IST Austria: PubRep (Institute of Science and Technology)
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Mountain glaciers recouple to atmospheric warming over the twenty-first century
No full textRecent studies have argued that air temperatures over many mountain glaciers are decoupled from their surroundings, leading to a local cooling which could slow down melting. Here we use a compilation of on-glacier meteorological observations to assess the extent to which this relationship changes under warming. Statistical modelling of the potential temperature decoupling of the world’s mountain glaciers indicates that currently glacier boundary layers warm ~0.83 °C on average for every degree of ambient temperature rise. Future projections under shared socioeconomic pathway (SSP) climate scenarios SSP 2-4.5 and SSP 5-8.5 indicate that decoupling, and thus relative cooling over glaciers, is maximized during the 2020s and 2030s, before widespread glacier retreat acts to recouple above-glacier air temperatures with its surroundings. This nonlinear feedback will lead to an increased sensitivity to warming from midcentury, with glaciers losing their capacity to affect the local climate and cool themselves
Diagonal cubic forms and the large sieve
No full textLet N(X) be the number of integral zeros (mathematical equation). Works of Hooley and Heath-Brown imply (mathematical equation), if one assumes automorphy and grand Riemann hypothesis for certain Hasse–Weil L-functions. Assuming instead a natural large sieve inequality, we recover the same bound on N(X). This is part of a more general statement, for diagonal cubic forms in (mathematical equation) variables, where we allow approximations to Hasse–Weil L-functions
Mechanism of mammalian transcriptional repression by noncoding RNA
No full textTranscription by RNA polymerase II (Pol II) can be repressed by noncoding RNA, including the human RNA Alu. However, the mechanism by which endogenous RNAs repress transcription remains unclear. Here we present cryogenic-electron microscopy structures of Pol II bound to Alu RNA, which reveal that Alu RNA mimics how DNA and RNA bind to Pol II during transcription elongation. Further, we show how distinct domains of the general transcription factor TFIIF control repressive activity. Together, we reveal how a noncoding RNA can regulate mammalian gene expression
Rate of convergence in multiple SLE using random matrix theory
No full textIn this paper, we provide a rate of convergence for a version of the Carathéodory convergence for the multiple SLE model with a Dyson Brownian motion driver towards its hydrodynamic limit, for β=1 and β=2. The results are obtained by combining techniques from the field of Schramm–Loewner Evolutions with modern techniques from random matrices. Our approach shows how one can apply modern tools used in the proof of universality in random matrix theory to the field of Schramm–Loewner Evolutions
Room temperature, cavity-free capacitive strong coupling to mechanical motion
No full textThe back-action damping of mechanical motion by electromagnetic radiation is typically overwhelmed by internal loss channels unless demanding experimental ingredients such as superconducting resonators, high-quality optical cavities, or large magnetic fields are employed. Here we demonstrate the first room temperature, cavity-free, all-electric device where back-action damping exceeds internal loss, enabled by a mechanically compliant parallel-plate capacitor with a nanoscale plate separation and an aspect ratio exceeding 1,000. The device has 4 orders of magnitude lower insertion loss than a comparable commercial quartz crystal and achieves a position imprecision rivaling optical interferometers. With the help of a back-action isolation scheme, we observe radiative cooling of mechanical motion by a remote cryogenic load. This work provides a technologically accessible route to high-precision sensing, transduction, and signal processing
Unsupervised extraction of rotational Lagrangian coherent structures
No full textLagrangian coherent structures (LCSs) are widely recognized as playing a significant role in turbulence dynamics since they can control the transport of mass, momentum or heat. However, the methods used to identify these structures are often based on ambiguous definitions and arbitrary thresholding. While LCSs theory provides precise and frame-indifferent mathematical definitions of coherent structures, some of the commonly used extraction algorithms employed in the literature are still case-specific and involve user-defined parameters. In this study, we present a new, unsupervised extraction algorithm that enables the extraction of rotational LCSs based on Lagrangian average vorticity deviation from an arbitrary 3D velocity field. The algorithm utilizes two alternative methods for the identification of the LCS core (ridge): an unsupervised clustering method and a streamline-based method. In a subsequent step, the ridge curve is parametrized through a pruning procedure of minimum spanning tree graphs. To assess the effectiveness of the algorithm, we test it on two cases: (i) direct numerical simulations of forced homogeneous and isotropic turbulence and (ii) three-dimensional Particle Tracking Velocimetry experiments of a turbulent gravity current
