Multiple oxygen sensors

Chapter 33, by Haddad, presents evidence for multiple oxygen sensors in the central neurons, which participate in acute as well as chronic responses to hypoxia in a variety of species including Drosophila and mammals. He states that acute responses to oxygen deprivation involve K efflux and Na influx, whereas chronic responses involve protein alteration in plasma membrane, cytosol, and mitochondria. The effects of hypoxia on central neurons described by Haddad are reminiscent of that described in the carotid body. Haddad concludes that there are multiple oxygen sensors in the central nervous system. 

These modern computer controlled ignition systems use multiple sensors to determine optimum firing. This may include double pick-up sensors on the flywheel to determine rpms under acceleration and deceleration, intake and atmospheric pressure compensation, oxygen sensor levels to maximize combustion, temperature sensors and exhaust emission sensors. All this data is constantly fed into the on-board computer and processed using complex algorithms to determine optimum firing and fuel consumption levels. 

This section reviews some recent developments on a multiple analyte sensor that is based on identical Alpg-based OLED pixels and monitors the serum analytes glucose, lactate, ethanol, and oxygen, which are of clinical, health, industrial, and environmental importance. These analytes were monitored sequentially or simultaneously comparable results were obtained using both approaches. 

Nitroxides are the most common of the oxygen-centred biradicals to be reported. As a model for spin-crossover molecules, the nitronyl nitroxide (105) was prepared and by oxidation with PbC>2 afforded the triplet biradical (106) which was characterized by ESR (Scheme 15).242 The one-electron oxidation of (105) afforded the singlet cation (107) which was seen to exist in equilibrium with (106) in solution. The authors claim that pH-controlled interconversion between two species of different spin multiplicities in this way may provide die basis for novel magnetic switches or pH sensors. The N.N-dialkylamino nitronyl nitroxides (108) were prepared and afforded die diplet-state biradical cation species by one-electron oxidation with iodine.243 The authors propose that, by the similarity of die electronic structures, diese structures can be regarded as hetero-analogues of trimethylenemethane. A paper confirms die conversion of 3,3-dimethyldioxetane into die corresponding ring-opened 1,2-diol but refutes the... 

Products obtained by propane-selective oxidation have been analyzed by gas sensor systems [19, 26]. Usually, several or multiple kinds of compounds are produced during the selective oxidation of propane. The formation of CO, C02, aldehydes such as acrolein, and ketone were observed over iron-silica catalysts [28, 29]. During the initial stage of catalyst investigation, the conversion of propane and the selectivity toward useful oxygenate products as chemical resources are of interest. Semiconductor-type gas sensors selective toward the oxygenate were employed to estimate the yield of oxygenate products, with a combination of the potentiometric CO sensor and the ND-IR C02 sensor [30]. 

Sensors may also use multiple electrolytes (referredto as electrolyte chains), and two examples of these are shown in Figure 13.Id and e. In both examples, a Na2SO4 auxiliary electrode is used with a sodium ion conductor so that the sensing electrode reaction is given by Equation (13.5). The difference between the two cases is that, in Figure 13.Id, the sodium ion conductor is used with another cation (strontium) conductor, whereas in Figure 13.le the sodium ion conductor is used with an anion (oxygen) conductor. In both cases, an equilibrium reaction is required to relate the... 

Oxygen ion conductors are used in amperometric sensors for a variety of gas species. The selectivity is controlled by selecting electrode materials that catalyze particular reactions hence, multiple electrodes are required for some multicomponent gas mixtures. In such cases, the system is designed so that each electrode removes a particular gas from the gas stream. The particular gas removed by a particular electrode can also be controlled by the voltage at the electrode, just as in cyclic voltammetry, which has also been used in solid-electrolyte based sensors [34]. In addition to providing selectivity, control of the applied voltage can be used to improve the magnitude of the response [35]. 

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