Changes In Structure Of Clusters Research Articles

Key grids based batch-incremental CLIQUE clustering algorithm considering cluster structure changes

In the network environment, data from various industries is dynamic and large-scale. Traditional clustering algorithms struggle to effectively utilize existing clustering results when faced with continuously evolving data, which makes the incremental grid-based clustering highly regarded. However, the existing incremental grid-based clustering algorithms fail to adequately consider the impact of newly added data on the original cluster structure. To address this issue, the key grids based batch-incremental CLIQUE clustering algorithm is proposed. The algorithm designates the incremental data mapping grids, which are or their neighbour girds are mixed with original data, as key grids to fully consider the cluster structure changes caused by the incremental data. Moreover, the cluster similarity coefficient based on grid features is introduced to measure density differences between the incremental data and the original clusters, and the cluster membership degree is defined to further consider the cluster membership of boundary sparse grid data and the identification of noise points. All of which ensures that the algorithm can adaptively create, merge or split clusters with the arrival of new data. Experimental results show that the proposed algorithm can adaptively adjust the cluster structure during incremental clustering, outperforming in accuracy and efficiency when clustering large-scale, dynamically changing data.

Cluster Appoach to Analyzing Registered Unemployment in the Region

The topic of the research is acute due to the fact that for a couple of years labour market of each region and Russia as a whole has been suffering turbulence because of changes in economic situation. It always responds sharply to all changes taking place in the field of economy. The article provides results of differentiation of cities and city districts of the Orenburg region by registered unemployment rate in 2017 and 2020. The choice of time slots for the research is stipulated by changes in regional labour market connected with the pass-over to digitalization, as well as impact of crisis events in economy. Estimation of varying parameters allows us to see heterogeneity in cities and city districts of Orenburzhiya. As a result of cluster analysis groups of administrative territories of the Orenburg region were found that are characterized by high, average and low level of registered unemployment indicators. Slight changes in cluster structure were identified. Results of cluster-groups comparison can be used as a foundation for devising regional employment policy aiming at smoothing differences between cities and city districts in the Orenburg region by key indicators of this sphere of economy development.

Global and regional changes in carbon dioxide emissions: 1970–2019

We introduce new frameworks to study spatio-temporal patterns in carbon dioxide emissions, demographic trends and economic patterns across 50 countries over the past 50 years. Our analysis is broken up into four sections. First, we introduce a new method to classify countries into one of three characteristic emissions classes based on a one, two or three-segment piecewise linear model. We reveal that most countries are best represented by a piecewise linear model with one change point. Next, we perform a decade-by-decade study of carbon dioxide trajectories. There, we demonstrate notable changes in cluster structures in each decade. We then study the spatial propagation of emissions over time, highlighting a peak in spatial dispersion in 2000, beyond which there has been a gradual decline in spatial emissions variance over space. Finally, we use carbon dioxide, GDP, and population data and apply dimensionality reduction and clustering to group countries based on similarity in their real and carbon economies.

Kinetics of structural change of pineapple (Ananas comosus) under the influence of PME (Pectin methylesterase)

The structure of pineapple ((Ananas comosus) is hard and brittle, but it is easy to soften under the influence of high temperature during processing. Understanding the structure, arrangement and chemical reactivity of pectin in the cell wall is key to predicting and controlling changes in cluster structure. There are many different methods to affect the pectin composition to create an insoluble calcium pectate complex to keep the connection between cells, keep the structure for pineapple. The addition of the pectin methylesterase enzyme (PME) extracted from tomato to pineapple is one of the recent researched trends with the aim of improving the structural change of pineapple due to heat. Based on the recommendations made from previous studies on enzyme addition to pineapple, in this study, experiments were conducted on the influence of the order of addition of PME and CaCl2, the effect of temperature of PME addition, and the influence of PME activity on the structural change of pineapple.

