By its very nature, vitamin A causes drying of the skin and exfoliation. A bevy of prescription and OTC vitamin A topical preparations make use of this side effect to treat a variety of skin concerns. The term Retinoid refers to any Vitamin A based molecule. It's a category, similar to saying antibiotic. They may be related, but some are stronger and more effective than others.
Pototype sheets for Weld Quality Workmanship Standard. Undercut. Definition: A groove cut at the toe of the weld by the welding arc and left. unfilled. Depth of undercut shall not exceed 1/32.
If the welder is too hot, or the persons technique is incorrect, or they are moving the rod to fast, the the path cut by the flame on the end of the rod is not properly filled, and the result is an undercut running along the side of the weld. This undercut causes the weld to be weak and makes it susceptible to failing.