This paper proposes a distributed nonsingular cooperative guidance law for multiple flight vehicles with Field-of-View(FOV)constraints.First,a novel time-to-go estimation is developed based on a FOV-constrained Propor...This paper proposes a distributed nonsingular cooperative guidance law for multiple flight vehicles with Field-of-View(FOV)constraints.First,a novel time-to-go estimation is developed based on a FOV-constrained Proportional Navigation Guidance(FPNG)law.Then,the FPNG law is augmented with a cooperative guidance term to achieve consensus of time-to-go with predefined-time convergence prior to the impact time.A continuous auxiliary function is introduced in the bias term to avoid the singularity of guidance command.Moreover,the proposed guidance law is extended to the three-dimensional guidance scenarios and the moving target with the help of a predicted interception point.Finally,several numerical simulations are conducted,and the results verify the effectiveness,robustness,and advantages of the proposed cooperative guidance law.展开更多
In the existing impact time control guidance (ITCG) laws for moving-targets, the effects of time-varying velocity caused by aerodynamics and gravity cannot be effectively con-sidered. Therefore, an ITCG with field-of-...In the existing impact time control guidance (ITCG) laws for moving-targets, the effects of time-varying velocity caused by aerodynamics and gravity cannot be effectively con-sidered. Therefore, an ITCG with field-of-view (FOV) constraints based on biased proportional navigation guidance (PNG) is developed in this paper. The remaining flight time (time-to-go) estimation method is derived considering aerodynamic force and gravity. The number of differential equations is reduced and the integration step is increased by changing the integral variable, which makes it possible to obtain time-to-go through integration. An impact time controller with FOV constraints is proposed by analyzing the influence of the biased term on time-to-go and FOV constraint. Then, numerical simulations are performed to verify the correctness and superiority of the method.展开更多
Optical microscopes are essential tools for scientific research,but traditional microscopes are restricted to capturing only two-dimensional(2D)texture information,lacking comprehensive three-dimensional(3D)morphology...Optical microscopes are essential tools for scientific research,but traditional microscopes are restricted to capturing only two-dimensional(2D)texture information,lacking comprehensive three-dimensional(3D)morphology capabilities.Additionally,traditional microscopes are inherently constrained by the limited space-bandwidth product of optical systems,resulting in restricted depth of field(DOF)and field of view(FOV).Attempts to expand DOF and FOV typically come at the cost of diminished resolution.In this paper,we propose a texture-driven FOV stitching algorithm specifically designed for extended depth-of-field(EDOF)microscopy,allowing for the integration of 2D texture and 3D depth data to achieve high-resolution,high-throughput multimodal imaging.Experimental results demonstrate an 11-fold enhancement in DOF and an 8-fold expansion in FOV compared to traditional microscopes,while maintaining axial resolution after FOV extension.展开更多
This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjuncti...This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjunction with the concept of biased Proportional Navigation Guidance(PNG). The guidance law developed leverages a nonlinear function to ensure the boundedness of velocity lead angle to cater to the seeker’s FOV limit. It is proven that the impact time error is nullified in a finite-time under the proposed method. Additionally, the optimality of the biased command is theoretically analyzed. Numerical simulations confirm the superiority of the proposed method and validate the analytic findings.展开更多
In this paper, a trajectory shaping guidance law,which considers constraints of field-of-view(FOV) angle, impact angle, and terminal lateral acceleration, is proposed for a constant speed missile against a stationary ...In this paper, a trajectory shaping guidance law,which considers constraints of field-of-view(FOV) angle, impact angle, and terminal lateral acceleration, is proposed for a constant speed missile against a stationary target. First, to decouple constraints of the FOV angle and the terminal lateral acceleration, the third-order polynomial with respect to the line-ofsight(LOS) angle is introduced. Based on an analysis of the relationship between the looking angle and the guidance coefficient,the boundary of the coefficient that satisfies the FOV constraint is obtained. The terminal guidance law coefficient is used to guarantee the convergence of the terminal conditions. Furthermore, the proposed law can be implemented under bearingsonly information, as the guidance command does not involve the relative range and the LOS angle rate. Finally, numerical simulations are performed based on a kinematic vehicle model to verify the effectiveness of the guidance law. Overall, the work offers an easily implementable guidance law with closed-form guidance gains, which is suitable for engineering applications.展开更多
Large field-of-view（FoV） three-dimensional（3 D） photon-counting imaging is demonstrated with a single-pixel single-photon detector based on a Geiger-mode Si-avalanche photodiode. By removing the collecting lens（C...Large field-of-view（FoV） three-dimensional（3 D） photon-counting imaging is demonstrated with a single-pixel single-photon detector based on a Geiger-mode Si-avalanche photodiode. By removing the collecting lens（CL）before the detector, the FoV is expanded to ±10°. Thanks to the high detection efficiency, the signal-to-noise ratio of the imaging system is as high as 7.8 dB even without the CL when the average output laser pulse energy is about 0.45 pJ/pulse for imaging the targets at a distance of 5 m. A 3 D image overlaid with the reflectivity data is obtained according to the photon-counting time-of-flight measurement and the return photon intensity.展开更多
