Influence of Absolute Humidity, Temperature and Population Density on COVID-19 Spread and Decay Durations: Multi-prefecture Study in Japan

This study analyzed the spread and decay durations of the COVID-19 pandemic in different prefectures of Japan. During the pandemic, affordable healthcare was widely available in Japan and the medical system did not suffer a collapse, making accurate comparisons between prefectures possible. For the 16 prefectures included in this study that had daily maximum confirmed cases exceeding ten, the number of daily confirmed cases follow bell-shape or log-normal distribution in most prefectures. A good correlation was observed between the spread and decay durations. However, some exceptions were observed in areas where travelers returned from foreign countries, which were defined as the origins of infection clusters. Excluding these prefectures, the population density was shown to be a major factor affecting the spread and decay patterns, with R2=0.39 (p<0.05) and 0.42 (p<0.05), respectively, approximately corresponding to social distancing. The maximum absolute humidity was found to affect the decay duration normalized by the population density (R2>0.36, p <0.05). Our findings indicate that the estimated pandemic spread duration, based on the multivariate analysis of maximum absolute humidity, ambient temperature, and population density (adjusted R2=0.53, p-value<0.05), could prove useful for intervention planning during potential future pandemics, including a second COVID-19 outbreak.Comment: Submitted to: International Journal of Environmental Research and Public Healt

Setting reference level in the human safety guidelines via nerve activation intercomparison at IF

International guidelines/standards have been published for human protection from electromagnetic field exposure. The research in the intermediate frequencies (IF: 300 Hz-10 MHz) is scattered unlike for other frequencies, and thus the limit prescribed in the guidelines/standards are different by a factor of 10. The IEEE International Committee on Electromagnetic Safety has published a research agenda for exploring the electrostimulation thresholds. However, the consistency of the excitation models for specific target tissue needs to be revised. For this purpose, we present the first intercomparison study using multiphysics modelling to investigate stimulation thresholds during transcranial magnetic stimulation (TMS). To define the stimulation threshold, a noninvasive technique for brain stimulation has been used. In this study, by incorporating individual neurons into electromagnetic computation in realistic head models, stimulation thresholds can be determined. The study case of one subject showed that the allowable external magnetic field strength in the current guidelines/standard is conservative

Human Exposure to Radiofrequency Energy above 6 GHz: Review of Computational Dosimetry Studies

International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity "absorbed/epithelia power density" has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 sec). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.Comment: 38 pages, 3 figure

Brain cortical stimulation thresholds to different magnetic field sources exposures at intermediate frequencies

Permissible field strengths in the international guidelines/standard for human protection are derived from peripheral nerve system stimulation at the intermediate frequencies where electrostimulation (attributable to axon activation) is more dominant than thermal effect. Recently, multiscale computation has been used to investigate neuron stimulation thresholds by incorporating individual neurons into realistic head models. However, the consistency of excitation models and permissible levels to specific target tissues (central nervous system) needs to be clarified. This article aims to investigate brain cortical stimulation thresholds using a multiscale computational approach for different scenarios of magnetic field exposures. The magnetic exposures include transcranial magnetic stimulation, uniform exposure, and wireless power transfer systems. Our results confirmed the consistency of the multiscale computations of the cortical thresholds between two independent groups for electromagnetic exposure of transcranial magnetic stimulation (thresholds in the range of motor cortex activation). We also quantified the conservativeness of permissible field strengths of international guidelines/standards at intermediate frequencies. Finally, with the multiscale approach, we confirmed that 10 000 kW of transmitting power of wireless power transfer (WPT) in an electric vehicle charging system may not induce an adverse effect for cortical activation

Reduction in human interaction with magnetic resonant coupling WPT systems with grounded loop

Wireless power transfer (WPT) systems have attracted considerable attention in relation to providing a reliable and convenient power supply. Among the challenges in this area are maintaining the performance of the WPT system with the presence of a human body and minimizing the induced physical quantities in the human body. This study proposes a magnetic resonant coupling WPT (MRC-WPT) system that utilizes a resonator with a grounded loop to mitigate its interaction with a human body and achieve a high-efficiency power transfer at a short range. Our proposed system is based on a grounded loop to reduce the leakage of the electric field, resulting in less interaction with the human body. As a result, a transmission efficiency higher than 70% is achieved at a transmission distance of approximately 25 cm. Under the maximum-efficiency conditions of the WPT system, the use of a resonator with a grounded loop reduces the induced electric field, the peak spatial-average specific absorption rate (psSAR), and the whole-body averaged SAR by 43.6%, 69.7%, and 65.6%, respectively. The maximum permissible input power values for the proposed WPT systems are 40 and 33.5 kW, as prescribed in the International Commission of Non-Ionizing Radiation Protection (ICNIRP) guidelines to comply with the limits for local and whole-body average SAR

Mapping Brain Motor Functions Using Transcranial Magnetic Stimulation with a Volume Conductor Model and Electrophysiological Experiments

Transcranial magnetic stimulation (TMS) activates brain cells in a noninvasive manner and can be used for mapping brain motor functions. However, the complexity of the brain anatomy prevents the determination of the exact location of the stimulated sites, resulting in the limitation of the spatial resolution of multiple targets. The aim of this study is to map two neighboring muscles in cortical motor areas accurately and quickly. Multiple stimuli were applied to the subject using a TMS stimulator to measure the motor-evoked potentials (MEPs) in the corresponding muscles. For each stimulation condition (coil location and angle), the induced electric field (EF) in the brain was computed using a volume conductor model for an individualized head model of the subject constructed from magnetic resonance images. A post-processing method was implemented to determine a TMS hotspot using EF corresponding to multiple stimuli, considering the amplitude of the measured MEPs. The dependence of the computationally estimated hotspot distribution on two target muscles was evaluated (n = 11). The center of gravity of the first dorsal interosseous cortical representation was lateral to the abductor digiti minimi by a minimum of 2 mm. The localizations were consistent with the putative sites obtained from previous EF-based studies and fMRI studies. The simultaneous cortical mapping of two finger muscles was achieved with only several stimuli, which is one or two orders of magnitude smaller than that in previous studies. Our proposal would be useful in the preoperative mapping of motor or speech areas to plan brain surgery interventions