Elastic Functional Changepoint Detection

Detecting changepoints in functional data has become an important problem as interest in monitory of climatologies and other various processing monitoring situations has increased, where the data is functional in nature. The observed data often contains variability in amplitude ($y$-axis) and phase ($x$-axis). If not accounted for properly, incorrect changepoints can be detected, as well as underlying mean functions at those changes will be incorrect. In this paper, an elastic functional changepoint method is developed which properly accounts for these types of variability. Additionally, the method can detect amplitude and phase changepoints which current methods in the literature do not, as they focus solely on the amplitude changepoint. This method can easily be implemented using the functions directly, or to ease the computational burden can be computed using functional principal component analysis. We apply the method to both simulated data and real data sets to show its efficiency in handling data with phase variation with both amplitude and phase changepoints

An index for T-wave pointwise amplitude variability quantification

The comparison between the pointwise amplitude of different T-waves provides insight into ventricular repolarization liability. However, T-wave pointwise amplitude variability can be confounded by time-domain variability. We, first, compared two algorithms for removing (warping) time-domain variability, one using the original and another one using a transformed T-wave (SRSF). We, next, compared the robustness against noise of two markers, dy and da, of pointwise amplitude variability, after warping the underlying temporal variability with the preferred warping algorithm. dy was obtained from the transformed T-waves while da was proposed in this work and was derived from the original T-waves. We, finally, used the most robust marker to measure the T-wave pointwise amplitude variability between every T-wave recorded during a Tilt test and their mean T-wave. Results showed that the preferred warping algorithm was the SRSF because it is not affected by differences between the amplitudes of the original T-waves. In addition, the marker da presented lower relative error values than dy for every level of noise. The analysis of electrocardiogram records showed that da was significantly lower during the tilt than in supine position (5.5 % vs 6.5 %, p<0.01). In conclusion, da robustly quantifies physiological variabilities of the T-wave amplitude, showing its potential to be used as an arrhythmic risk predictor in future clinical situations

An index for T-wave pointwise amplitude variability quantification

The comparison between the pointwise amplitude of different T-waves provides insight into ventricular repolarization liability. However, T-wave pointwise amplitude variability can be confounded by time-domain variability. We, first, compared two algorithms for removing (warping) time-domain variability, one using the original and another one using a transformed T-wave (SRSF). We, next, compared the robustness against noise of two markers, dy and da, of pointwise amplitude variability, after warping the underlying temporal variability with the preferred warping algorithm. dy was obtained from the transformed T-waves while da was proposed in this work and was derived from the original T-waves. We, finally, used the most robust marker to measure the T-wave pointwise amplitude variability between every T-wave recorded during a Tilt test and their mean T-wave. Results showed that the preferred warping algorithm was the SRSF because it is not affected by differences between the amplitudes of the original T-waves. In addition, the marker da presented lower relative error values than dy for every level of noise. The analysis of electrocardiogram records showed that da was significantly lower during the tilt than in supine position (5.5 % vs 6.5 %, p<0.01). In conclusion, da robustly quantifies physiological variabilities of the T-wave amplitude, showing its potential to be used as an arrhythmic risk predictor in future clinical situations

Variability of ventricular repolarization dispersion quantified by time-warping the morphology of the T-Waves

Objective: We propose two electrocardiogram (ECG)-derived markers of T-wave morphological variability in the temporal, d¿, and amplitude, da, domains. Two additional markers, d¿NL and daNL, restricted to measure the nonlinear information present within d¿ and da are also proposed. Methods: We evaluated the accuracy of the proposed markers in capturing T-wave time and amplitude variations in 3 situations: 1) In a simulated set up with presence of additive Laplacian noise, 2) when modifying the spatio-temporal distribution of electrical repolarization with an electro-physiological cardiac model, and 3) in ECG records from healthy subjects undergoing a tilt table test. Results:The metrics d¿, da, d¿NL, and daNL followed T-wave time- and amplitude-induced variations under different levels of noise, were strongly associated with changes in the spatio-temporal dispersion of repolarization, and showed to provide additional information to differences in the heart rate, QT and Tpe intervals, and in the T-wave width and amplitude. Conclusion: The proposed ECG-derived markers robustly quantify T-wave morphological variability, being strongly associated with changes in the dispersion of repolarization. Significance: The proposed ECG-derived markers can help to quantify the variability in the dispersion of ventricular repolarization, showing a great potential to be used as arrhythmic risk predictors in clinical situations

The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays, observing simultaneously at 250, 350, and 500 um. The diffraction-limited optical system provides a resolution of 30'' at 250 um. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/detector array. A rotating 4 K achromatic half-wave plate provides additional polarization modulation. With its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolution surveys and narrow field of view, and high resolution observations of substructure within molecular cloud cores. The first science flight will be from McMurdo Station, Antarctica in December 2010.Comment: 14 pages, 9 figures Submitted to SPIE Astronomical Telescopes and Instrumentation Conference 201

Comparison of prestellar core elongations and large-scale molecular cloud structures in the Lupus 1 region

Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 mum maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 mum with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics---including secondary filaments that often run orthogonally to the primary filament---and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core