INDEX stress experiments

Many publications use an absolute measure that denotes water security, frequently referring to an index that identifies a threshold of 1,700 CM per capita per year of renewable water, based on estimates of water requirements in the household, agricultural, industrial, and energy sectors as well as the needs of the enviromnent. Countries whose renewable water supplies cannot sustain this figure experience water stress. When supply falls below 1,000 m per capita per year, a country is said to experience water scarcity, and below 500 m per capita per year, absolute scarcity. However, these terms are easy to misinterpret, because they do not take into account possibilities for trade in agricultural products, efficiency of water use in agriculture, and other variables, and thus obscure the primacy of economic demand rather than physical need in determining water use [3-5]. 

The melt Index test measures the flow property at a fixed wall shear stress In the capillary. The shear stress depends on the load specified for the condition and it is provided in Table 3.8. The apparent shear rate at the capillary wall that the resin experiences depends on the Ml value measured, and it can be calculated using a modification of Eq. 3.33 as follows ... 

Some experiments have failed to demonstrate an effect of maternal odors on stressed offspring. The heart rate rose in rat pups removed from their home cage and placed in an unfamiliar environment this was taken as an index of fear. Tests with mothers and soiled bedding from mothers or other rat pups showed that tactile and thermal stimuli reduced fear in 16-day old pups, but olfactory cues from the mother or odors from the home cage did not (Siegel et ah, 1988). 

Aquatic microcosms and mesocosms offer the ideal situation to investigate populations of species interacting in their natural environment (i.e., to study communities stressed in structured systems see Section 4.5.1). It is, however, only recently that these experiments have been analyzed at the community level (Van Wijngaarden et al. 1995 Sparks et al. 1999 van den Brink and Ter Braak 1999). Until 10 years ago, experiments were evaluated at the population level, largely ignoring species interactions and energy flows in the systems. The development of community-level endpoints offered the possibility to evaluate the experiments on a community level (i.e., they offered the opportunity to scale up the level of evaluation Kedwards et al. 1999). Summary community-level endpoints calculated from the results of these experiments are mostly structural ones measures of diversity (e.g. numbers of species, and the Shannon-Weaver diversity index) and similarity of the treated systems compared to the untreated controls (e.g., the principal response curves method, Bray-Curtis dissimilarity, or Stander s index see van den Brink and Ter Braak 1998 for a comparison). 

It follows that for a constant refractive index the craze strain is also constant. Our observations on polystyrene indicate that neither the craze refractive index nor the ratios kB/kc and kB/kh are constant along the length of the craze (Figure 6). The values of A calculated from Equation 4 are shown in Figure 7. That the craze strain is not constant does not preclude the possibility that the craze stress is still constant, as might be the case for an ideal plastic material. However, the experiments on craze stress-strain properties by Kambour (10) and Hoare and Hull (11) indicate that this is not the case. 

As will be shown below, the experiment in the sliding plate rheometer does not allow one to determine Nl, since the normal force is in fact related to the second normal stress difference. For this reason, we studied the stress-optical law in shear by assuming that the principal directions of shear and refractive index are close to each other in the x-y plane. It is then straightforward to express the difference of principal stresses in the x-y plane... 

One of the most widely used indexes of community structure has been species diversity. Many measures for diversity are used, from such elementary forms as species number to measures based on information theory. A decrease in species diversity is usually taken as an indication of stress or impact upon a particular ecosystem. Diversity indexes, however, hide the dynamic nature of the system and the effects of island biogeography and seasonal state. As demonstrated in microcosm experiments, diversity is often insensitive to toxicant impacts. 

The majority of results so far available in this Held have been derived from spectra recorded on dispersive instruments. In order to test tl validity of Eq. (1) several independent experiments have been performed in which a highly oriented polyethylene terephthalate film is subjected stepwise to increasingly higher stresses in the stretching machine illustrated in Fig. 1 and FTIR spectra are taken at the relaxed stress levels with unpolarized radiation. In Fig. 4 the wavenumber shifts of the v(0—CH2) absorption band are plotted as a fimctimi of the applied stress for different experiments. From these systematic investigations, however, no linear relationship between the wavenumber shift Av and the plied stress good index of determination (0.98) was obtained for the power function ... 

The optical experiment setup used in other modulation experiments, shown in Figure 33, is quite similar to that used for vibrational circular dichroism experiments, described in detail elsewhere (234). Perhaps the experiment can best be understood from the following equations. Additional details can be found in the reference provided. The modulated beam is produced by the stress-induced difference in the index of refraction associated with the two perpendicular directions of a photoelastic modulator (PEM), in most cases a ZnSe crystal. Therefore, the... 

In this test, water was first imbibed by a specimen of Kunigel VI that was constrained from movement at both ends, allowing the developed swelling pressure to reach a constant value. Next, a short-term test sequence of consolidation and unloading was performed to obtain the compression index A and the swelling index k. After this procedure, a constant stress was applied and the displacement was measured. The procedure employed in the experiments is outlined in Table 10.1 and a schematic diagram of the apparatus is shown in Fig. 10.1. 

Here p is the density, t the time, Xi the three Cartesian coordinates, and o,- the components of velocity in the respective directions of these coordinates. In equation 2, the index j may assume successively the values 1, 2, 3 gj is the component of gravitational acceleration in the j direction, and atj the appropriate component of the stress tensor (see below). (A third equation, describing the law of conservation of energy, can be omitted for a process at constant temperature the discussion in this chapter is limited to isothermal conditions.) Now, many experiments are purposely designed so that both sides of equation 1 are zero, and so that in equation 2 the inertial and gravitational forces represented by the first and last terms are negligible. In this case, the internal states of stress and strain can be calculated from observable quantities by the constitutive equation alone. For infinitesimal deformations, the appropriate relations for viscoelastic materials involve the same geometrical form factors as in the classical theory of equilibrium elasticity they are described in connection with experimental methods in Chapters 5-8 and are summarized in Appendix C. 

---