Articles de revues : « Planar cluster »

1

Kawai, R., J. F. Tombrello et J. H. Weare. « Li5as a pseudorotating planar cluster ». Physical Review A 49, n^o 5 (1 mai 1994) : 4236–39. http://dx.doi.org/10.1103/physreva.49.4236.

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Wang, Meng-hui, Chen Chen, Sudip Pan et Zhong-hua Cui. « Planar hexacoordinate gallium ». Chemical Science 12, n^o 45 (2021) : 15067–76. http://dx.doi.org/10.1039/d1sc05089c.

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A star-like texture containing a planar hexacoordinate gallium center is reported in the lowest energy isomer of the GaBe6Au6+ cluster. High thermodynamic and kinetic stability of the title cluster makes it suitable candidate for experimental realization.

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Sucerquia, Daniel, Cristian Parra, Pilar Cossio et Olga Lopez-Acevedo. « Ab initio metadynamics determination of temperature-dependent free-energy landscape in ultrasmall silver clusters ». Journal of Chemical Physics 156, n^o 15 (21 avril 2022) : 154301. http://dx.doi.org/10.1063/5.0082332.

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Ab initio metadynamics enables the extraction of free-energy landscapes having the accuracy of first-principles electronic structure methods. We introduce an interface between the PLUMED code that computes free-energy landscapes and enhanced-sampling algorithms and the Atomic Simulation Environment (ASE) module, which includes several ab initio electronic structure codes. The interface is validated with a Lennard-Jones cluster free-energy landscape calculation by averaging multiple short metadynamics trajectories. We use this interface and analysis to estimate the free-energy landscape of Ag5 and Ag6 clusters at 10, 100, and 300 K with the radius of gyration and coordination number as collective variables, finding at most tens of meV in error. Relative free-energy differences between the planar and non-planar isomers of both clusters decrease with temperature in agreement with previously proposed stabilization of non-planar isomers. Interestingly, we find that Ag6 is the smallest silver cluster where entropic effects at room temperature boost the non-planar isomer probability to a competing state. The new ASE-PLUMED interface enables simulating nanosystem electronic properties under more realistic temperature-dependent conditions.

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SUBRAMANIAN, G., et DONALD L. KOCH. « Evolution of clusters of sedimenting low-Reynolds-number particles with Oseen interactions ». Journal of Fluid Mechanics 603 (30 avril 2008) : 63–100. http://dx.doi.org/10.1017/s0022112008000797.

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A theoretical framework is developed to describe, in the limit of small but finite Re, the evolution of dilute clusters of sedimenting particles. Here, Re =aU/ν is the particle Reynolds number, where a is the radius of the spherical particle, U its settling velocity, and ν the kinematic viscosity of the suspending fluid. The theory assumes the disturbance velocity field at sufficiently large distances from a sedimenting particle, even at small Re, to possess the familiar source--sink character; that is, the momentum defect brought in via a narrow wake behind the particle is convected radially outwards in the remaining directions. It is then argued that for spherical clusters with sufficiently many particles, specifically with N much greater than O(R0U/ν), the initial evolution is strongly influenced by wake-mediated interactions; here, N is the total number of particles, and R0 is the initial cluster radius. As a result, the cluster first evolves into a nearly planar configuration with an asymptotically small aspect ratio of O(R0U/N ν), the plane of the cluster being perpendicular to the direction of gravity; subsequent expansion occurs with an unchanged aspect ratio. For relatively sparse clusters with N smaller than O(R0U/ν), the probability of wake interactions remains negligible, and the cluster expands while retaining its spherical shape. The long-time expansion in the former case, and that for all times in the latter case, is driven by disturbance velocity fields produced by the particles outside their wakes. The resulting interactions between particles are therefore mutually repulsive with forces that obey an inverse-square law. The analysis presented describes cluster evolution in this regime. A continuum representation is adopted with the clusters being characterized by a number density field (n(r, t)), and a corresponding induced velocity field (u (r, t)) arising on account of interactions. For both planar axisymmetric clusters and spherical clusters with radial symmetry, the evolution equation admits a similarity solution; either cluster expands self-similarly for long times. The number density profiles at different times are functions of a similarity variable η = (r/t1/3), r being the radial distance away from the cluster centre, and t the time. The radius of the expanding cluster is found to be of the form Rcl (t) = A (ν a)1/3N1/3t1/3, where the constant of proportionality, A, is determined from an analytical solution of the evolution equation; one finds A = 1.743 and 1.651 for planar and spherical clusters, respectively. The number density profile in a planar axisymmetric cluster is also obtained numerically as a solution of the initial value problem for a canonical (Gaussian) initial condition. The numerical results compare well with theoretical predictions, and demonstrate the asymptotic stability of the similarity solution in two dimensions for long times, at least for axisymmetric initial conditions.

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Li, Fang, Jichun Liu et Yichao Yang. « Non-Planar Cluster Quivers from Surface ». Annals of Combinatorics 18, n^o 4 (13 novembre 2014) : 675–707. http://dx.doi.org/10.1007/s00026-014-0247-4.

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Hakula, Harri, et Mikael Laaksonen. « Subspace Reduction for Stochastic Planar Elasticity ». Applied Mechanics 3, n^o 1 (22 décembre 2021) : 1–13. http://dx.doi.org/10.3390/applmech3010001.