BACKGROUND It has been reported that deep learning-based reconstruction(DLR)can reduce image noise and artifacts,thereby improving the signal-to-noise ratio and image sharpness.However,no previous studies have evaluat...BACKGROUND It has been reported that deep learning-based reconstruction(DLR)can reduce image noise and artifacts,thereby improving the signal-to-noise ratio and image sharpness.However,no previous studies have evaluated the efficacy of DLR in improving image quality in reduced-field-of-view(reduced-FOV)diffusionweighted imaging(DWI)[field-of-view optimized and constrained undistorted single-shot(FOCUS)]of the pancreas.We hypothesized that a combination of these techniques would improve DWI image quality without prolonging the scan time but would influence the apparent diffusion coefficient calculation.AIM To evaluate the efficacy of DLR for image quality improvement of FOCUS of the pancreas.METHODS This was a retrospective study evaluated 37 patients with pancreatic cystic lesions who underwent magnetic resonance imaging between August 2021 and October 2021.We evaluated three types of FOCUS examinations:FOCUS with DLR(FOCUS-DLR+),FOCUS without DLR(FOCUS-DLR−),and conventional FOCUS(FOCUS-conv).The three types of FOCUS and their apparent diffusion coefficient(ADC)maps were compared qualitatively and quantitatively.RESULTS FOCUS-DLR+(3.62,average score of two radiologists)showed significantly better qualitative scores for image noise than FOCUS-DLR−(2.62)and FOCUS-conv(2.88)(P<0.05).Furthermore,FOCUS-DLR+showed the highest contrast ratio and 600 s/mm^(2)(0.72±0.08 and 0.68±0.08)and FOCUS-DLR−showed the highest CR between cystic lesions and the pancreatic parenchyma for the b-values of 0 and 600 s/mm2(0.62±0.21 and 0.62±0.21)(P<0.05),respectively.FOCUS-DLR+provided significantly higher ADCs of the pancreas and lesion(1.44±0.24 and 3.00±0.66)compared to FOCUS-DLR−(1.39±0.22 and 2.86±0.61)and significantly lower ADCs compared to FOCUS-conv(1.84±0.45 and 3.32±0.70)(P<0.05),respectively.CONCLUSION This study evaluated the efficacy of DLR for image quality improvement in reduced-FOV DWI of the pancreas.DLR can significantly denoise images without prolonging the scan time or decreasing the spatial resolution.The denoising level of DWI can be controlled to make the images appear more natural to the human eye.However,this study revealed that DLR did not ameliorate pancreatic distortion.Additionally,physicians should pay attention to the interpretation of ADCs after DLR application because ADCs are significantly changed by DLR.展开更多
In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the ba...In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.展开更多
For high precision calibration of camera with large field-of-view,massive calibration points will be needed if traditional methods are selected,which makes the calibration complex and time-consuming.In order to solve ...For high precision calibration of camera with large field-of-view,massive calibration points will be needed if traditional methods are selected,which makes the calibration complex and time-consuming.In order to solve this problem,a calibration method based on flexible planar target is proposed.In this method,distortion factor is firstly acquired by the invariance of cross ratio,and existing feature points are adjusted with the distortion factor.Then,a large number of points that will be used for the calibration are constructed with the adjusted feature points.Simultaneously,Tsai method is modified so as to reduce the complexity of calibration,which makes the process linear.The simulation and real experiments show that the method proposed in this paper is simple,linear,accurate and robust,and the precision of this method is close to that of Tsai method using abundant points.The method can satisfy the requirement of high precision calibration for camera with large field-of-view.展开更多
Augmented reality(AR)has garnered significant attention in recent years for its advanced display capabilities.Highperforming AR demands lightweight and integrated optical components.Metalenses offer a solution,as they...Augmented reality(AR)has garnered significant attention in recent years for its advanced display capabilities.Highperforming AR demands lightweight and integrated optical components.Metalenses offer a solution,as they can meet these requirements through their multifunctional and integrative potential.In this work,we propose a trans-reflective red-green-blue(RGB)achromatic AR metalens composed of titanium dioxide(TiO_2)nanopillars and a multiwavelength notch filter.The AR metalens achieves balanced focusing efficiencies for obliquely incident light,with a field of view exceeding 90°,which ensures excellent readability in various scenarios for AR devices.Additionally,ambient light can pass efficiently through the metalens.This design functions both as an eyepiece and an optical combiner,demonstrating strong potential for AR applications.展开更多
