\documentclass[a4paper,10pt]{scrreprt}
\usepackage{pstricks,pst-text}
\DeclareFixedFont{\SF}{T1}{phv}{b}{ol}{5mm}
\newcommand{\p}{\partial}
\newcommand{\vs}{\vspace{.1in}}
\begin{document}



\begin{pspicture}(-4,-4)(4,4)
  \pstextpath[c]{\psarcn[linestyle=none](0,0){2}{195}{110}}
{$dx/dt = \sigma(y-x)$}
  \pstextpath[c]{\psarcn[linestyle=none](0,0){2}{70}{-25}}
{$dy/dt = x(\rho-z) -y$}

  \pstextpath[c]{\psarc[linestyle=none](0,0){2}{230}{310}}
{$dz/dt = xy - \beta z$}

\end{pspicture}
\end{document}