Small Separation Research Articles

Measurement of the Taylor Microscale and the Effective Magnetic Reynolds Number in the Solar Wind With Cluster

AbstractWe use magnetic field data from the Cluster mission to estimate the value of the Taylor microscale and the effective magnetic Reynolds number in the interplanetary solar wind. Turbulent cascades can be characterized by the spatial scale at which dissipation begins to impact the local energy transfer, estimated by the Taylor microscale, as well as the separation between the injection and dissipation scales, estimated by the effective magnetic Reynolds number. Estimating the Taylor microscale requires measurements of the autocorrelation function at small separations. The Cluster spacecraft have exceptionally sensitive search coil magnetometers with high time resolution, making them ideal for measuring the Taylor microscale. We obtain a value of km; smaller than most previous measurements. We interpret this value as being smaller due to the higher time resolution, enabling the curvature of the autocorrelation function to be measured closer to the origin, giving a more accurate measurement. Combining the Taylor Microscale's computed value with concurrent correlation length measurements, we obtain a value of for the effective magnetic Reynolds number, which compares well to other observations. The four spacecraft of Cluster also allow directions transverse to the flow to be surveyed. The small separations (7 km) of Clusters 3 and 4 show that the Taylor microscale may vary as a function of direction to the mean magnetic field direction. The observed differences are small, requiring more observations to confirm this anisotropy.

Hydrodynamic shielding in radiative multicloud outflows within multiphase galactic winds

Abstract Stellar-driven galactic winds regulate the mass and energy content of star-forming galaxies. Emission- and absorption-line spectroscopy shows that these outflows are multiphase and comprised of dense gas clouds embedded in much hotter winds. Explaining the presence of cold gas in such environments is a challenging endeavour that requires numerical modelling. In this paper we report a set of 3D hydrodynamical simulations of supersonic winds interacting with radiative and adiabatic multicloud systems, in which clouds are placed along a stream and separated by different distances. As a complement to previous adiabatic, subsonic studies, we demonstrate that hydrodynamic shielding is also triggered in supersonic winds and operates differently in adiabatic and radiative regimes. We find that the condensation of warm, mixed gas in between clouds facilitates hydrodynamic shielding by replenishing dense gas along the stream, provided that its cooling length is shorter than the cloud radius. Small separation distances between clouds also favour hydrodynamic shielding by reducing drag forces and the extent of the mixing region around the clouds. In contrast, large separation distances promote mixing and dense gas destruction via dynamical instabilities. The transition between shielding and no-shielding scenarios across different cloud separation distances is smooth in radiative supersonic models, as opposed to their adiabatic counterparts for which clouds need to be in close proximity. Overall, hydrodynamic shielding and re-condensation are effective mechanisms for preserving cold gas in multiphase flows for several cloud-crushing times, and thus can help understand cold gas survival in galactic winds.

Numerical analysis of the fungibility of disclination dipole by dislocation array or dislocation monopole

Disclinations have been discovered and applied to a wide variety of materials, underscoring the importance of their analysis. Previous studies have demonstrated that a disclination dipole can be represented by a dislocation array in a deformation schematic and by a dislocation monopole in a stress state. Based on these observations, we propose that the elastic field of a disclination dipole can be substituted with that of a dislocation array or dislocation monopole, allowing the development of the disclination theory grounded in dislocation theory. In this study, we conducted a quantitative analysis of the elastic strain–energy of disclination dipoles, dislocation arrays, and dislocation monopoles using linear elasticity theory and molecular dynamics (MD) simulation. While linear elasticity theory facilitates a quantitative evaluation of the elastic field, it fails to account for out-of-plane deformation of the material. Therefore, MD analysis, which considers out-of-plane deformation, was employed to obtain versatile results applicable to a broader range of materials. Our findings from both theoretical analyses indicate that, in terms of strain–energy, a disclination dipole with a large separation can be represented by a dislocation array, whereas a dipole with a small separation can be represented by a dislocation monopole. This study newly performs strain–energy analysis of dislocations and disclinations using these two theoretical approaches.

Techno-Economic Analysis of a Carbon Molecular Sieve-Based Xylene Isomer Purification Process.

