Elasticity and Extensibility

The effect of heating on the strength and compressibility (under compressive stress) or extensibility (under tensile stress) at a given temperature follows [38, 39] 

Theoretically, p is in an inverse of the bulk modulus in dimension. However, t/2, does not contribute to the extensibility for the molten state as it approaches infinity at Tm- The Ni is the total number of bonds in the volume. Calibrated with the bulk value at Tq, the reduced temperature dependence of the linear extensibility for 

Note that the bond number density in the relaxed region does not change upon relaxation (Ni = Nbuik). For instance, bond relaxation never changes the bond number between the neighboring atoms in an MC (t = 1) whether it is suspended or embedded in the bulk, nor does it change the number density between the circumferential atomic layers of a solid. 

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Phospholipase A. Phospholipase A hydrolyzes the C2 ester linkage, converting lecithin into a free fatty acid and a lysophospholipid. This lysophospholipid is reported (50-51) to improve the elasticity and extensibility of dough, resulting in better bread quality. 

The /S-pleated structure is markedly different from the a helix in that it is like a sheet rather than a rod. The polypeptide chain is almost fully extended, and each chain forms many intermolecular hydrogen bonds with adjacent chains. Figure 25.13 shows the two different types of /S-pleated structures, called parallel and antiparallel. Silk molecules possess the /S structure. Because its polypeptide chains are already in extended form, silk lacks elasticity and extensibility, but it is quite strong due to the many intermolecular hydrogen bonds. 

The first part represents purely the effect of size, and the second part the joint effect of other stimuli. The effect of multi-filed coupling proceeds only in the surface up to skin depth, as seen from the second term in the second part. The undercoordinated atoms in the surface skin dictate the relative change of the elasticity and extensibility of the entire nanosolid whereas atoms in the core interior retain their bulk feamres. 

A third definition of surface mobility is essentially a rheological one it represents the extension to films of the criteria we use for bulk phases and, of course, it is the basis for distinguishing states of films on liquid substrates. Thus as discussed in Chapter IV, solid films should be ordered and should show elastic and yield point behavior liquid films should be coherent and show viscous flow gaseous films should be in rapid equilibrium with all parts of the surface. 

Over the years there have been many attempts to simulate the behaviour of viscoelastic materials. This has been aimed at (i) facilitating analysis of the behaviour of plastic products, (ii) assisting with extrapolation and interpolation of experimental data and (iii) reducing the need for extensive, time-consuming creep tests. The most successful of the mathematical models have been based on spring and dashpot elements to represent, respectively, the elastic and viscous responses of plastic materials. Although there are no discrete molecular structures which behave like the individual elements of the models, nevertheless... 

Interpretation of data obtained under the conditions of uniaxial extension of filled polymers presents a severe methodical problem. Calculation of viscosity of viscoelastic media during extension in general is related to certain problems caused by the necessity to separate the total deformation into elastic and plastic components [1]. The difficulties increase upon a transition to filled polymers which have a yield stress. The problem on the role and value of a yield stress, measured at uniaxial extension, was discussed above. Here we briefly regard the data concerning longitudinal viscosity. 

There are different techniques that have been used for over a century to increase the modulus of elasticity of plastics. Orientation or the use of fillers and/or reinforcements such as RPs can modify the plastic. There is also the popular and extensively used approach of using geometrical design shapes that makes the best use of materials to improve stiffness even though it has a low modulus. Structural shapes that are applicable to all materials include shells, sandwich structures, and folded plate structures (Fig. 3-8). These widely used shapes employed include other shapes such as dimple sheet surfaces. They improve the flexural stiffness in one or more directions. 

Elastomeric polypeptides are a class of very interesting biopolymers and are characterized by mbber-like elasticity, large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Their useful properties have motivated their use in a wide variety of materials and biological applications. Here, we focus on two elastomeric proteins and the recombinant polypeptides derived thereof. 

It has been shown in Chapter XI that the force of retraction in a stretched network structure depends also on the degree of cross-linking. It is possible therefore to eliminate the structure parameter ve/Vo) by combining the elasticity and the swelling equations, and thus to arrive at a relationship between the equilibrium swelling ratio and the force of retraction at an extension a (not to be confused with the swelling factor as). In this manner we obtain from Eq. (XI-44) and Eq. (39)... 

In order to simplify the discussion and keep the derivation of the formulae tractable, a fibre with a single orientation angle is considered. In a creep experiment the tensile deformation of the fibre is composed of an immediate elastic and a time-dependent elastic extension of the chain by the normal stress ocos20(f), represented by the first term in the equation, and of an immediate elastic, viscoelastic and plastic shear deformation of the domain by the shear stress, r =osin0(f)cos0(f), represented by the second term in Eq. 106. 

Gluten is a mixture of proteins that can be classified as glutenins and gliadins. Extensibility is provided by glutenins while the gliadins contribute elasticity and cohesiveness. 

Bromate treatment in the dough gives an increase in elasticity and a reduction in extensibility. These are of course the desired characteristics for making bread. 

Migration of nitrosamines into consumer products can occur via direct contact of materials such as waxed containers, elastic and rubber etc.81. Morpholine is used extensively as an industrial solvent for wax formulations. The wax formulations are used for coating fruits and vegetables to prevent moisture loss and increase shelf-life of the products. Paper and cardboard packed with morpholine was also found to give rise to NDMA, as these packaging materials were found to be contaminated with NDMA as well. Besides this, rubber products also provided a migratory source for both nitrosamines and nitros-able amine precursors, as trace levels of NDEA and TV-nitrosodibutylamine (NDBA) have been reported in cured meats with amine-based accelerators in the rubber nettings82. 

The elastic stress may be external or internal. External stresses are exerted on the chromatin during the cell cycle when the mitotic spindle separates chromosome pairs. The 30-nm fiber should be both highly flexible and extensible to survive these stresses. The in vitro experiments by Cui and Bustamante demonstrated that the 30-nm fiber is indeed very soft [66]. The 30-nm fiber is also exposed to internal stresses. Attractive or repulsive forces between the nucleosomes will deform the linkers connecting the nucleosomes. For instance, electrostatic interactions, either repulsive (due to the net charge of the nucleosome core particles) or attractive (bridging via the lysine-rich core histone tails [49]) could lead to considerable structural rearrangements. 

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