Low-density Regions Research Articles

Cosmological Prediction of the Void and Galaxy Clustering Measurements in the CSST Spectroscopic Survey

The void power spectrum is related to the clustering of low-density regions in the large-scale structure (LSS) of the Universe and can be used as an effective cosmological probe to extract information on the LSS. We generate galaxy mock catalogs from a Jiutian simulation and identify voids using the watershed algorithm for studying the cosmological constraint strength of the China Space Station Telescope spectroscopic survey. The galaxy and void autopower spectra and void−galaxy cross-power spectra at z = 0.3, 0.6, and 0.9 are derived from the mock catalogs. To fit the full power spectra, we propose to use the void average effective radius at a given redshift to simplify the theoretical model, and we adopt the Markov Chain Monte Carlo technique to implement the constraints on the cosmological and void parameters. The systematic parameters, such as galaxy and void biases and noise terms in the power spectra, are also included in the fitting process. We find that our theoretical model can correctly extract the cosmological information from the galaxy and void power spectra, which demonstrates its feasibility and effectivity. The joint constraint accuracy of the cosmological parameters can be improved by ∼20% compared to that of the galaxy power spectrum only. The fitting results of the void density profile and systematic parameters are also well constrained and consistent with the expectation. This indicates that the void-clustering measurement can be an effective complement to the galaxy-clustering probe, especially for the next-generation galaxy surveys.

Thermal Conductivity and Thermal Hall Effect in Dense Electron-Ion Plasma

In this study, we examine thermal conductivity and the thermal Hall effect in electron-ion plasmas relevant to hot neutron stars, white dwarfs, and binary neutron star mergers, focusing on densities found in the outer crusts of neutron stars and the interiors of white dwarfs. We consider plasma consisting of single species of ions, which could be either iron [56]Fe or carbon [12]C nuclei. The temperature range explored is from the melting temperature of the solid T∼109 K up to 1011 K. This covers both degenerate and non-degenerate electron regimes. We find that thermal conductivity increases with density and temperature for which we provide analytical scaling relations valid in different regimes. The impact of magnetic fields on thermal conductivity is also analyzed, showing anisotropy in low-density regions and the presence of the thermal Hall effect characterized by the Righi–Leduc coefficient. The transition froma degenerate to non-degenerate regime is characterized by a minimum ratio of thermal conductivity to temperature, which is analogous to the minimum observed already in the case of electrical conductivity. We provide also formulas fit to our numerical results, which can be used in dissipative magneto-hydrodynamics simulations of warm compact stars.

Dünn in der Fläche? Regionale Disparitäten in der Hospiz- und Palliativversorgung in Deutschland

IntroductionOutpatient and inpatient hospice and palliative care services have been significantly expanded in Germany in recent decades and are increasingly being supplemented by day care services. However, the availability of these services varies greatly from region to region. The extent to which the availability of these care structures is matched by a regional need based on local population structures is as yet unknown. MethodsIn four Poisson regression models, the relationship between population indicators from the areas of demographics, employment, income, education and health and the number of offers of outpatient and inpatient hospice work and palliative care is exploratively examined. The cumulated data at district level is drawn from the INKAR database of the Federal Institute for Research on Building, Urban Affairs and Spatial Development on living conditions in Germany and from the guide of the German Association for Palliative Medicine. By means of logistic regression, factors influencing the establishment of day care services will also be identified. ResultsThe analysis included 401 districts and cities in Germany. The number of inhabitants, settlement density, and the average age of inhabitants are the strongest predictors of the number of palliative care services. In metropolitan regions, both outpatient palliative care services and palliative care units tend to be more frequently available, while the number of outpatient hospice services and inpatient hospices increases in districts with a higher number of inhabitants regardless of settlement density. The regression model was unable to demonstrate a significant influence on the emergence of semi-inpatient care facilities, neither for the population indicators nor for the existing care structures. DiscussionRegional population structures can only partially explain the geographically uneven distribution of hospice and palliative care services in districts and cities in Germany. Despite an increase in hospice and palliative care services, fewer hospice and palliative care structures are available in low population density regions that tend to have a higher share of older inhabitants. ConclusionFuture health care planning should give more consideration to other population characteristics than to population size alone in order to improve care in regions with higher care needs that are, for example, due to a higher proportion of older residents. Subsequent studies should investigate which population characteristics can best describe the actual care needs.

