Cesium beam atomic clocks are widely used in various fields due to their excellent long-term stability. Compared to magnetic state selection clocks, optically pumped cesium beam clocks can concentrate more atoms in the clock transition state. However, traditional optical pumping with one laser still results in significant atomic loss, which limits the further improvement of optically pumped cesium beam clocks. Here, we implement and experimentally evaluate optical pumping with two lasers for state preparation to improve the population difference. We conduct a theoretical calculation of the population difference for the two-laser optical pumping scheme and develop a complete system for an optically pumped cesium beam clock. After experimental measurements, the estimated population difference of the two-laser pumping scheme reaches about five times that of the one-laser pumping scheme, thus improving the signal-to-noise ratio of the Ramsey fringes. The short-term frequency stability of the two-laser pumping scheme is 1.5×10−12/τ, which is improved by a factor of 1.47 compared with that of the one-laser pumping scheme with the same cesium beam and electric system.

Angular momentum coupling manifests widely in diverse physical systems, underpinning the emergent properties and collective dynamics across different scales. The tidal locking, which originates from the synchronization of rotational and orbital motions, has far-reaching impacts in celestial mechanics, reflecting fundamental processes of angular momentum transfer, energy dissipation, and evolution toward dynamical equilibrium. However, its counterpart in mesoscopic quantum fluids has remained largely unexplored. Here we demonstrate the emergence of quantum tidal locking in Bose-Einstein condensates undergoing central force motion in an anharmonic potential. The condensate follows a well-defined orbital trajectory in a static trap and experiences an effective rotating potential induced by the trap anharmonicity. The sustained geometric squeezing continuously deforms the condensate and drives a self-organized synchronization process, in which the intrinsic rotation gradually locks to the orbital motion. Numerical simulations further reveal the formation of a ring-shaped vortex array over longer timescales, arising from the coherent evolution of the rotating matter wave during the locking dynamics. Our findings establish quantum tidal locking in mesoscopic systems as a robust self-organized mechanism for generating and stabilizing circulating states.

Significance A gyroscope is a core sensor for measuring the angular velocity of an object's motion. It is designed to calibrate the position, attitude, and heading of navigation systems, with its precision directly determining the reliability of positioning systems. Traditional mechanical gyroscopes, micro-electro-mechanical system (MEMS) gyroscopes, and optical gyroscopes are constrained by factors such as mechanical wear, machining precision, and size, thus limiting their application scenarios and making it difficult to further improve long-term stability. Cold atom and ultracold atom interferometric gyroscopes based on the matter wave Sagnac effect utilize laser cooling technology to reduce atoms to the mu K to nK temperature range, significantly enhancing matter-wave coherence. Their theoretical sensitivity is 1011 times higher than that of optical interferometers, with long-term stability potentially reaching the order of 10-16 rad/s. This provides a new solution to overcoming traditional technological bottlenecks and achieving strategic-grade inertial navigation. Simultaneously, cold atom and ultracold atom interferometric gyroscopes can overcome the limitations of thermal atom gyroscopes, such as shorter atomic coherence time and bulky interferometric setups. While preserving the advantages of matter-wave interferometry, they possess the potential for integration and miniaturization, holding application significance in the fields of national defense and security, space science, and civil positioning. Progress Atom interferometric gyroscopes developed to date can be divided based on atomic source temperature characteristics into thermal atom, cold atom, and ultracold atom interferometric gyroscopes. Current experimental thermal atom interferometric gyroscopes have achieved long-term stability on the order of 10-10 rad/s. However, their short atomic coherence time and large interferometric setups have led to the proposal of various schemes adopting cold atoms as the interference source. Cold atom interferometric gyroscopes are primarily divided into two types based on the atomic source type and manipulation method, including the continuous atomic beam type and pulsed atomic cloud type. The method by employing continuous cold atomic beams preserves the advantage of high bandwidth characteristics of thermal atomic beam interferometric gyroscopes while effectively reducing device size without sacrificing sensitivity (Fig. 3). The pulsed cloud scheme for cold atom interferometric gyroscopes employs discretely launched cold atom clouds, utilizing designed laser pulse sequences to coherently split, reflect, and recombine atomic wave packets, and constructing spatially separated Sagnac interference loops. These devices typically adopt a projectile configuration (Figs. 4 and 5). Depending on the laser pulse sequence adopted during the interference experiment, they can be further divided into three-pulse and four-pulse types. Three-pulse sequence interferometers usually employ two identical, counter propagating atom clouds launched toward each other to form a dual interference loop. Four-pulse sequence interferometers often utilize a single atom cloud launched to form a butterfly shaped interference loop. Compared to atomic beam gyroscopes, they have advantages in the more flexible manipulation of coherent atoms. Ultracold atom interferometric gyroscopes developed from cold atom gyroscopes utilize laser cooling and evaporative cooling techniques to prepare neutral atoms (such as 87Rb) in the nK temperature range, forming Bose-Einstein condensates (BECs). Their unique quantum properties provide key advantages for building high-performance atom interferometric gyroscopes. On the one hand, longer coherence time allows for the design of more complex interference paths such as multi-loop circuits, enabling larger effective Sagnac interference areas within limited physical space. On the other hand, ultracold atoms can be precisely confined and guided by electromagnetic fields (magnetic traps, optical traps), enabling highly controllable, compact interference loop configurations that significantly enhance measurement sensitivity per unit volume (Figs. 6 -10). These schemes demonstrate the unique advantages of cold atom and ultracold atom interferometry in terms of sensitivity, stability, and multi-dimensional sensing, providing new avenues for the further development of inertial navigation technology. Conclusions and Prospects Cold atom and ultracold atom interferometric gyroscopes based on matter-wave interference principles feature significant development potential. Current research has validated the feasibility of various technical approaches and yielded notable results. However, much of the research remains at the laboratory stage, with a gap remaining to achieve theoretical precision limits and engineering applications. Future efforts should be focus on further integrating the advantages of multiple disciplines, improving measurement accuracy and stability, and intensifying research on engineering applications. In the long term, with the maturation of quantum control technology and micronano fabrication processes, practical, miniaturized, and integrated inertial units are expected to emerge. This will promote atomic gyroscopes from the laboratory stage into real applications, redefining the precision limits of inertial navigation.

