User-centric applications through visible light communication cooperative transmission constitute an architecture that has emerged in recent years. The resulting user-dependent cooperative clusters are observed to inevitably overlap. The training signals transmitted from the access points (APs) in each cluster or from the users who select identical APs in their clusters should be mutually orthogonal to avoid pilot contamination. Herein, we study the orthogonal training resource allocation problem for user-centric cooperative networks. Further, we formulate a joint pilot allocation and the user equipment (UE) selection problem to maximize the number of admitted UE with a fixed number of pilots. Finally, the analysis and numerical results denote a remarkable improvement when compared with the existing scheme and denote that the proposed method can effectively avoid pilot contamination and improve the utilization of training resources.

This paper proposes an all-optical-fiber high-precision magnetic field sensor based on magnetic fluid coating and cooling tapering to improve the sensitivity of optical fiber sensors in magnetic field detection and realizes high-precision real-time monitoring of field intensity under a weak magnetic field. The intermittent cooling method in the tapering process enhances the quality of the interference spectrum conveniently and slows the air-hole collapse of the photonic crystal fiber. Because of its simple manufacturing process, strong maneuverability, high sensitivity, and low degree of loss, the sensor realizes real-time online detection in a high-sensitivity magnetic field. Finally, the influence of the temperature variation of the sensor is discussed. Experimental results show that the photonic crystal fiber obtains a good interference spectrum at a tapering length of 5.5 mm and waist diameter of 75 μm. The sensor exhibits a highly linear response to external magnetic fields ranging from 0 to 78 Oe (1 Oe =^79.578 A·m -1) with a sensitivity of 95 pm·Oe -1. The degree of linear fitting is approximately 98.31%.

To address the shortcomings of the standard ant colony algorithm in cloud-computing resource allocation and scheduling, this study proposes an adaptive ant colony algorithm to improve load balance and reduce task execution time and costs. The proposed algorithm can solve tasks submitted by users with a short execution time, low cost, and balanced load rate. The traditional ant colony algorithm, the latest AC-SFL algorithm, and the improved adaptive ant colony algorithm are simulated using the CloudSim platform. Experimental results show that, the improved adaptive ant colony algorithm is able to quickly find a solution for the optimal cloud computing resource scheduling, shorten task completion time, reduce execution cost, and maintain the load balance of the entire cloud system center.

The critical dimension scanning electron microscope (CD-SEM) is a standard instrument for standardizing micro- to nano-sized line spacing samples. To improve the calibration accuracy of samples, this paper studies a measurement algorithm based on image processing technology. First, the characteristics of the developed samples are analyzed. Second, the algorithms for micro- to nano-sized line spacing measurement and linear approximation are researched and the line spacing standard samples with a single period from 100 nm to ~10 μm are measured. Finally, a nano-measuring machine is used in comparative experiments. The experimental results show that the relative error of the linear approximation algorithm is controlled within 0.45%. In contrast, the relative error obtained by the line spacing measurement algorithm is controlled within 0.35%, thus improving the measurement accuracy of the line spacing. The algorithm provides a measurement scheme for improving the reliability of the line spacing measurement instrument and ensuring the precision of semiconductor device manufacturing.

The measurement accuracy of the fringe projection three-dimensional system is mainly determined by the calibration accuracy of a camera and a projector. This study proposes an improved calibration method. Further, the projector is calibrated based on the inverse camera model. The phase coding method is employed to obtain the unwrapped phase, avoids the introduction of the camera calibration error, reduces the number of images projected by the projector, and simplifies and accelerates the calibration operation. Using two sets of fringe patterns, both horizontal and vertical, the projection by the projector corresponds with the camera image in case of system calibration. Thus, the pixel coordinate of the circular mark points in a projector image can be obtained. Subsequently, a radial distortion camera model is utilized for calibrating the projector. In addition, stereo calibration is the final step used to obtain a geometric relation between the camera and the projector. Furthermore, the experimental results demonstrate that the proposed calibration method is feasible.