On the Physical Nature of Lyα Transmission Spikes in High-redshift Quasar Spectra

We investigate Lyman-alpha (Lyα) transmission spikes at 5.2 < z < 6.8 using synthetic quasar spectra from the “Cosmic Reionization on Computers” simulations. We focus on understanding the relationship between these spikes and the properties of the intergalactic medium (IGM). Disentangling the complex interplay between IGM physics and the influence of galaxies on the generation of these spikes presents a significant challenge. To address this, we employ Explainable Boosting machines, an interpretable machine learning algorithm, to quantify the relative impact of various IGM properties on the Lyα flux. Our findings reveal that gas density is the primary factor influencing absorption strength, followed by the intensity of background radiation and the temperature of the IGM. Ionizing radiation from local sources (i.e., galaxies) appears to have a minimal effect on Lyα flux. The simulations show that transmission spikes predominantly occur in regions of low gas density. Our results challenge recent observational studies suggesting the origin of these spikes in regions with enhanced radiation. We demonstrate that Lyα transmission spikes are largely a product of the large-scale structure, of which galaxies are biased tracers.

Effects of Crystallinity and Branched Chain on Thermal Degradation of Polyethylene: A SCC-DFTB Molecular Dynamics Study.

As a widely used plastic, the aging and degradation of polyethylene (PE) are inevitable problems, whether the goal is to prolong the life of PE products or address the issue of white pollution. Molecular simulation is a vital scientific tool in elucidating the mechanisms and processes of chemical reactions. To obtain the distribution and evolution process of PE's thermal oxidation products, this work employs the self-consistent charge-density functional tight binding (SCC-DFTB) method to perform molecular simulations of the thermal oxidation of PE with different crystallinity and branched structures. We discovered that crystallinity does not affect the thermal oxidation mechanism of PE, but higher crystallinity makes PE more susceptible to cross-linking and carbon chain growth, reducing the degree of PE carbon chain breakage. The branched structure of PE results in differences in free volumes between the carbon chains, with larger pores leading to a concentrated distribution of O2 and chemical defects subsequently formed. The breakdown of PE is slowed down when chemical defects are localized in low-density regions of the carbon chain. The specifics and mechanism of PE's thermal oxidation are clearly revealed in this paper, which is essential for understanding the process in depth and for the development of anti-aging PE products.

A Survey of Dynamical and Gravitational Lensing Tests in Scale Invariance: The Fall of Dark Matter?

We first briefly review the adventure of scale invariance in physics, from Galileo Galilei, Weyl, Einstein, and Feynman to the revival by Dirac (1973) and Canuto et al. (1977). In the way that the geometry of space–time can be described by the coefficients gμν, a gauging condition given by a scale factor λ(xμ) is needed to express the scaling. In general relativity (GR), λ=1. The “Large Number Hypothesis” was taken by Dirac and by Canuto et al. to fix λ. The condition that the macroscopic empty space is scale-invariant was further preferred (Maeder 2017a), the resulting gauge is also supported by an action principle. Cosmological equations and a modified Newton equation were then derived. In short, except in extremely low density regions, the scale-invariant effects are largely dominated by Newtonian effects. However, their cumulative effects may still play a significant role in cosmic evolution. The theory contains no “adjustment parameter”. In this work, we gather concrete observational evidence that scale-invariant effects are present and measurable in astronomical objects spanning a vast range of masses (0.5 M⊙&lt; M &lt;1014M⊙) and an equally impressive range of spatial scales (0.01 pc &lt; r &lt; 1 Gpc). Scale invariance accounts for the observed excess in velocity in galaxy clusters with respect to the visible mass, the relatively flat/small slope of rotation curves in local galaxies, the observed steep rotation curves of high-redshift galaxies, and the excess of velocity in wide binary stars with separations above 3000 kau found in Gaia DR3. Last but not least, we investigate the effect of scale invariance on gravitational lensing. We show that scale invariance does not affect the geodesics of light rays as they pass in the vicinity of a massive galaxy. However, scale-invariant effects do change the inferred mass-to-light ratio of lens galaxies as compared to GR. As a result, the discrepancies seen in GR between the total lensing mass of galaxies and their stellar mass from photometry may be accounted for. This holds true both for lenses at high redshift like JWST-ER1 and at low redshift like in the SLACS sample. Of note is that none of the above observational tests require dark matter or any adjustable parameter to tweak the theory at any given mass or spatial scale.

