Mechanism Of Cluster Formation Research Articles

Uncovering the crystallography and formation mechanism of nanoscale clusters in Sb-rich SPPs of a p-type (Bi, Sb)2Te3 alloy.

Considering that the crystallographic characteristics of the Sb-rich secondary phase particles (SPPs) greatly affect the thermoelectric properties of Bi2Te3 based materials, it is of great significance to explore the mechanism behind the Sb-rich SPPs in the p-type (Bi, Sb)2Te3 material. Here a conventional TEM technique was used to characterize the composition, size and distribution of Sb-rich SPPs in a spark plasma sintered p-type (Bi, Sb)2Te3 alloy. The results indicated that two different morphologies of Sb-rich SPPs including elongated and circular Sb-rich SPPs were frequently observed. Combined with high-resolution transmission electron microscopy, this work provides atomic-scale evidence for the formation mechanism behind the Sb-rich SPPs in the (Bi, Sb)2Te3 material.

The longevity of the oldest open clusters. Structural parameters of NGC188, NGC2420, NGC2425, NGC2682, NGC6791,and NGC6819

The dynamical evolution of open clusters is driven by stellar evolution, internal dynamics, and external forces, which according to dynamical simulations will lead to their evaporation over a timescale of about 1\,Ga. However, about 10<!PCT!> of the known open clusters are older. These latter are special systems whose detailed properties are related to their dynamical evolution and the balance between mechanisms of cluster formation and dissolution. We investigated the spatial distribution and structural parameters of six open clusters older than 1\,Ga in order to constrain their dynamical evolution and longevity. We identified members using EDR3 data up to a distance of 150\,pc from the centre of each cluster. We investigated the spatial distribution of stars inside each cluster to understand their degree of mass segregation. Finally, in order to interpret the obtained radial density profiles, we reproduced them using the lowered isothermal model explorer with and the spherical potential escapers stitched ( models. All the studied clusters appear to be more extended than previously reported in the literature. The spatial distributions of three of them show some structures aligned with their orbits. These structures may be related to the existence of extra tidal stars. Moreover, we find that about 20<!PCT!> of their members have sufficient energy to leave the systems or are already unbound. Together with their initial masses, their distances to the Galactic plane may play significant roles in their survival. We find clear evidence that the most dynamically evolved clusters do not fill their Roche volumes, appearing more concentrated than the others. Finally, we find a cusp--core dichotomy in the central regions of the studied clusters, which shows some similarities to that observed among globular clusters.

Spatial Distribution Analysis of Urban Retail Industry Using POI Big Data

With the development of social economy, it is very important to identify urban functional areas and understand the spatial distribution characteristics of urban functional areas for urban scientific planning and government decision-making. Reasonable spatial distribution of urban retail industry is of great significance to promote urban economic development, optimize urban structure, and meet the consumption needs of urban residents. Based on the data of retail industry's POI, GDP, population and transportation in Nanning, China, this paper analyzes the spatial distribution characteristics and formation mechanism of different retail industry clusters in the city, and studies the spatial correlation between retail industry and population, economy, transportation, etc., using the methods of kernel density method, spatial correlation analysis, Getis-Ord G * index statistics, and average nearest neighbor distance. The results show that:(1)On the whole, the retail industry is concentrated in the central urban area of Nanning, spreading from the middle to the surrounding areas. (2)The retail hot spots have formed a multi-center development and surrounding spread pattern in spatial distribution. (3) The spatial distribution of the retail industry is highly related to the main traffic lines. At the same time, the concentration and distribution of the retail industry have a strong spatial correlation with the economy and population.

