In this paper, we study 3-d Hartree type fractional Schrödinger equations: $$ i\partial_{t}u-\vert\nabla\vert^{\alpha}u = \lambda \left ( |x|^{-\gamma} *\vert u\vert^{2} \right ) u,\;\;1 < \alpha < 2,\;\;0 < \gamma < 3,\; \lambda \in \mathbb R \setminus \{0\}. $$ In [7] it is known that no scattering occurs in $L^2$ for the long range ($0 < \gamma \le 1$). In [4, 10, 8] the short-range scattering ($1 < \gamma < 3$) was treated for the scattering in $H^s$. In this paper, we consider the critical case ($\gamma = 1$) and prove a modified scattering in $L^\infty$ on the frequency to the Cauchy problem with small initial data. For this purpose, we investigate the global behavior of $x e^{it |\nabla|^\alpha } u$, $x^2 e^{it |\nabla|^\alpha } u$ and $ \langle\xi\rangle ^5 \widehat{e^{it |\nabla|^\alpha } u}$. Due to the non-smoothness of $ |\nabla|^\alpha $ near zero frequency the range of $\alpha$ is restricted to $(\frac{17}{10}, 2)$.

In our previous papers, we introduce symphonic maps ([9]) and show a Hölder continuity of symphonic maps from domains of $\mathbb{R}^4$ into the spheres ([6], [7]). In this paper, we consider the heat flow of symphonic maps with values into spheres and prove a global existence of a weak solution to the Cauchy-Dirichlet problem for any given initial and boundary data.

We study the Cauchy problem of the Klein-Gordon-Zakharov system in spatial dimension $d \ge 5$ with initial datum $(u, \partial_t u, n, \partial_t n)|_{t=0} \in H^{s+1}(\mathbb{R}^d) \times H^s(\mathbb{R}^d) \times \dot{H}^s(\mathbb{R}^d) \times \dot{H}^{s-1} (\mathbb{R}^d)$. The critical value of $s$ is $s_c=d/2-2$. By $U^2, V^2$ type spaces, we prove that the small data global well-posedness and scattering hold at $s=s_c$ in $d \ge 5$.

We consider the long-time behavior of solutions to the fifth-order modified KdV-type equation. For the local-in-time well-posedness, we show that regularity conditions where by a tri-linear estimate holds in the Fourier restriction norm spaces, which is an extension of Kwon's result (2008). Using the method of testing by wave packets, we prove the small-data global existence and modified scattering. We derive the leading asymptotic in both the self-similar and oscillatory regions.