The Dynamics of ERP and Hemodynamic Responses at Very Short Stimulus Durations

Complementary non-invasive imaging methods on human subjects such as EEG and fMRI can provide new insights into the functioning of the brain and into neurovascular coupling. Particularly, short stimulus durations rather than commonly used standard durations in fMRI experiments are suitable to study the relationship between electrophysiological and vascular measures because of reduction of non-linearities of the hemodynamic response [1]. In this study, using very short stimulus durations (0.1 ms to 5 ms) and measurements with fMRI and EEG we have found that both N75 of the visual evoked potentials and BOLD signal increase and P100 decrease with stimulus duration. In addition, the BOLD signal poststimulus undershoot also tends to deviate more with stimulus duration. These results allow to shed light on whether and which ERP components correlate well with the BOLD signal

Assentication: User Deauthentication and Lunchtime Attack Mitigation with Seated Posture Biometric

Biometric techniques are often used as an extra security factor in authenticating human users. Numerous biometrics have been proposed and evaluated, each with its own set of benefits and pitfalls. Static biometrics (such as fingerprints) are geared for discrete operation, to identify users, which typically involves some user burden. Meanwhile, behavioral biometrics (such as keystroke dynamics) are well suited for continuous, and sometimes more unobtrusive, operation. One important application domain for biometrics is deauthentication, a means of quickly detecting absence of a previously authenticated user and immediately terminating that user's active secure sessions. Deauthentication is crucial for mitigating so called Lunchtime Attacks, whereby an insider adversary takes over (before any inactivity timeout kicks in) authenticated state of a careless user who walks away from her computer. Motivated primarily by the need for an unobtrusive and continuous biometric to support effective deauthentication, we introduce PoPa, a new hybrid biometric based on a human user's seated posture pattern. PoPa captures a unique combination of physiological and behavioral traits. We describe a low cost fully functioning prototype that involves an office chair instrumented with 16 tiny pressure sensors. We also explore (via user experiments) how PoPa can be used in a typical workplace to provide continuous authentication (and deauthentication) of users. We experimentally assess viability of PoPa in terms of uniqueness by collecting and evaluating posture patterns of a cohort of users. Results show that PoPa exhibits very low false positive, and even lower false negative, rates. In particular, users can be identified with, on average, 91.0% accuracy. Finally, we compare pros and cons of PoPa with those of several prominent biometric based deauthentication techniques

Analysis of topology aggregation techniques for QoS routing

We study and compare topology aggregation techniques used in QoS routing. Topology Aggregation (TA) is defined as a set of techniques that abstract or summarize the state information about the network topology to be exchanged, processed, and maintained by network nodes for routing purposes. Due to scalability, aggregation techniques have been an integral part of some routing protocols. However, TA has not been studied extensively except in a rather limited context. With the continuing growth of the Internet, scalability issues of QoS routing have been gaining importance. Therefore, we survey the current TA techniques, provide methodology to classify, evaluate, and compare their complexities and efficiencies. ©2007 ACM.postprin

Особливості та умови формування властивостей техногенних ґрунтів

This work utilises general numerical magnetic resonance imaging MRI simulations to predict the spatial specificity of the blood oxygenation level-dependent (BOLD) functional MRI (fMRI) signal. A Monte Carlo simulation approach was utilized on a microvascular structure consisting of randomly oriented cylinders representing blood vessels. This framework was employed to numerically investigate the spatial specificity, defined as ratio of pial vessel to microvascular signal, of the spin echo BOLD fMRI signal as a function of field strength, echo time and tissue types [grey matter (GM) and cerebrospinal fluid (CSF), respectively]. Spatial specificity of spin echo BOLD fMRI signal was determined to increase with field strength up to 16 T and with maximal specificity for echo time shorter than tissue T(2). In addition, it was found that, for large pial vessels, the extravascular signal decay could not be described using the oversimplified but nevertheless commonly employed mono-exponential signal decay approximation (MEA). Consequently, a recently proposed model relying on the MEA deviates substantially from our results on the spatial specificity. A refinement of this model is proposed based on an available, more detailed signal description. Finally, the effect of CSF on the spatial specificity was investigated. While a large spatial specificity of the spin echo BOLD fMRI signal is observed if a pial vessel is surrounded by grey matter, this is greatly reduced for a pial vessel situated on a GM/CSF interface, rendering the suppression of pial vessels on the cortex surface unlikely

