex showed a reduced BOLD during hand action observation, possibly preventing undesired overt imitation. This study provides a more detailed description of the location and reliability of sVx and proposes a model that extends the original idea of the MNS to include forward and inverse internal models and motor and sensory simulation, distinguishing the MNS from a more general concept of sVx