Dislocation‐induced local symmetry reduction in single‐crystal KNbO3 observed by Raman spectroscopy

AbstractIn recent years, dislocation‐tuned functionalized ceramics have become one of the focal points of modern materials research due to their outstanding properties. These range from improved electrical conductivity and ferroelectric properties to dislocation‐enhanced toughening and superconductivity, caused by local strain fields. The aim of this work is to investigate the dislocation‐induced structural changes in single‐crystal KNbO3 by micro‐Raman spectroscopy. Dislocation‐rich regions with tailored densities have been generated using the Brinell indenter scratching method. The influence of the dislocations on the single‐crystal structure can be observed in the Raman spectra. The activation of additional Raman modes is observed, which does not occur in regions of low dislocation density. This observation is confirmed by DFT calculations of vibrational modes and is attributed to a reduction in the crystal symmetry due to increased defect densities in plastically deformed KNbO3. In addition, an increase in compressive stress at higher dislocation densities can be demonstrated by a blueshift in Raman mode positions.

Two state model for the ML-BOP potential

The coarse-grained machine-learning derived ML-BOP model [Chan et al., Nature Commun. 10, 379 (2019)] provides a monoatomic representation of the water-water interaction potential in which orientational interactions are included as three-body contributions. Despite its simplicity, the model reproduces the phase diagram of water and its anomalies. Here, we show that a two-state Gibbs free energy expression – fitted simultaneously on the temperature and pressure dependence of the density and internal energy – predicts the existence of a liquid–liquid critical point, with critical parameters consistent with previous estimates. We also show that in this model: (i) while the low density liquid is pre-empted by crystal nucleation, the high-density liquid and its spinodal are accessible in numerical studies down to 100 K; (ii) crystallisation requires the presence of a local low density region. Thus, for densities larger than the critical density, spinodal decomposition (or nucleation of the low-density liquid) is a pre-requisite for ice nucleation.

Dataset Expansion with Pseudo-Labeling: Case Study for Optimizing Chatbot Intent Recognition

Purpose of the study: This study presents an approach for improving the performance of natural language processing (NLP) models in pseudo-labeling tasks, with a particular focus on enhancing chatbot model intent recognition for business use cases. Methodology: The employed case study approach explores the pseudo-labeling technique and demonstrates a practical and efficient way to iteratively expand the original set of labeled data for the purpose of refining model training to achieve superior intent recognition accuracy in chatbots. Main Findings: The approach results in notable increases in macro-averaged F1 score and overall accuracy, particularly by iteratively re-training the model with progressively larger datasets. While enhancing the model's ability to generalize through difficult cases was effective, the study found that incorporating a full range of examples, including easy ones, yielded the best results. This comprehensive approach made the model better suited for real-world applications. Applications of the study: As chatbots are increasingly deployed in various sectors, including business, customer service, healthcare, and education, it becomes crucial for research to examine their long-term impact, scalability, and adaptability to ensure their effectiveness and sustainability in diverse contexts. Therefore, building more accurate chatbots, capable of understanding a wide range of user intents, is particularly valuable in real-world applications where chatbots need to respond to diverse, often complex and unpredictable user queries. Novelty/Originality of the study: Unlike traditional approaches, this study introduces a novel strategy of filling low-density regions in the dataset with pseudo-labels, allowing the model to better separate classes and handle semantically similar but varied messages. These advancements contribute to a more effective and scalable chatbot solution across diverse industries.

