680 research outputs found
Complex singularities and PDEs
In this paper we give a review on the computational methods used to
characterize the complex singularities developed by some relevant PDEs. We
begin by reviewing the singularity tracking method based on the analysis of the
Fourier spectrum. We then introduce other methods generally used to detect the
hidden singularities. In particular we show some applications of the Pad\'e
approximation, of the Kida method, and of Borel-Polya method. We apply these
techniques to the study of the singularity formation of some nonlinear
dispersive and dissipative one dimensional PDE of the 2D Prandtl equation, of
the 2D KP equation, and to Navier-Stokes equation for high Reynolds number
incompressible flows in the case of interaction with rigid boundaries
Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions
Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes
equations are considered for the case of the two-dimensional uniform flow past
an impulsively-started circular cylinder. We show how Prandtl's solution
develops a finite time separation singularity. On the other hand Navier-Stokes
solution is characterized by the presence of two kinds of viscous-inviscid
interactions that can be detected by the analysis of the enstrophy and of the
pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
Cooperative particle filtering for tracking ERP subcomponents from multichannel EEG
In this study, we propose a novel method to investigate P300 variability over different trials. The method incorporates spatial correlation between EEG channels to form a cooperative coupled particle filtering method that tracks the P300 subcomponents, P3a and P3b, over trials. Using state space systems, the amplitude, latency, and width of each subcomponent are modeled as the main underlying parameters. With four electrodes, two coupled Rao-Blackwellised particle filter pairs are used to recursively estimate the system state over trials. A number of physiological constraints are also imposed to avoid generating invalid particles in the estimation process. Motivated by the bilateral symmetry of ERPs over the brain, the channels further share their estimates with their neighbors and combine the received information to obtain a more accurate and robust solution. The proposed algorithm is capable of estimating the P300 subcomponents in single trials and outperforms its non-cooperative counterpart
A Human-Centric Metaverse Enabled by Brain-Computer Interface: A Survey
The growing interest in the Metaverse has generated momentum for members of
academia and industry to innovate toward realizing the Metaverse world. The
Metaverse is a unique, continuous, and shared virtual world where humans embody
a digital form within an online platform. Through a digital avatar, Metaverse
users should have a perceptual presence within the environment and can interact
and control the virtual world around them. Thus, a human-centric design is a
crucial element of the Metaverse. The human users are not only the central
entity but also the source of multi-sensory data that can be used to enrich the
Metaverse ecosystem. In this survey, we study the potential applications of
Brain-Computer Interface (BCI) technologies that can enhance the experience of
Metaverse users. By directly communicating with the human brain, the most
complex organ in the human body, BCI technologies hold the potential for the
most intuitive human-machine system operating at the speed of thought. BCI
technologies can enable various innovative applications for the Metaverse
through this neural pathway, such as user cognitive state monitoring, digital
avatar control, virtual interactions, and imagined speech communications. This
survey first outlines the fundamental background of the Metaverse and BCI
technologies. We then discuss the current challenges of the Metaverse that can
potentially be addressed by BCI, such as motion sickness when users experience
virtual environments or the negative emotional states of users in immersive
virtual applications. After that, we propose and discuss a new research
direction called Human Digital Twin, in which digital twins can create an
intelligent and interactable avatar from the user's brain signals. We also
present the challenges and potential solutions in synchronizing and
communicating between virtual and physical entities in the Metaverse
Understanding minds in real-world environments : toward a mobile cognition approach
This work is supported by a scholarship from the University of Stirling and a research grant from SINAPSE (Scottish Imaging Network: A Platform for Scientific Excellence).There is a growing body of evidence that important aspects of human cognition have been marginalized, or overlooked, by traditional cognitive science. In particular, the use of laboratory-based experiments in which stimuli are artificial, and response options are fixed, inevitably results in findings that are less ecologically valid in relation to real-world behavior. In the present review we highlight the opportunities provided by a range of new mobile technologies that allow traditionally lab-bound measurements to now be collected during natural interactions with the world. We begin by outlining the theoretical support that mobile approaches receive from the development of embodied accounts of cognition, and we review the widening evidence that illustrates the importance of examining cognitive processes in their context. As we acknowledge, in practice, the development of mobile approaches brings with it fresh challenges, and will undoubtedly require innovation in paradigm design and analysis. If successful, however, the mobile cognition approach will offer novel insights in a range of areas, including understanding the cognitive processes underlying navigation through space and the role of attention during natural behavior. We argue that the development of real-world mobile cognition offers both increased ecological validity, and the opportunity to examine the interactions between perception, cognition and action—rather than examining each in isolation.Publisher PDFPeer reviewe
Understanding Minds in Real-World Environments: Toward a Mobile Cognition Approach
There is a growing body of evidence that important aspects of human cognition have been marginalized, or overlooked, by traditional cognitive science. In particular, the use of laboratory-based experiments in which stimuli are artificial, and response options are fixed, inevitably results in findings that are less ecologically valid in relation to real-world behavior. In the present review we highlight the opportunities provided by a range of new mobile technologies that allow traditionally lab-bound measurements to now be collected during natural interactions with the world. We begin by outlining the theoretical support that mobile approaches receive from the development of embodied accounts of cognition, and we review the widening evidence that illustrates the importance of examining cognitive processes in their context. As we acknowledge, in practice, the development of mobile approaches brings with it fresh challenges, and will undoubtedly require innovation in paradigm design and analysis. If successful, however, the mobile cognition approach will offer novel insights in a range of areas, including understanding the cognitive processes underlying navigation through space and the role of attention during natural behavior. We argue that the development of real-world mobile cognition offers both increased ecological validity, and the opportunity to examine the interactions between perception, cognition and action—rather than examining each in isolation
Enhancing brain-computer interfacing through advanced independent component analysis techniques
A Brain-computer interface (BCI) is a direct communication system between a brain
and an external device in which messages or commands sent by an individual do not
pass through the brain’s normal output pathways but is detected through brain signals.
