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Photoplethysmographic Waveform Versus Heart Rate Variability to Identify Low Stress States. Attention Test
摘要： Our long-term goal is the development of an automatic identifier of attentional states. In order to accomplish it, we should firstly be able to identify different states based on physiological signals. So, the first aim of this work is to identify the most appropriate features, to detect a subject high performance state. For that, a database of electrocardiographic (ECG) and photopletysmographic (PPG) signals is recorded in two unequivocally defined states (rest and attention task) from up to 50 subjects as a sample of the population. Time and frequency parameters of heart/pulse rate variability have been computed from the ECG/PPG signals respectively. Additionally, the respiratory rate has been estimated from both signals and also six morphological parameters from PPG. In total, twenty six features are obtained for each subject. They provide information about the autonomic nervous system and the physiological response of the subject to an attention demand task. Results show an increase of sympathetic activation when the subjects perform the attention test. The amplitude and width of the PPG pulse were more sensitive that the classical sympathetic markers (PLFn and RLF/HF) for identifying this attentional state. State classification accuracy reaches a mean of 89 ± 2%, a maximum of 93% and a minimum of 85%, in the hundred classifications made by only selecting four parameters extracted from the PPG signal (pulse amplitude, pulse width, pulse downward slope and mean pulse rate). These results suggest that attentional states could be identified by PPG.
关键词： Heart Rate Variability,Low Stress,Photoplethysmographic Waveform,Bagging
更新于2025-09-09 09:28:46
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Variability in monocular and binocular fixation during standard automated perimetry
摘要： The aim of this cross-sectional study was to use standard automated perimetry to compare fixation variability among the dominant eye fixation, non-dominant eye fixation, and binocular fixation conditions. Thirty-five eyes of 35 healthy young participants underwent standard automated perimetry (Humphrey 24–2 SITA-Standard) in dominant eye fixation, non-dominant eye fixation, and binocular fixation conditions. Fixation variability during foveal threshold and visual field measurement, which was recorded using a wearable eye-tracking glass and calculated using the bivariate contour ellipse area (deg2), was compared among the three fixation conditions. Further, the association of bivariate contour ellipse area with ocular position and fusional amplitude during binocular fixation was analysed. There were no significant differences in bivariate contour ellipse area during foveal threshold measurement among the dominant eye fixation (1.75 deg2), non-dominant eye fixation (1.45 deg2), and binocular fixation (1.62 deg2) conditions. In contrast, the bivariate contour ellipse area during visual field measurement in binocular fixation (2.85 deg2) was significantly lower than the bivariate contour ellipse area in dominant eye fixation (4.62 deg2; p = 0.0227) and non-dominant eye fixation (5.24 deg2; p = 0.0006) conditions. There was no significant difference in bivariate contour ellipse area during visual field measurement between dominant eye fixation and non-dominant eye fixation conditions. There was no significant correlation between bivariate contour ellipse area and either ocular position or fusional amplitude during both foveal threshold and visual field measurements. Thus, fixation variability might be improved in binocular fixation conditions during a long-duration test, such as visual field measurement.
关键词： binocular fixation,standard automated perimetry,monocular fixation,fixation variability,bivariate contour ellipse area
更新于2025-09-09 09:28:46
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Simulation of Cycle-to-Cycle Instabilities in SiOx- Based ReRAM Devices Using a Self-Correlated Process with Long-Term Variation
摘要： Cycle-to-cycle (C2C) current variability occurring in ReRAM devices is not only a stochastic feature inherent to electron transport in low dimensional conducting structures but also a consequence of the measurement protocol used to characterize the device evolution during resistance switching. In such latest case, C2C changes depend on the particular arrangement of the ions or vacancies that form the conducting filament spanning the dielectric film. In this work a discrete first order autoregressive model AR(1) with long-term variation is used to represent both the random and the “deterministic” behaviors of the high resistance state current. Simulation of C2C instabilities in SiOx is carried out through the quantum point-contact model for filamentary electron transport in dielectrics with fluctuating confinement potential barrier height. Simplicity is of utmost importance since the proposed approach is aimed for circuit simulation environments in which complex and time-consuming computations need to be avoided.
