Spheroidal structures

Semino CE, Merok JR, Crane GG et al (2003) Functional differentiation of hepatocyte-like spheroid structures from putative liver progenitor cells in three- dimensional peptide scaffolds. Differentiation 71 262-270... 

There now are known to be a whole family of caged carbon structures having various numbers of carbon atoms, including C30, C50, C7o, C72, C76, Cg4, and the huge C540. The name fullerene has replaced the unwieldy, Buckminsterfullerene used to describe this general spheroid structure of carbon, although they still are referred to as Buckyballs . 

When one thinks in terms of the many fused-ring isomers with unsatisfied valences at the edges that would naturally arise from a graphite fragmentation, this result seems impossible there is not much to choose between such isomers in terms of stability. If one tries to shift to a tetrahedral diamond structure, the entire surface of the cluster will be covered with unsatisfied valences. Thus a search was made for some other plausible structure which would satisfy all sp valences. Only a spheroidal structure appears likely to satisfy this criterion, and thus Buckminster Fuller s studies were consulted (see, for example, ref. 7). An unusually beautiful (and probably unique) choice is the truncated icosahedron depicted in Fig. 1. As mentioned above, all valences are satisfied with this structure, and the molecule appears to be aromatic. The structure has the symmetry of the icosahedral group. The inner and outer surfaces are covered with a sea of v electrons. The diameter of this C o molecule is 7 A, providing an inner cavity which appears to be capable of holding a variety of atoms. ... 

Spheroidal structures spontaneously formed in solution from amphiphilic (AB type) copolymers or block copolymers (ABA type), where A = hydrophobic, B = hydrophilic... 

Annealing. Annealing has two different purposes to relieve stresses induced by hot- or cold-working, and to soften the steel to improve its machinability or formability. It may involve only a subcritical heating to relieve stresses, recrystallize cold-worked material, or spheroidize carbides alternatively, it may involve heating above the upper critical temperature (A3) with subsequent transformation to pearlite or, less commonly, direcdy to a spheroidized structure on cooling. 

Modulus VS Composition. The modulus of IPNs as a function of composition 3rields information about their relative phase continuity. The first such study on polyacrylate/polyurethane latex interpenetrating elastomeric networks (lENs) was carried out by Matsuo and co-workers (Fig. 7) (43). Note that in the midrange of composition, the modulus begins to follow the parallel Takayanagi model (44). This suggests that the stiflfer acrylic phase is becoming a continuous phase, as predicted from percolation models of three-dimensional mosaics of compressed spheroidal structures. 

The morphologies using the 4a route were fibrous in nature (64) those utilizing route 4b resulted in a porous spheroidal structure for the PP phase (65). In all cases, the morphology was significantly finer than that available with the then commercial routes of preparing PP/EPDM thermoplastic IPNs. 

The microstructure of these steels has little effect on corrosion in the atmosphere or in neutral or alkaline solutions. In acids, however, microstructure can have a significant effect because the carbide morphology affects the hydrogen discharge reaction. Untempered martensitic and pearlitic structures generally show the lowest rates of attack in acids, whereas tempered martensite and spheroidized structures show much higher rates [2],... 

Castillon et al. analyzed the capacity of human airway epithehal ceUs cultured as three-dimensional (3D) spheroid structures to be efficiently transduced on long term by a pseudotyped lentiviral vector. They showed that lentiviral transduction does not alter the airway reconstitution and that the 3D spheroid structures were able to repopulate denuded basement membrane and reconstitute a well-differentiated human airway surface epithehum [76]. 

There are two simplifications of the Halpin-Tsai equations, en f approaches zero, approximating spheroidal structures, the Halpin-Tsai theory converges to the inverse rule of mixtures, and provides a lower bound modulus. Equation (10.8) expresses this relation, with an appropriate change in subscripts. 

A long standing discussion in the literature addresses the question of whether giant fullerenes prefer a faceted or a spherical shape. This question was raised considering pictures obtained by transmission electron microscopy (TEM) that have shown evidence of possible spheroidal structures in concentric carbon particles (lijima 1980 Ugarte 1992,1995). 

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