Dynamic stability and management of supramolecular structures of water

The cluster structure of water is a recognized basis for studying the special properties of this liquid and, in particular, when interacting with biological systems.  An attempt has been made to identify patterns for the appearance of short-lived cluster supramolecular structures in the composition of water. They determine its effectiveness in relation to such biological systems. Their appearance is based on the patterns of bifurcation transition with a doubling of the number of bound molecules H2O. This is possible in a border area with chaos in intermolecular of bonds water. The use of I. Prigogine's principle of high-intensity fluctuations is proposed. They appear independently of changes in cluster structures in triatomic molecular associations based on the accumulation of internal energy to minimize dissipative processes. This is the basis for the organization of such stable structures with minimal change in the entropy of the entire system. Prigozhin's algorithm was applied to calculate the thermodynamic instability and behavior of triatomics as a control method. The index of the operator Liouville and the comparable criterion of stability of Lyapunov are involved. The processes of instantaneous reversibility and stability of short-lived clusters based on molecules were investigated, in full accordance with the existing provisions on the dynamic structure of water. The features of the action of high-frequency random oscillations are shown, which determine the periodicity of the creation of short-lived associations in the composition of water. It also shows the stability of such periodic processes in a limited period of time, as a basis for identifying repetitive states of the system. Energy interrelation in such systems is proposed to be considered as the basis to maintain their optimal state in the structure of water. This is also an indicator of its relationship to the perceiving biological systems

The Dynamic Structure of Au38(SR)24 Nanoclusters Supported on CeO2 upon Pretreatment and CO Oxidation.

Atomically precise thiolate protected Au nanoclusters Au38(SC2H4Ph)24 on CeO2 were used for in-situ (operando) extended X-ray absorption fine structure/diffuse reflectance infrared fourier transform spectroscopy and ex situ scanning transmission electron microscopy–high-angle annular dark-field imaging/X-ray photoelectron spectroscopy studies monitoring cluster structure changes induced by activation (ligand removal) and CO oxidation. Oxidative pretreatment at 150 °C “collapsed” the clusters’ ligand shell, oxidizing the hydrocarbon backbone, but the S remaining on Au acted as poison. Oxidation at 250 °C produced bare Au surfaces by removing S which migrated to the support (forming Au+-S), leading to highest activity. During reaction, structural changes occurred via CO-induced Au and O-induced S migration to the support. The results reveal the dynamics of nanocluster catalysts and the underlying cluster chemistry.

Bell-shaped “dendrite velocity-undercooling” relationship with an abrupt drop of solidification kinetics in glass forming Cu-Zr(-Ni) melts

Abstract We analyze the crystal growth kinetics of rapidly solidifying glass-forming Cu50Zr50 alloy melts. Formulating a dendrite growth model we predict all features of crystallization kinetics in Cu50Zr50 from thermodynamically controlled growth (governed by the change in Gibbs free energy on solidification) to the kinetically limited regime (governed by atomic attachment at the solid/liquid interface). Comparing critical undercoolings observed in the crystallization kinetics with experimental data on melt viscosity, atomistic simulation's data on liquid microstructure and theoretically predicted dendrite growth velocity allows us to conclude that the dendrite growth kinetics strongly depends on the cluster structure changes of the melt.

Cluster structure changes during melting of 1-decanol: FTIR study and DFT calculations

Temperature dependence of 1-decanol FTIR spectra is studied from both sides of melting point with a step of 0.5°C near the phase transition. Using ab initio quantum-chemistry calculations of different cluster structures, authors show, that solid phase of alcohol is formed by clusters consisting of 3 molecules and liquid phase — by clusters consisting of 5 molecules. Unlike small alcohols, 1-decanol is formed by chain-like clusters. Gradual changes of spectral bands in process of heating are interpreted as a feature of amorphous phase.

