摘要 : The importance of habitat spatial variability as a key driver of soil biota patterning (e.g., soil nematodes) has lately gained a lot of attention. It is generally accepted that rhizosphere soil has a distinct faunal assemblage than bulk soil, but less is known about the patterning of soil nematodes and the causes of these changes in maize-alfalfa agroecosystems. As a result, the purpose of this study was to assess the dynamic changes in soil nematodes across bulk and rhizosphere soils when maize and alfalfa were grown separately and in a combination at varying levels of nitrogen fertilizer. The results of a field experiment in a 2 × 3 factorial completely randomized block design revealed that total nematode and omnivore-predator abundance, as well as nematode generic diversity and richness, maturity, and structure indices, were significantly increased in the rhizosphere of monoculture alfalfa and alfalfa grown in a mixture with maize when compared to the bulk soil. Furthermore, we discovered elevated levels of total sugars and organic acids in rhizosphere soils. Plant- and fungal-feeding nematodes increased in both bulk and rhizosphere soils, whereas omnivores and predators decreased in soils treated with monoculture and nitrogen fertilizer. Furthermore, we discovered a significant positive relationship between total nematode and omnivore-predator abundance and soil organic carbon and total nitrogen, soil moisture content, and microbial biomass C and N, implying that changes in these soil properties and rhizodeposition may shape the nematode community assemblage between the bulk and rhizosphere soils. Our findings suggest that crop mixes containing alfalfa would improve soil characteristics and rhizodeposition, resulting in increased nematode number and variety and contributing to sustainable agriculture. © 2023 The Author(s)

摘要 : Remote sensing satellites play a crucial role in both national defense and civil exploration. However, the imaging quality of high-resolution remote sensing satellites is significantly affected by atmospheric turbulence. We focus on the impact of camera aperture, satellite orbit altitude and atmospheric turbulence intensity on the imaging quality of space cameras during remote sensing satellite earth detection. Firstly, the turbulence wavefront simulation method based on the spherical wave model and Kolmogorov turbulence theory is analyzed. Subsequently, the disturbed wavefront, impacted by the camera aperture, satellite orbit height and atmospheric turbulence intensity, is analyzed, and a universal formula is derived. In addition, an equation for imaging resolution with camera aperture, satellite orbit height and atmospheric coherence length is developed. Finally, the effect of atmospheric turbulence on the Modulation Transfer Function (MTF) is studied. The variation of the relative error of MTF with camera aperture, satellite orbit height and atmospheric coherence length is simulated and analyzed, with reference to an MTF value of 0.15. This study provides a theoretical basis for designing, analyzing, and assessing high-resolution remote sensing satellites.

摘要 : To provide high-quality, intelligent, and healthy lighting sources, a linear dimming mixed lighting system is constructed using three-primary-color LED light sources. An optimization method for dimming and color mixing is proposed. The light chromaticity and light intensity of the mixed light source are set by color temperature and brightness level, which makes the mixed lighting effect more in line with the demand of "human-centric lighting". In the intelligent optimization of the system, the color temperature is converted into CIE $ {u}'{v}' $ chromaticity coordinates, and the brightness is converted into luminance to make the optimization calculations more accurate. The system adopts the linear dimming method, effectively avoiding the health and safety hazards caused by light source flicker, and effectively solves the problem of large linear dimming chromaticity drift with an optimization algorithm. Experiment results demonstate that the chromatic stability of the mixed light in the mixed lighting system is maintained within the first step of the CIE ${u}'{v}' $ chromaticity diagram in the color temperature range of 2000 K−8000 K. Moreover, the system exhibits imperceptible color deviation over the entire range of light intensity adjustments at the corresponding color temperature. This finding also indicates that linear dimming is better than the pulse-width dimming method in keeping the optical chromaticity stable. Theoretical exploration and experimental results demonstrate that the mixed lighting system is simple and feasible, with significant practical value.

摘要 : Unsafe explorations in the training phase hinder the practical deployment of reinforcement learning (RL) on autonomous robots. Some safe RL methods use safety constraints from prior or external knowledge to reduce or avoid unsafe explorations, but such knowledge is usually unavailable in practice, especially in unknown environments. In this work, we propose a few-shot reasoning-based safe reinforcement learning framework that includes a new few-shot learning method with dynamic support set to reason the safety of unexplored actions and hence guide safer action selection. Additionally, it endows robots with the capability of reverting to previous safe states and reflecting on failures to update the dynamic support set and further improve the accuracy of safety reasoning. Experimental results show that our new few-shot learning method is more accurate, and our proposed framework can significantly reduce the number of failures in the learning phase, especially for long-term autonomy.