Clustering characteristics of Fe-rich intermetallics in high vacuum die cast AlSiMgMn alloys with high resolution μ-CT inspection

The AlSiMgMn alloys with different Fe and Mn contents were prepared with high vacuum die casting (HVDC) process. The Fe-rich intermetallics in the surface layer and center of the alloys were inspected with high-resolution 3D X-ray micro-computed tomography (μ-CT), and the growth mechanism of the primary Fe-rich phase was analyzed through their different 3D morphographies. By combining Bisecting K-means and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) methods, the intermetallic clusters in the surface layer and center were quantified. The results show that the primary Fe-rich intermetallics were characterized as hexahedron and octagonal dendrite shapes with large size while the eutectic Fe-rich intermetallics were polyhedron and Chinese-script shapes. When Fe and Mn contents of the alloys were lower, the intermetallic clusters in the surface layer were with less cluster number and larger intermetallic distances showing uniform distribution whereas the clusters in the center were more and had shorter distances. In the case of alloys with higher Fe and Mn contents, the intermetallics showed clustering distribution in both the surface layer and center. The mechanism for the intermetallic cluster formation in the surface layer and center was further discussed.

HIO3-HIO2-Driven Three-Component Nucleation: Screening Model and Cluster Formation Mechanism.

Iodine oxoacids (HIO3 and HIO2)-driven nucleation has been suggested to efficiently contribute to new particle formation (NPF) in marine atmospheres. Abundant atmospheric nucleation precursors may further enhance HIO3-HIO2-driven nucleation through various multicomponent nucleation mechanisms. However, the specific enhancing potential (EP) of different precursors remains largely unknown. Herein, the EP-based screening model of precursors and enhancing mechanism of the precursor with the highest EP on HIO3-HIO2 nucleation were investigated. The formation free energies (ΔG), as critical parameters for evaluating EP, were calculated for the dimers of 63 selected precursors with HIO2. Based on the ΔG values, (1) a quantitative structure-activity relationship model was developed for evaluating ΔG of other precursors and (2) atmospheric concentrations of 63 (precursor)1(HIO2)1 dimer clusters were assessed to identify the precursors with the highest EP for HIO3-HIO2-driven nucleation by combining with earlier results for the nucleation with HIO3 as the partner. Methanesulfonic acid (MSA) was found to be one of the precursors with the highest EP. Finally, we found that MSA can effectively enhance HIO3-HIO2 nucleation at atmospheric conditions by studying larger MSA-HIO3-HIO2 clusters. These results augment our current understanding of HIO3-HIO2 and MSA-driven nucleation and may suggest a larger impact of HIO2 in atmospheric aerosol nucleation.

The Supersonic Project: Star Formation in Early Star Clusters without Dark Matter

The formation mechanism of globular clusters (GCs) has long been debated by astronomers. It was recently proposed that supersonically induced gas objects (SIGOs)–which formed in the early Universe due to the supersonic relative motion of baryons and dark matter at recombination–could be the progenitors of early GCs. In order to become GCs, SIGOs must form stars relatively efficiently despite forming outside of dark matter halos. We investigate the potential for star formation in SIGOs using cosmological hydrodynamic simulations, including the aforementioned relative motions of baryons and dark matter, molecular hydrogen cooling in primordial gas clouds, and explicit star formation. We find that SIGOs do form stars and that the nascent star clusters formed through this process are accreted by dark matter halos on short timescales (∼a few hundred megayears). Thus, SIGOs may be found as intact substructures within these halos, analogous to many present-day GCs. From this result, we conclude that SIGOs are capable of forming star clusters with similar properties to globular clusters in the early Universe, and we discuss their detectability by upcoming JWST surveys.

The effect of water molecules and air humidity on the cluster formation from benzoic acid with sulfuric acid/ammonia/dimethylamine: A molecular-scale investigation