Objective The compact cesium beam clock represents one of the most critical atomic clocks in the time-frequency field, where high-performance models provide essential support for navigation systems, high-speed communications, and related applications. Current compact cesium beam clocks can be categorized into three types, including magnetic state selection with magnetic detection (the traditional approach), magnetic state selection with optical detection, and optical pumping with optical detection (hereafter referred to as optically pumped compact cesium beam clocks). The traditional magnetic state selection-magnetic detection configuration operates without light-atom interactions, lasers, or laser-associated systems. In contrast, the latter two types incorporate light-atom interactions. Optical detection significantly improves cesium atomic state detection efficiency compared to magnetic detection, while optical pumping enhances cesium atomic state preparation efficiency relative to magnetic state selection. These dual improvements enable optically pumped compact cesium beam clocks to achieve superior frequency stability-a core performance metric. However, the integration of environmentally sensitive components like lasers and laser systems poses challenges for autonomous, long-term, continuous, and reliable operation in both light-enhanced configurations. Similar to other laser-dependent quantum precision measurement instruments, only well-designed, robust laser automatic frequency stabilization systems can ensure that optically pumped compact cesium beam clocks fully realize their performance advantages in practical applications. Methods The optically pumped compact cesium beam clock in our study employs an 852 nm laser (corresponding to the cesium D2 transition line) to generate pumping and detection beams. The laser system integrates miniaturized optical components, including isolators, acousto-optic modulators (AOMs), and polarization beam splitters (PBS) to achieve an effective optical power output of 3 -4 mW. A laser automatic frequency stabilization system is designed based on cesium atomic beam fluorescence spectroscopy and first-derivative frequency stabilization principles. This system features three core functions. The first is spectral identification and locking. After setting basic frequency stabilization parameters, the following steps are carried out. 1) Starting from an initial temperature of 50 degrees C , the laser temperature is reduced in large steps (--0.1 degrees C per 100 ms) until the detected fluorescence signal Vf exceeds the spectral threshold V-s (V-f> V-s), indicating proximity to the cesium D2 transition line. 2) The laser temperature is set at--0.5 degrees C above the current value, then gradually decreased in small steps (<= 0.01 degrees C per step). After each adjustment, a laser current scan is performed to verify fluorescence signal presence. If no signal is detected, the process reverts to step 1). 3) Upon spectral identification, the laser current performs scans for multiple times at this output frequency, with the system recording peak positions for several times. Temperature fine-tuning corrects drift in peak positions across scans. 4) Once the spectral peak stabilizes, proportional (P) and integral (I) feedback loops are sequentially activated to lock the laser frequency (Fig. 3). The second function is long-term maintenance. During prolonged operation, laser aging compromises conventional integral feedback, causing frequency drift or power fluctuations that degrade PI feedback performance. To this end, the system monitors integral current against a preset threshold I-m . If integral current exceeds I-m , the laser temperature is incremented by--0.0005 degrees C to reduce the current, while the temperature is decreased by--0.0005 degrees C if the integral current is below-I-m. Adjustments occur at a two-second interval to account for thermal relaxation (Fig. 4). The third is unlocking detection and recovery. The system ensures robustness in dynamic environments by the following processes. 1) Real-time fluorescence sampling and frequency servo control. When consecutive samples deviate beyond a preset threshold VT and the servo pauses, microwave frequency is reset to the center frequency, and an alert is triggered. 2) Fluorescence intensity determines laser lock status. 3) Upon unlocking, PI feedback is disabled, and a triangular current scan recenters the laser frequency. 4) Fluorescence exceeding the lock threshold reactivates PI feedback and microwave modulation. 5) Sampling resumes, and deviations below threshold VCrestore servo control and issue a lock signal. Results and Discussions The laser automatic frequency stabilization system is implemented in an optically pumped compact cesium beam clock for closed-loop operation and undergoes long-term comparative testing against UTC signals. In laboratory conditions, no laser unlocking occurs, with the frequency stabilization parameters effectively optimized. The output standard signal achieves frequency stability exceeding 1.5 x 10(-12)/ root r. After over 1500000 s of measurement, the frequency stability at 100000 s surpasses 5.0 x 10(-15), with a relative frequency deviation of 7.3 x 10(-14). The detailed results are shown in Table 1. The America-manufactured high-performance 5071A cesium beam clock remains a landmark product in compact cesium beam clocks and is still the most widely deployed worldwide. In recent years, few advanced technical specifications for compact cesium beam clocks have been reported internationally. In 2017, the European OSCC project achieved frequency stability of approximately 2.0 x 10(-12)/ root r for an optically pumped compact cesium beam clock. The same team reported short-term stability of 1.14 x 10(-12)/ root r in 2007 but failed to sustain long-term operation at this level. In 2001, the American compact cesium beam clock for GPSIII and France's Cs4 compact cesium beam clock in 2002 achieved 1.4 x 10(-12)/root rand 1.4 x 10-12/ r respectively, representing the best internationally reported long-term metrics. Domestic compact cesium beam clock technology has iteratively improved. Commercial products now match or exceed the short-term frequency stability of the 5071A but slightly lag in long-term stability. Recent research breakthroughs are listed as follows. A 2024 study employing modulation transfer spectroscopy for laser stabilization achieved 1.8 x 10(-12)/ root r. A 2023 study leveraging inverted transitions reported 3.0 x 10(-12)/root r. In summary, the performance metrics of this optically pumped compact cesium beam clock reach internationally advanced levels. As shown in Table 1, compared to the 5071A tube's frequency stability benchmarks, this system demonstrates a fivefold improvement. Conclusions We present a laser automatic frequency stabilization system for optically pumped compact cesium beam clocks. Based on cesium atomic beam fluorescence spectroscopy, the system employs a first-derivative frequency stabilization method to achieve automatic spectrum identification, laser locking, long-term stability maintenance, and features unlocking indication with locking recovery capability. This system significantly enhances the long-term reliability and operational stability of optically pumped compact cesium beam clocks, improving their environmental adaptability and enabling preliminary anomaly-handling capabilities. These advancements lay the foundation for developing optically pumped cesium beam clocks capable of fully adapting to dynamic and complex environments. Experimental findings indicate that the dynamic performance of such clocks is also influenced by system components like the cesium beam tube. Under the premise of maintaining effective laser frequency stabilization, establishing robust external vibration isolation, and implementing internal signal de-jittering with compensation methods are essential pathways to further optimize dynamic performance, thereby enabling reliable vehicular and naval applications of optically pumped compact cesium beam clocks.

