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Transition route to elastic and elasto-inertial turbulence in polymer channel flows

Viscoelastic shear flows support additional chaotic states beyond simple Newtonian turbulence. In vanishing Reynolds number flows, the nonlinearity in the polymer evolution equation alone can sustain inertialess “elastic” turbulence (ET) while “elasto-inertial” turbulence (EIT) appears to rely on an interplay between elasticity and finite-Re effects. Despite their distinct phenomenology and industrial significance, transition routes and possible connections between these states are unknown. We identify here a common Ruelle-Takens transition scenario for both of these chaotic regimes in two-dimensional direct numerical simulations of FENE-P fluids in a straight channel. The primary bifurcation is caused by a recently discovered “polymer diffusive instability” associated with small but nonvanishing polymer stress diffusion which generates a finite-amplitude, small-scale traveling wave localized at the wall. This is found to be unstable to a large-scale secondary instability which grows to modify the whole flow before itself breaking down in a third bifurcation to either ET or EIT. The secondary large-scale instability waves resemble “center” and “wall” modes, respectively—instabilities which have been conjectured to play a role in viscoelastic chaotic dynamics but were previously only thought to exist far from relevant areas of the parameter space. Published by the American Physical Society 2024

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Constraining dark energy with the integrated Sachs-Wolfe effect

We use the integrated Sachs-Wolfe (ISW) effect, by now detectable at ∼5σ within the context of Λ cold dark matter (ΛCDM) cosmologies, to place strong constraints on dynamical dark energy theories. Working within an effective field theory (EFT) framework for dark energy we find that including ISW constraints from galaxy–cosmic microwave background (CMB) cross-correlations significantly strengthens existing large-scale structure constraints, yielding bounds consistent with ΛCDM and approximately reducing the viable parameter space by ∼70%. This is a direct consequence of O(1) changes induced in these cross-correlations by otherwise viable dark energy models, which we discuss in detail. We compute constraints by adapting the ΛCDM ISW likelihood from Stölzner [] for dynamical dark energy models using galaxy data from 2 MASS, wide-field infrared survey explorer (WISE) × SuperCOSMOS, Sloan Digital Sky Survey Data Release 12, the catalog of photometric quasars and NRAO Very Large Array Sky Survey, CMB data from Planck 18, and baryon acoustic oscillation and redshift space distortion large-scale structure measurements from BOSS and 6dF. We show constraints both in terms of EFT-inspired αi and phenomenological μ/Σ parametrizations. Furthermore we discuss the approximations involved and related aspects of bias modeling in detail and highlight what these constraints imply for the underlying dark energy theories. Published by the American Physical Society 2024

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Fluid mechanics of luminal transport in actively contracting endoplasmic reticulum.

The endoplasmic reticulum (ER), the largest cellular compartment, harbours the machinery for the biogenesis of secretory proteins and lipids, calcium storage/mobilisation, and detoxification. It is shaped as layered membranous sheets interconnected with a network of tubules extending throughout the cell. Understanding the influence of the ER morphology dynamics on molecular transport may offer clues to rationalising neuro-pathologies caused by ER morphogen mutations. It remains unclear, however, how the ER facilitates its intra-luminal mobility and homogenises its content. It has been recently proposed that intra-luminal transport may be enabled by active contractions of ER tubules. To surmount the barriers to empirical studies of the minuscule spatial and temporal scales relevant to ER nanofluidics, here we exploit the principles of viscous fluid dynamics to generate a theoretical physical model emulating in silico the content motion in actively contracting nanoscopic tubular networks. The computational model reveals the luminal particle speeds, and their impact in facilitating active transport, of the active contractile behaviour of the different ER components along various time-space parameters. The results of the model indicate that reproducing transport with velocities similar to those reported experimentally in single-particle tracking would require unrealistically high values of tubule contraction site length and rate. Considering further nanofluidic scenarios, we show that width contractions of the ER's flat domains (perinuclear sheets) generate local flows with only a short-range effect on luminal transport. Only contractions of peripheral sheets can reproduce experimental measurements, provided they are able to contract fast enough.

