Preparation of ethyl 2-aryl 2,3-alkadienoates via palladium-catalyzed selective cross-coupling reactions

Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield.     

Microstructure and transport properties of various 90° grain boundaries in YBa2Cu3O7 thin films

The microstructure and transport properties of various 90° grain boundaries in (103) oriented YBa₂Cu₃O₇(YBCO) thin films grown epitaxially in situ by 90° off-axis sputtering are compared. The (103) films grown on (101) LaAlO₃ and (101) SrTiO₃ substrates have specific sets of 90° grain boundaries in both principal in-plane directions: 90° [010] twist boundaries along the [101] direction, and 90° [010] symmetrical tilt boundaries and 90° [010] basal-plane-faced tilt boundaries along the (301) direction. No weak-link behavior is observed across some of these boundaries by transport critical current density and normalized magnetic field dependence of J _c measurements along both those in-plane directions. High-resolution transmission electron microscopy reveals variations in the structure and microfaceting of the 90° boundaries, which may contribute to the absence of weak-link behavior. These results have important implications for understanding the behavior of step-edge Josephson junctions.     

Emission from a Rayleigh layer with irregular boundaries

A theory of microwave emission from an irregular layer of Rayleigh scatterers is developed by combining an existing matrix doubling method for volume scattering with the Kirchhoff method in surface scattering. Effects of the layer boundaries are illustrated by comparing layers with plane boundaries vs layers with rough top or bottom boundaries and irregular layers. It is found that the major effect of an irregular top layer boundary is to slow down the variation of the layer emission as a function of the nadir angle and the major effect of an irregular bottom boundary is to increase the level of the layer emission. Comparisons of the developed layer model with snow emission indicate the potential use of such models in data interpretation.     

An efficient step size control for continuation methods

In solving a nonlinear equation by the use of a continuation method one of the crucial problems is the choice of the step sizes. We present a model for the total computational cost of a standard numerical continuation process and solve the problem of optimal step size control for this model. Using the theoretical results as a basis, we develop an adaptive step size algorithm for Newton's method. This procedure is computationally inexpensive and it gives quite satisfactory results compared to some other numerical experiments found in the literature.     

Scanning tunneling spectroscopy of Ag films: the effect of periodic versus quasiperiodic modulation

By using scanning tunneling spectroscopy to probe a silver thin film that contains both periodic and quasiperiodic modulation, and by using Fourier analysis, we unravel the influences of individual Fourier components of the scattering potential (periodic versus quasiperiodic) on the electronic structure of a one-dimensional quasiperiodically modulated thin Ag film. Along the periodically modulated direction, a Bragg reflection-induced energy gap is observed in k space. On the other hand, the exotic E vs k spectrum with many minigaps was observed along the quasiperiodic direction.     

Phase-incoherent superconducting pairs in the normal state of Ba(Fe(1-x)Co(x))₂As₂

The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))?As? and a silver tip can be seen in the normal state of the film up to temperature T～1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.     

Strain-induced polarization rotation in epitaxial (001) BiFeO3 thin films

Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.     

Interface resistance dependence of spin transport in a ferromagnet–semiconductor hybrid structure

The spin transport signals from NiFe and Co into two-dimensional electron gas layers are measured for various thicknesses of transmission barriers. A stable and reproducible electrical detection of spin transport was obtained only when the barrier thickness is less than 10 nm. The typical interface resistance to observe spin signals in this experiment is about 0.5–250 Ω, which is a neither transparent nor a severe tunneling limit. The optimal interface resistance depends on the ferromagnetic materials, but severe tunneling barrier is not proper for fully electrical spin transport. Device size is also a critical factor to decide the proper range of interface resistance.     

Enthalpic effect of polyacrylonitrile on the concentrated solutions in dimethyl sulfoxide: Strong thixotropic behavior and formation of bound solvents

The effect of dipole–dipole interaction by nitrile groups of PAN on the bound state of solvent molecules and the concentrated solution properties in DMSO was investigated. Variation of a solution viscosity exhibited three overlap concentrations, C1*, C2*, and C3*, at 2.7, 8.6, and 16.3 wt%, respectively, representing the transition of concentration regions in the order of dilute, unentangled‐semi dilute, entangled‐semi dilute, and concentrated regions. The two‐dimensional mapping of FT‐IR analysis and dielectric measurement confirmed that the intermolecular interaction of PAN was suddenly enhanced at the C*s, inducing polarization to DMSO. In the ice‐melting process of PAN solutions, two different melting peaks (T_m2 and T_m3) of DMSO newly appeared at each C2* and C3*, suggesting the different types of bound solvents. In the concentrated solutions, the saturated dielectric constant and the strongly delayed evaporation of the solvent even at the boiling point of DMSO along with strong thixotropic behavior were indicative of the stronger confinement state of bound DMSO than in the semidilute solutions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1080–1089