This paper presents a finite-time cooperative guidance approach aimed at intercepting maneuverable targets while ensuring that multiple missiles adhere to field-of-view(FOV)constraints throughout the interception proc...This paper presents a finite-time cooperative guidance approach aimed at intercepting maneuverable targets while ensuring that multiple missiles adhere to field-of-view(FOV)constraints throughout the interception process.A model for the missile-target relative motion is constructed,where the FOV constraint is redefined as an asymmetric,time-varying limit on the missile's relative velocity perpendicular to the line-of-sight(LOS)direction.The proposed guidance method is divided into two components:one along the LOS direction and the other perpendicular to it.For the LOS direction,a multi-agent consensus protocol is employed alongside a finite-time disturbance observer,ensuring that the interception timing of multiple missiles converges to a consistent value within a finite period.Perpendicular to the LOS,a finite-time guidance law is formulated using a time-varying asymmetric barrier Lyapunov function(TABLF)combined with adaptive control theory,ensuring that all missiles achieve the desired impact angle while maintaining compliance with the FOV constraints.The finite-time stability of the guidance law is validated using Lyapunov theory.Finally,the effectiveness of the cooperative guidance strategy,including FOV compliance,is demonstrated through numerical simulations.展开更多
Compound eyes(CEs),renowned for their extraordinary visual capabilities,offer significant potential for advanced micro-optical systems.However,their applications in wide field-of-view(FOV)imaging and dynamic tracking,...Compound eyes(CEs),renowned for their extraordinary visual capabilities,offer significant potential for advanced micro-optical systems.However,their applications in wide field-of-view(FOV)imaging and dynamic tracking,for instance,microscopic particle image velocimetry(μ-PIV)for microfluidics,remain constrained by limited spatial resolution.We present a compound eye-on-a-chip(CEoC)system integrating a seven-ommatidium CE with a microfluidic platform.When fabricated via femtosecond laser two-photon polymerization(TPP),the CE exhibits exceptional surface smoothness(<4 nm roughness)and achieves wide-FOV imaging(>120°)with submicrometer resolution.Through quantitative calibration using TPP-fabricated microstructures,we established precise 3D spatial positioning capabilities.Proof-of-conceptμ-PIV experiments using fluorescent microparticles successfully reconstructed high-speed trajectories(10 mm/s)from real-time CE-captured images.This integrated CEoC system has promising potential for advancing microfluidic analysis and optofluidic manipulation technologies.展开更多
Wide field-of-view(FOV)optics are widely used in various imaging,display,and sensing applications.Conventional wide FOV optics rely on complicated lens assembly comprising multiple elements to suppress coma and other ...Wide field-of-view(FOV)optics are widely used in various imaging,display,and sensing applications.Conventional wide FOV optics rely on complicated lens assembly comprising multiple elements to suppress coma and other Seidel aberrations.The emergence of flat optics exemplified by metasurfaces and diffractive optical elements(DOEs)offers a promising route to expand the FOV without escalating complexity of optical systems.To date,design of large FOV flat lenses has been relying upon iterative numerical optimization.Here,we derive,for the first time,to the best of our knowledge,an analytical solution to enable computationally efficient design of flat lenses with an ultra-wide FOV approaching 180°.This analytical theory further provides critical insights into working principles and otherwise non-intuitive design trade-offs of wide FOV optics.展开更多
A homing guidance law combined with terminal angle constraint and seeker’s field-of-view limit is proposed in this paper for hitting a stationary target.The proposed guidance scheme is composed of proportional naviga...A homing guidance law combined with terminal angle constraint and seeker’s field-of-view limit is proposed in this paper for hitting a stationary target.The proposed guidance scheme is composed of proportional navigation guidance and a continuous feedback term with respect to a newly defined angle error.Considering that many existingmethods use switching logic strategy to address the specific constraint which will generate discontinuous acceleration command,the proposed scheme overcomes the limitation by not using switching logic.Furthermore,the finite-time convergence of angle error before interception is guaranteed via a Lyapunov-like approach,a shaping function is also designed to lengthen the range at which the error becomes zero.Numerical simulations demonstrate the characteristics and advantages of the proposed guidance law.展开更多
The consensus problem of impact time is addressed for multiple anti-ship missiles. A new distributed cooperative guidance law with the form of biased proportional navigation guidance （BPNG） is presented. The propose...The consensus problem of impact time is addressed for multiple anti-ship missiles. A new distributed cooperative guidance law with the form of biased proportional navigation guidance （BPNG） is presented. The proposed guidance law employs the available measurements of relative impact time error as the feedback information to achieve the consensus of impact time among mis- siles and, by exploiting the special structure of the biased cooperative control term, it can handle the seeker＇s field-of-view （FOV） constraint. The proposed scheme ensures convergence to consensus of impact time under either fixed or switching sensing/communication network, and the topological requirements are less restrictive than those in the existing results. Numerical examples are provided to illustrate the effectiveness of the proposed guidance law.展开更多