Introducing two pyrrole rings at the armchair edges of perylene creates the small, electron‐rich molecular bowl 1 , which can be viewed as a nitrogen‐doped end‐cap of C 70 . Despite numerous attempts since 2008, its synthesis has been hindered by strain and synthetic challenges. In this study, we present the synthesis and property analysis of molecular bowl 1 and its dimer, the wavy‐shaped nanographene 2 . Substituents on nitrogen atoms significantly affect the bowl depth, intermolecular interactions, and supramolecular behaviors. Consequently, the butyl‐substituted molecular bowl 1 a forms unusual polar crystals with all bowls oriented similarly, suggesting potential pyroelectric or ferroelectric applications. Due to the electron‐rich nature, compounds 1 exhibit significantly strong binding affinity towards fullerene, with 1 a forming a sandwich structure with C 70 . Furthermore, neutral bowls 1 display counter‐rotating ring currents similar to corannulene, while their dications exhibit global anti‐aromaticity. The wavy‐structured nanographene 2 demonstrates two continuously reversible oxidation processes, and its dication 2 2+ shows remarkably high stability under ambient conditions. In summary, this work constructs a small, electron‐rich molecular bowl and its nanographene dimer, highlighting their exceptional properties, promising applications, and potential as foundations for future advanced nanostructure fabrication.

