Onion-skin structure

Fig. 5.9. Schematic illustration (not to scale) of the onion-skin structure in the interior of a highly evolved massive star (25 M0). Numbers along the vertical axis show some typical values of the mass fraction, while those along the horizontal axis indicate temperatures and densities (gmcm-3). Adapted from Kippenhahn and Weigert (1990).

Fig. 7.3. Cross-section of a massive star. The onion-skin structure is specific to massive stars at the end of their existence.

Liquid crystals, liposomes, and artificial membranes. Phospholipids dissolve in water to form true solutions only at very low concentrations ( 10-10 M for distearoyl phosphatidylcholine). At higher concentrations they exist in liquid crystalline phases in which the molecules are partially oriented. Phosphatidylcholines (lecithins) exist almost exclusively in a lamellar (smectic) phase in which the molecules form bilayers. In a warm phosphatidylcholine-water mixture containing at least 30% water by weight the phospholipid forms multilamellar vesicles, one lipid bilayer surrounding another in an "onion skin" structure. When such vesicles are subjected to ultrasonic vibration they break up, forming some very small vesicles of diameter down to 25 nm which are surrounded by a single bilayer. These unilamellar vesicles are often used for study of the properties of bilayers. Vesicles of both types are often called liposomes.75-77... 

Amplification of DNA of chromosomes. During formation of oocytes parts of the DNA are "amplified" by repeated replication. This provides a way for the ovum to accumulate ribosomal RNA and various proteins in large amounts. Similarly, genes for two abundant proteins of the egg shell or chorion of insects are amplified. Bidirectional replication initiated at discrete positions yields an "onion skin" structure containing many copies of an 90-kb sequence containing the two genes. The polyploidy observed in some highly specialized cells such as the Purkinje cells... 

Fig. 1.10a,b. Mucocele of the appendix, a Cystoid lesion in the region of the appendix with an onion-skin structure, b The appendiceal mucocele appears as a cystoid enlargement of the appendix... 

Figure 4.30 shows the effect of temperature on the structure and a pitch fiber, with an onion skin structure, is preferred to a radial type structure. Possible cross sectional microstmctures of mesophase carbon fibers are given in Figure 4.34 and modification of the flow profile during extrusion can produce a less flow-sensitive product and higher tensUe strength. The lines within each section depict carbon layers, which are at least preferentially parallel to the fiber axis. 

Figure 12.7 Structure of carbon fiber, (a) A schematic iiiustralion of tree trunk or onion skin structure (ieft) and radial structure (right), (b) A typicai opticai micrograph of carbon fiber cross sections under polarized light in crossed nicols condition showing maltose cross patterns. Polarizer and analyzers are parallel to picture edges. Source Reprinted from Nyo H, Heckler AJ, Hoemschemeyer DL, Characterizing the structures of PAN based carbon fibers, 24 Nat Symposium, San Francisco, 179, 51-60, May 8-10.

The discovery of perfect geodesic dome closed structures of carbon, such as C o has led to numerous studies of so-called Buckminster fullerene. Dislocations are important features of the structures of nested fullerenes also called onion skin, multilayered or Russian doll fullerenes. A recent theoretical study [118] shows that these defects serve to relieve large inherent strains in thick-walled nested fullerenes such that they can show faceted shapes. 

Coarser spray droplets yield larger granules which tend to a raspberry coalesced, rather than an onion skin layered, structure. This effect is diminished the larger the ratio of granule size to droplet size. 

The Individual globules have a diameter of 10 -10 A and a peculiar structure similar to onion skin [5]. They contain (probably due to catalytic decomposition of CO on their surface) about... 

Figure 7.11 Typical transverse microstructures of pitch fibers showing radial, random, onion-skin, and quasionion-skin structures. Source Reprinted from Hamada T, Nishida SY, Furuyama M, Tomiaka T, Extended Abstracts of 1S Biennial Confon Carbon, Amer Carbon Soc, Worcester, MA, 225,1987, Hamada T, Nishida SY, Matsumoka M, Endo M, J Mater Res, 2, 850, 1987.

Nyo et examined PAN based Hitco carbon fibers using polarized light microscopy and found that high modulus fibers have a dual structure, with an onion skin like layer on the surface and a radial in the core (Figure 12.7). 

Products from Renewable Sources Surfactants are used in delivery systems for cosmetics. Rhodia has developed a system for fragrance and actives delivery for body washes known as Miracare SLB. The system is based on coconut-derived surfactant in a lamellar phase engineered to form onion-like vehicle that captures fragrances and actives. The onion-like structure has voids that can encapsulate and deliver active ingredients to hair and skin (13). Rhodia also has developed Mackine 301, a nonquartenized amidoamine surfactant. It is a vegetable-based product that offers an excellent alternative to conventional surfactants and is used as a hair conditioner and mask for both healthy and damaged hair (14). 

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