Cluster Core Research Articles

Structural Chemistry of Titanium (IV) Oxo Clusters, Part 2: Clusters without Carboxylate or Phosphonate Ligands.

Homometallic titanium oxo clusters (TOC) are one of the most important groups of metal oxo clusters. In a previous article, TOC structures with carboxylato and phosphonato ligands were reviewed and categorized. This work is now extended to clusters with other ligands. Comparison of the different cluster types shows how the interplay between condensation of the titanium polyhedra by means of bridging oxygen atoms and the coordination characteristics of the ligands influences the cluster structures and allows working out basic construction principles of the cluster core.

Hydrophobic Clusters Regulate Surface Hydration Dynamics of Bacillus subtilis Lipase A.

The surface hydration diffusivity of Bacillus subtilis Lipase A (BSLA) has been characterized by low-field Overhauser dynamic nuclear polarization (ODNP) relaxometry using a series of spin-labeled constructs. Sites for spin-label incorporation were previously designed via an atomistic computational approach that screened for surface exposure, reflective of the surface hydration comparable to other proteins studied by this method, as well as minimal impact on protein function, dynamics, and structure of BSLA by excluding any surface site that participated in greater than 30% occupancy of a hydrogen bonding network within BSLA. Experimental ODNP relaxometry coupling factor results verify the overall surface hydration behavior for these BSLA spin-labeled sites similar to other globular proteins. Here, by plotting the ODNP parameters of relative diffusive water versus the relative bound water, we introduce an effective "phase-space" analysis, which provides a facile visual comparison of the ODNP parameters of various biomolecular systems studied to date. We find notable differences when comparing BSLA to other systems, as well as when comparing different clusters on the surface of BSLA. Specifically, we find a grouping of sites that correspond to the spin-label surface location within the two main hydrophobic core clusters of the branched aliphatic amino acids isoleucine, leucine, and valine cores observed in the BSLA crystal structure. The results imply that hydrophobic clustering may dictate local surface hydration properties, perhaps through modulation of protein conformations and samplings of the unfolded states, providing insights into how the dynamics of the hydration shell is coupled to protein motion and fluctuations.

Redox-Active Boron Clusters.

ConspectusIn this Account, we discuss our group's research over the past decade on a class of functionalized boron clusters with tunable chemical and physical properties, with an emphasis on accessing and controlling their redox behavior. These clusters can be thought of as three-dimensional aromatic systems that have distinct redox behavior and photophysical properties compared to their two-dimensional organic counterparts. Specifically, our lab has studied the highly tunable, multielectron redox behavior of B12(OR)12 clusters and applied these molecules in various settings. We first discuss the spectroscopic and electrochemical characterization of B12(OR)12 clusters in various oxidation states, followed by their use as catholytes and/or anolytes in redox flow batteries and chemical dopants in conjugated polymers. Additionally, the high oxidizing potential and visible light-absorbing nature of fluoroaryl-functionalized B12(OR)12 clusters have been leveraged by our group to generate weakly coordinating, photoexcitable species that can promote photooxidation chemistry.We have further translated these solution-phase studies of B12(OR)12 clusters to the solid state by using the precursor [B12(OH)12]2- cluster as a robust building block for hybrid metal oxide materials. Specifically, we have shown that the boron cluster can act as a thermally stable cross-linking material, which enhances electron transport between metal oxide nanoparticles. We applied this structural motif to create TiO2- and WO3-containing materials that showed promising properties as photocatalysts and electroactive materials for supercapacitors. Building on this concept, we later discovered that B12(OCH3)12, the smallest of the B12(OR)12 family, could retain its redox behavior in the solid state, a previously unseen phenomenon. We successfully harnessed this unique behavior for solid-state energy storage by implementing this boron cluster as a cathode-active material in a Li-ion prototype cell device. Recently, our group has also explored how to tune the redox properties of clusters other than B12(OR)12 species by synthesizing a library of vertex-differentiated clusters containing both B-OR and B-halogen groups. Due to the additive qualities of different functional groups on the cluster, these species allow access to a region of electrochemical potentials previously inaccessible by fully substituted closo-dodecaborate alkoxy-based derivatives.Lastly, we discuss our research into smaller-sized redox-active polyhedral boranes (B6- and B10-based cluster cores). Interestingly, these clusters show significantly less redox stability and reversibility than their dodecaborate-based counterparts. While exploring the functionalization of closo-hexaborate to create fully substituted derivates (i.e., [B6R6Hfac]-), we observed unique oxidative decomposition pathways for this cluster system. Consequently, we leveraged this oxidative instability to generate useful alkyl boronate esters via selective chemical oxidation. We further explored a closo-decaborate cluster as a platform to access electrophilic [B10H13]+ species capable of directly borylating arene compounds with unique regioselectivity. Upon chemical oxidation of the arylated decaborate clusters, we successfully synthesized various aryl boronate esters, establishing the generality of the oxidative cluster deconstruction concept.Overall, our work shows that boron clusters are an appealing class of redox-active molecules, and this fundamental and understudied property can be leveraged for constructing novel materials with tunable physical and electrochemical properties, as well as producing unique chemical reagents for small molecule synthesis.

