The role of elasticity in slab bending

International audiencePrevious studies showed that plate rheology exerts a dominant control on the shape and velocity of subducting plates. Here, we perform a systematic investigation of the role of elasticity in slab bending, using fully dynamic 2-D models where an elastic, viscoelastic, or viscoelastoplastic plate subducts freely into a purely viscous mantle. We derive a scaling relationship between the bending radius of viscoelastic slabs and the Deborah number, De, which is the ratio of Maxwell time over deformation time. We show that De controls the ratio of elastically stored energy over viscously dissipated energy and find that at De>10-2, substantially less energy is required to bend a viscoelastic slab to the same shape as a purely viscous slab with the same intrinsic viscosity. Elastically stored energy at higher De favors retreating modes of subduction via unbending, while trench advance only occurs for some cases with De 1, where most zones have low De 0.1. Slabs with De<10-2 either have very low viscosities or they may be yielding, in which case our De estimates may be underestimated by up to an order of magnitude, potentially pointing towards a significant role of elasticity in ∼60% of the subduction zones. In support of such a role of elasticity in subduction, we find that increasing De correlates with increasing proportion of larger seismic events in both instrumental and historic catalogues

Earth curvature effects on subduction morphology: Modeling subduction in a spherical setting

We present the first application in geodynamics of a (Fast Multipole) Accelerated Boundary Element Method (Accelerated-BEM) for Stokes flow. The approach offers the advantages of a reduced number of computational elements and linear scaling with the problem size. We show that this numerical method can be fruitfully applied for the simulation of several geodynamic systems at the planetary scale in spherical coordinates, and we suggest a general approach for modeling combined mantle convection and plate tectonics. The first part of the paper is devoted to the technical exposition of the new approach, while the second part focuses on the effect played by Earth curvature on the subduction of a very wide oceanic lithosphere (W=6,000km and W=9,000km), comparing the effects of two different planetary radii (ER=6,371km, 2ER=2×6,371km), corresponding to an "Earth-like" model (ER) and to a "flat Earth" one (2ER). The results show a distinct difference between the two models: while the slab on a "flat Earth" shows a slight undulation, the same subducting plate on the "Earth-like" setting presents a dual behavior characterized by concave curvature at the edges and by a folding with wavelength of the order of magnitude of 1,000km at the center of the sla

Ascent of Bubbles in Magma Conduits Using Boundary Elements and Particles

AbstractWe investigate the use of the Multipole-accelerated Boundary Element Method (BEM) and of the Singularity Method for studying the interaction of many bubbles rising in a volcanic conduit. Observation shows that the expression of volcanic eruption is extremely variable, from slow release of magma to catastrophic explosive manifestation. We investigate the application of the Fast Multipole Method to the solution of (i) the Boundary Element Formulation of the Stokes flow and of (ii) the particle formulation using the Stokeslets, the Green Function of the Stokes flow law, as a particle kernel. We show how these implementations allow for the first time to numerically model in a dynamic setting a very large number of bubbles, i.e few thousands with the BEM models, allowing investigating the feedback between the single bubble deformation and their collective evolution, and few hundred of thousands of bubbles with the particle approach. We illustrate how this method can be used to investigate the intense interaction of a large number of bubbles and suggest a framework for studying the feedback between many bubbles and a complex thermal nonlinear magmati

Comparing state-of-the-art and emerging augmented reality interfaces for autonomous vehicle-to-pedestrian communication

In the last few years, a considerable literature has grown around the theme of how to provide pedestrians and other vulnerable road users (VRUs) with a clear indication about a fully autonomous vehicle (FAV)'s status and intentions, which is crucial to make FAVs and VRUs coexist. So far, a variety of external interfaces leveraging different paradigms and technologies have been created. Proposed designs include vehicle-mounted devices (like LED panels), short-range on-road projection, and road infrastructure interfaces (e.g., special asphalts with embedded displays). These designs have been experimented in different settings, using mockups, specially prepared vehicles, or virtual environments, with heterogeneous evaluation metrics. Some promising interfaces based on Augmented Reality (AR) have been proposed too, but their usability and effectiveness have not been tested yet. This paper aims to complement such body of literature by presenting a comparison of state-of-the-art interfaces and new designs under common conditions. To this aim, an immersive Virtual Reality-based simulation was developed, recreating a well-known scenario used in previous works represented by pedestrian crossing in urban environments under non-regulated conditions. A user study was then performed to investigate the various dimensions of vehicle-to-pedestrian interaction in both objective and subjective terms. Results showed that, although an interface clearly standing out over all the considered dimensions does not exists, one of the studied AR designs was able to provide state-of-the-art results in terms of safety and trust, at the cost of a higher cognitive effort and lower intuitiveness compared to LED panels showing anthropomorphic features. Together with rankings on the various dimensions, indications about advantages and drawbacks of the various alternatives that emerged from the study could be an important information source for next developments in the field

The Multi Crane Scheduling Problem: A Comparison Between Genetic Algorithm and Neural Network Approaches based on Simulation Modeling

