Refractive index measurement deflectometry for measuring gradient refractive index lens.

A method based on deflectometry to measure the refractive index distribution of radial gradient refractive index (GRIN) lens is proposed in this paper. The method establishes the relationship between the refractive index distribution and the direction of light ray by deriving the propagation equation of light in a non-uniform medium. By measuring the deflection angle using the principle of deflectometry and the assumption of central refraction, the refractive index distribution of the radial GRIN lens is determined. The specific principle of refractive index measurement deflectometry (RIMD) is described in detail, and the correctness and accuracy of the method are verified through numerical simulations. Furthermore, the effects of calibration error, lens surface shape on the accuracy of the measurement results are analyzed. In the experimental section, the proposed method is applied to measure a radial GRIN lens, and the results are compared with the nominal parameters in terms of shape distribution and numerical values, demonstrating good consistency. The measurement error is controlled within the order of 10-3. This method enables rapid and convenient acquisition of full-field information of GRIN lens and holds promising potential for playing an important role in lens manufacturing and production.

Frequency-domain searching algorithm in deflectometry for measuring the surface of a transparent planar element.

This Letter presents the frequency-domain searching algorithm in deflectometry (FSAD). By encoding specialized multi-frequency fringe patterns and employing a correlation searching algorithm, the limitations of existing frequency-domain methods can be overcome to some extent, thereby separating front and back surface reflections to obtain complete measurement data. The principles of FSAD are described in detail. In the experiment, a piece of window glass with thickness of 10 mm and a square area of 96 × 96 mm is measured to verify the proposed method.

Research on the Shock Wave Overpressure Peak Measurement Method Based on Equilateral Ternary Array.

The measurement process of ground shock wave overpressure is influenced by complex field conditions, leading to notable errors in peak measurements. This study introduces a novel pressure measurement model that utilizes the Rankine-Hugoniot relation and an equilateral ternary array. The research delves into examining the influence of three key parameters (array size, shock wave incidence angle, and velocity) on the precision of pressure measurement through detailed simulations. The accuracy is compared with that of a dual-sensor array under the same conditions. Static explosion tests were conducted using bare charges of 0.3 kg and 3 kg TNT to verify the numerical simulation results. The findings indicate that the equilateral ternary array shock wave pressure measurement method demonstrates a strong anti-interference capability. It effectively reduces the peak overpressure error measured directly by the shock wave pressure sensor from 17.73% to 1.25% in the test environment. Furthermore, this method allows for velocity-based measurement of shock wave overpressure peaks in all propagation direction, with a maximum measurement error of 3.59% for shock wave overpressure peaks ≤ 9.08 MPa.

Phase measuring deflectometry for convex aspheric surface measurement.

This paper introduces what we believe to be a novel approach to accurately measure the shape of convex aspherical surfaces with large slope gradients. This approach employs a pre-distortion system to enhance the visibility of the structured light pattern that is captured by camera. The data processing involves iterative methods to obtain surface shape data. The initial step in the experimental calibration involves establishing a reference plane, which serves as the starting point for the iterative process. The calculation for slope is subsequently utilized to determine the initial slope of the surface under test, and the height of the tested element is derived by integrating these slopes. Through multiple iterations and continuous updating of the surface height, the precise and authentic true surface height is ultimately achieved. The method's accuracy is assessed through the measurement of a highly steep convex aspherical area with a diameter of 5.2 mm and a radius of curvature of approximately 7.7 mm. The proposed method demonstrates root mean square accuracy that can reach half a wavelength when compared to the measurement results obtained from high-precision profilers.

A lightweight intrusion detection method for IoT based on deep learning and dynamic quantization.

Intrusion detection ensures that IoT can protect itself against malicious intrusions in extensive and intricate network traffic data. In recent years, deep learning has been extensively and effectively employed in IoT intrusion detection. However, the limited computing power and storage space of IoT devices restrict the feasibility of deploying resource-intensive intrusion detection systems on them. This article introduces the DL-BiLSTM lightweight IoT intrusion detection model. By combining deep neural networks (DNNs) and bidirectional long short-term memory networks (BiLSTMs), the model enables nonlinear and bidirectional long-distance feature extraction of complex network information. This capability allows the system to capture complex patterns and behaviors related to cyber-attacks, thus enhancing detection performance. To address the resource constraints of IoT devices, the model utilizes the incremental principal component analysis (IPCA) algorithm for feature dimensionality reduction. Additionally, dynamic quantization is employed to trim the specified cell structure of the model, thereby reducing the computational burden on IoT devices while preserving accurate detection capability. The experimental results on the benchmark datasets CIC IDS2017, N-BaIoT, and CICIoT2023 demonstrate that DL-BiLSTM surpasses traditional deep learning models and cutting-edge detection techniques in terms of detection performance, while maintaining a lower model complexity.

