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91.
热电器件能把废热转化为电能,减少二氧化碳排放,符合国家节能减排、逐步实现碳中和的发展需求. 该文通过建立多孔热电器件的热、电传导分析模型,解释了多孔热电泡沫高输出功率的内在机制,并揭示了几何结构及孔隙率对断裂破坏的影响机理. 在此基础上,阐明了断裂破坏对器件转化性能的影响规律. 研究发现,随着孔隙率的增加,热电泡沫与金属层之间的界面剪切应力减小. 同时,只要多孔热电泡沫的内部裂纹开始扩展就不会停止,直至器件完全破坏. 此外,随着裂纹扩展,输出功率呈现先增加后减小的趋势. 这是因为裂纹的形成间接增大了热电泡沫的孔隙率,导致器件与废热的接触面积增大,进而提高热电器件的输出功率;随着裂纹进一步扩展,其必然减弱热电器件的导热和导电性能,进而减小热电器件的输出功率. 相似文献
92.
ZHANG Zhirong;XIA Hua;SUN Pengshuai;YU Runqing;YANG Xi;LIN Yuqing;WU Bian;PANG Tao;GUO Qiang;LI Zhe;LIU Xu;CAI Yongjun;SIGRIST Markus W;CALSHAW Brain;SHU Chimin 《光子学报》2023,52(3):119-135
Stable isotope technology has been widely used in geochemistry, geophysics, agriculture, biology, clinical medicine and ecological environment science. It is very important for the study of atmosphere, soil, water quality and health to realize the accurate measurement of gas isotope abundance. At present, isotope abundance is measured and analyzed mostly by Isotope Ratio Mass Spectrometers. It is a relatively large, expensive and complex pre-processing, which is not conducive to real-time measurement of isotope abundance in the field. With the development of laser technology, the output wavelength can cover more and more wide bands, and the performance is more better. Many kinds of gases can be detected by laser absorption spectroscopy, and the detection sensitivity is further improved. This makes it possible to measure isotopic gases, which have attracted more and more attention and become one of the hot spots of laser spectroscopy. Compared with the traditional stable isotope analysis instruments, the isotope analysis technology based on laser absorption spectroscopy, as a relatively new isotope abundance measurement method, has the advantages of high selectivity, high accuracy, small volume, real-time online monitoring concentration and abundance, etc. So, the gas isotope analysis system based on laser absorption spectroscopy technology has important application value in environmental monitoring, ecosystem research, pollution tracing and tracing because of its miniaturization, fast response and real-time online measurement. Taking Tunable Diode Laser Absorption Spectroscopy （TDLAS）, Integrated Cavity Absorption Spectroscopy （ICOS） and Cavity Ring-Down Absorption spectroscopy （CRDS） as examples, the basic principle, spectrum line selection, system structure and some test results are described in this paper. Under the control of the PID system of temperature and pressure, the temperature control error is 0.003 ℃, and the pressure control error is 0.03mbar, which can meet the requirements of temperature and pressure control during the measurement of isotope gas. The 13C measurement accuracy of atmospheric CO2 is 0.3‰, the 13CH4 measurement accuracy of coalbed methane is 1.25‰, the 18O, 17O and D measurement accuracy of glacial H2O are 0.3‰, 0.2‰ and 0.5‰, respectively. And also, the “gold standard” for 13CO2 of detecting helicobacter pylori infection is also introduced. The feasibility and reliability of laser absorption spectroscopy in isotope measurement are verified. And it is also fully demonstrated that the measurement method based on laser absorption spectroscopy has a very good technical advantage. TDLAS, ICOS and CRDS have become the best choice for the high-sensitivity detection of trace gases and isotope gases. The three technologies have their characteristics： TDLAS technology has the simplest structure, but its cavity volume is large and requires the largest gas samples. The system structure of ICOS technology is relatively simple, but the technology is based on absorption intensity measurement technology, limited by laser intensity noise and frequency drift, which is also a major problem in applying ICOS technology in high sensitivity detection. Therefore, the signal-to-noise ratio and measurement accuracy of ICOS technology is slightly lower than that of CRDS technology. The structure of CRDS technology is relatively complex, and the conditions are relatively harsh, but it can achieve the absorption optical path that the above two technologies cannot reach, so it has the best sensitivity and measurement limits. Based on the above advantages and practical feasibility, laser absorption spectral isotope analysis system will be more and more applied to various fields. And the related system research still has a long way to go. At the same time, laser absorption spectroscopy is also faced with many shortcomings, such as： in these measurements, it is also necessary to consider the error sources such as the concentration dependence of the instrument and the time drift. A certain correction frequency should be set for periodic correction to eliminate the influence of the instrument drift, and the measurement results with accuracy and accuracy meeting the research needs should be obtained through appropriate correction strategies. 相似文献
93.
