The forming process of Selective Laser Melting (SLM) involves complex heat change and energy transfer, which changes the temperature distribution and morphology structure of the molten pool, thus affecting the performance of the forming parts. In this paper, a three-dimensional transient model was established by finite element software ANSYS to study the effects of laser power and scanning speed on the thermal behavior of NiTi monolayer formed by SLM. The results show that the scanned area will preheat the unscanned area, leading to the difference in peak temperature between the two scanning tracks, and the peak temperature and size of the molten pool will increase with the increase of laser power or the decrease of scanning speed. When the laser moves along different paths, the laser power has a greater impact on the temperature gradient of the molten pool than the scanning speed. Combined with the experiments, it can be seen that as power and scanning speed elevate, the microstructure of the NiTi alloy formed parts becomes more uniform. However, excessively low power or high scanning speeds can induce pores, impurities, and cracks within the NiTi alloy component's microstructure.

This study aims to predict the deformation distribution of thin-walled complex components formed via Selective Laser Melting (SLM), utilizing a thermal mechanical coupling analysis approach. The effectiveness of the results was evaluated by determining shape deviation. Numerical simulation was employed to depict the SLM forming process of TC4 alloy crowns, yielding the deformation distribution and shape discrepancy subsequent to SLM formation. SLM was executed on representative crown samples, which were later subjected to scanning by an ATOS CS5M 3D scanner. The resultant crown shapes were then aligned with the original crowns to assess their conformity. The results showed that the thermal mechanical coupling analysis method may serve as an effective tool for predicting crown deformation post-SLM processing.

The laser welding process is employed for sealing the metal bipolar plate of fuel cells. The targets for this method are stamped thin plates, no more than 0.1 mm in thickness. In the welding process, it is necessary to accurately control the depth of fusion to make it in a semi-penetration state. A heat source model that can accurately simulate the physical properties of welding is needed to quantitatively study the small-scale precision welding process by numerical simulation. In this paper, a modification was made to the existing laser welding heat source model to create a heat source model suitable for semi-penetration laser welding, with a focus on penetration control. By applying single factor analysis, the effect trend of each variable within the heat source model on heat flux output was determined. Through the welding experiment, the welding parameters and the weld cross-section shape of the small deformation bipolar plate are obtained. The trial-and-error method is used to adjust the value of each variable in the heat source model. The welding process is simulated by using the heat source model with the well-modulated parameters, and the simulation results are consistent with the real semi-penetration state. Consequently, this heat source model holds potential as a reference model for future numerical quantitative investigations in bipolar plate welding.

Laser shock strengthening, a non-contact method with superior control and enhancement effects, offers innovative modifications to gear surfaces. By manipulating the residual stress field spread over the gear surface, this technology significantly improves gear lifespan. This study delves into the impact of laser shock strengthening on gear surface′s residual stress, exploring four crucial process parameters: laser energy, laser spot size, laser spot bonding rate, and laser shock frequency. It provides an in-depth discussion of their influence on gear′s residual stress while reviewing the merits and demerits of composite laser shock strengthening techniques currently available. The regulatory impacts of combined methods such as laser shock strengthening-shot peening, laser quenching-laser shock strengthening, ultrasonic impact peening-laser shock strengthening, and electropulsing-assisted laser shock strengthening on residual stress are also assessed. In conclusion, it summarizes research advancements concerning gear surface residual stress reinforcement by laser shock technology and forecasts future developments and applications of laser shock.

Aiming at the color change of two-dimensional code laser marking on the surface of titanium alloy, this paper uses the method of experimental characterization analysis to explore the color change mechanism of two-dimensional code laser marking on the surface of titanium alloy. The influence of laser power, scanning line spacing, laser frequency and scanning speed on the color change of two-dimensional code laser marking is studied respectively. The spectrophotometer, scanning electron microscope, optical microscope, energy spectrometer and other equipment are used to characterize and analyze the mechanism of color change. The results show that with the increase of laser energy density, the surface color after laser marking gradually becomes black. On this basis, the reflectivity of the incident light of the two-dimensional code marked under different laser parameter combinations is analyzed, and its microscopic morphology is observed and its surface composition is measured. It is found that the main reason for the color change of the two-dimensional code marking is that the change of the micro-morphology causes the change of the reflectivity of the incident light on the surface of the two-dimensional code marking, and the nitrogen oxides produced during the processing process show different colors and the film thickness formed by the nitrogen oxides is different, causing different color changes.