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Stochastic eigenvalue problems are nonlinear and multiparametric. They require their own solution methods and remain one of the challenge problems in computational mechanics. For the simplest possible reference problems, the key is to have a cluster of at the low end of the spectrum. If the inputs, domain or material, are perturbed, the cluster breaks and tracing of the eigenpairs become difficult due to possible crossing of the modes. In this paper we have shown that the eigenvalue crossing can occur within clusters not only by perturbations of the domain, but also of material parameters. What is new is that in this setting, the crossing can be controlled; that is, the effect of the perturbations can actually be predicted. Moreover, the basis of the subspace is shown to be a well-defined concept and can be used for instance in low-rank approximation of solutions of problems with static loading. In our industrial model problem, the reduction in solution times is significant.

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Schmelzer, Jürn W. P., et Azat O. Tipeev. « Effect of Planar Interfaces on Nucleation in Melting and Crystallization ». Entropy 24, n^o 8 (26 juillet 2022) : 1029. http://dx.doi.org/10.3390/e24081029.

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The effect of planar interfaces on nucleation (namely, on the work of critical cluster formation and their shape) is studied both for crystallization and melting. Advancing an approach formulated about 150 years ago by J. W. Gibbs for liquid phase formation at planar liquid–liquid interfaces, we show that nucleation of liquids in the crystal at crystal–vapor planar interfaces proceeds as a rule with a much higher rate compared to nucleation in the bulk of the crystal. Provided the surface tensions crystal–liquid (σcl), liquid–vapor (σlv), and crystal–vapor (σcv) obey the condition σcv=σcl+σlv, the work of critical cluster formation tends to zero; in the range σcv<σcl+σlv, it is less than one half of the work of critical cluster formation for bulk nucleation. The existence of a liquid–vapor planar interface modifies the work of critical cluster formation in crystal nucleation in liquids to a much less significant degree. The work of critical crystal cluster formation is larger than one half of the bulk value of the work of critical cluster formation, reaching this limit at σcv=σcl+σlv. The shape of the critical clusters can be described in both cases by spherical caps with a radius, R, and a width parameter, h. This parameter, h, is the distance from the cutting plane (coinciding with the crystal–vapor and liquid–vapor planar interface, respectively) to the top of the spherical cap. It varies for nucleation of a liquid in a crystal in the range (h/R)≤1 and for crystal nucleation in a liquid in the range 2≥(h/R)≥1. At σcv=σcl+σlv, the ratio (h/R) of the critical cluster for nucleation in melting tends to zero ((h/R)→0). At the same condition, the critical crystallite has the shape of a sphere located tangentially to the liquid–vapor interface inside the liquid ((h/R)≅2). We present experimental data which confirm the results of the theoretical analysis, and potential further developments of the theoretical approach developed here are anticipated.

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Yildirim, E. K. « 2D quasi-planar or 3D structures ? A comparison between CrBn(n = 2 − 10) wheel-like clusters and their corresponding 3D pyramidal clusters, and their hydrogen storage capability ». International Journal of Modern Physics B 29, n^o 24 (30 septembre 2015) : 1550172. http://dx.doi.org/10.1142/s0217979215501726.

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In this study, we investigated stable structures for a transition metal atom–boron (CrB) wheel-like clusters and compared them with their corresponding 3D counterparts by means of density functional theory (DFT). In addition, hydrogen storage capability of the wheel-like system was investigated. All simulations were performed at the B3LYP/TZVP level of theory. We set out a complete route to the formation of CrB wheel-like clusters. Our results showed that, some of the clusters, investigated in this work (CrBn; n = 4, 6, 7, 8), either prefer to be in a 3D geometry rather than 2D quasi-planar or planar geometry. However, hydrogen doping has an interesting effect on both 2D quasi-planar and 3D geometries of this system. Simply it transforms the 3D structure, first, into a 2D quasi-planar, then a planar geometry. Furthermore, our results show that H–cluster interaction is too high for reversible hydrogen storage for these clusters.

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Yang, Yue-Ju, Shi-Xiong Li, De-Liang Chen et Zheng-Wen Long. « Structural Evolution and Electronic Properties of Selenium-Doped Boron Clusters SeBn0/− (n = 3–16) ». Molecules 28, n^o 1 (1 janvier 2023) : 357. http://dx.doi.org/10.3390/molecules28010357.

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A theoretical research of structural evolution, electronic properties, and photoelectron spectra of selenium-doped boron clusters SeBn0/− (n = 3–16) is performed using particle swarm optimization (CALYPSO) software in combination with density functional theory calculations. The lowest energy structures of SeBn0/− (n = 3–16) clusters tend to form quasi-planar or planar structures. Some selenium-doped boron clusters keep a skeleton of the corresponding pure boron clusters; however, the addition of a Se atom modified and improved some of the pure boron cluster structures. In particular, the Se atoms of SeB7−, SeB8−, SeB10−, and SeB12− are connected to the pure quasi-planar B7−, B8−, B10−, and B12− clusters, which leads to planar SeB7−, SeB8−, SeB10−, and SeB12−, respectively. Interestingly, the lowest energy structure of SeB9− is a three-dimensional mushroom-shaped structure, and the SeB9− cluster displays the largest HOMO–LUMO gap of 5.08 eV, which shows the superior chemical stability. Adaptive natural density partitioning (AdNDP) bonding analysis reveals that SeB8 is doubly aromatic, with 6 delocalized π electrons and 6 delocalized σ electrons, whereas SeB9− is doubly antiaromatic, with 4 delocalized π electrons and 12 delocalized σ electrons. Similarly, quasi-planar SeB12 is doubly aromatic, with 6 delocalized π electrons and 14 delocalized σ electrons. The electron localization function (ELF) analysis shows that SeBn0/− (n = 3–16) clusters have different local electron delocalization and whole electron delocalization effects. The simulated photoelectron spectra of SeBn− (n = 3–16) have different characteristic bands that can identify and confirm SeBn− (n = 3–16) combined with future experimental photoelectron spectra. Our research enriches the geometrical structures of small doped boron clusters and can offer insight for boron-based nanomaterials.