关键词： MIM,Resistive Switching,SiOx,Variability
更新于2025-09-09 09:28:46
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An expansive, cone-specific nonlinearity enabling the luminance motion system to process color-defined motion
摘要： To conclude that there is a dedicated color motion system, the hypothesis that the luminance motion pathway is processing color motion due to some nonlinearity must be rejected. Many types of nonlinearities have been considered. Cavanagh and Anstis (1991) considered interunit variability in equiluminance, but they found that adding a color-defined modulation to a luminance-defined drifting modulation increased the contribution to motion. This color contribution to motion cannot be due to interunit variability in equiluminance alone because such a luminance artifact would increase the effective luminance contrast for some luminance-sensitive units and decrease it for the others, resulting in no additional contribution to motion on average. Cavanagh and Anstis considered this color contribution to motion as evidence of a dedicated color motion system, but here we show that such a color contribution to motion varies with the phase difference between the luminance and color modulations, which would not be expected if luminance- and color-defined motion were processed separately. Specifically, the contribution to motion was greater when the luminance and color modulations were aligned (i.e., 08 or 1808 phase difference), than when they were not (908 or 2708 phase difference). Such a luminance-color phase interaction was also observed when spatially interleaving luminance and color information, which suggests that the interaction occurs after some spatial integration (i.e., not at the photoreceptors). To our knowledge, this luminance-color phase interaction cannot be explained by any previously considered nonlinearity. However, it can be explained by an expansive nonlinearity occurring before the summation of the L- and M-cone pathways (i.e., before ganglion cells) and after some spatial integration (i.e., after the photoreceptors). We conclude that there is a nonlinearity that has not been considered before, enabling some color motion processing by the luminance motion system.
关键词： color,luminance artifact,motion,expansive nonlinearity,interunit variability in equiluminance
更新于2025-09-04 15:30:14
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Exploring Test–Retest Variability Using High-Resolution Perimetry
摘要： Purpose: Test–retest variability (TRV) of visual field (VF) data seriously degrades our capacity to recognize true VF progression. We conducted repeated high-resolution perimetry with a test interval of 0.58 to investigate the sources of TRV. In particular, we examined whether the spatial variance of the observed sensitivity changes or if their absolute magnitude was of more importance. Methods: Sixteen eyes of 16 glaucoma patients were each tested three times at 61 VF locations along the superior-temporal 458 meridian using a modified protocol of the Octopus 900 perimeter. TRV was quantified as the standard deviation of the repeats at each point (retest-SD). We also computed the mean sensitivity at each point (retest-MS) and the running spatial-SD along the tested meridian. Multiple regression models investigated whether any of those variables (and also age, sex, and VF eccentricity) were significant independent determinants of TRV. Results: The main independent determinants of TRV were the retest-MS at (cid:2)0.04 dB TRV/dB loss (P , 0.0001, t-statistic 5.05), and the retest-SD at 0.47 dB spatial variance/dB loss (P , 0.0001, t-statistic 12.5). Conclusions: The larger effect for the spatial-SD suggested that it was perhaps a stronger determinant of TRV than scotoma depth per se. This might support the hypothesis that rapidly varying interactions between small perimetric stimuli, sensitivity across the field, and normal fixational jitter are strong determinants of TRV. Translational Relevance: Our study indicates that methods that might reduce the effects of jagged sensitivity changes, such as increasing stimulus size or better gaze tracking, could reduce TRV.
关键词： glaucoma,high-resolution perimetry,test–retest variability
更新于2025-09-04 15:30:14
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Revision of the Sun’s Spectral Irradiance as Measured by SORCE SIM
摘要： The Spectral Irradiance Monitor (SIM) instrument on board the Solar Radiation and Climate Experiment (SORCE) performs daily measurements of the solar spectral irradiance (SSI) from 200 to 2400 nm. Both temporal and spectral corrections for instrument degradation have been built on physical models based on comparison of two independent channels with different solar exposure. The present study derives a novel correction for SIM degradation using the total solar irradiance (TSI) measurements from the Total Irradiance Monitor (TIM) on SORCE. The correction is applied to SIM SSI data from September 2004 to October 2012 over the wavelength range from 205 nm to 2300 nm. The change in corrected, integrated SSI agrees within 0.1 W m?2 (1σ ) with SORCE TIM TSI and independently shows agreement with the SATIRE-S and NRLSSI2 solar models within measurement uncertainties.
关键词： Solar spectral irradiance,Degradation correction,Solar spectrum,Solar variability,Solar cycle
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Power Cycling of Commercial SiC MOSFETs
摘要： The robustness under power cycling of three comparable silicon carbide MOSFETs in TO-247 packages from three different manufacturers is investigated, with silicon IGBTs serving as reference. The power cycling method, especially the junction temperature measurement and best practices to ensure its accuracy, is described. The results give insight into reliability and variability as well as aging behavior and failure modes. We ?nd a large variability between samples, both in initial characteristics and measured cycling lifetime, as well as signs of semiconductor device degradation. There is a signi?cant spread in the extent of the variability, in the average and minimum observed lifetime, as well as in the failure mode. Some samples fail quickly due to bond wire defects, some due to semiconductor degradation, while others show very long lifetimes.
关键词： power cycling,SiC MOSFETs,variability,reliability,aging behavior,failure modes
更新于2025-09-04 15:30:14