Medium-sized Clusters Research Articles

Role of clustering in the anomalous properties of supercritical fluids

We propose that the anomalous (non-monotonic) behavior of physical properties of supercritical fluids (SCF) in the Widom delta is attributed to the formation of medium-sized clusters. This hypothesis is experimentally verified for carbon dioxide using both experimental methods and molecular dynamics simulations. From a microscopic point of view, the non-monotonic behavior of the nonlinear refractive index, speed of sound, and Raman scattering efficiency is caused by the formation of quasi-linear clusters of medium size (5–200 molecules per cluster). Within the clusters, the molecule concentration is close to that of the liquid phase, while outside the clusters, it resembles the gas phase, leading to experimentally observed high (∼15 %) density fluctuations. Isolated linear clusters exhibit high second-order hyperpolarizability, resulting in an increase in the molecular contribution to the nonlinear refractive index and the intensity of Raman scattering. The appearance of multiple Widom lines on the pressure–temperature (p-T) diagram, each associated with unique physical properties, arises from the combined effects of cluster-specific and density-related factors. This interplay results in the divergence of Widom lines and the formation of the characteristic feature known as the Widom delta.

Self-Generated Ions Modify the Pair Interaction and the Phase Separation of Chemically Active Colloids.

Chemically active colloids that release/consume ions are an important class of active matter, and exhibit interesting collective behaviors such as phase separation, swarming, and waves. Key to these behaviors is the pair-wise interactions mediated by the concentration gradient of self-generated ions. This interaction is often simplified as a pair-wise force decaying at 1/r2, where r is the interparticle distance. Here, we show that this simplification fails for isotropic and immotile active colloids with net ion production, such as Ag colloids in H2O2. Specifically, the production of ions on the surface of the Ag colloids increases the local ion concentration, c, and attenuates the pair-wise interaction force that scales with ∇c/c. As a result, the attractive force between an Ag colloid and its neighbor (active or passive) decays at 1/r or 1/r2 for small or large r, respectively. In a population, the attraction of a colloid by a growing cluster also scales with ∇c/c, so that medium-sized clusters grow fastest, and that the cluster coarsening slows with time. These results, supported by finite element and Brownian dynamic simulations, highlight the important role of self-generated ions in shaping the collective behavior of chemically active colloids.

Developing Vocational Education and Deepening the Integration of Industry and Education Providing Human Resources Support for Building a Strong Provincial Centre-Taking the Development of Vocational Education in Sanmenxia as an Example

Since the 18th National Congress of the Communist Party of China (CPC), China's vocational education has experienced significant improvement and optimisation, and the group of graduates from vocational colleges and universities has grown to become the backbone of China's industrial army, which not only provides a solid support for the vigorous development of small and medium-sized enterprise clusters, but also greatly promotes the transformation and upgrading of the regional industry, and accelerates the process of urbanization, which has become an important driving force for the socio-economic development of the society. In recent years, Sanmenxia City has paid special attention to the development of vocational education in the process of strengthening the construction of provincial centre city, and has cultivated a large number of high-quality technical talents, which has provided a solid talent foundation for the transformation and development of the city's economy and society. Taking the development of vocational education in Sanmenxia as an example, this paper focuses on the inevitability and positive contribution of vocational education to the construction of Sanmenxia as a provincial central city, analyses the current situation, and puts forward countermeasures and suggestions for the future of vocational education in the provision of talent support for the construction of a provincial central city.

Structural and spectral properties of Gas-phase FMgn (n = 2–20) clusters based on DFT

Structure, stability, electronic structure, spectroscopy and chemical bonding properties of a fluorine atom doped gas-phase small to medium-sized magnesium clusters, FMgn (n = 2–20), systematically investigated by CALYPSO software together with density functional theory (DFT). Structural calculations showed that FMgn has a structural diversity which is rarely reported in other magnesium-based clusters before. F atoms were always located in the outer layer of the Mgn host clusters and only two or three Mg atoms surround it. FMg18 was revealed to be supposed to have robust relative stability. Charge transfer and density of states were calculated for analyzing the electronic structure characteristics. Theoretical calculations of IR, Raman and UV–Vis spectra were computed to provide data guidelines for future experimental observations. Finally, the F–Mg and Mg–Mg chemical bonds of the FMgn clusters were analyzed, including the critical bonding points (BCPs) of Laplacian of electron density (Δρ), electron localization function (ELF) and interaction region indicator (IRI). The kind and strength of chemical bonds reveal the mechanism by which the F atom was rapidly stabilized by Mgn (n = 2–20) host clusters.

