COVID-19 Pandemic Analysis

The development of coronavirus disease (COVID-19) deaths in selected nations and states is compared to the result of calculations using a conventional SEIR model of pandemic development. The model is based on the infection multiplier, R0, defined as the number of people infected by each infectious person. The infection rate increases exponentially when R0 >1.0; it remains constant at R0 = 1.0 and decreases for R0 < 1.0. R0 is determined by population behavior (frequency and proximity of interactions) and the ease by which a victim is infected by an infectious person (virus' virulence). It is reduced by herd immunity when a large fraction of the population acquires immunity by vaccination or by recovering from infection. The daily death rates in the U.S. and northern Europe exhibited peaks in April/May 2020 and Dec. 2020/Jan. 2021 with more a modest rate during the summer of 2020 and a gradually decreasing rate since Jan. 2021. The model produces this type of oscillatory response if it assumes that the population's R0 responds to information reported about the pandemic, but with a delay between infections and resulting behavioral adjustments. Oscillatory behavior is typical of a control loop with delay in its feedback. The analysis concludes that: Given the history of R0 the model predicts the development of pandemic deaths. However, since R0 is determined by the population's behavior, control of the pandemic in democracies depends primarily on preparation and the persuasive power of political and scientific authorities. Data for S. Korea and New Zealand demonstrate the effectiveness of such methods. For each death in the U.S. about 169 persons were infected, but fewer than half of them were identified as cases. The pandemic was prolonged in the U.S. because the population chose to keep R0 near 1.0 by relaxing restrictions once the death rate subsided. Initial values of R0 as high as 5.0 were observed, leading to infections doubling about every 2 days. If unabated, the resulting exponential growth increases the infected population by a factor of about 5000 before the death from the first infections is recorded. Arrival from Italy probably initiated the pandemic in the eastern U.S., but, by the time the first death was recorded the number of domestic infections exceeded by far those that were imported. Import restrictions beyond this point are ineffective except in delaying the arrival of more virulent mutations. If no social restrictions had been adopted, approximately 1.6 million deaths would have resulted in the U.S. The vaccine, although developed and deployed at record speed, was too late to ameliorate this result. A third peak in death rate in Sept. 2021 may be prevented if more than 80% of the population is vaccinated.

Modulation of sensorimotor cortical oscillations in athletes with yips

The yips, an involuntary movement impediment that affects performance in skilled athletes, is commonly described as a form of task-specific focal dystonia or as a disorder lying on a continuum with focal dystonia at one end (neurological) and chocking under pressure at the other (psychological). However, its etiology has been remained to be elucidated. In order to understand sensorimotor cortical activity associated with this movement disorder, we examined electroencephalographic oscillations over the bilateral sensorimotor areas during a precision force task in athletes with yips, and compared them with age-, sex-, and years of experience-matched controls. Alpha-band event-related desynchronization (ERD), that occurs during movement execution, was greater in athlete with yips as compared to controls when increasing force output to match a target but not when adjusting the force at around the target. Event-related synchronization that occurs after movement termination was also greater in athletes with yips. There was no significant difference in task performance between groups. The enhanced ERD is suggested to be attributed to dysfunction of inhibitory system or increased allocation of attention to the body part used during the task. Our findings indicate that sensorimotor cortical oscillatory response is increased during movement initiation in athletes with yips.

Advanced Performance Metrics and their Application to the Sensitivity Analysis for Model Validation and Calibration

<pre>High quality generator dynamic models are critical to reliable and accurate power systems studies and planning. With the availability of PMU measurements, measurement-based approach for model validation has gained significant prominence. Currently, the model validation results are analyzed by visually comparing real--world PMU measurements with the model-based response measurements, and parameter adjustments rely mostly on engineering experience. This paper proposes advanced performance metrics to systematically quantify the generator dynamic model validation results by separately taking into consideration slow governor response and comparatively fast oscillatory response. The performance metric for governor response is based on the step response characteristics of a system and the metric for oscillatory response is based on the response of generator to each system mode calculated using modal analysis. The proposed metrics in this paper is aimed at providing critical information to help with the selection of parameters to be tuned for model calibration by performing enhanced sensitivity analysis, and also help with rule-based model calibration. Results obtained using both simulated and real-world measurements validate the effectiveness of the proposed performance metrics and sensitivity analysis for model validation and calibration.</pre>

Odor induces characteristic time courses of theta, beta and gamma oscillations in human olfactory cortex

Neuronal oscillations are fundamental to cognition, facilitating coordination and communication of information within and across brain regions. Studies on the spectral and temporal dynamics of oscillatory rhythms have contributed substantial insight to our understanding of mechanisms of human visual, auditory and somatosensory perception. However, these oscillations have been largely unexplored in the human olfactory system, where we lack basic understanding of fundamental spectrotemporal and functional properties. Determining if and how dynamic signatures of neural activity occur in human olfactory cortex is critical to understanding how we process odors. Here, we establish a characteristic oscillatory response to an odor in the human brain. Using direct electrical recordings from human piriform cortex, we identified three key odor-induced rhythms, in the theta (4-8Hz), beta (13-30Hz) and gamma (30-150Hz) frequency bands, each with distinct functional and temporal properties. While theta emerges and dissipates rapidly at the start of inhalation, beta and gamma emerge later, with beta persisting through exhalation, and gamma peaking around the transition between inhalation and exhalation. Beta and gamma amplitudes strongly predict odor identification ability, whereas theta does not. Theta phase modulates beta and gamma amplitudes during inhalation, only when odor is present. Our findings establish that smells elicit distinct neuronal rhythms in human olfactory cortex, which are dynamically interplayed over the course of a sniff. Our data further suggest a fundamental role for beta and gamma oscillations in human olfactory processing, and that their amplitudes--organized by theta phase--subserve odor identification in humans.

