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The accurate temperature measurement of high-power laser diode arrays is a considerable challenge due to their large temperature gradient and package structure. In this study, experiments based on the forward voltage method were set up to measure the transient temperature behavior of chips after the removal of heating load. A hybrid experimental/numerical method was developed to calculate multiple unknown interface thermal resistances and improve the prediction of the temperature distribution of high-power laser diode arrays by analyzing the transient temperature behavior of chips. The largest deviation between numerical and experimental results is 1.3 K. Based on the numerical results, thermal resistances for different layers and temperature distribution inside the chip were obtained and evaluated. Some suggestions for improving the thermal design of high-power laser diode arrays were derived.

High-power laser diode arrays (HPLDAs) have been widely used in pumps for solid-state lasers, medicine, optical data storage, and free-space optical communication due to their high efficiency, compact package, and long-term reliability. Similar to other high-power electronic chips, cooling is of great significance in maintaining the superior performance of HPLDAs including electro-optic conversion efficiency, beam quality, reliability, and long life span.

Land subsidence induced by excessive groundwater withdrawal has caused serious social, geological, and environmental problems in Beijing. Rapid increases in population and economic development have aggravated the situation. Monitoring and prediction of ground settlement is important to mitigate these hazards. In this study, we combined persistent-scatterer interferometric synthetic aperture radar with Grey system theory to monitor and predict land subsidence in the Beijing plain. Land subsidence during 2003–2014 was determined based on 39 ENVISAT advanced synthetic aperture radar (ASAR) images and 27 RadarSat-2 images. Results were consistent with global positioning system, leveling measurements at the point level and TerraSAR-X subsidence maps at the regional level. The average deformation rate in the line-of-sight was from −124 to 7 mm/year. To predict future subsidence, the time-series deformation was used to build a prediction model based on an improved Grey-Markov model (IGMM), which adapted the conv...

In this paper, the slamming pressure and load characteristics of a trimaran cross-section under various conditions were investigated by CFD (Computational Fluid Dynamics) simulations. The computation model was first validated against experimental results. After that, the simulation of different types of motion, i.e. free fall with different mass and entry velocity, entry with constant velocity and harmonic motion with different entry velocities were analysed. It was found that the characteristics of the dynamics during slamming strongly correlates to penetration depth, regardless of the types of entry. Distinguishing features during the wet-deck slam were observed for free fall motion under different conditions, including pressure drop under the main hull during wet-deck slam. The maximum acceleration would start to decrease after the mass has reached a certain value, and the second acceleration peak (corresponding to the wet-deck slam) would be smaller than the first one if the falling height is large enough.

In this study, a hybrid microchannel and slot jet array heat sink is designed and fabricated to achieve a better thermal performance of the high-power laser diode arrays. A standard commercial laser bar with wavelength of 808 nm is packaged on the heat sink and experiments are performed to assess the cooling performance of the hybrid heat sink. In the experiments, the forward voltage method is used to measure the chip temperature and the structure function method is applied to obtain the thermal resistance of the heat sink. Using the deionized water as coolant, the heat sink deals with a heat flux of up to 506 W/cm2 and the thermal resistance of the heat sink is only 0.23 K/W when the flow rate is 0.8 L/min (The average jet velocity is 13.3 m/s). The optical power can be up to 135.5 W corresponding to the wall plug efficiency of 64.2%. Compared with the published solutions related to cooling similar laser chips, the thermal resistance reduces by over 15%, indicating that this hybrid heat sink is an interesting solution to improve the cooling of the high-power laser diode arrays.

BACKGROUND Endogenous nitric oxide and adenosine increase simultaneously to keep the balance of energy demand and supply when the oxygen supply is insufficient, which suggests that nitric oxide and adenosine might exert a synergistic myoprotection during tissue hypoxia. In this study, we tested this hypothesis utilizing a canine model of prolonged global myocardial ischaemic reperfusion injury. METHODS In this double blind, controlled study, the hearts of 24 anaesthetized mongrel dogs were arrested for 2 hours with aortic cross clamping and blood cardioplegia. The treatment groups were those supplemented with 2 mmol/L L-arginine (ARG), supplemented with 1 mmol/L adenosine (ADO), ARG + ADO supplemented with both, and no supplementation (control) (n = 6 in each group). Haemodynamics, biochemical indices, adenosine triphosphate (ATP) content and myeloperoxidase activities of myocardium were determined to evaluate myocardial injury. Statistical comparison was performed by two way ANOVA. RESULTS Although the requirements for inotropic supports were higher, the cardiac outputs were lower in control group than in ARG, ADO and the combination groups. Plasma cardiac troponin I levels were higher and the areas of hydropic changes were larger in control group than in ARG and ADO groups. Combination of arginine and adenosine provided further myoprotection with respect to better cardiac performance, lower release of cardiac troponin I, and smaller areas of hydropic changes compared with ARG and ADO groups. ATP content was higher, but myeloperoxidase activities of myocardium were significantly lower in the combination group than in control, ARG and ADO groups (P < 0.05). CONCLUSIONS Combination of L-arginine and adenosine provides synergistic myoprotection in a canine model of global myocardial ischaemia. Thus, the combination is recommended when the heart is exposed to a prolonged ischaemia during cardiac surgery.

Fiber nonlinearity of optical orthogonal frequency division multiplexed (OFDM) system restricts the capacity improvement of optical fiber transmission. In this paper, we propose a novel digital coherent superposition (DCS) scheme to improve the tolerance to fiber nonlinearity in a coherent optical orthogonal frequency division multiplexed system. In simulation, 71.53 Gbit/s orthogonal frequency division multiplexed signal per channel with Hermitian symmetry is transmitted over 400 km standard single mode fiber in a wave division multiplexed-polarization-division multiplexed-coherent optical orthogonal frequency division multiplexed system with five channels. The 4-quadrature amplitude modulation is used for symbol mapping. For the receiver, after the conventional OFDM signal processing, we conduct DCS for OFDM subcarrier pairs, which requires only conjugation and summation in the x, y polarization direction, respectively. Firstly, the channel spacing is 25 GHz, the maximum signal-to-noise ratio improvement is 9.05 dB or 6.02 dB with or without symmetric dispersion compensation compared with a conventional orthogonal frequency division multiplexed system. The optimum launch power is increased by 2 dB. Secondly, the channel spacing is changed to 50 GHz to investigate the nonlinearity tolerance at different channel spacings in the wave division multiplexed system, the maximum signal-to-noise ratio improvement is 8.75 dB or 4.9 dB with or without symmetric dispersion compensation, respectively. Theoretical and simulation analysis show that the proposed method in this paper can effectively mitigate the first-order nonlinear distortions and hence improve the tolerance of coherent optical orthogonal frequency division multiplexed system with different channel spacings to fiber nonlinear effects.