Dense Clusters Research Articles

“Tidal Peeling Events”: Low-eccentricity Tidal Disruption of a Star by a Stellar-mass Black Hole

Close encounters between stellar-mass black holes (BHs) and stars occur frequently in dense star clusters and in the disks of active galactic nuclei. Recent studies have shown that in highly eccentric close encounters, the star can be tidally disrupted by the BH in a microtidal disruption event (microTDE), resulting in rapid mass accretion and possibly bright electromagnetic signatures. Here we consider a scenario in which the star might approach the stellar-mass BH in a gradual, nearly circular inspiral, under the influence of dynamical friction in a circum-binary gas disk or three-body interactions in a star cluster. We perform hydrodynamics simulations of this scenario using the smoothed particle hydrodynamics code PHANTOM. We find that under certain circumstances (for initial eccentricity e 0 ≳ 0.4 and penetration factor β = 1, or e 0 < 0.4 and β ≲ 0.67), the mass of the star is slowly stripped away by the BH. We call this gradual tidal disruption a “tidal-peeling event.” Additionally, we discover that some low-eccentricity microTDEs (e 0 < 0.4 and β = 1) are a new form of fast luminous transients similar to parabolic microTDEs. Depending on the initial distance and eccentricity of the encounter, these low-eccentricity microTDEs might exhibit significant accretion rates and orbital evolution distinct from those of a typical (eccentric) microTDE.

Detection algorithm for dense small objects in high altitude image

The high altitude images captured by drones often contain small-sized objects, which pose several challenges including significant scale variations and dense clustering. To tackle these challenges in small object detection, this paper presents EM-YOLO (Efficient Switching Network and Multi-Scale Feature Fusion Reinforced YOLO for Small Object Detection), an enhanced algorithm based on the YOLOv5s architecture. Firstly, to enhance the network's adaptability to varying object feature scales, the EM-YOLO redesigns the feature extraction backbone network by using different dilation rates in convolutions within the backbone. This flexible structure allows for improved extraction of object features, enhancing the network's feature extraction capability. Secondly, additional detection layer for small objects and combines it with the dynamic detection head. This combination addresses the issue of small object information loss due to multiple down-sampling operations on the feature maps. Finally, Focal-EIoU Loss is employed to enhance regression accuracy in EM-YOLO. Extensive experiments were conducted on the VisDrone2019-DET dataset. The results of these experiments demonstrate that the improved algorithm achieved a significant increase in performance. Specifically, the algorithm achieves 43.5% and 25.1% on the mAP0.5 and mAP0.5:0.95 metrics, which are 13.9% and 8.9% higher than YOLOv5s algorithm, respectively. Furthermore, comparative experiments with other mainstream algorithms indicate that EM-YOLO outperforms them in the task of small object detection.

The dragon-II simulations – III. Compact binary mergers in clusters with up to 1 million stars: mass, spin, eccentricity, merger rate, and pair instability supernovae rate

ABSTRACT Compact binary mergers forming in star clusters may exhibit distinctive features that can be used to identify them among observed gravitational-wave sources. Such features likely depend on the host cluster structure and the physics of massive star evolution. Here, we dissect the population of compact binary mergers in the dragon-II simulation data base, a suite of 19 direct N-body models representing dense star clusters with up to 106 stars and $\lt 33~{{\ \rm per\ cent}}$ of stars in primordial binaries. We find a substantial population of black hole binary (BBH) mergers, some of them involving an intermediate-mass BH (IMBH), and a handful mergers involving a stellar BH and either a neutron star (NS) or a white dwarf (WD). Primordial binary mergers, $\sim 30~{{\ \rm per\ cent}}$ of the whole population, dominate ejected mergers. Dynamical mergers, instead, dominate the population of in-cluster mergers and are systematically heavier than primordial ones. Around 20 per cent of dragon-II mergers are eccentric in the Laser Interferometer Space Antenna (LISA) band and 5 per cent in the LIGO band. We infer a mean cosmic merger rate of $\mathcal {R}\sim 30(4.4)(1.2)$ yr−1 Gpc−3 for BBHs, NS–BH, and WD–BH binary mergers, respectively, and discuss the prospects for multimessenger detection of WD–BH binaries with LISA. We model the rate of pair-instability supernovae (PISNe) in star clusters and find that surveys with a limiting magnitude mbol = 25 can detect ∼1–15 yr−1 PISNe. Comparing these estimates with future observations could help to pin down the impact of massive star evolution on the mass spectrum of compact stellar objects in star clusters.