The separation and purification of xylene isomers is critical to the production of polyethylene terephthalate (PET). These separations are complex to operate and demand tremendous amounts of energy and thus are an opportunity for reducing industrial energy consumption. Membranes provide a low-energy footprint technology with simpler operation, and recently, membrane materials have been developed that are capable of separating xylene isomers. While these materials have demonstrated the ability to separate xylenes, they have yet to be commercially deployed. This work conducts a techno-economic analysis (TEA) to provide insight on the commercial attractiveness of a p-xylene selective carbon molecular sieve (CMS) membrane from both a cost and energy standpoint. This TEA was conducted through the pairing of a Maxwell-Stefan transport framework for rigid microporous materials with process modeling. Single-stage organic solvent reverse osmosis (OSRO) and pervaporation processes were used to evaluate the effects of recovery, selectivity, and diffusivity on the energy intensity and cost of the xylene separation. The final analysis used two systems, a single pervaporation stage followed by two OSRO stages, which was compared against a three-stage OSRO cascade. These were benchmarked against the commercial Parex process. We estimate that the membrane processes have the potential to enable impressive cost savings compared to the Parex process. While both systems outperformed the Parex process in terms of cost, the pervaporation/OSRO hybrid process was able to achieve the lowest cost of all due to its reduced membrane surface area compared to standalone OSRO. These findings demonstrate the potential of membrane systems in the field of difficult small molecule solvent separations.

z ∼ 2 dual AGN host galaxies are disky: stellar kinematics in the ASTRID Simulation

We study dual AGN host galaxy morphologies at z=2 using the ASTRID simulation, selecting black hole (BH) pairs with small separation (), high mass ( MBH,12>107M⊙), and luminosity (). We kinematically decompose (using MORDOR) ∼1000 dual AGN hosts into standard components - a ‘disk’ (thin and thick disk, pseudo-bulge) and ‘bulge’ (bulge and halo) and define disk-dominated galaxies by the disk-to-total D/T≥0.5. In ASTRID, 60.9±2.1% of dual AGN hosts (independent of separation) are disk-dominated, with the D/T distribution peaking at ∼0.7. In dual-AGN hosts, the D/T increases from $17% $ at to $ 64% $ for , and the pseudo-bulge is the dominant component of the disk fraction at the high mass end. Moreover, dual AGN hosts exhibit a higher fraction of disk/large pseudo-bulge than single-AGN hosts. The Disk-to-Total ratio is approximately constant with BH mass or AGN luminosity. We also create mock images of dual AGN host galaxies, employing morphological fitting software Statmorph to calculate morphological parameters and compare them with our kinematic decomposition results. Around 83.3±2.4% of galaxies display disk-like profiles, of which ∼60.7±2.2% are kinematically confirmed as disks. Se'rsic indices and half-mass radii of dual AGN host galaxies align with observational measurements from HST at z∼2. Around 34% are identified as mergers from the Gini−M20 relation. We find two dual AGN hosted by galaxies that exhibit disk-like se'rsic index n12<1 and (D/T)12>0.5, which are in remarkable agreement with properties of recently discovered dual quasars in disk galaxies at z∼2.

Finite distance effects on the Hellings–Downs curve in modified gravity

There is growing interest in the overlap reduction function in pulsar timing array observations as a probe of modified gravity. However, current approximations to the Hellings–Downs curve for subluminal gravitational wave propagation, say v<1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$v<1$$\\end{document}, diverge at small angular pulsar separation. In this paper, we find that the overlap reduction function for the v<1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$v<1$$\\end{document} case is sensitive to finite distance effects. First, we show that finite distance effects introduce an effective cut-off in the spherical harmonics decomposition at ℓ∼1-v2kL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ell \\sim \\sqrt{1-v^2} \\, kL$$\\end{document}, where ℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ell $$\\end{document} is the multipole number, k the wavenumber of the gravitational wave and L the distance to the pulsars. Then, we find that the overlap reduction function in the small angle limit approaches a value given by πkLv2(1-v2)2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pi kL\\,v^2\\,(1-v^2)^2$$\\end{document} times a normalization factor, exactly matching the value for the autocorrelation recently derived. Although we focus on the v<1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$v<1$$\\end{document} case, our formulation is valid for any value of v.