During the camera calibration process, it is necessary to deal with the missed detection and redundancy of checkerboard corners caused by poor illumination conditions and lens distortion. In this study, we analyze the gray distribution properties of the corners and propose an algorithm for corner detection based on the checkerboard corners' gray distribution features. To ensure that the checkerboard corners are not missed under poor illumination conditions and lens distortion, the proposed algorithm firstly extracts candidate corners using the gray distribution characteristics of the corners. Then, we improve the accuracy of the candidate corners through iteration, and eliminate the fake corners based on the gray distribution characteristics of the checkerboard corners, avoiding the redundant corners. Finally, we extract the corner coordinates of the checkerboard by combining the nearest neighbor points. Experimental results show that there is no omission and redundancy in the corners under poor illumination conditions and lens distortion. By applying the checkerboard corners extracted by the proposed algorithm in camera calibration, a mean square error of the re-projection error less than 0.1 pixel has been achieved, which is better than those provided by existing algorithms.

This study proposes a reconfigurable microwave photonic bandpass filter based on an Add-Drop silicon nitride microring filter via optical single sideband modulation and optical carrier separation. The measured bandwidth and out-of-band rejection ratio of the proposed microwave photonic filter are 726 MHz and 37.0 dB, respectively. Further, a filter with a frequency tuning range of 1.64--23.41 GHz can be achieved by tuning the optical carrier's wavelength. In addition, the bandwidth can be adjusted to 0.683--2.246 GHz with an out-of-band rejection ratio of more than 26 dB by changing the coupling coefficients of the microring resonator.

A YAG pulsed laser welding system was used to analyze the microstructure of welded 1Cr17Ni2 stainless steel plates, tensile properties and microhardness of the joints, and effects of different defocusing distances on the microstructure and properties of the welded 1Cr17Ni2 stainless steel plates. The results show that the laser self-melting butt welding in the 1Cr17Ni2 stainless steel plate weld shows a microstructure division. The main structure of the base material area comprises ferrite and martensite, the heat-affected area comprises lath martensite and a small amount of banded ferrite, and the weld area comprises mainly martensite. Weld penetration gradually decreases with increasing defocusing distance. Further, the weld width increases and subsequently decreases, the martensite content at the weld gradually decreases, and the joint's tensile strength increases and subsequently decreases. The joint hardness in descending order is weld zone > heat affected zone > base material zone. Thus, the joint's overall hardness decreases with increasing defocusing distance. When the defocusing distance is -5.5 mm, the martensite beam group in the heat affected zone is fine and even, the welding forming quality is good, and the joint has excellent tensile performance.

In this paper, the rigorous coupled-wave analysis theory is used to simulate a hybrid Si/SiO2 high-contrast grating using a liquid crystal as a low refractive index material, which is suitable for liquid crystal tunable vertical-cavity surface-emitting lasers (VCSEL). Using 940-nm TM polarized incident light, the parameters of the grating structure can be optimized to obtain broadband (Δλ=256 nm), high reflectivity (R>99%), and polarization-stabilized characteristics that satisfy the VCSEL top mirror requirements. Changes in the refractive index of the liquid crystal do not affect the quality of the grating. Liquid crystal tunable VCSELs are expected to be combined with different high-contrast gratings and hybrid gratings in the future.

Considering the influence of matching of process parameters in selective laser melting (SLM) on forming quality, we choose three laser powers and conduct experiments at different scanning speeds and scan modes. The effect of laser power on the morphology of molten pool and residual stress is studied. Results show that an increase in the laser power leads to a corresponding increment in residual stress on formed parts and size of the molten pool. The main reason is that the heat flux density increases with the increasing laser power, the temperature gradient increases under the same thickness and cross section, and the temperature of the molten pool and its size increase. This results in a large interphase angle between crystal faces and large spacing between grain boundaries of different formed parts. It also results in excessive residual stress after cooling and solidification of the formed part corresponding to great thermal stress. Therefore, the thermal and residual stresses can be decreased by rationally selecting and matching the process parameters. Consequently, high-quality SLM parts can be produced.

In this paper, the laser surface remelting of ultra-high strength steel 300M was performed by using fiber lasers. The microstructure, hardness, and electrochemical corrosion behavior of the remelted surface at different laser powers and scanning rates were analyzed. The results show that the microstructures in the surface remelting zone primarily comprise martensite and retained austenite. The higher the scanning rate, the higher the microhardness. The average microhardness is about 704 HV. The electrochemical tests show that the self-corrosion potential of the surface of the material subsequent to laser remelting positively shifts, and the corrosion current density decreases. Thus, the corrosion resistance of the remelting layer is optimal when the laser power and scanning rate are 300 W and 33 mm/s, respectively.