Synthesis, spectral characterization, anti-cancer activity evaluation, and molecular docking of substituted 1,2-bis(3-butyl-2,6-diphenylpiperidin-4-ylidiene)hydrazone derivatives

A series of 1,2-bis(3‑butyl‑2,6-diphenylpiperidin-4-ylidiene)hydrazone derivatives of the substituted compounds 1–7, were confirmed by the characterization of IR & 1H-, NMR spectrum, together with X-ray crystallography and Mass spectroscopy also incredibly revealed. Docking analysis of the synthesized compounds employed under the protein from PDB code as 5cqh1, 4i40, 5fan, 7nud, 6Ya1 offers more inhibition values from 2D and 3D structures of the compounds, followed by Anti-cancer activity of the carcinoma cell line displayed that, highly potent to be active in nature. The in-vitro performance of -Cl substituted compound 6 (high anticancer activity) was in good correlation with its protein binding behaviour (strong binding). The increasing order of anticancer effect was 5>7>1>2>4>3>6 and the increasing order of binding ability on proteins were 7>3>4>1>2>5>6. The computational investigations were aligned with experimental techniques using Density Functional Theory (DFT) with a 6–31 G (d, p) basis set. Calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies revealed Mulliken charges and charge transfer phenomena occurring within the molecule. Analysis of the Molecular Electrostatic Potential (MEP) unveiled reactive sites, with high electron density regions depicted in red and low electron density regions in blue.

Probing the Linear-to-Plastic Transition in Polymer Nanocomposites via Atomistic Simulations: The Role of Interphases.

Polymer nanocomposites have found ubiquitous use across diverse industries, attributable to their distinctive properties and enhanced mechanical performance compared to conventional materials. Elucidating the elastic-to-plastic transition in polymer nanocomposites under diverse mechanical loads is paramount for the bespoke design of materials with desired mechanical attributes. In the current work, the elastic-to-plastic transition is probed in model systems of polyethylene oxide (PEO) and silica, SiO2, nanoparticles, through detailed atomistic molecular dynamics simulations. This comprehensive, multi-scale analysis unveils pivotal markers of the elastic-to-plastic transition, highlighting the quintessential role of microstructural and regional heterogeneities in density, strain, and stress fields, featuring the polymer-nanoparticle interphase region. At the atomic level, the behavior of polymer chains interacting with nanoparticle surfaces is traced, differentiating between free and adsorbed chains, and identifying the microscopic origins of the linear-to-plastic transition. The mechanical behavior of subregions are characterized within the PEO/SiO2 nanocomposites, focusing on the interphase and bulk-like polymer areas, probing stress heterogeneities and their decomposition into various force contributions. At the inception of plasticity, a disruption is discerned in isotropy of the polymeric density field, the emergence of low-density regions, and microscopic voids/cavities within the polymer matrix concomitant with a transition of adsorbed chains to free. The yield strain also emerges as an inflection point in the local versus global strain diagram, demarcating the elastic limit, and the plastic regime shows pronounced strain heterogeneities. The decomposition of the atomic Virial stress into bonded and non-bonded interactions indicates that the rigidity of the material is primarily governed by non-bonded interactions, significantly influenced by the volume fraction of the nanoparticle. These findings emphasize the importance of the microstructural and micromechanical environment at the polymer-nanoparticle interface on the linear-to-plastic transition, which is of great importance in the design of nanocomposite materials with advanced mechanical properties.

