Cluster Formation Process Research Articles

VizOPTICS: Getting insights into OPTICS via interactive visual analysis

Ordering points to identify the clustering structure (OPTICS) is a density-based clustering algorithm that allows the exploration of the cluster structure in the dataset by outputting an ordered queue called cluster ordering. However, this nonexplicit output makes it greatly more difficult for practitioners to identify cluster patterns and obtain high-quality clusters. In this paper, we firstly investigate OPTICS in depth and identify the challenges facing users of OPTICS for cluster analysis through a pilot user study. Then, integrating human intelligence deeply with the machine intelligence of OPTICS, a visual analytics approach, VizOPTICS, is proposed to support practitioners in understanding and applying OPTICS to extract meaningful clustering results. It includes an ordered lattice plot for observing the generation process of cluster ordering, a density scatter plot for analyzing the cluster structure in datasets, and a dynamic reachability plot for optimizing clustering results, and also provides several interaction modes, such as selecting and highlighting, to help users analyze the cluster formation and algorithm operation processes interactively. Finally, we assess our approach through four case studies and a user evaluation study. The results demonstrate the effectiveness and efficiency of the system.

Early-forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly

Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suite Torch, combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer, N-body dynamics, and stellar feedback, to model four initially identical 104 M ⊙ giant molecular clouds with a Gaussian density profile peaking at 521.5 cm−3. Using the Torch software suite through the AMUSE framework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100 M ⊙). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildup of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster.

Soft X-ray XAFS Analysis of Cluster Formation Process during 353 K Aging in Al–Mg–Si Alloys

Soft X-ray XAFS Analysis of Cluster Formation Process during 353 K Aging in Al–Mg–Si Alloys

Globular cluster metallicity distributions in the E-MOSAICS simulations

ABSTRACT The metallicity distributions of globular cluster (GC) systems in galaxies are a critical test of any GC formation scenario. In this work, we investigate the predicted GC metallicity distributions of galaxies in the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) simulation of a representative cosmological volume (L = 34.4 comoving Mpc). We find that the predicted GC metallicity distributions and median metallicities from the fiducial E-MOSAICS GC formation model agree well the observed distributions, except for galaxies with masses $M_\ast \sim 2 \times 10^{10} \, \rm {M}_{\odot }$, which contain an overabundance of metal-rich GCs. The predicted fraction of galaxies with bimodal GC metallicity distributions (37 ± 2 per cent in total; 45 ± 7 per cent for $M_\ast \gt 10^{10.5} \, \rm {M}_{\odot }$) is in good agreement with observed fractions ($44^{+10}_{-9}$ per cent), as are the mean metallicities of the metal-poor and metal-rich peaks. We show that, for massive galaxies ($M_\ast \gt 10^{10} \, \rm {M}_{\odot }$), bimodal GC distributions primarily occur as a result of cluster disruption from initially-unimodal distributions, rather than as a result of cluster formation processes. Based on the distribution of field stars with GC-like abundances in the Milky Way, we suggest that the bimodal GC metallicity distribution of Milky Way GCs also occurred as a result of cluster disruption, rather than formation processes. We conclude that separate formation processes are not required to explain metal-poor and metal-rich GCs, and that GCs can be considered as the surviving analogues of young massive star clusters that are readily observed to form in the local Universe today.

Environmental tourism potential of the Arctic regions of Russia

Tourism is an important field for international cooperation. The Arctic zone has a potential for the tourism activities development, the question remains on what policy principles should forming this industry be carried out. The goal of the work is to determine the advantages of the Arctic territories as a network cluster that takes into account modern security requirements and creates conditions for the development of territories based on tourist attractions. The work considers the best practices in the field of tourism clusters development in the world, Russian legislation aimed at activating the process of cluster formation in the field of tourism, key factors that determine the unique characteristics of the tourism sector of the Arctic. The main methods used were analytical generalization, comparative analysis, retrospective analysis of the legislative framework in the tourism sector of Russia. As a result, stating certain successes in the field of tourism development in the Arctic, the authors note the need for the development of the environment to attract the local population to forming cultural code of territory and note the key areas of digitalization that could contribute to improving the processes of tourist cluster formation in the Arctic territories.

