Migration length

The reproducibility of electrophoretic work is lower than most experimenters seem to wish. At the moment, migration length and even fractionation (e.g. Pi- and (32-gl°bulins) differ, according to the technique used and even from day to day in the same laboratory (P6). 

Another effect takes place when injecting different sample volumes in the capillary This may systematically change the migration length and, thus, migration times. A constant injection volume is, therefore, advised in cases of required high migration time reproducibility. 

Shock Layer Because the efficiency of actual columns is finite, concentration shocks are not stable. They are eroded by axial dispersion and the finite rate of mass transfer. A steep concentration gradient is formed instead. The steepness of the profile depends on the axial dispersion and the mass transfer resistance. In frontal analysis, a constant pattern, or steady-state profile, forms after an infinite period of time and an infinite migration length. In this case, the shock layer profile... 

In copolymers the exciton migration length is limited by the polymer structure available, and most importantly, by polymer conformation. When exciton migration involves excimers or exciplexes, long sequences of excimer-forming-sites (EFS) must be correctly orientated for maximum distance. 

Then the exciton migration length, L, assuming a one-dimensional random walk, is given by equation 4 ... 

Stern-Volmer plots were made from fluorescence spectral data and Ksy values calculated. Exciton migration lengths were calculated using equation (1) and equations (2), (3) and subsequently equation (4). This procedure gave three values of the migration length for comparison. 

Migration lengths in random copolymers of AON with AN are not greatly affected by composition. Copolymers containing 47 and 80 ... 

ACN had the longest migration length of 70A compared to 63 A for PACN using equation (1). The above percentages correspond to an overall monomer composition of 1 1 and 4 1. Random poly(ACN-co-AN) showed monomeric fluorescence at 355 nm and excimer fluorescence at 405 nm. The Iq/Im ratios were 0.88 and 0.61 for the 47 and 80 ACN copolymers, respectively, and the same value for PACN was 0.52. The incorporation of photo-inactive units such as AN in the copolymer increase chain flexibility and allows more excimer formation. 

The second type of copolymer studied in this work contained ACN and another monomer which was also a fluorophore. A series of copolymers of ACN and 2VN were prepared which varied in composition from 5.5 to 94.5 ACN. Calculated exciton migration lengths and Ksy values are given in Table III. A copolymer containing 53.5 ACN or ca. 1 1... 

Table VI gives the exciton migration lengths for five copolymers of ACN obtained by reacting poly(ACN-co-vinyl alcohol) with different acyl chlorides. The migration length as a percentage of the end-to-end distance is 167% for poly(ACN-co-l-vinyl naphthoate). For fluorophores 2-vinyl naphthoate, vinyl benzoate and vinyl cinnamate the average is 116% and for dimethyl-(2-naphthoxy)vinyloxysilane, 146%.

The quantity + r is usually denoted by and is known as the migration area and M as the migration length ... 

One of the merits of a water cooled plant is its compactness, i.e., that there is no need for wide cooling channels with a resulting decrease of the total density. The water pipes, as contrasted with the gas channels, reduce rather than increase the migration length of the neutrons. This results in a partial compensation of the decrease in A , as far as the size of the pile is concerned, even at low temperatures. 

One can define a characteristic distance 1/ac for every lattice. This is the migration length, divided by y/k — 1... 

As a consequence, l//c is proportional to the linear dimension of a going plant. In order to calculate /c, we have to calculate 1 first. The migration length consists of two parts... 

The migration lengths were assumed to be equal for metal- and oxide-containing lattices. We now go over to calculating the size of a pile, the center one eighth of which contains the uranium as metal, the outside as oxide or carbide. 

These flgures should be compared with the amounts needed, under similar assumptions for the multiplication factor and migration length, for a He-cooled system. We assumed that the multiplication constant is not affected in this case by the higher temperature of the U - an assumption which favors the He-cooled system. 

The second of these equations is capable of a very simple interpretation. The factor of grad in (5) is evidently the mean square of the total distance traveled by a neutron from creation to absorption, i.e. the square of the migration length L We can use a picture in which one free path is the migration length. Then q is the number of collisions per cm and sec and (5) becomes... 

Fujii and co-workers (1985) used such a membrane configuration to separate calcium isotopes with a migration length of 0.70m for a 0.5moll CaCli feed solution, resulting in enrichment factors smaller than those achieved by electromigration on the column. 

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