In this study, a laser-quenching experiment is conducted on the 40CrNiMoA steel base material of a reel spindle using a fiber laser. Further, the microstructure of sample surface is observed using a metallographic microscope, the microhardness of the phase-transformation hardening zone is evaluated using a Vickers hardness tester, and the friction and wear properties of the sample are evaluated using a vertical universal friction-and-wear tester. The macroscopic structure of the sample cross-section and morphology after wear are observed using a stereo microscope, and the corrosion resistance of the sample is verified using an electrochemical workstation. The results denote that after laser quenching of the 40CrNiMoA steel, a phase-transformation hardening zone can be observed on the surface with a microstructure that is mainly characterized by fine martensite, a small amount of retained austenite, and partially dispersed carbides. The hardened layer exhibits a depth of approximately 200 μm, and the hardness can become 638.3--711.2 HV, which is approximately 2.6--2.8 times that of the substrate. The average friction coefficient is 0.506, which is 42.5% lower than that of the substrate. The amount of wear is 1.3 mg, which is only 36.1% of that of the substrate. Herein, the abrasive wear is observed to be the main wear mechanism. Furthermore, the corrosion voltage is -0.497 V, which is slightly higher than that of the substrate, while the self-corrosion current density is 2.16789×10 -9 A/cm 2, which is lower than that of the substrate. The corrosion resistance is considerably improved.

High energy radiation such as γ ray induces a darkening effect on Yb-doped fiber (YDF), adversely affecting the reliability of Yb-doped fiber laser (YDFL). In this study, we assess the influence of the total dose of γ ray on the loss of large mode area YDF. The results show that the radiation induced loss (RIL) of the tested fiber linearly increases with the total dose. The optical efficiency of YDFL with different structural parameters after the generation of RIL is then investigated based on the measured value of RIL and rate equation model. The amplifier scheme pumped with 976-nm laser diodes exhibits the least sensitivity to the total dose of γ ray. The optimized central wavelength used herein is 1070 nm for the YDF; however, the efficiency difference is only 2% for wavelengths from 1060 nm to 1100 nm. This paper performs the research based on the YDFL system, providing a reference for further YDFL design and applications.

Fourier domain mode locking (FDML) technology can improve the scanning speed to achieve the designed limit of a tunable filter while the swept laser source maintains superior performance of the various parameters. To further improve the sweep frequency of the FDML swept laser source, an optical buffer device is introduced into the optical cavity of the laser to back up the swept light. In our experiment, the center wavelength of the swept laser source based on the optical buffer device within the ring cavity is 1310 nm, the sweep frequency range is 95 nm, the instantaneous line width is 0.1 nm, the scanning speed is raised to 202 kHz, and the average output optical power is 7.5 mW. In this paper, the optical buffer device is used to markedly increase the scanning speed of the traditional FDML high-speed swept laser source. It is important to improve the comprehensive imaging performance of swept source optical coherence tomography (SS-OCT) systems.

The superhydrophobic surface of titanium alloys with stable wettability is obtained by fabricating a microtexture on a titanium (Ti) alloy surface with a nanosecond laser and assisted with chemical treatment, and it exhibits properties similar to the “lotus effect”. Adjusting the laser processing parameters enables the production of micro/nanostructures with different surface wettabilities. On this basis, the titanium alloy surface is coated with a mixture of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane and ethanol solution. Scanning electron microscopy and energy spectrum analysis show that laser irradiation can induce the formation of multiscale porous Ti oxide microstructures in Ti alloys. The relationship between hydrophilicity of the Ti metal surface and micro/nanostructure surface change as well as the coating effect on the surface wettability are further investigated by evaluating the contact angle. This study can pave the road for applications in biomedical drug delivery.

