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Current algebra approach to two-dimensional interacting chiral metals
No full textWe reinterpret the chiral U(N) Wess-Zumino-Witten (WZW) model at level k>1 in (1+1) dimensions as an interacting chiral metal in two space dimensions. In this reinterpretation, spatial translations along one of the spatial dimensions in the two-dimensional chiral metal arise from a generator of the U(N) symmetry of the WZW model. The WZW model at k=1 is equivalent to Balents and Fisher's free chiral metal [L. Balents and M. P. A. Fisher, Phys. Rev. Lett. 76, 2782 (1996)]. Here, the U(N) symmetry corresponds to the IR symmetry of a chiral Fermi gas with (half of a) Fermi surface, with N equal to the number of points on the Fermi surface. We argue that exactly solvable interacting generalizations occur for levels k>1. Importantly, these interacting chiral metals maintain the U(N) symmetry of the free system. We calculate two-point correlation functions of the single-particle fermion operator, the U(1) number density, and current operators in these theories for general k. We find that interactions (k>1) produce 1/N corrections to scaling of the single-particle fermion operator as N→∞ and renormalize the amplitudes of the density and current two-point functions. This construction illustrates the ersatz Fermi liquid proposal of Else et al. [Phys. Rev. X 11, 021005 (2021)]
Effects of tidal emersion and marine heatwaves on cuttlefish early ontogeny
No full textAnthropogenic climate change has increased the frequency and intensity of extreme weather events, such as marine heatwaves (MHW). They exert a strong influence over the structure and functioning of marine ecosystems, considering temperature is one of the most critical environmental factors affecting marine life. Additionally, intertidal habitats are ecologically challenging ecosystems, and inhabiting organisms need to possess the necessary mechanisms to adapt to the periodic fluctuations in physical characteristics across tidal cycles. To assess the effect of simulated MHWs (categories I and IV) and low tide conditions (emersion) on the early development of the common cuttlefish Sepia officinalis, the development time and hatching success were evaluated, as well as the antioxidant enzymatic machinery, lipid peroxidation, HSP70 and total ubiquitin concentrations. Embryonic development time decreased significantly with temperature, but tidal emersion held no significant impact on development time or hatching success. Superoxide dismutase activity levels were significantly increased with temperature but lowered under emersion conditions. Glutathione-S-transferase activity significantly increased with temperature, while glutathione peroxidase activity was significantly enhanced under emersion. Catalase activity, lipid peroxidation, HSP70 content and total ubiquitin content were not affected by any of the treatments. These findings suggest that while development time is greatly conditioned by temperature, S. officinalis embryos are remarkably resilient to emersion conditions. Moreover, the simulated marine heatwaves did not elicit any sub-lethal oxidative stress-related effects, suggesting that such temperatures were still within the optimum range of the cuttlefish thermal window of aerobic performance
Geolocalization of Large-Scale DAS Channels Using a GPS-Tracked Moving Vehicle
No full textGeolocalization of distributed acoustic sensing (DAS) array channels represents a crucial step whenever the technology is deployed in the field. Commonly, the geolocalization is performed using point-wise active-source experiments, known as tap tests, conducted in the vicinity of the recording fiber. However, these controlled-source experiments are time consuming and greatly diminish the ability to promptly deploy such systems, especially for large-scale DAS experiments. We present a geolocalization methodology for DAS instrumentation that relies on seismic signals generated by a geotracked vehicle. We demonstrate the efficacy of our workflow by geolocating the channels of two DAS systems recording data on dark fibers stretching approximately 100 km within the Long Valley caldera area in eastern California. Our procedure permits the prompt calibration of DAS channel locations for seismic-related applications such as seismic hazard assessment, urban-noise monitoring, wavespeed inversion, and earthquake engineering. We share the developed set of codes along with a tutorial guiding users through the entire mapping process
