I need help with these questions for my homework What is the difference between
ID: 1805372 • Letter: I
Question
I need help with these questions for my homework What is the difference between steady state and non-steady state diffusion processes? Use mathematical expressions to explain them. List any two solutions corresponding to the non- steady state diffusion process as was demonstrated in class. What do you understand by fracture toughness? Write the expression for fracture toughness for the plane strain case. Identify your parameters. ii. What is fatigue failure? Give two examples where fatigue failures arise in an engineering application. Give examples of how it could be avoided. iii. What do you understand by the ductile to brittle transition temperature (DBTT)?Explanation / Answer
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All chemical potential gradients are zero at the equilibrium. Moreover, the principle of microscopic reversibility guarantees that, at equilibrium, the rate at which any process proceeds in the "forward" direction is exactly balanced by the rate of that process in the "reverse" direction. This holds for every individual process, and means that at equilibrium there can be no net flux through any enzyme, any ion channel, or any transport protein. This is easy to understand intellectually because a nonzero chemical potential difference is absolutely required to drive a net flux. But steady state and equilibrium are so commonly used as if they were synonyms, that you will likely have to think about these points for hours before you can parry the objections of scientists who are sure of their misinformation.
A widely misunderstood example is provided by the transport of ions across the plasma membrane of a cell. Take Na+ as an example. Because, in the normal state of the cell, there is no net flux of Na+ across the cell membrane, and because the Na concentration in the cytosol is not changing with time, this condition is sometimes thought to be an equilibrium state. It is not. It is a steady state. The fact that [Na+] is constant is sufficient to define a steady state, but is insufficient to distinguish a steady state from an equilibrium. That is because an equilibrium is a special case of a steady state; an equilibrium is a steady state that is achieved when all chemical potential gradients have decayed to zero and there are no further net movements of molecules via any process. This is in marked contrast to the steady state of Na in a living cell. Here, there is a substantial net flux of Na into the cell through Na channels in the cell membrane, and there is an opposite but equal net flux of Na extruded from the cell by the action of the Na+K+ATPase. There is a nonzero chemical potential gradient consisting of both chemical and electrical terms that propells Na+ into the cell, and there is a nonzero chemical potential gradient including a term for the hydrolysis of ATP that pumps Na+ from the cell. Neither the ion channels nor the Na pump can qualify as processes at equilibrium; there are net Na fluxes through both. The fact that there is no net flux across the membrane is simply a corrollary of the steady state, not an indication of equilibrium. This is because the equilibrium condition is a statement about processes, not about state variables. Consequently, equilibrium is attained only when there are no net fluxes through ion channels and no net fluxes through the pumps. Equilibrium is thus achieved only when the cell is dead. Far from being synonyms, the difference between steady state and equilibrium is the difference between life and death