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Ye, Fei, Hong Bo Xv, Jin Mei Liu et Ke Tong. « Effects of Uniaxial Strain on the Structures of Vacancy Clusters in FCC Metals ». Materials Science Forum 898 (juin 2017) : 1340–50. http://dx.doi.org/10.4028/www.scientific.net/msf.898.1340.

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The effects of [001] uniaxial strain on the stable structures and structural evolution of vacancy clusters in fcc metals, Cu, Ni, Al and Fe, have been studied and compared. Under uniaxial strain, the clusters in all these metals tend to align parallel or perpendicular to the strain axis under tensile or compressive strain. Moreover, both the body cluster and the {001} planar cluster become the dominant types. In addition, the stacking fault tetrahedron cluster becomes another dominant type in Al under compressive strain. The cluster structures in Fe are disordered under strain possibly because the pure fcc Fe is thermodynamically unstable under the current simulation condition.

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11

DANIEL, W. BRENT, ROBERT E. ECKE, G. SUBRAMANIAN et DONALD L. KOCH. « Clusters of sedimenting high-Reynolds-number particles ». Journal of Fluid Mechanics 625 (14 avril 2009) : 371–85. http://dx.doi.org/10.1017/s002211200900620x.

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We report experiments wherein groups of particles were allowed to sediment in an otherwise quiescent fluid contained in a large tank. The Reynolds number of the particles, defined as Re = aU/ν, ranged from 93 to 425; here, a is the radius of the spherical particle, U its settling velocity and ν the kinematic viscosity of the fluid. The characteristic size of a cluster, in a plane transverse to gravity, was measured by a ‘cluster variance’(〈r2t〉); the latter is defined as the mean square of the transverse coordinates of all constituent particles, averaged over a series of runs. The cluster variance, when plotted as a function of time, exhibited two regimes. There was a quadratic growth in the variance at short times(〈r2t〉 ∝ t2), while for long times, the cluster variance exhibited a slower sublinear growth with 〈r2t〉 ∝ t0.67. A theory, based on isotropic repulsive hydrodynamic interactions between particles, predicts the cluster variance to grow as t2/3 in the limit of long times. The theoretical framework was originally proposed to describe the long-time self-similar evolution of dilute clusters in the limit Re ≪ 1 Subramanian & Koch (J. Fluid Mech., vol. 603, 2008, p. 63), when the probability of wake-mediated interactions between particles remains asymptotically small; the latter requirement is satisfied for homogeneous spherical clusters larger than a critical radius, and is evidently satisfied for planar clusters oriented transversely to gravity. The isotropy of the interactions therefore stems from the isotropy, at large distances, of the disturbance velocity field produced by a single sedimenting particle outside its wake(which contains the compensating inflow to satisfy mass conservation). Herein, the theory is extended to large Re using an empirical correlation for the drag on a sedimenting particle. This allows one to predict, as a function of Re, the numerical prefactors in the expressions for the cluster variance of both spherical and planar clusters; the predictions for the growth exponent remain unchanged. The agreement between the theoretical and experimental growth exponents supports the hypothesis of a self-similar expansion at long times. The prefactor determined from the experimental observations is found to lie between the theoretical predictions for planar and spherical clusters.

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Zhou, Hong, Jun Qing Wen, Jun Feng Wang et Jun Fei Wang. « Study of Optical Characteristics of H₂S Molecule Adsorption on Ag_n (n=3,5) Clusters ». Advanced Materials Research 690-693 (mai 2013) : 611–14. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.611.

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All electronic structures and infrared adsorption spectra of AgnH2S (n=3, 5) clusters have been performed by using density functional theory. We obtain the lowest-energy structures of Ag3, Ag5, Ag3H2S and Ag5H2S clusters. The calculation results show that the lowest-energy structures of Ag3 and Ag5 clusters are planar geometries. The lowest-energy structures of Ag3H2S and Ag5H2S can be obtained by adsorbs immediately H2S on Ag3 and Ag5 clusters. The peak of infrared spectrum is 120cm-1 for Ag3 cluster, which is smaller than that of Ag5 cluster (180 cm-1). The peak of infrared spectrum is 350cm-1 for Ag3H2S cluster, which is larger than that of Ag5H2S cluster (290 cm-1). The comparison illustrates that adsorption H2S molecule make the peak of infrared spectrum shifting to shortwave.

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Eriksson, Henrik, Mikael Håkansson et Susan Jagner. « Pentamethylphenylcopper(I) : a square-planar tetranuclear cluster ». Inorganica Chimica Acta 277, n^o 2 (août 1998) : 233–36. http://dx.doi.org/10.1016/s0020-1693(97)06133-1.

