SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Distortion

165

BACKGROUND: The second-order, infinite impulse response notch filter is widely used to remove electrical power line noise in electrocardiograms (ECGs). However this filtering process often introduces spurious ringing artifacts in the vicinity of raw signal with sharp transitions. It is challenging to simultaneously remove these two types of noise without losing vital information about cardiac activities. OBJECTIVE: Our objective is to devise a method to remove the power-line interference without introducing artifacts nor losing vital information. To this end we have developed the “hybrid approach” involving two-sided filtration and multi-iterative approximation techniques. The two-sided filtration technique can suppress the interference but some cardiac components are lost. The lost information can be restored using multi-iterative approximation technique. RESULTS: For evaluation, four artificial data sets, each including 91 ECGs of different heart rates, were generated by a dynamical model. Four publicly-accessible sets of clinical data (MIT-BIH Arrhythmia, QT, PTB Diagnostic ECG, and T-Wave Alternans Challenge Databases) were also selected. Our new hybrid approach and the existing method were tested with these two types of signal under various pre-determined conditions. In contrast with the existing method, the hybrid approach can provide more than 27.40 dB and 37.77 dB reduction in signal distortion for 95% and 60% of artificial ECGs respectively; it can provide in excess of 11.78 dB and 17.48 dB reduction in distortion for 95% and 60% of these real records respectively. CONCLUSIONS: Overall, a significant reduction in signal distortion is demonstrated. These test results indicate that the newly proposed approach outperforms the traditional method assessed on both the artificial and clinical ECGs and suggest it could be of practical use for clinicians in the future.

Concepts: Signal processing, Digital signal processing, Noise, Distortion, Filter, Low-pass filter, Gibbs phenomenon, Ringing artifacts

28

Single crystal EPR studies of Ni(II) in hexaimidazolecobalt(II) dichloride tetrahydrate have been carried out at ambient temperature to obtain g and zero-field tensors, making it one of the very few systems having room temperature EPR data. The results show rhombic distortion around the Ni(II) ion, with the ion being entered the lattice substitutionally in place of Co(II). The optical data suggest trigonally distorted electronic structure around Ni(II) and collaboration with EPR data provided a few bonding parameters.

Concepts: Fundamental physics concepts, Atom, Valence electron, Algebraic structure, Solid, Crystal system, Distortion

27

During carrier multiplication (CM), also known as multiexciton generation (MEG), absorption of a single photon produces multiple electron-hole pairs, or excitons. This process can appreciably increase the efficiency of photoconversion, which is especially beneficial in photocatalysis and photovoltaics. This Account reviews recent progress in understanding the CM process in semiconductor nanocrystals (NCs), motivated by the challenge researchers face to quickly identify candidate nanomaterials with enhanced CM. We present a possible solution to this problem by showing that, using measured biexciton Auger lifetimes and intraband relaxation rates as surrogates for, respectively, CM time constants and non-CM energy-loss rates, we can predict relative changes in CM yields as a function of composition. Indeed, by studying PbS, PbSe, and PbTe NCs of a variety of sizes we determine that the significant difference in CM yields for these compounds comes from the dissimilarities in their non-CM relaxation channels, i.e., the processes that compete with CM. This finding is likely general, as previous observations of a material-independent, “universal” volume-scaling of Auger lifetimes suggest that the timescale of the CM process itself is only weakly affected by NC composition. We further explore the role of nanostructure shape in the CM process. We observe that a moderate elongation (aspect ratio of 6-7) of PbSe NCs can cause up to an approximately two-fold increase in the multiexciton yield compared to spherical nanoparticles. The increased Auger lifetimes and improved charge transport properties generally associated with elongated nanostructures suggest that lead chalcogenide nanorods are a promising system for testing CM concepts in practical photovoltaics. Historically, experimental considerations have been an important factor influencing CM studies. To this end, we discuss the role of NC photocharging in CM measurements. Photocharging can distort multiexciton dynamics, leading to erroneous estimations of the CM yield. Here, we show that in addition to distorting time-resolved CM signals, photocharging also creates spectral signatures that mimic CM. This re-emphasizes the importance of a careful analysis of the potential effect of charged species in both optical and photocurrent-based measurements of this process.