Development and Preliminary Application of Temperature Stress Test Machine for Cast-in-Place Inner Shaft Lining.

Over the past 20 years, as the depth and diameter of shaft lines increased in China, the cracking and water leakage of the inner walls of frozen shafts have become increasingly severe, resulting in significant safety threats and economic losses. Understanding the stress variation patterns of cast-in-place inner walls under the combined effects of temperature and constraint during construction is a prerequisite for evaluating the crack resistance performance of inner walls and preventing water leakage in frozen shafts. The temperature stress testing machine is an important instrument for studying the early-age crack resistance performance of concrete materials under the combined effects of temperature and constraint. However, existing testing machines have shortcomings in terms of applicable specimen cross-sectional shapes, temperature control methods for concrete structures, and axial loading capacity. In this paper, a novel temperature stress testing machine suitable for the inner wall structure shape, capable of simulating the hydration heat of the inner walls, was developed. Then, a reduced-scale model of the inner wall according to similarity criteria was manufactured indoors. Finally, preliminary investigations of the temperature, strain, and stress variations of the inner wall under 100% end constraint conditions were conducted by simulating the actual hydration heating and cooling process of the inner walls. Results show that the hydration heating and cooling process of the inner wall can be accurately simulated. After approximately 69 h of concrete casting, the accumulated relative displacement and strain of the end-constrained inner wall model were -244.2 mm and 187.8 µÎµ, respectively. The end constraint force of the model increased to a maximum value of 1.7 MPa and then rapidly unloaded, causing the model concrete to crack in tension. The temperature stress testing method presented in this paper provides a reference for scientifically formulating technical approaches to prevent cracking in cast-in-place concrete inner walls.

Density field measurement deflectometry for supersonic wind tunnels.

A method for the quantitative measurement of two-dimensional density field distributions based on deflectometry is proposed. With this method, from the point of view of the inverse Hartmann test, the light rays emitted from the camera reach the screen after being disturbed by the shock-wave flow field. After the coordinates of the point source are obtained by using the phase information, the deflection angle of the light ray can be calculated, and then the distribution of the density field can be determined. The principle of density field measurement deflectometry (DFMD) is described in detail. In the experiment, the density fields in wedge-shaped models with three different wedge angles are measured in supersonic wind tunnels, the experimental results from the proposed method are compared with the theoretical results, and the measurement error is found to be around 2.76 × 10-3kg/m3. This method has the advantages of fast measurement, a simple device, and low cost. It provides a new approach, to the best of our knowledge, to measuring the density field of a shock-wave flow field.

Wide-Viewing-Angle Integral Imaging System with Full-Effective-Pixels Elemental Image Array.

There exists a defect of the narrow viewing angle in the conventional integral imaging system. One reason for this is that only partial pixels of each elemental image contribute to the viewing angle and the others cause image flips. In this paper, a wide-viewing-angle integral imaging system with a full-effective-pixels elemental image array (FEP-EIA) was proposed. The correspondence between viewpoints and pixel coordinates within the elemental image array was built up, and effective pixel blocks and pixels leading to flipping images were deduced. Then, a pixel replacement method was proposed to generate the FEP-EIAs, which adapt to different viewing distances. As a result, the viewing angle of the proposed integral imaging system was effectively extended through the replacement of the pixels, which caused the image flips. Experiment results demonstrated that wide viewing angles are available for the proposed integral imaging system regardless of the viewing distances.

Front and back surface measurement of the transparent planar element based on multi-frequency fringe deflectometry.

As a highly accurate metrology, phase measuring deflectometry (PMD) can be used for in-situ surface shape measurement. However, due to the reflection off the back surface, PMD cannot measure both the front and back surfaces of the transparent planar element simultaneously. Therefore, this paper proposes a method for measuring the front and back surfaces of the transparent planar element. The phase distribution corresponding to the front and back surfaces can be firstly acquired by multi-frequency fringe deflectometry. Then, the front and back surface shapes can be obtained by inverse ray-tracing and nonlinear optimization. Numerical simulation and experiment verify the proposed method. The surface shape of window glass with a thickness of 10 mm is measured in the experiment. The surface shape error is around 50 nm in the root mean square with a diameter of 51 mm.

3D medical images security via light-field imaging.