Are there Marshallian industrial districts in Portugal? revisiting the canello and pavone algorithm

The present study maps and classifies industrial districts in Portugal, identifying the features of specialization and the current capacity of industrialization. It employs an adaptation of the algorithm developed by Canello and Pavone (2016) in 308 Portuguese municipalities based on six phases. In terms of methodological innovation, a new concentration ratio was introduced, making it possible to identify homogeneity in the industrial structure and to consider different sizes of companies, regarding the classification of Industrial Districts. It provides guidelines for policymakers in order to promote cross-fertilized industrial districts, considering the specificities of low-density industrial regions.

Void number counts as a cosmological probe for the large-scale structure

ABSTRACT Void number count (VNC) indicates the number of low-density regions in the large-scale structure (LSS) of the Universe, and we propose to use it as an effective cosmological probe. By generating the galaxy mock catalogue based on Jiutian simulations and considering the spectroscopic survey strategy and instrumental design of the China Space Station Telescope (CSST), which can reach a magnitude limit $\sim$23 AB mag and spectral resolution $R\gtrsim 200$ with a sky coverage of 17 500 deg2, we identify voids using the watershed algorithm without any assumption of void shape and obtain the mock void catalogue and data of the VNC in six redshift bins from $z=0.3$ to 1.3. We use the Markov chain Monte Carlo method to constrain the cosmological and VNC parameters. The void linear underdensity threshold $\delta _{\rm v}$ in the theoretical model is set to be a free parameter at a given redshift to fit the VNC data and explore their redshift evolution. We find that the VNC can correctly derive the cosmological information, and the constraint strength on the cosmological parameters is comparable to that from the void size function method, which can reach a few per cent level in the CSST full spectroscopic survey. This is because, since the VNC is not sensitive to void shape, the modified theoretical model can match the data better by integrating over void features, and more voids could be included in the VNC analysis by applying simpler selection criteria, which will improve the statistical significance. It indicates that the VNC can be an effective cosmological probe for exploring the LSS.

C9orf72 polyPR interaction with the nuclear pore complex

The C9orf72 gene associated with amyotrophic lateral sclerosis/frontotemporal dementia is translated to five dipeptide repeat proteins, among which poly-proline-arginine (PR) is the most toxic in cell and animal models, contributing to a variety of cellular defects. It has been proposed that polyPR disrupts nucleocytoplasmic transport (NCT) through several mechanisms including accumulation in the nuclear pore complex (NPC), accumulation in the nucleolus, and direct interactions with transport receptors. The NPC, which is the key regulator of transport between the cytoplasm and nucleus, plays a central role in these suggested mechanisms. Exploring polyPR interaction with the NPC provides valuable insight into the molecular details of polyPR-mediated NCT defects. To address this, we use coarse-grained molecular dynamics models of polyPR and the yeast NPC lined with intrinsically disordered FG-nucleoporins (FG-Nups). Our findings indicate no aggregation of polyPR within the NPC or permanent binding to FG-Nups. Instead, polyPR translocates through the NPC, following a trajectory through the central low-density region of the pore. In the case of longer polyPRs, we observe a higher energy barrier for translocation and a narrower translocation channel. Our study shows that polyPR and FG-Nups are mainly engaged in steric interactions inside the NPC with only a small contribution of specific cation-pi, hydrophobic, and electrostatic interactions, allowing polyPR to overcome the entropic barrier of the NPC in a size-dependent manner.

Numerical study of gas crossover effect on hydrogen-oxygen proton exchange membrane fuel cell

