Embodiments of the UMOs.

<p>The (a) and (d) are the embodiments of UMO 1; and (b) and (c) are the embodiments of UMO 2. We used (b) and (d) for the independent demonstration, and (a) and (c) for the chasing demonstration. In the test phase we had two pairs: (a) and (b); (c) and (d).</p>