Characterization of Neuroimage Coupling Between EEG and FMRI Using Within-Subject Joint Independent Component Analysis

The purpose of this dissertation was to apply joint independent component analysis (jICA) to electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to characterize the neuroimage coupling between the two modalities. EEG and fMRI are complimentary imaging techniques which have been used in conjunction to investigate neural activity. Understanding how these two imaging modalities relate to each other not only enables better multimodal analysis, but also has clinical implications as well. In particular, Alzheimer’s, Parkinson’s, hypertension, and ischemic stroke are all known to impact the cerebral blood flow, and by extension alter the relationship between EEG and fMRI. By characterizing the relationship between EEG and fMRI within healthy subjects, it allows for comparison with a diseased population, and may offer ways to detect some of these conditions earlier. The correspondence between fMRI and EEG was first examined, and a methodological approach which was capable of informing to what degree the fMRI and EEG sources corresponded to each other was developed. Once it was certain that the EEG activity observed corresponded to the fMRI activity collected a methodological approach was developed to characterize the coupling between fMRI and EEG. Finally, this dissertation addresses the question of whether the use of jICA to perform this analysis increases the sensitivity to subcortical sources to determine to what degree subcortical sources should be taken into consideration for future studies. This dissertation was the first to propose a way to characterize the relationship between fMRI and EEG signals using blind source separation. Additionally, it was the first to show that jICA significantly improves the detection of subcortical activity, particularly in the case when both physiological noise and a cortical source are present. This new knowledge can be used to design studies to investigate subcortical signals, as well as to begin characterizing the relationship between fMRI and EEG across various task conditions

LAPR: An experimental aircraft pushbroom scanner

A three band Linear Array Pushbroom Radiometer (LAPR) was built and flown on an experimental basis by NASA at the Goddard Space Flight Center. The functional characteristics of the instrument and the methods used to preprocess the data, including radiometric correction, are described. The radiometric sensitivity of the instrument was tested and compared to that of the Thematic Mapper and the Multispectral Scanner. The radiometric correction procedure was evaluated quantitatively, using laboratory testing, and qualitatively, via visual examination of the LAPR test flight imagery. Although effective radiometric correction could not yet be demonstrated via laboratory testing, radiometric distortion did not preclude the visual interpretation or parallel piped classification of the test imagery

Efficient coupling to an optical resonator by exploiting time-reversal symmetry

The interaction of a cavity with an external field is symmetric under time reversal. Thus, coupling to a resonator is most efficient when the incident light is the time reversed version of a free cavity decay, i.e. when it has a rising exponential shape matching the cavity lifetime. For light entering the cavity from only one side, the maximally achievable coupling efficiency is limited by the choice of the cavity mirrors' reflectivities. Such an empty-cavity experiment serves also as a model system for single-photon single-atom absorption dynamics. We present experiments coupling exponentially rising pulses to a cavity system which allows for high coupling efficiencies. The influence of the time constant of the rising exponential is investigated as well as the effect of a finite pulse duration. We demonstrate coupling 94% of the incident TEM00 mode into the resonator.Comment: 7 pages, 5 figure

Académie impériale de l’Opéra: Tannhäuser, Opéra en trois actes, de Richard Wagner

Transcript of ACADÉMIE IMPÉRIALE DE L’OPÉRA: TANNHÄUSER, OPÉRA EN TROIS ACTES, DE RICHARD WAGNER, by Jacques-Léopold Heugel, appearing in LE MÉNESTREL, 17 mars 1861, pp. 121 -123

Classical many-body time crystals

Discrete time crystals are a many-body state of matter where the extensive system's dynamics are slower than the forces acting on it. Nowadays, there is a growing debate regarding the specific properties required to demonstrate such a many-body state, alongside several experimental realizations. In this work, we provide a simple and pedagogical framework by which to obtain many-body time crystals using parametrically coupled resonators. In our analysis, we use classical period-doubling bifurcation theory and present a clear distinction between single-mode time-translation symmetry breaking and a situation where an extensive number of degrees of freedom undergo the transition. We experimentally demonstrate this paradigm using coupled mechanical oscillators, thus providing a clear route for time crystals realizations in real materials.Comment: 23 pages, 5 figures, comments are welcom

Method for Spatial Overlap Estimation of Electroencephalography and Functional Magnetic Resonance Imaging Responses

Background Simultaneous functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) measurements may represent activity from partially divergent neural sources, but this factor is seldom modeled in fMRI-EEG data integration. New method This paper proposes an approach to estimate the spatial overlap between sources of activity measured simultaneously with fMRI and EEG. Following the extraction of task-related activity, the key steps include, 1) distributed source reconstruction of the task-related ERP activity (ERP source model), 2) transformation of fMRI activity to the ERP spatial scale by forward modelling of the scalp potential field distribution and backward source reconstruction (fMRI source simulation), and 3) optimization of fMRI and ERP thresholds to maximize spatial overlap without a priori constraints of coupling (overlap calculation). Results FMRI and ERP responses were recorded simultaneously in 15 subjects performing an auditory oddball task. A high degree of spatial overlap between sources of fMRI and ERP responses (in 9 or more of 15 subjects) was found specifically within temporoparietal areas associated with the task. Areas of non-overlap in fMRI and ERP sources were relatively small and inconsistent across subjects. Comparison with existing method The ERP and fMRI sources estimated with solely jICA overlapped in just 4 of 15 subjects, and strictly in the parietal cortex. Conclusion The study demonstrates that the new fMRI-ERP spatial overlap estimation method provides greater spatiotemporal detail of the cortical dynamics than solely jICA. As such, we propose that it is a superior method for the integration of fMRI and EEG to study brain function