Cache controlled cluster networking protocol

When technologies such as Wireless Sensor Network, Internet of Things and Cloud Computing are coupled together, real-world issues can be remarkably resolved. Wireless Sensor Network sends enormous data to a cloud server via the internet. Some applications necessitate a huge number of sensors spread across a large area. Limited battery-powered sensors send lots of data to the Base Station. To save energy and extend sensor lifespan, sensors can be networked instead of talking directly with the Base Station. Our present research work proposes an innovative Cache-Controlled Cluster Networking Protocol (CCCNP). It is a cache-supervised dynamic cluster-based sensor networking technique. In CCCNP, as the complete network is under cache control, the number of caches established in the network and their location play a very crucial role. Therefore, we first formulate the equation for the appropriate number of caches and their location. Then the caches create a network cluster and support data transmission. It stabilizes cluster formation process and decreases sensor node overhead to increase network lifetime. We simulate the CCCNP, Low Energy Adaptive Clustering Hierarchy (LEACH), Improved LEACH (I-LEACH), and LEACH with Vice-cluster Head (LEACH-VH) algorithms for two different types of networks and compare them. CCCNP outperforms other algorithms both the configurations. The dead node rate decreased by three times for each round. Even the lifespan of nodes far from the BS improved by 3.51 and 2.87 times for both network configurations, respectively. The average throughput increased by 350%, and the average lifespan increased up to 289% of the rounds.

On the formation of an external cluster flow in a supersonic jet

In this work, the influence of the cluster formation process on the gas dynamics of a supersonic flow is studied by the method of electron-beam visualization. Corrections to the model for describing the transverse dimensions of supersonic flows under conditions of developed condensation are presented. Possible causes and conditions for the formation of a secondary cocurrent flow are analyzed. The influence of background gas penetration into the clastered flow has been studied. The conditions for the occurrence of an anomalous afterglow of a clastered flow upon initiation by an electron discharge are studied.

Reversible adhesion by type IV pili leads to formation of permanent localized clusters.

The formation of long-lived, multicellular clusters is a fundamental step in the physiopathology of many disease-causing bacteria. Experiments on abiotic surfaces suggest that bacterial colonization, including initial cluster formation, requires (1) irreversible adhesion, (2) cell proliferation, and (3) a phenotypic transition. However, here we show that on infection of a polarized MDCK epithelium, Pseudomonas aeruginosa (PA) forms long-lived- i.e., permanent- bacterial clusters without requiring irreversible adhesion, cell proliferation, or a phenotypic transition. By combining experiments and a mathematical model, we reveal that the cluster formation process is mediated by type IV pili (T4P). Furthermore, we unveil how T4P quantitatively operate during adhesion, finding that it is a stochastic process that involves an activation time, requires the retraction of pili, and results in reversible attachment. We explain how such reversible attachment process leads to the formation of permanent bacterial clusters and quantify the cluster growth dynamics.

Foreign experience if the formation and development of tourist clusters

Today, world practice shows that the formation of tourist clusters is one of the most effective ways not only to develop the territory for tourism purposes, but also to create unique conditions for the sustainable development of regional tourism in the long term. However, the process of cluster formation is quite complicated and necessitates the definition of clear mechanisms for integrating activities between tourism enterprises and state, educational, scientific and other public organizations involved in the cluster structure. Therefore, each country that implements the tourism clustering policy has developed its own experience in this area and creates a cluster based on the specifics of the relations formed between the local business community and the state. In this regard, the main purpose of writing this article is to review the foreign practice of clustering the tourism sector and identify the specific features of the various existing models of tourism clusters. From the scientific and practical point of view, the significance of the presented work is determined by identification of the distinctive properties of tourist clusters that contribute to a considerable increase in the attractiveness of the area for vacationers. As part of the study of the formation and development of tourist clusters in Europe, the USA and Asia, methods of comparative analysis, analogy and theoretical generalization were used.The value of study is that the results of study can be used as an information base in the course of determining the priorities for the development of tourism clusters in domestic practice.