Hydrogen-oxygen proton exchange membrane fuel cell (H2/O2 PEMFC) is a typical fuel cell for the applications of air-free environments, such as aerospace and underwater. Gas crossover has an adverse effect on the cell performance especially on open-circuit voltage (OCV), and this phenomenon would be severe for H2/O2 PEMFC. In this study, we develop a H2/O2 PEMFC model considering hydrogen and oxygen crossover, and investigate the gas crossover effect on H2/O2 PEMFC, and effects of temperature, relative humidity, inlet pressure and membrane thickness. The numerical results show that the gas crossover effect on the cell performance is obvious in the low current density region, and this effect becomes weak with current density. Although the crossover flux rate of hydrogen is generally greater than that of oxygen, the crossover current density of oxygen could be greater than that of hydrogen. Increasing temperature and relative humidity will decrease the OCV, and increase hydrogen and oxygen crossover current density. The temperature effect on OCV is more obvious at high relative humidity conditions. Increasing inlet pressure only slightly increases the OCV with considering the gas crossover effect. The OCV increases with increasing membrane thickness, and this positive effect becomes weak when the membrane thickness is greater than 75 μm in the investigated range. The work illustrates the basic influence rules and some quantified results of the critical parameters on the gas crossover effect and OCV of H2/O2 PEMFC.

Driving a deficient cathodic environment using anode to control selectivity for CO2 electroreduction

The anode has not been extensively studied in electrochemical CO2 reduction reaction (CO2RR) systems because it is believed to have no significant effect on the catalytic selectivity and activity of the cathode. Herein, we report that the anode can indeed influence the catalytic activity of the CO2RR by regulating the transfer of water and ions in a membrane electrode assembly. Despite employing identical cathode conditions, we observed optimal ethylene production at different current densities for distinct anode substrates: carbon paper (CP) and Ti meshes (TM). TM shows optimal ethylene Faradaic efficiency (31.1 %) in the high current density region, while CP demonstrates optimal ethylene Faradaic efficiency (20 %) in the low current density region. Based on the results of in situ/operando analysis and transparent cell tests, CP creates an environment deficient in water and cations, thereby promoting local pH effects. Consequently, this leads to a higher valence state of Cu during the CO2RR, resulting in increased catalytic activity for ethylene production. However, in the high-current-density region, the catalytic activity of CP degrades due to the uneven distribution of the reaction. Our study contributes to a deeper understanding of the reaction environment for CO2RR and offers insights for optimizing the catalytic activity of CO2RR systems.

ATOMS: ALMA three-millimetre observations of massive star-forming regions – XVI. Neutral versus ion line widths

ABSTRACT It has been suggested that the line width of ions in molecular clouds is narrower than that of the co-existing neutral particles, which has been interpreted as an indication of the decoupling of neutral turbulence from magnetic fields within a partially ionized environment. We calculate the principal component analysis (PCA) correlation coefficients of CCH versus H$^{13}$CO$^{+}$ and H$^{13}$CN versus H$^{13}$CO$^{+}$. We find aside from H$^{13}$CN, CCH could also be strongly spatial correlated with H$^{13}$CO$^{+}$ in high-mass star-forming regions. CCH and H$^{13}$CO$^{+}$ line emissions are strongly spatial correlated with each other in 48 per cent sources with a PCA correlation coefficient over 0.7. So, we investigate the ambipolar diffusion (AD) effect using CCH and H$^{13}$CO$^{+}$ lines as a neutral/ion pair in a sample of 129 high-mass star-forming clumps. We conduct a careful analysis of line widths of the CCH–H$^{13}$CO$^{+}$ pair pixel-by-pixel in 12 sources, which show a strong correlation in CCH–H$^{13}$CO$^+$ emission and no obvious outflows or multiple velocity components. The mean velocity dispersion of CCH is about the same as H$^{13}$CO$^{+}$ in 12 sources. In low-density regions of most sources, CCH shows a broader velocity dispersion than H$^{13}$CO$^{+}$. However, the AD effect is not significant from a statistical point of view.

