Gotowa bibliografia na temat „PVI threshold”

The current thesis aims to investigate cascaded processing in visual word recognition by testing the predictions of the Dual Route Cascaded (DRC) model of reading. Despite widespread acceptance of the idea that visual language processing is cascaded, there are circumstances in which such an account is not easily reconciled with the data produced by skilled readers. Recent experiments involving factorial manipulations in reading showed, in particular, additive effects of stimulus quality (i.e., clear vs. degraded stimuli) with letter string length and orthographic neighbourhood size in nonword reading and with word frequency and lexicality when words and nonwords were mixed in the task, thus suggesting that information processing implicated in visual word recognition must be at least partially thresholded. Six experiments have been presented in this thesis: on one hand, a new variable that has a role when the stimuli are degraded – the Total Letter Confusability – has been introduced; on the other hand, the effects due to list composition have been analyzed when the stimuli were degraded in the task. In general, the results obtained suggest a novel interpretation of the additivities previously observed; these findings have been explained within the DRC model which also correctly simulates a significant amount of the data. The empirical evidence collected so far clearly indicates that there is currently no need to assume thresholded processing in the reading system.

This thesis aims at providing a new approach for detecting R-waves in the ECG signal and generating the corresponding R-wave impulses with the delay between the original R-waves and the R-wave impulses being lesser than 100 ms. The algorithm was implemented in Matlab and tested with good results against 90 different ECG recordings from the MIT-BIH database. The Discrete Wavelet Transform (DWT) forms the heart of the algorithm providing a multi-resolution analysis of the ECG signal. The wavelet transform decomposes the ECG signal into frequency scales where the ECG characteristic waveforms are indicated by zero crossings. The adaptive threshold algorithms discussed in this thesis search for valid zero crossings which characterize the R-waves and also remove the Preventricular Contractions (PVC's). The adaptive threshold algorithms allow the decision thresholds to adjust for signal quality changes and eliminate the need for manual adjustments when changing from patient to patient. The delay between the R-waves in the original ECG signal and the R-wave impulses obtained from the algorithm was found to be less than 100 ms.<br>M.S.<br>Department of Electrical and Computer Engineering<br>Engineering and Computer Science<br>Electrical Engineering

Dissertação para obtenção do Grau de Mestre em Engenharia Civil – Perfil de Estruturas<br>The degradation of forests through the impacts of devastating wildfires increase unprotected soils area which consequently favours soil erosion processes. The sediment production is continuously reaching water courses in these areas which may result in important impacts in the flow morphodynamics and hydrodynamics. Sediment overfeeding induces important changes in the turbulent structure of the flow, mainly in momentum fluxes and exchange of momentum and mass between different layers in the flow structure, consequently affecting its ecological features. Coherent structures play an important role on sediment transport and mixing processes which are important in the fluxes that govern the turbulent structure. This study is aimed at evaluating the impacts of sediment transport on flow hydrodynamics, namely on the statistics characterizing coherent movements. In order to accomplish the purposed objective, experimental tests were undertook in laboratorial environment where two-dimensional instantaneous flow velocity fields in both directions, streamwise and vertical, were measured through means of Particle Image Velocimetry (PIV) technique. Two laboratory tests were simulated, consisting on a framework gravel bed with sand matrix and a framework gravel bed with sediment transport imposed at near capacity conditions. For both tests, the quadrant threshold analysis technique was employed and shear stress distribution statistics were analysed and discussed in what concerns their contribution and persistence. The results show that, in the near bed region, mobile bed conditions make sweep events assume a major role in the shear stress production processes. Also, larger events become less frequent in the pythmenic region, comparing with the immobile bed results. The impacts of mobile sediment in the near bed region over the flow structure are analysed and discussed in detail through probability density function distributions, in dimensional and non-dimensional data.<br>Fundação para a Ciência e Tecnologia - PTDC/ECM/099752/2008 ; undo de Europeu de Desenvolvimento Económico e Regional(FEDER) através do Programa Operacional Factores de Competitividade(COMPETE)FCOMP 01 0124 FEDER 009735

