Disparity between online and offline tests in accelerated aging tests of LED lamps under electric stress.

The accelerated aging tests under electric stress for one type of LED lamp are conducted, and the differences between online and offline tests of the degradation of luminous flux are studied in this paper. The transformation of the two test modes is achieved with an adjustable AC voltage stabilized power source. Experimental results show that the exponential fitting of the luminous flux degradation in online tests possesses a higher fitting degree for most lamps, and the degradation rate of the luminous flux by online tests is always lower than that by offline tests.

Analysis of junction temperature and modification of luminous flux degradation for white LEDs in a thermal accelerated reliability test.

An accelerated aging test is the main method in evaluation of the reliability of light-emitting diodes (LEDs), and the first goal of this study is to investigate how the junction temperature (Tj) of the LED varies during accelerated aging. The Tj measured by the forward voltage method shows an upward trend over the aging time, which gives a variation about 6°C-8°C after 3,000 h of aging under an ambient temperature of 80°C. The second goal is to investigate how the variation of Tj affects the lifetime estimation.

Pdx1 protein induces human embryonic stem cells into the pancreatic endocrine lineage.

Success in generating insulin-producing cells (IPCs) from human embryonic stem (hES) cells by genetic manipulation has recently revealed a new therapeutic potential for diabetes. However, clinical application has been hampered by the viral genome integration and the risk of insertion mutagenesis that are entailed. Herein, we report the induction of hEC into IPCs by direct delivery of human Pdx1 proteins per se.