摘要 : With the advantages of high flexibility, high safety, and good adhesion and wrapping, soft robots have a wide range of application prospects in complex environments such as automatic production lines and medical surgery. By coupling an active pneumatic drive structure and an interference variable stiffness mechanism, this paper designs a soft robot based on a variable stiffness pneumatic actuator. Based on kinematic analysis and finite element simulation based on the segmented constant curvature method, the Lagrange equations are applied to perform dynamic analysis, which in turn verifies the variable stiffness performance and bending performance of the variable-stiffness soft robotic arm. The soft manipulator adopts the structural design based on 2 mm thickness, jamming mechanism and coupling fiber layer, which can effectively resist 0–2.5 N force without large deviation and be adjustable in the stiffness range of (0.025–0.12) N/mm, under the condition that the vacuum degree does not exceed 80 kPa. The stiff stiffness and bending behavior of the proposed soft manipulator show excellent performance and can be applied to industrial automation, medical devices and other operations. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2024.

摘要 : This paper proposes and demonstrates a tunable filter using full conical mounting. The designed 1D resonant waveguide grating presents a tunable single reflection peak. The peak reflectance can theoretically reach 100%. The resonant wavelength can be tuned from 642.5 nm to 484.6 nm by changing the incident angle. The resonance between the 1st-order diffracted wave and fundamental transverse electric (TE) guided mode generates the reflection peak. This feature was achieved by optimizing the grating thickness to support the TE guided mode and suppress the transverse magnetic (TM) guided mode. The same concept can be applied to tunable filters with high dynamic range by increasing the thickness and period of grating in equal proportion. © 2024 Editorial Office of Chinese Optics. All rights reserved.

摘要 : Phase is an important parameter of light waves, but it cannot be directly observed. Based on the characteristics of Hartmann detectors that can detect wavefront rapidly, this paper studies the method of optical phase three-dimensional display and design an experimental system. Firstly, the parameters of optical system such as light sources and collimating lenses are optimized using Zemax software. Secondly, based on the modal method of wavefront reconstruction and Zernike polynomial defocusing and astigmatism coefficient, the method of the phase three-dimensional display is studied and the measuring instrument is developed. Three different lenses are measured with this instrument and realize the three-dimensional display, and the corresponding diopter measurement method is given. Finally, the experiment verifies the validity of three-dimensional display of light wave phase and diopter measurement, -2.00 D for a -2.07 D myopia lens, 0.91 D for a 1.00 D hyperopia lens, and 0.56 D for a 0.50 D astigmatism lens. The experimental results indicate that this system can approximately measure the diopter of the refractive correction lens and achieve three-dimensional display of the phase. The phase three-dimensional display instrument designed based on Hartmann detectors in this paper has better environmental adaptability and is convenient for researchers to visually observe the phase distribution of light.

摘要 : To solve the challenges associated with the inadequate separation of source image features, low interpretability, and difficulty of designing accurate fusion rules, this paper proposes an infrared (IR) and visible image fusion method based on mutual information feature separation and representation, which effectively separates features while preserving the typical information of the source image. First, a mutual information constrained coding network is used to extract the features, maximize the mutual information between the source image and features to retain the feature representation of the source image, and minimize the mutual information of private and public features to achieve separation and representation. In addition, the loss function adopts a soft weighted intensity loss to balance the distribution of IR and visible features. Objective and subjective evaluation results of comparison experiments indicate that the proposed method can effectively fuse important information regarding IR and visible images and has good visual perception.

摘要 : Single-atom Pd clusters anchored on t-BaTiO3 material was synthesized using hydrothermal and ultrasonic methods for the effective piezoelectric catalytic degradation of pollutants using vibration energy. XRD patterns of BaTiO3 loaded with monoatomic Pd were obtained before and after calcining, and showed typical cubic-phase BTO. TEM and HAADF-STEM images indicated single-atom Pd clusters were successfully introduced into the BaTiO3. The piezoelectric current density of the prepared Pd-BaTiO3 binary composite was significantly higher than that of the pristine BaTiO3. Under mechanical vibration, the nanomaterial exhibited a tetracycline decomposition rate of ~95 % within 7 h, which is much higher than the degradation rate of 56.7 % observed with pure BaTiO3. Many of the piezo-induced electrons escaped to the Pd-doped BaTiO3 interface because of Pd's excellent conductivity. Single-atom Pd clusters help promote the separation of the piezo-induced electrons, thereby achieving synergistic catalysis. This work demonstrates the feasibility of combining ultrasonic technology with the piezoelectric effect and provides a promising strategy for the development of ultrasonic and piezoelectric materials.