Structural evolution and electronic properties of medium-sized boron clusters doped with selenium

The exploration of boron-doped clusters' structures and properties significantly advances our understanding of nanomaterials at the microscopic level. This study employs density functional theory to systematically investigate the structural evolution and electronic properties of singly Se-doped boron-based clusters, SeBn− (n = 16–24). The dopant atom exhibits a distinct preference for positioning outside the Bn−/0 framework, mirroring the arrangement found in the corresponding pure boron skeleton. Predicting the structural and electronic properties of doped clusters using simulated photoelectron spectra. Notably, magic clusters SeB19− and SeB23− are identified, showcasing remarkable relative stability. Furthermore, SeB24− is suggested to potentially exist as a pseudo-tubular isomer, representing a unique three-dimensional structure. The natural population analysis uncovers an electron transfer from Se to B atoms. The electronic localization function highlights substantial electron delocalization in SeBn−. Additionally, isochemical shielding surface analysis reveals pronounced aromaticity in the pseudo-tubular SeB24− isomer, thereby significantly enhancing the overall stability of the clusters.

Muscle Sympathetic Action Potential Firing Patterns Following Intranasal Insulin Administration in Healthy Adults

Objective: Systemic insulin increases muscle sympathetic nervous system activity (MSNA) in healthy adults by augmenting firing frequency of medium-sized sympathetic action potentials (AP) and recruiting previously latent, larger axons. Whether these neural coding patterns are due to central or peripheral effects of insulin is unclear. We examined the impact of elevated central insulin on AP firing patterns in healthy adults. We hypothesized intranasal insulin administration, which increases central insulin levels, would increase MSNA via elevated firing frequency of APs and recruitment of previously latent, larger axons. Methods: Ten participants were assigned to time control [TC, n=6 (3M/3F)] or 160 IU of intranasal insulin [n=4 (3M/1F)] administered over 5 min. MSNA (fibular microneurography) was assessed at baseline and for 30 min following insulin administration. Sympathetic APs were identified using a matched mother wavelet and continuous wavelet transform. APs were divided into the proportion of those firing in small, medium, or large amplitude clusters. AP firing frequency, percent of APs firing within an MSNA burst (synchronous), and the probability of clusters firing more than once within an MSNA burst were identified. Data are reported as median (interquartile range). Results: MSNA burst frequency increased 15 min after intranasal insulin administration [24(20) to 31(23) bursts/min, p=0.03]. At this time, the percent of synchronous APs [72(27) to 90(24)%, p=0.02] and the probability of medium-sized AP clusters firing more than once within an MSNA burst [13(14) to 19(17)%, p=0.03] increased. No changes in MSNA burst frequency [23(14) to 25(13) bursts/min, p=0.27], percent of synchronous APs [74(15) to 75(34), p=0.48], nor firing probability of medium-sized AP clusters [6(12) to 8(7)%, p=0.97] occurred in TC. The total number of detected clusters did not change in either group (p>0.05). Conclusions: Intranasal insulin increases MSNA burst frequency due to a higher percent of synchronous APs, particularly medium-sized AP clusters; however, we did not observe recruitment of latent, larger axons. These exploratory data highlight potential differences in the sympathetic response to central versus peripheral insulin exposure in healthy adults. CAFNR Joy of Discovery (JKL, JP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Introducing hafnium to atomically small- and medium-sized tin clusters (HfSnn0/-/2- (n = 4–17)): A computational investigation of geometrical and growth behavior, spectral properties, electronic configuration and thermochemistry

The global and local minimum configurations of single Hf atom doped Sn clusters are conducted via density function theory (DFT) combined with artificial bee colony algorithm (ABCluster). Furthermore, DFT method is also used to systematically investigate on their structural growth evolution, spectral and electronic information, thermochemical properties following the size of tin clusters doped Hf atom. Structurally, the ground-state geometries of neutral, anion and di-anion are discovered that, from n = 4, the number of Sn atoms in cluster, HfSnn0/-/2- adsorb additional Sn atom on the prior architecture one by one until forming n = 17 for HfSnn-10/-, as well as forming n = 16 for HfSnn-12-. And for the HfSn110/- and HfSn102- as beginning the species veritably develop sealed architectures. The strongest vibrational modes of sealed nanoclusters are stretching modes of Hf atom with infrared actives and breathing modes of the Sn cage framework with Raman actives, respectively. The natural population analysis (NPA) elucidates the stronger relationship between the Hf atoms and the tin frameworks in sealed clusters than that in unsealed clusters. The results of thermochemical properties, molecular orbital shell (MOs), adaptive natural density partitioning (AdNDP) and ultraviolet visible absorption spectrum (UV–Vis) indicate that, the HfSn16 with high symmetry of Td exhibits thermochemical stability and optoelectronic properties, which is utilized potentially as zero-dimensional unit of self-assembling fluorescent nanomaterials.

