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A Seismological Study of the Michoacán-Colima, Mexico, Earthquake of 19 September 2022 (Mw7.6)
No full textMichoacán-Colima earthquake of 19 September 2022 (Mₛ 7.6, M_w 7.6) ruptured the NW end of the Cocos-North American plate interface, causing severe damage to many towns and cities in the states of Michoacán and Colima. The damage was further exacerbated by a major aftershock (M_w 6.7) on 22 September. The mainshock initiated below the coast at a hypocentral distance of 22 km from the seismic station of Maruata (MMIG) where peak ground acceleration and velocity, PGA and PGV, of ~ 1 g and 28 cm/s were recorded. The epicenter of the major aftershock was located ~ 30 km SE of the mainshock. Finite fault modeling of the mainshock by the U.S. Geological Survey reveals a rupture propagation along the strike towards the NW and yields a static stress drop, Δσₛ, of 3.7 MPa. Our estimated radiated energy, ER, is 3.44 x 10¹⁵ J, so that ER /M₀ is 1.27 × 10⁻⁵ similar to other large Mexican thrust earthquakes whose rupture areas do not extend to the trench.
Aftershocks of the 2022 mainshock overlap that of the Colima earthquake of 30 January 1973 (M_w7.6). Galitzin seismograms of the two earthquakes at DeBilt (DBN), The Netherlands, are reasonably similar so that they may be classified as quasi-repeated events. On the other hand, the DBN seismogram of the earthquake of 15 April 1941 (Mₛ 7.7), whose location is poorly known but occurred in the same region, differs greatly from those of the 1973 and 2022 earthquakes, suggesting a different source area for the 1941 event.
An analysis of the extensive regional recordings exhibits the effect of the directivity on the ground motion and on the ratio of ground motion during the mainshock to the major aftershock. The directivity explains the observed azimuthal dependence of PGA and PGV ratios, spectral ratios, and PGA and response spectra at 2s, Sa (T = 2 s). Because of the directivity, PGA, PGV, and Sa (T = 2 s) in the Valley of Mexico during the mainshock and the major aftershock were about the same in spite of the magnitude difference of 0.9. At CU (the reference, hard site in Mexico City), PGA and PGV during both events were ~ 6 cm/s² and 2 cm/s, respectively, lower than expected for the mainshock and higher than expected for the aftershock
Discovery and Binding Mechanism of Pyrazoloisoquinoline-Based Novel β-Arrestin Inverse Agonists of the Kappa-Opioid Receptor
No full textChronic exposure to stress or unwanted stimuli has been known to activate kappa opioid receptor/dynorphin (KOR/DYN) systems, which could induce depressive states and develop into some psychiatric disorders. Here, we report the first discovery of pyrazoloisoquinoline-based novel KOR β-arrestin inverse agonists through synthesis, structure–activity relationships, optimization, and the biological evaluations of μ/κ/δ opioid receptor activities with cAMP and β-arrestin recruitment assays. The optimized compound 7q shows potent and selective β-arrestin inverse agonism at KOR with an EC₅₀ value of 9.33 nM in contrast to lower activities at DOR and no activity at MOR. Moreover, we use molecular dynamics simulations to predict the binding mode of the inverse agonist and propose a mechanism for the inverse agonism. We find that the transmembrane helix 6 position of the activated state is different for the OR subtypes, leading to significantly different interactions between the receptor and β-arrestin
Human visual explanations mitigate bias in AI-based assessment of surgeon skills
No full textArtificial intelligence (AI) systems can now reliably assess surgeon skills through videos of intraoperative surgical activity. With such systems informing future high-stakes decisions such as whether to credential surgeons and grant them the privilege to operate on patients, it is critical that they treat all surgeons fairly. However, it remains an open question whether surgical AI systems exhibit bias against surgeon sub-cohorts, and, if so, whether such bias can be mitigated. Here, we examine and mitigate the bias exhibited by a family of surgical AI systems—SAIS—deployed on videos of robotic surgeries from three geographically-diverse hospitals (USA and EU). We show that SAIS exhibits an underskilling bias, erroneously downgrading surgical performance, and an overskilling bias, erroneously upgrading surgical performance, at different rates across surgeon sub-cohorts. To mitigate such bias, we leverage a strategy —TWIX—which teaches an AI system to provide a visual explanation for its skill assessment that otherwise would have been provided by human experts. We show that whereas baseline strategies inconsistently mitigate algorithmic bias, TWIX can effectively mitigate the underskilling and overskilling bias while simultaneously improving the performance of these AI systems across hospitals. We discovered that these findings carry over to the training environment where we assess medical students’ skills today. Our study is a critical prerequisite to the eventual implementation of AI-augmented global surgeon credentialing programs, ensuring that all surgeons are treated fairly
