Time effects

It is often more useful to use the discounted values, to allow for the time effect of money, hence... 

An example of the time effects in irreversible adsorption of a surfactant system is shown in Fig. XI-8 for barium dinonylnapthalene sulfonate (an oil additive) adsorbing on Ti02 (anatase). Adsorption was ineversible for aged systems, but much less so for those equilibrating for a short time. The adsorption of aqueous methylene blue (note Section XI-4) on TiOi (anatase) was also irreversible [128]. In these situations it seems necessary to postulate at least a two-stage sequence, such as... 

Thixotropy and Other Time Effects. In addition to the nonideal behavior described, many fluids exhibit time-dependent effects. Some fluids increase in viscosity (rheopexy) or decrease in viscosity (thixotropy) with time when sheared at a constant shear rate. These effects can occur in fluids with or without yield values. Rheopexy is a rare phenomenon, but thixotropic fluids are common. Examples of thixotropic materials are starch pastes, gelatin, mayoimaise, drilling muds, and latex paints. The thixotropic effect is shown in Figure 5, where the curves are for a specimen exposed first to increasing and then to decreasing shear rates. Because of the decrease in viscosity with time as weU as shear rate, the up-and-down flow curves do not superimpose. Instead, they form a hysteresis loop, often called a thixotropic loop. Because flow curves for thixotropic or rheopectic Hquids depend on the shear history of the sample, different curves for the same material can be obtained, depending on the experimental procedure. 

Experimentally, it is sometimes difficult to detect differences between a shear-thinning Hquid in which the viscosity decreases with increasing shear, and a thixotropic material in which the viscosity decreases with time, because of the combined shear and time effects that occur during a series of measurements. This is especially tme if only a few data points are collected. In addition, most materials that are thixotropic are also shear thinning. In fact. 

Fig. 6. Viscosity—time effects for a thixotropic material (a) shearing and (b) recovery. A nonthixotropic material would give horizontal lines in both cases.

Plasticization and Other Time Effects Most data from the literature, including those presented above are taken from experiments where one gas at a time is tested, with Ot calculated as a ratio of the two permeabihties. If either gas permeates because of a high-sorption coefficient rather than a high diffusivity, there may be an increase in the permeabihty of all gases in contact with the membrane. Thus, the Ot actually found in a real separation may be much lower than that calculated by the simple ratio of permeabilities. The data in the hterature do not rehably include the plasticization effect. If present, it results in the sometimes slow relaxation of polymer structure giving a rise in permeabihty and a dramatic dechne in selectivity. 

Measure of averaging time Cyclic factor measured Measurement method with same averaging time Effect with same averaging time... 

Ruths and Granick [95] have studied the self-adhesion of several monolayers and adsorbed polymers onto mica. For loose-packed monolayers, the adhesion, in excess of a constant value observed at low rate, increased as a power law with the square root of the separation rate. In the case of adsorbed diblocks, the excess adhesion increased linearly with logarithmic separation rate. The time effects were ascribed to interdigitation and interdiffusion between the contacting layers. 

Depletion of O3 results in an increased penetration of ultraviolet light with wavelengths in the range 290-320 nm which may in time effect changes in climate and perhaps lead also to an increased incidence of skin cancer in... 

Alixant, J-L., Real-time Effective Stress Evaluation in Shale Pore Pressure and Permeability Estimation, Ph.D. dissertation, Louisiana State University, p. 210, December 1989. 

It can be shown that the BBM is capable of universal computation ([fredkin82, marg84, marg88]). Unfortunately, as shown by Zurek [zurek84], the model is also unlikely to ever be realized in practice. Because BBM computations all depend so critically on initial ball and mirror placement, the fact that any errors in the initial placement grow exponentially in time effectively renders their results either suspect or meaningless. 

Table 8. Time effect in dissolution of Ca3(P04)2 (20 mg) at pH 7 collidine buffer and 37 °Ca...

From such curves, however, it would not be possible to determine whether the viscoelasticity is in fact linear. An experiment is needed where the time effect can be isolated. Typical of such experiments is stress relaxation. In this test, the specimen is strained to a specified magnitude at the beginning of the test and held unchanged throughout the experiment, while the monotonically decay-... 

Table V. Storage Time Effect of Iron and Aluminum on the Quality of Canned Beer ...

The concentration of UDP also affects the friction coefficient as shown in Fig. 39. It is discovered that the friction coefficient of pure PEG also decreases gradually and reaches a somewhat reduced value due to a time effect of the film thickness [16,18]. At the speed of 2 mm/s and pressure of 174 GPa, the friction coefficient of pure PEG is the highest. That for PEG + 0.5 % UDP ranks second. Those for PEG + 0.1 % UDP and PEG+ 0.3 %UDP are almost the same and have the lowest friction coefficient among all tested oils. Therefore, there is a good concentration extent of UDP in the basic oil. If the concentration is out of such extent, the effect... 

Another important factor in diffusion measurements that is often encountered in NMR experiments is the effect of time on diffusion coefficients. For example, Kinsey et al. [195] found water diffusion coefficients in muscles to be time dependent. The effects of diffusion time can be described by transient closure problems within the framework of the volume averaging method [195,285]. Other methods also account for time effects [204,247,341]. 

The effect differs according to time and place. So far as the time effect is concerned, there is a need to distinguish acute effect, which appears a short while after the substance penetration, from the long term or chronic effect, for which effects can be identified after several years of exposure. The action can be local, ie contact point with the substance, or systemic , reaching organs that are distant from the penetration point.The local effect affects skin and eyes and/or mucous membranes, especially the inhalation ones. The local effects are irritant and sensitive. 

Half-life, Effective—See Half-Time, Effective. 

Half-time, Effective—Time required for a radioactive element in an organ, tissue, or the whole body to be diminished 50% as a result of the combined action of radioactive decay and biological elimination, symbolized as Te or Teff. 

Figure 3. Seeded overflow CSTR, conversions vs. dimensionless time Effect of process variables (see also Table III).

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