Fabrication of green xylose-based nanofiltration membrane with enhanced performance and chlorine resistance

Nanofiltration technology has been widely used in drinking water purification due to its excellent permeance and selectivity properties, especially in small molecular solute separation. However, using oxidizing agents in the pretreatment process for fouling control threatens the nanofiltration membrane structure, leading to the deterioration of the separation performance. Herein, we fabricate a polyester nanofiltration membrane utilizing xylose as an aqueous monomer in the interfacial polymerization process. Due to abundant hydroxyl groups and low reactivity of xylose monomers, the polyester membrane possessed a hydrophilic and thin separation layer, which led to high water permeance with the optimal value of 28.7 L·m−2·h−1·bar−1. Possessing highly cross-linking structures and negatively charged surfaces, the fabricated polyester membranes showed an excellent Na2SO4 rejection of up to 95.4 %. In addition, the low electron-donating property of polyester membranes ensured their chemical stability toward active chlorine. This endows relatively stable performance of the polyester membrane after chlorine resistance tests in a wide pH range. This study presents a feasible approach employing green monomers for fabricating nanofiltration membranes with outstanding separation performance and robust chlorine resistance.

Establishing the temperature and orientation dependence of the threshold displacement energy in ThO2 via molecular dynamics simulations

ThO2 is a promising fuel for next-generation nuclear reactors. As a critical quantity measuring its radiation tolerance, the dependence of the threshold displacement energy on temperature and crystal orientation in ThO2 is unclear and established using comprehensive molecular dynamics simulations in this work. For both Th and O primary knock-on atoms (PKAs), the thresholds, denoted as EdTh and EdO, respectively, are calculated using two different interatomic potentials. Similar temperature and orientation dependence are observed, albeit with some quantitative differences. While on average over all orientations, higher energy is required for Th PKAs than O PKAs to displace atoms, the polar-averaged EdTh is significantly lower than that for EdO. Further, EdTh and EdO show different crystal orientation dependence and temperature dependence. Notably, the cubic symmetry in the fluorite structure is followed by EdTh, but does not hold for EdO because of the existence of two sublattices. The much higher average EdO than EdTh and their different temperature dependence are interpreted by the distinct recombination rates of Th and O Frenkel pairs in thermal spikes, resulting from the substantially lower migration barriers of O vacancies and interstitials. The recombination of O vacancies and interstitials, both of which are charged, is further enhanced by the Coulomb interaction at small Frenkel pair separations. The new findings are discussed for their generality in fluorite-structured oxides by comparing the results in ThO2 and UO2.

JWST/NIRCam 4–5 μm Imaging of the Giant Planet AF Lep b

With a dynamical mass of 3 M Jup, the recently discovered giant planet AF Lep b is the lowest-mass imaged planet with a direct mass measurement. Its youth and spectral type near the L/T transition make it a promising target to study the impact of clouds and atmospheric chemistry at low surface gravities. In this work, we present JWST/NIRCam imaging of AF Lep b. Across two epochs, we detect AF Lep b in F444W (4.4 μm) with signal-to-noise ratios of 9.6 and 8.7, respectively. At the planet’s separation of 320 mas during the observations, the coronagraphic throughput is ≈7%, demonstrating that NIRCam’s excellent sensitivity persists down to small separations. The F444W photometry of AF Lep b affirms the presence of disequilibrium carbon chemistry and enhanced atmospheric metallicity. These observations also place deep limits on wider-separation planets in the system, ruling out 1.1 M Jup planets beyond 15.6 au (0.″58), 1.1 M Sat planets beyond 27 au (1″), and 2.8 M Nep planets beyond 67 au (2.″5). We also present new Keck/NIRC2 L′ imaging of AF Lep b; combining this with the two epochs of F444W photometry and previous Keck L′ photometry provides limits on the long-term 3–5 μm variability of AF Lep b on timescales of months to years. AF Lep b is the closest-separation planet imaged with JWST to date, demonstrating that planets can be recovered well inside the nominal (50% throughput) NIRCam coronagraph inner working angle.

