Cluster Structures Research Articles

On the formation enthalpies and bandgaps of linear, cyclic and cubic neutral sodium chloride clusters (NaCl)n, n = 2, 3, 4, 5, 6, 10

We have taken a detailed molecular mechanics and DFT investigation of various linear, cyclic, cubic 2D and cubic 3D structures of neutral sodium chloride clusters. Our results explain the stability of these structures and calculate the lattice formation enthalpy and the bandgaps of these structures. We find that linear chains of NaCl clusters have a significantly smaller bandgap than cyclic and cubic clusters. This may find use in the use of new NaCl clusters geometries for applications in photovoltaics and high-speed infrared induced electronics.

Complex scaled nonlocalized cluster model for Be8

The nonlocalized cluster model provides a new perspective for describing nuclear cluster effects and has been successfully applied in the study of cluster structures in bound states, scattering states, and also resonant states. However, there is still some room for development when dealing with resonance problems with this new model. The complex scaling method (CSM) is an important method in research of the resonant states. We combine CSM with the nonlocalized cluster model [B. Zhou et al., Phys. Rev. Lett. 110, 262501 (2013)] for the first time, and such combination provides a new way to study the resonance in the nonlocalized cluster model. Here, we apply the CSM to $^{8}\mathrm{Be}$ as a simple example to illustrate its usages and advantages, while pointing out that the generalization to more complicated cluster systems is also natural.

Protein interactions in the biological assembly of iron-sulfur clusters in Escherichia coli: Molecular and mechanistic aspects of the earliest assembly steps.

This contribution focuses on the earliest steps of the assembly of FeS clusters and their insertion into acceptor apoproteins, that call for transient formation of a 2Fe2S cluster on a scaffold protein from sulfide and iron salts. For the sake of simplicity, this report is essentially limited to the Escherichia coli isc‐encoded proteins and does not take into account agents that modulate the enzymatic synthesis of sulfide by protein in the same operon or the redox events associated with both sulfide generation and conversion of 2Fe2S structures in clusters of higher nuclearity. Therefore, the results discussed here are based on chemical reconstitution systems using inorganic sulfide, ferric salts, and excess thiols. This simplification offers the possibility to address some mechanistic issues related to the role of protein/protein interaction as for modulating: (a) the rate of cluster assembly on scaffold proteins; (b) the stability of the cluster on the scaffold protein; and (c) the rate of transfer to acceptor apoproteins as also influenced by the acceptor concentration. The emerging picture highlights the mechanistic versatility of the systems, that is discussed in terms of the capability of such an apparently simple combination of proteins to cope with various physiological situation. The hypothetical mechanism presented here may represent an additional way of modulating the rate and outcome of the overall process while avoiding potential toxicity issues.

Two-dimensional Sb cluster superlattice on Si substrate fabricated by a two-step method

Nanoclusters consisting of a few atoms have attracted a lot of research interests due to their exotic size-dependent properties. Here, well-ordered two-dimensional Sb cluster superlattice was fabricated on Si substrate by a two-step method and characterized by scanning tunneling microscopy. High resolution scanning tunneling microscope measurements revealed the fine structures of the Sb clusters, which consist of several Sb atoms ranging from 2 to 7. Furthermore, the electronic structure of the nanocluster displays the quantized energy-level which is due to the single-electron tunneling effects. We believe that the fabrication of Sb cluster superlattice broadens the species of the cluster superlattice and provides a promising candidate to further explore the novel physical and chemical properties of the semimetal nanocluster.

Intermolecular binding between bulk water and dissolved gases in earth's magnetic field.

Elucidation of the static states and dynamic behavior of oxygen and nitrogen dissolved in water is one of the most important issues in the life sciences. In the present study, experimental trials and theoretical calculations were performed based on the hypothesis that the dissolution of gas molecules in water is related to excitation by the Earth’s magnetic field. Using quantum theories such as those used to describe electro magnetic resonance and nuclear magnetic resonance, this study investigated the states of oxygen, nitrogen and hydrogen dissolved in water. The results indicate that the Earth’s magnetic field is involved in the bonding and dissociation of molecules at the gas-liquid interface. These calculations assessed the effect of a field strength of 1.0 x 10−4 T and reproduced the influences of temperature changes on dissolved gas concentrations. Molecular interactions caused by electromagnetic properties and the external geomagnetic field were found to affect intermolar bonding associated with water cluster structures. It is concluded that the binding between molecules typically attributed to Coulomb coupling by magnetic charge and van der Waals forces results from excitation in the Earth’s magnetic field.

