Carbon clusters: From ring structures to nanographene

The lowest energy configurations of Cn(n =< 55) clusters are obtained using the energy mini- mization technique with the conjugate gradient (CG) method where a modified Brenner potential is invoked to describe the carbon and hydrocarbon interaction. We found that the ground state configuration consists of a single ring for small number of C atoms and multi-ring structures are found with increasing n, which can be in planar, bowl-like or cap-like form. Contrary to previous predictions, the binding energy Eb does not show even-odd oscillations and only small jumps are found in the Eb(n) curve as a consequence of specific types of edges or equivalently the number of secondary atoms. We found that hydrogenation of the edge atoms may change the ground state configuration of the nanocluster. In both cases we determined the magic clusters. Special attention is paid to trigonal and hexagonal shaped carbon clusters and to clusters having a graphene-like configuration. Trigonal clusters are never the ground state, while hexagonal shaped clusters are only the ground state when they have zigzag edges.Comment: Accepted for publication in Phys. Rev.

Theoretical study of the stable states of small carbon clusters Cn (n = 2-10)

Both even- and odd-numbered neutral carbon clusters Cn (n = 2-10) are systematically studied using the energy minimization method and the modified Brenner potential for the carbon-carbon interactions. Many stable configurations were found and several new isomers are predicted. For the lowest energy stable configurations we obtained their binding energies and bond lengths. We found that for n < 6 the linear isomer is the most stable one while for n > 5 the monocyclic isomer becomes the most stable. The latter was found to be regular for all studied clusters. The dependence of the binding energy for linear and cyclic clusters versus the cluster size n (n = 2-10) is found to be in good agreement with several previous calculations, in particular with ab initio calculations as well as with experimental data for n = 2-5.Comment: Submitted to Phys. Rev.

Upheaval buckling of underground pipelines of complex configuration located in liquefied soils

The problem of loss of stability of underground pipelines with a middle part in the form of a straight or П-shaped part located in liquefied soils is considered in the article. The pipeline lifting process occurs under the action of buoyancy force in the liquefied soil zone and then under the action of the longitudinal compressive force that appears due to the temperature of the transported product and its pressure. The problem is solved by the finite element method. The results are presented as a table and graphs of changes in the values of transverse displacements along the coordinate depending on the pipeline geometric characteristics and the soil rheological properties. It is established that the П-shaped part is a damper against pipeline buckling

First-principles modeling of the polycyclic aromatic hydrocarbons reduction

Density functional theory modelling of the reduction of realistic nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen evidences for the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase of the binding energy between nanographenes during reduction is also discussed as possible cause of the experimentally observed limited hydrogenation of studied nanographenes.Comment: 18 pages, 7 figures, accepted to J. Phys. Chem.

The concept of peace and man in the Uzbek and Russian literature of the 20th century

This article is about mutual relations between Uzbek and Russian literature and also is about development tendencies of small prose in the 60 th - 80 th years of XX th centur

The concept of peace and man in the Uzbek and Russian literature of the 20th century

This article is about mutual relations between Uzbek and Russian literature and also is about development tendencies of small prose in the 60 th - 80 th years of XX th centur

THE GROWTH AND DEVELOPMENT OF RASPBERRY CULTIVARS IN THE CONDITION OF UZBEKISTAN

In the article during the growing season the occurence of phenological phases, the buds formation, buds opening, the beginning of flowering, full flowering and the duration and the end of flowering, the time of flowering and the condition of the plants of the raspberry cultivars grown in Uzbekistan are evaluated in points. The results of research to study the beginning of fruit ripening, full ripening, the differences and quality indicators of fruits, the average and maximum weight of the fruit, acidity and sugar content of the fruit are given. Raspberry cultivars with high yields, depending on the ripening period of the fruit, are also recommended herei

Combined Tillage Unit

Based on the test results, a section of working bodies was selected for strip tillage, the height, the length of the soil-shifting plate of its flat-cutting paw and the angle of attack of the disks were determined experimentally. As well as the test results showed that the most acceptable for strip tillage is a combination of working bodies, consisting of a one-sided flat-cutting paws with a soil-shifting plate, a pointed arm and a pair of disk working bodies, providing high rates of soil crumbling quality and leveling of the surface of the treated strips, as well as cleansing them of stubble and roots