Cell decelerating phase

After the exponential growth phase, the cell growth is limited by the availability of nutrients and the accumulation of waste products of metabolism. Consequently, the growth rate gradually decreases, and this phase is called the decelerating phase. 

The onset of the deceleration phase is identified as the time when the net rate of cell growth decreases. Decreases observed in the rate of increase of the number of cells are a direct consequence of the effects enumerated in Section 13.1.1. The point at which the net rate of cell growth becomes zero marks the onset of the stationary phase. 

In case the Monod equation holds for the rates of cell growth in the exponential growth, with decelerating and stationary phases in a uniformly mixed fermentor operated batchwise, a combination of Equations 4.2 and 4.6 gives... 

If cells are synchronised at the G1 /S boundary and then released, the rate of DNA synthesis is initially slow but accelerates to reach a maximum at about 3h and then decelerates until S-phase is essentially complete in 6-7 h (Stubblefield and Mueller, 1962 Adams, 1969b). As replication occurs different numbers of replicons are active at any one time, and so it is not surprising that more careful labelling reveals bursts of tritiated thymidine incorporation throughout S-phase rather than a steady even progression (Klevecz, 1969 Lett and Sun, 1970 Klevecz et al., 1974). 

Cells growth is described as an autocatalytic reaction. All growth requires an initial seed or inoculum of cells. As the cells are given nutrients, they metabolize this food to make more cells. The nutrient requirements vary considerably with cell type, but all cells undergo the growth phases shown in Fig. 1—stationary, exponential, deceleration, stationary, and death phases. 

The experiments on the overall power train (see Sect, 7,5) refer to the European R40 driving cycle, shown in Fig, 7,2 and already described in Sect, 6,5 (Fig, 6,21b), It is composed by three phases, the first two being characterized by a sequence of acceleration, constant speed and deceleration steps, while the last one presents two steps at constant speed, before returning to zero speed. This driving cycle is used in this chapter to evaluate the performance of the fuel cell power train on a road mission typical of urban areas,... 

This behavior is evidenced in Fig. 7.46, where the individual cell voltages corresponding to five significant instants of the cycle are reported, in particular just before acceleration (f = 0 s), just after acceleration (f = 10 s), two instants of the stationary phase (f = 20 and 34 s), and at the end of deceleration step (t = 45 s). An evident problem of stack malfunctioning is observed at f = 10 s, especially for the last 10 cells, due to difficulties of air compressor in assuring the necessary... 

After nutrients and substrate begin to diminish, cell growth decelerates and enters a period of no apparent growth. This phase is known as the stationary phase. In the stationary phase, the rate of growth equals the rate of cell death and no net change in cell mass concentration occurs. Fermentation products produced during the stationary phase are known as non-growth associated products. 

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