Oxidation of graphene on metals

We use low-energy electron microscopy to investigate how graphene is removed from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding Ru surface, decreasing their concentration below the equilibrium value. This undersaturation causes a flux of carbon from graphene to the monomer gas. In this initial mechanism, graphene is etched at a rate that is given precisely by the same non-linear dependence on carbon monomer concentration that governs growth. Thus, during both growth and etching, carbon attaches and detaches to graphene as clusters of several carbon atoms. At later times, etching accelerates. We present evidence that this process involves intercalated oxygen, which destabilizes graphene. On Ir, this mechanism creates observable holes. It also occurs mostly quickly near wrinkles in the graphene islands, depends on the orientation of the graphene with respect to the Ir substrate, and, in contrast to the first mechanism, can increase the density of carbon monomers. We also observe that both layers of bilayer graphene islands on Ir etch together, not sequentially.Comment: 15 pages, 10 figures. Manuscript revised to improve discussion, following referee comments. Accepted for publication in Journal of Physical Chemistry C, Feb. 11, 201

Phase field theory of polycrystalline solidification in three dimensions

A phase field theory of polycrystalline solidification is presented that is able to describe the nucleation and growth of anisotropic particles with different crystallographic orientation in three dimensions. As opposed with the two-dimensional case, where a single orientation field suffices, in three dimensions, minimum three fields are needed. The free energy of grain boundaries is assumed to be proportional to the angular difference between the adjacent crystals expressed here in terms of the differences of the four symmetric Euler parameters. The equations of motion for these fields are obtained from variational principles. Illustrative calculations are performed for polycrystalline solidification with dendritic, needle and spherulitic growth morphologies.Comment: 7 pages, 4 figures, submitted to Europhysics Letters on 14th February, 200

PECULIAR FEATURES OF TEACHING HISTORY TO ECONOMIST STUDENTS IN RUSSIAN UNIVERSITIES

The purpose of the article: The article is aimed at studying of key issues of the set of methods and methodology of teaching history to students of the direction "Economics"; identifying of key aspects of the history course, competent understanding whereof is important for development of professional competencies of future economists, is of special attention.Materials and methods: The leading approach to the study of this problem is the analysis of key problem issues of the history course, a competent understanding of which is important for the formation of professional competencies of economists.Results of the research: The article shows that in the history of economics there are a lot of controversial, controversial issues on which quite superficial, subjective judgments and conclusions can occur in the journalistic, and sometimes academic literature. A number of similar questions are considered, the features of their study with students are revealed. The work identifies key aspects of the course of history, a competent understanding of which is important for the formation of professional competencies of future economists. The recommendations of the methodological and methodological plan for their study are proposed to increase the effectiveness of training future economists. Applications: This research can be used for the universities, teachers, and students. Novelty/Originality: In this research, the model of peculiar features of teaching history to economist students in Russian universities is presented in a comprehensive and complete manner

Ocean Colour remote sensing in the Southern Laptev Sea: evaluation and applications

Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigeneous matter into Arctic coastal waters. We used optical operational satellite data from the Ocean Colour sensor MERIS onboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigeneous matter in the southern Laptev Sea. MERIS satellite data from 2006 on to 2011 were processed using the Case2Regional Processor, C2R, installed in the open-source software ESA BEAM-VISAT. Since optical remote sensing using Ocean Colour satellite data has seen little application in Siberian Arctic coastal and shelf waters, we assess the applicability of the calculated MERIS parameters with surface water sampling data from the Russian-German ship expeditions LENA2010 and TRANSDRIFT-XVII taking place in August and September 2010 in the southern Laptev Sea. The surface waters of the southern Laptev Sea are characterized by low transparencies, due to turbid river water input, terrestrial input by coastal erosion, resuspension events and, therefore, high background concentrations of Suspended Particulate Matter, SPM, and coloured Dissolved Organic Matter, cDOM. The mapped calculated optical water parameters, such as the first attenuation depth, Z90, the attenuation coefficient, k, and Suspended Particulate Matter, SPM, visualize resuspension events that occur in shallow coastal and shelf waters indicating vertical mixing events. The mapped optical water parameters also visualize that the hydrography of the Laptev Sea is dominated by frontal meanders with amplitudes up to 30 km and eddies and filaments with diameters up to 100 km that prevail throughout the ice-free season. The meander crests, filaments and eddy-like structures that become visible through the mapped MERIS C2R parameters indicate enhanced vertical and horizontal transport energy for the transport of terrigenous and living biological matter in the surface waters during the ice-free season

Changing nutrient stoichiometry affects phytoplankton production, DOP accumulation and dinitrogen fixation – a mesocosm experiment in the eastern tropical North Atlantic