Dense Cold Quark–Gluon Matter Clusters and Their Study at the NICA Collider

In this paper, the production of particles outside the region of nucleon–nucleon kinematics due to interactions involving dense cold clusters of quark-gluon matter in nuclei is calculated. The possibility of observing this process in the region of central rapidities and large transverse momenta in heavy ion collisions at low energies with MPD detector at the NICA collider is demonstrated.

To the biology of Ligularia sibirica in the South Ural Reserve

The article presents the results of studying the life and reproductive characteristics of plants of the relict for Europe Eurasian polymorphic species Ligularia sibirica (L.) Cass. in three coenopopulations in the conditions of the South Ural Nature Reserve. The plant is little studied in the Ural region, medicinal and very effective, therefore in many ways promising for study in introduction purposes. In natural coenopopulations it grows in fairly moist areas, occurs sparsely in meadows, and in dense clusters under the forest canopy. In forest cenoses, Ligularia sibirica plants are tall and look much larger than in meadow cenoses. In different ecotopes, the variability of morphometric characters is not the same and is specific to a particular habitat. The characteristics of the generative sphere vary to a greater extent relative to the vegetative one. Analysis of variance revealed the dependence of the height of the generative shoot on the plant habitat (56.8%), as well as the length and width of the stem leaves on the ecotope conditions (51.3-69.2%). The age structure of the CP has a right-sided single-vertex type of spectrum with a predominance of young generative plants and a low proportion of mature ones. The superiority of generative plants in the spectra is due to the seed renewal of this species. Ligularia sibirica is distinguished by high reproductive rates with a fairly high coefficient of seed productivity (91%). However, the germination rate of its seeds is quite low, since the seeds are characterized by shallow organic dormancy, from which the seeds can be removed by short stratification or by storing the seeds in dry conditions. In the Southern Urals, this species requires further study.

Deep Learning-Based Microscopic Cell Detection using Inverse Distance Transform and Auxiliary Counting.

Microscopic cell detection is a challenging task due to significant inter-cell occlusions in dense clusters and diverse cell morphologies. This paper introduces a novel framework designed to enhance automated cell detection. The proposed approach integrates a deep learning model that produces an inverse distance transform-based detection map from the given image, accompanied by a secondary network designed to regress a cell density map from the same input. The inverse distance transform-based map effectively highlights each cell instance in the densely populated areas, while the density map accurately estimates the total cell count in the image. Then, a custom counting-aided cell center extraction strategy leverages the cell count obtained by integrating over the density map to refine the detection process, significantly reducing false responses and thereby boosting overall accuracy. The proposed framework demonstrated superior performance with F-scores of 96.93%, 91.21%, and 92.00% on the VGG, MBM, and ADI datasets, respectively, surpassing existing state-of-the-art methods. It also achieved the lowest distance error, further validating the effectiveness of the proposed approach. These results demonstrate significant potential for automated cell analysis in biomedical applications.