To realize InP-based monolithic integrated optoelectronic devices and systems, the quantum well intermixing (QWI) technology has been experimentally investigated for the InGaAsP/InGaAsP confinement heterojunction multiple quantum well laser structures herein. The active-area QWI technology realized under P-ion implantation with different energies, different rapid thermal annealing (RTA) conditions, and cycle annealing is investigated, and the experimental results are characterized using photoluminescence (PL) spectra. Experimental results show that the QWI effect can be observed for all the samples with different variables, where the annealing temperature has the most significant effect and the cycle annealing can further enhance the QWI effect. The blue-shift in PL spectra increases with the annealing temperature and time and implantation energy, and the annealing temperature has the greatest effect on the blue shift. Finally, the maximum blue-shift achieved is approximately 116 nm with secondary annealing at 750 ℃ for 150 s when the injection dose and energy are 1×10 14 ion/cm 2 and 600 keV, respectively. Our findings will benefit future design and fabrication of monolithic integrated optoelectronic devices and systems using QWI technology.

In this study, dense and defect-free specimens of a single track are fabricated at a high deposition rate using the plasma arc deposition, in which the 316L stainless steel powder is used as the deposition material. The effects of the deposition current, scanning speed, and powder feeding rate on the deposition height, width, and angle of the specimens are studied. Moreover, the microstructure and composition of the deposited samples are examined and analyzed. The results indicate that the deposition angle increases with increase in the powder feeding rate and decreases with increase in the deposition current. The deposition angles of the specimens fabricated under different deposition parameters are mainly sharp angles, which is beneficial for the deposition of the lapped samples. Among all the process parameters, the width of the single track is mostly affected by the deposition current, while its height is mostly affected by the scanning speed. The dilution rate decreases under a higher scanning speed, lower deposition current, or higher powder feeding rate. The composition distribution of the deposition specimens is uniform. The solidified microstructure comprises austenite and ferrite phases.

In this study, single-layer homogeneous samples are rapidly prototyped using fused deposition modeling (FDM) based on the preparation of graphene/polylactide (PLA) composite. Further, the effects of different graphene contents on the electromagnetic parameters are investigated. The wave absorption effect is calculated and analyzed according to the transmission line theory. A composite exhibiting low graphene content is selected as the printing material of transparent layer, whereas a composite exhibiting high graphene content is selected as the printing material of absorption and reabsorption layers. Furthermore, the matching thickness range of the absorption and reabsorption layers is determined using the quarter-wavelength matching model. Subsequently, a three-layer wave absorber comprising different graphene/PLA composite is designed and manufactured. The experimental results denote that a three-layer wave absorber performs significantly better than a single-layer homogeneous wave absorber. The optimal wave absorption effect can be observed when the composites with the graphene mass fractions of 5%, 7%, and 8%, are used as the printing materials of transparent, absorption, and reabsorption layers, respectively. Finally, the reflectivity of such wave absorber in the band of 13.3-18 GHz is less than -10 dB, and the maximum absorption peak is -30 dB at 17 GHz.

In this study, an optical system of total-reflection night-light remote sensing is designed using the off-axis three-mirror optical structure of COOK TMA based on the development requirements of the urban night-light remote sensing cameras. Its field of view is 5°×2°, focal length is 500 mm, F number is 3.8, and working waveband is 0.4-0.8 μm. The optical axes of the primary, second, and third mirrors are designed to be coaxial to improve the feasibility of optical installation and adjustment. Initially, the appropriate initial structural parameters are selected. Then, ray tracing and optimization are performed using the CODE V software. Results show that the root-mean-square diameter of the spot is 2.305 μm, which is less than one eighth of a pixel. Further, the optical modulation transfer function is greater than 0.92 at Nyquist frenquency of 25 lp/mm, which is close to the diffraction limit. The external baffle, blocking rings, diaphragm, and matte paint are used to decrease the stray-light level. Subsequently, the stray light of the optical-mechanical system is simulated and analyzed using the Tracepro software. The results denote that the point source transmittance is between 10 -11 and 10 -3 when the off-axis field of view is 1°-80°. Furthermore, the point source transmittance is less than 1×10 -9 when the solar suppression angle is 65.96°-80°, which satisfies the application requirements.