Introduction Inflammatory diseases, such as diabetes mellitus, rheumatoid arthritis, and inflammatory bowel disease, lead to systemic immune microenvironment disturbances, contributing to bone loss, yet the mechanisms by which specific receptors regulate this process in inflammatory bone loss remain poorly understood. As a G-protein-coupled receptor, the Apelin receptor plays a crucial role in the regulation of inflammation and immune microenvironment. However, the precise mechanisms governing its role in inflammatory bone loss remain incompletely understood. Objective This study aims to investigate how APJ regulates macrophage polarization to mitigate inflammatory bone loss. Methods Lipopolysaccharide induced systemic inflammatory bone loss model in mice was used to explore the relationship between bone loss and osteoclast activation, macrophage polarization and APJ. In vitro studies, Bone marrow derived macrophages and siRNA were used to elucidate the regulatory influence of APJ on the immune microenvironment and osteoclast differentiation, while high-throughput sequencing is leveraged to uncover the underlying mechanisms through which APJ modulates macrophage polarization. Results Our study established a link between APJ and macrophage M1 polarization in systemic inflammatory bone loss mice. The activation of APJ effectively mitigated M1 polarization in macrophages, suppressed excessive osteoclast activation, and alleviated systemic inflammatory bone loss. In vitro high-throughput sequencing analysis revealed that APJ modulates macrophage polarization, linking to mitochondrial autophagy and the NOD-like receptor signaling pathway and the involvement of the AMPK and MAPK signaling pathways in signal transduction after APJ activation was also suggested. Subsequent experiments substantiated that APJ predominantly enhances mitophagy and diminishes the accumulation of reactive oxygen species by regulating the AMPK/BNIP3/PINK1/PARKIN axis, thereby suppressing the activation of macrophage M1 polarization and osteoclastogenesis. Conclusion This study elucidated the underlying mechanism by which APJ modulates macrophage polarization, thereby proposing a new therapeutic target for addressing inflammatory bone loss.

Vaginal delivery and resulting pelvic floor muscle (PFM) dysfunction are significant risk factors for pelvic floor dysfunction (PFD). Despite this, the biological basis underlying PFD after childbirth remain unclear. This study was aimed at assessing the early response of the vaginal wall and PFM to simulated birth injury (SBI) in rats. Forty female Sprague–Dawley rats were divided into four groups: control (sham operation), and 1, 4, and 14 days post-injury. In the SBI groups, a catheter was inserted into the vagina with 130 g of weight attached to the end, and the balloon was inflated to 5 ml for 2 h. Evaluation of vaginal tissues and PFMs included histological, immunohistochemical, Western blot, and uniaxial biomechanical testing. In the vaginal wall, the SBI group showed significantly lower COL1A1 expression and higher MMP-2 and MMP-9 expression. At 4 and 14 days post-injury, there was a significant decrease in PFM fiber area and increased collagen content. The SBI group also exhibited significant increases in the expression of Nrf2, NQO1, HO-1, and SOD-2, indicating involvement of oxidative stress in both the vaginal wall and PFMs. Protein expression of Pax7 and MyoG, as well as the number of fibers with centralized nuclei, continued to increase significantly after SBI. Additionally, the vaginal wall of the SBI group showed a decreasing trend in tensile strength and elastic modulus, with a greater ultimate strain. Extracellular matrix remodeling, oxidative stress, decreased biomechanical properties, and muscle dysmyogenesis may collectively contribute to increased susceptibility to PFD development.

