Elongational rate

Fig. 1. Elongation rate of stem intemode 12 (A), silks (A), leaf 8 ( ), and nodal roots (O) of maize at various water potentials. Elongation rates are the average per hour for 24 h of growth in a controlled environment chamber. Water potentials were measured in the growing region of each organ in the same plants. Samples were taken immediately after the growth period when the plants had been in the dark for the last 10 h. Each point is from a single plant. Modified from Westgate Boyer (1985a).

Table 1. Primary root elongation rate of several species at various vermiculite water potentials... 

Seedlings were transplanted to the different water potentials 30 h after planting, and were grown in the dark at 29 °C and near saturation humidity. Elongation rates were constant when the measurements were made. Data of R.E. Sharp and G. Voetberg (unpublished). 

Fig. 4. Spatial distribution of (a) relative elemental elongation rate (longitudinal growth rate) and (p) osmotic potential in the apical 10 mm of maize primary roots growing at various vermiculite water contents (see Fig. 3). Growth distributions were obtained by time-lapse photographic analysis of the growth of marked roots points are means from 5 or 6 roots. Osmotic potentials were measured on bulked samples from 30-50 roots points are means s.d. (n = 3-7). Root elongation rates (a, inset) were constant when the measurements were made. Modified from Sharp et al. (1988, 1989).

Taylor, H.M. Ratliff, L.F. (1969). Root elongation rates of cotton and peanuts as a function of soil strength and soil water content. Soil Science, 108, 113-19. 

Green, P.B., Erickson, R.O. Buggy, J. (1971). Metabolic and physical control cell elongation rate in vivo studies in Nitella. Plant Physiology, 47, 423-30. 

Figure 3. PME isoform patterns in cell wall extracts fiom active and resting cells, a cell wall extracts from successive segments (A, B, C and D) sectioned along mui bean hypocotyb and exhibiting decreasing elongation rates a, and y m c the main PME isoforms present in the extracts, tteir pi are respectively around 7.5, S.5 and above 9.1. b cell wall extracts obtained from poplar cambium and inner bark tissues during cambial active (may) and rest (december and march) periods 1, 2 and 3 represent the activity of 3 groups of PME isoforms with pi around 5-6, 7.5 and above 9.1. Activities expressed as percent of total PME activity present in each extract.

These flow features are of importance in a great number of technical processes, especially for high process velocities when extremely high shear rates can be observed. For polymeric systems this can lead to a so-called non-Newtonian behaviour, i.e. the rheological material functions become dependent on the shear or elongational rate. 

Strong and weak zones are divided into subzones that allow for a distribution of shear and elongation rates and residence times. 

Figure 7. Green strength of different rubbers. Elongation rate, 0.3 m/min compound, 55 parts carbon black N 330 NR, natural rubber IR, synthetic cis-1,4-...

Consider a stream of liquid that is subject to a purely elongational flow in the x-direction. The elongational rate of strain may be defined as the velocity gradient in the direction of flow, ie dvjdx. Now consider the case in which the elongational strain rate is constant ... 

Thus, even when the elongation rate, as defined by equation 3.76, is constant, the separation of two material points increases exponentially with time. As stress relaxation occurs exponentially, it is clear that at high elongation rates the stress will increase very rapidly. In a purely viscous liquid the stress relaxes instantaneously and consequently this high resistance to stretching does not occur. 

Tensile testing was performed on an Instron A1020C at elongation rates of 50%/min and 100%/min. A minimum of 7 samples were tested per material type. Both melt-pressed films and in situ disks were examined. Some saunples were also conditioned in a hxunidity chamber before testing to insure that the samples contained the same amount of water which acts as plasticizer. 

Because the concentration of capped filaments is a denominator term, we immediately recognize that the elongation rate will be retarded by capping. 

For the unfilled polystyrene melt at low elongational rates a constant value of Tjg is achieved given by three times the zero shear viscosity according to Trou-... 

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