No presente trabalho foi avaliado o efeito da microestrutura e da capacidade de suportar carregamento de camadas nitretadas produzidas em aços ferramenta AISI H13 e AISI D2 sobre a aderência e a resistência ao desgaste microabrasivo de revestimentos de TiN-PVD. Em cada um desses aços, foram produzidas camadas nitretadas de diferentes estruturas e espessuras, e foram determinadas experimentalmente as curvas potencial início de formação de camada branca, para a nitretação a 520oC. Para o aço ferramenta AISI H13, o emprego de tempos de pré-tratamento de nitretação mais prolongados ( aproximadamente 11 h) foi necessário para aprofundar a camada nitretada e, conseqüentemente, aumentar a capacidade de suportar carregamento dos revestimentos, evitando a formação de bordas que provocam o lascamento e a escamação das camadas de TiN. Observou-se que esse tipo de falha persiste se a zona de endurecimento for pouco profunda, uma vez que a transição de propriedades mecânicas da camada de TiN para o núcleo não nitretado continua abrupta e a capacidade de suportar carregamento da camada nitretada ainda é baixa. Por outro lado, curtos tempos de nitretação (aproximadamente 42 min.) foram suficientes para aumentar a aderência das camadas de TiN ao aço ferramenta D2, pois o núcleo não nitretado desse aço possui uma capacidade de suportar carregamento razoável. Observou-se que a resistência ao desgaste microabrasivo e a aderência dos revestimentos são prejudicadas com a presença de uma camada preta na interface camada de TiN/camada nitretada. Quando a superfície dos revestimentos é carregada, falhas do tipo “casca de ovo” facilmente ocorrem.<br>In this work, the influence of both the microstructure and the load-bearing capacity of nitrided layers, formed on top of AISI D2 and AISI H13 tool steels, on adhesion and wear resistance of PVD-TiN coatings was studied. The threshold nitriding potential curves for the above mentioned steels and the optimum conditions of the pre-treatments which increased the adhesion as well as the wear resistance of the PVD-TiN were determined experimentally. By using longer nitriding times (about 11 h) and lower nitrogen contents in the gas mixture (about N2-5%vol.), it was possible to minimize the pile-up degree of the TiN/H13 nitrided substrates and, consequently, the occurrence of coatings chipping. This flaw persists when the nitrided layer is thin, due to an abrupt transition of mechanical properties at the TiN coating / steel core interface. Shorter nitriding times (about 42 min.) and lower nitrogen contents (about N2-5%vol.), on the other hand, are sufficient to guarantee a better adhesion of TiN coatings on AISI D2 tool steel, as the core of such steel possesses relatively better load-bearing capacity than the AISI H13 tool steel. The presence of a black layer at the TiN/nitrided layer interface was observed in all coatings deposited over nitrided layers produced above the threshold nitriding potential curves. This layer affects adversely the wear resistance and the adhesion of the TiN coatings. When higher loads are applied on the coated surface, “egg shell” type flaws easily occur.

Ce travail a pour motivation de fournir des données expérimentales importantes pour l'interprétation de la chimie des ionosphère planétaires, en particulier pour le plus grand satellite de Saturne, Titan. On s'intéresse spécifiquement à la réactivité des espèces ioniques excitées. Cette thèse porte, d'une part, sur des expériences de préparation des cations (CH3+ et CF3+) sélectionnés en énergie interne par photoionisation VUV d'espèces neutres, et d'autre part, sur des réactions de cations sélectionnés en énergie interne avec des molécules, O+ avec CH4 et N+(3P) avec C3H4, C3H6 et C3H8.L'étude de la préparation des cations CH3+ et CF3+ sélectionnés dans des niveaux vibrationnels a été réalisée par la technique de coïncidence TPEPICO et du rayonnement VUV synchrotron à SOLEIL. Un spectromètre de type PFI-ZEKE qui permet d'atteindre une résolution de 0.84 cm-1 a été construit pour la réalisation d'études complémentaires avec le rayonnement laser VUV du Centre Laser de l'Université Paris Sud (CLUPS), à Orsay en France.Les expériences pour la