Novel flexible aromatic Cu3 metal-organic π-cluster for electrocatalytic CO2 reduction reaction

Producing Cn products through electrocatalytic CO2 reduction reaction (CO2RR) is of great significance in addressing the global warming crisis. Organic-inorganic hybrid catalysts, characterized by precise and controllable active sites and metal-ligand synergistic interactions, can enhance the reaction activity and stability of Cu-based catalysts. Herein, based on density functional theory (DFT), a novel flexible aromatic Cu3 metal-organic π-cluster (Cu3-π cluster) was constructed, consisting of triple-atom active centers and pentalyne ligands. During the catalytic CO2RR process, the adsorption of H can promote the activation of CO2, this converts the competing hydrogen evolution reaction (HER) into promoting CO2RR. Enhanced aromaticity of its cluster core is credited with stabilizing the coadsorption of H and CO2 (H* + CO2*), consequently lowering the reaction free energy of the CO2 activation process. Research has shown that Cu3-π cluster have high catalytic activity for electrocatalytic CO2 generation of C2H4. Considering the solvation effect, the limit potential of this reaction is −0.60 V. Furthermore, the reaction free energies suggest that the Cu3-π cluster is more inclined to yield C2H4(g) products via COCO* coupling. Moreover, the high CO coverage at the triple-atom active centers not only makes it more challenging for this cluster to adsorb H, but also reduces the energy barrier of the COCO* coupling reaction.In the entire reaction pathway of C2H4(g), there exhibits dynamic self-adaptive behavior in the bond lengths and bond angles of the three Cu atoms in the cluster core, leading to fluctuations in aromaticity. The flexibility and aromaticity changes in this structure enable the Cu3-π cluster to better stabilize intermediates. This work provides theoretical guidance for the application of metal-organic π-clusters, accelerates the screening of catalysts for CO2RR, and provides powerful theoretical guidance for the structure-activity relationships between aromaticity and catalytic activity.

Regulation mechanism of the quorum sensing regulator AphA on the type Ⅵ secretion system VflT6SS2 in Vibrio fluvialis

Objective: To explore the regulation mechanism of the quorum sensing regulator AphA on the functional activity of type Ⅵ secretion system VflT6SS2 in Vibrio fluvialis. Methods: Western Blot analysis was used to detect the relative expression and secretion of VflT6SS2 signature component hemolysin-coregulated protein (Hcp) in wild type (WT), ΔaphA, and corresponding complementary strains. Quantitative reverse transcription PCR and luminescence activity assay of the promoter-lux fusion system was used to measure the mRNA expression levels and promoter activity of the VflT6SS2 core and accessory gene-cluster representative genes tssB2, hcp (tssD2) and vgrG (tssI2), and the quorum sensing regulator HapR in WT and ΔaphA strains. A point mutation experiment combined with a luminescence activity assay was used to verify the regulatory binding site of AphA in the tssD2b promoter region. Electrophoretic mobility shift assay (EMSA) was used to determine AphA binding to the hapR promoter. Results: The mRNA expression levels of tssB2, hcp(tssD2), vgrG (tssI2), and hapR as well as the protein expression and secretion levels of Hcp in ΔaphA strain, were significantly higher than those in the WT strain. The promoter activities of the VflT6SS2 core cluster, tssD2a, tssI2a, and hapR were higher in ΔaphA strain than in the WT strain, while the promoter activity of tssD2b showed the opposite trend. The promoter sequence analysis of tssD2a and tssD2b found significant differences in the region from -335 bp to -229 bp, and two potential AphA binding sites on tssD2b. The promoter activity of tssD2b decreased significantly after the point mutation of the two potential AphA binding sites. EMSA results showed that AphA binds directly to the promoter region of hapR. Conclusions: AphA indirectly inhibits the regulation of the VflT6SS2 core and accessory gene clusters at the promoter level by directly repressing the expression of hapR. AphA showed opposite regulation patterns for tssD2a and tssD2b, and AphA could positively regulate the expression of tssD2b by directly binding to the tssD2b promoter region (-335 bp to -229 bp).