In the atmosphere, benzoic acid (BA) is one of the most abundant aromatic acids and contributes to new particle formation (NPF). Sulfuric acid (SA), ammonia (NH3), and dimethylamine (DMA) have been identified as critical nucleation precursors. Since water (H2O) is abundant in the atmosphere, the hydration effect is a significant concern. However, the hydration effect on the precise mechanisms of cluster formation remains unclear. In this study, theoretical calculation method was used to investigate the interactions between BA and NH3/DMA/SA in the presence of up to six water molecules at the PW91PW91/6-311++G(3df,3pd) using geometrical analysis, topological analysis, and the Gibbs free energies analysis. Hydrated distributions of clusters under different relative humidity (RH) levels and their atmospheric implications were also estimated. This study shows water molecules have mild impacts on the interaction between BA and NH3/DMA, but have relatively strong effect on the interaction between BA and SA. Hydrated distributions for the three types of clusters show that they are insensitive to different RH levels, and a completely unhydrated (BA)(NH3) cluster dominates the hydrated distributions. When the concentrations of BA are particularly high, especially in heavily polluted areas, the concentrations of (BA)(SA) can reach the same order of magnitude or higher than those of (SA)2. Thus, the importance of BA in prompting NPF has been revealed to a certain extent.

Polyhedral Colloidal Clusters Assembled from Amphiphilic Nanoparticles in Deformable Droplets.

Polyhedral colloidal clusters assembled from functional inorganic nanoparticles have attracted great interest in both scientific research and applications. However, the spontaneous assembly of colloidal nanoparticles into polyhedral clusters with regular shape and tunable structures remains a grand challenges. Here, we successfully construct Mackay icosahedral and regular tetrahedral colloidal clusters assembled from gold nanoparticles grafted with a mixture of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) homopolymers by precisely tuning the interfacial interaction between the nanoparticles and the oil/water interface. By increasing the proportion of hydrophilic P2VP ligands on the surface of gold nanoparticles, the Mackay icosahedral clusters can transform into regular tetrahedral clusters in order to maximize the surface area of the polyhedral assembly. Furthermore, we reveal the formation mechanism of these regular polyhedral colloidal clusters. The formation of polyhedral colloidal clusters is not only dependent on the entropy but also determined by the interfacial free energy. This finding demonstrates an effective approach to organize nanoparticles into polyhedral colloidal clusters with potential applications in various fields.

MD Simulations of Collision Cascades in α-Ti. Cluster Statistics and Governing Mechanisms of Point Defect Cluster Formation

MD Simulations of Collision Cascades in α-Ti. Cluster Statistics and Governing Mechanisms of Point Defect Cluster Formation

MD Simulations of Collision Cascades in α-Ti. Statistics and Governing Mechanisms of Point Defect Cluster Formation

The outcomes of molecular dynamics simulations of primary damage formation in collision cascades initiated by primary knock-on atoms (PKA) with PKA energy 5 keV ≤Epka≤ 25 keV in α-titanium at 100 K ≤T≤ 900 K temperatures have been analysed. The fraction of vacancies, εv, and self-interstitial atoms (SIA), εi, in point defect clusters created in isolated collision cascades was evaluated. The corresponding averages ⟨εv⟩ and ⟨εi⟩ over cascade series with the same (Epka, T) parameters, the average size ⟨Nvac⟩ and ⟨Nsia⟩ of vacancy and SIA clusters, respectively, and the average vacancy ⟨Yvac ⟩ and SIA ⟨Ysia ⟩ cluster-per-cascade yield were found as well. Possible governing mechanisms have been suggested to explain ⟨εv⟩, ⟨εi⟩ , ⟨Nvac⟩, ⟨Nsia⟩, ⟨Yvac⟩ and ⟨Ysia⟩ dependence on (Epka,T).

Silicon tracker for cluster-knockout reactions at intermediate energies

The cluster-knockout reaction project, ONOKORO, has been launched to elucidate the formation mechanism of clusters in atomic nuclei. For the inverse-kinetics cluster-knockout reaction experiments, a new detector array is under development to measure energies and angles of light ions emitted in the reactions. The silicon tracker tracks the particles with good angular and energy-loss resolutions. A performance test of the silicon strip detectors with a thickness of 100μm and a strip width of 100μm was performed using prototype silicon detectors. The mono-energetic proton and α-particle beams were irradiated on the silicon detectors. The energy-loss spectra in silicon detectors showed a good signal-to-noise ratio. The threshold level for signal detection is seven sigma of noise level. Their dynamic ranges were optimized wide enough to detect charge number Z= 1 and Z= 2 ions emitted in the cluster-knockout reactions.

