COVID-19 vaccine: factual reporting, dynamic preferences, and gender hesitancy

At different rates in different countries, one can observe the phenomenon of COVID-19 vaccine hesitancy. In June 2021, we surveyed 1,068 people in France and Italy to inquire about individual potential acceptance, focusing on time preferences, in a risk-return framework: getting the jab today, in a month, and in 3 months; perceived risks of vaccination and COVID-19; and expected benefit of the vaccine. We conducted a randomized controlled trial to understand the impact of daily stimuli, such as factual news about vaccines, on audience acceptance of vaccination. In the main experiment, participants were asked to read two different articles extracted from two Italian newspapers about vaccine-related thrombosis, one using a more abstract description and language and the other using a more anecdotical description and concrete language. We find that individual preferences for vaccination are variable and unstable over time, and individual choices of accepting, refusing, or delaying may be affected by the way news is written. To understand these dynamic preferences, we propose a new model based on seven categories of human behaviours that was validated by a neural network. We observe a treatment effect: participants who red the articles significantly shifted to vaccine hesitancy categories. Furthermore, we detect a peculiar gender effect, showing that the type of language that results in a higher vaccination rate for men is correlated with women’s lower vaccination rate and vice versa. This outcome should be taken into consideration for an appropriate gender-based communication campaign to achieve herd immunity

Reconstruction of the geometry of volcanic vents by trajectory tracking of fast ejecta - the case of the Eyjafjallajökull 2010 eruption (Iceland)

Two methods are introduced to estimate the depth of origin of ejecta trajectories (depth to magma level in conduit) and the diameter of a conduit in an erupting crater, using analysis of videos from the Eyjafjallajökull 2010 eruption to evaluate their applicability. Both methods rely on the identification of straight, initial trajectories of fast ejecta, observed near the crater rims before they are appreciably bent by air drag and gravity. In the first method, through tracking these straight trajectories and identifying a cut-off angle, the inner diameter and the depth level of the vent can be constrained. In the second method, the intersection point of straight trajectories from individual pulses is used to determine the maximum possible depth from which the tracked ejecta originated and the width of the region from which the pulses emanated. The two methods give nearly identical results on the depth to magma level in the crater of Eyjafjallajökull on 8 to 10 May of 51 ± 7 m. The inner vent diameter, at the level of origin of the pulses and ejecta, is found to have been 8 to 15 m. These methods open up the possibility to feed (near) real-time monitoring systems with otherwise inaccessible information about vent geometry during an ongoing eruption and help defining important eruption source parameters

A study on the influence of internal structures on the shape of pyroclastic particles by X-ray microtomography investigations

1.X-Ray computed microtomography is a non-destructive 3D imaging technique that can be used for the investigation of both the morphology and internal structures of a solid object. Thanks to its versatility, it is currently of common use in many research fields and applications, from medical science to geosciences. The latter include volcanology, where this analytical technique is becoming increasingly popular, in particular for quantifying the shape as well as the internal structure of particles constituting tephra deposits. Particle morphology plays a major role in controlling the mobility of pyroclastic material in the atmosphere and particle-laden flows, while the internal structure (e.g. vesicles and crystal content) is of importance for constraining the processes occurring in magmatic chamber or volcanic conduits. In this paper, we present results of X-Ray microtomography morphological and textural analyses on volcanic particles carried out to study how particle shape is influenced by their internal structures. Particles were selected from tephra generated during explosive eruptions of different magnitude and composition. Results show how particle morphology is strongly influenced by their internal structure, which is characterized by textural features like vesicularity, vesicle and solid structure distribution, vesicles inter-connection and distance between adjacent vesicles. These have been found to vary with magma composition, vesiculation and crystallization history. Furthermore, our results confirm that X-Ray microtomography is a powerful tool for investigating shape and internal structure of particles. It both allows us to characterize the particle shape by means of tridimensional shape parameters and to relate them to their internal structures

Inverting sediment bedforms for evaluating the hazard of dilute pyroclastic density currents in the field

Pyroclastic density currents are ground hugging gas-particle flows associated to explosive volcanic eruptions and moving down a volcano's slope, causing devastation and deaths. Because of the hostile nature they cannot be analyzed directly and most of their fluid dynamic behavior is reconstructed by the deposits left in the geological record, which frequently show peculiar structures such as ripples and dune bedforms. Here, a set of equations is simplified to link flow behavior to particle motion and deposition. This allows to construct a phase diagram by which impact parameters of dilute pyroclastic density currents, representing important factors of hazard, can be calculated by inverting bedforms wavelength and grain size, without the need of more complex models that require extensive work in the laboratory

The terminal velocity of volcanic particles with shape obtained from 3D X-ray microtomography

New experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of Reynolds number Re. Experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size, density and shape. Particle shape, which strongly influences fluid drag, was measured in 3D by High-resolution X-ray microtomography, by which sphericity Φ3D and fractal dimension D3D were obtained. They are easier to measure and less operator dependent than the 2D shape parameters used in previous papers. Drag laws that make use of the new 3D parameters were obtained by fitting particle data to the experiments, and single-equation terminal velocity models were derived. They work well both at high and low Re (3 × 10− 2 < Re < 104), while earlier formulations made use of different equations at different ranges of Re. The new drag laws are well suited for the modelling of particle transportation both in the eruptive column, where coarse and fine particles are present, and also in the distal part of the umbrella region, where fine ash is involved in the large-scale domains of atmospheric circulation. A table of the typical values of Φ3D and D3D of particles from known plinian, subplinian and ash plume eruptions is presented. Graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions

