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Thermal stress can induce birefringence in a laser medium, which can cause depolarization of the laser. The depolarization effect will be very severe in a high-average-power laser. Because the depolarization will make the frequency doubling efficiency decline, it should be compensated. In this paper, the thermal characteristics of two kinds of materials are analyzed in respect of temperature, thermal deformation and thermal stress. The depolarization result from thermal stress was simulated. Depolarization on non-uniform pumping was also simulated, and the compensation method is discussed.
The high repetition rate 10 J/10 ns Yb:YAG laser system and its key techniques are reported. The amplifiers in this system have a multi-pass V-shape structure and the heat in the amplifiers is removed by means of laminar water flow. In the main amplifier, the laser is four-pass, and an approximately 8.5 J/1 Hz/10 ns output is achieved in the primary test. The far-field of the output beam is approximately 10 times the diffraction limit. Because of the higher levels of amplified spontaneous emission (ASE) in the main amplifier, the output energy is lower than expected. At the end we discuss some measures that can improve the properties of the laser system.
Previous studies showed an inconsistent association of fruit and vegetable consumption with bone health. We assessed the associations in Chinese adolescents, young and postmenopausal women.
A cross-sectional study conducted in China during July 2009 to May 2010.
Bone mineral density (BMD) and content (BMC) at the whole body, lumbar spine and left hip were measured with dual-energy X-ray absorptiometry. Dietary intakes were assessed using an FFQ. All these values were separately standardized into Z-scores in each population subgroup.
One hundred and ten boys and 112 girls (11–14 years), 371 young women (20–34 years, postpartum within 2 weeks) and 333 postmenopausal women (50–70 years).
After adjustment for potential covariates, analysis of covariance showed a significantly positive association between fruit intake and BMD and BMC in all participants combined (P-trend: < 0·001 to 0·002). BMD Z-score increased by 0·25 (or 2·1 % of the mean), 0·22 (3·5 %), 0·23 (3·0 %) and 0·25 (3·5 %), and BMC Z-score increased by 0·33 (5·7 %), 0·25 (5·8 %), 0·34 (5·9 %) and 0·29 (4·7 %), at the total body, lumbar spine, total hip and femoral neck in participants belonging to the top tertile compared with the bottom tertile of fruit intake (all P < 0·05), respectively. There was no significant association between vegetable intake and bone mass at all bone sites studied except for total body BMD (P = 0·030). Relatively more pronounced effects were observed in boys and postmenopausal women.
Our findings add to the existing evidence that fruits and vegetables may have a bone sparing effect.
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