This week I read something about network flow from Algorithm Design. But I am confused about some concepts. We say, if a graph G contains some nodes with demands, positive or negative, how to define the min cut for these graphs? If we still use the definition for simple graph, the value of max flow is not equal to the capacity of min cut. Or is it totally meaningless to talk about min-cut in a network with demands on some nodes. Another thing is  how to define the capacity of a min-cut for graph with lower bound on its edges. Still the sum of capacities of edges out of starting set? Or say, now we have a lower bound for this cut which is the sum of lower bounds of edges out of starting set. 
Min-cut in graph with demands/lower bounds
network flow;minimum cuts