This Letter proposes a selective encryption scheme for three-dimensional (3D) medical images using light-field imaging and two-dimensional (2D) Moore cellular automata (MCA). We first utilize convolutional neural networks (CNNs) to obtain the saliency of each elemental image (EI) originating from a 3D medical image with different viewpoints, and successfully extract the region of interest (ROI) in each EI. In addition, we use 2D MCA with balanced rule to encrypt the ROI of each EI. Finally, the decrypted elemental image array (EIA) can be reconstructed into a full-color and full-parallax 3D image using the display device, which can be visually displayed to doctors so that they can observe from different angles to design accurate treatment plans and improve the level of medical treatment. Our work also requires no preprocessing of 3D images, which is more efficient than the method of using slices for encryption.

Deep-learning-based 3D object salient detection via light-field integral imaging.

This Letter proposes an effective light-field 3D saliency object detection (SOD) method, which is inspired by the idea that the spatial and angular information inherent in a light-field implicitly contains the geometry and reflection characteristics of the observed scene. These characteristics can provide effective background clues and depth information for 3D saliency reconstruction, which can greatly improve the accuracy of object detection and recognition. We use convolutional neural networks (CNNs) to detect the saliency of each elemental image (EI) with different viewpoints in an elemental image array (EIA) and the salient EIA is reconstructed by using a micro-lens array, forming a 3D salient map in the reconstructed space. Experimental results show that our method can generate high-quality 3D saliency maps and can be observed simultaneously from different angles and positions.

Phase measuring deflectometry based on calibration of the entrance pupil center of the camera lens.

A camera calibration method for phase measuring deflectometry (PMD) based on the entrance pupil center (EPC) of the camera lens is proposed. In our method, the position of the entrance pupil of the camera lens is first measured; next the absolute coordinates of the EPC are calibrated by using a reference flat and an external stop that is mounted in front of the camera lens; then the EPC as the camera coordinates is used for PMD. The feasibility of the proposed method is verified by simulation. The surface shapes of a planar optical element and a planar window glass are separately measured in our experiments, and a subwavelength accuracy level is achieved. Meanwhile, the effects of the camera lens with different aperture settings on captured images are investigated (including exposure time, image contrast, and measurement accuracy). The experimental results show that the exposure time required declines with the decrease in the f-number, and the measurement accuracy is higher than others when the f-numbers are changed from f/5.6 to f/11.

Color ghost imaging through the scattering media based on A-cGAN.

Ghost imaging plays an important role in the field of optical imaging. To realize color ghost imaging through the scattering media, we propose a deep learning method with high generation ability. Through our method, we can efficiently reconstruct color images with rich details, in line with human perception and close to the target color pictures. Experimental results show that our method can image through the scattering media with different scattering intensities and achieve good results even at a sampling rate of 0.1.

Cryptanalysis for a light-field 3D cryptosystem based on M-cGAN.

Integral imaging, as an excellent light-field three-dimensional (3D) imaging technique, is considered as one of the most important technologies for 3D encryption because of its obvious advantages of high robustness, security, and computational feasibility. However, to date, there is no effective cryptanalysis technology for the light-field 3D cryptosystem. In this Letter, a cryptanalysis algorithm based on deep learning for the light-field 3D cryptosystem is presented. The 3D image can be optically retrieved by the trained network model without encryption keys. The experimental results verify the feasibility and effectiveness of our proposed method.

Active speckle deflectometry based on 3D digital image correlation.

A method based on 3D digital image correlation (DIC) to measure the shape of specular surface is proposed. The proposed active speckle deflectometry (ASD) utilizes a stereo-camera system to monitor the liquid crystal display (LCD), which is deliberately moved during the measurement. Another testing camera (TC) is used to capture the single-shot speckle pattern displayed on the LCD screen after reflection by the test surface. With this proposal, the movement of the LCD screen can be arbitrary as long as the TC can capture the reflection of speckle pattern. The distance as well as the direction of the movement is not required to be known. The coordinates of the point source are determined by applying the 3D DIC technique with the monitoring stereo-cameras (MSC) before and after the movement of the LCD screen, then the slope and surface shape are obtained. The measurement accuracy of this method is evaluated by measuring a flat glass with a diameter of about 80 mm, compared with the measurement results of interferometer, the shape measurement difference is 0.278um in root mean square (RMS). The shape of two wafers is also measured, and the measurement results are compared to that of the traditional phase measuring deflectometry (PMD). ASD has the advantages of fast measurement, low cost, arbitrary LCD movement, tolerance for the out-of-plane shape of the LCD screen. It provides a new method for specular surface measurement.

