Wakefulness systems

For the hydrodynamic instability model, Lienhard and Dhir (1973b) extended the Zuber model to the CHF on finite bodies of several kinds (see Sec. 2.3.1, Fig. 2.18). Lienhard and Hasan (1979) proposed a mechanical energy stability criterion The vapor-escape wake system in a boiling process remains stable as long as the net mechanical energy transfer to the system is negative. They concluded that there is no contradiction between this criterion and the hydrodynamic instability model. 

Matching the flow between the impeller and the diffuser is complex because the flow path changes from a rotating system into a stationary one. This complex, unsteady flow is strongly affected by the jet-wake of the flow leaving the impeller, as seen in Figure 6-29. The three-dimensional boundary layers, the secondary flows in the vaneless region, and the flow separation at the blades also affects the overall flow in the diffuser. 

Tsutsumi, A., Nieh, J.Y. and Fan, L.S., 1991. Role of the bubble wake in fine particle production of calcium carbonate in bubble column systems. Industrial and Engineering Chemistry Research, 30, 2328-2333. 

A medication that causes induction of sleep. The majority of currently available hypnotics (for example benzodiazepine receptor agonists) act via potentiating the brain s inhibitory GABAergic systems, in turn reducing the activity of arousal (i.e. wake promoting) neurotransmitter systems. 

Pathological conditions in which the VLPO system is weakened (i.e. less drive for sleep) could, therefore, result in more frequent changes between wakefulness and sleep, as has been demonstrated in animal models. Interestingly, elderly individuals have significantly reduced numbers - often by as much as 50% - of sleep-promoting VLPO neurones, an age-related loss of VLPO cells that may explain, at least partially, this population s characteristic difficulty in falling and staying asleep. 

Since the publication of the Standardised Sleep Manual by Rechtshaffen and Kales (Eds) in 1968, human sleep has been described using a classification system based on a combination of EEG, EMG and EOG features. The acquisition and use of such data is known as polysomnography. Note, that when including the state of WAKE in the classification, these are most accurately described as arousal states in place of sleep stages. 

---