This study applies terrestrial laser scanning technology for data measurement in brick-concrete structures, using wall length as the primary index to monitor deformation. Firstly, after determining the two distance thresholds based on thickness, the single wall point cloud is acquired by building point cloud segmentation and wall point cloud redistribution. Secondly, using the single wall as the fundamental unit, the wall boundary points are estimated. This estimation method is changed from the point cloud boundary estimation method based on normal. It only needs to calculate the normal once and convert the coordinate system once. Thirdly, with the constraint that two adjacent top boundary lines intersect at a point, the top boundary line is fitted by the weighted iterative least squares method. Fourthly, for single wall, a downward-translatable interest region is created and the structural length in the region is calculated. Finally, for two consecutive measurements, the wall lengths obtained of the same translations times are difference to extract the deformation values. The results show that the deformation discerned from the wall length calculated through this method aligns with the deformation represented by wall fractures. Furthermore, the computational error associated with the wall length ranges between -3 mm and 7 mm, thereby attaining millimeter level precision.

The building facade structure is one of the essential features to describe the architectural model. To solve the problems of the existing algorithms such as the long time to extract the building facade structure, the spatial projection error, and the missing point cloud after conversion, this paper proposes a building facade structure extraction method based on point cloud segmentation. This method uses single clustering segmentation to extract windows, and dilutes the main structure through a point cloud Downsampling algorithm to reduce the density and complexity of point clouds. Introduce standard vector algorithm to remove high-density main point cloud to edge point cloud. Finally, the improved 3D line segment detection algorithm traverses the edge point cloud to achieve feature extraction of building facade structures. Comparative experiments using self-testing point clouds and Semantic 3D publicly available data demonstrate that the proposed method effectively extracts building facade structures, enhances efficiency, and improves the filtering of disordered line segments. This method offers a new approach for structural processing in point cloud facade processing and model construction.

This paper presents the design of a small off-axis meter-scattering lidar atmospheric detection system to address the issues of large volume and complex structure associated with traditional atmospheric detection lidar. Firstly, the self-built small-scale meter-scattering lidar experimental system was used to carry out 24-hour continuous atmospheric detection in Changchun, and the variation of the contour of the extinction coefficient of atmospheric aerosols is consistent with the actual local situation, which proved that the experimental system was feasible. Secondly, the various factors affecting the accuracy of aerosol inversion are discussed, and appropriate methods are used to remove background noise to improve the inversion accuracy, and it is found that the backscatter extinction logarithmic ratio k and boundary value σm increase with the increase of its value within a certain range, and the lidar ratio Sa is inversely proportional to the atmospheric aerosol extinction coefficient value within a certain value range. Finally, the modification of the system overlapping factor is introduced to enhance the inversion accuracy of near-ground aerosols.

Low-level wind shear has been recognized as one kind of dangerous weather for aviation. To study the 1.55 μm wind lidar′s detection capabilities for low-level wind shear, a typical process of low-level wind shear caused by thunderstorm gale has been analysed by using data from FC-III wind lidar and Doppler weather radar. FC-III wind lidar adopts pulse coherent system and all fiber structure. A combined scanning strategy was implemented to achieve detection of wind shear which includes Doppler-beam-swinging (DBS) scan, plan-position-indicator (PPI) scans at the tangles of 4-and 6-degree, range-height-indicator (RHI) scans, and glide-path (GP)scans. Results demonstrate that the combined scanning strategy can effectively detect the three stages of low-level wind shear: vertical shear of horizontal wind in the environment before the thunderstorm gale, horizontal wind shear caused by the gusty front, and vertical shear of horizontal wind caused by the gale behind the gust front. The study shows that the vertical and horizontal structure and evolution of low-level wind shear can be clearly detected during these stages. Utilizing the combined scanning strategy, forecasters can provide an early warning for this wind shear 5 minutes in advance.

