Absorption and Emission of Light in III–V Semiconductors

Previous chapters discussed the crystal structure and bandstructure of III–V semiconductors. This chapter shifts to the book’s second major topic: electronic interactions with light. It introduces the main ideas about how light waves propagate in semiconductor crystals and induce absorption, spontaneous emission, and stimulated emission in bulk semiconductors. It also considers the differences between the electronic interactions with light in zinc-blende and wurtzite crystals and what happens as the energy gap of the semiconductor is reduced to zero or when the crystal is two-dimensional.

Time-Interval Emphasis in an Aeronautical Dual-Task Context: A Countermeasure to Task Absorption

Objective: We tested a training method intended to prevent unsafe aeronautical behavior (i.e., too much time spent gazing inside the cockpit) induced by the modern cockpit, by teaching individuals to perform a task complementing the see-and-avoid mandatory safety task within a limited time interval. Background: Aeronautical activities led crews to perform several tasks simultaneously in an ergonomic environment under constant change. See and avoid remains one of the main safety tasks during visual flight. However, modern cockpits induce absorption and impair performance of this safety task. Many laboratory studies showed the relevance of training methods for managing dual-task situations and estimating time intervals. Method: A specific virtual environment was developed to expose participants to a dual-task situation in which time-interval emphasis was provided in real time. Two types of emphasis training were tested: a permissive one that allowed participants to pursue the inside-cockpit task beyond the time limit and a nonpermissive one that did not. Results: The best time-interval acquisition, with retention up to 24 hr later, was observed in the nonpermissive condition, but task performances immediately after the training sessions were equivalent across conditions. Conclusion: Time-emphasis training appears to be an efficient means of promoting absorption resistance while preserving task performance. Transferability of time-interval estimation skills has yet to be tested. Application: Most areas of application for absorption resistance (aviation, shipping, rail, road, etc.) could benefit from this type of training to manage multitask situations.

Analysis of the naphthalene vapour absorption bands at 3200 Å. II. Naphthalene d -8

The absorption spectrum of octadeuteronaphthalene near 3200 Å has been measured and partially analyzed. The origin is at 32138.2 cm -1 , 118 cm -1 higher than that of naphthalene h -8. The analysis of the spectrum shows a nearly complete similarity to naphthalene h -8, with differences only in the relative ability of non-totally symmetrical vibrations to induce absorption along the shorter in-plane molecular axis. In naphthalene this ability is largely confined to two b 3 g vibrations of 438 cm -1 and 911 cm -1 in the upper state; in naphthalene d -8 the b 3 g vibration of 422 cm -1 behaves analogously to 438 cm -1 and induces the strongest bands in the system, but there are several higher b 3 g frequencies giving false origins, indicating important changes in the vibrational modes on deuteration. As in naphthalene, long-axis polarized bands show single maxima and short-axis polarized bands two maxima spaced by 2 to 3 cm -1 . The band group with principal head 490 cm -1 below the origin shows a structure unique in the whole system: it is proposed that this is due to Coriolis coupling of the a g fundamental 493 cm -1 to a newly identified b 3 g fundamental 490 cm -1 . Several upper-state fundamentals are reported for the first time.