Searching for stellar population in the molecular cloud GRSMC 045.49+00.04

Abstract Understanding the characteristics of young stellar populations is essential for deriving insights into star formation processes within parent molecular clouds and the influence of massive stars on these processes. This study primarily aims to investigate the young stellar objects (YSOs) within the molecular cloud G 045.49+00.04, including three ultra-compact HII (UC HII) regions: G 45.48+0.13 (IRAS 19117+1107), G 45.45+0.06 (IRAS 19120+1103), and G 45.47+0.05. We used near-, mid-, and far-infrared photometric data along with radiation transfer models and the modified blackbody fitting to identify and study the YSOs and the interstellar medium (ISM). In total, we identified 1482 YSOs in a 12 arcmin radius covering GRSMC 045.49+00.04, with a mass range from 1.5 M ${}_{\odot}$ to 22 M ${}_{\odot}$ . Of these, 315 objects form relatively dense clusters in the UC HII regions, close to the IRAS 19120+1103 and 19117+1107 sources. In each UC HII region, several high-mass stars have been identified, which in all likelihood are responsible for the ionization. The YSOs with 21.8 M ${}_{\odot}$ and 13.7 ± 0.4 M ${}_{\odot}$ are associated with IRAS 19120+1103 and 19117+1107, respectively. The non-cluster YSOs (1168) are uniformly distributed on the field. The distribution of YSOs from both samples on the colour-magnitude diagram and by the evolutionary ages is different. About 75% of objects in the IRAS clusters are concentrated around the Zero Age Main Sequence and have a well-defined peak at an age of Log(Age[years]) $\approx$ 6.75, with a narrow spread. The non-cluster objects have two concentrations located to the right and left of the 0.1 Myr isochrone and two well-defined peaks at Log(Age) $\approx$ 6.25 and 5.25. The fraction of the near-infrared excess stars, as well as the mass function confirm that the evolutionary age of the cluster is about 1 Myr. The K luminosity functions’ α slopes for the IRAS clusters and non-cluster objects are 0.32 ± 0.04 and 0.72 ± 0.13, respectively. The steeper α slope is suggesting that the non-cluster objects are less evolved, which is well consistent with the evolutionary age. Similar results – including evolutionary age, narrow age spread, and the less evolved nature of non-cluster objects – were also observed for the YSOs in the neighbouring G 45.14+00.14. The both regions (G 045.49+00.04 and G 45.14+00.14) are located and distinguished by their brightness and density at the edge of the bubble around the highly variable X-ray binary GRS 1915+105, which includes a black hole and a K-giant companion. Based on the above, we can assume that the process of star formation in the young IRAS clusters was triggered by the GRS 1915+105-initiated shock front inside the ISM massive condensation, through the process of ‘collecting and collapse’. Most non-cluster objects probably belong to a later generation. Their formation could be triggered by the recurrent activity of GRS 1915+105 and/or through the edge collapse scenario and mass accumulation through the gas flows along the ISM filaments.

Single Millisecond Pulsars from Dynamical Interaction Processes in Dense Star Clusters

Globular clusters (GCs) are particularly efficient at forming millisecond pulsars. Among these pulsars, about half lack a companion star, a significantly higher fraction than in the Galactic field. This fraction increases further in some of the densest GCs, especially those that have undergone core collapse, suggesting that dynamical interaction processes play a key role. For the first time, we create N-body models that reproduce the ratio of single-to-binary pulsars in Milky Way–like GCs. We focus especially on NGC 6752, a typical core-collapsed cluster with many observed millisecond pulsars. Previous studies suggested that an increased rate of neutron star binary disruption in the densest clusters could explain the overabundance of single pulsars in these systems. Here, we demonstrate that binary disruption is ineffective and instead we propose that two additional dynamical processes play dominant roles: (1) tidal disruption of main-sequence stars by neutron stars and (2) gravitational collapse of heavy white dwarf binary merger remnants. Neutron stars formed through these processes may also be associated with fast radio bursts similar to those observed recently in an extragalactic GC.

Advancements in Remote Sensing Image Dehazing: Introducing URA-Net with Multi-Scale Dense Feature Fusion Clusters and Gated Jump Connection

Advancements in Remote Sensing Image Dehazing: Introducing URA-Net with Multi-Scale Dense Feature Fusion Clusters and Gated Jump Connection

Capillary imbibition of confined monodisperse emulsions in microfluidic channels.

