Structure hollow

The carbon-arc plasma of extremely high temperatures and the presence of an electric field near the electrodes play important roles in the formation of nanotubes[ 1,2] and nanoparticles[3]. A nanoparticle is made up of concentric layers of closed graphitic sheets, leaving a nanoscale cavity in its center. Nanoparticles are also called nanopolyhedra because of their polyhedral shape, and are sometimes dubbed as nanoballs because of their hollow structure. 

In addition to nanocapsules filled with metals and carbides, various exotic carbon materials with hollow structures, such as single-wall (SW) tubes[9,10], bamboo-shaped tubes, and nanochains[l 1], are produced by using transition metals as catalysts. 

Nanoscale diameter, hollow structure, high conductivity, mechanical strength and inertness of CNTs are also very useful for macroscale applications. MWCNTs have been more widely used for macroscopic applications since they are more readily available in larger quantities and are more stable than SWCNTs. 

A hollow waveguide (HWG) is essentially a hollow tube that transports light from one end to the other either by multiple mirror reflection or by total internal reflection. The hollow structure gives them several advantages (i) a high power threshold, (ii) low insertion losses, (iii) no end reflections, (iv) a small beam divergence, (v) robustness and - especially important for sensor applications - (vi) a wide spectral transmission range. 

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

Embryonic stem cells are derived from pre-implant-stage human embryos, usually at the blastocyst stage (the blastocyst is a thin-walled hollow structure containing a cluster of cells, known as the inner cell mass, from which the embryo arises). These embryos are invariably ones initially generated as part of in vitro fertilization procedures but which are destined to be discarded, either due to poor quality or because they are in excess to requirement. There are an estimated 400 000 in vitro fertilization-produced embryos in frozen storage in the USA alone, of which some 2.8 per cent are likely to be discarded. 

Smooth muscle is distributed throughout the body, largely around hollow structures such as blood vessels, the gastrointestinal tract and the genitourinary system. Normal function requires that the smooth muscles contract and relax at appropriate times, and abnormalities of contraction underlie such important pathologies as hypertension, incontinence and abnormal childbirth. Since contraction is initiated by an increase of cytoplasmic Ca2+ concentration then normal function requires appropriate Ca2+ handling. 

The main difference between titania nanotube and the ID nanostructures discussed before is the presence of an hollow structure, but which has significant consequences for their use as catalytic materials (i) in the hollow fiber nanoconfinement effects are possible, which can be relevant for enhancing the catalytic performance (ii) due to the curvature, similarly to multi-wall carbon nanotubes, the inner surface in the nanotube is different from that present on the external surface this effect could be also used to develop new catalysts and (iii) different active components can be localized on the external and internal walls to realize spatially separated (on a nanoscale level) multifunctional catalysts. 

The detection of other molecules, such as ammonia, requires the use of a porous catalytic metal. To obtain a gas response from the NH3 molecule, it is believed that active sites of triple points are required where the molecules are in contact with the metal, insulator, and ambient [30, 31]. It has been shown that gas species such as hydrogen atoms or protons also diffuse out onto the exposed oxide surface in between the metal grains [Figure 2.1(b)] [32, 33]. Furthermore, Lofdahl et al. have performed experiments that provide clear evidence that hydrogen atoms or protons also diffuse under the metal from the triple point [34]. The hollow structure of the metal surface facing the insulator has been revealed by Abom et al. [35]. 

Traditionally, opium is smoked with a pipe, typically around 20 inches long. Opium pipes are usually made of wood, and the type of wood used often denotes the wealth of the smoker. Poor smokers typically use pipes made from bamboo, while wealthier smokers may have pipes constructed of ebony. About three-quarters down the shaft of the pipe rests the bowl, a hollow structure that can be made of metal, porcelain, or clay, again depending on the quality of the pipe. The hollow pipe is sealed on one end and has an opening on the other, through which the user takes in the smoke. 

Though Ceo has not (so far) found any major applications, the influence of C6o is now pervasive in chemistry and beyond.8 C6o is a kind of ideal nanoscale building block that can be picked up and manipulated with nanotechnological tools.9 Importantly, its curved, hollow structure has made us familiar with another view of carbon materials, different and complementary to that of flat sheets of carbon atoms in graphite. Ultimately, all the interest generated around such carbon allotropes has driven the research in the field and introduced the perhaps most notable representatives of the present nanoworld, carbon nanotubes (NTs). 

PeritheciuM In fungi, an ascocarp consisting of a spherical, cylindrical, or flash shaped, hollow structure, which contains the asci and usually opens by a terminal pore. 

The broad classes of packings for vapor-liquid contacting are either random or structured. The former are small, hollow structures with... 

Foams have a large variety of applications. Solid foams are widely used as insulating materials. Due to the presence of air bubbles they have a low thermal conductivity. Polyurethane foams and Styrofoam are examples. Styrofoam is also used as a packing material. The light weight of polymer foams makes them attractive as filling materials to stabilize otherwise hollow structures. A natural solid foam is pumice stone. Metal foams are used in the automotive and aerospace industry as light and stable materials [567], Ceramic foams are developed for electronic applications as piezoelectric transducers and low dielectric constant substrates [568],... 

The eye globe is a hollow structure filled anteriorly by the aqueous humor and posteriorly by the vitreous. The aqueous humor (Figure 24.1) is continuously formed by the ciliary body. It is secreted into the posterior chamber from which it passes through the pupil into the anterior chamber and is drained at the anterior chamber periphery. Due to the blood aqueous barrier formed by zonulae occludentes of the nonpigmentary ciliary epithelium, macromolecules such as proteins can pass to the aqueous in very small quantities, regardless of their plasma concentrations. In humans, the aqueous humor protein level is around 20 mg/100 mL, less than 0.5% of the normal plasma total protein levels (Table 24.1) [22]. In the human eye, the rate of aqueous formation is around 2.5 pL/min, whereas in the case of rabbit eye it is... 

Hollow planar waveguides have been fabricated by several techniques, including physical vapor deposition and CVD of silver and dielectric layers on metallic substrates. Nevertheless, better results can be obtained by taking advantage of silicon micromachining techniques. Perhaps the most important advantage of silicon hollow waveguides over other hollow structures is the... 

The omnidirectional guide is most useful for sensing applications owing to the open hollow core. In honeycomb-type structures [31,32], light is confined to the small central air hole, which is difficult to fill with analyte gas for sensing owing to considerable back-pressure building up in the hollow structure. 

Figure 10 A novel micron-sized hybrid of silk fibroin and CaCOj, with a hollow structure and unusual rice-like shape is synthesized in the presence of regenerated silk fibroin via aggregation-mediated crystallization (a) mineralization of HAP on the electrospun mat of silk fibroin (b).

Tubulin is a self-assembling protein that forms microtubules (MTs) within the cell. MTs are involved in a variety of cell functions including vesicle movement, chromosome segregation, and cell motility. MTs are assemblies of heterodimeric proteins, a/p-tubulins. The protein consists of two subunits, a modified a-tubulin and a modified P-tubulin. The two monomers have about 40% of the same amino acid sequences and their structures are similar except for a few differences in the loops. Each monomer contains a pair of central P sheets surrounded by a helices. The tubulin monomers self-assemble into hollow structures, termed microtubules. 

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