Ejection velocities, age, and formation process of SPE meteoroid cluster

Context. Meteoroid clusters represent a unique opportunity to study processes of meteoroid disruptions in interplanetary space. We follow our previous work about the September epsilon Perseid (SPE) meteoroid cluster from 2016 with a detailed analysis of the observed data and cluster formation conditions. Aims. Our goal is to determine ejection velocities of the cluster members and SPE’s age, as well as to estimate the most probable formation process. Methods. We precisely determined mutual positions and masses of all meteoroids including the errors. We assumed that the massdominated meteoroid is the parent body of the cluster and that the observed positions of meteoroids are controlled by the ejection velocities and the action of solar radiation pressure. A formula for the dependence of meteoroid ejection velocities on the mutual positions, masses, and cluster age was derived. It was assumed that the time at which the initial kinetic energy of all meteoroids reached a minimum value corresponds to the age of the cluster. Knowing values and directions of ejection velocities together with meteoroid masses then allowed us to determine the most likely process of cluster formation. Results. The meteoroids occupy a volume of 66 × 67 × 50 km and are shifted in the antisolar direction by 27 km relative to the parent meteoroid. The age of the cluster is 2.28 ± 0.44 days. The ejection velocities range from 0.13 ± 0.05 m s−1 to 0.77 ± 0.34 m s−1 with a mean value of 0.35 m s−1. The ejection velocity directions are inside the cone with an apex angle of 101 ± 5°. The axis of the cone is ~45° away from the solar direction and ~34° away from the mean direction of the flux of small meteoroids’ incident on the parent meteoroid. Formation due to the separation of part of the surface due to very fast rotation is the least likely thing to occur. We estimate the rotation frequency to be about 2 Hz and the corresponding stress is several orders of magnitude lower than the predicted strength limit. It is also difficult to explain the formation of the cluster by an impact of a small meteoroid on the parent body. However, this possibility, although not very likely, cannot be completely ruled out. The most probable process is the exfoliation due to thermal stresses. Their estimated magnitude is sufficient and the derived ejection velocities are consistent with this process of formation.

Analysis of the concept of "cluster" and its characteristic features

The paper analyzes the concept of "cluster" in foreign and domestic literature, as well as in regulatory legal acts of the Russian Federation. Foreign and domestic sources on cluster topics are analyzed, aspects of the processes of cluster formation and development are highlighted, on the basis of which the analyzed concepts were proposed. In conclusion, the author provides the author's definition of "cluster".

A potential new phase of massive star formation

Context. Due to the sparsity and rapid evolution of high-mass stars, a detailed picture of the evolutionary sequence of massive protostellar objects still remains to be drawn. Some of the early phases of their formation are so short that only a select number of objects throughout the Milky Way currently find themselves spending time in those phases. Aims. Star-forming regions going through the shortest stages of massive star formation present different observational characteristics than most regions. By studying the dust continuum and line emission of such unusual clouds, one might be able to set strong constraints on the evolution of massive protostellar objects. Methods. We present a detailed analysis of the G345.88-1.10 hub filament system, which is a newly discovered star-forming cloud that hosts an unusually bright bipolar infrared nebulosity at its centre. We used archival continuum observations from Berschel, WISE, Spitzer, 2MASS, and SUMSS in order to fully characterise the morphology and spectral energy distribution of the region. We further made use of APEX 12CO(2–1), 13CO(2–1), C18O(2–1), and H30α observations to investigate the presence of outflows and map the kinematics of the cloud. Finally, we performed RADMC-3D radiative transfer calculations to constrain the physical origin of the central nebulosity. Results. At a distance of 2.26-0.21+0.30 kpc, G345.88-1.10 exhibits a network of parsec-long converging filaments. At the junction of these filaments lie four infrared-quiet fragments. The fragment H1 is the densest one (with M = 210 M⊙, Reff = 0.14 pc) and sits right at the centre of a wide (opening angle of ~90 ± 15°) bipolar nebulosity where the column density reaches local minima. The 12CO(2–1) observations of the region show that these infrared-bright cavities are spatially associated with a powerful molecular outflow that is centred on the H1 fragment. Negligible radio continuum and no H30α emission is detected towards the cavities, seemingly excluding the idea that ionising radiation drives the evolution of the cavities. Radiative transfer calculations of an embedded source surrounded by a disc and/or a dense core are unable to reproduce the observed combination of a low-luminosity (≲500 L⊙) central source and a surrounding high-luminosity (~4000 L⊙) mid-infrared-bright bipolar cavity. This suggests that radiative heating from a central protostar cannot be responsible for the illumination of the outflow cavities. Conclusions. This is, to our knowledge, the first reported object of this type. The rarity of objects such as G345.88-1.10 is likely related to a very short phase in the massive star and/or cluster formation process that has been unidentified thus far. We discuss whether mechanical energy deposition by one episode or successive episodes of powerful mass accretion in a collapsing hub might explain the observations. While promising in some aspects, a fully coherent scenario that explains the presence of a luminous bipolar cavity centred on an infrared-dark fragment remains elusive at this point.

