A novel notion of turbulent structure-the local cascade structure-is introduced to study the convection phenomenon in a turbulent channel flow. A space-time cross-correlation method is used to calculate the convection velocity. It is found that there are two characteristic convection speeds near the wall, one associated with small-scale streaks of a lower speed and another with streamwise vortices and hairpin vortices of a higher speed. The new concept of turbulent structure is powerful to illustrate the dominant role of coherent structures in the near-wall convection, and to reveal also the nature of the convection-the propagation of patterns of velocity fluctuations-which is scale-dependent.
The low-lying structures of the self-conjugate ( N = Z ) nuclei 8241Nb41 and 8643Tc43 have been investigated using isomeric-decay spectroscopy following the projectile fragmentation of a 107Ag beam. These represent the heaviest odd®Codd N = Z nuclei in which internal decays have been identified to date. The resulting level schemes shed light on the shape evolution along the N = Z line between the doubly-magic systems 5628Ni and 10050Sn and support a preference for T = 1 states in T z = 0 odd®Codd nuclei at low excitation energies associated with a T = 1 neutron®Cproton pairing gap. Comparison with Projected Shell Model calculations suggests that the decay in 82Nb may be interpreted as an isospin-changing K isomer.