152 research outputs found
3D Morphology of Open Clusters in the Solar Neighborhood with Gaia EDR3: its Relation to Cluster Dynamics
We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located
within 500 pc of the Sun, using Gaia EDR3 and kinematic data from literature.
Members of OCs are identified using the unsupervised machine learning method
StarGO, using 5D parameters (X, Y, Z, ). The
OC sample covers an age range of 25Myr--2.65Gyr. We correct the asymmetric
distance distribution due to the parallax error using Bayesian inversion. The
uncertainty in the corrected distance for a cluster at 500~pc is 3.0--6.3~pc,
depending on the intrinsic spatial distribution of its members. We determine
the 3D morphology of the OCs in our sample and fit the spatial distribution of
stars within the tidal radius in each cluster with an ellipsoid model. The
shapes of the OCs are well-described with oblate spheroids (NGC2547, NGC2516,
NGC2451A, NGC2451B, NGC2232), prolate spheroids (IC2602, IC4665, NGC2422,
Blanco1, Coma Berenices), or triaxial ellipsoids (IC2391, NGC6633, NGC6774).
The semi-major axis of the fitted ellipsoid is parallel to the Galactic plane
for most clusters. Elongated filament-like substructures are detected in three
young clusters (NGC2232, NGC2547, NGC2451B), while tidal-tail-like
substructures (tidal tails) are found in older clusters (NGC2516, NGC6633,
NGC6774, Blanco1, Coma Berenices). Most clusters may be super-virial and
expanding. -body models of rapid gas expulsion with an SFE of
are consistent with clusters more massive than , while clusters
less massive than 250 tend to agree with adiabatic gas expulsion
models. Only six OCs (NGC2422, NGC6633, and NGC6774, NGC2232, Blanco1, Coma
Berenices) show clear signs of mass segregation.Comment: 35 pages, 17 figures, accepted by Ap
Binary Star Evolution in Different Environments: Filamentary, Fractal, Halo and Tidal-tail Clusters
Using membership of 85 open clusters from previous studies (Pang et al.
2021a,b, 2022b; Li et al. 2021) based on Gaia DR3 data, we identify binary
candidates in the color-magnitude diagram, for systems with mass ratio q > 0.4.
The binary fraction is corrected for incompleteness at different distances due
to the Gaia angular resolution limit. We find a decreasing binary fraction with
increasing cluster age, with substantial scatter. For clusters with a total
mass > 200, the binary fraction is independent of cluster mass. The
binary fraction depends strongly on stellar density. Among four types of
cluster environments, the lowest-density filamentary and fractal stellar groups
have the highest mean binary fraction: 23.6% and 23.2%, respectively. The mean
binary fraction in tidal-tail clusters is 20.8%, and is lowest in the densest
halo-type clusters: 14.8%. We find clear evidence of early disruptions of
binary stars in the cluster sample. The radial binary fraction depends strongly
on the cluster-centric distance across all four types of environments, with the
smallest binary fraction within the half-mass radius , and increasing
towards a few . Only hints of mass segregation is found in the target
clusters. The observed amount of mass segregation is not significant to
generate a global effect inside the target clusters. We evaluate the bias of
unresolved binary systems (assuming a primary mass of 1) in 1D
tangential velocity, which is 0.1-1. Further studies are
required to characterize the internal star cluster kinematics using Gaia proper
motions
3D Morphology of Open Clusters in the Solar Neighborhood with Gaia EDR 3. II. Hierarchical Star Formation Revealed by Spatial and Kinematic Substructures
We identify members of 65 open clusters in the solar neighborhood using the machine-learning algorithm StarGO based on Gaia EDR3 data. After adding members of 20 clusters from previous studies we obtain 85 clusters, and study their morphology and kinematics. We classify the substructures outside the tidal radius into four categories: filamentary (f1) and fractal (f2) for clusters 100 Myr. The kinematical substructures of f1-type clusters are elongated; these resemble the disrupted cluster Group X. Kinematic tails are distinct in t-type clusters, especially Pleiades. We identify 29 hierarchical groups in four young regions (Alessi 20, IC 348, LP 2373, LP 2442); 10 among these are new. The hierarchical groups form filament networks. Two regions (Alessi 20, LP 2373) exhibit global orthogonal expansion (stellar motion perpendicular to the filament), which might cause complete dispersal. Infalling-like flows (stellar motion along the filament) are found in UBC 31 and related hierarchical groups in the IC 348 region. Stellar groups in the LP 2442 region (LP 2442 gp 1–5) are spatially well mixed but kinematically coherent. A merging process might be ongoing in the LP 2442 subgroups. For younger systems (≲30 Myr), the mean axis ratio, cluster mass, and half-mass–radius tend to increase with age values. These correlations between structural parameters may imply two dynamical processes occurring in the hierarchical formation scenario in young stellar groups: (1) filament dissolution and (2) subgroup mergers
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Association of increased Treg and Th17 with pathogenesis of moyamoya disease
