Extended Cesáro operators from generally weighted Bloch spaces to Zygmund space

AbstractLet g be a holomorphic function of the unit ball B in the n-dimensional complex space, and denote by Tg the extended Cesáro operator with symbol g. Starting with a brief introduction to well-known results about Cesáro operator, we investigate the boundedness and compactness of Tg from generally weighted Bloch spaces Blogα (0<α<∞) to Zygmund space Z in the unit ball, and also present some necessary and sufficient conditions

Energy-based drag decomposition analyses for a turbulent channel flow developing over convergent–divergent riblets

Direct numerical simulations of a turbulent channel flow developing over convergent-divergent (C-D) riblets are performed at a Reynolds number of Re-b = 2800, based on the half channel height delta and the bulk velocity. To gain an in-depth understanding of the origin of the drag generated by C-D riblets, a drag decomposition method is derived from kinetic energy principle for a turbulent channel flow with wall roughness. C-D riblets with a wavelength, lambda, ranging from 0.25 delta to 1.5 delta, are examined to understand the influence of secondary flow motions on the drag. It is found that as lambda increases, the intensity of the secondary flow motion increases first and then decreases, peaking at lambda / delta = 1. At lambda / delta & GE; 1, some heterogeneity appears in the spanwise direction for the turbulent kinetic energy (TKE) and vortical structures, with the strongest enhancement occurring around regions of upwelling. All the riblet cases examined here exhibit an increased drag compared to the smooth wall case. From the energy dissipation/production point of view, such a drag increase is dominated by the TKE production and the viscous dissipation wake component. While the drag contribution from the TKE production shear component decreases as lambda increases, the drag contribution from the wake component of both the TKE production and viscous dissipation follows the same trend as the intensity of the secondary flow motion. From the work point of view, the drag increase in the riblet case at lambda / delta = 0.25 comes mainly from the work of the Reynolds shear stresses, whereas at lambda / delta & GE; 1, the drag augmentation is dominated by the work of the dispersive stresses. At lambda / delta = 0.5, both components play an important role in the increase in the drag, which also exhibits a peak

Enhanced Orbital Degeneracy in Momentum Space for LaOFeAs

The Fermi surfaces (FS) of LaOFeAs (in $k_z$=0 plane) consist of two hole-type circles around $\Gamma$ point, which do not touch each other, and two electron-type co-centered ellipses around M point, which are degenerate along the M-X line. By first-principles calculations, here we show that additional degeneracy exists for the two electron-type FS, and the crucial role of F-doping and pressure is to enhance this orbital degeneracy. It is suggested that the inter-orbital fluctuation is the key point to understand the unconventional superconductivity in these materials.Comment: 4 pages, 5 figure