Impact of Surface Ligand Identity and Density on the Thermodynamics of H Atom Uptake at Polyoxovanadate-Alkoxide Surfaces.

An understanding of how molecular structure influences the thermodynamics of H atom transfer is critical to designing efficient catalysts for reductive chemistries. Herein, we report experimental and theoretical investigations summarizing structure-function relationships of polyoxovanadate-alkoxides that influence bond dissociation free energies of hydroxide ligands located at the surface of the cluster. We evaluate the thermochemical descriptors of O-H bond strength for a series of clusters, namely [V6O13-x(OH)x(TRIOLR)2]-2 (x = 2, 4, 6; R = NO2, Me) and [V6O11-x(OMe)2(OH)x(TRIOLNO2)2]-2, via computational analysis and open circuit potential measurements. Our findings reveal that modifications to the TRIOL ligand (e.g., changing from the previously reported electron withdrawing nitro-backed ligand to the electron-donating methyl variant) have limited influence on the strength of surface O-H bonds as a result of near complete thermodynamic compensation in these systems (i.e., correlated changes in redox potential and cluster basicity). In contrast, changes in surface density of alkoxide ligands via direct alkoxylation of the polyoxovanadate-alkoxide surface result in measurable increases in bond dissociation free energies of surface O-H bonds for the mixed-valent derivatives. Our findings indicate that the extent of (de)localization of electron density across the cluster core has an impact on the bond dissociation free energies of surface O-H bonds across all oxidation states of the assembly.

Noema formIng Cluster survEy (NICE): Discovery of a starbursting galaxy group with a radio-luminous core at z = 3.95

The study of distant galaxy groups and clusters at the peak epoch of star formation is limited by the lack of a statistically and homogeneously selected and spectroscopically confirmed sample. Recent discoveries of concentrated starburst activities in cluster cores have opened a new window to hunt for these structures based on their integrated IR luminosities. Here, we carry out a large NOEMA (NOrthern Extended Millimeter Array) program targeting a statistical sample of infrared-luminous sources associated with overdensities of massive galaxies at z > 2, the Noema formIng Cluster survEy (NICE). We present the first result from the ongoing NICE survey, a compact group at z = 3.95 in the Lockman Hole field (LH-SBC3), confirmed via four massive (M⋆ ≳ 1010.5 M⊙) galaxies detected in the CO(4–3) and [CI](1–0) lines. The four CO-detected members of LH-SBC3 are distributed over a 180 kpc physical scale and the entire structure has an estimated halo mass of ∼1013 M⊙ and total star formation rate of ∼4000 M⊙ yr−1. In addition, the most massive galaxy hosts a radio-loud active galactic nucleus with L1.4 GHz, rest = 3.0 × 1025 W Hz−1. The discovery of LH-SBC3 demonstrates the feasibility of our method to efficiently identify high-z compact groups or cluster cores undergoing formation. The existence of these starbursting cluster cores up to z ∼ 4 provides critical insights into the mass assembly history of the central massive galaxies in clusters.

Insights into Temporal Evolution of Induced Earthquakes in the Southern Delaware Basin Using Calibrated Relocations from the TXAR Catalog (2009–2016)

