High-stress limit

In the PTIS spectrum of P [49], lines have also been observed at 12.630, and 12.660meV (101.87, and 102.11cm-1), with semi-experimental excited state energy values of 0.256 and 0.226 meV, respectively, which can be ascribed to 8p i and 8/i i levels [20]. The positions of the 4/o, 5po, 6po, and 6/o lines of Sb extrapolated from absorption measurements in the high-stress limit [14] are 73.40, 75.72, 77.76, and 78.40 cm-1 (9.100, 9.388, 9.641, and 9.720 meV), respectively. It is interesting to note that in this study, no value is reported at the position expected (76.75 cm-1) for 5/o. This absence is correlated with a calculated OS for that line about two orders of magnitude smaller than those for the other lines of the series (see Table 5.21). 

Fig. 8.3. Energy levels of shallow donors in silicon (not to scale) showing the allowed transitions between the Is (Ai) state and the stress-split sublevels of npo and np i for F / / [100], In the high-stress limit, the stress dependence of the Is (Ai), npo (Ai + B2) and np (2E) are the same so that the transitions between these states are stress-independent (after [123]). Reproduced with permission from the Institute of Physics...

The stress splitting of the Sb donor lines in germanium has also been studied in the high-stress limit (HSL) by Baker and Fisher [8]. In this limit, due to thermalization and changes in the relative intensities, the transitions from Is (Ai) to npo(—) (and n/o(—)) of Fig. 8.6 are predominant. They are denoted ripq1 —) (°°) in this reference and a high-resolution spectrum of Ge Sb taken... 

Fig. 8.19. Stress dependence of the computed binding energies for the first odd-parity excited acceptor states in germanium for F//<100>. The energy origin is the top of the T6+ (mj = 1/2) VB Dah symmetry). The labelling on the LHS corresponds to the attributions of zero-stress acceptor lines of germanium given in Table 7.9. The one on the RHS corresponds to the high-stress limit (after [24]). Copyright 1987 by the American Physical Society...

Energies and wave functions of shallow acceptor states in silicon and germanium for stresses along the <100> and < 111 > axes have also been calculated by Buczko [27] using the full stress-dependent Hamiltonian up to the high-stress limit. The results of these calculations will be discussed in comparison with the experimental results. 

As discussed in the introduction, disruptions cause the most severe thermomechanical loading experienced in a tokamak. In each of the 500 or so disruptions expected in ITER, approximately 10-20 MJ/m will be deposited onto the first wall in 0.01 to 3 seconds. Such a disruption will cause very high thermal stresses and significant material erosion (Section 4). As these events are transient in nature, the ability of the PFC to withstand the disruption depends on the material s ability to both conduct and to absorb the deposited heat, before reaching a temperature or stress limit. For comparative purposes, a disruption figure of merit takes this into account ... 

Deformation contributes significantly to process-flow defects. Melts with only small deformation have proportional stress-strain behavior. As the stress on a melt is increased, the recoverable strain tends to reach a limiting value. It is in the high stress range, near the elastic limit, that processes operate. 

This recommended practice summarizes the results of experimental tests and actual data acquired from operating plants to establish practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures. The effects on the resistance of steels to hydrogen at elevated temperature and pressure that result from high stress, heat treating, chemical composition, and cladding are discussed. 

Dislocations move when they are exposed to a stress field. At stresses lower than the critical shear stress, the conservative motion is quasi-viscous and is based on thermal activation that overcomes the obstacles which tend to pin the individual dislocations. At very high stresses, > t7crit, the dislocation velocity is limited by the (transverse) sound velocity. Damping processes are collisions with lattice phonons. 

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