Stakeholder contribution to tourism collaboration: Exploring stakeholder typologies, networks and actions in the cluster formation process

Business clustering as a collaboration strategy has proven successful in many regional destinations but research is still nascent in this domain. While recent research has offered insights into the cluster formation process, research is still yet to understand stakeholder typologies, networks and stakeholder actions and how they contribute to cluster formation. The present research utilised a Participatory Action Research (PAR) approach in regional Queensland, Australia, to understand stakeholder interactions and actions between participants from local tourism businesses, local council, the local, regional and state tourism organisations. Findings reveal how different stakeholder typologies and stakeholder networks contribute to cluster formation. This study offers advancement of stakeholder theory through describing stakeholder typologies, presenting the Stakeholder Collaboration Continuum and unpacking stakeholder relationships and their contribution to cluster formation.

Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation

ABSTRACT We investigate whether spatial-kinematic substructure in young star-forming regions can be quantified using Moran’s I statistic. Its presence in young star clusters would provide an indication that the system formed from initially substructured conditions, as expected by the hierarchical model of star cluster formation, even if the cluster were spatially smooth and centrally concentrated. Its absence, on the other hand, would be evidence that star clusters form monolithically. The Moran’s I statistic is applied to N-body simulations of star clusters with different primordial spatial-velocity structures, and its evolution over time is studied. It is found that this statistic can be used to reliably quantify spatial-kinematic substructure, and can be used to provide evidence as to whether the spatial-kinematic structure of regions with ages ≲6 Myr is best reproduced by the hierarchical or monolithic models of star formation. Moran’s I statistic is also able to conclusively say whether the data are not consistent with initial conditions that lack kinematic substructure, such as the monolithic model, in regions with ages up to, and potentially beyond, 10 Myrs. This can therefore provide a kinematic signature of the star cluster formation process that is observable for many Myr after any initial spatial structure has been erased.

Theoretical study of the formation of large, astronomically relevant PAH-organic molecule clusters

Context. Polycyclic aromatic hydrocarbon (PAH) molecules play an essential role in the prebiotic compound evolution network in the interstellar medium (ISM). A recent experimental study revealed that large, astronomically relevant PAH-organic molecule clusters are gradually formed through the ion-molecule collision reaction pathway in the presence of a strong radiation field. Aims. We present a theoretical survey for the formation processes of PAH-organic molecule clusters (e.g., such as the graphene carbon cluster (C48) organic molecule (Pyroglutaminol, pgn, C5H9NO2) cluster cations, (pgn)nC48+, n = [1,6]), to illustrate the building block mechanism for the formation of large prebiotic compounds. Methods. To investigate the stability and the building block formation mechanisms of PAH-organic molecule clusters in the ion-molecule collision reaction process, we carried out theoretical calculations with DFT, including the hybrid density functional B3LYP, as implemented in the Gaussian 16 program. The basis set of the 6-311++G** and 6-31+G** was selected and used for different cluster systems. Results. We investigated the structure of newly formed species and the energy for these reaction pathways. The ion-molecule reaction between ((C5H9NO2)nC48+, n = [0,5]) with C5H9NO2 readily occur, resulting in a very large number of reaction pathways and very complex newly formed molecular clusters. An expanded tree (in building block pathways) shows the trunk and branches of these various formation pathways. These clusters (e.g., the graphene carbon cluster and its organic molecules) provide a possible formation and chemical-evolution route for the large complex prebiotic compounds in bottom-up and energy allowed processes in the ISM. Conclusions. The gas-phase reactions between large PAH species and organic molecules occur relatively easily, resulting in a very large number of reaction pathways and very complex newly formed molecular clusters. These PAH-organic molecule clusters will lead to large organic molecules, which may contain some of the critical molecular configurations that can characterize living material.

