  We study mixed-moment models (full zeroth moment, half higher moments) for a
Fokker-Planck equation in one space dimension. Mixed-moment minimum-entropy
models are known to overcome the zero net-flux problem of full-moment minimum
entropy Mn models. Realizability theory for these mixed moments of arbitrary
order is derived, as well as a new closure, which we refer to as Kershaw
closures. They provide non-negative distribution functions combined with an
analytical closure. Numerical tests are performed with standard first-order
finite volume schemes and compared with a finite-difference Fokker-Planck
scheme.
