Traction fiber

Hypotheses of Force Production. This discussion will center on the molecular mechanisms by which poleward forces might be produced. Given the mechanical and physiological attributes of the area between the kinetochores and the poles, and the presence there of chromosomal spindle fibers, it is hardly surprising that current speculations revive an old idea—the traction fiber. These speculations are briefly reviewed here. For critiques of the ingenious alternatives advanced earlier, see Schrader, 1953 Mazia, 1961 and Taylor, 1965a. 

Cornman, I. 1944. A summary of evidence in favor of the traction fiber in mitosis. Amer. Natur., 78 410-422. 

Treatments used for various types of fractures are cast immobilization, traction, and internal fixation. A plaster or fiber glass cast is the most commonly used device for fracture treatment. Most broken bones heal successfiiUy once properly repositioned, ie, fixed in place via a cast. This type of cast or brace is known as an orthosis. It allows limited or controlled movement of nearby joints. This treatment is desirable for certain fractures. 

In fiber-reinforced composites the deformation of the matrix is then used to transfer stresses by means of shear tractions at the fiber-matrix interface, to the embedded high-strength fibers. On the other hand, fibers retard the propagation of cracks and thus produce a material of high strength. 

Pagano, N.J. and Tandon. G.P. (1990). Thermo-elastic model for multidirectional coated fiber composites Traction formulation. Composites Sci. Technol. 38, 247 269. 

Fig. 6. Proposed push-pull model for nematode sperm locomotion. Assembly and bundling of MSP filaments into fiber complexes (dark band spanning the lamellipo-dium) pushes the membrane at the leading edge forward. At the same time a second force, associated with disassembly of the fiber complexes at the base of the lamellipo-dium, pulls the cell body forward. In this model, attachments where the cytoskeleton is linked to the membrane and the membrane anchored to the substratum establish traction and separate mechanically the forces produced at opposite ends of the fiber complexes. Thus, rather than canceling each other, these forces can be exerted independently against the substratum. Reproduced from The Journal of Cell Biology, 2000, vol. 149, pp. 7-12 by copyright permission of the Rockefeller University Press.

The fiber is suspended in the liquid, which means that due to small time scales given by the pure viscous nature of the flow, the hydrodynamic force and torque on the particle are approximately zero [26,51]. Numerically, this means that the velocity and traction fields on the particle are unknown, which differs from the previous examples where the velocity field was fixed and the integral equations were reduced to a system of linear equations in which velocities or tractions were unknown, depending on the boundary conditions of the problem. Although computationally expensive, direct integral formulations are an effective way to find the velocity and traction fields for suspended particles using a simple iterative procedure. Here, the initial tractions are assumed and then corrected, until the hydrodynamic force and torque are zero. 

The approach used to simulate Mode I cracking under monotonic loading is to define tractions [Pg.38]

For SDE, with a constant sliding stress, t0, the sliding distance,/, in the absence of fiber failure, is related to the crack surface tractions, ab, by14,31... 

The preceding basic results can be used to obtain solutions for matrix cracking.14,29,31 58,83,86 Present understanding involves the following factors. Because the fibers are intact, a steady-state condition exists wherein the tractions on the fibers in the crack wake balance the applied stress. This special case may be addressed by integrating Eqn. (23) up to a limit u = uq. This limit... 

In structural ceramic composites, the principal effect considered was one of crack-face closure tractions, or cohesive forces, brought about, for instance, by bridging fibers. A rigorous evaluation of the crack tip fields where the crack faces are not traction free has not yet been attempted. However, an approximate approach for the small-scale creep case is to assume that the crack tip fields are not functionally altered by crack-face tractions, with the effect of the traction being only to introduce a zone of crack tip shielding. This allows for the development of preliminary models for creep crack growth which is inclusive of the role of crack bridging. These preliminary models predict that,... 

Studies of craze microstructure and the surrounding displacements of crazes have established that the only parts around a craze that undergo plastic deformation are concentrated into a process zone at the tip of the craze, and into a fringing layer all around the entire craze body. In the process zone craze matter is generated by one of the two processes discussed above, and fibrils are necked down to the final extension ratio. In the fringing layer, additions are made to craze fibrils by drawing polymer out of half space. Outside the idetifiable parts of a craze, the solid polymer remains entirely elastic while inside the craze body the fully drawn fibers carry the required craze tractions purely elastically in their orientation hardened state at the... 

Shen G, Lee HK. HoUow fiber-protected liquid phase microex-traction of tiiazine herbicides. Anal Chem 2002 74 648-654. 

Before reviewing in detail the fundamental aspects of elastomer blends, it would be appropriate to first review the basic principles of polymer science. Polymers fall into three basic classes plastics, fibers, and elastomers. Elastomers are generally unsaturated (though can be saturated as in the case of ethylene-propylene copolymers or polyisobutylene) and operate above their glass transition temperature (Tg). The International Institute of Synthetic Rubber Producers has prepared a list of abbreviations for all elastomers [3], For example, BR denotes polybutadiene, IRis synthetic polyisoprene, and NBR is acrylonitrile-butadiene rubber (Table 4.1). There are also several definitions that merit discussion. The glass transition temperature (Tg) defines the temperature at which an elastomer undergoes a transition from a rubbery to a glassy state at the molecular level. This transition is due to a cessation of molecular motion as temperature drops. An increase in the Tg, also known as the second-order transition temperature, leads to an increase in compound hysteretic properties, and in tires to an improvement in tire traction... 

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