Tham khảo tài liệu 'supply chain, the way to flat organisation part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A Physics Approach to Supply Chain Oscillations and Their Control 171 1 v dv dt X - 21 N dN dx 5 The rationale for this expression is that when the inventory of the level below the level of interest is less than normal the production rate v will be diminished because of the smaller number of production units being introduced to that level. At the same time when the inventory of the level above the level of interest is larger than normal the production rate will also be diminished because the upper level will demand less input so that it can catch up in its production through-put. Both effects give production rate changes proportional to the negative of the gradient of N. It is reasonable also that the fractional changes are related rather than the changes themselves since deviations are always made from the inventories at hand. We note in passing that the quantity 1 is somewhat arbitrary and reflects an equally arbitrary choice of a scale factor that relates the continuous variable x and the discrete level variable n. A time scale for the response is missing from Eq. 5 . We know that a firm must make decisions on how to react to the flow of production units into the firm. Assume that the time scale of response Tresponse is given by Tresponse 1 tprocessing where Tprocessing is the processing time for a unit as it passes through the firm and for simplification we are assuming and Tprocessing are constant throughout the chain. Because of a natural inertia associated with cautious decision-making it is likely that will be less than unity corresponding to response times being longer than processing times. Then Eq. 5 becomes 1 v dv dt - 2 1 Tprocessing N dN dx 6 Since by definition the steady state production rate velocity is given by V0 1 Tprocessing this gives finally for the effective internal force that changes production flow rates F dv dt - 2 V02 1 N dN dx 7 Insertion of this expression into Eq. 3 then yields ổf dt vổf dx - 2 V02 1 N dN dx ổf ổv 0 8 In the steady .