介绍了北京大学利用光抽运小铯钟相比于传统的磁选态小铯钟有更高的铯原子利用率的优势,在频率稳定度方面取得的突破性进展;总结出了光抽运小铯钟达到高性能的关键因素在于铯束管优值、激光稳频和电路地噪声;最终优化后的光抽运小铯钟频率稳定度均超过了5071A优质管2倍以上,典型值为3×10-12/τ1/2;近三年来陆续研制出8台光抽运小铯钟,初步实现了高性能光抽运小铯钟工程化.

Objective: Previous studies have shown a relationship between retinopathy and cognition including population with and without chronic kidney disease (CKD) but data regarding peritoneal dialysis (PD) are limited. This study aims to investigate the relationship between retinopathy and cognitive impairment in patients undergoing peritoneal dialysis (PD). Methods: In this observational study, we recruited a total of 107 participants undergoing PD, consisting of 48 men and 59 women, ages ranging from 21 to 78 years. The study followed a cross-sectional design. Retinal microvascular characteristics, such as geometric changes in retinal vascular including tortuosity, fractal dimension (FD), and calibers, were assessed. Retinopathy (such as retinal hemorrhage or microaneurysms) was evaluated using digitized photographs. The Modified Mini-Mental State Examination (3MS) was performed to assess global cognitive function. Results: The prevalence rates of retinal hemorrhage, microaneurysms, and retinopathy were 25%, 30%, and 43%, respectively. The mean arteriolar and venular calibers were 63.2 and 78.5 & mu;m, respectively, and the corresponding mean tortuosity was 37.7 & PLUSMN; 3.6 and 37.2 & PLUSMN; 3.0 mm-1. The mean FD was 1.49. After adjusting for age, sex, education, mean arterial pressure, and Charlson index, a negative association was revealed between retinopathy and 3MS scores (regression coefficient: -3.71, 95% confidence interval: -7.09 to -0.33, p = 0.03). Conclusions: Retinopathy, a condition common in patients undergoing PD, was associated with global cognitive impairment. These findings highlight retinopathy, can serve as a valuable primary screening tool for assessing the risk of cognitive decline.

Pelvic organ prolapse (POP) harms the quality of life of elderly patients. Transvaginal polypropylene mesh repair for POP was a frequently reported complication and was banned by the FDA in 2019. New therapeutic strategies are urgently required, and tissue engineering technology could be a novel therapy. Here, we developed a tissue engineering mesh out of three components: silk fibroin (SF) knitted mesh loaded with basic fibroblast growth factor (bFGF) and adipose-derived stem cells (ADSCs). We used coaxial electrospinning technology to achieve local bFGF release to promote regeneration. Additionally, ADSCs were loaded to demonstrate their paracrine ability of immune regulation and angiogenesis. Meanwhile, knitted silk fibroin mesh provided mechanical support. In vitro, SF/bFGF/ADSC tissue engineering mesh can stably release bFGF and has good biocompatibility, promoting cell proliferation and extracellular matrix synthesis. Six months after the SF/bFGF/ADSC tissue engineering mesh was implanted in a SD rat model, extracellular matrix reorganization, angiogenesis, and immunomodulatory effect, as well as mechanical properties of the implanting position were improved. Hence, SF/bFGF/ADSC tissue engineering mesh could be regarded as a promising option with excellent collagen synthesis, low foreign body response, and early angiogenic ability, providing potential ideas for POP treatment.

