共查询到19条相似文献,搜索用时 765 毫秒
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主要回顾了中国科学院精密测量科学与技术创新研究院在液氮低温钙离子光频标的物理系统设计、不确定度评估与稳定度的优化与测量等方面的工作。液氮低温系统为钙离子创造了液氮的温度环境(~ 80 K),极大降低了钙离子光频标的黑体辐射频移,使钙离子光频标的系统不确定度降至3.0 × 10-18,成为第五种不确定度进入10-18的原子/离子光频标体系。为了优化钙离子光频标的稳定度,将钟激光频率参考在Ramsey条纹上,并引入了参考条纹判定算法及自动寻峰算法,使钙离子光频标可长期稳定运行,长期稳定度达到6.3 × 10-18@524 000 s。 相似文献
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针对镱离子光钟实验中激光冷却并操控离子时,激光器频率漂移影响原子钟系统的问题,基于数字PID控制方法,设计了一种新的多通道频率-数字信号转换稳频方法,将多路多波长激光频率锁定在波长计的参考频率上。对激光器锁定前和锁定后的频率进行一定时长的数据采集及数据对比,激光频率漂移由800 MHz控制在± 0.8 MHz,激光频率稳定度由9.29 × 10-10@1 s优化至2.79 × 10-10@1 s,频率千秒稳达到3.85 × 10-12。该系统简单、易实现,具有小型化、适应性强的优点。 相似文献
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通过分析带有声学放大器的行波热声发电系统中直线发电机的电-力-声类比图,发现直线发电机的最佳工作状态与行波热声发动机的输出声阻抗特性相关。采用DeltaEC软件计算带有声学放大器的行波热声发动机(以下简称系统)的输出声阻抗特性。计算结果发现,输出声阻抗虚部Xa为-1×107 Pa·s·m-3时,系统的最大输出声功率545.47 W,最大热声转换效率为7.2%;当输出声阻抗虚部Xa在-3.9×106~-1×107 Pa·s·m-3之间变化,实部Ra在1.37×106~2.31×107 Pa·s·m-3之间时,等效位移在1.89~6 mm之间变化,符合直线发电机的位移要求;结合输出声阻抗对压力与体积流率的相位差及系统工作频率的影响,发现声阻抗实部Ra应在1.37×106~2.31×107 Pa·s·m-3之间,声阻抗虚部Xa在-7.5×106~-1.0×107 Pa·s·m-3之间时,系统具有较好的工作状态。 相似文献
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一种锁定半导体激光器频率的新方法 总被引:1,自引:0,他引:1
报道了一种实现半导体激光器频率锁定的新方法:通过交流磁场对法拉第反常色散光学滤波器(FADOF)的透射谱进行调制,将半导体激光器的频率锁定在FADOF的透射谱上。在B=1.76×10~(-2)T、T=120℃条件下,利用一阶导数稳频技术,测得1s和10s取样时间的频率稳定度分别为1.5×10~(-10)和5.8×10~(-11)。 相似文献
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超高冲击加速度传感器在武器研制、航空航天等高过载测量中发挥了重要的作用,为解决超高冲击加速度的校准问题,基于激光绝对法,建立了超高冲击加速度校准系统。本文介绍了系统的组成和优化方案,设计了合适的解调程序和滤波算法,对原始多普勒信号进行解调,实现了冲击加速度峰值1 × 104 g ~ 2.5 × 105 g,脉宽20 ~ 50 μs范围内半正弦冲击波形的绝对复现。最后对影响测量结果的不确定分量进行评定,超高冲击加速度测量不确定度为8%,对2 × 105 g以上冲击加速度校准具有重要意义。 相似文献
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Hsin-Yao Lin Wan-Ru Chen Li-Chia Lu Hsuen-Li Chen Yu-Hsuan Chen Michael Pan Chi-chia Chen Chihchen Chen Tzung-Hai Yen Dehui Wan 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(28):2207404
Surface-enhanced Raman spectroscopy (SERS)-based biosensors have attracted much attention for their label-free detection, ultrahigh sensitivity, and unique molecular fingerprinting. In this study, a wafer-scale, ultrasensitive, highly uniform, paper-based, portable SERS detection platform featuring abundant and dense gold nanopearls with narrow gap distances, are prepared and deposited directly onto ultralow-surface-energy fluorosilane-modified cellulose fibers through simple thermal evaporation by delicately manipulating the atom diffusion behavior. The as-designed paper-based SERS substrate exhibits an extremely high Raman enhancement factor (3.9 × 1011), detectability at sub-femtomolar concentrations (single-molecule level) and great signal reproductivity (relative standard deviation: 3.97%), even when operated with a portable 785-nm Raman spectrometer. This system is used for fingerprinting identification of 12 diverse analytes, including clinical medicines (cefazolin, chloramphenicol, levetiracetam, nicotine), pesticides (thiram, paraquat, carbaryl, chlorpyrifos), environmental carcinogens (benzo[a]pyrene, benzo[g,h,i]perylene), and illegal drugs (methamphetamine, mephedrone). The lowest detection concentrations reach the sub-ppb level, highlighted by a low of 16.2 ppq for nicotine. This system appears suitable for clinical applications in, for example, i) therapeutic drug monitoring for individualized medication adjustment and ii) ultra-early diagnosis for pesticide intoxication. Accordingly, such scalable, portable and ultrasensitive fibrous SERS substrates open up new opportunities for practical on-site detection in biofluid analysis, point-of-care diagnostics and precision medicine. 相似文献
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Zehui Li Rongji Liu Cheng Tang Zhuoya Wang Xiao Chen Yuheng Jiang Chizhong Wang Yi Yuan Wenbo Wang Dongbin Wang Shuning Chen Xiaoyuan Zhang Qiang Zhang Jingkun Jiang 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(15)
In situ monitoring of hydrogen peroxide (H2O2) during its production process is needed. Here, an electrochemical H2O2 sensor with a wide linear current response range (concentration: 5 × 10?8 to 5 × 10?2 m ), a low detection limit (32.4 × 10?9 m ), and a high sensitivity (568.47 µA mm ?1 cm?2) is developed. The electrocatalyst of the sensor consists of cobalt nanoparticles and atomic Co‐Nx moieties anchored on nitrogen doped carbon nanotube arrays (Co‐N/CNT), which is obtained through the pyrolysis of the sandwich‐like urea@ZIF‐67 complex. More cobalt nanoparticles and atomic Co‐Nx as active sites are exposed during pyrolysis, contributing to higher electrocatalytic activity. Moreover, a portable screen‐printed electrode sensor is constructed and demonstrated for rapidly detecting (cost ≈40 s) H2O2 produced in microbial fuel cells with only 50 µL solution. Both the synthesis strategy and sensor design can be applied to other energy and environmental fields. 相似文献
