Radial Density Research Articles

Distances, Radial Distribution, and Total Number of Galactic Supernova Remnants

We present a table of 215 supernova remnants (SNRs) with distances. New distances are found to SNR G51.26 + 0.11 of 6.6 ± 1.7 kpc using H i absorption spectra and to five other SNRs using maser/molecular cloud associations. We recalculate the distances and errors to all SNRs using a consistent rotation curve and provide errors where they were not previously estimated. This results in a significant distance revisions for 20 SNRs. Because of observational constraints and selection effects, there is an apparent deficit of observed number of Galactic SNRs. To investigate this, we employ two methods. The first method applies correction factors for the selection effects to derive the radial density distribution. The second method compares functional forms for the SNR surface density and selection function against the data to find which functions are consistent with the data. The total number of SNRs in the Galaxy is ∼3500 (Method 1) or in the range from ∼2400 to ∼5600 (Method 2). We conclude that the current observed number of SNRs is not yet complete enough to give a well-determined total SNR number or radial density function.

Detection of Intracluster Globular Clusters in the First JWST Images of the Gravitational Lens Cluster SMACS J0723.3–7327 at z = 0.39

We present a survey of globular clusters (GCs) in the massive gravitational lens cluster SMACS J0723.3–7327 at z = 0.39 based on the early released JWST/NIRCam images. In the color–magnitude diagrams of the point sources, we clearly find a rich population of intracluster GCs that are spread over a wide area of the cluster. Their ages, considering the cluster redshift, are younger than 9.5 Gyr. The F200W (AB) magnitudes of these GCs, 26.5 mag < F200W0 < 29.5 mag, correspond to −15.2 mag < M F200W < −12.2 mag, showing that they belong to the brightest GCs (including ultracompact dwarfs). The spatial distributions of these GCs show a megaparsec-scale structure elongated along the major axis of the brightest cluster galaxy. In addition, they show a large number of substructures, some of which are consistent with the substructures seen in the map of diffuse intracluster light. The GC number density map is, in general, consistent with the dark matter mass density map based on the strong lensing analysis in the literature. The radial number density profile of the GCs in the outer region is steeper than the dark matter mass profile obtained from lensing models. These results are consistent with those for the GCs found in the deep HST images of A2744, another massive cluster at z = 0.308, and in simulated galaxy clusters. This shows that the intracluster GCs are an excellent independent tool to probe the dark matter distribution in galaxy clusters, as well as reveal the cluster assembly history in the JWST era.

Pedestal fluctuation measurements with charge exchange imaging at the DIII-D tokamak

A new high radial resolution 2D multichannel Charge eXchange Imaging (CXI) diagnostic is under development for deployment at DIII-D. The diagnostic system will measure low-to-intermediate radial wavenumber carbon density fluctuations by observing the n = 8 - 7 (λ = 529.06 nm) C-VI emission line, resulting from charge exchange collisions between heating neutral beam atoms and the intrinsic carbon ion density. The new CXI diagnostic will provide measurements with ΔR ∼ 0.4 cm to access higher kr instabilities (kr < 8cm-1) predicted to arise in the steep-gradient region of the H-mode pedestal. The CXI system will feature 60 fiber bundles in a 12 × 5 arrangement, with each bundle consisting of four 1mm fibers. A custom optical system has been designed to filter and image incoming signals onto an 8 × 8 avalanche photodiode array. Additionally, a novel electronics suite has been designed and commissioned to amplify and digitize the relatively low-intensity carbon signal at a 2MHz bandwidth. Forward modeling results of the active C-VI emission suggest sufficient signal to noise ratios to resolve turbulent fluctuations. Prototype measurements demonstrate the ability to perform high frequency pedestal measurements.

Tracing the Giant Outer Halo of the Mysterious Massive Disk Galaxy M104. I. Photometry of the Extended Globular Cluster Systems

M104 (NGC 4594, the Sombrero galaxy) is a mysterious massive early-type galaxy that shows a dominant bulge and a prominent disk. However, the presence of a halo in M104 has been elusive, and it is not yet known how M104 has acquired such a peculiar structure. Using wide (∼2 deg2) and deep ugi images of M104 obtained with the CFHT/MegaCam, we detect a large number of globular clusters (GCs) found out to (∼100 kpc). The color distribution of these GCs shows two subpopulations: a blue (metal-poor) system and a red (metal-rich) system. The total number of GCs is estimated to be N GC = 1610 ± 30 and the specific frequency to be S N = 1.8 ± 0.1. The radial number density profile of the GCs is steep in the inner region at and becomes shallow in the outer region at . The outer region is dominated by blue GCs and is extended out to . This shows clearly the existence of a giant metal-poor halo in M104. The inner region is composed of a bulge hosting a disk, corresponding to a metal-rich halo as seen in early-type galaxies. At least two clumps of blue GCs are found in the outer region. One clump is overlapped with a faint stellar stream located in the southwest, indicating that it may be a remnant of a disrupted dwarf galaxy. Our results imply that the metal-rich inner halo of M104 formed first via major mergers, and the metal-poor outer halo grew via numerous minor mergers.