The internal logistics for warehouses of many industrial applications, based on the movement of heavy goods, is commonly solved by the installment of a multi-crane system. The job scheduling of a multi-crane system is an interesting problem of optimization, solved in many ways in the past. This paper describes a comparison between the optimization by the use of Genetic Algorithms (GA) and introduce a framework for the solution of the problem using machine learning driven by Neural Networks (NN). Even though this last approach is not implemented in this paper, performances very close to GA ones are expected with NN. A case-study for steel coil production is proposed as a test frame for two different simulation software tools, one based on a heuristic solution and one on machine learning; performances and data achieved from reviews and simulations are compared

Building trust in autonomous vehicles: Role of virtual reality driving simulators in HMI design

The investigation of factors contributing at making humans trust Autonomous Vehicles (AVs) will play a fundamental role in the adoption of such technology. The user's ability to form a mental model of the AV, which is crucial to establish trust, depends on effective user-vehicle communication; thus, the importance of Human-Machine Interaction (HMI) is poised to increase. In this work, we propose a methodology to validate the user experience in AVs based on continuous, objective information gathered from physiological signals, while the user is immersed in a Virtual Reality-based driving simulation. We applied this methodology to the design of a head-up display interface delivering visual cues about the vehicle' sensory and planning systems. Through this approach, we obtained qualitative and quantitative evidence that a complete picture of the vehicle's surrounding, despite the higher cognitive load, is conducive to a less stressful experience. Moreover, after having been exposed to a more informative interface, users involved in the study were also more willing to test a real AV. The proposed methodology could be extended by adjusting the simulation environment, the HMI and/or the vehicle's Artificial Intelligence modules to dig into other aspects of the user experience

Incidence of uterine rupture in second-trimester abortion with gemeprost alone compared to mifepristone and gemeprost

OBJECTIVES: To compare uterine rupture rates in women having a medical abortion receiving gemeprost alone to those receiving mifepristone plus gemeprost. STUDY DESIGN: We reviewed the records of women undergoing medical abortion at 13 0/7-23 6/7 weeks from January 2007 to December 2014 at a single center in Italy. Prior to January 2011, we used gemeprost 1 mg vaginally every 3 h up to a maximum of five doses. After January 2011, we added mifepristone 200 mg orally 24 h prior to the same gemeprost protocol. The primary outcome of the study was the incidence of uterine rupture. We compared the outcome between women receiving gemeprost alone with the combination of gemeprost and mifepristone. RESULTS: One thousand and sixty-one (58.5%) and 753 (41.5%) women underwent medical abortion in the gemeprost-alone and the gemeprost/mifepristone groups, respectively. Five (0.47%) uterine ruptures occurred in the gemeprost and four uterine ruptures occurred in the gemeprost/mifepristone groups, respectively (0.53%) (p=.89). All uterine ruptures occurred in women with prior cesarean delivery. CONCLUSIONS: We rep orted no difference in the incidence of uterine rupture between the gemeprost-alone and gemeprost and mifepristone groups. IMPLICATIONS: Uterine rupture is a rare complication of second-trimester medical abortion with gemeprost. Use of mifepristone prior to gemeprost does not affect this risk

Could YouTubeTM encourage men on prostate checks? A contemporary analysis

Objectives: To assess YouTube™ videos' quality on prostate checks, especially on the digital rectal exam (DRE), and to investigate if they can inform patients correctly and eradicate their beliefs and myths.Methods: A search using as keywords "digital rectal exam for prostate cancer" was performed on the YouTubeTM platform. We selected the first 100 videos. To assess video quality content, Patient Education Materials Assessment Tool for audio-visual content (PEMAT A/V) and Misinformation tool were used.Results: Seventy-three videos were suitable for the analyses. The median PEMAT A/V Understandability score and PEMAT A/V Actionability score were 46.2% (interquartile range [IQR]: 30.8-76.9) and 50.0% (IQR: 25.0-75.0), respectively. The medi-an PEMAT A/V Understandability and Actionability scores were 69.2% (IQR: 46.2-88.5) vs 46.2% (IQR: 30.8-61.5) (p = 0.01) and 100.0% (IQR: 87.5-100.0) vs 25.0% (IQR: 25.0-68.8)(p < 0.001), for healthcare workers vs patients, respectively. According to the Misinformation tool, the median misinforma-tion score of the overall videos was 2.2 (IQR:1.7-2.8). According to the target audience, the misinformation score was 2.8 (IQR: 2.4-3.5) vs 2.0 (IQR: 1.5-2.8) (p = 0.02), for healthcare workers vs patients, respectively. Conclusions: Currently, based on our analyses, YouTubeTM videos' quality on DRE resulted unsatisfactory according to the PEMAT A/V score and the Misinformation tool. Videos targeted to healthcare workers got higher quality scores if compared to videos targeted to patients. Therefore, YouTubeTM videos' may not be considered a reliable source of information on DRE for patients