Twist elastic properties

For the CB0n0.fSj2MB series with n - 7 and 9 a blue phase was observed but not for n = 6 and 8 thus, the chiral properties of these materials do indeed exhibit an odd-even effect as expected. This was rationalised in terms of the smaller pitch for the odd relative to the even membered dimers which arises from the smaller twist elastic constant of odd dimers and is related to their lower orientational order. Surprisingly, the helical twisting power of the dimers in a common monomeric nematic solvent appears to depend solely on the nature of the chiral group, the 2-methylbutyl chiral centre, and not on its environment. Thus similar helical twisting powers are observed for both odd and even membered dimers. We will return to the nature of the phases exhibited by some of these chiral dimers in Sect. 4.4. 

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

In addition, PLCL scaffolds can be easily twisted and bent. In contrast, PLGA scaffolds largely deform and are broken even at strains as low as 20%. These data indicate that PLCL scaffolds are flexible and highly elastic, whereas PLGA scaffolds are stiff and brittle. To further examine the elastic properties of PLCL scaffolds, scaffolds with varying porosity were subjected to cyclic strain at 10% amplitude and 1 Hz frequency for 27 days in culture medium (Jeong, 2004b). PLCL scaffolds of all tested porosities maintained excellent elasticity even in the hydrolytic medium over a 27-day experimental period. 

In this equation now, Tq will be the residual tension existing at the entrance to or the exit from the knot where the suture ends are positively gripped by the compressive forces, n will be equivalent to the number of throws, is the twist angle, and ji is the coefficient of friction. The tension T can be obtained directly from the measurements of the KHF by the loop method and can be equated by empirical means to suture size, tensile and frictional properties, and parameters of knot construction. The value of T, the actual tension existing along the inner loop ends and exerted by the tissues, however, remains to be determined but can be expected to depend upon, among other factors, the size of the suture loop, the tension used to tie the knot and the mechanical and visco-elastic properties of tissues approximated. 

It was determined that the main endowment into the frictional component of the viscosity has the relative movement of the twisted between themselves into m-ball polymeric chains. Such relative movement takes into account the all possible linkages effects. Elastic component of the viscosity rj is determined by the elastic properties of the conformational volume of the m-ball of polymeric chains at its shear deformation. 

To predict the shape of an adherent tissue cell and quantify the stress distribution inside it, the fibrous actin cytoskeleton or the ECM can be modeled as a two-dimensional network of elastic cables. Previously, elastic cable network provided remarkable quantitative predictions of erythrocyte elastic properties and micropipette aspiration experiments. The cable networks have the additional feature that filaments buckle under compressive load. This model has already been tested successfully to model cell poking, magnetic twisting cytometry, magnetic bead microrheometry experiments. Although the cable network is far from representing the complexity of the actin network mechanics, it incorporates some of its essential features. This model is extended to include the effect of spatial distribution of adhesion points along the periphery of the cell. 

One optical feature of helicoidal structures is the ability to rotate the plane of incident polarized light. Since most of the characteristic optical properties of chiral liquid crystals result from the helicoidal structure, it is necessary to understand the origin of the chiral interactions responsible for the twisted structures. The continuum theory of liquid crystals is based on the Frank-Oseen approach to curvature elasticity in anisotropic fluids. It is assumed that the free energy is a quadratic function of curvature elastic strain, and for positive elastic constants the equilibrium state in the absence of surface or external forces is one of zero deformation with a uniform, parallel director. If a term linear in the twist strain is permitted, then spontaneously twisted structures can result, characterized by a pitch p, or wave-vector q=27tp i, where i is the axis of the helicoidal structure. For the simplest case of a nematic, the twist elastic free energy density can be written as ... 

A textile composite reinforced by woven or nonwoven fabrics, knits, or braids is a material of great interest Conventional textile composites are developed as the combination of various synthetic fibers and resins. On the other hand, material developed by the combination of natural fibers and natural-resource-based resin may be called a textile biocomposite. Natural fibers are first changed into bundle form, known as slivers, and then spun into a continuous yam. Spun yams are often twisted around each other to make a heavier yarn, called a twisted or plied yarn. Such spun yams are processed into final textile products such as woven fabrics, knits, and braids. The textile biocomposites described in this chapter are natural-resource-based resin composites reinforced by such spun yarns or textile products. Section 10.1 describes the elastic properties oftwisted yam biocomposites of ramie, and Section 10.2 introduces the development and evaluation of bladed yarn composites made from jute. 

Elastic Properties of Twisted Yarn Biocomposites 339 Table 10.1 Tensile properties of unidirectional composites with various yarn twist angles. 

Nakamura, R., Goda, K., Noda, J., and Netravali, A.N. (2010) Elastic properties of green composites reinforced with ramie twisted yarn. /. Solid Mech. Mater. 

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