Polarity sensors

Typical input data for a moment tensor inversion consist of the network geometry (coordinates of the sensors) knowledge of sensor polarity (i.e. whether an upwards deflection at the sensor indicates a compression or dilatation) sensor orientation source coordinates P and/or S-wave displacement amplitudes recorded at each sensor (time-domain inversion) or P and/or S-wave spectral amplitudes (frequency-domain inversion) and the polarities of the wave phases. 

A modified carbon paste electrode (CPE) using asolectin, cytochrome c, and cytochrome oxidase were applied for amperometric determination of cyanide [56]. The modified CP matrix mimics a biological membrane environment. The sensor, polarized at —0.15 V versus Ag/AgCl, generates the reduced form of cytochrome c, which in turn is oxidized by the enzyme cytochrome oxidase. The resulting current is related to the enzyme activity and is depressed by inhibitors of cytochrome oxidase such as cyanide. Concentrations of cyanide as low as 0.5 pM can be measured with half-maximal response at about 12 pM. The inhibition is reversible and reproducible (RSD = 4%), allowing cyanide determination for more than 2 months using the same probe. Possible use of this biosensor in flow systems was illustrated. 

Electric Field Meter These meters are calibrated to indicate the polarity and magnitude of the electric field (V/m) at the sensor. They should have only one calibrated meter/surface spacing and should be... 

In the perpendicular recording, the magnetic polarity is perpendicular to the media surface and can be read with a GMR sensor similar to the sensor used in LMR. In this case, the media is effectively situated within the head gap, potentially relaxing many limits on both head and media design experienced in longitudinal recording. 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

Indicator electrodes are used both for analytical purposes (in determining the concentrations of different substances from values of the open-circuit potential or from characteristic features of the polarization curves) and for the detection and quantitative characterization of various phenomena and processes (as electrochemical sensors or signal transducers). One variety of indicator electrode are the reference electrodes, which have stable and reproducible values of potential and thus can be used to measure the potentials of other electrodes. 

The problem of measuring small concentration of oxygen in a buffer gas can be solved by using the semiconductor sensor with a sensitive element consisting of a zinc oxide film immersed in a polar or, better, a protodonor liquid (see Section 3.4). 

Fig. 2.6.1 Schematic of an experiment with remote detection. The basic steps are (a) the polarization of the sensor medium, (b) NMR or MRI encoding using rf pulses and magnetic field gradients and (c) signal detection. The NMR or MRI information travels between the locations (b) and (c).

Selective Complexations of Polar Guests by Hosts Containing Functional Sensors ... 

A novel approach for ion sensing is based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) and was presented first106 in 1987. PSDs are charge dyes and typically located at the interface between a lipophilic sensor phase and a hydrophilic sample phase. The transport of an ion into the lipophilic sensor layer causes the PSD to be displaced from the hydrophilic/hydrophobic interface into the interior of the respective phase (or vice versa), thereby undergoing a significant change in its fluorescence properties107 110. 

The ion sensing scheme based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) was extended to other anions. Both the clinically significant chloride ion124 and the environmentally important nitrate anion125 can be sensed in the desired concentration ranges. Such sensors have the unique advantage of having a virtually pH-insensitive response. 

Mohr G.J., Werner T., Oehme I., Preininger C., Klimant I., Kovacs B., Wolfbeis O.S., Novel optical sensor materials based on solubilization of polar dyes in apolar polymers. Advanced materials 1997 14 1108-1113. 

---