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\usepackage{authblk}
\usepackage{fancyhdr}
\geometry{top=2.5cm, bottom=2.5cm, left=2.5cm, right=2.5cm}

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\fancypagestyle{plain}{
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    \fancyhead[C]{\normalfont\normalsize \it Low Energy Nuclear Dynamics: FUSION27}
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\begin{document}

\title{\fontsize{16pt}{19pt}\selectfont \bf Title of the Abstract}

\author[1]{Author 1}
\author[2,3]{Author 2}
\affil[1]{Author 1 Affiliation}
\affil[2]{Author 2 Affiliation 1}
\affil[3]{Author 2 Affiliation 2}
\date{}
\maketitle	

\vspace{3ex}

Body of the abstract. It should not exceed one page~\cite{ref1}.


\begin{thebibliography}{00}
\bibitem{ref1} Reference 1.
\end{thebibliography}
\end{document}