\documentclass[11pt]{article}
\setlength{\oddsidemargin}{-0.1in}
\setlength{\topmargin}{-0.8in}
\setlength{\textheight}{9.0in}
\setlength{\textwidth}{6.8in}
\renewcommand{\baselinestretch}{1.2}
\title{An Article's Title}
\author{Art I.~Cle\\
        Electrical Engineering Department\\
        University of Rhode Island\\
        Kingston, Rhode Island, 02881
\thanks{This work was supported by ...}}
\date{}

\begin{document}
\maketitle
\begin{abstract}
An abstract should be short and to the point.
\end{abstract}

\section{Introduction}
The paper is organized as follows. This is the introduction, and Section
2 follows.

\section{A Section of the Article}

\subsection{A Sub-section}


\noindent We wish to include some math examples.  To do so we
assume that the \({\rm i}^{\rm th}\) word  is characterized by the 
probability density function (PDF) 
\(p_{i}(x_{t_{i-1}},\;...,\;x_{t_{i}-1};\;
{\mbox{\boldmath $\theta$}}_{i}
)\), where
\({\mbox{\boldmath $\theta$}}_{i}\) is a vector of unknown parameters.
A mathematical equation is created by:
\begin{equation}
\prod_{i=1}^{N_{s}}p_{i}(x_{t_{i-1}},\;...,\;x_{t_{i}-1};
{\mbox{\boldmath $\theta$}}_{i})
\end{equation}

\vspace{0.2 in}
 
\subsection{A Second Sub-section}

This sub-section will use a citation. Here it is: ``Don't take wooden 
nickels'' \cite{dad}.  Note to get the references correct, you'll need
to run latex twice.

\begin{thebibliography}{99}
\bibitem{dad}
Pops I.~Cle, {\it Digital Processing Tips },
Frosty Publishers, Newark NJ, 1978.

\end{thebibliography}

\setcounter{equation}{0}
\renewcommand{\theequation}{A-\arabic{equation}}
\appendix
\section{The First Appendix}
\indent Let us not worry about filling up the appendix with 
useless info. But we will show a fraction and some other 
ideas:
\begin{equation}
p({\bf x};{\mbox{\boldmath $\theta$}})\simeq
\frac{1}{(2\pi \sigma^{2})}
e^{-\frac{1}{2\sigma^{2}}(x - \mu)^2}
\end{equation}

\setcounter{equation}{0}
\renewcommand{\theequation}{B-\arabic{equation}}

\section{The Second Appendix}

We can show some nifty arrays by using the array command. \\
\vspace{0.1in}

$\left[ \begin{array}{l}
{\bf Q}_{k-1}\\
{\bf s}_{k}^{T}
\end{array} \right] =
\left[ \begin{array}{c}
l \times j\\
r \times p
\end{array} \right]$ \\
\vspace{0.1in}

And equations will now have the prefix B
\begin{equation}
 \lim_{n \rightarrow \infty} k^{-n} = 0
\end{equation}


\end{document}