On Photoeffect in the Few-Electron Atomic Systems

Closed analytical formulas are derived for the differential and total cross sections of the non-relativistic photoelectric effect in the three main classes of few-electron atomic systems: (a) neutral atoms and positively charged atomic ions which contain more than one bound electron, (b) negatively charged atomic ions, and (c) one-electron atoms and ions. Our procedure developed in this study is a combination of QED methods and results of the density functional theory obtained for atoms and ions. In all these systems the photoelectric effect is considered as photodetachment of the outer-most electron and our analysis is based on the results of density functional theory obtained for the electron density (radial) distribution in these atomic systems. Analytical formulas (similar to ours) for the differential and total cross sections of photoelectric effect for atomic systems from classes (a) and (b) contribute to our understanding of these systems and have not appeared in the literature, to the best of our knowledge.

Correlation between radial peripapillary vascular density and reduced central corneal thickness in glaucoma suspect patients

BackgroundOptical coherence tomography (OCT) angiography (OCTA) provides a quantitative assessment of the microcirculation of the retina and choroid. It may precede the retinal nerve layer (RNFL) and optic disc head defects. Retinal nerve fiber layer defects and reduced central corneal thickness (CCT) are important parameters in the assessment of a glaucoma suspect patients. The aim of this study is to investigate any possible relationship between the reduced central corneal thickness and the radial peripapillary capillary (RPC) density defect in glaucoma suspect.MethodsIn this cross sectional study, 92 eyes were incorporated. Peripapillary OCT angiography (4.5 mm) and Anterior segment OCT for corneal pachymetry were done. C/D Ratio, thickness of nerve fiber layer, the blood flow indices and central corneal thickness also were evaluated.ResultsIn eyes of glaucoma suspect patients; a significant positive correlation between CCT and total RPC density was detected (r = 0.38, P < 0.001). A strong positive correlation was also found between total RPC and peripapillary RNFL thickness (r = 0.55, P < 0.001).ConclusionReduced central corneal thickness and peripapillary capillary density are two screening parameters for glaucoma suspect patients. The radial peripapillary capillary density is a valid diagnostic tool for glaucoma.

New Findings in Early-Stage Keratoconus: Lamina Cribrosa Curvature, Retinal Nerve Fiber Layer Thickness, and Vascular Perfusion

PurposeOur aim was to investigate the involvement of posterior pole structures in eyes affected by keratoconus (KC). Optical coherence tomography (OCT) and OCT angiography (OCTA) were used to determine the status of lamina cribrosa (LC), peripapillary retinal nerve fiber layer (RNFL), macular and peripapillary microvasculature. DesignObservational, cross-sectional, case-control analysis. MethodsSingle-center investigation involving patients with KC and healthy control subjects. Enrolled subjects underwent anterior segment OCT combined with Placido-disk topography, macular and optic nerve head swept-source OCT and swept-source OCTA scans, and 3D wide glaucoma module for peripapillary RNFL thickness measurement. The LC curvature index was used to express the degree of LC posterior bowing. We calculated the vessel density and vessel length density at the macular superficial capillary plexus, deep capillary plexus, choriocapillaris, and nerve radial peripapillary capillary plexus. ResultsOverall, 32 eyes with KC and an equal number of age- and axial length–matched control eyes were included in the analysis. Almost all (97%) of eyes with KC were classified as early stage. KC displayed a reduction in peripapillary RNFL thickness (104.8 ± 11.9 µm vs 110.7 ± 10.5 µm; P = .039) and nerve radial peripapillary capillary plexus vessel density (46.31% ± 3% vs 43.82% ± 4%; P = .006) when compared with control subjects; these differences were more evident in the temporal sector and were associated with a higher LC curvature index (9.9% ± 2.6% vs 8.48% ± 1.7%; P = .012). Mean macular superficial capillary plexus vessel density was 3 percentage points lower in eyes with KC than in healthy controls (P < .001). ConclusionEarly-stage KC may be characterized by a posterior bowing of the LC along with a subtle peripapillary RNFL thinning and vascular impairment. These findings support the hypothesis that KC may be a corneal manifestation of a more generalized “eye collagen disease.”

