Spherical harmonic decomposition applied to spatial-temporal analysis of human high-density EEG

We demonstrate an application of spherical harmonic decomposition to analysis of the human electroencephalogram (EEG). We implement two methods and discuss issues specific to analysis of hemispherical, irregularly sampled data. Performance of the methods and spatial sampling requirements are quantified using simulated data. The analysis is applied to experimental EEG data, confirming earlier reports of an approximate frequency-wavenumber relationship in some bands.Comment: 12 pages, 8 figures, submitted to Phys. Rev. E, uses APS RevTeX style

Responses to Two Weight Training Protocols--One with Integrated High-Intensity Interval Training

Purpose: To examine the physiological effects (energy expenditure, oxygen consumption [VO2], heart rate [HR], blood lactate [BLa-], excess post-exercise oxygen consumption [EPOC]) and perception (rating of perceived exertion [RPE] and enjoyment) of the combination of high-intensity interval training (HIIT) exercise with conventional circuit weight training (CWT; nine consecutive exercises)(CWIT) compared to HIIT exercise with tri-set training (3 three-exercise mini-circuits)(TRIIT). Methods: Fourteen trained men completed two separate resistance exercise protocols. CWIT consisted of six HIIT bouts prior to three rounds of a nine exercise CWT protocol. TRIIT consisted of three rounds of three mini-circuits consisting of three exercises with the integration of three HIIT bouts between the first and second mini-circuits and second and third mini-circuits. Both protocols were matched for exercise load and time. VO2 was measured via indirect calorimetry, BLa- was measured via portable lactate analyzer, exertion was measured via Borg scale (6-20) and enjoyment was measured via Physical Activity Enjoyment Scale (PAES). Differences between CWIT and TRIIT protocols were analyzed as group means by using paired t-tests and as protocol by time using a 2 x 5 repeated measures ANOVA (SPSS v22.0). Results: Average values for CWIT and TRIIT were similar (p\u3e.05) for VO2, HR and RPE. Energy expenditure was significantly higher during the CWIT compared to the TRIIT protocol, as well as EPOC. BLa- was significantly higher at all post-exercise time points (immediate, 5 min, 10 min and 20 min post-exercise) following the CWIT compared to the TRIIT protocol. Both protocols were considered enjoyable according to the PAES. Conclusions: Performing HIIT prior to CWT elicits higher metabolic perturbation in comparison to the integration of HIIT with mini-circuits. CWIT also required greater energy requirements during and after the protocol compared to TRIIT. This may be useful for fitness trainers when determining how to implement HIIT into a CWT workout

The Micro Slit Gas Detector

We describe the first tests with a new proportional gas detector. Its geometry consists in slits opened in a copper metallized kapton foil with 30 micron anode strips suspended in these openings. In this way the multiplication process is similar to a standard MSGC. The fundamental difference is the absence of an insulating substrate around the anode. Also the material budget is significantly reduced, and the problems related to charging-up or polarization are removed. Ageing properties of this detector are under study.Comment: 13 pages tex file, 10 figures ep

Black hole - D-brane correspondence: An example

We explore the connection between D-branes and black holes in one particular case: a $D3$-brane compactified to four dimensions on $T^6/Z_3$. Using the $D$-brane boundary state description we show the equivalence with a double extremal N=2 black hole solution of four dimensional supergravity.Comment: 15 pages, LaTeX. Contribution by C. Nunez to the conference Quantum Gravity in the Southern Cone, Bariloche 7-10 January 1998; to appear in the proceeding

Model of Low-pass Filtering of Local Field Potentials in Brain Tissue

Local field potentials (LFPs) are routinely measured experimentally in brain tissue, and exhibit strong low-pass frequency filtering properties, with high frequencies (such as action potentials) being visible only at very short distances ($\approx$10~$\mu m$) from the recording electrode. Understanding this filtering is crucial to relate LFP signals with neuronal activity, but not much is known about the exact mechanisms underlying this low-pass filtering. In this paper, we investigate a possible biophysical mechanism for the low-pass filtering properties of LFPs. We investigate the propagation of electric fields and its frequency dependence close to the current source, i.e. at length scales in the order of average interneuronal distance. We take into account the presence of a high density of cellular membranes around current sources, such as glial cells. By considering them as passive cells, we show that under the influence of the electric source field, they respond by polarisation, i.e., creation of an induced field. Because of the finite velocity of ionic charge movement, this polarization will not be instantaneous. Consequently, the induced electric field will be frequency-dependent, and much reduced for high frequencies. Our model establishes that with respect to frequency attenuation properties, this situation is analogous to an equivalent RC-circuit, or better a system of coupled RC-circuits. We present a number of numerical simulations of induced electric field for biologically realistic values of parameters, and show this frequency filtering effect as well as the attenuation of extracellular potentials with distance. We suggest that induced electric fields in passive cells surrounding neurons is the physical origin of frequency filtering properties of LFPs.Comment: 10 figs, revised tex file and revised fig

Absence of a structural transition up to 40 Gpa in MgB2 and the relevance of magnesium non-stoichiometry

We report measurements on MgB2 up to ~40GPa. Increasing pressure yields a monotonous decrease of the lattice parameters and of the c/a ratio, but no structural transition down to parameters smaller than those of AlB2. The transition superconducting temperature also decreases with temperature in a sample dependent way. The results are explained by an increase of the filling of the 2D pxy bands with pressure, the Mg stoichiometry determining the starting position of the Fermi level. Our measurements indicate that these hole bands are the relevant ones for superconductivity.Comment: submitted March 9th 2001, PRB accepte