Definition. 1  Troponins are specific proteins found in heart muscle. Troponin testing is done to diagnose heart attacks (myocardial infarctions). 2  When heart muscle is damaged, as in a myocardial infarction (MI), troponins leak out of cells and into the bloodstream.
Variable Ratio Schedule (VR) This is going to be a little confusing at first, but hang on and it will become clear. A variable ratio schedule (VR) is a type of operant conditioning reinforcement schedule in which reinforcement is given after an unpredictable (variable) number of responses are made by the organism. This is almost identical to a Fixed-Ratio Schedule but the reinforcements are given on a variable or changing schedule.
According to the VR research team at Valve, all of the following are needed to establish presence. 1  A wide field of view (80 degrees or better) 2  Adequate resolution (1080p or better) 3  Low pixel persistence (3 ms or less) 4  A high enough refresh rate (>60 Hz, 95 Hz is enough but less may be adequate)