An optical element comprises an organic resin and bubbles distributed to have a number density increasing from a first plane of the optical element toward a second plane of the optical element, where a diameter of the bubbles is less than or equal to a wavelength of light which enters the optical element. A portable audio player or radio can be inserted into the sleeve and connected to a pre-installed wiring and speaker system that is integrated into the fabric seams of the cap. As all synchronization objects contain searchable partner lists, actual simulated and runtime deadlocks including any type of synchronization object can be detected, and the full system can be analyzed to identify potential deadlocks. Advantageously, a user to may displace excretions downwardly into the bag while seated on the present invention. The stove element is adapted for fuel to dispose therein. Photo-curable compositions of the present invention exhibit faster cross-linking rates than similar compositions containing no endgroup-modified polymers.