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Subduction earthquake sequences in a non-linear visco-elasto-plastic megathrust
No full textWe present a 2-D thermomechanical computational framework for simulating earthquake sequences in a non-linear visco-elasto-plastic compressible medium. The method is developed for a plane-strain problem and incorporates an invariant formulation of the classical rate- and state-dependent friction law and an adaptive time-stepping, which allows the time step to vary by many orders of magnitude during a simulation. Long-term tectonic convergence is imposed by displacing a boundary at a constant rate, whereas temperature-dependent viscosity is solved using a rapidly converging Newton–Raphson scheme. The 2-D volume is discretized using finite differences on a fully staggered grid and marker-in-cell techniques. An adaptive free-surface approximation is used to modulate the air viscosity with the time step, which allows stresses to vanish on the free surface during the propagation of fast slipping events. We present a set of increasingly complex models in which we investigate how inertia, radiation damping, thermally activated non-linear rheology and off-megathrust splay-fault events affect sequences of seismic and aseismic slip on a simplified subduction megathrust. The new method provides a unique computational framework to analyse earthquake sequences and to connect forearc deformation with the dynamic properties of the megathrust, thus providing a physical link between observations spanning from slow interseismic strain accumulation to localized coseismic slip of individual earthquakes and post-seismic viscoelastic relaxation
The extent of ionization in simulations of radio-loud AGNs impacting kpc gas discs
No full textWe use the results of relativistic hydrodynamic simulations of jet-interstellar medium (ISM) interactions in a galaxy with a radio-loud AGN to quantify the extent of ionization in the central few kpcs of the gaseous galactic disc. We perform post-process radiative transfer of AGN radiation through the simulated gaseous jet-perturbed disc to estimate the extent of photo-ionization by the AGN with an incident luminosity of 10⁴⁵ erg s⁻¹. We also map the gas that is collisionally ionized due to shocks driven by the jet. The analysis was carried out for simulations with similar jet power (10⁴⁵ erg s⁻¹) but different jet orientations with respect to the gas disc. We find that the shocks from the jets can ionize a significant fraction (up to 33 per cent of dense gas (n > 100 cm⁻³) in the disc, and that the jets clear out the central regions of gas for AGN radiation to penetrate to larger distances in the disc. Jets inclined towards the disc plane couple more strongly with the ISM and ionize a larger fraction of gas in the disc as compared to the vertical jet. However, similar to previous studies, we find that the AGN radiation is quickly absorbed by the outer layers of dense clouds in the disc, and is not able to substantially ionize the disc on a global scale. Thus, compared to jet–ISM interactions, we expect that photo-ionization by the AGN radiation only weakly affects the star-formation activity in the central regions of the galactic disc (≲ 1 kpc), although the jet-induced shocks can spread farther out
Scintillation time-scale measurement of the highly active FRB20201124A
No full textScintillation of compact radio sources results from the interference between images caused by multipath propagation, and probes the intervening scattering plasma and the velocities of the emitting source and scattering screen. In FRB20201124A, a repeating fast radio burst (FRB) that entered a period of extreme activity, we obtained many burst detections in observations at the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Effelsberg 100-m Radio Telescope. Bursts nearby in time show similar scintillation patterns, and we measure a scintillation time-scale of 14.3 ± 1.2 and 7 ± 2 min at Effelsberg (1370 MHz) and uGMRT (650 MHz), respectively, by correlating burst pair spectra. The scintillation bandwidth scaled to 1 GHz is 0.5 ± 0.1 MHz, and the inferred scintillation velocity at Effelsberg is V_(ISS) ≈ (59 ± 7) √(d₁/2 kpc km s⁻¹), higher than Earth’s velocity for any screen beyond a lens distance of d₁ ≳ 400 pc. From the measured scintillation bandwidth, FRB20201124A has comparatively lower scattering than nearby pulsars, and is underscattered by a factor of ∼30 or ∼1200 compared to the NE2001 and YMW16 model predictions, respectively. This underscattering together with the measured scintillation velocity is consistent with a scattering screen more nearby the Earth at d₁ ~ 400 pc, rather than at 2 kpc spiral arm that NE2001 predicts to be the dominant source of scattering. With future measurements, the distance, geometry, and velocity of the scattering screen could be obtained through modelling of the annual variation in V_(ISS), or through interstation time delays or interferometric observations. Scintillation/scattering measurements of FRBs could help improve Galactic electron density models, particularly in the Galactic halo or at high Galactic latitudes