Scaling up global kinetic models of pulsar magnetospheres using a hybrid force-free-PIC numerical approach

Context. The particle-in-cell approach has proven effective in modeling neutron-star and black-hole magnetospheres from first principles, but global simulations are plagued with an unrealistically small separation between the scales where microphysics operates and the system-size scales due to limited numerical resources. A legitimate concern is whether the scale separation achieved to date is large enough for results to be safely extrapolated to realistic scales. Aims. In this work, our aim is to explore the effect of scaling up physical parameters and to check whether salient features uncovered by pure kinetic models at smaller scales are still valid, with a special emphasis on particle acceleration and high-energy radiation emitted beyond the light cylinder. Methods. To reach this objective, we developed a new hybrid numerical scheme coupling the ideal force-free and the particle-in-cell methods to optimize the numerical cost of global models. We propose a domain decomposition of the magnetosphere based on the magnetic-field topology using the flux function. The force-free model is enforced along open field lines while the particle-in-cell model is restricted to the reconnecting field line region. Results. As a proof of concept, this new hybrid model is applied to simulate a weak millisecond pulsar magnetosphere with realistic scales using high-resolution axisymmetric simulations. Magnetospheric features reported by previous kinetic models are recovered, and strong synchrotron radiation above 100MeV consistent with the Fermi-LAT gamma-ray pulsar population is successfully reproduced. Conclusions.This work further consolidates the shining-reconnecting current sheet scenario as the origin of the gamma-ray emission in pulsars, as well as firmly establishing pulsar magnetospheres as at least teraelectronvolt particle accelerators.

Protostellar Outflows at the EarliesT Stages (POETS)

Context. Understanding the launching mechanism of winds and jets remains one of the fundamental challenges in astrophysics. The Protostellar Outflows at the EarliesT Stages (POETS) survey has recently mapped the 3D velocity field of the protostellar winds in a sample (37) of luminous young stellar objects (YSOs) at scales of 10–100 au via very long baseline interferometry (VLBI) observations of the 22 GHz water masers. In most of the targets, the distribution of the 3D maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk wind (DW). Aims. Our goal is to assess the launching mechanism of the protostellar wind in the YSO IRAS 21078+5211, the most promising MHD DW candidate from the POETS survey. Methods. We have performed multi-epoch Very Long Baseline Array (VLBA) observations of the 22 GHz water masers in IRAS 21078+5211 to determine the 3D velocities of the gas flowing along several wind streamlines previously identified at a linear resolution of ~1 au. Results. Near the YSO at small separations along (xl ≤ 150 au) and across (R ≤ 40 au) the jet axis, water masers trace three individual DW streamlines. By exploiting the 3D kinematic information of the masers, we determined the launch radii of these streamlines with an accuracy of ~1 au, and they lie in the range of 10–50 au. At increasingly greater distances along the jet (110 au ≤ xl ≤ 220 au), the outflowing gas speeds up while it collimates close to the jet axis. Magneto-centrifugal launching in a radially extended MHD DW appears to be the only viable process to explain the fast (up to 60 km s−1) and collimated (down to 10°) velocities of the wind in correspondence with launch radii ranging between 10 and 50 au. At larger separations from the jet axis (R ≥ 100 au), the water masers trace a slow (≤20 km s−1), radially expanding arched shock-front with kinematics inconsistent with magneto-centrifugal launching. Our resistive-magnetohydrodynamical simulations indicate that this shock-front could be driven by magnetic pressure. Conclusions. The results obtained in IRAS 21078+5211 demonstrate that VLBI observations of the 22 GHz water masers can reliably determine the launching mechanism of protostellar winds.

Optimizing measurement tradeoffs in multiparameter spatial superresolution

The quantum Cramér-Rao bound for the joint estimation of the centroid and the separation between two incoherent point sources cannot be saturated. As such, the optimal measurements for extracting maximal information about both at the same time are not known. In this paper, we ascertain these optimal measurements for an arbitrary point spread function, in the most relevant regime of a small separation between the sources. Our measurement can be adjusted within a set of tradeoffs, allowing more information to be extracted from the separation or the centroid while ensuring that the total information is the maximum possible. Published by the American Physical Society 2024

Epoxy Coating as a Novel Method to Prevent Avian Electrocutions and Electrical Faults on Distribution Pylons with Grounded Steel Crossarms