PbS Clusters Embedded in Sodalite Zeolite Cavities of Different Compositions: Unraveling the Structural Evolution and Optical Properties Using ab Initio Calculations

The structure and properties of the PbS quantum dots (QDs) encapsulated in the zeolite host, a system reported to exhibit extremely high nonlinear optical properties, were determined employing a combination of a robust structure prediction tool based on genetic algorithm approach and density functional calculations (DFT) including state-of-the-art two component time-dependent DFT implementation for hybrid exchange correlation functionals. Sizable changes in cluster structures and even isomer stability ordering are observed either with respect to the gas phase or as a result of the change of the sodalite zeolite composition (extra-framework cations and Si:Al ratio). The presence of very small clusters in the zeolite cavities such as monomers or dimers is predicted which are stabilized mostly via dispersion and to lesser extent electrostatic interaction with the host. The optical excitations of the PbS-zeolite composite are confined mostly to the QDs, i.e., the zeolite can be regarded as a confining dielect...

Distributed and Weighted Clustering based on d-Hop Dominating Set for Vehicular Networks

Clustering is one of the key technologies in vehicular networks. Constructing and maintaining stable clusters is a challenging task in high mobility environments. DWCM (Distributed and Weighted Clustering based on Mobility Metrics) is proposed in this paper based on the d-hop dominating set of the network. Each vehicle is assigned a priority that describes the cluster relationship. The cluster structure is determined according to the d-hop dominating set, where the vehicles in the d-hop dominating set act as the cluster head nodes. In addition, cluster maintenance handles the cluster structure changes caused by node mobility. The rationality of the proposed algorithm is proven. Simulation results in the NS-2 and VanetMobiSim integrated environment demonstrate the performance advantages.

Monitoring of changes in cluster structures in water under AC magnetic field

A fundamental possibility of visualizing cluster structures formed in distilled water by an optical method based on the analysis of dynamic speckle structures is demonstrated. It is shown for the first time that, in contrast to the existing concepts, water clusters can be rather large (up to 200 -m in size), and their lifetime is several tens of seconds. These clusters are found to have an internal spatially inhomogeneous structure, constantly changing in time. The properties of magnetized and non-magnetized water are found to differ significantly. In particular, the number of clusters formed in magnetized water is several times larger than that formed in the same volume of non-magnetized water.

Structure of Self-Assembled Free Methanol/Tetrachloromethane Clusters

The structure of molecular clusters of diameters at or below a nanometer is important both in nucleation phenomena and potentially for the preparation and application of nanoparticles. Little is known about the relationship between the structure and composition of the cluster and about the interplay between cluster composition, size, and temperature. The present project explores how the structure of mixed CH3OH/CCl4 clusters vary with composition and size; implicitly by changing the amount of noncondensing backing gas and thus the capacity to remove heat during cluster condensation, and explicitly through theoretical models. Experimentally, molecular clusters were produced by coexpansion of helium and a vapor of azeotropic methanol/tetrachloromethane composition in a supersonic nozzle flow. The clusters were subsequently characterized by means of carbon 1s photoelectron spectroscopy. Additional information was obtained by molecular-dynamics simulations of clusters at 3 different sizes, 4 different compositions and several temperatures, and using polarizable force fields. Mixed clusters were indeed obtained in the coexpansion experiments. The clusters show an increasing degree of surface coverage by methanol as the backing pressure is lowered, and at the lowest helium pressure the cluster signal from tetrachloromethane has almost vanished. The MD simulations show a gradual change in cluster structure with increasing methanol contents, from that of isolated rings of methanol at the surface of a tetrachloromethane core, to a contiguous methanol cap covering more than half of the cluster surface, to that of subclusters of tetrachloromethane submerged in a methanol environment. Both experimental and computational results support a thermodynamical driving force for methanol to dominate the surface structure of the mixed clusters. At high helium pressure, the growing clusters may cool efficiently, possibly impeding the diffusion of methanol to the surface. At low helium pressure, methanol is completely dominating the outermost few layers of the clusters, possibly in parts caused by preferential loss of tetrachloromethane through evaporative cooling.