Objective:To further improve the quality of doctoral dissertations in clinical medicine and stomatology.Methods:Taking the 1 122 experts' comments on the 2016-2018 clinical/stomatological doctoral dissertations of a university, the paper made a statistical analysis from such aspects as the source of topic selection, the type of topic selection, the literature review, paper innovation, writing standards, etc. SPSS 20.0 was used for statistical analysis.Results:The results showed that 61.0% (614/1006) dissertations were selected from applied research and 30% (302/1006) from non project research; 83.9% (941/1122) dissertations were evaluated as good and excellent, and the first three items with poor evaluation were: innovation (3.3%, 37/1122), content (2.2%, 25/1122) and writing standard (0.9%, 10/1122).Conclusion:It is suggested that the school and tutors should make clear the training orientation of clinical/stomatological doctoral graduate students, strengthen the training of their scientific research ability and thesis writing ability, and pay attention to clinical practice training without reducing their academic requirements.

目的 监测我国主要城市三级甲等医院住院患者分离的革兰氏阴性菌的细菌耐药状况,掌握耐药流行趋势,为抗生素合理使用提供科学数据.方法 定点收集来自全国19家医院临床分离细菌,由中心实验室统一用平皿/肉汤二倍稀释法测定抗菌药物最低抑菌浓度(MIC)值.结果 对2019年7月至2020年6月来自全国19座城市19家医院的4795株临床分离致病菌进行了MIC测定.结果 显示,大肠埃希菌和肺炎克雷伯菌中超广谱β内酰胺酶(ESBLs)表型检出率分别为52.8％和23.6％,均持续下降,碳青霉烯类耐药肺炎克雷伯菌比例与前次监测持平.对肠杆菌目细菌抗菌作用较好的药物包括碳青霉烯类、阿米卡星、拉氧头孢、β内酰胺类合剂、磷霉素氨丁三醇和西他沙星等.非发酵革兰阴性菌中铜绿假单胞菌和鲍曼不动杆菌对亚安培南的耐药率分别为27.1％和70.7％,多重耐药菌(MDR)检出率分别为39.7％和74.9％,泛耐药菌(XDR)检出率分别为11.8％和69.0％.不同病房、不同年龄以及不同标本来源菌株耐药率比较提示,重症监护病房分离肺炎克雷伯菌、鲍曼不动杆菌和铜绿假单胞菌中MDR占比更高,儿童患者分离肺炎克雷伯菌中ESBLs检出率高于成人和老年人,我国儿童中细菌耐药问题不容忽视.结论 ESBLs检出率有所下降;碳青霉烯类耐药肺炎克雷伯菌、铜绿假单胞菌、鲍曼不动杆菌比例稳定;鲍曼不动杆菌对米诺环素耐药率有所升高,值得注意.

Herein, we report the scheme of an optically pumped atomic clock based on a cold cesium atomic beam source. We propose the laser system and physical mechanism of this atomic clock, wherein the atomic beam travels in an upper parabolic trajectory, thereby eliminating the light shift effect. In the experiments, when the length of the free evolution region was 167 mm, the line width of the Ramsey fringe was 37 Hz. When the expected signal-to-noise ratio of the Ramsey fringe that can be achieved is 36,000, the expected short-term frequency stability is about 3.6 × 10 –14 /√τ, which is significantly higher than that of a conventional optically pumped cesium clock of similar volume.

对于小型化光抽运铯束原子钟来说,最重要的指标之一是它的频率稳定度,尤其是长期频率稳定度.小型化光抽运铯束原子钟当中的各项频移机制会导致其运行过程中频率的移动,它们是恶化原子钟长期频率稳定度的源头.本文从理论上分析了小型化光抽运铯束原子钟当中的Rabi牵引,对其频移贡献的大小和对各项参数的敏感度进行计算,并提出了调整合适的C场大小,控制合适的系统参数可以减小该频移对小型化光抽运铯束原子钟频率稳定度的影响.结果表明,Rabi牵引在小型化光抽运铯束原子钟的研究当中非常重要,文中提到的方法对原子钟的频率稳定度有改善作用.