Electrical faults caused by power escaping electric systems can lead to power outages, equipment damage, and fires. Faults sometimes occur when birds perched on power structures are electrocuted. Distribution power lines supported by concrete and steel pylons are particularly fault-prone because small separations between conductors and grounded components allow even small birds to inadvertently create faults while being electrocuted. Most conservation solutions focus on covering energized wires and components to prevent contact by birds and, although usually effective when installed correctly, covers can sometimes be dislodged thus becoming ineffective. Glass Flake Epoxy (GFE) is a non-conductive thermoset plastic that can adhere to steel crossarms and not be dislodged. We hypothesized that GFE-coated crossarms might reduce faults (proxies for avian electrocutions), and we conducted laboratory and field trials to evaluate that hypothesis. In the laboratory, we found a 2000 micrometer (μm)-thick layer of GFE coating that created a dielectric strength of 12.30 ± 0.21 kV, which was sufficient to prevent the formation of a phase-to-ground fault on up to 20 kV distribution lines. This should allow birds to perch on metal crossarms without being electrocuted. In field trials, we substituted 24% of a 20 kV distribution pylon’s crossarms with GFE-treated crossarms and found that doing so correlated with a 28% decrease in faults. Although we did not measure avian electrocutions directly, our findings suggest GFE coatings may offer a novel method of reducing avian electrocutions on power lines.

MODEL&amp;CO: exoplanet detection in angular differential imaging by learning across multiple observations

ABSTRACT Direct imaging of exoplanets is particularly challenging due to the high contrast between the planet and the star luminosities, and their small angular separation. In addition to tailored instrumental facilities implementing adaptive optics and coronagraphy, post-processing methods combining several images recorded in pupil tracking mode are needed to attenuate the nuisances corrupting the signals of interest. Most of these post-processing methods build a model of the nuisances from the target observations themselves, resulting in strongly limited detection sensitivity at short angular separations due to the lack of angular diversity. To address this issue, we propose to build the nuisance model from an archive of multiple observations by leveraging supervised deep learning techniques. The proposed approach casts the detection problem as a reconstruction task and captures the structure of the nuisance from two complementary representations of the data. Unlike methods inspired by reference differential imaging, the proposed model is highly non-linear and does not resort to explicit image-to-image similarity measurements and subtractions. The proposed approach also encompasses statistical modelling of learnable spatial features. The latter is beneficial to improve both the detection sensitivity and the robustness against heterogeneous data. We apply the proposed algorithm to several data sets from the VLT/SPHERE instrument, and demonstrate a superior precision-recall trade-off compared to the PACO algorithm. Interestingly, the gain is especially important when the diversity induced by ADI is the most limited, thus supporting the ability of the proposed approach to learn information across multiple observations.

Comparisons between full molecular dynamics simulation and Zhang's multiscale scheme for nanochannel flows.

In a very small surface separation, the fluid flow is actually multiscale consisting of both the molecular scale non-continuum adsorbed layer flow and the intermediate macroscopic continuum fluid flow. Classical simulation of this flow often takes over large computational source and is not affordable owing to using molecular dynamics simulation (MDS) to model the adsorbed layer flow, if the flow field size is on the engineering size scale such as of 0.01-10mm or even bigger like occurring in micro or macro hydrodynamic bearings. The present paper uses full MDS to validate Zhang's multiscale flow model, which yields the closed-form explicit flow equations respectively for the adsorbed layer flow and the intermediate continuum fluid flow. Here, full MDS was carried out for the pressure-driven flow of methane in the nano slit pore made of silicon respectively with the channel heights 5.79nm, 11.57nm, and 17.36nm. According to the number density distribution, the flow areas were respectively discriminated as the adsorbed layer zone and the intermediate fluid zone. The values of the characteristic parameters for Zhang's multiscale scheme were extracted from full MDS and input to Zhang's multiscale flow equations respectively for calculating the flow velocity profile and the volume flow rates of the adsorbed layers and the intermediate fluid. It was found that for these three channel heights, the flow velocity profiles calculated from Zhang's model approximate those calculated from full MDS, while the total flow rates through the channel calculated from Zhang's model are close to those calculated from full MDS. The accuracy of Zhang's multiscale flow model is improved with the increase of the channel height. The recent modification of the optimized potential for liquid simulation (MOPLS) model was used to calculate the interaction force between two methane molecules. In order to calculate the interaction force between the wall atoms and the methane molecules accurately, our previous non-equilibrium multiscale MDS was used. The interaction forces between the methane molecule and the wall atom were obtained from the coupled potential function by the L-B mixing rule when the fluid molecules arrived at near wall. The methane molecule diameter was obtained from the radial distribution function by using equilibrium MDS under the same initial conditions. The local viscosities across the adsorbed layer were obtained from the local velocity profile by using the Poiseuille flow method. The motion equation of the methane molecule was solved by the leapfrog method. The temperature of the simulation system was checked by Bhadauria's method, i.e., the system temperature was rectified by the velocities in the y- and z-directions. The flow velocity distributions across the channel height and the volume flow rates through the channel were also calculated from Zhang's closed-form explicit flow equations respectively for the adsorbed layer flow and the intermediate fluid flow. The results respectively obtained from full MDS and Zhang's multiscale flow equations were then compared.