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low nitrogen to phosphorus (N : P) ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified nitrate availability as a control of primary production, while a possible co-limitation of nitrate and phosphate could not be ruled out. To better understand the impact of changing N : P ratios on primary production and N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67–48). Silicic acid was supplied at 15 µmol L−1 in all mesocosms. We monitored nutrient drawdown, biomass accumulation and nitrogen fixation in response to variable nutrient stoichiometry. Our results confirmed nitrate to be the key factor determining primary production. We found that excess phosphate was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low inorganic phosphate availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where nitrate was still available, indicating that bioavailable N does not necessarily suppress N2 fixation. We observed a shift from a mixed cyanobacteria–proteobacteria dominated active diazotrophic community towards a diatom-diazotrophic association of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially influencing primary productivity and carbon export

The fat oxidation rate at rest and under exercise load «until exhaustion» in Nordic skiers

Objective: to study the fat oxidation rate during physical exercises of different intensity and to identify factors influencing this process in athletes. Materials and methods: highly qualified Nordic skiers (26 men, 11 women) were examined. Fat oxidation (FO) was determined by the indirect colorimetric technique within stepwise increasing cycle load in the test «to failure». Results: FO for highly skilled skiers (MS and MSIL) was 0.17 g/min at rest and 0.77 g/min at the peak of the load, corresponding to the range of 40-60% of the maximal oxygen consumption (MOC). The level of skill was associated with a higher peak FO and its longer retention up to a load of 80-90% of the MOC. Age differences appeared only at the peak of the load, in the range of 60-70% of the MOC. There was a higher base and maximum FO in men, unlike women. Conclusions: the fat oxidation rate during exercise should be used in assessing the functional state of athletes when planning load regimes and preventing overtraining

In situ observation of stress relaxation in epitaxial graphene

Upon cooling, branched line defects develop in epitaxial graphene grown at high temperature on Pt(111) and Ir(111). Using atomically resolved scanning tunneling microscopy we demonstrate that these defects are wrinkles in the graphene layer, i.e. stripes of partially delaminated graphene. With low energy electron microscopy (LEEM) we investigate the wrinkling phenomenon in situ. Upon temperature cycling we observe hysteresis in the appearance and disappearance of the wrinkles. Simultaneously with wrinkle formation a change in bright field imaging intensity of adjacent areas and a shift in the moire spot positions for micro diffraction of such areas takes place. The stress relieved by wrinkle formation results from the mismatch in thermal expansion coefficients of graphene and the substrate. A simple one-dimensional model taking into account the energies related to strain, delamination and bending of graphene is in qualitative agreement with our observations.Comment: Supplementary information: S1: Photo electron emission microscopy and LEEM measurements of rotational domains, STM data of a delaminated bulge around a dislocation. S2: Movie with increasing brightness upon wrinkle formation as in figure 4. v2: Major revision including new experimental dat

Investigation of Non-Equilibrium Structural-Phase Transformations and Development of Methods for Control of Structure Formation of Aluminum-Based Alloys under Local Beam Influence

В настоящей статье изучено формирование микроструктуры в сплавах систем Al–ПМ, Al–Mg–ПМ и Al–Cu–Mg–Mn–ПМ (где ПМ — переходные металлы Fe, Ni, Cr, Mn, Zr) в зависимости от мощности лазерного излучения, температуры и структуры подложки и стратегии сканирования лазерного луча. Также сформирована база микроструктур и размеров структурных составляющих сплавов в зависимости от условий кристаллизации. Разработан алгоритм и создана компьютерная модель, позволяющая моделировать процесс кристаллизации сплавов, используя вероятности за рождения и роста зерен.The formation of the microstructure in alloys of the Al–PM, Al–Mg–PM, and Al–Cu–Mg–Mn–PM systems (where PM are transition met als Fe, Ni, Cr, Mn, Zr) depending on the laser power, temperature, and substrate structures and laser beam scanning strategies were investigated. A database of microstructures and sizes of structural components of alloys has been formed depending on the conditions of crystallization. An algorithm has been developed and a computer model has been created that makes it possible to simulate the process of crystallization of alloys using the probabilities of grain nucleation and growth.Работа выполнена при финансовой поддержке Российского Фонда Фундаментальных Исследований (проект №19-38-60037 «Перспектива»).The work was carried out with the financial support of the Russian Foundation for Basic Research (project No. 19–38–60037 “Perspektiva”)

Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There are numerous feedbacks between oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. We investigated the pelagic biogeochemistry of OMZs in the eastern tropical North Atlantic and eastern tropical South Pacific during a series of cruise expeditions and mesocosm studies. The following summarizes the current state of research on the influence of low environmental oxygen conditions on marine biota, viruses, organic matter formation and remineralization with a particular focus on the nitrogen cycle in OMZ regions. The impact of sulfidic events on water column biogeochemistry, originating from a specific microbial community capable of highly efficient carbon fixation, nitrogen turnover and N2O production is further discussed. Based on our findings, an important role of sinking particulate organic matter in controlling the nutrient stochiometry of the water column is suggested. These particles can enhance degradation processes in OMZ waters by acting as microniches, with sharp gradients enabling different processes to happen in close vicinity, thus altering the interpretation of oxic and anoxic environments