The acquisition of the high-density strain information is of great significance in the aeronautics and astronautics field. Strain can directly reflect the mechanical state of the structure and the structural health state can be inferred from the strain. The optical fiber-based strain measurement technology can densely obtain the distributed strain on the optical fiber, and the strain field distribution on the structure can be obtained by laying the optical fiber on the surface of the measured structure. In recent years, various distributed optical fiber sensing technologies can realize the multiplexing of large-scale sensors on a single optical fiber. Improving the spatial measurement resolution on a single optical fiber has always been a concern in this field. The paper begins by introducing space-intensive strain measurement scenarios and their requirements. It then examines typical distributed fiber-optic strain sensing technologies with millimeter-level spatial resolution, and finally explores the future development direction of dense fiber-optic strain sensing methods.

The detection of crop quality is essential for ensuring the safety of crop circulation and storage. This involves the use of biochemical and optical detection technologies, with optical detection being preferred due to its high efficiency, non-destructive nature, and rapid characteristics. Terahertz wave technology offers favorable conditions for crop quality detection due to its unique properties, including transient, transmission, coherence, and low-energy attributes. In recent years, terahertz technology has demonstrated significant potential in crop quality detection. This paper provides a summary of the terahertz detection system, detection principle, and advantages, along with an in-depth analysis of the recent progress in the application of terahertz technology in crop quality detection. This includes disease detection, variety origin identification, transgenic identification, and other detection methods. Furthermore, the paper identifies and discusses the existing problems in the research and application of terahertz technology in crop quality detection, while also presenting potential development directions.

The accurate measurement of the temporal-spatial distribution of laser intensity is crucial for analyzing the atmospheric propagation effect of high-power lasers and evaluating the beam control and aiming ability of high-power laser systems. Currently, the most reliable method for measuring high-energy laser power intensity distribution is the photoelectric array detection method, offering high temporal-spatial resolution, response sensitivity, and low measurement error. A photoelectric detection unit comprises a laser attenuation sampling apparatus, cooling system, integrating sphere attenuator, optical fiber attenuator, photoelectric detection module, and data processing terminal. Utilizing the photoelectric array detector based on this unit enables the measurement of large area laser spot, high-energy laser, and high temporal-spatial resolution, providing essential technical support for the development of high-power laser photoelectric array detectors.

Using the rate equation of quantum dot laser (QDL) and the filtering model of fiber Bragg grating (FBG), the property of the photon microwave signals generated by a QDL subject to optical injection and FBG optical feedback is numerically investigated. The quality of the microwave signals is judged using optical spectrum, frequency spectrum, and linewidth techniques. The results show that for the fixed frequency detuning, the microwave frequency is robust to injection intensity and the microwave intensity first increases and then decreases with the increase of injection intensity. Considering that the microwave linewidth generated by optical injection is about 0.5 MHz, which is relatively wide, FBG filtering optical feedback is introduced to narrow the microwave linewidth. It is found that by adjusting the feedback parameters appropriately, the microwave linewidth can be compressed to around 1 kHz, and the linewidth compression effect is obvious. The research results can provide theoretical support for the application of the QDL in photogenerated microwaves.