Abstract The Texas Seismological Network (TexNet) has enabled real-time monitoring of induced earthquakes since 2017. Before 2017, location uncertainties and temporal gaps in seismic data obscure correlations across Texas between seismicity and saltwater disposal or hydraulic fracturing. Depth biases also complicate linking anthropogenic stress changes to faults. We relocate 73 M 1.5+ earthquakes from the TXAR catalog (2009–2016) relative to the centroid of a calibrated core cluster consisting of 116 earthquakes from the TexNet catalog post-2020, in the southern Delaware basin south of the Grisham fault zone. Hypocentroidal decomposition relocation reduces spatial uncertainties of the TXAR events to <5 km and provides updated depths. The core cluster has uncertainties less than <300 m and depth constrained from near-source stations and S−P differential times. The majority of relocated TXAR events indicate the triggering of northwest-trending faults at a mean depth of 1 km below sea level, suggesting a causal connection with shallow saltwater disposal and consistency with post-2017 seismicity. Spatiotemporal patterns of pre-2017 seismicity and saltwater disposal highlight initial triggering via pore-pressure stress perturbations from nearby low-volume injections and later from southeastward pressure diffusion along permeable anisotropic conduits and fracture zones. The comparison between pre- and post-2017 seismicity indicates shallow fault reactivation through similar triggering mechanisms since 2009.

Triptolide Administration Alters Immune Responses to Mitigate Insulin Resistance in Obese States.

Individuals who are overweight or obese are at increased risk of developing prediabetes and type 2 diabetes, yet the direct molecular mechanisms that connect diabetes to obesity are not clear. Chronic, sustained inflammation is considered a strong risk factor in these interactions, directed in part by the short-lived gene expression programs encoding for cytokines and pro-inflammatory mediators. In this study, we show that triptolide administration in the C57BL/6 diet-induced obese mice at up to 10 μg/kg/day for 10 weeks attenuated the development of insulin resistance and diabetes, but not obesity, in these animals. Significant reductions in adipose tissue inflammation and improved insulin sensitivity were observed in the absence of changes in food intake, body weight, body composition, or energy expenditure. Analysis of the core cluster of biomarkers that drives pro-inflammatory responses in the metabolic tissues suggested TNF-α as a critical point that affected the co-development of inflammation and insulin resistance, but also pointed to the putatively protective roles of increased COX-2 and IL-17A signaling in the mediation of these pathophysiological states. Our results show that reduction of diet-induced inflammation confers partial protection against insulin resistance, but not obesity, and suggest the possibility of achieving overweight phenotypes that are accompanied by minimal insulin resistance if inflammation is controlled.

GeRu6(CO)18HI]: A Germanium-Centered Ruthenium Carbonyl Cluster with Aromatic Ring Current.

The carbonyl cluster compound [GeRu6(CO)18HI] is unique in regard to its structure and bonding with a GeRu6 cluster core, a planar GeRu4HI unit, extensive multi-center bonding, and an aromatic ring current similar to benzene (9-10nAT-1). The open-shell cluster core is a Ge-centered five-membered Ru4(Ru2) ring with CO ligands and an additional H and I atom, each bridging two Ru atoms on opposite sides of the cluster core. The compound is prepared at 130°C in a weakly-coordinating ionic liquid.

First evidence of a connection between cluster-scale diffuse radio emission in cool-core galaxy clusters and sloshing features

Radio observations of a few cool-core galaxy clusters have revealed the presence of diffuse emission on cluster scales, similar to what was found in merging clusters in the form of radio halos. These sources might suggest that a minor merger, while not sufficiently energetic to disrupt the cool core, could still trigger particle acceleration in the intracluster medium on scales of hundreds of kiloparsecs. We aim to verify the occurrence of cluster-scale diffuse radio emission in cool-core clusters and test the minor merger scenario. With the LOw Frequency ARray (LOFAR) at 144 MHz, we observed a sample of twelve cool-core galaxy clusters presenting some level of dynamical disturbances, according to X-ray data. We also performed a systematic search of cold fronts in these clusters, re-analysing archival Chandra observations. The clusters PSZ1G139.61+24, A1068 (new detection), MS 1455.0+2232, and RX J1720.1+2638 present diffuse radio emission on a cluster scale ($r $). This emission is characterised by a double component: a central mini-halo confined by cold fronts and diffuse emission on larger scales, whose radio power at 144 MHz is comparable to that of radio halos detected in merging systems with the same cluster mass. The cold fronts in A1068 are a new detection. We also found a candidate plasma depletion layer in this cluster. No sloshing features are found in the other eight clusters. Two of them present a mini-halo, with diffuse radio emission confined to the cluster core. We also found a new candidate mini-halo. Whereas, for the remaining five clusters, we did not detect halo-like emission. For clusters without cluster-scale halos, we derived upper limits to the radio halo power. We found that cluster-scale diffuse radio emission is not present in all cool-core clusters when observed at a low frequency, but it is correlated to the presence of cold fronts. The coexistence of cluster-scale diffuse radio emission and cold fronts in cool-core clusters requires a specific configuration of the merger and so it puts some constraints on the turbulence, which deserves to be investigated in the future with theoretical works.

