Acceleration ratio

As the Ca2+ concentration is lowered, the rate of the uncatalyzed hydrolysis decreases more rapidly than the catalyzed process, producing an increase in the rate acceleration ratio. For example, as the ratio of Ca2+ to cycloheptaamylose is decreased from 1 1 to 0.33 1, the rate acceleration for the hydrolysis of diphenyl pyrophosphate increases from 4.4 to 27. At lower Ca2+ concentrations, catalysis by the cycloamyloses was described as absolute catalysis since the rate of the spontaneous hydrolysis could not be measured. The term absolute catalysis is misleading, however, since the uncatalyzed rate, no matter how slow, must be finite. 

Other types of ester have been studied (Fendler and Fendler, 1975 Bender and Komiyama, 1978 Szejtli, 1982), though in much less detail. Brass and Bender (1973) studied the cleavage of two diaryl carbonates and three diaryl methylphosphonates in basic buffers (Table A5.ll). For the carbonates, reacting with /1-CD, introduction of p-nitro groups increases the acceleration ratio and worsens substrate binding, so that KTs barely alters. More interesting are the results for the phosphonates in that the effects of nitro groups depend on their position and on the CD. 

Table 6. Effect of Accelerator Ratio on 300% Modulus, MPaa...

At certain frequencies, the amplitude of the acceleration ratio goes through local resonant peaks. 

As sulfur content increased, the change in sulfur bond ratios exhibit a transition from a semi-efficient , or lower sulfur/accelerator ratio, to a conventional ,or higher sulfur/accelerator ratio, cure system (4). Overall, the... 

Figure 22.9 plots the peak surface acceleration to peak base acceleration ratios as computed for each vertical array for both the flights. All values are larger than unity indicating an amplification of the acceleration from the base to the surface. The amplification ratio decreases with an increase of the input motion amplitude, due to the non-linear soil behavior. The response of the reference array (ESB box) is always larger than the soil. The amplification along the tunnel array is... 

Likewise, for performance, sometimes a sulfur donor is needed as well. Elemental sulfur gives rise to variable cross-link lengths, regulated to some extent by sulfur-to-accelerator ratio. In some applications, particularly those which require very high temperature and or oxidative stability, one may need a preponderance of cross-links of very low rank, mostly monosulfidic. For this purpose, organic sulfur donors may be useful (24). 

Fig. 8.6. Course of the CBS-accelerated sulphur vulcanization of natural rubber at 140T with a high sulphur accelerator ratio (2-5 0-6). (x) Total cross-links ( ) poly sulphide ( ) monosulphide ( ) disulphide. The upper and lower figures on the curve relating to total cross-links are values of E and E, respectively. (After Moore, 1965.)...

In the presence of sulphenamide accelerators little difference is observed between ENR and NR. Similar types of crosslink, mono-, di- and poly-sulphidic, are produced and their ratio varies with the sulphur/accelerator ratio as with other highly unsaturated polymers. 

Another interesting approach to evaluating field data versus accelerated data is the mean acceleration ratio and coefficient of variation [37],... 

To compare data from a field exposure to data from an accelerated test for a set of panels, the acceleration ratio/or each type of material (i.e., coating and substrate) is calculated by dividing the average result from the accelerated test by the corresponding reference value, usually from field exposure. These results are then summed up for all the panels in the set and divided by the number of panels in the set to give the mean acceleration ratio. That is,... 

Another commonly quoted value is the ratio of the maximum trough acceleration to g (as opposed to the previously defined vertical acceleration ratio), K, the dynamic machine... 

The seismic coefficient is specified as a fraction, roughly 1/2, of the peak horizontal acceleration ratio a Jg at the crest of an earth dam because the lateral inertial force is applied for only a short interval during transient earthquake loading. ... 

Seismic Design of Earth-Retaining Structures, Fig. 3 Seismic displacements plotted as a function of the critical to maximum acceleration ratio... 

The complex dynamic Young s modulus can be determined from the response of a bar-shaped test specimen in a forced-resonance method (186). A shaker drives one end of the specimen (nominally 100 x 6 x 6 mm). Miniature accelerometers are used to measure the driving point acceleration at the shaker and the response of the test specimen as shown in Figure 6. The output signals from the accelerometers are analyzed by a dual-channel fast Fourier transform spectrum analyzer. The analyzer determines the acceleration ratio and phase difference of the two accelerometers, and also provides a random noise source to drive the shaker over... 

These accelerators (ratio MBTS 0.65, CBS 0.48 and DPG 0.15) had also been used to vulcanise the original SBR rubber compound (along with 2 phr sulfur, 5 phr zinc oxide and 1 phr stearic acid) that was being devulcanised in these experiments ... 

This article describes the effect of changes in the crosslinking system on the fatigue life and other properties in natural rubber suspension bushings. The effect of sulphur/accelerator ratio was determined for several properties that included fatigue life, crystallisation, friction and creep. 5 refs. 

Two blends of isoprene mbber, filled with carbon black, had chemical compositions which differed only in the sulphur/accelerator ratio. After curing, the final mechanical stiffness was almost the same for each of the blends. After the determination of optimal compositions and vulcanisation conditions, the elastomer sheets were... 

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