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We study transition form factors for decays of D mesons. That is, we consider matrix elements of the weak left-handed quark current for the transitions D → P and D → V, where P and, V are light pseudoscalar or vector mesons, respectively. Our motivation to perform the present study of these form factors is future calculations of nonleptonic decay amplitudes. We consider the transition form factors within a class of chiral quark models. Especially, we study how the large energy effective theory limit works for D-meson decays. In this paper, we extend previous work on the case B → π to the case D → P ¼ π, K. Further, we extend our previous model based on the large energy effective theory to the entirely new case D → V ¼ ρ; K Ã ; … To determine some of the parameters in our model, we use existing data and results based on some other methods like lattice calculations, light-cone sum rules, and heavy-light chiral perturbation theory. We also obtain some new predictions for relations between form factors.

We present results of an initial study of Kelvin‐Helmholtz instability in a stratified shear flow using a three‐dimensional, nonlinear, compressible, spectral collocation model. The simulation was performed at an intermediate Reynolds number and significantly extends previous studies of homogeneous and stratified shear flows. Our major findings include a secondary instability oriented along the two dimensional velocity field, with counter‐rotating vortices arising due to both buoyancy and shear sources of eddy kinetic energy within the billow structures. The vortices occupy the outer regions of the billows and contribute significant eddy transports of momentum and potential temperature within the billows. The resulting KH evolution differs in important respects from the corresponding two‐dimensional or unstratified flows.

the polymer persistence length and corresponding potential/thermal energy ratio.