天体物理学讲座第二讲 活动星系核物理

星系的活动是星系核心大质量黑洞吸积周围的气体释放巨大的辐射功率的过程,它是强引力场物理,高能物理和辐射流体物理的天然实验室,文章介绍了活动星系核中黑洞吸积,发射线形成和外流的观测事实和基本物理过程等,指出了现有理论存在的一些问题。     

中低温能源全流发电螺杆膨胀机的性能及实验研究

一、前言 全流系统是把地热(或余热)流体(包括汽、水)全部直接地引入动力机膨胀作功,因而可以充分利用热源汽液两相的可用能,获得比闪蒸或双循环系统更高的能量利用率。研究全流动力机是全流发电技术的关键性课题。在全流动力机中,螺杆膨胀机被认为是比较有希望的二种动力机,它以较适于汽液两相等优点而日益受到重视。本文研究螺杆膨胀机性能,提出了适于汽液两相的理想螺杆膨胀机概念,建立了机组的效     

CO_2跨临界循环高压侧压力控制的热力学分析

本文介绍了ＣＯ_２跨临界循环高压侧压力控制的基本原理;通过循环分析,阐述了不同压力运行条件对制冷量和制冷效率的影响。通过对所得结果的分析论证,提供并优化出一种简单、实用的压力控制调节方案,该方案对汽车空调、热泵系统更有实用意义。     

吸收式制冷循环系统的热力学分析

从热力学观点讨论了工作温度对于制冷循环系统性能的影响。分析了与循环时间有关的温度效率和熵产数。对于一个相对较短的循环时间,吸收/解吸收热量转换器的温度效率在200秒后可以达到92%。熵产数Ns由在一个循环系统内生成的不可逆性参数和热量转换器流体有效性参数之间的比率决定。结果显示,在使用一个30℃冷源的情况下高级吸收式循环系统的熵产数Ns在热水温度是45℃至55℃之间时是相对较小的,而对于传统循环,在使用相同冷源温度的情况下,热水温度在65℃到75℃之间时,Ns是相对较小的。     

单频偏振激光干涉仪中波片对非线性误差的影响

研究了用于纳米测量的激光干涉仪中光学波片对非线性误差的影响,基于琼斯矩阵理论建立了多波片的误差分析模型,分析了λ/2和λ/4波片引起的干涉仪非线性误差,对波片位置引起的非线性误差进行了实验研究.结果表明,波片位置调整精度对干涉仪测量影响巨大,在0～5°范围内,λ/2波片和λ/4波片引起的非线性误差分别为6.5 nm和9...     

Acceleration test of substrate-packaged fiber Bragg grating sensor北大核心CSCD

To test whether the fiber Bragg grating (FBG) sensor can endure the steady-state inertial loads caused by the acceleration and the sensing properties during the loads, a FBG strain and temperature sensor with aluminium alloy substrate package was designed, and the acceleration performance on the sensor was tested. The sizes of FBG strain and temperature sensor were designed and its package process was described. The strain and temperature sensing mechanisms of FBG sensor were analyzed, and the spectrum detection and demodulation system based on volume phase grating and linear array photodetector was developed. Finally, the acceleration test equipment was established, and the acceleration performance test of the selected FBG strain and temperature sensor was carried out in accordance with the requirements and methods of GJB150.15A acceleration test. The experimental results show that in the 2 min performance test before and after the acceleration test, the wavelength offset is below to ±50 pm, and the change of light intensity is below to 0.3 V. In acceleration test, the maximum fluctuation of wavelength offset is ±7 pm, and the light intensity is in the range of 1.3 V~4.003 V. It is proved that the designed FBG sensor has the ability to endure the acceleration loads and has the good sensing performance during the acceleration loads. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

A compact graphene Q-switched erbium-doped fiber laser using optical circulator and tunable fiber Bragg grating

We demonstrate a passively Q-switched tunable erbium-doped fiber laser(EDFL)based on graphene as a saturable absorber(SA).A three-port optical circulator(OC)and a strain-induced tunable fiber Bragg grating(TFBG)are used as the two end mirrors in an all-fiber linear cavity.The Q-switched EDFL has a low pump threshold of 23.8 mW.The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from23.8 mW to 219.9 mW.The minimum pulse duration is 1.7μs and the highest pulse energy is 25.4 nJ.The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.     

用作光学蝶互边网络的全息互连光栅的研究

提出了利用平面倾斜条纹透射体全息光栅等光强的０级和１级衍射光实现蝶互连网络中的直连和交连。在红敏光致聚合物干版上面制备出了这种光栅互连器件，并给出了这种器件的设计原理和制备方法。     

一种基于圆内接直角三角形的圆检测方法

提出一种基于圆内接直角三角形的圆检测方法.创建基于有效像素位置的数组存储空间,将图像空间的搜索任务转移到压缩的数组空间中完成,配以特定的搜索算法,降低了该方法复杂度.在存储空间中分级别搜索直角三角形,将圆参量的求解转化为三角形参量的计算,避免了反复的平方、开方运算,减少了运算时间.在结果计算过程中,将单个直角三角形求解结果进行聚合,最终得到合理全局解.合成图以及实际图像的实验结果表明,该方法用于一般图像的圆检测时,具有独特的抑制噪声以及非圆上边缘点干扰的优势,实验快速、可靠,具有可重复性,检测精度小于1 pixel.     

基于飞秒光学频率梳相关探测的绝对测距

提出了一种基于飞秒光学频率梳相关探测的绝对距离测量方法,通过检测测量信号与参考信号的相关条纹,实现了绝对距离测量。研究了一阶相关函数的测量模型,建立了基于非平衡迈克耳孙干涉光路的测量系统,通过拟合一阶相关函数包络并提取其峰值精确判断脉冲重合位置,获得了被测距离。设计并配合长导轨进行了3 m的绝对距离测量实验,并与商用干涉仪测量结果进行实时比对。基于大量实验数据,针对环境因素及系统误差进行了分析,并进行了误差消除与补偿。研究结果表明,所提方法在500 min长期测量中,在3 m的测量范围内的最大测量误差为5.85μm,测量标准差为2.20μm。