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.
The VRA is a special authority by which agencies can appoint an eligible veteran without competition. The VRA is an excepted appointment to a position that is otherwise in the competitive service. After 2 years of satisfactory service, the veteran is converted to a career-conditional appointment in the competitive service. (Note, however, that a veteran may be given a noncompetitive temporary or term appointment based on VRA eligibility. These appointments do not lead to career jobs.) When two or more VRA applicants are preference eligibles, the agency must apply veterans' preference as required by law.