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Schmitz, Sebastian, Tim Secker, Mariam Batool, Jan van Leusen, Muhammad Arif Nadeem et Paul Kögerler. « A planar decanuclear cobalt(II) coordination cluster ». Inorganica Chimica Acta 482 (octobre 2018) : 522–25. http://dx.doi.org/10.1016/j.ica.2018.06.005.

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15

Guo, Jin-Chang, Lin-Yan Feng, Jorge Barroso, Gabriel Merino et Hua-Jin Zhai. « Planar or tetrahedral ? A ternary 17-electron CBe5H4+ cluster with planar pentacoordinate carbon ». Chemical Communications 56, n^o 59 (2020) : 8305–8. http://dx.doi.org/10.1039/d0cc02973d.

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Planar or tetrahedral? Global searches discover a 17-electron CBe₅H₄⁺ cluster with planar pentacoordinate carbon. The 18-electron neutral features a tetrahedral carbon.

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Nhat, Pham Vu, Nguyen Thanh Si, Nguyen Ngoc Khanh Anh, Long Van Duong et Minh Tho Nguyen. « The Au12 Gold Cluster : Preference for a Non-Planar Structure ». Symmetry 14, n^o 8 (11 août 2022) : 1665. http://dx.doi.org/10.3390/sym14081665.

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The transition point from a two-dimensional (2D) to a three-dimensional (3D) structure in a series of small gold clusters remains a topic of continuing debate. In the present study, coupled-cluster CCSD(T) and DFT calculations are performed to re-examine the relative energies of several low-lying isomers of Au12, aiming to shed new light on this issue. At odds with many previous reports on the preference of a planar di-capped elongated-hexagon structure, the Au12 size is found to energetically prefer a globular cup-like form with C2v symmetry. While DFT results are not able to assign the most stable form of Au12 as the relative energies between the lowest-lying isomers are strongly functional-dependent, coupled-cluster theory calculations point out the preference of a 3D structure for having a D3h symmetry. Such a prediction is further supported by a comparison of the vibrational spectra computed using the revTPSS density functional with the available experimental infrared ones that were previously recorded from the far-IR multiple photon dissociation (FIR-MPD) experiment.

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Das, Prasenjit, et Pratim Kumar Chattaraj. « Structure and Bonding in Planar Hypercoordinate Carbon Compounds ». Chemistry 4, n^o 4 (15 décembre 2022) : 1723–56. http://dx.doi.org/10.3390/chemistry4040113.

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The term hypercoordination refers to the extent of the coordination of an element by its normal value. In the hypercoordination sphere, the element can achieve planar and/or non-planar molecular shape. Hence, planar hypercoordinate carbon species violate two structural rules: (i) The highest coordination number of carbon is four and (ii) the tetrahedral orientation by the connected elements and/or groups. The unusual planar orientations are mostly stabilized by the electronic interactions of the central atom with the surrounding ligands. In this review article, we will talk about the current progress in the theoretical prediction of viable planar hypercoordinate carbon compounds. Primary knowledge of the planar hypercoordinate chemistry will lead to its forthcoming expansion. Experimental and theoretical interests in planar tetracoordinate carbon (ptC), planar pentacoordinate carbon (ppC), and planar hexacoordinate carbon (phC) are continued. The proposed electronic and mechanical strategies are helpful for the designing of the ptC compounds. Moreover, the 18-valence electron rule can guide the design of new ptC clusters computationally as well as experimentally. However, the counting of 18-valence electrons is not a requisite condition to contain a ptC in a cluster. Furthermore, this ptC idea is expanded to the probability of a greater coordination number of carbon in planar orientations. Unfortunately, until now, there are no such logical approaches to designing ppC, phC, or higher-coordinate carbon molecules/ions. There exist a few global minimum structures of phC clusters identified computationally, but none have been detected experimentally. All planar hypercoordinate carbon species in the global minima may be feasible in the gas phase.

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Guo, Shihui, Yu Zhang, Ping Wang, Huang Tang, Wei Dai, Genquan Li, Jie Bi et Benchao Zhu. « Insights into the structural evolution and electronic properties of deficient-electron sodium chloride clusters ». Materials Express 10, n^o 9 (30 septembre 2020) : 1404–11. http://dx.doi.org/10.1166/mex.2020.1782.

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We have explored the structural evolution and electronic properties of cationic sodium chloride (NaCl)+n (n = 1–8) clusters. The global minimum of cationic (NaCl)+n clusters have been extensively searched using CALYPSO method combined with DFT calculations. The structural evolution of (NaCl)+n clusters can be divided into three stages: linear structure, planar ring-like structure and three-dimensional structure. It is worth to note that cuboid structure is more common in the cluster series as the cluster size increases. (NaCl)+4 clusters is identified as "magic number" clusters by means of the relative stabilities analyses. The following chemical bonding analysis indicate that the stability of (NaCl)+ 4cluster mainly comes from the interaction between Na 3s and Cl 3p atomic orbitals.

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Huang, Wei, Alina P. Sergeeva, Hua-Jin Zhai, Boris B. Averkiev, Lai-Sheng Wang et Alexander I. Boldyrev. « A concentric planar doubly π-aromatic B19− cluster ». Nature Chemistry 2, n^o 3 (24 janvier 2010) : 202–6. http://dx.doi.org/10.1038/nchem.534.

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Cheung, F., A. Samarian et B. James. « Angular Velocity Saturation in Planar Dust Cluster Rotation ». Physica Scripta T107, n^o 5 (2004) : 229. http://dx.doi.org/10.1238/physica.topical.107a00229.