Linear Scaling Incremental Scheme for Correlation Energies with Embedding Generated Virtuals.

A novel incremental scheme is presented including an incremental expansion of the virtual space for the calculation of electron correlation energies, which is compatible with any size-extensive correlation method and scales asymptotically linear for large molecules. The performance is studied for organic molecules, water clusters, and a La(III)-water complex, where the compatibility with pseudopotentials is also examined. The computational requirements are already reduced tremendously for medium-sized water clusters and hydrocarbons with respect to the canonical CCSD as well as the ordinary incremental scheme references. Correlation energies within chemical accuracy have been observed for all studied systems. The novelty of the method is that relatively small virtual spaces are used in combination with tuples of localized occupied spaces. The corresponding orthonormal occupied and virtual orbitals are obtained from QM/QM embedding calculations and can thus be used with standard quantum chemistry codes for correlation calculations. It is presented how relevant virtual spaces are selected and the correlation energies are linked in the new virtual space expansion.

A Vicsek-type model of confined cancer cells with variable clustering affinities.

Clustering of cells is an essential component of many biological processes from tissue formation to cancer metastasis. We develop a minimal, Vicsek-based model of cellular interactions that robustly and accurately captures the variable propensity of different cells to form groups when confined. We calibrate and validate the model with experimental data on clustering affinities of four lines of tumor cells. We then show that cell clustering or separation tendencies are retained in environments with higher cell number densities and in cell mixtures. Finally, we calibrate our model with experimental measurements on the separation of cells treated with anti-clustering agents and find that treated cells maintain their distances in denser suspensions. We show that the model reconstructs several cell interaction mechanisms, which makes it suitable for exploring the dynamics of cell cluster formation as well as cell separation. Insight: We developed a model of cellular interactions that captures the clustering and separation of cells in an enclosure. Our model is particularly relevant for microfluidic systems with confined cells and we centered our work around one such emerging assay for the detection and research on clustering breast cancer cells. We calibrated our model using the existing experimental data and used it to explore the functionality of the assay under a broader set of conditions than originally considered. Future usages of our model can include purely theoretical and computational considerations, exploring experimental devices, and supporting research on small to medium-sized cell clusters.

Effects of bromine-containing counterion salts in directing the structures of medium-sized silver nanoclusters.

The preparation and structural determination of silver nanoclusters (especially the medium-sized Ag clusters) remain more challenging relative to those of their gold counterparts because of the comparative instability of the former. In this work, three medium-sized Ag clusters were controllably synthesized and structurally determined, namely, [Ag52(S-Adm)30Br4H20]2- (Ag52 for short), Ag54(S-Adm)30Br4H20 (Ag54 for short), and [Ag58(S-Adm)30Br4(NO3)2H22]2+ (Ag58 for short) nanoclusters. Specifically, the introduction of PPh4Br gave rise to the generation of Ag52 and Ag54 nanoclusters with homologous compositions and configurations, while the TOABr salt selected Ag58 as the sole cluster product, whose geometric structure was completely different from those of Ag52 and Ag54 nanoclusters. In addition, the optical absorptions and emissions of the three medium-sized silver nanoclusters were compared. The findings in this work not only provide three uniquely medium-sized nanoclusters to enrich the silver cluster family but also point out a new approach (i.e., changing the counterion salt) for the preparation of new nanoclusters with novel structures.

Predicting Binding Energies and Electronic Properties of Boron Nitride Fullerenes Using a Graph Convolutional Network.

As isoelectronic counterparts of carbon fullerenes, medium-sized boron nitride clusters also prefer cage structures composed of even-sized polygons. As the cluster size increases, the number of cage isomers grows rapidly, and determining the ground state structure requires a tremendous amount of DFT calculations. Herein, we develop a graph convolutional network (GCN) that can describe the energy of a (BN)n cage by its topology connection. We define a vertex feature vector on a dual polyhedron by the permutation of the neighbor vertices' degree and aggregate the information on vertices by two graph convolutional layers to learn the local feature of the dual polyhedron. The GCN is trained on (BN)28 and subsequently tested on (BN)23 and (BN)24 data sets, which satisfactorily reproduce the order of isomer energies from DFT calculations. We further employ the trained GCN to predict the ground state structures within the size range of n = 25-32, which agree well with DFT results. Using the same GCN framework, we also successfully trained the highest-occupied or lowest-unoccupied orbital energies of (BN)28 isomers. The present graph convolutional network establishes a direct mapping between the topological connection and the energetic or electronic properties of a cage-like cluster or molecule.

