Disordered media

Bismuth subgaHate [12552-60-2] (basic bismuth gaHate), Dermatol, is a bright yellow powder that can be prepared by the interaction of bismuth nitrate and gaUic acid in an acetic acid medium. It has been employed as a dusting powder in some skin disorders and as an ingredient of suppositories for the treatment of hemorrhoids (183,185). It has been taken orally for many years by colostomy patients in order to control fecal odors, but the dmg may cause serious neurological problems (186). 

In Sec. 3 our presentation is focused on the most important results obtained by different authors in the framework of the rephca Ornstein-Zernike (ROZ) integral equations and by simulations of simple fluids in microporous matrices. For illustrative purposes, we discuss some original results obtained recently in our laboratory. Those allow us to show the application of the ROZ equations to the structure and thermodynamics of fluids adsorbed in disordered porous media. In particular, we present a solution of the ROZ equations for a hard sphere mixture that is highly asymmetric by size, adsorbed in a matrix of hard spheres. This example is relevant in describing the structure of colloidal dispersions in a disordered microporous medium. On the other hand, we present some of the results for the adsorption of a hard sphere fluid in a disordered medium of spherical permeable membranes. The theory developed for the description of this model agrees well with computer simulation data. Finally, in this section we demonstrate the applications of the ROZ theory and present simulation data for adsorption of a hard sphere fluid in a matrix of short chain molecules. This example serves to show the relevance of the theory of Wertheim to chemical association for a set of problems focused on adsorption of fluids and mixtures in disordered microporous matrices prepared by polymerization of species. 

Conducting polymer composite materials are typical disordered structures consisting of randomly (or according to a certain law) arranged particles of a conducting filler that are submerged into a polymer medium. In this case the filler particles have macro-... 

Figure 57.15. The structural correlation between the trigonal Ni2Al3 (the thick outline) and the bcc structure of the disordered Ni-Al phase. The large circles are Ni, the medium ones are A1 and the small ones are voids (11).

Since equal numbers of disordered and ordered residues were used for training and testing, prediction success would be about 50% if disordered and ordered sequences were the same. In contrast to this 50% value, prediction success rates for the short, medium, long, and merged datasets were 69% 3%, 74% 2%, 73% 2%, and 60% 3%, respectively (Romero et al., 1997b), where the standard errors were determined over about 2200, 2600, 2000, and 6800 individual predictions, respectively. 

The success rate of every prediction set was greater than the value of 50% expected by chance. Specifically, the various sets of predictions differed from the 50% value by about 3 standard deviations (for the lowest success rate, which was for the merged data) to about 12 standard deviations (for the highest success rates, which were for the medium and long regions of disorder). Overall, these data provided very strong support for our hypothesis that disorder is encoded by the amino acid sequence (Romero et al., 1997b). 

Effect of off-diagonal dynamic disorder (off-DDD). The interaction of the electron with the fluctuations of the polarization and local vibrations near the other center leads to new terms VeP - V P, Vev - Vev and VeAp - VAPd, VA - VAd in the perturbation operators V°d and Vfd [see Eqs. (14)]. A part of these interactions corresponding to the equilibrium values of the polarization P0l and Po/ results in the renormalization of the electron interactions with ions A and B, due to their partial screening by the dielectric medium. However, at arbitrary values of the polarization P, there is another part of these interactions which is due to the fluctuating electric fields. This part of the interaction depends on the nuclear coordinates and may exceed the renormalized interactions of the electron with the donor and the acceptor. The interaction of the electron with these fluctuations plays an important role in processes involving solvated, trapped, and weakly bound electrons. 

Additional effect of diagonal dynamic disorder. The variations of the electron densities near the centers A and B due to polarization fluctuations and local vibrations lead to changes in the interaction of the electron with the medium and, hence, to changes in the shape of the potential energy surfaces Ut and Uf as compared... 

According to Table 1, our results showed that disordered cancrinite can also be formed by using a medium carbonate concentration (0.86 mol. L"1) and a low temperature (80°C), but higher reaction times (96 and 336 h) are necessary. A low temperature and low NaOH concentration (80°C, 3.07 mol. L"1) and short reaction times (96 h) did not allow the dissolution of the starting material. On the contrary, a high NaOH and carbonate concentration totally dissolved the starting material and any solid phase is determined in this experiment. 

The nanorods obtained are well cylindrically shaped and well crystalline (Fig. 4), although disorder is probably present at the surface as shown by HRTEM image (see Fig. 4), probably due to the strong bonding of the amine which cover the entire surface. This is demonstrated also from the fact that the nanorods display very different solubilities at different pH values in aqueous solutions due to the amphiphilic behavior of the amine group. In an acidic medium (pH < 3), the amine group is protonated, and the nanorods cannot be precipitated because they form a stable suspension.164 When the pH is increased to basic conditions (pH > 9), the nanorods precipitated within a few minutes. This could be another interesting way to develop... 

One final type of laser resonator, which is also applicable for molecular glasses, should be mentioned The random laser, based on coherent backscat-tering in an amplifying medium [212, 213]. In these structures, strongly scattering nanoparticles like Ti02 colloids are randomly dispersed in the amorphous films leading to self-contained optical paths and thus to the localization of optical modes. Since disordered structures are much easier to produce than ordered... 

Negative values for redox couple entropy have also been obtained for the Cu(II)/Cu(I) reduction, in aqueous medium, of the blue copper proteins stellacyanin, plastocyanin and azurin.14 The decrease in molecular disorder has been attributed in this case to the fact that the charge neutralization of the redox site (from + 1 to 0) favours the formation of hydrogen bonds between the solvent (water) and the copper centre.17... 

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