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In the autonomous navigation of drones, improving positioning accuracy is of significant importance to obtain highly accurate information on flight velocity. Traditional microwave and acoustic velocity measurement methods have the disadvantages of poor precision and susceptibility to interference. In this study, an unmanned aerial vehicle (UAV)-mounted two-dimensional laser Doppler velocimeter was developed and investigated, and a relevant drone flight navigation and positioning experiment was carried out. The UAV-mounted two-dimensional laser Doppler velocimeter (LDV) prototype developed in this study applies a scheme of dual-beam measurement light, sharing a focusing lens group. After process integration, the performance of the prototype was measured. It shows that a velocity measurement effect with a high signal-to-noise ratio can be achieved by using two measurement probe beams within a working distance range of 40 m–60 m. In the flight experiment, the flight trajectory calculated using the LDV-measured velocity data was compared with the global navigation satellite system (GNSS)-recorded trajectory. The result shows that LDV can achieve an odometer accuracy of 4.8‰. This study has validated the feasibility of the laser Doppler velocimeter in drone navigation and positioning, providing a novel method for reliable and high-precision velocity measurement in autonomous drone navigation.

In contrast to those deployed on land vehicles, the single-beam Laser Doppler velocimeter (LDV) used for velocity acquisition on airborne vehicles requires a focusing transmitter. The effects of spherical aberration in focusing transmitters on the distant velocity measurement of single-beam Laser Doppler velocimeters are demonstrated in this work. The calculations of the numerical simulations based on the generated theories and the subsequent experiments are in agreement with the theoretical analyses. The impact of spherical aberration on the signal-to-noise ratio (SNR) of single-beam Laser Doppler velocimeters is explained. Also illustrated is the generalized analysis for single-beam Laser Doppler velocimeters equipped with complex optics. An efficient approach for evaluating and advancing the SNR performance of single-beam Laser Doppler velocimeters used for distant velocity measurement is demonstrated. Works in this paper pave way for the design of airborne LDV.

Spin-based comagnetometers have essential applications in studying new physical effects such as the fifth force, Lorentz violations, and spin-gravity interactions. In this paper, a transfer function model of the spin precession phase (frequency) is derived to analyze the comagnetometer's noise mechanism. The theory combined with experiments reveals that the output frequency noise of the spin oscillator above 5 Hz is mainly phase noise from the phase-locked loop. The noise below 5 Hz is mainly from the biased magnetic field noise. When building a comagnetometer using two spin oscillators, the symmetry of the spin oscillator is significant. When the intrinsic physical parameters cannot be symmetrical, the comagnetometer's common-mode suppression capability to magnetic field fluctuations can be enhanced by optimizing the control parameters. In addition, the closed-loop control of Bz can significantly weaken the effect of system asymmetry in the low-frequency band. Finally, when considering the comagnetometer system in nuclear magnetic resonance gyroscopes, a trade-off between the bandwidth and sensitivity can be achieved using theory. This paper is an excellent reference for both the research and application of comagnetometers.

Previous Chinese research revealed that diarsenic trioxide (As2O3) inhibits acute promyelocytic leukemia (PML) cell proliferation and initiates apoptosis through degradation of the PML-retinoic acid receptor protein. This study was to analyse whether As2O3 also had an effect on hepatocellular carcinoma (HCC) cells. As2O3 effects on various HCC cell lines and primary HCC cells were investigated in time and dose series, including measurements of cell growth, PML mRNA and protein expression, xenografted tumor formation, and the self-renewal Oct4 and hepatocyte marker expressions in mouse model xenografts or cells treated with PML siRNA. The results were analyzed by immunocytochemistry, quantitative reverse transcription PCR and western blotting as well as indocyanine green and Periodic Acid Schiff staining. As2O3 inhibited HCC cell and HCC cell-derived xenograft tumor formation in a time-dependent manner and reduced PML protein expression in HCC cells, but had limited effects on PML mRNA levels in cell nuclei. The HCC cell line HuH7 treated with As2O3 showed a decreased expression of alpha-fetoprotein and increased expression and transcription of mature hepatocyte markers, indicating differentiation of HCC cells into hepatocytes. Cytokeratin 18 protein and mRNA levels as well as tyrosine aminotransferase and apolipoprotein B mRNA transcriptions were enhanced by As2O3 as were the numbers of indocyanine green and Periodic Acid Schiff stained cells. In addition, As2O3 downregulated the expression of Oct4. In conclusion, since As2O3 inhibited HCC cell proliferation and HCC cell-derived xenograft tumor formation it is suggested that an appropriate concentration of As2O3 might be a promising therapy to treat HCC.

In dual-fiber optical traps, two counter-propagating laser beams emitted from opposing laser fibers trap and manipulate particles. We describe the operation and performance of a dual-fiber optical trap created using spherical-tapered ended fiber pigtailed to 1436 nm laser diodes. Compared with the dual flat ended fiber optical trap, the dual spherical-tapered ended fiber optical trap increased the axial stiffness from 0.44 pN/µm to 0.99 pN/µm, and increased the lateral stiffness from 1.68 pN/µm to 1.76 pN/µm. The dual-fiber optical trap fabricated by spherical-tapered ended fiber enhanced the trapping efficiency of the optical trap. It expanded the application range and reliability of the dual-fiber optical trap. Additionally, we integrated the dual-fiber optical trap into an optical chip, thereby improving the stability of the system.

