Induced unfit

We think that protein (or RNA) machines that convert free energy of chemical reactions into mechanical work operate by a series of induced fit and induced unfit (Fig. 14.4). Here, we define fit and unfit in a broad sense and do not distinguish them from conformational selection (we discuss energetics rather than kinetics). 

Humans have always used the environment as a source of resources. However, for a lengthy period of time their activity did not markedly affect the biosphere. Only in the late 19th century did changes in the biosphere induced by human activity drop on human civilization like a ton of bricks. Trying to improve living standards and profit margins, humans continue to step up the rate of material production without little regard for the consequences (Tables 2.2-2.6). With such an approach, most of the resources taken from nature return to nature as waste, often poisonous or unfit for utilization. This threatens the existence of both the biosphere and humankind (Moiseev, 1990 Schwarzenbach, 2002). 

Stress-corrosion cracking of steel was first encountered in a practical way in riveted steam boilers. Stresses at rivets always exceed the elastic Unfit, and boiler waters are normally treated with alkalies to minimize corrosion. Crevices between rivets and boiler plate allow boiler water to concentrate, until the concentration of alkali suffices to induce S.C.C., sometimes accompanied by explosion of the boiler. Because alkalies were recognized as one of the causes, failures of this kind were first called caustic embrittlement. With the advent of welded boilers and with improved boiler-water treatment, S.C.C. of boilers has become less common. Its occurrence has not been eliminated entirely, however, because significant stresses, for example, may be established at welded sections of boilers or in tanks used for storing concentrated alkalies. 

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