Understanding Metal–Organic Framework Nucleation from a Solution with Evolving Graphs

A mechanistic understanding of metal-organic framework (MOF) synthesis and scale-up remains underexplored due to the complex nature of the interactions of their building blocks. In this work, we investigate the collective assembly of building units at the early stages of MOF nucleation, using MIL-101(Cr) as a prototypical example. Using large-scale molecular dynamics simulations, we observe that the choice of solvent (water and N,N-dimethylformamide), the introduction of ions (Na+ and F-) and the relative populations of MIL-101(Cr) half-secondary building unit (half-SBU) isomers have a strong influence on the cluster formation process. Additionally, the shape, size, nucleation and growth rates, crystallinity, and short and long-range order largely vary depending on the synthesis conditions. We evaluate these properties as they naturally emerge when interpreting the self-assembly of MOF nuclei as the time evolution of an undirected graph. Solution-induced conformational complexity and ionic concentration have a dramatic effect on the morphology of clusters emerging during assembly. While pure solvents lead to the rapid formation of a small number of large clusters, the presence of ions in aqueous solutions results in smaller clusters and slower nucleation. This diversity is captured by the key features of the graph representation. Principle component analysis on graph properties reveals that only a small number of molecular descriptors is needed to deconvolute MOF self-assembly. Descriptors such as the average coordination number between half-SBUs and fractal dimension are of particulalr interest as they can be can be followed experimentally by techniques like by time-resolved spectroscopy. Ultimately, graph theory emerges as an approach that can be used to understand complex processes revealing molecular descriptors accessible by both simulation and experiment.

Securing Cluster Formation and Cluster Head Elections in Wireless Sensor Networks

In wireless sensor networks, clustering plays a very important role for energy savings at each node because it reduces the number of transmissions through TDMA based communication. For secure clustering, it is very crucial to find compromised nodes and remove them during the initial cluster formation process. If some nodes are compromised and survive from the exclusion process of normal nodes, they can make some nodes have a different membership view in the same cluster and consequently separate a cluster into multiple clusters. To resolve these problems, we propose a robust scheme against such attacks in this paper. First, our scheme generates large sized clusters to improve the quality of clusters. Second, our scheme exploits the verification of two hop distant nodes to maintain the quality of the large sized clusters and avoids the separation of the clusters. In addition, our scheme prefers broadcast transmissions to reduce the energy consumption of nodes. We prove that our scheme generates fewer clusters and is more secure and energy-efficient than its rival scheme through security analysis and simulation results. With regard to CH election, we also propose a scheme which securely elects CHs by recognizing the compromised nodes and depriving them of their CH candidacy. To this aim, each node in a cluster calculates reputation values of other CH candidates according to their behavior and distributes them through a broadcast. Then each node extracts substantial reputation values of CH candidates using the distributed reputation values. Next, each node evaluates the substantial reputation values of other CH candidates and excludes some disreputable nodes from CH candidates. The scheme greatly improves non-manipulability and agreement property of CH election results in comparison with other rival schemes. Moreover, the scheme guarantees higher non-manipulability and agreement property than other rival schemes, even in a loss-prone environment.