A cylindrical resonator gyroscope is a kind of Coriolis gyroscope, which measures angular velocity or angle via processing of the standing wave. The symmetry of a cylindrical resonator is destroyed by different degrees of geometric nonuniformity and structural damage in the machining process. The uneven mass distribution caused by the asymmetry of the resonator can be expressed in the form of a Fourier series. The first three harmonics will reduce the anti-interference ability of the resonator to the external vibration, as well as increase the angular random walk and zero-bias drift of the gyroscope. In this paper, the frequency split of different modes caused by the first three harmonic errors and the displacement of the center of the cylindrical resonator bottom plate are obtained by simulation, and the relationship between them is explored. The experimental results on five fused silica cylindrical resonators are consistent with the simulation, confirming the linear relationship between the n = 1 frequency split and second harmonic error. A method for evaluating the first three harmonic errors of fused silica cylindrical resonators is provided.

The cylindrical resonator gyroscope (CRG) is a kind of solid-state gyroscope with a wide application market. The cylindrical resonator is the key component of CRG, whose quality factor and symmetry will directly affect the performance of the gyroscope. Due to the material properties and fabrication limitations, the actual resonator always has some defects. Therefore, frequency trimming, i.e., altering the local mass or stiffness distribution by certain methods, is needed to improve the overall symmetry of the resonator. In this paper, we made further derivation based on the chemical trimming theory proposed by Basarab et al. We built up the relation between the frequency split and the balanced mass to determine the mass to be removed. Chemical trimming experiments were conducted on three cylindrical fused silica resonators. The frequency splits of the three resonators were around 0.05 Hz after chemical trimming. The relation between frequency split and balanced mass established from experimental data was consistent with the theoretical calculation. Therefore, frequency split can be reduced to lower than 0.05 Hz under rigorous theoretical calculation and optimized chemical trimming parameters.

A fast and accurate determination of longitudinal relaxation time is put forward for hyperpolarized 129Xe. The theoretical framework for the method is developed. Measurement of the longitudinal relaxation time is by the determination of a close-loop response of 129Xe magnetization to the external magnetic fields and is implemented with a highly sensitive Rb magnetometer. The indirect measurement dramatically reduces the time consuming than the conventional inversion-recovery method and is more suitable for the samples with long longitudinal relaxation time.

Radiationless electromagnetic interference (REI) has been used to achieve focusing below Abbe’s diffraction limit. Here, we demonstrate an approach to REI that uses the Fano resonance of subwavelength slits to achieve subdiffraction focusing. Two main features of the Fano resonance are critical: (1) The Fano resonance suppresses radiation by destructive interference, thereby allowing for REI, and (2) the Fano resonance creates a resonant field enhancement allowing one to overcome evanescent decay, which is different from past approaches to REI. An analytic theory is introduced to explain these results. While the analytic theory is formulated for a perfect electric conductor, comprehensive numerical simulations show the applicability in the visible regime, where losses and plasmonic effects play a role.

Object detection in remote sensing plays a crucial role in various ground identification tasks. However, due to the limited feature information contained within small targets, which are more susceptible to being buried by complex backgrounds, especially in extreme environments (e.g., low-light, motion-blur scenes). Meanwhile, event cameras offer a unique paradigm with high temporal resolution and wide dynamic range for object detection. These advantages enable event cameras without being limited by the intensity of light, to perform better in challenging conditions compared to traditional cameras. In this work, we introduce the Multi-Vision Transformer (MVT), which comprises three efficiently designed components: the downsampling module, the Channel Spatial Attention (CSA) module, and the Global Spatial Attention (GSA) module. This architecture simultaneously considers short-term and long-term dependencies in semantic information, resulting in improved performance for small object detection. Additionally, we propose Cross Deformable Attention (CDA), which progressively fuses high-level and low-level features instead of considering all scales at each layer, thereby reducing the computational complexity of multi-scale features. Nevertheless, due to the scarcity of event camera remote sensing datasets, we provide the Event Object Detection (EOD) dataset, which is the first dataset that includes various extreme scenarios specifically introduced for remote sensing using event cameras. Moreover, we conducted experiments on the EOD dataset and two typical unmanned aerial vehicle remote sensing datasets (VisDrone2019 and UAVDT Dataset). The comprehensive results demonstrate that the proposed MVT-Net achieves a promising and competitive performance.

The current SMT reflow soldering process usually adopts experimental methods to predict the temperature curve, and the disadvantages of high cost and low efficiency are urgent problems. In view of the high heat capacity and poor wetting of the product during the reflow soldering process, this paper optimizes the temperature curve prediction model. First, the existing furnace temperature model is simplified, and then a method based on genetic algorithm is proposed by introducing heating factors. Based on the above, we established a reflow temperature curve optimization model. Finally, the MAPE evaluation method is used to compare the predicted results with the production data, and the results show that the predicted values meet the error accuracy requirements. Therefore, it is proved that the mathematical model of genetic algorithm established can effectively predict the temperature curve, and provide guidance for the production process of the reflow soldering of the enterprise.

A fast and accurate determination of longitudinal relaxation time is put forward for hyperpolarized 129Xe. The theoretical framework for the method is developed. Measurement of the longitudinal relaxation time is by the determination of a close-loop response of 129Xe magnetization to the external magnetic fields and is implemented with a highly sensitive Rb magnetometer. The indirect measurement dramatically reduces the time consuming than the conventional inversion-recovery method and is more suitable for the samples with long longitudinal relaxation time. [ABSTRACT FROM AUTHOR]