détermination de l'influence de l'excitation du cation O+ (2S,2D,2P) sur sa réactivité avec le méthane ont été réalisées par les techniques de coïncidence TPEPICO et de guides d'ions. Elles ont été réalisées sur la ligne de rayonnement VUV DESIRS du synchrotron SOLEIL. Les études pour déterminer la constante de vitesse et les rapports de branchement entre produits des réactions de N+(3P) avec C3H4, C3H6 et C3H8 ont été réalisées par l'utilisation de la technique SIFT sur un montage de type commercial de petite taille à l'Institut de Physico-Chimie J. Heyrovský à Prague, en République Tchèque<br>This work has the motivation to provide experimental data relevant to the interpretation of the chemistry of planetary ionospheres, particularly for the largest satellite of Saturn, Titan. Here we have a particular interest in studying the reactivity of excited ionic species. The first part of this work concerns the production of CH3+ and CF3+ state selected cations by VUV photoionization of neutral species and the second part, the reactions of state selected cations with molecules: O+ with methane and N+(3P) with C3H4, C3H6 and C3H8.The study of the preparation of the CH3+ and CF3+ cations in selected vibrational levels was performed by using the TPEPICO coincidence technique and VUV radiation at the french synchrotron, SOLEIL. A PFI-ZEKE spectrometer, that allowed us to obtain a resolution down to 0.84 cm-1, was constructed to conduct additional studies involving laser VUV radiation at the Laser Center of the University Paris Sud XI, at Orsay in France.Experiments to determine the influence of the O+ (2S,2D,2P) cation excitation on its reaction with methane were performed using the TPEPICO coincidence and the guide ion beam technique. These experiments were performed on the VUV DESIRS beamline at the synchrotron SOLEIL. Rate constants and products branching ratio for the reacion of N+(3P) with C3H4, C3H6 and C3H8 were measured with the SIFT technique in a small commercial apparatus at the Institute of Physical Chemistry J. Heyrovský in Prague, Czech Republic<br>Este trabalho tem como motivação fornecer dados experimentais importantes para a interpretação da química de ionosferas planetárias, em particular para o maior Satélite de Saturno, Titan. Aqui temos o interesse específico pelo estudo de reatividades de espécies iônicas excitadas. Uma parte deste trabalho consistiu de experiências de preparação de cátions (CH3+ e CF3+) selecionados em energia interna via a fotoionização VUV de espécies neutras e de reações de cátions selecionados em massa e energia interna com moléculas (O+ com metano e N+(3P) com C3H4, C3H6 e C3H8).O estudo de preparação dos cátions CH3+ e CF3+ selecionados energia interna (vibracional) foi realizado pela utilização da técnica de coincidência TPEPICO com a radiação VUV do síncrotron SOLEIL. Um espectrômetro do tipo PFI-ZEKE que nos permite obter uma resolução de até 0.84 cm-1 foi construído para a realização de estudos complementares envolvendo a radiação VUV laser do Centro de Laser da Universidade Paris Sud XI, em Orsay na França.Experiências para determinar a influência da excitação do cátion O+ (2S,2D,2P) na produção de íons devido a sua reação com o metano foram realizadas com a utilização da técnica de coincidência TPEPICO e da técnica de guia de íons. Estes experimentos foram realizados na linha de radiação VUV DESIRS do síncrotron SOLEIL. Estudos de determinação de constantes de velocidade e dos produtos formados da reação N+(3P) com C3H4, C3H6 e C3H8 foram realizados a partir da utilização da técnica SIFT em uma montagem do tipo comercial de pequeno porte no Instituto de Físico-Química J. Heyrovský em Praga, na República Checa

This dissertation discusses the use of secret sharing cryptographic protocols for distributing and sharing of secret documents, in our case PDF documents. We discuss the advantages and uses of such a system in the context of collaborative environments. Description of the cryptographic protocol involved and the necessary Public Key Infrastructure (PKI) shall be presented. We also provide an implementation of this framework as a “proof of concept” and fundament the use of a certificate extension as the basis for threshold cryptography. Details of the shared secret distribution protocol and shared secret recovery protocol shall be given as well as the associated technical implementation details. The actual secret sharing algorithm implemented at this stage is based on an existing well known secret sharing scheme that uses polynomial interpolation over a finite field. Finally we conclude with a practical assessment of our prototype.