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Abstract A measurement of the frequency noise at the relaxation oscillation frequency of a Nd:YAG monolithic non-planar ring laser is presented. By careful monitoring of various applied calibration signals, a limit to the frequency noise level of ~ 6.3 × 10?2 Hz/√Hz is set over the relaxation oscillation bandwidth and it is shown that this is approximately at the level to be expected, based on the relaxation oscillation induced time varying refractive index. 相似文献
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Dhinesh Babu Velusamy Jehad K. El‐Demellawi Ahmed M. El‐Zohry Andrea Giugni Sergei Lopatin Mohamed N. Hedhili Ahmed E. Mansour Enzo Di Fabrizio Omar F. Mohammed Husam N. Alshareef 《Advanced materials (Deerfield Beach, Fla.)》2019,31(32)
MXenes have recently shown impressive optical and plasmonic properties associated with their ultrathin‐atomic‐layer structure. However, their potential use in photonic and plasmonic devices has been only marginally explored. Photodetectors made of five different MXenes are fabricated, among which molybdenum carbide MXene (Mo2CTx) exhibits the best performance. Mo2CTx MXene thin films deposited on paper substrates exhibit broad photoresponse in the range of 400–800 nm with high responsivity (up to 9 A W?1), detectivity (≈5 × 1011 Jones), and reliable photoswitching characteristics at a wavelength of 660 nm. Spatially resolved electron energy‐loss spectroscopy and ultrafast femtosecond transient absorption spectroscopy of the MXene nanosheets reveal that the photoresponse of Mo2CTx is strongly dependent on its surface plasmon‐assisted hot carriers. Additionally, Mo2CTx thin‐film devices are shown to be relatively stable under ambient conditions, continuous illumination and mechanical stresses, illustrating their durable photodetection operation in the visible spectral range. Micro‐Raman spectroscopy conducted on bare Mo2CTx film and on gold electrodes allowing for surface‐enhanced Raman scattering demonstrates surface chemistry and a specific low‐frequency band that is related to the vibrational modes of the single nanosheets. The specific ability to detect and excite individual surface plasmon modes provides a viable platform for various MXene‐based optoelectronic applications. 相似文献
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The power dynamic range of an YBa2Cu3O7−x
frequency-selective Josephson detector for the Hilbert-transform spectroscopy was experimentally studied in the subterahertz
frequency range. At a temperature of 80 K, the dynamic range of 2×105 was achieved at a noise equivalent power of 8×10−15 W/Hz1/2. 相似文献
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An earlier modification of the Paris law for the growth of deep cracks in the linear elastic fracture mechanics regime is extended to include a term enabling the prediction of cyclic crack growth rates at low frequencies. The relation requires (i) a reference growth law under continuous cycling at the appropriate elevated temperature and (ii) a specified, dimensionless degradation term, defined as Dc, the creep/oxidation damage per cycle, which increases as the applied frequency decreases or as the dwell time at peak load is prolonged. The relationship is validated against data from the previous analysis on low alloy ferritic and austenitic steels in the range 538–650°C and against further published results on Ni-based alloys at temperatures up to 700°C. It appears that for the former series oxidation is the dominant damaging mode, whereas a linear creep damaging mechanism is manifest in the Ni-based alloys. Moreover, levels of cyclic damage in terms of Dc are higher in the latter, ranging between 10?3 and 5 × 10?1 compared with 10?4 to 5 × 10?2 for the steels. A brief comparison is made with damage factors arising from the high strain fatigue deformation mode at elevated temperatures and other models for the prediction of frequency effects are discussed. 相似文献
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Abstract The FDTD method is used to calculate the specific extinction cross section of the powder of brass 70Cu/30Zn with 1.35×104 to 2.56×105 particles in the infrared frequency range. A digitized model of body‐center‐like structures is used for the calculations of specific extinction cross‐section. From theoretical calculations, the value of a specific extinction cross section of the powder of brass 70Cu/30Zn is between 0.14 to 4.0 m2/g. While the experimental measurement shows the value of specific extinction cross section to be between 0.58 to 3.78 m2/g. The theoretical results concur with those obtained from the experimental measurement for the cell sizes of particles in the range of 0.05 to 0.4 p.m. There are some differences between the theoretical value and measurement data of specific extinction cross section for other particle sizes outside the range of 0.05 to 0.4μm. 相似文献