Molecular dynamics simulations of the microscopic mechanism of thermal conductivity enhancement of ethylene Glycol–Water–Au nanofluids

With an increase of the heat load of internal combustion engines, the heat dissipation of the equipment increases accordingly. Traditional ethylene glycol (EG)–water coolants are unable to meet the heat dissipation demands of high heat load internal combustion engines. Nanofluids have better heat transfer performances than conventional fluids, suggesting they can be used to solve the problem of the insufficient heat dissipation capacity of internal combustion engines. In this paper, EG–water–Au nanofluids are formed by adding Au nanoparticles with a volume fraction of 1.5% to EG–water solutions. These are used to investigate the effect of the EG mass concentration on the thermal conductivity of the EG–water solutions and their nanofluids, and to analyze the microscopic mechanism of thermal conductivity enhancement of the nanofluids. It is found that the thermal conductivity of the EG–water solutions are positively correlated with the water content of the system, and the higher the water content of the system, the better the diffusion performance of the system components. The thermal conductivity of the EG–water solutions increase for all EG mass concentrations after the addition of Au nanoparticles, up to 17.20%. The presence of an adsorption layer of base liquid molecules on the surface of the nanoparticles is an important reason for the improved thermal conductivity of the nanofluids. According to the analysis of molecular radius of gyration, end-to-end distance and intermolecular interaction energy in the systems, it is found that the addition of the nanoparticles has no significant effect on the conformation of EG molecular chain, and the van der Waals interaction energy in the nanofluid systems is slightly enhanced. Through an analysis of the radial distribution function and density distribution of the nanofluid systems, it is found that the base liquid molecules that adsorb on the surface of the nanoparticles are stratified. The high-density interval of EG molecules is (0.65, 1.25) nm, while water molecules mostly gather in the form of clusters in the (1.15, 1.65) nm interval, and the arrangement of base liquid molecules in the adsorption layer is similar to the orderly arrangement of solids. The properties of some components in the nanofluids show a solid-like microstructure, which makes the thermal conductivity of the nanofluids higher than that of the base solution. These research results can provide an important reference for improving the heat transfer performance of traditional alcohol–water coolants.

OCT and OCTA evaluation of vascular and morphological structures in the retina in recovered pediatric patients with COVID-19

BackgroundUsing OCT and OCTA imaging, we aimed to determine whether COVID-19 induces pathological changes in vascular and morphological structures in the pediatric retina. MethodsThe current prospective, cross-sectional, observational clinical study included recovered pediatric patients with COVID-19 evaluated between May 2020 and June 2020. Retinal vascular (radial peripapillary, superficial, and deep capillary plexus vessel densities) and morphological (peripapillary retinal nerve fiber, ganglion cell layer, retinal, and choroidal thickness) in the optic disk and macula regions were quantitively assessed using OCT and OCTA. Data were compared between COVID-19 patients and age-matched controls. ResultsThe COVID-19 group included 32 eyes of 16 patients and the control group included 32 eyes of 16 cases. Fundus and biomicroscopic examinations revealed no signs of pathology in the COVID-19 group. Mean peripapillary retinal nerve fiber, ganglion cell layer, and choroidal thickness values were significantly greater in the COVID-19 group than in the control group (p<0.05). OCTA indicated that mean superficial and deep capillary plexus vessel densities, and choriocapillaris flow area values were significantly lower in the COVID-19 group than in the control group, whereas mean radial peripapillary capillary plexus vessel density values were significantly higher (p<0.05). ConclusionsEven if fundus examination results appear normal in pediatric patients with COVID-19, vascular and morphological changes may be observed in the retina. Further studies with larger numbers of patients are needed to elucidate the clinical significance of vascular and morphological changes in this population.

