Fast visible imaging of turbulent plasma in TORPEX

Fast framing cameras constitute an important recent diagnostic development aimed at monitoring light emission from magnetically confined plasmas, and are now commonly used to study turbulence in plasmas. In the TORPEX toroidal device [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], low frequency electrostatic fluctuations associated with drift-interchange waves are routinely measured by means of extensive sets of Langmuir probes. A Photron Ultima APX-RS fast framing camera has recently been acquired to complement Langmuir probe measurements, which allows comparing statistical and spectral properties of visible light and electrostatic fluctuations. A direct imaging system has been developed, which allows viewing the light, emitted from microwave-produced plasmas tangentially and perpendicularly to the toroidal direction. The comparison of the probability density function, power spectral density, and autoconditional average of the camera data to those obtained using a multiple head electrostatic probe covering the plasma cross section shows reasonable agreement in the case of perpendicular view and in the plasma region where interchange modes dominate.This work is partly funded by the “Fonds National Suisse de la Recherche Scientifique.

Micro helical polymeric structures produced by variable voltage direct electrospinning

Direct near field electrospinning is used to produce very long helical polystyrene microfibers in water. The pitch length of helices can be controlled by changing the applied voltage, allowing to produce both micro springs and microchannels. Using a novel high frequency variable voltage electrospinning method we found the helix formation speed and compared the experimental buckling frequency to theoretical expressions for viscous and elastic buckling. Finally we showed that the newmethod can be used to produce new periodic micro and nano structures.Comment: accepted for publication in Soft Matte

Aberrant High-Order Dependencies in Schizophrenia Resting-State Functional MRI Networks

The human brain has a complex, intricate functional architecture. While many studies primarily emphasize pairwise interactions, delving into high-order associations is crucial for a comprehensive understanding of how functional brain networks intricately interact beyond simple pairwise connections. Analyzing high-order statistics allows us to explore the nuanced and complex relationships across the brain, unraveling the heterogeneity and uncovering patterns of multilevel overlap on the psychosis continuum. Here, we employed high-order independent component analysis (ICA) plus multivariate information-theoretical metrics ($O$-information and $S$-information) to estimate high-order interaction to examine schizophrenia using resting-state fMRI. The results show that multiple brain regions networks may be altered in schizophrenia, such as temporal, subcortical, and higher-cognitive brain regions, and meanwhile, it also shows that revealed synergy gives more information than redundancy in diagnosing schizophrenia. All in all, we showed that high-order dependencies were altered in schizophrenia. Identification of these aberrant patterns will give us a new window to diagnose schizophrenia.Comment: 7 pages, 4 figures, Accepted to InfoCog@NeurIPS 2023 (https://sites.google.com/view/infocog-neurips-2023/home

Methodology for turbulence code validation: Quantification of simulation-experiment agreement and application to the TORPEX experiment

A methodology for plasma turbulence code validation is discussed, focusing on quantitative assessment of the agreement between experiments and simulations. The present work extends the analysis carried out in a previous paper [P. Ricci et al., Phys. Plasmas 16, 055703 (2009)] where the validation observables were introduced. Here, it is discussed how to quantify the agreement between experiments and simulations with respect to each observable, how to define a metric to evaluate this agreement globally, and-finally-how to assess the quality of a validation procedure. The methodology is then applied to the simulation of the basic plasma physics experiment TORPEX [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], considering both two-dimensional and three-dimensional simulation models. [doi: 10.1063/1.3559436

Enhanced dynamic functional connectivity (whole-brain chronnectome) in chess experts

Multidisciplinary approaches have demonstrated that the brain is potentially modulated by the long-term acquisition and practice of specific skills. Chess playing can be considered a paradigm for shaping brain function, with complex interactions among brain networks possibly enhancing cognitive processing. Dynamic network analysis based on resting-state magnetic resonance imaging (rs-fMRI) can be useful to explore the effect of chess playing on whole-brain fluidity/dynamism (the chronnectome). Dynamic connectivity parameters of 18 professional chess players and 20 beginner chess players were evaluated applying spatial independent component analysis (sICA), sliding-time window correlation, and meta-state approaches to rs-fMRI data. Four indexes of meta-state dynamic fluidity were studied: i) the number of distinct meta-states a subject pass through, ii) the number of switches from one meta-state to another, iii) the span of the realized meta-states (the largest distance between two meta-states that subjects occupied), and iv) the total distance travelled in the state space. Professional chess players exhibited an increased dynamic fluidity, expressed as a higher number of occupied meta-states (meta-state numbers, 75.8 ± 7.9 vs 68.8 ± 12.0, p = 0.043 FDR-corrected) and changes from one meta-state to another (meta-state changes, 77.1 ± 7.3 vs 71.2 ± 11.0, p = 0.043 FDR-corrected) than beginner chess players. Furthermore, professional chess players exhibited an increased dynamic range, with increased traveling between successive meta-states (meta-state total distance, 131.7 ± 17.8 vs 108.7 ± 19.7, p = 0.0004 FDR-corrected). Chess playing may induce changes in brain activity through the modulation of the chronnectome. Future studies are warranted to evaluate if these potential effects lead to enhanced cognitive processing and if "gaming" might be used as a treatment in clinical practice

Runaway electron energy measurement using hard x-ray spectroscopy in "Damavand" tokamak

Set of experiments has been developed to study existing runaway electrons in "Damavand" tokamak plasma upon characteristics of hard x-ray emissions produced by collision of the runaway electrons with the plasma particles and limiters. As a first step, spatial distribution of hard x-ray emissions on the equatorial plane of the torus was considered. Obtained spectra of hard x-ray emissions for different alignments of shielded detector indicate isotropic emissivity in the equatorial plane. This is in agreement with wide angle cone of bremsstrahlung radiations, deduced from the mean value of energy of the runaway electrons. The mean energy was calculated from the slope of the energy spectrum of hard x-ray photons. In the second stage in order to investigate time evolution of energy of the runaway electrons, similar technique were applied to obtain hard x-ray energy in every 3 ms intervals, from the beginning to the end of plasma. The mean energy of the runaway electrons increases during the ramp up phase and reaches its maximum between 3 and 9 ms after plasma formation. Also considering the time dependence of the counted photons in each energy range shows that energetic photons are emitted during the ramp up phase of the plasma current in Damavand tokamak

Statistical properties of electrostatic turbulence in toroidal magnetized plasmas (Invited paper)

A unique parabolic relation is observed to link skewness and kurtosis of density fluctuation signals, measured over the whole cross-section of the simple toroidal device TORPEX for a broad range of experimental conditions. This relationship is also valid for density fluctuation signals measured in the scrape-off layer of the TCV tokamak. All the probability density functions (PDFs) of the measured signals, including those characterized by a negative skewness, are universally described by a special case of the beta distribution. In TORPEX, fluctuations in the drift-interchange frequency range are necessary and sufficient to assure that PDFs can be described by this specific beta distribution. For a more detailed plasma scenario, it is shown that electron temperature and plasma potential fluctuations have different statistical properties compared with the density