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Stoyan, Dietrich, et Helga Stoyan. « Estimating Pair Correlation Functions of Planar Cluster Processes ». Biometrical Journal 38, n^o 3 (1996) : 259–71. http://dx.doi.org/10.1002/bimj.4710380302.

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Paolini, E., et A. Tamagnini. « Minimal cluster computation for four planar regions with the same area ». Geometric Flows 3, n^o 1 (1 avril 2018) : 90–96. http://dx.doi.org/10.1515/geofl-2018-0007.

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Abstract The topology of a minimal cluster of four planar regions with equal areas and smallest possible perimeter was found in [9]. Here we describe the computation used to check that the symmetric cluster with the given topology is indeed the unique minimal cluster.

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Pan, Sudip, José Luis Cabellos, Mesías Orozco-Ic, Pratim K. Chattaraj, Lili Zhao et Gabriel Merino. « Planar pentacoordinate carbon in CGa5+ derivatives ». Physical Chemistry Chemical Physics 20, n^o 18 (2018) : 12350–55. http://dx.doi.org/10.1039/c8cp01009a.

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IKESHOJI, T. « MOLECULAR DYNAMICS SIMULATION FOR THE CLUSTERING PROCESS BY TEMPERATURE CONTROL ». Surface Review and Letters 03, n^o 01 (février 1996) : 247–51. http://dx.doi.org/10.1142/s0218625x96000486.

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The clusterization process from gas states of Lennard–Jones (L–J) potential atom and water molecule of the TIP4P model was simulated by the molecular dynamics calculation with a constant-temperature thermostat at 0.1 (reduced unit) for the L–J atom system and at 200 K for the water molecule. The linear relationship between the logarithm of the populatlon and the cluster size was observed with no significant peak. The inner temperature of clusters was higher than the system temperature. Structure parameters derived from the inertia of clusters gave the following information on the structure. Clusters grow at first in linear or planar structure. Dipole interaction of water molecules favors more linear structure at the beginning of the cluster formation. Clusters around 13 L–J atoms become highly spherical and water clusters of 3–5 members become rings, after lowering of the temperature.

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Deka, Ajanta. « Preferential Sites for Adsorption of CO on Au6 Clusters Using Density Functional Theory Based Reactivity Descriptors ». Journal of Nanoscience and Nanotechnology 20, n^o 8 (1 août 2020) : 5288–93. http://dx.doi.org/10.1166/jnn.2020.18531.

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Nanoarchitectonics of neutral Au6 cluster upon addition and removal of one electron have been studied using density functional based reactivity descriptors. We studied the response of various sites of cationic, neutral and anionic Au6 clusters towards impending electrophilic and nucleophilic attacks using DFT based local reactivity descriptors, viz, Fukui function for nucleophilic attack f+. Fukui function for electrophilic attack f−, relative nucleophilicity f+/f− and relative electrophilicity f+/f−. Based on these parameters different types of unique atoms have been identified for each cluster. Reactivity predictions for the unique atoms of the minimum energy planar triangular Au6 structure have been verified by using CO as a probe molecule. It has been found adsorption of CO molecules on gold cluster brings about structural changes in the cluster and that the CO molecule prefers the apex site for adsorption onto the triangular Au6 cluster as compared to the mid site.

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Wang, Yong Juan, Jie Cheng, Xian Fang Yue et De Sheng Liu. « The Magnetism of DNA Molecular Materials ». Advanced Materials Research 306-307 (août 2011) : 46–49. http://dx.doi.org/10.4028/www.scientific.net/amr.306-307.46.

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In this paper, the atomic magnetic moments and spin-splittings of the six-member ring N2C4 cluster with planar and folding configurations in DNA bases are studied, respectively. The results show that the surprising interplay between the molecular structure and their magnetic property. In the planar configuration, the cluster exhibits antiferromagnetism and ferromagnetism in the ground state and metastable state, respectively. In the folding configuration, it exhibits antiferromagnetism and ferrimagnetism in the ground state and metastable state, respectively.

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Tang, Xiaoyan, Ye Xu, Wenpeng Ye, Yan Tang, Yunsheng Ma et Rongxin Yuan. « Mn(II)2Gd(III)3 Phosphonate as a Molecular Refrigerant ». Australian Journal of Chemistry 68, n^o 12 (2015) : 1926. http://dx.doi.org/10.1071/ch15520.

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3d-Gd phosphonate clusters are attractive for their potential applications as magnetic coolers. A new pentanuclear cluster [Mn(II)2Gd(III)3(OH)(dtbmfPO3)2(tBuCO2)8(HO2CtBu)(H2O)2]·HO2CtBu·CH3CN (1) (dtbmfPO3H2 = (2,7-di-tert-butyl-9-methyl-9H-fluoren-9-yl)phosphonic acid) has been synthesised and characterised. The cluster has a planar structure in which the trinuclear {MnGd2(OH)} and dinuclear {MnGdO2} units are joined together by two phosphonate groups. The magnetic studies reveal that 1 shows antiferromagnetic interactions and a large magnetocaloric effect (ΔS = 20.9 J kg–1 K–1 at ΔH = 7 T).

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Solar-Encinas, José, Alejandro Vásquez-Espinal, Luis Leyva-Parra, Osvaldo Yañez, Diego Inostroza, Maria Luisa Valenzuela, Walter Orellana et William Tiznado. « Planar Elongated B12 Structure in M3B12 Clusters (M = Cu-Au) ». Molecules 28, n^o 1 (28 décembre 2022) : 236. http://dx.doi.org/10.3390/molecules28010236.