Strategic aspects of cluster organization of agricultural production

The article examines the main strategic aspects of the cluster organization of agricultural production. Existing research on this topic was analyzed, and the possibilities of cluster organization of agricultural production under modern conditions were studied. It is emphasized that the formation of self-governing cluster agro-industrial associations is one of the critical components of reforming the system of managing the development of agro-industrial production in the conditions of decentralization of power, European integration, and the development of inter-economic and public self-government. A semantic scheme of the cluster organization of agricultural production has been developed, the object of which is agricultural products, the subjects of which are agricultural enterprises, and which provides for the creation of closed cycles of "production" - "storage", - "processing" - "sale" of agricultural products based on integration with using mechanisms of corporatization and cooperation to achieve competitive products and increase profitability for cluster participants. The main strategic aspects of the cluster organization of agricultural production are highlighted, in particular: increasing competitiveness: the formation of agricultural clusters allows increasing the competitiveness of the industry by combining resources, knowledge and innovations; optimization of production processes: the cluster organization contributes to the optimization of the supply chain, reducing costs and increasing the quality of products due to more effective coordination between participants; stimulation of innovation: clusters create a favorable environment for innovation through joint use of scientific research, development of new technologies and exchange of experience; development of human capital: agrarian clusters contribute to the development of personnel potential through training, training and exchange of knowledge between cluster participants; support for regional development: the formation of clusters contributes to the development of regional branches of the economy and the creation of new jobs in rural areas; increasing resilience to external influences: clusters can provide protection against external shocks, such as changes in market conditions or natural disasters, through joint problem-solving and resource provision. Keywords: strategic management, agricultural sector, cluster, clusterization, cluster organization, cluster structures, agricultural production, agricultural enterprises.

An Improved Self-Adaptive Differential Evolution with the Neighborhood Search Algorithm for Global Optimization of Bimetallic Clusters.

Global optimization of multicomponent cluster structures is considerably time-consuming due to the existence of a vast number of isomers. In this work, we proposed an improved self-adaptive differential evolution with the neighborhood search (SaNSDE) algorithm and applied it to the global optimization of bimetallic cluster structures. The cross operation was optimized, and an improved basin hopping module was introduced to enhance the searching efficiency of SaNSDE optimization. Taking (PtNi)N (N = 38 or 55) bimetallic clusters as examples, their structures were predicted by using this algorithm. The traditional SaNSDE algorithm was carried out for comparison with the improved SaNSDE algorithm. For all the optimized clusters, the excess energy and the second difference of the energy were calculated to examine their relative stabilities. Meanwhile, the bond order parameters were adopted to quantitatively characterize the cluster structures. The results reveal that the improved SaNSDE algorithm possessed significantly higher searching capability and faster convergence speed than the traditional SaNSDE algorithm. Furthermore, the lowest-energy configurations of (PtNi)38 clusters could be classified as the truncated octahedral and disordered structures. In contrast, all the optimal (PtNi)55 clusters were approximately icosahedral. Our work fully demonstrates the high efficiency of the improved algorithm and advances the development of global optimization algorithms and the structural prediction of multicomponent clusters.

A Study on the Spatial Association Network of CO2 Emissions from the Perspective of City Size: Evidence from the Yangtze River Delta Urban Agglomeration