The Design and Integrated Performance of SPT-3G
No full textSPT-3G is the third survey receiver operating on the South Pole Telescope dedicated to high-resolution observations of the cosmic microwave background (CMB). Sensitive measurements of the temperature and polarization anisotropies of the CMB provide a powerful data set for constraining cosmology. Additionally, CMB surveys with arcminute-scale resolution are capable of detecting galaxy clusters, millimeter-wave bright galaxies, and a variety of transient phenomena. The SPT-3G instrument provides a significant improvement in mapping speed over its predecessors, SPT-SZ and SPTpol. The broadband optics design of the instrument achieves a 430 mm diameter image plane across observing bands of 95, 150, and 220 GHz, with 1.2′ FWHM beam response at 150 GHz. In the receiver, this image plane is populated with 2690 dual-polarization, trichroic pixels (∼16,000 detectors) read out using a 68× digital frequency-domain multiplexing readout system. In 2018, SPT-3G began a multiyear survey of 1500 deg² of the southern sky. We summarize the unique optical, cryogenic, detector, and readout technologies employed in SPT-3G, and we report on the integrated performance of the instrument
Euclid preparation. XVII. Cosmic Dawn Survey: Spitzer Space Telescope observations of the Euclid deep fields and calibration fields
No full textWe present a new infrared survey covering the three Euclid deep fields and four other Euclid calibration fields using Spitzer Space Telescope’s Infrared Array Camera (IRAC). We combined these new observations with all relevant IRAC archival data of these fields in order to produce the deepest possible mosaics of these regions. In total, these observations represent nearly 11 % of the total Spitzer Space Telescope mission time. The resulting mosaics cover a total of approximately 71.5 deg² in the 3.6 and 4.5 μm bands, and approximately 21.8 deg² in the 5.8 and 8 μm bands. They reach at least 24 AB magnitude (measured to 5σ, in a 2″.5 aperture) in the 3.6 μm band and up to ∼5 mag deeper in the deepest regions. The astrometry is tied to the Gaia astrometric reference system, and the typical astrometric uncertainty for sources with 16 Spitzer Space Telescope has now been decommissioned, these mosaics are likely to be the definitive reduction of these IRAC data. This survey therefore represents an essential first step in assembling multi-wavelength data on the Euclid deep fields, which are set to become some of the premier fields for extragalactic astronomy in the 2020s
Automated reconstruction of dendritic and axonal arbors reveals molecular correlates of neuroanatomy
No full textNeuronal anatomy is central to the organization and function of brain cell types. However, anatomical variability within apparently homogeneous populations of cells can obscure such insights. Here, we report large-scale automation of arbor reconstruction on a dataset of 802 inhibitory neurons characterized using the Patch-seq method, which enables measurement of multiple properties from individual neurons, including local morphology and transcriptional signature. We demonstrate that these automated reconstructions can be used in the same manner as manual reconstructions to understand the relationship between many cellular properties used to define cell types. We uncover molecular correlates of laminar innervation on multiple molecularly defined neuronal subclasses and types. In particular, our results reveal molecular correlates of the variability in Layer 1 (L1) innervation even in a transcriptomically defined subpopulation of Martinotti cells in the adult mouse neocortex
Weak cubic CaSiO₃ perovskite in the Earth’s mantle
No full textCubic CaSiO₃ perovskite is a major phase in subducted oceanic crust, where it forms at a depth of about 550 kilometres from majoritic garnet. However, its rheological properties at temperatures and pressures typical of the lower mantle are poorly known. Here we measured the plastic strength of cubic CaSiO₃ perovskite at pressure and temperature conditions typical for a subducting slab up to a depth of about 1,200 kilometres. In contrast to tetragonal CaSiO₃, previously investigated at room temperature, we find that cubic CaSiO₃ perovskite is a comparably weak phase at the temperatures of the lower mantle. We find that its strength and viscosity are substantially lower than that of bridgmanite and ferropericlase, possibly making cubic CaSiO₃ perovskite the weakest lower-mantle phase. Our findings suggest that cubic CaSiO₃ perovskite governs the dynamics of subducting slabs. Weak CaSiO₃ perovskite further provides a mechanism to separate subducted oceanic crust from the underlying mantle. Depending on the depth of the separation, basaltic crust could accumulate at the boundary between the upper and lower mantle, where cubic CaSiO₃ perovskite may contribute to the seismically observed regions of low shear-wave velocities in the uppermost lower mantle, or sink to the core–mantle boundary and explain the seismic anomalies associated with large low-shear-velocity provinces beneath Africa and the Pacific
