Critical time

These are illustrated in Figure 3-18. Flat belts are used chiefly for conveyer belt systems rather than power transmission. I oothed (or timing) belt are generally used for control of critically timed rotating elements of a mechanical systems and are not used in power transmission application. The V section and the ribbed power belting systems are used exclusively for power transmission, and thus the discussion in this section will be confined to these categories of belting. 

Figure 3. A typical variation of the critical time, i.e. the time to buckle, and the compressive load for a plastic column. The plot show the time (sec) versus the load (N). (Reprinted with permission from ref. 13. Copyright 1988 Soc. of Plastic Engineers.)...

By applying a multipipe feed system, Unt can be significantly reduced the critical time will be inversely proportional to the number of pipes. However, too many nozzles could result in intermingling of the local reaction zones, thus affecting the selectivity. The critical time is roughly two orders of magnitude longer than the blend time t99, which is defined later in this section. 

Another commonly used approximation for which there is an analytical solution is to assume that the root acts as a zero sink for uptake. Here the solute concentration at the root surface is taken to be zero and uptake is therefore completely controlled by the diffusive flux to the root (21,40,41). The implicit assumption is that root uptake is very rapid in comparison to resupply by transport and hence the root very rapidly depletes the solute concentration at the root surface to zero and maintains it there. The validity of this assumption depends on the value of X and it is inapplicable unless X is greater than or about 10 (38). For such large X, there is a nondimensional critical time (/,.) after which it is reasonable to assume a zero sink (38,42). Approximate values of /, are... 

Using the standard parameter values for maize presented in Table 2, the dimensional critical times after which a zero-sink approximation is valid are 180 s for P and 89 s for K. The zero sink assumption is not valid at all for NO," N ( l = 0.04). 

The critical time for organogenesis is during the first eight weeks of pregnancy thus, the risk for birth defects is highest during the first trimester. 

FIGURE 44-1. Embryonic development. (Reprinted, with permission, from Moore KL, The Developing Human. New York Elsevier, 1874 p 96 copyright 1974.) The horizontal bars represent potential sensitivity to teratogens. The pink areas represent the more critical times. 

At the critical time, there is a change in slope in the cube root law plot [37,39]. 

The fraction undissolved data until the critical time can be least-square fitted to a third degree polynomial in time as dictated by Eq. (29). The moments of distribution ij, p2, and p3 can be evaluated from Eqs. (30) through (32), with three equations used to solve for three unknowns. These values may be used as first estimates in a nonlinear least-squares fit program, and the curve will, hence, reveal the best values of both shape factor, size distribution, and A -value. 

Figure 8.12 illustrates the general effect of creep, plotted as a function of log strain versus log time. Under applied load a sample gradually deforms until a critical time (tc) after which it deforms rapidly. If creep is allowed to go unchecked, the sample may break abruptly. 

Sokol RZ Health Research Association, Inc., Los Angeles, CA Pb exposure in utero may induce an inherited change in DNA methylation patterns in Pb exposed pups, the mechanism by which Pb exposure during the critical time of sexual differentiation induces reproductive axis abnormalities in adulthood National Institute of Environmental Health Sciences... 

The concept of a measurement of an induction period is based upon determination of critical time of the reaction progress that leads to the catastrophic change of the useful properties of the material. This may be demonstrated on the... 

Female ability to control exposure to male scent at critical times may help to explain why similar pregnancy-blocking stimuli have produced conflicting results in different experiments. For example in one study manipulating male social status (Labov 1981a), females were housed directly below males, while a similar study (Huck 1982) housed females adjacent to males, separated by mesh. The pregnancy... 

All indications are that we are only just beginning to see a few threads of the rich fabric of chemical signals that link lobsters to each other and to their environment. Exoskeleton, bladders, glands, and control of currents all indicate that these animals can be chemically quiet and release specific signals at critical times during aggression and courtship. Chemical signals appear to be used to remember individuals and to facilitate stable dominance hierarchies. 

Over the past years, some symposia and colloquia groups have provided especially valuable insights at critical times, and I would like to thank colleagues at the New Trends in the History of Science conference in Utrecht in August 1986, the Beckman Center symposium, Chemical Sciences in the Modern World, in May 1990, the International Summer School in History of Science in Uppsala in June 1990, and the conference on research schools in New Haven in December 1990. 

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