City size expansion in China creates substantial economic circulation, which impacts CO2 emissions. Since CO2 production primarily comes from human activities, CO2 emissions are mainly in cities. To achieve China’s carbon neutrality and provide specific implementation guidance for future carbon-reduction policies, it is worth assessing China’s pressure on carbon reduction in the urban aspect. Highly developed social productivity and a market economy lead to a dramatic increase in the interconnection between cities, and the spatial distribution of CO2 emissions emerges in a spatial association. Therefore, it is of great significance to investigate the interaction of CO2 emissions with spatial effects. Taking the Yangtze River Delta urban agglomeration (YRDUA) as the research target area, this paper utilizes city-size indices to construct spatial-association networks of CO2 emissions for the first time. It employs social network analysis to explore the structures of whole networks, clusters, and city nodes. The main results show that: (1) the spatial associations of CO2 emissions in the YRDUA’s cities have become tighter over time. (2) The networks of CO2 emissions in the YRDUA’s cities have noticeable spatial-spillover effects, and the interaction of CO2 emissions between cities is dominant. (3) Nanjing is the paramount “bridge” node in the networks. (4) Nanjing, Hangzhou, Wuxi, Shanghai, Changzhou, Suzhou, Nantong, and Hefei will be the decisive cities for efficient CO2 emission control in the future. Overall, this paper reveals the role of carbon reduction in the YRDUA’s cities and proposes suggestions for establishing a transboundary energy-saving mechanism to improve the efficiency of energy conservation and emission reduction.

Black Titanium-Oxo Clusters with Ultralow Band Gaps and Enhanced Nonlinear Optical Performance.

A series of catecholate-functionalized titanium-oxo clusters (TOCs), PTC-271 to PTC-277, with atomically precise structures were synthesized and characterized, including distinctive "boat" and "chair" conformations in PTC-273 and PTC-274, respectively. These cluster compounds are prominent for their ultralow optical band gaps, as is visually evident from the rather unusual black TOCs (B-TOCs), PTC-272 to PTC-277. The cluster structures were found to be ultrastable with respect to air, water, organic solvents, and even acidic or basic aqueous solutions in a wide pH range (pH 0-13), owing to the stabilizing effects of catecholate and its derivatives, as well as the carboxylate ligands. Another prominent feature is the occurrence of third-order nonlinear optical (NLO) performance, which has previously been unreported in the field of homometallic titanium-oxo clusters. Open-aperture Z-scan experiments show significant solid-state optical limiting (OL) applications of these B-TOCs, with high laser irradiation stability and low minimum normalized transmittance (Tmin) of PTC-273 as ∼0.17. Meanwhile, theoretical calculations indicate that the smaller band gaps of B-TOCs were beneficial for strengthening the NLO response. This work not only represents a significant milestone in the construction of stable low-band gap black titanium oxide materials but also contributes to the mechanism insights into their optical applications.

An Improved Three-Way Clustering Based on Ensemble Strategy

As a powerful data analysis technique, clustering plays an important role in data mining. Traditional hard clustering uses one set with a crisp boundary to represent a cluster, which cannot solve the problem of inaccurate decision-making caused by inaccurate information or insufficient data. In order to solve this problem, three-way clustering was presented to show the uncertainty information in the dataset by adding the concept of fringe region. In this paper, we present an improved three-way clustering algorithm based on an ensemble strategy. Different to the existing clustering ensemble methods by using various clustering algorithms to produce the base clustering results, the proposed algorithm randomly extracts a feature subset of samples and uses the traditional clustering algorithm to obtain the diverse base clustering results. Based on the base clustering results, labels matching is used to align all clustering results in a given order and voting method is used to obtain the core region and the fringe region of the three way clustering. The proposed algorithm can be applied on the top of any existing hard clustering algorithm to generate the base clustering results. As examples for demonstration, we apply the proposed algorithm on the top of K-means and spectral clustering, respectively. The experimental results show that the proposed algorithm is effective in revealing cluster structures.

Towards cluster duality for Lagrangian and orthogonal Grassmannians

In (2019), Rietsch and Williams relate cluster structures and mirror symmetry for type A Grassmannians Gr(k,n), and use this interaction to construct Newton-Okounkov bodies and associated toric degenerations. In this article we define a cluster seed for the Lagrangian Grassmannian, and prove that the associated Newton-Okounkov body agrees up to unimodular equivalence with a polytope obtained from the superpotential defined by Pech and Rietsch on the mirror Orthogonal Grassmannian in Pech and Rietsch (2013).

Clusteromics III: Acid Synergy in Sulfuric Acid-Methanesulfonic Acid-Base Cluster Formation.

