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For substance is a single genus of being , so that the principles can differ only as prior and posterior , not in genus ; in a single genus there is always a single contrariety , all the other contrarieties in it being held to be reducible to one . In the section with closed rings " quantum mechanical principles can restrict the energies of the electrons , explains Cohen [ of Berkeley ] , forcing them to occupy separate energy levels , like electrons in a semiconductor . Computer simulations based on physical and chemical principles can complement experiments and provide novel insights into the behavior of biomolecules at an atomic level of detail . It also shows that the introduction of ecologically sound organic principles can have very quick positive impacts on the productivity and well-being of smallholder farmers so that they do not necessarily have to face a conversion period of reduced yields as they change from chemical to organic production . Despite the uncertainty , following three basic principles can help anyone move toward a healthy weight . Computer simulations based on physical and chemical principles can complement experiments and provide novel insights into the behavior of these systems at an atomic level .