Recentemente è stato dimostrato che la Stimolazione Magnetica Transcranica (TMS), applicata anche ad aree diverse da V1, può generare fosfeni. In particolare, sono stati riportati fosfeni in seguito alla stimolazione del Solco Intraparietale (IPS). Tuttavia, non è stato ancora chiarito se i fosfeni parietali siano generati direttamente dalla corteccia parietale indipendentemente dal contributo delle aree occipitali. In primo luogo, è stato svolto un esperimento per confrontare i più comuni metodi di misurazione della soglia di detezione dei fosfeni, dato che la stessa rappresenta il cuore del mio progetto di dottorato. Nello specifico, sono stati misurati il metodo degli stimoli costanti (MOCS), il “Modify Binary Search” (MOBS), ed il “Rapid Estimation of Phosphene Threshold” (REPT) in 17 partecipanti. I dati ottenuti suggeriscono che il MOCS sia il metodo più stabile da utilizzare nei successivi esperimenti: nonostante la sua lunghezza è risultato essere consistente nelle somministrazioni consecutive riportando soglie invariate indipendentemente dal numero di somministrazioni. Il MOBS è risultato invece altamente variabile, mentre il REPT è meno affidabile del MOCS, rimanendo comunque affidabile indipendente dal numero di somministrazioni. Il secondo esperimento si proponeva di descrivere sistematicamente le caratteristiche dei fosfeni parietali in modo da trovare eventuali differenze con i fosfeni classicamente evocati in occipitale in termini di soglia di detezione, eccentricità, grandezza, vividezza e luminosità. I siti di stimolazione sono stati identificati funzionalmente attorno a P3 e O1 e il metodo degli stimoli costanti è stato utilizzato per determinare la soglia dei fosfeni. Ai soggetti è stato anche richiesto di disegnare i fosfeni alla fine della procedura di soglia per determinare eccentricità e grandezza e di stimare vividezza e luminosità delle percezioni evocate. I risultati hanno mostrato una soglia più alta per i fosfeni in parietale (72.4%) rispetto a quelli evocati da stimolazione occipitale (63.1%). Inoltre, le due curve psicofisiche dei due tipi di fosfeni hanno mostrano una diversa forma riportando valori che correlano solo al 50% delle rispettive curve. Luminosità ed eccentricità sono poi risultate essere modulate dal sito di stimolazione, ottenendo rispettivamente, in seguito a stimolazione parietale, fosfeni meno luminosi (e più difficili da percepire) e stabili nella posizione indipendentemente dall’intensità di stimolazione, contrariamente a quanto avviene con i fosfeni in occipitale. Questo dato è probabilmente dovuto ad una peggiore organizzazione retinotopica dello spazio nella regione del solco intraparietale. Dato che l’attivazione di V1 è ritenuta necessaria nella percezione di fosfeni, la possibilità che V1 sia implicata nei fosfeni parietali non può essere totalmente rifiutata con i dati del secondo esperimento. Pertanto, è stata testata una paziente affetta da emianopsia omonima, la cui area visiva primaria danneggiata non mostrava alcuna attività rimanente, per indagare il ruolo del solco intraparietale nell’esperienza visiva cosciente. La paziente ha riportato fosfeni del tutto simili a quelli evocati nell’emisfero sano in seguito a stimolazione parietale dell’emisfero ipsilaterale la lesione occipitale. Inoltre la soglia riportata non è risultata differente da quella ottenuta nel lobo parietale sui soggetti sani. Infine, lo scopo dell’ultimo esperimento era di identificare il network corticale attivato nell’induzione di fosfeni da lobo parietale. In particolare la percezione dei fosfeni parietali è stata esplorata usando la combinazione simultanea di due diverse tecniche: TMS e fast optical imaging (event-related optical signal – EROS), capace di offrire una buona risoluzione spaziale unita ad un’ottima capacità di risoluzione temporale. I dati preliminari ottenuti da cinque partecipanti hanno rivelato pattern di attivazione diversi in base alla presenza o assenza di percezione del fosfene. Tuttavia, poiché molte delle attivazioni evidenziate sono di segno negativo, questi dati risultano di non facile interpretazione e trarre conclusioni certe risulta impossibile prima di un allargamento del campione. Concludendo, questi risultati, valutati insieme a precedenti evidenze sperimentali, sostengono l’ipotesi di un lobo parietale capace di generare esperienze visive coscienti, indipendentemente dalle aree visive primarie, e andando dunque contro le teorie che teorizzano che V1 sia necessaria per la consapevolezza visiva (Tong, 2003).