Acid–base molecular clusters are an important stage in atmospheric new particle formation. While such clusters are most likely multicomponent in nature, there are very few reports on clusters consisting of multiple acid molecules and multiple base molecules. By applying state-of-the-art quantum chemical methods, we herein study electrically neutral (SA)1(MSA)1(base)0–2 clusters with base = ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA) and ethylenediamine (EDA). The cluster structures are obtained using a funneling approach employing the ABCluster program, semiempirical PM7 calculations and ωB97X-D/6-31++G(d,p) calculations. The final binding free energies are calculated at the DLPNO-CCSD(T0)/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory using the quasi-harmonic approximation. Based on the calculated cluster geometries and thermochemistry (at 298.15 K and 1 atm), we find that the mixed (SA)1(MSA)1(base)1–2 clusters more resemble the (SA)2(base)1–2 clusters compared to the (MSA)2(base)1–2 clusters. Hence, some of the steric hindrance and lack of hydrogen bond capacity previously observed in the (MSA)2(base)1–2 clusters is diminished in the corresponding (SA)1(MSA)1(base)1–2 clusters. Cluster kinetics simulations reveal that the presence of an MSA molecule in the clusters enhances the cluster formation potential by up to a factor of 20. We find that the SA–MSA–DMA clusters have the highest cluster formation potential, and thus, this system should be further extended to larger sizes in future studies.

Subscales in the National Student Survey (NSS): Some considerations on their structure

ABSTRACT Measures of student satisfaction are commonly used to compare universities. Student satisfaction with higher education institutions in the UK is assessed yearly using the National Student Survey (NSS). The most recent revision of the NSS suggests that the satisfaction questions form eight different subscales. The aim of this research was to empirically test whether the NSS questions form eight separate subscales. We used the public data from the NSS from 2019 and clustering methods to examine the structure of the data. We tested the structure of the NSS questions when the data was analysed as a whole (i.e. at the ‘top’ national level across all universities and courses). We also assessed the clustering of data for 78 course subjects separately to see the most frequent number of clusters across courses (i.e. at the ‘bottom’ individual course level). At the top (national) level, we found a four cluster or two cluster solution (when excluding both an item on the student union and a general satisfaction item), rather than an eight cluster solution. At the bottom (course) level, the most common cluster solution was two clusters, but with considerable variation, ranging from one to eight clusters. Our findings thus suggest that there is considerable variation in the structure of the NSS and that this variation can depend on analytical level (top national level vs. bottom course level). We review the implications of differing cluster structures for how the NSS is used.

Assessing the development of agro-industrial clusters in the European cluster collaboration platform network

Subject. This article examines the integration processes in cluster structures operating in various sectors of the economy of European countries. Objectives. The article aims to identify the features of organizational and economic relations within cluster structures in European countries on the basis of their classification by territorial and sectoral characteristics. Methods. For the study, we used the localization and formalization techniques, and the case study and cartographic methods. Results. The article offers an author-developed approach to the classification of European economic clusters. This classification helps identify the regional and sectoral specifics of cluster structures, and determine the areas of their cooperation and main trends in their development. Conclusions. Cooperation at the national and international levels contributes to the achievement of the goals of strategic development of economic clusters.

En route from metal alkoxides to metal oxides: metal oxo/alkoxo clusters

Molecular metal oxo or oxo/alkoxo clusters, MwOx(OH/OR)y(L/X)z (L or X = organic ligands), can often be isolated upon (partial) hydrolysis of metal alkoxides. Investigation of such clusters leads to a better understanding of the basic processes of sol–gel chemistry. The ligands not only stabilize the cluster core but also influence to some extent the cluster structures. They can easily change their position on the cluster surface, thus adapting to changing cluster geometries, and can be exchanged under certain conditions. A close inspection of titanium oxo/alkoxo cluster structures, taken as an informative example, shows that Ti3O units (with or without organic ligands) are the basic building blocks. Clusters with higher nuclearities appear to be predominantly formed by cluster–cluster or by cluster–monomer condensations. Ligand substitution or condensation reactions within a cluster unit are also possible.Instead of extended metal oxide networks, metal oxo/alkoxo clusters may be formed upon hydrolysis of metal alkoxides.