Designing TOGAXSI: Telescope for inverse-kinematics cluster-knockout reactions

We have launched a new research project named “ONOKORO” to elucidate the formation mechanism of clusters in atomic nuclei. The project comprehensively investigates clustering phenomena in the medium-to-heavy mass region with inverse-kinematics cluster-knockout reactions at the intermediate energy facilities. The new detector array named “TOGAXSI” is under construction for this purpose. It measures scattering angles and the energies of deuterons, tritons, 3He, and α particles emitted at forward angles from the cluster-knockout reactions. It also measures the recoil protons emitted from the scattering events at large angles. High-angular and high-energy resolutions with wide solid angles are required to achieve a good cluster separation energy resolution and a reasonably high yield. The designed telescope consists of silicon trackers and GAGG:Ce calorimeters. This paper shows the required conditions and design concepts of TOGAXSI.

Initialization of Nanowire or Cluster Growth Critically Controlled by the Effective V/III Ratio at the Early Nucleation Stage.

For self-catalyzed nanowires (NWs), reports on how the catalytic droplet initiates successful NW growth are still lacking, making it difficult to control the yield and often accompanying a high density of clusters. Here, we have performed a systematic study on this issue, which reveals that the effective V/III ratio at the initial growth stage is a critical factor that governs the NW growth yield. To initiate NW growth, the ratio should be high enough to allow the nucleation to extend to the entire contact area between the droplet and substrate, which can elevate the droplet off of the substrate, but it should not be too high in order to keep the droplet. This study also reveals that the cluster growth between NWs is also initiated from large droplets. This study provides a new angle from the growth condition to explain the cluster formation mechanism, which can guide high-yield NW growth.

Review of bismuth‐doped fibers used in O‐band optical amplifiers‐scientific challenges and outlook

AbstractBismuth‐doped phosphosilicate fibers have become the most promising gain medium for O‐band amplifiers. Yet scientific challenges on understanding the nature of bismuth active centers (BACs), mechanisms of bismuth cluster formation in the phosphosilicate glass network still exist. It is likely that multiple BACs with different oxidation states in different structural sites all contribute to the broad, nonsymmetric luminescence and gain spectra. Due to the progress in the fundamental understanding of bismuth‐doped phosphosilicate glass, various designs of optical amplifiers with decent performances have been demonstrated.

Effective mechanism for the region sustainable development based on a tourist cluster formation

The article is devoted to the analysis of key aspects of the region sustainable development based on the tourist cluster formation mechanism: the study of the infrastructure of the territory, the demand for tourist destinations in the region. The topic of the study is relevant, given the geopolitical tension and unstable situation in the international arena, the consequence of which was the introduction of restrictions on a number of foreign tourist destinations. The combination of foreign policy and economic factors gave a positive impetus for the development of domestic tourism. The object of the study is the tourism sector, as one of the key areas for increasing the region competitiveness and sustainability. The subject of the study is the mechanism for the formation of a tourist and recreational cluster on the example of the city. Zhigulevsk, Samara region. The purpose of the study is to analyze the key positions of the mechanism for forming a tourist cluster in the region. Research objectives: • study of the essence of the tourist and recreational cluster; • identification of key positions of the mechanism of effective formation of the tourist cluster; • study of the potential of the territory of the tourist and recreational cluster of the city of Zhigulevsk, Samara Region. Methodologists and research methods. The authors applied a systematic approach to the study of the mechanism of forming a tourist cluster in the region: analyzed the engineering infrastructure, transport infrastructure, as well as cultural and historical objects on the example of the tourist cluster of the city of Zhigulevsk, Samara region. The analysis of demand for services of the tourism sector of the Samara region was carried out using an online survey of consumers of this type of services, the results of which are presented using a graphical method. Degree of scientific development of the topic. The study of the process of forming a tourist and recreational cluster in the region is widely covered in scientific literature, affecting such areas of knowledge as sociology, economics, culture, history, ecology. The authors of the article analyze, on the one hand, the desires and opportunities of consumers of tourist services, on the other hand, the possibilities of a tourist and recreational cluster to meet the needs of tourists. The key to the effective formation of a tourist and recreational cluster is a comprehensive analysis of the tourist and recreational territory.