摘要 : MethodsWe take Rogers RT5880 copper-clad substrate with a thickness of 1.57 mm as the substrate of the microstrip cavity and CRLH-TLs. The thickness of the copper layer is 0.035 mm. A Fabry-Perot (FP) cavity is formed inside a microstrip line. Two SRRs are placed in the cavity and located at the antinode and node of the electromagnetic field in the FP cavity respectively to construct a unidirectional EIT-like structure. The excitation port of the EIT-like effect is determined by the sequence of the antinode and node in the FP cavity. Tunable composite right/left-handed transmission lines (CRLH-TLs) loaded with varactors are added at the two ends of the FP cavity (marked as left and right CRLH-TLs respectively) to change the electromagnetic field distribution in the cavity. By optimizing all parameters, the electrical lengths of CRLH-TLs are quarter wavelength and half wavelength respectively under different bias voltages. Therefore, since the distribution of the nodes and antinodes in the cavity can be switched by changing the electric length of the CRLH-TLs, the sequence of the antinode and node where the two split ring resonators (SRRs) lie in the cavity is also switched, which leads to a switched EIT-like excitation port. Finally, a sample is fabricated and tested to validate the unidirectional EIT-like effect with the electrically switchable excitation port.Results and DiscussionsThis structure realizes the unidirectional EIT-like effect to bring a unidirectional reflection with high contrast ratio. It is validated both in simulation and experiments that the contrast ratio of the unidirectional reflection can reach more than 95%, and the excitation port of the unidirectional EIT-like effect is determined by the sequence of nodes and antinodes in the FP cavity. The capacitance of the varactors in the CRLH-TLs varies along with the bias voltage. Thus, different bias voltages are simulated by setting different capacitance values. In case I, the capacitance of varactors in the left CRLH-TLs is set as 2.5 pF (Csl=2.5 pF) and that in the right is set as 1.5 pF (Csr=1.5 pF). The magnitude of the reflection coefficient of port 1 S11 and port 2 S22 at 3.97 GHz are 0.007 and 0.538 respectively, showing that the EIT-like effect is only excited through port 1. Case II has swapped the capacitance of the varactors in the right and left CRLH-TLs units. Thus the reflection spectra S11 and S22 will also be exchanged due to the geometric symmetry of the switchable EIT-like effect. At last, the excitation port of the EIT-like effect has been switched to port 2, indicating that switching the bias voltage can achieve a unidirectional EIT-like effect with an electrically switchable excitation port (Fig. 2). When the capacitance of the varactors is set as 1.5 pF and 2.5 pF, the transmission amplitudes of the CRLH-TLs are both larger than 0.7 and ∠S21 are close to -90° and -180° at 3.97 GHz respectively (Fig. 3). Since the transmission phase difference between the CRLH-TLs units with the capacitance of 2.5 pF and 1.5 pF is -90°, once the capacitance of the varactors in the left and right CRLH-TLs is exchanged, the sequence of the nodes and antinodes in the FP cavity is reversed. As a result, the port to excite the unidirectional EIT-like effect is switched (Fig. 4). For the fabricated sample, when the bias voltage on the left and right sides of the CRLH-TLs are V1=0 V and V2=6 V respectively, only when the wave is incident from port 1, the EIT-like effect can be excited. Through exchanging the bias voltages, the unidirectional EIT-like excitation port is switched. This shows that the structure can achieve a unidirectional EIT-like effect with an electrically switchable excitation port.ObjectiveUnidirectional electromagnetically induced transparency-like effect is a special kind of EIT-like effect, which is caused by its asymmetric structure. The EIT-like effect can be excited by the asymmetric structure only when a wave is incident from a certain port. The unidirectional EIT-like effect plays a significant role in realizing directional reflection and transmission and is crucial in unidirectional invisibility. With the development of tunable metamaterials, various kinds of reconfigurable metamaterials are also proposed to realize a tunable EIT-like effect. However, the dynamically switchable unidirectional EIT-like effect has been barely reported. The excitation port of the unidirectional EIT-like effect is usually fixed and determined by the structure topology. To realize a reflection-type unidirectional EIT-like effect, an electrically switchable excitation port based on tunable CRLH-TLs and a two-port microstrip cavity embedded with two SRRs is proposed. The reflection-type EIT-like effect can only be excited when an electromagnetic wave is incident from a certain port. The contrast ratio of the asymmetric reflection coefficient of the two ports in our paper reaches 98.7%. On this basis, the coupling between the microstrip cavity and the SRRs is dynamically modulated by the tunable CRLH-TLs, thereby changing the excitation port of the unidirectional EIT-like effect. Finally, a unidirectional EIT-like effect with an electrically switchable excitation port is achieved, and the applications of the EIT-like effect in optical storage, optical modulation, sensing, and other fields are promoted.ConclusionsWe propose a reflection-type unidirectional EIT-like effect with an electrically switchable excitation port, and validate it in simulation and experiments. To switch the excitation port of the unidirectional EIT-like effect, our paper reverses the sequence of nodes and antinodes in the FP cavity by changing the bias voltages of CRLH-TLs on both sides of the cavity. This unidirectional EIT-like effect with an electrically switchable excitation port provides a feasible scheme for tunable asymmetric EIT-like effects and is expected to be applied in directional reflection and multifunctional unidirectional stealth devices.