Spindle mechanical properties

Spindle Mechanical Properties. How does the spindle respond to the mitotic forces so that force directionality is controlled and orderly chromosome motion results Artificial forces have been used to study chromosome attachment to the spindle. Especially informative are the centrifugation studies of Schrader (1934), Shimamura (1940), and Yamamoto (1964), and the micromanipulation experiments of Carlson (1952). Recent micromanipulation results (Nicklas and Staehly, 1967) add some details to the earlier observations and confirm them during normal prometaphase and anaphase motion. Artificial forces sufficient to stretch the chromosome cause little or no increase in the distance from the pole to the kinetochore, but there is much less resistance to lateral or poleward displacement. The spindle as a whole behaves in micromanipulation and during isolation as a single body it is a mechanical unit independent of the rest of the cell (reviewed by Mazia, 1961). The simplest, and the classic, interpretation attributes these mechanical properties to individual spindle fibers in order to account for the... 

Alloy 600 plates ( 6 mm thick) were butt welded using a PCBN tool. Spindle speed was 450 rpm, and travel rate was 56 mm/min (2.2 in./min). Substantial grain refinement was observed in the stir zone. Mechanical properties were excellent. Yield strength and ultimate strength were 370 and 720 MPa (54 and 104 ksi), respectively, compared with 265 and 630 MPa (38 and 92 ksi) for the base metal. Elongation was reduced from 50% in the base metal to 27% in the transverse weld specimen. However, it is important to recognize that the non-... 

These considerations will center on the usual course of chromosome motion occurring when the spindle is present—prometaphase through anaphase. Three questions suggest the analytical Tormat. First, descriptive cytology What are the phenomena to be explained Second, mechanics What forces and mechanical properties are necessary to account for chromosome motion Third, preliminary attempts at molecular explanation How are mitotic forces produced and controlled This gives a progression from the best to the least understood features of chromosome motion. 

Summary and Conclusions. The following cytological and mechanical features yield a general explanation of both prometaphase and anaphase. Beyond this, they provide numerous tests for the adequacy of molecular hypotheses of force production and control. The conclusions not beyond dispute have been put in parentheses. Their justification, beyond that given above, is their consistency with one another in leading from spindle structure to forces and mechanical properties and to the explanation of the observed motions. Some entries on this list also appear on those of Mazia (1961, p. 285) and Forer (1969, pp. 572-573). 

This model proposes a functional differentiation of chromosomal and interpolar spindle fibers in good accord with the cytological features of prometaphase congression and separate poleward motion and spindle elongation in anaphase, with the static mechanical properties, and with the slight evidence for differences in chromosomal and interpolar fibers from their differing responses to colchicine and chloral hydrate (p. 245). Any more extended discussion is unwarranted until the motions of granules and displaced chromosomes have been fully described in a variety of forms specific predictions are readily formulated. 

Understanding the rheology of the fiber-spinning dope solutions is important to enable the fabrication of the polyaniline fibers with reproducible electrical and mechanical properties. In our studies, a Brookfield RVDV-III cone and plate rheometer was used to measure the viscosity of the concentrated EB solutions. The gelation studies of these solutions were conducted at 25°C and a constant shear rate of 0.8 using cone spindle (CP-52) with a semivertical cone angle of 87°. Figure 2.10 illustrates the viscosity... 

The majority part of the interior of the fiber mass is the cortex, which, from the point of view of mechanical properties, is also the most important component. The cortex consists of elongated, spindle-shaped cells aligned in the direction of the fiber axis. Within these cells resides the major part of the keratinized protein in the form of macrofibrils, which in turn are formed by lower levels of organization, i.e., microfibrils and finally protofibrils. The latter two are low-sulfur proteins and more or less crystalline in nature with their a-helical parts as crystalline lattice components. They are embedded in a noncrystalline, nonfibrillar matrix of disulfide cross-linked, globular proteins. 

The Mooney viscosity is the torque generated on a spindle rotating at constant angular velocity, immersed in a polymeric material between heated dies. It is one of the most widely used industrial measures of bulk viscoelastic properties of polymeric materials, especially elastomers and rubbers. Oftentimes, the Mooney viscosity is of greater practical significance than the dynamic mechanical determination of G and G". The notion of Mooney viscosity is well grounded in the principles of continuum mechanics but involves the empirically determined Mooney viscosity and related parameters. 

The cortical layer, the cortex, is located tmder the cuticle and forms the main mass of the fiber and, consequently, defines basic physico-mechanical and many other properties of the wool. Cortex is composed of spindle-shaped cells connivent to one another. Protein substance is also located between the cells. 

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