Simulation of the TAEs’ saturation phase in the Large Helical Device: MHD burst

The aim of the present study is to analyze the saturation regime of the toroidal Alfven eigenmodes (TAE) in the Large Helical Device plasma, particularly the MHD burst. The linear and nonlinear evolution of the TAEs are simulated by the FAR3d code that uses a reduced MHD model for the thermal plasma coupled with a gyrofluid model for the energetic particle (EP) species. The linear simulations indicate the overlapping of 1/2 − 1/1, 2/3–2/4 and 3/5–3/6 TAEs in the inner-middle plasma region and frequency range of 45–75 kHz, triggered by EPs with an energy of T f = 45 keV and EP β = 0.022. The nonlinear simulations show that 2/3–2/4 and 3/4–3/5 TAEs are further destabilized due to the energy transfer from the 1/1–1/2 TAE, leading to broad TAE radial overlapping and triggering of the MHD burst. The energy of the 1/1–1/2 TAE is also nonlinearly transferred to the thermal plasma destabilizing the 0/0 and 0/1 modes, inducing the generation of shear flows and zonal currents, as well as large deformations in the thermal pressure and EP density radial profiles. The nonlinear simulation reproduces the same succession of instabilities and the same frequency range with respect to the experiment. The instability propagates outward during the bursting phase, showing a large decrease of the EP density profile between the middle-outer plasma, indicating the loss of part of the EP population that explains the decrease in the plasma heating efficiency observed during the MHD burst.

A Comprehensive Study of Five Intermediate-age Pismis (2, 3, 7, 12, 15) Clusters Using Photometric and Astrometric Data from Gaia EDR3

Open clusters are groups of stars that form simultaneously; hence, these are excellent probes to test theories of star formation, stellar evolution, and dynamics in the Milky Way disk. We carry out a detailed photometric and kinematic study of five poorly studied intermediate-age open clusters, Pismis 2 (Pi 2), Pismis 3 (Pi 3), Pismis 7 (Pi 7), Pismis 12 (Pi 12), and Pismis 15 (Pi 15), using the Gaia EDR3 database. By estimating the membership probabilities of stars, we recognized 635, 1488, 535, 368, and 494 most probable members for these clusters by using proper-motion and parallax data taken from Gaia EDR3. The radial density profiles of cluster members provide cluster radii of 4.′5–6.′5 for these clusters. Their ages range from 0.9 to 2.5 Gyr, and distances range, using parallax, from 2.15 to 5.10 kpc. The overall mass function slopes for main-sequence stars are found as 0.27 ± 0.16 (for 1.0–1.6 M ⊙ stars), 0.86 ± 0.27 (for 1.0–2.1 M ⊙ stars), 1.08 ± 0.32 (for 1.0–2.2 M ⊙ stars), 0.89 ± 0.38 (for 1.0–2.2 M ⊙ stars), and 1.07 ± 0.28 (for 1.0–2.1 M ⊙ stars) for clusters Pi 2, Pi 3, Pi 7, Pi 12, and Pi 15. Our obtained values of slopes are flatter in comparison with Salpeter’s value (x = 1.35) within uncertainty. The present study demonstrates that all these Pismis clusters are dynamically relaxed. We found that these objects follow a circular path around the Galactic center. We compute these clusters’ apex coordinates (A, D) and other kinematic parameters.

Nonlinear Force and Vibration Analysis of an Interior Permanent Magnet Synchronous Generator With Eccentricity Detection

In this article, an in-depth study on eccentricities and their resultant vibration characteristics of an interior permanent magnet synchronous generator (IPMSG) for portable power generation is proposed. Also, this article introduces the eccentricity detection through vibration tests, since the vibration patterns caused by eccentricities are unique. Three basic eccentricity cases are investigated, namely the static, dynamic, and elliptical. Air-gap radial flux density and radial force density profiles are theoretically analyzed through mathematical modeling. With the help of finite-element analysis, the unique force profiles are verified for IPMSG of different cases, and the tooth force chopping process is studied. With modal analysis and testing, the harmonic vibration responses are predicted. An IPMSG prototype is fabricated and an overall eccentricity evaluation is reported through vibration tests.

