Fiber structure

The temperature dependence of the thermal conductivity of CBCF has been examined by several workers [10,13,14]. Typically, models for the thermal conductivity behavior include a density term and two temperaUrre (7) terms, i.e., a T term representing conduction within the fibers, and a term to account for the radiation contribution due to conduction. The thermal conductivity of CBCF (measured perpendicular to the fibers) over the temperature range 600 to 2200 K for four samples is shown in Fig. 6 [14]. The specimen to specimen variability in the insulation, and typical experimental scatter observed in the thermal conductivity data is evident in Fig. 6. The thermal conductivity of CBCF increases with temperature due to the contribution from radiation and thermally induced improvements in fiber structure and conductivity above 1873 K. 

In an earlier study (44) on the effect of viscosity ratio on the morphology of PP-LCP blends we found that the viscosity ratio is a critical factor in determining the blend morphology. The most fibrillar structure was achieved when the viscosity ratio (i7lcp i7pp) ranged from about 0.5-1. At even lower viscosity ratios the fiber structure was coarser, while at viscosity ratios above unity, the LCP domains tended to be spherical or clusterlike (Fig. 1)=... 

For increased power requirements, electrode constructions have been developed which bring the electronic conductors in closer contact with the active material particles first, around 1930, the sinter electrode [110], recently in sealed cells largely replaced by the nichel-foam electrode, and then, around 1980, the fiber structure electrode [111]. In order to take full advantage of their increased perform-... 

Polk et al. reported27 that PET fibers could be hydrolyzed with 5% aqueous sodium hydroxide at 80°C in the presence of trioctylmethylammonium bromide in 60 min to obtain terephthalic acid in 93% yield. The results of catalytic depolymerization of PET without agitation are listed in Table 10.1. The results of catalytic depolymerization of PET with agitation are listed in Table 10.2. As expected, agitation shortened the time required for 100% conversion. Results (Table 10.1) for the quaternary salts with a halide counterion were promising. Phenyltrimethylammonium chloride (PTMAC) was chosen to ascertain whether steric effects would hinder catalytic activity. Bulky alkyl groups of the quaternary ammonium compounds were expected to hinder close approach of the catalyst to the somewhat hidden carbonyl groups of the fiber structure. The results indicate that steric hindrance is not a problem for PET hydrolysis under this set of conditions since the depolymerization results were substantially lower for PTMAC than for die more sterically hindered quaternary salts. 

In contrast to single-crystal work, a fiber-diffraction pattern contains much fewer reflections going up to about 3 A resolution. This is a major drawback and it arises either as a result of accidental overlap of reflections that have the same / value and the same Bragg angle 0, or because of systematic superposition of hkl and its counterparts (-h-kl, h-kl, and -hkl, as in an orthorhombic system, for example). Sometimes, two or more adjacent reflections might be too close to separate analytically. Under such circumstances, these reflections have to be considered individually in structure-factor calculation and compounded properly for comparison with the observed composite reflection. Unobserved reflections that are too weak to see are assigned threshold values, based on the lowest measured intensities. Nevertheless, the number of available X-ray data is far fewer than the number of atomic coordinates in a repeat of the helix. Thus, X-ray data alone is inadequate to solve a fiber structure. 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

Of special interest to intercalation studies are complex non-stoichiometric systems, such as the so-called misfit layer chalcogenides that were first synthesized in the 1960s [45]. Typically, the misfit compounds present an asymmetry along the c-axis, evidencing an inclination of the unit cell in this direction, due to lattice mismatch in, say, the -axis therefore these solids prefer to fold and/or adopt a hollow-fiber structure, crystallizing in either platelet form or as hollow whiskers. One of the first studied examples of such a misfit compound has been the kaolinite mineral. 

For thermal protection during reentry from space, Dornier manufactured some model shingles from SiC/SiC and C/SiC. Fig. 13 shows two shingles each reinforced with two beads. For these parts a special prepreg was developed which had a 2.5 D fiber structure and enabled easy forming by autoclave tools to be carried out. 