Xiao-Qin Liu 《中国物理 B》2022,31(11):114205-114205
Yb3+:CaF2-YF3 transparent ceramics with excellent optical quality was successfully fabricated by hot-pressed method. Pulsed laser properties of this ceramics were investigated for the first time. Laser diode (LD) was applied as the pump source to generate a dual-wavelength mode-locked (ML) laser. The maximum average output power was 310 mW, which represents the highest output power of ultrafast calcium fluoride ceramic laser. The spectrum separated at 1048.9 nm and 1049.7 nm with a total pulse duration of 8.9 ps. The interval period between the beating signals was about 4.3 ps, corresponding to a 0.23 THz beat pulse repetition rate. These results demonstrate its potential in producing dual-wavelength ultrashort pulses. These Yb3+:CaF2-YF3 ceramics with low-cost and short-preparation period are ideal candidate materials for ultrafast lasers. 相似文献
94.
CO是碳氢燃料不完全燃烧的重要产物,常常被作为反应燃烧效率的标志物,燃烧场CO组分浓度的精确测量对提高燃烧效率、减少污染物排放具有重要意义。离轴积分腔输出光谱(OA-ICOS)是一种利用物质对激光的特异性吸收,实现对该物质分析和测量的技术,具有非接触、稳定和高灵敏度等优点。针对燃烧场CO浓度低,背景信号干扰强等特点,采用分布反馈式(DFB)激光器搭建基于离轴积分腔输出光谱的CO浓度测量系统,通过直接吸收光谱的测量方法实现对高温燃烧场CO浓度测量。利用仿真模拟的方法,在所用激光器中心波长的附近选出了常温下谱线强度较为突出,高温下不受其他燃烧产物干扰的第一泛频带R(10)吸收谱线。通过固定光程池对比吸光度的方法标定了OA-ICOS系统的有效光程;通过比较不同扫描频率下吸收谱线的信噪比和线型拟合残差标准差,得到最佳波长扫描频率;通过测量不同浓度CO混合气体的吸收信号分析了系统误差。探究了不同燃烧情况下CH4/Air预混平焰炉上CO的产生情况,根据燃烧场测量区域温度分布情况描述了温度分布不确定度对CO测量结果的影响。当量比为1.0时,在10 ms的测量时间分辨率下,噪声等... 相似文献
95.