Geometric and electronic structures of medium-sized boron clusters doped with plutonium

Doping metal heteroatoms is an effective strategy to regulate the geometric and electronic structure of boron based nanoclusters. However, the exploration of the ground state structures of metal-boron-based nanoclusters is still a challenge duo to the complexity of the bonding interactions between heterogeneous atoms and boron cluster and the number of isomers on the potential energy surface increases exponentially with cluster size. Here, we use the CALYPSO cluster structural search method in combination with density functional theory calculations to study the geometries and electronic properties of anionic boron clusters doped with plutonium (PuB, n = 10–20). Our results show that the medium-sized PuB cluster exhibits excellent stability with highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of 2.30 eV. The remarkable stability of the anionic PuB cluster is due to the robust interactions between the Pu metal and the B14 skeleton, along with the strong covalent interactions between the B atoms. These findings enrich the geometric structure database of metal doped clusters and provide valuable insights for the future synthesis of boron based nanomaterials.

Cell clusters in intervertebral disc degeneration: an attempted repair mechanism aborted via apoptosis.

Cell clusters are a histological hallmark feature of intervertebral disc degeneration. Clusters arise from cell proliferation, are associated with replicative senescence, and remain metabolically, but their precise role in various stages of disc degeneration remain obscure. The aim of this study was therefore to investigate small, medium, and large size cell-clusters. For this purpose, human disc samples were collected from 55 subjects, aged 37-72 years, 21 patients had disc herniation, 10 had degenerated non-herniated discs, and 9 had degenerative scoliosis with spinal curvature <45°. 15 non-degenerated control discs were from cadavers. Clusters and matrix changes were investigated with histology, immunohistochemistry, and Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Data obtained were analyzed with spearman rank correlation and ANOVA. Results revealed, small and medium-sized clusters were positive for cell proliferation markers Ki-67 and proliferating cell nuclear antigen (PCNA) in control and slightly degenerated human discs, while large cell clusters were typically more abundant in severely degenerated and herniated discs. Large clusters associated with matrix fissures, proteoglycan loss, matrix metalloproteinase-1 (MMP-1), and Caspase-3. Spatial association findings were reconfirmed with SDS-PAGE that showed presence to these target markers based on its molecular weight. Controls, slightly degenerated discs showed smaller clusters, less proteoglycan loss, MMP-1, and Caspase-3. In conclusion, cell clusters in the early stages of degeneration could be indicative of repair, however sustained loading increases large cell clusters especially around microscopic fissures that accelerates inflammatory catabolism and alters cellular metabolism, thus attempted repair process initiated by cell clusters fails and is aborted at least in part via apoptosis.

Structures, Electronic, and Magnetic Properties of CoKn (n = 2-12) Clusters: A Particle Swarm Optimization Prediction Jointed with First-Principles Investigation.

Transition-metal-doped clusters have long been attracting great attention due to their unique geometries and interesting physical and/or chemical properties. In this paper, the geometries of the lowest- and lower-energy CoKn (n = 2-12) clusters have been screened out using particle swarm optimization and first principles relaxation. The results show that except for CoK2 the other CoKn (n = 3-12) clusters are all three-dimensional structures, and CoK7 is the transition structure from which the lowest energy structures are cobalt atom-centered cage-like structures. The stability, the electronic structures, and the magnetic properties of CoKn clusters (n = 2-12) clusters are further investigated using the first principles method. The results show that the medium-sized clusters whose geometries are cage-like structures are more stable than smaller-sized clusters. The electronic configuration of CoKn clusters could be described as 1S1P1D according to the spherical jellium model. The main components of petal-shaped D molecular orbitals are Co-d and K-s states or Co-d and Co-s states, and the main components of sphere-like S molecular orbitals or spindle-like P molecular orbitals are K-s states or Co-s states. Co atoms give the main contribution to the total magnetic moments, and K atoms can either enhance or attenuate the total magnetic moments. CoKn (n = 5-8) clusters have relatively large magnetic moments, which has a relation to the strong Co-K bond and the large amount of charge transfer. CoK4 could be a magnetic superatom with a large magnetic moment of 5 μB.

