\documentclass[a0paper,twocolumn]{a0poster}
\usepackage{tikz,pgf}
\usepackage{graphics, times}
\usepackage[absolute]{textpos}
\usepackage{amsmath,amssymb}
\TPGrid[40mm,40mm]{23}{12}   
\usepackage[Kashida]{xepersian}

\begin{document}



\begin{textblock}{15}(15,1.23)
\tikzstyle{mybox} = [draw=red, fill=red!40!yellow!50, very thick,
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\tikzstyle{fancytitle} =[very thick,draw=black,fill=red, text=blue, inner ysep=20pt]

\begin{tikzpicture}
\setRTL
\node [mybox] (box){%
    \begin{minipage}{0.50\textwidth}
      این یک معادله هست 
        \begin{align}
            \dot{n} &= u -v\delta_\psi \\
            \dot{e} &= u\delta_\psi + v
        \end{align}
    \end{minipage}
};
\node[fancytitle,above=0pt] at (box.north) {
%\hboxR{یک عنوان}
\begin{minipage}{0.50\textwidth}
      این یک عنوان برای معادله است
    \end{minipage}
};
\end{tikzpicture}%
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\end{textblock}
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\end{document}
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