Example Stepped surface near

Most fiindamental surface science investigations employ single-crystal samples cut along a low-index plane. The single-crystal surface is prepared to be nearly atomically flat. The surface may also be modified in vacuum. For example, it may be exposed to a gas that adsorbs (sticks) to the surface, or a film can be grown onto a sample by evaporation of material. In addition to single-crystal surfaces, many researchers have investigated vicinal, i.e. stepped, surfaces as well as the surfaces of polycrystalline and disordered materials. 

In Chapter 11, we will discuss a fourth category of elements, one with vertical profiles nearly opposite to the biolimiting elements. These elements have surfece-water enrichments and bottom-water depletions. Most are trace metals that adsorb onto sinking particles enabling their transport to the sediments. These elements tend to have shorter residence times than the biolimiting elements because they lack the remineralization step. Still other elements have a foot in both camps in some locations, they exhibit biolimiting behavior and have profiles with surface-water depletion and bottom-water enrichments, and in other locations, the profiles appear to be controlled by particle adsorption. Iron is an example of such an element. 

Some cellular responses occur too rapidly following steroid hormone exposure to involve the multi-step process of nuclear receptor activation. For example, 17/6-estradiol can rapidly stimulate adenylate cyclase and cause a near-instantaneous increase in intracellular cAMP in cultured prostate cells. These effects are mediated by the interaction of steroid hormones with cell surface proteins. 

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