This paper reports a design scheme for a two-vision and two-light-path telecentric system based on machine vision. With a refractive prism as the boundary, the telecentric system is divided into two parts: the objective part and the eyepiece part. By adding and replacing the eyepiece, different optical magnifications are realized in the original system to ensure the applicability of telecentric systems in different situations. A double telecentric system with dual vision is designed. In the proposed system, the working distance is 130 mm, and the object fields of view are 40 mm and 80 mm, respectively. With an imaging chip SN5000A made by ON Semiconductor company, the optical magnifications are -0.275 and -0.1375, respectively. The system achieves low distortion (0.3 at 105 lp/mm), and high telecentricity (<0.1°), and also meets other design requirements.

This study determines the initial structural parameters based on the theory of coaxial three-mirror aberrations to satisfy the design requirements using a simulation software. Through the optical design concept of coaxial three mirrors, incident beam off-axis, primary mirror, and third-mirror vertex intersecting, an off-axis three-mirror optical system, which can be easily adjusted and exhibits high accuracy, is designed and combined with a digital micromirror device target generator, thereby providing a dynamic real-time simulation target for an armored vehicle. The system has a working waveband of 200--1200 nm. Further, the effective focal length is 2800 mm, the field of view is 2°, and the diameter of entrance pupil is 350 mm. The design results prove that the maximum relative distortion of the optical system is 0.1056%. Furthermore, the wave aberration of each field of view is better than λ/40 (the dominant wavelength λ=636.3 nm), and the modulation transfer function (MTF) is greater than 0.54 at 70 lp/mm, which is close to the diffraction limit. The system also exhibits a good imaging quality, satisfying the requirements of an infinite dynamic target simulation. In addition, by the analysis of the machining and assembly tolerance, the MTF of the optical system greater than 0.4 can be obtained.

To obtain high-quality iris images, a phone iris-recognition lens is designed using the optical design software ZEMAX in this study. The phone lens comprises four plastic aspheric lenses. The total working distance, total length, and F number of the phone lens are 200--330 mm, 4.09 mm, and 2.4, respectively. In the design results, the modulation transfer function at 275 mm exceeds 0.4 at one-half the Nyquist frequency of the lens. The distortion is lower than 0.6%, and the relative illumination exceeds 83%. Image evaluation and tolerance analysis confirm that the system has small distortion, a large variable working distance, excellent image quality, and stable performance, thus meeting the processing requirements of iris recognition lenses.

This paper proposes an improved optical path system to solve two problems caused by domestic traditional sulfur dioxide detectors: less optical path fluorescence and low acquisition accuracy. The point light source is collimated and concentrated using a lens, and a narrow slit is used to reduce interference of stray light, thereby improving the defect of the light intensity convergence effect on the conventional optical path structure and improving the detection precision as well. Zemax is used to simulate the new and original light paths. By comparing the point map and detection view, the root-mean-square radius and geometric maximum radius of the new light path are reduced to 35.439 μm and 50.194 μm, respectively, and the light intensity of the contact area between the gas and light source is improved. The experimental test shows that, compared with the conventional instrument, the sulfur dioxide concentration indication value error of the improved optical path system is reduced from 2% to 1%, improving detection accuracy. This newly developed optical path system can effectively solve above problems and is suitable for the design of sulfur dioxide detectors.

Considering the disadvantages of the direct inverse model for the back propagation (BP) neural network, such as low precision, excessive time consumption, and easy to concussion, this paper proposes an inverse modeling method for the BP neural network that combines an improved ant colony algorithm and a Bayesian regularization algorithm. This method improves the ant colony algorithm, which sets the volatilization factor based on the search stage, updates the pheromone based on the degree of pros and cons of the path, and considers the distance between the starting point and the nodes and the distance between the end point and the nodes in the heuristic factor, to optimize the weight of the forward model and improve the accuracy of the overall model. Then the Bayesian regularization algorithm with L1/2 norm is used to reverse the input of the forward model, which improves the stability of the network. It is applied to a reconfigurable power amplifier. Experimental results show that the accuracy of the method, compared with that of the direct inverse modeling method and the adaptive η inverse modeling method, is improved by 99.77% and 90.70%, respectively, with the average running time for the modeling being shorten by 35.76% and 2.05%, respectively. Thus, the complexity of designing a power amplification module is reduced and its design speed is accelerated.