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Here, it is shown that the M3B12 (M = Cu-Au) clusters’ global minima consist of an elongated planar B12 fragment connected by an in-plane linear M3 fragment. This result is striking since this B12 planar structure is not favored in the bare cluster, nor when one or two metals are added. The minimum energy structures were revealed by screening the potential energy surface using genetic algorithms and density functional theory calculations. Chemical bonding analysis shows that the strong electrostatic interactions with the metal compensate for the high energy spent in the M3 and B12 fragment distortion. Furthermore, metals participate in the delocalized π-bonds, which infers an aromatic character to these species.

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Pradeep, T., et N. Sandhyarani. « Structure and dynamics of monolayers on planar and cluster surfaces ». Pure and Applied Chemistry 74, n^o 9 (1 janvier 2002) : 1593–607. http://dx.doi.org/10.1351/pac200274091593.

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Organized molecular assemblies have been one of the intensely pursued areas of contemporary chemistry. Among the various methodologies used to make organized monolayer structures, self-assembled monolayers (SAMs) have been attractive to many materials chemists owing to the simplicity of the preparative method and high stability. Advances in various techniques and their application in the study of SAMs have significantly improved our understanding of these molecular systems. These studies have been further intensified since the successful preparation of stable metal clusters protected with monolayers. This article reviews the structure, temperature-induced phase transitions, and associated dynamics of monolayers, principally in the context of our own work in this area. Alkanethiols on Au(111) and Ag(111) are taken as archetypal systems to discuss the properties of 2D SAMs; studies from our laboratory have been on evaporated thin films. Alkanethiols on Au and Ag cluster surfaces are taken as examples of 3D SAMs. Although our principal focus will be on alkanethiols, we will touch upon a few other adsorbate systems as well.

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Scherer, K., A. Noack, J. Kleimann, H. Fichtner et K. Weis. « The interaction of multiple stellar winds in stellar clusters : potential flow ». Astronomy & ; Astrophysics 616 (août 2018) : A115. http://dx.doi.org/10.1051/0004-6361/201832696.

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Context. While several studies have investigated large-scale cluster winds resulting from an intra-cluster interaction of multiple stellar winds, as yet they have not provided details of the bordering flows inside a given cluster. Aims. The present work explores the principal structure of the combined flow resulting from the interaction of multiple stellar winds inside stellar clusters. Methods. The theory of complex potentials is applied to analytically investigate stagnation points, boundaries between individual outflows, and the hydrodynamic structure of the asymptotic large-scale cluster wind. In a second part, these planar considerations are extended to fully three-dimensional, asymmetric configurations of wind-driving stars. Results. We find (i) that one can distinguish regions in the large-scale cluster wind that are determined by the individual stellar winds, (ii) that there are comparatively narrow outflow channels, and (iii) that the large-scale cluster wind asymptotically approaches spherical symmetry at large distances. Conclusions. The combined flow inside a stellar cluster resulting from the interaction of multiple stellar winds is highly structured.

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Chen, Zilu, Yanling Shen, Lingling Li, Huahong Zou, Xiaoxiao Fu, Ziyuan Liu, Kai Wang et Fupei Liang. « High-nuclearity heterometallic clusters with both an anion and a cation sandwiched by planar cluster units : synthesis, structure and properties ». Dalton Transactions 46, n^o 43 (2017) : 15032–39. http://dx.doi.org/10.1039/c7dt02881d.

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Mealli, Carlo, Davide Maria Proserpio, Giuseppe Fachinetti, Tiziana Funaioli, Giovanni Fochi et Pier Francesco Zanazzi. « The electron-deficient planar tetrairon cluster octacarbonyltetrakis(pyridine)tetrairon ». Inorganic Chemistry 28, n^o 6 (mars 1989) : 1122–27. http://dx.doi.org/10.1021/ic00305a023.

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Garban, Christophe, Gábor Pete et Oded Schramm. « Pivotal, cluster, and interface measures for critical planar percolation ». Journal of the American Mathematical Society 26, n^o 4 (13 juin 2013) : 939–1024. http://dx.doi.org/10.1090/s0894-0347-2013-00772-9.

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Oger, Esther, Nathan R M. Crawford, Rebecca Kelting, Patrick Weis, Manfred M Kappes et Reinhart Ahlrichs. « Boron Cluster Cations : Transition from Planar to Cylindrical Structures ». Angewandte Chemie International Edition 46, n^o 44 (12 novembre 2007) : 8503–6. http://dx.doi.org/10.1002/anie.200701915.

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FUKUDA, Ryoji, et Nobuo TANAKA. « Cluster Control of a Distributed-Parameter Planar Structure Using Acoustic Cluster Filtering. Experimental Verification of Acoustic Cluster Filtering. » Transactions of the Japan Society of Mechanical Engineers Series C 69, n^o 678 (2003) : 371–78. http://dx.doi.org/10.1299/kikaic.69.371.

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Hudiyanti, Dwi, Tri Joko Raharjo, Narsito Narsito et Sri Noegrohati. « INVESTIGATION ON THE MORPHOLOGY AND PROPERTIES OF AGGREGATE STRUCTURES OF NATURAL PHOSPHOLIPIDS IN AQUEOUS SYSTEM USING CRYO-TEM ». Indonesian Journal of Chemistry 12, n^o 1 (14 février 2012) : 57–61. http://dx.doi.org/10.22146/ijc.21372.

