Time scale, extension

The solutes were benzene, ethyl benzene, butyl benzene, hexyl benzene, octyl benzene and decyl benzene and it is seen that the silica could easily resolve any two solute pairs having a difference of only two methylene groups. In fact, solutes having only one methylene group difference would have been discerned as two peaks. The disadvantage of the system can be seen from the time scale. The separation took over 10 hours to complete and this extensive time period was necessary even when using the maximum inlet pressure available of 6,000 p.s.i. 

Although the idea of generating 2D correlation spectra was introduced several decades ago in the field of NMR [1008], extension to other areas of spectroscopy has been slow. This is essentially on account of the time-scale. Characteristic times associated with typical molecular vibrations probed by IR are of the order of picoseconds, which is many orders of magnitude shorter than the relaxation times in NMR. Consequently, the standard approach used successfully in 2D NMR, i.e. multiple-pulse excitations of a system, followed by detection and subsequent double Fourier transformation of a series of free-induction decay signals [1009], is not readily applicable to conventional IR experiments. A very different experimental approach is therefore required. The approach for generation of 2D IR spectra defined by two independent wavenumbers is based on the detection of various relaxation processes, which are much slower than vibrational relaxations but are closely associated with molecular-scale phenomena. These slower relaxation processes can be studied with a conventional... 

For a classical diffusion process, Fickian is often the term used to describe the kinetics of transport. In polymer-penetrant systems where the diffusion is concentration-dependent, the term Fickian warrants clarification. The result of a sorption experiment is usually presented on a normalized time scale, i.e., by plotting M,/M versus tll2/L. This is called the reduced sorption curve. The features of the Fickian sorption process, based on Crank s extensive mathematical analysis of Eq. (3) with various functional dependencies of D(c0, are discussed in detail by Crank [5], The major characteristics are... 

For folded proteins, relaxation data are commonly interpreted within the framework of the model-free formalism, in which the dynamics are described by an overall rotational correlation time rm, an internal correlation time xe, and an order parameter. S 2 describing the amplitude of the internal motions (Lipari and Szabo, 1982a,b). Model-free analysis is popular because it describes molecular motions in terms of a set of intuitive physical parameters. However, the underlying assumptions of model-free analysis—that the molecule tumbles with a single isotropic correlation time and that internal motions are very much faster than overall tumbling—are of questionable validity for unfolded or partly folded proteins. Nevertheless, qualitative insights into the dynamics of unfolded states can be obtained by model-free analysis (Alexandrescu and Shortle, 1994 Buck etal., 1996 Farrow etal., 1995a). An extension of the model-free analysis to incorporate a spectral density function that assumes a distribution of correlation times on the nanosecond time scale has recently been reported (Buevich et al., 2001 Buevich and Baum, 1999) and better fits the experimental 15N relaxation data for an unfolded protein than does the conventional model-free approach. 

On the contrary, are(j u/0red clearly shows some dependence on the structure of the crosslinks, changing from around 0.27 to 0.10 as the branching density z increases from 0.01 to 0.5. The different time scale of the experiments can not have effected the results, because is was proved that G is independent of frequency. The deformation ratio X is 1.00005 in case of torsional vibrations and 1.02-1.04 in case of uniaxial extension. Hence it ap-... 

The incorporation of 14C into compounds at a suitable site often requires extensive and complicated syntheses, and thus a relatively long time. This usually means that 14C-labeled compounds are unsuitable for studies to be carried out during discovery. There are however, very rapid methods for incorporating 3 H into compounds. The newer methods, generally involving metal-catalyzed exchange reactions [15-18], in our experience, mean that suitable labels can often be prepared in 2 or 3 weeks. These time scales make the approach viable for discovery support. Additionally, and importantly, these methods can lead to specific incorporation of tritium. 

For h < 26, the situation is much more complex. One not only needs to know 4>(z) for each layer, but how 4>(z) changes as the two particles approach, i.e. 4>(z,h) this may well depend on the time-scale of the approach, i.e. the equilibrium path may not be followed. Scheutjens and Fleer (25) in an extension of their model for polymer adsorption have analysed the situation for two interacting uncharged parallel, flat plates carrying adsorbed, neutral homopolymer, interacting under equilibrium conditions. Only a semi-quantitative picture will be presented here. 

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