[O] closing column mode for beamer export

[Larrabee Strow]

I am trying to put a second row of two columns in a org beamer slide.

No problems with doing the first row, two column.

I can't figure out any way to put in the second row of two columns.
(I am trying to show a 2x2 grid of images, with titles.)

It appears to me I need something that produces and \end{columns}
after my first row of columns.

I have seen in the maillist and manual statement about using
ignoreheading property, but nothing I tried worked, I am sure I just
don't understand the instructions on this.  What I want is below, but
I need something after the first row that starts a new column

*** 
  :PROPERTIES:
  :BEAMER_col: 0.5
  :END:
\centering L2 Bias

#+ATTR_LaTeX: :width \linewidth  
[[./g039__bias_z1.pdf]]

*** 
  :PROPERTIES:
  :BEAMER_col: 0.5
  :END:
\centering L2 Std.

#+ATTR_LaTeX: :width \linewidth  
[[./g039__std_z1.pdf]]


**************HERE a need equivalent to a carriage return/line feed ************

*** 
  :PROPERTIES:
  :BEAMER_col: 0.5
  :END:
\centering L2 Bias Row Number 2

#+ATTR_LaTeX: :width \linewidth  
[[./g039__bias_z1_v2.pdf]]

*** 
  :PROPERTIES:
  :BEAMER_col: 0.5
  :END:
\centering L2 Std. Row Number 2

#+ATTR_LaTeX: :width \linewidth  
[[./g039__std_z1_v2.pdf]]


Thanks.