Analysis of plasma-derived small extracellular vesicle characteristics and microRNA cargo following exercise-induced skeletal muscle damage in men.

Extracellular vesicle (EV) cargo is known to change in response to stimuli such as muscle damage. This study aimed to assess particle size, concentration and microRNA (miR) content within small EV-enriched separations prepared from human blood taken before and after unaccustomed eccentric-biased exercise-induced muscle damage. Nine male volunteers underwent plyometric jumping and downhill running, with blood samples taken at baseline, 2, and 24 h post-exercise. EVs were separated using size exclusion chromatography (SEC) and their characteristics evaluated by nanoparticle tracking. No changes in EV size or concentration were seen following the muscle-damaging exercise. Small RNA sequencing identified 240 miRs to be consistently present within the EVs. RT-qPCR analysis was performed: specifically, for known muscle-enriched/important miRs, including miR-1, -206, -133a, -133b, -31, -208b, -451a, -486 and - 499 and the immune-important miR-21, -146a and - 155. Notably, none of the immune-important miRs within the EVs tested changed in response to the muscle damage. Of the muscle-associated miRs tested, only the levels of miR-31-5p were seen to change with decreased levels at 24 h compared to baseline and 2 h, indicating involvement in the damage response. These findings shed light on the dynamic role of EV miRs in response to exercise-induced muscle damage.

Impact of single and two successive droplets on a liquid pool

The interaction between droplets and a liquid pool is a widely observed fluid phenomenon with significant relevance to various industrial applications. This study numerically investigates the impact of both a single droplet and two successive droplets on a liquid pool with a fixed thickness. Particular emphasis was focused on the evolution of cavity depth and width during the deformation process. For single droplet impacts, the cavity depth exhibits linear growth with time in the early stage, consistent with predictions based on energy balance. This growth is independent of the Weber number (We) within the explored range of 96&amp;lt;We&amp;lt;345. Similarly, the cavity width shows weak dependence on the Weber number during early development, deviating and reaching a maximum width at later times. The maximum cavity width follows a power-law relationship with the Weber number, with a 0.5 exponent. In the case of successive droplet impacts with small initial separation, cavity depth also evolves linearly with time in the early stage but over an extended period. This prolonged growth is attributed to droplet merging, resulting in an effectively larger merged droplet. However, for successive droplets with large separation, the two linear growth stages exhibit intermittent interruptions due to the second impact occurring at a later time. The variation in cavity width due to different initial spacings between two successive droplets still exhibits similarity until a larger spacing causes a change in the rate of cavity width development.