Alterungsverhalten von Li-Ionen-Zellen mit siliziumhaltigen Anoden - chemische und physikalische Untersuchungen

Silizium gewinnt als Anoden-Aktivmaterial für Lithium-Ionen Zellen kontinuierlich an Bedeutung. Vor allem als Teilsubstituent des standardmäßig verwendeten Anoden-Aktivmaterials Graphit wird Silizium bzw. Siliziumoxid bereits heute kommerziell eingesetzt. Der Zusammenhang von Silizium bzw. Siliziumanteil und dessen Einfluss auf das Alterungsverhalten der Zellen wurde für viele Einzelaspekte in der Fachliteratur ausführlich untersucht, allerdings bedingen und beeinflussen sich die einzelnen Alterungseffekte gegenseitig, sodass eine ganzheitliche Untersuchung von Partikel- über Elektroden- bis hin zur Zellebene notwendig ist. Durch ebendiese ganzheitliche Betrachtung konnten in der vorliegenden Arbeit zuvor unbeachtete Wirkzusammenhänge identifiziert und untersucht werden. Es wurde der Zusammenhang unterschiedlicher Alterungseinflüsse mit dem in den Zellen enthaltenen Silizium und der Lebensdauer ebendieser betrachtet. Dazu wurden unterschiedlichste elektrochemische, chemisch-physikalische und mechanische Untersuchungsmethoden an unterschiedlichen Zellformaten und Zelltypen durchgeführt. Zunächst wurde der Einfluss des Siliziumgehalts auf Lade- und Entladekurven, irreversiblen Kapazitätsverlust, Innenwiderstand, Dickenänderung und Alterungsverhalten untersucht. Die betrachteten Zellen wurden mit gleichen Zellparametern (d. h. Aktivmaterialien, Elektrolyten, Separatoren, Flächenkapazitäten, Binderanteilen, Porositäten, etc.) hergestellt. Einzig der SiOx-Anteil in den Anoden wurde variiert. Zunächst fanden systematische Messungen der o. g. Zellparameter an Laborzellen im Halb- und Vollzellformat statt. Mit Hilfe ausführlicher differentieller Spannungsanalysen an Anoden und Kathoden konnte so der Einfluss auf die jeweiligen Aktivmaterialien und deren Alterungsverhalten untersucht werden. Auch unterschiedliche Spannungsfenster und der Einfluss des zur Reaktion verfügbaren Lithiums wurden betrachtet. Im weiteren Verlauf wurden aus den zuvor ausführlich charakterisierten Elektroden mehrlagige Laborpouchzellen hergestellt und unter unterschiedlichen äußeren Drücken über einen ausgedehnten Zeitraum (d. h. viele Vollzyklen) untersucht. Im Verlauf der Langzeitzyklisierung wurden regelmäßig differentielle Spannungsanalysen und Innenwiderstandsbestimmungen durchgeführt, um so den detaillierten Alterungsverlauf abbilden zu können. Am Ende der Langzeituntersuchungen wurden die Zellen geöffnet und ausführliche Post-mortem-Analysen mit Hilfe unterschiedlichster chemisch-physikalischer Analysemethoden durchgeführt. Zuletzt wurden die in den vorherigen Kapiteln erarbeiteten Erkenntnisse auf kommerziell erhältliche, siliziumhaltige Rundzellen angewendet. Nach ausführlicher Charakterisierung der verwendeten Zellen und ihrer Bestandteile, wurden diese in unterschiedlichen Spannungsfenstern gezykelt und untersucht und dabei der Einfluss auf die Zellalterung, d. h. den Kapazitätsverlust und Innenwiderstandsanstieg, aber vor allem auch das Zelldickenwachstum, die Wickelverformung und Materialalterung genau analysiert. So konnten direkte Zusammenhänge der Alterungseinflüsse, hervorgerufen u. a. durch das enthaltene Silizium, gefunden werden, die zu einem Kapazitätsverlust und schließlich zum Zelltod führen

Observation of opto-mechanical multistability in a high Q torsion balance oscillator

We observe the opto-mechanical multistability of a macroscopic torsion balance oscillator. The torsion oscillator forms the moving mirror of a hemi-spherical laser light cavity. When a laser beam is coupled into this cavity, the radiation pressure force of the intra-cavity beam adds to the torsion wire's restoring force, forming an opto-mechanical potential. In the absence of optical damping, up to 23 stable trapping regions were observed due to local light potential minima over a range of 4 micrometer oscillator displacement. Each of these trapping positions exhibits optical spring properties. Hysteresis behavior between neighboring trapping positions is also observed. We discuss the prospect of observing opto-mechanical stochastic resonance, aiming at enhancing the signal-to-noise ratio (SNR) in gravity experiments.Comment: 4 pages, 5 figure