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

The evolution of early Spermophilus in eastern Europe and the antiquity of the Old World ground squirrels

Spermophilus is the most diverse and abundant genus of Eurasian sciurids. Even though many species have been described, the early evolution of the group is poorly understood. Here we present a review of the evolution and taxonomy of early Spermophilus, based on analysis of more than 1500 specimens from the late Pliocene and Early–Middle Pleistocene of Ukraine and European Russia, representing the most complete and continuous fossil record of the early Old World ground squirrels known to date. In addition to documenting previously unpublished specimens of Spermophilus nogaici, we describe a new species, Spermophilus praecox sp. nov., the oldest member of the genus, from the late Pliocene and Early Pleistocene (middle Villanyian to earliest Biharian) of southern Ukraine. It is intermediate in size between a somewhat smaller Spermophilus nogaici and larger Spermophilus polonicus and Spermophilus primigenius. Morphologically, the new species can be distinguished from all known Spermophilus by the retention of primitive traits including a small P3; rudimentary lingual metaloph; large metaconule and mesostyle; presence of P4–M2 endoloph; and premolariform p4 lacking a lingual metalophid. The patterns of dental evolution in eastern European early Spermophilus throughout 2.15 My indicates the existence of a single gradually evolving S. praecox–S. nogaici lineage characterized by a decrease of molar size but enlargement of premolars; the tendency toward high-crowned teeth with more expanded anterior and reduced posterior lobes; well-developed transverse ridges and anterostyles; reduced endolophs, anteroconules, metaconules, and mesostyles of P4–M2; molariform p4; complete m1–m2 metalophids; and stronger m3 hypoconid, hypoconulid, and entoconulid. Dental character regression suggests that Spermophilus evolved from a relatively large-sized sciurid having generalized Otospermophilus-like dentition, probably an unknown North American member of stem Marmotina. Copyright © 2019 M.V. Sinitsa and N.V. Pogodina. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Government Council on Grants, Russian FederationWe would like to thank Dmitry V. Ivanoff, Oleksandr M. Kovalchuk, Vadym O. Yanenko (all National Museum of Natural History, Kiev, Ukraine), Olga V. Makarova (Zoological Institute of the Russian Academy of Sciences, Saint Petersburg, Russia), Mihály Gasparik and Piroska Pazonyi (both Hungarian Museum of Natural History, Budapest, Hungary) for access and guidance during MVS’s visits to their respective institutions. We are also grateful to Alexey S. Tesakov (Geological Institute of the Russian Academy of Sciences, Moscow, Russia) for discussions on fossil ground squirrels and southern Ukraine stratigraphy. Finally, we thank Thomas H. Goodwin (Andrews University, Berrien Springs, USA), William W. Korth (Rochester Institute of Vertebrate Paleontology, New York, USA), and the Editor, Olivier Lambert (Royal Belgian Institute of Natural Sciences, Brussels, Belgium) for their constructive comments that greatly improved the manuscript. The research was supported by Act 211 of the Government of the Russian Federation, contract No. 02.A03.21.0006; and by INQUA Project 1606:‘Ground Squirrels on the March: Expansion and Speciation in the Quaternary of the Circum-Pontic Area and Surroundings’

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

New Bryokhutuliinia species (bryophyta) with sporophytes from the upper jurassic of Transbaikalia

A new species of the moss genus Bryokhutuliinia, B. crassimarginata is described from the Upper Jurassic deposits from the Olov, Transbaikal Area of South Siberia. Its excellent preservation demonstra- tes that the leaves were not only complanate, but truly distichous. In addition to anatomically pre- served gametophytes, sporophytes on short lateral branches were found, although carbonized and not exhibiting structural details. Possible relationships with pleurocarpous mosses and with Fissidentaceae are discussedyesBelgorod State National Research Universit

Squirrels (Rodentia, Sciuridae) of the Early Miocene Tagay fauna in Eastern Siberia