Towards a fully consistent Milky Way disk model

Context. The semi-analytic Just-Jahreiß (JJ) model of the Galactic disk is a flexible tool for stellar population synthesis with a fine age resolution of 25 Myr. The model has recently been calibrated in the solar neighbourhood against the Gaia DR2 stars. We have identified two star-formation bursts within the last ∼4 Gyr of the local star-formation rate (SFR) history. Aims. In this work we present a generalised version of the JJ model that incorporates our findings for the solar neighbourhood and is applicable to a wide range of galactocentric distances, 4 kpc ≲R ≲ 14 kpc. Methods. The JJ model includes the four flattened and two spheroidal components of the Milky Way, describing it as an axisymmetric system. The thin and thick disks, as well as atomic and molecular gas layers, are assumed to have exponential radial surface density profiles. Spherical stellar halo and dark matter in the form of a cored isothermal sphere are also added to the model. The overall thickness of the thin disk is assumed to be constant at all radii, though model realisations with a flaring disk can also be tested. The adopted radial variation in the thin-disk SFR reflects the inside-out disk growth scenario. Motivated by our findings for the solar neighbourhood, we allow a smooth power-law SFR continuum to be modified by an arbitrary number of Gaussian peaks. Additionally, the vertical kinematics of the stellar populations associated with these episodes of star-formation excess is allowed to differ from the kinematics prescribed by the age-velocity dispersion relation for the thin-disk populations of the same age. Results. We present a public code of the JJ model complemented by the three sets of isochrones generated by the stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code (PARSEC), the Modules and Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST), and a Bag of Stellar Tracks and Isochrones (BaSTI). Assuming a plausible set of parameters, we take the first step towards calibrating the JJ model at non-solar radii. Using metallicity distributions of the red clump giants from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), we constrain the radial variation of the JJ-model age-metallicity relation and propose a new analytic form for the age-metallicity relation function. Conclusions. The generalised JJ model is a publicly available tool for studying different stellar populations across the Milky Way disk. With its fine age resolution and flexibility, it can be particularly useful for reconstructing the thin-disk SFR, as a variety of different SFR shapes can be constructed within its framework.

THE ROLE OF OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH PREECLAMPSIA.

To investigate the changes in the microvascular structure of the retina and optic disk by comparing the optical coherence tomography angiography findings in preeclamptic patients with those in healthy pregnant women and healthy nonpregnant women and also to evaluate the preeclamptic patients after delivery by showing whether the changes are permanent or not. Fifty preeclamptic, 50 healthy pregnant, and 50 healthy nonpregnant women enrolled in three groups (preeclamptic pregnant women group, healthy pregnant women group, and nonpregnant women group; respectively). Patients in the preeclamptic pregnant women group were evaluated at three different time points including up to 3 hours before delivery (Group 1), 2, or 3 days after delivery (Group 2), and 6 weeks after delivery (Group 3), and compared with each other. All patients underwent a comprehensive ophthalmologic examination including optical coherence tomography angiography. Choriocapillaris blood flow area, deep foveal density, deep temporal density, deep nasal density, and radial peripapillary capillary inside disk density values were significantly lower in the preeclamptic pregnant women group than in the healthy pregnant women group. Deep foveal density and deep nasal density values were significantly higher in Group 3 than in Group 1 and 2, and deep temporal density was significantly higher in Group 3 than in Group 1. Optical coherence tomography angiography diagnosed decreased deep retinal capillary density values in the macula of patients with preeclampsia, but these results improved after delivery.

Addressing the critical parameters for overdamped underwater electrical explosion of wire

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub-μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron–neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

Development of an x-ray radiography platform to study laser-direct-drive energy coupling at the National Ignition Facility.

A platform has been developed to study laser-direct-drive energy coupling at the National Ignition Facility (NIF) using a plastic sphere target irradiated in a polar-direct-drive geometry to launch a spherically converging shock wave. To diagnose this system evolution, eight NIF laser beams are directed onto a curved Cu foil to generate Heα line emission at a photon energy of 8.4keV. These x rays are collected by a 100-ps gated x-ray imager in the opposing port to produce temporally gated radiographs. The platform is capable of acquiring images during and after the laser drive launches the shock wave. A backlighter profile is fit to the radiographs, and the resulting transmission images are Abel inverted to infer radial density profiles of the shock front and to track its temporal evolution. The measurements provide experimental shock trajectories and radial density profiles that are compared to 2D radiation-hydrodynamic simulations using cross-beam energy transfer and nonlocal heat-transport models.

Study of Creeping Discharges Propagating Along a Solid Insulating Surface Immersed in Mineral Oil and Palm Kernel Oil Methyl Ester Under Negative Lightning Impulse Voltage

This article presents the results of an experiment designed to study creeping discharges on a solid insulating surface immersed in palm kernel oil methyl ester (PKOME) compared with those produced from mineral oil (MO). The investigation takes place under standard negative lightning impulse voltage application, and for the three following solid insulating surfaces: hardened glass (HG), porcelain (PO), and simple glass (SG). The distributions of the radial discharge occupancy densities as a function of the thickness of the solid material and the insulating liquid are evaluated. A statistical study of the total and final length of the branches produced by the discharges is presented, as well as the current amplitudes and the charge produced by this phenomenon. A fractal analysis of the phenomenon is also presented. The experimental results show that the distribution of the average radial density of the discharge, the total and final lengths of the branches, and fractal dimension depend strongly on the physicochemical characteristics of the insulation system.