Superdiffusive transport in chaotic quantum systems with nodal interactions
No full textWe introduce a class of interacting fermionic quantum models in d dimensions with nodal interactions that exhibit superdiffusive transport. We establish nonperturbatively that the nodal structure of the interactions gives rise to long-lived quasiparticle excitations that result in a diverging diffusion constant, even though the system is fully chaotic. Using a Boltzmann equation approach, we find that the charge mode acquires an anomalous dispersion relation at long wavelength ωðqÞ ∼ qz with dynamical exponent z ¼ min½ð2n þ dÞ=2n; 2, where n is the order of the nodal point in momentum space. We verify our predictions in one-dimensional systems using tensor-network techniques
Angle dependence as a unifying feature of root graviresponse modules
No full textGravitropism, the patterning of postembryonic growth in relation to the gravity vector, allows plants to optimize the use of limited and nonhomogenous resources in their immediate environment. Since the current model of root gravitropism has not been able to integrate all aspects of the response (perception, response, and behavior), research on gravitropism has been dominated by different theories attempting to conceptualize each aspect individually. In this work, we sought to reevaluate all the main components of the root graviresponse through the lens of angle dependence. We show angle dependence in Cholodny–Went-based auxin asymmetry and growth response, which we tracked back to angle-dependent variation in PIN asymmetry and statolith sedimentation in the columella. Thanks to this approach, we were able to suggest distinct roles for PINs and columella cell tiers, and a potential function for auxin vertical flux through the columella. Our findings provide a unifying framework to further explore the mechanisms that regulate angle-dependent gravitropic response, with major implications of time-dependent features of root graviresponse
Mean estimation in high-dimensional binary timeinhomogeneous Markov Gaussian mixture models
No full textWe explore the problem of mean estimation for a high-dimensional binary symmetric Gaussian mixture model, where the label (sign) follows a time-inhomogeneous Markov chain. We propose a spectral estimator based on a partition of a subset of the samples to blocks. We develop a computationally efficient algorithm to find the optimal blocks, and derive minimax lower bounds on the estimation loss of any estimator, which establish the effectiveness of our proposed estimator. The resulting minimax rate illuminates the interplay between the sample size, dimension, signal strength, and the memory on the loss
The light echo of a high-redshift quasar mapped with Lyα tomography
No full textUltraviolet (UV) radiation from accreting black holes ionizes the intergalactic gas around early quasars, carving out highly ionized bubbles in their surroundings. Any changes in a quasar’s luminosity are therefore predicted to produce outward-propagating ionization gradients, affecting the Lyα absorption opacity near the quasar’s systemic redshift. This “proximity effect” is well-documented in rest-UV quasar spectra but only provides a one-dimensional probe along our line of sight. Here we present deep spectroscopic observations with the James Webb Space Telescope (JWST) of galaxies in the background of a superluminous quasar at zQSO ≈ 6.3, which reveal the quasar’s “light echo” with Lyα tomography in the transverse direction. This transverse proximity effect is detected for the first time toward multiple galaxy sightlines, allowing us to map the extent and geometry of the quasar’s ionization cone. We obtain constraints on the orientation and inclination of the cone, as well as an upper limit on the obscured solid angle fraction of fobsc < 91%. Additionally, we find a timescale of the quasar’s UV radiation of tqso = 10^5.6+0.1-0.3 yr, which is significantly shorter than would be required to build up the central supermassive black hole (SMBH) with conventional growth models, but is consistent with independent measurements of the quasars’ duty cycle. Our inferred obscured fraction disfavors a scenario where short quasar lifetimes can be explained exclusively by geometric obscuration, and instead supports the idea that radiatively inefficient accretion or growth in initially heavily enshrouded cocoons plays a pivotal role in early SMBH growth. Our results pave the way for novel studies of quasars’ ionizing geometries and radiative histories at early cosmic times