Oxygen sensors prevention

It should also be mentioned that low oil viscosity at low temperatures is desirable in the new small 4 cylinder and V-6 cylinder fuel economy automobiles ( 5, 6). This is to permit sufficient speed of engine cranking for cold weather starting at winter temperatures. Low oil volatility must be maintained to prevent oil misting and blowby from poisoning the catalyst system and oxygen sensors in the anti-pollution devices (7). 

The initial sensors and subsequent signal transduction systems of hypoxic vasoconstriction (HPV) remain an area of intense investigation (21,22). At the cellular level, pulmonary artery smooth muscle (PASM) contraction depends on an increase in cytosolic calcium from the extracellular space as well as release from intracellular stores, and membrane depolarization due to closure of K+ channels. Many argue that the mitochondria is a primary oxygen sensor such that electron transport chain inhibitors can specifically inhibit HPV and/or prevent the hypoxia-specific response. Reactive oxygen species are also implicated in HPV. Two different models are proposed one describes an increase in mitochondrial ROS mediated via increased intracellular calcium release, and the second describes a decrease in mitochondrial ROS mediated via inhibition of the Kv channel (Figure 8.2). 

Currently, in the biochemical industries continuous sensing and measurement is generally limited to pH, carbon dioxide concentration and oxygen concentration. Other quantities would ideally be measured on a continuous basis but the lack of a suitable sensor prevents this. One major exception within a large pharmaceutical company is the use of a mass spectrometer to analyse fermenter vent gas continuously. The results are rapidly obtained and precise. The machine is linked to 64 fermenters and this spreads the substantial capital cost over a number of products. 

It should be noted that in a vapour phase the liquid layer on the surface of a sensitive element of the sensor (zinc oxide) must be sufficiently thin, so that it would not produce any influence on the diffusion flux of oxygen through this layer. Possible lack of the film continuity (the presence of voids) does not prevent determination of concentration of oxygen in the bulk of the cell by the vapour - gas method. In this case, one deals with a semi-dry method. On the contrary, the presence of a thick liquid layer causes considerable errors in measuring t, because of different distribution of oxygen in a system gas - liquid layer -semiconductor film (this distribution is close to that in the system semiconductor film - liquid), in addition to substantial slowing down of oxygen diffusion in such systems. 

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