Automatic reduction of four-loop bubbles

We give technical details about the computational strategy employed in a recently completed investigation of the four-loop QCD free energy. In particular, the reduction step from generic vacuum bubbles to master integrals is described from a practical viewpoint, for fully massive as well as QED-type integrals.Comment: 5 pages. Talk presented at RADCOR/Loops and Legs 2002, Kloster Banz, German

RadioAstron probes the ultra-fine spatial structure in the H2_2O maser emission in the star forming region W49N

H$_2$O maser emission associated with the massive star formation region W49N were observed with the Space-VLBI mission RadioAstron. The procedure for processing of the maser spectral line data obtained in the RadioAstron observations is described. Ultra-fine spatial structures in the maser emission were detected on space-ground baselines of up to 9.6 Earth diameters. The correlated flux densities of these features range from 0.1% to 0.6% of the total flux density. These low values of correlated flux density are probably due to turbulence either in the maser itself or in the interstellar medium.Comment: Accepted for publication in Advances in Space Researc

Electron Spin Dynamics of the Superconductor CaC6 probed by ESR

Conduction Electron Spin Resonance (CESR) was measured on a thick slab of CaC6 in the normal and superconducting state. A surprising increase of the CESR intensity below Tc can not be explained by the theoretically predicted change in spin susceptibility. It is interpreted as a vortex enhanced increase of the effective skin depth. Non-linear microwave absorption measurements in the superconducting state describe CaC6 as an anisotropic BCS superconductor. The study of the spin dynamics in the superconducting state and the discovery of the vortex enhanced increase of the skin depth poses a challenge to theory to provide a comprehensive description of the observed phenomena. CESR data in the normal state characterize CaC6 as a three-dimensional (3D) metal. The analysis suggests that the scattering of conduction electrons is dominated by impurities and supports the description of superconductivity in the dirty limit.Comment: 4 pages, 3 figure

ОБНАРУЖЕНИЕ СПОНТАННОГО МУТАГЕНЕЗА, ОБУСЛОВЛЕННОГО МОБИЛЬНЫМИ ГЕНЕТИЧЕСКИМИ ЭЛЕМЕНТАМИ, ОТНЕСЕННЫМИ К КЛАССУ ТРАНСПОЗОНОВ ПОЛОВЫХ КЛЕТОК, И СЕЛЕКЦИЯ ПАСЛЕНОВЫХ КУЛЬТУР

In Solanaceae crops the spontaneous mutagenesis caused by mobile genetic elements referred by authors to the class of the transposones of germ cells (ТGC) was found. Mutagenic activity of TGC was sown on the examples of monogenic point mutations of the gene of color tomato fruits epidermis: y + _y _y +.The transposition of TGS in chromosome «switches on – switches off» the y-gene changing its allele status. Detected in Solanaceae crops TGC is differed from founded out earlier controlling elements causing only chimeric somatic spotting.Application of the TGS-mutants can accelerate the breeding process. Using the spontaneous mutagenesis allowed to develop six varieties.На пасленовых культурах обнаружен спонтанный мутагенез, обусловленный мобильными генетическими элементами, отнесенными авторами к классу транспозонов половых клеток (ТПК). Их перемещения по геному приводят к моногенным мутационным изменениям на уровне целого организма. Мутагенная функция ТПК продемонстрирована на многократных примерах моногенных точковых мутаций гена окраски эпидермиса плода томата: y+ -y -y+. Перемещения ТПК в хромосоме «включают – выключают» ген y, меняя состояние его аллелей: доминантное – рецессивное – доминантное на уровне всего растения. Обнаруженное ТПК у пасленовых культур отличается от ранее открытых у растений контролирующих элементов, вызывающих только химерную соматическую пятнистость. Использование ТПК-мутантов позволяет ускорить селекционный процесс. С применением спонтанного мутагенеза создано шесть сортов

The theory of long-range Josephson current through a single-crystal ferromagnet nanowire