<br>It has recently been shown that TMS applied to visually responsive areas other than V1 can generate light sensations, called “phosphenes”, in absence of visual stimulation in the environment. In particular, contralateral phosphenes have been obtained by stimulating the intraparietal sulcus. However, a question that still remains open is whether parietal phosphenes are generated by the parietal cortex, independently from the contribution of occipital areas. Since the phosphene threshold represented the heart of my project, a preliminary experiment comparing the most common thresholding methods was carried out in order to assess which methods was the most reliable. We thus tested the “method of constant stimuli” (MOCS), the “Modify Binary Search” (MOBS) and the “Rapid Estimation of Phosphene Threshold” (REPT) in seventeen participants. Each of the three methods was repeated three times per participant in the same week. The data suggested using MOCS in the next experiments because, despite its length, it resulted to be consistent across days, with thresholds not changing depending on the number of administrations. On the other hand, MOBS appeared highly variable, while REPT tended to be less reliable than MOCS but still remaining unaffected by the number of administrations. The aim of the second experiment was to provide a characterization of parietal phosphenes to find possible differences in terms of phosphene threshold, eccentricity, size, vividness and brightness with those evoked by stimulation of the occipital cortex. Single-pulse magnetic stimulations were administered with a figure-of-eight coil, assisted by a neuronavigational system. Individual stimulation sites were functionally identified around P3 and O1 (10-20 system). To determine phosphene threshold the “method of constant stimuli” was used: randomly intermixed intensities were employed (ranging from 45% to 90%) and twenty stimulations were given for each output intensity. Subjects were also requested to draw the phosphenes as to obtain eccentricity and size and to rate vividness and brightness of evoked perceptions. Fourteen subjects participated in the study. Results showed that the threshold was reliably lower for occipital lobe (63.1% of maximum stimulator output, MSO) than for parietal lobe (72.4% MSO) TMS stimulation and that the two psychophysical curves had a significantly different shape, with correlating values only at the 50% threshold. In addition, brightness and eccentricity were modulated by the site of stimulation, respectively obtaining less bright phosphenes (and thus more difficult to perceive) following parietal stimulation and no changes in the location of parietal phosphenes by changing the intensity of stimulation, contrary to what happened for the occipital phosphenes. This was probably due to the coarser retinotopic organization of space within the parietal cortex. Given that the activation of V1 is generally thought to be involved in conscious perception of phosphenes, the possibility that V1 was implicated in parietal phosphenes could not be totally dismissed with the second experiment. Therefore, a hemianopic patient, who showed no residual activity in her left V1, was tested to further investigate the role of intraparietal sulcus in visual conscious experience. She crucially reported parietal phosphenes (broadly similar to those evoked in the intact hemisphere and in sighted individuals) when TMS was applied over the damaged hemisphere (P3), in absence of V1. Additionally, her threshold values were not very different from those of healthy participants. Finally, we sought to identify the cortical neural network activated while inducing phosphenes with parietal TMS. In particular, parietal phosphene perception was explored using a simultaneous combination of TMS and a fast optical imaging tool (event-related optical signal – EROS), which offer a good spatial resolution in conjunction with the ability to map out the time course of feed-forward and feedback processes. The phosphene threshold value was employed to compare phosphene awareness to no phosphene awareness under identical stimulation parameters and to investigate which regions critically determined the parietal phosphene perception. Preliminary data from five participants seemed to reveal different activation patterns depending on the presence/absence of phosphenes but, since a lot of negative activations were highlighted, these data were not easy to be interpreted, as often happens with fMRI data. Therefore, the current sample needs to be enlarged and more data to be collected before any serious inferences can be drawn. In sum, these findings, along with previous evidence, corroborated the hypothesis that the parietal lobe is able to generate conscious visual experience, independently from early visual areas, and that parietal phosphenes may have a different neural basis from those elicited in occipital lobe. Such a result, therefore, goes against theories suggesting that primary visual area is necessary for awareness (Tong, 2003).