An integrated cooperative guidance framework for multi-missile cooperatively attacking a single stationary target is proposed in this paper by combining both the centralized and decentralized communication topologies....An integrated cooperative guidance framework for multi-missile cooperatively attacking a single stationary target is proposed in this paper by combining both the centralized and decentralized communication topologies. Once missiles are distributed into several groups, missiles within a single group communicate with the centralized leader-follower framework, while the leaders from different groups communicate using the nearest-neighbor topology. To implement the integrated cooperative guidance framework, a group of Finite-Time Cooperative Guidance（FTCG） laws considering the saturation constraint on FOV（FTCG-FOV） are firstly derived within the centralized leader-follower framework to satisfy the communication topology of missiles in a single group.Then, an improved sequential approach is developed to adapt the FTCG-FOV to satisfy the communication topology between groups. The numerical simulations demonstrate the effectiveness and high efficiency of the integrated cooperative guidance framework and the cooperative guidance laws, as well as the superiority of the developed sequential approach.展开更多
An impact-time-control guidance law is required for the simultaneous attack of suicide attack unmanned aerial vehicles.Based on the nonlinear model,a two-phase guidance strategy is proposed.The impact time is derived ...An impact-time-control guidance law is required for the simultaneous attack of suicide attack unmanned aerial vehicles.Based on the nonlinear model,a two-phase guidance strategy is proposed.The impact time is derived in a simple analytical form of initial states and switching states,and it can be controlled by switching at an appropriate range.Firstly,a two-phase guidance law is designed to make the magnitude of the heading error decrease monotonically from its initial value to zero.And then,the feasible interval of the switching ranges and of the impact times under the acceleration constraint are given analytically in sequence.Furthermore,a general form of twophase guidance law is proposed,which allows the magnitude of the heading error to increase in the first phase,to improve the applicability of the methodology.Having the same structure as proportional navigation guidance with a time-varying gain,the proposed algorithms are simple and easy to implement.The corresponding feedback form is presented for realistic implementation.When a predefined impact time is taken within its permissible set,the constraints on the acceleration and fieldof-view will not be violated during the interception.Finally,simulations validate the effectiveness of the methodology in impact time control and salvo attack.展开更多
The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problem...The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problems of the SeaDAS (SeaWiFS Data Analysis System) algorithm applied to China coastal waters, a new atmospheric correction algorithm is discussed, developed, and used for the SSC of East China coastal waters. The advantages of the new algorithm are described through the comparison of the results from different algorithms.展开更多
In many ultrafast imaging applications, the reduced field-of-view（r FOV） technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic ...In many ultrafast imaging applications, the reduced field-of-view（r FOV） technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporallyencoded（SPEN） method offers an inherent applicability to r FOV imaging. In this study, a flexible r FOV imaging method is presented and the superiority of the SPEN approach in r FOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging（EPI） experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the r FOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest（ROIs） with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging.展开更多
In this paper,an integrated estimation guidance and control(IEGC)system is designed based on the command filtered backstepping approach for circular field-of-view(FOV)strapdown missiles.The threedimensional integrated...In this paper,an integrated estimation guidance and control(IEGC)system is designed based on the command filtered backstepping approach for circular field-of-view(FOV)strapdown missiles.The threedimensional integrated estimation guidance and control nonlinear model with limited actuator deflection angle is established considering the seeker's FOV constraint.The boundary time-varying integral barrier Lyapunov function(IBLF)is employed in backstepping design to constrain the body line-of-sight(BLOS)in IEGC system to fit a circular FOV.Then,the nonlinear adaptive controller is designed to estimate the changing aerodynamic parameters.The generalized extended state observer(GESO)is designed to estimate the acceleration of the maneuvering targets and the unmatched time-varying disturbances for improving tracking accuracy.Furthermore,the command filters are used to solve the"differential expansion"problem during the backstepping design.The Lyapunov theory is used to prove the stability of the overall closed-loop IEGC system.Finally,the simulation results validate the integrated system's effectiveness,achieving high accuracy strikes against maneuvering targets.展开更多
基金supported by the National Natural Science Foundation of China(No.91216304)。
文摘This paper proposes a distributed nonsingular cooperative guidance law for multiple flight vehicles with Field-of-View(FOV)constraints.First,a novel time-to-go estimation is developed based on a FOV-constrained Proportional Navigation Guidance(FPNG)law.Then,the FPNG law is augmented with a cooperative guidance term to achieve consensus of time-to-go with predefined-time convergence prior to the impact time.A continuous auxiliary function is introduced in the bias term to avoid the singularity of guidance command.Moreover,the proposed guidance law is extended to the three-dimensional guidance scenarios and the moving target with the help of a predicted interception point.Finally,several numerical simulations are conducted,and the results verify the effectiveness,robustness,and advantages of the proposed cooperative guidance law.
