You can create pictures within LaTeX using a limited set of picture
symbols. These include vector, line, oval, and
others. They are fairly difficult to use, and you have to set them up
by hand. For more information you should refer to the LaTeX manual.
This picture was made with the following LaTeX code.
\begin{picture}(80,80)(0,0)
\put(60,77){\vector(1,0){7}}
\put(60,85){$\theta^+$}
\put(60,40){\line(1,5){10}}
\put(60,40){\line(0,1){50}}
\put(60,40){\oval(40,40)[l]}
\put(60,20){\line(0,1){40}}
\put(0,40){\vector(1,0){40}}
\put(0,43){flow}
\end{picture}