Hamiltonian Hopf bifurcation with symmetry

In this paper we study the appearance of branches of relative periodic orbits in Hamiltonian Hopf bifurcation processes in the presence of compact symmetry groups that do not generically exist in the dissipative framework. The theoretical study is illustrated with several examples.Comment: 35 pages, 3 figure

Graph Signal Processing: Overview, Challenges and Applications

Research in Graph Signal Processing (GSP) aims to develop tools for processing data defined on irregular graph domains. In this paper we first provide an overview of core ideas in GSP and their connection to conventional digital signal processing. We then summarize recent developments in developing basic GSP tools, including methods for sampling, filtering or graph learning. Next, we review progress in several application areas using GSP, including processing and analysis of sensor network data, biological data, and applications to image processing and machine learning. We finish by providing a brief historical perspective to highlight how concepts recently developed in GSP build on top of prior research in other areas.Comment: To appear, Proceedings of the IEE

Plasma Soluble Human Elastin Fragments as an Intra-Aneurysmal Localized Biomarker for Ruptured Intracranial Aneurysm

Background—Fragmentation of the tunica media is a hallmark of intracranial aneurysm formation, often leading to aneurysmal progression and subsequent rupture. The objective of this study is to determine the plasma level of elastin fragments in the lumen of ruptured versus unruptured human intracranial aneurysms. Methods and Results—One hundred consecutive patients with/without ruptured saccular intracranial aneurysms undergoing endovascular coiling or stent-assisted coiling were recruited. Blood samples were collected from the lumen of intracranial aneurysm using a microcatheter. The tip of the microcatheter was placed inside the aneurysm’s sac in close proximity to the inner wall of the dome. Plasma levels of elastin fragments were measured using an ELISA-based method. Mean plasma level of soluble human elastin fragments was significantly greater in ruptured aneurysms when compared with nonruptured aneurysms (102.0±15.5 versus 39.3±9.6 ng/mL; P\u3c0.001). Mean plasma level of soluble human elastin fragments did not have significant correlation with age, sex, size, or aneurysm location. Conclusions—The present study revealed that a significantly higher concentration of soluble human elastin fragments in the lumen of ruptured intracranial aneurysms when compared with nonruptured ones. © 2018 The Authors

Graph-Based vs Depth-Based Data Representation for Multiview Images

In this paper, we propose a representation and coding method for multiview images. As an alternative to depth-based schemes, we propose a representation that captures the geometry and the dependencies between pixels in different views in the form of connections in a graph. In our approach it is possible to perform compression of the geometry information and to preserve a direct control of the effect of geometry approximation on view reconstruction. This is not possible with classical depth-based representations. As a results, our method leads to more accurate view prediction, when compared to conventional lossy coding of depth maps operating at the same bit rate. We finally show in experiments that our representation adapts the amount of transmitted geometry to the complexity of the predictions that are performed at the decoder

Schumann Resonance spectral characteristics: A useful tool to study Transient Luminous Events (TLEs) on a global scale

© International Conference on Atmospheric Electricity, ICAE 2014 The background Schumann Resonance (SR) spectra require a natural stabilization period of ~10-12 minutes for the three modal parameters, namely, the frequency, intensity and Q-factor to be derived from Lorentzian fitting. Before the spectra are computed and the fitting process is initiated, the raw time series data need to be properly filtered for local cultural noise, narrow band interference as well as large transients in the form of global Q-bursts. Mushtak and Williams [2009] describe an effective technique named as Isolated Lorentzian (I-LOR), in which, the contribution from local cultural and various other noises are minimized to a great extent, and enabling the problem of inter-modal interference to be more effectively addressed in the SR background spectra. An automated technique based on median filtering of time series data and the rejection of events exceeding 16 core standard deviations (CSD) (where \u27core\u27 pertains to the central portion of the spectral power content ) from the average of the period of interest has also been developed by Mushtak et al. [2012]. This cleaning of data before obtaining the modal parameters is essential for work related to the background SR, for example, finding the source strength of tropical \u27chimney\u27 regions by inversion of multi-station data. The methodology used for removing the effect of Q-bursts from background SR spectra could also be used to search for big sprite-producing positive lightning flashes in mesoscale convective systems worldwide. These special lightning flashes are known to have greater contribution in the ELF range (below 1 kHz) compared to negative CG strikes [Cummer 2006]. The global distributions of these Q-bursts have been studied by Huang et al., [1999] and Hobara et al. [2006] by wave impedance methods from single station ELF measurements at Rhode Island, USA. The present work aims to demonstrate the effect of Q-bursts on SR spectra using GPS time-stamped observation of TLEs and average energy data from the VLF World Wide Lightning Location Network (WWLLN). It is observed that the Q-bursts selected for the present work do alias with the background spectra over a five second period, through the amplitudes of these Q-bursts are far below the 16 CSD limit so that they do not strongly alias the background spectra of 10-12 minute duration. The extent of this aliasing is yet to be investigated thoroughly. It is expected that the spectral ELF methodology could be used effectively to detect TLEs globally with a small number of networked stations, especially during daylight conditions, when optical measurements of sprites are not possible