基金supported by the National Natural Science Foundation of China(U21B2028).
文摘In the existing impact time control guidance (ITCG) laws for moving-targets, the effects of time-varying velocity caused by aerodynamics and gravity cannot be effectively con-sidered. Therefore, an ITCG with field-of-view (FOV) constraints based on biased proportional navigation guidance (PNG) is developed in this paper. The remaining flight time (time-to-go) estimation method is derived considering aerodynamic force and gravity. The number of differential equations is reduced and the integration step is increased by changing the integral variable, which makes it possible to obtain time-to-go through integration. An impact time controller with FOV constraints is proposed by analyzing the influence of the biased term on time-to-go and FOV constraint. Then, numerical simulations are performed to verify the correctness and superiority of the method.
基金supported by Science Foundation of Donghai Lab-oratory(No.DH-2022KF01001).
文摘Optical microscopes are essential tools for scientific research,but traditional microscopes are restricted to capturing only two-dimensional(2D)texture information,lacking comprehensive three-dimensional(3D)morphology capabilities.Additionally,traditional microscopes are inherently constrained by the limited space-bandwidth product of optical systems,resulting in restricted depth of field(DOF)and field of view(FOV).Attempts to expand DOF and FOV typically come at the cost of diminished resolution.In this paper,we propose a texture-driven FOV stitching algorithm specifically designed for extended depth-of-field(EDOF)microscopy,allowing for the integration of 2D texture and 3D depth data to achieve high-resolution,high-throughput multimodal imaging.Experimental results demonstrate an 11-fold enhancement in DOF and an 8-fold expansion in FOV compared to traditional microscopes,while maintaining axial resolution after FOV extension.
文摘This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjunction with the concept of biased Proportional Navigation Guidance(PNG). The guidance law developed leverages a nonlinear function to ensure the boundedness of velocity lead angle to cater to the seeker’s FOV limit. It is proven that the impact time error is nullified in a finite-time under the proposed method. Additionally, the optimality of the biased command is theoretically analyzed. Numerical simulations confirm the superiority of the proposed method and validate the analytic findings.
基金supported by the Defense Science and Technology Key Laboratory Fund of Luoyang Electro-Optical Equipment Institute,Aviation Industry Corporation of China (6142504200108)。
文摘In this paper, a trajectory shaping guidance law,which considers constraints of field-of-view(FOV) angle, impact angle, and terminal lateral acceleration, is proposed for a constant speed missile against a stationary target. First, to decouple constraints of the FOV angle and the terminal lateral acceleration, the third-order polynomial with respect to the line-ofsight(LOS) angle is introduced. Based on an analysis of the relationship between the looking angle and the guidance coefficient,the boundary of the coefficient that satisfies the FOV constraint is obtained. The terminal guidance law coefficient is used to guarantee the convergence of the terminal conditions. Furthermore, the proposed law can be implemented under bearingsonly information, as the guidance command does not involve the relative range and the LOS angle rate. Finally, numerical simulations are performed based on a kinematic vehicle model to verify the effectiveness of the guidance law. Overall, the work offers an easily implementable guidance law with closed-form guidance gains, which is suitable for engineering applications.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11774095,11722431 and 11621404the Shanghai Basic Research Project under Grant No 18JC1412200+2 种基金the National Key R&D Program of China under Grant No2016YFB0400904the Program of Introducing Talents of Discipline to Universities under Grant No B12024the Shanghai International Cooperation Project under Grant No 16520710600
文摘Large field-of-view（FoV） three-dimensional（3 D） photon-counting imaging is demonstrated with a single-pixel single-photon detector based on a Geiger-mode Si-avalanche photodiode. By removing the collecting lens（CL）before the detector, the FoV is expanded to ±10°. Thanks to the high detection efficiency, the signal-to-noise ratio of the imaging system is as high as 7.8 dB even without the CL when the average output laser pulse energy is about 0.45 pJ/pulse for imaging the targets at a distance of 5 m. A 3 D image overlaid with the reflectivity data is obtained according to the photon-counting time-of-flight measurement and the return photon intensity.
