Small fibers

Fiber-Bed Scrubbers Fibrous-bed structures are sometimes used as gas-liquid contactors, with cocnrrent flow of the gas and hqnid streams. In such contactors, both scrubbing (particle deposition on droplets) and filtration (particle deposition on fibers) may take place. If only mists are to be collected, small fibers may be used, but if solid particles are present, the use of fiber beds is limited by the tendency of the beds to phig. For dnst-cohectiou service, the fiber bed must be composed of coarse fibers and have a high void fraction, so as to minimize the tendency to plug. The fiber bed may be made from metal or... 

Small organisms frequently become embedded within corrosion products and deposits. The organisms may make up a sizable fraction of the deposit and corrosion product. Seed hairs and other small fibers often blow into cooling towers, where they are transported into heat exchangers. The fibers stick to surfaces, acting like sieves by straining particulate matter from the water. Deposit mounds form, reinforced by the fibers (see Case History 11.5). 

Surfaces exposed to water contained many localized areas of wastage (Fig. 6.22). Corroded areas were covered by brittle black or brown caps over irregular metal-loss regions. Many small fibers were embedded in corrosion products, and many more were wrapped around surfaces. Most fibers were about 0.001 in. (0.003 cm) in diameter and were hollow. 

Figure 6.22 A thermocouple housing showing localized wastage. Small fibers containing high concentrations of salt were found in corroded areas.

The earliest information dealing with this phenomenon dates back to 600 B.c. It was found that a piece of amber after it had been rubbed was able to attract small fibers. More recent observations are from the 17th century, when William Gilbert noticed that amber, sulfur, and other dielectrics charged by friction could attract smoke. Similar observations were made by Boyle (1675) and Otto von Guericke (1672). Francis Hauksbee (1709) reported that he had discovered a phenomenon which is now called ionic wind or electric wind. Ionic wind and the glow from the corona discharge was discussed by Isaac Newton (1718). 

Epidermal nerve fiber analysis by immunocytochemical techniques using the panaxonal marker protein gene product 9.5 (PGP 9.5) allows the study of epidermal innervation by small fiber C and A5 nerve fibers (McCarthy et al. 1995 Holland et al. 1997). Studies of skin biopsies of HIV infected patients with DSP or ATN showed reduction in the number of epidermal fibers in distal areas of the lower extremities with an inverse correlation between neuropathic pain intensity and epidermal nerve fiber density (Polydefkis et al. 2002) (Fig. 4.3). There were also fewer epidermal fibers in HIV seropositive patients without clinical evidence of neuropathy, suggesting that HIV infection may be associated with the loss of cutaneous innervation even before the onset of sensory symptomatology (McCarthy et al. 1995). 

Several agents are currently used for plugging high permeability strata. These include small fibers that are carried in the waterflood and deposited in the high permeability zgnes and chemical reactions forming insoluble precipitations. Some of the current methods available, for example polymers or foams, are subject to deterioration and are costly. This gives them limited application as they are not able to penetrate deep into the strata. 

In general, optical-based pH measurement techniques require relatively expensive and cumbersome instruments, and their sophisticated method cannot be easily carried out for routine assay. Interfering contact and reactions of the dye molecules, particularly considering in-vivo measurements, cannot be excluded [34], Some other possible factors, such as a weaker signal at shorter response times, complications in microfabrication, and difficulties in attaching the chemical or biological agents to the small fiber tip, are potential limitations for the application of these optical sensors to in-vivo measurements in micro environments [35]. 

The latest results of a controlled crystallization of macromolecules are the polymer fibrids which are a completely new modification of synthetic polymers as far as the micro- and macro-structure is concerned. They exist of small fibers having a length of up to some millimeters, which are highly oriented, and which have a macro-morphology similar to that of cellulose pulp. 

Breuer O, Sundararaj U (2004). Big returns from small fibers a review of polymer/carbon nanotube composites. Polymer Composites 25 630-645. 

Size. Fiber size is very crucial in OFCD development. Small fibers allow miniaturization of the probe so it may be positioned within a single cell to measure various physical parameters. The core size, the size of the path through which light traverses... 

In view of the fact that the above techniques examine single fibers embedded in a matrix block, application of the experimental measurements to practical fiber composites may be limited to those with small fiber volume fractions where any effects of interactions between neighboring fibers can be completely neglected. To relate the interface properties with the gross performance of real composites, the effects of the fiber volume fraction have to be taken into account. To accommodate this important issue, a modified version of the fiber pull-out test, the so-called microbundle pull-out test, has been developed recently by Schwartz and coworkers (Qui and Schwartz, 1991, 1993 Stumpf and Schwartz, 1993 Sastry et al., 1993). In... 

Some asbestos materials can break into small fibers that can float in the air, and these fibers can be inhaled. These tiny fibers are small, cannot be seen, and can pass through the filters of normal vacuum cleaners and get back into the air. Once inhaled, asbestos fibers can become lodged in tissue for a long time. After many years, cancer or other sickness can develop. In order to be a health risk, asbestos fibers must be released from the material and be present in the air for people to breathe. A health risk exists only when asbestos fibers are released from the material or product. Soft, easily crumbled asbestos-containing material, previously defined as friable asbestos, has the greatest potential for asbestos release and therefore has the greatest potential to create health risks. 

Microfibers allow a fabric to be woven that is lightweight and strong. They can be tightly woven so that wind, rain, and cold do not easily penetrate. Rainwear manufacturers use microfibers for this reason. They also have the ability to allow perspiration to pass through them. Thus, so-called microfiber athletic-wear is becoming more commonplace. Microfibers are also very flexible because the small fibers can easily slide back and forth on one another. The first fabric made from microfiber was Ultrasuede in which short polyester microfibers were imbedded into a PU base. Today microfibers are made mainly from polyesters, nylon, acrylic, and rayon fibers. 

Materials called composites are also in widespread use. A composite consists of small fibers of one substance embedded in a matrix of another substance. The fibers reinforce the matrix, adding stiffness. One of the first composites was fiberglass, in which thin fibers of glass reinforce a plastic material. Fiberglass is strong yet light in weight. 

Local anesthetics preferentially block small fibers because the distance over which such fibers can passively propagate an electrical impulse is shorter. During the onset of local anesthesia, when short sections of a nerve are blocked, the small-diameter fibers are the first to fail to conduct electrical impulses. For myelinated nerves, at least two and preferably three successive nodes of Ranvier must be blocked by the local anesthetic to halt impulse propagation. Therefore, myelinated nerves tend to become blocked before unmyelinated nerves of the same diameter. For this reason, the preganglionic fibers are blocked before the smaller unmyelinated C fibers involved in pain transmission. 

Huffman (87) studied the transient emissions from terbium in a vinylic resin matrix. His compound was Tb tris-[4,4,4-trifluoro-l-(2-thienyl)-1,3-butaneodione] in polymethylmethacrylate. This may be conveniently abbreviated as TbTTA in PMMA. The compound EuTTA in PMM A had previously been reported by Wolff and Pressley (99) to give laser oscillation. Working with small fibers at 77°K, Huffman found distortions from the normal fluorescent decay curves when the optical pumping was large. He interprets this as evidence for stimulated emission. A comparison of these distorted decays with EuTTA in PMMA indicated a similar behavior, thus tending to substantiate his hypothesis. 

Preparations of carbon fibers are similar to those of GC, with two important exceptions caused by the small fiber diameter. Fibers are mounted quite differently from GC, particularly for in vivo applications that require a small overall electrode diameter. In addition, fibers can experience much higher current densities during electrochemical pretreatment, which can qualitatively alter ECP effects. 

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