%----------preamble----------------
\makeatletter
%%%%
\renewcommand\@maketitle{%
\newpage
\null
\vskip 2em%
\begin{center}%
\let \footnote \thanks
{\LARGE \@title \par}%
\vskip 1.5em%
{\large
\lineskip .5em%
\begin{tabular}[t]{c}%
\@author
\end{tabular}\par}%
\vskip 1em%
{\large \@date}%
\end{center}%
\par
\vskip 1.5em%
\begin{center}%
\abstract@produce
\end{center}%
\vskip 1.5em}
%
%%%
\newbox\abstractbox
\renewenvironment{abstract}{%
\lrbox\abstractbox
\minipage{.8\textwidth}%
\centerline{\bfseries\large\abstractname}%
\bigskip\small\it
}{%
\endminipage\endlrbox}
\def\abstract@produce{%
\leavevmode\box\abstractbox\par
}
\makeatother
%--------------------------------------