Select exclude

To obtain isolated polymer chains, a solvent must be present. The solvent might be selectively excluded or imbibed by the coil, depending on the free energy of interaction, and thereby perturb the coil dimensions. 

However, the size of the pores is the most important initial consideration because, if a molecule is to be adsorbed, it must not be larger than the pores of the adsorbent. Conversely, by selecting an adsorbent with a particular pore diameter, molecules larger than the pores may be selectively excluded, and smaller molecules can be allowed to adsorb. 

Graphical techniques can be applied for single-frequency measurements when the frequency selected excludes the contributions of confounding phenomena. For example, impedance measurements on a semiconductor diode at a sufficiently high frequency exclude the influence of leakage currents and of electronic transitions between deep-level and band-edge states. Thus, as discussed in Section 16.4, the capacitance can be extracted from the imaginary part of the impedance as... 

This principle prevents a priori prejudicing of the constitutive equations by selectively excluding certain dependencies. It is usually this principle which makes the general approach impractical, since it forces us to include dependencies for which there is no physical evidence. In practice, however, this principle has to be compromised. 

The excitation was chopped at a frequency of 34Hz and phase-sensitive detection was used. In this way, the long-lived (seconds at 20K) phosphorescence and delayed fluorescence were selectively excluded from these data, and only the "prompt" fluorescence was analyzed. Data including the long-lived signals were measured in separate experiments, and will be reported elsewhere. 

In blood, 70-80% of " Tc-pertechnetate is bound to proteins. Perchlorate has been shown to displace pertechnetate from plasma protein-binding sites (Oldendorf et al. 1970). The unbound fraction is preferentially concentrating in the thyroid gland and other related structures, such as salivary glands, gastric mucosa, choroid plexus, and mammary tissue. " Tc-pertechnetate is selectively excluded from the cerebrospinal fluid (Andros et al. 1965). 

Similar to the behavior of Nafion, poly(ester sulphonic acid) ionomers selectively exclude anionic species and large particles, but cations and neutral molecules are permeable. Of the three Eastman Kodak AQ 29, AQ 38, and AQ 55 polymers, AQ 55 (see the polymer backbone in Fig. 11.12) is the most studied and most applied in biosensor preparation. Wang and coworkers described have features of this polymer as an electrode material, including strong affinity toward hydrophobic counterions, prevention of electrode fouling from proteins, stability of the polymer film on the electrode, ability to preconcentrate catalysts in the film, and lowering the overpotential of many species difficult to oxidize or reduce. Several workers also showed that this poly(ester sulphonic acid) polymer is very stable as an organic phase electrode material. ... 

In this chapter, the traditional method is used, with a sliding window of 40 m.y. and rejection of all poles >25° from the mean pole, a value suggested by the distribution of poles for the past 1 m.y. discussed above (Figure 3.8). The resulting UgjS are probably minimum values because the selection excludes those poles that lie beyond the 25° limit that otherwise meet the palaeomagnetic criteria. 

It is regretted that the size of the volume has rendered the insertion of literature references impossible the Selected Bibliography (A,5) may partly compensate for this omission. Section numbers are now included in the headings of the pages—a feature introduced in response to requests by many readers. The volume comprises virtually at least three books under one cover, viz., experimental technique, preparations, and qualitative organic analysis. It should therefore continue to be of value as a one volume reference work in the laboratory. Students at all levels will find their requirements for laboratory work (excluding quantitative organic analysis) adequately provided for and, furthermore, the writer hopes that the book will be used as a source of information to supplement their theoretical studies. 

Likewise, Grieco, while working with amphiphile-like reactants, observed an enhanced preference for endo-adduct in aqueous solutions, which he attributed to orientational effects within the micelles that were presumed to be present in the reaction mixture ". Although under the conditions used by Grieco, the presence of aggregates cannot be excluded, other studies have clearly demonstrated that micelle formation is not the reason for the improved selectivities . Micellar a peg tes even tend to diminish the preference for endo adduct. ... 

Every effort has been made to select the most useful and most reliable information and to record it with accuracy. However, the editor s many years of involvement with handbooks bring a realization of the opportunities for gremlins to exert their inevitable mischief. It is hoped that users of this handbook will offer suggestions of material that might be included in, or even excluded from, future editions and call attention to errors. These communications should be directed to the editor at his home address (or by telephone). 

Zeohte 5A is used because its pores can size-selectively adsorb straight-chain molecules while excluding branched and cycHc species. The normal hydrocarbon fraction has better than 95% purity, and the higher octane isomer fraction contains less than 2% normal hydrocarbons (64). 

An example of unique selectivity is provided by the use of 5A molecular sieves for the separation of linear hydrocarbons from branched and cycHc types. In this system only the linear molecules can enter the pores others are completely excluded because of their larger cross section. Thus the selectivity for linear molecules with respect to other types is infinite. In the more usual case, all the feed components access the selective pores, but some components of the mixture are adsorbed more strongly than others. A selectivity between the different components that can be used to accomplish separation is thus established. 

Of interest is the manner in which cavities of the appropriate size are introduced into ion-selective membranes. These membranes typically consist of highly plasticized poly(vinyl chloride) (see Membrane technology). Plasticizers (qv) are organic solvents such as phthalates, sebacates, trimelLitates, and organic phosphates of various kinds, and cavities may simply be the excluded volumes maintained by these solvent molecules themselves. More often, however, neutral carrier molecules (20) are added to the membrane. These molecules are shaped like donuts and have holes that have the same sizes as the ions of interest, eg, valinomycin [2001-95-8] C H QN O g, and nonactin [6833-84-7] have wrap around stmctures like methyl monensin... 

---