We study imbibition of a monodisperse emulsion into high-aspect ratio microfluidic channels with the height h comparable to the droplet diameter d. Two distinct regimes are identified in the imbibition dynamics. In a strongly confined system (the confinement ratio d/h = 1.2 in our experiments), the droplets are flattened between the channel walls and move more slowly compared to the average suspension velocity. As a result, a droplet-free region forms behind the meniscus (separated from the suspension region by a sharp concentration front) and the suspension exhibits strong droplet-density and velocity fluctuations. In a weaker confinement, d/h = 0.65, approximately spherical droplets move faster than the average suspension flow, causing development of a dynamically unstable high-concentration region near the meniscus. This instability results in the formation of dense droplet clusters, which migrate downstream relative to the average suspension flow, thus affecting the entire suspension dynamics. We explain the observed phenomena using linear transport equations for the particle-phase and suspension fluxes driven by the local pressure gradient. We also use a dipolar particle interaction model to numerically simulate the imbibition dynamics. The observed large velocity fluctuations in strongly confined systems are elucidated in terms of migration of self-assembled particle chains with highly anisotropic mobility.

Role of interaction range on the microstructure and dynamics of attractive colloidal systems.

Colloidal gelation phase diagram has been traditionally characterized using three key factors: particle volume fraction, strength of attraction, and range of attraction. While there's a rich body of literature on the role of attraction strength and particle volume fraction, majority of studies have been limited to short range interactions. Using Brownian dynamics simulations, we explored the effect that the range of attractions has on the microstructure and dynamics of both weakly and strongly attractive colloidal systems. Although gelation occurs significantly faster at high attraction strength, by an order of magnitude compared to low strength, we did not observe any clear trend in gelation-rate with respect to a change in the range of interaction. However, as the attraction range increases in both systems, the final structure undergoes a transition from a single connected network to a fluid of dense clusters. This results in a new gelation phase boundary for long range attractive colloids.

Mining method of students’ learning behavior characteristics in online classroom of Colleges and Universities based on dense clustering method

Mining method of students’ learning behavior characteristics in online classroom of Colleges and Universities based on dense clustering method

Mining method of students' learning behaviour characteristics in online classroom of colleges and universities based on dense clustering method

Mining method of students' learning behaviour characteristics in online classroom of colleges and universities based on dense clustering method

Percolation transitions in a binary mixture of active Brownian particles with different softness.

Homogeneous active Brownian particle (ABP) systems with purely repulsive interactions are considered to exhibit a simple phase behavior, but various physical attributes of active entities can lead to variation in the collective dynamics. Recent studies have shown that even homogeneous ABPs exhibit complex behavior due to an interplay between particle softness and motility. However, the heterogeneity in the composition of ABPs has not been explored yet. In this paper, we study the structural properties of a binary mixture of ABPs with different particle softness by varying the relative softness and composition. We found that upon varying the motility parameter, the system underwent a motility-induced phase separation (MIPS) followed by a percolation transition similar to the homogeneous systems. However, we observed a novel feature: the formation of a space-filling structure made of particles with higher stiffness, within the dense cluster of MIPS containing both types of particles. Our systematic analysis shows that this structure formation occurs only if the difference in softness of both types of particles is sufficiently large. Furthermore, the presence of a non-linear scaling for different compositions of binary ABPs suggests that there is a complex relationship between the composition and the structural properties. Our study demonstrates that the composition heterogeneity of ABPs can lead to complex phase behavior.

Phase behaviour and dynamics of three-dimensional active dumbbell systems.

We present a comprehensive numerical study of the phase behavior and dynamics of a three-dimensional active dumbbell system with attractive interactions. We demonstrate that attraction is essential for the system to exhibit nontrivial phases. We construct a detailed phase diagram by exploring the effects of the system's activity, density, and attraction strength. We identify several distinct phases, including a disordered, a gel, and a completely phase-separated phase. Additionally, we discover a novel dynamical phase, that we name percolating network, which is characterized by the presence of a spanning network of connected dumbbells. In the phase-separated phase we characterize numerically and describe analytically the helical motion of the dense cluster.