Correction: Single and dual metal atom catalysts for enhanced singlet oxygen generation and oxygen reduction reaction
No full textCorrection for ‘Single and dual metal atom catalysts for enhanced singlet oxygen generation and oxygen reduction reaction’ by Mohsen Tamtaji et al., J. Mater. Chem. A, 2023, https://doi.org/10.1039/D2TA08240C
Measurement of the Angular Momenta of Pre-main-sequence Stars: Early Evolution of Slow and Fast Rotators and Empirical Constraints on Spin-down Torque Mechanisms
No full textWe use TESS full-frame imaging data to investigate the angular momentum evolution of young stars in the Orion Complex. We confirm recent findings that stars with rotation periods faster than 2 days are overwhelmingly binaries, with typical separations of tens of au; such binaries quickly clear their disks, leading to a tendency for rapid rotators to be diskless. Among (nominally single) stars with rotation periods slower than 2 days, we observe the familiar gyrochronological horseshoe-shaped relationship of rotation period versus T_(eff_, indicating that the processes that govern the universal evolution of stellar rotation on gigayear timescales are already in place within the first few megayears. Using spectroscopic v sin i, we determine the distribution of sin i, revealing that the youngest stars are biased toward more pole-on orientations, which may be responsible for the systematics between stellar mass and age observed in star-forming regions. We are also able for the first time to make empirical, quantitative measurements of angular momenta and their time derivatives as functions of stellar mass and age, finding these relationships to be much simpler and monotonic as compared to the complex relationships involving rotation period alone; evidently, the relationship between rotation period and T_(eff) is largely a reflection of mass-dependent stellar structure and not of angular momentum per se. Our measurements show that the stars experience spin-down torques in the range of ∼10³⁷ erg at ∼1 Myr to ∼10³⁵ erg at ∼10 Myr, which provide a crucial empirical touchstone for theoretical mechanisms of angular momentum loss in young stars
Location-Dependent Spatiotemporal Antialiasing in Photoacoustic Computed Tomography
No full textPhotoacoustic computed tomography (PACT) images optical absorption contrast by detecting ultrasonic waves induced by optical energy deposition in materials such as biological tissues. An ultrasonic transducer array or its scanning equivalent is used to detect ultrasonic waves. The spatial distribution of the transducer elements must satisfy the spatial Nyquist criterion; otherwise, spatial aliasing occurs and causes artifacts in reconstructed images. The spatial Nyquist criterion poses different requirements on the transducer elements’ distributions for different locations in the image domain, which has not been studied previously. In this research, we elaborate on the location dependency through spatiotemporal analysis and propose a location-dependent spatiotemporal antialiasing method. By applying this method to PACT in full-ring array geometry, we effectively mitigate aliasing artifacts with minimal effects on image resolution in both numerical simulations and in vivo experiments
Reliability Function for Streaming Over a DMC With Feedback
No full textConventionally, posterior matching is investigated in channel coding and block encoding contexts – the source symbols are equiprobably distributed and are entirely known by the encoder before the transmission. In this paper, we consider a streaming source, whose symbols progressively arrive at the encoder at a sequence of deterministic times. We derive the joint source-channel coding (JSCC) reliability function for streaming over a discrete memoryless channel (DMC) with feedback. We propose a novel instantaneous encoding phase that operates during the symbol arriving period and achieves the JSCC reliability function for streaming when followed by a block encoding scheme that achieves the JSCC reliability function for a classical source whose symbols are fully accessible before the transmission. During the instantaneous encoding phase, the evolving message alphabet is partitioned into groups whose priors are close to the capacity-achieving distribution, and the encoder determines the group index of the actual sequence of symbols arrived so far and applies randomization to exactly match the distribution of the transmitted index to the capacity-achieving one. Surprisingly, the JSCC reliability function for streaming is equal to