Transformation of amorphous carbon clusters to fullerenes

Transformation of amorphous carbon clusters into fullerenes under high temperature is studied using molecular dynamics simulations at microsecond times. Based on the analysis of both structure and energy of the system, it is found that fullerene formation occurs in two stages. Firstly, fast transformation of the initial amorphous structure into a hollow sp$^2$ shell with a few chains attached occurs with a considerable decrease of the potential energy and the number of atoms belonging to chains and to the amorphous domain. Then, insertion of remaining carbon chains into the sp$^2$ network takes place at the same time with the fullerene shell formation. Two types of defects remaining after the formation of the fullerene shell are revealed: 7-membered rings and single one-coordinated atoms. One of the fullerene structures obtained contains no defects at all, which demonstrates that defect-free carbon cages can be occasionally formed from amorphous precursors directly without defect healing. No structural changes are observed after the fullerene formation, suggesting that defect healing is a slow process in comparison with the fullerene shell formation. The schemes of the revealed reactions of chain atoms insertion into the fullerene shell just before its completion are presented. The results of the performed simulations are summarized within the paradigm of fullerene formation due to selforganization of the carbon system.Comment: 35 pages, 9 figure

Formation of nickel-carbon heterofullerenes under electron irradiation

arXiv.-- et al.A way to produce new metal-carbon nanoobjects by transformation of a graphene flake with an attached transition metal cluster under electron irradiation is proposed. The transformation process is investigated by molecular dynamics simulations by the example of a graphene flake with a nickel cluster. The parameters of the nickel-carbon potential (I. V. Lebedeva et al., J. Phys. Chem. C, 2012, 116, 6572) are modified to improve the description of the balance between the fullerene elastic energy and graphene edge energies in this process. The metal-carbon nanoobjects formed are found to range from heterofullerenes with a metal patch to particles consisting of closed fullerene and metal clusters linked by chemical bonds. The atomic-scale transformation mechanism is revealed by the local structure analysis. The average time of formation of nanoobjects and their lifetime under electron irradiation are estimated for the experimental conditions of high-resolution transmission electron microscopy (HRTEM). The sequence of images of nanostructure evolution with time during its observation by HRTEM is also modelled. Furthermore, the possibility of batch production of studied metal-carbon nanoobjects and solids based on these nanoobjects is discussed.AS, IL, AK and AP acknowledges Russian Foundation of Basic Research (14-02-00739-a). AP acknowledges Samsung Global Research Outreach Program. IL acknowledges support from the Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme (Grant Agreement PIIF-GA-2012-326435 RespSpatDisp), Grupos Consolidados del Gobierno Vasco (IT-578-13) and the computational time on the Supercomputing Center of Lomonosov Moscow State University and the Multipurpose Computing Complex NRC “Kurchatov Institute.” EB acknowledges EPSRC Career Acceleration Fellowship, New Directions for EPSRC Research Leaders Award (EP/G005060), and ERC Starting Grant for financial support.Peer Reviewe

Manifestations of politeness and power in problem-solving business telephone calls

The article features some of the research findings obtained during an analysis of patterns of polite behaviour typical of subordinate and superior speakers in business telephone settings. The overall objective of the research was to describe how politeness manifests itself in opening, message and closing routines of business telephone calls and what factors play out in the choice of politeness strategies. The aims of the research presuppose the solution of the following research questions. Is there any discernible correlation between the degree of politeness and the social factor of power/social role in problem-solving business telephone interaction? Does the ranking of imposition affect the use of politeness? How does the setting affect politeness? What impact does the business telephone call environment and its restrictions have on patterns of polite behaviour? Are patterns of politeness different in different problem-solving call routines? The study is conducted within the framework of the lingua-pragmatic, socio-cultural and conversation analyses. The research methods include data collection, observation, quantitative analysis, comparative analysis, and evaluation. The corpus used for the analysis features samples of authentic problem-solving business telephone interaction which include transcripts of task-oriented calls made in the workplace. The materials have been obtained from the audio sections of Business English textbooks. The analysis reinforces assumptions about the heterogeneity of business telephone interaction. Manifestations of politeness show a lot of variability and dependence on a vast range of variables, including social (power / acquired social role, distance between the interactants, gender). The opening and closing routines of problem-solving calls are inherently formulaic and show the interactants’ adherence to positive politeness. The message part is more task-oriented and structurally complex, hence the greater diversity of patterns of polite behaviour observed here

Interlayer interaction, shear vibrational mode, and tribological properties of two-dimensional bilayers with a commensurate moir\'e pattern

The potential energy surface (PES) of interlayer interaction of infinite twisted bilayer graphene is calculated for a set of commensurate moir\'e patterns using the registry-dependent Kolmogorov-Crespi empirical potential. The calculated PESs have the same shape for all considered moir\'e patterns with the unit cell size of the PES which is inversely related to the unit cell size of the moir\'e pattern. The amplitude of PES corrugations is found to decrease exponentially upon increasing the size of the moir\'e pattern unit cell. An analytical expression for such a PES including the first Fourier harmonics compatible with the symmetries of both layers is derived. It is shown that the calculated PESs can be approximated by the derived expression with the accuracy within 1%. This means that different physical properties associated with relative in-plane motion of graphene layers are interrelated and can be expressed analytically as functions of the amplitude of PES corrugations. In this way, we obtain the shear mode frequency, shear modulus, shear strength and barrier for relative rotation of the commensurate twisted layers to a fully incommensurate state for the considered moir\'e patterns. This barrier may possibly lead to the macroscopic robust superlubricity for twisted graphene bilayer with a commensurate moir\'e pattern. The conclusions made should be valid for diverse 2D systems of twisted commensurate layers.Comment: 9 pages, 3 figures; Supplemental Material: 2 pages, 1 figur

