Thermal Conductivity Tensor in YBa2_2Cu3_3O7−x_{7-x}: Effects of a Planar Magnetic Field

We have measured the thermal conductivity tensor of a twinned YBa$_2$Cu$_3$O$_{7-x}$ single crystal as a function of angle $\theta$ between the magnetic field applied parallel to the CuO$_2$ planes and the heat current direction, at different magnetic fields and at T=13.8 K. Clear fourfold and twofold variations in the field-angle dependence of $\kappa_{xx}$ and $\kappa_{xy}$ were respectively recorded in accordance with the d-wave pairing symmetry of the order parameter. The oscillation amplitude of the transverse thermal conductivity $\kappa^0_{xy}$ was found to be larger than the longitudinal one $\kappa^0_{xx}$ in the range of magnetic field studied here ($0 T$$\le B \le 9$$T$). From our data we obtain quantities that are free from non-electronic contributions and they allow us a comparison of the experimental results with current models for the quasiparticle transport in the mixed state.Comment: 9 Figures, Phys. Rev. B(in press

ОСОБЕННОСТИ ДЕФОРМИРОВАНИЯ РАЗЛИЧНЫХ МОДЕЛЕЙ ГРАФЕНА ПРИ РАСТЯЖЕНИИ

Young’s modulus and Poisson’s ratio for graphene sheet models have been calculated in the framework of the finite element method as well as using semi-empirical PM6 and ab initio and DFT approaches. All three groups of the methods predict a monotonic increase of Young’s modulus with increasing a sample size with turning the curves to asymptote for bulk samples. Young’s modulus value calculated using quantum-chemical method PM6 converges to 1.01 TPa, reaching this value for the 9 × 15 model (C304H50). This value is in a good agreement with the literature data obtained both experimentally and theoretically for a bulk sample of graphene.Выполнены расчеты величин модуля Юнга и коэффициента Пуассона моделей графена в зависимости от их размера с использванием трех принципиально различающихся методов: конечных элементов, полуэмпирического квантовохимического метода PM6, методов ab initio и DFT. Все три группы методов предсказывают монотонное увеличение модуля Юнга с ростом размера образца с выходом графиков на асимптоту. Рассчитанное в рамках полуэмпирического метода PM6 значение модуля Юнга сходится к 1,01 ТПа, достигая указанного значения для модели 9 × 15 (C304H50). Эта величина хорошо согласуется с имеющимися литературными данными, полученными экспериментальными и расчетными методами для массивного образца графена

Superconductor-ferromagnet junction phase qubit

We propose a scheme for a phase qubit in an SIFIS junction, consisting of bulk superconductors (S), a proximity-induced ferromagnet (F), and insulating barriers (I). The qubit state is constituted by 0 and $\pi$ phase states of the junction, in which the charging energy of the junction leads to the superposition of the two states. The qubit is operated by the gate voltage applied to the ferromagnet, and insensitive to the decoherence sources existing in other superconducting qubits. We discuss a scalable scheme for qubit measurement and tunable two-qubit coupling.Comment: 3 pages, 3 figure

Extrinsic Fluorescent Dyes as Tools for Protein Characterization

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization

Enantioselective Synthesis of Planar Chiral Ferrocene Triflones

International audienceA multi-gram scale synthesis of ferrocenetriflone was optimised fromferrocenesulfonyl fluoride and Me3SiCF3 (Ruppert reagent).Enantioselective deprotolithiations were then optimised usingalkyllithiums in the presence of catalytic (+)-sparteine to afford 2-substituted ferrocene triflones in 79-84% ee. The use of chiral lithiumamides in the presence of in situ traps was also optimised and wasfound to outperform alkyllithium∙chiral diamine chelates for the firsttime in the ferrocene series, with 89-93% ee. Crystallisation ofderivatives afforded enantiopure compounds that were engaged indeprotolithiation-electrophilic trapping sequences, a halogen ‘dance'reaction and transition metal-promoted coupling to afford a wide rangeof variously polysubstituted ferrocene triflones

Self-assembled bifunctional surface mimics an enzymatic and templating protein for the synthesis of a metal oxide semiconductor

The recent discovery and characterization of silicatein, a mineral-synthesizing enzyme that assembles to form the filamentous organic core of the glassy skeletal elements (spicules) of a marine sponge, has led to the development of new low-temperature synthetic routes to metastable semiconducting metal oxides. These protein filaments were shown in vitro to catalyze the hydrolysis and structurally direct the polycondensation of metal oxides at neutral pH and low temperature. Based on the confirmation of the catalytic mechanism and the essential participation of specific serine and histidine residues (presenting a nucleophilic hydroxyl and a nucleophilicity-enhancing hydrogen-bonding imidazole nitrogen) in silicatein’s catalytic active site, we therefore sought to develop a synthetic mimic that provides both catalysis and the surface determinants necessary to template and structurally direct heterogeneous nucleation through condensation. Using lithographically patterned poly(dimethylsiloxane) stamps, bifunctional self-assembled monolayer surfaces containing the essential catalytic and templating elements were fabricated by using alkane thiols microcontact-printed on gold substrates. The interface between chemically distinct self-assembled monolayer domains provided the necessary juxtaposition of nucleophilic (hydroxyl) and hydrogen-bonding (imidazole) agents to catalyze the hydrolysis of a gallium oxide precursor and template the condensed product to form gallium oxohydroxide (GaOOH) and the defect spinel, gamma-gallium oxide (γ-Ga(2)O(3)). Using this approach, the production of patterned substrates for catalytic synthesis and templating of semiconductors for device applications can be envisioned