Applied field strength

Top typical saturation curve and variation of mean electron energy with applied field. Middle fraction of the electron swarm exceeding the specific energy at each field strength. Calculated assuming constant collision cross-section and Maxwell-Boltzman distribution. Bottom variation of products typical of involvement of ionic precursors (methane) and excited intermediates (ethane) with applied field strength... 

From Eq. 17.35 it can be observed that N is directly proportional to the applied field strength, the migration distance from injection to detection and the apparent mobility of a solute. The diffusion coefficient and the length of the capillary are inversely related to the efficiency. ... 

The potential is the potential difference between the plane of shear (or slipping plane) and the bulk solution. From Eq. (4), it is clear that for a given situation of water (electrolyte) in the interstitium, the Ueo is proportional to the zeta potential and to the applied field strength. Also in a real situation of EOD, it is necessary to use the so called length-averaged value of the zeta potential in order to take into account the effect of the axially variable zeta potential on the electroosmotic velocity. 

For the two commercial FIFFF models, symmetric and asymmetric, it is possible to modulate the applied field strength during a run by programming the cross-flow rate however, there are few examples of programmed analyses since, in FIFFF, the whole flowrate control is complex because of the presence of two flow axes, one for channel flow and the other for cross-flow. The back pressures on the channel and cross-flow outlets have to be adjusted, so that each pair of entering and... 

Fig. 2.27 (a) Theoretical potential energy curves for 4HeRh2+ in different applied field strengths. At zero field, the binding energy of the system is about 0.34 eV, and the equilibrium separation is about 2 A. In an applied field of over 4 V/A, the potential barrier reduces rapidly, and dissociation by particle tunneling becomes possible. 

Fig. 27. Quantum efficiency of sensitized hole injection in organic crystals (injected holes per incident photon) versus applied field strength (ratio of voltage to crystal thickness) Pe = perylene. Ar = anthracene, Ch = chrysene, Phen = phenanthrene...

Fig. 10. Magnetization of a-iron oxide samples in Fig. 8 at 1.7 K. as a function of applied field strength. Sample size (a) 2.5 nm, (b) 7.5 nm, (c) 9.5 nm, (d) 14.5 nm, and (e) 25 nm. The curve for y-Fe203 is included for comparison. From ref. 56, reprinted with permission, copyright 1984 by the American Chemical Society.

Another format of chromatography which has been performed on electrophoresis chips is micellar electrokinetic capillary chromatography (MECC). This technique represents a very powerful extension of CE for the separation of both neutral species and ionic compounds, and has been originally developed by Terabe et al. [76]. Transfer of MECC to CE microchips has been first demonstrated by Moore et al. [77]. The experimental procedure used is identical to high speed CE, apart from the fact that a MECC buffer with 50 mM SDS and 10% methanol was used. Again three coumarin dyes were used as a model sample. Separation was achieved within a few minutes. At low applied field strengths (< 400 V/cm), the reproducibility was found to be excellent (below 1 %). 

Fig. 10.3. Electrochromatograms exhibiting the effect of the length of the bare-silica segment on the separation of benzene and alkylbenzenes. Capillary, 100 pm i.d. with a 20 cm ODS segment and a variable-length bare-silica segment of (a), 0 cm (b), 6 cm and (c), 28 cm. Mobile phase, 1.25 mM sodium dihydrogenphosphate, pH 6.0, containing 75% (v/v) acetonitrile. Applied field strength, 625 V/cm. Detection, UV at 254 nm. Solutes 1, benzene 2, toluene 3, ethylbenzene 4, propylbenzene 5, butylbenzene 6, pentylbenzene. Reproduced with permission from Yang and El Rassi [12].

Induction of New Phenomena by Imposed Gradients. Studies on the effects of imposed electric fields on chemical waves (see below on signal propagation) show that phenomena can be induced in the system by the imposed gradient that do not exist in the field free medium. For example, it was found (l l) that for a system wherein only one type of wave existed in the field free case, two stable types of waves exist in the system subject to the field. This "induction of multiplicity" implies that beyond a critical value of the applied field strength new phenomena may set in that are not simple distortions of field free patterns. Another strictly imposed field effect is found in the case of a new two dimensional crescent shaped wave that occurs when a circular wave is subjected to a supracritical field (15). 

It was also found that the electrical resistivity of ceramics based on silicon carbide, and, more recently, zinc oxide could be made sensitive to the applied field strength. This has allowed the development of components that absorb transient surges in power lines and suppress sparking between relay contacts. The non-linearity in resistivity is now known to arise because of potential barriers between the crystals in the ceramic. 

Many ferroelectrics possess very high permittivity values which vary considerably with both applied field strength and temperature. The permittivity reaches a peak at the Curie point and falls off" at higher temperatures in accordance with the Curie-Weiss law... 

Fig. 6.12 Dependence of tan <5 on the applied field strength for barium titanates curve A, technically pure barium titanate curve B, barium titanate containing lead and 1-2 at. % Ti4 replaced by Co3+, unpoled curve C as B but poled.

The EOF is inversely proportional to the viscosity r] of the electrolyte, proportional to its dielectric constant e, the applied field strength E and the -potential (zeta-potential). For FS capillaries, the EOF diminishes with increasing electrolyte concentration, and increases with the degree of dissociation of the surface... 

The quadratic effect of an externally applied field on the absorption coefficient is described by the imaginary part of the third-order susceptibility -o) a),0,0). influences the molar decadic absorption coefficient of the solute. The absorption coefficient in the presence of the field is a quadratic function of the applied field strength (118),... 

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