Fiber differentiation

Figure 5 X-ray reflexes of PET fibers differentiated by draw ratio (in %).

Tohyama, I., Kameyama, M., and Kimura, H. (1998) Quantitative morphometric analysis of two types of serotonin-immunoreactive nerve fibers differentially responding to p-chlorophenylalanine treatment in the rat brain. Neuroscience 26 (3), 971-991. 

A major advance made since the 1965 edition of the volumes lA-16 on developmental physiology in the first series of this Encyclopedia was prepared has been the quantitative elucidation of hormonal control of sieve-tube differentiation during regeneration in stems. In addition, the earlier quantitative studies of tracheary differentiation have been extended and amplified. An unexpectedly close connection between sieve tubes and tracheary cells in their regeneration and normal differentiation has been revealed and a unifying picture of vascular differentiation in the shoot has resulted. A start has recently been made in unraveling the controlling factors for fiber differentiation. These advances will be described and discussed below. 

Aloni took up the problem of fiber differentiation and developed a physio-logical-anatomical approach, which, when combined with multiple-comparison statistics, resulted in two excellent papers (1976, 1979). Concentrating on the primary phloem fibers of Coleus, he used a technique of staining cleared material (Aloni and Sachs 1973) which allowed large samples to be processed efficiently. 

Excision of the leaves reduced to zero the number of fibers differentiated. The presence of a single pair of mature leaves was sufficient to restore fiber differentiation to normal levels, but this inductive effect only operated on internodes below the leaf-pair (Fig. 4.10). Further evidence that the induction moved basipetally came from regeneration experiments in which a transverse slit was made two-thirds of the way through internode 5 fiber differentiation occurred everywhere except directly below the wound if the wound was kept open with parafilm (Fig. 4.10). If the wound was not kept open, fiber differentiation did occur directly below the wound, but the number of such cells was much smaller (Aloni 1976). 

Aldaba VC (1927) The structure and development of the cell wall in plants. I. Bast fibers of Boehmeria and Linum. Am J Bot 14 16-24 Aloni R (1976) Polarity of induction and pattern of primary phloem fiber differentiation in Coleus. Am J Bot 63 877-889... 

The other major benefit of RF heating was in reduced presstimes. A typical steam-heated MDF press was operated at about 163°C. Presstimes, not including deadtime, for 19-mm (3/4 in.) board would be about 7 min. With RF, this time could be reduced to about 5 min. It will be noted that these presstimes, even with the use of RF, are longer than those requited for particleboards and this, in addition to the more costiy base fiber and the higher resin requirements, explains much of the manufacturing cost differential between MDF and particleboard. 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

Bicomponent fibers have also provided a route to self-texturing (self-crimping) fibers. The crimp results from the length differential developed during processing caused by differential shrinkage in the two polymers in side-by-side or eccentric core—sheath configurations (50). 

A significant advantage of the PLM is in the differentiation and recognition of various forms of the same chemical substance polymorphic forms, eg, brookite, mtile, and anatase, three forms of titanium dioxide calcite, aragonite and vaterite, all forms of calcium carbonate Eorms I, II, III, and IV of HMX (a high explosive), etc. This is an important appHcation because most elements and compounds possess different crystal forms with very different physical properties. PLM is the only instmment mandated by the U.S. Environmental Protection Agency (EPA) for the detection and identification of the six forms of asbestos (qv) and other fibers in bulk samples. 

In general, once the curtain of filaments has been produced, it is necessary to attenuate the filaments in order to provide strength and resistance to deformation. The most commonly practiced approach is to utilize a single slot, which is at least the width of the curtain, at a point below the spinning plate and above the laydown screen. There are two practical approaches taken. The first utilizes the injection of low pressure air at a point above the slot so that the fibers attain sufficient acceleration in the slot to provide adequate draw (22) (Fig. 7). The second utilizes a low pressure vacuum below a venturi to provide the pressure differential requited for sufficient acceleration and resulting attenuation (30). 

CeUulosic fibers, powdered limestone, gHsonite, and asphalt are frequently added to both water and oH muds at levels of 10 to 25 kg/m (4—10 lb /bbl) when high differential pressures are encountered to control seepage losses to the formation. This treatment also is used to improve the quaHty of the mud filter cake to reduce the chance of differential pressure sticking. 

Another clinical consideration is the abiUty of local anesthetic agents to effect differential blockade of sensory and motor fibers. In surgical procedures such as obstetrics or postoperative pain rehef, an agent which produces profound sensory block accompanied by minimal motor block is desirable. On the other hand some procedures such as limb surgery require both deep sensory and motor blockade. In clinical practice, bupivacaine ( 22,... 

Muscle tissue is unique in its ability to shorten or contract. The human body has three basic types of muscle tissue histologically classified into smooth, striated, and cardiac muscle tissues. Only the striated muscle tissue is found in all skeletal muscles. The type of cells which compose the muscle tissue are known as contractile cells. They originate from mesenchymal cells which differentiate into myoblasts. Myoblasts are embryonic cells which later differentiate into contractile fiber cells. 

Air Permeability. Air permeabiUty is an important parameter for certain fabric end uses, eg, parachute fabrics, boat sails, warm clothing, rainwear, and industrial air filters. Air permeabiUty of a fabric is related to its cover, or opacity. Both of these properties are related to the amount of space between yams (or fibers in the case of nonwovens). The most common method for specifying air permeabiUty of a fabric involves measuring the air flow per unit area at a constant pressure differential between the two surfaces of the fabric. This method, suitable for measuring permeabiUty of woven, knitted, and nonwoven fabrics, is described in ASTM D737. Units for air permeabiUty measured by this method are generally abbreviated as CFM, or cubic feet per square foot per minute. 

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