Constraining the Densities of the Three Kepler-289 Planets with Transit Timing Variations
No full textKepler-289 is a three-planet system containing two sub-Neptunes and one cool giant planet orbiting a young, Sun-like star. All three planets exhibit transit timing variations (TTVs), with both adjacent planet pairs having orbital periods close to the 2:1 orbital resonance. We observe two transits of Kepler-289c with the Wide-field InfraRed Camera on the 200″ Hale Telescope at Palomar Observatory, using diffuser-assisted photometry to achieve space-like photometric precision from the ground. These new transit observations extend the original four-year Kepler TTV baseline by an additional 7.5 yr. We rereduce the archival Kepler data with an improved stellar activity correction and carry out a joint fit with the Palomar data to constrain the transit shapes and derive updated transit times. We then model the TTVs to determine the masses of the three planets and constrain their densities and bulk compositions. Our new analysis improves on previous mass and density constraints by a factor of two or more for all three planets, with the innermost planet showing the largest improvement. Our updated atmospheric mass fractions for the inner two planets indicate that they have hydrogen-rich envelopes, consistent with their location on the upper side of the radius valley. We also constrain the heavy element composition of the outer Saturn-mass planet, Kepler-289c, for the first time, finding that it contains 30.5 ± 6.9 M_⊕ of metals. We use dust evolution models to show that Kepler-289c must have formed beyond 1 au, and likely beyond 3 au, and then migrated inward
CO and CO₂ Productions Rates of Comets Observed by NEOWISE within Year 1 of the Reactivated Mission
No full textWe report on the observed fluxes of the comets detected by NEOWISE during the first year of operations after the spacecraft’s reactivation. The sample included 57 comets. Of the comets detected, 30 were short-period comets (27 Jupiter-family comets, 1 Centaur, 2 Halley-type comets), and 27 were long-period comets. From the measured fluxes in the two NEOWISE bands, proxies for the gas production and coma dust are derived. We find a relationship between heliocentric distance, perihelion distance, and the gas-to-dust proxy fractions
Early Results from GLASS-JWST. XI. Stellar Masses and Mass-to-light Ratio of z > 7 Galaxies
No full textWe exploit James Webb Space Telescope (JWST) NIRCam observations from the GLASS-JWST-Early Release Science program to investigate galaxy stellar masses at z > 7. We first show that JWST observations reduce the uncertainties on the stellar mass by a factor of at least 5–10, when compared with the highest-quality data sets available to date. We then study the UV mass-to-light ratio, finding that galaxies exhibit a a two orders of magnitude range of M/L_(UV) values for a given luminosity, indicative of a broad variety of physical conditions and star formation histories. As a consequence, previous estimates of the cosmic stellar-mass density — based on an average correlation between UV luminosity and stellar mass — can be biased by as much as a factor of ∼6. Our first exploration demonstrates that JWST represents a new era in our understanding of stellar masses at z > 7 and, therefore, of the growth of galaxies prior to cosmic reionization
Numerical simulation of turbulent, plane parallel Couette-Poiseuille flow
No full textWe present numerical simulation and mean-flow modelling of statistically stationary plane Couette–Poiseuille flow in a parameter space (Re,θ) with Re = √[Re꜀² + Re²_M] and θ = arctan (Re_M/Re꜀, where Re꜀, Re_M are independent Reynolds numbers based on the plate speed U꜀ and the volume flow rate per unit span, respectively. The database comprises direct numerical simulations (DNS) at Re = 4000, 6000, wall-resolved large-eddy simulations at Re = 10000, 20000, and some wall-modelled large-eddy simulations (WMLES) up to Re = 10¹⁰. Attention is focused on the transition (from Couette-type to Poiseuille-type flow), defined as where the mean skin-friction Reynolds number on the bottom wall Re_(τ,b), changes sign at θ = θ꜀(Re). The mean flow in the (Re,θ) plane is modelled with combinations of patched classical log-wake profiles. Several model versions with different structures are constructed in both the Couette-type and