Microscopic Insights Into the Formation of Methanesulfonic Acid–Methylamine–Ammonia Particles Under Acid-Rich Conditions

Understanding the microscopic mechanisms of new particle formation under acid-rich conditions is of significance in atmospheric science. Using quantum chemistry calculations, we investigated the microscopic formation mechanism of methanesulfonic acid (MSA)–methylamine (MA)–ammonia (NH3) clusters. We focused on the binary (MSA)2n-(MA)n and ternary (MSA)3n-(MA)n-(NH3)n, (n = 1–4) systems which contain more acid than base molecules. We found that the lowest-energy isomers in each system possess considerable thermodynamic and dynamic stabilities. In studied cluster structures, all bases are protonated, and they form stable ion pairs with MSA, which contribute to the charge transfer and the stability of clusters. MA and NH3 have a synergistic effect on NPF under acid-rich conditions, and the role of NH3 becomes more remarkable as cluster size increases. The excess of MSA molecules does not only enhance the stability of clusters, but provides potential sites for further growth.

Stepwise pesudopolyrotaxane nanostructure formation from supramolecular self-assembly by inclusion complexation of fast violet B with α- and β-cyclodextrins

The current work deals with fast violet B (FVB) and cyclodextrins (α-CD and β-CD) inclusion complex into pesudopolyrotaxane nanorod by supramolecular self-assembly. FVB/α-CD forms 2:2 from 1:1 and FVB/β-CD forms 1:2 from 1:1 inclusion complexes, which further self assembled to form nanorod and nano cluster structures. The nanorods formed through step-by-step process after FVB encapsulation into cyclodextrins nano cavities. Wide angle powder X-ray diffraction exposed the crystallinity of the materials, thermal analysis, Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance spectroscopy (1H NMR and 2D ROESY) confirmed FVB encapsulation into the CDs cavities. Amido functionality of FVB molecule is twisted when it is encapsulated within α-CD and β-CD cavities. Computational studies further divulge that the complex formation is an enthalpy-entropy driven process.

Parameters and Structure of Neural Network Databases for Assessment of Learning Outcomes

The purpose of this study is to determine the methodology, develop a theory of construction, put into practice algorithmization and implement the functionality of a hybrid intelligent system for assessment of educational outcomes of trainees on the basis of the identified keyword parameters and structure of the artificial neural network using expert systems and fuzzy simulation; to develop a methodology for the construction of structural-logic, hierarchical, functional and fractal schemes for structuring databases of the didactic field of learning elements; to determine the content, structure of parameters and database components, selection criteria and the content of complexes of educational standards. The methodology of introducing intelligent systems into mathematical education is on the basis of the Hegelian triad: thesis (implementation of the coherence principle) – antithesis (implementation of principles of the fractality and historiogenesis) – synthesis (implementation of the principles of self-organization and reflection of the complex system inversion integrity). Requirements for the organization and construction of the artificial neural network for assessment of personal achievements on the basis of fuzzy simulation have been developed. In the direction of using elements of fractal geometry, the technological structures of clusters that constitute the basis of generalized structures have been developed. In particular, it is revealed that the didactic field of learning elements is equipped with a system of multi-level hierarchical databases of exercises, motivational-applied, research, practice-oriented tasks using expert systems and integration of mathematical, information, natural-science and humanities knowledge and procedures.

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Molecular dynamics simulation of initial thermal decomposition mechanism of DNTF.

In order to understand the thermal decomposition characteristics of 3,4-Bis(3-nitrofurazan-4-yl)furoxan (DNTF), the thermal decomposition reaction of DNTF at 300-4000K temperature programmed and constant temperatures of 2000K, 2500K, 3000K, 3500K, and 4000K was simulated by ab initio computational molecular dynamics method. The thermal decomposition mechanism of DNTF at different temperatures was analyzed from the aspects of product evolution, cluster, potential energy curve, and reaction path. The analysis of products shows that the initial small molecular products are NO, NO2, CO, CO2, and N2, and the final small molecular products are CO2 and N2. In the early stage, the ring-opening reaction of furoxan in DNTF structure is the main trigger reaction, and the C-C bond is broken at the initial stage of reaction. The carbon chain structure produced by decomposition forms various cluster structures in the form of C-N bond. In addition, it was found that temperature significantly affects the decomposition rate of DNTF, but does not change its initial decomposition path.