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Cryogenic transmission electron microscopy (Cryo-TEM) was used to investigate the aggregates morphology and properties of candle tree (Aleurites moluccana) endosperm, sesame (Sesamum indicum L. syn.) seeds, and coconut (Cocos nucifera) endosperm phospholipids in dilute aqueous system. The micrographs showed that candle tree phospholipids formed planar bilayer and cluster of vesicles with lipid droplets, while coconut and sesame phospholipids formed well-defined unilamellar vesicles. The vesicles size could be as small as 50 nm in diameter. Coconut phospholipids also showed a good bending ability. Formation of clusters of vesicles was also found in coconut phospholipids dispersion, but this cluster was easily broken by extrusion through a small pore membrane.

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Wang, Chao Gang, Xin Zhang et Ke Han. « A Study of the Model which Can Improve LEACH Protocol ». Applied Mechanics and Materials 721 (décembre 2014) : 736–39. http://dx.doi.org/10.4028/www.scientific.net/amm.721.736.

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In the application process of wireless sensor network, LEACH protocol solves the problem of data fusion well, and reduces data exchanges between nodes and bases. Based on the research, this paper proposes an advanced LEACH protocol, which is fused by the data of cluster head, and each time when transmits data to the neighbor shortest cluster head, this protocol gets reduction in the aspects of theoretical existing and energy consumption, and improvement in using efficiency. The LEACH protocol Low Energy Adaptive Clustering Hierarchy (LEACH) [1] is designed by Hein Zelman W et al from college of electronic engineering and computer science of MIT University for the wireless sensor network. The protocol divides all nodes in the network into several clusters, in which the cluster members are responsible for the collection of user needs in the news, and the cluster head is responsible for the management of cluster member cluster members, for the allocation of communication time slot to receive the cluster members messages, and these messages are forwarded to fusion processing, the processed data to the base station node. Compared with the planar routing, the cluster structure through data fusion, can eliminate redundant data, reduce network traffic, effectively save energy, and prolong the network survival time. But the protocol still has some problems, such as the burden of cluster heads is too heavy, more energy consumption, cost of frequent building clusters bring and network load balancing.

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ESRAFILI, MEHDI D., FATEMEH ELMI et NASSER L. HADIPOUR. « DENSITY FUNCTIONAL THEORY STUDY OF BINDING ENERGIES, 7Li NUCLEAR MAGNETIC SHIELDING, AND ELECTRIC FIELD GRADIENT TENSORS ON THE SMALL CLUSTERS OF LinHm (m ≤ n ≤ 4) ». Journal of Theoretical and Computational Chemistry 06, n^o 04 (décembre 2007) : 959–73. http://dx.doi.org/10.1142/s021963360700343x.

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The binding energies, geometries, 7 Li magnetic shielding, and electric field gradient tensors of hydrogenated lithium clusters, Li n H m (m ≤ n ≤ 4), were studied via density functional theory approach. We optimized the structures using B3LYP functional and 6-311++G (2d,2p) basis set. The calculated binding energies of lithium hydride clusters indicate that hydrogenation energy of Li n H m clusters decreases as the number of hydrogen atoms within the cluster increases. Our calculations also showed that for n = 4 clusters, the three-dimensional structure is more stable than the planar one. The study of the trends in the 7 Li magnetic shielding isotropy, σiso, and anisotropies, Δσ, values are explained in terms of the interplay between the electronic and geometrical effects. The variations in the 7 Li nuclear quadrupole coupling constants, χ, and their associated asymmetry parameters, ηQ, for different isomers of the lithium hydride clusters and the influence of hydrogenation on the EFG tensors are also discussed. For n = 4, we obtained a noticeable difference in the χ value from the planar to the three-dimensional structures. The atoms in molecules (AIM) analysis at the Li–H bond critical point reveals remarkably different topographical properties of the charge density and associated Laplacian fields for the planar and three-dimensional lithium hydride clusters.

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Carotenuto, G., S. De Nicola et L. Nicolais. « Fluorescent Thiol-Derivatized Gold Clusters Embedded in Polymers ». Advances in Materials Science and Engineering 2013 (2013) : 1–6. http://dx.doi.org/10.1155/2013/548284.

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Owing to aurophilic interactions, linear and/or planar Au(I)-thiolate molecules spontaneously aggregate, leading to molecular gold clusters passivated by a thiolate monolayer coating. Differently from the thiolate precursors, such cluster compounds show very intensive visible fluorescence characteristics that can be tuned by alloying the gold clusters with silver atoms or by conjugating the electronic structure of the metallic core with unsaturated electronic structures in the organic ligand through the sulphur atom. Here, the photoluminescence features of some examples of these systems are shortly described.

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Nhat, Pham Vu, Nguyen Thanh Si, Nguyen Thi Nhat Hang et Minh Tho Nguyen. « The lowest-energy structure of the gold cluster Au₁₀ : planar vs. nonplanar ? » Physical Chemistry Chemical Physics 24, n^o 1 (2022) : 42–47. http://dx.doi.org/10.1039/d1cp04440k.

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Stamatovic, Biljana, et Goran Kilibarda. « Algorithm for Identification of Infinite Clusters Based on Minimal Finite Automaton ». Mathematical Problems in Engineering 2017 (2017) : 1–7. http://dx.doi.org/10.1155/2017/8251305.

