Inhomogeneous magnetic field without

By Earnshaw s theorem, it is impossible to make a trap for ions static electric fields, but Penning in 1936 developed a stable ion trap that was a combination of a static uniform magnetic field and inhomogeneous electrostatic fields. In 1958 Paul and his associates made a successful electric quadrupole ion trap without a magnetic field by having the electric field oscillate sinusoidally at radio frequencies. 

In the following, we discuss a method to measure model free the residual dipolar van VIeck moments without contributions from inhomogeneous spin interactions originating from static magnetic field inhomogeneities, local susceptibility effects, and heteronuclear dipolar interactions (70). Moreover, in the first approximation this method is insensitive to the transverse relaxation produced by the fluctuating dipolar interactions. 

An externally applied torque on the director can only be transmitted to the surfaces of a vessel without shear, if the director rotation is homogeneous throughout the sample as assumed in Sect. 8.1.2 for the rotational viscosity. Otherwise this transmission occurs partially by shear stresses. The resulting shear flow is called backflow. As there is usually a fixed director orientation at the surfaces of the sample container, a director rotation in the bulk of the sample by application of a routing magnetic field leads to an inhomogeneous rotation of the director and to a backflow [42]. 

---