The placement of obstacles in front of doors is believed to be an effective strategy to increase the flow of pedestrians, hence improving the evacuation process. Since it was first suggested, this ...counterintuitive feature is considered a hallmark of pedestrian flows through bottlenecks. Indeed, despite the little experimental evidence, the placement of an obstacle has been hailed as the panacea for solving evacuation problems. In this work, we challenge this idea and experimentally demonstrate that the pedestrians flow rate is not necessarily altered by the presence of an obstacle. This result-which is at odds with recent demonstrations on its suitability for the cases of granular media, sheep and mice-differs from the outcomes of most of existing numerical models, and warns about the risks of carelessly extrapolating animal behaviour to humans. Our experimental findings also reveal an unnoticed phenomenon in relation with the crowd movement in front of the exit: in competitive evacuations, an obstacle attenuates the development of collective transversal rushes, which are hazardous as they might cause falls.
The Juno spacecraft reached the mid‐point of its nominal mission in December 2018, after completing 17 perijove passes. Ten of these were dedicated to the determination of the gravity field of the ...planet, with the aim of constraining its interior structure. We provide an update on Jupiter's gravity field, its tidal response and spin axis motion over time. The analysis of the Doppler data collected during the perijove passes hints to a non‐static and/or non‐axially symmetric field, possibly related to several different physical mechanisms, such as normal modes or localized atmospheric or deeply‐rooted dynamics.
Plain Language Summary
Jupiter's gravity field has been updated with the use of Juno's data collected up to the mid‐point of its mission. The field is largely symmetric about the rotation axis, and shows conspicuous north‐south asymmetry. Possible non‐static and/or non‐axially symmetric field is compatible with the data.
Key Points
Juno updates Jupiter's gravity field halfway through its mission, revealing a largely axially symmetric, north‐south asymmetric field
Hints to a non‐static and/or non‐axially symmetric field, possibly related to several different physical mechanisms, appear in the data
The tidal response is evaluated and compared to interior model predictions
The combination of the Doppler data from the first two Juno science orbits provides an improved estimate of the gravity field of Jupiter, crucial for interior modeling of giant planets. The ...low‐degree spherical harmonic coefficients, especially J4 and J6, are determined with accuracies better than previously published by a factor of 5 or more. In addition, the independent estimates of the Jovian gravity field, obtained by the orbits separately, agree within uncertainties, pointing to a good stability of the solution. The degree 2 sectoral and tesseral coefficients, C2,1, S2,1, C2,2, and S2,2, were determined to be statistically zero as expected for a fluid planet in equilibrium.
Key Points
The Jupiter gravity field has been evaluated for the first two Juno orbits
The zonal harmonics J4 and J6 improve over previous results by factors of 5 and 22, respectively, providing strong constraints on Jupiter interior models
Jupiter's atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. Whether this is also true of the gas giant's interior has been ...unknown, limiting our ability to probe the structure and composition of the planet. The discovery by the Juno spacecraft that Jupiter's gravity field is north-south asymmetric and the determination of its non-zero odd gravitational harmonics J
, J
, J
and J
demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops. Here we report an analysis of Jupiter's even gravitational harmonics J
, J
, J
and J
as observed by Juno and compared to the predictions of interior models. We find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. Moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. This depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation. Given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in Saturn and to be shallower in massive giant planets and brown dwarfs.
We report experimental results on the competitive passage of elongated self-propelled vehicles rushing through a constriction. For the chosen experimental conditions, we observe the emergence of ...intermittencies similar to those reported previously for active matter passing through narrow doors. Noteworthy, we find that, when the number of individuals crowding in front of the bottleneck increases, there is a transition from an unclogged to a clogged state characterized by a lack of convergence of the mean clog duration as the measuring time increases. It is demonstrated that this transition-which was reported previously only for externally vibrated systems such as colloids or granulars-appears also for self-propelled agents. This suggests that the transition should also occur for the flow through constrictions of living agents (e.g., humans and sheep), an issue that has been elusive so far in experiments due to safety risks.
► State of the art in panic egress are computer simulations that still need validation. ► We study the evacuation of ants from a chamber. ► Ants were forced to egress using a repellent in different ...concentrations. ► Behavior of evacuating ants are different when compared with humans. ► We advise not to apply the results of experiments with ants directly to human systems.
The faster is slower effect is a self-organized phenomena first described for pedestrian dynamics. Although it has been obtained in computer simulations, it has not been observed in real systems yet. To achieve this goal, we carried out experiments with ants, which are self-propelled biological agents. The ants were placed inside a bidimensional chamber with a narrow exit, and a paper imbibed with repellent was placed in the opposite wall of the chamber. Using different concentrations of citronella, which produced different degrees of repellency, the ants were forced to egress from the chamber and the evacuation time was measured. A minimum evacuation time is observed for intermediate concentrations of citronella, compatible with the faster is slower effect. However, this effect was not generated by the occurrence of blocking clusters right before the exit as the ants did not display a selfish evacuation behavior.