Graph-based representation for multiview image geometry

In this paper, we propose a new representation for multiview image sets. Our approach relies on graphs to describe geometry information in a compact and controllable way. The links of the graph connect pixels in different images and describe the proximity between pixels in the 3D space. These connections are dependent on the geometry of the scene and provide the right amount of information that is necessary for coding and reconstructing multiple views. This multiview image representation is very compact and adapts the transmitted geometry information as a function of the complexity of the prediction performed at the decoder side. To achieve this, our GBR adapts the accuracy of the geometry representation, in contrast with depth coding, which directly compresses with losses the original geometry signal. We present the principles of this graph-based representation (GBR) and we build a complete prototype coding scheme for multiview images. Experimental results demonstrate the potential of this new representation as compared to a depth-based approach. GBR can achieve a gain of 2 dB in reconstructed quality over depth-based schemes operating at similar rates

Aliasing of the Schumann resonance background signal by sprite-associated Q-bursts

© 2017 The Authors The Earth\u27s naturally occurring Schumann resonances (SR) are composed of a quasi-continuous background component and a larger-amplitude, short-duration transient component, otherwise called ‘Q-burst’ (Ogawa et al., 1967). Sprites in the mesosphere are also known to accompany the energetic positive ground flashes that launch the Q-bursts (Boccippio et al., 1995). Spectra of the background Schumann Resonances (SR) require a natural stabilization period of ∼10–12 min for the three conspicuous modal parameters to be derived from Lorentzian fitting. Before the spectra are computed and the fitting process is initiated, the raw time series data need to be properly filtered for local cultural noise, narrow band interference as well as for large transients in the form of global Q-bursts. Mushtak and Williams (2009) describe an effective technique called Isolated Lorentzian (I-LOR), in which, the contributions from local cultural and various other noises are minimized to a great extent. An automated technique based on median filtering of time series data has been developed. These special lightning flashes are known to have greater contribution in the ELF range (below 1 kHz) compared to general negative CG strikes (Huang et al., 1999; Cummer et al., 2006). The global distributions of these Q-bursts have been studied by Huang et al. (1999) Rhode Island, USA by wave impedance methods from single station ELF measurements at Rhode Island, USA and from Japan Hobara et al. (2006). The present work aims to demonstrate the effect of Q-bursts on SR background spectra using GPS time-stamped observation of TLEs. It is observed that the Q-bursts selected for the present work do alias the background spectra over a 5-s period, though the amplitudes of these Q-bursts are far below the background threshold of 16 Core Standard Deviation (CSD) so that they do not strongly alias the background spectra of 10–12 min duration. The examination of one exceptional Q-burst shows that appreciable spectral aliasing can occur even when 12-min spectral integrations are considered. The statistical result shows that for a 12-min spectrum, events above 16 CSD are capable of producing significant frequency aliasing of the modal frequencies, although the intensity aliasing might have a negligible effect unless the events are exceptionally large (∼200 CSD). The spectral CSD methodology may be used to extract the time of arrival of the Q-burst transients. This methodology may be combined with a hyperbolic ranging, thus becoming an effective tool to detect TLEs globally with a modest number of networked observational stations