Helicity, as one of only two inviscid invariants in three-dimensional turbulence, plays an important role in the generation and evolution of turbulence. From the traditional viewpoint, there exists only one channel of helicity cascade similar to that of kinetic energy cascade. Through theoretical analysis, we find that there are two channels in helicity cascade process. The first channel mainly originates from vortex twisting process, and the second channel mainly originates from vortex stretching process. By analysing the data of direct numerical simulations of typical turbulent flows, we find that these two channels behave differently. The ensemble averages of helicity flux in different channels are equal in homogeneous and isotropic turbulence, while they are different in other type of turbulent flows. The second channel is more intermittent and acts more like a scalar, especially on small scales. Besides, we find a novel mechanism of hindered even inverse energy cascade, which could be attributed to the second-channel helicity flux with large amplitude.Helicity exists in many natural phenomena, such as hurricanes, tornadoes, and rotating "supercell" thunderstorms in the atmosphere, Langmuir circulation in the ocean, and  -effect and  -effect in the magnetic field [1,2]. In the past few decades, there have been numerous theoretical and numerical conclusions indicating that helicity could reduce the aerodynamic drag, nonlinearity of Navier-Stokes equations (NSEs), and improve the mixing effectiveness of reactants [1,3]. Helicity, the integral of the scalar product of velocity and vorticity, is the second inviscid invariant of the three-dimensional(3D) NSEs, which indicate that helicity cascade exists in 3D turbulent flows. Recently, a new research has shown that helicity is a conservative quantity even in viscous flows [4,5]. Helicity is a topological variable, which measures the degree of the linkage of the vortex lines in the flow field [6], and consists of linking, twisting and writhing [4].The classical Richardson-Kolmogorov-Onsager picture of 3D turbulence is based on the concept of energy cascade, which ignores the topology of vortices [7]. Theoretically, there are two possibilities describing the dynamical properties of helicity and energy cascades. One is simultaneous energy and helicity cascades toward smaller scales, and the other is a pure helicity cascade with no cascade of energy, leading to broken -5/3 power law solutions in the turbulent magnetohydrodynamical, convective and atmospheric flows [8,9]. While many studies revealed that through direct numerical simulations (DNS) and shell model there exists a transfer of energy and helicity to small scales simultaneously in turbulent flows at a high Reynolds number [8,[10][11][12][13]. In the process of the joint cascade of energy and helicity in helical turbulence, helicity flux is more

Nano‐peapods: Magnetically responsive photonic nanochains have been produced by inducing chain alignment of uniform magnetic particles during their silica coating process and then allowing additional deposited silica to wrap entire structures. The optical diffraction of these nanochains can be switched on and off by applying magnetic fields.