Negative climb

Fig. 3.47 This force is acting in the negative y direction, because tensile stress induces the negative climb of a dislocation. Note that the width at the lower edge of the curve is less by b than at the upper edge, since a dislocation is defined by the extra half-plane [14]...

The positive climb process requires long-range transport of matter and consumes vacancies. Continuous deformation will hence lead to a depletion of vacancies and eventually limit the effectiveness of the mechanism. Roitsch et al. [50] showed that besides the metadislocation loops, a second set of dislocations is involved in the deformation mechanism, which compensates the depletion of vacancies. The second set of dislocations consists of loops on (0 01) habit planes with [010] Burgers vectors [51]. These dislocations move by pure negative climb, that is, the expansion of the loops is connected to a production of vacancies, and hence the systems acts as a vacancy source. The interaction of the two loop systems in the form of vacancy exchange ensures continuous operation of the deformation mechanism. 

The x axis is again an asymptote and the line crosses the y axis at 1. This time the curve climbs to infinity as x becomes more negative. This is because — x is now becoming more positive. The curve is simply a mirror image, around the y axis, of the positive exponential curve seen above. ... 

Thus, to drive a current through the external circuit, the potential of the electron sink has to become more positive and thal of the electron source more negative (Fig. 7.182). But under zero-current, or equilibrium, conditions, the electrode that tends to be a sink is negative with respect to the electrode that tends to be a source. This means that in the course of driving a current, the potentials of the two electrodes climb toward each other the cell potential decreases with cell current in a self-driving cell. 

If the vacancies are subsaturated, the dislocation tends to produce vacancies and therefore acts as a vacancy source. In that case, Eq. 11.5 will still hold, but fiy will be negative and the climb force and climb direction will be reversed. Equation 11.5 also holds for interstitial point defects, but the sign of will be reversed. 

One would think that a woman with such a history and reputation would be fearless. But apparently, this is not the case. Amie tells us that she has always been afraid of heights, and had chosen rock climbing to face her fears. The hazard of the sport is apparent. After all, a long fall can kill. But in a twist to Amies story, it turns out that she was only three feet off the ground and attached by a rope to a skilled partner who loved her. Therefore, the probability of a negative consequence was extremely low. It is clear then that our own sense of risk can frighten us even if the activity is not likely to cause harm. 

The obvious value to insert for cFe21 is zero in which case Nemst s equation for the electrode potential of the Fe2+ + 2e Fe equilibrium indicates a value that would be highly negative. Since this potential is negative with respect to the equilibrium potential of any possible electronation reaction, the iron will start dissolving and building Fe2+ concentration in the solution layer that is in contact with the electron-sink area of the iron. If this layer is stagnant and the Fe2+ ions are not removed by a chemical reaction, e.g., precipitation, the Fe2+ concentration will climb up from zero. Clearly, the Fe2+ ion concentration adjacent to the metal is determined by the amount of metal that has dissolved, and how fast this diffuses away. 

The initial results reported from a metrics system will often indicate performance below expectations. Initial data may be skewed until metrics data collection is reliably implemented, and performance may continue to drop as improvement opportunities are defined and implemented. This sometimes occurs when the historical perspective of performance is too optimistic because objective measures had not been used in the past. Implementing near-miss data collection is one example The number of reported near misses will probably increase as reliability of reporting improves, so the number of reported near misses is likely to climb during the initial implementation phases of near-miss data collection. Audiences of metrics reports should be prepared for such situations, so the result is expected and potential negative reactions are managed. 

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