Anisotropic Strange Star Model Beyond Standard Maximum Mass Limit by Gravitational Decoupling in f(Q)$f(Q)$ Gravity

AbstractThe current theoretical development identified as the gravitational decoupling via Complete Geometric Deformation (CGD) method that has been introduced to explore the nonmetricity Q effects in relativistic astrophysics. In the present work, we have investigated the gravitationally decoupled anisotropic solutions for the strange stars in the framework of gravity by utilizing the CGD technique. To do this, we started with Tolman metric ansatz along with the MIT Bag model equation of state related to the hadronic matter. The solutions of the governing equations of motions are obtained by using two approaches, namely the mimicking of the θ sector to the seed radial pressure and energy density of the fluid model. The obtained models describe the self‐gravitating static, compact objects whose exterior solution can be given by the vacuum Schwarzschild Anti‐de Sitter spacetime. In particular, we modeled five stellar candidates, viz., LMC X‐4, PSR J1614‐2230, PSR J0740+6620, GW190814, and GW 170817 by using observational data. The rigorous viability tests of the solutions have been performed through regularity and stability conditions. We observed that the nonmetricity parameter and decoupling constant show a significant effect on stabilizing to ensure the physically realizable stellar models. The innovative feature of this work is to present the stable compact objects with masses beyond the without engaging of exotic matter. Therefore, the present study shows a new perception and physical significance about the exploration of ultra‐compact astrophysical objects.

Cotton gravity and 84 galaxy rotation curves

Recently, as a generalization of general relativity, a gravity theory has been proposed in which gravitational field equations are described by the Cotton tensor. That theory allows an additional contribution to the gravitational potential of a point mass that rises linearly with radius as $\Phi = -GM/r + \gamma r/2$, where $G$ is the Newton constant. The coefficients $M$ and $\gamma$ are the constants of integration and should be determined individually for each physical system. When applied to galaxies, the coefficient $\gamma$, which has the dimension of acceleration, should be determined for each galaxy. This is the same as having to determine the mass $M$ for each galaxy. If $\gamma$ is small enough, the linear potential term is negligible at short distances, but can become significant at large distances. In fact, it may contribute to the extragalactic systems. In this paper, we derive the effective field equation for Cotton gravity applicable to extragalactic systems. We then use the effective field equation to numerically compute the gravitational potential of a sample of 84 rotating galaxies. The 84 galaxies span a wide range, from stellar disk-dominated spirals to gas-dominated dwarf galaxies. We do not assume the radial density profile of the stellar disk, bulge, or gas; we use only the observed data. We find that the rotation curves of 84 galaxies can be explained by the observed distribution of baryons. This is due to the flexibility of Cotton gravity to allow the integration constant $\gamma$ for each galaxy. In the context of Cotton gravity, "dark matter" is in some sense automatically included as a curvature of spacetime. Consequently, even galaxies that have been assumed to be dominated by dark matter do not need dark matter.

Rotating thermal flow of water near its density inversion point in a vertical annulus: flow regime transition and heat transfer enhancement

Three-dimensional simulations are performed to identify the flow regimes of the rotating thermal flow of cold water near its density inversion point within a vertical annulus and evaluate the commensurate heat transfer abilities. The development of flow regimes and the variation in heat transfer behaviors in the special case with the density inversion parameter Θm=0.5 are explored over a wide range of parameters, with the Rayleigh number 104≤Ra≤106 and the Reynolds number Re≤150. The convection flow is radially separated into two layers by the density-maximum isosurface, with the inner and outer layers dominated by a positive and negative radial density gradient, respectively. Three axisymmetric and four non-axisymmetric basic flow regimes with different generation mechanisms are defined to describe the double-layer convection flow. Eleven flow regimes are identified, each of which consists of one, two or three basic flow regimes. The spatio-temporal features of the flow regimes depend on Ra and Re. The mixed convection parameter is demonstrated to be capable of qualitatively measuring the relative strength of the flow between the inner and outer layers in certain ranges of Ra. The mechanisms of both the flow regime transitions and the mode transitions between steady and oscillatory states are explored in terms of the combined action of density inversion effect, centrifugal effect and buoyancy effect. The heat transfer behaviors depend on the spatio-temporal features of flow regimes. The mechanism of heat transfer enhancement and that for the non-monotonic variation of heat transfer ability are revealed. The limitation of the axisymmetric assumption is quantified.