On 29 September 2022 the Juno spacecraft flew within 354 km of Europa's surface while several instruments probed the moon's surroundings. During the close flyby, radio occultations were performed by ...collecting single‐frequency Doppler measurements. These investigations are essential to the study of Europa's ionosphere and represent the first repeat sampling of any set of conditions since the Galileo era. Ingress measurements resulted in a marginal detection with a peak ionospheric density of 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude. A more significant detection emerged on egress, with a peak density of 6,000 ± 3,000 cm−3 (3σ) at 320 km altitude. Comparison with Galileo measurements reveals a consistent picture of Europa's ionosphere, and confirms its dependence on illumination conditions and position within Jupiter's magnetosphere. However, the overall lower densities measured by Juno suggest a dependence on time of observation, with implications for the structure of the neutral atmosphere.
Plain Language Summary
On 29 September 2022, NASA's Juno spacecraft flew very close to Jupiter's moon Europa. During the encounter, a radio occultation experiment was performed, where radio signals are exchanged between the spacecraft and ground stations as the former sets behind or rises from the moon as seen from the Earth. The scope of this experiment was studying the ionosphere of Europa, a layer of electrons and ions surrounding the moon. The Juno measurements confirmed the presence of the layer, with a structure similar to the one observed by the Galileo mission in the late 1990s.
Key Points
Europa's ionosphere was detected from Juno's X‐band Doppler data via NASA's Deep Space Network during a close encounter in 2022
Peak densities were 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude during ingress and 6,000 ± 3,000 cm−3 (3σ) at 320 km during egress
The Juno ionospheric profiles are consistent with Galileo measurements, and show a dependence on solar zenith and magnetospheric ram angles
. We report a thorough analysis of the intermittent flow of pedestrians through a narrow door. The observations include five different sets of evacuation drills with which we have investigated the ...effect of door size and competitiveness on the flow dynamics. Although the outcomes are in general compatible with the existence of the faster-is-slower effect, the temporal evolution of the instantaneous flow rate provides evidence of new features. These stress the crucial role of the number of people performing the tests, which has an influence on the obtained results. Once the transients at the beginning and end of the evacuation are removed, we have found that the time lapses between the passage of two consecutive pedestrians display heavy-tailed distributions in all the scenarios studied. Meanwhile, the distribution of burst sizes decays exponentially; this can be linked to a constant probability of finding a long-lasting clog during the evacuation process. Based on these results, a discussion is presented on the caution that should be exercised when measuring or describing the intermittent flow of pedestrians through narrow doors.
The Juno Extended Mission presented the first opportunity to acquire gravity measurements of Ganymede since the end of the Galileo mission. These new Juno data offered the chance to carry out a joint ...analysis with the Galileo data set, improving our knowledge of Ganymede's gravity field and shedding new light upon its interior structure. Through reconstruction of Juno's and Galileo's orbit during the Ganymede flybys, the gravity field of the moon was estimated. The results indicate that Ganymede's degree‐2 field is compatible with a body in hydrostatic equilibrium within 1−𝜎 and hint at regional gravity anomalies with amplitudes exceeding those inferred by Cassini for Titan. Our explicit treatment of non‐hydrostatic effects leads to wider confidence intervals for the derived moment of inertia with respect previous analyses. The higher central value of the derived moment of inertia indicates a lesser degree of Ganymede's differentiation.
Plain Language Summary
On 7 June 2021, Juno performed the first close flyby of Ganymede, the largest satellite of Jupiter (and the largest moon in the Solar System), since the end of the Galileo mission. The gravity field of Ganymede was reconstructed using the radio tracking data from all of the Ganymede encounters of both the Galileo and Juno missions. The data analysis hints at localized gravity anomalies. Interpretation of the gravity data suggests a slightly higher moment of inertia with respect previous publications, indicating a lesser degree of differentiation.
Key Points
Joint analysis of the Juno and Galileo data leads to a Ganymede's degree‐2 gravity compatible with hydrostatic equilibrium within 1−σ
The data hints at regional gravity anomalies with amplitudes exceeding those inferred by Cassini for Titan
Treatment of non‐hydrostatic effects leads to wider confidence intervals for the derived moment of inertia with respect to previous studies
•The experimental egress of ants was compared with human egress in emergency conditions.•The behavior of ants and humans was very different when evacuating under threatening situations.•Ants did not ...jam nor clog near the door, thus always producing efficient evacuations.
In this work we studied the trajectories, velocities and densities of ants when egressing under controlled levels of stress produced by a chemical repellent at different concentrations. We found that, unlike other animals escaping under life-and-death conditions and pedestrian simulations, ants do not produce a higher density zone near the exit door. Instead, ants are uniformly distributed over the available space allowing for efficient evacuations. Consequently, the faster-is-slower effect observed in ants (Soria et al., 2012) is clearly of a different nature to that predicted by de social force model. In the case of ants, the minimum evacuation time is correlated with the lower probability of taking backward steps. Thus, as biological model ants have important differences that make their use inadvisable for the design of human facilities.
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