The Tagay vertebrate fauna (Olkhon Island, Lake Baikal, Russia) dated to the late Early Miocene yielded a diverse association of sciurine rodents, including flying squirrel Hylopetes sp., tree squirrels Sciurus cf. lii, Sciurus sp., and Blackia cf. miocaenica, and a numerically dominant small marmotine Miospermophilus debruijni. The presence of flying and tree squirrels indicates the presence of wooded biotopes. The record of Blackia is remarkably distant (more than 4000 km) from the nearest synchronous records in western Asia (Anatolia) and Eastern Europe thus implying a continuous distribution range of this genus stretching through the middle latitudes of the Holarctic and likely marking the continental belt of temperate forests in late Early Miocene. Marmotines of North American origin document direct faunal communication between temperate faunas of the Old and New Worlds at that time. © 2023 Sinitsa and Tesakov.Russian Foundation for Basic Research, РФФИ: 14-04-00575; Russian Science Foundation, RSF: 23-24-00267The research was supported by the project of the Russian Science Foundation, no. 23-24-00267.Funding: The research was supporte

A Jurassic ornithischian dinosaur from Siberia with both feathers and scales

Feathers, not just for the birds? Theropod dinosaurs, thought to be the direct ancestors of birds, sported birdlike feathers. But were they the only feathery dino group? Godefroit et al. describe an early neornithischian dinosaur with both early feathers and scales. This seemingly feathery nontheropod dinosaur shows that feathers were not unique to the ancestors of birds and may even have been quite widespread. Science , this issue p. 451 </jats:p

Study (301)-(000) D2O band in 10200 - 10450 cm-1 spectral region

Measurements of D2O absorption spectra in the visible spectral region near 0.98 μm are performed using FT-spectrometer IFS-125M and Light-emitting diode (LED) as source of radiation. Water vapor spectrum has been obtained by averaging over 17136 scans recorded at 24 m optical path length, temperature 24 С and pressure of sample 27 mBar. Due to strong emission of LED source it was possible to achieve signal-to-noise ratio about 104 and to record weak lines with intensities of 6 10-27 cm/molecule. Comparisons with results of early works are made. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Palynology of Middle Jurassic deposits from the Kulinda locality (Transbaikalia): Biostratigraphy and biofacies

The Kulinda section belongs to the base of the Ukurey Formation in the Orlov Depression (Transbaikalia). The site has yielded numerous bones and associated integumentary structures belonging to the primitive ornithischian dinosaur. However, the age of the Kulinda deposits has not been investigated in detail so far. Palynological studies discussed in this paper clarify this question and provide the data on the palaeoenvironments. The Kulinda section is composed of siltstone and sandstone with admixture of volcanogenic material. Ten samples were collected from the bone-bearing deposits as well as the underlying and overlying sediments. The samples were treated by 15% hydrochloric and 30% hydrofluoric acids. Mineral and organic matters were separated by centrifugation in cadmium heavy liquid with specific gravity 2.25. Spore-pollen assemblage contains the species, which are important for Middle Jurassic stratigraphy: Podocarpidites rousei Pocockand, Eboraciato rosa (Sachanova et Iljina) Timochina. Their lowermost occurrences are revealed in the Bathonian in Western Siberia (Palynozone 10) and Kansk-Achinsk basin. The domination of Pseudopicea variabiliformis Bolchovitina and abundant Cyathidites are also characteristic features of the Bathonian of Western Siberia. Palynological zones in this region are calibrated against ammonite Boreal standard and foraminiferal successions that give the reliable age constraints. Spore-pollen assemblage from the Kulinda section shows that neighboring areas were occupied by coniferous forests with an admixture of pteridosperms, podocarpaceans and ginkgoaleans. More humid habitats near the lake were mostly occupied by cyatheaceous/dipteridaceous ferns. The climate was temperate and rater humid. The water genesis of deposits is confirmed by the presence of green algae Botryococcus and Leiosphaeridia. The age of the Ukurey Formation was broadly regarded as the Late Jurassic according to palaeontological data, isotope dating and its general position in the section. New palynological data show that its lower stratigraphic extend is wider, than it is was assumed earlier, and changed over the territory. The Bathonian age of the Ukurey Formation does not contradict to the general geological situation in Transbaikalia. Biofacial analysis confirms lacustrine genesis of the Ukurey Formation and evidences temperate warm and rather humid conditions on the nearby land areas