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.
A series of monodispersed oligo(p-phenyleneethynylene)s were synthesized bearing intramolecular hydrogen bonds between side chains of adjacent phenylene units in the backbone. Thus, all repeating units of the molecules are constrained in a coplanar orientation. Such planarized conformation is considered favorable for single-molecule conductance. Photophysical characterization results show narrowed bandgaps and extended conjugation lengths, consistent with a rigid, planar backbone framework as a result of intramolecular hydrogen bonding.
For the time being, Integrated Optics is able to produce a range of devices able of efficiently modulating phase, amplitude and frequency of guided waves in single mode structures implemented at the surface of active materials such as Lithium Niobate. In most of the cases, their basic principle relies on the interference pattern of two guided waves and the classical implementations of such modulators were mainly related to COBRA switch type directional couplers or to MACH ZEHNDER type interferometers. Only very recently a structure combining the coupled waveguides of a COBRA and the Y junction of the MACH ZEHNDER interferometer was designed. This paper is an analysis of the switching characteristics of this Y-fed directional coupler and of its high frequency modulation properties.