Hydraulic Effect of Vegetation Zones in Open Channels: An Experimental Study of the Distribution of Turbulence

The development of vegetation in riverbeds is an important part of river engineering, and an in-depth understanding of its hydraulic influence is greatly needed. Our research focuses primarily on common reed (Phragmites australis) in riverbeds. To date, little is known about the hydraulic impact of the Phragmites australis reed and both field and laboratory data are still very scarce. Consequently, the main goal of our study was to evaluate the effect of vegetation zones on the spatial distribution of turbulence. Based on laboratory measurements of local instantaneous velocities, the values of the turbulence intensity (degree) Tu were determined, and its spatial distribution was illustrated. Analysis of the results showed that the relatively dense clusters of plants (reeds) act as “openwork deflectors” of the current and very clearly shape its spatial distribution. This can also be observed in the case of the distribution of the turbulence parameter Tu. For example, in the case of the development of riparian vegetation in the form of quasi-triangular communities of common reed (Phragmites australis) located alternately, there is a channelization of the flow, but also spatial changes in its character that occur. This work only presents results for preliminary hydraulic tests for Phragmites reed. These experiments should also be continued for other species of flexible riparian vegetation such as wicker. In the laboratory, the hydraulic influence of only triangle-shaped vegetation zones has been studied. Therefore, there is also a need for further hydraulic studies on vegetation zones of shapes other than triangular, e.g., rectangular, as well as vegetation zones with irregular shapes The authors see the need for such research and have already planned its continuation. Research on the interactions between vegetation and the structure of water flow in the riverbed is a very important aspect of contemporary trends in river environment management. Conscious, planned, and model-tested locating (or removing) of vegetation in a stream allows for shaping hydraulic and morphological conditions, thus controlling the processes of erosion, transport, and accumulation of debris.

MOLECULAR GENETIC CHARACTERIZATION OF UKRAINIAN REPRESENTATIVES OF THE COMPLEX SPECIES ACONITUM ANTHORA BASED ON THE ITS1-5.8S- ITS2 REGION OF THE NUCLEAR GENOME

Problem. The question of determining the boundaries of a species, in addition to the fundamental aspects, is of practical importance for nature conservation activities. One of the taxonomically problematic groups is the complex species A. anthora s. l. In the flora of Ukraine, four taxa with controversial status are distinguished within its borders, A. anthora L., A. eulophum Rchb., A. jacquinii Rchb. and A. pseudanthora Błocki ex Pacz. The last two species are included in the Red Book of Ukraine and the IUCN list. Determining the taxonomic position of these closely related forms requires the use of molecular genetic approaches. The ITS1-5.8S-ITS2 region of 35S rDNA is considered the most popular and informative marker for plant taxonomy and barcoding. Aim. To clarify the taxonomic status and phylogenetic relationships of representatives of A. anthora s. l. using the molecular marker ITS1-5.8S-ITS2 of 35S rDNA. Methods. Herbarium specimens of four representatives of the group A. anthora s. l. were collected on the territory of Western Ukraine. DNA was isolated by a modified CTAB method and then used for PCR amplification of the ITS1-5.8S-ITS2 region. PCR products were purified and Sanger sequenced. The sequences obtained were aligned with the sequences deposited in the GenBank database for representatives of two subgenera of the genus Aconitum, i.e. the nominative subgenus and the subgenus Lycoctonum. The resulting matrix was used for principal component analysis (PCA) and phylogenetic analysis using the Maximum Likelihood method. Main results. The sequences of ITS1-5.8S-ITS2 that we obtained for A. anthora, A. eulophum, A. jacquinii, and A. pseudanthora samples were found to be almost identical. They differed from each other in only five of the 641 alignment positions. Among them, four out of five positions appeared to be polymorphic even within individual genomes. According to the results of PCA analysis, all four samples of A. anthora s. l. formed a dense cluster separated by significant distances from the clusters formed by representatives of the subgenera Aconitum and Lycoctonum. In the generated phylogenetic tree, three main monophyletic clades are present, which correspond to the subgenera Aconitum and Lycoctonum and the A. anthora s. l. group. The Lycoctonum clade was sister to other members of the genus, and the Aconitum and A. anthora s. l. clades were sister to each other. Conclusions. The use of the ITS1-5.8S-ITS2 region of 35S rDNA for phylogenetic analysis confirms the need to grant the A. anthora s. l. group the status of a separate subgenus within the genus Aconitum. The high genetic affinity between samples of A. anthora s. l. from the territory of Ukraine indicates that the species names A. eulophum, A. jacquinii, and A. pseudanthora should be considered synonyms of A. anthora.