Some severe motor impairments, such as Amyothrophic Lateral Sclerosis, head
trauma, spinal injuries and other diseases may cause the patients to lose their muscle
control and become unable to communicate with the outside environment. Currently
no effective cure or treatment has yet been found for these diseases. Therefore using a
BCI system to rebuild the communication pathway becomes a possible alternative
solution. Among different types of BCIs, an electroencephalogram (EEG) based BCI
is becoming a popular system due to EEG’s fine temporal resolution, ease of use,
portability and low set-up cost. However EEG’s susceptibility to noise is a major
issue to develop a robust BCI. Signal processing techniques such as coherent
averaging, filtering, FFT and AR modelling, etc. are used to reduce the noise and
extract components of interest. However these methods process the data on the
observed mixture domain which mixes components of interest and noise. Such a
limitation means that extracted EEG signals possibly still contain the noise residue or
coarsely that the removed noise also contains part of EEG signals embedded.
Independent Component Analysis (ICA), a Blind Source Separation (BSS)
technique, is able to extract relevant information within noisy signals and separate the
fundamental sources into the independent components (ICs). The most common
assumption of ICA method is that the source signals are unknown and statistically
independent. Through this assumption, ICA is able to recover the source signals.
Since the ICA concepts appeared in the fields of neural networks and signal
processing in the 1980s, many ICA applications in telecommunications, biomedical
data analysis, feature extraction, speech separation, time-series analysis and data
mining have been reported in the literature. In this thesis several ICA techniques are
proposed to optimize two major issues for BCI applications: reducing the recording
time needed in order to speed up the signal processing and reducing the number of
recording channels whilst improving the final classification performance or at least
with it remaining the same as the current performance. These will make BCI a more
practical prospect for everyday use.
This thesis first defines BCI and the diverse BCI models based on different
control patterns. After the general idea of ICA is introduced along with some
modifications to ICA, several new ICA approaches are proposed. The practical work
in this thesis starts with the preliminary analyses on the Southampton BCI pilot
datasets starting with basic and then advanced signal processing techniques. The
proposed ICA techniques are then presented using a multi-channel event related
potential (ERP) based BCI. Next, the ICA algorithm is applied to a multi-channel
spontaneous activity based BCI. The final ICA approach aims to examine the
possibility of using ICA based on just one or a few channel recordings on an ERP
based BCI.
The novel ICA approaches for BCI systems presented in this thesis show that ICA
is able to accurately and repeatedly extract the relevant information buried within
noisy signals and the signal quality is enhanced so that even a simple classifier can
achieve good classification accuracy. In the ERP based BCI application, after multichannel
ICA the data just applied to eight averages/epochs can achieve 83.9%
classification accuracy whilst the data by coherent averaging can reach only 32.3%
accuracy. In the spontaneous activity based BCI, the use of the multi-channel ICA
algorithm can effectively extract discriminatory information from two types of singletrial
EEG data. The classification accuracy is improved by about 25%, on average,
compared to the performance on the unpreprocessed data. The single channel ICA
technique on the ERP based BCI produces much better results than results using the
lowpass filter. Whereas the appropriate number of averages improves the signal to
noise rate of P300 activities which helps to achieve a better classification. These
advantages will lead to a reliable and practical BCI for use outside of the clinical
laboratory
Estimation of single trial ERPs and EEG phase synchronization with application to mental fatigue
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
A Novel Analysis of Performance Classification and Workload Prediction Using Electroencephalography (EEG) Frequency Data
Across the DOD each task an operator is presented with has some level of difficulty associated with it. This level of difficulty over the course of the task is also known as workload, where the operator is faced with varying levels of workload as he or she attempts to complete the task. The focus of the research presented in this thesis is to determine if those changes in workload can be predicted and to determine if individuals can be classified based on performance in order to prevent an increase in workload that would cause a decline in performance in a given task. Despite many efforts to predict workload and classify individuals with machine learning, the classification and predictive ability of Electroencephalography (EEG) frequency data has not been explored at the individual EEG Frequency band level. In a 711th HPW/RCHP Human Universal Measurement and Assessment Network (HUMAN) Lab study, 14 Subjects were asked to complete two tasks over 16 scenarios, while their physiological data, including EEG frequency data, was recorded to capture the physiological changes their body went through over the course of the experiment. The research presented in this thesis focuses on EEG frequency data, and its ability to predict task performance and changes in workload. Several machine learning techniques are explored in this thesis before a final technique was chosen. This thesis contributes research to the medical and machine learning fields regarding the classification and workload prediction efficacy of EEG frequency data. Specifically, it presents a novel investigation of five EEG frequencies and their individual abilities to predict task performance and workload. It was discovered that using the Gamma EEG frequency and all EEG frequencies combined to predict task performance resulted in average classification accuracies of greater than 90%
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