All-in-one rheology of multicellular aggregates

Tissues are generally subjected to external stresses, a potential stimulus for their differentiation or remodelling. While single-cell rheology has been extensively studied, mechanical tissue behavior under external stress is still poorly known because of a lack of adapted set-ups. Herein we introduce magnetic techniques designed both to form aggregates of controlled size, shape and content (magnetic molding) and to deform them under controlled applied stresses over a wide range of timescales and amplitudes (magnetic rheometer). We explore the rheology of multicellular aggregates (F9 cells) using both standard assays (creep and oscillatory response) and an innovative broad spectrum solicitation coupled with inference analysis. We find that multicellular aggregates exhibit a power-law response with non-linearities leading to tissue stiffening at high stress. Comparing magnetic measurements on aggregates to isolated F9 cells characterization by parallel-plates rheometry, we reveal the role of cell-cell adhesions in tissue mechanics. Thanks to its versatility, the magnetic rheometer thus stands as an essential tool to investigate model tissue rheology.

Economic fluctuations in a model with an overlapping structure of employment

This study presents a dynamic general equilibrium model with an explicit employment period and investigates economic fluctuations to a temporary productivity shock. Numerical experiments indicate oscillatory responses of new hiring and employment to the shock which are not observed in a standard flexible price model. The explicit employment period constructs an overlapping structure of employment which results in the oscillatory response. This study also examines the effects of change in employment period to economic fluctuations and shows that the variations in new hiring are higher when the employment period is long.

The gamma response to colour hue in humans: Evidence from MEG

It has recently been demonstrated through invasive electrophysiology that visual stimulation with extended patches of uniform colour generates pronounced gamma oscillations in the visual cortex of both macaques and humans. In this study we sought to discover if this oscillatory response to colour can be measured non-invasively in humans using magnetoencephalography. We were able to demonstrate increased gamma (40–70 Hz) power in response to full-screen stimulation with four different colour hues and found that the gamma response is particularly strong for long wavelength (i.e. red) stimulation, as was found in previous studies. However, we also found that gamma power in response to colour was generally weaker than the response to an identically sized luminance-defined grating. We also observed two additional responses in the gamma frequency: a lower frequency response around 25–35 Hz that showed fewer clear differences between conditions than the gamma response, and a higher frequency response around 70–100 Hz that was present for red stimulation but not for other colours. In a second experiment we sought to test whether differences in the gamma response between colour hues could be explained by their chromatic separation from the preceding display. We presented stimuli that alternated between each of the three pairings of the three primary colours (red, green, blue) at two levels of chromatic separation defined in the CIELUV colour space. We observed that the gamma response was significantly greater to high relative to low chromatic separation, but that at each level of separation the response was greater for both red-blue and red-green than for blue-green stimulation. Our findings suggest that the stronger gamma response to red stimulation cannot be wholly explained by the chromatic separation of the stimuli.

Dissociable components of oscillatory activity underly information encoding in human perception

Brain decoding can predict visual perception from non-invasive electrophysiological data by combining information across multiple channels. However, decoding methods typically confound together the multi-faceted and distributed neural processes underlying perception, so it is unclear what specific aspects of the neural computations involved in perception are reflected in this type of macroscale data. Using MEG data recorded while participants viewed a large number of naturalistic images, we analytically separated the brain signal into a slow 1/f drift (<5Hz) and a oscillatory response in the theta frequency band. Combined with a method for capturing between-trial variability in the way stimuli are processed, this analysis revealed that there are at least three dissociable components that contain distinct stimulus-specific information: a 1/f component, reflecting the temporally stable aspect of the stimulus representation; a global phase shift of the theta oscillation, related to differences in the speed of processing between the stimuli; and differential patterns of theta phase across channels, likely related to stimulus-specific computations. We demonstrate that common cognitive interpretations of decoding analysis can be flawed if the multicomponent nature of the signal is ignored, and suggest that, by acknowledging this fact, we can provide a more accurate interpretation of commonly observed phenomena in the study of perception.

Advanced Performance Metrics and Sensitivity Analysis for Model Validation and Calibration

<pre>High quality generator dynamic models are critical to reliable and accurate power systems studies and planning. With the availability of PMU measurements, measurement-based approach for model validation has gained significant prominence. Currently, the model validation results are analyzed by visually comparing real--world PMU measurements with the model-based response measurements, and parameter adjustments rely mostly on engineering experience. This paper proposes advanced performance metrics to systematically quantify the generator dynamic model validation results by separately taking into consideration slow governor response and comparatively fast oscillatory response. The performance metric for governor response is based on the step response characteristics of a system and the metric for oscillatory response is based on the response of generator to each system mode calculated using modal analysis. The proposed metrics in this paper is aimed at providing critical information to help with the selection of parameters to be tuned for model calibration by performing enhanced sensitivity analysis, and also help with rule-based model calibration. Results obtained using both simulated and real-world measurements validate the effectiveness of the proposed performance metrics and sensitivity analysis for model validation and calibration.</pre>