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Refined cyclic renormalization group in Russian doll model

Focusing on Bethe-Ansatz integrable models, robust to both time-reversal symmetry breaking and disorder, we consider the Russian Doll Model (RDM) for finite system sizes and energy levels. Suggested as a time-reversal-symmetry breaking deformation of Richardson’s model, the well-known and simplest model of superconductivity, RDM revealed an unusual cyclic renormalization group (RG) over the system size NN, where the energy levels repeat themselves, shifted by one after a finite period in \ln NlnN, supplemented by a hierarchy of superconducting condensates, with the superconducting gaps following the so-called Efimov (exponential) scaling. The equidistant single-particle spectrum of RDM made the above Efimov scaling and cyclic RG to be asymptotically exact in the wideband limit of the diagonal potential. Here, we generalize this observation in various respects. We find that, beyond the wideband limit, when the entire spectrum is considered, the periodicity of the spectrum is not constant, but appears to be energy-dependent. Moreover, we resolve the apparent paradox of shift in the spectrum by a single level after the RG period, despite the disappearance of a finite fraction of energy levels. We also analyze the effects of disorder in the diagonal potential on the above periodicity and show that it survives only for high energies beyond the energy interval of the disorder amplitude. Our analytic analysis is supported with exact diagonalization.

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Self-regulated growth of galaxy sizes along the star-forming main sequence

We present a systematic analysis of the spatially-resolved star formation histories (SFHs) using Hubble Space Telescope imaging data of ∼997, intermediate redshifts 0.5≤z≤2.0 galaxies from GOODS-S field, with stellar mass range 9.8≤logM⋆/M⊙≤11.5. We estimate the SFHs in three spatial regions (central region within the half-mass radii R50s, outskirts between 1−3R50s, and the whole galaxy) using pixel-by-pixel spectral-energy distribution (SED) fitting, assuming exponentially declining tau model in individual pixels. The reconstructed SFHs are then used to derive and compare the physical properties such as specific star-formation rates (sSFRs), mass-weighted ages (t 50), and the half mass-radii to get insights on the interplay between the structure and star-formation in galaxies. The correlation of sSFRs ratio of the centre and outskirts with the distance from the main sequence (MS) indicates that galaxies on the upper envelope of the MS tend to grow outside-in, building up their central regions, while those below the MS grow inside-out, with more active star-formation in the outskirts. The findings suggest a self-regulating process in galaxy size growth when they evolve along the MS. Our observations are consistent with galaxies growing their inner bulge and outer disc regions, where they appear to oscillate about the average MS in cycles of central gas compaction, which leads to bulge growth, and subsequent central depletion possibly due to feedback from the starburst resulting in more star formation towards the outskirts from newly accreted gas.

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Confirmatory Factor Analysis of the Hyperacusis Impact Questionnaire, Sound Sensitivity Symptoms Questionnaire, and Screening for Anxiety and Depression in Tinnitus, Including Preliminary Analyses of the Parent Versions for Use with Children.

We previously reported the results of exploratory factor analysis (EFA) of the Hyperacusis Impact Questionnaire (HIQ), the Sound Sensitivity Symptoms Questionnaire (SSSD), and the Screening for Anxiety and Depression in Tinnitus (SAD-T). Confirmatory factor analysis (CFA) is necessary to confirm the latent constructs determined using EFA. CFA should use different samples but with similar characteristics to those used for EFA. The aim was to use CFA to confirm latent constructs derived using EFA of the HIQ, SSSQ, and SAD-T. We further evaluated the psychometric properties of parent versions of these questionnaires (indicated by -P), which are intended for use with children. This was a retrospective cross-sectional study. Data for 323 consecutive adults and 49 children who attended a Tinnitus and Hyperacusis Therapy Clinic in the United Kingdom within a 6-month period were included. Data were collected retrospectively from the records of patients held at the Audiology Department. CFA with the weighted least-squares mean and variance-adjusted estimator was applied to assess the previously proposed factor structures of the HIQ, SSSQ, and SAD-T. The internal consistency of the scales was assessed via Cronbach's α (α). The items of the HIQ, SSSQ, and SAD-T were tested for measurement invariance regarding age and gender using the multiple indicator multiple cause (MIMIC) model. All questionnaires showed good to excellent internal consistency, with α = 0.93 for the HIQ, 0.87 for the SSSQ, and 0.91 for the SAD-T. The parent versions showed acceptable to good internal consistency, with α = 0.88 for the HIQ-P, 0.71 for the SSSQ-P, and 0.86 for the SAD-T-P. CFA showed that the HIQ, SSSQ, and SAD-T were all one-factor questionnaires and the factors generally were similar to those obtained for the EFA. The MIMIC model showed that all three questionnaires can be considered as measurement invariant, with scores similar across genders and ages. The HIQ, SSSQ, and SAD-T are internally consistent one-factor questionnaires that can be used in clinical and research settings to assess the impact of hyperacusis, the severity of sound sensitivity symptoms, and to screen for anxiety and depression symptoms. Future studies should further explore the psychometric properties of the parent versions of the HIQ, SSSQ, and SAD-T.

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