Accurate measurement and influence on device reliability of defect density of a light-emitting diode

A method of accurately measuring the defect density of a high-power light-emitting diode （LED） is proposed. The method is based on measuring the number of emitting photons in the magnitude of 105 under the injection current as weak as nA and calculating the non-radiative recombination coefficient which is related to defect density. Defect density is obtained with the self-developed measurement system, and it is demonstrated that defect density has an important influence on LED optical properties like luminous flux and internal quantum efficiency （IQE）. At the same time, a batch of GaN-based LEDs with the chip size of 1 minx 1 mm are selected to conduct the accelerated aging tests lasting for 1000 hours. The results show that defect density exhibits a greater variation and is more sensitive to LED reliability than luminous flux during aging tests. Based on these results, it is concluded that for the GaN-based LED with a chip size of 1 mm ~ I mm, if its defect density is over 1017/cm3, the LED device performance suffers a serious deterioration, and finally fails.

PFNA-Ⅱ combined with preoperative accurate measurement evaluation for the treatment of senile femoral fractures between rotor

Objective:Research PFNA-Ⅱcombined with preoperative accurate measurement of senile femoral fracture between the rotor of the clinical application value.Methods:Fiftytwo patients with intertrochanteric fractures admitted to our hospital from January 2017 to October 2019 were selected and divided into the traditional group and the measurement group according to the random number table method,with 26 patients in each group.The traditional group could not make accurate measurement before operation,but the measurement group could make accurate measurement before operation.Postoperative follow-up was conducted for at least 6 months to compare The Times of intraoperative X-ray fluoroscopy,operation time,intraoperative blood loss,and TAD,Harris score and improved BADL score of the hip joint between the two groups.Results:The number of intraoperative X-ray fluoroscopy in the measured group was less than that in the conventional group(15.08+/-2.10 vs 19.81±2.21 times,t=7.920,P=0.000).The operation time of the measured group was lower than that of the traditional group(78.46+/-3.68 vs 89.62+/-5.28 minutes,t=8.841,P=0.000).Intraoperative blood loss was less in the measured group than in the conventional group(146.15+/-24.18 vs 163.46+/-22.62 ml,t=2.666,P=0.010).There was no statistically significant difference in TAD values between the two groups(23.73+/-2.49 vs 24.04+/-2.63 mm,t=0.433,P=0.667).There is no interaction between intervention mode and time factor(F=0.362,P=0.698).There was statistical difference in Harris scores between different timepoints before and after the operation,in other words,there was time effect(F=378.110,P=0.000).There was no statistical difference in Harris scores between the 2 groups,in other words,there was no group effect(F=0.874,P=0.354).All the Harris scores of the two groups increased with time,and the increase trend was consistent(39.69+/-3.27,68.27+/-5.06,82.54+/-6.21 points,F=49.333,P=0.000;39.15+/-3.46,67.00+/-4.24,80.84+/-7.12 points,F=53.460,P=0.000).There was no significant difference in the improved BADL score between the two groups 6 months after surgery(t=0.587,P=0.560).Conclusion:PFNA-Ⅱcombined with preoperative accurate measurement in the application of the elderly femoral fracture between the rotor is safe and effective,not only can shorten the operation time,less intraoperative blood loss and the number of perspective,while reducing the risks of medical radiation.

Accurate measurement of ultrasonic velocity by eliminating the diffraction effect

The accurate measurement method of ultrasonic velocity by the pulse interference method with eliminating the diffraction effect has been investigated in VHF range experimentally. Two silicate glasses were taken as the specimens, their frequency dependences of longitudinal velocities were measured in the frequency range 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect were calculated using A. O. Williams' theoretical expression. For the frequency dependences of longitudinal velocities, the measurement results were in good agreement with the simulation ones in which the phase advances were included. It has been shown that the velocity error due to diffraction effect can be corrected very well by this method.

An Accurate and Safe Small Raman Gain Measurement for Installed Fiber Optic Cables

Novel small Raman gain measurement method for installed fiber optic cables using a modulated pump light is proposed. We have demonstrated accurate Raman gain measurement in small Raman gain less than 1dB and we also measured Raman gain for the installed fiber optic cable by using average pumping power of about only 25mW.

A new method and instrument for accurately measuring interval between ultrashort pulses

Using second-order autocorrelation conception, a novel method and instrument for accurately measuring interval between two linearly polarized ultrashort pulses with real time were presented. The experiment demonstrated that the measuring method and instrument were simple and accurate (the measurement error < 5 fs). During measuring, there was no moving element resulting in dynamic measurement error.

An apparatus for accurately measuring solubilities of gases in liquids at elevated temperatures and pressures

An apparatus for measuring solubilities of gases in liquids at elevated temperatures and pressures has been constructed. Using this apparatus, the slubilities of N_2 and CO_2 in some solvents have been determined in the temperature range between 20 and 230℃, and at pressures up to 130 atm. The experimental results obtained generally agree well with literature values. It is shown that this apparatus is reliable; attainment of equilibria needs only about 5 hours; precision of the measure- ments is ±0.2％.