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

Evaluation of the microstructure and mechanical properties of a new modified cast and laser-melted AA7075 alloy

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. © 2019 by the authors.Ministry of Science and Higher Education of the Russian FederationThe author (Asmaa M. Khalil) gratefully acknowledges financial support from the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of MISiS (Support project for young research engineers)

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

Coverage of the Indian Art Exhibition at the British Museum (October 1922) on the Pages of Rupam Magazine (Calcutta, 1922)

Статья посвящена выставке Индийского искусства в Британском музее в 1922 г. как одному из событий, способствующему знакомству западной публики с изобразительным искусством региона и включению индийской живописи в общемировой художественный контекст.The article is devoted to the exhibition of Indian art in the British Museum in 1922, as one of the events that contribute to the acquaintance of the Western public with the visual arts of the region and the inclusion of Indian painting in the global artistic context

Development of the optimal mode of bleaching of linen materials by periodic method

The article presents the results of research on the operational properties of linen material bleached by the developed combined periodic method. The influence of the composition and concentration of components in the working solution on the quality indicators of bleaching was studied. The results of the study show that the use of the proposed combined method for bleaching linen and mixed fabrics allows you to obtain high values of the degree of whiteness and capillarity with the preservation of strength indicators and minimal destruction of cellulose fiber

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

THE USE OF NEW REAGENT KITS FOR DETECTION AND DESCRIPTION OF ADDITIONAL ALLELES

During the screening typing of recruited volunteers with Volga Federal District for unrelated hematopoietic stem cell registry on the loci (HLA)-A, B, DRB1, DRB345 in sample No 1758 identified a new allele at locus A. The use of basic kit AlleleSEQR HLA-A Sequencing in combination with HARP – A2F98A allowed to determine the genotype of this sample – А*30:01:01, a new allele А*25, В*13, 44, DRB1*03, 09, DRB3*02, DRB4*01

Structure and magnetism in ultrathin iron oxides characterized by low energy electron microscopy

We have grown epitaxial films a few atomic layers thick of iron oxides on ruthenium. We characterize the growth by low energy electron microscopy. Using selected area diffraction and intensity vs. voltage spectroscopy, we detect two distinct phases which are assigned to wustite and magnetite. Spin polarized low energy electron microscopy shows magnetic domain patterns in the magnetite phase at room temperature.Comment: 21 pages, 10 figures, for J. Phys Cond Matt special LEEM/PEEM issue in honor of E. Baue

Investigation of influence of parameters of laser welding on microstructure and mechanical properties of Al-4.7%Mg -0.32%Mn-0.21%Sc-0.09%Zr alloy

В работе исследовано влияние пиковой мощности (0,64–1,31 кВт) при напряжениях из диапазона 330–430 В при лазерной сварке со стандартным диаметром пучка и длительностью импульса 8 мс. Изучена микроструктура, сформированная сваркой. Установлено, что существует разноообразие в размерах и форме зерен в зоне шва. Показано, что с увеличением пиковой мощности ширина и глубина области шва увеличивается.In the present work the influence of peak power of laser beam welding were studied at voltage range from 330 to 430 V and peak power (0,64; 0,75; 0,87; 1,01; 1,15; 1,31) kW , and laser beam diameter is standard and duration 8 ms. The microstructure after welding was studied. It was concluded that there is a variant in grain size and shape in the welded zone and pre-welded area. The dimensions of welded zone was measured. From measuring data, it was observed, that as increasing the peak power the width and depth of welding increased.The work was performed as part of the state work "Carrying out of research work (basic research, applied research and experimental development)" state task MES of Russia in the sphere of scientific activities 2014–2016. (Task № 2014/113)

Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified Alznmgcu with 4%si Alloys

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc + Zr, 4%Si-Ti + B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500◦ C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3 (Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was partially funded by Russian Foundation for Basic Research (RFBR) with project number 19-38-60037