Immuno-inflammation has been shown to play a pivotal role in the pathogenesis of moyamoya disease (MMD). However, how did circulating Treg/Th17 cells involve in MMD patients remains unclear. 26 MMD, 21 atherothrombotic stroke, and 32 healthy controls were enrolled in this study. MMD patients have a significantly higher percentage of circulating Treg and Th17 cells as well as their dominantly secreting cytokines than other groups (P < 0.0001), whereas no difference was found in the ratio of Treg/Th17 between patients in MMD and atherothrombotic stroke group or control subjects (P = 0.244). However, the increased Treg in MMD patients which were enriched with FrIII Treg cells had deficient suppressive functions (P = 0.0017) compared to healthy volunteers. There was a positive correlation between Treg or TGF-β and MMD Suzuki’s stage. And the level of circulating Treg was as an independent factor associated with MMD stage. Besides, TGF-β was also correlated with the increased expression of VEGF in MMD patients. Our findings indicated an important involvement of circulating Treg in the pathogenic development of MMD and TGF-β in Treg induced VEGF
The Altered Reconfiguration Pattern of Brain Modular Architecture Regulates Cognitive Function in Cerebral Small Vessel Disease
Background: Cerebral small vessel disease (SVD) is a common cause of cognitive dysfunction. However, little is known whether the altered reconfiguration pattern of brain modular architecture regulates cognitive dysfunction in SVD.Methods: We recruited 25 cases of SVD without cognitive impairment (SVD-NCI) and 24 cases of SVD with mild cognitive impairment (SVD-MCI). According to the Framingham Stroke Risk Profile, healthy controls (HC) were divided into 17 subjects (HC-low risk) and 19 subjects (HC-high risk). All individuals underwent resting-state functional magnetic resonance imaging and cognitive assessments. Graph-theoretical analysis was used to explore alterations in the modular organization of functional brain networks. Multiple regression and mediation analyses were performed to investigate the relationship between MRI markers, network metrics and cognitive performance.Results: We identified four modules corresponding to the default mode network (DMN), executive control network (ECN), sensorimotor network and visual network. With increasing vascular risk factors, the inter- and intranetwork compensation of the ECN and a relatively reserved DMN itself were observed in individuals at high risk for SVD. With declining cognitive ability, SVD-MCI showed a disrupted ECN intranetwork and increased DMN connection. Furthermore, the intermodule connectivity of the right inferior frontal gyrus of the ECN mediated the relationship between periventricular white matter hyperintensities and visuospatial processing in SVD-MCI.Conclusions: The reconfiguration pattern of the modular architecture within/between the DMN and ECN advances our understanding of the neural underpinning in response to vascular risk and SVD burden. These observations may provide novel insight into the underlying neural mechanism of SVD-related cognitive impairment and may serve as a potential non-invasive biomarker to predict and monitor disease progression
Serum Fetuin-A Associates with Type 2 Diabetes and Insulin Resistance in Chinese Adults
Previous studies have demonstrated that fetuin-A is related to insulin resistance among subjects with normal glucose tolerance but not patients with type 2 diabetes. There are limited data available concerning fetuin-A and insulin resistance in Chinese. We aimed to study the association of fetuin-A with insulin resistance among participants with or without type 2 diabetes in a large sample size of adults aged 40 and older.A community-based cross-sectional study was performed among 5,227 Chinese adults. The average age of our study was 61.5±9.9 years. Serum fetuin-A concentrations were not significantly different between male and female (296.9 vs. 292.9 mg/l, p = 0.11). Compared with the lowest quartile, the highest quartile of serum fetuin-A revealed a significant higher proportion of type 2 diabetic patients (34.8% vs. 27.3%, p<0.0001). In the multinomial logit models, the risk of type 2 diabetes was associated with each one quartile increase of serum fetuin-A concentrations when referenced not only to normal glucose tolerance (OR 1.24, 95% CI 1.07-1.43, p = 0.004) but also to impaired glucose regulation (OR 1.25, 95% CI 1.08-1.44, p = 0.003, respectively), after adjustment for age, sex, community, current smoking, and current drinking. The logistic regression analysis showed that fetuin-A were associated with elevated HOMA-IR and fasting serum insulin both among the participants with or without type 2 diabetes in the full adjusted analysis. There was no significant association between elevated serum fetuin-A concentrations and impaired glucose regulation (all p≥0.12).Higher fetuin-A concentrations were associated with type 2 diabetes and insulin resistance in middle aged and elderly Chinese
Active screen plasma surface co-alloying of 316 austenitic stainless steel with both nitrogen and niobium for the application of bipolar plates in proton exchange membrane fuel cells
AbstractAustenitic stainless steel has been researched as a promising candidate material for bipolar plates in proton exchange membrane fuel cells. However, its interfacial contact resistance (ICR) is about 16 times higher that of the Department of Energy (DOE) target (10 mΩ cm2), which leads to undesirable fuel cell performance. In this work, a new hybrid plasma surface engineering process, based on active screen plasma co-alloying, has been developed to simultaneously alloy 316 austenitic stainless steel (316 SS) surfaces with both nitrogen and niobium. The results demonstrated that the layer structure of the modified surfaces can be tailored by adjusting the treatment conditions. All the plasma treated 316 SS samples exhibited significantly reduced ICR below the DOE target of 10 mΩ cm2. The corrosion resistance of the N/Nb co-alloyed 316 SS was much better than active screen plasma nitrided and marginally better than the untreated material
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