A realistic vascular model for BOLD signal up to 16.4 T

The blood oxygenation level-dependent (BOLD) signal using functional magnetic resonance imaging (fMRI) is currently the most popular imaging method to study brain function non-invasively. The sensitivity of the BOLD signal to different types of MRI sequences and vessel sizes is currently under investigation [1]. Gradient echo (GRE) sequences are known to be sensitive to larger vessels (venules and veins), whereas spin-echo (SE) sequences are generally more sensitive to smaller vessels (venules and capillaries), especially at high magnetic field strength [2, 3]. However, the widely used single vessel model is only an approximation to the realistic vascular distribution. Realistic vascular models have been proposed by Marques and Bowtell [4] and, recently, by Chen et al.[5]. We herein present a realistic vascular model (RVM) where diffusion is accounted for by a Monte-Carlo random walk

Encaminhamento óptimo do tráfego em redes Triple Play

A Internet é responsável pelo surgimento de um novo paradigma de televisão – IPTV (Televisão sobre IP). Este serviço distingue-se de outros modelos de televisão, pois permite aos utilizadores um elevado grau de interactividade, com um controlo personalizado sobre os conteúdos a que pretende assistir. Possibilita ainda a oferta de um número ilimitado de canais, bem como o acesso a conteúdos de Vídeo on Demand (VoD). O IPTV apresenta diversas funcionalidades suportadas por uma arquitectura complexa e uma rede convergente que serve de integração a serviços de voz, dados e vídeo. A tecnologia IPTV explora ao máximo as características da Internet, com a utilização de mecanismos de Qualidade de Serviço. Surge ainda como uma revolução dentro do panorama televisivo, abrindo portas a novos investimentos por parte das empresas de telecomunicações. A Internet também permite fazer chamadas telefónicas sobre a rede IP. Este serviço é denominado VoIP (Voz sobre IP) e encontra-se em funcionamento já há algum tempo. Desta forma surge a oportunidade de poder oferecer ao consumidor final, um serviço que inclua os serviços de Internet, de VoIP e de IPTV denominado serviço Triple Play. O serviço Triple Play veio obrigar a revisão de toda a rede de transporte de forma a preparar a mesma para suportar este serviço de uma forma eficiente (QoS), resiliente (recuperação de falhas) e optimizado (Engenharia de tráfego). Em redes de telecomunicações, tanto a quebra de uma ligação como a congestão nas redes pode interferir nos serviços oferecidos aos consumidores finais. Mecanismos de sobrevivência são aplicados de forma a garantir a continuidade do serviço mesmo na ocorrência de uma falha. O objectivo desta dissertação é propor uma solução de uma arquitectura de rede capaz de suportar o serviço Triple Play de uma forma eficiente, resiliente e optimizada através de um encaminhamento óptimo ou quase óptimo. No âmbito deste trabalho, é realizada a análise do impacto das estratégias de encaminhamento que garantem a eficiência, sobrevivência e optimização das redes IP existentes, bem como é determinado o número limite de clientes permitido numa situação de pico de uma dada rede. Neste trabalho foram abordados os conceitos de Serviços Triple Play, Redes de Acesso, Redes Núcleo, Qualidade de Serviço, MPLS (Multi-Protocolo Label Switching), Engenharia de Tráfego e Recuperação de falhas. As conclusões obtidas das simulações efectuadas através do simulador de rede NS-2.33 (Network Simulator versão 2.33) serviram para propor a solução da arquitectura de uma rede capaz de suportar o serviço Triple Play de uma forma eficiente, resiliente e optimizada.Orientador: Paulo Nazareno Maia Sampai

