Shift factor time-pressure

The experimental ranges of strain rates (or strains) are summarized in Table 2 for the various types of experiments. Time-temperatiire superposition was successfully applied on the various steady shear flow and transient shear flow data. The shift factors were foimd to be exactly the same as those obtained for the dynamic data in the linear viscoelastic domain. Moreover, these were found to be also applicable in the case of entrance pressure losses leading to an implicit appUcation to elongational values. 

While an increase in temperature speeds up the viscoelastic response, an increase in pressure slows it down. In the so-called piezorheologically simple systems, all the response times have the same dependence on pressure, and the generalized shift factor is expressed by the Fillers-Moonan-Tschoegl equation (17)... 

The following discussion will first address models of dynamic and naturalistic decision making. These models both illustrate naturalistic decision-making strategies and explain their relation to experience and task familiarity. A brief discussion wftl also be provided on teams and team leadership, in naturalistic settings. Attention wdl then shift to the issue of time pressure and stress and how this factor influences performance in naturalistic decision making. 

In addition to the free volume [36,37] and coupling [43] models, the Gibbs-Adams-DiMarzo [39-42], (GAD), entropy model and the Tool-Narayanaswamy-Moynihan [44—47], (TNM), model are used to analyze the history and time-dependent phenomena displayed by glassy supercooled liquids. Havlicek, Ilavsky, and Hrouz have successfully applied the GAD model to fit the concentration dependence of the viscoelastic response of amorphous polymers and the normal depression of Tg by dilution [100]. They have also used the model to describe the compositional variation of the viscoelastic shift factors and Tg of random Copolymers [101]. With Vojta they have calculated the model molecular parameters for 15 different polymers [102]. They furthermore fitted the effect of pressure on kinetic processes with this thermodynamic model [103]. Scherer has also applied the GAD model to the kinetics of structural relaxation of glasses [104], The GAD model is based on the decrease of the crHiformational entropy of polymeric chains with a decrease in temperature. How or why it applies to nonpolymeric systems remains a question. 

The nominal human error rates can be reduced or increased based on operator-related environmental factors (quality of displays, control layout and clarity, control area environment, procedures, access), personnel faotors (training, experience), and stress factors (personal, shift schedules, response time pressure, severity or magnitude-of-safety condition). The best source for determining the human error rate would be company/facility-specific historical data, but in most organizations, this is not available. Therefore, an owner/operator often uses other published, acknowledged sources and adjusts the human error rate for their application and circumstances accordingly. 

The shift factor ap can be used to combine time-dependent or frequency-dependent data measured at different pressures, exactly as ap is used for different temperatures in Section A above, and with a shift factor ar,p data at different temperatures and pressures can be combined. It is necessary to take into account the pressure dependence of the limiting values of the specific viscoelastic function at high and low frequencies, of course, in an analogous manner to the use of a temperature-dependent Jg and the factor Tp/Topo in equations 19 and 20. The pressure dependence of dynamic shear measurements has been analyzed in this way by Zosel and Tokiura. A very comprehensive study of stress relaxation in simple elongation, with the results converted to the shear relaxation modulus, of several polymers was made by Fillers and Tschoegl. An example of measurements on Hypalon 40 (a chlorosulfonated polyethylene lightly filled with 4% carbon black) at pressures from 1 to 4600 bars and a constant temperature of 25°C... 

The inclusion of values in Table 1 l-III derived from dynamic bulk viscoelastic measurements implies the concept that the relaxation times describing time-de-pendent volume changes also depend on the fractional free volume—consistent with the picture of the glass transition outlined in Section C. In fact, the measurements of dynamic storage and loss bulk compliance of poly(vinyl acetate) shown in Fig. 2-9 are reduced from data at different temperatures and pressures using shift factors calculated from free volume parameters obtained from shear measurements, so it may be concluded that the local molecular motions needed to accomplish volume collapse depend on the magnitude of the free volume in the same manner as the motions which accomplish shear displacements. Moreover, it was pointed out in connection with Fig. 11 -7 that the isothermal contraction following a quench to a temperature near or below Tg has a temperature dependence which can be described by reduced variables with shift factors ay identical with those for shear viscoelastic behavior. These features will be discussed more fully in Chapter 18. 

The effect of pressure on linear viscoelastic properties can also be accounted for in terms of shift factors. One can define an isothermal time-shift factor flp(P) that accounts for the effect of pressure on the relaxation times at constant temperature, and it has been found that this factor follows the well-known Bams equation ... 

Much of the experimental success of asymmetric epoxidation lies in exercising proper control of Eq. 6A.4 [6]. Both TI(OR)4 and Ti(tartrate)(OR)2 are active epoxidation catalysts, and because the former is achiral, any contribution by that species to the epoxidation will result in loss of enantioselectivity. The addition to the reaction of more than one equivalent of tartrate, relative to Ti, will have the effect of minimizing the leftward component of the equilibrium and will suppress the amount of Ti(OR)4 present in the reaction. The excess tartrate, however, forms Ti(tartrate)2, which has been shown to be a catalytically inactive species and will cause a decrease in reaction rate that is proportional to the excess tartrate added. The need to minimize Ti(OR)4 concentration and, at the same time, to avoid a drastic reduction in rate of epoxidation is the basis for the recommendation of a 10-20 mol % excess of tartrate over Ti for formation of the catalytic complex. After the addition of hydroperoxide and allylic alcohol to the reaction, the concentration of ROH will increase accordingly, and this will increase the leftward pressure on the equilibrium shown in Eq. 6A.4. Fortunately, in most situations this shift apparently is extremely slight and is effectively suppressed by the use of excess tartrate. A shift in the equilibrium does begin to occur, however, when the reaction is run in the catalytic mode and the amount of catalyst used is less than 5 mol % relative to allylic alcohol substrate. Loss in enantioselectivity then may be observed. This factor is the basis of the recommendation for use of 5-10 mol % of Ti-tartrate complex when the catalytic version of asymmetric epoxidation is used. 

M REC, as the TREC, does not depend on the reaction path. In addition, there is no dependence on the membrane-permeation properties (related to the time required for species permeation).1 In any case, the final value reached depends on the extractive capacity of the system, for example, the pressure and composition on the permeate side. The composition on the permeate side, similarly to the feed molar ratio, can be expressed by considering the ratio (named sweep factor) between the initial molar number of nonpermeating species (present on the permeate side) and the initial molar number of the reference reactant, for example, methane for methane steam reforming, or carbon monoxide for water gas shift). The sweep factor was defined for a closed M Ras ... 

Figure 4.17 Frequency shift as a function of time measured for a gold-coated SAW device exposed to an Na gas stream containing CH3(CH2)isSH at tproximately 25% of its saturation vapor pressure. Leveling of the frequency shift at approximately 1.15 monolayers indicates that the polycrystalline gold Him has a roughness factor of 1.15. The kinetic data fit a simple, first-order Langmuir rate law. (Reprinted with permission. See Ref. [143J. 1991 American Chemical Society.)...

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