Asteroseismic measurement of core and envelope rotation rates for 2006 red giant branch stars

Context. Tens of thousands of red giant stars in the Kepler data exhibit solar-like oscillations. The mixed-mode characteristics of their oscillations enable us to study the internal physics from the core to the surface, such as differential rotation. However, envelope rotation rates have only been measured for about a dozen red giant branch (RGB) stars so far. This limited the theoretical interpretation of angular momentum transport in post-main sequence phases. Aims. We report the measurements of g-mode properties and differential rotation in the largest sample of Kepler RGB stars. Methods. We applied a new approach to calculate the asymptotic frequencies of mixed modes, which accounts for so-called near-degeneracy effects (NDEs) and leads to improved measurements of envelope rotation rates. By fitting these asymptotic expressions to the observations, we obtained measurements of the properties of g modes (period spacing, ΔΠ1, coupling factor, q, g-mode offset term, εg, small separation, δν01) and the internal rotation (mean core, Ωcore, and envelope, Ωenv, rotation rates). Results. Among 2495 stars with clear mixed-mode patterns, we found that 800 show doublets and 1206 show triplets, while the remaining stars do not show any rotational splittings. We measured core rotation rates for 2006 red giants, doubling the size of pre-existing catalogues. This led us to discover an over-density of stars that are narrowly distributed around a well-defined ridge in the plane, showing core rotation rate versus evolution along the RGB. These stars could experience a different angular momentum transport compared to other red giants. With this work, we also increased the sample of stars with measured envelope rotation rates by two orders of magnitude. We found a decreasing trend between envelope rotation rates and evolution, implying that the envelopes slow down with expansion, as expected. We found 243 stars whose envelope rotation rates are significantly larger than zero. For these stars, the core-to-envelope rotation ratios are around Ωcore/Ωenv ∼ 20 and show a large spread with evolution. Several stars show extremely mild differential rotations, with core-to-surface ratios between 1 and 2. These stars also have very slow core rotation rates, suggesting that they go through a peculiar rotational evolution. We also discovered more stars located below the ΔΠ1–Δν degeneracy sequence, which presents an opportunity to study the history of plausible stellar mergers.

A Survey of Protoplanetary Disks Using the Keck/NIRC2 Vortex Coronagraph

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations of protoplanetary disks in the millimeter continuum have shown a variety of radial gaps, cavities, and spiral features. These substructures may be signposts for ongoing planet formation, and therefore these systems are promising targets for direct imaging planet searches in the near-infrared. To this end, we present results from a deep imaging survey in the L′ band (3.8 μm) with the Keck/NIRC2 vortex coronagraph to search for young planets in 43 disks with resolved features in the millimeter continuum or evidence for gaps/central cavities from their spectral energy distributions. Although we do not detect any new point sources, using the vortex coronagraph allows for high sensitivity to faint sources at small angular separations (down to ∼0.″1), allowing us to place strong upper limits on the masses of potential gas giant planets. We compare our mass sensitivities to the masses of planets derived using ALMA observations, and while we are sensitive to ∼1 M Jup planets in the gaps in some of our systems, we are generally not sensitive to planets of the masses expected from the ALMA observations. In addition to placing upper limits on the masses of gas giant planets that could be interacting with the dust in the disks to form the observed millimeter substructures, we are also able to map the micron-sized dust as seen in scattered light for 8 of these systems. Our large sample of systems also allows us to investigate limits on planetary accretion rates and disk viscosities.

Regulation of MOF-74 nanosheet channels for precise H2 purification

Mixed matrix membranes (MMMs), composed of functional fillers and a polymer matrix, are considered effective demonstrations for overcoming the trade-off limitation of polymeric membrane-based gas separations. MOF-74, with its high density of open metal sites and one-dimensional straight honeycomb channels, is an extremely attractive filler material. However, the intrinsically large pore aperture and micron-sized, spindle-shaped grain morphology hinder the use of high-performance, interfacial defect-free MMMs for small gas separations. Herein, we report novel mixed matrix membranes integrated with dual-metallic MOF-74 nanosheets and poly(vinylamine) for precise molecular sieving for H2 purification applications. The nanosheets of parallel orientation within the membrane maximize the exposure of channels for polymeric chain penetration. The amino side groups anchored on the polymeric chains coordinate with the open metal sites on the channel walls of MOF-74 nanosheets, exposing the hydrophobic alkyl backbones to shrink the originally large channel apertures and simultaneously enhancing the interfacial compatibility between MOF-74 and the polymer matrix. Benefiting from the merits of these elegant channel regulations, MMMs exhibit superior H2/CH4 and H2/CO2 separation performances toward binary, ternary and even quaternary feedstocks, along with remarkable long-term separation stability. This MMM is expected to constitute a new membrane paradigm that holds great promise for practical H2 purification and separation.