Measurement of the response time of magnetorheological fluids and ferrofluids based on the magnetic susceptibility response

From a technological point of view one of the most important characteristics of magnetorheological fluids and ferrofluids is their fast (on the [Formula: see text] s time scale) response to external magnetic fields. We report response time measurements based on the time domain magnetic susceptibility response of commercially available fluids. The dynamic susceptibility is measured over time in the presence of external magnetic field by a method using an inductive resonant circuit. The response time of the fluids is extracted as the characteristic time constant from the response to ramp excitation. We investigated the influence of the slope of the ramp excitation on the response time. The macroscopic response times were correlated with the characteristic time scales of the microscopic processes behind the susceptibility response. In case of the magnetorheological fluids the overall response time have been associated with the characteristic times of structure formation. The relatively slow response of the ferrofluid corresponded to a relaxation dominated by Brownian mechanism, which indicated the presence of multi-core clusters.

Air pollution perception in ten countries during the COVID-19 pandemic

As largely documented in the literature, the stark restrictions enforced worldwide in 2020 to curb the COVID-19 pandemic also curtailed the production of air pollutants to some extent. This study investigates the perception of the air pollution as assessed by individuals located in ten countries: Australia, Brazil, China, Ghana, India, Iran, Italy, Norway, South Africa and the USA. The perceptions towards air quality were evaluated by employing an online survey administered in May 2020. Participants (N = 9394) in the ten countries expressed their opinions according to a Likert-scale response. A reduction in pollutant concentration was clearly perceived, albeit to a different extent, by all populations. The survey participants located in India and Italy perceived the largest drop in the air pollution concentration; conversely, the smallest variation was perceived among Chinese and Norwegian respondents. Among all the demographic indicators considered, only gender proved to be statistically significant.

Consistent large-scale response of hourly extreme precipitation to temperature variability

<p>Hourly precipitation extremes can intensify with higher temperatures at higher rates than theoretically expected from thermodynamic increases explained by the Clausius-Clapeyron (CC) relationship (~6.5%/K), but local scaling with surface air temperature is highly variable. Here, we use daily dewpoint temperature, a direct proxy of absolute humidity, as the scaling variable instead of surface air temperature. Using a global dataset of over 7000 hourly precipitation gauges, we estimate the at-gauge local scaling across six macro-regions; this ranges from CC to 2xCC for more than 60% of gauges. We find positive scaling in subtropical and tropical regions in contrast to previous work. Moreover, regional scaling rates show surprisingly universal behaviour at around CC, with higher scaling rates in Europe. Our results show a much greater consistency of scaling across the globe than previous work, usually at or above the CC rate, suggesting the relevance of dewpoint temperature scaling to understand future changes.   </p>