In this study, the quantum simulation of the Heisenberg spin XY model is realized by obtaining the effective Hamiltonian of the atom-microcavity coupled systems via adiabatic approximation. Further, the quantum coherence between any two-body quantum systems is analyzed based on the criterion of relative entropy to obtain quantum resources. The long-range quantum coherence decreases exponentially with increasing the two-body spacing. Furthermore, when the system parameters are varied, it is found that there is a numerical mutation in the long-range quantum coherence near the quantum critical point, which provides a possible order parameter for characterizing the quantum phase transition. After considering the influence of external light-field noise on the quantum coherence, it is found that the quantum coherence decays with time and gradually disappears.

With the development of wireless communication, visible light communication (VLC) has become very promising technology owing to its many advantages. However, the nonlinear effect of VLC introduces many challenges for signal processing and deteriorates system performance. As machine learning has many advantages and significant potential for solving nonlinearity issues, the VLC that utilizes machine learning algorithms is bound to have tremendous research value. Existing research shows that traditional machine learning algorithms, such as K-means, DBSCAN, and support vector machine, perform well in pre-equalization, post-equalization, anti-system jitter, and phase correction. A deep neural network can further improve the performance of the VLC system because of its strong nonlinear fitting ability. In this article, we analyze the aforementioned methods and introduce their application to the signal processing in VLC. We hope this paper provides a reference for solving the nonlinearity problems related to machine learning in VLC.

Chronic liver injury induces liver fibrosis that must be diagnosed and treated within an appropriate timeframe. Otherwise, it can easily evolve into liver cirrhosis, or other more severe liver diseases. In recent years, fluorescence imaging and spectral analysis techniques have greatly promoted the detection and research of liver fibrosis diseases because they offer rapid, simple, and non-instrusive detection, and thus have great potential. This review highlights the latest achievements of fluorescence imaging and spectral analysis techniques in the investigation of tissue, cell, and molecular mechanisms of liver fibrosis. The research difficulties and potential application prospects of the technique regarding liver fibrosis are also discussed.

Fluorescence spectroscopy is an important testing method. Recently, the optical-fiber-probe-based fluorescence testing technology has become a popular research topic. This technology exhibits the advantages of high efficiency, micro, real-time, in-situ, small size, and easy integration. This review briefly describes the principle of fluorescence analysis, the spatial conduction theory of laser emission and fluorescence collection using optical-fiber probes, the typical structure and preparation of the optical-fiber fluorescent probes, and the status of research in the fields of biology, environment, and food safety. Finally, this review looks forward to the development trend of optical-fiber fluorescent probes.

Ultra-short and ultra-high-energy pulsed laser is a powerful tool for investigating the interaction between laser and matter, and they have thereby been extensively investigated. A chirped-pulse amplification (CPA) system is the critical component for generating ultra-short and ultra-high-energy laser pulses. A pulse-compression grating (PCG) is an essential part of CPA, and it plays an important role in CPA performance. Metal/multilayer-dielectric gratings (MMDGs) have attracted considerable attention owing to their characteristics of high diffraction efficiency, broad bandwidth, and high laser-induced-damage threshold. To improve the understanding of metal/multilayer-dielectric pulse compression grating, we provide a comprehensive review of the status, design principles, and manufacturing processes of MMDGs. Finally, we discuss the prospects for future developments of MMDGs.

Ultra-fast laser heating technology has been gradually applied in many fields, and the thermal conduction mechanism has received significant attention. The traditional Fourier heat-transfer law is insufficient for correctly describing the thermal conduction mechanism in the ultra-fast process. Therefore, based on the results of the previous researches on heat-transfer theory of ultra-fast laser heating technology, this paper summarizes an overview of the heat transfer of ultra-fast laser heating technology. Simultaneously, applications of the lattice Boltzmann, Monte Carlo, and molecular dynamics methods in ultra-fast laser heating heat-transfer theory research, which have attracted considerable attention in recent years, are briefly introduced. Finally, future prospects for heat transfer theory in ultra-fast laser heating technology are examined in this paper.

Virtual reality (VR) and its derivatives, namely augmented reality (AR) and mixed reality (MR), can overlap the three-dimensional virtual scene with the real world and can significantly improve the intuition, accuracy, and real-time nature of the user's sensory world. The popularization and application of this technology is expected to revolutionize the medical field. Herein, the concept of VR/AR/MR is analyzed and its development process is briefly described. The applications of VR and AR in the medical field are elaborated, and the advantages of solutions based on MR are analyzed based on HoloLens. Finally, the deficiencies of VR/AR/MR applications in the medical field are summarized, and the future development trend is prospected.