文摘BACKGROUND It has been reported that deep learning-based reconstruction(DLR)can reduce image noise and artifacts,thereby improving the signal-to-noise ratio and image sharpness.However,no previous studies have evaluated the efficacy of DLR in improving image quality in reduced-field-of-view(reduced-FOV)diffusionweighted imaging(DWI)[field-of-view optimized and constrained undistorted single-shot(FOCUS)]of the pancreas.We hypothesized that a combination of these techniques would improve DWI image quality without prolonging the scan time but would influence the apparent diffusion coefficient calculation.AIM To evaluate the efficacy of DLR for image quality improvement of FOCUS of the pancreas.METHODS This was a retrospective study evaluated 37 patients with pancreatic cystic lesions who underwent magnetic resonance imaging between August 2021 and October 2021.We evaluated three types of FOCUS examinations:FOCUS with DLR(FOCUS-DLR+),FOCUS without DLR(FOCUS-DLR−),and conventional FOCUS(FOCUS-conv).The three types of FOCUS and their apparent diffusion coefficient(ADC)maps were compared qualitatively and quantitatively.RESULTS FOCUS-DLR+(3.62,average score of two radiologists)showed significantly better qualitative scores for image noise than FOCUS-DLR−(2.62)and FOCUS-conv(2.88)(P<0.05).Furthermore,FOCUS-DLR+showed the highest contrast ratio and 600 s/mm^(2)(0.72±0.08 and 0.68±0.08)and FOCUS-DLR−showed the highest CR between cystic lesions and the pancreatic parenchyma for the b-values of 0 and 600 s/mm2(0.62±0.21 and 0.62±0.21)(P<0.05),respectively.FOCUS-DLR+provided significantly higher ADCs of the pancreas and lesion(1.44±0.24 and 3.00±0.66)compared to FOCUS-DLR−(1.39±0.22 and 2.86±0.61)and significantly lower ADCs compared to FOCUS-conv(1.84±0.45 and 3.32±0.70)(P<0.05),respectively.CONCLUSION This study evaluated the efficacy of DLR for image quality improvement in reduced-FOV DWI of the pancreas.DLR can significantly denoise images without prolonging the scan time or decreasing the spatial resolution.The denoising level of DWI can be controlled to make the images appear more natural to the human eye.However,this study revealed that DLR did not ameliorate pancreatic distortion.Additionally,physicians should pay attention to the interpretation of ADCs after DLR application because ADCs are significantly changed by DLR.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11174280,60990323,and 60990320)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.YYYJ-1123)
文摘In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.
基金Sponsored by the Fundamental Research Funds for the Central Universities(Grant No.HIT.NSRIF.2014019)
文摘For high precision calibration of camera with large field-of-view,massive calibration points will be needed if traditional methods are selected,which makes the calibration complex and time-consuming.In order to solve this problem,a calibration method based on flexible planar target is proposed.In this method,distortion factor is firstly acquired by the invariance of cross ratio,and existing feature points are adjusted with the distortion factor.Then,a large number of points that will be used for the calibration are constructed with the adjusted feature points.Simultaneously,Tsai method is modified so as to reduce the complexity of calibration,which makes the process linear.The simulation and real experiments show that the method proposed in this paper is simple,linear,accurate and robust,and the precision of this method is close to that of Tsai method using abundant points.The method can satisfy the requirement of high precision calibration for camera with large field-of-view.
