102 research outputs found
Electromyogram (EMG) Removal by Adding Sources of EMG (ERASE) -- A novel ICA-based algorithm for removing myoelectric artifacts from EEG -- Part 2
Extraction of the movement-related high-gamma (80 - 160 Hz) in
electroencephalogram (EEG) from traumatic brain injury (TBI) patients who have
had hemicraniectomies, remains challenging due to a confounding bandwidth
overlap with surface electromyogram (EMG) artifacts related to facial and head
movements. In part 1, we described an augmented independent component analysis
(ICA) approach for removal of EMG artifacts from EEG, and referred to as EMG
Reduction by Adding Sources of EMG (ERASE). Here, we tested ERASE on EEG
recorded from six TBI patients with hemicraniectomies while they performed a
thumb flexion task. ERASE removed a mean of 52 +/- 12% (mean +/- S.E.M)
(maximum 73%) of EMG artifacts. In contrast, conventional ICA removed a mean of
27 +/- 19\% (mean +/- S.E.M) of EMG artifacts from EEG. In particular,
high-gamma synchronization was significantly improved in the contralateral hand
motor cortex area within the hemicraniectomy site after ERASE was applied. We
computed fractal dimension (FD) of EEG high-gamma on each channel. We found
relative FD of high-gamma over hemicraniectomy after applying ERASE were
strongly correlated to the amplitude of finger flexion force. Results showed
that significant correlation coefficients across the electrodes related to
thumb flexion averaged 0.76, while the coefficients across the homologous
electrodes in non-hemicraniectomy areas were nearly 0. Across all subjects, an
average of 83% of electrodes significantly correlated with force was located in
the hemicraniectomy areas after applying ERASE. After conventional ICA, only
19% of electrodes with significant correlations were located in the
hemicraniectomy. These results indicated that the new approach isolated
electrophysiological features during finger motor activation while selectively
removing confounding EMG artifacts
Artifactual log-periodicity in finite size data: Relevance for earthquake aftershocks
The recently proposed discrete scale invariance and its associated
log-periodicity are an elaboration of the concept of scale invariance in which
the system is scale invariant only under powers of specific values of the
magnification factor. We report on the discovery of a novel mechanism for such
log-periodicity relying solely on the manipulation of data. This ``synthetic''
scenario for log-periodicity relies on two steps: (1) the fact that
approximately logarithmic sampling in time corresponds to uniform sampling in
the logarithm of time; and (2) a low-pass-filtering step, as occurs in
constructing cumulative functions, in maximum likelihood estimations, and in
de-trending, reddens the noise and, in a finite sample, creates a maximum in
the spectrum leading to a most probable frequency in the logarithm of time. We
explore in detail this mechanism and present extensive numerical simulations.
We use this insight to analyze the 27 best aftershock sequences studied by
Kisslinger and Jones [1991] to search for traces of genuine log-periodic
corrections to Omori's law, which states that the earthquake rate decays
approximately as the inverse of the time since the last main shock. The
observed log-periodicity is shown to almost entirely result from the
``synthetic scenario'' owing to the data analysis. From a statistical point of
view, resolving the issue of the possible existence of log-periodicity in
aftershocks will be very difficult as Omori's law describes a point process
with a uniform sampling in the logarithm of the time. By construction, strong
log-periodic fluctuations are thus created by this logarithmic sampling.Comment: LaTeX, JGR preprint with AGU++ v16.b and AGUTeX 5.0, use packages
graphicx, psfrag and latexsym, 41 eps figures, 26 pages. In press J. Geophys.
Re
Tunneling Between Parallel Two-Dimensional Electron Gases
The tunneling between two parallel two-dimensional electron gases has been
investigated as a function of temperature , carrier density , and the
applied perpendicular magnetic field . In zero magnetic field the
equilibrium resonant lineshape is Lorentzian, reflecting the Lorentzian form of
the spectral functions within each layer. From the width of the tunneling
resonance the lifetime of the electrons within a 2DEG has been measured as a
function of and , giving information about the density dependence of the
electron-impurity scattering and the temperature dependence of the
electron-electron scattering. In a magnetic field there is a general
suppression of equilibrium tunneling for fields above T. A gap in the
tunneling density of states has been measured over a wide range of magnetic
fields and filling factors, and various theoretical predictions have been
examined. In a strong magnetic field, when there is only one partially filled
Landau level in each layer, the temperature dependence of the conductance
characteristics has been modeled with a double-Gaussian spectral density.Comment: LaTeX requires REVTeX macros. Eighteen pages. Fourteen postscript
figures are included. (All figures have been bitmapped to save space. The
original can be requested by email from [email protected]). Accepted for
publication in Phys. Rev.
In vitro analysis of the cytotoxicity and the antimicrobial effect of four endodontic sealers
<p>Abstract</p> <p>Introduction</p> <p>The aim of this study was to investigate <it>in vitro </it>the cytotoxicity and antibacterial properties of four different endodontic sealers using human periodontal ligament fibroblast cell proliferation and visual analysis of growth inhibition.</p> <p>Methods</p> <p>A silicone (GuttaFlow), silicate (EndoSequence BC), zinc oxide eugenol (Pulp Canal Sealer EWT) and epoxy resin (AH Plus Jet) based sealer were incubated with PDL fibroblasts (10<sup>4 </sup>cells/ml, n = 6) up to 96 h. Cell proliferation (RFU) was determined by means of the Alamar Blue assay. Cell growth and morphology was visualized by means of fluorescent dyes. Possible antibacterial properties of the different sealers were visualized by means of SEM (<it>Enterococcus faecalis; Parvimonas micra</it>).</p> <p>Results</p> <p>Fibroblast proliferation depended on sealer and cultivation time. After 72 and 96 h GuttaFlow and EndoSequence BC showed relatively non-cytotoxic reactions, while Pulp Canal Sealer EWT and AH Plus Jet caused a significant decrease of cell proliferation (p < 0.001). Visualization of cell growth and morphology with various fluorescent dyes supplemented the results. No antibacterial effect of EndoSequence BC to <it>P. micra </it>was found, whereas GuttaFlow showed a weak, Pulp Canal Sealer EWT and AH Plus Jet extensive growth inhibition. Also, no antibacterial effect of GuttaFlow, EndoSequence BC or AH Plus Jet to <it>E. faecalis </it>could be detected.</p> <p>Conclusions</p> <p>These <it>in vitro </it>findings reveal that GuttaFlow and EndoSequence BC can be considered as biocompatible sealing materials. However, prior to their clinical employment, studies regarding their sealing properties also need to be considered.</p
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