Metal enrichment: the apex accretor perspective

The goal of this work is to devise a description of the enrichment process in large-scale structure that explains the available observations and makes predictions for future measurements. We took a spartan approach to this study, employing observational results and algebra to connect stellar assembly in star-forming halos with metal enrichment of the intra-cluster and group medium. On one hand, our construct is the first to provide an explanation for much of the phenomenology of metal enrichment in clusters and groups. It sheds light on the lack of redshift evolution in metal abundance, as well as the small scatter of metal abundance profiles, the entropy versus abundance anti-correlation found in cool core clusters, and the so-called Fe conundrum, along with several other aspects of cluster enrichment. On the other hand, it also allows us to infer the properties of other constituents of large-scale structure. We find that gas that is not bound to halos must have a metal abundance similar to that of the ICM and only about one-seventh to one-third of the Fe in the Universe is locked in stars. A comparable amount is found in gas in groups and clusters and, lastly and most importantly, about three-fifths of the total Fe is contained in a tenuous warm or hot gaseous medium in or between galaxies. We point out that several of our results follow from two critical but well motivated assumptions: 1) the stellar mass in massive halos is currently underestimated and 2) the adopted Fe yield is only marginally consistent with predictions from synthesis models and SN rates. One of the most appealing features of the work presented here is that it provides an observationally grounded construct where vital questions on chemical enrichment in the large-scale structure can be addressed. We hope that it may serve as a useful baseline for future works.

Role of jianxin granules in heart failure: evidence from network pharmacology, molecular docking and experimental verification.

Jianxin (JX) granules is a traditional Chinese medicine widely used in the treatment of heart failure (HF), but the mechanism is unclear. This study aimed to investigate the mechanism of JX granules in the treatment of HF based on network pharmacology analysis and in-vivo experiments. A series of network pharmacology methods was employed to ascertain potential targets and critical pathways implicated in the therapeutic action of JX granules against HF. Subsequently, molecular docking was utilized to investigate the binding affinity of key active constituents within JX granules to these targets. In-vivo experiments, echocardiography, hematoxylin and eosin, Masson's trichrome assay, and western blot analysis were conducted to validate the efficacy and mechanism of JX granules in treating rats with HF. A total of 122 active components, 896 drug targets, 1216 HF-related targets, and 136 targets pertinent to drug-disease interactions were identified. 151 key targets and 725 core clusters were detected through protein-protein interaction network analysis. Among these, interleukin 6 (IL-6), vascular endothelial growth factor a (VEGFA), and serine/threonine kinase 1 (AKT1) were core hub genes. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis revealed the critical pathways, including epidermal growth factor receptor (EGFR), advanced glycation end products (AGEs) and their receptors (RAGE) pathway, along with hypoxia-inducible factor 1 (HIF-1) signaling pathway. Molecular docking studies demonstrated high binding affinities between key targets and the pivotal active ingredients of Danshenol A, salvianolic acid B, and arachidonic acid. Furthermore, animal studies corroborated that JX granules improve cardiac function and reduce myocardial fibrosis, potentially by modulating the expression of IL-6, VEGFA, and p-AKT1. The bioactive components within JX granules, such as Danshenol A, salvianolic acid B, and arachidonic acid may exert therapeutic effects on HF through modulation of IL-6, VEGFA, and AKT1 gene expression. This study provides a scientific basis for subsequent clinical application of JX granules and an in-depth investigation of their mechanisms of action.