Size-dependent structural characteristics and phonon thermal transport in silicon nanoclusters

We investigate the size effects on the structures and thermal conductivity of silicon nanoclusters (SiNCs) using molecular dynamics simulations. We demonstrate that as the diameter of the SiNCs increases from 1.80 nm to 3.46 nm, the cluster structure changes from an amorphous state to a crystalline state at 300 K, which is in good agreement with the experimental findings. Our calculated thermal conductivity of the SiNCs shows a size-dependent effect due to the remarkable phonon-boundary scattering and can be about three orders of magnitude lower than that of bulk Si.

Clustering of the Self-Organizing Time Map

This paper extends the use of recently introduced Self-Organizing Time Map (SOTM) by pairing it with classical cluster analysis. The SOTM is an adaptation of the Self-Organizing Map for visualizing dynamics in cluster structures. While enabling visual dynamic clustering of temporal and cross-sectional patterns, the stand-alone SOTM lacks means for objectively representing temporal changes in cluster structures. This paper combines the SOTM with clustering and illustrates the usefulness of second-level clustering for representing changes in cluster structures in an easily interpretable format. This provides means for identification of changing, emerging and disappearing clusters over time. Experiments are performed on two toy datasets and two real-world datasets. The first real-world application explores evolution dynamics of European banks before and during the global financial crisis. Not surprisingly, the results indicate a build-up of risks and vulnerabilities throughout the European banking sector prior to the start of the crisis. The second application identifies the cyclicality of currency crises through changes in the most vulnerable clusters.

Influence of the block hydrophilicity of AB2 miktoarm star copolymers on cluster formation in solutions

We investigated the formation of various micelle shapes of lipid-like amphiphilic AB(2) miktoarm star copolymers in a solution, by performing dissipative particle dynamics simulations. AB(2) miktoarm star copolymer molecules are modeled with coarse-grained structures that consist of a relatively hydrophilic head (A) group with a single arm and a hydrophobic tail (B) group with double arms. A decrease in the hydrophilicity of the head group leads to a reduction of the polymer-solvent contact area, causing cluster structure changes from spherical micelles to vesicles. Consequently, a spherical exterior with multi-lamellar or cylindrical phase interior structures forms under poor solvent conditions without the introduction of spherical hard-wall containers. Furthermore we observed that, for small head group lengths, vesicles were formed in much wider range of solvent-head interaction strength than for long head groups, indicating that molecules with short head group offer a superior vesicle forming property. A phase diagram, the structure and kinetics of the cluster formation, a density profile, and a detailed shape analysis are presented to discuss the molecular characteristics of potential candidates for drug carriers that require superior and versatile vesicle forming properties. We also show that, under certain solvent-hydrophilic head group interaction conditions, initially formed cylindrical micelles transform to bilayer fragments through redistribution of copolymers within the cluster.

Energy Efficient and Stable Weight Based Clustering for Mobile Ad Hoc Networks

Recently several weighted clustering algorithms have been proposed, however, to the best of our knowledge; there is none that propagates weights to other nodes without weight message for leader election, normalizes node parameters and considers neighboring node parameters to calculate node weights. In this paper, we propose an Energy Efficient and Stable Weight Based Clustering (EE-SWBC) algorithm that elects cluster heads without sending any additional weight message. It propagates node parameters to its neighbors through neighbor discovery message (HELLO Message) and stores these parameters in neighborhood list. Each node normalizes parameters and efficiently calculates its own weight and the weights of neighboring nodes from that neighborhood table using Grey Decision Method (GDM). GDM finds the ideal solution (best node parameters in neighborhood list) and calculates node weights in comparison to the ideal solution. The node(s) with maximum weight (parameters closer to the ideal solution) are elected as cluster heads. In result, EE-SWBC fairly selects potential nodes with parameters closer to ideal solution with less overhead. Different performance metrics of EE-SWBC and Distributed Weighted Clustering Algorithm (DWCA) are compared through simulations. The simulation results show that EE-SWBC maintains fewer average numbers of stable clusters with minimum overhead, less energy consumption and fewer changes in cluster structure within network compared to DWCA.

