Polarisation ratio

The macroscopic alignment of polymer chains was also achieved by depositing soluble poly(p-phenylenes), such as 37 or poly(3-thiophenes) such as 26, from solution by the Langmuir-Blodgett technique. However, low polarisation ratios ( u/ x) were found for electroluminescence (3 1). 

Low polarisation ratios (<2 1) for absorption had also been found for amorphous PPV (1) deposited from solution by spin-coating on rubbed poly(tetrafluoroethylene) [PTFE]. It is evident that this could be improved on by making use of the high order parameter and self-organising properties of the nematic phase of liquid crystalline electroluminescent polymers such as those (16, 28 and 78-82) shown in Table 6.16. - 2 ° This was then found subsequently to be the case using thermotropic liquid crystalline polyfluorenes, such as 28 and 80 shown in Table 6.6 and segmented PPV derivatives, such as 81. The nematic phase exhibits the lowest viscosity of... 

Center of mass differential cross sections (presented here only for 0( D) + H2) present a (juasi forward-backward symmetry and small rmdulations. The degree of polarisation (ratio of DCS for forwcu d/sideways or backward/sideways) is high ( 3) for initial rotational state j = 0 and decreases with j. The for-... 

The research in this field is very active and even higher polarisation ratios could be obtained in the near future. 

In both of the examples (8), the chemiluminescence is associated with a "parallel transition the positive polarisation ratios found experimentally reflect the expected negative alignment, i.e, a tendency for J j. k However, the ultimate spectator stripping limit was only attained at superthermal collision energies, see Fig. 1 [28]. Despite the low mass of the H atom there is a significant release of orbital motion in the separating products and a clear indication of a preferred non-linear collision geometry. 

The halogen substituents ( — 7 +M) owe their o p-orientating effect, achieved in spite of the deactivation, to polarisability by the conjugative process. The strength of the inductive deactivation is seen in the sequence of the two ratios quoted. 

It follows from (1) that the more negative metal, at a bimetallic junction, can be subject to more aggravated attack because of this lowered cathodic polarisation. In part, this may result from the greater ease of replenishment of dissolved oxygen under conditions where the ratio of surface area to electrolyte volume is very high. Rosenfel d has also produced evidence to show that rapid convective mixing in the condensed layer, under conditions of lowered relative humidity which permit rapid evaporation, further hastens the arrival of dissolved oxygen at the cathode and results in an additional... 

Schematic polarisation curves for phases a and 0 showing the selection of optimum dilTerential etch ratio conditions...

The Hull cell cathode has a continuous variation of current density along its length, and there are equations which give the primary current density at any point not too near the end. If the local thickness is measured at two points for which P is known, Tcan be calculated. The real current distribution is a function of cathode and anode polarisation as well as of the resistance of the electrolyte. The metal distribution ratio will be... 

As A will be a function of current density, T will be a function of electrode area, and comparisons should therefore be made with cells of standard size. Equation 12.12 shows that high throwing indices will result when polarisation rises steeply with current (AE, AEj) and cathode efficiency falls steeply (cj >> f i)- The primary current ratio, P = affects the result because... 

An increase in conductivity usually increases T because it increases the proportion of polarisation in the total cell potential difference and lowers the ratio ( V A )/( V - AEj). Changing the conductivity of an acid copper bath with sulphuric acid produced the following result (291 A/m average c.d., P = 5) ... 

Throwing indices measured in a Hull cell differ from those in a Haring-Blum cell because of the differences in geometry. In a Hull cell several pairs of points can be found which have the same primary current ratio, but for which M and hence T are found to vary because of polarisation changes. 

Fig. 19.20 Schematics of reactivation polarisation curves, (a) Single loop EPR test method, (<>) double loop EPR test method and (c) reactivation ratio EPR test method...

The sequence of polarisation steps is shown in Figure 19.20b. The surface is first polarised anodically from the corrosion potential to -l-3(X)mV (S.C.E.) at a rate of 1-67 mV s . As soon as this potential is reached, the scanning direction is reversed and the potential is decreased at the same rate to the corrosion potential. The ratio of the maximum current in the reactivation loop, to that in the larger anodic loop, is used as a measure of the degree of sensitisation. 

The conclusion of Brown et a/.346,347 viz. that the increased reactivity along a series of alkyl halides is due to the increased polarisation of the carbon-halogen bond has been challenged by Allen and Yats348, who found constant meta para isomer ratios for methylation, ethylation, and isopropylation of toluene, and since this ratio reflects the selectivity and hence reactivity of the electrophile they con-... 

Satchell476 also measured the first-order rate coefficients for dedeuteration of [4-3H]-anisole by acetic acid or acetic acid-hydrochloric acid media containing zinc and stannic chlorides (Table 128). The rates here paralleled the indicator ratio of 4-nitrodiphenylamine and 4-chloro-2-nitroaniline, so that the implication is that a linear relationship exists between log k and the unknown H0 values. The results also show the rate-enhancing effect of these Friedel-Crafts catalysts, presumably through additional polarisation of the catalysing acid, for in the absence of them, exchange between acetic acid and anisole would be very slow. Other studies relating to the effect of these catalysts are reported below (p. 238). 

Cross-polarisation (CP) in the rotating frame has been introduced as a means of transferring polarisation between different nuclear species in solids [168], and has become of central importance for obtaining spectra of rare spins with low gyromagnetic ratios such as 13C, since a significant sensitivity enhancement may be achieved. Cross-polarisation can be used either for direct observation of low-sensitivity nuclei or for indirect detection of such nuclear species via high-sensitivity nuclei such as protons [169]. 

Magnetisation densities and polarised neutron diffraction optimised flipping ratio measurements... 

Before going further, it may be noted that the flipping ratio does not depend either on the Lorentz factor or on absorption in the sample. Certain instrumental parameters such as the polarisation of the neutron beam for the two spin states, the half wavelength contamination of the neutron beam and the dead-time detector can readily be taken into account when analysing the data. On the other hand, the extinction which may occur in the scattering process is not so easy to assess, but must also be included [14]. Sometimes, it is even possible to determine the magnetisation density of twinned crystals [15]. 

With the new VME/UNIX control system on the polarised hot-neutron normal-beam diffractometer D3 at ILL, each measurement cycle for both peak and background intensities lasts 2 s, and the (+)/(-) counting-time fractions are defined with a 1 MHz clock. There are two detector scalers and two monitor scalers ((+) and (-) states). In Table 1, we compare the flipping ratio measured for the strong 200 and the weak 600 Bragg peak reflections of a CoFe sample. As expected, the standard deviation cr (if) is improved in the case of the strong reflection (16%). 

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