Concepts: Addition, Nanotechnology, Nanomaterials, Semiconductor, Aspect ratio, Yield, Distortion, Multiplication

24

Electromagnetic (EM) tracking systems are highly susceptible to field distortion. The interference can cause measurement errors up to a few centimeters in clinical environments, which limits the reliability of these systems. Unless corrected for, this measurement error imperils the success of clinical procedures. It is therefore fundamental to dynamically calibrate EM tracking systems and compensate for measurement error caused by field distorting objects commonly present in clinical environments. We propose to combine a motion model with observations of redundant EM sensors and compensate for field distortions in real-time. We employ a simultaneous localization and mapping (SLAM) technique to accurately estimate the pose of the tracked instrument while creating the field distortion map. We conducted experiments with 6 degrees-of-freedom motions in the presence of field distorting objects in research and clinical environments. We applied our approach to improve the EM tracking accuracy and compared our results to a conventional sensor fusion technique. Using our approach, the maximum tracking error was reduced by 67% for position measurements and by 64% for orientation measurements. Currently, clinical applications of EM trackers are hampered by the adverse distortion effects. Our approach introduces a novel method for dynamic field distortion compensation, independent from pre-operative calibrations or external tracking devices, and enables reliable EM navigation for potential applications.

Concepts: Measurement, Metrology, Error, Test method, Calibration, Observational error, Distortion, Interference

19

Self-estimates of intelligence (SEI), which influence to what extent people engage in and how well they perform at a task, are subject to distortion. Here, the distortion effects of individual differences in intelligence (IQ), gender, and proximal (with reference to test performance) and distal (with reference to IQ score distributions) assessments of SEI were tested in a sample of 200 British adults. The results showed that (1) people with lower IQ misestimated their SEI to a greater extent than people with high IQ; (2) this effect was more pronounced in distal than proximal measures of SEI; (3) SEI means did not differ significantly across gender but the IQ-related level of SEI distortion did; (4) this effect was greater for distal than proximal measurement; and (5) proximal SEI were on average less distorted than distal SEI scores and also correlated more closely with IQ. Overall, the findings suggest that the distal SEI assessment method resulted in greater gender- and IQ-related distortions of SEI.

Concepts: Effect, Affect, Educational psychology, Psychometrics, Intelligence quotient, Intelligence, Distortion, Race and intelligence

13

Autism spectrum disorder (ASD) has been associated with a reduction in resting state functional connectivity, though this assertion has recently been challenged by reports of increased connectivity in ASD. To address these contradictory findings, we examined both inter- and intrahemispheric functional connectivity in several resting state data sets acquired from adults with high-functioning ASD and matched control participants. Our results reveal areas of both increased and decreased connectivity in multiple ASD groups as compared to control groups. We propose that this heterogeneity stems from a previously unrecognized ASD characteristic: idiosyncratic distortions of the functional connectivity pattern relative to the typical, canonical template. The magnitude of an individual’s pattern distortion in homotopic interhemispheric connectivity correlated significantly with behavioral symptoms of ASD. We propose that individualized alterations in functional connectivity organization are a core characteristic of high-functioning ASD, and that this may account for previous discrepant findings.

Concepts: Autism, Pervasive developmental disorder, Vector space, Asperger syndrome, Autism spectrum, PDD-NOS, Pattern, Distortion

4

When humans draw maps, or make judgments about travel-time, their responses are rarely accurate and are often systematically distorted. Distortion effects on estimating time to arrival and the scale of sketch-maps reveal the nature of mental representation of time and space. Inspired by data from rodent entorhinal grid cells, we predicted that familiarity to an environment would distort representations of the space by expanding the size of it. We also hypothesized that travel-time estimation would be distorted in the same direction as space-size, if time and space rely on the same cognitive map. We asked international students, who had lived at a college in London for 9 months, to sketch a south-up map of their college district, estimate travel-time to destinations within the area, and mark their everyday walking routes. We found that while estimates for sketched space were expanded with familiarity, estimates of the time to travel through the space were contracted with familiarity. Thus we found dissociable responses to familiarity in representations of time and space. This article is protected by copyright. All rights reserved.

