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A premature ventricular contraction (PVC) is a common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node. PVCs may cause no symptoms or may be perceived as a "skipped beat" or felt as palpitations in the chest. PVCs do not usually pose any danger. [1]
An R wave follows as an upward deflection, and the S wave is any downward deflection after the R wave. The T wave follows the S wave, and in some cases, an additional U wave follows the T wave. To measure the QRS interval start at the end of the PR interval (or beginning of the Q wave) to the end of the S wave.
In a fire, PVC can form hydrogen chloride fumes; the chlorine serves to scavenge free radicals, making PVC-coated wires fire retardant. While hydrogen chloride fumes can also pose a health hazard in their own right, it dissolves in moisture and breaks down onto surfaces, particularly in areas where the air is cool enough to breathe, so would ...
N-O• + R• → N-O-R Although they are traditionally considered as light stabilizers, they can also stabilize thermal degradation. Even though HALS are extremely effective in polyolefins, polyethylene and polyurethane, they are ineffective in polyvinyl chloride (PVC). It is thought that their ability to form nitroxyl radicals is disrupted.
The chlorine content may vary from manufacturer to manufacturer; the base can be as low as PVC 56.7% to as high as 74% by mass, although most commercial resins have chlorine content from 63% to 69%. [citation needed] As the chlorine content in CPVC is increased, its glass transition temperature (T g) increases significantly. Under normal ...
Important examples can be distinguished by the R group in the monomer H 2 C=CHR: Polyethylene R = H; polypropylene from propylene, R = CH 3; Polystyrene is made from styrene, R = C 6 H 5; Polyvinyl chloride (PVC) is made from vinyl chloride, R= Cl; Polyvinyl acetate (PVAc) is made from vinyl acetate, R = O 2 CCH 3; Polyacrylonitrile is made ...
A permanent virtual circuit (PVC) is a virtual circuit established for repeated/continuous use between the same DTE. In a PVC, the long-term association is identical to the data transfer phase of a virtual call. Permanent virtual circuits eliminate the need for repeated call set-up and clearing. Frame Relay is typically used to provide PVCs.
The bodies of fittings for pipe and tubing are often the same base material as the pipe or tubing connected: copper, steel, PVC, CPVC, or ABS. Any material permitted by the plumbing, health, or building code (as applicable) may be used, but it must be compatible with the other materials in the system, the fluids being transported, and the ...
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