Heat:generated by ohmic losses is a critical parameter for performance and lifetime of light-emitting diodes (LEDs). The temperature of InGaN MQW LEDs during operation has been investigated depending on the forward current using three independent methods. First, the temperature of the active region was derived from the electroluminescence spectra of the devices. Second, temperature dependent micro-Raman scattering by phonons was used to determine,the local temperature. Finally a finite element simulation was performed to get a full temperature profile of the device. While the first method yields the temperature of the active region, the latter two can map the thermal distribution. All three independent methods reveal maximum operation temperatures about 120 to 130 degrees C at a forward current of 30 mA, corresponding to a power density of 705 W cm(-2).

AIM:The purpose of this study was to examine quantitatively the change of muscle thickness and echo intensity caused by muscle exercise in healthy persons.METHOD:16 healthy volunteers (7 women, 9 men), aged 23 to 37 years, underwent static exercises of the rectus abdominis, rectus femoris/vastus intermedius, and tibialis anterior muscles. In addition, the rectus femoris/vastus intermedius muscles were exercised dynamically. Thicknesses of these muscles were measured before and during/after exercise using the electronic caliper and computer-assisted gray-scale analysis of the echo signals.RESULTS:Short, maximal isometric contraction resulted in an increase of thickness by 5 to 18% depending on the examined muscle (p < 0.01). The echo intensity of the rectus femoris and vastus intermedius muscles decreased significantly (-8% and -26%, p < 0.01). The increase of muscle thickness immediately after isometric exercise for up to 90 s was significantly correlated to the duration of contraction (r = 0.26 to 0.49, p < 0.05). Muscle echo intensities did not significantly correlate with the duration of the contraction. After dynamic exercise on a bicycle ergometer both thickness of the rectus femoris/vastus intermedius muscles (+12.5%, p < 0.01) and echo intensity of the vastus intermedius muscle increased (+19.5%, p < 0.01). The change of echo intensity of the vastus intermedius muscle after static and dynamic exercise was significantly different (-26% vs. +18%, p < 0.001).CONCLUSION:Muscle thickness increases during and after static as well as dynamic exercise. Echo intensity may be unchanged, decreased or increased, depending on the exercised muscle and mode of exercise.