The Fate of Star Clusters near the Galactic Center. I. Analytic Considerations

A star cluster in a galactic nucleus sinks toward the galactic center because of dynamical friction. As it spirals inward, the cluster loses mass through stellar evolution, relaxation driven evaporation, and tidal stripping, eventually dissolving in the galactic tidal field. We model the in-spiral of dense young star clusters near the center of our Galaxy to study the extent of the region of parameter space in which the cluster can reach the inner parsec of the Galaxy within a few million years. Since we neglect changes in cluster structure due to internal evolution, the present study is most applicable to star clusters less than about one initial relaxation time old. We find that only star clusters with initial masses 105 M☉ can reach the Galactic center from an initial distance of 60 pc within one initial relaxation time or a few million years, whichever is smaller.

Spatial structure of the globular cluster M15

The spatial structure of the metal-poor globular cluster M15 is studied as a function of magnitude interval ΔB and the limiting B magnitude of star counts. Astrometric and photometric measurements of two plates obtained with the 2-m reflector of the National Academy of Sciences of Bulgaria were used. Analysis of the differential and integrated apparent (ΔF(r) and F(r)) and spatial (Δf(r) and f(r)) stellar density distributions in different ΔB intervals and to different limiting magnitudes reaching B=21.5m indicates that the cluster structure changes systematically as we consider fainter stars, beginning with the transition region between the subgiant branch and the main-sequence turnoff in the (V, B-V) diagram. This variation is manifest in two ways: a homological growth in the radii of spatial zones of the cluster and of the cluster radius in accordance with a single law, and variations in the stellar density, with the rate of increase in the number of faint stars growing toward the outer zones of the cluster. Empirical relations describing these variations and parameters determining the cluster structure are obtained.

The structure of Ni46, Ni47, and Ni48

The geometrical structures of Ni46, Ni47, and Ni48 are investigated by the chemical probe method using molecular nitrogen as the probe molecule. Nitrogen saturation levels are determined and found to be consistent with cluster structures derived from two geometries, one having face-centered-cubic (fcc) packing and the other fcc/hcp (hexagonal-close-packed) layered packing. The fcc-based structures provide the best overall agreement with the experimental measurements. The saturation levels are inconsistent with icosahedral or decahedral packing, a structure found for Ni49 and larger clusters in earlier experiments. The change in cluster structure between Ni48 and Ni49 (most likely from fcc to icosahedral packing) is clearly evident in the nitrogen adsorption experiments at both low and high coverages, as well as with other reagent molecules.

The interaction of gold clusters with methanol molecules: Ab initio molecular dynamics of Aun+CH3OH and AunCH3OH

Structural, dynamical, and electronic properties of adducts obtained by adsorbing one methanol molecule onto charged and neutral gold clusters, Aun+–CH3OH and Aun–CH3OH, are investigated using Car–Parrinello ab initio molecular dynamics as a function of the cluster size n. The absorption process occurs by the formation of a Au⋆–O coordination bond to one particular gold atom Au⋆ without altering the structure of the underlying cluster. This chemical bond is much stronger for the charged metal clusters Aun+ than for the neutral analogs Aun. In the charged case, the C–O stretching vibration of the interacting methanol molecule is found to increase discontinuously as the underlying cluster structure changes from two-dimensional to three-dimensional. The weaker C–O bond in the neutral species however has “insufficient strength” to be sensitive to changes in coordination number and cluster structure. This leads to a constant C–O stretching frequency as the size of the cluster increases, including the regime where the Aun cluster changes from planar to three-dimensional.