Single photon counting detection technology has become an important development direction in the field of 3D imaging because of its high sensitivity. Complex targets have become important research objects because of their diverse structures and rich features, but their response mechanism of photon imaging is too complex to be analyzed by simple models. In this paper, a single photon 3D imaging data simulation method based on 3D model is proposed for the feature analysis of complex targets. Based on the typical Avalanche Photodiodes (APD) single photon detector array, combined with the single photon 3D imaging detection model, a single photon detection data simulation method based on 3D structure model of complex target is proposed. Firstly, the object body coordinate system was established and the 3D structure was transformed to the imaging coordinate system at fixed point according to the affine transformation model. Then, according to the imaging relationship, the different resolution units in the field of view were divided into background units, foreground units, target units and noise units. The original photon data was generated for different units according to the photon number Poisson distribution model. Through computer simulation, the method is applied to simulate single photon 3D imaging detection data of typical civil aviation targets, laying a theoretical and data foundation for 3D measurement and structural characteristic analysis of targets.

Aiming at the problems of serious feature loss and more holes in the traditional point cloud simplification algorithm, a point cloud simplification algorithm considering the features and integrity of point clouds was proposed. Firstly, the whole feature points of the model are extracted by using the neighborhood normal Angle of the point cloud. Then the fuzzy C-means clustering algorithm is used to extract the local feature points according to the curvature of the point cloud and the fast point feature histogram. Then the non-local feature points are subsampled using the improved voxel reduction method to obtain the non-feature points. Finally, the point clouds obtained from each step are fused to obtain the final reduced point cloud. The proposed algorithm is compared with the traditional methods and method of other literature, and the Hausdorff distance, a quantitative index describing the error between datasets, is used as the evaluation index of the simplification accuracy. The experimental results show that the Hausdorff distance of the proposed algorithm on Bunny dataset and Skull dataset is about 25% and 39% lower than that of the random reduction method, about 86% and 95% lower than that of the curvature reduction method, and about 86% and 81% lower than method of other literature. It can be seen that the simplification algorithm in this paper has high simplification accuracy.

The recurrence of orthodontic issues after treatment is a common clinical concern. Addressing how to minimize recurrence and shorten the retention period is a prominent research focus in orthodontics. Low-level laser therapy (LLLT) is a treatment method that stimulates cell proliferation and differentiation through photobiomodulation, characterized by effective penetration and biosafety compared to other methods for reducing recurrence. Most research findings indicate that when combined with traditional retainers, LLLT can decrease the orthodontic recurrence rate and retention period within specific parameter ranges. Studies have suggested that LLLT influences tissue remodeling and repair by impacting Matrix metalloproteinases (MMPs), Adenosine Triphosphate (ATP), protein synthesis, cytokines, and more. It can enhance the stability of orthodontic treatment, with its mechanism linked to the remodeling of periodontal ligament (PDL) fibers and alveolar bone. Further exploration of LLLT′s application in orthodontic retention holds significant scientific research and clinical guidance implications. This paper provides a review of experimental studies, mechanisms, and key parameters of LLLT in orthodontic retention.

OBJECTIVE To investigate the effect of multiband-light-emitting diode (LED) in regulating cutaneous cells’ functions after skin injury. METHOD The epidermal keratinocytes (HaCaT) and dermal fibroblasts (HS27) of human were injured by mechanical injury, respectively. The injured cells were treated by a LED light that with four peak bands (460 nm, 590 nm, 640 nm, and 940 nm) and output energy density of 400 mW/cm2. The proliferation and migration of HaCaT cells were evaluated by CTG assay and wound healing assay, respectively. Moreover, the proinflammatory factors in HS27, such as interlukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), were detected by ELISA. In addition, the extracellular matrix (ECM) proteins production of HS27 were evaluated by western blotting and ELISA. RESULTS Low level light therapy (LLLT) with the multiband-LED i) accelerated cell proliferation and migration of injured keratinocytes, ii) decreased the protein levels of IL-6 and TNF-α in the injured fibroblasts, iii) increased the production of Collagen-I, Collagen-III, and hyaluronic acid. Furthermore, a better improved wound healing effect were seen after two treatments, compared with that after only one treatment. CONCLUSION The multiband-LED mediated photobiomodulation accelerated re-epithelialization, ameliorated dermal inflammation and stimulated ECM production, promoting wound healing of skin.