In this study, the Raman spectra of three brands of wood lacquer samples, such as Chenyang brand, are examined to realize the rapid nondestructive detection as well as the accurate identification and classification of wood lacquer. Subsequently, the processing effects of different preprocessing methods, such as the baseline correction, Savitzky-Golay nine-point smoothing, first derivative, and second derivative, are investigated. Three models of characteristic-band ratio, Fisher discriminant, and K nearest neighbor (KNN) are also established. The experimental results indicate that the characteristic-band ratio method is capable of characterizing the features of the three wood lacquer samples with 1358 cm -1/1239 cm -1; further, the Raman spectral model combined with Fisher discriminant based preprocessing methods of baseline correction, smoothing, and second derivative exhibits an optimal classification accuracy of 100%. However, the accuracy of the KNN discriminant model is limited to 88.5% under the same preprocessing. Therefore, the second-derivative based Raman spectroscopy combined with the characteristic-band-Fisher-KNN method can provide a new rapid nondestructive analysis method for the accurate detection of different brands of wood lacquer, exhibiting universality and certain reference significance.

In this study, the feasibility of the rapid non-destructive testing method for the pomegranate quality in the Sichuan and Yunnan Provinces is investigated based on the visible/near-infrared diffuse transmission spectroscopy technique. First, the near-infrared spectra of pomegranates are obtained using a dynamic online detection device which can effectively suppress the effect of stray light, and the actual sugar content value is measured. In combination with the principal component analysis method, the cluster analysis of pomegranates from different producing areas can approximately divide the samples into two categories. Further, a partial least squares discrimination analysis model is developed for the pomegranates from two distinct producing areas, which exhibits an accuracy greater than 97%. Meanwhile, multiple pretreatment methods, such as Savitzky-Golay smoothing, normalization, baseline correction, and multiplicative signal correction, are employed to establish a single model for two pomegranate types. Based on the obtained results, the baseline correction method is observed to be better than the other examined methods. In particular, the correlation coefficient of the prediction set (Rp) of the established Sichuan pomegranate model is 0.82, the root mean square error of prediction set (RMSEP) is 0.37, the correlation coefficient of the calibration set (Rc) is 0.90, and the root mean square error of calibration set (RMSEC) is 0.31. However, for the Yunnan pomegranate model, the Rp is 0.81, the RMSEP is 0.33, the Rc is 0.87, and the RMSEC is 0.27. In the post-sorting verification experiment for samples not involved in modeling, the discriminating rate of pomegranates in both the producing areas is 95%, whereas the sugar content sorting accuracy is 92.5%. Thus, the near-infrared spectroscopy is of considerable significance with respect to the discrimination of the pomegranate producing area and the sorting of its sugar content and may form the basis for future pomegranate online sorting research.

For gamut mapping of spectral color management, this study propose a nonlinear multispectral dimension reduction method that tackles serial problems in the calculation of high-dimensional spectral data in the process of establishing a look-up table. The method performs a partial least squares analysis on metameric black, extracts the potential components, obtains the KMN vector, and combines the result with Lab vector, yielding a six-dimensional vector which is used as an intermediate conversion space LabKMN. Within this space, the interconversion between the high-dimensional spectral data and low-dimensional base vector can be realized. The LabPQR space is divided into two three-dimensional spaces. The first three dimensions are the CIELAB values under specific lighting conditions, and the remaining dimensions (PQR) describe the spectral reconstruction dimensions of metameric black. The spectral and colorimetric accuracies of the two methods are compared. On 1600 Munsell sample dataset, the proposed method achieves a root-mean-square error of 0.0139 (versus 0.0164 in LabPQR), and a colorimetric reconstruction error of 1.8138 (versus 2.8706 in LabPQR). Compared with LabPQR, the proposed method improves the spectral accuracy by 15.24% and reduces the colorimetric reconstruction error by 36.81%. The reconstruction accuracy is greatly improved after dimension reduction by the proposed method, and the original color spectrum space is described with higher precision.