Pumping cells characteristics

Experimental current-voltage characteristic of a pumping cell having the structure shown in Fig. 3b for two different O2 concentrations in N2. The temperature of the device was 750 C. 

Figure 3.14 shows a cross-section of the novel HC sensor that consists of an oxygen pump cell and a gas-detection cell [82], In this sensor, Pt is used for the active electrode of the gas-detection cell and PrgO, is used for the inactive electrode owing to its low catalytic activity and relatively high electric conductivity. The sensing characteristics to 500 ppm of C3Hg of the proposed sensor at a temperature of 800°C are shown in Figure 3.15. The published results [82] allowed identifying...

The effect of an ambiguous pumping current characteristic at 7<1 can be avoided by exposing the anode to a reference atmosphere, favorably to ambient air (Fig. 17.15.9) like a potentiometric cell generating a superimposed Nernst voltage,... 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

Flow of the liquid past the electrode is found in electrochemical cells where a liquid electrolyte is agitated with a stirrer or by pumping. The character of liquid flow near a solid wall depends on the flow velocity v, on the characteristic length L of the solid, and on the kinematic viscosity (which is the ratio of the usual rheological viscosity q and the liquid s density p). A convenient criterion is the dimensionless parameter Re = vLN, called the Reynolds number. The flow is laminar when this number is smaller than some critical value (which is about 10 for rough surfaces and about 10 for smooth surfaces) in this case the liquid moves in the form of layers parallel to the surface. At high Reynolds numbers (high flow velocities) the motion becomes turbulent and eddies develop at random in the flow. We shall only be concerned with laminar flow of the liquid. 

The primary plasma-membrane Ca2+ transporter (PMCA) is a P-type pump with high affinity for Ca2+ (Km = 100-200 nmol/1) but relatively low transport capacity [19]. The stoichiometry of PMCA is one Ca2+ transported for each ATP hydrolyzed. These pumps probably do not carry out bulk movements of Ca2+ but are most effective in maintaining very low concentrations of cytosolic Ca2+ in resting cells. A distinguishing characteristic of the PMCAs is that, in addition to binding Ca2+ as a substrate, they are further activated by binding... 

The sodium and calcium pumps can be isolated to near purity and still exhibit most of the biochemical properties of the native pump. Some kinetic properties of these pumps in native membranes are altered or disappear as membrane preparations are purified. For example, when measured in intact membranes, the time-dependencies of phosphorylation and dephosphorylation of the pump catalytic sites exhibit biphasic fast to slow rate transition this characteristic progressively disappears as the membranes are treated with mild detergents. One suggested explanation is that, as the pumps begin to cycle, the catalytic subunits associate into higher oligomers that may permit more efficient transfer of the energy from ATP into the ion transport process [29, 30], Some structural evidence indicates that Na,K pumps exist in cell membranes as multimers of (a 3)2 [31]. 

Figure 2. Sodium and chloride uptake across an idealised freshwater-adapted gill epithelium (chloride cell), which has the typical characteristics of ion-transporting epithelia in eukaryotes. In the example, the abundance of fixed negative charges (muco-proteins) in the unstirred layer may generate a Donnan potential (mucus positive with respect to the water) which is a major part of the net transepithelial potential (serosal positive with respect to water). Mucus also contains carbonic anhydrase (CA) which facilitates dissipation of the [H+] and [HCO(] to CO2, thus maintaining the concentration gradients for these counter ions which partly contribute to Na+ import (secondary transport), whilst the main driving force is derived from the electrogenic sodium pump (see the text for details). Large arrow indicates water flow...

Batch operation in a larger scale - in laboratory or even industrial applications - frequently is reahzed using a flowthrough cell with optimized flow characteristics, which is coupled by circulating pumps with reservoirs that contain the reaction solutions. 

The red blood cell has no mitochondria and is totally dependent on anaerobic glycolysis for ATP. In pyruvate kinase deficiency, the decrease in ATP causes the erythrocyte to lose its characteristic biconcave shape and signals its destruction in the spleen. In addition, decreased ion pumping by Na /K -ATPase results in loss of ion balance and causes osmotic fragility, leading to swelling and lysis. 

In Figure 4.1, the CSTR is connected to a recycle loop and measurement cells. If the cells and recycle loop have a volume V and the pump has a volumetric pumping speed of Vp then the characteristic residence time is With our various... 

Electrochemical gas detection instruments have been developed which use a hydrated solid polymer electrolyte sensor cell to measure the concentration of specific gases, such as CO, in ambient air. These instruments are a spin-off of GE aerospace fuel cell technology. Since no liquid electrolyte is used, time-related problems associated with liquid electrolytes such as corrosion or containment are avoided. This paper describes the technical characteristics of the hydrated SPE cell as well as recent developments made to further improve the performance and extend the scope of applications. These recent advances include development of NO and NO2 sensor cells, and cells in which the air sample is transported by diffusion rather than a pump mechanism. 

The excitable membrane of nerve axons, like the membrane of cardiac muscle (see Chapter 14) and neuronal cell bodies (see Chapter 21), maintains a resting transmembrane potential of -90 to -60 mV. During excitation, the sodium channels open, and a fast inward sodium current quickly depolarizes the membrane toward the sodium equilibrium potential (+40 mV). As a result of this depolarization process, the sodium channels close (inactivate) and potassium channels open. The outward flow of potassium repolarizes the membrane toward the potassium equilibrium potential (about -95 mV) repolarization returns the sodium channels to the rested state with a characteristic recovery time that determines the refractory period. The transmembrane ionic gradients are maintained by the sodium pump. These ionic fluxes are similar to, but simpler than, those in heart muscle, and local anesthetics have similar effects in both tissues. 

Calcium ions are usually released in distinct pulses or "quanta." The kinetic characteristics of the system of receptors, diffusing InsP3, calcium buffers, and calcium pumps in the cell membrane, and the membrane potential may account for this behavior.174 301-306 Since... 

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