\documentclass[12pt]{article}
\newcommand{\talk}[1]{\noindent\parbox{\textwidth}{\large\textbf{#1}}\\[1ex]}
\newcommand{\speaker}[1]{\parbox{\textwidth}{\textbf{#1}}\\[1ex]}
\newcommand{\affiliation}[1]{\parbox{\textwidth}{#1}\\[2ex]}
\renewcommand{\abstract}[1]{\parbox{\textwidth}{#1}}

\begin{document}
\talk{}
\speaker{}
\affiliation{}
\abstract{}
\end{document}

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%%% mode: latex
%%% TeX-master: t
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