In this paper, we study the regularity criteria for axisymmetric weak solutions to the MHD equa- tions in R3. Let we, Jo and ue be the azimuthal component of w, J and u in the cylindrical coordinates, respectively. Then the axisymmetric weak solution （u,b） is regular on （0, T） if （wo,Jo） E Lq（O,T;Lp） or （oae,V（uoeo）） e Lq（0,T;Lp） with 3 ＋ 2 〈 2, 3 〈 p 〈 oo. In the endpoint case, one needs conditions （we, Jo） C LI（0, T;B∞∞） or （wo, V（uoeo）） C LI（0, T;B ∞∞）.
Using the fibering method introduced by Pohozaev, we prove existence of positive solution for a Diriclhlet problem with a quasilinear system involving p-Laplacian operator.
With a Hǒlder type inequality in Besov spaces, we show that every strong solution θ（t, x） on （0, T ） of the dissipative quasi-geostrophic equations can be continued beyond T provided that ⊥θ（t, x） ∈L 2γ/γ-2δ （（0, T ）; B^δ-γ/2 ∞∞（R^2）） for 0 〈 δ 〈 γ/2 .