Investigating the post-stimulus undershoot of the BOLD signal – A simultaneous fMRI and fNIRS study

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Cortical depth dependent functional responses in humans at 7T: improved specificity with 3D GRASE

Ultra high fields (7T and above) allow functional imaging with high contrast-to-noise ratios and improved spatial resolution. This, along with improved hardware and imaging techniques, allow investigating columnar and laminar functional responses. Using gradient-echo (GE) (T2* weighted) based sequences, layer specific responses have been recorded from human (and animal) primary visual areas. However, their increased sensitivity to large surface veins potentially clouds detecting and interpreting layer specific responses. Conversely, spin-echo (SE) (T2 weighted) sequences are less sensitive to large veins and have been used to map cortical columns in humans. T2 weighted 3D GRASE with inner volume selection provides high isotropic resolution over extended volumes, overcoming some of the many technical limitations of conventional 2D SE-EPI, whereby making layer specific investigations feasible. Further, the demonstration of columnar level specificity with 3D GRASE, despite contributions from both stimulated echoes and conventional T2 contrast, has made it an attractive alternative over 2D SE-EPI. Here, we assess the spatial specificity of cortical depth dependent 3D GRASE functional responses in human V1 and hMT by comparing it to GE responses. In doing so we demonstrate that 3D GRASE is less sensitive to contributions from large veins in superficial layers, while showing increased specificity (functional tuning) throughout the cortex compared to GE

Comparing the emergence of Echinochloa crus- galli populations in different locations. Part I: Variations in emergence timing and behaviour of two populations

Echinochloa crus-galli (L.) P. Beauv. is one of the most important weeds. It is distributed worldwide and has adapted to diverse habitats and climatic conditions. This study aimed to compare the emergence patterns of two populations of E. crus-galli from different environments at 11 locations across Europe and the Middle East. Seeds of the two populations were collected from maize in Italy and from spring barley in Norway and were then buried in soil in autumn 2015. In the spring of 2016, the soil was disturbed around the usual seedbed preparation date in each location and emergence was recorded. The soil was again disturbed a year later and emergence was recorded for a second season. Total emergence, the times of onset, end and to 50% emergence and the period between 25% and 75% of emergence were analysed by two-way ANOVA and principal components analysis. The Italian population showed a higher emergence than the Norwegian population in Southern locations, while the ranking was reversed in Northern locations. In almost all locations, a tendency to emerge earlier was recorded for the Norwegian population, but the periods from 25% to 75% emergence were similar for both populations. Total emergence, and the times of onset and end of emergence seemed to be mainly under genotypic (plus maternal) control, suggesting there were different temperature thresholds for seedling emergence in each population. Conversely, the duration of emergence seemed to be mainly under environmental control. This research confirms the high variability between populations and suggests the need to continue identifying key characteristics for the development of efficient models for seedling emergence in specific climates and/or latitudes.The authors thank all the technicians, students and institutions that have contributed to establishing and maintaining the field experiment. We also thank Dr. Frank Forcella and James Eklund from the USDA‐ARS in Morris (MN) for providing the dataloggers and facilitating the collection of soil temperature data in each location. Our thanks also to the Spanish Ministry of Economy and Competitiveness for funding to Royo‐Esnal through the AGL2017‐83325‐C4‐2‐R; Duzce Üniversitesi, Turkey, for funding to Uludag (Project No: 2015.11.02.375); and the Norwegian Research Funding for Agriculture and the Food Industry and project partners in Research Council of Norway Project no. 267700 for supporting Tørresen in the experiment. Uludag thanks his two graduate students Miss Buyukkurt and Zambak, and Murdoch thanks MSc student, Mr Guangxing Xie, who carried out the germination assays. Finally, the authors are also grateful to the European Weed Research Society for providing funds to enable the working group participants to meet and discuss the collaborative experiment