Cosmic Vine: A z = 3.44 large-scale structure hosting massive quiescent galaxies

We report the discovery of a large-scale structure at z = 3.44 revealed by JWST data in the Extended Groth Strip (EGS) field. This structure, called the Cosmic Vine, consists of 20 galaxies with spectroscopic redshifts at 3.43 < z < 3.45 and six galaxy overdensities (4 − 7σ) with consistent photometric redshifts, making up a vine-like structure extending over a ∼4 × 0.2 pMpc2 area. The two most massive galaxies (M* ≈ 1010.9 M⊙) of the Cosmic Vine are found to be quiescent with bulge-dominated morphologies (B/T > 70%). Comparisons with simulations suggest that the Cosmic Vine would form a cluster with halo mass Mhalo > 1014 M⊙ at z = 0, and the two massive galaxies are likely forming the brightest cluster galaxies (BCGs). The results unambiguously reveal that massive quiescent galaxies can form in growing large-scale structures at z > 3, thus disfavoring the environmental quenching mechanisms that require a virialized cluster core. Instead, as suggested by the interacting and bulge-dominated morphologies, the two galaxies are likely quenched by merger-triggered starburst or active galactic nucleus (AGN) feedback before falling into a cluster core. Moreover, we found that the observed specific star formation rates of massive quiescent galaxies in z > 3 dense environments are one to two orders of magnitude lower than that of the BCGs in the TNG300 simulation. This discrepancy potentially poses a challenge to the models of massive cluster galaxy formation. Future studies comparing a large sample with dedicated cluster simulations are required to solve the problem.

Discovery of Astrometric Accelerations by Dark Companions in the Globular Cluster ω Centauri

We present results from the search for astrometric accelerations of stars in ω Centauri using 13 yr of regularly scheduled Hubble Space Telescope WFC3/UVIS calibration observations in the cluster core. The high-precision astrometry of ∼160,000 sources was searched for significant deviations from linear proper motion. This led to the discovery of four cluster members and one foreground field star with compelling acceleration patterns. We interpreted them as the result of the gravitational pull by an invisible companion and determined preliminary Keplerian orbit parameters, including the companion’s mass. For the cluster members, our analysis suggests periods ranging from 8.8 to 19+ yr and dark companions in the mass range of ∼0.7 to ∼1.4M ☉. At least one companion could exceed the upper mass boundary of white dwarfs and can be classified as a neutron star candidate.

Environmental regulation and corporate environmental performance: A bibliometric analysis

Under the concept of green development, enterprises will face more environmental constraints. Whether government environmental regulation (ER) can effectively promote corporate environmental performance (CEP) has not yet been unified among scholars, and few studies have conducted bibliometric analysis on ER and CEP. Based on the above, this study has three purposes: first, to fill the research gap by analyzing and visualizing 72 articles on ER and CEP through Biblioshiny and VOSviewer; second, to help scholars easily understand the research development and quickly find promising research directions; and lastly, to enable the government and corporate managers gain a more comprehensive view of ER’s impacts on CEP, which can assist in policy making and business management. The research found that: (a) the number of articles and citations in the field is on the rise. China is the most academically influential country in terms of publications, citations, and collaborations. Journal of Cleaner Production is the top-ranked journal. Ramanathan R, Testa F, and Zhang Y are the top three authors. Environmental management, sustainability, and China are the most popular keywords. Collaboration between authors, institutions, and countries is relatively weak and isolated. (b) ER and CEP have three emerging clusters: Climate Change, FDI, as well as Environmental Awareness, and three core clusters: Environmental Management, Data Envelopment Analysis, and Economic Analysis. The evolution of themes shows a trend from decentralized to centralized and then back to decentralized. (c) Future research can take the Regulatory Framework, Green Technological Innovation, and Environmental Management System as breaking points.

The Emergence of a Brightest Cluster Galaxy in a Protocluster Core at z = 2.24

We report the detection of a pair of massive quiescent galaxies likely in the process of merging at the center of the spectroscopically confirmed, extremely massive protocluster BOSS1244 at z = 2.24 ± 0.02. These galaxies, BOSS1244-QG1 and BOSS1244-QG2, were detected with Hubble Space Telescope grism slitless spectroscopic observations. These two quiescent galaxies are among the brightest member galaxies, with z = 2.223–2.255 in BOSS1244, and reside at redshifts z = 2.244 and z = 2.242, with a half-light radius of 6.76 ± 0.50 kpc and 2.72 ± 0.16 kpc, respectively. BOSS1244-QG1 and BOSS1244-QG2 are separated by a projected distance of about 70 physical kpc, implying that the two galaxies likely merge to form a massive brightest cluster galaxy (BCG) with size and mass similar to the most massive BCGs in the local Universe. We thus infer that BCG formation through dry major mergers may happen earlier than the full assembly of a cluster core, which broadens our previous understanding of the coevolution of mature galaxy clusters and BCGs in the nearby Universe. Moreover, we find a strong density–star formation relation over a scale of ∼18 comoving Mpc in BOSS1244, i.e., star formation activity decreases as density increases, implying that the quenching of star formation in BCGs and their progenitors is likely governed by environment-related processes before the virialization of the cluster core.