© 2017 Elsevier B.V. Theoretical model of the singlet long-range Josephson transport is proposed. Taking into account the mismatch of the electron effective masses of majority and minority spin subbands the Eilenberger-like equations are obtained with renormalized effective exchange interaction. The critical Josephson current is calculated through ferromagnet nanowire. It is shown that the effective exchange field can be completely compensated and thereby the long-range spatial supercurrent arises. Within the proposed theoretical model, the long-range proximity effect observed in the Co single-crystalline nanowire (Wang et al., 2010) can be qualitatively understood

Current switches based on asymmetric ferromagnet-superconductor nanostructures with allowance for a triplet channel in an external magnetic field

We analyze the properties of asymmetric three-layer (FSF and FFS) heterostructures consisting of a ferromagnet (F) and a superconductor (S) in an external magnetic field. The asymmetry of FS systems can be due to the difference in the parameters characterizing the F layers (in particular, noncollinearity of the magnetizations of the ferromagnets, leading to the generation of the long-range triplet component of the superconducting condensate). We consider the case of strong scattering of conduction electrons from non-magnetic impurities (the so-called dirty limit), for which we derive the equations for the pair amplitude and corresponding boundary conditions to these equations, which are valid in the presence of an external magnetic field. We discuss possible applications of these FS heterostructures as spin switches on the basis of analysis of their phase diagrams, and we give recommendations for determining the optimal parameters required for their stable operation. The occurrence of peculiar re-entrant superconductivity in the FFS systems on an increase of the external magnetic field is predicted. © 2013 Pleiades Publishing, Inc

Solitary superconductivity in a ferromagnet–superconductor heterostructure

© 2015, Pleiades Publishing, Inc. A ferromagnet (F)–superconductor (S) (F1F2S) three-layer heterostructure has been studied using Usadel equations with allowance for the pair electron–electron interaction in ferromagnetic layers. The appearance of regions with solitary superconductivity on the phase diagram has been predicted for the antiparallel configuration of the magnetization in F layers. Conditions for the possible experimental observation of solitary superconductivity in FFS three-layer structures, as well as for the detection of the electron–electron interaction in ferromagnets, have been discussed

A Dramatic Reading of Vizenor's Bear Island at the University of Michigan

A brief report on a dramatic reading of Vizenor's Bear Island: The War at Sugar Point staged at the Univeristy of Michigan in March 2018 in conjunction with Vizenor's presentation of the third annual Berkhofer Lecture

Long-range spin-singlet proximity effect for a Josephson system with a single-crystal ferromagnet due to its band-structure features

© 2018 American Physical Society. A possible explanation for the long-range proximity effect observed in single-crystalline cobalt nanowires sandwiched between two tungsten superconducting electrodes [Nat. Phys. 6, 389 (2010)NPAHAX1745-247310.1038/nphys1621] is proposed. The theoretical model uses properties of a ferromagnet band structure. Specifically, to connect the exchange field with the momentum of quasiparticles the distinction between the effective masses in majority and minority spin subbands and the Fermi-surface anisotropy are considered. The derived Eilenberger-like equations allowed us to obtain a renormalized exchange interaction that is completely compensated for some crystallographic directions under certain conditions. The proposed theoretical model is compared with previous approaches

A Peculiar Solitary Re-entrant Superconductivity Induced by an External Magnetic Field in Ferromagnet-Superconductor Heterostructures

© 2014, Springer Science+Business Media New York. We solve the boundary value problem for the Usadel-like equations in the dirty limit case for thin-film three-layered ferromagnet (F) - superconductor (S) structures. Our theoretical approach taking into account of the asymmetry and triplet superconducting correlations is valid in the external magnetic field presence as in the real experimental setup for the FS spin valve explorations. Based on the recent experimental data obtained for the symmetrical (FSF) trilayer in an external magnetic field, we expand the theoretical description to the asymmetrical FSF and FFS trilayers. We also consider the peculiar re-entrant superconductivity and solitary superconductivity induced by the external magnetic field for the FFS trilayer