Spin-Offs, Innovation Spillover and the Formation of Agricultural Clusters: The Case of the Vegetable Cluster in Shouguang City, Shandong Province, China

Agricultural clusters play a powerful role in promoting the agricultural transformation and rejuvenation of rural areas. However, no in-depth exploration has been made on how agricultural clusters form and evolve, especially in the context of China’s long-term small-scale rural economy. The purpose of this article is to reveal the formation process and evolution mechanism of agricultural clusters by case study research. With the knowledge flow as the starting point, this article takes the Vegetable Cluster in Shouguang City of Shandong Province, China as an example to construct a theoretical framework in the three dimensions of points (spin-offs of enterprises or farmers), lines (network-spillovers of various innovation) and planes (the formation of new regional industry spaces) and put forward theoretical hypotheses. It is shown that: (1) The local spin-off of seed farmers is the main path in the transformation of traditional farmers into enterprises. (2) The network-spillover and adoption of innovative knowledge promote the derivation of specialized farmers or enterprises and realize regional agricultural specialization and spatial agglomeration. (3) The formation of the agricultural cluster resulted from the joint effects of spin-off derived from the entrepreneurial spirit of the farmers, network-spillover of various agricultural innovations and spatial integration of the agricultural landscape. The formation of local agricultural innovation systems marks the maturity of an agricultural cluster. This article contribute to the field by studying one source of Alfred Marshall’s knowledge of external economy from the perspective of spin-offs and innovative spillovers, analyzing the agricultural increasing returns to scale neglected by Krugman, and exploring the micro mechanism of farmers’ enterprise-oriented evolution and the formation of agricultural clusters in underdeveloped rural areas. The research results are of profound referential significance for the cultivation of agricultural clusters in developing countries.

Capturing the Trajectory of Metal-Ion-Cluster Formation: Stepwise Accumulation of Zn(II) Ions in a Robust Coordination Space Formed by a Rigid Tridentate Carboxylate Ligand.

Organic ligand-directed synthesis of metal-ion clusters with a well-defined number and arrangement of metal ions is an important subject toward the development of functional inorganic-organic nanohybrids. Here we report the synthesis of multinuclear Zn-oxo clusters using a triptycene-based rigid ligand (H3L) featuring three metal-coordination sites arranged in a triangular shape. Upon complexation of H3L with zinc acetate dihydrate, a decanuclear Zn-oxo cluster and multinuclear Zn-oxo clusters with a smaller number of Zn(II) ions were formed as the final product and its intermediates, respectively. A comparison of the X-ray structure of the final product with those of the intermediates revealed the cluster-formation process, where four triptycene ligands preorganize to form a robust coordination space to which Zn(II) ions accumulate in a stepwise manner. This stepwise metal-ion accumulation, along with the formation of a large tetrahedral decanuclear Zn-oxo cluster, highlights the potential of ligand design using 1,8,13-substituted triptycenes for the development of various metal-ion clusters.

Chemical reaction zone measurements in pressed trinitrotoluene (TNT) and comparison with triaminotrinitrobenzene (TATB)

Photonic Doppler velocimetry and digital high-speed shadowgraphy have been used to characterize the chemical reaction zone parameters of pressed trinitrotoluene (TNT) samples with an initial density of 1.568 g cm−3. Comparison of the nanosecond time-resolved particle velocity histories of the free surfaces of detonating charges in air and light vacuum and of the interfaces between TNT detonation products and lithium fluoride or polymethyl methacrylate windows allow one to bracket the von Neumann spike pressure between 24.8 and 28.8 GPa. Our velocity waveforms confirm the two-step reaction pathway already observed in TNT, triaminotrinitrobenzene (TATB), and nitromethane, with a first fast energy release over 80 ns followed by a slower release over 250 additional ns. We consider the end of the first release zone as the locus of the Chapman–Jouguet (CJ) state, and the CJ pressure thus lies between 17.6 and 17.7 GPa. The energy release is not completed in this Jouguet plane but only after about ≈280 ns when the carbon cluster formation process ends. This corresponds to both the end of the slow release part of the interface velocity profiles and to the moment at which the free surface velocity profiles reach their maximum. Our shadowgraphy images confirm that carbon formation occurs very rapidly after the detonation breakout, in good agreement with previous time-resolved small-angle x-ray scattering measurements. The comparison with similar results previously obtained on TATB allows one to further highlight their similarities, which mainly result from their excess carbon production at late times.