Graphene superlattice with periodically modulated Dirac gap

Graphene-based superlattice (SL) formed by a periodic gap modulation is studied theoretically using a Dirac-type Hamiltonian. Analyzing the dispersion relation we have found that new Dirac points arise in the electronic spectrum under certain conditions. As a result, the gap between conduction and valence minibands disappears. The expressions for the position of these Dirac points in ${\bf k}$-space and threshold value of the potential for their emergence were obtained. At some parameters of the system, we have revealed interface states which form the top of the valence miniband.Comment: 5 pages, 4 figures, accepted to Physical Review

Geometry-induced reduction of the critical current in superconducting nanowires

Reduction of the critical current in narrow superconducting NbN lines with sharp and rounded bends with respect to the critical current in straight lines was studied at different temperatures. We compare our experimental results with the reduction expected in the framework of the London model and the Ginsburg-Landau model. We have experimentally found that the reduction is significantly less than either model predicts. We also show that in our NbN lines the bends mostly contribute to the reduction of the critical current at temperatures well below the superconducting transition temperature

Critical fields for vortex expulsion from narrow superconducting strips

We calculate the critical magnetic fields for vortex expulsion for an infinitely long superconducting strip, using the Ginzburg-Landau formalism. Two critical fields can be defined associated with the disappearance of either the energetic stability or metastability of vortices in the center of the strip for decreasing magnetic fields. We compare the theoretical predictions for the critical fields in the London formalism with ours and with recently published experimental results. As expected, for narrow strips our results reproduce better the experimental findings.Comment: 5 pages, 5 figure

Anomalies of Density, Stresses, and the Gravitational Field in the Interior of Mars

We determined the possible compensation depths for relief harmonics of different degrees and orders. The relief is shown to be completely compensated within the depth range of 0 to 1400 km. The lateral distributions of compensation masses are determined at these depths and the maps are constructed. The possible nonisostatic vertical stresses in the crust and mantle of Mars are estimated to be 64 MPa in compression and 20 MPa in tension. The relief anomalies of the Tharsis volcanic plateau and symmetric feature in the eastern hemisphere could have arisen and been maintained dynamically due to two plumes in the mantle substance that are enriched with fluids. The plumes that originate at the core of Mars can arise and be maintained by the anomalies of the inner gravitational field achieving +800 mGal in the region of plume formation, - 1200 mGal above the lower mantle-core transition layer, and -1400 mGal at the crust.Comment: 9 pages, 5 figure

Hysteretic characteristics of a double stripline in the critical state

Analytical investigations of the critical state are carried out for a superconducting stripline consisting of two individual coplanar strips with an arbitrary distance between them. Two different cases are considered: a stripline with transport current and strips exposed to a perpendicular magnetic field. In the second case, the obtained solutions correspond to "fieldlike" (for unclosed strips) and "currentlike" (for a long rectangular superconducting loop) states in an isolated strip to which both a transport current and a magnetic field are applied with constant ratio.Comment: 8 pages, 6 figures. accepted by SS

Magnetic-field dependence of the critical currents in a periodic coplanar array of narrow superconducting strip

We calculate the magnetic-field dependence of the critical current due to both geometrical edge barriers and bulk pinning in a periodic coplanar array of narrow superconducting strips. We find that in zero or low applied magnetic fields the critical current can be considerably enhanced by the edge barriers, but in modest applied magnetic fields the critical current reduces to that due to bulk pinning alone.Comment: 23 pages, 7 figure

Microfossils of the late proterozoic debengdinskaya formation of the olenekskiy uplift

Microfossils from the Middle Riphean Debengdinskaya formation of the Olenekskiy uplift have been studied. Various stenoorganic forms of acritarchs and cyanobacteries are described. Morphological groups which are preliminary compared with large flora taxons are allocated among acritarchs : brown and green seaweed, mushrooms, seaweed located in symbiotic relations (?) with cyanobionts. The prematurity of radical conclusions about age of the deposit based on majority of Proterozoic microfossils is underline

Change in Structure, Phase Composition, and Properties during Soft Hardening of Titanium Alloy VST5553

Методами оптической, растровой, просвечивающей, ориентационной электронной микроскопии, рентгенографии, МРСА, микроиндентирования рассмотрены особенности формирования структурно-фазового состояния, текстуры и свойств (твердости, модуля упругости) в высокопрочном титановом сплаве VST5553 после мягкой закалки на воздухе при температуре нагрева в b‑ и (a+b)-областях.The features of the formation of the structural-phase state, texture and properties (hardness, contact elastic modulus) in the high-strength titanium alloy VST5553 after soft quenching in air with heating temperatures in b- and (a+b) -areas.Работа выполнена в рамках государственного задания Минобрнауки (№ 0836-2020-0020).The work was carried out within the framework of the state task of the Ministry of Education and Science (№ 0836–2020–0020)

Abstract P-27: The 30S Ribosomal Subunit Assembly Factor Rbfa Plays a Key Role in the Formation of the Central Pseudoknot and in the Correct Docking of Helix 44 of the Decoding Center

Background: Ribosome biogenesis is a complicated multi-stage process. In the cell, 30S ribosomal subunit assembly is fast and efficient, proceeding with the help of numerous assembly protein factors. The exact role of most assembly factors and mechanistic details of their operation remain unclear. The combination of genetic modification with cryo-EM analysis is widely used to identify the role of protein factors in assisting specific steps of the ribosome assembly process. The strain with knockout of a single assembly factor gene accumulates immature ribosomal particles which structural characterization reveals the information about the reactions catalyzed by the corresponding factor. Methods: We isolated the immature 30S subunits (pre-30S subunits) from the Escherichia coli strain lacking the rbfA gene (ΔrbfA) and characterized them by cryo-electron microscopy (cryo-EM). Results: Deletion of the assembly factor RbfA caused a substantial distortion of the structure of an important central pseudoknot which connects three major domains of 30S subunit and is necessary for ribosome stability. It was shown that the relative order of the assembly of the 3′ head domain and the docking of the functionally important helix 44 depends on the presence of RbfA. The formation of the central pseudoknot may promote stabilization of the head domain, likely through the RbfA-dependent maturation of the neck helix 28. The cryo-EM maps for pre-30S subunits were divided into the classes corresponding to consecutive assembly intermediates: from the particles with completely unresolved head domain and unfolded central pseudoknot to almost mature 30S subunits with well-resolved body, platform, and head domains and with partially distorted helix 44. Cryo-EM analysis of ΔrbfA 30S particles revealing the accumulation of two predominant classes of early and late intermediates (obtained at 2.7 Å resolutions) allowed us to suggest that RbfA participate in two stages of the 30S subunit assembly and is deeper involved in the maturation process than previously thought. Conclusion: In summary, RbfA acts at two distinctive 30S assembly stages: early formation of the central pseudoknot including the folding of the head, and positioning of helix 44 in the decoding center at a later stage. An update to the model of factor-dependent 30S maturation was proposed, suggesting that RfbA is involved in most of the subunit assembly process