High-density cluster core-based [formula omitted]-means clustering with an unknown number of clusters

The k-means algorithm, known for its simplicity and adaptability, faces challenges related to manual cluster number selection and sensitivity to initial centroid placement. This paper introduces an innovative framework aimed at overcoming these challenges. By proposing a data-driven cluster number estimation method and a robust initialization strategy based on high-density cluster cores, our approach revolutionizes k-means, unlocking its full unsupervised potential and ensuring superior performance, even in scenarios involving overlapping clusters. The method employs a novel density-based technique to accurately identify cluster cores, resulting in substantial improvements over existing methods. Rigorous experimentation on synthetic and real-world datasets demonstrates an average performance enhancement of 15% in terms of the Adjusted Rand Index for datasets with overlapping clusters, surpassing the capabilities of state-of-the-art density-based clustering methods and traditional k-means. Moreover, our method autonomously determines the optimal number of clusters, facilitating true unsupervised learning and eliminating the impact of initial centroid placement on clustering outcomes. This leads to stable and consistent results, addressing key limitations of the conventional k-means algorithm. The practical applicability of our approach is exemplified in image segmentation tasks, showcasing its versatility and reliability in real-world scenarios.

A two-stage clustering ensemble algorithm applicable to risk assessment of railway signaling faults

Knowledge graph (KG) modeling constructs a connected network of hazard/fault events by drawing on historical reports, helping extract risk factors and propagation features in railway signaling safety. For the huge graph structure of the knowledge system, efficiently and accurately transforming the event information with text for risk level prediction is the crucial topic of this paper. To establish a quantitative risk assessment method based on KG modeling, we innovatively introduce text clustering technology to intelligently divide the entity short text data set in the KG, assign standardized entity names to the cluster partitions, and then complete the calculation and analysis according to the characteristic parameter formula, greatly reducing the labor and time consumption of data annotation and approximate text repetitive processing. Significantly, a two-stage clustering ensemble algorithm (TSCEA) integrating base clusterer optimization and hierarchical clustering prediction is proposed, whose innovative approach lies in describing sample similarity by the co-association matrix, while considering the contribution discrepancy of samples for decision-making. Specifically, Stage One selects and optimizes various base clusterers with different method kernels, while Stage Two emphasizes the contribution discrepancy of the cluster core and the cluster halo to make the final clustering decision, with the ensemble strategy serving as the bridge between these two. The KG established on field investigation is used to complete the experiment and analysis of the novel algorithm. Another clustering ensemble algorithm (based on a direct weighting strategy) and each base clusterer are applied to verify clustering performance, while the evaluation depends on external indicators. The results indicate that the proposed clustering ensemble algorithm outperforms others in various indicators, significantly improving clustering accuracy and robustness.

Context of Male Single Parenting in Nigeria

Most studies have documented experiences of single parents focusing more predominantly on realities of females. This is especially so in studies on Africa where single parenting has been commonly narrated as core cluster of patriarchy and feminization of gender oppression. In this article, the authors contribute to knowledge by examining single parenting from experiences of men – male single parents in patriarchal context of Africa thereby nuancing essentialist explanations of single parenting that have reified traditional patriarchy as mainstreaming single parenting into existences of a particular gender. This empirical article explores male single parenting through 30 in-depth interviews triangulated with autoethnography leveraging over 10 years of the authors’ primary insights, contextual lived experiences and observation. Issues examined include: worldviews about male single parents, consequences of male single parenting, companionship deficits occasioned by male single parenting, support systems and perceived benefits of male single parenting in context. Findings show many male single parents do not get formal supports, like from government agencies and non-governmental organizations, but they get informal supports from their kinship and social networks like families, friends and neighbours. Sense of maleness – sense of wanting to show being a strong man – do not make many male single parents seek supports from people as they do not want to be seen as weak if they seek supports. While some single fathers enjoy emotional supports from networks, they suffer serious financial pressures and insufficiency as they are not able to get financial assistance from anyone or organization. This is very important against the background of poor economic system in which male single parents live.