Method for measuring the radius of mean curvature of a spherical surface based on phase measuring deflectometry.

In this paper, a method for measuring the radius of mean curvature (Rm) of the spherical surface based on phase measuring deflectometry is proposed. With our method, the average of the Rm in a small region is constrained by a preknown radius of curvature (Rp), and the height of an anchor point in this region can be calculated with iterative and optimization methods. Then both the height and slope data of the spherical surface can be obtained, and the Rm of each point of the spherical surface can be calculated by a differential geometric method. The feasibility of the proposed method is verified by simulation. In the experiment, a spherical surface with 88.652 mm radius of curvature is measured to demonstrate the effectiveness of this method, which can be used to accurately measure the Rm of each point on the spherical surface by online or in situ measurement.

SP1-induced lncRNA DANCR contributes to proliferation and invasion of ovarian cancer.

Transcription factor SP1 could manipulate pathways involved in ovarian cancer progression. LncRNAs are involved in SP1-mediated tumorigenesis. LncRNA DANCR could promote metastasis of ovarian cancer. However, the regulatory function and involvement of SP1-induced lncRNA DANCR in ovarian cancer remain elusive. Data from this study showed that SP1 was up-regulated in ovarian cancer tissues and cells (CAOV3, SKOV3, A2780), and SP1 could bind to the promoter region of DANCR through chromatin immunoprecipitation and leuciferase activity assays. Therefore, DANCR was transcriptionally induced by SP1 in ovarian cancer tissues and cells (CAOV3, SKOV3, A2780). Functionally, reduced expression of DANCR suppressed cell viability, migration and invasion of CAOV3, while enhanced DANCR expression contributed to SKOV3 growth. Over-expression of SP1 reversed the suppressive effects of DANCR interference on ovarian cancer progression. In conclusion, SP1-induced DANCR contributed to oncogenic potential of ovarian cancer, suggesting a promising therapeutic target for ovarian cancer.

Speckle pattern shifting deflectometry based on digital image correlation.

A method based on digital image correlation (DIC) for the surface shape measurement of specular surface by shifting a speckle pattern, which is displayed on an LCD screen, is proposed in this paper. With this method, the deformed information of test surface is encoded within the displacement distribution between the two recorded speckle images before and after the speckle pattern shifted. The displacement distribution is calculated by the DIC algorithm, then the slope data and the surface shape are obtained. The principle and algorithm of speckle pattern shifting deflectometry (SPSD) are described in detail. The correctness and feasibility of the proposed method are verified by simulation, and the source of error is analyzed as well. Finally, the shape of an acrylic plastic plate and a silicon wafer are measured. The experimental result of the proposed method is compared with that of PMD, and the figure error is around 1µm RMS with a measured diameter of about 100mm. This method has the advantages of fast measurement, simple device, low cost and needlessness of reference element. It provides a new approach to measure the shape of specular surface.

Integral imaging-based 2D/3D convertible display system by using holographic optical element and polymer dispersed liquid crystal.

An integral imaging-based 2D/3D convertible display system is proposed by using a lens-array holographic optical element (LAHOE), a polymer dispersed liquid crystal (PDLC) film, and a projector. The LAHOE is closely attached to the PDLC film to constitute a projection screen. The LAHOE is used to realize integral imaging 3D display. When the PDLC film with an applied voltage is in the transparent state, the projector projects a Bragg matched 3D image, and the display system works in 3D mode. When the PDLC film without an applied voltage is in the scattering state, the projector projects a 2D image, and the display system works in 2D mode. A prototype of the integral imaging-based 2D/3D convertible display is developed, and it provides 2D/3D convertible images properly.

Evolution of optical properties and electronic structures: band gaps and critical points in MgxZn1-xO (0 ≤ x ≤ 0.2) thin films.

MgxZn1-xO (ZMO) thin films with tunable Mg content were deposited by atomic layer deposition (ALD) on silicon substrates at 190 °C. The elemental and structural properties were acquired by X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Spectroscopic ellipsometry measurements were performed to reveal the evolution of the dielectric functions and critical points in the ZMO thin films by point-by-point fit in the photon energy range of 1.2-6.0 eV. The dependence of the dielectric functions on doping content is clearly demonstrated and physically explained. The critical point energies and the types of interband optical transitions were extracted from standard lineshape analysis of the second derivatives of the dielectric functions. The critical point features were discussed in terms of band structure modification and structural homogeneity arisen by introducing the Mg dopant into the films. Controlling these transitions by changing the doping content will be of practical significance in emerging ZMO-based thin-film photonic and optoelectronic devices.