Concepts: Time, Mathematics, Map, Estimation, All rights reserved, Distortion, Copyright, Cartography

3

We report here an unexpectedly robust ability of healthy human participants ( n = 40) to recognize extremely distorted needle-like facial images, challenging the well-entrenched notion that veridical spatial configuration is necessary for extracting facial identity. In face identification tasks of parametrically compressed internal and external features, we found that the sum of performances on each cue falls significantly short of performance on full faces, despite the equal visual information available from both measures (with full faces essentially being a superposition of internal and external features). We hypothesize that this large deficit stems from the use of positional information about how the internal features are positioned relative to the external features. To test this, we systematically changed the relations between internal and external features and found preferential encoding of vertical but not horizontal spatial relationships in facial representations ( n = 20). Finally, we employ magnetoencephalography imaging ( n = 20) to demonstrate a close mapping between the behavioral psychometric curve and the amplitude of the M250 face familiarity, but not M170 face-sensitive evoked response field component, providing evidence that the M250 can be modulated by faces that are perceptually identifiable, irrespective of extreme distortions to the face’s veridical configuration. We theorize that the tolerance to compressive distortions has evolved from the need to recognize faces across varying viewpoints. Our findings help clarify the important, but poorly defined, concept of facial configuration and also enable an association between behavioral performance and previously reported neural correlates of face perception.

Concepts: Psychology, Cognition, Summation, Face, Faces, Face transplant, Distortion

3

We propose a method to calculate field maps from the phase of each EPI in an fMRI time series. These field maps can be used to correct the corresponding magnitude images for distortion caused by inhomogeneity in the static magnetic field. In contrast to conventional static distortion correction, in which one ‘snapshot’ field map is applied to all subsequent fMRI time points, our method also captures dynamic changes to B0 which arise due to motion and respiration. The approach is based on the assumption that the non-B0-related contribution to the phase measured by each radio-frequency coil, which is dominated by the coil sensitivity, is stable over time and can therefore be removed to yield a field map from EPI. Our solution addresses imaging with multi-channel coils at ultra-high field (7T), where phase offsets vary rapidly in space, phase processing is non-trivial and distortions are comparatively large. We propose using dual-echo gradient echo reference scan for the phase offset calculation, which yields estimates with high signal-to-noise ratio. An extrapolation method is proposed which yields reliable estimates for phase offsets even where motion is large and a tailored phase unwrapping procedure for EPI is suggested which gives robust results in regions with disconnected tissue or strong signal decay. Phase offsets are shown to be stable during long measurements (40min) and for large head motions. The dynamic distortion correction proposed here is found to work accurately in the presence of large motion (up to 8.1°), whereas a conventional method based on single field map fails to correct or even introduces distortions (up to 11.2mm). Finally, we show that dynamic unwarping increases the temporal stability of EPI in the presence of motion. Our approach can be applied to any EPI measurements without the need for sequence modification.

Concepts: Magnetic field, Mathematics, Fundamental physics concepts, Measurement, Distortion, Coil, Electronics terms, Cartography

3

Although memory can be hazy at times, it is often assumed that memories of violent or otherwise stressful events are so well encoded that they are effectively indelible and that confidently retrieved memories are almost certainly accurate. However, findings from basic psychological research and neuroscience studies indicate that memory is a reconstructive process that is susceptible to distortion. In the courtroom, even minor memory distortions can have severe consequences that are partly driven by common misunderstandings about memory - for example, that memory is more veridical than it may actually be.

Concepts: Psychology, Cognitive psychology, Sleep, Neuroscience, Cognition, Memory, Cognitive neuroscience, Distortion