Precursory Signal Detected for the 2018 Sierra Negra Volcanic Eruption, Galápagos, Using Seismic Ambient Noise
No full textThe changes in physical properties leading up to a volcanic eruption provide clues to processes occurring within volcanoes and may reveal premonitory signals. The Sierra Negra shield volcano, located in the Galápagos Islands, erupted on 26 June 2018 after months of continued inflation and escalating earthquake activity. We applied ambient noise interferometry to five months of continuous seismic data from 12 broadband stations to calculate crustal shear-wave velocity changes before and during the eruption. Using the Moving Window Cross-Spectral technique and a pre-eruption stack of ambient seismic data as reference, we found a −0.27% decrease in velocity 17 days before the eruption in station-pairs that pass beneath the caldera's north-eastern sector. Sensitivity kernels suggest that the velocity changes of this precursory signal are greatest at depths corresponding to the shallow sill (∼2 km) beneath the wide caldera. Our results, considered in light of geodetic, seismicity, and petrological results, suggest that this velocity decrease is in part caused by dilatation from a M_L 4.8 earthquake, and degassing after a possible magma intrusion below or at the base of the sill. The precursory velocity decrease within the sill region offers an important tool for forecasting future eruptions at Sierra Negra
Hysteresis in electrochemical systems
No full textHysteresis is a phenomenon that pervades both the physical and social sciences. While commonly associated with magnetism, it also occurs in a wide variety of other materials, including ferroelectrics and shape memory alloys. Hysteresis emerges when a particular property has a history dependence. It is exploited in microelectronic memory, logic, and neuromorphic devices. In electrochemical systems, such as Li-ion batteries, hysteresis is undesirable as it leads to energy losses during each round trip charge–discharge cycle. Unfortunately, many new battery concepts that promise significant increases in energy density, including those that rely on displacement and conversion reactions, or on anion-redox mechanisms, suffer from severe hysteresis that prevents their commercialization. This article surveys different forms of hysteresis in electrochemical systems with a focus on Li-ion batteries and establishes thermodynamic and kinetic principles with which to understand and rationalize electrochemical hysteresis. The ability to control hysteresis in rechargeable batteries will enable the implementation of promising electrode chemistries. It will also open the door to many new device applications. As on-chip batteries become more prominent, new possibilities will emerge to incorporate them not only as local energy sources but also as active components of new device concepts that exploit electrochemical hysteresis
Mentalizing During Social Interaction: The Development and Validation of the Interactive Mentalizing Questionnaire
No full textStudies have shown that during social interaction a shared system underlies inferring one’s own mental state, and the mental states of others – processes often referred to as mentalization. However, no validated assessment has been developed to measure second order mentalization (one’s beliefs about how transparent one’s thoughts are to others), or whether this capacity plays a significant role in social interaction. The current work presents a interactive mentalization theory, which divides these directional and second order aspects of mentalization, and investigates whether these constructs are measurable, stable, and meaningful in social interactions. We developed a 20-item, self-report interactive mentalization questionnaire (IMQ) in order to assess the different sub-components of mentalization: self–self, self–other, and other–self mentalization (Study 1). We then tested this scale on a large, online sample, and report convergent and discriminant validity in the form of correlations with other measures (Study 2), as well as correlations with social deception behaviors in real online interaction with Mturk studies (Study 3 and Study 4). These results validate the IMQ, and support the idea that these three factors can predict mentalization in social interaction