Poiseuille-type flow regions. Model calculations of Re_(τ,b)(Re,θ), Re_(τ,t)(Re,θ) (the skin-friction Reynolds number on the top wall) and θ꜀ show general agreement with both DNS and large-eddy simulations. Both model and simulation indicate that, as θ is increased at fixed Re, Re_(τ,t) passes through a peak at approximately θ = 45°, while Re_(τ,b) increases monotonically. Near the bottom wall, the flow laminarizes as θ passes through θ_(c) and then re-transitions to turbulence. As Re increases, θ꜀ increases monotonically. The transition from Couette-type to Poiseuille-type flow is accompanied by the rapid attenuation of streamwise rolls observed in pure Couette flow. A subclass of flows with Re_(τ,b) = 0 is investigated. Combined WMLES with modelling for these flows enables exploration of the Re → ∞ limit, giving θ꜀ → 45° as Re → ∞
Chemo-mechanical-microstructural coupling in the tarsus exoskeleton of the scorpion Scorpio palmatus
No full textThe multiscale structure of biomaterials enables their exceptional mechanical robustness, yet the impact of each constituent at their relevant length scale remains elusive. We used SAXD analysis to expose the intact chitin-fiber architecture within the exoskeleton on a scorpion's claw, revealing varying orientations, including Bouligand and unidirectional regions different from other arthropod species. We uncovered the contribution of individual components’ constituent behavior to its mechanical properties from the micro- to the nanoscale. At the microscale, in-situ micromechanical experiments were used to determine site-specific stiffness, strength, and failure of the biocomposite due to fiber orientation, while metal-crosslinking of proteins is characterized via fluorescence maps. At the constituent level, combined with FEA simulations, we uncovered the behavior of fiber-matrix deformation with fiber diameter <53.7 nm and protein modulus in the range 1.4-11 MPa. The unveiled microstructure-mechanics relationship sheds light on the evolved structural functionalities and constituents' interactions within the scorpion cuticle
Neural mechanisms underlying the hierarchical construction of perceived aesthetic value
No full textLittle is known about how the brain computes the perceived aesthetic value of complex stimuli such as visual art. Here, we used computational methods in combination with functional neuroimaging to provide evidence that the aesthetic value of a visual stimulus is computed in a hierarchical manner via a weighted integration over both low and high level stimulus features contained in early and late visual cortex, extending into parietal and lateral prefrontal cortices. Feature representations in parietal and lateral prefrontal cortex may in turn be utilized to produce an overall aesthetic value in the medial prefrontal cortex. Such brain-wide computations are not only consistent with a feature-based mechanism for value construction, but also resemble computations performed by a deep convolutional neural network. Our findings thus shed light on the existence of a general neurocomputational mechanism for rapidly and flexibly producing value judgements across an array of complex novel stimuli and situations
High-contrast Imaging around a 2 Myr-old CI Tau with a Close-in Gas Giant
No full textGiant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. CI Tau is a 2 Myr-old classical T Tauri star hosting an eccentric hot Jupiter, CI Tau b. The standard formation scenario of a hot Jupiter predicts that planets formed further out and migrated inward. A high eccentricity of CI Tau b may be suggestive of high-e migration due to secular gravitational perturbations by an outer companion. Also, the Atacama Large Millimeter/submillimeter Array 1.3 mm-continuum observations show that CI Tau has at least three annular gaps in which unseen planets may exist. We present high-contrast imaging around CI Tau taken from the Keck/NIRC2 _(L')-band filter and vortex coronagraph that allows us to search for an outer companion. We did not detect any outer companion around CI Tau from angular differential imaging (ADI) using two deep imaging data sets. The detection limits from ADI-reduced images rule out the existence of an outer companion beyond ∼30 au that can cause the Kozai–Lidov migration of CI Tau b. Our results suggest that CI Tau b may have experienced type II migration from ≲2 au in megayears. We also confirm that no planets with ≥ 2–4 M_Jup are hidden in two outer gaps