Population inversion in optically pumped asymmetric quantum well terahertz lasers
Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga1−xAlxAs quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation.
Engineering the electron - phonon scattering rates in the active regions of quantum cascade lasers operating beyond
This theoretical work explores an aspect of carrier scattering rate design in the active region of intersubband quantum cascade lasers operating in the far-infrared (30 - ) or terahertz (1 - 10 THz) region of the spectrum, namely the depopulation of the lower laser level. Envelope function calculations of eigenstates and non-radiative scattering rates are presented for the active layer of an intersubband laser under the influence of an electric field and at room temperature. Two methods of depopulating the lower laser level to engineer a population inversion are explored, namely depopulation by resonant longitudinal optic phonon emission and depopulation to a strongly coupled state, as can occur at an anti-crossing.
[Effects of dance exercise on exercise intention and exercise-related affect of postmenopausal women].
PURPOSE
A dance exercise program was performed to investigate the effects of exercise on exercise intention and exercise-related affect as these are important determinants of exercise behavior.


METHOD
The subjects were overweight (23< or =BMI< or =25) or obese (BMI> or =25) postmenopausal women (n=14), who participated in an exercise program from May, 2003 through November, 2003 at one public health center located in Kyong-gi Province. Data was analyzed with an SAS PC program.


RESULT
Exercise intention was significantly increased after the exercise program (t=-2.24, P=0.04). Exercise-related affect was also increased, but there was no statistically significant change (t=1.81, P=0.09).


CONCLUSION
This study suggests that exercise participation can increase the level of future exercise behavior by increasing exercise intention and exercise-related affect.