基金supported by the National Key R&D Program of China(No.2024YFB2809200)the National Natural Science Foundation of China(No.12374363)+4 种基金the Guangdong Basic and Applied Basic Research Foundation(Nos.2025A1515011514and 2020B0301030009)the Guangdong Provincial Natural Science Fund Projects(No.2024B1515040013)the Guangdong Provincial Quantum Science Strategic Initiative(Nos.GDZX2306002 and GDZX2206001)the“GDTZ”Plan(No.2021TQ06X161)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.241gqb016)。
文摘Augmented reality(AR)has garnered significant attention in recent years for its advanced display capabilities.Highperforming AR demands lightweight and integrated optical components.Metalenses offer a solution,as they can meet these requirements through their multifunctional and integrative potential.In this work,we propose a trans-reflective red-green-blue(RGB)achromatic AR metalens composed of titanium dioxide(TiO_2)nanopillars and a multiwavelength notch filter.The AR metalens achieves balanced focusing efficiencies for obliquely incident light,with a field of view exceeding 90°,which ensures excellent readability in various scenarios for AR devices.Additionally,ambient light can pass efficiently through the metalens.This design functions both as an eyepiece and an optical combiner,demonstrating strong potential for AR applications.
基金National Natural Science Foundation of China(Grant No.62303380)and the Aeronautical Science Foundation of China(Grant No.201907053001)。
文摘This paper presents a finite-time cooperative guidance approach aimed at intercepting maneuverable targets while ensuring that multiple missiles adhere to field-of-view(FOV)constraints throughout the interception process.A model for the missile-target relative motion is constructed,where the FOV constraint is redefined as an asymmetric,time-varying limit on the missile's relative velocity perpendicular to the line-of-sight(LOS)direction.The proposed guidance method is divided into two components:one along the LOS direction and the other perpendicular to it.For the LOS direction,a multi-agent consensus protocol is employed alongside a finite-time disturbance observer,ensuring that the interception timing of multiple missiles converges to a consistent value within a finite period.Perpendicular to the LOS,a finite-time guidance law is formulated using a time-varying asymmetric barrier Lyapunov function(TABLF)combined with adaptive control theory,ensuring that all missiles achieve the desired impact angle while maintaining compliance with the FOV constraints.The finite-time stability of the guidance law is validated using Lyapunov theory.Finally,the effectiveness of the cooperative guidance strategy,including FOV compliance,is demonstrated through numerical simulations.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFB4600400)the National Natural Science Foundation of China(Grant Nos.T2325014,62205174)the Natural Science Foundation of Jilin Province(Grant No.20230101350JC)。
文摘Compound eyes(CEs),renowned for their extraordinary visual capabilities,offer significant potential for advanced micro-optical systems.However,their applications in wide field-of-view(FOV)imaging and dynamic tracking,for instance,microscopic particle image velocimetry(μ-PIV)for microfluidics,remain constrained by limited spatial resolution.We present a compound eye-on-a-chip(CEoC)system integrating a seven-ommatidium CE with a microfluidic platform.When fabricated via femtosecond laser two-photon polymerization(TPP),the CE exhibits exceptional surface smoothness(<4 nm roughness)and achieves wide-FOV imaging(>120°)with submicrometer resolution.Through quantitative calibration using TPP-fabricated microstructures,we established precise 3D spatial positioning capabilities.Proof-of-conceptμ-PIV experiments using fluorescent microparticles successfully reconstructed high-speed trajectories(10 mm/s)from real-time CE-captured images.This integrated CEoC system has promising potential for advancing microfluidic analysis and optofluidic manipulation technologies.
基金supported by the Defense Advanced Research Projects Agency Defense Sciences Office(DSO)Program,EXTREME Optics and Imaging(EXTREME)(No.HR00111720029)MIT Skoltech Seed Fund Program,and MIT Deshpande Center for Technological Innovation。
文摘Wide field-of-view(FOV)optics are widely used in various imaging,display,and sensing applications.Conventional wide FOV optics rely on complicated lens assembly comprising multiple elements to suppress coma and other Seidel aberrations.The emergence of flat optics exemplified by metasurfaces and diffractive optical elements(DOEs)offers a promising route to expand the FOV without escalating complexity of optical systems.To date,design of large FOV flat lenses has been relying upon iterative numerical optimization.Here,we derive,for the first time,to the best of our knowledge,an analytical solution to enable computationally efficient design of flat lenses with an ultra-wide FOV approaching 180°.This analytical theory further provides critical insights into working principles and otherwise non-intuitive design trade-offs of wide FOV optics.
基金supported by the Shanghai Academy of Spaceflight Technology and Shanghai Jiao Tong University(SAST-SJTU)Advanced Space Technology Joint Research Fund(No.USCAST 2020-8)the National Natural Science Foundation of China(No.U20B2054).