Finally, we were led to the last stage of research where we treated the crystallization from the melt in multiple chain systems [22-24]. In most cases, we considered relatively short chains made of 100 beads they were designed to be mobile and slightly stiff to accelerate crystallization. We could then observe the steady-state growth of chain-folded lamellae, and we discussed the growth rate vs. crystallization temperature. We also examined the molecular trajectories at the growth front. In addition, we also studied the spontaneous formation of fiber structures from an oriented amorphous state [25]. In this chapter of the book, we review our researches, which have been performed over the last seven years. We want to emphasize the potential power of the molecular simulation in the studies of polymer crystallization. 

With both the extreme values 5.9 10 2 respectively 31.8 10 2 kJ/m h °C the term C becomes 59.3 10"3 or 11 10 3 and rMD (5 9) = 9.1 h, respectively fMD (1,8) = 2.5 h. The heat conductivity in the product becomes the decisive value. It is a function of the chamber pressure, but changes in the interesting pressure range of 0.5 mbar to 1 mbar by only 15 %. However it varies with the solid content by a factor of 2 and is dependent on the structure. The A,r of turkey meat parallel to the fiber structure is three times larger than given above. 

Fiber spinning, 11 174, 175, 170-171 carbon-nanotube, 13 385-386 methods of, 16 8 models of, 11 171-172 of polyester fibers, 20 12-15 Fiber structure, of aromatic polyamides, 19 727... 

Figure 16.8 Three different kinds of bolaamphiphiles containing different apo-lar spacers and/or polar head groups. The cartoons representthe orthogonal and nonorthogonal arrangements proposed to explain the fiber structures observed in solution...

Hilakus, W., Resin impregnation of fiber structures, US Patent 4 728 387, 1986. 

In summary what have we learned in 25 years In some areas, surprisingly little— for example, we cannot say that we really understand the condensed chromatin fiber structure much better than we did in 1978. Although the significance of the great majority of histone variants remains unknown, replacement histones appear now to be involved in major chromosomal functions. There are areas in which we have accrued incredible amounts of detailed information yet still do not quite know what to do with it. Histone acetylation is a prime example. Allfrey et al. [56] could predict its role in a general sense in 1964. We now know a whole rogue s gallery of acetylases and deacetylases plus the specific histone sites for many. Nevertheless, authorities in the field must still write in 2000, The mechanisms by which histone acetylation affects chromatin structure and transcription is not yet clear [58]. 

Beard, D.A. and Schlick, T. (2001) Computational modeling predicts the structure and dynamics of chromatin fiber. Structure (Camb) 9, 105-114. 

Although chemically modifying DNA have distinctive implications for chromatin transitions and fiber structure in the presence of HI [250], in vivo these effects appear to work in concert with chromosomal proteins. 5 -Methylcytosines are specifically bound by members of the MBD (methyl-CpG-binding-domain) family, such as MeCP2 (Methyl-Cytosine binding Protein 2) and MBDl. These proteins have been shown to interact with HDACs and provide a casual link between DNA methylation, histone deacetylation and transcriptional repression [251-253]. 

The insight from AFM images may be greatly boosted by sophisticated image analysis. Fritzsche and Henderson [30,31] have extracted cross-sections of nucleosomes at half-maximum height and have fitted them to virtual ellipsoids. These ellipsoids had relatively smooth perimeter and an aspect ratio of 1.2 1.4 moreover, the orientation of the ellipsoids was correlated with the direction of the fiber axis, with more than 50% of nucleosomes aligned with the axis. While this orientation effect may result from surface interactions, as discussed by the authors themselves, it may also represent an actual, and structurally important, feature of fiber structure. Ellipsoid-shaped nucleosomes have been reported in electron EM studies [32,33], and have been predicted in models of chromatin... 

Three-dimensional fiber structure summary of results... 

The structure of the condensed chromatin fiber is still under discussion [1,23,54], with two competing models the original solenoid model of Finch and Klug [16], and the straight-linker model [12,14,55]. Assessing the structure in vivo or in situ has proven impossible thus far, due to technical limitations. Chromatin fibers released from nuclei into solution by nuclease treatment have been widely used as models for fiber structure such fibers are extended at low ionic strength and condensed at ionic strengths believed to be close to those found in vivo ( 150 mM Na" " or 0.35 mM Mg " "). The salt-induced fiber compaction has been extensively studied in the past but is still poorly understood in terms not only of the details of the structure but also in terms of the molecular mechanisms of the compaction process. 

---