The rate of sedimentation from turbulent suspension: an experimental model with application to pyroclastic density currents and discussion on the grain-size dependence of flow runout

Large‐scale experiments generating ground‐hugging multiphase flows were carried out with the aim of modelling the rate of sedimentation, of pyroclastic density currents. The current was initiated by the impact on the ground of a dense gas‐particle fountain issuing from a vertical conduit. On impact, a thick massive deposit was formed. The grain size of the massive deposit was almost identical to that of the mixture feeding the fountain, suggesting that similar layers formed at the impact of a natural volcanic fountain should be representative of the parent grain‐size distribution of the eruption. The flow evolved laterally into a turbulent suspension current that sedimented a thin, tractive layer. A good correlation was found between the ratio of transported/sedimented load and the normalized Rouse number of the turbulent current. A model of the sedimentation rate was developed, which shows a relationship between grain size and flow runout. A current fed with coarser particles has a higher sedimentation rate, a larger grain‐size selectivity and runs shorter than a current fed with finer particles. Application of the model to pyroclastic deposits of Vesuvius and Campi Flegrei of Southern Italy resulted in sedimentation rates falling inside the range of experiments and allowed definition of the duration of pyroclastic density currents which add important information on the hazard of such dangerous flows. The model could possibly be extended, in the future, to other geological density currents as, for example, turbidity currents

PARTIcle Shape ANalyzer PARTISAN – an open source tool for multi-standard two-dimensional particle morphometry analysis

In volcanology, 2D morphometric analysis is a method often applied for quantitative characterization of eruptive products, used to compare tephra from different events or phases, infer eruptive styles and underlying clast generating mechanisms, or describe the aerodynamic behavior of tephra. Such particle shape analyses can be conducted using particle silhouettes or cross-sectional slices, obtained under by means of electron or optical microscope imagery. Over the course of the last years, a number of different morphometric systems have been used. Each of them uses its own nomenclature and mathematical definitions of shape-describing parameters, some of which can only be obtained using specific commercial software. With the PARTIcal Shape ANalyzer PARTISAN we present a freeware tool which parameterizes 2D shapes and provides a suite of shape descriptors, following the respective standards of the five most commonly used 2D morphometric systems. Use of PARTISAN will enable the user to study and archive the results of particle shape analysis in a format compatible with various published routines, thus increasing the potential for linking new work with results of work previously published by other groups. It will allow as well the cross-comparison of results obtained by these morphological routines. PARTISAN hence could be seen as a "Rosetta Stone" for volcanological particle morphometry, and opens the way towards an inter-group effort for a standardized 2D description of particle shapes

Volcanic jets, plumes, and collapsing fountains: evidence from large-scale experiments, with particular emphasis on the entrainment rate

The source conditions of volcanic plumes and collapsing fountains are investigated by means of large-scale experiments. In the experiments, gas-particle jets issuing from a cylindrical conduit are forced into the atmosphere at different mass flow rates. Dense jets (high particle volumetric concentration, e.g., C 0 > 0.01) generate collapsing fountains, whose height scales with the squared exit velocity. This is consistent with Bernoulli's equation, which is a good approximation if air entrainment is negligible. In this case, kinetic energy is transformed into potential energy without any significant loss by friction with the atmosphere. The dense collapsing fountain, on hitting the ground, generates an intense shear flow similar to a pyroclastic density current. Dilute hot jets (low particle volumetric concentration, e.g., C 0 3). © 2014 Springer-Verlag Berlin Heidelberg

A review of statistical tools for morphometric analysis of juvenile pyroclasts

Post-printMorphometric analyses are based on multiparametric datasets that describe quantitatively the shapes of objects. The stochastic nature of fracture-formation processes that break up magma during explosive eruptions yields mixtures of particles that have highly varied shapes. In volcanology morphometric analysis is applied to these mixtures of particles with diverse shapes for two purposes: (1) to fingerprint tephra from individual eruptions and use the fingerprints to distinguish among tephra layers and determine their extents, and (2) to reconstruct eruption processes, by linking particles formed by known fragmentation processes in experiments with particles from natural pyroclastic deposits. Here we review the most commonly adopted statistical techniques for morphometric analysis of pyroclasts. We provide sets of objects with different shapes, along with their morphometric data, in order to demonstrate and illustrate the methods. They can be used not only for addressing the processes of fragmentation during explosive eruptions, but also for the characterization of other types of solid particles with complex morphologies.Icelandic Centre for Research, grant Nr. 206527-051Peer Reviewe

Interaction between pyroclastic density currents and buildings: Numerical simulation and first experiments

The interaction between pyroclastic density currents and buildings is investigated by means of numerical simulation and large-scale experiments. Numerical simulation is performed with the Euler-Lagrange approach using a two-way coupling between gas and particles of three sizes. The collapse of an eruptive column consisting of a mixture of gas and pyroclasts is produced experimentally, and the impact of the resulting shear current with mock-ups representing buildings is monitored. A combination of results from simulations and experiments shows that, upon impact with a building, the multiphase current develops strong turbulence intensity, which significantly affects particle dispersion. The flow recirculation around the building induces forced deposition at the front and wake in the back wall, with flow reattachment farther away. These changes produce a variation in the dynamic pressure, which is the most important parameter for assessing the impact of pyroclastic density currents moving over inhabited areas