that for a fully accessible source, implying that the knowledge of the entire symbol sequence before the transmission offers no advantage in terms of the reliability function. For streaming over a symmetric binary-input DMC, we propose a one-phase instantaneous small-enough difference (SED) code that not only achieves the JSCC reliability function, but also, thanks to its single-phase time-invariant coding rule, can be used to stabilize an unstable linear system over a noisy channel. For equiprobably distributed source symbols, we design low complexity algorithms to implement both the instantaneous encoding phase and the instantaneous SED code. The algorithms group the source sequences into sets we call types, which enable the encoder and the decoder to track the priors and the posteriors of source sequences jointly, leading to a log-linear complexity in time. While the reliability function is derived for
non-degenerate DMCs, i.e., DMCs whose transition probability
matrix has all positive entries, for degenerate DMCs, we design
a code with instantaneous encoding that achieves zero error for
all rates below Shannon’s joint source-channel coding limit
Cell-specific occupancy dynamics between the pioneer-like factor Opa/ZIC and Ocelliless/OTX regulate early head development in embryos
No full textDuring development, embryonic patterning systems direct a set of initially uncommitted pluripotent cells to differentiate into a variety of cell types and tissues. A core network of transcription factors, such as Zelda/POU5F1, Odd-paired (Opa)/ZIC3 and Ocelliless (Oc)/OTX2, are conserved across animals. While Opa is essential for a second wave of zygotic activation after Zelda, it is unclear whether Opa drives head cell specification, in the Drosophila embryo. Our hypothesis is that Opa and Oc are interacting with distinct cis-regulatory regions for shaping cell fates in the embryonic head. Super-resolution microscopy and meta-analysis of single-cell RNAseq datasets show that opa’s and oc’s overlapping expression domains are dynamic in the head region, with both factors being simultaneously transcribed at the blastula stage. Additionally, analysis of single-embryo RNAseq data reveals a subgroup of Opa-bound genes to be Opa-independent in the cellularized embryo. Interrogation of these genes against Oc ChIPseq combined with in situ data, suggests that Opa is competing with Oc for the regulation of a subgroup of genes later in gastrulation. Specifically, we find that Oc binds to late, head-specific enhancers independently and activates them in a head-specific wave of zygotic transcription, suggesting distinct roles for Oc in the blastula and gastrula stages
Hydrodynamics Change Tafel Slopes in Electrochemical CO₂ Reduction on Copper
No full textThe hydrodynamics of electrochemical CO₂ reduction (CO₂R) systems is an insufficiently investigated area of research that has broad implications on catalyst activity and selectivity. While most previous reports are limited to laminar and CO₂-sparged systems, herein we address a wide range of hydrodynamics via electrolyte recirculation systems. We find that increased hydrodynamics at the electrode surface results directly in changes to the ethylene and methane Tafel slopes, demonstrating that mass transport is on equal footing with catalyst active sites in determining reaction mechanisms and the ensuing product distribution. Mass transport is traditionally considered to be in the purview of systems-level engineering, yet the present work shows that CO₂R mechanistic work must be considered in the context of the mass transport conditions. We extend our analysis to organic coatings, demonstrating that the films shield the active sites from variability in hydrodynamics and increase the residence time of CO so that it may be further reduced to desirable products
Rydberg Excitons and Trions in Monolayer MoTe₂
No full textMonolayer transition metal dichalcogenide (TMDC) semiconductors exhibit strong excitonic optical resonances which serve as a microscopic, non-invasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS₂, MoSe₂, WS₂ and WSe₂), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe₂). Here, we report an experimental investigation of excitonic luminescence properties of monolayer MoTe₂ to understand the excitonic Rydberg series, up to 3s. We report significant modification of emission energies with temperature (4K to 300K), quantifying the exciton-phonon coupling. Furthermore, we observe a strongly gate-tunable exciton-trion interplay for all the Rydberg states governed mainly by free-carrier screening, Pauli blocking, and band-gap renormalization in agreement with the results of first-principles GW plus Bethe-Salpeter equation approach calculations. Our results help bring monolayer MoTe₂ closer to its potential applications in near-infrared optoelectronics and photonic devices