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Nonlinear effects in optical fiber frequency transfer have a significant impact on the precision of frequency transfer. We investigate the main nonlinear effects, including the Brillouin scattering and the Raman scattering, in optical fiber frequency transfer through theoretical and simulation calculations in detail. The calculation results show that the threshold powers of the Brillouin scattering and the Raman scattering decrease with the increase in the fiber length; however, the fiber length has little to no impact on the threshold powers when the fiber length is greater than 10 km. The threshold powers, including the Brillouin scattering and the Raman scattering, increase as the attenuation coefficient increases. Conversely, when it comes to the gain coefficients, the outcomes exhibit a reverse trend. When the linewidth Δvlaser of the laser source is from 1 Hz to 1 MHz, the linewidth Δvlaser does not affect the threshold powers of the Brillouin scattering. This study seeks to offer design guidance aimed at mitigating nonlinear effects in optical fiber frequency transfer. The calculated results hold considerable potential in guiding various applications reliant on Brillouin and Raman scattering properties, such as laser technology and optical fiber sensing.

The Arithmetic Optimization Algorithm (AOA) is a meta-heuristic algorithm inspired by mathematical operators, which may stagnate in the face of complex optimization issues. Therefore, the convergence and accuracy are reduced. In this paper, an AOA variant called ASFAOA is proposed by integrating a double-opposite learning mechanism, an adaptive spiral search strategy, an offset distribution estimation strategy, and a modified cosine acceleration function formula into the original AOA, aiming to improve the local exploitation and global exploration capability of the original AOA. In the proposed ASFAOA, a dual-opposite learning strategy is utilized to enhance population diversity by searching the problem space a lot better. The spiral search strategy of the tuna swarm optimization is introduced into the addition and subtraction strategy of AOA to enhance the AOA’s ability to jump out of the local optimum. An offset distribution estimation strategy is employed to effectively utilize the dominant population information for guiding the correct individual evolution. In addition, an adaptive cosine acceleration function is proposed to perform a better balance between the exploitation and exploration capabilities of the AOA. To demonstrate the superiority of the proposed ASFAOA, two experiments are conducted using existing state-of-the-art algorithms. First, The CEC 2017 benchmark function was applied with the aim of evaluating the performance of ASFAOA on the test function through mean analysis, convergence analysis, stability analysis, Wilcoxon signed rank test, and Friedman’s test. The proposed ASFAOA is then utilized to solve the wireless sensor coverage problem and its performance is illustrated by two sets of coverage problems with different dimensions. The results and discussion show that ASFAOA outperforms the original AOA and other comparison algorithms. Therefore, ASFAOA is considered as a useful technique for practical optimization problems.

Since the beginning of the 21st century, the net primary productivity (NPP) of grassland in the Three-Rivers Headwaters (TRH) region has changed significantly. In this study, NPP was assessed by the Carnegie-Ames-Stanford approach (CASA) model in TRH from 2000 to 2019. The abrupt changes of NPP and meteorological factors were analyzed by cumulative departure, MK test, and Pettitt test. The contributions of meteorological and human factors to changes in grassland NPP were quantitatively assessed using the scenario simulation method. The obtained results showed that: (1) From 2000 to 2019, the NPP of grasslands increased from 135.72 to 141.16 gC/m−2a−1. However, the overall growth trend was not significant, and the proportion of significant growth was only 31.45%; (2) An abrupt increase in meteorological factors occurred around 2005, while an abrupt increase in NPP occurred around 2008, which showed that 2008 was the year when human factors, such as ecological projects and policies, began to show a significant impact on the growth of NPP; and (3) The contribution of human factors to the abrupt increase in NPP was significantly greater than the contribution of meteorological factors. The contribution of human factors exceeded 70% in 93.68% of the studied area, reaching 98% in general, while the contribution of meteorological factors was less than 2%. Among them, the human contributions to the Yangtze River Source, the Yellow River Source, and the Lancang River Source all exceeded 95%. The negative effects of meteorological factors on the growth of NPP in the abovementioned three regions were as high as 47.35%, 48.66%, and 36.91%, respectively. Human factors have contributed greatly to the increase in NPP in most of the source areas of the Yellow River, the eastern part of Tanggulashan County, the southeastern part of Zhiduo County, and the western part of Zaduo County at the source of the Yangtze River.

Brownian thermal noise (TN) of ultra-stable cavities (USCs) imposes a fundamental limitation on the frequency stability of ultra-narrow linewidth lasers. This work investigates the TN in cylindrical USCs with the four support pads in detail through theoretical estimation and simulation. To evaluate the performance of state-of-the-art ultra-narrow linewidth lasers, we derive an expression of the TN for a cylindrical spacer according to the fluctuation–dissipation theorem, which takes into account the front face area of the spacer. This estimation is more suitable for the TN of the cylindrical USC than the previous one. Meanwhile, we perform detailed studies of the influence of the four support pads on the TN in cylindrical USCs for the first time by numerical simulations. For a 400 mm long cylindrical USC with an ultra-low expansion spacer and fused silica substrates, the displacement noise contributed from the four support pads is roughly four times that of the substrates and the GaAs/AlGaAs crystalline coating. The results show that the four support pads are the primary TN contributors under some materials and geometries of USCs.

