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Fields of science or learning include law , medicine , theology , accounting , actuarial computation , engineering , architecture , teaching , various types of physical , chemical and biological sciences , pharmacy and other occupations that have a recognized professional status and are distinguishable from the mechanical arts or skilled trades where the knowledge could be of a fairly advanced type , but is not in a field of science or learning . Missing from most discussions is what really occurs in American visual art - - the huge mass of artists who are still tied to realism , classicism , various forms of impressionism and hundreds of other styles . To help you grasp the core principles at work , Switching to VoIP uses a combination of strategy and hands-on " how-to " that introduce VoIP routers and media gateways , various makes of IP telephone equipment , legacy analog phones , IPTables and Linux firewalls , and the Asterisk open source PBX software by Digium . With a complete disregard for age or conditions of health , the Soviet citizens were compelled , under threat of torture , shooting or death by starvation , to perform , gratuitously , various kinds of heavy work , including work of a military nature . Using metallic copper as catalyst in aprotic solvents such as DMF , various nitroalkanes can be easily converted to the corresponding carbonyl compounds and nitrous acid in the presence of N-donor ligands .