Window size, effective

In the case of zeolite A, three different cation sites have been identified most of the cations occupy comer sites in the central cavity (Type I sites), but some of the total of twelve univalent ions (e.g. Na+ or K+) ions per cage must occupy sites within the eight-ring windows and therefore partially obstruct the channels. The effective window size of NaA (i.e. the 4A sieve) is thereby reduced from 0.42 nm to c. 0.38 nm. Since the K+ ion is somewhat larger, the window size becomes even smaller (i.e the 3A sieve). When the Na+ cations are exchanged for Ca2+ or Mg2+, the number of requisite cations is reduced and the effective aperture size and pore volume are both increased (the 5A sieve). 

This smoother is one way to improve the signal-to-noise ratio of the data, as shown in Figure 5.4. The original data has some visible random noise and a large spike. The mean smoother with a 3-point window reduces the noise significantly, but does not remove the spike. Witli the largest window size (21 point), the spike is removed but the shape of the peak has changed (broader and lower intensity). The apparent shift in the peak to lower variable number is due to the end effect (i.c., 10 points from each end of the sample vector have been removed). 

Figure 6.5 a Product distribution for hydrocracking catalyzed by an ERI-type zeolite, showing the window effect observed by Chen et ai. b simulation of n-C- in an ERI cage (window size = 0.36 nm xO.51 nm). Thanks to Dr. David Dubbeldam for the zeolite simulation snapshot. 

The size of the polyplex is also crucial to its function. The threshold for first-pass elimination by the kidneys is approximately lOnm in diameter defining a rough lower size limit for nanoparticles (21). Upper size limits are more difficult to establish as they depend on a variety of factors that are variable within tumors including penetration of capillary endothelium, diffusion rates in tumor interstitium and intracellular spaces (22). Macromolecular complexes preferentially accumulate in tumors through the enhanced permeability and retention (EPR) effect (23). Ideally, a nanoparticle would be in a size window such that it could take advantage of the EPR effect. The size of the polyplex can be readily modified during complexation by altering the DNA to polymer ratio (24). 

Anomalous diffusion in zeohtes is expected to happen only in structures which possess cages separated by windows, and the concept of the window effect depends both on the cage and window sizes. An unusual behavior may occur in systems where the sizes of the molecule and of the aperture between cavities are similar, and when the characteristic length scales of the molecifle and of the cavity are comparable. If a molecule is too long to fit comfortably... 

Hadley et al. (1997) also examined the effect of window size in computing the engagement index. In all of the studies described earlier, the index was based upon 40 seconds of EEG activity. Hadley et al. argued that an improvement in system sensitivity might be obtained with a smaller window width. Thus, they compared system operation with window sizes of 40 and 4 seconds. 

---