Ultra-stable optical cavities (USOCs) as fragile precision instruments have many important applications in space. In order to protect them from being damaged during a rocket launch, we analyzed a USOC by means of finite element methodology. The shock acceleration limits that the USOC can withstand in different directions and under various conditions are given. To increase the shock acceleration limit, the midplane thickness and the fixed hole diameter should be selected to be as high as possible. It is worth noting that the launch direction of the USOC should be selected as the horizontal direction, for which the shock acceleration limit that the USOC can withstand is approximately two times that of the vertical direction. In this paper, results provide guidance for the design of USOCs for space applications, especially the design to prevent the damage caused by a shock. The method could then be applied to other space optical cavities, providing a tool to improve the effect of shock at high accelerations.

Thermal noise in optical cavities sets a fundamental limit to the frequency instability of ultra-stable lasers. Numata et al. derived three equations based on strain energy and the fluctuation–dissipation theorem to estimate the thermal noise contributions of the spacer, substrates, and coating. These equations work well for cylindrical cavities. Extending from that, an expression for the thermal noise for a cubic spacer based on the fluctuation–dissipation theorem is derived, and the thermal noise in cubic optical cavities is investigated in detail by theoretical analysis and finite element simulation. The result shows that the thermal noise of the analytic estimate fits well with that of finite element analysis. Meanwhile, the influence of the compressive force Fp on the thermal noise in cubic optical cavities is analyzed for the first time. For a 50 mm long ultra-low expansion cubic cavity with fused silica substrates and GaAs/AlGaAs crystalline coating, the displacement noise contributed from every Fp of 100 N is about three times more than that of the substrate and coating.

A polarization-insensitive recirculating delayed self-heterodyne method (PI-RDSHM) is proposed and demonstrated for the precise measurement of sub-kilohertz laser linewidths. By a unique combination of Faraday rotator mirrors (FRMs) in an interferometer, the polarization-induced fading is effectively reduced without any active polarization control. This passive polarization-insensitive operation is theoretically analyzed and experimentally verified. Benefited from the recirculating mechanism, a series of stable beat spectra with different delay times can be measured simultaneously without changing the length of delay fiber. Based on Voigt profile fitting of high-order beat spectra, the average Lorentzian linewidth of the laser is obtained. The PI-RDSHM has advantages of polarization insensitivity, high resolution, and less statistical error, providing an effective tool for accurate measurement of sub-kilohertz laser linewidth.

The National Time Service Center of China is developing a compact, highly stable, 698 nm external-cavity diode laser (ECDL) for dedicated use in a space strontium optical clock. This article presents the optical design, structural design, and preliminary performance of this ECDL. The ECDL uses a narrow-bandwidth interference filter for spectral selection and a cat’s-eye reflector for light feedback. To ensure long-term stable laser operation suitable for space applications, the connections among all the components are rigid and the design avoids any spring-loaded adjustment. The frequency of the first lateral rocking eigenmode is 2316 Hz. The ECDL operates near 698.45 nm, and it has a current-controlled tuning range over 40 GHz and a PZT-controlled tuning range of 3 GHz. The linewidth measured by the heterodyne beating between the ECDL and an ultra-stable laser with 1 Hz linewidth is about 180 kHz. At present, the ECDL has been applied to the principle prototype of the space ultra-stable laser system.

In this research, monthly hydrological and daily meteorological data were collected across China for the period 1956–2012. Modified Mann–Kendall tests, double mass curve analysis, and correlation statistics were performed to identify the long-term trends and interrelation of the hydrometeorological variables and to examine the influencing factors of streamflow and sediment. The results are as follows: (1) In the last 60 years, the streamflow in northern China has shown different decreasing trends. For the southern rivers, the streamflow presented severe fluctuations, but the declining trend was insignificant. For the streamflow in western China, an increasing trend was shown. (2) In the northern rivers, the streamflow was jointly controlled by the East Asian monsoon and westerlies. In the southern rivers, the runoff was mainly influenced by the Tibet–Qinghai monsoon, the South Asian monsoon, and westerlies. (3) Sediment loads in the LCRB (Lancang River Basin) and YZRB (Yarlung Zangbo River Basin) did not present significant change trends, although other rivers showed different degrees of gradual reduction, particularly in the 2000s. (4) Underlying surface and precipitation changes jointly influenced the streamflow in eastern rivers. The water consumption for industrial and residential purposes, soil and water conservation engineering, hydraulic engineering, and underlying surface changes induced by other factors were the main causes of streamflow and sediment reduction.

Recombinant human fibroblast growth factor 10 (rhFGF-10) is frequently used to treat patients with skin injuries. It can also promote hair growth. However, the effective application of rhFGF-10 is limited because of its poor stability and transdermal absorption. In this study, polymerase chain reaction (PCR) and Southern blotting were used to identify transgenic safflowers carrying a gene encoding an oleosin-rhFGF-10 fusion protein. The size and structural integrity of oleosin-rhFGF-10 in oil bodies extracted from transgenic safflower seeds was characterized by polyacrylamide gel electrophoresis and western blotting. Oil body extracts containing oleosin-rhFGF-10 were topically applied to mouse skin. The absorption of oleosin-rhFGF-10 was studied by immunohistochemistry. Its efficiency in promoting wound healing and hair regeneration were evaluated in full thickness wounds and hair growth assays. We identified a safflower line that carried the transgene and expressed a 45 kDa oleosin-rhFGF-10 protein. Oil body-bound oleosin-rhFGF-10 was absorbed by the skin with higher efficiency and speed compared with prokaryotically-expressed rhFGF-10. Oleosin-rhFGF-10 also enhanced wound closure and promoted hair growth better than rhFGF-10. The application of oleosin-rhFGF-10 in oil bodies promoted its delivery through the skin, providing a basis for improved therapeutic effects in enhancing wound healing and hair growth.