A beam source is proposed for the production of an intense cold cesium atomic beam that can be used in cesium beam atomic clocks. The source is based on a two-dimensional magneto-optical trap (2D-MOT), but introduces hollow cooling and pushing lights in the axial direction to create a 2D+-MOT, which separates the cooling and pushing functions while the low-power pushing light pushes atoms out to form a cold atomic beam. This cold cesium atomic beam source reduces the light shift due to leakage light and retains longitudinal cooling to increase the flux of the cold atomic beam compared with that of the conventional 2D+-MOT scheme. The specifics of the design are investigated, the atomic velocity and beam flux are calculated, and the results are experimentally verified. The results demonstrate that when the power of the pushing light is 180 µW and when its frequency resonates with the 4 → 5′ transition of the Cs D2 line, the most probable longitudinal velocity of the outgoing cold atomic beam, the width of velocity distribution, and the atomic beam flux are 19.38 m/s, 8.1 m/s, and 1.7 × 1010 atoms/s, respectively.

目的 探讨腹膜透析合并糖尿病患者眼底血管参数(血管直径、曲率、分形维数)和认知功能评估的临床应用研究.方法 将26行腹膜透析合并糖尿病患者按认知功能测定结果分为认知功能正常组和认知功能受损组.对比2组人口统计学资料、相关指标、视网膜血管参数的差异.结果 认知功能正常组患者12例,认知功能受损组患者14例.与认知功能正常组比较,认知功能受损组合并症较多,残余肾功能较低,差异有统计学意义(P＜0.05).认知功能受损组动脉平均管径、静脉平均管径、动静脉比率和静脉平均曲率数值略低于认知功能正常组;动脉平均曲率及血管分形维数数值略高于认知功能正常组,但差异无统计学意义(P＞0.05).认知功能受损组微血管瘤发生率高于认知功能正常组,差异有统计学意义(P＜0.05).结论 微血管瘤可能是腹膜透析合并糖尿病患者认知功能异常的眼底标志.

SummaryThe short-term frequency stability of compact optically pumped cesium beam atomic clock is directly affected by signal-to-noise ratio of its Ramsey spectrum. In this paper, the noise sources of compact optically pumped cesium beam atomic clock are analyzed. On the basis of the parameters in our optically pumped cesium beam atomic clock, the noise contributions of different sources within 1Hz bandwidth are studied, and the corresponding signal-to-noise ratios are calculated. According to the evaluation results, one of the main noise sources of the compact optically pumped cesium beam atomic clock is the frequency noise of the detection laser.

The research of optically pumped cesium beam atomic clock (OPCB) at Peking University has lasted for decades. At present, the short-term frequency stability is 3×10−12/τ and the long-term (5-day) frequency stability can reach 7 × 10 −15 . The optimization methods of the short-term frequency stability are using laser induced beam spectrum to stabilize the laser frequency, using cyclic transition to detect the atomic state and using a cesium oven with a collimator to generate the cesium atomic beam. The methods of obtaining the good long-term frequency stability are controlling the microwave power based on the atomic transition probability, controlling the C-field intensity based on Zeeman frequency and controlling the laser power using fluorescence. The compact optically pumped cesium beam atomic clock of Peking University is expected to contribute to the field of timing, positioning, navigation and high speed digital communication.

北京大学光抽运铯束原子钟小组致力于发展连续式光抽运铯束原子钟的关键技术,为长时间守时、导航定位等军事和科研领域的应用提供关键设备.本文总结了国内外守时型小铯钟的研究现状,分析和比较了不同小组的磁选态、光抽运等小铯钟的方案、特点和结果.其中,北京大学光抽运铯束原子钟小组所研制的小铯钟通过长达90 d的长期测试,在保持了 3×10-12/τ1/2短期稳定度的情况下,进一步得到了 7×10-15的5 d稳定度,准确度优于3×10-13.另外,本文还介绍基于二维磁光阱的冷原子铯束光抽运原子钟的研究结果,我们得到了线宽为40 Hz的Ramsey信号,这为下一步获得连续冷原子束原子钟奠定了基础.

Because of the excellent long-term stability of cesium beam atomic clocks, they are widely used in the field of punctuality. The research of cesium beam atomic clocks is to optimize and improve their stability gradually. In order to improve the stability of our optically pumped cesium beam atomic clock, we have optimized the circuit system in the atomic clock, including the microwave source and other circuits. Compared to the result in 2020 year, the final stability has been improved by nearly 30%. It shows that circuit noise is an important source which affects the signal-to-noise ratio in compact optically pumped cesium beam clocks. It is necessary to consider and reduce the influence of circuit noise in the design and manufacture of atomic clocks.