文摘A homing guidance law combined with terminal angle constraint and seeker’s field-of-view limit is proposed in this paper for hitting a stationary target.The proposed guidance scheme is composed of proportional navigation guidance and a continuous feedback term with respect to a newly defined angle error.Considering that many existingmethods use switching logic strategy to address the specific constraint which will generate discontinuous acceleration command,the proposed scheme overcomes the limitation by not using switching logic.Furthermore,the finite-time convergence of angle error before interception is guaranteed via a Lyapunov-like approach,a shaping function is also designed to lengthen the range at which the error becomes zero.Numerical simulations demonstrate the characteristics and advantages of the proposed guidance law.
基金supported by the National Natural Science Foundation of China (No. 61273058)
文摘The consensus problem of impact time is addressed for multiple anti-ship missiles. A new distributed cooperative guidance law with the form of biased proportional navigation guidance （BPNG） is presented. The proposed guidance law employs the available measurements of relative impact time error as the feedback information to achieve the consensus of impact time among mis- siles and, by exploiting the special structure of the biased cooperative control term, it can handle the seeker＇s field-of-view （FOV） constraint. The proposed scheme ensures convergence to consensus of impact time under either fixed or switching sensing/communication network, and the topological requirements are less restrictive than those in the existing results. Numerical examples are provided to illustrate the effectiveness of the proposed guidance law.
基金supported by the National Natural Science Foundation of China(No.11532002)
文摘An integrated cooperative guidance framework for multi-missile cooperatively attacking a single stationary target is proposed in this paper by combining both the centralized and decentralized communication topologies. Once missiles are distributed into several groups, missiles within a single group communicate with the centralized leader-follower framework, while the leaders from different groups communicate using the nearest-neighbor topology. To implement the integrated cooperative guidance framework, a group of Finite-Time Cooperative Guidance（FTCG） laws considering the saturation constraint on FOV（FTCG-FOV） are firstly derived within the centralized leader-follower framework to satisfy the communication topology of missiles in a single group.Then, an improved sequential approach is developed to adapt the FTCG-FOV to satisfy the communication topology between groups. The numerical simulations demonstrate the effectiveness and high efficiency of the integrated cooperative guidance framework and the cooperative guidance laws, as well as the superiority of the developed sequential approach.
文摘An impact-time-control guidance law is required for the simultaneous attack of suicide attack unmanned aerial vehicles.Based on the nonlinear model,a two-phase guidance strategy is proposed.The impact time is derived in a simple analytical form of initial states and switching states,and it can be controlled by switching at an appropriate range.Firstly,a two-phase guidance law is designed to make the magnitude of the heading error decrease monotonically from its initial value to zero.And then,the feasible interval of the switching ranges and of the impact times under the acceleration constraint are given analytically in sequence.Furthermore,a general form of twophase guidance law is proposed,which allows the magnitude of the heading error to increase in the first phase,to improve the applicability of the methodology.Having the same structure as proportional navigation guidance with a time-varying gain,the proposed algorithms are simple and easy to implement.The corresponding feedback form is presented for realistic implementation.When a predefined impact time is taken within its permissible set,the constraints on the acceleration and fieldof-view will not be violated during the interception.Finally,simulations validate the effectiveness of the methodology in impact time control and salvo attack.
文摘The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problems of the SeaDAS (SeaWiFS Data Analysis System) algorithm applied to China coastal waters, a new atmospheric correction algorithm is discussed, developed, and used for the SSC of East China coastal waters. The advantages of the new algorithm are described through the comparison of the results from different algorithms.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474236,81171331,and U1232212)
文摘In many ultrafast imaging applications, the reduced field-of-view（r FOV） technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporallyencoded（SPEN） method offers an inherent applicability to r FOV imaging. In this study, a flexible r FOV imaging method is presented and the superiority of the SPEN approach in r FOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging（EPI） experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the r FOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest（ROIs） with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging.
文摘In this paper,an integrated estimation guidance and control(IEGC)system is designed based on the command filtered backstepping approach for circular field-of-view(FOV)strapdown missiles.The threedimensional integrated estimation guidance and control nonlinear model with limited actuator deflection angle is established considering the seeker's FOV constraint.The boundary time-varying integral barrier Lyapunov function(IBLF)is employed in backstepping design to constrain the body line-of-sight(BLOS)in IEGC system to fit a circular FOV.Then,the nonlinear adaptive controller is designed to estimate the changing aerodynamic parameters.The generalized extended state observer(GESO)is designed to estimate the acceleration of the maneuvering targets and the unmatched time-varying disturbances for improving tracking accuracy.Furthermore,the command filters are used to solve the"differential expansion"problem during the backstepping design.The Lyapunov theory is used to prove the stability of the overall closed-loop IEGC system.Finally,the simulation results validate the integrated system's effectiveness,achieving high accuracy strikes against maneuvering targets.