Morphological transformation of perfluorinated sulfonic acid ionomer via ionic complex formation at a high entropy state

Proton exchange membranes (PEMs) act as conductors in PEM fuel cells (PEMFCs) to transport protons from the anode to the cathode in the membrane electrode assembly (MEA). Because protons are transported via the hydrophilic channels of the PEMs, the morphological control of these channels has been considered a key issue that influences their electrochemical performance. In this study, we propose a simple route that provides fast proton transport pathways via the morphological transformation of hydrophilic channels in a commercially available perfluorinated sulfonic acid (PFSA) ionomer, Nafion®. It is based on the formation of ionic complexes when metallic salts are added during the membrane fabrication process, instead of using PFSA ionomers with tuned chemical structures. The effectiveness of this strategy is theoretically verified by performing molecular simulations for the ionic cluster formation mechanism. The formation of the ionic complexes in a high entropy state is found to be advantageous in decreasing the distance between ionic clusters, improving proton transport efficiency resulting in higher proton conductivity and single cell performance without any additional chemical and processing step causing the production cost increase.

Temperature-dependent synergistic evolution mechanism of rhenium and irradiation defects in tungsten-rhenium alloys

We have systemically investigated the synergistic evolution of rhenium (Re) and irradiation defects in tungsten (W)-Re alloys under different temperatures and irradiation doses using object Kinetic Monte Carlo method. Our results revealed the underlying mechanism for the transition of Re effect on W from beneficial to harmful during the Re-defects evolution with the increase of irradiation dose, in which temperature always plays a critical role. On the one hand, Re will significantly promote the defect annihilation at low irradiation doses and high temperatures, thereby effectively reducing their sizes and number densities. This is due to the formation of stable Re-SIAs complexes that can be eliminated by the mobile vacancy-type defects, whereas the transition of the migration pattern of SIAs only plays a weak role in the defect recombination in W-Re system. On the other hand, with the increase of irradiation dose, Re will aggregate to form Re-rich clusters or even precipitates. Interestingly, the formation mechanism of Re-rich clusters is also dependent on temperature. At low temperatures, the interstitial-mediated mechanism plays a crucial role in the Re-rich cluster formation, while at high temperatures, both SIA-type and vacancy-type defects will act as the transport carriers of Re to promote their clustering. Accordingly, the critical conditions for the transition of Re from beneficial to harmful and the formation of Re-rich clusters at different temperatures and irradiation doses are given with the help of the phase diagram. Our work presents the temperature dependence of the synergy of Re and irradiation defects in W-Re in fusion-relevant environment, which provides a good reference for the development of radiation-resistant materials and the prediction of W performance in fusion reactors.

Fast hardening response of martensitic stainless steel by copper-rich cluster formation under pulsed electric current

The pursuit of excellent comprehensive mechanical properties using a rapid aging process is of practical significance in the field of aging strengthening. A pulsed electric current assisted aging process can effectively accelerate aging and reduce the energy consumption caused by long-term thermal aging. The mechanism of a Cu-rich cluster formation promoted by a pulsed electric current was investigated to better understand the fast-hardening response process. The size and structure of the Cu-rich cluster were characterized using transmission electron microscopy (TEM); the results indicated that the pulsed electric current did not change the mechanism of aging strengthening but accelerated the process. The time required to achieve peak aging decreased owing to the athermal effect (interaction between atoms and electrons) induced by the pulsed electric current. The athermal effect decreased as the temperature increased, and a relationship between the athermal effect and temperature was obtained. When a current density of 7 × 107 A/m2 was applied, the precipitation activation energy of the Cu-rich clusters decreased by 91 kJ mol−1; this was owing to the following two aspects. (1) The pulsed electric current lowered the vacancy formation energy and resulted in an increase in vacancy concentration and (2) the current density gradient caused by the difference in conductivity between the matrix and Cu-rich clusters accelerated the substitution of the Cu atoms and vacancies and reduced the atomic migration energy. These results provide insights into the effect of a pulsed electric current on the kinetics of precipitation in the martensitic stainless steel and a deduction for the mechanism of the rapid growth of Cu-rich clusters.