Lei HU;Deyao LI;Jianping LIU;Aiqin TIAN;Dan WANG;Tao ZHANG;Si WU;Peng XU;Hui YANG 《光子学报》2022,51(2):99-104
Gallium Nitride（GaN）-based materials have the characteristics of large band gap, high electron mobility, high thermal conductivity, etc., which are used in various electronic devices and optoelectronic devices, and have received extensive attention. High power GaN-based blue laser diodes （LDs） have great prospects in laser display, laser lighting, metal processing and other fields. However, the development of high-power GaN-based blue lasers is extremely difficult, mainly related to the difficulties of epitaxial growth, processing and packaging technology. Firstly, the epitaxial structure of blue laser is complicated, and the crystal quality needs to be ensured while improving the luminous efficiency of the quantum well and reducing the light absorption loss. Secondly, the sidewall loss and cavity surface loss need to be reduced during the manufacturing process. Last but not least, a low thermal resistance packaging technology needs to be developed, so that high-power GaN-based blue lasers can effectively dissipate heat. In this work, by adopting the double-sided packaging method for GaN-based blue lasers, which use the copper fully attached to the N-side of the blue laser to increase the heat dissipation. According to the change in the forward voltage caused by the junction temperature change, the thermal resistance of the single-sided packaged blue laser is 8.5 K/W, while the double-sided packaged blue laser has a thermal resistance of 6.7 K/W. It can be found that the GaN-based blue laser with double-sided packaging has lower thermal resistance and can dissipate heat more effectively, which is beneficial for the high-power blue laser to work under continuous room temperature conditions. According to the power-current curves of the blue laser from room temperature to 65 ℃, the characteristic temperature of the single-sided packaged blue laser is 132 K, and the characteristic temperature of the double-sided packaged blue laser is 235 K, it is found that the characteristic temperature of the double-sided packaged blue laser is higher, which means that has better temperature stability. Finally, we demonstrate the double-sided packaged blue lasers with a ridge width of 45 μm and a cavity length of 1 200 μm which have a threshold current density of 1.1 kA/cm2 and a slope efficiency of 1.4 W/A. The light output power reaches 7.5 W at 6 A under continuous-wave operation at room temperature, it means that the double-sided packaged blue laser has good material quality, structure and packaging. 相似文献
96.
Cost minimization multi-product production problems with static production resource usage and internal product flow requirements have been solved by linear programming (LP) with input/output analysis. If the problem is complicated by interval resource estimates, interval linear programming (ILP) can be used. The solution of realistic problems by the above method is cumbersome. This paper suggests that linear goal programming (LGP) can be used to model a multi-product production system. LGP's unique modeling capabilities are used to solve a production planning problem with variable resource parameters. Input/output analysis is used to determine the technological coefficients for the goal constraints and is also used to derive an information sub-model that is used to reduce the number of variable resource goal constraints. Preliminary findings suggest that the LGP approach is more cost-efficient (in terms of CPU time) and in addition provides valuable information for aggregate planning. 相似文献
97.
NdxLu1−xVO4 (x = 0, 0.005, 0.02, 0.023, 0.03 and 0.05) series crystals have been grown by the Czochralski method. The results of X-ray powder diffraction experiments show that these crystals belong to the zircon-type structure. The cutoff wavelength of LuVO4 is 330 nm and the transmittance is about 80% in 540-3010 nm. The functional relation of absorption coefficient α at 808 nm on Nd3+-doped concentration Nd in units of atomic % is obtained to be α = 7.649 Nd. The results of Judd-Ofelt analysis show that there is no obvious concentration quenching effect below 3 at.% doped concentrations. The highest output power at 1.06 μm is 1090 mW for Nd0.02Lu0.98VO4 at the pumping power of 6.58 W of a laser diode, the optical-optical conversion efficiency is 16.6% and slope efficiency is 19.4%. 相似文献
98.
A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly. 相似文献
99.
This paper presents the planar Fiber Bragg Grating （FBG） hydrophone probe sensing principle, and theoretically and experimentally researches the probe structure sensitivity, the receiving sensitivity frequency response characteristic and the acceleration response property. Planar sheet is made of stainless steel, its thickness is 0.15 mm, its diameter is 15mm, and the length of hollow circular shell is 20 mm. For this size of the structure, the probe structure sensitivity is up to 23 fm/Pa, which is about 7300 times of the value of the bare fiber. The resonance frequency is 6.5 kHz, and the amplitude-frequency curve of the receiving sensitivity response is relatively flat within the frequency range of 100 Hz to 5.5 kHz. The output yielded by one unit acceleration （1m/s2） is equivalent to （2.52 to 3.26 Pa） acoustic pressure acting output. This probe structure is easy to form FBG hydrophone array by multiplexing technique. The research shows that this planar structure not only can form FBG hydrophone probe, but also can constitute optical FBG laser hydrophone probe. The structure can realize different bandwidth, different range acoustic pressure measurement by adjusting the geometrical size of the sheet. 相似文献
100.