Arp2/3 complex and the pentose phosphate pathway regulate late phases of neutrophil swarming

Neutrophil swarming is an essential process of the neutrophil response to many pathological conditions. Resultant neutrophil accumulations are hallmarks of acute tissue inflammation and infection, but little is known about their dynamic regulation. Technical limitations to spatiotemporally resolve individual cells in dense neutrophil clusters and manipulate these clusters in situ have hampered recent progress. We here adapted an invitro swarming-on-a-chip platform for the use with confocal laser-scanning microscopy to unravel the complexity of single-cell responses during neutrophil crowding. Confocal sectioning allowed the live visualization of subcellular components, including mitochondria, cell membranes, cortical actin, and phagocytic cups, inside neutrophil clusters. Based on this experimental setup, we identify that chemical inhibition of the Arp2/3 complex causes cell death in crowding neutrophils. By visualizing spatiotemporal patterns of reactive oxygen species (ROS) production in developing neutrophil swarms, we further demonstrate a regulatory role of the metabolic pentose phosphate pathway for ROS production and neutrophil cluster growth.

Two-step nucleation and crystal growth in a metastable solution

This study is concerned with a theory of two-step nucleation and growth of crystals in a metastable liquid. This mechanism is that crystalline nuclei formation occurs in dense liquid clusters suspended in the solution. These clusters contain higher solution concentration and viscosity, leading to a lower surface free energy barrier and faster phase transition route. The theory is based on growth laws of crystals during the two-step bulk phase transformation. At the initial stage, the crystals evolve in a diffusion-limited environment with almost unchanged supersaturation. At the second stage, they become larger, move beyond these clusters, and evolve in accordance with a hyperbolic tangent law. A generalized particle growth law joining the first and second stages is obtained by stitching the diffusion limited and hyperbolic tangent laws. On this basis, an integrodifferential model of the evolution of a polydisperse ensemble of crystals was formulated and solved. The crystal-size distribution function increases and the solution supersaturation remains practically unchanged until the particle size corresponds to a transition in the particle growth rate from a diffusion-limited branch to a hyperbolic tangent branch. This is followed by an increase in the crystal growth rate, a decrease in the distribution function and solution supersaturation. Then the distribution function increases up to the maximum size of crystals grown in the solution. A sufficiently long time interval of almost constant supersaturation and the N-shaped behavior of the distribution function are the consequences of a two-step nucleation and growth mechanisms.

The function of ER-phagy receptors is regulated through phosphorylation-dependent ubiquitination pathways

Selective autophagy of the endoplasmic reticulum (ER), known as ER-phagy, is an important regulator of ER remodeling and essential to maintain cellular homeostasis during environmental changes. We recently showed that members of the FAM134 family play a critical role during stress-induced ER-phagy. However, the mechanisms on how they are activated remain largely unknown. In this study, we analyze phosphorylation of FAM134 as a trigger of FAM134-driven ER-phagy upon mTOR (mechanistic target of rapamycin) inhibition. An unbiased screen of kinase inhibitors reveals CK2 to be essential for FAM134B- and FAM134C-driven ER-phagy after mTOR inhibition. Furthermore, we provide evidence that ER-phagy receptors are regulated by ubiquitination events and that treatment with E1 inhibitor suppresses Torin1-induced ER-phagy flux. Using super-resolution microscopy, we show that CK2 activity is essential for the formation of high-density FAM134B and FAM134C clusters. In addition, dense clustering of FAM134B and FAM134C requires phosphorylation-dependent ubiquitination of FAM134B and FAM134C. Treatment with the CK2 inhibitor SGC-CK2-1 or mutation of FAM134B and FAM134C phosphosites prevents ubiquitination of FAM134 proteins, formation of high-density clusters, as well as Torin1-induced ER-phagy flux. Therefore, we propose that CK2-dependent phosphorylation of ER-phagy receptors precedes ubiquitin-dependent activation of ER-phagy flux.