Mechanism of Magic Number NaCl Cluster Formation from Electrosprayed Water Nanodroplets.

Events taking place during electrospray ionization (ESI) can trigger the self-assembly of various nanoclusters. These products are often dominated by magic number clusters (MNCs) that have highly symmetrical structures. The literature rationalizes the dominance of MNCs by noting their high stability. However, this argument is not necessarily adequate because thermodynamics cannot predict the outcome of kinetically controlled reactions. Thus, the mechanisms responsible for MNC dominance remain poorly understood. Molecular dynamics (MD) simulations can provide atomistic insights into self-assembly reactions, but even this approach has thus far failed to provide pertinent answers. The current work overcomes this limitation. We focused on salt clusters formed from aqueous NaCl solutions during ESI. The corresponding mass spectra are dominated by the Na14Cl13+ MNC. Simulations of ESI droplets showed nonspecific association of Na+ and Cl-, culminating in gaseous clusters via solvent evaporation to dryness (charged residue mechanism). These nascent clusters did not show any preference for MNCs. In mass spectrometry experiments, analyte ions undergo in-source activation prior to detection. We emulated in-source activation by heating nascent clusters in our MD runs. Heating triggered structural fluctuations and dissociation events, generating MNC-dominated product distributions. Why are MNCs preferred after in-source activation? Thermally excited clusters frequently adopt structures consisting of a preformed MNC and a stringlike protrusion that contains the surplus ions. Facile separation of these protrusions releases the MNC (Clusterhot → MNC-protrusion → MNC + protrusion). This work marks the first time that MD simulations were able to capture cluster self-assembly with subsequent "molecular pruning", generating MNC-dominated product distributions that agree with experiments.

ЗАКОНОМЕРНОСТИ ПЕРЕХОДНОГО РЕЖИМА В ДИССИПАТИВНОЙ КЛЕТОЧНОЙ МОДЕЛИ ЗЕМЛЕТРЯСЕНИЙ

The purpose of this work was to analyze the mechanisms of the growth of drop clusters,leading on a finite-size lattice to a state close to a critical one with a power-law size distribution ofclusters similar to that observed in a seismic process. At the same time, the question of applicabilityof this model to the description of processes in a real geophysical medium remains. Analysis ofthe elements coupling in the one-dimensional OFC model with open boundary conditions allowsan estimation of the variability of the incoming energy to the lattice elements located at differentdistances from the boundaries. The constructed computational model makes it possible toestimate the size of the boundary areas of high average incoming energy variability at differentvalues of the coupling parameter α. It is shown that, as α grows, the boundary region of inhomogeneityexpands. It is shown that there are two different modes of synchronous drop fo rmation,simulating an earthquake. Both mechanisms are determined by the capture of a neighboringelement and the subsequent synchronization of the drops. This process forms a stabledrop of a larger size. The presence of boundary regions with a high gradient of the input energyrate is the main mechanism for the formation of clusters of lattice elements, demonstrating thesimultaneous drop of the accumulated energy. Such a synchronization is achieved due to thehigh mutual variability of energy at each iteration step. The second important mechanism ofcluster growth is typical for the formed clusters that exceed the size of the near-boundary regionof high inhomogeneity of the energy inflow. As the cluster size grows, the capture area ofneighboring elements that are not included in the cluster expands. Accordingly, the probabi litythat the energy of the neighboring element is in the capture area increases. The calculationsshow that the mean time of reaching the given size of the cluster on the lattice at different sp atialdimensions d and at different coupling parameters confirms the presence of two time intervalswith a different mechanism of cluster formation. In this case, the growth of large clusters hasa power-law character, with an exponent determined by the dimension d.