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We propose a finite automaton based algorithm for identification of infinite clusters in a 2D rectangular lattice with L=X×Y cells. The algorithm counts infinite clusters and finds one path per infinite cluster in a single pass of the finite automaton. The finite automaton is minimal according to the number of states among all the automata that perform such task. The correctness and efficiency of the algorithm are demonstrated on a planar percolation problem. The algorithm has a computational complexity of O(L) and could be appropriate for efficient data flow implementation.

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Yamaguchi, Tadashi, Nozomu Nishimura, Ken-ichi Shirakura et Tasuku Ito. « Triangular Platinum(II) Cluster Complexes and Cluster Core Transformation from Square-Planar to Triangular Type ». Bulletin of the Chemical Society of Japan 73, n^o 4 (avril 2000) : 775–84. http://dx.doi.org/10.1246/bcsj.73.775.

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Sizov, N. E., S. P. Pozdniakov et N. N. Muromets. « Impact of planned heterogeneity of hydraulic conductivity on the results of pumping in an isolated unconfined layer ». Moscow University Bulletin. Series 4. Geology 1, n^o 3 (28 janvier 2022) : 113–23. http://dx.doi.org/10.33623/0579-9406-2021-3-113-123.

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The paper presents the results of numerical simulation of cluster pumping test in an heterogeneous aquifer with transmissivtyvariability described by the model of a stationary random field of its logarithm with a given scale of correlation in the plan. The case of comparable planar distance to observation wells and correlation scale is considered. Parameters of the model of transmissivity heterogeneity of the simulated aquifer are obtained from the data of experimental tests carried out within the limits of the South Voronezhskoye groundwater field. The simulation has shown that the average results of interpretation of these cluster pumping data correspond to the geometric value of the transmissivity, which confirms the previously obtained approximate theoretical result for the model of small-scale heterogeneity and extends it to an almost important case of similarity of cluster well test planar sizes and spatial scale of heterogeneity. Thus, the present study has confirmed the possibility to apply standard methods in processing of cluster pumping data under planned heterogeneity conditions to estimate the equivalent aquifer transmissivity in the well cluster location area.

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Sun, Rui, Bo Jin, Bin Huo, Caixia Yuan, Hua-Jin Zhai et Yan-Bo Wu. « Planar pentacoordinate carbon in a sulphur-surrounded boron wheel : the global minimum of CB₅S₅⁺ ». Chemical Communications 58, n^o 15 (2022) : 2552–55. http://dx.doi.org/10.1039/d1cc07313c.

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Chkhartishvili, Levan. « Relative stability of planar clusters B11, B12, and B13 in neutral- and charged-states ». Characterization and Application of Nanomaterials 3, n^o 2 (20 juillet 2020) : 73. http://dx.doi.org/10.24294/can.v3i2.761.

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Theoretically, within the diatomic model, the relative stability of most abundant boron clusters B11, B12, and B13 with planar structures in neutral, positive and negative charged-states is studied. According to the specific (per atom) binding energy criterion, B12+ (6.49 eV) is found to be the most stable boron cluster, while B11– + B13+ (5.83 eV) neutral pair is expected to present the preferable ablation channel for boron-rich solids. Obtained results would be applicable in production of boron-clusters-based nanostructured coating materials with super-properties such as lightness, hardness, conductivity, chemical inertness, neutron-absorption, etc., making them especially effective for protection against cracking, wear, corrosion, neutron- and electromagnetic-radiations, etc.

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Pham, Hung Tan, Jules Tshishimbi Muya, Fernando Buendía, Arnout Ceulemans et Minh Tho Nguyen. « Formation of the quasi-planar B50 boron cluster : topological path from B10 and disk aromaticity ». Physical Chemistry Chemical Physics 21, n^o 13 (2019) : 7039–44. http://dx.doi.org/10.1039/c9cp00735k.

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The lowest-lying isomer of the B₅₀ boron cluster is confirmed to have a quasi-planar shape with two hexagonal holes. This cluster is derived from a topological (leapfrog) path from B₁₀ and its high thermodynamical stability is due to a disk aromaticity.

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Duminil-Copin, Hugo, et Vincent Tassion. « Renormalization of Crossing Probabilities in the Planar Random-Cluster Model ». Moscow Mathematical Journal 20, n^o 4 (2020) : 711–40. http://dx.doi.org/10.17323/1609-4514-2020-20-4-711-740.

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Rahane, Amol B., et Vijay Kumar. « B84 : a quasi-planar boron cluster stabilized with hexagonal holes ». Nanoscale 7, n^o 9 (2015) : 4055–62. http://dx.doi.org/10.1039/c4nr06026a.

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Tanaka, Nobuo, Ryoji Fukuda et Colin H. Hansen. « Acoustic cluster control of noise radiated from a planar structure ». Journal of the Acoustical Society of America 117, n^o 6 (juin 2005) : 3686–94. http://dx.doi.org/10.1121/1.1920187.

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Kalita, Amlan J., Shahnaz S. Rohman, Chayanika Kashyap, Sabnam S. Ullah, Indrani Baruah et Ankur K. Guha. « Planar Pentacoordinate Nitrogen in a Pseudo-Double-Aromatic NBe5H4+ Cluster ». Inorganic Chemistry 59, n^o 24 (10 décembre 2020) : 17880–83. http://dx.doi.org/10.1021/acs.inorgchem.0c03045.

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