Innovation Development of an Enterprise: Modeling Dynamics

At the present stage of economic development, the leading role in ensuring the competitiveness of both an singular enterprise and the country as a whole, as well as in creating conditions for the transition to sustainable development, is played by the successful implementation of the latest scientific developments in production processes, comprehensive support for the strategy of innovative development. The development and implementation of innovations is a complex dynamic process that requires the use of special research methods. Such a method is system dynamics, which makes it possible to take into account the nonlinearity of the impact of innovation on the state of the economy. The paper considers the methodology for building a model for managing innovation processes, taking into account the self-organization of the logistic type. The main danger that can accompany the evolution of innovation processes is the emergence of unacceptable dynamic modes, so one of the tasks of the study was to determine the conditions capable of ensuring the stability of equilibrium states of a complex dynamic system according to the proposed models. The object of research is a complex dynamic system, between the elements of which there is both positive and negative feedback. To build a model of the dynamics of innovation processes, the mathematical apparatus of the theory of differential equations was applied, which made it possible to consider the development of the innovation process in continuous time. With the help of the instrumentarium of nonlinear dynamics, a study of the stability of diffusion of innovations depending on the parameters of the control influence was carried out. The conditions for the transition of the system to a critical state, which may be accompanied by the occurrence of bifurcations and chaos, have been determined. Particular attention was paid to determining the structural stability of the regulated innovation process in the case when both equilibrium positions are close in terms of parameter values. It is expedient to apply the proposed model to solve the problem of innovation management both at the State level and at the level of an individual industry or an individual enterprise. The obtained theoretical conclusions were confirmed through the use of simulation modeling

Nanotube-Based NEMS: Control vs. Thermodynamic Fluctuations

Multi-scale simulations of nanotube-based nanoelectromechanical systems (NEMS) controlled by a nonuniform electric field are performed by an example of a gigahertz oscillator. Using molecular dynamics simulations, we obtain the friction coefficients and characteristics of the thermal noise associated with the relative motion of the nanotube walls. These results are used in a phenomenological one-dimensional oscillator model. The analysis based both on this model and the Fokker-Planck equation for the oscillation energy distribution function shows how thermodynamic fluctuations restrict the possibility of controlling NEMS operation for systems of small sizes. The parameters of the force for which control of the oscillator operation is possible are determined.Comment: 40 pages, 12 figure

The effect of zinc complex of N-isopropenylimidazole on the morphological characteristics of gum tissues in experimental endodontic-periodontal lesions in rats Authors

Introduction: Combined inflammatory and destructive processes affecting the dental pulp and tissues of the periodontal complex are among the most problem diseases of the dental system. Current therapy with use of available pharmacological agents does not always allow achieving the expected positive result. In addition, often the lack of information about morphological processes in the tissues of the dental system, in particular the gums, with endodontic-periodontal lesion (EPL) limits the ability of dentists to carry out targeted pharmacotherapy with both traditional and, in particular, new medications. The aim of the study was to evaluate the morphological characteristics of gum tissues in a therapeutic context of N-isopropenylimidazole zinc complex derivative in experimental endodontic-periodontal lesion in rats. Materials and Methods: A simulation of EPL in rats was performed in two ways: simultaneous induction of acute periodontitis and parodontitis by pulp extraction and natural infection of the pulp cavity, as well as by ligation of the necks of lower incisors. The research protocols included 5 groups of animals: 1st – intact group (control-1); 2nd – animals with simulated EPL (control-2); 3rd – animals with simulated EPL and treated with Metrogyl Denta® gel (M-D); 4th – animals with simulated EPL and treated with N–isopropenylimidazole zinc complex derivative gel under the laboratory code Pilim-1; and 5th – animals with simulated EPL and treated with the combination of M-D + Pilim-1. The gum of the lower incisors was taken for morphological studies. Slides were stained with hematoxylin and eosin. Computer morphometry was performed using the ImageJ software. Results and Discussion: The substances M-D, Pilim-1 and, especially, the combination of M-D+Pilim-1 (against the background of chlorhexidine bigluconate used as oral rinse) for 14 days in rats with simulated EPL cause a significant improvement of the morphological structure of the gum with minimal residual dystrophy and sclerosis. The combination M-D + Pilim-1 led to a 1.3-time increase in epithelial thickness, and a 1.5-time decrease in acanthosis depth in comparison with M-D, while the number of capillaries and their diameter had no significant differences. Compared with Pilim-1, the epithelial thickness increased 1.5 times, and the acanthosis depth and the number of capillaries decreased 1.6 and 1.4 times, respectively, whereas the diameter of the capillaries did not change significantly. The pronounced protective effect of the combination M-D + Pilim-1 on the morphological structure of the gingival mucosa of rats with simulated EPL may be associated with antimicrobial, anti-inflammatory, regenerating, angioprotective and antioxidant properties of both M-D and Pilim-1 separately, and, possibly to a greater extent, of the combination M-D + Pilim-1. Conclusion: The substances M-D, Pilim-1 and, especially, the combination M-D + Pilim-1 (against the background of chlorhexidine bigluconate used as oral rinse) for 14 days in rats with simulated EPL have a protective effect on the epithelial structure and the connective tissue of the proper mucous plate, manifested in active normalization of pathological changes and significant restoration of their organotypic structure