Theoretical study of geometry and electronic properties of medium-sized doped clusters Li2Bn0/− (n = 1–12)

Theoretical study of geometry and electronic properties of medium-sized doped clusters Li2Bn0/− (n = 1–12)

Algebraic Graph-Based Machine Learning Model for Li-Cluster Prediction.

In cluster research, determining the ground-state structure of medium-sized clusters is hindered by a large number of local minimum on potential energy surfaces. The global optimization heuristic algorithm is time-consuming due to the use of DFT to determine the relative size of the cluster energy. Although machine learning (ML) is proved to be a promising way to reduce the DFT computational costs, a suitable method to represent clusters as input vectors is one of the bottlenecks in the application of ML to cluster research. In this work, we proposed a multiscale weighted spectral subgraph (MWSS) as an effective low-dimension representation of clusters and build an MWSS-based ML model to discover the structure-energy relationships in lithium clusters. We combine this model with the particle swarm optimization algorithm and DFT calculations to search for globally stable structures of clusters. We have successfully predicted the ground-state structure of Li20.

Pivotal role of the B12-core in the structural evolution of B52-B64 clusters.

An icosahedral B12 cage is a basic building block of various boron allotropes, and it also plays a vital role in augmenting the stability of fullerene-like boron nanoclusters. However, the evolution of compact core-shell structures is still a puzzle. Using a genetic algorithm combined with density functional theory calculations, we have performed a global search for the lowest-energy structures of Bn clusters with n = 52-64, which reveals that bilayer and core-shell motifs frequently alternate as the ground state. Their structural stability is assessed, and the competition mechanism between various patterns is also elucidated. More interestingly, an unprecedented icosahedral B12-core half-covered structure is identified at B58, which bridges the gap between the smallest core-shell B4@B42 and the complete core-shell B12@B84 cluster. Our findings provide valuable insights into the bonding pattern and growth behavior of medium-sized boron clusters, which facilitate the experimental synthesis of boron nanostructures.

STRUCTURE AND VIBRATIONS OF FREE NIN CLUSTERS (N &lt; 20)

The binding energy, equilibrium geometry, and vibration frequencies of small free Nin clusters (n &lt; 20) were calculated using interatomic interaction potentials calculated in an embedded atom method. Calculations of the energy parameter of stability АЕ2 and dissociation energy showed that the most energetically stable clusters are those with the magic numbers of atoms n = 4, 6, 13, 19. Calculations of atomic vibrations revealed that the dynamic contribution to the stability of clusters is determined by the minimum vibration frequency, whose extreme values fall on clusters with the magic numbers of atoms n = 4, 6, 13, 19. The maximum vibration frequency varies nonmonotonically and for clusters with n &lt; 19 it has no clear extreme values. This result is consistent with available experimental data on stable structures of small and medium-sized metal clusters.

Structural evolution, charge transfer and bonding properties of medium-sized atomic rubidium-doped boron clusters

In this work, the bonding properties of B8Rb2 cluster were characterized by molecular orbitals and bonding order. The electrostatic potentials of the clusters were also analyzed, and the interaction of particles between the alkali metal orbitals and the boron backbone was found.

Cooperativity and reactivity properties of medium-sized boron clusters: a combined density functional theory and information-theoretic approach study

In continuation of our previous work of small boron clusters [Phys. Chem. Chem. Phys. 23, 24118 (2021)], we systematically examined the neutral and negatively charged boron clusters B n /B − (nε{8–38}) with planar or quasi-planar conformations, whose exotic properties have aroused considerable interest in the literature. We make use of two total energy partition schemes, conceptual density functional theory, and the information-theoretic approach to appreciate the cooperativity and reactivity properties. We found that neutral boron clusters are positively cooperative, but negatively charged boron clusters are negatively cooperative. Our results show that the origin of the cooperativity effect for the negatively cooperative boron clusters is much more complicated than the neutral boron clusters. For chemical reactivity, we unveil that the reactive sites are around the cluster periphery and boron atoms can be both electrophilic and nucleophilic. Global and local aromaticity for the boron clusters can be totally different. For the first time, we have observed helical spin density distributions for negatively charged boron clusters (B16 – and B20 – ), which is reminiscent of helical molecular orbitals [Chem. Sci. 4, 4278 (2013)] in allenes, cumulenes, and oligoynes (polyalkynes). Collectively, our results should provide more insights to understand the exotic properties of boron clusters and henceforth yield novel potential applications.