Does the Inter-Provincial Floating Population Affect Regional Economic Development in China? An Empirical Analysis

In recent decades, significant changes in the urban–rural structure of population mobility have profoundly impacted provincial development, urbanization, and population redistribution in China. Based on China’s fifth, sixth, and seventh national population census datasets, this study explores the effects of the inter-provincial floating population on regional economic development through statistical and empirical analysis, identifying both the scale and structural impacts of the floating population on regional economic development. The results found that while the scale of China’s floating population has been continuously increasing, the spatial distribution pattern remains relatively unchanged, and the pattern is summed up as low in the middle and high on both sides. The floating population exerts both scale and structural effects on the economic development of both inflow and outflow regions, altering regional populations and production efficiency, and thereby influencing regional economic outcomes. Specifically, this study finds that the inflow population has no significant differential impact on high- and low-density regions. In contrast, the outflow population exhibits a significant differential impact, with the negative impact of the outflow population on low-density regions being more substantial than that on high-density regions. Inter-provincial migration supports achieving sustainable development goals (SDG-8 and 11) by shaping regional economic development. To address these dynamics, the high-density regions of China should transform and upgrade the industrial and population structure by promoting the trend of population return to low-density regions. This can be achieved by transferring low-end industries and low-skilled labor, thereby alleviating the pressure of overcrowding. Meanwhile, low-density regions should seize the opportunities for population return and industrial transfer, implement talent introduction, and accurately undertake industrial transfer. This approach can foster the in-depth development of new urbanization and rural revitalization initiatives, promoting balanced regional growth and sustainability.

Rossby wave instability and substructure formation in 3D non-ideal MHD wind-launching discs

ABSTRACT Rings and gaps are routinely observed in the dust continuum emission of protoplanetary discs (PPDs). How they form and evolve remains debated. Previous studies have demonstrated the possibility of spontaneous gas rings and gaps formation in wind-launching discs. Here, we show that such gas substructures are unstable to the Rossby wave instability (RWI) through numerical simulations. Specifically, shorter wavelength azimuthal modes develop earlier, and longer wavelength ones dominate later, forming elongated (arc-like) anticyclonic vortices in the rings and (strongly magnetized) cyclonic vortices in the gaps that persist until the end of the simulation. Highly elongated vortices with aspect ratios of 10 or more are found to decay with time in our non-ideal magnetohydrodynamic (MHD) simulation, in contrast with the hydro case. This difference could be caused by magnetically induced motions, particularly strong meridional circulations with large values of the azimuthal component of the vorticity, which may be incompatible with the columnar structure preferred by vortices. The cyclonic and anticyclonic RWI vortices saturate at moderate levels, modifying but not destroying the rings and gaps in the radial gas distribution of the disc. In particular, they do not shut-off the poloidal magnetic flux accumulation in low-density regions and the characteristic meridional flow patterns that are crucial to the ring and gap formation in wind-launching discs. Nevertheless, the RWI and their associated vortices open up the possibility of producing non-axisymmetric dust features observed in a small fraction of PPDs through non-ideal MHD, although detailed dust treatment is needed to explore this possibility.

The Structural and Orbital Effects of Active Galactic Nuclei Feedback on SMBH Binaries Embedded in Gaseous Circumbinary Disks

Using subparsec-scale-resolution radiation+hydrodynamical adaptive mesh refinement simulations deployed with the RAMSES code, we study the dynamics of supermassive black hole (SMBH) binaries embedded in gaseous nuclear circumbinary disks, where we investigate the effects of active galactic nucleus feedback on the SMBH binaries' migration behavior and disk structure. The radiative feedback effects are modeled by injecting photons that interact with the gas, through the adoption of a grid of BH emission spectra. We run simulations with initial conditions that lead by pure gravity plus hydrodynamics both to the formation of a low-density tidal cavity and to systems where gas–viscous diffusion is efficient enough to maintain a sizable gas reservoir surrounding the binary. For gap-forming binaries we find that orbital evolution is unchanged with the inclusion of feedback, but ionizing radiation photoevaporates gas that is at the outer edge of the low-density region. For non-gap-forming systems we find that when feedback is included a strong initial disruption of the circumbinary disk is followed by an eventual stabilization of the medium that can usher a return to a fast binary migration regime. All of this is possible as a result of how our simulations capture the ionization states of the nuclear disk region and how this affects the coupling efficiency decrease with respect to the radiative feedback.